hytrel(r) design guide - module v - cbucc.comcbucc.com/pds_file/2002061583146.pdfhytrel ® is the...

dthermoplastic polyester elastomerHytrel

Design Guide—Module V

®

Miner Elastomer’s TecsPak® devices are used in avariety of energy management applications. Suchdevices can undergo severe deformation repeatedlywithout deterioration in properties, like energyabsorption, reliability, and durability.

Hytrel® permits a new degree of freedom in designingtough, resilient, shock- and noise-isolating connectorsand fasteners with integral hinges, springs, and seals.

Copyright © 2000 E.I. du Pont de Nemours and Company. All rights reserved.

Table of Contents

General Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Properties and Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Mechanical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Tensile Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Tensile Stress-Strain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Tensile Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Yield Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Elastic Modulus in Tension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Tensile Set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Poissons’ Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Compressive Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Elastic Modulus in Compression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Flexural Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Flexural Modulus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Creep Modulus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Compressive Creep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Fatigue Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Flexural Fatigue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Heat Generation and Flexural Fatigue in Compression . . . . . . . . . . . . . . . . . . . . . . . 18Resistance to Flex Cut Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Ross Flex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18DeMattia Flex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19Impact Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19Notched Izod Impact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19Instrumented Impact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Brittleness Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Thermal Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Thermal Conductivity and Specific Heat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Dynamic Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Electrical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Abrasion and Wear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Friction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Wear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

(continued)

Table of Contents (continued)

Effect of Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Moisture Pickup and Drying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Shrinkage and Post-Molding Shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Annealing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Dimensional Tolerances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29The Molding Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Concentrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Gas Permeability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Radiation Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40Resistance to Mildew and Fungus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Agency Approvals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42Food and Drug Administration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42Underwriters Laboratories Recognition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45General Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45Design Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47Undercuts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48Realistic Tolerances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48Assembly Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49Overmolding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55Bearings and Seals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55Gears . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56Boots and Bellows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56Rolling Diaphragms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57Belts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58Coiled Tubing and Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58Reinforced Hose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

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General InformationDescriptionHytrel® is the DuPont registered trademark forits brand of thermoplastic polyester elastomers. Tpolyether-ester block copolymers combine manythe most desirable characteristics of high-perfor-mance elastomers and flexible plastics. Hytrel®

offers a unique combination of mechanical, physcal, and chemical properties that qualifies it fordemanding applications. The various grades ofHytrel® exhibit a wide range of flexibility/stiffnessand processing capabilities.

This brochure is intended to assist design enginein the successful and efficient design of parts ofHytrel® thermoplastic polyester elastomers. Manyof the same design considerations that apply tometals and other engineering materials of constrtion apply to Hytrel®. It is common practice to usestandard engineering equations for designing witHytrel®. However, because all engineering materiare affected to some extent by temperature, moisture, and other environmental service conditions,it is necessary to determine the extreme operatinconditions and to design a part so that it will per-form satisfactorily under all these conditions.

The selection of the best material for any application requires a knowledge of the properties ofall candidate materials and how they satisfy therequirements of the application. Hytrel® may bechosen for a job because of one, or a combinatioof its properties.

Much of the engineering data needed to design wHytrel® is given in the following pages and shouldbe helpful to the designer. However, it is alwaysimportant to test prototypes of a proposed designand material under realistic conditions beforemaking production commitments.

Description, typical characteristics and typicalapplication areas of various Hytrel® grades arelisted in Table 1.

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Properties and CharacteristicsHytrel® is a thermoplastic polyester elastomer thacombines many of the most desirable characteristics of high-performance elastomers and flexibleplastics. It features exceptional toughness andresilience; high resistance to creep, impact, and ffatigue; flexibility at low temperatures; and goodretention of properties at elevated temperatures. addition, it resists deterioration from many indus-trial chemicals, oils, and solvents.*

Typical properties of various Hytrel® grades arelisted in Table 2, in SI units (pages 4–5), andfollowed by English units (pages 6–7).

ProcessingHytrel® can be readily formed into high-perfor-mance products by a variety of thermoplasticprocessing techniques, including injection moldinextrusion, blow molding, rotational molding, andmelt casting. Hytrel® is processed at temperaturesbetween 177 and 260°C (350 and 500°F), depend-ing on the process and polymer type. All standardgrades have a sharp melting point and very goodmelt stability.

ApplicationsThe excellent properties of Hytrel® qualify it for anumber of demanding applications where mechacal strength and durability are required in a flexibcomponent. Examples include seals, belts, bush-ings, pump diaphragms, gears, protective boots,hose and tubing, springs, and impact-absorbingdevices. In many of these applications, Hytrel®

allows a multipiece rubber, plastic, or even metalcomposite assembly to be replaced with a singlepart. For outdoor applications, Hytrel® should beprotected from ultraviolet (UV) attack.

Some of the industries where Hytrel® can alreadybe found include: automotive, fluid power, electri-cal/electronic, appliance and power tool, sportinggoods, footwear, wire and cable (including fiberoptics), furniture, and off-road transportationequipment. The potential for using Hytrel® in otherindustries is limited only by one’s imagination.

* Property data sheets and other Hytrel® processing guides, as wellas this brochure, are available through the world wide web,http://www.dupont.com/enggpolymers/americas.

Typical Uses

Applications requiring flex lifecoupled with good flexibility atlow temperatures. Thin, flexiblemembranes. Good for highoriginal color retention.

TubingHose jacketsWire and cable jacketsFilm sheetingMolded products

Applications requiring highoriginal color retention.Molded and extruded productsfor consumer use.

TubingHose jacketsWire and cable jacketsProfilesMolded products

TubingMolded and extruded products forconsumer use.

Same as Hytrel® G4774.

Characteristics*

Very flexible grade of Hytrel®.Excellent flex resistance, especiallyat low temperatures. Moldableeven in thin sections. Can be usedin light-colored products.

Excellent heat-aging resistanceand resistance to oils at hightemperatures. Best low modulusmolding and extrusion grade.

Like Hytrel® G4074, except thatheat-aging resistance is reduced.Can be used in light-coloredproducts.

Excellent heat-aging resistanceand resistance to oils at hightemperatures. Good resistanceto oils, fuels, and solvents.

Good balance of low and hightemperature properties.

Excellent heat-aging resistanceand resistance to oils at hightemperatures.

Hytrel® G3548L

Hytrel® G4074

Hytrel® G4078W

Hytrel® G4774

Hytrel® G4778

Hytrel® G5544

Description

Low modulus molding andextrusion grade. Containsimproved color-stableantioxidants.

Low modulus molding andextrusion grade. Contains adiscoloring antioxidant.

Low modulus molding andextrusion grade. Containsimproved color-stableantioxidants.

Low to medium modulus moldingand extrusion grade. Contains adiscoloring antioxidant.

Low to medium modulus moldingand extrusion grade. Containscolor-stable antioxidants.

Medium modulus molding andextrusion grade. Contains adiscoloring antioxidant.

(continued)* The characteristics shown are those of the unmodified standard composition. Special stabilizers and additives can be mixed with Hytrel® to improve

its resistance to UV light, heat aging, and moisture.

Grade

Table 1Compositions of Hytrel®

General Purpose Hytrel® ResinsThese grades offer the best balance of properties and cost.

High-Performance Hytrel® ResinsThese grades provide an extra measure of strength or serviceability in the most demanding

applications and can be used in light-colored products.

Description

Low modulus extrusion grade.Contains color-stableantioxidants.

Low modulus molding andextrusion grade. Contains color-stable antioxidants.

Medium-low modulus moldingand extrusion grade. Containscolor-stable antioxidants.

Medium modulus moldinggrade. Contains color-stableantioxidants.

Medium modulus extrusiongrade. Contains color-stableantioxidants.

Hytrel® 4056

Hytrel® 4069

Hytrel® 4556

Hytrel® 5526

Hytrel® 5556

Characteristics*

Excellent low-temperatureproperties. Excellent flex-fatigueresistance. Excellent creepresistance.

Low modulus grade similar toHytrel® 4056 with a highermelting point.

Same as Hytrel® 4069.

Combine the best balance ofproperties of the product line.

Grade Typical Uses

Hose jacketsWire and cable jacketsFilm and sheetingBeltingSeals

Same as Hytrel® 4056 andmolded products.

Same as Hytrel® 4056 andmolded products.

Seals, packing, and gasketsGears and bearings

Tubing and hoseWire and cable jacketsFilm and sheetingBelting

2

Table 1Compositions of Hytrel® (continued)

High-Performance Hytrel® Resins (continued)

Description

Medium-high modulus moldingand extrusion grade. Containscolor-stable antioxidants.

High modulus molding andextrusion grade. Contains color-stable antioxidants.

Highest modulus molding andextrusion grade. Containscolor-stable antioxidants.

Hytrel® 6356

Hytrel® 7246

Hytrel® 8238

Characteristics*

Very good resistance to oils,hydraulic fluids, and fuels. Verygood resistance to permeation bygases and liquids.

High service temperature. Retainsgood low-temperature flexibility.Excellent resistance to oils, fuels,and solvents. Low fuel permeability.

Highest service temperature. Bestresistance to oils, fuels, andsolvents. Lowest fuel permeability.

* The characteristics shown are those of the unmodified standard composition. Special stabilizers and additives can be mixed with Hytrel® to improveits resistance to UV light, heat aging, and moisture.

Grade Typical Uses

Tubing and hoseFilmProfilesSealsGears and sprocketsFuel tanks

TubingWire and cable jacketsGears and sprocketsOil field parts

TubingWire and cable jacketsGears and sprocketsOil field partsElectrical connectors

Description

Very low modulus molding andextrusion grade. Containscolor-stable antioxidants.

Pigmented black. Particularlysuitable for extrusion blowmolding and extrusion.

Heat-stabilized grade of Hytrel®

5556. Contains a discoloringantioxidant.

Pigmented black. Particularlysuitable for extrusion blowmolding and extrusion.

Medium-low modulus grade.Contains color-stableantioxidants.

Medium-low modulus molding andextrusion grade. Flame retardedantidrip compound.

Medium modulus, high viscositygrade, pigmented black.Particularly suitable for extrusionand extrusion blow molding.

Characteristics*

Most flexible grade of Hytrel®

with good strength and toughnessover a wide temperature range.

Good balance of propertiescombined with high viscosity forextrusion and blow moldingapplications.

Combine the best balance ofproperties of the product line.

Good balance of propertiescombined with high viscosity forextrusion and blow moldingapplications.

Low permeability to oils, fuels,and plasticizers—approximatelyone-third that of other grades ofsimilar stiffness. High clarity inthin films.

Meets requirements ofUL-94 class V-0 at 1.57 mm(1/16 in) thickness.

Excellent flex fatigue resistanceand excellent performance at lowtemperature. Formulated forimproved surface lubricity.

Typical Uses

Applications requiring flex lifecoupled with good flexibilityat low temperatures. Thin,flexible membranes.

Hollow thin-walled partsBlow film and sheetingLarge diameter tubingHose mandrelsProfilesAutomotive boots and covers

Tubing and hoseWire and cable jacketsFilm and sheetingBeltingUsed where increased heat-aging stability is required.

Hollow thin-walled partsBlow film and sheetingLarge diameter tubingHose mandrelsProfilesAutomotive boots and covers

Applications requiring goodflexibility coupled with lowpermeability to fuels, oils, andplasticizers. Coextrudablebarrier membrane over morepermeable substrates.

Tubing and hoseWire and cable jacketsFilm and sheeting

Hollow thin-walled partsBlow film and sheetingLarge diameter tubingProfilesAutomotive boots and covers

Grade

Hytrel® 3078

Hytrel® HTR4275BK

Hytrel® 5555HS

Hytrel® HTR5612BK

Hytrel® HTR6108

Hytrel® HTR8068

Hytrel® HTR8139LV

Specialty Hytrel® Resins

3

Propertya ASTM ISO Unit G3548L G4074 G4078W G4774 G4778 G5544

Hardness, durometer D D 2240 868 35 40 40 47 47 55

Flexural Modulusd D 790 178at –40°C MPa 62 207 166 320 320 850

23°C MPa 32.4 65.5 65.5 117 117 193100°C MPa 7 33 16 69 69 125

Tensile Stress at Breake D 638 R527 MPa 10.3 16 17 20.7 20.7 31

Elongation at Breake D 638 R527 % 200 310 310 275 300 375

Tensile Stress at 5% Straine D 638 R527 MPa 1.7 2.4 3.0 3.8 5.0 6.0

Tensile Stress at 10% Straine D 638 R527 MPa 2.6 4.3 4.5 6.0 7.0 10.5

Izod Impact (notched)f D 256 R180at –40°C Method A J/m No Break 27 27 144 165 133

23°C J/m No Break No Break No Break No Break No Break No Break

Resistance to Flex Cut Growth, D 1052 — cycles >1 x 106 >1 x 106 >1 x 106 >1 x 106 >1 x 106 8 x 105

Ross (pierced) to 5x cutgrowth

Initial Tear Resistance,g Die C D 1004 34 kN/m 51 96 88 94 91 123

Melt Flow Rate D 1238 1133 g/10 min 10 5.2 5.3 11 13 10Test Conditions: Temperature, °C

at 2.16 kg load 190 190 190 230 230 230

Melting Pointh D 3418 3146 °C 156 170 170 208 208 215

Vicat Softening Point D 1525 306 °C 77 112 119 174 175 196Rate B

Deflection Temperature D 648 75under Flexural Load

at 0.5 MPa °C 42 50 50 72 80 111at 1.8 MPa °C 32 N/A N/A 45 46 51

Specific Gravity D 792 R1183 — 1.15 1.19 1.18 1.20 1.20 1.22

Water Absorption, 24 hr D 570 62 % 5 2.1 3 2.5 2.3 1.5

Abrasion Resistance at 1 kg load D 1044 — mg/1000(Modified) rev

Taber, CS-17 Wheel 30 9 20 13 12 9Taber, H-18 Wheel 310 193 260 168 162 116

Method IProcedure BST

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General Purpose GradescTest Methodsb

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a All properties were measured on injection-molded specimens at 23°C (73°F) unlessspecified otherwise. The values shown are for unmodified grades. Colorants oradditives of any kind may alter some or all of these properties. The data listed herefall within the normal range of product properties, but they should not be used toestablish specification limits or used alone as the basis of design.

b All of the values reported in this table are based on ASTM methods. ISO methodsmay produce different test results due to differences in test specimen dimensionsand/or test procedures.

c The High-Productivity and High-Performance grades of Hytrel® are namedaccording to the following product key: first two digits: Hardness durometer D (ingeneral, the greater the hardness, the stiffer the polymer); third digit: A measure ofinherent viscosity; fourth digit: Type of antioxidant: 0–5 Discoloring, 6–9 Non-discoloring; Letter suffix: Special functions or colors.

d Crosshead speed 12.5 mm/min (0.5 in/min).e ASTM Type IV dumbbells diecut from injection molded slab 2 mm (0.079 in) thick.

Head speed 50 mm/min (2 in/min).f Specimens 6.35 mm (0.25 in) thick.g Specimens 2 mm (0.079 in) thick.h Differential Scanning Calorimeter (DSC), peak of endotherm.i Hardness, Rockwell R.

Table 2Typical Properties of Hytrel®

(SI Units)

4

4056 4069 4556 5526 5556 6356 7246 8238 3078 HTR4275BK 5555HS HTR5612BK HTR6108 HTR8068 HTR8139LV

40 40 45 55 55 63 72 82 30 55 55 50 60 46 46(104) i

155 172 230 760 760 1,800 2,410 3,030 145 910 760 510 2,010 650 22062 55 84 207 207 330 570 1,110 28 160 207 124 193 174 9527 28 44 110 110 150 207 255 14 59 110 46 60 50 45

21 20 31 40 40 41 45.8 48.3 26.2 40 40 36 38.6 12.4 34

700 700 600 500 500 420 360 350 700 450 500 530 400 340 600

2.4 2.4 4.1 6.9 6.9 12 14 27.6 1.3 7.6 6.9 5.5 7.6 3.9 4.5

3.6 3.5 5.7 10.3 10.3 16 20 30.3 2.1 10.3 10.3 8.3 9.6 5.2 6.3

No Break No Break No Break 128 170 48 40 30 No Break 70 43 110 20 90 No BreakNo Break No Break No Break No Break No Break No Break 210 40 No Break No Break No Break No Break No Break No Break No Break

>1 x 106 >1 x 106 >1 x 106 5 x 105 5 x 105 5 x 105 3 x 104 N/A >1 x 106 5 x 104 1 x 105 6 x 105 6 x 105 — >1 x 106

101 95 116 158 158 175 200 253 77 163 158 145 150 75 123

5.3 8.5 8.5 18 7.5 8.5 12.5 12.5 5.0 1.8 8.5 3.0 5.2 4.6 3.3

190 220 220 220 220 230 240 240 190 230 220 230 190 190 230

150 193 193 203 203 211 218 223 170 196 203 196 168 169 192

108 134 158 180 180 195 207 212 83 174 180 155 148 110 161

54 55 60 90 90 115 130 140 46 68 90 62 50 — 68N/A N/A 43 49 49 51 52 55 N/A 45 49 44 42 — 46

1.17 1.11 1.14 1.20 1.20 1.22 1.25 1.28 1.07 1.16 1.20 1.16 1.24 1.43 1.15

0.6 0.7 0.6 0.5 0.5 0.3 0.3 0.3 0.8 0.5 0.7 0.4 0.2 1.9 0.7

3 15 3 7 6 7 13 9 2 20 — 38 9 25 4100 80 72 70 64 77 47 20 90 227 112 186 116 — 65

High-Performance Gradesc Specialty Grades

5

Propertya ASTM ISO Unit G3548L G4074 G4078W G4774 G4778 G5544

Hardness, durometer D D 2240 868 35 40 40 47 47 55

Flexural Modulusd D 790 178at –40°F psi 9,000 30,000 24,000 47,000 47,000 123,000

73°F psi 4,700 9,500 9,500 17,000 17,000 28,000212°F psi 1,010 4,750 2,320 10,000 10,000 18,000

Tensile Stress at Breake D 638 R527 psi 1,490 2,000 2,460 3,000 3,000 4,500

Elongation at Breake D 638 R527 % 200 310 310 275 300 375

Tensile Stress at 5% Straine D 638 R527 psi 240 350 440 550 670 875

Tensile Stress at 10% Straine D 638 R527 psi 380 550 650 875 980 1,520

Izod Impact (notched)f D 256 R180at –40°F Method A ft⋅lbf/in No Break 0.5 0.5 2.7 3.1 2.5

73°F ft⋅lbf/in No Break No Break No Break No Break No Break No Break

Resistance to Flex Cut Growth, D 1052 — cycles >1 x 106 >1 x 106 >1 x 106 >1 x 106 >1 x 106 8 x 105

Ross (pierced) to 5x cutgrowth

Initial Tear Resistance,g Die C D 1004 34 lbf/in 290 460 500 535 520 700

Melt Flow Rate D 1238 1133 g/10 min 10 5.2 5.3 11 13 10Test Conditions: Temperature, °F

at 2.16 kg load 374 374 374 446 446 446

Melting Pointh D 3418 3146 °F 312 338 338 406 406 419

Vicat Softening Point D 1525 306 °F 171 233 246 345 347 385Rate B

Deflection Temperature D 648 75under Flexural Load

at 66 psi °F 108 122 122 162 176 232at 264 psi °F 90 N/A N/A 113 115 124

Specific Gravity D 792 R1183 — 1.15 1.19 1.18 1.20 1.20 1.22

Water Absorption, 24 hr D 570 62 % 5 2.1 3 2.5 2.3 1.5

Abrasion Resistance at 1 kg load D 1044 — mg/1000(Modified) rev

Taber, CS-17 Wheel 30 9 20 13 12 9Taber, H-18 Wheel 310 193 260 168 162 116

Method IProcedure BST

IFFN

ESS

THER

MA

L

General Purpose GradescTest Methodsb

TOU

GH

NES

SST

RESS

/STR

AIN

MIS

CELL

AN

EOU

S

a All properties were measured on injection-molded specimens at 23°C (73°F) unlessspecified otherwise. The values shown are for unmodified grades. Colorants oradditives of any kind may alter some or all of these properties. The data listed herefall within the normal range of product properties, but they should not be used toestablish specification limits or used alone as the basis of design.

b All of the values reported in this table are based on ASTM methods. ISO methodsmay produce different test results due to differences in test specimen dimensionsand/or test procedures.

c The High-Productivity and High-Performance grades of Hytrel® are namedaccording to the following product key: first two digits: Hardness durometer D (ingeneral, the greater the hardness, the stiffer the polymer); third digit: A measure ofinherent viscosity; fourth digit: Type of antioxidant: 0–5 Discoloring, 6–9 Non-discoloring; Letter suffix: Special functions or colors.

d Crosshead speed 12.5 mm/min (0.5 in/min).e ASTM Type IV dumbbells diecut from injection molded slab 2 mm (0.079 in) thick.

Head speed 50 mm/min (2 in/min).f Specimens 6.35 mm (0.25 in) thick.g Specimens 2 mm (0.079 in) thick.h Differential Scanning Calorimeter (DSC), peak of endotherm.i Hardness, Rockwell R.

Table 2Typical Properties of Hytrel®

(English Units)

6

4056 4069 4556 5526 5556 6356 7246 8238 3078 HTR4275BK 5555HS HTR5612BK HTR6108 HTR8068 HTR8139LV

40 40 45 55 55 63 72 82 30 55 55 50 60 46 46(104) i

22,500 25,000 33,000 110,000 110,000 260,000 350,000 440,000 21,000 132,000 110,000 74,000 292,000 93,700 31,9009,000 8,000 13,000 30,000 30,000 48,000 83,000 160,000 4,000 23,200 30,000 18,000 28,000 25,200 13,7803,900 4,060 6,400 16,000 16,000 22,000 30,000 37,000 2,030 8,550 16,000 6,700 8,700 7,300 6,530

3,000 2,900 4,500 5,800 5,800 5,950 6,650 7,000 3,800 5,800 5,800 5,230 5,600 1,800 4,930

700 700 600 500 500 420 360 350 700 450 500 530 400 340 600

350 350 600 1,000 1,000 1,740 2,030 4,000 190 1,100 1,000 800 1,100 570 650

525 510 830 1,500 1,500 2,320 2,900 4,400 300 1,500 1,500 1,200 1,400 750 910

No Break No Break No Break 2.4 3.2 0.9 0.8 0.5 No Break 1.4 0.8 2.1 0.4 1.7 No BreakNo Break No Break No Break No Break No Break No Break 3.9 0.8 No Break No Break No Break No Break No Break No Break No Break

>1 x 106 >1 x 106 >1 x 106 5 x 105 5 x 105 5 x 105 3 x 104 N/A 1 x 106 5 x 104 1 x 105 6 x 105 6 x 105 — >1 x 106

580 550 660 900 900 1,000 1,150 1,440 440 930 900 830 855 430 700

5.3 8.5 8.5 18 7.5 8.5 12.5 12.5 5.0 1.8 8.5 3.0 5.2 4.6 3.3

374 428 428 428 428 446 464 464 374 446 428 446 374 374 446

302 379 379 397 397 412 424 433 338 385 397 385 334 336 378

226 273 316 356 356 383 405 414 181 345 356 311 298 230 322

129 131 140 194 194 239 266 284 115 154 194 144 122 — 154N/A N/A 110 120 120 124 126 131 N/A 113 120 111 108 — 115

1.17 1.11 1.14 1.20 1.20 1.22 1.25 1.28 1.07 1.16 1.20 1.16 1.24 1.43 1.15

0.6 0.7 0.6 0.5 0.5 0.3 0.3 0.3 0.8 0.5 0.7 0.4 0.2 1.9 0.7

3 15 3 7 6 7 13 9 2 20 — 38 9 25 4100 80 72 70 64 77 47 20 90 227 112 186 116 — 65

High-Performance Gradesc Specialty Grades

7

Mechanical PropertiesTensile Properties (ASTM D 638)Tensile elongation and tensile modulus measure-ments are among the most important indicationsof strength in a material and are the most widelyspecified properties of plastic materials. The tensitest is a measurement of the ability of a materialto withstand forces that tend to pull it apart andto determine to what extent the material stretchesbefore breaking. The tensile modulus of elasticity an indication of the relative stiffness of a materialand can be determined from a stress-strain diagraDifferent types of materials are often compared onthe basis of tensile strength, elongation, and tensimodulus.

Tensile Stress-StrainA stress-strain curve shows the relationship of anincreasing force on a test sample to the resultingelongation of the sample. Some of the factors thataffect the curve are: temperature, type of resin, raof testing, etc.

Tensile properties over a range of temperaturesare shown in Figures 1–10. Because of the elasto-meric nature of Hytrel®, elongation before break ishigh; as a result, low-strain-level and high-strain-level curves are presented separately to facilitateselection of strain levels.

Tensile StrengthThe tensile strength values are obtained from strestrain curves by noting the maximum stress on thecurve. The maximum tensile values are given inTable 2 and can be used in rating the relative resinstrengths.

Generally, the stiffer grades of Hytrel® show highertensile strengths and shorter elongations than thesofter grades. The stiffer grades are higher in thecrystalline polyester hard segment and thereforebehave more like typical engineering plastics.

Yield StrengthThe yield strength, also taken from the stress-stracurve, is the point at which the material continuesto elongate (strain) without additional stress. Theyield strength often has a lower value than thetensile strength. For Hytrel®, the maximum stressis usually at the breaking point; however, for someof the harder grades at low temperatures, themaximum stress may be at the yield point. Themore flexible grades of Hytrel® behave more likeelastomeric materials. They do not show any yieldunder the conditions used in the tests.

8

le

is

m.

le

te

ss-

in

In the design of plastic parts, yield strength is themost common reference, as it is uncommon for apart to be stressed beyond the yield point. Unlessone is designing gaskets and washers, which areoften stressed beyond the yield point, it is goodpractice to design within the proportional limit,which is substantially below the yield point.

100 200 300 400 50000 0

10

20

30

40

ASTM D 638Test Specimen:ASTM Type IV

Dumbbells diecut from injection molded slab 2 mm (0.079 in) thickStrain Rate: 50 mm/min (2 in/min)

Strain, %

1000100°C (212°F)120°C (248°F)

65°C (149°F)

23°C (73°F)

0°C (32°F)

–20°C (–4°F)

–40°C (–40°F)

2000

3000

4000

5000

Ten

sile S

tress, p

si

Ten

sile S

tress, M

Pa

302520151050012

34

56

78

9

1011

1213

14

15

ASTM D 638

Strips: 6.35 mm (0.25 in) wide

Strain Rate: 25.4 mm/min (1 in/min)

Strain, %

500

1000

1500

2000

0

Ten

sile S

tress, p

si

Ten

sile S

tress, M

Pa

100°C (212°F)120°C (248°F)

65°C (149°F)

23°C (73°F)

0°C (32°F)

–20°C (–4°F)

–40°C (–40°F)

Figure 1. Tensile Properties—Hytrel® G4074

Figure 2. Tensile Stress at Low Strain—Hytrel® G4074

100°C (212°F)

120°C (248°F)

65°C (149°F)

23°C (73°F)

0°C (32°F)–20°C (–4°F)

–40°C (–40°F)

30252015105001

2

34

5

67

8

910

1112

Strain, %

500

1000

1500

0

Ten

sile S

tress, M

Pa

Ten

sile S

tress, p

si

ASTM D 638



100°C (212°F)120°C (248°F)

150°C (302°F)

65°C (149°F)

23°C (73°F)0°C (32°F)–20°C (–4°F)

–40°C (–40°F)

800 90070060050040030020010000

10

20

30

40

50

60

Strain, %

1000

2000

3000

4000

5000

6000

7000

8000

0

Ten

sile S

tress, M

Pa

Ten

sile S

tress, p

si

ASTM D 638

Test Specimen:

ASTM Type IV

Dumbells diecut from injection molded slab 2 mm (0.079 in) thick

Strain Rate: 50 mm/min (2 in/min)

100°C (212°F)120°C (248°F)150°C (302°F)

65°C (149°F)

23°C (73°F)

0°C (32°F)

–20°C (–4°F)

–40°C (–40°F)

30252015105002

4

6

8

10

12

14

16

18

20

22

24

26

28

30

Strain, %

500

1000

1500

2000

2500

3000

3500

4000

0

Ten

sile S

tress, M

Pa

Ten

sile S

tress, p

si

ASTM D 638



100°C (212°F)

120°C (248°F)

65°C (149°F)

23°C (73°F)0°C (32°F)

–20°C (–4°F)

–40°C (–40°F)

600 70050040030020010000

10

20

30

40

50

60

70

ASTM D 638

Test Specimen:

ASTM Type IV

Dumbells diecut from injection molded slab 2 mm (0.079 in) thick

Strain Rate: 50 mm/min (2 in/min)

Strain, %

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0

Ten

sile S

tress, M

Pa

Ten

sile S

tress, p

si

Figure 5. Tensile Properties—Hytrel® 5526/5556Figure 3. Tensile Properties—Hytrel® 4056

Figure 6. Tensile Stress at Low Strain—Hytrel® 5526/5556

Figure 4. Tensile Stress at Low Strain—Hytrel® 4056

9

100°C (212°F)120°C (248°F)

150°C (302°F)

65°C (149°F)23°C (73°F)

0°C (32°F)–20°C (–4°F)

–40°C (–40°F)

800 90070060050040030020010000

10

20

30

40

50

60



Strain, %

1000

2000

3000

4000

5000

6000

7000

8000

0

Ten

sile S

tress, M

Pa

Ten

sile S

tress, p

si

100°C (212°F)120°C (248°F)

65°C (149°F)

23°C (73°F)0°C (32°F)

–20°C (–4°F)

600 70050040030020010000

10

20

30

40

50

60

70

Strain, %

1000

0

2000

3000

4000

5000

6000

7000

8000

9000

10000

Ten

sile S

tress, M

Pa

Ten

sile S

tress, p

si



ASTM D 638



100°C (212°F)120°C (248°F)150°C (302°F)

65°C (149°F)

23°C (73°F)

0°C (32°F)

–20°C (–4°F)

–40°C (–40°F)

3025201510500

10

20

30

40

50

60

Strain, %

1000

2000

3000

4000

5000

6000

7000

8000

0

Ten

sile S

tress, M

Pa

Ten

sile S

tress, p

si

100°C (212°F)120°C (248°F)150°C (302°F)

65°C (149°F)

23°C (73°F)

0°C (32°F)

–20°C (–4°F)

–40°C (–40°F)

3025201510500

10

20

30

40

50

60

70

Strain, %

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0

Ten

sile S

tress, M

Pa

Ten

sile S

tress, p

si

ASTM D 638



Figure 9. Tensile Properties—Hytrel® 7246Figure 7. Tensile Properties—Hytrel® 6356



10

t

n

l

h

.

Elastic Modulus in Tension(ASTM D 638)The elastic modulus is calculated from the linearportion of the stress-strain curves, that is, below elastic limit, which is approximately between 7 an10% strain for Hytrel®. This modulus changes withtime under load (see creep data), and this factormust be included in the calculation for part design

This modulus is the ratio of stress to correspondistrain below the proportional limit of a material.This is also known as modulus of elasticity, orYoung’s modulus, and is a measure of a materiastiffness. It is represented in Figure 11.

ASTM D 638Strips: 6.35 mm (0.25 in) wide


Temperature, °F

Temperature, °C

G4074

G40746356

5526/5556

4056

4056

7246

160140120100806040200–20–4010

2030406080

100

200300400600800

1000

2000

1.52

5

10

20

50

100

200

300 3402602201801401006020–20

Ela

sti

c M

od

ulu

s, M

Pa

Ela

sti

c M

od

ulu

s, p

si

× 10

3

Figure 11. Elastic Modulus in Tension versusTemperature—Hytrel®

Tensile Set (ASTM D 412)Tensile set represents residual deformation whicis partly permanent and partly recoverable afterstretching and retraction. For this reason, theperiods of extension and recovery and other testconditions must be controlled to obtain comparabresults. Tensile sets of representative Hytrel® gradesare shown in Figures 12 and 13.

1

hed

.

g

’s

le

18016014012010080604020 200

4056

6356

5526/5556

See Figure 13

7246

00

20

40

60

80

100

120

140ASTM D 412

Strain, %

Ten

sile S

et,

%

Figure 12. Tensile Set—Hytrel®

ASTM D 412

11 12109

4056

6356

7246

5526/5556

8765432100

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Strain, %

Ten

sile S

et,

%

Figure 13. Tensile Set at Low Strain—Hytrel®

Poissons’ RatioPoissons’ ratio measures the relative ability of amaterial to deform at right angles to applied stressIt permits the mathematical determination of amaterial’s physical characteristics and values in adirection perpendicular to the direction of loading.

Poissons’ ratio is defined as the ratio of the trans-verse strain to the longitudinal strain of a material.For plastics, the ratio is affected by time, tempera-ture, stress, sample size, etc.

Poissons’ ratio for most Hytrel® resins at 23°C(73°F) is 0.45. The value does not change signifi-cantly from Hytrel® resin to resin.

1

a

n

Compressive Properties(ASTM D 575)Compressive properties describe the behavior ofa material when it is subjected to a compressiveload at a relatively low and uniform rate of loadingProperties in compression are generally strongerthan in tension. In practical applications, thecompressive loads are not always applied instantneously. The results of impact, creep, and fatiguetests must also be considered during part design.

Table 3 lists the compression set values at differetemperatures. Compression set can be significantimproved by annealing for 24–48 hr at 100°C(212°F) for Hytrel® G4074 and 4056 and at 121°C(250°F) for all other Hytrel® types.

Compressive stress-strain properties are obtainedby using ASTM D 575, “Rubber Properties inCompression.” Two molded discs of 28.6 mm(1.13 in) diameter and 6.25 mm (0.25 in) highare stacked together and placed in a compressiontesting apparatus.

Figures 14–18 illustrate the compressive stressversus strain properties generated by the use ofthis method at various temperatures.

Figure 14. Compressive Properties—Hytrel® G4074

ASTM D 575

100°C (212°F)

120°C (248°F)

150°C (302°F)

65°C (149°F)

23°C (73°F)

0°C (32°F)

–20°C (–4°F)

–40°C (–40°F)

30252015105002

4

6

8

10

12

14

16

18

20

22

24

26

2830

Strain, %

500

1000

1500

2000

2500

3000

3500

4000

0

Co

mp

ressiv

e S

tress, M

Pa

Co

mp

ressiv

e S

tress, p

si

1

.

-

tly

ASTM D 575

100°C (212°F)

120°C (248°F)

150°C (302°F)

65°C (149°F)

23°C (73°F)

0°C (32°F)

–20°C (–4°F)

–40°C (–40°F)

30252015105002

4

6

8

10

12

14

16

18

20

22

24

26

Strain, %

500

1000

1500

2000

2500

3000

3500

0

Co

mp

ressiv

e S

tress, M

Pa

Co

mp

ressiv

e S

tress, p

si

Figure 15. Compressive Properties—Hytrel® 4056

Figure 16. Compressive Properties—Hytrel® 5526/5556

ASTM D 575

100°C (212°F)120°C (248°F)150°C (302°F)

65°C (149°F)23°C (73°F)

0°C (32°F)

–20°C (–4°F)

–40°C (–40°F)

3025201510500

10

20

30

40

50

60

Strain, %

1000

2000

3000

4000

5000

6000

7000

8000

0

Co

mp

ressiv

e S

tress, M

Pa

Co

mp

ressiv

e S

tress, p

si

Table 3Compression Set Resistance

ASTM D 395, Method A, 9.3 MPa (1350 psi) Load

Compression Set, %After 22 hr at

23°C 70°C 100°CType of Hytrel® (73°F) (158°F) (212°F)

4056 11 27 33

G4074 10 28 51

5526/5556 <1 4 8

6356 <1 2 4

7246 <1 2 5

2

,

ASTM D 575

100°C (212°F)

120°C (248°F)150°C (302°F)

65°C (149°F)

23°C (73°F)

0°C (32°F)

–20°C (–4°F)

–40°C (–40°F)

3025201510500

10

20

30

40

50

60

70

80

90

Strain, %

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

11000

12000

13000

0

Co

mp

ressiv

e S

tress, M

Pa

Co

mp

ressiv

e S

tress, p

si


ASTM D 575

100°C (212°F)120°C (248°F)

150°C (302°F)

65°C (149°F)

23°C (73°F)

0°C (32°F)

–20°C (–4°F)–40°C (–40°F)

3025201510500

10

20

30

40

50

60

70

80

90

100

Strain, %

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

11000

12000

14000

13000

0

Co

mp

ressiv

e S

tress, M

Pa

Co

mp

ressiv

e S

tress, p

si


1

Elastic Modulus in CompressionFigure 19 shows values for elastic modulus incompression versus temperature. These numbersare calculated from the linear portions of thestress-strain curves, that is, those portions belowthe elastic limit, which is approximately 7–10%for Hytrel®. Modulus changes with time under loadhowever, and this factor must be included in partdesign.

ASTM D 575Temperature, °F

Temperature, °C

G4074

63565526/5556

4056

7246

160 180140120100806040200–20–4010

2030406080

100

200300400600800

1000

1.52

5

10

20

50

100

300 3402602201801401006020–20

Ela

sti

c M

od

ulu

s, M

Pa

Ela

sti

c M

od

ulu

s, p

si

× 10

3

Figure 19. Elastic Modulus in Compression versusTemperature—Hytrel®

3

n

to

dn

s

,

a

gl

tors

,

t.

Flexural Properties (ASTM D 790)The stress-strain behavior of polymers in flexureis of interest to anyone designing a part to be beFlexural strength is the ability of the material towithstand bending forces applied perpendicular its longitudinal axis. The stress induced due to thflexural load is a combination of compressive antensile stress. Flexural properties are reported acalculated in terms of the tangent modulus ofelasticity (or modulus of elasticity in bending).

Flexural ModulusVariation of flexural modulus with temperature isshown in Figure 20. Differences in modulus valuefor tension, compression, and flexure will occur dto differences in strain rates, shapes of samplesAlso, flexure tests emphasize the surface of thesample, which will have molded-in stresses that different from those in the interior of the sample,which cools more slowly in the molding process.

ASTM DTemperatu

Temperatu86040200–20–40

10

2030406080

100

200300400600800

1000

2000

11401006020–20

Fle

xu

ral M

od

ulu

s, M

Pa

Figure 20. Flexural Modulus versus Temperature—Hyt

1

t.

e

d

ueetc.

re

Creep Modulus (ASTM D 2990)An important factor to consider when designingwith thermoplastics is that the modulus of a givenmaterial will change due to many factors includinstress level, temperature, time, and environmentaconditions. Figures 21–24 are plots of creep orapparent modulus versus time at various stresslevels, all at room temperature. Generally, linearcreep modulus plots can be extrapolated by a facof ten in the time axis with reasonable safety. Thihas been done on the creep modulus plots and issignified by dashed lines. For critical applicationshowever, testing for the full expected life of thepart should be done to verify these results. Thehighest stress level shown on each plot is themaximum recommended stress level for eachmaterial under long-term loading. Higher stresslevels may result in catastrophic failure of the parIn all cases, testing should be performed on thefabricated part to verify satisfactory performanceof the material in each application.

Figure 25 presents limited creep modulus data at100°C (212°F). These plots are not extrapolateddue to the unpredictable effects that heat agingunder stress can have on materials.

790re, °F

re, °C

63565526/5556

4056

7246

160 18014012010001.52

5

10

20

50

100

200

500300 34026022080

Fle

xu

ral M

od

ulu

s, p

si

× 10

3rel®

4

ASTM D 299023°C (73°F)

Time, hr

10000500010005002001005020105210.50.20.11

2

34

68

10

20

3040

6080

100

200

500

1000

2000

5000

10000Applied Stress1.4 MPa (200 psi)3.4 MPa (500 psi)3.8 MPa (550 psi)4.3 MPa (625 psi)4.8 MPa (700 psi)

5.5 MPa (800 psi)5.9 MPa (850 psi)

Cre

ep

Mo

du

lus, M

Pa

Cre

ep

Mo

du

lus, p

si

Extrapolated

ASTM D 2990

23°C (73°F)

Time, hr

100005000200010005002001005020105210.5

Extrapolated

0.20.11

2

34

68

10

20

3040

6080

100

200

200

500

1000

2000

5000

10000

20000

Applied Stress

3.4 MPa (500 psi)

5.5 MPa (800 psi)

8.3 MPa (1200 psi)

9.7 MPa (1400 psi)

11.0 MPa (1600 psi)12.4 MPa (1800 psi)

Cre

ep

Mo

du

lus, M

Pa

Cre

ep

Mo

du

lus, p

si

Figure 22. Tensile Creep Modulus—Hytrel® 5526/5556

Figure 21. Tensile Creep Modulus—Hytrel® 4056

15

ASTM D 2990

23°C (73°F)

Time, hr

1000050001000 20005002001005020105210.50.20.110

20

3040

6080

100

200

300400

600800

1000

2

5

10

20

50

100

Applied Stress

5.5 MPa (800 psi)

8.3 MPa (1200 psi)10.3 MPa (1500 psi)13.1 MPa (1900 psi)

13.8 MPa (2000 psi)

Cre

ep

Mo

du

lus, M

Pa

Extrapolated

Cre

ep

Mo

du

lus, p

si

× 10

3

ASTM D 299023°C (73°F)

Time, hr

1000050001000 20005002001005020105210.50.20.110

20

3040

6080

100

200

300400

600800

1000

2

5

10

20

50

100

Applied Stress5.5 MPa (800 psi)

12.4 MPa (1800 psi)

18.9 MPa (2730 psi)

Cre

ep

Mo

du

lus, M

Pa

Cre

ep

Mo

du

lus, p

si

× 10

3

Extrapolated



16

ASTM D 2990100°C (212°F)

Time, hr

10005002001005020105210.50.20.110

20

30

40

50

60

70

80

90

100110120130140150

200

2000

5000

7246

7246

6356

6356

5556/5526

5.5 MPa (800 psi)

5.5 MPa (800 psi)

5.5 MPa (800 psi)

Applied Stress

8.3 MPa (1200 psi)

8.3 MPa (1200 psi)

20000

10000

Cre

ep

Mo

du

lus, M

Pa

Cre

ep

Mo

du

lus, p

si

Figure 25. Tensile Creep Modulus at 100°C (212°F)—Hytrel®

Compressive CreepCompressive creep results for a load of 6.9 MPa(1000 psi) at 23°C (73°F) and 50°C (122°F) arepresented in Table 4. Creep in compression ismuch less than in tension, as can be seen by comparing the values for compressive creep with thosfor tensile creep shown in the same table. Valuesfor tensile creep were obtained by converting cremodulus data to creep strain with the formula:

Creep strain =stress

creep modulus

1

-e

ep

Table 4Creep Strain

100 hr at 6.9 MPa (1000 psi) Stress

Compressive TensileCreep, % Creep, %

23°C 50°C 23°CType of Hytrel® (73°F) (122°F) (73°F)

4056 5.4 8.9 —

G4074 6.0 11.5 —

5526/5556 0.6 1.3 8.0

6356 0.5 0.7 5.8

7246 0.5 0.5 2.5

7

e

Fatigue ResistanceThe behavior of materials subjected to repeatedcycle loading in terms of flexing, stretching,compressing, or twisting is generally described asfatigue. Such repeated cyclic loading eventuallyconstitutes a permanent mechanical deteriorationand progressive fracture, which can lead to com-plete failure. Fatigue life is defined as the numberof cycles of deformation required to bring about thfailure of the test specimen under a given set ofoscillating conditions.

Flexural Fatigue (ASTM D 671)The ability of a material to resist permanent dete-rioration from cyclic stress is measured in this testby using a fixed cantilever-type testing machinecapable of producing a constant amplitude of forceon the test specimen each cycle. The specimen isheld as a cantilever beam in a vice at one end andbent by a concentrated load applied through a yokfastened to the opposite end. The alternating forceis produced by the unbalanced, variable eccentricmounted on a shaft. A counter is used to record thnumber of cycles along with a cutoff switch to stopthe machine when the specimen fails.

Table 5 lists the fatigue limits of four types ofHytrel®. Sample size and shape, frequency offlexing, ambient temperature, and heat transferall have significant effects on fatigue.

For design purposes, a test simulating actual end-use conditions should be performed to determinethe expected fatigue limit.

Table 5Flex FatigueASTM D 671

Fatigue Limit*

Type of Hytrel® MPa psi

4056 5.2 750

5556 6.9 1000

6356 6.9 1000

7246 11.0 1600

*Samples tested to 2.5 × 106 cycles without failure.

1

e

e

e

Heat Generation and FlexuralFatigue in Compression(ASTM D 623)Because of wide variations in service conditions,no correlation between accelerated test and servicperformance exists. This test helps to estimaterelative service quality of Hytrel®. It may be usedto compare the fatigue characteristics and rate ofheat generation when Hytrel® is subjected todynamic compressive strain.

In this method, which uses the Goodrich Flex-ometer, a definite compressive load is applied toa test specimen through a lever system havinghigh inertia, while imposing on the specimen anadditional high-frequency cyclic compression ofdefinite amplitude. The increase in temperature atthe base of the test specimen is measured.

Table 6 gives data on the temperature rise due tohysteresis after 20 min for two grades of Hytrel®.Temperature rises fairly quickly and then remainsroughly constant for the balance of the test.

Table 6Goodrich Flexometer

ASTM D 6232.54 mm (0.1 in) Stroke, 1.0 MPa (145 psi)

Static Load, 23°C (73°F)

Sample TemperatureAfter 20 min

Type of Hytrel® °C °F

4056 48 118

5556 66 151

Resistance to Flex Cut GrowthThis test gives an estimate of the ability of Hytrel®

to resist crack growth of a pierced specimen whensubjected to bend flexing. Due to the varied natureof operating service condition of a part molded inHytrel®, no correlation exists between these testresults and actual end-use conditions.

Ross Flex (ASTM D 1052)A pierced strip test specimen of 6.35 mm (0.25 in)thick is bent freely over a rod to a 90° angle andthe cut length is measured at frequent intervals todetermine the cut growth rate. The cut is initiatedby a special shape piercing tool.

The test results are reported in Table 7 as thenumber of cycles it took the specimen to grow fivetimes the original pierced length. These results arealso reported in Table 2, Typical Properties ofHytrel®.

8

-

Table 7Resistance to Flex Cut Growth, Ross (Pierced)

ASTM D 1052Cycles to Five Times Cut Growth

Type of Hytrel® 23°C (73°F)

G3548W >1 × 106

G4074, G4078W >1 × 106

G4774, G4778 >1 × 106

G5544 8 × 105

4056 >1 × 106

4069 >1 × 106

4556 >1 × 106

5526, 5556 5 × 105

6356 5 × 105

7246 3 × 104

8238 —

HTR3078 >1 × 106

HTR4275BK 5 × 104

5555HS 1 × 105

HTR5612BK 6 × 105

HTR6108 6 × 105

HTR8068 —HTR8139LV >1 × 106

HTR8171 >1 × 106

HTR8206 —

DeMattia Flex (ASTM D 813)A pierced strip test specimen of 6.35 mm (0.25 in)thick with a circular groove restrained so that itbecomes the outer surface of the bend specimen,with 180° bend, and the cut length is measured atfrequent intervals to determine the cut growth rate

The test results are reported in Table 8 as thenumber of cycles it took for the specimen toreach failure.

Table 8De Mattia Flex Life (Pierced)

ASTM D 813Cycles to Failure

Type of Hytrel® 23°C (73°F)

G3548W 3.6 × 104

G4074, G4078W 3.6 × 104

G4774, G4778 1.6 × 105

G5544 7 × 103

4056 >1 × 106

4069 1.7 × 105

4556 3.6 × 103

5526, 5556 >1 × 106

HTR4275BK 5.4 × 104

HTR5612BK 1.1 × 105

HTR6108 5.4 × 103

1

.

Impact ResistanceThe impact properties of polymeric materials aredirectly related to their overall toughness, whichis defined as the ability of the polymer to absorbapplied energy. Impact resistance is the ability of amaterial to resist breaking under shock loading orthe ability to resist the fracture under stress appliedat high speed.

Most polymers, when subjected to impact loading,seem to fracture in a characteristic fashion. Thecrack is initiated on the polymer surface by theimpact loading. The energy to initiate such a crackis called the crack-initiation energy. If the loadexceeds the crack-initiation energy, the crackcontinues to propagate. A complete failure occurswhen the load exceeds the crack-propagationenergy. Thus, both crack initiation and crackpropagation contribute to the measured impactstrength.

The speed at which the specimen or part is struckwith an object has a significant effect on thebehavior of the polymer under impact loading. Atlow rates of impact, relatively stiff material canstill have good impact strength; while at high ratesof impact, even highly elastomeric material likeHytrel® may exhibit brittle failure at low tempera-tures. All materials have a critical velocity in whichthey behave as glassy, brittle materials.

Impact properties are highly dependent on temperature. Generally, plastics are tougher and exhibitductile modes of failure at temperatures above theirglass transition temperature (T

g), and are brittle well

below their Tg.

A notch in a test specimen, which creates a local-ized stress concentration, or a sharp corner in amolded part drastically lowers impact strength.

Notched Izod Impact (ASTM D 256)The objective of the Izod impact test is to measurethe behavior of a standard notched test specimento a pendulum-type impact load. The specimen isclamped vertically and the swinging pendulum isreleased with the notch on the opposite side. Theresults are expressed in terms of kinetic energyconsumed by the pendulum in order to break thespecimen. The energy required to break a standardspecimen is actually the sum of energies needed todeform it, to initiate its fracture, and to propagatethe fracture across it, and the energy needed tothrow the broken ends of the specimen. Thesetest results are reported in Table 2, pages 6–9, atroom temperature and at –40°C (–40°F).

9

Instrumented Impact(ASTM D 3763)One of the drawbacks of the conventional impacttest method is that it provides only one value, thetotal impact energy; it does not provide data on thtype of fracture (ductile, brittle), dynamic tough-ness, fracture, yield loads or fracture behaviorbased on the geometry of the specimen.

The falling weight instrumented impact testerprovides a complete load and energy history ofspecimen fracture mechanism. Such a systemmonitors and precisely records the entire impactevent, starting from the rest position to initialimpact, plastic bending to fracture initiation,and propagations to complete failure.

Measurement is done by mounting the strain gauginto the striking tup, and an optical device triggersthe microprocessor just before striking the speci-men. The output of the strain gauge records theapplied load variations to the specimen throughouthe entire fracturing process. A complete load-timhistory (fracturing) of the entire specimen is ob-tained. The apparent total energy absorbed by thespecimen is calculated and plotted against time.

Figures 26–30 show drop-weight-impact resultsfor representative grades of Hytrel®. The plots showenergy dissipated in rupturing the sample, and themaximum force experienced by the tup as itpunches through the sample.

ASTM D 376315.9 mm (0.63 in) spherical tup

31.8 mm (1.25 in) diameter support

Temperature, °F

Temperature, °C100806040200–20–40

10

10

20

30

40

50

5526/5556

4056

60

70

0

10

20

30

40

50

60

70

80

90

1801401006020–20

En

erg

y, J

En

erg

y, ft

⋅lb

Figure 26. Drop Weight Impact Failure Energyversus Temperature—Hytrel®

2



Temperature, °F

Temperature, °C100806040200–20–40

0

10

20

30

40

50

7246

6356

60

90

70

0

10

20

30

40

50

60

70

80

90

100

110

ductile failure

brittle failure

1801401006020–20

En

erg

y, J

80

En

erg

y, ft

⋅lb



Temperature, °F

Temperature, °C100806040200–20–40

0

1

2

3

4

5

5526/5556

4056

6

7

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1801401006020–20

Lo

ad

, N

× 1

03

Lo

ad

, lb

× 1

03

e

e

te

Figure 27. Drop Weight Impact Failure Energyversus Temperature—Hytrel®

Figure 28. Drop Weight Impact Failure Loadversus Temperature—Hytrel®

0



Temperature, °F

Temperature, °C100806040200–20–40

0

1

2

3

4

57246

6356

6

8

7

0

0.2ductile failure

brittle failure

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.81801401006020–20

Lo

ad

, N

× 1

03

Lo

ad

, lb

× 1

03

ASTM D 3763Drop Weight Impact Tests

15.9 mm (0.63 in) spherical tup31.8 mm (1.25 in) diameter support

Temperature, °F

Temperature, °C100–10–40 –30 –20–50–60

0

10

20

30

40

50

60

70

80

90

100

6356

7246

0 20 40–20–40–60

Bri

ttle

Failu

res, %

Figure 29. Drop Weight Impact Failure Loadversus Temperature—Hytrel®

Figure 30. Percentage of Brittle Failuresversus Temperature—Hytrel®

2

Brittleness Temperature (ISO 974)This test method establishes the temperature atwhich 50% of the specimens tested fail whensubjected to the test conditions. The test evaluateslong-term effects such as crystallization. Thermo-plastic elastomers are used in many applicationsrequiring low-temperature flexing with or withoutimpact. Data obtained by this test may be used topredict the behavior of elastomeric materials at lowtemperatures only in applications in which theconditions of deformation are similar to the testconditions. Table 9 lists the brittleness tempera-tures for representative grades of Hytrel®.

Table 9Brittleness Temperature

ASTM 746

Brittleness Temperature


G3548W –60 –76G4074, G4078W –66 –87G4774 –56 –67G4778 –65 –85G5544 –60 –76

4056 <–100 <–1484069 <–105 <–1574556 <–105 <–1575526 <–70 <–965556 <–100 <–1486356, 7246 <–70 <–948238 –92 –134

3078 <–105 <–157HTR4275BK <–100 <–1485555HS <–70 <–94HTR5612BK <–100 <–148HTR6108 –98 –144HTR8068 –48 –51HTR8139LV <–100 <–148HTR8171 –63 –81HTR8206 –67 –88

1

-

Thermal PropertiesThermal Conductivity andSpecific HeatThermal conductivity data are shown in Table 10,and coefficients of linear thermal expansion in theflow direction measured by Thermo MechanicalAnalysis (TMA) are presented in Table 11. Figure31 is a plot of specific heat versus temperature forfour types of Hytrel®.

Table 10Thermal Conductivity

Thermal Conductivity (k)

Type of Hytrel® J/sec·m·°C Btu/hr·ft·°F

G4074 0.165 0.095

4056 0.190 0.110

5526/5556 0.156 0.090

6356 0.152 0.088

7246 0.149 0.086

Table 11Coefficient of Linear Thermal Expansion,

SI Units

Temperature CoefficientType of Hytrel® Range, °C mm/mm/°C × 10–5

4056 –40–23 1523–55 1355–100 11

5526/5556 –50–23 1823–55 2055–120 21

7246 –40–23 1323–55 1755–120 11

2

Dynamic Properties(ASTM D 4065–95)These measurements are made by Dynamic Me-chanical Analysis (DMA) technique. The measurements are made at varying temperatures. Thedynamic modulus represented in Figure 32 repre-sents the load-bearing capability or stiffness of theplastic materials, while the tan ∂ or the dampingfactor represented in Figure 33 represents the glasstransition temperature, below which the plasticgoes into a glassy state. These data are useful inthe design of parts used in dynamic applicationssuch as motor mounts and couplings.

Temperature, °F

Temperature, °C–40 –20 0 20 40 60 80 100 120

0

0.1

0

1

2

63567246

5526/55564056

100 140 180 220 2606020–20

Sp

ecif

ic H

eat,

kJ/k

g⋅K

Sp

ecif

ic H

eat,

Btu

/lb⋅°F

0.2

0.3

0.4

0.5

0.6

Figure 31. Specific Heat versus Temperature

2

ASTM D 4065–95

Temperature, °F

Temperature, °C200 220

1.510

20

3040

6080

100

200

400

600800

1000

2000

3000

4000

6356

4056

5556/5526

7246

–140 –100 –60 –20 20 60 100 140 180 220 260 300 340 380 420D

yn

am

ic E

lasti

c M

od

ulu

s, M

Pa

Dyn

am

ic E

lasti

c M

od

ulu

s, p

si

× 10

3

180160140120100806040200–20–40–60–80–100

2

5

10

20

50

100

200

500

ASTM D 4065–95

Temperature, °F

Temperature, °C200 220

0.01

0.02

0.03

0.04

0.050.06

0.08

0.1

0.2

0.3

6356

4056

5556/5526

7246

–140 –100 –60 –20 20 60 100 140 180 220 260 300 340 380 420

Tan

δ

180160140120100806040200–20–40–60–80–100

Figure 32. Dynamic Modulus versus Temperature (at 1 Hz frequency)

Figure 33. Damping Factor versus Temperature (at 1 Hz frequency)

23

r

s

Electrical PropertiesElectrical measurements show that Hytrel® engi-neering thermoplastic elastomers are suitable folow-voltage applications. High-mechanicalstrength, coupled with excellent resistance to oilsolvents, and chemicals, also makes Hytrel®

suitable for many jacketing applications. Theproperties shown in Table 12 were measured on

Figure 34. Dielectric Strength vs. Thickness—Hytrel® 5

2000

1800

1600

1400

1200

1000

800

600

400

200

0 10 20 30 4

0

mils

mm 0.25 0.50 0.75 1

Sample

Die

lectr

ic S

tren

gth

,vo

lts/m

il

ASTM

TabElectrical Properties at Roo

ASTM HProperty Test Method

Volume Resistivity, Ω⋅cm D 257 8

Dielectric Strength, kV/mm (V/mil) D 149 16

Dielectric Constant D 1500.1 kHz1 kHz1000 kHz

Dissipation Factor D 1500.1 kHz1 kHz1000 kHz

2

,

injection molded plaques with the dimensions76 × 127 × 1.9 mm (3 × 5 × 0.075 in).

As with all polymeric materials, the dielectricstrength in kV/mm (V/mil) varies depending onthe sample thickness used in the measurement.Figure 34 shows this relationship for Hytrel® 5556.The same relationship applies to all other grades.

556

0 50 60 70 80

.0

Thickness

Die

lectr

ic S

tren

gth

,KV

/mm

1.25 1.50 1.75 2.0

10

20

30

40

50

60

70

80

D 149

le 12m Temperature and 50% RH

ytrel® Hytrel® Hytrel® Hytrel® Hytrel®

4056 5526 5556 6356 7246

.2 × 1010 1.2 × 1011 1.1 × 1011 9.7 × 1011 1.8 × 1012

.1 (410) 17.3 (440) 15.7 (400) 16.1 (410) 18.1 (450)

5.2 4.5 4.6 4.4 4.05.1 4.5 4.5 4.2 3.94.6 4.2 4.1 3.7 3.5

0.005 0.006 0.006 0.018 0.0160.008 0.009 0.009 0.02 0.0190.06 0.04 0.04 0.04 0.03

4

Abrasion and WearFrictionMeasurements of frictional properties may be maon a film or sheeting specimen when sliding overitself or over another substance. The coefficientsfriction are related to the slip properties of plastic

The coefficient of friction—the ratio of the fric-tional force to the force, usually gravitational,acting perpendicular to the two surfaces in contaThis coefficient is a measure of the relative diffi-culty with which the surface of one material willslide over an adjoining surface of itself, or ofanother material. The static or starting coefficientof friction is related to the force measured to begmovement of the surfaces relative to each other.The kinetic or dynamic or sliding coefficient offriction is related to the force measured in sustaining this movement.

Values for the coefficient of friction of Hytrel®

measured by two different methods are shownin Table 13. As can be seen from the data, testmethods have a great influence on the results;therefore, it is difficult to predict frictional forcesunless testing is performed under conditions thatsimulate the end use.

Wear (ASTM D 1044, Modified)Measurement of wear is determined by the weighloss and/or thickness loss on the test specimenunder the force of abrasive wheel held underspecified load against the test specimen mounteda rotating turntable.

Hytrel® engineering thermoplastic elastomer hasexcellent wear properties in many applications.Table 14 lists results from Taber and NBS abrasiotests. For information on wear in bearing applica-tions, see “Bearings and Seals,” page 51.

2

de

ofs.

ct.

in

-

t

on

n

Table 13Coefficient of Friction

Hytrel® on Steel Hytrel® on SteelMoving Sled— Thrust Washer—ASTM D 1894 ASTM D 3702

Type of Hytrel® Static Dynamic

4056 — 0.82

5526/5556 0.32 0.44

6356 0.26 0.31

7246 0.22 0.28

Table 14Abrasion Resistance

ASTM D 1044mg/1000 rev

Taber Abrasion

CS-17 H-18Type of Hytrel® Wheel Wheel

General Purpose

G3548L 30 310

G4074 9 193

G4078W 20 260

G4774 13 168

G4778 12 162

G5544 9 116

High Performance

4056 3 100

4069 15 80

4556 3 72

5526 7 70

5556 6 64

6356 7 77

7246 13 47

8238 9 20

Specialty

3078 2 90

HTR4275BK 20 227

5555HS — 112

HTR5612BK 38 186

HTR6108 9 116

HTR8068 25 —

HTR8139LV 4 65

5

Effect of EnvironmentMoisture Pickup and DryingHytrel® granules are supplied in moisture-resistantpackaging. However, when exposed to air, thegranules pick up moisture. Moisture levels above0.10% may seriously impair the processing, causinhighly variable melt pressure, varying extruderoutput, degradation of the resin, and, possibly,bubbles in the melt as it exits the die.

At temperatures above the melting point, excessivmoisture causes hydrolytic degradation of the polymer. Such degradation results in poor physicalproperties and brittleness, particularly at lowtemperatures.

Equilibrium moisture levels depend on the gradeand are shown in Table 15 (ASTM D 570 testmethod). The rate of moisture absorption forHytrel® 5556 is shown inFigure 35.

Table 15Equilibrium Moisture Levels of Hytrel®

Equilibrium MoistureType of Hytrel® Level, % After 24 hr

General Purpose

G3548W 5.0G4074 2.1G4078W 3.0G4774, G4778 2.5G5544 1.5

High Performance

4056 0.64069 0.74556 0.65526 0.55556 0.56356 0.37246 0.38238 0.3

Specialty

3078 3.0HTR4275BK 0.35555HS 0.7HTR5612BK 0.4HTR6108 0.2HTR8068 1.9HTR8139LV 0.7

26

g

e-

1.00.8

0.6

0.4

0.2

0.10.08

0.06

0.04

0.02

0.010.1 0.2 0.4 0.6 1 2 4 6 10

100%RH

50% RH

Time, hr

Mo

istu

re G

ain

, w

t%

ASTM D 570

Hytrel® thermoplastic elastomer must be dried priorto processing, which is critical to making qualityparts that will give good service performance.

Also, in the case of critical extrusion operations,such as vacuum calibration of tubes to smalltolerances, it has been found that extruder outputmay fluctuate slightly with changing moisturelevels and temperature of the granules in thehopper. For this reason, drying of Hytrel® granulesin a desiccant (dehumidifying) drier underconditions of fixed temperature and time isrecommended.

Drying time and temperature will depend on theinitial moisture level in the material, as well asthe type of drier or oven used. However, generalguidelines for drying Hytrel®, which are based onlaboratory and industrial experience, are shown inFigure 36.

Figure 35. Moisture Absorption at AmbientTemperature—Hytrel® 5556

ed

Shrinkage and Post-MoldingShrinkageShrinkage of Hytrel® in injection molding dependson factors such as:• Grade of Hytrel®

• Molding conditions (injection pressure, screwforward time [SFT], mold temperature, etc.)

• Part geometry and thickness• Mold design, runner, sprue system, gate size

Shrinkage is measured at room temperature and 50% RH on a standard test specimen 24 hr aftermolding. Shrinkage increases significantly aftermolding, but tends to reach a maximum after 24 hThis section provides information on how shrink-age varies with these parameters.

Unless stated, these shrinkage values were obtainon test specimens of 3.2 mm (0.125 in) thicknessmolded at standard conditions:• Mold temperature: 45°C (113°F)• Injection pressure: 70 MPa (10,150 psi)• SFT: optimum

Table 16 gives the nominal shrinkage values forvarious grades of Hytrel®, obtained under thesestandard conditions.

Figure 36. Recommended Guidelines for DryingHytrel® (Drying Time versus Temperature)

0

150

140

130

120

110

100

90

Tem

pera

ture

, °C

Time, hr

1 32 4 5 6 7 8

Max. (low melting point grades)

Max. (most grades)

300

275

250

225

200

Tem

pera

ture

, °F

2

Table 16Shrinkage of Hytrel®

ASTM D 955Measured on standard test specimen, in flow

direction 3.2 mm (0.125 in) thick,molded at recommended conditions

Type of Hytrel® Shrinkage, %

General Purpose

G3548W 0.5

G4074 0.8

G4078W 0.8

G4774, G4778 1.4

G5544 1.6

High-Performance

4056 0.5

4069 0.8

4556 1.1

5526 1.4

5556 1.4

6356 1.5

7246 1.6

8238 1.6

Specialty

5555HS 1.4

Figures 37–39 show the influences on shrinkage ofdifferent injection molding parameters. The dataprovides a general guideline to help in predictingshrinkage. The values should be added to orsubtracted from the nominal shrinkages given inTable 16 in order to get a first approximation of thefinal shrinkage. The shrinkage evaluation forprecision parts should be made on a prototypetool.

at

r.

7

g

0.20

0.15

0.10

0.05

0.00

–0.05

–0.10

–0.15

–0.2025 5030 60 70

Mold Temperature, °C

ASTM D 955

Mold Temperature, °F

Ab

so

lute

Ch

an

ge o

f S

hri

nkag

e, %

9080 100

65

At recommendedmelt temperatureOptimum SFTInj. press 70 MPa(10.2 kpsi)

35 40 45 55 75

110 120 130 140 150 160

0.8

0.6

0.4

0.2

0.0

–0.2

–0.40 2 4 6 8 10

Part Thickness, mm

ASTM D 955

Part Thickness, in

Ab

so

lute

Ch

an

ge

of

Sh

rin

ka

ge

, %

All processing parameters are standard.

0.500.300.200.10 0.40

12 14

Figure 38. Influence of Part Thickness on Shrinkagein Length

Figure 37. Influence of Mold Temperature onShrinkage

2

0.4

0.3

0.2

0.1

0.0

–0.1

–0.2

–0.3

–0.440 50 7060 80 100

Injection Pressure, MPa

ASTM D 955

Injection Pressure, psi

Ab

so

lute

Ch

an

ge o

f S

hri

nkag

e, %

11,00090007000 13,000

90

At recommendedmelt temperatureOptimum SFTMold temperature45°C (113°F)

For example, an approximation of the shrinkage ofa part made of Hytrel® can be done as follows:

Nominal shrinkage ofHytrel® 5526: 1.40% (Table 16)

Part is molded using a64°C mold temperature(versus 45°C): 0.08% (Figure 37)

Part has a thicknessof 2 mm (versus 3.2 mm): –0.13% (Figure 38)

Part is molded using aninjection pressure of900 bar (versus 700 bar): –0.15% (Figure 39)

Total shrinkage isapproximately: 1.20%

AnnealingPost-molding shrinkage is measured after annealinparts at 120°C (248°F) for 4 hr. Even for the stifferand more crystalline grades, the absolute value ofpost-molding shrinkage for parts molded at recom-mended conditions is low (less than 0.1%).

Figure 39. Influence of Injection Pressure onShrinkage

8

e

.

ey

il

-

t

e

s

nd

.

Dimensional TolerancesAllowable variations in the dimensions of aninjection molded part are called the tolerances ofthe part and greatly affect the cost of manufactureA realistic view of the purchased cost of toleranceoften helps avoid high manufacturing charges witno detriment to the performance of the part.

Regardless of the economics, it may be unreasonable to specify close production tolerances on a pwhen it is designed to operate within a wide rangof environmental conditions. Dimensional changedue to temperature variations alone can be threefour times as great as the specified tolerances. Ain many applications such as bearings and gearsclose tolerances with plastics are not as vital aswith metals, because of the resiliency of plastics.

Some general suggestions are:• The design for a part should indicate conditions

under which the dimensions shown must be he(temperature, humidity, etc.).

• On a drawing, overall tolerances for a part shoube shown in mm/mm (in/in), not in fixed values.A title block should read, “All decimal dimen-sions ±0.00X mm/mm (±0.00X in/in),not ±0.00X mm (±0.00X in), unless otherwisespecified.”

• The number of critical dimensions per part shoube as low as possible. A part with several criticadimensions will naturally be more difficult tomold than a part with few critical dimensions.

• Tight tolerances should not be put on dimensionacross a parting line or on sections formed bymovable cores or sliding cams.

• Where compromises in tolerances could beacceptable from a performance standpoint, thetolerances in question should be discussed withthe molder in view of possible economics.

Factors that must be considered when establishintolerances for injection-molded parts are:• Thermal expansion and contraction• Nature of the surroundings• Processing conditions and part molding shrinka• Molding tolerances

Multicavity molds will result in a cost savingsbut can increase tolerance limits from 1–5% percavity. Therefore, a tolerance that would be specfied for a single-cavity mold would have to beincreased to allow for production variables.

2

.sh

-art

e

tolso,,

ld

ld

ldl

s

g

ge

i-

Whether or not the part can withstand this variancwill depend on the function of the part and shouldalways be considered.

The ability to maintain minimum tolerances isdependent on part design, the number of cavities,mold design, the injection molding system used,molding conditions, and the ability of the molder.Only through an optimization of all of these vari-ables can the tightest of tolerances be maintained

The Molding OperationIn the injection molding of thermoplastics, parts armade by injecting molten resin into a shaped cavitthat has been built into an appropriate mold. In thecavity, the molten resin is held under pressure untit solidifies. Simultaneously, it is shrinking due tothe change from liquid to solid and thermal contraction. The solid part thus formed reproduces thecavity shape in detail and is removed from themold. Ejector pins or rings in the mold free the parfrom it. Molten resin is produced by melting rawmaterial in the cylinder of the molding machinewhile the part just formed is cooling in the mold.

This overall procedure is repeated on a rigidlymaintained cycle until the required number ofparts is produced. Cycle time is determined largelyby the rate at which heat can be removed from thecooling part. This rate is approximately propor-tional to the wall thickness of the part and is slowbecause of low thermal conductivity. For thisreason, parts should be designed with walls asthin as is consistent with design requirementsand ease of fabrication.

The configuration and dimensions of the moldingtool depend on the size and shape of the part to bproduced as well as the number of cavities to beemployed in production. At the same time, molddimensions must be governed by the dimensionsof standard molding machines. Mold costs oftencan be reduced by the use of standard mold frameinto which the part-forming cavities are fitted.

The molding process and the injection mold offerthe designer an opportunity to add both value andfunction to the design. A close relationship betweethe functional designer and the molder is suggesteto optimize these opportunities.

ConcentratesHytrel® resins should be protected from excessivetemperature, UV light, and hot, moist environment

9

.

Table 17Concentrates*

(in a base of Hytrel® 4056)

Grade Description Characteristics and Typical Uses

Hytrel® 10MS Hydrolytic stabilizer concentrate. For blending with other grades of Hytrel® to improve serviceabilityin hot, moist environments. Recommended letdown ratio is 9:1.

Hytrel® 20UV UV light stabilizer concentrate. Used for protection of light-colored parts against UV degradation.Recommended letdown ratio is 25:1 or less.

Hytrel® 30HS Heat stabilizer concentrate. For blending with other grades of Hytrel® to retard thermal oxidativedegradation and extend useful life at elevated temperatures.Recommended letdown ratio is between 16:1 and 40:1, usuallyabout 20:1.

Hytrel® 40CB Concentrate of a fine Hytrel® must be protected against degradation from exposure toparticle size carbon black. UV light when used outdoors or when exposed to sunlight. Hytrel®

40CB provides the most effective protection. Recommended let-down ratio for direct outdoor exposure is 7:1.

Hytrel® 51FR Flame retardant concentrates. 51FR and 52FR are concentrates containing 67% by weight ofHytrel® 52FR a brominated flame retardant and antimony oxide synergist

dispersed in Hytrel® 4056 and 5556 respectively. A let-down ratioof 10:1 will yield oxygen indices of 21–30 (ASTM D2863) and aUL rating of V-2.

*All concentrates are supplied in pellet form. They can be dry-blended with pellets of unmodified grades, then melt-mixedin the screw of an extruder or injection molding machine.

Hytrel® 10MS

Blending with Hytrel® 10MS concentrate is sug-gested for such products as tubing, hose, cablejackets, seals, packings, gaskets, and moldedappliance parts, which require a greater degree

TabAddition of Hytrel® 10MS I

Property 40Parts Hytrel® 10MS/Parts Regular Hytrel® 0/100Final Concentration of PCD, % (by weight) 0Stress/Strain Properties (Injection-Molded Slabs)OriginalTensile Strength, MPa 25.5

(psi) (3700)Elongation at Break, % 450After Immersion in Water at 70°C (158°F)

1 MonthTensile Strength, % of Original 66Elongation, % of Original 107

3 MonthsTensile Strength, % of Original 55Elongation, % of Original 100



12 MonthsTensile Strength, % of Original NotElongation, % of Original Tested

of moisture resistance than is available with theregular types of Hytrel® alone.

Hytrel® 10MS is not color-stable. It is not recom-mended for use in light-colored or painted articles

le 18mproves Hydrolytic Stability

Type of Hytrel®

D 55D 63D 72D10/90 0/100 10/90 0/100 10/90 0/100 10/90

2 0 2 0 2 0 2

30.2 37.9 40.5 39.3 34.3 38.8 37.4(4375) (5500) (5875) (5700) (4975) (5625) (5425)

450 450 440 320 360 330 350

72 Not Not 86 95 100 10099 Tested Tested 103 100 118 101

70 Not Not 72 99 63 9797 Tested Tested 105 101 39 92

64 51 82 15 92 18 93106 71 96 2 104 1 92

65 Not Not Failed 78 Failed 79101 Tested Tested 90 86

Not 43 76 — Not — NotTested 69 82 — Tested — Tested

(continued)30

Table 18Addition of Hytrel® 10MS Improves Hydrolytic Stability (continued)

Type of Hytrel®

Property 40D 55D 63D 72DParts Hytrel® 10MS/Parts Regular Hytrel® 0/100 10/90 0/100 10/90 0/100 10/90 0/100 10/90Final Concentration of PCD, % (by weight) 0 2 0 2 0 2 0 2Stress/Strain Properties (Injection-Molded Slabs)

After Immersion in Water at 100°C (212°F)2 Weeks

Tensile Strength, % of Original Not Not Not Not 39 92 41 94Elongation, % of Original Tested Tested Tested Tested 3 90 2 101

1 MonthTensile Strength, % of Original 21 61 47 105 Failed 67 Failed 74Elongation, % of Original 11 104 13 104 74 73

3 MonthsTensile Strength, % of Original Failed in 47 Failed 63 — Failed — FailedElongation, % of Original 35–38 Days 108 90 — —

6 MonthsTensile Strength, % of Original — 14 — 62 — — — —Elongation, % of Original — 6 — 99 — — — —

Hytrel® 20UV

Hytrel® 20UV concentrate or other protection fromUV light should be incorporated in all products ofHytrel® that are used outdoors or exposed to direcsunlight via windows or reflective surfaces. In verythin parts, especially those less than 0.55 mm(0.02 in) thick, degradation due to UV radiation

TabHytrel® 20UV Extends S

During Weather-

Parts Hytrel® 5556 100Parts Hytrel® 20UV —Letdown Ratioa —

Originalb

Tensile Strength at Break,c MPa (psi) 50.8 (7Elongationc at Break, % 720

Exposure Time, hr 48

Tensile Strength at Break, MPa (psi)Elongation at Break, %

Exposure Time, hr —Tensile Strength at Break, MPa (psi) —Elongation at Break, % —

a Pellets dried, extrusion blended, pelletized, and dried again.b Compression molded film, 0.275 mm (0.011 in) thick.c Tensile and elongation measurements were carried out using

3

t

can be caused by exposure to incandescent orfluorescent lighting.

Hytrel® 20UV blended with Hytrel® may discolorwith time. Where color is important, the use ofpigments in combination with Hytrel® 20UV isrecommended.

le 19erviceability of Hytrel®

ometer Exposure

100 1002.5 4

40:1 25:1

375) 53.4 (7750) 41.6 (6025)750 730

300 300

16.8 (2425) 19.8 (2875)410 460

658 1000

11.2 (1625) 10.8 (1575)30 50

a head speed of 50 mm/min (2 in/min).

1

Hytrel® 30HS

Addition of Hytrel® 30HS improves aging/thermalstability. Hytrel® 5555HS is a specialty gradecontaining a thermal stabilizer package. Specialprecautions should be taken to make sure thatthe concentrate and Hytrel® resin are dry beforeprocessing.

Hytrel® 30HS is not color-stable. It is not recom-mended for use in light colored or painted articles

Time, week

0

10

20

40

60

80

100

5555HS

30

50

70

90

110

120

Rete

nti

on

of

Elo

ng

ati

on

at

Bre

ak, %

0 2 4 6 8 10 12 14 16 18 20 22 24

5556

5556 with 30HS

Time, day

0

20

40

60

80

100

7246 with 30HS

50% relative retention

50% absolute retention

Rete

nti

on

of

Elo

ng

ati

on

at

Bre

ak, %

0 2 4 6 8 10 12 14 16 18 20 22

7246

Failed priorto next test

Figure 41. Comparison of Hytrel® 7246 with Hytrel®

7246 containing Hytrel® 30HS—Oven Aging at 177°C (351°F)

Figure 40. Comparison of Hytrel® 5556 and Hytrel®

5556 Containing Hytrel® 30HS withHytrel® 5555HS—Oven Aging at 121°C (250°F)

3

.

Time, week

0

20

40

60

80

100

4056 with 30HS

G4074

G4074 with 30HS

Rete

nti

on

of

Elo

ng

ati

on

at

Bre

ak, %

0 2 6 10 14 18 22 262420161284

4056Samples failed priorto seven-week test

Figure 42. Comparison of Hytrel® 4056 and Hytrel®

G4074 containing Hytrel® 30HS—Oven Aging at 121°C (250°F)

Notes: All test specimens used in the oven aging were“Die C” dumbbells cut from injection molded slabs76 mm × 127 mm × 9.5 mm (3 in × 5 in × 0.075 in).Tests were made using an Instron Tensile Testeraccording to ASTM D 638-82 at 50 mm/min (2 in/min) for Hytrel® 5555HS, Hytrel® 5556, and Hytrel®7246, and at 500 mm/min (20 in/min) for Hytrel®4056 and Hytrel® G4074. A letdown ratio of 20:1was used for all samples. The figures present datafor Hytrel® 30HS. Colorants or additives of any kindor processing conditions may alter some or all ofthese properties. The data listed here fall within thenormal range of product properties, but theyshould not be used to establish specification limitsor used alone as the basis of design.

2

Hytrel® 40CB

Hytrel® 40CB concentrate or other protection fromUV light should be incorporated in all products ofHytrel® that are used outdoors or exposed to diresunlight via windows or reflective surfaces.

TabEffect of Level of Carbon Black on 2.5 mm

ConcentrateLetdown Ratio

(Hytrel® 5556/Hytrel® 40CB) —Total Carbon Black, % 0

Originalb

Tensile Strength at Break, MPa (psi) 31.4 (4Elongation at Break, % 430

Exposure Time, hr 50Tensile Strength at Break, MPa (psi)Elongation at Break, %

Exposure Time, hrTensile Strength at Break, MPa (psi)Elongation at Break, %



a Pellets of Hytrel® 40CB and Hytrel® 5556 were tumble blendemade by compression molding; Weather-ometer Carbon Arc

b Properties determined at a crosshead speed of 50.8 mm/min

TabEffect of Level of Carbon Black on 2.5 mm

ConcentrateLetdown Ratio

(Hytrel® 5556/Hytrel® 40CB) —Total Carbon Black, % 0

Originalb

Tensile Strength at Break, MPa (psi) 31.4 (4Elongation at Break, % 430

Exposure Time, month 3Tensile Strength at Break, MPa (psi)Elongation at Break, %

Exposure Time, monthTensile Strength at Break, MPa (psi)Elongation at Break, %

Exposure Time, monthTensile Strength at Break, MPa (psi)Elongation at Break, %

a Pellets of Hytrel® 40CB and Hytrel® 5556 were tumble blendemade by compression molding; outdoor aging in Florida, 5°S

b Properties determined at a crosshead speed of 50.8 mm/min

3

ct

Also very thin parts, especially those less than0.55 mm (0.02 in) thick, should be protected asdegradation due to UV radiation can be caused byexposure to incandescent or fluorescent lighting.

le 20 (0.1″) Films of Hytrel® after Weatheringa

Hytrel® 5556

16:1 7:11.47 3.13

550) 36.4 (5275) 38.8 (5625)535 535

50 5034.8 (5050) 36.6 (5300)

700 725

150 15034.2 (4975) 33.8 (4900)

605 710

600 60016.8 (2450) 27.0 (3925)

335 540

1000 100014.4 (2075) 15.6 (2250)

130 235

d and extruder melt blended prior to film preparation; film was.(2 in/min).

le 21 (0.1″) Films of Hytrel® Exposed in Floridaa

Hytrel® 5556

16:1 7:11.47 3.13

550) 36.4 (5275) 38.8 (5625)535 535

3 326.0 (3775) 30.4 (4400)

565 680

6 621.6 (3125) 25.2 (3650)

485 550

9 919.4 (2800) 23.0 (3350)

380 455

d and extruder melt blended prior to film preparation; film wasouth.(2 in/min).

3

y

Hytrel® 51FR and 52FR Flame RetardantConcentrates

Flame RetardancyTables 22 and 23 summarize oxygen index when51FR or 52FR is blended into Hytrel® 4056,Hytrel® 5556, Hytrel® 7246 and Hytrel® 8238.Tensile properties are also shown. A let-down ratiof 10:1 (i.e., 10 parts Hytrel® to 1 part flameretardant concentrate) is required to attain anoxygen index of 21–30).

Heat Aging51FR is recommended for the use in softer Hytrel®

resins with hardness <55D. Hytrel® resins contain-ing 51FR with hardness <55D, show very goodretention of melt flow after heat aging at 100°C(see Table 24), however, incorporation of 5lFRinto Hytrel® resins with hardness ≥55D gave poordispersion. 52FR is recommended for the use instiffer Hytrel® resins with hardness ≥55D.

Incorporation of 52FR in the Hytrel® resins withhardness ≥55D improves the dispersion (see Table25) with good retention of tensile properties andmelt flow after prolonged aging; however, incorporation of 52FR in Hytrel® resins with hardness<55D, increased the stiffness and hardness of theblend noticeably. Incorporation of 5lFR and 52FRin the Hytrel® resins shows excellent color stabilityof the blends after heat aging.

ProcessingTrials at melt temperatures tip to 232°C (450°F)have shown that 51 FR and 52FR are non-corrosito nitrided and heat-hardened screws. When operting above this temperature or when employinglong equipment residence times, orrosion-resistanequipment (e.g., chrome plating on screws) shoulbe considered.

Additional processing information is containedin bulletin “Rheology and Handling,” which isavailable from your local Engineering Polymerssales representative.

1 Numerical values measured by ASTM D 635, D 2863 or UL-94 arenot intended to reflect hazards presented by this or any other mateunder actual fire conditions.

3

o

-

vea-

td

Safety During ProcessingDuring processing, several precautions should betaken.• The Hytrel® flame retardant concentrates may

form gaseous decomposition products if pro-cessed wet or if overheated or held at processingtemperatures longer than 10 minutes.

• If extensive decomposition of 51FR and/or 52FRoccurs, shut off heat and purge machine withpolyethylene.

Combustion: No test results available on combus-tion products of 51FR/52FR alone, as well as afterlet down.

Waste DisposalThe Hytrel® flame retardant may be disposed of bylandfill provided the method is in compliance withfederal, state and local regulations. Leachate testsshow that the antimony trioxide is well encapsu-lated. Using the EP toxicity text (Fed. Reg. May 19,1980) the arsenic concentration was 0.005 mg/L(arsenic is found as an impurity in most antimonycompounds compared to the EPA standard of5 mg/L maximum. Antimony was well below thislevel at 2.3 mg/L; antimony is not regulated byEPA.

ToxicitySome operations such as machining may producedust from 51FR and 52FR. Therefore, toxicity ofthe ingredients may be of importance. Inhalation ofdust should be avoided. Antimony trioxide (Sb

2O

3),

although not highly toxic in acute tests, has chronictoxicity potential.

Exposure to antimony trioxide dust should be keptbelow 0.5 mg/m3. (ACGIH intended change.)

In a chronic inhalation study sponsored byASARCO Inc., rats exposed to 4.2 mg/m3 Sb

2O

3dust for one year subsequently developed lungtumors, while rats receiving 1.6 mg/m3 and controlsshowed no tumors. The Sponsor informed EPA ofthese results under Section 8(e). In another study bNIOSH (reported in a letter to customers of theHarshaw Chemical Co., 8-29-80), rats exposed to50 mg/m3 Sb

2O

3 (no other concentrations tested)

deve-loped lung tumors also after a one-yearexposure.

Hytrel® has an oral approximate lethal dose (ALD)greater than 25 g/kg of body weight in rats. Normalprecautions should be taken to avoid undue expo-sure during handling.

rial

4

Table 23Blends of 52FR in Hytrel® 4056, 5556, 7246, and 8238 (Injection Molded Test Pieces)

Polymer Hytrel® 4056 Hytrel® 5556 Hytrel® 7246 Hytrel® 8238

FR Concentrate — 52FR 52FR — 52FR 52FR — 52FR 52FR — 52FR 52FRLetdown — 12:1 10:1 — 12:1 10:1 — 12:1 10:1 — 12:1 10:1% FR Concentrate 0 5.2 6.1 0 5.2 6.1 0 5.2 6.1 0 5.2 6.1Carrier Type — 5556 5556 — 5556 5556 — 5556 5556 — 5556 5556

Oxygen Indexa (ASTM D 2863)

Flex Bars (0.125") % 19.1 26.0 25.9 20.0 24.3 25.2 20.6 26.3 23.3 21.5 21.9 20.1

Vertical Burn (ASTM D 3801)

Thickness 3.06 mm (1/8") HB V-2 V-2 HB V-2b V-2 HB V-2 V-2b HB V-2 V-21.57 mm (1/16") HB V-2 V-2 HB V-2b V-2 HB V-2 V-2 HB V-2 V-20.08 mm (1/32") HB V-2 V-2 HB V-2 V-2 HB V-2 V-2 HB V-2 V-2

Original Physical Properties

Hardness Durometer D (ASTM D2240) 43 52 50 58 60 58 71 72 72 80 75 72Tensile Strength, MPa (ASTM D 638) 23 20 20 31 27 30 37 27 31 39 31 33Elongation at Break, % (ASTM D 638) 551 625 618 482 470 514 381 287 326 295 252 285Flex Modulus, MPa (ASTM D 790) 81 155 164 212 269 280 680 746 761 1180 1586 1500Melt Flow g/10 min. (ASTM D 1238) 5.15 0.45 —c 7.8 10.21 8.62 13.0 14.1 15.8 21 20 20Condition, at °C and 2.16 Kg load 190 190 190 220 220 220 240 240 240 240 240 240

a Numerical Values measured by D 2863 are not intended to reflect hazards presented by this or any other material underactual fire conditions.

b Ret. UL Listing Card, Guide QMQS2, File No. E63766. (This listing card also includes use of 52FR in Hytrel® 5555HS up to aminimum thickness of 1.52 mm giving UL-94 rating of V-2.)

c No flow (with 52FR addition to Hytrel® 4056 the melt flow at 190°C was very low/or the melt did not flow at all due to theHytrel® 5556 base in 52FR with higher melting characteristics)

Note: 52FR not recommended for Hytrel® resins with Durometer hardness of <55D.—see *—higher hardness In Hytrel® 4056 containing 52FR—higher stiffness In Hytrel® 4056 containing 52FR

Table 22Blends of 51FR in Hytrel® 4056, 5556, 7246, and 8238 (Injection Molded Test Pieces)

Polymer Hytrel® 4056 Hytrel® 5556 Hytrel® 7246 Hytrel® 8238

FR Concentrate — 51FR 51 FR — 51FR 51 FR — 51FR 51FR — 51FR 51FRLetdown — 12:1 10:1 — 12:1 10:1 — 12:1 10:1 — 12:1 10:1% FR Concentrate 0 5.2 6.1 0 5.2 6.1 0 5.2 6.1 0 5.2 6.1Carrier Type — 4056 4056 — 4056 4056 — 4056 4056 — 4056 4056

Oxygen Indexa (ASTM D 2863)

Flex Bars (0.125") % 19.1 26.0 26.0 20.0 20.3 24.7 20.6 22.4 26.9 21.5 26.4 27.1

Vertical Burn (ASTM D 3801)

Thickness 3.06 mm (1/8") HB V-2 V-2b HB V-2 V-2 HB V-2 V-2 HB V-2 V-21.57 mm (1/16") HB V-2 V-2b HB V-2 V-2 HB V-2 V-2 HB V-2 V-20.08 mm (1/32") HB V-2 V-2 HB V-2 V-2 HB V-2 V-2 HB V-2 V-2

Original Physical Properties

Hardness Durometer D (ASTM D2240) 43 43 47 58 58 58 71 71 66 80 75 75Tensile Strength, MPa (ASTM D 638) 23 19 20 31 26 25 37 30 25 39 25 27Elongation at Break, % (ASTM D 638) 651 768 583 482 468 457 381 417 304c 295 <100c <50c

Flex Modulus, MPa (ASTM D 790) 81 87 108 212 261 164 680 752 750 1180 1586 156Melt Flow g/10 min (ASTM D 1238) 5.15 5.14 5.16 7.5 9.52 8.44 13.0 17.1 15.0 21 22.4 193Condition, at °C and 2.16 Kg load 190 190 190 220 220 220 240 240 240 240 240 240

a Numerical Values measured by D 2863 are not intended to reflect hazards presented by this or any other material underactual fire conditions.

b Ret. UL Listing Card, Guide QMQS2, File No. E63766d Poor dispersionNote: 51FR is not recommended in blends of Hytrel® resins with hardness ≥55D

—the dispersion of 51FR into Hytrel® resins with hardness ≥55D is poor.

35

Table 24Heat Aging: Blends of 51FR in Hytrel® 4056 (Injection Molded Test Pieces)

Polymer Hytrel® 4056

FR Concentrate — 51FR 51FRLetdown — 12:1 10:1% FIR Concentrate 0 5.2 6.1Carrier Type — 4056 4056

Original PropertiesTensile Strength, MPa (ASTM D 638) 23 19 20Elongation at Break, % (ASTM D 638) 551 768 583Melt Flow g/10 min. (ASTM D 1238) 5.15 5.14 5.16Condition, at °C and 2.16 Kg load 190 190 190

Heat Aging at 100°C—2 weeksTensile Strength, MPa (ASTM D 638) 24 18 20Elongation at Break, % (ASTM D 638) 579 769 603Melt Flow g/10 min. (ASTM D 1238) 5.75 5.84 6.19Condition, at °C and 2.16 Kg load 190 190 190

4 weeksTensile Strength, MPa (ASTM D 638) 24 19 20Elongation at Break, % (ASTM D 638) 598 673 612Melt Flow g/10 min. (ASTM D 1238) 6.1 6.8 6.8Condition, at °C and 2.16 Kg load 190 190 190

6 weeksTensile Strength, MPa (ASTM D 638) 23 18 19Elongation at Break, % (ASTM D 638) 605 674 650Melt Flow g/10 min. (ASTM D 1238) 7.3 7.7 7.7Condition, at °C and 2.16 Kg load 190 190 190

Heat Aging at 125°C—2 weeksTensile Strength, MPa (ASTM D 638) 21 18 17Elongation at Break, % (ASTM D 638) 640 653 655Melt Flow g/10 min. (ASTM D 1238) 10 27 12Condition, at °C and 2.16 Kg load 190 190 190

4 weeksTensile Strength, MPa (ASTM D 638) 17 15 15Elongation at Break, % (ASTM D 638) 699 691 655Melt Flow g/10 min. (ASTM D 1238) 30 TF 28Condition, at °C and 2.16 Kg load 190 190 190

6 weeksTensile Strength, MPa (ASTM D 638) 11 11 11Elongation at Break, % (ASTM D 638) 467 460 389Melt Flow g/10 min. (ASTM D 1238) TF TF TFCondition, at °C and 2.16 Kg load 190 190 190

Comment on discoloration after aging pink No change No change

Note: Hytrel® 4056 sample after oven aging showed pink discoloration, while the same containing 51FR showed nodiscoloration.

TF: too fluid to measure the melt flow under described conditions.

36

Table 25Heat Aging: Blends of 52FR in Hytrel® 5556, 7246 and 8238 (Injection Molded Test Pieces)

Polymer Hytrel® 5556 Hytrel® 7246 Hytrel® 8238

FR Concentrate — 52FR 52FR — 52FR 52FR — 52FR 52FRLetdown — 12:1 10:1 — 12:1 10:1 — 12:1 10:1% FR Concentrate 0 5.2 6.1 0 5.2 6.1 0 5.2 6.1Carrier Type — 5556 5556 — 5556 5556 — 5556 5556

Original PropertiesTensile Strength, MPa (ASTM D 638) 31 27 30 37 27 31 39 31 33Elongation at Break, % (ASTM D 638) 482 470 514 381 287 326 295 252 285Melt Flow g/10 min (ASTM D 1238) 7.8 10.21 8.62 13.0 14.1 15.8 21 20 20Condition, at °C and 2.16 Kg load 220 220 220 240 240 240 240 240 240

Heat Aging at 100°C—2 weeksTensile Strength, MPa (ASTM D 638) 29 22 27 36 29 34 33 37 30Elongation at Break, % (ASTM D 638) 480 350 500 333 290 302 383 280 420Melt Flow g/10 min (ASTM D 1238) 8.98 10.38 9.29 14.1 14.1 15.2 15.1 14.1 14.6Condition, at °C and 2.16 Kg load 220 220 220 240 240 240 240 240 240

4 weeksTensile Strength, MPa (ASTM D 638) 30 25 24 40 29 34 43 41 40Elongation at Break, % (ASTM D 638) 483 470 473 410 333 316 294 249 215Melt Flow g/10 min (ASTM D 1238) 9.2 10.5 10.1 16 14.9 15.8 15.9 14.2 15.1Condition, at °C and 2.16 Kg load 220 220 220 240 240 240 240 240 240

6 weeksTensile Strength, MPa (ASTM D 638) 28 25 27 35 30 35 41 41 41Elongation at Break, % (ASTM D 638) 483 466 505 400 337 310 355 225 249Melt Flow g/10 min (ASTM D 1238) 10 12 12.1 16.4 16.6 18.1 22.1 20.1 19.4Condition, at °C and 2.16 Kg load 220 220 220 240 240 240 240 240 240

Heat Aging at 125°C—2 weeksTensile Strength, MPa (ASTM D 638) 28 24 25 39 — 34 31 31 42Elongation at Break, % (ASTM D 638) 481 495 523 330 — 340 346 100 <50Melt Flow g/10 min (ASTM D 1238) 14.2 14.7 12.9 22.1 — 20.2 17 23 27Condition, at °C and 2.16 Kg load 220 220 220 240 240 240 240 240 240

4 weeksTensile Strength, MPa (ASTM D 638) 29 25 25 41 32 33 38 31 42Elongation at Break, % (ASTM D 638) 525 516 532 463 369 341 322 <50 <50Melt Flow g/10 min (ASTM D 1238) 16.8 15.7 15.6 30.5 24.0 24.4 22 26 26condition, at °C and 2.16 Kg load 220 220 220 240 240 240 240 240 240

6 weeksTensile Strength, MPa (ASTM D 638) 27 22 23 34 23 36 29 41 43Elongation at Break, % (ASTM D 638) 552 491 486 391 360 354 249 <50 <50Melt Flow g/10 min (ASTM D 1238) TF TF TF 35 26 30 45 41 30Condition, at °C and 2.16 Kg load 220 220 220 240 240 240 240 240 240

Heat Aging at 135°C—2 weeksTensile Strength, MPa (ASTM D 638) 29 23 22 39 26 35 31 42 43Elongation at Break, % (ASTM D 638) 557 505 444 451 10026 340 <50 <50 <50Melt Flow g/10 min (ASTM D 1238) 17.2 16.8 15.2 22.5 27 23.8 18 43 49Condition, at °C and 2.16 Kg load 220 220 220 240 240 240 240 240 240

4 weeksTensile Strength, MPa (ASTM D 638) 16 16 16 23 22 25 23 38 43Elongation at Break, % (ASTM D 638) <50 93 90 297 331 355 76 <50 <50Melt Flow g/10 min (ASTM D 1238) TF TF TF 49.6 50.7 53.5 23 44 58Condition, at °C and 2.16 Kg load 220 220 220 240 240 240 240 240 240

6 weeksTensile Strength, MPa (ASTM D 638) failed failed failed 31 28 25 27 32 39Elongation at Break, % (ASTM D 638) failed failed failed <50 <50 56 <50 <50 <50Melt Flow g/10 min (ASTM D 1238) — — — 60 64 66 53 58 61Condition, at °C and 2.16 Kg load 220 220 220 240 240 240 240 240 240

Comment on discoloration after aging pink no no pink no no pink no no

Note: Hytrel® 5566, 7246 and 8238 samples after oven aging showed pink discoloration, while the same containing 52FRshowed no discoloration.

37

Fluid Resistance

Hytrel® has excellent resistance to nonpolar mateals, even at elevated temperatures. Polar materiaat elevated temperatures may have severe effectsHytrel®. In general, fluid resistance of Hytrel®

improves as the stiffness of the grade increases.

Table 26 offers some general guidelines to assist selecting the most suitable grade of Hytrel® for aspecific application. More detailed product data aravailable and should be referred to prior to makinfinal material selection.

For simplicity, the Hytrel® products have beengrouped into three hardness ranges. Their abilityto meet end-use requirements is rated either verysuitable, generally suitable, or not suitable.

TabFluid Re

35

Mineral oils and greases,Other nonaromatic hydrocarbons

Benzene, toluene, otheraromatic hydrocarbons,chemicals, and solvents

Water, alcohols, glycols

• ambient temperature

• >50°C (>122°F) with 10MS

without 10MS

Acids and bases

• diluted

• concentrated

Very suitable

Generally suitable

Not suitable

ri-ls on

in

eg

Often, the starting point in selecting the rightmaterial is to consider the end-use environment—to what conditions will the application be exposed(e.g., temperature or chemicals).

The best heat and chemical resistance is typicallyprovided by the hardest, stiffest Hytrel® grades;whereas the softer, more flexible Hytrel® gradesusually provide better performance in low-temperature environments.

It is important to keep in mind that the part designmust accommodate the mechanical behavior ofthe material selected based on the environmentalconditions. In addition, physical properties,methods of assembly, and other criteria all playa part in making the best material selection forthe specific application.

le 26sistance

Hardness

D–40D 45D–55D 63D–104R

38

s,

Gas PermeabilityHytrel® polyester elastomers have an unusual cobination of polarity, crystallinity, and morphology.As a result, they have a high degree of permeabto polar molecules, such as water, but are resistato permeation by nonpolar hydrocarbons andrefrigerant gases (see Table 27).

TabPermeabilitya of

Hytrel®

Gas 4056

Air 2.4 × 10–8

Nitrogen 1.7 × 10–8

Carbon Dioxide 3.5 × 10–7

Helium 15.7 × 10–8

Propane <0.2 × 10–8

Waterb 3.1 × 10–5

Freon 12 Fluorocarbon 1.4 × 10–8

Freon 22 Fluorocarbon 0.47 × 10–8

Freon 114 Fluorocarbon 41 × 10–8

a Units of permeability: cm3 (at standard temperature and pres(at STP)⋅cm/atm⋅sec⋅cm2 at 71°F and ∆P = 5 psi

b Values obtained at 90% RH, 25°C (77°F), assuming that perme

3

m-

ilitynt

In permeability to moisture, Hytrel® is comparableto the polyether-based urethanes and, therefore,is useful as a fabric coating for apparel. Its lowpermeability to refrigerant gases and hydrocarbonsuch as propane, makes Hytrel® of interest for usein refrigerant hose or in flexible hose or tubing totransmit gas for heating and cooking.

le 27 Hytrel® to Gases

Hytrel® Hytrel® Hytrel®

5556 6346 7246

1.8 × 10–8 — —

1.4 × 10–8 — —

1.8 × 10–7 — —

9.9 × 10–8 — 3.2 × 10–8

<0.2 × 10–8 <0.2 × 10–8 —

2.4 × 10–5 — —

1.2 × 10–8 1.2 × 10–8 0.82 × 10–8

0.59 × 10–8 <0.2 × 10–8 —

28 × 10–8 4.6 × 10–8 2.7 × 10–8

sure, STP)⋅mm/Pa⋅s⋅m2 at 21.5°C and ∆P = 34.5 kPa or cm3

ability laws hold for water.

9

Radiation ResistanceThe increasing use of nuclear energy, for examplin power plants, military areas, and medicine,places new requirements on many rubber com-pounds as well as other materials. Some factorsof importance to market development of nuclearenergy include, for example: the maximum dosagto which the material can be subjected withoutdamaging effects, the possible use of additivesto provide additional stabilization to radiation,and the effect of radiation on physical properties.

Three uncompounded grades of Hytrel® polyesterelastomer show excellent retention of physicalproperties after irradiation at 23°C (73°F) in air.(The combined effect of heat-aging or steam-aging concurrent with radiation exposure wasnot studied.)

Injection-molded slabs of Hytrel® 4056, Hytrel®

5556, and Hytrel® 7246, 2 mm (0.079 in) thick,were exposed to a 1.5 MeV electron beam atRadiation Dynamics Ltd., Swindon, Wiltshire, U.KThe slabs were then tested by ASTM test method

For the most part, the radiation of prime interestfrom the standpoint of insulation damage hasenergy of the order of 1 MeV, which is principallygamma photons and fast neutrons. Damage iscaused by collisions of this radiation with electron

TabStability of Hytrel® Polyes

Electron Beam, 1.5 MeV, 23°C (73°F), 7

ASTMTest Method

Original

Tensile Strength, MPa (psi) D 638Elongation at Break, % D 638100% Modulus, MPa (psi) D 638Hardness, Durometer D D 2240

Exposure 5 Mrad, kJ/kg

Tensile Strength, MPa (psi)Elongation at Break, %100% Modulus, MPa (psi)Hardness, Durometer D





4

e

e

.s.

s

and nuclei in the elastomer where the energy inputfrom such collisions may be greater than the bondenergies in the elastomer.

Most elastomers are embrittled by radiation expo-sure, which induces cross-links between molecules.This eventually gives a three-dimensional network,such as is seen in hard rubber or phenolic resins.A few polymers, notably butyl rubber, degrade byreversion to low-molecular-weight tars and oils.

Although upgrading changes can occur undercontrolled low dosage (radiation cross-linkedpolyolefins), long exposure normally producesdegradation. Thus, the amount of change is depen-dent on radiation flux rate, total radiation dose,energy of radiation, chemical composition of thepolymer, environment (ambient temperature, airversus inert gas, steam exposure, etc.), and theinitial properties of the elastomeric compound. Theamount of change is independent of the type ofradiation at equal energy,* whether alpha, beta,or gamma rays, or neutrons. This is known as theequal-energy, equal-damage concept.

Table 28 summarizes the effect of radiation onthree hardness grades of Hytrel®. It will be seen thatthe exposure to 150 kJ/kg (15 Mrad) produces verylittle change in the properties of Hytrel®.

* R. B. Blodgett and R. G. Fisher, IEEE Transactions on PowerApparatus and Systems, Vol. 88, No. 5, p. 529, (May 1969).

le 28ter Elastomer to Radiation0% RH, Radiation Dosage in J/kg (rad)

Hytrel® Hytrel® Hytrel®

4056 5556 7246

24.1 (3495) 27.2 (3945) 35.7 (5175)550 390 430

6.8 (985) 14.4 (2090) 22.0 (3190)40 55 72

50 50 50

22.8 (3305) 28.3 (4105) 36.6 (5305)510 470 410

7.3 (1060) 14.5 (2100) 23.6 (3420)40 55 72

100 100 100

22.8 (3305) 28.9 (4190) 37.4 (5425)500 470 370

6.2 (900) 14.5 (2100) 23.9 (3465)40 55 72

150 150 150

22.1 (3205) 30.3 (4395) 38.6 (5595)490 490 390

6.1 (885) 14.2 (2060) 24.6 (3565)40 55 72

0

s
Resistance to Mildew and FungusThe resistance of a high-performance 40 duromeD hardness grade of Hytrel® polyester elastomer tocertain fungi was determined according to ASTMD 1924-63, using the following cultures.
Culture Observed GrowthAspergillus niger NoneAspergillus flavus NoneAspergillus versicolor Very slight, sparsePenicillin funiculosum NonePullularia pullulans NoneTrichloderma sp. None

4

Samples of the same grade Hytrel® were also buriedfor one year in Panama. Instron test results were afollows:

OriginalDurometer D Hardness 40Tensile Strength, MPa (psi) 25.5 (3700)Elongation at Break, % 450100% Modulus, MPa (psi) 6.9 (1000)300% Modulus, MPa (psi) 8.8 (1275)

Retention after 1 yr Soil Burial in Panama, %Durometer Hardness 98Tensile Strength 82Elongation at Break 82100% Modulus 99300% Modulus 98

The harder grades of Hytrel® were not includedin these tests but should show at least equivalentresistance, because they are based on the sameraw materials.

ter

1

s

ge

Agency ApprovalsFood and Drug AdministrationThe following grades of Hytrel® meet Food andDrug Administration (FDA) guidelines for foodcontact use in the U.S. The stabilizer system usedin these grades is in full compliance with FDAregulations.

The following grades of Hytrel® may be used incompliance with the Federal Food, Drug, andCosmetic Act, specifically:

Contact with Dry Repeated Use Contact

Bulk Food with Fatty or Wet Food(Regulation (Regulation

Hytrel® 21CFR177.1590) 21CFR177.2600)

4069 √ √4556 √ √5526 √ √5556 √ √6356 √ √7246 √ √8238 √ √3078 √ √4056 √HTR6108 √

Essentially all high performance grades of Hytrel®

meet FDA guideline for bulk dry food contact usein the U.S. If the customer uses compliant additiveand follows the temperature and alcohol contentrequirements of the application, then the applica-tion should be in compliance with the repeateduse regulation.

This information, based upon our experience, is offered without charas part of our service to customers. It is intended for use by personshaving technical skill, at their own discretion and risk. We do notguarantee favorable results, and we assume no liability in connectionwith its use. The information is not intended as a license to operateunder, or a recommendation to infringe, any patent of DuPont orothers.

4

None of the high productivity grades of Hytrel®

have FDA approval in the U.S.—not because of thepresence of toxic extractable material, but ratherbecause they have not been tested due to theenormous expense of extraction and animal feedingtests required by the FDA.

Underwriters LaboratoriesRecognitionUnderwriters Laboratories (UL) is an independent,nonprofit testing laboratory that evaluates the safetyof equipment offered for sale. Many state and localgovernments require that electrical appliances inthe U.S. carry UL approval before they can be soldwithin their jurisdiction.

The UL listing cards for Hytrel® base resins andcompositions with 51FR and 52FR flame-retardantconcentrates are attached.

2

QMFZ2Component -- Plastics

March 3, 1993

E I DUPONT DE NEMOURS & CO INC E51284 (R)(B—cont. from A card)

——0

—0

—0

—0

——5

—6

————

—00

—0

—0

—0

—00000000

—43334443

—858550505050——

—858550505050——

90909050505050——

—94HB94HB94HB94HB94HB94HB94HB94HB

0.711.473.051.573.181.563.181.573.21

NC

NC

NC

NC

G4074 G5548 4069 3078

Replaces E51284B dated February 9, 1993, filed E I DuPont de Nemours & Co., Inc., DuPont Polymers, Engineering Polymers.

Underwriters Laboratories Inc.®

Reports: November 5, 1984; April 30, 1990; July 14, 1987; November 5, 1984.

324299212 N7047 D11/0019036

(Cont. on B1 card)

68

Mech


March 3, 1993

E I DUPONT DE NEMOURS & CO INCDUPONT POLYMERS, ENGINEERING POLYMERS,TEEE RESINS, PO BOX 80713, CHESTNUT RUNPLAZA, WILMINGTON DE 19880-0713

E51284 (R)(A card)

——0

—0

——0

——5

—5

——5

—0000

—00

—0000

—00

—4343

—33

—85858585—7580

—85858585—8585

9090909090858585

—94HB94HB94HB94HB

—94HB94HB

0.711.473.051.473.050.711.473.05

NC

NC

NC

5555HS 8238 5556, 4556

Thermoplastic elastomer-ether-ester, designated "Hytrel", furnished in the form of pellets.

CTI

D495

HVTR

HAI

HWI

w/oImp

withImp

ElecUL94FlameClass

MinThkmmColMtl Deg

RTI

Replaces E51284A dated February 9, 1993, filed E I DuPont de Nemours & Co., Inc., DuPont Polymers, Engineering Polymers.


Reports: June 30, 1986; June 30, 1986; November 5, 1985.

324299212 H7047 D11/0019035

(Cont. on B card)

67


April 1, 1998

E I DUPONT DE NEMOURS & CO INC E51284 (R)(B1—cont. from B card)

—0

—0

—0

—0

—0

—6

—6

—6

—6

—6

—0

—0

—0

—0

—0

0000000000

3232433233

5050————————

5050————————

5050————————

94HB94HB94HB94HB94HB94HB94HB94HB94HB94HB

1.573.181.573.171.503.001.573.121.573.05

NC

NC

NC

NC

NC

G4778 G3548, G4078G3548W, G4078WG4774, G55444059FG

—0

——

—0

0—

4—

5050

5050

5050

94HB94HB

1.503.00

NCG3548L

Replaces E51284B1 dated April 16, 1996.Underwriters Laboratories Inc.®

Reports: July 14, 1987; July 14, 1987; November 5, 1984; April 30, 1990; July 14, 1987.

324299212 N7047 D1I/0215721

(Cont. on C card)

224

43


March 3, 1993

E I DUPONT DE NEMOURS & CO INC E51284 (R)(D—cont. from C card)

Replaces E51284D dated February 9, 1993, filed E I DuPont de Nemours & Co., Inc., DuPont Polymers, Engineering Polymers.


UL94 small-scale test data does not pertain to building materials, furnishings and related contents.UL94 small-scale test data is intended solely for determining the flammability of plastic materialsused in the components and parts of end-product devices and appliances, where the acceptability ofthe combination is determined by ULI.

324299212 N7047 D11/0152205

71

See General Information Preceding These Recognitions.


March 3, 1993

E I DUPONT DE NEMOURS & CO INC E51284 (R)(C—cont. from B1 card)

——————1

—0

—

——————6

—6

—

——————2

—0

—

————00000

—

———233142

—

——————————

——————————

——————————

94HB94HB94HB94HB94V-094V-194-V094HB94HB94HB

1.471.571.473.181.571.573.181.573.300.91

NCNCNC

NCBKBKNCBKNC

4056, 724663565526 HTR8068 HTR5612

8238

Replaces E51284C dated February 9, 1993, filed E I DuPont de Nemours & Co., Inc., DuPont Polymers, Engineering Polymers.


Reports: January 12, 1978; January 12, 1978; November 5, 1984; March 28, 1988; March 28, 1988; July 31, 1990.

324299212 N7047 D11/0144472

(Cont. on D card)

70

Thermoplastic elastomer-ether-ester, designated "Hytrel", furnished in the form of pellets.

Marking: Company name and material designation on container, wrapper or molded on finished part.

Concentrate Dsg

QMQS2Component -- Flame Retardant And/Or Color Concentrates

July 27, 1994

E I DUPONT DE NEMOURS & CO INC E63766 (R)(A card)

Report: January 12, 1978.

DUPONT ENGINEERING POLYMERS,CHESTNUT RUN PLAZA, PO BOX 80713, WILMINGTON DE 19880-0713

Hytrel 50FRHytrel 50FRHytrel 50FRHytrel 51FRHytrel 52FRHytrel 52FRHytrel 52FRHytrel 52FR

Flame retardant concentrates, furnished in the pellet form, for use in the specified Recognizedthermoplastic elastomer-ether-ester resins shown below.

DuPontDuPontDuPontDuPontDuPontDuPontDuPontDuPont

Hytrel 4056Hytrel 5526Hytrel 7246Hytrel 4056

Hytrel 5555HSHytrel 5556Hytrel 7246Hytrel 8238

NCNCNCNCNCNCNCNC

0.0620.0630.0660.060.060.060.120.06

(1.57)(1.60)(1.67)(1.52)(1.52)(1.52)(3.00)(1.52)

1:6.71:101:101:101:101:101:101:10

94V-294V-294V-294V-294V-294V-294V-294V-2

Base ResinManufacturer Mtl Dsg LD Col In. (mm)

MinimumLet-Down

Ratio

UL94FlameClass

Min Thk

Underwriters Laboratories Inc.®324299182 H3082 D11/0010940(Cont. on B card)

58

Replaces E63766A dated February 9, 1993.

44

.

le

ApplicationsGeneral ConsiderationsThe following general stepwise procedure isintended to help minimize problems during thegrowth of a design and to aid in the rapid development of a successful commercial product.

As an initial step, the designer should list theanticipated conditions of use and the performancrequirements of the article to be designed. He/shmay then determine the limiting design factors anby doing so realistically, avoid pitfalls that cancause loss of time and expense at later stages ofdevelopment. Use of the checklist (below) will behelpful in defining design factors.

Design Checklist

General Information• What is the function of the part?• How does the assembly operate?• Can the assembly be simplified by using Hytrel?• Can it be made and assembled more

economically?• What tolerances are necessary?• Can a number of functions be combined in a

single molding to eliminate future assemblyoperations and simplify design?

• What space limitations exist?• What service life is required?• Is wear resistance required?• Can weight be saved?• Is light weight desirable?• Are there acceptance codes and specifications

such as SAE or UL?• Do analogous applications exist?

Structural Considerations• How is the part stressed in service?• What is the magnitude of stress?• What is the stress versus time relationship?• How much deflection can be tolerated in service

Environment• Operating temperature?• Chemicals, solvents?• Humidity?• Service life in the environment?

4

-

eed,

?

Appearance• Style?• Shape?• Color?• Surface finish?• Decoration?

Economic Factors• Cost of present part?• Cost estimate of Hytrel® part?• Are faster assemblies and elimination of finishing

operations possible?• Will redesign of the part simplify the assembled

product and thus give rise to savings in installedcost?

Manufacturing Options• Should the proposed design be machined, blow

molded, melt cast, injection molded, or extrudedconsidering the number of parts to be made,design geometry, and tolerances?

• If injection molding is chosen, how can molddesign contribute to part design?

• In subsequent assembly operations, can theproperties of the chosen material be used further(e.g., spin welding, snap fits)?

• After preliminary study, several steps remain toconvert design ideas into production.

Drafting the Preliminary Design

After considering end-use requirements, the de-signer is ready to define the part geometry. Thismay be done in several stages with preliminarydrawings indicating the basic design and functions.More detailed sketches provide information onthickness, radii, and other structures, as workedout from end-use considerations.

Prototyping the Design

Prototypes can be prepared by several techniquesA common approach is to machine the part fromrod or slab stock (see the Machining Hytrel®

bulletin). If machining operations are expected tobe elaborate or expensive, it is sometimes advisabto x-ray the part to avoid using material with voids.A medical type unit will show voids as small as1.58 mm (0.0625 in) diameter, and even greaterresolution can be obtained with some industrialunits.

5

d

The melt stability of Hytrel® permits production ofprototypes by melt casting, which is a process usian extruder to fill an inexpensive aluminum mold.This method can also be advantageous for shortproduction runs because setup costs are low. Forfurther information, see the “Melt Casting” bulletin

In any large and important development, thepreparation of prototypes, using the fabricationmethod intended for production, can provide addeassurance against failure in use. For injection-molded parts, the use of an inexpensive alumi-num, brass, or copper beryllium mold is frequentlyconsidered an important step between conceptionand production. In addition, molded prototypesprovide information on gate location and on moldshrinkage.

Additional reasons why the molded prototype ispreferred to the machined prototype are:• Machine marks may result in variable behavior.• Orientation effects in the molded parts resulting

from gate location or knockout pins may influ-ence toughness.

Testing the Design

Every design should be subjected to some form otesting while in the prototype stage to check theaccuracy of calculations and basic assumptions.• Actual end-use testing of a part in service is the

most meaningful kind of prototype testing. Hereall of the performance requirements are encountered, and a complete assessment of the designcan be made.

• Simulated service tests are often conducted witprototype parts. The value of this type of testingdepends on how closely the end-use conditionsare duplicated. For example, an automobileengine part might be given temperature, vibra-tion, and hydrocarbon resistance tests; a luggagfixture could be subjected to impact and abrasiotests; and a radio component might undergo tesfor electrical and thermal insulation.

• Standard test procedures, such as those develoby the ASTM, generally are useful as a designguide but normally cannot be drawn upon topredict accurately the performance of a part inservice. Again, representative field testing maybe indispensable.

4

ng

.

d

f

,-

h

ents

ped

Long-term performance must sometimes be pre-dicted on the basis of “severe” short-term tests.This form of accelerated testing is widely usedbut should be used with discretion, because therelationship between the long-term service and theaccelerated condition is not always known.

Taking a Second Look

A second look at the design helps to answer thebasic question: “Will the product do the right job atthe right price?” Even at this point, most productscan be improved by redesigning for productioneconomies or for important functional and aestheticchanges. Weak sections can be strengthened, newfeatures added, and colors changed. Substantial anvital changes in design may necessitate completeevaluation of the new design. If the design has heldup under this close scrutiny, specifications thendetails of production can be established.

Writing Meaningful Specifications

The purpose of a specification is to eliminate anyvariations in the product that would prevent it fromsatisfying the functional, aesthetic, or economicrequirements. The specification is a complete setof written requirements that the part must meet. Itshould include such things as: generic name, brandand grade of material, finish, parting line location,flash, gating, locations where voids are intolerable,warpage, color, and decorating and performancespecifications.

Setting Up Production

Once the specifications have been carefully andrealistically written, molds can be designed andbuilt to fit the processing equipment. Tool designfor injection molding should be left to a specialistor able consultant in the field, because inefficientand unnecessarily expensive production can resultfrom improper design of tools or selection ofmanufacturing equipment.

Controlling the Quality

It is good inspection practice to schedule regularchecking of production parts against a givenstandard. An inspection checklist should includeall the items that are pertinent to satisfactoryperformance of the part in actual service at itsassembled cost. The end user and molder shouldjointly establish the quality control procedures thatwill facilitate production of parts within specifica-tions. (See DuPont Engineering Polymers, ModuleI, for general design principles.)

6

e
Design MethodsUsing Physical Property Data
The designer who is new to Hytrel® polyesterelastomer and plastics can rely on much of his/hbackground with other materials (such as metalsto form a basis for design analysis and synthesisof a molded or extruded part of Hytrel®. Two basicareas that must be considered most carefully areproperty data and effect of environment.

Whereas property data in this book are presentethe same fashion as for metals, the use of the dain conventional engineering design formulas canvary. For example, the stress-strain relationship not linear below the yield point and does changewith time under load. A single number cannot beused for modulus as is done with metals. For shoterm loading, the stress-strain curves can be consulted for the secant modulus at a particular loadand temperature. The secant modulus is thensubstituted for elastic modulus in the appropriateequation. In applications involving long-termloading, the creep modulus curves must be usedestimate the modulus at a given point in time. Thprocedure is illustrated by the following example

Problem: A part design calls for a 135 N load to suspended from the center of a beam 25 mm tal6.5 mm thick, and 165 mm long supported at itsends. The part specification requires that the beanot sag more than 15 mm after 30 days continuoloading. The designer wishes to use Hytrel® 6356for this part. Will it meet the sag requirement?

s

er)

d inta

is

rt--

tois:

bel,

mus

Solution: The first step is to calculate the stresslevel in the part. The maximum stress occurs in thoutermost fibers and is calculated by the followingequation:

σ =

where σ = stress in outer fibersM = bending momentZ = distance from neutral axisI = moment of inertia

Calculating the bending moment:

M =

where F = loadl = length of beam between supports

Therefore, M =

= 5569 N⋅mm

For a rectangular cross section of base (b, mm) andheight (h, mm):

I = =

= 8464 mm4

Finally, calculating the stress,

σ =

= 8.22 MPa

Referring to Figure 23, the modulus for Hytrel®

6356 at a stress level of 8.22 MPa after 30 days iap-proximately 126 MPa.

Using the appropriate equation to calculatedeflection:

Y max. =

where Y max.= deflection at center of beamE = Young’s modulus. In this case,

the modulus determined fromFigure 23 is to be used.

Therefore, Y max. =

= 11.8 mm

Hytrel® 6356 will meet the requirements of theapplication.

MZ

I

Fl

4

(135)(165)

4

bh3

12

(6.5)(25)3

12

(5569)(12.5)

8464

Fl3

48 El

(135)(165)3

48(126)(8464)

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Figure 43. Types of Undercut

UndercutsUndercuts, classified as internal and external,are molded in parts for functional reasons or fordecoration. Undercuts may increase tooling costsand lengthen cycles, but this is dependent on thetype and location of the undercuts on the part.Undercuts are formed by using split cavity moldsand collapsible cores and stripping the part fromcore or cavity (see Figure 43).

The allowable undercut will vary with type ofHytrel®, wall thickness, and diameter. The undercshould be well rounded and filleted to allow foreasy removal of the part from the mold and tominimize stress concentrations during stripping.

Also, the undercut part must be free to stretch orcompress; that is, the wall of the part opposite theundercut must clear the mold or core before ejec-tion is attempted. Adequate part contact area shobe provided during stripping so that penetration othe part does not occur by the knock-out system othe wall does not collapse.

Realistic TolerancesOne of the most important steps in the design ofgears is the specification of realistic tolerances.Plastic gears do not require the high tolerances ometal gears. The best tolerances that can normalbe met with injection-molded gears are in the ranof AGMA Quality No. 5, 6, 7. This means that totacomposite error may be held between 0.08 and0.13 mm (0.003 and 0.005 in), with tooth-to-toothcomposite error between 0.03 and 0.05 mm (0.00and 0.002 in).

Closer tolerances can be held in an injection-molded gear, but the designer must expect to paya premium because higher tooling cost, fine controf the molding conditions, and close inspection ofthe gears usually will be required.

External*undercuts

Parting linenecessitated bysplit cavity Internal

undercuts

*Undercut exaggerated for clarity

4

AssemblyA Coined Hinge

Coining can be used as an assembly method. InFigure 44, a housing is coined near the coverportion so that it can be permanently closed andsealed. The advantage of the coining method is ththe coined section, though only 25% the thicknessof the adjoining walls, has an equivalent strength.This would not be true were the hinge area moldedwith a 0.38 mm (15 mil) wall.

Designing for Ultrasonic Assembly

Sonic welding is a satisfactory way to assembleparts fabricated from the harder types of Hytrel®.The design in Figure 45 for an automotive valvecomponent is a good example. The step joint isplaced on the exterior of the lower part. The webof the lower part will then retain or support thediameter of the weld surface, and the mating weldsurface on the upper part can be retained by an encircling fixture. This overcomes the possibility ofthe weld surface on the upper part distorting in-wardly. This distortion, of course, could affect theweld strength. Make the axial length of the upperweld surface 2.03 mm (0.080 in) greater than theaxial length of the lower weld surface 1.9 mm(0.075 in) to ensure that the parts will bottom outon the welding line.

ut

uldfr

flyel

1

ol

0.38 mm (0.015 in)

Folded 90°

As molded

Coining tools

1.52 mm (0.060 in)

16.28 mm (0.641 in)

80.2

9 m

m (

3.16

1 in

)

1.52 mm(0.060 in)

2.36 mm(0.093 in)

1.58 mm(0.0625 in)

Figure 44. A Coined Hinge

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Designing for Vibration/Weld Assembly

For rigid parts with a large weld area, the pre-ferred assembly method is vibration welding. As example, the carbon cannister used for automotivfuel vapor emission control is an ideal candidate.Because it is rectangular, spin welding is not practical; its large weld area precludes the use of sonwelding because of the need for a high energysource, and a hermetic seal is required. The typeof vibration weld used in Figure 46 is linear, thecover plate and body moving relative to each othalong an axis down the long centerline of the opeend of the body. The flange that forms the weldsurface is ribbed to maintain proper flatness durinthe welding operation. Note the clearance allowebetween the recessed portion of the cover and thinside of the body.

2.03 mm(0.080 in)

2.03 mm(0.080 in)

2.03 mm(0.080 in)

0.38 mm(0.015 in)

12.05 mm(0.075 in)

Clearance forwelding vibration

Figure 46. Design for Vibration Weld Assembly

Figure 45. Designing for Ultrasonic Assembly(Automotive Valve Component)

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Assembly TechniquesBonding of Hytrel® to Metal

1. Grit-blast the metal surface using clean, sharp90-mesh aluminum oxide grit.

2. Degrease the grit-blasted surface with tolueneor methyl ethyl ketone. Use a clean, lint-freecloth.

3. Brush-apply a thin coat of Chemlok AP-134adhesion promoter as soon as possible aftergrit-blasting and degreasing. Allow the coat todry for 40 min at room temperature. The dryfilm should be no more than 25 µm (1 mil)thick; heavier coats will reduce bond strength.

4. Brush-apply a coat of mixed Tycel primer (100parts Tycel 7000 adhesive with 5 parts Tycel7203 curing agent—pot life, 12 hr). Allow theprimer coat to dry 30 min at room temperatureThe dry primer film should be approximately50 µm (2 mil) thick; total adhesion promoter +primer film thickness = 75 µm (3 mil).

5. Protect cleaned and primed surfaces fromcontamination by dirt, oil, or grease duringstorage.

6. Injection-mold Hytrel® onto the primed surfaceusing a normal molding cycle. (See the bulletin“Injection Molding,” for standard injectionmolding conditions.)

a. For optimum bond strength, molding mustbe done within 2.5 hr after priming.

b. Preheating of the metal insert is not neces-sary if the substrate is steel. However, someincrease in bond strength to aluminum canbe achieved by preheating the insert to190°C (375°F).

Preparation of Metal SurfaceProper preparation of the metal surface is veryimportant, because any trace of oil, grease, mois-ture, or oxide film will reduce adhesion. Properpreparation consists of grit-blasting and degreasinfollowed by priming. Degreasing must be doneafter grit-blasting, because the grit may be con-taminated with oil. Avoid using fast-evaporatingsolvents (e.g., acetone or methylene chloride) todegrease; they can cause moisture to condense othe metal surface when they evaporate.

Adhesion will not be obtained unless the cleansurface is primed. Grit-blasting and degreasingalone are not sufficient preparation.

9

s

Primer SystemOne primer system that produces acceptable bonstrength is a coat of Chemlok1 AP-134 primer,followed by a coat of Tycel 7000/Tycel 7203adhesive. Use of Chemlok AP-134 as an adhesivpromoter yields a substantial increase in bondstrength compared to that obtained with the Tyce7000/Tycel 7203 system alone (see Table 29).

Thixon2 406 bonding agent can also be used as aprimer system, but good bond strength is achieveonly if the metal insert is preheated within aspecific temperature range (Table 30).

Open TimeOpen time is the time period between applicationof the primer and use of the primed insert in theinjection molding operation. For optimum bondstrength, open time should be no more than 2.5 hBond strength is reduced considerably at longeropen times (see Table 29). If open time exceeds4 hr, there will be essentially no adhesion betweeHytrel® and the metal insert.

Table 29Effect of Open Time on Bond Strength

Bond Strength (90° peel),Open Time, hr* kN/m (lb/in)

1.0 5.2 (30)

1.5 8.8 (50)

2.0 7.9 (45)

2.5 8.4 (48)

3.0 5.2 (30)

3.5 4.9 (28)

4.0 1.8 (10)

16.0 0 (0)

Notes: Same bonding procedurePrimer system—Chemlok AP-134 plus Tycel 7000/7203Substrate temperature: 24°C (75°F)Polymer—55D Hytrel®

Standard injection molding conditions for 55D Hytrel®

Bonds aged 5 days at 24°C (75°F) before testing

1 Chemlok is a trademark of Lord Corporation.2 Thixon is a trademark of Morton InternationalNote: Before processing Hytrel® polyester elastomer, read the

bulletin, “Handling and Processing Precautions for Hytrel®.”

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Substrate Type and TemperatureWorkable levels of adhesion can be obtained inbonding Hytrel® to tool steel, stainless steel,aluminum, and brass, using the specified primersystem (see Tables 30–31). With a steel insert, noin-crease in bond strength is achieved by heatingthe substrate; with an aluminum insert, however,some benefit is gained by preheating to 190°C(375°F).

Type of Hytrel®

All types of Hytrel® polyester elastomer can bebonded to a variety of substrates using the proce-dure and primer system shown (Table 30). Bondstrength tends to be greater for the lower hardnespolymers and decreases slightly as polymer hard-ness increases.

Table 30Effect of Primer and Substrate Temperature

on Bond Strength

BondSubstrate Strength

Primer Temperature, (90° peel),Substrate System °C (°F) kN/m (lb/in)

Steel Tycel 7000/7203 24 (75) 8.2 (47)with Chemlok 121 (250) 7.7 (44)AP-134 primer 190 (375) 8.4 (48)

Steel Tycel 7000/7203 24 (75) 3.5 (20)alone 121 (250) 2.6 (15)

190 (375) 3.3 (19)

Steel Thixon 406 24 (75) 0.2 (1)121 (250) 7.9 (45)190 (375) 0 (0)

Aluminum Tycel 7000/7203 24 (75) 6.0 (34)with Chemlok 121 (250) 6.1 (35)AP-134 primer 190 (375) 7.7 (44)

Aluminum Tycel 7000/7203 24 (75) 3.0 (17)alone 121 (250) 3.0 (17)

190 (375) 7.7 (44)

Notes: Same bonding procedure except for the primer systemOpen time—less than 1.5 hrPolymer—55D Hytrel; thickness—3.2 mm (0.125 in)Standard injection molding conditions for 55D Hytrel®


0

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er

Table 31Effect of Polymer and Metal Type on

Bond Strength

Bond Strength(90° peel),

Polymer Substrate kN/m (lb/in)

40D Hytrel® Steel 12.8 (73)Aluminum 8.1 (46)Brass 14.7 (84)Stainless Steel 14.9 (85)




Notes: Same bonding procedurePrimer System—Chemlok AP-134 plus Tycel 7000/7203Open time—less than 1.5 hrSubstrate temperature: 24°C (75°F)Standard injection molding conditions for the varioustypes of Hytrel®


Bonding During Compression Molding orMelt Casting

Considerably stronger bonds between Hytrel® andmetal can be achieved during compression moldior metal casting than during injection molding,because a substantially longer contact time undeheat and pressure is inherent in these operations

Procedure for Bonding Hytrel® to Metal DuringCompression Molding or Melt Casting

1. Grit-blast the metal surface using clean, shar90-mesh aluminum oxide grit.

2. Degrease the grit-blasted surface with toluenor methyl ethyl ketone. Use a clean, lint-freecloth.

3. Brush-apply a prime coat of Thixon 406bonding agent as soon as possible after grit-blasting and degreasing. Allow the coat to dryfor 30 min at room temperature. The drycoating should be approximately 25 µm (1 mil)thick; heavier coats will reduce bond strength

5

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4. If desired, brush-apply a second coat of Thixonbonding agent and allow it to dry for 30 min atroom temperature.

5. Protect cleaned and primed surface fromcontamination by oil, grease, and mold lubri-cants during storage.

6. Preheat metal to molding temperature if desire(see text).

7. Melt cast or compression mold Hytrel® onto theprimed metal, using standard techniques forthese operations.

Preparation of Metal SurfaceThe same precautions cited in the discussion ofpreparation of metal surfaces for bonding duringinjection molding apply to the compression mold-ing and melt casting operations as well. The metalsurface must first be grit-blasted and degreased toremove all traces of oil, grease, or oxide film, andthen must be primed with a commercial adhesivebonding agent.

Primer SystemThixon 406 bonding agent gives excellent adhesionbetween 55D Hytrel® and heated or unheated brassor steel, producing bond strength in excess of87.5 kN/m (500 lb/in), see Table 31. It shouldalso be satisfactory for use with other types ofHytrel® polyester elastomer.

A two-part curing system of Thixon bonding agents403 and 404 can also be used, but it produces lowbond strength than the preferred primer.

Substrate Type and TemperatureExcellent adhesion between Hytrel® and brass orsteel is obtained with the bonding agents cited(Table 32). Although no data are shown, adhesionto other metals should also be satisfactory if thepreferred primer is used.

Pressure on the MeltSlightly better adhesion is obtained if pressureis applied to the polymer melt, as in compressionmolding. Applied pressure probably produces moreintimate contact between the melt and the primedsurface.

1

Table 32Bonding 55D Hytrel® to Brass and Steel

BondSubstrate Strength

No. of Temperature, (90° peel),Substrate Prime Coats °C (°F) kN/m (lb/in)

Steel 1 24 (75) 87.5 (500)Steel 2 24 (75) 87.5 (500)Steel 1 204 (400) 92.8 (530)Steel 2 204 (400) 91.0 (520)Brass 1 24 (75) 103.2 (590)Brass 2 24 (75) 101.5 (580)Brass 1 204 (400) 87.5 (500)Brass 2 204 (400) 101.5 (580)

Notes: See procedure for bonding Hytrel® to metal duringcompression molding or melt casting.Primer—Thixon 406

Welding

Hytrel®, being a thermoplastic material, may bewelded to itself and to some other plastics by mosconventional plastic welding techniques.

Each of these has certain advantages, and thechoice depends on such things as: size/shape ofparts, shape and type of joint required, grade ofHytrel®, and equipment available. This informationcovers five basic welding methods and describesthe applications that are appropriate in each case.These are:• Hot plate/hot knife method• Sheet welding by hot air and other methods

– Hot air– Hot air and hot melt extrusion– Hot wedge

• High frequency welding– Dielectric heating– Inductive heating

• Ultrasonics• Spin/friction welding• Welding to other thermoplastics

Hot Plate/Hot Knife MethodThis method is simple to operate and suitablefor welding many Hytrel® items, particularlyinjection molded parts and solid section profiles(e.g., V-belts).

5

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“Hot plate” welding is the term generally applied tothe technique used with injection molded parts,where the two halves are brought into contact witha heated plate (flat or profiled) until both surfaceshave been melted. The components are then re-moved from contact with the plates and quicklybrought together at a preset pressure for severalseconds until the joint has set.

All grades of Hytrel® may be used for hot platewelding; however, it may be difficult to achievea good weld with blow molding grades such asHTR4275. This is because the low melt flow makesit more difficult for the two melted surfaces to flowtogether. If this problem occurs, higher tempera-tures (up to 280°C [536°F]) may help.

“Hot knife” refers to the type of tool used forwelding small solid profiles such as V-belts.Otherwise the principle is the same.

For successful welding, it is important to ensurethe following:• Plate surface temperature 20–50° above melting

point of the Hytrel®, depending on grade.• Best results obtained with nonstick plate surface

(e.g., use self-adhesive PTFE/glass fiber tape).• Holding pressure should be low during melting

stage, then higher pressure is required whenmaking the joint.

• Parts should be lined up accurately. Melting andapplication of pressure must be uniform aroundthe joint.

• Joint design should provide for flow of materialfrom the weld line.

Sheet Welding by Hot AirThis method can be used for welding and heatsealing Hytrel® sheeting in applications such astank and pit liners (typical sheeting thicknesses0.5 to 1.5 mm [0.02 to 0.06 in]). A handheld elec-tric blower provides a temperature-controlled jet ofhot air through a specially shaped flat nozzle that ismoved along slowly between the overlapping sheetedges. The inside surfaces of both sheets of Hytrel®

are melted and then forced together by a rubberhand roller that is applied along the top of the jointabout 10 cm (25.4 in) behind the nozzle.

AdvantageEquipment is relatively inexpensive and light-weight. It is convenient to use for field (i.e., on-site)weld-ing inside tanks and other places wherefactory prefabrication of all joints is not possible.

2

Disadvantages• Difficult to achieve consistent, reliable results.

Success depends on the skill of the operator.• Sensitive to temperature changes—insufficient

heat will not melt the surfaces, while too muchheat may cause blow holes, etc.

• Only suitable for certain grades of Hytrel®, suchas 4056, G4075, 5556. Very high or very lowmelt flow grades (e.g., 5526 and HTR4275), aswell as those with additives such as 10MS, havebeen found to be difficult to weld by this method

Welding with Hot Air Combined with HotMelt ExtrusionA modification of the above method is to applya molten bead of Hytrel® to the joint area, com-bined with hot air preheating of the sheet surfacesfollowed by hand roller pressure. Good welds havbeen produced using this equipment with severalgrades of Hytrel® sheeting, including those con-taining 10MS.

Hot WedgeThis technique uses a seam welding machine thacontains an electrically heated wedge, which ispassed between the two sheet edges to be joinedThe handheld machine is moved along by twopowered rollers, which also press the sheetingtogether behind the wedge. A device of this typehas been successfully used for factory prefabrication of Hytrel® sheeting for tank liners.

High Frequency (HF) WeldingDielectric HeatingThis method can generally only be applied to shewelding (up to 1.5 mm [0.06 in]) but is very suit-able for factory (i.e., prefabrication) welding ofnozzles and similar areas for tank linings. Theprinciple of this method is that the material to bewelded becomes the dielectric between two capator plates (formed by the steel work table and themetal electrode), which are part of a high-frequenAC circuit. The frequency used is allocated by lawand in most cases is 27.12 MHz. When the circuitis energized, heat is generated in the dielectricmaterial; the amount of heat is dependent on:• Frequency used (usually fixed by law and by

machine manufacturers).• Voltage applied—this is the normal means of

controlling the power available for heat genera-tion in the weld, after other parameters have beestablished. However, excessive voltage cancause dielectric breakdown of the material,resulting in “burn holes.”

• Electrode area—the bigger the area, the morepower is required from the machine, all other

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conditions being equal. The electrode, andhence the weld area, is therefore limited bythe capacity of the machine. For Hytrel®, whichhas a lower dielectric loss than other plastics, theoptimum electrode area for a 1.5 kW machine isabout 150 mm × 12 mm (5.9 in × 0.5 in) (i.e.,1800 mm2 [2.95 in2]).

• Thickness of material to be welded—the maxi-mum sheet thickness that can be easily weldedwith a 1.5 kW machine is approximately 1.5 mm(0.06 in).

• Type of material—materials with low dielectricloss factors, such as Hytrel®, require higher volt-age or smaller electrodes than other materialssuch as PVC.

• Loss—the loss of heat from the joint by conduc-tion through the metal electrodes. It is advanta-geous (see below) to cover the work table andelectrode with heat-insulating material (whichmay itself act as a dielectric and generate heat).Another technique is to use an electrically-heatedelectrode.

• Time—the temperature reached in the weld areawill rise over several seconds until an equilibriumis reached where heat energy being generated isequal to heat losses (conduction, radiation, etc.).If the power applied by the machine is not suf-ficient, then this equilibrium temperature will bebelow the melting point of the material, and noweld is possible. Provided sufficient power isavailable, the operator then determines whenwelding has occurred (by visual indication ofthe joint area and power meter) and switches offthe power. This time varies between 3 and 8 secdepending on the grade of Hytrel®, thickness, etc.

For successful welding of Hytrel® by this method,the following points are also important:• A heated (temperature-controlled) electrode is

best for consistent results, because the powersetting required for a particular material type andthickness depends on the electrode temperature.A heated electrode reduces heat conduction fromthe joint and eliminates variability caused by acold electrode, which warms as it is used.

• Heat generation at the joint can be assisted byuse of a thin paper/Mylar® laminate—known as“elephant hide”—on top of the work table. Anadditional layer of varnished cloth under theelephant hide has been used to further increasethe heat. Also, a self-adhesive PTFE tape over theelectrode surface can be used for similar reasons,although this should not be necessary with aheated electrode.

3

• Where possible, the joint line should fall approxmately midway between the electrode and thework table, i.e., use two sheets of equal thickneThis way the surfaces to be welded are at thepoint where maximum heat is generated.

The 40D and 55D grades have been very succesfully welded by this method. Harder grades ofHytrel® sheet up to 1 mm (0.04 in) may be weldedbut longer times may be required.

Inductive (Electromagnetic) WeldingThis technique is based on the principle that heatcan be induced in certain materials by alternatingelectromagnetic fields. The most effective result iobtained when a magnetic material is subjected ta high-frequency field produced by an inductiongenerator via water-cooled work coils. Thefrequency is normally determined by legallyestablished values in the range of 4–40 MHz.

For welding applications, the magnetic materialtakes the form of fine metal, graphite, or ferriteparticles that are dispersed in a tape or rod of thematerial to be welded. This tape is then positionein the joint area, and by action of the appliedelectromagnetic field and external pressure, thetape material fuses with the two surfaces to forma welded joint.

This method can be applied to sheeting applica-tions as well as to injection molded or other partsas long as the geometry of the weld line will allowcoils to be placed so as to provide a magnetic fielof sufficient intensity to melt the weld material.

Ultrasonic WeldingUltrasonic energy is transmitted to thermoplasticsin the form of high-frequency mechanical vibra-tions that cause the areas in contact to melt byfrictional heat and to fuse together, producing ahigh-strength joint.

A power supply converts a line voltage of50–60 Hz to an ultrasonic frequency, generally20 kHz. A transducer then converts the 20 kHzelectrical energy to mechanical energy of the samfrequency. The horn (metal tool that contacts thework) transmits the mechanical vibrations of thetransducer to the parts being assembled. Hytrel® hasbeen successfully welded using ultrasonics; how-ever, the rate of welding is slower than for othermethods because the contact area of the horn isrelatively small.

The following considerations are important indetermining the applicability of this method toHytrel®.

5

• The more rigid plastics are easier to weld.Hytrel® requires high-power input because ofits flexibility.

• The higher the modulus, coefficient of friction,and thermal conductivity, the easier it is to weld.

• The lower the melt temperature, density, andspecific heat, the easier it is to weld.

• Mold release agents and lubricants can reducefrictional heating and must be removed.

• If different grades of Hytrel® are being assembled,the melting points of these grades should differ byno more than 10–15°C (18–27°F).

Spin/Friction WeldingFriction welding is generally considered to meanrotary or spin welding, where one part is rotatedat high speed against the other while a steadypressure is applied. Frictional heat develops atthe surface, and when a prescribed amount of meltis developed, rotation is stopped while pressureis maintained on the joint until the bond hassolidified.

Basic variables of spin welding are rotationalspeed, joint pressure, and spin time. If two differentHytrel® grades having differing melting points areto be assembled by this process, these variablesmust be adjusted such that both polymer surfacesare melted.

A limitation of the spin welding technique is thedifficulty in using it for very flexible polymersor thin cross sections. Spinning parts of theseflexible materials under pressure will cause dis-tortion of the bonded area.

Welding Hytrel ® to Other ThermoplasticsA limited amount of work has been done onwelding Hytrel® to other thermoplastics, usingthe hot plate method.

It should be noted that in some cases it is necessaryto use plate temperatures that are higher than thosenormally recommended for Hytrel®-to-Hytrel®

welding. This may cause stringing of the moltenHytrel®. It is sometimes necessary to use differentplate contact times and pressures for the twomaterials.

The following results were obtained when severalother thermoplastic materials were hot plate weldedto Hytrel®. Plate temperatures were normally 300°C(572°F) with melt and weld times of 7–9 sec.

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Good Welds Questionable No WeldPolycarbonate Styrene ABSSAN Polyether sulphone PolypropyleneCellulose acetate EVA Nylon 6,6PVC Polyethylene

Acrylic

It is emphasized that these are general conclusioand in any application involving welding of Hytrel®

to other plastics, trials should be made with theparticular grades of material being considered.

OvermoldingOvermolding (or insert molding) is a process inwhich a thermoplastic material is molded directlyonto a second thermoplastic material (the insert).Hytrel® generally overmolds best when used withother grades of Hytrel®; however, other materialscan be used.

The optimum process requires that the insert gradhave a relatively low melting point (<190°C[<374°F]), and preferably with a broad meltingrange for slower crystallization. In order to achieva good bond, the material used as the overmoldshould be injected at least 30°C (54°F) higher inmelt temperature and be processed at a somewhhigher temperature than is typically used forinjection molding. This ensures that the highermelting resin can melt the surface of the insert,thus establishing a good bond.

If these requirements cannot be met, then thedesign may incorporate a mechanical bond(molded- in mechanical locking devices) or designwith some flash or projection that can melt togethto form a bond. The insert can also be mechanicaabraded or may even require an adhesive to achia good bond. In all cases, the insert should be dryand free of grease and oil, which could interferewith a good bond.

Bearings and SealsHytrel® engineering thermoplastic elastomer hasbeen used in a number of bearing and seal appli-cations where flexibility, chemical resistance, oruseful temperature range not found in other elas-tomers or plastics is required.

A convenient way to assess the suitability ofa material for use in unlubricated bearing appli-cations is to determine whether the pressure andvelocity (PV) of the proposed bearing is lower thathe PV limit for the material under the operatingconditions foreseen. The PV limit for a material isthe product of limiting bearing pressure MPa (psi)and peripheral velocity m/min (fpm), or bearingpressure and limiting velocity, in a given dynamic

5

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system (Tables 33 and 34). It describes a critical,easy to recognize change in the bearing perfor-mance of the material in the given system. Whenthe PV limit is exceeded, one of the followingmanifestations may occur:• melting• cold flow or creep• unstable friction• transition from mild to severe wear

PV limit is generally related to rubbing surfacetemperature limit. As such, PV limit decreases withincreasing ambient temperature. The PV limitsdetermined on any given tester geometry andambient temperature can rank materials, buttranslation of test PV limits to other geometriesis difficult.

For a given bearing application, the product of PVis independent of the bearing material. Wear isdependent on PV for any material.

The use of experimentally determined PV limitsin specific applications should be consideredapproximate because all pertinent factors are noteasily defined. This means that a generous safetyfactor is an important consideration in bearingdesign. Some factors known to affect PV limits are:• absolute pressure• velocity• lubrication• ambient temperature• clearances• type of mating materials• surface roughness

Table 33PV Limit and Wear Factor

ASTM D 3702, SI Units

PV Limit Wear Factor, K

MPa × × 10–3

G4074 1.1 39

4056 2.1 22

5556 2.1 2.0

6346 6.3 2.1

7246 8.4 0.48

ft

min

in3⋅min

ft⋅lb/hrType of Hytrel

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Table 34PV Limit and Wear FactorASTM D 3702, English Units

PV Limit Wear Factor, K

× × 10–10

G4074 500 32,200

4056 1,000 17,900

5556 1,000 1,620

6346 3,000 1,750

7246 4,000 400

As indicated previously, the PV limit decreaseswith any change that results in increase of thecoefficient of friction or reduced heat dissipationfrom the bearing zone. This observation and in-dustrial experience leads to the following sugges-tions for bearing design:• Design bearing sections as thin as is consistent

with application requirements. This maximizesheat conduction through the plastic materialadjacent to the bearing surface and reducesthermal expansion.

• Metal/plastic bearing interfaces run coolerthan plastic/plastic interfaces, because heat isconducted from the interface more rapidly bymetal than plastic. Metal/plastic bearings havehigher PV limits than plastic/plastic bearings.

• Provision for air circulation about the bearingcan bring about cooler operation.

• Lubrication can greatly increase the PV limit,depending on type and quantity of lubrication.Where lubricants are used, these must be stablat the bearing temperature.

• For unlubricated bearings of Hytrel® on metal, themetal should be as hard and smooth as is constent with bearing life requirements and bearingcost.

• Bearing clearance is essential to allow for thermexpansion or contraction and other effects.

• Surface grooves should be provided in the bearing so that wear debris may be cleared from thebearing area. For lubricated bearings, the groovcan increase the supply of lubricant. Bearingpressure will increase with grooving.

• For the bearing applications in dirty environ-ments, use of seals or felt rings can increasebearing life if they are effective in preventingpenetration of dirt into the bearing.

m

min

mm3⋅min

m⋅N/hrType of Hytrel

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GearsA growing number of applications have shownHytrel® engineering thermoplastic elastomer to bean excellent material for gears. Two factors giveHytrel® a decided advantage over some materials certain applications.• Greater flexibility compared to plastics and

metals used in gears results in quieter operation• The ability of Hytrel® to be melt cast means

that large gears with thick sections can be pro-duced—much larger than is possible by injectionmolding.

Some other advantages of using Hytrel® in gearsare as follows:• Post-machining operations or burr removal are

usually not required• Possible combination of gears with other

elements, such as springs, bearings, ratchets,cams, and other gears

• Low weight• Corrosion resistance• Electrical insulation• Shock absorption

Boots and BellowsFigure 47 shows a blow-molded CVJ boot forautomotive axles. Hytrel® replaces vulcanizedrubber in boots previously used in this application.The higher modulus allows thinner wall thicknessat the same strength and lower weight. The prodution cost of a blow-molded boot is considerablylower than for an injection-molded rubber boot.

An optimized thermoplastic boot differs from themany available rubber boots. The folded edges arflat and have small radii at the tip as depicted inFigure 48. It is very important that the boot doesnot kink when it is being bent as this would lead toa premature failure. Excessive stretching of theboot leads to kinking at the inside. It is vital that thboot be designed in such a way that the originallength, as produced, is identical to the maximumextended length in use. This way, the boot is onlystressed in compression, and kinking is avoided.

The advantage of a thermoplastic axle boot, ascompared with a rubber boot, is that the impactresistance is higher. The Hytrel® boot has a longeruseful life, and it retains its shape better at highspeeds. In addition, the Hytrel® boot shows superiorlow temperature properties.

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Under dynamic loads, stresses will develop at thetips of the folds. When loaded in flexure up to themaximum deformation, the stress will increaseproportionally to the wall thickness in the outerregions of the boot. The flex fatigue resistance,consequently, can be optimized by reducing thewall thickness. However, the tear resistance and timpact resistance are also important considerationTherefore, the wall thickness can only be reducedto the point that all mechanical requirements arestill being met. All these factors combined lead toa lower cost boot.

Figure 47. Automotive CVJ Boot

Figure 48. Boot Design

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Rolling DiaphragmsBecause of its flexibility and fatigue resistance,Hytrel® is suitable for use in many diaphragmapplications. Its high modulus, compared to vul-canized rubber, allows a thinner cross section andpossible elimination of fabric reinforcement, whichcombined with thermoplastic processing, oftenresult in a lower cost part.

Pictured in Figure 49 is a rolling type diaphragm,which provides a longer stroke than a flat dia-phragm. A plastic diaphragm of this type must bedesigned so that there is no circumferential com-pression of the diaphragm as it rolls from thecylinder wall to the piston, which causes wrinklingor buckling and results in early failure. There aretwo ways to accomplish this design:• Use a piston with a tapered skirt to keep the com

pression to a minimum, as shown in Figure 50.• Design the system so that the piston moves only

in the direction that will roll the diaphragm fromthe piston to the cylinder wall, as related to themolded shape of the diaphragm.

Reprinted with permission from Bellofram Corp.

DP

DP + Convolution width

Reprinted with permission from Bellofram Corp.

hes.

Figure 49. Rolling Type Diaphragm

Figure 50. Tapered Piston Skirt

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BeltsHytrel® has proven to be an excellent material forpower transmission and conveyor belting. It can bmade in “V,” round, flat, and other configurations.Its high tensile modulus, compared to rubber, eliminates the need for reinforcing cord in many appli-cations, which means that belting can be extrudedin long lengths and stocked in rolls. When a belt isneeded, a length is cut off and heat spliced to maa finished belt.

Belts of Hytrel® should be made to the samedimensions as the belts being replaced. In applications involving large diameter pulleys and moderaspeeds, belts of Hytrel® have outlasted vulcanizedrubber belts by a wide margin. Small-diameterpulleys and high speeds should be avoided, asthese result in excessive heat buildup and failureof the belt.

Heat splicing of the belt is a simple process, butmust be done properly for best results. A 45° biascut will generally give the best splice. After cuttingthe ends to be spliced are heated above the meltipoint of the material with a heating paddle and thejoined together. Two important points are:• The belt ends must not be pushed so tightly

together that the melt is squeezed from betweenthe ends.

• The ends must be held motionless until the melhas solidified. A fixture that will hold the beltends properly will help ensure a good splice.Flash is trimmed from the splice with a knifeor clippers.

Excessive moisture content will cause degrada-tion of the melt in the splice as it does during anyother processing operation (see the “Rheology anHandling” bulletin). For best results, the ends ofthe belt should be dried before splicing or thebelting should be stored in a dry atmosphere,such as a heated cabinet.

Coiled Tubing and CablesProducts such as coiled pneumatic tubing andcoiled electrical cables are made from Hytrel® bywinding an extruded profile around a mandreland then heat setting. The coil will spring back tosome extent when released so the mandrel must smaller than the desired final diameter of the coil.Exact mandrel size must be determined for eachapplication by trial and error.

Recommended temperatures for heat setting areshown in Table 35. Parts must be held at the settintemperature only long enough to heat the entirecross section of the part to the setting temperatur

5

Parts may be cooled by air at room temperatureand should remain on the mandrel until cooled.

Table 35Heat Setting Temperature

Temperature


4056 107 225

5556 125 255

6346 125 255

7246 150 300

Reinforced HoseIn the design of reinforced hose, three importantfactors to consider in the choice of the tube andcover materials are: resistance to the environmentin which the hose must operate, strength, andflexibility of the material. Based on these factorsand others, Hytrel® thermoplastic elastomer hasbeen chosen for several hose applications such ashydraulic and paint spray hose. As a cover, Hytrel®

offers excellent resistance to abrasion and weather-ing. UV stabilizer concentrate, Hytrel® 20UV, shouldbe added to the cover material if it will be exposedto sunlight. Similarly, thin-walled hose linings ofHytrel® must be protected from UV light that passesthrough the cover. Carbon black is an effectivescreen (see Effect of Environment on p. 26).

In fire hose and other lay-flat hoses, it is possible touse a tube of Hytrel®, which is thinner than avulcanized rubber tube, making the hoses lighterand easier to handle. Hytrel® can be used inSAE100R7 and R8 thermoplastic hydraulic hoses,which offer the advantages of lighter weight and awider color selection than steel-reinforced rubberhose.

In the design of thin-walled tubing of Hytrel®, caremust be taken that the expansion of the liningagainst the cover does not exceed the elastic limitof Hytrel®.

If the finished hose is to be coupled, creep, thermalexpansion, and cut or notch sensitivity must beconsidered in the fitting design. Creep data forHytrel® may be calculated from the creep modulusplots (see pages 15 and 16). Sharp edges andburrs should be avoided when designing fittingsfor hoses based on Hytrel®. In all cases, the finalfitting design should be tested under actual orclosely simulated service conditions to ensuresatisfactory performance.

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Identity and Trademark Standards

Guidelines for Customer Use—Joint ventures and authorizedresellersOnly joint ventures and resellers who have signed special agreements with DuPont to resell DuPontproducts in their original form and/or packaging are authorized to use the Oval trademark, subject to theapproval of an External Affairs representative.

Guidelines for Customer Use—All other customersAll other customer usage is limited to a product signature arrangement, using Times Roman typography,that allows mention of DuPont products that serve as ingredients in the customer’s products. In this signa-ture, the phrase, “Only by DuPont” follows the product name.

Hytrel®

Only by DuPont

A registration notice ® or an asterisk referencing the registration is required. In text, “Only by DuPont”may follow the product name on the same line, separated by two letter-spaces (see above example). Whena DuPont product name is used in text, a ® or a reference by use of an asterisk must follow the productname. For example, “This device is made of quality DuPont Hytrel® thermoplastic polyester elastomer fordurability and corrosion resistance.”

*Hytrel® is a DuPont registered trademark. Only DuPont makes Hytrel®.

Hytrel® Only by DuPont or

thermoplastic polyester elastomerHytrel®

e

Printed in U.S.A.[Replaces: H-57474] (95.1)Reorder No.: H-81098 (00.2)

For more information onEngineering Polymers:

For Automotive Inquiries: (800) 533-1313

1-800-441-0575

StartwithDuPont

U.S.A.EastDuPont Engineering PolymersChestnut Run Plaza 713P.O. Box 80713Wilmington, DE 19880-0713(302) 999-4592

AutomotiveDuPont Engineering PolymersAutomotive Products950 Stephenson HighwayTroy, MI 48007-7013(248) 583-8000

Asia PacificDuPont Asia Pacific Ltd.P.O. Box TST 98851Tsim Sha TsuiKowloon, Hong Kong852-3-734-5345

CanadaDuPont Canada, Inc.DuPont Engineering PolymersP.O. Box 2200Streetsville, MississaugaOntario, Canada L5M 2H3(905) 821-5953

EuropeDuPont de Nemours Int’l S.A.2, chemin du PavillonP.O. Box 50CH-1218 Le Grand-SaconnexGeneva, SwitzerlandTel.: ##41 22 7175111Telefax: ##41 22 7175200

JapanDuPont Kabushiki KaishaArco Tower8-1, Shimomeguro 1-chomeMeguro-ku, Tokyo 153Japan(011) 81-3-5434-6100

MexicoDuPont S.A. de C.V.Homero 206Col. Chapultepec Morales11570 Mexico D.F.(011 525) 722-1456

South AmericaDuPont America do SulAl. Itapecuru, 506Alphaville—CEP: 06454-080Barueri—São Paulo, BrasilTel.: (055-11) 7266-8182Fax: (055-11) 7266-8513Telex: (055-11) 71414 PONT BR

DuPont Argentina S.A.Avda.Mitre y Calle 5(1884) Berazategui-Bs.As.Tel.: (541) 319-4484/85/86Fax: (541) 319-4417

The data listed here fall within the normal range of properties, but they should not be used to establish specification limits nor used alone as the basis ofdesign. The DuPont Company assumes no obligations or liability for any advice furnished or for any results obtained with respect to this information.All such advice is given and accepted at the buyer’s risk. The disclosure of information herein is not a license to operate under, or a recommendation toinfringe, any patent of DuPont or others. DuPont warrants that the use or sale of any material that is described herein and is offered for sale by DuPontdoes not infringe any patent covering the material itself, but does not warrant against infringement by reason of the use thereof in combination with othermaterials or in the operation of any process.

CAUTION: Do not use in medical applications involving permanent implantation in the human body. For other medical applications, see “DuPontMedical Caution Statement,” H-50102.

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