LONG FIBER COMPOUNDSMold Design And

Processing ConditionsA Guide to Processing

Long Fiber Specialty Compounds

English/Standard and SI Metric

web site: www.rtpcompany.com

Table of Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

Molding Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . .3-4

Processing Conditions . . . . . . . . . . . . . . . . . . . . . . . . . .5

Troubleshooting Guide . . . . . . . . . . . . . . . . . . . . . . . . . .6

No information supplied by RTP Company constitutes a warranty regarding product performance or use. Any information regarding performance or use is only offered as suggestion forinvestigation for use, based upon RTP Company or other customer experience. RTP Company makes no warranties, expressed or implied, concerning the suitability or fitness of any ofits products for any particular purpose. It is the responsibility of the customer to determine that the product is safe, lawful and technically suitable for the intended use. The disclosure ofinformation herein is not a license to operate under, or a recommendation to infringe any patents.

LONG FIBER COMPOUNDSMOLD DESIGN & PROCESSING CONDITIONS

2

Engineering Design ConsiderationsRTP Company’s Long Fiber Compounds produce tough, yet lightweight injection molded parts. The propertyadvantages of the long fibers make these materials ideal replacements for metal. The reinforcement additivessuch as glass, aramid, carbon, and stainless steel fibers require design considerations very similar to thatrequired by short fiber reinforced materials. These reinforcing fibers provide the higher mechanical propertiesneeded for metal replacement by acting in an anisotropic manner (directionally non-uniform).

To maximize the benefits of Long Fiber Compounds, gate location should be evaluated for alignment of optimummechanical properties relative to the part’s structural requirements. Other issues such as placement of weld linesin the part design need to be considered much in the same manner as short fiber reinforced materials.

Comparison of Long & Short Fiber Pellets

• 0.43 in/11 mm long

• 0.12 in/3 mm diameter

• Parallel fibers run length of the pellet

• 30-60% fiber by weight

• Fibers encapsulated with resin

Characteristics of RTP Company’s long fiber pellets:

LONG FIBER COMPOUNDSMOLD DESIGN & PROCESSING CONDITIONS

Need Assistance?

For more information, pleasecontact your local sales repre-sentative or one of our experi-enced technical support repre-sentatives who can assist youwith:

•

•

•

•

For technical assistance, Call:(800) 433-4787 or(507) 454-6900

or Email:rtp@rtpcompany.com

Evaluating mold design andsetup

Optimizing processingconditions based on material

New material considerations

Problem investigation andresolution

• Pellets typically 0.12 in/3 mm long

• Fibers typically 0.04 in/1 mm long

• Random fibers varying in length and

orientation

Characteristics of short fiber pellets:

ToolingConsiderations• Full round runners with a diameter

of 0.25” (5.56 mm) are preferred

• Runners should have no sharp corners• Minimum gate thickness of 0.080”

(2 mm)

• Sprues as short as possible, withinitial diameter of 0.25” (5.56 mm),tapered to 11/32” (8.73 mm)

• Open channel type hot runnersystems are acceptable

• Use same materials for molds asfor other reinforced materials

ProcessingConsiderations• Feed throat from hopper to

machine must have sufficientopening to prevent bridging oflong pellet composition

• Reverse barrel profile to “pre-soak” or “soften fibers”

• Minimum back pressure shouldbe used, typically 25-50 psi(0.17-0.34 MPa)

Molding TemperatureRefer to the Processing Conditionsfor recommended starting tempera-tures. Normally, reinforced materialsrequire higher mold temperaturesthan non-reinforced materials. Thishelps achieve a smoother, moreblemish free surface by providing aresin rich skin on the molded part.

Minimizing Wear in Processing EquipmentHighly-filled engineering plastics cancause wear on conventional steelmolds constructed with insufficienthardness. Of the factors causingwear, fiberglass content has the mostinfluence with a Mohs hardness of 5to 7. Comparatively, carbon fiber hasa Mohs hardness of 2, and commontool steels have a hardness of 4.

Wear can be minimized by properprocessing and properly hardenedtool steel cavities, cores, runner sys-tems and sprue bushings. Cavitiesmust be vented at the end of fill tominimize trapped gasses, whichcould cause pitting from high temper-atures. Gates can be affected by thefast injection speeds used in process-ing glass-filled Long FiberCompounds. These speeds cancause high temperatures and a lossof hardness.

The mold cavity and core finish playan important role in tool longevity,and machining marks have beenshown to accelerate wear. A 4microinch (0.0001 mm) or better fin-ish is recommended for high produc-

When processed properly, Long Fiber Compounds retain their fiber length during molding. Correct process-ing is critical to maintaining high-quality parts; breaking the fibers during processing can result in sharplyreduced material properties.

These molding guidelines are offered as suggestions and may be subject to modification, depending on yourspecific material or design. Please contact RTP Company’s technical service representatives for assistance.

Equipment ConsiderationsA general purpose screw that utilizes a typical three-zone style is best for pro-cessing RTP Company Long Fiber Compounds. The screw has three sec-tions: feed, compression, and metering. Metering should be done with anL/D ratio of 16:1 to 22:1, with a low compression ratio of 2:1 to 2.5:1.

A 100% “Free Flow” fluted screw tip valve assembly is required to allowsmooth melt flow. The nozzle/sprue orifice should have generous dimen-sions (0.250”/5.56mm) and be without sharp edges or severe convolutions.Do not use internally tapered tips or tips without a constant diameter path-way.

Material construction for screws and barrels can be the same as for standardreinforced materials.

3

Three Piece Screw Tip Ring Valve

Passagewayssized to provide

smooth open melt flow

High Polish

Precision ground matingsurfaces for effective sealing

100% “Free Flow” design

All components made from highquality, high puritytool steel.

LONG FIBER COMPOUNDSMOLDING GUIDLINES

(continued on page 4)

(continued from page 3)

Vacuum Loader

Material Hopper(Maintain Full Hopper) Insulated

Dry Air HoseAir Spreader Cone

Dry Air

Humid Air Hose

Blower

MaterialCatch Pan

Afterheater

Bedheater

Desiccant Bed

Filtered Air Hose_<125¡F

Molding Machine Filter Dryer

Long Fiber Compound

Wet Air

tion cores and cavities. Gatesshould be hardened and replaceableto obtain mold longevity.

Many tool steels are able to resist theerosion caused by glass filled materi-als. The choice of tool steel is dictat-ed by economics, location within themold and life expectancy required.The following are tool steels withgood abrasion resistance:

• A-2 Steel resists serious abrasionwhen hardened to 58-60 RockwellC(Rc)

• D-2 Steel contains more chromium,is more resistant to abrasion, and issomewhat harder to machine thanA-2. D-2 is limited to smaller com-ponents due to its brittleness.

Mold plating is an excellent way toimprove the service life of a mold.

Effective abrasion-resistant coatingsinclude electroless nickel plating,slow deposition dense chrome, andnye-carb plating.

For long production molds, A-2 or D-2tool steel hardened to RockwellC~60+ is recommended. Of these,A-2 steel is a little more flexible andforgiving. For low volume runs, S-7and H-13 are acceptable softersteels.

Drying Long FiberCompoundsMoisture may be present in somematerials, either on the surface orabsorbed by the resin system.Without proper drying, this moisture

may be converted to steam in theinjection cylinder and cause blisters,splay, internal voids, and laminationof the molded part’s surface.Undried hygroscopic materials cansuffer degradation of properties.

RegrindRegrind materials may be used to amaximum level of 5% without signifi-cantly changing Long FiberCompound properties. Higher per-centages reduce average fiberlength, negatively affecting impactresistance and other structural prop-erties. Accurately mix ground run-ners, sprue, and rejects with the vir-gin pellets, being careful to keep themixture free of contamination.

4

LONG FIBER COMPOUNDSMOLDING GUIDLINES

In the hopper, the drying units force hot dehumidi-fied air through the plastic granule by way of a closedair circulating system. The moisture is removed by thesieve desiccant, which traps the moisture molecules.The dry air is then heated to a preset temperature anddelivered to the material in the insulated hopper.

The majority of water is absorbed in the initial con-tact with the desiccant bed. When the bed becomes

saturated, it is regeneratedby heating to more than500°F (290°C), purging itselfof moisture. Properly main-tained dryer systems giveconsistently dry resin, high-er yields, and improvedstream time, which can yieldgreater profits. Desiccantsshould be replaced everytwo years, and dryer filtersshould be checked andcleaned once each shift toinsure adequate air flow tothe bed.

Typical Dehumidifying Closed Systems for Drying Long Fiber Compounds

Rear Center Front

216-232 210-227 204-221260-285 254-279 249-274249-271 232-266 221-260282-293 277-288 274-282249-271 232-266 221-260299-321 288-304 277-293221-238 216-232 204-221177-199 188-216 199-227243-275 238-252 232-246249-271 243-299 238-260309-321 299-309 288-299343-360 349-366 343-360354-383 349-371 343-360382-416 362-385 343-366216-232 210-227 204-221309-324 304-318 299-313271-282 257-268 240-251

Melt Mold

210-249 37-77271-299 65-122243-271 54-93277-299 82-124243-271 54-93288-316 82-121210-249 38-66193-238 21-66238-271 65-121313-329 93-149313-329 135-177349-399 135-177349-382 121-163360-399 163-232227-271 52-93304-329 135-163240-282 82-148

Injection Back

69-103 1.75-3.534-124 1.75-3.569-124 1.75-3.569-124 1.75-3.569-124 1.75-3.569-124 17.5-3.569-103 1.75-3.569-124 1.75-3.569-124 1.75-3.569-103 1.75-3.569-103 1.75-3.569-124 1.75-3.569-124 1.75-3.569-124 1.75-3.569-103 1.75-3.569-124 1.75-3.569-124 1.75-3.5

Drying Time@ Temp. (°C)

4 hrs @ 822-4 hrs @ 79

2 hrs @ 822 hrs @ 792 hrs @ 82

2-4 hrs @ 792 hrs @ 822 hrs @ 794 hrs @ 1214 hrs @ 1496 hrs @ 1494 hrs @ 1494 hrs @ 1353 hrs @ 1496 hrs @ 1074 hrs @ 1214 hrs @ 60

Dew MoisturePoint (°F) Content

-29 0.02%-18 0.20%-29 0.20%-18 0.02%-29 0.20%-29 0.02%N/A N/A-29 0.20%-29 0.02%-71 0.04%N/A 0.04%-32 0.04%-29 0.02%-29 0.02%-32 0.01%-32 0.05%-32 0.02%

Processing Temperatures (°C) Pressures (MPa)

Injection and Screw Speeds: A slow injection speed of 12.7-25.4 mm/second and a screw speed of 30 to 70 RPMare recommended for all polymers in the above chart.

5

Polymer

RTP 100 Series PPRTP 200 Series Nylon 6/6RTP 200A Series Nylon 6RTP 200B Series Nylon 6/10RTP 200D Series Nylon 6/12RTP 300 Series PCRTP 400 Series PSRTP 700 Series HDPERTP 1000 Series PBTRTP 1100 Series PETRTP 1300 Series PPSRTP 1400 Series PESRTP 2100 Series PEIRTP 2200 Series PEEKRTP 2300 Series RTPURTP 4000 Series PPARTP 4500 Series PK

English/Standard Measurements

Melt Mold

410-480 100-170520-570 150-255470-520 130-200530-570 180-250470-520 130-200550-600 180-250410-480 100-150380-450 70-150460-520 150-250480-560 275-350595-625 275-350660-750 275-350660-720 250-325680-750 325-450430-470 125-200580-625 275-325465-540 180-300

Injection Back

10,000-15,000 25-505,000-18,000 25-50

10,000-18,000 25-5010,000-18,000 25-5010,000-18,000 25-5010,000-18,000 25-5010,000-15,000 25-5010,000-18,000 25-5010,000-18,000 25-5010,000-15,000 25-5010,000-15,000 25-5010,000-18,000 25-5010,000-18,000 25-5010,000-18,000 25-5010,000-15,000 25-5010,000-18,000 25-5010,000-18,000 25-50

Drying Time@ Temp. (°F)

4 hrs @ 1802-4 hrs @ 175

2 hrs @ 1802 hrs @ 1752 hrs @ 180

2-4 hrs @ 1752 hrs @ 1802 hrs @ 1754 hrs @ 2504 hrs @ 3006 hrs @ 3004 hrs @ 3004 hrs @ 2753 hrs @ 3006 hrs @ 2254 hrs @ 2504 hrs @ 140

Dew MoisturePoint (°F) Content

-20 0.02%0 0.20%

-20 0.20%0 0.02%

-20 0.20%-20 0.02%N/A N/A-20 0.20%-20 0.02%-40 0.04%N/A 0.04%-25 0.04%-20 0.02%-20 0.02%-25 0.01%-25 0.05%-25 0.02%

Processing Temperatures (°F) Pressures (psi)

Polymer

RTP 100 Series PPRTP 200 Series Nylon 6/6RTP 200A Series Nylon 6RTP 200B Series Nylon 6/10RTP 200D Series Nylon 6/12RTP 300 Series PCRTP 400 Series PSRTP 700 Series HDPERTP 1000 Series PBTRTP 1100 Series PETRTP 1300 Series PPSRTP 1400 Series PESRTP 2100 Series PEIRTP 2200 Series PEEKRTP 2300 Series RTPURTP 4000 Series PPARTP 4500 Series PK

Rear Center Front

420-450 410-440 400-430500-545 490-535 480-525480-520 450-510 430-500540-560 530-550 525-540480-520 450-510 430-500570-610 550-580 530-560430-460 420-450 400-430350-390 370-420 390-440470-495 460-485 450-475480-520 470-570 460-500590-610 570-590 550-570670-700 660-690 650-680670-720 660-700 650-680720-780 685-725 650-690420-450 410-440 400-430590-615 580-605 570-595520-540 495-515 465-485

S.I. Metric Measurements

Injection and Screw Speeds: A slow injection speed of 0.5-1”/second and a screw speed of 30 to 70 RPM arerecommended for all polymers in the above chart.

LONG FIBER COMPOUNDSPROCESSING CONDITIONS

Change Gate LocationClean Mold FacesClean VentsCheck for Material ContaminationCheck for Uneven Mold TemperatureCheck Mold Faces for Proper FitDry MaterialIncrease Amount of MaterialIncrease Back PressureIncrease Clamp PressureIncrease Cooling TimeIncrease Holding PressureIncrease Injection Hold TimeIncrease Injection PressureIncrease Injection SpeedIncrease Injection TimeIncrease Mold TemperatureIncrease Size of GatesIncrease Size of RunnersIncrease Size of SprueIncrease Size of VentLocate Gates Near Heavy Cross SectionsRaise Material TemperatureRedesign Ejection MechanismReduce Amount of RegrindReduce Back PressureReduce Cylinder TemperatureReduce Holding PressureReduce Injection PressureReduce Injection SpeedReduce Mold TemperatureReduce Molded StressReduce Overall Cycle TimeReduce Screw Speed

SUGGESTED REMEDIESTry in numerical order

Blisters

Brittleness

Excessive Flash

Gas B

urnsO

versized Part

Poor Surface Finish

Silver S

treakingS

ink Marks

Poor Weld Lines

Short S

hots

Undersized Part

VoidsW

arping

PROBLEM

1

111

1

1 1 1

1

11

1

1

2

2

2 22 2

2

2 22

3 3

33

3

33 3

3

3

4

4

4

4

44

4

4

4

4

4

2

2

2

3

3

34

4

55

5

5

55

5

5

5

5

5 5

5

66

6 6 6

6 6

6

66

6

6

6

7

7

7

7

7

7

7

7

7

7

78

8

8

8

8

8

8

8

8

8

9

9

9

9

9

9 9

10

10

10

10

10

10

11

11

11

11

12

12

12

6

Perform in numerical order by column

LONG FIBER COMPOUNDSTROUBLESHOOTING GUIDE

Headquarters:RTP Company580 East Front StreetWinona, MN 55987-0439(507) 454-6900(800) 433-4787Fax: (507) 454-2089Web site: www.rtpcompany.comEmail: rtp@rtpcompany.com

Manufacturing Facilities:

Winona, Minnesota

South Boston, Virgina

Dayton, Nevada

Beaune, France

Fort Worth, Texas

Indianapolis, Indiana

This information is intended to be used only as a guideline for designers and processors of modified thermoplastics for injection molding. Because injection mold design and processingis complex, a set solution will not solve all problems. Observation on a “trial and error” basis may be required to achieve desired results.

No information supplied by RTP Company constitutes a warranty regarding product performance or use. Any information regarding performance or use is only offered as suggestion forinvestigation for use, based upon RTP Company or other customer experience. RTP Company makes no warranties, expressed or implied, concerning the suitability or fitness of any ofits products for any particular purpose. It is the responsibility of the customer to determine that the product is safe, lawful and technically suitable for the intended use. The disclosure ofinformation herein is not a license to operate under, or a recommendation to infringe any patents.