Manufacturing Benefits of Ductile Iron Components in High Pressure Systems

Molly StieberUndergraduate Research Assistant, Milwaukee School of

Engineering (MSOE), Fluid Power Institute

John SchultzNational Account Manager, Dura-Bar

1

Continuous Cast Iron Bar Stock

A high-quality alternativefor low-medium carbon

steel and castings

Grades:Ductile, Gray, Ni-Resist

Shapes:Rectangles/Squares, Rounds, Custom

2

The Continuous Casting Process

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The Continuous Casting Process

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Advantages of Continuous Casting

Water Flow

Cast BarGraphite DieRefractory Lining

Molten Iron

Water Cooler

Water Flow

Cast BarGraphite DieRefractory Lining

Molten Iron

Water Cooler

Impurities that cause gas and slag defects float to the top of the molten iron and cannot enter the dieEliminates Gas & Slag Defects

The head pressure in the bottom of the bar machine constantly feeds iron into the solidifying bar

Eliminates Shrink and Provides Excellent Surface Finishes

The bar exits the die extremely hot and cools to room temperature in still air

Eliminates Hard Spots and Provides Very Consistent Machinability

5

Benefits of Ductile Iron Chips over Steel

Simpler Chip Management

– More easily removed from crevices (deburring)

– More compact– Can handle

without gloves if need be

– Ductile iron chips are cleaner

– Lead free

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Advantages of Ductile Iron vs. SteelDuctile Iron

ASTM A536 65-45-12Steel

AISI 1045/ JIS S45C

Surface Finish ---

Pressure

Quality

Noise/Vibration Damping ---

Machinability/Tool Life ---

Deburring ---

Availability ---

Size Ranges ---

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Typical Applications in Fluid Power

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Ductile Iron Pressure Ratings

Problem:There is no industry

standard for ductile iron pressure ratings.

Solution:Daman, Dura-Bar and

MSOE team up to determine ductile iron

pressure ratings.

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The Steel AlternativeMSOE Research

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Ductile Iron Pressure RatingsBarlow Formula:

Pressure (psi) = 2 * (Wall Thickness (in.)) * (Material Strength (psi))(Inner Diameter of Cylinder (in.))

Variables:Fatigue Strength (psi): 40000 (true for all ductile iron grades)

Safety Factor: 4 10000 psi

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How Stress is Calculated

. .2

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What is the maximum hydraulic pressure?

Depends: Assume 45,000psi maximum stress and a 3”

diameter cylinder with 1/8” wall.

4,0903”

1/8”

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If we increase wall thickness to 1”…

Depends: Assume 45,000psi maximum

stress and a 3” diameter cylinder with 1” wall.

180,0003”

1”

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Minimum Allowable Wall Thickness (inches)

Bore Size (inches)

Maximum Operating System Pressure (bar)

4000 5000 5500 60000.250 0.05 0.06 0.07 0.080.500 0.10 0.13 0.14 0.150.750 0.15 0.19 0.21 0.231.000 0.20 0.25 0.28 0.301.250 0.25 0.31 0.34 0.381.500 0.30 0.38 0.41 0.451.750 0.35 0.44 0.48 0.532.000 0.40 0.50 0.55 0.60

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Maximum System Pressure (psi)

Bore Size (inches)

Burst Area Wall Thickness (inches)

0.125 0.250 0.375 0.500 0.6250.250 10000 20000 30000 40000 500000.500 5000 10000 15000 20000 250000.750 3333 6667 10000 13333 166671.000 2500 5000 7500 10000 125001.250 2000 4000 6000 8000 100001.500 1667 3333 5000 6667 83331.750 1429 2857 4286 5714 71432.000 1250 2500 3750 5000 6250

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Statement of Challenge

Prove and expand table

Data to be used to optimize manifold design

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Pressure Rating Testing by MSOE

Test pressure = 6,000

psi

Rated pressure = 5,172

psi

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Explanation of NFPA Standard T2.6.1 R2-2001

Cyclic Test Pressure = Rated Fatigue Pressure x Kv

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Component Test Results

No manifold failures

Only o-ring extrusions

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Mechanical Property ComparisonDuctile Iron

ASTM A536 65-45-12Steel

AISI 1045

Tensile Strength 65,000 psi/ 448 MPa 81,900 psi

Yield Strength 45,000 psi/ 310 MPa 45,000 psi

Elongation 12% 16%

Hardness- Average 180 BHN 163 BHN

Machinability Rating (1212=100%) 170% 56%

Pieces/ Insert Edge* 340 112

*Relative tool life comparison done at 450 sfm, .010” feed and .125” doc

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Ductile Iron vs. Steel Testing, program overview

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Design Comparison

Varying bore sizes and wall thicknesses

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Ductile Iron vs. Steel Testing Results

No failures of either material

Allowed minimum wall thicknesses in this

configuration to be rated for 6,500 psi

*Method of verifying the rated fatigue pressure (or establishing the rated burst pressure; or both) of the pressure containing envelope conforms to NFPA/T2.6.1 R2-2000, Fluid power components - Method for verifying the fatigue and establishing the burst pressure ratings of the pressure containing envelope of a metal fluid power component, for the values, categories and special conditions (if any) as specified. The configuration shown above has an RFP = 44.82 MPa (6,500 psi), category C/90/ where k0 for ductile iron = 0.14Testing, verification, and rating performed by the Fluid Power Institute at the Milwaukee School of Engineering.

Rated System Pressure*: 6,500 psiBore Size (in) Minimum Allowable Wall

Thickness (in)0.5 0.161 0.332 0.65

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Industry Benefits

Allows ductile iron to be designed into high pressure systems

Increases the maximum pressure at which systems can be run

Decreases manufacturing costs for manifolds

More intelligently, compactly designed manifolds

25

Future Plans

Burst testing

Run test with smaller wall thicknesses to achieve failures

Develop design tool for manifold design

Validate stress equations through testing

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Questions?

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