Project presentationMasters Project in Mechanical Engineering

Rensselaer Polytechnic Institute

Reduction of Friction in a plastic reciprocating arm

By Swamy Ranga

Introduction / Problem Description :

Forward Stroke

Return Stroke

•Reciprocating plastic part

•Life - Number of

operations

•External condition

•Friction

Methodology/Approach :

•Focus on component “ARM” – FMEA

•No Change in any other component design – High investment,

Performance

• Friction properties

•Temperature withstand capability

•Mouldability

•Availability and Cost

•Risk mitigation

Potential Materials:

• Liquid Crystal polymer + PTFE (Self Lubricating)

• Liquid Crystal polymer + Glass + PTFE (Self Lubricating)

Relatively unique class of partially crystalline aromatic polyesters based on p-

hydroxybenzoic acid and related monomers. PTFE addition make it self

lubricating. Glass fibres improves the strength. Features include

1) Good lubricating property with Teflon (PTFE)

2) Superior heat aging performance and retention of properties with

temperature

3) Inherently flame retardant

4) Excellent chemical resistance

5) Superior dielectrics over a wide temperature range

6) Outstanding flow - long paths, thin walls, complex shapes

7) Exceptional dimensional stability, low mold shrinkage, low thermal

expansion.

Potentiel Materials

•Polybutylene Terepthalate + Glass + Internal lubricant

Thermoplastic crystalline polymer, and a type of polyester. PBT is resistant to

solvents, shrinks very little during forming, is mechanically strong, heat-resistant

up to 150°C (or 200°C with glass-fibre reinforcement) and can be treated with

flame retardants to make it noncombustible. Features include

1) Lubricated

2) Flame Retardant

3) Good Chemical Resistance

4) Good Dimensional Stability

5) Good Processability

6) High Impact Resistance

7) Low Moisture Absorption

Material comparison :

MaterialPBT (Current material)

Liquid crystal polymer + PTFE (Self Lubricating)

Liquid crystal polymer + Glass + PTFE (Self Lubricating)

PBT with 30% glass filled, With internal lubricant (Additive)

unit of measurement

Density 1.63 1.5 1.62 1.67 gm/Cu cm

Mold Shrink, Linear flow

0.0010 to 0.0030 in/in (0.1 to 0.3%) 0.0025 in/in

Mold Shrinkage - parallel 0.00% 0.10%Mold Shrinkage - normal 0.70% 0.40%

Mechanical propertiesTensile modulus 1.45E+06 1.02E+06 1.60E+07 1.19E+06 PsiTensile stress at break 18100 23206 25381 15200 PsiTensile strain at break 2% 6% 3% 3.5%Flexural modulus 1.38E+06 1.02E+06 1.52E+06 Psi

Co-efficient of friction - 0.18 0.11(Improved

Lubrication)

Impact

Charpy unnotched impact strength @ 23deg C

23.8 ft.lb/sq in (50.028 KJ/sq mt) 86 KJ/sq mt 38 KJ/sq mt 28.6 ft.lb/sq in

1 ft lb - 1.355818 KJ

Charpy notched impact strength @ 23deg C

3.33 ft.lb/sq in (7 KJ/sq mt) 28 KJ/sq mt 26 KJ/sq mt 5.23 ft.lb/sq in

1 sq inch - 0.000645 sq mt

Izod unnotched impact strength @ 23deg C

21.4 ft.lb/sq in (44.98 KJ/sq mt) 67 KJ/sq mt 33 KJ/sq mt 20.9 ft.lb/sq in

Izod notched impact strength @ 23deg C

3.81 ft.lb/sq in (8 KJ/sq mt) 35 KJ/sq mt 23 KJ/sq mt 4.76 ft.lb/sq in

Rockwell 119 (R Scale) 55 (M Scale) 55 (M Scale)

MaterialPBT (Current material)

Liquid crystal polymer + PTFE (Self Lubricating)

Liquid crystal polymer + Glass + PTFE (Self Lubricating)

PBT with 30% glass filled, With internal lubricant (Additive)

Unit of measurement

Thermal PropertiesHDT B(0.45 Mpa) 220 205 Deg CHDT A(1.8 Mpa) 195 185 Deg CDTUL @ 1.8 Mpa 165 230 Deg CDTUL @ 0.45 Mpa 227 250 Deg CDTUL @ 8.0 Mpa 89 162 Deg C

Electrical propertiesSurface resistivity 1.00E+15 1.00E+15 1.00E+15 1.00E+14 ohmsVolume resistivity 1.00E+15 1.00E+15 1.00E+13 1.00E+15 ohm mtrCTI 225 180 175 330 VDi-electric properties 480 3600 690 V/mmRelative permitivity at 1+06 Hz 3.3 3.3 4Flamability - UL0.0280 in V0 V0 V0 V0

UL746RTI str 140 130 130 140 Deg CRTI imp 130 130 130 130 Deg CRTI elec 130 130 130 140 Deg C

Material comparison :

Samples:•Minimum 4 samples from each material type

•Checked for dimensions, finish etc.

•Assembled in the product and the product marked with material type of Arm.

Test setup & details:•PLC controlled test setup to fire the voltage & control operation rate and

sequence

•600 operations per hour for 24 hours a day

•Target 100,000 operations

•Test will run till failure or till a certain a degree of confidence.

Mechanical Endurance Test Results:

SamplesSample number Arm material

No. of operations (Test running)

No. of operations

(Test stopped) Remarks

1 AC1 PBT (BL) - 62246 Failed due to Friction2 AC2 PBT (BL) 91433 - -3 AC3 PBT (BL) - 58737 Failed due to Friction4 AC4 PBT (BL) 104733 - -5 AC5 PBT (BL) - 79813 Failed due to Friction6 AC6 PBT (BL) - 112525 Failed due to Friction7 AC7 PBT (BL) - 54078 Failed due to Friction8 AC8 PBT (BL) - 54030 Failed due to Friction1 AD1 LCP (GF) 267726 - Test in progress

2 AD2 LCP (GF) 267723 - Test in progress

3 AD3 LCP (GF) 259554 - Test in progress

4 AD4 LCP (GF) 267670 - Test in progress

5 AD5 LCP 184342 - Test in progress

6 AD6 LCP 175473 - Test in progress

7 AD7 LCP 192184 - Test in progress

8 AD8 LCP 192213 - Test in progress

9 AD9 PBT(Lubricated) 91823 Test in progress

10 AD10 PBT(Lubricated) - 89212 Failed due to Friction

11 AD11 PBT(Lubricated) 91824 Test in progress

12 AD12 PBT(Lubricated) 91716 Test in progress

Conclusion :

Material chosen •Liquid Crystal polymer + Glass + PTFE (Self Lubricating) -

Material for usage

•Liquid Crystal polymer + PTFE (Self Lubricating) – Alternate

Material