Advanced Troubleshooting of Polyurethane Elastomers. By Nick Skirkanich. Sales Development Manager, COIM USA Inc.

Transcription

1 Advanced Troubleshooting of Polyurethane Elastomers By Nick Skirkanich Sales Development Manager, COIM USA Inc.

2 Troubleshoo*ng Main Categories Raw Material Issues Processing Problems Appearance Problems Field Failures

3 Review Processing Procedures Raw Material Inventory and Storage Prepolymer/Curative Meltdown Prepolymer/Curative Transfer Prepolymer Degassing Mixing Prepolymer and Curative Mold Preparation Casting Cure Demold Postcure Finishing

4 Raw Material Issues

5 Raw Material Issues Prepolymer High Viscosity Prepolymer Difficult Degas Pot Life Changes Gel Time Changes

6 Prepolymer High Viscosity Causes: - Overheated prepolymer Ø Heat history Accumulative - Low prepolymer temperature - Use of inappropriate prepolymer

7 Prepolymer High Viscosity Solutions: - Adhere to melting guidelines - Log heat history of prepolymer - Thermocouple temperature check - Choose proper prepolymer - Manage package size to resin use.

8 Prepolymer Difficult Degas Causes: - High prepolymer viscosity - Insufficient degas vacuum - No degassing agent - Moisture contaminated prepolymer (no N2 cap),excessive degassing time

9 Prepolymer Difficult Degas Solutions: - Check prepolymer temperature and heat history - Check vacuum pump gauge - Add degassing agent - Change prepolymer

10 Pot Life Changes Causes: - Degraded prepolymer - Degraded curative - Improper catalyst addition - Incorrect temperature

11 Pot Life Changes Solutions: - Minimize heat history - Check catalyst addition - Monitor temperatures

12 Gel Time Changes Causes: - Degraded prepolymer - Degraded curative - Improper catalyst addition - Incorrect temperatures

13 Gel Time Changes Solutions: - Minimize heat history - Check catalyst addition - Monitor temperatures

14 Processing Problems

15 Processing Problems Poor Physical Properties Low Hardness

16 Poor Physical Proper*es Causes: - Incorrect stoichiometry - Overheated prepolymer - Incomplete cure

17 Poor Physical Proper*es Solutions: - Calibrate equipment regularly - Minimize heat history - Calculate curative on specific %NCO - Use elemental analyzer (Cl) - Follow supplier guidelines - Test sheets for daily production (ref)

18 Low Hardness Causes: - Overheated prepolymer - Incomplete cure (TDI/ triols) - Incorrect stoichiometry - Inadequate mixing

19 Low Hardness Solutions: - Minimize heat history - Calculate curative on specific %NCO - Mix adequately - Follow curing guidelines

20 Helpful Guidelines Raw Materials & Processing Complete melting of prepoymer - not just enough to use (MW range) Low NCO, (low duro) prepolymers more sensitive NCO content important tool, easy and quick to use Tracking heat history Production check list establishes references for YOUR process Add catayst to bulking agent to accurately meter

21 Helpful Guidelines Raw Materials & Processing II Vacuum trap for degassing (curative like HQEE) Check curative blend compatability / temp dependent (BDO/polyol) Temperature! Temperature! Temperature! v Measure oven temps with thermocouple (Oven hot spots) v Use temperature tape to confirm drum temps v Measure actual mold temperatures at pour. v Know your prepolymer temperature v Measure exotherms for your materials

22 Appearance Problems

23 Appearance Problems Large Voids in Parts Small Bubbles in Parts Excessive Shrinkage, Cracking or Warping Swirls/Streaks in Parts Surface cosmetics

24 Large Voids in Parts Causes: - Air entrapment during pour - Short pot life - Leaking mold

25 Large Voids in Parts Solutions: - Redesign mold/vents - Alter pour technique - Use lower viscosity prepolymer - Add degassing agent

26 Small Bubbles in Parts Causes: - Moisture contamination - Inadequate degassing - Poor pouring technique - Failed seal in machine - Mold leakage (during cure)

27 Small Bubbles in Parts Solutions: - Store products under dry N 2 - Degas all components pre- and post mixing - Mold properly heated - Maintain mix head seals

28 Excessive Shrink/Crack/ Warp Causes: - Incompatible resin and mold temperatures - Localized temperature variation - Low stoichiometry

29 Excessive Shrink/Crack/Warp Solutions: - Balance exotherm and mold temperatures - Heat molds adequately - Monitor raw material temperatures

30 Swirls/Streaks in Parts Causes: - Improper mixing - Unevenly dispersed filler - Knit lines

31 Swirls/Streaks in Parts Solutions: - Ensure mixing all components - Disperse fillers in plasticizer - Use smaller size filler particles - Use high viscosity materials - Use increased pot life systems

32 Surface Cosme*cs Causes - Cool mold temperatures ( lakeing ) surface shrinkage - Leak in mold seal ; drawing air onto surface - Excess mold release

33 Surface Cosme*cs Solutions - Insure mold temps are uniform - Improve seal at mold joints where air intake is located - Monitor/gauge mold release amount and frequency

34 Field Failures

35 Field Failures Part Softening in Use Part Hardening in Use Deformed Part Blowout

36 Field Failures Fatique (cracking/chunking) Polyurethane to Non- Polyurethane Bond Failure Swelling Abrasion Failure

37 Part SoOening in Use Causes: - Contact with solvents - Exposure to excessively high temperatures - Hydrolysis of Ester based resins

38 Part SoOening in Use Solutions: - Shield elastomer from solvents - Insulate elastomer from heat source - Choose proper prepolymer

39 Part Hardening in Use Causes: - Soft segment crystallization - Insufficient cure - Low stoichiometry - Plasticizer leaching

40 Part Hardening in Use Solutions: - Choose correct prepolymer - Use stoichiometry above 90% - Ensure plasticizer compatibility - Follow curing guidelines

41 Deformed Part Causes: - Softening by heat - Poor abrasion resistance - Tendency to be thermoplastic - High compression set

42 Deformed Part Solutions: - Reduce heat exposure - Higher abrasion resistance formula - Reduce load/redesign part - Process at correct stoichiometry

43 Blowout Causes: - Improper system choice - Wrong hardness elastomer - Incorrect stoichiometry - Uneven loading - Too great of a load/speed

44 Blowout Solutions: - Choose correct system - Choose correct hardness - Optimize stoichiometry - Load evenly - Redesign part/application

45 PU to Non- PU Bond Failures Causes: - Poor initial bond - Too much stress at bond line - Overheating - Water/solvent permeation

46 PU to Non- PU Bond Failures Solutions: - Use correct primer/adhesive - Apply adhesive properly (Clean room concept) - Design to minimize stress - Provide cooling - Need correct urethane system

47 Swelling Causes: - Exposure to harmful solvents

48 Swelling Solutions: - Choose proper elastomer - Shield elastomer from solvent - Test elastomer before exposure

49 Abrasion Failure Causes: - Incorrect stoichiometry - Excessive heat buildup - Incorrect system choice

50 Abrasion Failure Solutions: - Choose correct stoichiometry - Minimize heat buildup - Choose correct system

51 References

52 References Trouble Shooting Guide For Polyurethane Elastomers - Brochure Polyurethane Elastomers by Hepburn Castable Polyurethane Elastomers by Clemitson

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