Extrusion Resistance of Elastomers: A study of factors that affect performance

Transcription

1 Extrusion Resistance of Elastomers: A study of factors that affect performance RubberCon 212 Peter Warren Previously presented at High Performance Elastomers & Polymers for Oil and Gas Applications Aberdeen, 212 High Performance Sealing Technology James Walker 212

2 Outline Examples and mechanisms of extrusion damage Test procedure Extrusion resistance of bisphenol fluoroelastomers Extrusion resistance of peroxide fluoroelastomers Extrusion resistance of peroxide HNBR s Influence of filler level Influence of crosslink density Other reinforcements Increased groove fill and constant pressure Summary of findings

3 Examples of Extrusion Damage - 1 Lace type extrusion damage Clearance generally small Occurs over medium to long periods of time

4 Localised anti-extrusion device failure Examples of Extrusion Damage - 2

5 Examples of Extrusion Damage - 3 Nibbling damage Normally observed with pressure cycling System pressure causes housing to lift or dilate so clearance increases Nub of elastomer extrudes into clearance, and is nibbled off when pressure drops and clearance reduced.

6 Examples of Extrusion Damage - 4 Schematic of Nibbling damage

7 Examples of Extrusion Damage - 5 Shaving extrusion damage Normally associated with continuous application of pressure Most often occurs with O-rings Seal forced into clearance, and over time unwinds into clearance.

8 Examples of Extrusion Damage - 6 Shaving extrusion damage otherwise known as the Rizla Effect

9 Test Equipment - 1 Diametral extrusion gaps.4 and.8mm (radial.2 and.4mm) Normally recommend max. diametral gaps of.2mm max, and back-up rings >1bar Test temperatures 1 C and 15 C O-ring squeeze 14% Low initial level of groove fill (58%) Worst possible conditions large overspill area on bobbin

10 Test Equipment - 2.4mm Diametral Gap

11 Test Equipment - 3.4mm Diametral Gap - Offset

12 Test Equipment - 4 Seals fitted and air removed from system with oil at min. pressure Stabilised at test temp for 1 hour Pressure ramped up at 4bar/minute until significant pressure drop occurred Seals removed and examined Normally 3 test runs for each set of conditions Pressure and temperature logged via a PC

13 Pressure (bar) Test Equipment 5 Ramp Test Data Time (seconds)

14 Pressure in Bar Bisphenol Cured Fluoroelastomers - 1 Extrusion test failure 1C bar Increased filler level bar Bisphenol 9.4mm Bisphenol 9.8mm Bisphenol 9 + black.4mm Bisphenol 9 + black.8mm Material and extrusion gap

15 Pressure in Bar Bisphenol Cured Fluoroelastomers - 2 Extrusion test failure 15C bar 22 bar Increased filler level Bisphenol 9.4mm Bisphenol 9.8mm Bisphenol 9 + black.4mm Bisphenol 9 + black.8mm Material and extrusion gap

16 Pressure in Bar Peroxide Cured Fluoroelastomers - 1 Extrusion test failure 1C Bisphenol 9.4mm LT Peroxide FKM 9.4mm Peroxide Terpolymer FKM 9.4mm Material and extrusion gap

17 Pressure in Bar Peroxide Cured Fluoroelastomers Extrusion test failure 15C Bisphenol 9.4mm LT Peroxide FKM 9.4mm Material and extrusion gap Peroxide Terpolymer FKM 9.4mm

18 Pressure in Bar Peroxide Cured Fluoroelastomers 3: Extrusion test failure 1C Modified formulation Cure system and filler as terpolymer Median values only LT Peroxide FKM 9.4mm LT Peroxide FKM 9.8mm LT Peroxide FKM 9 EXP.4mm Material and extrusion gap LT Peroxide FKM 9 EXP.8mm

19 Pressure in Bar Peroxide Cured Fluoroelastomers 4: 12 Extrusion test failure 15C Modified formulation LT Peroxide FKM 9.4mm LT Peroxide FKM 9.8mm LT Peroxide FKM 9 EXP.4mm LT Peroxide FKM 9 EXP.8mm Material and extrusion gap Cure system and filler as terpolymer

20 Pressure in Bar 1% 1C and 5% 1C Peroxide Cured Fluoroelastomers 5: Overview Extrusion test failure 1C Hardness 87 to 92 Material and extrusion gap Extrusion resistance not directly related to tensile modulus or hardness Tear strengths of BP and P FKM s similar

21 Pressure in Bar Peroxide Cured Fluoroelastomers 6: Extrusion test failure 1C Influence of viscosity MU higher, otherwise identical formulations Type 3 FKM Supplier 1 FKM 9 S1.4mm Supplier 1 FKM 9 S1.8mm Supplier 2 Peroxide FKM 9 S2.4mm Material and extrusion gap Supplier 2 Peroxide FKM 9 S2.8mm

22 Pressure in Bar Peroxide Cured Fluoroelastomers 7: Extrusion Test failure 15C Influence of viscosity Supplier 1 FKM 9 S1.4mm Supplier 1 FKM 9 S1.8mm Supplier 2 Peroxide FKM 9 S2.4mm Polymer type and formulation appear more influential within this viscosity range Supplier 2 Peroxide FKM 9 S2.8mm Material and extrusion gap

23 Pressure in Bar HNBR Elastomers Extrusion test failure 1C LT Peroxide FKM 9.4mm LT Peroxide FKM 9.8mm Medium ACN HNBR 9.4mm Medium ACN HNBR 9.8mm LT HNBR 9.4mm LT HNBR 9.8mm Material and extrusion gap

24 Pressure in Bar HNBR Elastomers Extrusion Test failure 15C LT Peroxide FKM 9.4mm LT Peroxide FKM 9.8mm Medium ACN HNBR 9.4mm Medium ACN HNBR 9.8mm LT HNBR 9.4mm LT HNBR 9.8mm Material and extrusion gap HNBR shows less decay at higher temperature

25 Pressure in Bar 1% 1C and 5% 1C HNBR Elastomers - 3 Extrusion test failure 1C LT Peroxide FKM 9.4mm LT Peroxide FKM 9.8mm Medium ACN HNBR 9.4mm Medium ACN HNBR 9.8mm LT HNBR 9.4mm LT HNBR 9.8mm Material and extrusion gap Again, modulus does not coincide with extrusion resistance outside polymer type

26 Pressure in Bar HNBR Elastomers 4: Influence of filler level Extrusion test failure 1C Reduced black level / hardness LT HNBR 9.4mm LT HNBR 9.8mm LT HNBR 75.4mm LT HNBR 75.8mm Material and extrusion gap

27 Pressure in Bar HNBR Elastomers 4: Influence of filler level Extrusion Test failure 15C LT HNBR 9.4mm LT HNBR 9.8mm LT HNBR 75.4mm LT HNBR 75.8mm Material and extrusion gap

28 Crosslink Density - 1 Aubert Y Coran. Vulcanisation Science & Technology of Rubber, Academic Press, New York, 1978

29 Pressure in Bar Crosslink Density - 2 Extrusion test failure 1C 1 Post-cured Medium ACN HNBR 9.4mm Medium ACN HNBR 9.8mm Medium ACN HNBR 9 No Post Cure.4mm Material and extrusion gap Medium ACN HNBR 9 No Post Cure.8mm

30 Pressure in Bar Crosslink Density Extrusion test failure 15C Medium ACN HNBR 9.4mm Medium ACN HNBR 9.8mm Medium ACN HNBR 9 No Post Cure.4mm Material and extrusion gap Medium ACN HNBR 9 No Post Cure.8mm

31 Pressure in Bar Other Reinforcements 1 8 Extrusion test failure 1C LT HNBR 9.4mm LT HNBR 9.8mm LT HNBR 9 MWNT.4mm Material and extrusion gap LT HNBR 9 MWNT.8mm LT HNBR 9 Aramid.4mm LT HNBR 9 Aramid.8mm Increase in tensile modulus, decrease in E at B Small decrease in extrusion resistance

32 Pressure in Bar Other Reinforcements LT HNBR 9.4mm Extrusion Test failure 15C LT HNBR 9.8mm LT HNBR 9 MWNT.4mm LT HNBR 9 MWNT.8mm Material and extrusion gap LT HNBR 9 Aramid.4mm LT HNBR 9 Aramid.8mm

33 Other Reinforcements 3 Particle alignment may assist particularly for smaller gaps

34 Reduction in Capabilities Under Constant Pressure - 1 Failure pressure after ramping Selected materials assessed under constant pressure Decreased in increments of 1% Evidence of some seal rotation Housing volume reduced Constant pressure trials run avoided seal rotation

35 Reduction in Capabilities Under Constant Pressure - 1

36 Reduction in Capabilities Under Constant Pressure - 2

37 Conclusions thus far Extrusion resistance difficult to estimate using conventional laboratory tests High modulus values alone do not predict comparative extrusion resistance outside of polymer types Polymer appears main consideration in obtaining good performance Increased filler levels improves resistance with narrow gaps and lower temperatures Crosslink density can make modest improvements within limitations Best results obtained by careful optimisation. Need to consider influence on other properties Constant pressure capability for.4mm diametric clearance thought to be in the region of 4% to 5% of ramped failure pressure

38 Acknowledgements Thanks to: Steve Winterbottom and Andrew Douglas for their work on the paper James Wilkinson for the extrusion test work Duncan Smith and Paul Bowman for designing and procuring the extrusion test fixture

39 Thank you for listening This information is based on our general experience, but because of factors which are outside our knowledge and control, no warranty is given or is to be implied with respect to such information. If any doubt exists, please seek advice from James Walker. James Walker 212 Peter Warren High Performance Sealing Technology James Walker 212