Guarantee for O-rings? Factors influencing their service life.

Transcription

1

2 Guarantee for O-rings? Factors influencing their service life.

3 Guarantee for O-rings? How long will the O-ring last, and can you guarantee that? WE OFFER YOU NO MATTER HOW YOU USE THEM A 5 YEAR GUARANTEE ON YOUR NEW CAR TIRE

4 Contents Classification of a machine s components How O-rings work Factors that influence their service life Manufacturing process Material properties Environment Fitting/Layout Medium Operating conditions Summary

5 Component classification A-parts High risk but calculable C-parts Risk neutral B-parts High risk but not calculable

6 How O-rings work Surface pressure Surface pressure Pressure P O-ring pressed into installation area without compression load O-ring pressed into installation area under compression load

7 Factors that influence their service life Operating conditions Vibrations, glide path, temperature, pressure, number of starts/stops, centric/eccentric bearings, extrusion gap, speed Manufacturing process Mixing process, vulcanisation conditions, cross-linking type, tempering, composition of the compound P Material properties Temperature resistance, chemical resistance, cold flow/creepage, resistance to ageing, wear, hardness, yield point Component to be sealed Material, wear resistance, coating, hardness, diameter, wetting behaviour, corrosion behaviour, roughness, ripple, processing structure, manufacturing procedure, heat dissipation, damage, abrasion, adhesion Medium Chemical composition, impurities, temperature, ph value, concentration Fitting/Layout Condition of groove, sharp edges, cleanliness, damage, closed/open groove, fitting (pushing in) Environment Dirt/dust, temperature, routing, strippers, ozone, UV rays, water Ʃ = 54 influencing factors

8 Manufacturing process Defined and reproducible formula Mixing process Vulcanisation conditions Cross-linking type, tempering

9 Material properties Properties must be appropriate for the process Hardness must be in accordance with the pressure range Observe maximum/minimum operating temperature Material must be compatible with the medium Use defined materials Gap extrusion Pressure

10 Environment Environmental influences High temperatures Ozone Source: istockphoto.com, HHakim

11 Fitting/Removing Wherever possible, use suitable assembly grease or oil. Warning when using O-rings made from EPDM: Do not use mineral oil-based oils and grease!

12 Fitting/Removing The O-ring s inner diameter can be temporarily stretched by up to 20 % during installation. Otherwise: maximum stretching 6 %. d max d + 20 % max d + 6 % Warning! Observe the tolerances of all components!

13 Fitting/Removing Wherever possible use fitting aids. Fitting direction Assembly grease or coat the O-ring Mounting cone Do not draw O-rings over sharp edges or threads!

14 Fitting/Removing Use appropriate tools.

15 Fitting/Removing Damage to the O-ring caused by using unsuitable installation tools.

16 Assembly summary Condition of groove, sharp edges Cleanliness, damage Closed/open groove Lubricate the O-ring Prevent mixing up materials Use appropriate tools Use fitting aids

17 Constructional measures Never draw O-rings over sharp edges. Never run over drill holes Fitting direction Fitting direction Piston seal z z Rod seal

18 Design of installation areas Installation areas in compliance with ISO or the brochure O-ring Basics Extreme process data such as high temperatures, pressures or vacuum -> special installation areas

19 Design of installation areas Input values Nominal dimension Fit Upper tolerance Lower tolerance Maximum dimension Minimum dimension Hole diameter d4[mm]= 50 H Shaft diameter d9[mm]= 50 f Groove base diameter d3[mm]= 44.5 h Groove width bx[mm]= Radius in groove base f[mm]= ISO 3601 O-ring inner diameter[mm]= 44 ISO O-ring cross section diameter[mm]= 3.53 ISO Material: EPDM Temperature [ C]= 100 Expansion coefficient a [10^-6/K]= 175 OK O-ring inner diameter[mm] at 100 C = O-ring cross section diameter[mm] at 100 C = 3.58 Results nominal max min Inspection Compression inc swelling [%]= OK Compression inc swelling [mm]= Groove filling [%]= OK Expansion [%]= OK Groove depth t [mm]= Gap g [mm]= OK Lead-in chamfer at 15 z [mm]= 3.0 Lead-in chamfer at 20 z [mm]= 2.3

20 Design of installation areas % 100 % % % P % % 100 % 100 % Warning! The real cross section diameter must be used Take into account cross-sectional alterations after expansion Thermal expansion of the ring See ISO Observe tolerances

21 Design of installation areas O-ring cross section diameter depends on component diameter in accordance with ISO 3601 Diameter O-ring cross section diameter 4 to > 12 to > 24 to > 46 to > 124 to Do not choose an O-ring cross section that is too thin! O-ring cross section diameter d/mm Permitted deviation /mm ± Relative deviation 16% 12% 10% 8% 6% 6% 4% 4%

22 Design of installation areas Damage to the O-ring due to incorrectly dimensioned installation area.

23 Resistance to media Physical processes Chemical processes Temperature

24 Resistance to media Severely swollen O-ring FKM in phorone (paint thinner)

25 Resistance table A = 0 to 5 % volume swelling. Elastomer exhibits no or minimal swelling. B = 5 to 10 % volume swelling. Elastomer exhibits low to moderate swelling. C = 10 to 20 % volume swelling. Elastomer exhibits moderate to strong swelling. D = Not recommended E = No data available.

26 Resistance NBR: Oil, hydraulic oil, lubricating grease, petrol, aliphatic hydrocarbons, diluted acids and alkaline solutions Standard FKM/FPM (Copolymer): Mineral oil, aliphatic and aromatic hydrocarbons, chlorinated hydrocarbons, concentrated acids, weak alkalines Special FKM (Tetrapolymer): As standard FKM, plus extraordinary resistance to hot water, steam, biogenic media (biodiesel, E10 etc) FFKM/FFPM: Resistance comparable to PTFE (Teflon) EPDM: Highly resistant to hot water and steam, resistant to ageing and ozone, excellent chemical resistance to oxidising agents VMQ: Wide operating temperature range: (-55 C to +200 C), air, oil resistance comparable to NBR, no hot water and steam

27 Summary of resistance to media Resistance table Temperature Observe the Arrhenius equation Empirical values Suitability tests in borderline cases If in doubt, use a higher quality material, NBR FKM FFKM

28 Operating conditions Vibrations Dynamic/static Temperature Medium Environment Number of starts/stops

29 Storage Information on proper storage of O-rings can be found in ISO 2230 General information on O-ring structural design, fitting, resistances, storage etc. can be found in COG O-ring basics

30 Summary Service life prognosis is difficult/impossible Suitability tests under real installation and operating conditions Resistance table Temperature Observe the Arrhenius equation Empirical values If in doubt, use a higher quality material, NBR FKM FFKM Consult the seal manufacturer (AWT)

31 A presentation from C. Otto Gehrckens GmbH & Co. KG Gehrstücken Pinneberg, Deutschland Contact details: info@cog.de or sales-export@cog.de Tel.: +49 (0) Fax: +49 (0) Your instructor: Mr. Thomas Lucht awt@cog.de Copyright: This presentation is only intended for informational purposes subsequent to our webinar of 9 December Any reproduction or further use even only of excerpts without the prior written permission of C. Otto Gehrckens GmbH & Co. KG is expressly prohibited!