Scooterotica

Fluoroelastomers (FPM/FKM)
Well known compounds include Viton® from DuPont Performance Elastomers, Tecnoflon® from Ausimont Spa, and Dyneon® from 3M Dyneon.

Chemical properties
Fluoroelastomers operate efficiently under severe chemical conditions and at higher temperatures where many other seal materials cannot survive. According to grade, they are well suited to arduous conditions with petroleum fuels and mineral-based hydraulic fluids, and many solvents.

Typical operating temperatures
-15°C to +200°C continuous, or +230°C intermittent. Some grades are available for temperatures from -30°C to +250°C.


General purpose fluoroelastomers

FR10: Dipolymer-based range with hardnesses of 50-90 IRHD. These grades are ideal for general applications and are approved to UK Ministry of Defence low compression set specifications.

FR17: Terpolymer-based range with hardnesses of 65-95 IRHD. This range has better high temperature flexibility characteristics than FR10, although these properties are - to some extent - at the expense of compression set resistance.

FR44: Dipolymer-based range with hardnesses of 50-90 IRHD. This range comes in a distinctive shade of green for easy identification. These low compression set grades meet many regularly used specifications.

Special fluoroelastomer grades

FR58/90 & 98: These terpolymer-based grades are rapid gas decompression (RGD) resistant for oilfield duties, and have good all round elastomeric properties. We are the market leader in seals for RGD environments. FR58/90 grade is qualified to the stringent Norsok M-710 standard for RGD resistance and sour gas (H2S) ageing.

FR64/70 & 80: Dipolymer-based compounds developed to offer enhanced performance in steam, hot water and mineral acids.

LR5853: Tetrapolymer-based range with hardnesses of 80, 90 and 98 IRHD. These have enhanced fluid resistance, especially with methanol and gasoline-alcohol blends that adversely affect other fluoroelastomers. They will stiffen at below -5°C, thus LR6316 and FR25 are recommended for low temperature use.

LR6316: Available in hardnesses of 75 and 90 IRHD, these compounds are based on a special tetrapolymer with a similar fluid resistance to LR5853, plus improved low temperature characteristics for services down to -28°C.

FR25: Tetrapolymer-based range with hardnesses of 70-90 IRHD. It offers fluid resistance approaching that of the FR10 range plus improved low temperature characteristics for service down to -33°C. FR25/90 is compounded for rapid gas decompression (RGD) resistance in oilfield applications, and is qualified to the stringent Norsok M-710 standard for RGD resistance and sour gas (H2S) ageing.

Spoke to an old racer (motorbike/ sidecar) about viton seals the other day he thought they were a bit like "the kings new clothes". But the interesting/ shocking thing about them was that if they are burnt, the ash from them is highly corrosive, if you get it on your skin it cannot be washed off and keeps burning
I dont know how true this is perhaps someone could confirm ?
At first this may not seem a problem... i dont normally burn my seals but like a lot of people i heat the mag housing up with a blow torch to get the bearings out so may burn a seal once in a while

When these seals are overheated they create an acid which, as Carlos said "keeps on burning" the only cure is amputation. This material was (is?) used to seal cylinder liners in cars and people were maimed when handling burnt out cars.

This is really nasty stuff . . is it worth using it to stretch rebuild time a little . . especially on something as unreliable as a lammie which will probably have broken before benefitting anyway.

it sounds like hydroflouric acid (HFl) i used to work with it when i worked in a lab in a university.. unlike most acids you cant wash it off with water you have to neutralise it with the correct solution.. im not sure of the chemistry (flunked my A level) but normally acid neutralises itself as it burns as part of the chemical reaction but this doesnt happen with HFl and it keeps on burning, its other property is its the only acid that will dissolve glass (we used it to etch silicon wafers)..

i would have thought the amounts produced will be minimal but still its as well to know these things.. although i would guess that lots of stuff we come into contact with can be potentially nasty, thinners, old engine oil and burnt plastics are particularly carcinogenic..

Thanks for all the replies I feel its been a good education for me... I have learnt more through the replies to date than I thought... By a long way and then some... Thanks All, for sharing the information...

As a sort of postcript to this thread, I have been able to order some Viton seals through my firm. My supplier wasn't able to get all the sizes in the 6mm thick and could only get certain ones in 7mm, which from another poster who stated that these 7mm were just too thick. It does appear that the most important seals, namely the drive side and mag side are obtainable in the exact correct sizes, and as these are really the only ones exposed to unleaded fuel and its constituents, and work in the harshest atmosphere, are the only ones to bother favouring, whereas all other seals can remain Rolf.