What material is this brown o-ring?

The buckets full of stuff are probably the accelerants - the things they need to take the gummy polymer base and turn it into cross-linked rubbery stuff. "Buckets" would be a pretty big batch - I watched a 20kg batch of Viton get mixed up last November, and they used about a quart-sized plastic bag full. It got mixed up in a screw machine mixer, it was essentially a 3 foot diameter motor (50 hp+) directly attached to a pair of wide paddle screws in a little mixing chamber, and that was the whole thing. The amount of power density in that machine was staggering. The rubber mix would cause the whole unit to bounce and shake while it was being churned.

After that, it gets rolled out into sheets and sliced into preforms and used. You are correct that at this stage room temperature storage can start the curing process, so it typically will get used within 1-2 days, if not immediately. Viton/FKM does need post cure, but I've never heard of a microwave oven to do the job, it's usually a large forced air convection oven.

Also, once the molding process is done the rubber is permanently, fundamentally changed on a chemical level, so if any of the molded scrap is recycled and reused, that is a serious cut-rate manufacturer and should not be trusted for any kind of sealing devices. Scrap from the preforming process when the uncured material is rolled out into a sheet and the sheet is trimmed can be re-mixed, but that is usually kept to 10% or less at reputable places.

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Firebrick43 said:

as far as o rings go, the best is buna N,,,,,,IF,,,,,, you dont have special needs. certain oils(PAG oil comes to mind require hnbr) or very high heat (viton). Viton is good up to 400 degrees but only down to 0-5 degrees F. Most mobile or even industrial application never see that high heat.

Buna N is good up to 250 but down to -22F. So almost all mobile applications are buna N. Also long term I have noticed that long term(as in decades) viton tends to actually erode a grove more so than Buna N. I know most of you wont ever see that but the machines and engines I work on have 20,000 hour plus overahaul intervals and do have issues with erosion of sealing surfaces.

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HNBR is used for high heat. It is basically a more heat (but not chemical) resistant form of buna N. HNBR is used in air conditioning systems, because the compressor fittings and condensor inlet fitting will get too hot for buna N. It has nothing to do with oil resistance.

Viton does have a higher breakdown temperature, but really, Viton is used where organic solvents may damage buna N. Viton is also a little less abrasion/wear resistant than buna N. As such, it does not make a good substitute in most cases.

Skin said:

...Real Viton is brown and sometimes black, not red. Anything really red is probably silicone...

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Bright red is usually silicone. Most Viton I've seen is a purpley cast of brown. Kind of earthworm is how I'd describe it.

Qualitytools said:

Don't forget Teflon for petroleum applications also as it is considered better than the Viton

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Teflon is not very compressible, so it cannot be substituted for another type of o-ring, since it will not fit in the same dimensions. Plus teflon o-rings don't tend to fail unless they're damaged when you remove them. For these reasons, it makes absolutely no sense to stock a selection of teflon o-rings.

If you want to throw all options out there, there is also polyurethane (these are often clear). I've used them for CO2 seals in air guns, but I haven't seen them elsewhere.

HNBR is used for high heat. It is basically a more heat (but not chemical) resistant form of buna N. HNBR is used in air conditioning systems, because the compressor fittings and condensor inlet fitting will get too hot for buna N. It has nothing to do with oil resistance.Viton does have a higher breakdown temperature, but really, Viton is used where organic solvents may damage buna N. Viton is also a little less abrasion/wear resistant than buna N. As such, it does not make a good substitute in most cases.Bright red is usually silicone. Most Viton I've seen is a purpley cast of brown. Kind of earthworm is how I'd describe it.Teflon is not very compressible, so it cannot be substituted for another type of o-ring, since it will not fit in the same dimensions. Plus teflon o-rings don't tend to fail unless they're damaged when you remove them. For these reasons, it makes absolutely no sense to stock a selection of teflon o-rings.If you want to throw all options out there, there is also polyurethane (these are often clear). I've used them for CO2 seals in air guns, but I haven't seen them elsewhere.

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