Cleanliness specification

[dgallup]

Anybody know of an existing ISO/SAE/ASTM/etc. cleanliness specification for o-rings? I hate inventing my own if there is some industry standard I can reference.

Some background:

We normally buy o-ring direct from the manufacture, they come in sealed plastic bags and we take them straight into our clean room without washing. We have a couple of applications that use fluorosilicone o-rings which are somewhat delicate and rather easy to damage during installation so we have been having those o-rings shipped from the manufacture to another supplier who applies an anti-friction coating. These go back to the manufacture who repackages them and ships to us. Even though we 100% leak test the finished assemblies before shipping, we have had some field returns for leakage. When we test them we verify the leakage and on disassembly have found small fibers on the coated o-rings. We did a complete process walk of our clean room procedures and have determined that the fibers are on the coated o-rings when we receive them. We want to establish a cleanliness requirement for the incoming o-rings, hence my request.

I don't understand quite how these units pass initial testing and fail later but I'm pretty sure that won't happen if we don't have any fibers.

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[gerhardl]

Standards for allowed particle content of fluids (hydraulic oils, fuel oils) exists, and might be well adaptable in your case.

Not my area, but one of the links below might help you to search further. I got hits in Scandinavian and European standards.

http://www.sis.se/fluidsystem-och-d...-föroreningar-av-fluider/sis-iso-tr-163862014

See page 10 in

http://www.parkerhfde.com/pdf/conmon/dd015/DD0000015_NO.pdf

 

[dgallup]

Most (all?) of the fluid specs run the fluid through a filter and then you size & count the particles on the filter paper. I don't want to use any fluid, just somehow limit what is on my part. I've seen some specs for large flat surfaces but nothing for small torus.

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[dgallup]

Parker handbook has only this to say:

Cleanliness is vitally important to assure proper sealing
action and long O-ring life. Every precaution must be taken
to insure that all component parts are clean at time of
assembly. Foreign particles — dust, dirt, metal chips, grit,
etc.— in the gland may cause leakage and can damage the
O-ring, reducing its life.

I don't see anything saying how clean their o-rings are on delivery.

We have found that the problem o-rings are getting contaminated after they initially leave the manufacturer. It's happening either at the people applying the coating or when they are repackaged later. We are eliminating the repackaging and are running a trial eliminating the coater.

I'd still like to find a cleanliness spec for o-rings.

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[btrueblood]

I vaguely recall a cleanliness standard, involving rinsing (a certain number of) o-rings in (a certain volume of) clean fluid, collecting the fluid, passing it through a membrane filter, and performing a particle count.

The procedure was never used, as it was deemed easier to procure the o-rings to a vendor's standard packaging spec (believe it was Parker).

Why not use a little silicone grease on the o-ring at the time of application?

 

[dgallup]

The most common cleanliness spec I have found (ISO 16232) is like that. You wash the parts, filter the wash fluid and then quantify what is washed off. That does not seem practical for a coated o-ring as either 1) the wash is not effective and the fibers are still on the o-rings or 2) the wash is effective and the o-rings are no longer coated. We may well end up going that route but it will have to be a destructive test on a small sample lot.

These are very small o-rings, it's difficult to pick them up (we use vacuum devices) and trying to lubricate them by hand would be a nightmare. Plus even in the clean room it's possible to get something on your gloves and then transfer it to the o-rings.

We have very tight leakage requirements on these products and even when the part passes initial testing we find some that fail later, usually because of a fiber on the o-ring. I can only surmise that the o-rings move in the glands enough during pressurization / de-pressurization cycles that a fiber that originally did not compromise the seal works it's way into a position where it does cause a leak.

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