Im now needing to occasionally replace o-rings in machine tools and whatnot and need to purchase a selection of them to keep in the truck.
Most applications will be for air, in an oily environment, though a few will be for hydraulic fluids. Is there some material best suited for general use?
And will they degrade in a short period of time, in the back of my service truck in hot weather?
What material should I be using?
I will likely purchase from ebay one of those 400 piece selections for $10 or so, unless someone has better suggestions.
Grants recent thread on O/A o rings brought this to mind.
Thanks in advance
Gunner
"A prudent man foresees the difficulties ahead and prepares for them; the simpleton goes blindly on and suffers the consequences."
O-Rings are available in five different materials from Scientific Instrument Services. Each type has its advantages and disadvantages as listed in the O Ring Comparison Chart. Of the various types of O-Rings available from SIS, Buna-N is the most sidely used type of O ring in the seal ring. It is also the least expensive type of O-Ring seal. It does however have severe temperature and chemical resistance limitations.
NITRILE OR BUNA N (NBR) Typical Trade Names:
Chemigum Goodyear Tire & Rubber Co. Paracril Uniroyal Hyvcar Goodrich Chemical Co. Krynac Polysar, Ltd. Ny Syn Copolymer Rubber & Chem. Corp. Buna N or Nitrile, is a copolymer of butadiene and acrylonitrile. Acrylonitrile content is varied in commercial products from 18% to 48%. As the nitrile content increases, resistance to petroleum base oils and hydrocarbon fuels increases, but low temperature flexibility decreases. Due to its excellent resistance to petroleum products, and its ability to be compounded for service over a temperature range of -65 to + 275 degrees F (- 54 to +135 degrees C), Nitrile is the most widely used etastomer in the seal industry today. Most military rubber specifications for fuel and oil resistant MS and AN 0-rings require nitrile base compounds. It should be mentioned, however, that to obtain good resistance to low temperature with nitrile compounding, it is almost always necessary to sacrifice some high temperature fuel and oil resistance. Nitrile compounds are superior to most elastomers with regard to compression set or cold flow, tear and abrasion resistance. Inherently, they do possess good resistance to ozone, sunlight or weather but this can be substantially improved through compounding. However, since ozone and weather resistance are not always built in, seals from nitrile bases should not be stored near electric motors or other equipment which may generate ozone, or in direct sunlight.
Nitrile Is Recommended for:
General purpose sealing. Petroleum oils and fluids. Cold Water. Silicone greases and oils Di-ester base lubricants (MIL-L-7808). Ethylene glycol base fluids (Hydrolubes) Nitrile is not recommended for:
O-Rings are available in sizes (sizes 0, 1, 2 and 3) which correspond to the diameter of the cross section of the O-Ring. Within these groups the O-Rings are classified according to their inside diameter. To see a complete selection of the various sizes and types of O-Rings available from Scientific Instrument Services, just click on the hyperlink on the size list above. If the size you require is not listed, it may still be available. Contact us with your requirements.
Although I've not done business with these folks before.
And if that doesn't cover it, you should find a list for Parker Seals. I have an hard copy with 15-20 pages just on materials and compatibility charts...
I think Viton is hard to beat as the best general purpose material to stock. More expensive than Buna or nitrile but much more chemically resistant when you need that. I don't think I've ever run into an application that called for Buna or nitrile that Viton wouldn't work in, and I've had several applications that called for Viton either for chemical resistance or high temperatures or low outgassing in a vacuum system. Probably safe for a year or three in a truck toolbox, at least. It will eventually start to check and then crack when you flex it so it will be pretty obvious when it's time to toss them. The Parker catalog is a great resource on materials and especially on oring groove design.
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has a great selection, as well as
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(as someone else mentioned - I've bought several items from them over the years and think a lot of them, but I am friends with the owners :-)).
-- Regards, Carl Ijames carl.ijames at verizon.net
I agree with Carl. The Viton "o" rings are pretty much impervious to most common oils and common industrial chemicals. The extra cost will be repaid in reliability. If you want to maximise the shelf life of them, keep them in a dark, sealed container.
Yes, until you need to make a "special" by cutting out a section and re-joining it. Cyanoacrylate (super-glue) works surprisingly well with natural or nitrile rubber, but it won't work with viton (or silicone).
I wonder what material one could expect from the Harbor Freight kit. Sort of scary to think about it. I have dozens of Buna-N and Viton O rings that have been stored in a drawer for at least 15 years at room temp and none of them show any degradation. And when I take apart hydraulic cylinders that have been operating for 20 to 40 years, I don't see a lot of degradation either. Many of these systems run at elevated temperatures, so I don't see why storing them in the back of the truck would be a problem.
I use viton exclusively, I'm in the chemistry dept. at a university. Also, you know you can buy o-ring cord stock for making your own special sizes. I've got a little teflon V block for aligning the ends. I should make a fixture to make square end cuts with a razor blade too. Randy Replogle
First Apple Rubber Products is another maker of Orings. Their web site has a lot of information, probably more information than you want. Parker and Apple both sent me some techincal literature some years back when I needed info on how to size the Oring grooves ( and a few samples of Orings ).
Second Harbor Freight sells assortments and also a make your own kit. The kit is just Oring stock, adhesive, and a simple jig and razor blade to get a nice straight cut. I would probably buy both if I were you. I am sure Harbor Freight sell Buna N Orings.
If I recall correctly buna Orings do not have a shelf life. Not too sure about this. It has been a while. Will check at work tomorrow.
And last but not least, you might want to turn some tapered bits of steel similar to the things sold for sizing finger rings. I have done this. Handy for sizing Orings, but also for measuring holes. Stick the taper tool into the hole and then measure the diameter of the tapered tool with a caliper flush with the surface that has the hole. Much easier than trying to use the inside caliper measurement ears. Good for Orings because they stay round and you measure the tapered steel which does not distort.
I just look in my Parker O-ring book, chemical compatibility section. I work in the chemical industry. Viton will go to hell in a handbasket if it sees an amine. EPDM is very good. Buna is fine for some stuff. I hate Kalrez and won't use it unless I positively have to (temperatures above high temp silicone).
Thats the problem...I never know. Last week I needed some tiny ones for the inside of a Hardinge Auto-threader..2 weeks before that..some that were about 5/8" in diameter for a hydraulic unit..a month before that..
Which is why I need to keep an assortment on hand. Like OD & ID snap rings. and the occasional E clip.
If I were bringing the machines to my shop for repair..I could keep a shitload of stuff on hand ..but since I work out of my truck....it becomes a bit more problematic.
And there is another bitch of mine..snap rings. They are hard to find since the end of the old time hardware store..and the bearing houses are more than happy to sell you some, assuming they have any...but will only sell you a full bag of 20is or so.
And I hate driving 50 miles round trip to the nearest place that sells snap rings, even in So. California...for a single snap ring.
Gunner
"A prudent man foresees the difficulties ahead and prepares for them; the simpleton goes blindly on and suffers the consequences."
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