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Old 03-06-2013, 06:36 PM   #125
Bill Harris
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Joined: Sep 2008
Location: backwoods Alabama
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For sure. Oil seal technology has changed so much in the past few years. And I'm accustomed to the old-school lipped seal with the garter spring and the little spiral grooves to persuade oil to go back in. This filled teflon seal is much akin to magick, but I'll have to get used ot it.

--Bill

Quote:
Originally Posted by Plaka View Post
Teflon (Polytetrafluoroethylene (PTFE) really isn't all that slippery. Compare it to UHMW-PE or even Nylon and they're all close. Teflon has very low surface energy so things don't stick to it. But again, compare it to the polyethelenes and it's close. Try sticking something to them, especially HMW-PE and UHMW-PE. Where teflon shines is it's ability to take heat. Line a frying pan with PE and it will melt all over your stir fry. But Teflon is also very soft. handle a sheet or block of it and you get a very different feeling for it than poking a frying pan. You can dent it with your fingernail. it takes abrasion just as poorly in contrast to UHMW-PE which is one of the most abrasior resistant of polymers.

Used in a seal, Teflon will take heat, will have low intrinsic friction and will wet poorly---just as poorly with oil as with water or glue. At a microscopic level oil wets out a steel surface but beads up on a Teflon one. So what's happening at the interface of the seal lip and the shaft is quite different that what's happening with something like a Viton (another floropolymer) seal.

I'd say the upshot is if you have a polished surface to run the seal lip on I'd use it. In general textured surfaces have lower friction, especially when coated with oil but given the softness of Teflon I'd be concerned with wear. The polished surface may give longer life.

The Teflon may be filled with something (like graphite or Moly) and if it isn't white or light tan this is likely. Nylon is commonly filled with graphite which makes an interesting material. You would have to look at a seal under a microscope to see what's happening there. (if someone wants to send me one I'll check it out. Needs to fit an '83 R100 motor). Anyway the filler could both stiffen it and give it some abrasion resistance.

Making a seal that can be installed dry isn't for the field people, it's for manufacturing. You can load a magazine with them and just punch them into the blocks as they come by on the line, fully automated if it's set up, and you don't have a mess or the need to accurately control lubricants automatically. So the seal salesman tells the OEM, "look at our new seal, you can install it dry!" (if the manufacturer didn't request it in the first place). What trickles down to the field is, "don't lube them".
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