Surface finish for steel sliding on Teflon

[Revelation19]

I am interested in using Teflon (or other polymer) to act as a slide on the inner surface of a steel cylinder. The cylinder has an ID of 15 inches (0.38 m). It needs to slide slong its axis a length of 1.75 inches (44.5 mm). It is used in a test rig and will move only occasionally (once a month or less), however it needs to be able to move the full distance in about 1 second. It also has to act as a marginal pressure seal, though this is a secondary function. I envision using a strip of Teflon bonded into a groove cut into the inner cylinider. (The Teflon strip I can purchase has an etched side for bonding.)

My question is: Is there some particular (or minimum) surface finish I need to use on the inside of the steel cylinder?

 

[rnd2]

Minimum is a fine evenly ground finish. There is no need to polish the inside sliding surface of the steel cylinder.

 

[plastx]

I agree that a fine even finish should work. Some PTFE bearing manufacturers give guidelines like 8 to 16 µ inch Ra if you need to spec it out. The following link is for linear bearing material that calls out this finish guideline:

http://www.rulon-meldin.com/Media/Documents/S0000000000000001016/epprulon142.pdf

Check with your supplier to see if they have a recommendation.

Regards,
Mike

 

[Pressed]

[URL unfurl="true"]http://www.nhbb.com/engineering/astro/liners.cfm[/URL]

Down towards the end of the document.

_______________________________________
Feeling frisky.........

http://www.tailofthedragon.com

 

[rnd2]

Do you mean this?
extract from website: "......Surface Finish and Hardness

Surface finish and hardness for the surfaces running against a TEFLON® liner are important for maximum liner life, whether on the shaft, ball, or other running surface.

For maximum life, NHBB recommends a finish of 8 Ra maximum, achieved by lapping, buffing, or honing after grinding. Anything higher than 8 Ra will reduce life.

Hardness should be Rc50 minimum. As hardness drops below Rc50, the mating surface begins to wear............" end of website extract.
From my direct experience with plain (simple) bearings, whereby the shaft is metal; either carbon steel or stainless steel, THAT SLIDES (not rolls) against a bearing surface, free of extraneous abrasive particles, and made from PTFE, Phenolic, UHMWPE, Nylon, etc. I have never observed an obvious benefit of having a polished surface. For the same application, I have never observed an obvious benefit of the shaft having a special hardened surface either.

 

[Pressed]

[URL unfurl="true"]http://www.polylube.com/pdfs/Fiber_Series.pdf[/URL]

[URL unfurl="true"]http://www.sdp-si.com/D780/PDF/D780BRG012.PDF[/URL]

[URL unfurl="true"]www.parker.com/packing/cat/english/5315_FlexiSeal.pdf[/URL]   page 8

[URL unfurl="true"]http://www.nhbb.com/assets/pdfs/catalog/AstroEng.pdf[/URL]

[URL unfurl="true"]http://mdmetric.com/or/applicgb.htm[/URL]

If you have evidence to the contrary, all I can say is that the experts have differences in opinions. Nothing new to that.

_______________________________________
Feeling frisky.........

http://www.tailofthedragon.com

 

[damienk]

from my knowledge, sliding between polymer aand metal can lead to a so cladde stick slip process which means that your "realtive sliding" is not so good. And what about wear of PTFE ?

 

[Revelation19]

We have only in passing considered wear of the Teflon. I have raised this question (I assume we will get wear) but as we are building a prototype test rig, we are glossing over these details for now. I, for one, have added that to the observation data to be collected at the completion of the testing. I am also thinking of having the leading and trailing edges of the Teflon strip chamfered a bit to ease entry and assembly.

For now, the consensus in our design group is going with a mere 64 finish on the ID of the cylinder.....