×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Surface finish for steel sliding on Teflon

Surface finish for steel sliding on Teflon

Surface finish for steel sliding on Teflon

(OP)
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?

RE: Surface finish for steel sliding on Teflon

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

RE: Surface finish for steel sliding on Teflon

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

RE: Surface finish for steel sliding on Teflon

CODE

http://www.nhbb.com/engineering/astro/liners.cfm

Down towards the end of the document.

_______________________________________
Feeling frisky.........
www.tailofthedragon.com

RE: Surface finish for steel sliding on Teflon

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.

RE: Surface finish for steel sliding on Teflon

CODE

http://www.polylube.com/pdfs/Fiber_Series.pdf

http://www.sdp-si.com/D780/PDF/D780BRG012.PDF

www.parker.com/packing/cat/english/5315_FlexiSeal.pdf   page 8

http://www.nhbb.com/assets/pdfs/catalog/AstroEng.pdf

http://mdmetric.com/or/applicgb.htm

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.........
www.tailofthedragon.com

RE: Surface finish for steel sliding on Teflon

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 ?

RE: Surface finish for steel sliding on Teflon

(OP)
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.....

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources