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Teflon Disk In Place of a Slew Bearing

Teflon Disk In Place of a Slew Bearing

Teflon Disk In Place of a Slew Bearing

(OP)
I am using a steel plate resting on a teflon disk in place of a slew bearing. The material in contact with the teflon is steel. I know that the co-efficient of friction for teflon on steel is pretty low but is there any type of lubricant that would make it even lower? I have looked and looked but can't find the answers I need. Any help/guidance would be much appreciated!!

RE: Teflon Disk In Place of a Slew Bearing

Most any kind of grease should help a bit.

Mike Halloran
Pembroke Pines, FL, USA

RE: Teflon Disk In Place of a Slew Bearing

Also, make the steel plates more smooth and more flat.

Mike Halloran
Pembroke Pines, FL, USA

RE: Teflon Disk In Place of a Slew Bearing

You might take a look at the recommended maximum PV (pressure & velocity) data for ptfe bearings contained on page numbers 4&5 of the following:

Bunting Bearings Catalog

There are thrust bearing pressure values listed.

Guidance with teflon is not possible like with a conventional slewing bearing. Once some eccentricity creeps in, the teflon can move where it wants. Hard to say whether teflon will perform without seeing some details about your application. Some sort of teflon flanged sleeve bearing might serve your purposes if the PV values concur.

RE: Teflon Disk In Place of a Slew Bearing

A. Are you sure PTFE is what you need per some above comments.

B. What Mike said about the finish of the steel - also bare steel may corrode over time (increasing friction) so what plating does it have (if any) as that will impact things.

C. Anecdotal information from an old colleague suggested that PTFE on UHMWPE was actually lower coefficient of friction than PTFE against PTFE.

D. If the answer to A is 'no' consider materials such as Turcite or PTFE impregnated acetal and similar.

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Teflon Disk In Place of a Slew Bearing

Teflon is very soft and can abrade easily. It also can allow the mating part to embed. Even if the sliding friction is low, once dug in, the resistance to motion can go up.

HMWPE is probably better. It is a little higher friction, but it is much harder and won't displace and resists embedment.

The only application I've seen where teflon was chosen as a high load bearing material was replaced with greased bronze soon after.

No matter what, I expect the friction to be 10 to 100 times what a roller/ball bearing produces.

RE: Teflon Disk In Place of a Slew Bearing

The P values given in the referenced Bunting catalog seem a little high to me.

For a particular carbon-filled TFE with which I have some experience, there was a 'sweet spot' at around 100 psi, above which the wear rate (at low speed) was excessive, and below which, in my particular special case, the leak rate between a stainless plate and plastic surface, both lapped to a couple of light bands, became excessive.

YMMV.

Mike Halloran
Pembroke Pines, FL, USA

RE: Teflon Disk In Place of a Slew Bearing

(OP)
The metal plate was machined flat and as smooth as possible. The max pressure is only about 40 PSI. The velocity is negligible. The same design worked amazing in a previous project but the pressure was a little less than half of the current requirement. I'm just surprised in the drastic difference in performance from 20 PSI to 40 PSI. Maybe I am over looking something. Thanks for the help!

RE: Teflon Disk In Place of a Slew Bearing

"The metal plate was machined flat and as smooth as possible" well that's almost meaningless. Flat and smooth in my world would be less than .0002 flatness and perhaps 8RA microinches. This may be smoother or not smooth enough for your application.

However, as you've done similar before and it worked, I'd look again at suggestions of both surfaces being low friction material of some kind.

Have you tried googling, a quick search got me:

http://machinedesign.com/mechanical-drives/enginee...

http://info.craftechind.com/blog/bid/259158/Top-5-...

http://www.glt.ibg-monforts.com/en/ptfe-bearings-g...

http://www.tss.trelleborg.com/remotemedia/media/gl...

http://mtsandtg.com/system/ckeditor_assets/attachm... (mentions specific lubricant at the end)

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Teflon Disk In Place of a Slew Bearing

(OP)
Thank you Kenat. Your links provided me with exactly what I needed. What i meant was with the tools available at our shop, the plate is as smooth as it is going to get.

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