Best material for low friction coefficient

[ndhtally]

Hi,

I'm in need of some advice on which material to use please.

I need a polymer which can handle high temperature with very low wear, very low friction and no abrasion characteristics.

The one's which I'm considering so far are

1) Acetal Homopolymer (Delrin)
2) Torlon 4301 PAI
3) Vespel SP21

If anyone could point me in the right direction as to which of these materials would be considered best suited for the above mentioned application, or if there is a (better) more suitable material. I would be very grateful indeed.

Kindest regards

Martin

 

[ndhtally]

Sorry,

I forgot to add that the application is to (button) a piston to prevent metal to metal contact abrasion. The piston will be travelling at high speed under fairly high heat conditions.

Regards

Martin

 

[patprimmer]

I am presuming this is a button on the skirt.

PTFE works fine. It is soft, but that helps it conform to the bore. This will help reduce slap and reduce scuffing, but will not noticeably reduce friction. It was a trick in the late 70's early 80's, but went out of fashion, probably because the benefits were never proved.

Graphite and molly filled nylon 6.6 or nylon 4.6 or PAI could also work.

Acetal homopolymer is doubtful re temperature resistance.

Carbon fibre filler could improve the high temperature properties of the polymers while not diminishing the bearing properties.

Piston skirt buttons became a new trick in the 70's 80's era, but dropped out of fashion, probably because benefits were difficult to confirm.



Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
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[plasgears]

Compression molded Vespel would be my choice because of its high temp resistance and lubricity. I first saw use of Vespel in jet engine compressor stator blade trunnion bearings. These bearings facilitated rotation of compressor stator blades as a means of stall avoidance, among other things.

Torlon would be a close second choice because it may be injection molded.

 

[ndhtally]

Many thanks for your help gentlmen,

I'm looking into your suggestions. Availability may be an issue with some of these polymers....

I'll let you know how I get on and how well they perform for the task.

Regards

Martin

 

[aspearin1]

Dicronite....

http://www.dicronite.com

I'm not quite familiar with the piston design, but I do find dicronite to be a neat material. It's meant for high temperature/high pressure applications. It is an extremely thin coating, molecularly bonded to substrate. Coefficient of friction is 0.03.

ChemE, M.E. EIT
"The only constant in life is change." -Bruce Lee

 

[patprimmer]

There are a large number of suppliers of dry lube surface coatings. Most automotive ceramic coatings manufacturers offer one.

I thought you were looking for buttons to control piston rock with large bore clearance and or short piston skirts.

Nylon or PTFE (Teflon) will do the job, and both are readily available as bar stock or as moulding compounds. Nylon must be injection moulded or extruded, while PTFE must be compression moulded

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[pierrig]

For this application, Torlon would be the best choice. High temperature resistance and low coeff of friction. It is also very easy to use in injection-molding applications.