Re: Tin & lead based babbitt

Posted by Dennis Novotny ( on 04:33:56 15/06/05

In Reply to: Tin & lead based babbitt posted by Raghav

The use of lead and tin based babbit dates back to the earliest days of sleeve bearings. I don't recall for sure but I do believe that Sn based babbit is superior in strength to Pb based material. However, babbit thickess plays a much more signifigant role in determining the fatigue properties of babbit.

The key to increasing the fatigue resistance of babbit is to DECREASE THE THICKNESS of the materials. This way, the babbit simply provides surface action (conformability, siezure resistance, etc). A proven way to do this was to plate the babbit over a copper/lead based lining material. The F77/F112 materials that were pioneered by Clevite were made this way and similar materials were/are still suplied this way.

A movement is underway to replace PB with Sn and Copper with Aluminum Alloy bearing materials but the principals remain the same. Use a lining material for load carrying properies and use the babbit for surface action.

Another way to achieve the "tri-metal process" (steel back, cu-pb liner and babbit overplate) is to sinter a copper lead matrix onto the steel back and then pour babbit over top. The sintered cu-pb is not machined prior to the casting of the babbit which allows the peaks and valleys of the cu-pb matrix to be infiltrated with babbit.

This provides a hi-bred of sorts that has the strength of the cu-pb lining with the surface action of the babbit. When done optimally, you can see a copper "haze" thru the babbit when the cast babbit is finish machined.

Aluminum alloyed with tin and other alloys are replacing Cu/Pb bearings for cost and size control reasons. They are MUCH stronger than babbit bearings and have surface action that is more than adequate with properly finished journals.

There is a very good SAE paper written by Bill Yahraus called "Fundamentals of lubrication and sleeve bearing performance". In it you will find a lot of information about building and maintaining oil films which related directly to bearing temperatures. THe paper is a "must read" for any sleeve bearing engineer.

From my experience with sleeve bearings and bushings, I've not seen where a change from Sn to Pb based babbit (or vise versa) has an appreciable affect on bearing temperature. However, clearance and bearing geometry DO signifigantly affect the oil film thickness which DOES have a very pronounced affect on bearing temperature.

By the way, copper wants to sieze to steel under marginal oil films or during metal to metal contacte unless it is alloyed with either tin or lead which provide lubricity (aka "surface action"). IF you do use copper as part of your attempt to create a multi-layer bearing, I'd strongly suggest that you use it as a substrate with babbit cast over top or plated over top. I think you'll find this to be a MUCH more forgiving and reliable bearing surface.

Also check out SAE Spec J459 and J460 for insight into overplate and bearing substrate materials.

: Dear Gordon,
: I would be thankful if you could help me with an application of babbitting on mill counter shaft bearings. On these bearings presently lead based babbitting is done through pouring process. We are looking at going with a tin based babbitt instead. With the lead based babbitt the oil film temperature is around 65 deg C, if we go with a tin based babbitt would there be a change in the temperature of the oil film ? What is the kind of change that could occur ?
: Also if the temperature of the oil film is to be reduced - would a layer of copper after bond coat help in reducing the temperature ? If yes how much coat of copper can be given & what would be the effect on bonding ? (Bondarc-copper- Tin based Babbitt)
: Thanks in Advance,
: Regards,
: Raghav Bagri

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