Subject: Cast Babbitt And Bronze Bearings
Date: Sun, 3 Dec 2000 03:03:49 -0800 (PST)From: Richard Allen Hi all,About babbitt bearings, I made a discovery in an unrelated area several years ago that may be the key to selecting the right bearing alloy, and also why they work so well. In silver soldering copper tubing for refrigeration, air conditioning, and some plumbing applications, a very popular brazing alloy is Silphos. It is, as you can well guess from the name, an alloy containing silver and phosphorous. It makes quick, easy, and strong brazed joints on many NON-FERROUS metals (copper, brass, gilding metal, sterling silver, to name a few), but will not stick in any way, shape, or form, to iron, steel, and stainless steel. The principal that prevents bonding to iron and its alloys is the phosphorous.
A while back I bought some lead-free plumbers soft solder to use as a low temperature babbitt for some cast plain bearings in my jewelers rolling mill, and found out the hard way it will not stick to ferrous alloys, either. It does not contain phosphorous. It does contain a lot of bismuth, though. Eureka! From a chemical standpoint, I discovered that members of the group "V-a" family of elements (nitrogen, phosphorous, arsenic, antimony, and bismuth) when used in many non-ferrous alloys, such as lead and/or tin solder, silver-copper-zinc brazing alloys, etc, WILL NOT STICK TO IRON AND ITS ALLOYS! So, phosphorous, arsenic, antimony, and bismuth are all good candidates for anti-friction additives in bearing metals (I'm still up in the air whether nitrogen in the form of nitrides has any use here, nitrides are usually diamond hard).
I have made cast babbitt bearings several times, and the instructions always state to FIRST "tin" all iron surfaces to be babbitted with 50% lead 50% tin solder so the babbitt will stick. One time I tried it without the solder, and the babbitt shell popped right out! It is the antimony in the babbitt that keeps crankshaft bearings from soldering themselves to the crankshaft. Arsenic works very well as an anti-solder for ferrous materials! , also, but has undesirable properties such as possibly hardening bearing metals too much to be useful in internal combustion engines, and being way too poisonous to work with. Bismuth is excellent, but for low temperatures only. Its alloys soften excessively at modern internal combustion engine running temperatures, however, it may be okay for open air crankshaft engines.
Also, Silphos and Phoscopper make excellent HARD BRONZE bearings. If you care to, read about their brazing properties at: . I have used Silphos as a clutch shaft pilot bearing in a 327 Chevy crankshaft by carefully centering a highly polished correct size steel mandrel in the worn out brass bearing shell then melting in the Silphos around it with a propane torch. When cool, I pressed the steel mandrel out, leaving a precisely finished hard bronze bearing surface. Usually, cast bearings must be machined after casting to be correctly centered, square, the exact diameter, and have the finish necessary. Using Silphos or Phoscopper this way may get around needing to machine small cast bearings. Work and play safely,-------Richard Allen
relayed a success story of babbit...Almost a year ago I asked the SEL about babbit pouring and received alot of info, tips, etc. Well I FINALLY got around to it. So a year later.... here are some pics at the lower portion of this page: http://www.oldengine.org/members/luket/novo1/novojunior.html It takes more time to make a jig and all the other monkey work than it does to actually pour the bearing. I used JB Weld to hold the shafts to the flat plate. I think it turned out fair for my very first pour. The next one I do will come out much better. I think this one is good enough to keep and not have to melt out to do over. The con rod has a new bronze bush in the small end. Dummy wrist pin in jig was inserted into an existing wallered out hole in the flat plate. JB welded dummy wrist pin while it was clamped to a machinists square, or one of the "X" shaped machinist square things, which was clamped to the flat plate too. This insured the dummy wrist pin and con rod was square to my flat plate. Or so I think any way. Once that was dry I laid out where my dummy journal needed to be. Dummy journal was turned 1 or 2 thousandths bigger than existing crank journal and end was faced off square. JB weld was put on dummy crank journal and placed in the proper spot on the flat plate. Didn't use anything to insure it was square to the world. End was faced off in lathe so figured that was good enough. Once that was dry I cut down a golf tee to fit into the oil hole and that extended almost to the dummy crank journal but not quite touching it. Blackened up shims and dummy journal and assembled all together. I'll try to explain this so try to paint a picture....... When I placed the dummy crank journal on the flat plate, a tiny amount of jb weld squeezed out on half the circumference of the shaft. When I assembled all together one shim wasn't able to make contact with the flat plate when slid all the way down, it rested on the jb weld creating a small gap and not totally seperating the two bearing halves. After I dammed it all up with play-doh and poured into half of one bearing, the babbit flowed through this small void and started to fill up the other side of my bearing. Not good. As it started to cool it couldn't flow through the small gap and stopped filling the other side, once the side was full that I was pouring in I had to start pouring on the other side of the 'half' full side. I topped it off and it looked good. But after taking it apart you can see the seam where the two pours came together. I think it will be ok and work just fine. I need to file the sides to the proper thickness, cut in an oil groove, get some prussian blue and see how good it fits up. It was really easy to do. I ordered babbit from mcmaster carr. I figured out how much volume I would need to fill my void, doubled the amount to be safe, and cut off a slab from my ingot. Ended up with just enough.