Metal finishing Q&As since 1989

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Prep for tin plating

Hi,

I'm not a plater by trade, more of a researcher/inventor type. Anyway, I am trying to get a uniform tin plating on a large number of tiny carbon steel balls (20-30 mesh Cast Steel Shot specifically.)

I have gotten some tinning butter (tin + acid flux mix) and I have noticed that it will put a nice tin plating on just about any clean steel surface, but it would appear that the balls are not clean enough to accept the tinning as provided by my source. As I will not be able to mechanically clean each ball, I am looking for a simple and relatively safe (I hope) method for prepping my steel balls before the tinning process.

Any suggestions would be greatly appreciated.

Thanks,

William Gray
Engineer - Brooklyn, New York, USA
2005

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Mr. Gray, I don't think anyone can give you a good answer to your problem without knowing something about the nature of the soil on the balls. For example, if it is an oil, a detergent may suffice. Oxidation usually requires an acidic cleaner. Check with your supplier of the balls to get an idea, and then we may be able to help. James Totter, CEF - Tallahassee, Florida 2005 Rock Tumbler on Amazon (affil links) For starters, pick up a cheap or used rock tumbler [affil links]. Think lapidary or jewelry. Michaels has cheap imported ones.Use with an appropriate media to cut rather than polish. You might be able to get small amounts from a vendor from broken bags or from a user of say 120 grit aluminum oxide. Any that sticks into the steel when you are through can be eaten out with a weak Draino solution. This will also clean the shot, so it will rust rapidly when you take it out and dry it. If you like the results, you can proceed to a small bowl vibratory unit which will do more, better and faster. James Watts - Navarre, Florida 2005

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2005

Q. Thanks so much for the help. I've gotten this process to work sort of, by soaking my balls (the little steel ones :-) in muriatic acid [affil links]. Then coating then in tinning butter and heating in a metal dish.

The issue is that this process relies on tinning butter which is pretty expensive and it is quite hard to do any significant quantity this way.

I have found that the surface tension of the tin is a big problem when I try and drop individual steel balls into a tin bath. Basically I am taking a steel ball out of a bath of a water containing hydrochloric acid and zinc chloride (commercial aggressive flux) and dropping them into a pool of molten tin.

I am finding that the balls are not becoming tinned as I have hoped, but are rather floating on the surface while the flux boils off and never making it into the tin, but rather becoming a part of the gunk that ends up floating on the surface of the molten tin.

I have found that if I dry the balls out before I try and dunk them, the flux is inactive.

Perhaps I should try a paste flux?

Perhaps I sould try to do this in a oxygen free environment?

Perhaps I should try to pressure inject the tin over a set of ball wet with flux (sounds dangerous!)

All thoughts are very welcome.

Thanks,

William Gray
- Brooklyn, New York, USA

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William, I would NOT use hydrochloric acid (muriatic acid) to clean steel balls. This is a very aggressive acid and chloride ions are renowned for causing corrosion. This leads me to think you will have many more longer term problems. I would suggest you use a sulfuric acid based acid dip (say 20%), preferably with a good wetting agent. Thoroughly rinse the balls after treatment in a mildly acidic water. Then you can plate your balls with tin.
As far as cleaning them, I would also suggest you may want to consider a ball mill. This is a pair of parallel rollers onto which sits a cylindrical container. As the rollers rotate the cylinder rotates and its contents are agitated. You can put your balls in this container along with a suitable abrasive agent (say sand, sawdust or even rose petals) and the balls will come out lovely and clean. Discard the abrasive agent after a time as it becomes contaminated with dirt and grease. I have seen rose petals used to polish gold artifacts and it works really well.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2005