White metal - its availability & uses ?

While paging through some of my ME back issues last night I came across an article in the Oct 2007 issue entitled "Basic casting in white metal"

This looks to be a relatively pain free way of metal casting, but what was not clear, is what white metal is, where one gets it, and more importantly what uses it may have in a model engineering context.

Tiranti's sell various grades and all the other items you will likely need, also gives a brief explanation of what it is.

Its a bit soft for most of our uses but I suppose if you want to hold something without marking it may have a use as a jaw lining or could be machined into a nesting holder for machined work. Not to forget the bearing grade which is often refered to a babbit.

J

Edited By JasonB on 29/02/2012 20:10:59

Edited By JasonB on 29/02/2012 20:13:26

I made a feed nut from white metal for a milling machine some 35 years ago no sign of wear after all this time, and it has been well used.

The bearing metal material has very specific amounts of antimony and copper in with the lead and tin to give it the wear resistant properties. Related to printers' type metal. It is quite amazing that they managed to find the formula with the technology of 400 years ago. Ordinary white metal starts with around equal parts lead and tin so is a form of solder but probably with more unknown 'crud' but it has a low melting point like solder and is therefore easy to cast. Very high levels of tin make it Pewter as in tankards.

It may be that there is a lot of bearing grade around so it gets used for general casting but if you just get the solder version it will be a really crap bearing.

In model engineering bronze is more likely to be used for a bearing but white metal is commonly used for casting axle box/spring assemblies for G1 down to smaller gauges. I'd say G1 is counted as a model engineering rather than a model railway size.

When looking for white metal don' t be fooled by aluminium now used for eg car door handles and carburettas or cast zinc that used to be used for these things and Dinky toys. Zinc will bubble in vinegar, aluminium in caustic soda, pewter won't react with either but white metal might depending on its impurities but not as readily.

The unusual property of antimony is that (like water) it expands on freezing. Its use in type metal, AIUI, is largely because of this property, which makes the finished letter much crisper; most metals shrink on freezing and the edges tend to round and blur a little. I think the copper may be for increased wear resistance. For all I know the antimony may help this as well, but I doubt it would be the additive of choice for this purpose as it is rather toxic.

David

I do a bit of spin casting of tin alloys in silicone rubber moulds using a centricast machine. As Jason has said, Tiranti's is a good starting point . There are many different alloys for different uses, For a ME low temp casting can be very useful for making small quantities of identical parts such as nameplates, bezels, cases and lineside models of all kinds. One route is to make an original in brass or plastic then make a two part silicone rubber mould then cast directly into the mould.

You can do most moulding tricks e.g. use nylon rods to make cast in holes, install bushes into the mould to be cast in and join complex parts by soldering. Imagination is the major limit. You don't have to use silicone rubber moulds or centrifical casting, simple jobs can be cast into alloy moulds, cuttlefish or whatever else that will withstand 300 degrees C for a few seconds but it is vital to be certain that the mould is completly dry before pouring the metal in.

Finally I would point out that most "Pewter" is tin, copper and antimony , it has been in use for thousands of years as drinking vessels and plates without mass extinction.

Billy.

I've heard that a good source of white metal is diecast model cars, matchbox/corgi sort of thing. You may get a load from a bootsale, but beware some of the older ones are worth £££!

For low stressed parts the metal is quite good - better than Mazak!

Neil

As David Littlewood has alreadt mentioned, *type* netal is perhaps the only metal that I know of whihc can be cast and create an exact copy without a press or other equipment (centrifugal e.t.c.).

If old *letters* can not be found, similar metal cab be bought from sources selling matl to bullet loaders called hard (25% Antimony and 75% Lead) at $ 2.5 to 3 . pound.

One can make a mould from dentist;s plaster and reproduce parts from a plastic original (or your creation if artistic enough).

Regarding the poison thing, well, both metals can be poisonus under conditions, but I am 70 and was making my own tin *lead* sokdiers since 10. I suggest you mekt the metal in open space and avoid inhaling aby fumes (invisible). Be carefull but not hysteric about it.

Further information can be given f wanted.

George

Thanks all, some really useful information , much appreciated

There's a photo in my album of a traction engine I assembled for a friend, I think the kit was by Fine Cast, or some similar name, it's white metal. To go with it I carved a little man in a boiler suit, and made a wheelbarrow, and a bucket. Ian S C

Antimony is put into the mix to make it harder, in fact with heat treatment the hardness can be increased.

Clive

I am thinking that whitemetal may be useful for model tracion engine parts. Steering wheels, brake wheels etc.

It will be too weak, best to fabricate with steel spokes and steel or stainles steel rim.

J

Er.. I think Dinky cars are made of mazak (sometimes called zamak) and cast in rigid moulds. Whitemetal is softer and heavier and has a lower melting point. A lot of model railway kits are centrifugally cast white metal either in vulcanised rubber or silicon rubber moulds. It's base constituents are closely related to tin/lead solder. It can also be simply poured in to an open rubber mould although centrifugal casting tends to have less of a bubble problem. Dusting the moulds in talc first helps.

David,

Antimony does shrink slightly on freezing (liquid density 6.5, room temp solid density 6.7). As you say, it does modify the type metal alloy so that it shrinks very little on casting. Bismuth is one of the few metals that does expand on freezing (liquid density 10, room temp solid density 9.8). Plutonium also expands on freezing (not very useful for the home workshop though).

cheers,

Rod

Edited By Roderick Jenkins on 28/12/2012 19:09:33

We used white metal in bearings in the 60s Citroen cars used them extensivly in there engines for bearings, I still have a set of scrapers somewhere in my workshop

Bob

Good write up of some "babbitt" being poured on a model engine on HMEM

J

Edited By JasonB on 28/12/2012 19:49:13

Used to work for Corgi Toys in Northamton, The metal used in the diecasting of the model cars was called Mazak, Low melt and rejects could be remelted and used again over and over,

Remetaling bearings in cars was a routine job for the motor mechanic of yesteryear. Our HR 6 Ruston Hornsby has just had its big end remetaled in the last month or so. Ian S C