‹ Back

4^th October 2023

 

White Metal Casting, by Chris Cox

 

At the October meeting we had a talk and demonstration of the white metal casting process. Firstly Chris dicussed how he got started with it, from making his own projects and then kits for London Brighton south coast models that were not available commercially elsewhere.

He was able to have assistance from members of his local group at that time, the Brighton Circle, to begin learning how to cast his own components. Drawings were sourced via the Brighton Circle, and also from the National Archives, the British Library and patents drawings.

 

The process was outlined, beginning with making the master components in styrene plastic, usually assembled with Humbrol liquid poly glue. Chris pointed out that some parts (like coach sides or other flat items) had a tendency to curl up, so it was important to apply layers to the back of the piece as well, to maintain balance helping it stay flat.

These masters are then used to create a mould, into which molten metal can be poured to replicate them.

The metal pouring is done in a centrifuge machine, so the moulds are designed in a circular shape to fit in the centrifuge.

A mould is made by taking half of the mould casing, filling it with a special malleable clay type substance, then pressing the masters into the surface. The other half of the mould casing is added, and a moulding rubber liquid poured in. Once the liquid has set, the clay is removed from the other part of the mould, the surface sprayed with wax, and more rubber liquid poured into the remaining space, thus filling the mould in two seperable halves.

Once all the mould rubber is set, the layers can be prised apart and the master components removed, hopefully leaving behind a perfect replica of the masters, in negative form as spaces within the pair of rubber moulds.

 

Once the moulds are completely cured, they can be repeatedly used for casting white metal. To do so, Chris noted that suitable protective equipment was used - as molten metal can clearly do some damage, and some fumes are given off in the melting process.

The moulds are dusted with french talc or graphite, and the excess brushed off. The mould is then carefully assembled into the centrifuge, making sure the halves of the mould align with each other the same way as when they were made.

The white metal was melted in a ladle over a gas burner until liquid, during which time a scum can appear on the surface, which is scooped out and disposed of.

With the centrifuge machine spinning, the metal is then poured into a hole at the centre and by the nature of centrifuge, is propelled outward into all the open spaces inside the mould.

After allowing some cooling time, the mould is then dissassembled, revealing the components now reproduced in white metal.

 

Thanks to Chris for his demonstration, it was a great insight into casting. Many of us will have used cast parts in projects, and now we know how they get made!

 

Andrew Vaughan.