Casting Metal Parts


One of the questions most often asked regarding the manufacturing of our kits is how the metal detail parts are made. So I thought we could show you a brief step by step of how it's done. The process itself is called spin casting, where a rubber mold is spun at high speed while hot liquid metal is poured into it, using a spin caster machine.

First you need some metal and it needs to be melted into liquid form to about 700 degrees; this is done with a gas or electric melting pot. The metal used is a tin alloy. The pot is always kept full to help maintain temperature.

Then you need a mold of the items you are casting. In this case it's an HO scale set of fire safety parts that includes a fire call box, standpipe valve and alarm bell. These are often seen on the walls of industrial buildings. Making the original master parts is another story which we can get to another time. But to make the vulcanized rubber molds, you need multiples of the original master pattern, usually machined in brass. You first make a mold that produces one, use that mold to make a few dozen production masters, then those go into a production mold - so there are a few steps missing here. But we'll jump right to using the finished production mold.

The mold is 9" round and is in two parts. The upper layer has a centered hole for the metal to pour into while the machine is spinning. By the way, these molds are very durable, the vulcanized rubber, made under extreme heat and pressure are similar to tire rubber. They can last many years; you can see above this one is 15 years old.

Once in the machine, it's clamped in place by a top plate and air from a compressor.
You can see the top plate features a hole as well, where the metal will pass through and it's locked in place by the aluminum finger holds.

The machine is already set to spin the appropriate RPMs and also for a set time.
Metal is poured in place once the mold starts spinning. No time is wasted as the we want the metal as hot as possible. As it spins inside the mold, centrifugal force sends it to all corners of the mold.
Once removed from the machine after about 40 seconds of spinning, we remove the mold. Often there is a stem of metal from the pour. The mold is pulled apart, revealing finished parts inside.
 

Often on the first spin, a few parts might not form correctly or at all.  The metal flows better once they are warmed up. Also, I forgot to mention, before the mold is put in the machine, it's dusted with a talc powder that also helps the metal flow.
Now there is a sprue of completed parts. They can either be twisted right off the sprue or cut with nippers depending on the part.
Once the parts are removed from the sprue, the excess metal is immediately put back into the pot to be re-used.
Parts are sorted as they are cast and eventually bagged specifically for each kit. 
Detail parts really make the scene and help tell a story with your structure kits. Aside from including these details in our kits, we do offer many of them separately so you can add them to a kit or any scratch building or kit bashing projects. You can find them here: