Low melt alloy casting - anyone done any?

[thor]

No amount of reading can substitute for actual experience, I'm hoping someone has tried this. I heard about low melt alloys like Cerrobend that can be melted in a double boiler and I'm wanting to have a go at it.  I'll probably start off with something small - like a lamp post but eventually I'd like to try making English style open wagons and maybe even a loco shell one day.

I have had some experience in sandcasting aluminum - I was a shop teacher - and hot metal type casting (I was a Monotype guy) but not at the hobby/jewellery level so I don't know anything useful about techniques suitable for this.

I've spent a day or so reading up on the various alloys and mold materials such as cured rubber and silicone rubber but as I say, there's nothing like getting the straight griff from someone that's done it. I dont want to buy something that turns out to be not good enough for what I need.

[trigtrax]

I have done investment casting of silver and gold. In that case a wax model is encased in plaster and then melted out after the plaster sets. The molten metal is then spun into the mold.. To make a proper plaster cast you'll need a good vacuum chamber. This draws disolved air out of the mold which would otherwise form bubbles on the surface.

The lowest temperature molding I've done is casting lead sinkers. For best results the aluminum molds need to be heated before pouring in the lead. this keeps the metal from cooling during the pouring and causing voids and defects.

The low temperature alloys you're taking about are used for proofing, or making casts of the internals of machined parts.. They are very expensive, and most machine shops reuse the metal after measurements are made.

The vulcanized rubber and silicone rubber is again a spinning process which requires high temperature models and a heated press to set the rubber disks.. Going on line to an outfit like Romanoffs for spinner, vulcanizing press and melting furnace gives you a start-up cost of $7-8K.

You'll find used equipment on e-bay.. Good luck