Investment Casting

[Splint]

These are some pictures I took when I toured a jewlery factory in Thailand. The process is lost wax (investment) casting. The shaft at the bottom of the ring in the picture is put in the hole in the rectangular cavity so that it is centeralised and then liquid rubber is poured in until the rubber reaches the top of the cavity. When the rubber solidifies it is removed from the cavity and cut appart so the pattern can be removed (the two halves of a finished rubber mold can be seen on the left of the picture).

[Splint]

This picture shows the wax which is melted down and injected into the cavity between the two halves of the mold where it cools down and solidifies leaving a shape identicle to that of the pattern.

[Splint]

This picture shows a man opperating the wax injection machine. The mating faces of the rubber mold are sprinkled with some powder which acts as a seperating agent, the mold halves are put together with sheet metal plates on the backs of each half to make sure the molds hold their true shape and the a rubber band is put around the assembley to keep it together. The wax is then injected and the mold assembly is put aside for a few minutes while the wax in the mold cools and solidifies.

[Splint]

After the wax has solidifid the halves of the mold are sepperated and the wax ring is removed. The molds are then reused to make more rings, hundreds of rings can be made with the rubber molds before the condition of the molds deteriorates and new molds are required.

[Splint]

The rings are attached to a wax tree. The wax tree in this picture was for demonstration and the rings at the top of the tree had broken away from the trunk because people were continually touching and picking it up.

[Splint]

A tube is put around the tree and then casting powder is tipped in where it sets around the wax tree. Once it has set the wax is melted out of the casting powder and a cavity in the shape of the tree is left in the powder. Molten silver is poured into the cavity and left to cool down.

[Splint]

When the silver is cool the casting powder can be smashed away to expose the tree. The individual componants are cut from the tree for processing and the trunk goes back into the melting pot.

[Splint]

The casting is debured, polished, may have stones fitted, even sand blasted to achieve a porus finish.
Jewlery factories can be very interesting places to visit, they are usually close to tourist destinations and they encourage tourists to come in to look and hopefully spend some money, unfortunately the tour guides are in a big hurry to get through the factory and into the showroom. I went back into the factory for a better look after the tour was over.
Cheers
Splint

[ynneb]

Hey Splint, That was a real good post. It would be a pity for that effort to eventually be lost in the abyss of old threads. Why dont you format the whole thing into a html document, and upload it to the tutorial section.
If you cant be bothered, let me know, and I will compile it for you.

[dbassett74]

That was awesome indeed! Gave me a very good sense of how this investment casting works. We need more articles like this!!