About the Lost Wax Process
Although an ancient practice, the lost wax
process today may vary from foundry to foundry.
However, the steps which are usually used in
casting small bronze sculptures in a modern
bronze foundry are generally quite standardized.
Here at WH Casting we use a very unique vacuum
cast machine. This one-of-a-kind casing
machine was originally built specifically for
NASA. We acquired it in 2009.
What sets us apart in the casting world is the fine tuned precision pours under pressure and vacuum this machine provides. Other foundries use the older technique of having to create a shell of investment slurry (a plaster of Paris type solution) around their waxes and then after the wax is melted out they use giant vats of molten bronze to pour into the empty shell. With our machine we don't have to go through the waiting stages of a shell investment to set up. That process can take upwards of a week or more to create a thick enough shell around the wax before the molten metal pouring can begin. Our process uses specialty fit cans or flasks that are built specifically for this machine. These cans are filled with as many waxes as we can fit at a time and then our investment is poured around it, filling the can. We also vacuum the invested cans in their liquid state to help eliminate any air trapped around the wax. The slurry content of these cans set up in about an hour and can go directly to into the Burnout oven.
The other difference with our process vs. the standard casting method is that we only melt enough bronze at a time to cast exactly what we need for each can. By weighing out the wax weight and using a conversion code we can determine the exact amount of bronze needed for each can. What really sets us apart is the fact that once the door shuts on the casting chamber vacuum begins and nitrogen gas is introduced to create a completely inert, pollution-free casting environment resulting in perfect castings.
After the bronze drops into the can it can almost immediately be removed and set aside to cool. There are two methods of breaking out bronze from the investment cans: quenching or air hammer. The air hammer is a good solution when it's too cold to play in the water outdoors.
The finishing process is quite simple around here, we do a bath of Liver of Sulfur and polish back to create a lovely natural bronze contrast.