Pressure casting is the process of using a pressure chamber and compressor to eliminate bubbles from a casting resin or mould rubber. It is the best method for ensuring that castings are bubble free. The pressure casting method is commonly used by professional prototype model makers who cannot tolerate a single bubble. A single bubble on the surface of a casting will result in the casting being discarded.

How Pressure Casting Works

A liquid plastic (Smooth-Cast® Plastics, Crystal Clear® Plastics or TASK® plastics) is mixed and poured into a rubber mould.
The entire mould structure is placed into a pressure chamber.
The door or lid to the pressure chamber is closed and tightly secured.
A compressor hose is then connected to an air port on the pressure chamber.
The compressor is then turned on and the mould and resin are subjected to 60 psi pressure until the resin gels.
The bubbles are collapsed into solution and the result is a bubble free casting.

Making the mould Under Pressure

If you are going to use a rubber mould on a regular basis for pressure casting, it is suggested to make the rubber mould under pressure as well. This means mixing and pouring mould rubber over your original model, placing the structure in your pressure chamber and applying 60 psi until the mould cures.

Reason: If you pressure cast resin in a rubber mould that has not also been pressurized, any bubbles present in the rubber mould may implode under the pressure and the collapsed bubbles may be reflected in the finished casting as bubble positives or "dimples".
Important Notices

Note: when making a mould of a hollow model under pressure it may collapse under pressure
Warning: use commercial pressure chambers only. More than one resin caster has learned the hard way that "home-made" pressure chambers can explode violently and cause serious injury.
Important: ensure that the air running from your compressor (used to pressurize the pressure chamber) is dry. Moisture in the air line will react with urethane resins and rubbers causing bubbles or foaming. Air line driers are available from industrial supply stores.