An introduction to Room Temperature Vacuum Casting

This process of RTV molding is applied with the utilization of a vacuum chamber to extract the liquefied material into the mold. The method of vacuum casting is applicable when the mold that is desired has complex details or undercuts. It is also utilized when there is a concern of air entrapment or if the material has fibrous properties or wire reinforces.

A two piece silicone mold is placed in a vacuum chamber while the raw liquefied material is mixed and degassed; this is done when dissolved gasses are removed from liquid materials called degasification applied to prevent gas bubbles formation that is undesirable when a smooth finish is required. After the extraction of gasses is completed, the liquid material is then poured into the mold. The vacuum is then released and the mold is taken out of the vacuum chamber.

After this procedure, the vacuum casting is cured in an oven. Curing is a process of toughening or hardening of the liquefied material. This can also be applied to polyurethane and other plastics like acrylic. The silicone mold can be reused to up to 20 times maximum where it will start to deteriorate and can no longer be useful. 

In the oven, it takes to up to hours for the liquid material to be cured depending on its size. After an exothermic reaction of the plastics, the cavity is opened and the molded plastic is removed. The silicone cavity is the closed and the procedure done again.

The disadvantage of Vacuum Casting is that it is expensive and is not preferred for mass production. However a substitute is available instead of this method known as Reaction Injection Molding. This process does not require expensive vacuum chambers and mixing facilities. The process utilizes simple plastic injection system with a couple of pressurized chambers.


vacuum casting or casts with silicone moulds for low volume plastic production in china (RTV or room temperature vulcanisation.) or poly urethane cast from china.