PRESS

The Importance of Vacuum in the Rubber Injection Molding Process

The importance of vacuum in rubber injection cannot be overstated.

Vacuum is an often used but a commonly misunderstood technique in rubber injection molding. The main purpose of vacuum is to remove air entrapments during the injection and vulcanization process that occurs once rubber is packed inside an injection mold. This sounds simple in theory but to achieve a good vacuum in a repeatable injection process is a bit more complex.

Vacuum is achieved by evacuating air and developing gasses inside the mold or mold cavity prior to and during the injection process. A properly designed mold will have strategically located vacuum connections and dump grooves to assist cavity filling without voids in the product. Often these vacuum locations, or the vacuum achieved at these locations is insufficient, improperly designed or in many cases hindered by an inadequate working vacuum pump system outside the mold.

A “near perfect” vacuum is considered 0.996 bar or 29.4 mm hg. Many times this is difficult to achieve due to poorly sealed mold plates or is caused by a variety of other factors. Proper vacuum is a function of both sound machinery maintenance, vacuum pump and vacuum line maintenance as well as a properly sealed mold plate and cavity design. DESMA USA’s NAMC division considers vacuum a key criteria in any new project design phase.

Another way to achieve adequate vacuum in rubber injection molding is to utilize a vacuum chamber where the mold is placed completely inside a controlled environment. To remove air, a properly sized vacuum pump with an accumulator tank evacuates the air completely within the chamber (versus cavity only) prior to or during injection. Special features within the hydraulic circuitry of the press must be incorporated in conjunction with vacuum for optimum process stability.

DESMA has many years of experience not only in process development using vacuum, but also in the development of machinery and molds that require vacuum. Our DESMA Trainer, Walter Frick, has decades of experience in this subject. Walter offers several classes on rubber processing that touch on vacuum. These classes were designed for in person instruction but have been updated and are now available online.

Contact DESMA Training for more information.

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