The process of rubber molding has helped shape the way that we use rubber in today’s world. Rubber molding consists of shaping rubber into the desired shape.
Following is a list of some of the technologies/molding practices used when creating rubber solutions.
Compression Molding
Compression molding is a method of molding in which the rubber material or compound is placed in a mold cavity. The mold is closed using hydraulic or electric pressure, compressing the material to conform to the mold cavity’s shape. Next, rubber is cured through the heating of the rubber from the heated mold. The cured rubber is then taken out and given time to cool. Excess material, also known as “flash,” is trimmed.
Compression molding has the longest cure/cycle time but represents the simplest and lowest-cost tooling.
Injection Molding
Next to liquid injection molding, injection molding offers the shortest cure/cycle time, with moderately complicated tooling. In this custom rubber molding method, rubber material or compound is fed into an injection barrel and warmed by the temperature-controlled barrel or through the shearing action of an auger-type screw or plunger. The material is then fed into the runner system and mold cavity through hydraulic or electric ram pressure.
Next, rubber is cured through the heating of the rubber from the injection process and the heated mold. The cured rubber part is removed and allowed to cool, with excess material removed.
Liquid Injection Molding
Liquid injection molding, sometimes referred to as LIM, delivers the shortest cure/cycle time. In this process, a two-part silicone is fed into a mixing head through hydraulic ram pressure. From this mixing head, the mixed liquid silicone is fed into an injection barrel. From this barrel, the mixed liquid silicone is funneled into a runner system and mold cavity via hydraulic or electric ram pressure.
The liquid silicone is cured through the heating of the material from the hold mold. The curing time of liquid injection molding is usually about one-third to one-sixth the time required for solid or gum rubber. The cured rubber part is removed and allowed to cool, with any excess material trimmed.
Transfer Molding
Transfer molding has a slightly more-complicated tooling process compared with compression molding. In this process, rubber material or compound is placed into a mold “pot,” located above the top mold plate. Using hydraulic pressure, the tight-fitting plunger squeezes rubber material from the pot through the gates into the mold cavity. Rubber is then cured through the heating of the rubber from the heated mold. After the rubber is cured, the mold opens, with the plunger raised up from the pot and the “transfer pad” removed and discarded.
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