Different Types of Rubber Molding Process
#1 Injection Molding
Injection molding is one of the most common molding process. With injection molding, the press unit and injection unit act as two separate entities with separate controls. The press unit allows for molds to be placed horizontally or vertically. An extruder unit can also serve several presses by moving in a pre-programmed pattern. All of these result in short injection processes with high amounts of pre-heating. With this type of molding, the handling of blanks is eliminated, processes can be automated and difficult cavities and flow channels can easily be filled.
#2 Compression Molding
Compression molding is similar to injection molding in the respect that it also utilizes heat and pressure. However, the application of heat and pressure are quite different, explained as follows. The mold has two halves, each carrying a portion of the cavity. At first, the uncured raw material, known as the charge, is pre-heated and placed in the lower half. The mold sections are also heated beforehand. Once the operator is content with the material’s placement, the plug (the movable half of the mold), lowers down into the fixed mold. Due to the pressure from the plug, the charge takes the mold cavity shape. The mold applies heat to cure the rubber in its new shape. Finally, the molded rubber comes out as the final product.
#3 Transfer Molding
Transfer molding is a natural progression in development to limit the disadvantages of compression molding. The process starts out with a blank being loaded in the chamber, which is then distributed into several cavities. In this beginning stage, pre-heating takes place in the rubber, forcing the rubber to flow through channels. This pre-heating reduces the curing time and allows the rubber to flow easier and fill mold cavities efficiently. However, the molds are more complicated and expensive.
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