This molding process is the compressing of an uncured rubber preform in a cavity of a compression mold bolted up in a hydraulic press. Under heat and pressure the rubber flows and fills a mold cavity. Over time, the rubber gains cross link density and cures out into a finished part.
Compression molding is an efficient, low waste, cost effective molding method. It is best suited for all but the closest dimensional tolerances, medium volumes, and medium to large size parts. Compression molding tools are inexpensive compared to other methods. Advantages of compression molding are low tooling cost, short set-up times, and the ability to process a wide range of elastomers, including higher durometer materials.
This production method is a simplified version of injection molding. A rubber preform is compressed in a transfer pot through sprue holes. The rubber flows through these sprue holes into the mold/part cavity. This molding method is excellent for more complicated designs, close tolerances, and small to medium part sizes. Tooling tends to be more expensive than compression molds, but significantly less expensive than injection tools. Advantages of transfer molding are less reject, shorter cycle times, maintaining tight dimensions, excellent uniformity, and low cost.