Rubber compression molding produces elastomeric parts by placing a pre-measured amount of rubber into a mold, closing the tool, and applying heat and pressure. This pre-measured material is called a charge or load, and the mold is usually pre-heated so that the material flows more readily and fills the tool as it’s compressed. When molding is complete, the part is cooled, ejected, and trimmed or de-flashed.
Often, rubber compression molding is used to produce larger or heavier parts – especially ones that are flat or have simple contours. Yet this molding technique can also be used with smaller parts and can produce threads, holes, and grooves. Compression molding supports a wide range of elastomers, but it’s generally used for low-to-medium part volumes.
Rubber Compression Molding Advantages and Disadvantages
The advantages of compression molding start with its lower tooling costs. Because compression-molded materials are placed directly into a mold, they don’t need to flow through a complex series of channels and openings as with injection molding. Consequently, compression molding supports the use of heavier and harder-to-flow materials.
Rubber compression molding isn’t used for fine part tolerances, but compression-molded parts still have good dimensional accuracy. They also have a smooth, attractive surface finish and can achieve a good level of detail. Because they’re strong and lightweight, compression-molded parts can replace metal ones in structural components and assemblies.
Compression molding is not a good choice for complex parts with sharp edges, steep angles, or intricate details despite its many advantages. Generally, the part geometries are relatively simple so compression molds don’t need to include ejection mechanisms that increase the cost of tooling. Longer cycle times are also a disadvantage, but
Ask The Rubber Group
Is compression molding the right choice for your project? Is injection molding or transfer molding a better option instead? Ask The Rubber Group. We offer all three services for both standard and custom molded rubber products.