The Protolis guide to compression molding
In this guide, you will find comprehensive instructions for Compression Molding, a widely used method for crafting precise, high-quality rubber components.
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What is compression molding?
• Introduction of compression molding
Compression molding is a manufacturing process in which a pre-shaped material, known as a preform such as silicone or rubber, is placed into a heated mold cavity. The mold is then closed, and the combined application of heat and pressure causes the material to flow, ensuring complete cavity filling while eliminating air voids. Heat simultaneously initiates the curing reaction, while pressure maintains dimensional accuracy and prevents defects. The thermoset material must then be allowed sufficient time to cure fully, developing the required mechanical strength, durability, and dimensional stability. This technique is widely employed across industries to produce high-quality, precision components, particularly those with low Shore hardness.
• The history of rubber compression molding
Rubber compression molding is the earliest known technique in rubber molding, with origins dating back to the 1890s. The method was pioneered by Harvey Firestone, who employed it in the production of the first consumer rubber products. Since its introduction, the core principles of the process have remained largely consistent. Owing to its simplicity and effectiveness, rubber compression molding has long been regarded as a dependable approach for manufacturing a wide range of rubber components. This foundational method also played a pivotal role in enabling the development of more advanced molding techniques that are widely used in modern production.
• Key terms
- Preform: A precisely measured and often shaped amount of raw rubber or silicone placed into the mold.
- Curing (Vulcanization): The chemical process (heat + pressure) that cross‑links polymer chains and hardens thermoset materials.
- Flash: Excess material that escapes the mold cavity during compression.
- Degassing: The release of trapped air from the material during molding to prevent voids.
- Durometer (Shore Hardness): A scale (e.g., Shore A, D) used to measure the hardness of elastomers.
- Deflashing: The post-molding process of trimming away flash for precise part dimensions.
Continue your exploration of compression molding in other chapters:
How does compression molding work?
Benefits and limitations of compression molding
When to choose compression molding for prototypes and low volume manufacturing?