Elastomer manufacturing has many steps, and one of the most important is post-curing. Without this process, the materials that make up elastomers like silicone and fluoroelastomers would fail in the operations they’re used in. Our latest blog will tell you what you need to know about post-curing, including the types of materials that most need it, and the operations where you can find these elastomers.
What is Post-Curing?
Post-cure is the second step in the vulcanization of certain elastomers. Post-cure is used to get rid of leftover decomposition from initial vulcanization. If you’re unaware what vulcanization is, it’s a heat-based process of converting basic visco-elastic liquids into durable products. In fact, this term has the same meaning as “cure.” Post-curing has a big impact on the performance and durability of the final product.
Post-curing means subjecting the rubber part to high temperatures for an extended period to complete cross-linking, which can enhance physical properties like strength, hardness, heat and chemical resistance, and other environmental factors. Post-curing prevents future defects like blistering or cracking by driving out volatile byproducts under controlled conditions, making sure they don’t outgas and damage the material once the part is put into service.
What Type of Elastomers Need Post-Curing?
The most common materials in elastomers that need post-curing are silicone, fluoroelastomer (FKM), fluorosilicone (FVMQ), and peroxide-cured ethyl propyl diene monomer (EPDM). Silicone needs to be post-cured in a heated air-circulated oven usually around 150ºC (302ºF) to 200ºC (392ºF) for several hours to remove volatile byproducts like potential chemicals that are inside the rubber, as well as to eliminate outgassing, and complete cross-linking. Post-curing silicone helps to ensure proper safety compliance and improves its strength.
Post-curing FKM parts, which is commonly done at 200ºC (392ºF) to 232ºC (450ºF) involves two stages: primary curing happens under pressure during injection molding, and the secondary post-cure takes place in an oven to complete cross-linking and increase tensile strength, compression set, and stability. For FKM, post-curing removes residual process aids like waxes, maximizes thermal stability, and improves compression set resistance. To avoid adverse reactions, FKM parts should not be cured alongside components made from other elastomers like silicone rubber, which can be damaged because of chemical interactions in the oven environment.
FVMQ, unlike regular silicone, requires stricter, more precisely-controlled post-cure cycles due to its fluoro-modified polymer chains and higher tendency for volatile trapping. FVMQ has a higher shrinkage rate during vulcanization and post-curing than standard silicone. It also needs extended heat cycles (usually 4–8 hours) to prevent thermal degradation. FVMQs have a different limit than regular silicone, being around 177ºC (351ºF) to 200ºC (392ºF), but utilizes fluorine groups to resist fuels, oils, and harsh solvents.
Peroxide-cured EPDM stabilizes the physical properties and addresses effects caused by residual peroxide decomposition and trapped radical recombination. Depending on the temperature, it can take between 1–4 hours for post-curing. This process helps prevent outgassing in sensitive environments, enhances the material performance in high-temperature environments without premature aging or hardening, and helps the component meet strict purity and safety requirements regulated by industries like the Food and Drug Administration.
Where Are Post-Cured Materials Typically Found?
In a broad sense, post-cured elastomers are used in multiple fields, such as industrial, automotive, aerospace, food and beverage, and medical. Their usage in these areas makes sense because these operations require high safety and reliability, thermal stability, and strict purity from their fluid and gas sealing. Within the medical field, equipment like silicone tubing and catheters use seals to ensure biocompatibility. Chemicals need to be eradicated from these elastomers to be safe for body contact, almost like a form of sterilization. In the automotive sector, FKM and silicone are frequently used for fuel system hoses and engine seals.
For the food and beverage area, post-cured materials are located in kitchenware and fluid-handling equipment to ensure compliance with food-safety standards by removing residual peroxides. Aerospace uses post-cured seals and gaskets to help their technology withstand extreme temperature without releasing volatile compounds that can ruin systems or optics. Industrial-wise, they’re found in heavy-duty machinery and chemical processing plants, where the materials come into contact with acids and gases.
The Post-Blog Question
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