Scorching in EPDM rubber parts usually occurs when vulcanization begins earlier than intended during processing. The main causes relate to temperature, processing time, compound formulation, equipment condition, and raw material quality. Controlling these factors helps reduce the risk of premature vulcanization before molding is complete.
Improper temperature control
Excessive temperatures during rubber mixing or molding can accelerate reactions involving curing agents and other additives. For example, an internal mixer with poor temperature control may cause the rubber compound to begin vulcanizing too early. High workshop temperatures during summer can create a similar risk, particularly when the production area lacks effective cooling.
Operators need to monitor processing temperatures and keep them within the ranges specified for the compound and production process.
Excessive processing time
Rubber compound that remains inside processing equipment for too long has a greater risk of premature vulcanization. An extruder running at an excessively low screw speed may allow the compound to remain inside the barrel longer than intended.
Delays between mixing and molding can also increase this risk. When the compound waits too long before the next processing stage, prolonged exposure to air may contribute to changes in its processing condition and increase the likelihood of scorching.
Problems with the compound formulation
Excessive amounts of curing agents or accelerators can speed up vulcanization and cause the compound to scorch before the intended curing stage. An unsuitable ratio between different additives can also alter the reaction rate and lead to premature vulcanization.
The compound formulation therefore needs to match the processing requirements. Inconsistent proportions of curing agents and accelerators can make the vulcanization process more difficult to control.
Equipment-related problems
Rubber accumulation inside equipment can create another source of scorching. Dead corners may allow compound to build up and partially vulcanize. During subsequent production, this material can mix with fresh compound and affect the quality of the finished parts.
Faulty temperature control systems can cause similar problems. If the actual processing temperature exceeds the set value, the compound may begin to vulcanize earlier than expected. Regular equipment checks and effective temperature monitoring help identify these problems before they affect more production material.
Raw material quality and storage
Variations in raw material properties can affect the vulcanization process. Large fluctuations in the Mooney viscosity of the rubber, for example, can change its processing behavior. Differences in additive activity can also affect the rate and consistency of vulcanization.
Storage conditions matter as well. If raw materials or additives are exposed to moisture or excessive heat, or undergo unwanted reactions during storage, their properties may change. These changes can increase the risk of premature vulcanization during subsequent processing.
Custom precision component machining services
In addition to discussing rubber processing issues, Hansheng Automation provides drawing based custom machining for precision components used across different industries. Our services cover yacht components and RC racing car parts, as well as nonstandard parts for tobacco packaging and filling machinery. We manufacture components according to customer drawings and specified dimensions to support different equipment and application requirements.
