Heat Cured Rubber (HCR)

- Heat cured rubber is processed by heating and curing the base compounding composed of silicone polymer, supplement fillings and other additives with the addition of vulcanization agents.
Compared to other organic rubber materials, it has superior thermal stability, oil resistance, and electrical properties. HCR is widely used in every industry and can be manufactured with compression, transfer, injection ,extrusion and calender molding. It also has short curing time and relatively weak odor during the manufacturing process.


● Molding Techniques

▶ Compression Molding
Compression molding is the typical method for molding HCR. The stock is usually preformed to the approximate size and weight of the final part. It is then placed in the heated cavity of the mold, where it is cured under heat and pressure

▶ Transfer Molding
Transfer molding is a process by which uncured rubber compound is transferred from a holding vessel (transfer pot) to the mold cavities, using a hydraulically operated piston. It is mainly used for producing flash-less parts.

▶ Calendering
Calendering is for producing long runs of uniformly thick sheets of silicone rubber. Firm compound with good green strength and resistance to over-milling may work best for calendering. It is suggested that soft stocks be aged a minimum of 24 hours after milling to help build up structure prior to calendering.

▶ Injection Molding
Silicone rubber's low relative viscosity and fast cure rate make it an excellent material for injection molding which insures constant feed and minimizes handling of the uncured compound. Injection molding cure cycles are typically in the range of 0.5 - 3 minutes.

▶ Extrusion Molding
Extrusion is used for production of tubing, wire and cable insulation. Typically, the screw may have a compression ratio in the range of 2:1 to 4:1 and an Length/Diameter ratio of 8:1 to 12:1. Stainless steel screens of 40 to 150 mesh may help remove contamination increase backpressure, reduce porosity, and provide better dimensional control.

● Curing Techniques

▶ Extrusion Curing
HAV Curing: HAV uses of a heated tunnel through which the profile is fed con tinuously on a moving conveyor. Curing time is 3 to 12 seconds at a high temperature range from 300°F to 1200°F.
CA Curing: Steam cure commonly refers to systems (used by the wire and cable industry) that consist of chambers with 4" to 6" in diameter and 100 to 150 feet in length. Steam pressure varies from 50 psig to 225 psig, depending on processing level.

▶ Oven Curing
Oven Curing: Oven curing is the process of removing volatiles and peroxide decomposition form cured silicone parts and the process can improve dimensional stability and high temperature performance.

● Momentive Performance Materials

● Dongjue Silicone Group

● Daeil Advanced Materials