Thermally vulcanized silicone rubber is a type of silicone product with the largest output and wide application. Silicone rubber has excellent high and low temperature resistance, can be used for a long time in the range of -60 ~ 250 ° C, and has excellent electrical insulation properties, ozone resistance, weather aging resistance, water repellency, moisture resistance, and good physiological inertia.

Add reinforcing filler, vulcanizing agent (or do not add) and other additives to hot vulcanized silicone rubber raw rubber, and then knead to form a mixed rubber, which can be processed into various silicone rubber by general rubber processing methods such as molding and extrusion. rubber products.

Mixed silicone rubber can generally be prepared on a general-purpose rubber open mill, and large-scale production is carried out in a kneader or closed mixing equipment.

Detailed description of each process:

1. Mixing:

      When using a mill for mixing (not commonly used), it is best to equip a dust-proof or ventilation device above the roller of the mill to reduce the flying of white carbon black. During the mixing process, no other impurities or colloidal particles should be mixed in, the temperature should be controlled below 40°C, and enough cooling water should be used. The mixing and eating of powder by the open mill is slow, and the mixing time of each batch of rubber is about 20 to 40 minutes. Mixing with an internal mixer can not only improve production efficiency and reduce labor intensity, but also reduce the flying of white carbon black and improve the operating environment.

     The operation sequence of internal mixer mixing (not commonly used) is basically similar to that of open mixer, but the requirement for interval time is not strict. The mixing time of each batch of rubber is about 8-18 minutes, and the filling factor of the internal mixer should be controlled in the range of 0.7-0.75, which is more suitable. The debinding temperature is related to the type of filler, and should usually be controlled within the range of 50°C to 70°C.

    Special kneader for silica gel, vacuuming. Generally use a special kneader of 800-2000L, put raw rubber, white carbon black, silicone oil, mechanism control agent, small materials with special requirements, etc. into the kneader for mixing, usually 2-3 hours, the temperature rises to 130°C-150°C , after another half an hour of vacuuming, the material is poured through the open mill and the sheet is parked.

2. Heat treatment:

When using non-surface-modified fumed silica as a reinforcing agent, a structure control agent must be added to the compound. Therefore, the heat treatment of the rubber has become a necessary process. The main purpose of heat treatment is to further combine the structure control agent with the surface of silica (Si-OH) and eliminate low molecular volatiles in the glue. The general heat treatment conditions are: under the protection of nitrogen or in a kneader under reduced pressure, treat at 160°C-200°C for 1-1.5h.

3. Filtration:

For extruded products, calendered products, rubberized products, and film products, mechanical impurities and undispersed compounding particles are one of the main factors leading to product quality problems. Therefore, the sizing material used for the above-mentioned products must be filtered. When filtering, a rubber filter can be used, or an ordinary extruder can be used instead. The temperature of the machine barrel and screw should be controlled to the lowest level, and the filter size should be 120-200 mesh.

4. Refining:

After the rubber is parked, because the gel content increases and the plasticity decreases, it must be re-milled when it is used. The re-milling of the rubber should be done in moderation. If the re-milling is insufficient, the softness of the rubber material will be poor and the surface will be uneven; if the re-milling is excessive, the surface of the rubber material will be sticky, which is not conducive to operation.

About liquid silicone rubber, please check the details:
https://www.siliconefoam.net/product-iota-f663a,b-liquid-silicone-rubber-foam-.html