Production Technology and Material Proportion of Mixed Silicone rubber
Thermally vulcanized silicone rubber is a kind of product with large output and wide application. Silicone rubber has excellent resistance to high and low temperature. It can be used for a long time in the range of - 60 - 250 C. It also has excellent electrical insulation, ozone resistance, weather aging resistance, water repellency, moisture resistance, and good physiological inertia. A kind of reinforcing filler, vulcanizing agent (or without adding) and other additives are added to the raw rubber of hot vulcanized silicone rubber, which is then mixed into rubber, and can be processed into various silicone rubber products by common rubber processing methods such as die pressing and extrusion. A kind of Mixed silicone rubber can be prepared in general purpose rubber mill, while large-scale production is carried out in kneader or closed mixing equipment. The following are the basic coordination processes:
Detailed description of each process:.
1. Blending:.
When mixing with an open mill, it is better to equip a dust-proof or air-suction device above the roller of the converter to reduce the flying of silica. No other impurities or colloidal particles should be mixed in the mixing process. The temperature should be controlled below 40 C and enough cooling water should be boiled. The mixing time of each batch of rubber is between 20 and 40 minutes. Mixing with internal mixer can not only improve production efficiency and reduce labor intensity, but also reduce the flying of silica and improve operation environment. A kind of the mixing sequence of internal mixer is similar to that of open mixer, but the requirement of interval time is not strict. The mixing time of each batch of rubber is about 8 to 18 minutes, and the filling coefficient of the mixer should be controlled in the range of 0.7 to 0.75. The gum discharge temperature is related to the type of filler, and should be controlled in the range of 50 ~70 ~C. 
2. Heat treatment:
When fumed silica without surface modification is used as reinforcing agent, structural control agent must be added to the compound.  Therefore, the heat treatment of rubber materials has become a necessary process. The main purpose of heat treatment is to further combine the structure control agent with the silica surface (Si-OH) and eliminate the low molecular volatiles in the gum. The general heat treatment conditions are as follows: under the protection of nitrogen or in the kneader of decompression, the kneader is treated at 160 200 for 1 1.5 h. 
3. Filtration:
For extruded products, calendered products, coated products and diaphragm products, mechanical impurities and undispersed particles are one of the main factors leading to product quality problems. Therefore, the rubber used for the above products must be filtered. It can be replaced by rubber filter or ordinary extruder. The temperature of barrel and screw should be controlled to the lowest level, and the specifications of filter screen should be 120-200 mesh. 
4. Refining:.
When the rubber is stopped, the gel content increases and the plasticity decreases, so it is necessary to refine it when used. Rubber refining should stop at the right time, insufficient refining, poor softness and uneven surface; and excessive refining, the surface of the rubber will stick, which is not conducive to operation.