The raw silicone rubber is relatively soft and has a certain plasticity, and can be directly mixed with an open mill or an internal mixer without mastication. The mixing methods can be as follows:

(1) Kneading with open mill
The roller speed ratio of the double-roll mill is preferably (1.2~1.4):1, the fast roller is behind, a higher speed ratio leads to faster mixing, and a low speed ratio can make the film smooth. The roller must have cooling water, and the mixing temperature should be below 40℃ to prevent scorch or volatilization loss of vulcanizing agent. When mixing, the roll distance is small (1 ~ 5mm) at the beginning, and then gradually increases. Feeding and operation sequence: raw rubber (roll wrapping) - reinforcing filler - structure control agent - heat-resistant additives - colorant - thin pass 5 times - blanking, oven heat treatment - re-melting - vulcanizing agent - thin pass - parking Overnight - Refining - Filming. The rubber compound can also not be heat treated in an oven. After adding heat-resistant additives, adding a vulcanizing agent and then thinning it, park it overnight for re-melting, and then park it for several days to re-melt and use it. The mixing time is 20 to 40 minutes.

When the silicone rubber is added to the rubber mixing machine, it is wrapped with a slow roll (front roll), and it is quickly wrapped with a fast roll (rear roll) when mixing. It must be able to operate on both sides during rubber mixing. Since the silicone rubber compound is relatively soft, it can be operated with an ordinary putty knife during mixing. When it is thin, the sheet cannot be pulled off like ordinary rubber, but it is scraped off with a steel, nylon or wear-resistant plastic scraper.

In order to facilitate cleaning and prevent the leakage of lubricating oil into the glue, a movable glue plate should be used. Fumed silica is easy to fly and is harmful to human body, so corresponding protective measures should be taken. If powder peroxide is used directly during mixing, explosion-proof measures must be taken, preferably paste peroxide.

(2) Mixing by internal mixer
When mixing with a laboratory 2L internal mixer, the mixing time is 6-16min. There is no particular difficulty in mixing. When the charging coefficient is 0.74, the mixing can be carried out normally with a Φ160mm open mill. The discharge temperature is related to the type of reinforcing filler. When using weak reinforcing filler and precipitation method silica, the discharge temperature is below 50℃; when using fumed silica, the discharge temperature is 70℃ about.

(3) Rubber compound parking and regrinding
After the silicone rubber compound is mixed, the parking time should be no less than 24h, so that various compounding agents (especially structural control agents) can fully work with the raw rubber. After parking, the rubber material becomes hard and the plasticity value decreases, so it must be re-melted before use. The back-mixing adopts an open mill, and the roll distance is large (3-5mm) at the beginning. At this time, the rubber compound is hard and the surface is wrinkled, which is wrapped on the front roll. With the extension of the back-melting time, the rubber compound gradually becomes soft; the roll distance is gradually reduced (0.25-0.5mm), and the rubber compound is quickly wrapped on the rear roll. After the rubber material becomes soft and the surface is smooth and flat, the material can be unloaded. Insufficient re-refining will cause wrinkles on the surface of the film; if re-refining is excessive, the rubber will become sticky and stick to the roller. The tempering temperature is generally controlled at room temperature.