A rubber mixing machine, also known as a sealed rubber mixing machine, is mainly used for plasticizing and mixing rubber. A rubber mixer generally consists of a mixing chamber, two relatively rotating rotors, an upper top bolt, a lower top bolt, a temperature measurement system, a heating and cooling system, an exhaust system, a safety device, a discharge device, and a recording device.

When the rubber mixer is working, the two rotors rotate relative to each other, clamping the material from the feeding port and bringing it into the roller gap under the compression and shear of the rotor. After passing through the roller gap, it hits the lower top bolt edge and is divided into two parts, which respectively travel along the gap between the front and rear chamber walls and the rotor before returning to the upper part of the roller gap. During the flow around the rotor, the material is subjected to shear and friction everywhere, causing the temperature of the rubber material to rise sharply and the viscosity to decrease, increasing the wettability of the rubber on the surface of the compounding agent and ensuring full contact between the rubber and the compounding agent surface. The clumps of the compounding agent, together with the rubber material, pass through the gaps between rotors, between rotors and upper and lower top bolts, and between rotors and the interior walls of the mixing chamber. They are sheared and broken, surrounded by stretched and deformed rubber, and stabilized in a broken state. At the same time, the convex edges on the rotor cause the rubber material to move along the axial direction of the rotor, playing a role in stirring and mixing, so that the mixing agent is evenly mixed in the rubber material. The compounding agent is repeatedly sheared and broken, causing the rubber material to undergo deformation and recovery. The continuous stirring of the rotor ribs ensures that the compounding agent is evenly dispersed in the rubber material and reaches a certain degree of dispersion. Due to the much greater shear force on the rubber material during mixing in the internal mixer compared to the open mixer, the rubber mixing temperature is higher, resulting in a significantly higher efficiency of rubber mixing in the internal mixer than in the open mixer. The quality of the rubber material mixed by the internal mixer depends not only on the feeding sequence, but also on the mixing temperature, feeding capacity, rotor speed, mixing time, top bolt pressure, and rotor type.

In the mixing process of rubber mixer, the order of adding raw rubber, carbon black, and liquid softener, as well as the mixing time, are particularly important. Generally, raw rubber is added first, followed by carbon black, and the liquid softener is added after the carbon black is basically dispersed in the rubber material. This is beneficial for mixing, improves the mixing effect, and shortens the mixing time. Adding liquid softeners too early or too late is not conducive to refining, as it can cause uneven dispersion, prolonged mixing time, and high mixing temperature. This is beneficial for the plastic flow and deformation of raw rubber and rubber materials, as well as for the wetting and powder feeding of rubber on the surface of solid compounding agent particles. However, it also reduces the viscosity of the rubber material, which is not conducive to the crushing and dispersion of compounding agent particles. Excessive mixing temperature can accelerate the thermal oxidative aging of rubber, leading to a decrease in the physical and mechanical properties of vulcanized rubber, resulting in the phenomenon of mixing; It can also cause the rubber material to burn, so effective cooling measures must be taken during the mixing process of the internal mixer; But the temperature cannot be too low, otherwise there will be a phenomenon of rubber material dispersion.

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