Release time:

2020-10-21

1. Rotor The type and number of rotor lobes affect mixing. More lobes result in faster shear speed, higher heat generation, shorter mixing time, but may compromise mixing quality. Different rotor types impact mixing. Shear-type rotors have a large dispersion zone between the rotor lobes and the mixing chamber, resulting in a wide and strong shear force, high efficiency, and good mixing quality. Intermeshing rotors have a dispersion zone between the two rotors, resulting in lower shear force, lower heat generation, longer mixing time, and better dispersion. 2. Upper Ram Pressure The upper ram keeps the material within the mixing chamber's working area. Insufficient pressure causes material slippage on the chamber walls and rotor surfaces. Appropriate pressure reduces voids in the material and increases contact force. High pressure increases material temperature and mixing power. Insufficient loading capacity prevents the upper ram pressure from being fully effective, resulting in uneven material dispersion. 3. Temperature Each rubber type has an optimal mixing temperature range. The type and amount of raw rubber, reinforcing agents, and softeners determine the temperature rise during mixing. At the same temperature, longer mixing times lead to better dispersion. 4. Fill Level This depends on the effective volume of the internal mixer, the type of raw rubber in the formulation, and the amount of reinforcing fillers and plasticizers. The fill level should be higher for raw rubbers with high plasticity. The filling factor (by weight) should be between 0.65 and 0.75. Insufficient fill level prevents the necessary shear force from being achieved. 5. Material Addition Sequence The order of material addition affects the mixing results. In automated systems, a typical sequence (using multi-stage mixing, according to material requirements) is: raw rubber - pre-mixing - addition of fillers/compounds - pre-mixing - addition of softeners - pre-mixing - final mixing - discharge. 6. Rotor Speed Rotor speed is directly proportional to shear rate. Higher shear rates accelerate uniform mixing. Increasing rotor speed raises the rubber temperature, reducing viscosity and shear stress. 7. Time Mixing time depends on the fill level and the temperature rise of the formulation. The mixing temperature affects the time for different rubber types. The internal mixer's speed and upper ram pressure also affect mixing time. Therefore, auxiliary and feeding times should be minimized in the mixing process. 8. Cooling Water The cooling water temperature is typically set to 15 degrees Celsius. Low-viscosity materials should not be cooled with hot water to avoid sticking to the rotor. High-viscosity materials can be cooled with hot water. Increasing the cooling water temperature shortens mixing time, reduces energy consumption, and improves production efficiency.