That is, mixing capacity. Insufficient capacity will reduce the shearing and kneading effects on the rubber, even rubber slip and rotor idling, resulting in poor mixing effect. On the contrary, excessive capacity makes it difficult for the rubber material to turn over, which makes the top bolt not in the right position, and makes part of the rubber material stay at the feeding mouth neck, thus making the rubber material mixed unevenly, mixing for a long time, and easily leading to equipment overload and high energy consumption. Therefore, the mixing capacity should be appropriate, usually 60%~70% of the total effective volume of the airtight chamber. The material capacity during mixing of internal mixer can be calculated by the following empirical formula:
Q -- loading capacity, Kg;
K - filling coefficient, usually 0.6~07;
V -- total effective volume of air tight chamber, L;
ρ—— Density of rubber compound, g/cm3.
The selection and determination of the filling coefficient K shall be based on the type of raw rubber and the characteristics of the formula, the characteristics of the equipment and the degree of wear, and the top bolt pressure. For NR and formula with high gum content, K should be appropriately increased; For synthetic rubber and formula with low rubber content, K should be appropriately reduced; For old equipment with high wear degree, K shall be increased; The new equipment should be smaller; K of intermeshing rotor internal mixer shall be less than that of shearing rotor internal mixer; When the pressure of upper jacking bolt increases, K should also increase accordingly. In addition, K of inverse mixing method must be as large as possible. During mixing in the internal mixer, the rubber must be subject to a certain pressure of the upper jack bolt. It is generally considered that the upper jacking bolt pressure should be 0.6-0.8MPa. When the rotor speed is constant, the effect of further increasing the pressure is not significant. When the mixing capacity is insufficient, the pressure of top plug can not fully play its role. Increasing the pressure of the upper jacking bolt can reduce the unfilled space in the air tight chamber and increase its filling degree by about 10%. With the increase of capacity and rotating speed, the pressure of upper jacking bolt must be increased.