Factors Affecting Mixing Effect of Internal Mixer
Time of issue：
2022-12-20
Compared with open mixer mixing, internal mixer mixing has the advantages of short mixing time, high efficiency, high degree of mechanization and automation, good rubber quality, low labor intensity, safe operation, small loss of flying medicine, and good environmental sanitation conditions, etc. Advantages, but the heat dissipation in the mixing chamber of the internal mixer is difficult, the mixing temperature is high and difficult to control, which limits the temperature-sensitive rubber materials, and is not suitable for light-colored rubber materials and rubber materials with frequent variety changes. In addition, the internal mixer needs to be equipped with a corresponding unloading device for mixing.
Compared with open mixer mixing, internal mixer mixing has the advantages of short mixing time, high efficiency, high degree of mechanization and automation, good rubber quality, low labor intensity, safe operation, small loss of flying medicine, and good environmental sanitation conditions, etc. Advantages, but the heat dissipation in the mixing chamber of the internal mixer is difficult, the mixing temperature is high and difficult to control, which limits the temperature-sensitive rubber materials, and is not suitable for light-colored rubber materials and rubber materials with frequent variety changes. In addition, the internal mixer needs to be equipped with a corresponding unloading device for mixing.
(1) Glue volume
A reasonable amount of glue should be able to ensure that the rubber is subjected to maximum friction and shear in the mixing chamber, so that the compounding agent can be evenly dispersed. The amount of glue loaded depends on the characteristics of the equipment and the characteristics of the glue. Generally, it is calculated according to the total volume of the mixing chamber and the filling factor, and the filling factor is 0.55 to 0.75. If the equipment has been used for a long time, due to the wear and tear of the mixing chamber, the filling factor can take a large value, and the amount of glue can be increased. If the pressure of the upper bolt is relatively high, or the plasticity of the rubber material is relatively large, the amount of glue installed can also be increased accordingly.
(2) The pressure of the upper ejector pin
Increasing the pressure of the top bolt can not only increase the amount of rubber loaded, but also make the rubber and equipment and parts inside the rubber contact and squeeze each other faster and more effectively, and accelerate the mixing process of the auxiliary agent into the rubber. Thereby shortening the mixing time, improving production efficiency, reducing the sliding of materials on the contact surface of equipment, increasing the shear stress of rubber, improving the dispersibility of compounding agents, and improving the quality of rubber at the same time. Therefore, at present, measures such as increasing the diameter of the top bolt fan cylinder or increasing the wind pressure are often taken to improve the mixing efficiency and rubber quality of the internal mixer.
(3) Rotor speed and rotor structure shape
During the mixing process, the shear rate of the rubber compound is proportional to the rotor speed. Increasing the shear speed of the rubber material can shorten the mixing time, which is the main measure to improve the efficiency of the internal mixer. At present, the speed of the internal mixer has been increased from 20 r/min to 40 r/min, 60 r/min, and up to 80 r/min, which shortens the mixing cycle from 12 to 15 min to the shortest 1 to 1.5 min. In recent years, in order to meet the requirements of the mixing process, a multi-speed or variable-speed internal mixer has been used for mixing. The speed can be changed at any time according to the characteristics of the rubber material and the process requirements to obtain the best mixing effect. The structural shape of the rotor of the internal mixer has a great influence on the mixing process. The ridges of the elliptical rotor of the internal mixer are increased from two to four, which can play a more effective role of shearing and stirring. It can increase production efficiency by 25-30% and reduce energy consumption. In recent years, in addition to the oval shape, there are also triangular, cylindrical and other rotor-shaped internal mixers that have been used in production.
(4) Mixing temperature
During the mixing process of the internal mixer, the heat generated is large and heat dissipation is difficult, so the temperature of the rubber material rises quickly and the temperature is high. Generally, the refining temperature is 100-130°C, and 170-190°C is also used for high-temperature refining. This process has been used in the mixing of synthetic rubber. The debinding temperature is generally controlled at 125°C during slow-speed mixing. ~135°C, and the debinding temperature is above 160°C during rapid banburying. I kun kneading, temperature is too high can reduce the mechanical shear effect to rubber material, make mixing uneven, and can aggravate the thermo-oxidative cracking of rubber molecule, make rubber material physical and mechanical performance reduce, simultaneously, also can promote rubber and Excessive chemical bonding between carbon blacks will generate too much gel, which will reduce the plasticity of the rubber material, and the surface of the rubber material will be rough, resulting in difficulties in calendering and extrusion processing.
(5) Dosing sequence
The plastic compound and masterbatch should be added first to form a whole, and then other compounding ingredients should be added in sequence. Solid softeners and small medicines are added before carbon black and other fillers are added to ensure sufficient mixing time. The liquid softener must be added after adding carbon black to avoid agglomeration of carbon black and make it difficult to disperse; the super accelerator and sulfur are added after the tablet machine cools down, or in the internal mixer during the second-stage mixing, but the other The debinding temperature should be controlled below 100°C.
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