Release time:

2020-09-29

Characteristics of Internal Mixer Mixing Mixing rubber and various compounding agents in the high-temperature, high-pressure internal mixer mixing chamber, after a short period of kneading, dispersion, and mixing, the required mixed rubber can be obtained. The mixing process is: lifting the top ram → adding materials → lowering the top ram → pressurizing and mixing → mixing completion → opening the bottom ram → turning over → discharging → returning to the original position → closing the bottom ram. Advantages of internal mixer mixing: ① Short mixing time, high production efficiency, and good quality of mixed rubber; ② Large rubber loading capacity, high degree of automation of mixing and other operations, low labor intensity, and safe operation; ③ Small loss of compounding agents, small pollution, and hygienic workplace. Disadvantages of internal mixer mixing: ① The internal mixer is slow to dissipate heat, and the mixing temperature is difficult to accurately control. For rubber materials sensitive to temperature, scorching is easily produced during mixing, and the cooling water consumption is large; ② The mixed rubber is in an irregular block shape and must be subjected to supplementary processing such as pressing; ③ Internal mixer mixing is not suitable for light-colored rubber materials, special rubber materials, rubber materials with frequent changes in varieties, and rubber materials sensitive to temperature. Mixing Methods of Internal Mixer The mixing methods of internal mixers include one-stage mixing, two-stage mixing, feeding method, and reverse mixing method. (1) Working Stages of Internal Mixer Mixing Internal mixer mixing is divided into three stages: wetting, dispersion, and kneading. (2) BIT Value In the internal mixer mixing process, the wetting and dispersion stages play a leading role in mixing. In production, the mixing performance of the rubber material is often measured by the time required for the compounding agent to be uniformly dispersed in the rubber material. Generally, the end time of dispersion is taken as the second power peak point appearing on the mixing time-power curve, which is called the Black Ink Time (BIT) value. The smaller the BIT value, the better the mixing performance of the rubber material, that is, the easier it is to mix. (3) Cooling and Standing a. Cooling is to avoid scorching and mutual adhesion caused by high temperature of the mixed rubber. Generally, it is cooled strongly to below 35℃. b. Standing allows the stress of the rubber molecules to relax, reducing shrinkage. It also allows the compounding agents to continue to disperse, and the carbon black and rubber to further combine, improving the physical and mechanical properties of the rubber material. Rapid Inspection of Internal Mixers Controlling and ensuring the quality of mixed rubber is one of the key links in the production of rubber products. Rapid inspection is a rapid quality inspection of mixed rubber. The rapid inspection method is to take one sample from the front, middle, and rear parts of each batch of mixed rubber during the sheeting process, and determine its plasticity, vulcanization characteristics, hardness, tensile strength, elongation at break, permanent set, and density, etc., and compare the measured results with the specified standard values to determine whether the quality meets the requirements. The inspection methods for the relevant items can be found in the corresponding national standards.