Blog_Wuxi Tengyu Environmental

2020-10

Factors Affecting the Mixing Effect of a Internal Mixer

1. Rotor The type and number of rotor lobes affect mixing. More lobes result in faster shear speed, higher heat generation, shorter mixing time, and potentially compromised mixing quality. Different rotor types impact mixing. Shear-type rotors have a large and wide shear zone between the rotor lobes and the mixing chamber, resulting in high shear force, high efficiency, and good mixing quality. Intermeshing rotors have a shear 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 rubber compound within the mixing chamber's working area. Insufficient pressure causes the compound to slip along the chamber walls and rotor surfaces. Appropriate pressure reduces voids in the material and increases contact force. High pressure increases the compound temperature and mixing power. Insufficient loading capacity prevents the upper ram pressure from being fully effective, resulting in uneven dispersion of the compound. 3. Temperature Each type of rubber 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. Charging Sequence The order of adding materials affects the mixing results. In automated systems, a common sequence (using multi-stage mixing, according to material requirements) is: raw rubber - pre-mixing - addition of fillers/compounding agents - pre-mixing - addition of softeners - pre-mixing - discharge. 6. Speed Speed is directly proportional to shear rate. Higher shear rates accelerate uniform mixing. Increasing speed raises the rubber temperature, reducing viscosity and shear stress. 7. Time Mixing time is related to the fill level and the temperature rise of the formulation. The mixing temperature affects the time for various rubber compounds. The internal mixer speed and upper ram pressure also affect mixing time. Therefore, auxiliary and charging times should be minimized in the mixing process. 8. Cooling Water The cooling water temperature is typically set to 15 degrees Celsius. Low-viscosity rubber compounds are not easily cooled with hot water, as they tend to stick to the rotor. High-viscosity rubber compounds use hot water cooling. Increasing the cooling water temperature shortens mixing time, reduces energy consumption, and improves production efficiency.

2020-10-21

2020-09

Characteristics and advantages of kneading in a Banbury mixer

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.

2020-09-29

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