News and Information_DY R&P Machinery

2020-10

Factors Affecting the Mixing Effect of a Banbury 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, 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.

2020-10-21

2020-09

Characteristics and advantages of kneading in an internal 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, less pollution, and clean workplace. Disadvantages of internal mixer mixing: ① The internal mixer is slow to dissipate heat, and the mixing temperature is difficult to accurately control. Materials sensitive to temperature are prone to scorching 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, special rubber, rubber with frequent changes in variety, and rubber 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 dominant role. In production, the mixing performance of the rubber is often measured by the time required for the compounding agent to be uniformly dispersed in the rubber. Generally, the end time of dispersion is considered to be when the second power peak appears 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, i.e., 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. Rapid Inspection of Internal Mixers Controlling and ensuring the quality of mixed rubber is a key link in the production of rubber products. Rapid inspection is a rapid quality inspection of mixed rubber. The rapid inspection method is to take a sample from the front, middle, and rear parts of each batch of mixed rubber during sheeting, and determine its plasticity, vulcanization characteristics, hardness, tensile strength, elongation at break, permanent set, and density, 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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