Industry News_DY R&P Machinery

2021-07

The working principle of an intensive mixer

A kneader is a machine that uses a pair of rotors with specific shapes that rotate relative to each other. Under adjustable temperature and pressure in a closed state, it intermittently plasticizes and mixes polymer materials. Below, the editor of Xianji.com will detail the working principle, structure, uses, operation methods, and precautions of the kneader.

2021-07-26

2020-11

What are the mixing principles of an open mill?

What are the mixing principles of an open mill? The mixing process of an open mill generally includes three stages: wrapping, feeding, and mixing. (1) Wrapping Several states of rubber in an open mill: 1—Rubber is difficult to enter the roll gap; 2—Tightly wrapped around the front roll; 3—Forms a bag-like shape after leaving the roll; 4—Viscous flow wrapping the roll (2) Feeding Before the rubber is wrapped around the roll and the compounding agents are added, an appropriate amount of rubber should be kept at the upper end of the roll gap. An appropriate amount of accumulated rubber is a necessary condition for feeding. (3) Mixing Circumferential: Most even mixing; Axial: Uneven; Radial: Least even Factors Affecting Open Mill Mixing 1. Rubber Loading Capacity The rubber loading capacity should be reasonably determined based on the specifications of the open mill and the characteristics of the rubber compound formula. If the capacity is too large, the mixing and dispersion effect will be reduced, the mixing temperature will increase, and scorching may occur, affecting the quality of the rubber compound; if the capacity is too small, it will reduce production efficiency. Formula: V—Rubber loading capacity, L; D—Roll diameter, cm; L—Roll length; 2. Roll Gap The roll gap is generally 4~8mm. Reducing the roll gap increases the shearing effect, but also increases heat generation. 3. Mixing Temperature If the roll temperature is too low, the rubber will be too hard and easily damage the equipment. Increasing the roll temperature helps reduce the viscosity of the rubber and accelerate the mixing and feeding speed, but if the temperature is too high, it is easy to cause the rubber to leave the roll and scorch, making it difficult to operate. The roll temperature is generally maintained between 50~60℃ through cooling. However, when mixing rubber compounds containing high-melting-point compounding agents (such as high-melting-point coumarone resin), the roll temperature needs to be appropriately increased.

2020-11-26

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

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