Six reference quantities to determine the production condition of the Co-rotation parallel twin screw extruder#twin screw and barrel#parallel twin screw and barrel#Co-rotation parallel twin screw extruder

The Co-rotation parallel twin screw extruder used in our production process has six key parameters: temperature peak, pressure peak, viscosity dissipation, mixing index, average residence time, and torque results. The transformation of these six parameters will affect the quality and output of the products, and even damage the extruder.

Let's take a look at these parameters together here.

Temperature

The heat sources of the material temperature increase during the extrusion process mainly include:
1)Heat conduction of the barrel to the material;
2) The viscosity dissipation caused by shear in the barrel.

Temperature will directly affect the viscosity of the material, and the temperature increases. For temperature-sensitive materials, when the temperature exceeds a certain limit value, combustion and explosion will occur in other accidents, so the temperature should be strictly controlled in the actual operation process, and the operation should be carried out within a safe temperature range.

In the extruder, the lead of the forward thread element decreases or the lead of the reverse thread element increases, the peak temperature will increase significantly. In the process of double screw mixture, the reverse thread element and the forward thread element of the small guide can contribute to the establishment of the pressure in the mixing process, improve the filling rate of the material in the screw, increase the friction between the material and the barrel, and increase the material temperature.

Pressure

In the process of double screw mixture, the material will be subject to a certain external pressure, and the pressure has a certain impact on the mobility of the material. Under pressure, the intermolecular distance will narrow, the molecular chain movement will decrease, the intermolecular interaction will increase, and the viscosity will increase. In the actual production process, if the pressure is too large, the material viscosity will be too high, and the processing process will become difficult. For the pressure-sensitive material, when the pressure exceeds the limit value, it will cause combustion or explosion accidents.

Viscidity

Scky dissipation is the work done to overcome the resistance caused by its own viscosity in the process of material mixing, and further transformed into the energy of the material itself.

Double screw extruder mixing process, the polymer fluid in the flow of shear rate directly affect the viscosity of the material, affecting the material mixing process viscosity dissipation, shear rate is too large, the greater the viscosity dissipation, polymer melt rupture, even mechanical degradation, too small does not meet the needs of polymer processing, affect the final quality of the product.

Mixing index

Mixing is a process that reduces homogeneity between materials. According to the Brodkey mixing mechanism, the mixing process involves three forms of molecular motion: molecular diffusion, volume diffusion and vortex diffusion. In the double screw extruder, the material is stretched or cut under the rotation of the screw, producing tensile flow or rotating flow. In order to quantitatively characterize the mixing degree of the material, the concept of mixing index is introduced, which is the ratio of the stretching rate tensor to the sum of the stretching rate tensor and the rotation tensor.

In the mixing process of double screw extruder, the mixing index reflects the relationship between shear and stretching. The larger the mixing index, the more significant the influence of stretching in the material mixing process.

The increase of forward kneading block lead and reverse thread element lead will lead to the enhanced stretching of the material in the double screw extruder, promoting the more uniform mixing of materials in the extruder. However, in the actual production, the mixing index is difficult to directly explain the mixing effect of materials, so it can only be used as a reference.

Mean detention time

The residence time of the material in the double-screw extruder directly affects the quality of the final product. Generally, the longer the residence time of the material in the double screw extruder, the more the continuous mixing of the material in the cylinder. After a long enough residence time, the mixing of the material will reach the best state.

The reverse thread element and kneading block can prolong the residence time of the material in the barrel and enhance the mixing effect.

Torque

Torque is an important parameter for double screw extruder, which can reflect the carrying capacity of double screw extruder and protect the safe operation of double screw extruder. In the actual processing process, the viscoelasticity of the polymer should be studied according to the torque limit of the twin-screw extruder to ensure that the extrusion process is within a safe and controllable range.

1. The peak temperature increases with the reverse thread element lead and decreases with the forward thread element lead.

2. The reverse thread element can establish greater pressure than the reverse pinch block. In practical engineering, the reverse thread element or reverse kneading block is generally placed in front of the screw exhaust section to establish a certain vacuum degree.

3. The addition of the reverse screw element and the reverse kneading block element will increase the screw filling degree and viscosity dissipation.

4. The mixing index increases with the forward kneading block lead and the reverse thread element lead.

5. The reverse thread element and the pinch block can prolong the residence time of the material in the double screw.

6. Significant effects of torque: forward thread element lead and reverse thread element lead.