Process temperature Optimization of Twin Screw Extruder
1. The setting and control of extrusion process temperature should be based on PVC-U melt plasticizing degree of 60% -65%, the melt temperature of screw tube should be controlled between 180 ℃ and 185 ℃, and the die temperature should be controlled between 190-210 ℃, so that the melt can reach the best plasticizing degree at a moment. Extrude immediately from the die. It can not only be extruded from the best plasticizing degree, but also can prevent the material overheating time too long, produce decomposition, and reduce some properties.
2. Properly raise the set temperature of feed section: to provide sufficient external heat to the material, ensure the good plasticization of the material, effectively reduce the temperature difference between the set temperature and the display temperature of the metering section, and slow down the wear of the screw tube and screw of the extruder due to the shear action; It is not better to lower the set temperature of the metering section, but to take the display temperature no more than 185 ℃ -190 ℃ as the benchmark to ensure the steady and balanced plasticization of the material and prevent local superthermal decomposition. When the extrusion quantity is large, the external heating has been stopped, the cooling system does not stop working and the temperature is still higher than 190 ℃, the screw setting temperature or feeding speed can be reduced appropriately according to the conditions.When the extrusion quantity is small and the display temperature is lower than 180 ℃, the screw tube should be raised properly, and the screw setting temperature or feeding speed should be improved.
3. Under certain extrusion speed, feed speed is an effective means to control shear heat: when the feed speed is reduced and the temperature difference between the set temperature and the display temperature is adjusted in the metering section, the temperature difference between the set temperature and the display temperature in the feed section is larger, It is necessary to reduce extrusion speed in order to prolong the residence time of material in feed section, absorb external heating and promote plasticization.
4. The setting temperature of the combined core is based on ensuring the equilibrium and consistency of the melt cross section temperature: if the setting temperature is too low, the melt surface flow speed will be too slow, which will affect the molding quality of the extrusion products from the die, and the setting temperature will be too high, The melt surface flow speed is too fast, which also affects the molding quality of extrusion products from the die.
5. replacement screw and screw: when changing, we must strictly check and adjust the axial clearance of each section of the screw to prevent the overheating of the material or melt partly because of a certain gap. The extruder will work in a certain time and adjust the radial gap between the screw and the screw in time in order to prolong its working life.
6. Optimization of extrusion process temperature: can achieve different specifications, shear performance extruder, under different extrusion volume conditions, as long as the display temperature is in a controllable state, can be extruded at the same process temperature. In order to improve the quality of products, slow down the wear and tear of extruder, prolong its working life, further reduce the cost, facilitate management, timely detection and effective treatment of faults multi-layer goal.
7. there are preconditions for optimizing the process: when the extruder is overloaded, the equipment, electrical appliances and instruments are in a malfunction state, and the temperature is not controlled, the raw materials, ingredients and other factors affecting the plasticizing degree of the material are affected. All should take the corresponding countermeasure treatment, thus establishes the good foundation for the optimization craft.