The extruder barrel screw is not well plasticized because the solid phase cannot flow like a fluid, so the heat generated by shear is small. The heat source of solid phase melting mainly relies on the heat source conducted by the heater on the barrel and the heat source generated by the shear in the melt film. Its conduction speed is related to the barrel temperature, contact area, porosity of the plastic and thermal conductivity and other physical parameters.
When these conditions are certain, the screw speed (actually represents the time the plastic is heated) will directly affect the heat conduction. Therefore, in the first part of the screw, that is, the feeding section and the compression section, it is necessary to ensure that the plastic has enough residence time to heat it into a substantially molten flow state. Then it is further subjected to shearing, plasticization and homogenization in the metering section to ensure good product quality.
But when the speed is increased, the residence time of the plastic in the front of the extruder barrel and screw is shortened, and the solid phase enters the metering section before it is too late, so that unplasticized plastic may appear in the product.
The extruder barrel screw is not plasticized well. Check the reason:
1. Check carefully, starting from the hopper, the inner spring nozzle.
2. The plastic head has been cleaned or replaced! Remove the head and use fire to completely burn the remaining material on the rubber head;
3. Whether the pipes conveying raw materials are anti-static hoses or stainless steel pipes. When the raw materials are conveyed, they will generate static electricity when they rub against ordinary PVC hoses, and static electricity will cause black spots on the product;
4. Check whether toner is added to the raw material of the lower screw and barrel, whether the temperature is set properly, there may be oil in the barrel of the new machine, and so on;
5. Check the dehumidification dryer of the raw material. The regeneration temperature is very high. If the quality of the heating tube is not good, it is easy to have black flakes falling off the outer wall of the heating tube, and then fall into the molecular sieve, and then enter the entire system. In this way, you make The product has black spots.
6. Special screw and barrel are needed, because PC material is very corrosive, and black material will come out when the screw rots.More about:Extruder screw barrel Manufacturers