What are the main factors that the screw affects the quality of plasticization?

Update:26 Feb 2021

The main factors affecting the quality of plasticization are: aspect ratio, compression ratio, back pressure, screw speed, barrel heating temperature, etc.
1. Length-to-diameter ratio: the ratio of the effective working length of the screw to the screw diameter.
a. If the ratio of length to diameter is large, the food will be more uniform;
b. Plastics with better thermal stability can be used with longer screws to improve mixing performance without scorching. Plastics with poor thermal stability can be used with shorter screws or without threads at the end of the screw. Considering the characteristics of plastics, the general flow length ratio is as follows: thermosetting is 14\'16, heat sensitivity such as rigid PVC, high-viscosity PU is 17\'18, general plastic is 18\'22, and high temperature stable plastics such as PC and POM are 22\'24.
2. Compression ratio: It is the ratio of the depth of the last groove of the feed section to the depth of the first groove of the metering section.
a. Considering the effects of material compressibility, filling degree, backflow, etc., products should be dense, heat transfer and exhaust;
b. Appropriate compression ratio can increase the density of plastics, make molecules and molecules more tightly bound, help reduce air absorption, reduce temperature rise due to pressure, and affect the difference in output, improper compression Than will destroy the physical properties of plastic;
c. The higher the compression ratio, the higher the temperature rise of the plastic during the plasticization process in the material tube, the better the mixing uniformity of the plastic during the plasticization, and the relative output is greatly reduced.
d. High compression ratio is suitable for non-meltable plastics, especially plastics with low melting viscosity and thermal stability; low compression ratio is suitable for fusible plastics, especially high melting viscosity, heat-sensitive plastics.
3. Back pressure
a. Increasing the back pressure can increase the work done by the screw on the molten resin, eliminate unmelted plastic particles, and increase the density and uniformity of the raw materials in the barrel;
b. The back pressure is used to increase the temperature of the barrel, and its effect is the most significant;
c. If the back pressure is too large, it is easy to decompose the heat-sensitive plastics, and it may cause salivation to the low-viscosity plastics. If the back pressure is too small, the injection molded product may have bubbles.
4. Screw speed
a. The rotation speed of the screw directly affects the shear of the plastic in the spiral groove;
b. The small screw groove is shallow and absorbs the heat source quickly, which is enough to promote the softening of the plastic during the compression period. The frictional heat energy between the screw and the barrel wall is low, which is suitable for high-speed rotation and increases the plasticizing capacity;
5. Electric heating temperature setting
a. Melt the chilled plastics remaining in the barrel and screw to facilitate the rotation of the screw and provide a part of the heat required for the melting of the plastic;
b. The setting is 5\'10℃ lower than the melt temperature (partly provided by frictional heat energy);More about:Extruder screw barrel Manufacturers

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