What is the difference between high speed extrusion process control and low speed extrusion for UPVC profiles?

Apr 17,2025

What is the difference between high speed extrusion process control and low speed extrusion for UPVC profiles?

The differences between high speed extrusion and low speed extrusion of UPVC profiles are:

（1）In terms of the control of barrel temperature, for parallel twin screw extruders, usually the material needs more heat in the first zone and the second zone during high-speed extrusion, and the temperature setting should be higher, generally 180~185 ° C is appropriate. Because the material at the end of the barrel is subjected to large shear friction heat here, and the material has been semi-plasticized, the high temperature is easy to cause material decomposition, so it is generally controlled at 165~175℃. The transition section is the connection section between the barrel and the mold, where the two strands of material converge and change from spiral movement to linear movement, the movement state is complex, the movement speed is reduced, and the material passes for a long time. At the same time, this is the highest pressure in the entire extrusion system, in order to prevent over-plasticization, the temperature here is generally set slightly lower than the temperature of the last area of the barrel;
（2）The temperature of the mold is relatively high, generally 190~200℃;
（3）Extrusion pressure is high, the general twin-screw extruder high-speed extrusion die pressure should be controlled at 25~32MPa;
（4）The screw speed is high, for the twin screw, the screw speed should generally be set at about 2/3 of the maximum allowable speed of extrusion is more economical and reasonable, the speed is too high, resulting in the extruder overload operation, accelerate the wear of the machine, reduce its service life;
（5）High-speed extrusion water temperature is generally controlled at 12~16℃, the effective water pressure is above 0.2MPa, the water is best softened, and the water supply should meet the cooling requirements of profiles;
（6） The exhaust vacuum degree of the main engine should be generally controlled in 0.05~0.07MPa to discharge the gas and low molecular volatiles in the material to ensure the compactness and physical and mechanical properties of the product;
（7） Generally, the first section of the dry mold should use a vacuum pump alone, the vacuum degree is maintained above 0.075MPa, and the vacuum degree of the dry mold behind can be slightly lower in the case of ensuring the molding of the product. Vacuum type water tank vacuum degree is generally controlled in 0.01~0.02MPa.
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