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Knowledge of injection molding machine screw

- Jul 03, 2018 -

Injection molding machine SCREW is the main core component of the injection molding machine. Its function is to transport, compact, melt, stir and press various kinds of plastics, which are all done by the rotation of the screw in the barrel. When the screw rotates, the plastic will rub against each other on the inner wall of the barrel, the bottom surface of the screw groove, the screw advance surface, and between the plastic and the plastic. The forward movement of the plastic is the result of this combination of motion, and the heat generated by the friction is also absorbed to increase the temperature of the plastic and melt the plastic. The design of the screw will directly affect the extent of these effects. Injection molding machine screw use method, material classification, segmentation description, parameter description, good and bad evaluation standards, common problems and solutions.

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 How to choose the injection machine screw? Knowledge induction of injection molding machine screw

How to choose injection machine screw

1. The screw diameter (D) is related to the required injection volume: injection volume = 1/4 * π * D2 * S (injection stroke) * 0.85;

2. The screw diameter (D) is inversely proportional to the highest injection pressure and proportional to the plasticizing capacity;

3, responsible for the transportation, pushing and preheating of plastics, should ensure preheating to the melting point;

4, crystalline plastics should be long (such as POM, PA); amorphous materials second (such as PS, PU, ABS); heat sensitivity is the shortest (such as PVC);

5, DKM injection molding machine screw is responsible for plastic mixing, compression and pressurized exhaust, almost all of the raw materials through this section melt, but not necessarily evenly mixed;

6. The plastic gradually melts, and the volume of the screw groove must be correspondingly decreased to correspond to the decrease of the geometric volume of the plastic. Otherwise, the material pressure is not real, the heat transfer is slow, and the exhaust gas is poor;

7. The compression section generally accounts for more than 25% of the working length of the screw, but the nylon screw accounts for about 15%. The plastic screw with high viscosity, fire resistance, low conductivity and high additive accounts for about 40%, and the PVC screw can account for 100%. Proportion to avoid intense shear heat;

8. The length of the metering section is good for mixing. If it is too long, the melt will stay too long and cause thermal decomposition. If it is too short, the temperature will be uneven. Generally, it will account for about 20%, ensuring that the plastic is completely melted and the temperature is uniform. Mixing evenly;

9. The deeper the depth of the feed screw groove, the larger the conveying volume, but the screw strength of the injection molding machine should be considered. The shallower the metering groove depth, the plasticizing heat and the higher the mixing performance index, but the metering groove depth is too shallow. The shear heat increases, the self-generated heat increases, and the temperature rise is too high, causing discoloration or charring of the plastic, especially for heat sensitive plastics.

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