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Screw design considerations

Update:10-10-2017
Summary:

   Extruder barrel with plastic and tight fit with the […]

   Extruder barrel with plastic and tight fit with the screw, in order to normal operation, should pay attention to the following important features.
1. The barrel is straight.
2. The design of the barrel should be able to withstand the working pressure of the extruder. These pressures can be as high as 70-140MPa (10000-20000psi), even higher in the injection molding.
3. The inner wall of the barrel should be more wear-resistant than the extruder screw, because the screw is easier to replace than the barrel, re-processing is also cheaper than the barrel.
4. The support of the rear end of the barrel shall be slidably supported and allowed to expand when the barrel is heated. Rigid support can cause bending of the barrel, which may cause serious damage to the screw and the barrel.
5. In order to improve the transport of the group, the feeding section of the barrel can be slotted. The grooving section should ensure good cooling capacity to take away the heat generated by high friction and prevent the melting of the material in the tank. In addition, the groove should be tilted open, the depth gradually shallow, to minimize the material in the structure of the hanging material opportunities.
6. If there is no air intake, it should be biased and the opening side wall is tangent to the inner wall of the barrel to reduce the chance that the plastic melt will hang on the front of the exhaust port, see Figure 2.20. More traditional symmetrical exhaust port design, easy to make the material in the bottom of the exhaust port constantly blocked. The opening of the exhaust port can be designed to be tilted downwards to avoid cooling the extruder barrel.

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