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Problems when selecting the screw for the injection molding machine

Update:09-10-2019
Summary:

Opening the injection molding plant and contacting the […]

Opening the injection molding plant and contacting the injection molding machine will naturally touch the important part of the injection molding machine - the screw. As one of the wearing parts of injection molding, the screw often requires the injection molding manufacturer to buy a few more for the needs. Then, how to choose the screw of the injection molding machine, what parameters do we need to look at when picking the screw? Below Feng Tiejun came to everyone for science.

What is the function of the injection molding machine screw?

The screw is a key component in the plasticizing mechanism. It is in direct contact with the plastic. The plastic passes through the effective length of the screw. After a long thermal history, it undergoes a three-state (glass state, viscoelastic state, viscous flow state) transformation. The length, geometry and geometric parameters of the functional segment will directly affect the conveying efficiency and plasticizing quality of the plastic, which will ultimately affect the injection molding cycle and product quality.

What parameters do you need to look at when selecting a screw?

1. Screw diameter - related to the required injection volume, inversely proportional to the highest injection pressure, and proportional to the plasticizing capacity.

2. The length of the feeding section - the feeding section is also called the conveying section or the feeding section. In order to improve the conveying capacity, the surface of the groove must be smooth and the length should ensure that the material has sufficient conveying length.

3. The length of the thread of the melting section - helps to stabilize the fluctuation of the melt in the groove, and has the effect of stabilizing the pressure, so that the material is extruded from the head of the screw with a uniform amount of material, so it is also called the metering section.

4. The depth of the molten section thread - the melting section of the thread depth is small, the screw groove is shallow, which improves the plasticizing effect of the plastic melt, which is conducive to the homogenization of the melt. However, if the thread depth of the molten section is too small, the shear rate will be too high, and the shear heat will be too large, causing degradation of the macromolecular chain and affecting the melt quality. On the other hand, if the thread depth of the molten section is too large, the reflowing effect by the back pressure of the screw is enhanced during the pre-molding, and the plasticizing ability is lowered.

5. Plasticizing section (compression section) thread length - plasticizing section length will affect the material from the solid state to the viscous flow state of the conversion process, too short will not be able to convert, so that the material is blocked at the end of the length of the plasticizing section, forming very High pressure, torque or axial force, too long will increase the torque of the screw and unnecessary energy consumption.

6. Pitch - its size affects the helix angle B, which affects the efficiency of the groove.

7. Width of the spiral edge - the width and width affect the volume of the groove, the leakage of the melt, and the degree of wear resistance of the screw.

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