What is the operating theory of the screw and barrel of the injection molding machine?

Update: 2021/03/08
Summary:

When the material of the screw and barrel of the inject […]

When the material of the screw and barrel of the injection molding machine moves forward, it is heated due to the heat generated by the conflict and the heat conducted by the barrel heater. When the temperature of the material exceeds its melting point, a molten film is formed on the inside and outside of the barrel, and the plasticizing section starts from this. It is necessary to point out that the starting point of the plasticizing section is generally not the starting point of the compacting section. The dividing line of each functional section depends on the function of the polymer, the geometry of the extruder and the operating conditions. Therefore, the dividing line can be changed due to changes in operating conditions. However, the geometric section of the screw is determined by the plan and will not change due to changes in operating conditions. When the material moves forward, the amount of solid material in each direction will be reduced due to melting. When all the solid polymer disappears, it reaches the end of the plasticizing section, and the melt conveying section begins. In the solid conveying section, the melt is evenly conveyed to the die.
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When the polymer flows into the die, the shape of the die flow channel appears in the screw and barrel of the injection molding machine. Therefore, when the polymer leaves the die, its shape more or less fits the cross section of the last part of the die flow channel. shape. Because of the movement resistance of the die, pressure is required to force the material through the die. This pressure is generally called die pressure. The die pressure is determined by the shape of the die (especially the runner), the temperature of the polymer melt, the flow rate through the die, and the rheological properties of the polymer melt. Die pressure is generated by the die and not by the extruder. The extruder only generates enough pressure to force the material through the die. If the polymer, extrusion volume, die and die temperature are all the same, no matter whether the extruder is a gear pump single screw extruder or a double screw extruder, there will be no difference, and the head force is the same. .
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The operation of the screw and barrel of the injection molding machine is actually very simple. The material enters from the hopper. Generally, materials flow into the extruder barrel from the hopper by gravity. Some materials are not easy to move in dry conditions, it is necessary to use special methods to avoid materials hanging in the hopper. Once the material falls into the extruder, it is in the annular space between the screw and barrel of the extruder, and is then surrounded by the automatic spiral web of the spiral edge and the forced spiral groove of the butterfly belly. The machine stopped and the cicada rod rotated. Therefore, the conflicting forces all act on the material and the appearance of the barrel and screw. At least the material is in a solid state (below the melting point), and these conflicting forces serve to transport materials forward.

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