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Extruders The Fundamental Mechanism
- Sep 05, 2017 -

Extruders The fundamental mechanism

The fundamental mechanism of extrusion is simple - a screw rolling in the cylinder and the plastic forward. The screw is actually a slope or slope, wrapped around the base layer. Its intention is to add pressure in order to overcome the greater resistance. In the case of an extruder, there are three resistance requirements to overcome the conflicting force of the solid particles (feed) to the cylinder wall and the distance between them in the first few laps (feed zone) The adhesion on the cylinder wall; the flow resistance of the melt when it is advanced forward.

        Newton has explained that if an object does not move in a given direction, then the force on this object is balanced in this direction. The screw does not move in the axial direction, although it may scroll horizontally in the circumference. Thus, the axial force on the screw is balanced, and if it exerts a large forward thrust on the plastic melt, it also applies an equal thrust to an object together. Here, the thrust applied by it is on the bearing-thrust bearing that is behind the inlet.

        Most single screws are right-hand threads, like screw and bolts used in carpentry and machines. If they look from the back, they are reverse rolling, because they have to push back the cylinder. In some twin-screw extruders, the two screws in the two cylinders in the reverse rolling and interspersed with each other, so one is necessary to the right, the other is necessary to the left. In the other bite double screw, the two screws roll in the same direction so that it is necessary to have the same orientation. However, no matter what the situation has to absorb the backward force of the thrust bearing, Newton's principle is still applicable.

    2. Hot criteria

    The extrudable plastic is a thermoplastic - they melt upon heating and re-solidify upon cooling. Where does the heat of molten plastic come from? The feed preheat and the barrel / mold heater may work and are very important at the start, however, the motor input energy - the resistance of the motor to overcome the viscosity of the melt when the rolling screw is generated in the cylinder. Plastic is the most important heat source, small system, low speed screw, high melt temperature plastic and extrusion coating except for the application.

    With regard to all the other operations, it is important to recognize that the cylinder heater is not the primary heat source in operation, so the effect on extrusion may be smaller than we might have (see rule 11). The posterior cylinder temperature may still be paramount, as it affects the speed at which the solid matter is transported. The die and mold temperatures should generally be the desired melt temperatures that may be close to this temperature unless they are used for a detailed intention to glare, fluid distribution may be pressure controlled.