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Twin Screw Extruder Screw Structure
- Sep 18, 2017 -

Twin Screw Extruder Screw structure

The Structure and Temperature Principle of Twin Screw Extruder

Structural principles:

For the basic mechanism of the extrusion process, simply a screw is rotated in the cylinder and the plastic is pushed forward. The screw structure is a bevel or slope wound around the center layer, the purpose is to increase the pressure in order to overcome the greater resistance. For the extruder, there are three kinds of resistance to work to overcome: First, the friction, which contains the solid particles (feed) on the cylinder wall friction and the screw rotation before a few laps (feed area) between them Mutual friction between the two; the second is the adhesion of the melt in the cylinder wall; Third, the melt is pushed forward when the internal logistics resistance.

According to the Newton theorem, if an object is in a certain direction at rest, then the object in this direction in the balance of balance. For the circumferential movement of the screw, it is no axial movement, that is to say the axial force on the screw in equilibrium. So if the screw to the plastic melt to exert a large forward thrust, then it also to another object to exert a similar size but the direction of the back thrust. Obviously, the thrust it exerts is on the thrust bearing behind the inlet. Most of the single screws are right-handed, and if they are in the reverse direction, they are rotated backwards and rotated out of the cylinder by rotary motion. In some twin-screw extruders, the two screws in the two barrels in the reverse rotation and cross each other, it must be a right, a left, for the bite double screw, the two screws are the same The direction of rotation, and therefore must have the same orientation. However, no matter what the situation has to withstand the backward force of the thrust bearing, still meet the Newton theorem.

Temperature principle:

The extrudable plastic is a thermoplastic which melts upon heating and solidifies again upon cooling. So in the extrusion process requires heat, to ensure that the plastic can reach the melting temperature. So where does the heat of molten plastic come from? First, the loader preheat and the cylinder / mold heater may function and are very important at start-up. In addition, the motor input energy, that is, the resistance of the motor to overcome the viscosity of the melt. When the screw is rotated, the friction heat generated in the cylinder is All plastic is the most important heat source, of course small system, low speed screw, high melt temperature plastic and extrusion coating applications except. In operation, it is important to realize that the cylinder heater is not a major heat source, and it may have less effect on extrusion than we might expect. The rear cylinder temperature is more important because it affects the speed of solids transfer in the feed or feed. In general, the die and mold temperature should reach the desired temperature of the melt or close to this temperature, for some specific purpose (eg glazing, fluid distribution or pressure control).