Most single screw profile extruder
is right-handed threads, like screws and bolts used in woodworking and machinery. If they look from the back, they are turning in the opposite direction because they try to spin out the barrel as far as possible. In some twin-screw extruders, the two screws rotate in opposite directions in two cylinders and cross each other, so one must be right-handed and the other must be left-handed.
2. Deceleration principle
In most extruders, the change in screw speed is achieved by adjusting the speed of the motor. The motor typically rotates at full speed of approximately 1750 rpm, but this is too fast for an extruder screw. If it is rotated at such a fast speed, too much frictional heat is generated and the residence time of the plastic is too short to produce a uniform, well-stirred melt.
3. Feeding as coolant
Extrusion is the transfer of energy to the unheated plastic to melt it, and the input feed is at a lower temperature than the barrel and screw surfaces in the feed zone. The surface temperature of the barrel in the feed zone is at the melting point of the plastic, cooled by contact with the feed particles, but the heat is retained by the heat transferred back from the hot front and controlled heating. Even after the current end heat is held by the viscous friction and no barrel heat input is required, the post heater may be required.
4. Screw end pressure is very important
This pressure reflects the resistance of all objects downstream of the screw: the filter screen and the contaminated shredder plate, the adapter transfer tube, the fixed stirrer, and the mold itself. It depends not only on the geometry of these components but also on the temperature in the system, which in turn affects resin viscosity and throughput. Measuring temperature is important for safety reasons - if the temperature is too high, the die and mold may explode and cause damage to the machine and nearby personnel.
Why is the control effect of the cylinder not always the same as expected? If the cylinder is heated, the viscosity of the material layer at the wall of the cylinder becomes smaller, the motor requires less energy to operate in this smoother cylinder, and the motor current decreases. On the contrary, if the cylinder is cooled, the viscosity of the melt at the wall of the cylinder increases, the motor must be rotated more forcefully, the amperage is increased, and some of the heat removed by the cylinder is returned by the motor.