Views:302 Author:Site Editor Publish Time: 2019-10-24 Origin:Site
Several key elements in the plastic extrusion process, including the screw design of the extruder, the stability of the process operation, the heating temperature, the pressure at the end of the screw, the control of the residence time of the plastic melt in the die, and the monitoring of various process parameters, as well as training for operating staff. By mastering these factors, we can save production costs, improve product quality, and fully utilize the performance of plastic extrusion machines.
1 Mechanical principle
In some twin-screw extruders, the two screws reverse in two simplifications and cross each other, so one must be right and the other must be left. In other occlusal twin-screws, the two screws rotate in the same direction and must therefore have the same orientation. However, in either case, there is a thrust bearing that absorbs the backward force, and Newton's principle still applies.
2. Feeding as a coolant
Extrusion transfers the energy of the motor, sometimes the heater, to the cold plastic, converting it from solid to melt. The input feed is lower than the simplified and screw surface temperatures in the feed zone. However, the simplified surface in the feed zone is almost always above the melting range of the plastic. It cools by contact with the feed particles, but the heat is transferred back and forth by the hot front end and controlled heating. Even after the current end heat is held by viscous friction and no simple heat input is required, the rear heater may be required. The most important exception is the slotted feed cartridge, which is used exclusively for HDPE pipe extrusion machine.
3. Heating temperature control
The extrudable plastic is a thermoplastic that melts upon heating and solidifies again upon cooling. The heat of the melt is mainly the preheating of the feed and the barrel/die heater. The motor can also input energy—the frictional heat generated by the screw against the resistance of the viscous melt when the motor turns the screw is the most important heat source. In order to improve the intrinsic quality of the extruded products, thermal degradation of the melt should be prevented as much as possible, that is, the residence time of the melt in the die should be avoided, which is an important guiding for the correct usage of plastic extrusion machines
4. Control of melt residence time in the die
The residence time of the plastic melt in the handpiece has a great influence on the quality of the product. During the plastic pipe extrusion manufacturing process, the residence time of the melt should be controlled between relaxation time and heat settling time. If the residence time is too short, the expansion of the die is relatively large, and the extruded product will have a large residual stress; if the residence time is too long, the material will affect the quality of the extruded product due to thermal degradation caused by heat.
5. Control of the main motor of the extruder
The main motor of all extruders is opposite to the cylinder, and the barrel body is also opposite to the main motor. The control effect of the barrel is not always the same as expected, especially in the temperature measurement area. Because if the barrel is heated, the viscosity of the material layer at the wall of the barrel becomes smaller, and the main motor requires less energy to operate in this smoother barrel, at which point the motor current drops.