Screw back pressure and speed control The high back pre […]
Screw back pressure and speed control
The high back pressure allows the melt to be strongly sheared, and the low rotational speed also allows the plastic to have a longer plasticizing time in the barrel. Therefore, the control of the simultaneous design of the back pressure and the rotational speed is currently used more.
For example, the screw measures the full stroke first high speed, low back pressure, then switches to lower speed, higher back pressure, then switches to high back pressure, low speed, and finally plasticizes at low back pressure and low speed. In this way, the pressure of the melt at the front of the screw is mostly released, reducing the moment of inertia of the screw, thereby improving the accuracy of screw metering.
Excessive back pressure often results in:
The degree of discoloration of the colorant increases; the mechanical wear of the screw of the pre-plastic machine is increased; the pre-plasticization period is prolonged, the production efficiency is decreased; the nozzle is prone to runny, and the amount of recycled material is increased; even if the self-locking nozzle is used, if the back pressure is higher than The designed spring blocking pressure also causes fatigue damage. Therefore, the back pressure must be adjusted properly.