Most melt transfer or pumping problems in plastic pelletizers are caused by inappropriate metering section designs. Below Shuliy Machinery introduces the common problems and possible solutions of plastic granulators in use.
The first most common problem in the melt conveying of plastic granulators is that the grooves are too deep; the second most common problem is the insufficient length of the metering section. If the groove is too deep, the metering section of the screw can be cooled to reduce the effective depth.
Conversely, if the threaded groove is too shallow, the metering section of the screw can be heated to increase the effective depth of the threaded groove and increase the melt transfer capacity. However, if the depth of the metering section is incorrect, it is best to change the screw design with an appropriate metering section size.
In some cases, simply changing the design of the screw does not effectively improve melt transfer capacity. For example, there is a two-stage extruder screw that must be operated at high outlet pressures. If the second-order length of the screw is insufficient, it may not be possible to use the screw to generate the required high pressure.
Such conditions will cause exhaust gas flow, that is, the molten polymer flows out of the exhaust holes. One possible solution to this problem is to place a gear pump between the extruder and the die. In this method, the gear pump can generate the required head pressure, and only the screw can generate enough pressure to feed the gear pump.
Other possible solutions for exhaust flow are:
1. Reduce pressure.
2. Increase the length of the extruder.
3. Use the internal heating of the screw in the second stage of the screw.
4. Reduce the barrel temperature in the second stage.