The quality of molten plastics has a great influence on product quality. Therefore, we must mention the quality of plastics. In general, the main factors influencing the plasticization and the plasticization problems may be the conditions of a screw with a high compression ratio, a short compression section length, and a short length of the entire screw. The shorter plastic pelletizing machines with screws take the extrusion required to melt-related instability problems to be lower than the long plastic pelletizers. This is one of the underlying reasons why the plastic granulator industry tends to have a longer plastic granulator.
In the 1950s and 1960s, the L/D aspect ratio of most single screw plastic granulators was approximately 20:1.
In the 1970s and 1980s, the aspect ratio of most plastic granulators was about 25:1. Between 1990 and 2000, the aspect ratio of most single screw plastic granulators was about 30:1.
Instability caused by insufficient melting capacity can be diagnosed by preheating the raw material. If preheating can reduce or eradicate instability, then the cause of the problem is most likely caused by insufficient melting capacity. Melting conditions can be improved by changing the processing conditions or changing the screw geometry.
The methods for improving melting include: preheating the raw materials; increasing the barrel temperature when the plastic granulator is running at a low speed; lowering the barrel temperature when the plastic granulator is running at a high speed; decreasing the screw speed; increasing the barrel pressure.
Screw design changes that can increase melting capacity include: increasing the thread angle in this transition section; reducing the helix edge clearance in the transition section; increasing the length of the transition section; using multiple thread designs in the transition section; ending at this transition section The groove mixing section is used.
From: Single Screw and Barrel