(2) Cleaning of the barrel, screw and its accessories
In order to prevent contamination of raw materials and the presence of old materials or impurities in the recesses of screws and accessories, resins with poor thermal stability are present. Therefore, the screws are cleaned before use and after shutdown to prevent impurities from sticking. When there is no screw cleaning agent, the screw can be cleaned with a resin such as pe or ps.
When temporarily stopping, in order to prevent the raw material from staying at high temperature for a long time, causing the solution to fall, the temperature of the dryer and the barrel should be lowered. For example, the temperature of the barrel such as pc and pmma should be reduced to below 160 °C. (The hopper temperature should be reduced to below 100 °C for pc)
(3) Problems that should be paid attention to in mold design (including product design)
In order to prevent the occurrence of poor back flow, or uneven cooling, resulting in poor plastic molding, surface defects and deterioration, generally in the mold design, should pay attention to the following points.
a) the wall thickness should be as uniform as possible, and the draft angle should be large enough;
b) The transition should be gradual. Smooth transition to prevent sharp corners. Sharp edges are produced, especially PC products must not have gaps;
c) Gate. The flow channel should be as wide and thick as possible, and the gate position should be set according to the shrinkage condensation process, and if necessary, a cold well should be added;
d) the surface of the mold should be smooth and the roughness is low (preferably less than 0.8);
e) Vent hole. The tank must be sufficient to vent the air and the gas in the melt;
f) Except for pet, the wall thickness should not be too thin, generally not less than lmm.