For each type of plastic or plastic part, there is a limit to the surface temperature of the mold beyond which one or more adverse effects (eg, component burrs) may occur. Higher mold temperatures mean less flow resistance, which on the injection molding machine naturally means that the material flows faster through the gate and cavity. However, because the injection flow control valve used does not correct this change, faster filling will result in higher effective pressures in the runners and cavities, which is likely to cause flash burrs. The high-heat model prevents the program from freezing the plastic that enters the edge of the flash before the high pressure is formed, as it was previously set, causing the melt to burr around the ejector rod and overflow into the gap of the dividing line.
Generally, an increase in mold temperature reduces the effectiveness of the plastic in the cavity layer, allowing the molten material to flow more easily within the cavity, resulting in greater part weight and better surface quality. At the same time, the increase in mold temperature also increases the tensile strength of the part. Many molds, especially engineering thermoplastics, operate at relatively high temperatures. If the mold is not insulated, the heat lost to the air and the injection molding machine can easily be lost as much as the shot cylinder. Therefore, the mold and the board should be insulated and, if possible, the surface of the mold should be insulated. If a hot runner mold is considered, an attempt is made to reduce the heat exchange between the hot runner portion and the cooled injection molded part, such a method can reduce energy loss and warm-up time.
Temperature control necessity
(1) Temperature control on the result of forming
The appearance of the molded article, the physical properties of the material, the forming cycle, etc., are all affected by the temperature of the mold, and the relationship is quite remarkable. In the case of molding, the temperature of the mold core is kept low, and the number of shots can be increased. On the contrary, the forming cycle related to the shape of the molded article (the structure of the mold core) and the type of the finished material depends on the increase of the filling temperature of the mold.
(2) Temperature control should be taken to prevent stress
In relation to the molded material, reducing the stress only slows down by lowering the temperature. If the cooling time is short, even if a part of the hardening is still soft, the stress caused by the uneven shrinkage can be avoided. That is, proper temperature control can improve the cooling stress properties.
(3) The degree of crystallization of the forming material is adjusted, and temperature control is required.
Crystalline materials such as polysulfide (nylon), polyacetic acid, and polypropylene have improved crystallization degree and improved mechanical properties, and generally require higher mold temperature.