A hot mold surface keeps the plastic surface liquid long enough to build pressure in the cavity. If the cavity is filled and the cavity pressure can press the soft plastic against the metal before the frozen skin hardens, the cavity surface replication is high. On the other hand, if the plastic entering the cavity under low pressure pauses, no matter how short, its slight contact with the metal will cause stains, sometimes called gate stains.
For every plastic and plastic part, there is a mold surface temperature limit beyond which one or more adverse effects may occur (for example, the component may flash). Higher mold temperatures mean less resistance to flow. On many injection moulding machines, this naturally means faster flow through the runners, gates, and cavities, and because the
injection mould flow control valves used do not correct for this change, faster filling will cause higher effective pressures in the runners and cavities. Flash may be caused. Because the hotter model does not freeze the plastic that enters the flash area before high pressure is formed, the melt can flash around the ejector pin and overflow into the parting line gap. This indicates that good injection rate control is required, and some modern flow control programmers can indeed do this.
Generally, an increase in mold temperature will reduce the condensation layer of plastic in the cavity, making it easier for the molten material to flow in the cavity, resulting in larger part weight and better surface quality. At the same time, an increase in mold temperature will also increase the tensile strength of the part. Many plastic injection moulds, 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 as much as the loss of the shot cylinder. So insulate the mold from the machine plate and, if possible, the surface of the mold. If you are considering using a hot runner mold, try to reduce the heat exchange between the hot runner section and the cooled injection molded part. This method can reduce energy loss and preheating time.
The purpose and function of temperature control on formability, the appearance of molded products, the physical properties of materials, and the forming cycle are significantly affected by the mold core temperature. Under normal molding conditions, it is ideal to keep the mold core temperature at a lower level to increase the number of injections, but the forming cycle related to the molded product shape (mold core structure) and the type of finished product material also depends on the need to increase the mold core filling temperature.
This is a problem of the material of the molded product. The only requirement for this is the cooling speed. If the cooling time is short, even if one part is hardened and another part is still soft, stress caused by uneven shrinkage can still be avoided. In other words, proper temperature control can improve the cooling stress properties.
