Temperature control and pressure control for injection molding

Injection molding is also known as injection molding, which is a kind of injection and molding method. The advantages of injection molding method are fast production speed, high efficiency, automatic operation, variety of colors, simple to complex shapes, large to small sizes, accurate product sizes, easy to update products, and the ability to form complex shaped precision mold parts, injection molding is suitable for mass production and complex shaped products and other molding processing fields.

Injection molding temperature control

1、Barrel temperature

The process of precision injection molding needs to control the temperature of the barrel temperature, nozzle temperature and mold temperature. The first two temperatures mainly affect the plasticization and flow of plastic, while the latter temperature mainly affects the flow and cooling of plastic. Each kind of plastic has different flow temperature, the same kind of plastic, due to different sources or grades, its flow temperature and decomposition temperature is different, this is due to the average molecular weight and molecular weight distribution is different, plastic plasticization process in different types of injection machines is also different, so the choice of barrel temperature is also different.

2、Nozzle temperature

Nozzle temperature is usually slightly lower than the maximum temperature of the barrel, this is to prevent the melt in the straight-through nozzle may occur "salivation phenomenon". Nozzle temperature can not be too low, otherwise it will cause early condensation of the melt and the nozzle will be blocked, or due to early condensation of the material into the cavity and affect the performance of the product.

3、Mold temperature

Mold temperature has a great impact on the intrinsic performance and apparent quality of the product. The temperature of injection molding mold is determined by the presence or absence of plastic crystallinity, the size and structure of the product, performance requirements, and other process conditions (melt temperature, injection speed and injection pressure, molding cycle, etc.).

Injection molding pressure control

The pressure in the injection molding process includes plasticizing pressure and injection pressure, and directly affects the plasticization of plastic and the quality of products.

1、Plasticizing pressure

When using screw injection machine, the top of the screw melt in the screw rotation back pressure is called plasticizing pressure, also known as back pressure. The size of this pressure can be adjusted by the relief valve in the hydraulic system. In injection, the magnitude of the plasticizing pressure varies with the design of the screw, the quality requirements of the product and the type of plastic. If these conditions and the speed of the screw are said to be constant, increasing the plasticizing pressure will strengthen the shearing effect, i.e., it will increase the temperature of the melt, but it will reduce the efficiency of plasticization, increase backflow and leakage, and increase the driving power.

In addition, increasing the plasticizing pressure often leads to uniform temperature of the melt, uniform mixing of the color and discharge of gas from the melt. In general operation, the decision of plasticizing pressure should be in the premise of ensuring the excellent quality of the product, the lower the better, the specific value is different with the variety of plastic used, but usually rarely exceed 20 kg / cm2.

2、Injection pressure

In current production, the injection pressure of almost all injection machines is based on the pressure applied to the plastic by the top of the plunger or screw (converted from the oil circuit pressure). The role of injection pressure in injection molding service is to overcome the resistance to the flow of plastic from the barrel to the cavity, to give the rate of molten material filling the mold and to compact the molten material.