Shot Injection Molding Important Process Conditions
Injection molding is an engineering technique that involves converting plastics into useful products that maintain their original properties. 2 Shot Injection Molding The important technological condition of injection molding is to influence the temperature, pressure and the corresponding time of the plastic flow and cooling.
Injection molding process need to control the temperature of the barrel temperature, nozzle temperature and mold temperature. The first two temperatures mainly affect the plasticizing and flow of plastics, and then a temperature mainly affects the flow and cooling of plastics. 2 Shot Injection Molding Each plastic has a different flow temperature, the same kind of plastic, due to different source or brand, its flow temperature and decomposition temperature is different, this is due to the weight and molecular weight distribution, plastic in different types of injection molding process is different, so choose the barrel temperature is not the same.
The 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 "casting phenomenon." 2 Shot Injection Molding Nozzle temperature can not be too low, otherwise it will cause premature solidification of the melt and the nozzle will be blocked, or due to early coagulation injection mold cavity and affect the performance of products.
The mold temperature has great influence on the intrinsic performance and apparent quality of the products. Mold temperature depends on the crystallinity of plastic, 2 Shot Injection Molding product size and structure, performance requirements, as well as other process conditions (melt temperature, injection speed and injection pressure, molding cycle, etc.).
During injection molding, 2 Shot Injection Molding pressure includes plasticizing pressure and injection pressure, and directly affects the plastic and product quality.
1, plasticizing pressure
(back pressure) using screw-type injection machine, screw the top of the melt material in the screw rotation back when the pressure is called plasticizing pressure, 2 Shot Injection Molding also known as back pressure. The size of the pressure can be adjusted by the overflow valve in the hydraulic system. In the injection, the size of the plastic pressure is the same as the rotational speed of the screw, the increase in plasticizing pressure will increase the melt temperature, but will reduce the speed of plasticizing.
In addition, the increase in plasticizing pressure can often make the melt temperature uniformity, the mixing of color materials and the discharge of gas in the melt. In general operation, the decision of plasticizing pressure should be in the premise of guaranteeing the quality of the product is good, 2 Shot Injection Molding the lower the better, the specific value of the plastic with the variety of different, but usually rarely more than 20 kg/cm.
2. Injection pressure
In current production, almost all injection presses are based on the pressure (from the oil circuit pressure) on the top of the plunger or screw. The effect of injection pressure in injection molding is to overcome the flow resistance of plastic from the barrel to the cavity, and to give the rate of the melt filling and compaction of the melt.