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Injection Molding Turn Plastics Into Useful Products That Retain Their Original Properties
Oct 13, 2017

Injection molding is an engineering technique that involves converting plastics into useful products that maintain their original properties. The important technological condition of injection molding is to influence the temperature, pressure and corresponding time of plastic flow and cooling.

One, temperature control 1, barrel temperature: Injection Molding process need to control the temperature of the barrel temperature, nozzle temperature and mold temperature. The first two-way temperature mainly affects the plastic and flow of plastics, and then a temperature mainly affects the flow and cooling of plastics. 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. 2, nozzle temperature: 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." Nozzle temperature can not be too low, otherwise it will cause premature solidification of the melt and the nozzle will be blocked, or influence the performance of the products due to the injection mould cavity of the early-injection molding machine Simple maintenance Injection moulding knowledge selection Injection molding machine simple process processing molding and modification method of polyvinyl chloride in China the demand for engineering plastics daily increase gas Auxiliary injection molding System 3, Mould temperature: The mold temperature has a great influence on the intrinsic performance and apparent quality of the product. Mold temperature depends on the crystallinity of plastic, product size and structure, performance requirements, as well as other process conditions (melt temperature, injection speed and injection pressure, molding cycle, etc.).

Second, pressure control: injection molding process pressure including plastic pressure and injection pressure, and directly affect 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, 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 of 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, the lower the better, the specific value of the plastic with the variety of different, but usually rarely more than 20 kg/cm 2. 2, injection pressure: In the current production, almost all injections of injection pressure is the plunger or screw the top of the plastic pressure (from the oil circuit pressure conversion) prevail. The role of injection pressure in injection molding is to overcome the flow resistance of the plastic from the barrel to the cavity, to give the rate of the melt filling and compaction of the molten material.

Third, the molding cycle to complete an injection molding process required time called the molding cycle, also known as the mold-plastic cycle. It actually consists of the following sections: Forming period: The molding cycle directly affects the labor-health rate and equipment utilization ratio. Therefore, in the production process, should be in the quality assurance premise, as far as possible to shorten the molding cycle of each relevant time. During the entire molding cycle, the injection time and cooling time are the most important, They have a decisive effect on the quality of the products. The filling time in injection time is inversely proportional to the mold filling rate, and the mold filling time in production is generally about 3-5 seconds. The holding time in injection time is the pressure time of plastic inside the cavity, the overall injection time accounted for a larger proportion, generally about 20-120 seconds (the extra thick workpiece can be up to 5-10 minutes). At the gate of the melt before freezing, the number of holding time, the product size accuracy has an impact, if in the future, There is no effect. The holding time also has the most beneficial value, it is known to depend on the temperature of the material, the mold temperature and the size of the sprue and gate. If the main channel and the gate size and the process conditions are normal, usually to get the product shrinkage fluctuation range of the minimum pressure value. Cooling time depends on the thickness of the product, Plastic tears and crystallization performance, and mold temperature and so on. But the end of time, should be to ensure that the product demoulding without causing changes in principle, cooling time is generally about 30-120 seconds, cooling time is not necessary, not only to reduce production efficiency, the complex workpiece will also cause demoulding difficulties, Release stress is even produced when forced demoulding. Other time in the molding cycle is related to the continuity and automation of the production process and the degree of the two.