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Injection Molding The Molten Material Is Completely Melted By Means Of A Screw
Sep 21, 2017

Injection molding, refers to a certain temperature, through the screw mixing completely molten plastic material, with high pressure into the mold cavity, after cooling and curing, to get the molding method. This method is suitable for batch production of complex parts, which is one of the important processing methods. Mainly have a mold, shot plastic, pressure, cooling, open mold, the product out of six stages.

Injection molding process

temperature control

⒈ barrel temperature: injection molding process need to control the temperature of the barrel temperature, nozzle temperature and mold temperature. The first two kinds of temperature mainly affect the plasticization and flow of plastic, and then a temperature is mainly affecting the flow of plastic and cooling. Each plastic has a different flow temperature, the same kind of plastic, due to the different sources or grades, the flow temperature and decomposition temperature is different, it is due to the average molecular weight and molecular weight distribution caused by different plastic in different types of injection Machine plastic process is also different, so choose the cylinder temperature is not the same.

⒉ nozzle temperature: nozzle temperature is usually slightly lower than the maximum temperature of the barrel, which is to prevent the melt in the straight-through nozzle may occur "salivation phenomenon." The nozzle temperature can not be too low, otherwise it will cause the melt early coagulation and nozzle clogging, or because the early injection into the cavity and affect the performance of products.

⒊ mold temperature: mold temperature on the product's inherent performance and apparent quality of a great impact. The temperature of the mold depends on the presence or absence of the crystallinity of the plastic, the size and structure of the product, the performance requirements, and other process conditions (melt temperature, injection speed and injection pressure, molding cycle, etc.).

Pressure control

Pressure during injection molding, including plasticization pressure and injection pressure of two, and a direct impact on plastic plastic and product quality.

⒈ plasticization pressure: (back pressure) with screw-type injection machine, the top of the screw in the screw rotation back when the pressure is called plasticization pressure, also known as back pressure. The size of this pressure can be adjusted by the relief valve in the hydraulic system. In the injection, the size of plasticizing pressure is with the screw design, product quality requirements and the type of plastic and need to change, if these conditions and the screw speed are unchanged, then increase the plasticization pressure will strengthen the shear Role, which will increase the melt temperature, but will reduce the efficiency of plasticization, increase the counter current and leakage, increase the driving power.

In addition, increasing the plasticizing pressure often results in a uniform temperature of the melt, uniform mixing of the colorants, and removal of the gas from the melt. In general operation, the decision to plasticize the pressure should be to ensure that the quality of products under the premise of the lower the better, the specific value is different with the use of plastic varieties, but usually rarely more than 20 kg / square centimeter.

⒉ injection pressure: in the current production, almost all of the injection machine injection pressure is the top of the plunger or screw on the plastic

The pressure applied (by the oil pressure conversion) shall prevail. The effect of injection pressure on injection molding is to overcome the flow resistance of the plastic from the cartridge to the cavity, the rate at which the melt is charged, and the melt to be compacted.

Forming cycle

The time required to complete an injection molding process is called a molding cycle, also known as a molding cycle. It actually includes the following parts: Molding cycle: The molding cycle directly affects labor productivity and equipment utilization. Therefore, in the production process, should ensure the quality of the premise, as far as possible to shorten the molding cycle of the relevant time. In the entire molding cycle, the injection time and the cooling time of the most important, they have a decisive impact on the quality of the product. The filling time in the injection time is directly proportional to the filling rate, and the filling time in the production is generally about 3-5 seconds. Injection time in the holding time is the pressure on the plastic cavity time, the injection of the proportion of the larger time, generally about 20-120 seconds (especially thick parts can be up to 5 to 10 minutes). In the gate before the melt frozen, the number of holding time, the accuracy of the size of the product impact, if in the future, no effect. The holding time also has the most value, it is known that it depends on the material temperature, mold temperature and the size of the main channel and gate. If the size of the main channel and the gate and the process conditions are normal, usually to produce the product shrinkage range of the minimum pressure range prevail. The cooling time is mainly determined by the thickness of the product, the thermal and crystalline properties of the plastic, and the mold temperature. The end of the cooling time should be to ensure that the product does not cause changes in the principle of mold release, cooling time is generally about 30 to 120 seconds between the cooling time is too long is not necessary, not only reduce the production efficiency of complex parts will Resulting in stripping difficult, forced release even when the mold release stress. The other times in the molding cycle are related to whether the production process is continuous and automated as well as the degree of continuity and automation.