Injection molding process parameters
DATE：2022/8/30 8:50:06 / READ： / SOURCE：This station
Injection molding process parameters
The temperature to be controlled in the injection molding process includes barrel temperature, nozzle temperature and mold temperature. The first two temperatures mainly affect the plasticization and flow of plastics, and the second temperature mainly affects the flow and cooling of plastics. Before injection molding, make sure that the injection cylinder, drying hopper mold and hydraulic oil are at the appropriate temperature. Hollow plate production line www.handern.comEach plastic has different flow temperature. The same plastic has different flow temperature and decomposition temperature due to different sources or brands. This is due to different average molecular weight and molecular weight distribution. The plasticizing process of plastics in different types of injection molding machines is also different, so the barrel temperature is also different. Hollow plate production line www.handern.com
The temperature of the plastic is controlled by the barrel, so the temperature of the barrel is related to the plasticizing quality of the plastic. When selecting the barrel temperature, the main focus is to ensure that the plastic is plasticized well and can be injected smoothly without causing local degradation of the plastic. The temperature of the barrel is first related to the nature of the plastic. Generally, the plastic must be heated to its viscous flow temperature T (or melting point TM) or above before it can flow and inject. Therefore, the maximum temperature at the end of the barrel should be higher than t or TM but lower than the decomposition temperature T of the plastic. For heat sensitive plastics with narrow temperature between T and T, and plastics with low molecular weight and wide molecular weight distribution, the barrel temperature should be lower, i.e. slightly higher than t; For the plastics with wide temperature and high molecular weight between T and T, the higher value can be appropriately selected to give full play to the advantage of low viscosity. When determining the barrel temperature, it is also necessary to consider the residence time of the plastic in the heating barrel, which is particularly important for heat sensitive plastics such as polyoxymethylene. Therefore, in addition to strictly controlling the maximum temperature of the barrel, the residence time of the plastic in the barrel (i.e. the influence of the production cycle on the material temperature) should also be controlled during production. Hollow plate production line www.handern.com
When determining the barrel temperature, the structural characteristics of products and molds shall also be considered. When forming thin-walled products, the flow resistance of plastic is very large, and it is very easy to cool and lose the flow capacity, so a higher barrel temperature should be selected; When forming thick wall products, the flow resistance is small, and because the cooling time of thick wall products is long, the injection molding cycle is increased, and the plastic is heated in the barrel for a long time, so a lower material temperature should be selected; For products with complex shapes or inserts, the melt flow is longer and more tortuous than the injection molding process technology and production management, and higher barrel temperature should also be selected. Hollow plate production line www.handern.com
The temperature control of plastics with different properties is also emphasized. For example, the degree of abspc and ABS is very little affected by the temperature. Therefore, when ABS reaches the deformation flow temperature, it is not effective to increase the barrel temperature through continuous training in the hope of reducing the viscosity to help mold filling. Especially when making ABS color products, it is harmful but not beneficial. Most of the color pigments are organic substances, and most of them are unstable at high temperature, which makes the color of the products fade, Uneven color spots appear. In contrast to ABS, the viscosity of PC decreases obviously when the temperature is slightly increased. According to the data, within the processing temperature range, the injection pressure can be reduced by half if the barrel temperature is increased by 10 ~ 20 ℃. Conversely, if the temperature is lower than the normal processing temperature by 10 ~ 20 ℃, the injection pressure will be doubled. This reaction effect is more prominent when the nozzle and mold temperature are low. Therefore, sufficient material temperature and mold temperature must be ensured during the production of PC parts.
Nozzle temperature: when the melt passes through the nozzle, a large temperature rise will occur due to the high shear rate. In order to prevent the molten plastic from flowing, the nozzle temperature should be adjusted to be slightly lower than the maximum temperature of the barrel; If an extended nozzle is used, a heating ring matching the long nozzle shall be used or the temperature shall be adjusted higher to prevent the nozzle from being blocked by cold materials. The temperature of the nozzle should not be too low. Generally, it can be 5 ~ 10 ℃ lower than the maximum temperature of the barrel. Otherwise, the injection pressure will increase or the material will set early, affecting the product quality. Hollow plate production line www.handern.com
Melt temperature melt temperature is the melt temperature at the time of injection according to the production cycle after the completion of plastic plasticization. The melt temperature is the actual temperature of plastic plasticization. The temperature of the barrel is determined by the glue temperature and screw speed of the production management center of Chengzhou Jiangyi Technology Expo. Back pressure, injection quantity and injection cycle. The melt temperature can be measured at the nozzle or by the air injection method. The profile temperature is only for guidance. If there is no experience in processing a specific grade of plastic, the profile temperature should start from the lowest setting. Mold temperature directly affects the melt filling and product cooling, and determines the molding cycle.
Mold temperature is one of the main factors affecting product quality. The choice of mold temperature depends on the nature of the material, the size and shape of the product and the mold structure. For amorphous plastics, the mold temperature mainly affects the viscosity (fluidity) of the baked body. If the melt viscosity of the material is low (such as PS), the lower mold temperature can be selected to improve the production efficiency; If the melt viscosity of the material is high (such as PC), a higher mold temperature should be used to meet the needs of mold filling. For crystalline plastics, when the mold temperature is high, the material cooling time is long, the crystallinity is high, the product hardness is high, the strength is high, but the shrinkage rate is large; When the mold temperature is low, the cooling time of the material is short, the crystallinity is low, the product is soft and the flexibility is good. For parts with high dimensional accuracy, lower mold temperature shall be selected to control shrinkage; For the parts with high surface gloss or thin and complex parts, a higher mold temperature should be selected to facilitate mold filling; For thick wall parts, a higher mold temperature Tm shall be selected. If the mold temperature is low, the temperature difference between the inner and outer layers of the parts is large, which may cause depression and internal space.
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