At present, the mold industry has begun to use high-speed injection molding machines in injection molding. Products of different sizes need to use injection molding machines of different tonnages, but in general, the injection speed of the injection molding machine is very important.
During injection, in order to make the melt fill the cavity in time, the injection molding machine should have a certain injection speed in addition to sufficient injection pressure to ensure a faster flow rate of the melt. During production, choosing a reasonable injection speed is an important factor to ensure the quality of plastic products. Usually, low-speed injection of molten material, long filling time, products prone to defects such as weld lines, uneven density and large residual stress, especially for crystalline plastics and thin-walled products with a narrow processing temperature range.
Although high-speed injection can reduce the temperature difference of the melt in the mold cavity, improve the pressure transmission effect, obtain precision products with uniform density and low stress, and shorten the molding cycle, however, the excessive injection speed causes the melt to flow through the nozzle. The frictional heat may cause plastic decomposition and discoloration, as well as disadvantages such as inhalation of gas and poor exhaust, which directly affect the surface quality of the product. At the same time, the requirements for program control are higher.
At present, the injection speed has an increasing trend. Because increasing the injection speed can not only shorten the injection time, but also obtain high-quality products at a lower mold temperature and shorten the molding cycle. Especially when injection molding various thin-walled and long-run products, high injection speed is a prerequisite for obtaining high-quality products. In order to meet the processing requirements of different plastics and products of different structures, the injection speed of the injection molding machine also has a certain adjustment range. The adjustment of the injection speed can be achieved by controlling the flow of pressure oil into the injection cylinder. In addition, multi-stage injection is currently used to meet the requirements of product structure.
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