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Plasticizing pressure

by:CSSSLD     2021-01-23
Another determinant of plastic flow resistance is plastic and mould gating system and the coefficient of friction between mold and melt viscosity, the greater the friction coefficient and the melt viscosity, injection molding processing and the higher the pressure should be. The same kind of plastic friction coefficient and the melt viscosity is vary with the material barrel temperature and mould temperature, in addition, but also to the whether with lubricant. Cavity is filled, the effect of injection pressure is within the mold on the compaction of melting.

in order to shorten the molding cycle, determining the mold can be used two ways. One way is to put the mold temperature as low as possible, to speed up the cooling speed to shorten the cooling time. Another method requires the mold temperature to keep in the condition of heat deformation temperature lower, in order to under the high temperature will be plastic mold release, and then by its natural cooling, it also can shorten the cooling time of plastic parts in the mold. Specific use what method, need according to the plastic variety and the complexity of the plastic parts.

the function of injection pressure is to overcome the flow resistance of plastic melt flowing from cylinder cavity, to melt a certain rate of filling and compaction of the melt, and so on. The size of the injection pressure depends on the type of injection molding machine, plastic varieties, mould gating system structure, size and surface roughness, mold temperature, plastic pieces of wall thickness and size of the process, such as relationship is very complex, at present is difficult to make a quantitative relationship. The same situation in other conditions, plunger type injection machine screw injection molding machine injection pressure should be better than the role of the injection pressure, the reason for this is that the plastic inside the plunger cylinder injection molding pressure loss is bigger than screw injection molding machine.

the injection molding pressure including the plasticization and injection pressure in the process of two kinds, they have a direct impact on the plasticizing plastic and plastic parts quality. Plasticizing pressure is also called the back pressure, refers to the screw injection machine, screw head molten material in the screw rotating back pressure. The size of the pressure can be found on the overflow valve to adjust the hydraulic system. Injection, plasticizing pressure is depending upon the design of the screw, the size of the plastic parts quality requirements and the type of plastic and certain. If these conditions and the screw rotation speed is constant, the pressure increase plasticizing when raise the temperature of the melt, and make the melt temperature uniformity, color mixing and exclude the gases in the melt.

increase plasticizing pressure, will reduce the plasticizing rate, extend the molding cycle, and may even lead to the degradation of plastic. General operations, on the premise of guarantee the quality of plastic parts, plasticizing should pressure is lower, the better, the concrete numerical value with the varieties of the plastic used, generally is about 6 mpa, usually rarely more than 20 mpa. Injection polyformaldehyde, higher plasticizing pressure can increase the surface quality of plastic parts, but it could also make plastic color, plasticizing rate is reduced and less liquidity.

in order to change the polycarbonate, polysulfone and polyphenylene oxide for the flow of high viscosity plastic and molding performance, and strive to make them obtain the compact structure, need to adopt a higher mold temperature, injection tooling on the other hand, for small viscosity of polyethylene, polypropylene, polyvinyl chloride, polystyrene and polyamide, such as plastic, can adopt a lower mould temperature, which can shorten the cooling time, improve production efficiency. For wall thickness of the parts, because the mold filling and the cooling time is longer, if the temperature is too low, it is easy to internal vacuum plastic bubble and larger stress, should not be so use low mold temperature.

for polyamide, plasticizing pressure must be reduced, otherwise the plasticizing rate cut soon, this is because the screw in the upstream and the increase in the amount of leakage flow. If you want to increase the temperature, the method should be adopted to increase the temperature of the cylinder. Polyethylene high thermal stability, improve plasticizing risk of reduced pressure, this is advantageous to the mixing and mixed color, but the plasticizing rate decreases. Injection molding machine injection pressure refers to the piston or screw head axial moving their head of plastic melt pressure. Table is commonly used in the injection molding machine pressure indicates the size of the injection pressure, typically in the 40 - 130 mpa, the size of the pressure can be adjusted by injection molding machine control system.

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