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Injection molding machine processing when the back pressure is how form?

by:Hisson     2020-04-09
A, the formation of the back pressure in the process of plastic melting and plasticizing, constantly moving to cylinder front-end (melting Measuring indoor) More and more, and gradually formed a pressure, push the screw back. In order to prevent the screw back too fast, to ensure that the molten material uniform compaction, need to provide a screw in the opposite direction, the pressure of the opposite direction to prevent the screw back pressure is called the back pressure. Back pressure which is also called plasticizing pressure, it is controlled by adjusting the injection cylinder oil return of throttle valve. Pre plasticizing injection screw injection molding machine oil cylinder is set at the back of the back pressure valve, adjusting screw rotation back when the speed of the cylinder oil injection, keep the oil cylinder pressure; The motor speed of screw back ( Resistance) Is controlled by AC servo valve. Second, the appropriate adjustment back pressure the benefits of 1, can the molten material compaction within the gun barrel, increase density, increasing resin shot, the stability of the goods weight and size. 2, can be the gas 'crowd out' within the molten material, reducing gas, internal air bubbles on the surface of the products, improve gloss uniformity. To slow down the speed of the screw back, make the liquid inside the gun barrel fully plasticizing, adding pigments, masterbatch and mixing evenness of melting, avoid products appear mixed color phenomenon. 3, slow speed of the screw back, make the liquid inside the gun barrel fully plasticizing, adding pigments, masterbatch and mixing evenness of melting, avoid products appear mixed color phenomenon. 4, appropriately increase back pressure, can improve shrink and products around the glue on the surface of the products. 5, can increase the temperature of the molten material, make the molten material plasticizing quality improvement, improve the liquidity when molten material molding, product surface without cold glue lines. Third, when the back pressure is too low, easy to appear the following questions 1, when the back pressure is too low, screw back too fast, into the gun barrel front-end of molten material density is small, Relatively loose) , into the air. 2, can lead to poor quality of plasticizing, glue quantity is not stable, the product weight, dimension change is big. 3, product surface will shrink, gas, cold material grain, luster as well as the uneven phenomenon. 4, easy appear bubbles inside the product, the product and bone around an easy walk with glue. Fourth, the high back pressure, easy to appear the following questions 1, gun barrel front high pressure is too high, material temperature, melting viscosity decreased, molten material in the screw groove upstream and cylinder and the screw clearance leakage flow rate increases, will reduce the plasticizing efficiency ( The plasticizing rate of per unit time) 。 2, for the thermal stability of plastics ( Such as: PVC, POM, etc. ) Or coloring, because of the melting temperature and heating time growth and cause thermal decomposition in the cylinder, or coloring colour degree increasing, product surface color/gloss variation. 3, high back pressure, screw back slowly, plastic material long time back, will increase the cycle time, resulting in a decline in production efficiency. 4, high back pressure, liquid pressure is high, after glue nozzle is easy to melt salivate occur the next time you shoot glue, nozzle flow passage of slag can be plugged nozzle or products in cold spots. 5, in the process of plastic beer, often because of back pressure is too large, the nozzle glue leakage phenomenon, waste of raw materials and lead to fever circle burn out near the nozzle. 6, the plastic body and screw barrel increase mechanical wear. Five, the set-up of back pressure injection of back pressure adjustment should be according to the condition of the performance of the raw material, dry, product structure and quality condition and decide, back pressure calibration in commonly 3 - 15kg/cm 3 。 When the product surface has a little gas, mixed color, shrink and product size, weight, change is big, can be appropriately increase the back pressure. When the nozzle leakage on glue, salivate, molten material overheating decomposition, product color and back slowly to consider appropriate to reduce back pressure. Back pressure control in injection molding process is one of the important parameters of molten material quality and product quality, the right back pressure has important role in improving the product quality, can not be ignored!
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