Detailed introduction

05

2022

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09

The benefits of properly adjusting the back pressure of the barrel screw


Appropriate adjustmentbarrel screwBenefits of back pressure

  

机筒螺杆


The barrel screw can compress the molten material in the barrel, increase the density, and improve the stability of the product injection volume, weight and size.barrel screwThe gas in the melt can "squeeze", reduce the air flowers and internal bubbles on the surface of the product, and improve the uniformity of gloss. The retreat speed of the barrel screw makes the molten material in the barrel fully plasticized, increases the mixing uniformity of toner, masterbatch and molten material, and avoids color mixing. Appropriately increasing the back pressure can improve the shrinkage of the product surface and the glue walking around the product. It can improve the humidity of the melt, improve the plasticizing quality of the melt, improve the fluidity of the melt filling mold, and there are no cold colloidal particles on the surface of the product.

When the back pressure of the barrel screw is too low, the following problems are prone to occur: when the back pressure is too low, the screw retreats too fast, the density of the molten material before flowing into the fan cylinder is small (relatively loose), and there is more trapped air.barrel screwIt will lead to poor plasticizing quality, unstable injection volume, and large changes in product weight and product size. The surface of the product will shrink, empty flowers, cold lines, uneven gloss and other undesirable phenomena. Bubbles are easy to appear inside the product, and glue is easy to go around the product and bone position.

The high back pressure of the barrel screw is prone to the following problems: the melting pressure at the front end of the barrel is too high, the material temperature is high, the viscosity is reduced, the melt countercurrent in the screw groove increases, and the leakage flow between the barrel and the screw increases, which will reduce the plastic chemical efficiency (The amount of plasticized material per unit time). For plastics with poor thermal stability (such as PVC, POM, etc.) or colorants, thermal decomposition is caused by the increase of heating time in the barrel due to the increase of melt temperature, or the degree of discoloration of colorants increases, and the surface color of the product becomes worse. The back pressure is too high, the screw retreats slowly, and the pre-plastic glue back time is long, which will increase the cycle time and lead to a decrease in production efficiency. The back pressure is high, the melt pressure is high, and the glue liquid is prone to drooling after spraying. When spraying glue next time, the cold material in the nozzle channel will block the nozzle or extrude the product.

In the injection molding process, often due to excessive back pressure, leakage phenomenon, waste of raw materials and lead to near the hot ring burn. The mechanical wear of the preforming mechanism and the screw barrel increases. The adjustment of injection molding back pressure should be based on factors such as raw material performance, drying conditions, product structure and quality. The adjustment of back pressure is generally 3-15kg/cm3. When the product surface has a little empty flowers, color mixing, shrinkage and product size, weight changes, can be appropriately increased back pressure. In case of glue leakage, drooling, melting overheating decomposition, product discoloration, slow backwater, etc., the pressure of glue back can be reduced. Back pressure is one of the important parameters to control the quality of molten materials and products in injection molding process. Appropriate back pressure plays an important role in improving product quality that cannot be ignored!