The role of screw back pressure in injection molding machine


The back pressure ensures that the screw can generate e […]

The back pressure ensures that the screw can generate enough mechanical energy to melt and mix the plastic during the rotary reset. The back pressure also has the following applications.
  1 Discharge volatile gases, including air, out of the shooting tank.
  2 Evenly add the additives (such as toner, color, antistatic agent, talc, etc.) and the melt.
  3 Homogenize the melt flowing through different screw lengths.
  4 Provide a uniform and stable plasticized material to obtain accurate finished product weight.
 The back pressure can increase the temperature of the melt in the barrel of the injection molding machine, and the increase range is related to the set back pressure value. The larger injection molding machine [screw diameter over 70mm (2.75in) can be as high as the back pressure of the oil line. 2.5-4MPa], but it should be noted that too high oil line back pressure or resistance induced back pressure causes the melt back pressure to be too high, and the melt temperature in the barrel is too high. This case is sensitive to heat sensitive plastic. Production is destructive.
Moreover, the too high back pressure also causes the screw to be too large and the irregular offside condition, so that the amount of glue is extremely unstable. The offside of the screw is related to the viscoelastic properties of the plastic; the offside of the screw is related to the energy stored in the melt. The more energy, the greater the offside distance of the screw, the energy of these stores causes the screw to suddenly jump backwards when it stops rotating, some thermoplastic.
 Plastic beating is more severe than other plastics, such as LDPE, HDPE, PP, EVA, PP/EPDM composites and PPVC. It is more prone to beating than GPPS, HIPS, POM, PC, PPO-M and PMMA. In order to achieve optimum production conditions, the correct back pressure setting is critical, and the proper back pressure setting allows the melt to be properly mixed and the offside range of the screw does not exceed 0.4 mm (0.016 in).