What is the back pressure in the injection molding machine?
Back pressure: screw back when applied to the rod end of rubber pressure. It can reduce material consumption and bubble phenomenon.A: when the back pressure is adjusted properly, the density of the melt can be increased, the air discharged by the air in the cylinder can be discharged, and the rubber material is compacted, so that the cycle of the beer mould is stable, and the production efficiency is improved.B: back pressure is high, screw speed is slow, the resistance is large, the barrel screw is easily damaged, because the screw friction heat, heat increase in external heating unchanged, will make the temperature rise, the viscosity decreased, resulting in leakage and countercurrent flow, the nozzle is easy to produce salivation phenomenon.C: low back pressure and screw speed is fast, but it is difficult to put the rubber barrel compaction, the particles is not uniform, resulting in flower phenomenon, such as adding toner material will appear in different shades of color.Note: feed back when the screw rotation should be shaped, injection should be straight. 1, can melt inside the barrel compaction, increase density, improve the stability of injection quantity, weight and size of the products.2. The gas in the melt can be extruded to reduce the gas, the inner bubbles and the gloss uniformity of the products. Slow speed screw back, so that melt inside the barrel full plasticizing, mixing and melting toner, color uniformity, avoid product color mixing phenomenon.3, slow speed screw back, so that melt inside the barrel full plasticizing, mixing and melting toner, color uniformity, avoid product color mixing phenomenon.4, appropriately increase the back pressure, can improve the product surface shrinkage and product periphery walk glue situation.
Jin Xin offers you:Jin Xin explain the injection molding machine screw back pressure what role?Back pressure allows the screw to produce enough mechanical energy in the rotation of the reset to melt and mix the plastic, and the back pressure has the following uses.The volatile gases, including air, are discharged to the outer cylinder.Mix the additives (e.g., toner, color, antistatic agent, talc, etc.) and melt evenly.Homogenizing the melt flowing through different screw lengths.Providing uniform and stable plasticizing material to obtain accurate weight of finished products.The back pressure can make up the melt temperature of injection molding machine barrel, rise and set pressure value associated with a large injection molding machine, screw diameter more than 70mm [(2.75in) of the oil pressure can be up to 2.5-4MPa], but need to pay attention to the oil pressure is too high, or is caused by the melt pressure back pressure resistance induction high temperature molten material in the barrel is too high, this kind of situation for heat sensitive plastics production is destructive.And too high back pressure also caused excessive screw and irregular offside, so that the amount of plastic is very unstable. The viscoelastic properties of offside and plastic screw the screw; offside and melt the stored energy. The more energy, the greater the offside screw distance, the energy stored in the screw stops rotating, suddenly beat back, some thermoplasticPlastic beating phenomenon is more severe than other plastic, such as LDPE, HDPE, PP, EVA, PP/EPDM composite and PPVC, compared with GPPS, HIPS, POM, PC, PPO - M and PMMA, more prone to beating phenomenon. For optimum production conditions, the correct back pressure setting is critical. Proper back pressure setting allows the mixture to be properly mixed, and the offside range of the screw does not exceed 0.4mm (0.016in).
