The plasticizing process of a vertical phenolic injection molding machine is affected by a variety of factors, including back pressure, screw speed, and material temperature.
- Back pressure: A large back pressure facilitates the full and uniform plasticization of the molten material. However, excessively high temperatures can cause the molten material to cure prematurely, lose its flowability, and make it impossible to inject. Conversely, too little back pressure will result in insufficient plasticization of the molten material, poor flowability, and inability to fill the mold. Therefore, the appropriate back pressure should be adjusted according to the actual situation of the raw material and the degree of wear of the screw barrel.
- Screw speed: The faster the screw speed, the shorter the plasticizing time, and the molten material may not be fully plasticized. Slower screw speeds increase friction during the plasticizing process, resulting in high temperatures of the molten material, premature solidification, gas generation, and increased corrosion and wear of the screw barrel.
- Material temperature: If the material temperature is too high, the melt will quickly solidify under the action of screw shear force, which will aggravate the wear of the screw barrel, which will not be able to be injected and may clog the nozzle; If the temperature of the material is too low, the melt plasticization is insufficient, the injection process is slow, the mold cavity cannot be filled sufficiently, and the melt traces are obvious. In general, the material temperature should be controlled between 70 and 90 °C, for example, the temperature of the raw material PF-161J should be kept between 72 and 78 °C.
- Injection speed and pressure: too fast injection speed will cause a large frictional heat between the melt and the mold, which will partially solidify or even scorch, and the water vapor and gas generated during the curing process cannot be discharged, forming holes or lack of glue similar to acne; If the injection speed is too slow, flow marks and melt marks are likely to occur.
- Injection pressure: Excessive injection pressure can ensure the good molding and mechanical properties of the melt, but it will also increase the stress inside the plastic parts, making the burr thicker and larger (the burr is best able to transmit light); If the injection pressure is too small, the product is prone to glue shortage, and repeated glue shortage will cause the mold adhesive to turn black, and the product surface will lose its luster and turn white.
- Curing molding conditions: the higher the mold temperature, the longer the cooling time, the shorter the mold molding cycle, and the higher the production efficiency. However, too high a mold temperature may cause the phenolic powder to burn, pinholes to appear, and the filled molten material to solidify rapidly, producing gas that is difficult to discharge, and at the same time, it may burn the mold, resulting in defects such as mold agent and whitening. If the mold temperature is too low, the melt front will have poor fluidity, the mold core cannot be filled, the curing of the melt is not tight, the mechanical strength is poor, and the gloss is low.
- Cooling time: The higher the mold temperature, the longer the cooling time, and the better the cooling effect. The annealing after demoulding should be done by natural cooling.
