二、The relationship between the injection rate and pressure of segmented injection molding:
1. In the segmented injection molding process, no matter how many stages of the filling process changes, the injection pressure is only one pressure, that is, one pressure, and the speed of the pressure holding stage is only one regardless of the number of stages.
2. Sectional injection molding example:
(1) The same finished product can be molded with a small clamping force, so as to prolong the life of the machine and the mold;
(2) Segmented deceleration: Mastering the correct pressure holding switching point can effectively ensure the stability of quality;
(3) When the flow of the molded plastic is too good, in order to prevent the burr from occurring, low-speed injection is taken, but the raw material is not allowed to be cooled and solidified, and the molten resin passes through the thickness of the flesh and then increases the injection rate to quickly fill the mold cavity, and the flow mark (which is the striped pattern of the molten grease gradually centered on the gate) is caused by the junction formed between the resin that initially flows into the mold cavity and cools too quickly and the resin that flows into the mold second.
(4) If the glue inlet (i.e. gate) part is thick, the injection rate is too fast and will cause turbulence, and the cold material is easy to remain in the channel and form flow marks, so the slow and low-pressure glue feeding should push away the cold material head so that the plastic behind can enter smoothly.
(5) In the injection molding project, the nozzle is in contact with the mold because the mold cooling water cools the mold temperature is lower than that of the nozzle, and part of the heat is taken away by the mold, and the nozzle is easy to produce cold material heads, which are injected into the mold, which will be blocked at the gate and cause flow patterns or silver stripe traces.
(6) Precision small parts, fine gate size, and most of the cavity gate balance production is extremely difficult and difficult, the gate can be opened with the same size and then used multi-stage injection molding technology to overcome.
(7) The change of the switching position at the junction of the first stage of low-speed injection molding and the second stage of high-speed injection molding can be corrected by moving the local part of the welding line, such as moving the obvious part in appearance to a less obvious position (such as the label).
(8) The phenomenon of depression and poor fusion is opposed to each other in molding, and can be improved at the same time by this method; the injection rate of the sunken part of the product drops sharply, and the injection rate of filling the mold cavity is quickly increased after filling the surface layer to cold and solidifying, and the welding line part should be shot quickly to prevent poor fusion (generally the surface subsidence of the molded product occurs at the thickness of the meat, which is caused by the volume shrinkage of the molten resin when it is cooled and cured).
(9) In the process of pressure holding, the residual stress of the molded product can be reduced by reducing the segmentation.
(10) The molding conditions of thin molded products and long flow distance require high pressure to be successfully completed, but high-speed and high-pressure injection is easy to cause residual stress at the gate part, which affects the quality, so high-speed glue feeding, medium-speed filling, and low-speed pressure holding are adopted to eliminate residual stress, so as to prevent the deformation of the finished product.
(11) Mold cooling to improve: if the moving mold temperature is low and the fixed mold temperature is high, the molded product will not warp inward, and if the moving mold temperature is high, the molded product may have outward warping.
(12) Scorching (a phenomenon caused by compressed combustion of gas in the cavity) is most likely to occur at the parting line or welding, and the surface of the resin shows traces of black carbonization, and the air gas can be discharged smoothly from the cavity, and the injection rate must be reduced.