We have defects in the gate area during the injection molding process. What are the reasons for this phenomenon?
How To Solve The Defect In The Product Gate Area?
In the design of the point gate perpendicular to the direction of the injection molded part, a radiation system composed of different color depths and glosses centered on the gate appears on the surface of the part during injection molding, called the ray line. There are basically three kinds of performance, namely dark lines on a dark background, dark lines on a dark background, and dark lines around the gate are dense and whitish.
Most of these defects occur during the injection of polystyrene and modified polystyrene mixtures, and are related to the following factors: the two materials have differences in rheology, coloring, etc., the flow rate of the stratospheric and turbulent layers of the casting system, and there are differences in heating conditions; plastics are burned by thermal decomposition; gaseous substances interfere when plastics enter the mold.
①. When using mixed plastic, the plastic should be mixed well, and the particle size of the plastic should be the same and uniform.
②. Plastic and colorant should be mixed evenly, if necessary, appropriate dispersant should be added and mixed mechanically.
③. The plasticization should be complete, and the plasticization performance of the machine should be good.
④. Reduce the injection molding pressure and speed, shorten the injection molding inject and pressure holding time, at the same time increase the mold temperature, increase the nozzle temperature, and reduce the front furnace temperature.
⑤. To prevent the melt and coking material from increasing the viscosity caused by the degradation of plastics: if pay attention to whether the screw and barrel are worn and there is a dead angle or the heating system is out of control, improper processing operation will cause the plastic to decompose due to long-term heating. The inner surface of the front end of the screw and barrel can be polished.
⑥.Improve the gate design, such as enlarge the gate diameter, change the gate position, change the gate to fillet transition, try to locally heat the gate, and add cold material well at the end of the runner.
Cold spots mainly refer to the parts with fog or bright stripes near the gate or curved scars from the gate that is like earthworms attached to them. They are caused by the plastic front entering the cavity or due to excessive pressure. It is caused by cold material that is later squeezed into the cavity;
The forward material transfers heat due to the cooling effect of the nozzle or runner and is cooled and solidified before entering the cavity. When it is expanded into the cavity through the narrow gate, the melt fractures, and then it is subsequently heated The molten material pushed, so it became a cold spot.
①. Cold feed well should be set up. Also consider the form, size, and position of the gate to prevent the cooling rate of the material from being disparate.
②. The center of the nozzle should be adjusted, and the matching size of the nozzle and the mold inlet should be designed to prevent leakage or cold material from being brought into the cavity.
③. The exhaust degree of the mold is good. Gas interference can cause turbid markings on the gate.
④. Increase the mold temperature. Slow down the injection speed, increase the injection molding pressure, reduce the pressure and injection time, and reduce the pressure.
⑤. Dry the plastic. Use less lubricant to prevent powder contamination.