In the whole
injection molding process, gas grain defects are a common defect in the processing of plastic parts. What causes such defects are generally caused?
1. Injection molding equipment does not match the injection molding products.
The selection of injection molding equipment should be reasonable. If the sum of the weight of the product and the gate aggregate is less than 20% of the maximum injection amount, the remaining raw materials will be decomposed by the shearing force generated by the rotation of the screw and the heating of the barrel. . If it is greater than 80% of the maximum injection amount, the melt may be unevenly heated, and it is difficult to form a precision product. If the screw design is reasonable and matches the type of plastic being processed, the molding process will be relatively wide; otherwise the molding process may be narrow or even impossible to form.
2. The design of the venting groove of the injection molding die is too small or too small.
In the case of high temperature and high pressure, the low-viscosity molten plastic suddenly passes through the narrow gate, and the molten material is injected into the mold cavity for a short time, entering the cavity with a large free space, forming a high-pressure injection state, entraining the flow channel and The air that exists in the cavity. The filling process of the raw materials in the mold is a process in which the gas is discharged. The mold parting surface lacks necessary exhaust holes or exhaust holes, and is blocked, the position is not good, and there is no machining gap and venting such as inserts and thimbles. The air in the flow channel and the cavity cannot be removed while the plastic enters, and the gas is easily trapped in the high-temperature melt. As the melt flows, the gas escapes from the surface of the melt to form a flow trace.
3. The plastic melt itself continuously generates gas.
If the injection molding equipment is suitable for the production of a certain product, the plastic mold is designed reasonably and the exhaust gas is smooth, but the plastic itself continuously generates gas, and the plastic melt still generates gas lines during the injection molding process and the cooling molding process.
4. The environmental humidity of the injection molding equipment is large.
When the injection molding machine is in a humid environment, the humidity of the air is too high, the humidity of the air is too large, and the water droplets that are condensed into water when the mold is cold (such as the mold temperature is lower than the dew point) cause a trace amount of moisture in the cavity of the mold. This moisture is vaporized by the melt to form water vapor, and the gas will not be discharged when it is discharged.
