Four common causes of airline defects in injection molded products
February 23, 2022
Throughout the injection molding process, airline defects are a common defect in the processing of plastic parts. What are the general causes of this defect?
1. Mismatch between injection molding equipment and injection molded products.
The choice 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 volume, the remaining raw material will be decomposed by the shearing force generated by the screw rotation and the heating of the barrel. . If it is greater than 80% of the maximum injection volume, the melt may be unevenly heated and it will be difficult to form a precision product. If the screw is well designed to match the type of plastic being processed, the molding process will be relatively wide; otherwise, the molding process may be narrow or even unmoldable.
2. The venting slot of the injection mold is designed too small or too small.
Under high temperature and 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 into the mold cavity with a large free space, forming a high pressure injection state, entrapping the air present in the runner and the mold cavity. The filling process of the raw material in the mold is a process of gas discharge. The mold parting surface lacks the necessary venting holes or venting holes, which are blocked, poorly positioned, without machining gaps and vents such as inserts and ejectors. While the plastic is entering, the air in the runners and cavities cannot be removed and the gas is easily trapped in the hot melt. As the melt flows, the gas escapes from the surface of the melt and forms flow marks.
3. The plastic melt itself continuously produces gas.
If the injection molding equipment is suitable for producing a certain product, the plastic mold is well designed and the exhaust is smooth, but the plastic itself keeps producing gas, the plastic melt will still produce gas lines during the injection molding process and the cooling molding process.
4. High humidity in the environment of injection molding equipment.
When the injection molding machine is in a humid environment, the humidity of the air is too high and the humidity of the air is too high. When the mold is cold (such as the temperature of the mold is below the dew point), water droplets condense into water, resulting in a trace amount of moisture in the mold cavity. This moisture is vaporized by the melt and forms water vapor, which is not discharged when the gas is discharged.
