Handling of defective sinkers in injection molded products
June 11, 2022
Gate dizziness, also known as sun spots, fog spots, that is, the circular color change produced near the gate. The shape is an ellipse or a circle, usually determined by the method of pouring and the size of the gate, due to melt fracture.
Defect mechanism
There are many reasons for creating a sprue, the main reasons are:
The barrel, nozzle and mold temperature are low;
The injection pressure is too high and the mold temperature is too low. If the mold temperature is too low, the plastic will cool too quickly, causing too much cold material, and then rushing to the surface of the product, resulting in defects;
The gate setting is unbalanced; the gate is too small or the cavity at the pouring is too thin. When the glue flow is large and the cross-sectional area is small (gate, cavity thickness), the shear rate is large, the shear stress increases, and the molten rubber is broken to cause the gate halo phenomenon. Cracking of the melt can also cause other defects such as flow marks, discoloration, and fog.
Final solution:
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forming
Process
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➤ Reduce injection speed, injection pressure, multi-stage injection pressure and position exchange;
➤ Increase the melt temperature and mold temperature to improve the fluidity of the material during the filling process.
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Mold
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➤Adjust the gate position so that the gate does not affect the appearance quality of the product as much as possible;
➤Appropriate gate section, the gate and runner section are preferably rounded to reduce the flow resistance of the stream;
➤With the appropriate gate type, the side-injection and lap-type infusion effects are better than the latent pouring effect;
➤ reasonable arrangement of cold wells;
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simulation
analysis
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➤The numerical simulation can be used to predict the temperature, shear rate and shear stress of the melt passing through the above narrow zone. According to the analysis results, the corresponding adjustment can be made, and the appropriate gate size and cavity wall thickness at the glue can be found very quickly.
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