Under what circumstances should a mold temperature controller be used to heat the mold, and when should a chiller be used to cool the plastic mold? Below are some conditions for injection molding.
1. Mold Closing Pressure: In principle, it should be greater than the total pressure of the plastic injected into the mold, with the goal of preventing burrs.
2. Pressure and speed have a partial relationship acting on the mold. The purpose is to ensure that the raw material enters the mold evenly, thoroughly, and appropriately, filling all corners. Too low a pressure will result in short shots and shrinkage; too high a pressure will result in burrs, overfilling, sticking, burning, mold damage, and high internal stress.
3. Speed: The speed determines the condition of the raw material in the mold runner and in the finished product. Too high a speed will result in burrs, overfilling, and burning; too low a speed will result in short shots, shrinkage, poor bonding, and breakage.
4. Temperature: Different raw materials require different temperatures. Too low a temperature will result in uneven color of the solution and increased internal stress in the finished product. Excessive pressure due to low temperature can cause screw breakage. Too high a pressure will result in burrs on the product, and the temperature difference during cooling will cause shrinkage. Raw materials will decompose, turn yellow, discolor, and become brittle. Prolonged cooling time makes it difficult for gas to escape, potentially leading to gas leaks.
5. Back pressure: The resistance encountered when the screw retracts during feeding is called back pressure. Its function is to make the raw material more compact during conveying and compression. It allows air and moisture in the raw material to escape from the back of the screw, ensuring the sol does not contain gaseous components that affect the surface of the finished product. Low back pressure will result in bubbles and silver streaks on the surface. High back pressure will cause overheating, clumping, glue overflow, prolonged cycle time, and the screw not retracting. The application of loosening the screw is also very important: with low back pressure, some materials require loosening, while others do not. With high back pressure, loosening must be used, and the distance must be carefully controlled to prevent air intrusion and glue overflow.
6. The mold temperature and cooling time affect the finished product's sticking, shrinkage, dimensional tolerances, surface gloss, and cycle time, and should be adjusted in a timely manner according to the actual situation. In addition, for acrylic and PC products with thick walls, mold temperature is required to prevent the generation of air bubbles and stress.
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