Analysis and solution of shrinkage and depression of injection molded products
| During the injection molding process, shrinkage of the product is a common phenomenon. The main reasons for this are: 1. Machine side: (1) The nozzle hole is too large to cause the melt to recirculate and shrink, and when it is too small, the resistance is insufficient and the shrinkage occurs. (2) If the clamping force is insufficient, the flash will also shrink. Check whether the clamping system has any problems. (3) If the amount of plasticization is insufficient, a machine with a large amount of plasticization should be used to check whether the screw and the barrel are worn. 2. Mold aspect: (1) The design of the parts should be such that the wall thickness is uniform and the shrinkage is consistent. (2) The cooling and heating system of the mold should ensure that the temperature of each part is consistent. (3) The pouring system should be ensured to be unobstructed, and the resistance should not be too large. For example, the size of the main channel, the runner, and the gate should be appropriate, the finish should be sufficient, and the transition zone should have a circular transition. (4) For thin parts, the temperature should be raised to ensure smooth flow, and the mold temperature should be reduced for thick-walled parts. (5) The gate should be opened symmetrically, as far as possible in the thick part of the part, and the volume of the cold well should be increased. 3. Plastics: Crystalline plastics shrink than conventional non-crystalline plastics. When processing, the amount of material should be increased appropriately, or a replacement agent should be added to the plastic to accelerate crystallization and reduce shrinkage and depression. 4. Processing: (1) The temperature of the cylinder is too high, and the volume changes greatly, especially the temperature of the front furnace. For plastics with poor fluidity, the temperature should be properly increased to ensure smoothness. (2) The injection pressure, speed, back pressure is too low, and the injection time is too short, so that the amount or density is insufficient and the contraction pressure, speed, back pressure is too large, and the time is too long, causing the flash to shrink. (3) The feeding amount means that the injection pressure is consumed when the cushion is too large, and when the amount is too small, the amount of the material is insufficient. (4) For parts that do not require precision, after the injection pressure is maintained, the outer layer is basically condensed and hardened, and the part with the sandwich part is still soft and can be ejected, and the mold is released early, and it is slowly cooled in air or hot water. It can make the shrinkage depression smooth and not conspicuous and does not affect the use. |
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