Related Causes Of Dents In Mold Products

- Jan 26, 2021-

1. Causes of dents


  1 The thickness of each part of the product is different


  2 The internal pressure of the mold is insufficient


  3 Insufficient mold cooling


  4 Deformation due to insufficient cooling time


   2. Related knowledge


1 In the process of producing products, dents are the most frequent occurrence of undesirable phenomena. The plastic injected into the mold shrinks in volume when it is cooled. The early cooling part, that is, the surface hardens first, and bubbles are generated inside. The so-called dent is slow cooling. The part of the bubble produces a conspicuous concave surface in the direction of the bubble shrinkage.


  2 Materials with high shrinkage are also prone to dents. When changing the molding conditions to eliminate dents, the setting conditions should be set in the direction of small shrinkage. That is, the mold temperature and barrel temperature decrease, and the injection pressure increases, but it should be noted that this may cause residual internal stress.


  3 Because the dents are better to be inconspicuous, if they do not affect the appearance, they are deliberately processed into a corroded pattern on the mold, such as grain and grain. Also, if the molding material is HIPS, lowering the mold temperature to reduce the finish is also effective. However, once dents occur in these methods, it is difficult to repair polished products.


   2. Related knowledge


1 In the process of producing products, dents are the most frequent occurrence of undesirable phenomena. The plastic injected into the mold shrinks in volume when it is cooled. The early cooling part, that is, the surface hardens first, and bubbles are generated inside. The so-called dent is slow cooling. The part of the bubble produces a conspicuous concave surface in the direction of the bubble shrinkage.


  2 Materials with high shrinkage are also prone to dents. When changing the molding conditions to eliminate dents, the setting conditions should be set in the direction of small shrinkage. That is, the mold temperature and barrel temperature decrease, and the injection pressure increases, but it should be noted that this may cause residual internal stress.


  3 Because the dents are better to be inconspicuous, if they do not affect the appearance, they are deliberately processed into a corroded pattern on the mold, such as grain and grain. Also, if the molding material is HIPS, lowering the mold temperature to reduce the finish is also effective. However, once dents occur in these methods, it is difficult to repair polished products.


   Three, the solution


  1 Instant: Increase injection pressure, extend injection holding time, reduce barrel temperature and mold temperature, and force cooling where dents occur.


  2 Short-term: Fill up the flow edge where the dent is generated. When the material in the dented area has a narrow place, make this part thick.


  3 Long-term: The thickness difference of the designed product should be completely avoided. Reinforcing ribs that are prone to dents should be as short as possible.


  4. Differences in materials


  1 Materials with large mold shrinkage have large dents. For example, PE, PP, even if only a slight reinforcement ribs, will produce dents.