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Reasons and solutions for shortage of plastic products

  1. Reasons for material shortage Reasons and solutions for shortage of plastic products
  2. The injection molding machine has insufficient pressure and the injection time is too short.
  3. Insufficient pressure in the mold means that the injection pressure loss is too great during the injection cycle. ​
  4. Insufficient material fluidity. ​
  5. Poor air escape from the mold cavity. ​
  6. The gate is unbalanced (when one mold has multiple holes). ​
    1. Related knowledge
  7. Material shortage is generally determined by the shape of the mold and the fluidity of the material. When there is a shortage of material due to molding condition settings, the molding condition settings should be set in the direction of good material fluidity, that is, increase the mold temperature, barrel temperature, injection speed and injection pressure. ​https://doi.org/10.1016/j.powtec.2023.118848
  8. If the exhaust design in the mold cavity is not clever, the air in the mold will be difficult to escape. In addition to causing the product to be short of material, it is also the cause of burnt spots and fusion marks on the product. ​
    1. Solution
  9. Immediately: Increase the temperature of the mold and barrel, increase the injection pressure, and add a gas escape groove (depth 0.02~0.04mm) 5~10mm wide on the parting surface. ​
  10. Short term: enlarge the gate and increase the flow edge (overflow edge). When a large number of molds are produced, if the cavity is short of material, the gate of that cavity will be enlarged, the configuration of the flow edge will be changed, and a gas escape pin will be added to improve the smoothness of the mold. ​
  11. Long-term: Avoid designing products with different thicknesses. Add gates where the thickness of the product is thick. Understand the occasions where the product will be used. If appropriate, try to use materials with good fluidity. ​https://solidcomould.com/product/office-chair-backrest-mould-18/

 4. Due to differences in materials

When the mold temperature is not high, resins whose material fluidity deteriorates significantly, such as polycarbonate PC, polyphenylene ether PPO, polyethylene terephthalate, commonly known as polyester resin PETP, etc., require the mold temperature to be heated to 80 degree or above (use a mold temperature regulator). ​

 5. Reference matters
  1. The so-called fluidity of material generally refers to the measurement of the weight of material flowing into the injection hole under a certain temperature and pressure within a certain period of time. Indicates the flow properties of the material such as the melting index of the material. ​
  2. As a method of measuring resin fluidity, a spiral flow (vortex) mold is used. This can be used to measure the resin filling length. ​

    (1) The injection holding time above a certain time has nothing to do with the filling length, but if it is too short, it will cause insufficient filling (lack of material). ​
    (2) It has nothing to do with the time the material stays in the barrel. ​
    (3) If the injection speed is too slow, filling will become insufficient. However, speed above a certain value will have little effect. ​
    (4) The higher the mold temperature is, the better it will have less impact. ​
    (5) If there is a little left in the plasticizing stroke of the screw, the filling length will become longer. ​
    (6) There is generally a linear relationship between injection pressure and filling length. ​
    (7). In the appropriate area of molding, the material temperature is generally linearly proportional to the filling length. ​
    (8) The thickness of the cavity is roughly in linear proportion to the filling length. ​
  3. The ratio L/T of the maximum filling length (L) to the thickness of the cavity (T) is used as the standard for the fluidity of the molding material.
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