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Reasons for blow molding failure of blow molding machine

Update:16-04-2021
Summary:

1. Blow molding failure factor of hollow blow molding m […]

1. Blow molding failure factor of hollow blow molding machine-blowing pressure
When making blow-molded products, we have to blow in compressed air for two purposes. One is to inflate the parison to make it close to the inner wall of the cavity and blow out the shape. The second purpose is to play a cooling role, because in the process of hollowing the parison will be directly deformed due to the action of gravity, which will affect the quality, shape and structure of the product.
Due to the different types of our blow molded products, the temperature will be different, and the required compressed gas pressure will also be different. Generally, it is between 0.2-0.7 MPa. Between this value, it is determined according to the actual situation to make the pattern and appearance of the product clear after molding. For large blow molding products, higher blowing pressure will be adopted, and vice versa.

Second, the blow molding failure factor of the hollow blow molding machine-inflation speed

In order to make the wall thickness of the finished product more uniform and the appearance more smooth and shiny, the blowing time will be shortened, and the inflating speed should be as fast as possible, but with a degree. Otherwise it will be blown or partially collapsed. The reason is that a vacuum created at the air inlet will cause a depression in this part of the product. When the parison is inflated and molded, the depression becomes a diaphragm.
On the other hand, it is because the preform at the die site may be broken by the extremely fast airflow. Therefore, it is necessary to switch to a larger blowpipe caliber, or reduce the inflation speed a bit.

Three, blow molding failure factors of hollow blow molding machine-blow up ratio

The blow-up ratio is the ratio of the large diameter of the product to the parison. It mainly refers to the relationship between the large radial size of the product and the size of the die in the extruder head. When the size and quality of the produced parison are set, the blow-up ratio will change according to the size of the product. If the inflation ratio is large, the product will be thin, and inflation will be more difficult, but the material is saved. A large blow-up ratio will cause the product to become thicker and increase the consumption of raw materials. It will also reduce the effective volume of the product, prolong the cooling time, and increase the cost. Therefore, the general inflation ratio is between 0.2-0.4.

Fourth, the blow molding failure factor of the hollow blow molding machine-mold temperature

1. Mold temperature and product quality are inseparable. Generally, the temperature of mold cooling water is between 10-20 degrees Celsius. Too low temperature will cause the product to weaken elongation and not easy to inflate, not only is it difficult to form, but the appearance is not clear because many places are stuck together because of the inability to blow. Too high temperature will cause the cooling time to be prolonged and the product is easy to deform.

⒉The mold temperature depends on the type of plastic.

3. The wall thickness of the product is related to the cooling time. Not only the mold is cooled, but the inside of the mold is also cooled.

Fifth, the blow molding failure factor of the hollow blow molding machine-cooling time

After the parison is inflated, it has already begun to cool, and the cooling time determines the appearance, performance and production efficiency of the product. Prolonging the cooling time will prevent the shape change of the plastic caused by the elasticity, and the product has a neat appearance and good quality. If the cooling time is too short, it will cause stress and porosity in the product. Under the premise of ensuring product cooling and shaping, speed up cooling and improve production efficiency.

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