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Reasons for failure of blow molding products-control factors in extrusion blow molding machines

In the blow molding process, what factors will cause the blow molding product to fail? Are you often distressed by this situation? There are many parts for blow molding machines. Which aspects should be considered? What are the control factors in extrusion blow molding machines?

1. Control factors in extrusion blow molding machine-blowing pressure

When making blow-molded products, we must pass in compressed air for two purposes. One is to inflate the tube blank to make it close to the inner wall of the mold cavity and blow out the shape. The second purpose is to play a cooling role! Because the parison will be directly deformed due to gravity during the extrusion process, which will affect the quality, shape and structure of the product

Due to the different varieties of our blow molded products, the temperature and air pressure are also different. It is usually between 0.2-0.7 MPa. Between these values, the pattern and appearance of the product after molding can be made clear. For large blow molding products, higher blowing pressure will be adopted,

2.The controlling factor in the extrusion blow molding machine-inflation speed

In order to make the wall thickness of the product more uniform, and the appearance more smooth and shiny, the blowing time will be shortened, and the inflation speed should be as fast as possible, but it must be moderate. Otherwise, the product will be disfigured. The reason is that the vacuum created at the air inlet will cause this part of the product to dent. When the parison is completely inflated into a fat man, the dented part becomes the 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 increase the diameter of the blowpipe, or reduce the inflation rate a little.

3. The control factor in the extrusion blow molding machine-blow up ratio

The blow-up ratio is the ratio of the maximum diameter of the product to the preform. It mainly refers to the relationship between the maximum radial dimension 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 small, 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.

4. The control factor in the extrusion 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 lead to reduced product extensibility, not easy to inflate, not only difficult to form, the appearance is also ugly, and the pattern is not clear. Too high temperature will cause the cooling time to be prolonged and the product is easy to deform.

2. The 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.

5. The control factors in extrusion blow molding machine-cooling time

After the parison is inflated, it has already begun to cool. 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.

OK, let’s make a summary. The advantage of the extrusion blow molding machine is that it is suitable for a variety of plastics, has high production efficiency, uniform wall thickness of the parison, can produce large containers, and requires less equipment investment.


Post time: Feb-26-2021