Influencing factors in the blow molding process

(1) Blowing pressure

Compressed air in blow molding has two effects, inflation and cooling. Low-viscosity, small-volume or thick-walled parts should use low pressure; high-viscosity, large-volume or thin-walled parts should use higher pressure.

(2) Air blowing speed

In order to shorten the blowing time, so that the product can obtain a more uniform thickness and a better appearance, the blowing speed should be as large as possible, but the following phenomena may occur if the speed is too fast: 1. A vacuum is formed at the air inlet, so that this part of the parison is When the parison is fully inflated, the indented part will form a diaphragm; ② the parison in the die part is also easily broken by the faster airflow.

(3) Inflation ratio

The inflation ratio is generally 2-4 times. If the inflation ratio is too large, the shape stability of the product will be poor, and if the inflation ratio is too small, the wall thickness will be uneven.

⑷ Mold temperature and cooling time

If the mold temperature is too low, the extensibility of the plastic at the jaw will decrease, it will not be easy to blow up, and the part will be thickened, making it difficult to form; if the mold temperature is too high, the cooling time will be prolonged, and the production cycle will be long. If the cooling time is too short, insufficient cooling will easily lead to deformation of the product, increased shrinkage, and dull appearance.

⑸ Molding cycle

Including the process of extruding the parison, cutting the parison, closing the mold, blowing, cooling, deflating, opening the mold, and taking out the product. The selection principle of the molding cycle is to shorten it as much as possible on the premise of ensuring that the product can be shaped.