Influencing factors in the blow molding process
(1) blowing pressure
The compressed air in blow molding has two effects, blowing and cooling. Low pressure should be selected for low viscosity, small volume or thick wall parts; High viscosity, large volume or thin wall parts should choose higher pressure.
(2) Blowing speed
In order to shorten the blowing time, in order to facilitate the product to obtain a more uniform thickness and better appearance, the blowing speed should be as large as possible, but the speed is too fast, the following phenomena are easy to occur: ① A vacuum is formed at the air inlet, so that this part of the billet is indented, and when the billet is completely blown, the indented part will form a diaphragm; ② The blank of the die part is also easy to be pulled off by faster air flow.
(3) Blowing ratio
Blowing ratio is generally 2-4 times, blowing ratio is too large, the shape stability of the product is poor, too small easy to cause uneven wall thickness.
⑷ Mold mild cooling time
The mold temperature is too low, it will make the plastic elongation at the clip decrease, not easy to blow, and make the part thicker, forming difficult; The mold temperature is too high, the cooling time is prolonged, and the production cycle is long. The cooling time is too short, insufficient cooling is easy to cause deformation of the product, shrinkage and increase, and the appearance is dull.
⑸ Forming cycle
Including extruding billet, intercepting billet, closing mold, blowing, cooling, deflating, opening mold, taking out products and other processes. The selection principle of the molding cycle is to shorten as much as possible under the premise of ensuring that the product can be shaped.
