Several important points to note about hollow blow molding machines

　　1. Inflation Pressure of the Blow Molding Machine

　　In blow molding, compressed air serves two purposes: firstly, it expands the parison to tightly adhere to the mold cavity wall, forming the desired shape; secondly, it provides cooling. The air pressure varies depending on the type of plastic and the parison temperature, generally controlled between 0.2-0.7 MPa. The most suitable pressure is one that allows the product's appearance, patterns, etc., to be clearly visible after molding. Lower values are used for plastics with lower viscosity and easier deformation; higher values are used for plastics with higher viscosity and modulus; high pressure is suitable for large-volume and thin-walled products; lower pressure is used for small-volume and thick-walled products.

　　2. Inflation Speed of the Blow Molding Machine

　　To shorten the inflation time, facilitating a more uniform thickness and better surface for the product, the inflation speed (volume of air flowing per unit time) should be as large as possible, but not excessively so. Otherwise, it will negatively impact the product: firstly, a vacuum may be created at the air inlet, causing the parison to indent in that area, and when the parison is fully inflated, the indented part will form a diaphragm; secondly, the parison in the die area may be torn by the extremely fast airflow, resulting in defective products.

　　Therefore, it is necessary to increase the blow pipe diameter or appropriately reduce the inflation speed.

　　3. Blow Ratio of the Blow Molding Machine

　　The ratio of the product's dimensions to the parison's dimensions is usually called the blow ratio. When the parison's dimensions and weight are constant, the larger the product's dimensions, the larger the parison's blow ratio. The size of the blow ratio is determined based on the type, properties, shape, and size of the product, as well as the size of the parison. The blow ratio is usually controlled within 2-4 times.

　　4. Mold Temperature and Cooling Time of the Blow Molding Machine

　　To ensure product quality, the mold temperature should be evenly distributed, generally maintained at 20-50℃. If the mold temperature is too low, the extensibility of the plastic at the weld line will decrease, making it difficult to inflate and causing the product to thicken in this area. It also makes molding difficult, and the product's contours and patterns will not be clear. If the mold temperature is too high, the cooling time is prolonged, extending the production cycle. The product will deform after demolding, and shrinkage will increase.

　　The mold temperature depends on the type of plastic. When the glass transition temperature of the plastic is high, a higher mold temperature can be used; otherwise, the mold temperature should be lowered as much as possible.

　　Generally, the cooling time increases with the increase in product wall thickness. Sometimes, in addition to cooling the mold, the molded product can also be internally cooled by introducing various cooling media (such as liquid nitrogen, carbon dioxide, etc.) for direct cooling.

　　5. Molding Cycle of the Blow Molding Machine

　　The blow molding cycle includes processes such as extruding the parison, cutting the parison, closing the mold, inflation, cooling, deflation, opening the mold, removing the product (subsequent trimming, assembly, and packaging are not included).