Mold design directly impacts product precision, production efficiency, and material adaptability in plastic bottle manufacturing. Injection blow molding, in particular, places specific demands on mold structure. Taking common plastic raw materials such as PE, PP, and PET as examples, molds must simultaneously meet the dual technical requirements of injection molding and blow molding expansion.
The core principle of injection blow molding is two-stage molding: first, a preform with a neck is formed by injection molding; then, compressed air is used to inflate the preform to complete the bottle body. This design requires precise control of the mold cavity temperature distribution and venting structure to avoid problems such as obvious parting lines or uneven wall thickness. Differences in shrinkage rates among different plastic raw materials (e.g., PET shrinkage is approximately 1.5-2.2%, PP approximately 1.0-2.5%) directly affect the mold's dimensional compensation design.
The industry typically classifies blow molds into two categories: Injection blow molds and injection stretch blow molds. The former is suitable for general-purpose plastics such as PE/PP, while the latter is mostly used for crystalline materials such as PET. The runner system of injection blow molds requires special optimization to ensure uniform melt filling of the preform cavity while avoiding excessive shearing that could lead to material degradation. The selection of mold steel must also consider the balance between wear resistance (e.g., using S136 stainless steel) and thermal conductivity.
In actual production, a mold production line with an annual capacity of 800 sets requires special attention to the design efficiency of the cooling system. For thin-walled products such as cosmetic bottles, molds typically employ multi-point hot runner systems to shorten the molding cycle; while large chemical drum molds place greater emphasis on draft angles and the reliability of the ejection mechanism. These design differences are essentially aimed at resolving the contradiction between different plastic properties and the requirements of the end product.
