Hollow blow molding is a process that uses extrusion blow molding. For large products, two key molding technologies are crucial: First, the need to rapidly supply the required amount of melt to reduce preform sagging and diameter reduction due to the large size and weight of the product; second, the long cooling time of large products, which prevents continuous extrusion, leading to the development of die heads with accumulators. Hollow thermoformed products with a volume exceeding 20L are considered large hollow blow-molded containers.
The process involves storing the plasticized melt from the extruder in a accumulator. Once the accumulator reaches a predetermined volume, a pressure liner forces it through an annular die at a high rate, forming a tubular shape of a certain length. To further improve the uniformity of wall thickness in large blow-molded products, variable annular die and programmable controllers are used in these accumulator-equipped blow molding machines to automatically control the axial wall thickness distribution of the preform according to a pre-set program, thereby further improving the uniformity of wall thickness in large blow-molded products.
