What is the difference between injection blow molding and extrusion blow molding?
Answer: Extrusion blow molding blows compressed air into molten plastic to make it expand into a formed mold and is used only to make hollow parts with little surface detail, such as bottles and jugs. Injection molding injects molten plastic into a mold and is used to make primarily solid parts with high degrees of intricacy.
Extrusion blow molding:
Between both methods, the extrusion blow molding method tends to be the more popular choice. Plastic pellets are fed from a hopper into an extruder, which uses friction to heat the plastic into a liquified state. The molten plastic is extruded into a hollow tube, called a parison. Pressurized air is then blown into the parison, forming it into shape. Excess plastic on the bottom of the container is trimmed. Containers are then sent to a second trimming station, where the top is trimmed. When possible, this excess is recycled back through the process to limit waste.
Injection molding creates greater detail than extrusion blow molding. Resin pellets are fed from a hopper into an extruder. The pellets are then melted and injected into a preform mold around a core rod. Pressurized air forces the plastic to take the shape of the mold.
The final step in both blow molding processes is to check for leaks. If a leak is detected the container is recycled back into production to limit waste. MDI offers both extrusion and injection blow molding services, with extensive custom capabilities.
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