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What is extrusion blow molding

Blow moulding machine is a manufacturing process used for the production of plastic bottles, containers, and custom shapes. This manufacturing process can be accomplished through different methods, but at Apex Plastics we use extrusion blow molding and injection stretch blow molding (ISBM). For this blog, we will focus on the EBM process.The extrusion blow molding process can be broken down into two subcategories continuous extrusion blow molding and intermittent extrusion blow molding. In continuous blow molding, the plastic is extruded constantly while the machine runs. With intermittent extrusion blow molding, the extruder runs for a designated amount of time and fills a reservoir with plastic; after the reservoir has been filled, a ram is activated and pushes the material from the reservoir through the extrusion head.An EBM machine can be used to manufacture a wide variety of bottles, containers, and shapes commonly used to make products we use in daily life such as oil bottles, peroxide bottles, shampoo, and personal care items among many others. 

Intermittent EBM machines are often used to make large parts or products that require thick walls, such as gallon water coolers and gasoline containers.At Apex Plastics, we produce bottles, containers, and shapes from less than  ounces to over  gallon on continuous EBM machines.  Materials processed in our EBM include high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polypropylene.The continuous extrusion blow molding process begins by loading the resin into a hopper on the top part of the machine, which is then fed into an extruder. The plastic can be processed in its natural state, or it can be blended with a wide variety of colors and additives.

The material handling systems, composed of blenders, grinders, surge bins, and other components, are used to manage and move material within the facility. Material blenders provide consistent batches of material throughout the production process.The extruder contains a screw that continuously turns, pushing the plastic resin down the barrel. Through mechanical friction, the plastic is transformed from a solid pellet form, into a molten state. Heaters strategically placed on the barrel and head help maintain a uniform heat during the extrusion process. The melt strength is important to maintain a uniform wall thickness to avoid holes in the final product. The molten plastic is then pushed through an extrusion head, and past the die tooling that forms the parison. The parison is a hollow tube of molten plastic that will become the final product. The extrusion head and die tooling determine the length and shape of the parisons. For heavy or large parts, a single extrusion head may be used allowing only one part to be made during each cycle of the machine.

Smaller parts use extrusion heads capable of making multiple parisons at the same time.  Making multiple parts at a time increases productivity time during a machine's cycle.The mold encloses around the parison, and then a blow pin enters the top of the parison sealing the tube. The pins compress air into the parison to mold the plastic into the final shape of the product. Molds are commonly made of aluminum or other metals. The mold is then cooled to facilitate the quick formation of the finished part. Once the plastic has cooled and hardened, the mold opens up and the final product is ejected.  After the part is ejected, excess plastic, or flash, is then removed manually or by machine. The flash is sent through a grinder where it is cut into small pieces and then transferred to a surge bin. The recycled material, or regrind as it is commonly called, can be reintroduced to the manufacturing process through the material handling system keeping waste to near zero.