Blow molding machines are used within the plastics manufacturing industry to make bottles of all types. Like other molding processes, blow molding machines generate their finished product through use of heated plastic and a mold cavity in which the liquid is shaped and cooled into its final form under pressure.
Extrusion blow molding machines use a plastic manufacturing process to produce bottles of various sizes and shapes. Plastic resin in the form of pellets are fed into an extruder which uses a rotating flighted screw to melt the resin and push it through the head of the extrusion blow molding machine. The tube-like plastic that exits the head is called a parison. clamp with molds in the shape of the final product close around the parison. A blow pin inserts into the middle of the parison and blows the plastic into the shape of the surrounding mold, which then cools to form the bottle. Many heads are programmable to form parisons with varying wall thickness along the length of the parison. This method is used to counter the effects of the temperature gradient along the length of the parison that would otherwise lead to bottles with non-uniform wall thicknesses.
Injection blow molding machines are used for high volume production of smaller bottles such as medical vials and other pharmaceutical bottles, single serve bottles, and jars. Injection molding machines employ the use of three stations arranged in a rotary fashion. The first station is the injection station where the injection blow molding machine injects melted plastic into a heated mold that contains a core rod. By the time the process at this station is complete the pre-form has been made which contains the finished neck of the bottle or jar being made, attached to a polymer tube which will form the body. The mold opens and the core rod is rotated to the next station where a hollow, chilled blow mold clamps around it before compressed air flows through an opening in the core rod to blow the body of the part into the finished shape. Once sufficiently cooled, the injection blow molding machine rotates the finished part to the final station for ejection. Typical material run on these machines includes LDPE, HDPE, PP, and PVC.
Accumulator blow molding machines employ a type of blow molding process called intermittent extrusion blow molding. These machines are similar to continuous extrusion blow molding machines except that the plastic that exits the extruder first builds up in an accumulator head before a hydraulic system pushes the accumulated plastic out through the die to form the parison. The two halves of the mold are clamped around the parison which is blown with air into the form of the mold. This system is ideal for larger and heavier products in which the weight of the parison tends to cause a large amount of pull upon exiting the die head, thus creating forces that lead to non-uniform wall thickness. Allowing the plastic to accumulate first and then get rapidly pushed through the die via a hydraulic system such as a press ram helps to mitigate the wall thickness dilemma. Many well-built machines include parison programming which allows the machine to alter the thickness of the parison as it is being formed. The combination of the above processes allows accumulator blow molding machines to efficiently produce heavy, hollow plastic products with uniform wall thickness. Examples of the types of products made on accumulator blow molding machines are large drums, garbage cans, and gas tanks using resins such as HDPE, PP, and PP
For more information on Injection molding Machines or other machines you might need please see our article about What Type of Plastics and Metal Machinery do I Need?
Interested in Injection Molding Machines? Get more information at Injection Molding Machines Guide
Interested in Extrusion Molding Machines? Then get more information at What are Extrusion Molding Machines?