Three Types of PET Blowing Machine Processes

PET Blowing Machine is the process of forming a molten tube (referred to as the parison or preform) of thermoplastic material

 

PET Blowing Machine is the process of forming a molten tube (referred to as the parison or preform) of thermoplastic material (polymer or resin) and placing the parison or preform within a mold cavity and inflating the tube with compressed air, to take the shape of the cavity and cool the part before removing from the mold.

The world of plastics and manufacturing is multifaceted and quite complex, featuring a large number of different process that can be used to produce plastic items. One of the methods available today is that of blow moulding. Blow moulding is a plastic manufacturing process commonly used to create hollow plastic parts, like liquid containers, plastic drums and storage tanks. Blow moulding enables companies to mass-produce plastic items quickly and effectively.

The manufacturing process for blow moulding involves the melting of raw material, which is generally a thermoplastic. Thermoplastics include polyethene, polypropylene and polyvinyl chloride. The thermoplastic used starts off the form of small granules or pellets, which are melted before being formed.

Blow Molding Processes

Blow molding is a manufacturing process that creates hollow plastic parts. There are three unique processes for creating blow molded parts, they include the following:

Stretch Blow Molding

This blow molding process involves the production of hollow objects, such as bottles, having biaxial molecular orientation. Biaxial orientation provides enhanced physical properties, clarity, and gas barrier properties, which are all important in products such as bottles for carbonated beverages.

There are two distinct stretch blow molding techniques. In the one-stage process, preforms are injection molded, conditioned to the proper temperature, and blown into containers—all in one continuous process. This technique is most effective in specialty applications, such as wide-mouthed jars, where very high production rates are not a requirement.

In the two-stage process, preforms are injection molded, stored for a short period of time (typically 1 to 4 days), and blown into containers using a reheat-blow (RHB) machine. Because of the relatively high cost of molding and RHB equipment, this is the best technique for producing high volume items such as carbonated beverage bottles.

Injection blow molding

The process of injection blow molding (IBM) is used for the production of hollow glass and plastic objects in large quantities. In the IBM process, the polymer is injection molded onto a core pin; then the core pin is rotated to a blow molding station to be inflated and cooled. This is the least-used of the three blow molding processes, and is typically used to make small medical and single serve bottles. The process is divided into three steps: injection, blowing and ejection.

The injection blow molding machine is based on an extruder barrel and screw assembly which melts the polymer. The molten polymer is fed into a hot runner manifold where it is injected through nozzles into a heated cavity and core pin. The cavity mold forms the external shape and is clamped around a core rod which forms the internal shape of the preform. The preform consists of a fully formed bottle/jar neck with a thick tube of polymer attached, which will form the body. similar in appearance to a test tube with a threaded neck.

The preform mold opens and the core rod is rotated and clamped into the hollow, chilled blow mold. The end of the core rod opens and allows compressed air into the preform, which inflates it to the finished article shape.

After a cooling period the blow mold opens and the core rod is rotated to the ejection position. The finished article is stripped off the core rod and as an option can be leak-tested prior to packing. The preform and blow mold can have many cavities, typically three to sixteen depending on the article size and the required output. There are three sets of core rods, which allow concurrent preform injection, blow molding and ejection.

Extrusion Blow Molding

The extrusion blow molding process begins with the conservative extrusion of a parison or tube, using a die like those used for making plastic pipe. The parison is then extruded downward between the two halves of an open blow mold. When the parison reaches the proper length, the mold closes, catching and holding the neck end open and pinching the bottom end closed. A rod-like blow pin is inserted into the neck end of the hot parison to simultaneously form the threaded opening and to inflate the parison inside the mold cavity. After the bottle cools, the mold opens to eject the bottle. The excess plastic is trimmed from the neck and bottom pinch-off areas.

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