Blow Molding is a plastics extrusion process used to create a one-piece hollow plastic product or one with a cavity void of plastics material. Examples of this would be a milk jug or water bottle. Complex items such as car parts that have several bends or compartments may also be blow molded.
The process of blow molding involves melting plastic resin in an extruder via the friction of a turning screw and conveying that plastic parison via gravity to the molds. The parison is placed in a mold, an air pin is inserted and the plastic is “blown” to the shape of the mold, much as if you blew up a balloon in a box, it would take the shape of that box. The air pin is retracted and the plastic cools. The cooling process can take anywhere from seconds to minutes based on the process and the size of the product. The mold separates and the product is discharged.
Categories of Blow Molding Machinery
At Arlington Machinery we carry blow molding machinery in five distinct categories: Accumulator Head, Reciprocating Screw, Continuous, Injection Blow and Injection Stretch.
Intermittent Extrusion Blow Molding Machines
Accumulator Head and Reciprocating Screw are both types of Intermittent Extrusion Blow Molding. In this method, the extruder moves backward and forward similar to an injection molder. The molds are located under the die head remain in the same place and open and close. Intermittent Extrusion machines are very fast cycle times are possible. They typically run HDPE resin. Accumulator Machines are actually a reciprocating screw with a larger shot size. In order for the shot to be larger, the extruder allow the plastic to “accumulate” before it is shot into the mold. Shot sizes for Accumulator heads usually range from three to 75 lbs.
- Typical applications for accumulator blow molding machines include automotive panels, industrial containers, and large housewares items.
- Typical Accumulator Head Manufacturers: Sterling, Davis Standard, Krupp Kautex, Uniloy, Battenfeld, Graham, Hartig, Cincinnati
- Typical Reciprocating Screw Manufacturers: Impco, Graham Engineering, Rochleau, Uniloy, Milacron, Cincinnati
Continuous Blow Molding Machines
Continuous Blow Molding Machines can be subdivided into Rotary Wheel and Shuttle. Continuous blow molding is typically necessary for high production runs for a large output of product. In this process the screw is continually turning and pushing out plastic. As the plastic parison moves in a constant stream, the molds move to meet it and clamp over the section and move away, allowing for the next mold to do the same. The molds either are a shuttle clamp and move to the side or are on a wheel that spins either horizontally or vertically.
- Typical Continuous Manufacturers: Wilmington, Battenfeld Fischer, Bekum, Hayssen
Injection Blow Molding Machinery
Injection Blow Machines inject the plastic onto rods that are then indexed to a blow station and then are indexed to a removal station. (An additional station(s) can also be incorporated for longer cooling times.)
- Typical products include small medical/research containers and small personal hygiene/convenience bottles.
- Typical Injection Blow Manufacturers: Jomar, Milacron
Injection Stretch Blow can be broken down into 1-step and 2-step. Injection stretch uses a preform, either made in the machine itself for one-step or created in a separate injection molding machine for 2-step, that is then reheated. As the parison is reheated it is stretched by a rod. This stretching aligns the molecules bi-axially. This biaxial orientation provides an increase in strength of the product while using minimal raw material. The neck and screw top remain in the shape of original injection. Injection stretch machines are used almost exclusively for PET and are ideal for producing bottles used in carbonated soda bottles.
- Typical Injection Stretch Blow Manufacturers: Husky, Nissei, Krupp, Sidel, Side, Cincinnati
Vast Selection of Blow Molding Machines and Equipment
Arlington Machinery’s vast selection of blow molding equipment and industry experience ensure that we either have or can source the ideal machinery for your needs. See our available equipment online or reach out to us with your specifications.