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Blow Molding |
Blow molding, or blow foaming, is a novel molding process by which big hollow plastic parts like plastic beverage bottles and fuel tanks are manufactured. The  process of blow molding involves melting the polymers and and forming it into a parison, which is a a plastic tube like structure with a hole in one end in which compressed air can pass through. The concept of this novel molding process came from the idea of blowing glass. Enoch Ferngren and William Kopitke were the first verified people who used the blow molding process.
The process
The whole process of blow molding begins with melting down the granular plastic material and forming it into the parison, which is then clamped into a mold and air is pumped into it. The pressure of the air makes the plastic assume the desired shape.
Different types of Blow Molding
Extrusion Blow Molding : This process is exclusively employed to manufacture dairy containers, shampoo bottles, hoses/pipes, and hollow industrial parts such as drums. There are two types of extrusion blow molding:
Continuous extrusion blow molding
Intermittent extrusion blow molding which is further divided into the straight intermittent process and the accumulator process.
Injection Blow Molding: The process of injection blow molding employs three stages : injection, blowing and ejection. First the polymer is injection molded onto a core pin. The core pin is then rotated to a blow molding station where it is inflated. It is cooled hereafter and the molds are ejected. This method is used to make single serve and medical bottles.
Stretch Blow Molding: Stretch blow molding is extensively used to produce bottles, jars and other containers. In this process infrared heaters are used to heat the  preforms above their glass transition temperature after which high air pressure is employed to blow them into bottles.
Advantages of Blow Molding
- Low tool Cost
- Low die cost
- Rapid production rate
- Ability to mold complex part
- Produces recyclable parts
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