Blow molding (also known as blow moulding or blow forming) is a manufacturing process by which hollow plastic parts are formed. In general, there are three main types of blow molding: extrusion blow molding, injection blow molding, and stretch blow molding. The blow molding process begins with melting down the plastic and forming it into a parison or preform. The parison is a tube-like piece of plastic with a hole in one end in which compressed air can pass through.
The parison is then clamped into a mold and air is pumped into it. The air pressure then pushes the plastic out to match the mold. Once the plastic has cooled and hardened the mold opens up and the part is ejected.
TYPES OF BLOW MOLDING MACHINE
There are two types of blow molding – Extrusion & Injection blow molding. In Extrusion Blow Molding, plastic resin is heated up to melt and extruded into a tubular shape called Parison. This Parison is then trapped inside two halves of the required mold and blown by air to the shape of mold. In Injection Blow molding, first the material is injected to form a preform and then it is blown to the shape. Extrusion Blow molding is used to produce all types of drums, cans, bottles etc. and injection blow molding is used to produce bottles.
Continuous Type Blow Moulding:
In continuous blow molding the Parison – tubular molten raw material – is extruded continuously and the mold moves sidewards after receiving the Parison. The blowing will be done in the blowing station and the blown containers ejected. The mold will again move towards the Parison and next cycle starts.
Intermittent Type Blow Molding:
In intermittent blow molding the molten material is stored in a chamber called accumulator and Parison is ejected intermittently during the start of each cycle. Hence these machines are known as accumulator type blow molding machines. In Accumulator machines Parison is ejected intermittently at the starting of each cycle. During the blowing time the molten material processed by extruder is stored in the accumulator chamber on the die head.
Injection Blow Molding:
In normal injection Blow molding process, the Preform made by injection moulding is directly blown to the required shape of mold. The injection process allows generating better neck formation to the container.
Injection Stretch Blow Molding:
In normal injection stretch Blow molding process, the Preform made by injection moulding is first stretched along the axis to orient the structure and then blown to the required shape of mould. This allows creating transparent containers with very low wall thickness and better strength.
Single Stage Injection Blow Molding:
In single stage molding, the preform is made and immediately blown to shape in the same machine. The normal injection blow molding is done by this process. The stretch blow molding also done in single stage process.
Two Stage Injection Blow Molding:
In two stage process, first the preform made like any injection mold process. The ready preform then re-heated, stretched and blown to the required shape. Here the preform making and blow molding are done in two different machines. This process is used normally for stretch blow molding.