Blow Molding: Types, Benefits, Applications

Blow molding also called Blow Forming, as it is manufacturing process through which hollow plastic parts are formed.

PROCESS OF BLOW MOLDING:

1. The process begins with melting the plastic and forming it into parison (in tube form).
2. The air pressure pushes the plastic and presses it against mold cavity.
3. When the plastic become cool and hard, the mold opens and part is released.

TYPES OF BLOW MOLDING:

Following are the types of blow molding:

1. EXTRUSION BLOW MOLDING:

In this molding, first plastic is melted and press out into hollow tube. This hollow tube is then hold by closing it into cooled mold cavity. Air passed through the plastic and making it into desire shape of part. After the plastic has cooled, the mold is opened and removed the solidified part.

Extrusion blow molding is of two types:

1. Continuous extrusion blow molding:

In this molding, plastic is continuously extruded and the individual parts are cut off by knife.

2. Intermittent extrusion molding:

In intermittent extrusion, extruder screw run, stops and pushes melt out. Here, accumulator is used to gather mold.

2. INJECTION BLOW MOLDING:

This type of molding is used for producing hollow parts in large quantity.

In this type, molten polymer is injected into a heated preform mold. Then this preform is passed to the hollow, chilled blow mold. Air is blown out to preform part, forcing it against the mold. Then blow formed polymer is cooled and remove from blow mold.

3. STRETCH BLOW MOLDING:

In this process, first using injection molding process we molded the plastic into preform. These preforms are formed with the necks of bottles, these preforms are packed and after cooling fed into reheat stretch blow molding machine. The preforms are heated and then using metal blow molds high pressure air blown into bottles.

ADVANTAGES OF BLOW MOLDING:

• Fast production rate.
• Low tooling cost.
• Producing large hollow parts.
• Ability to mold complex parts.

DISADVANTAGES OF BLOW MOLDING:

• Thick parts cannot be manufactured.
• Inability to form bottles with proper neck finishes.
• Limited to hollow parts.
• To make wide neck jars spin trimming is necessary.

BLOW MOLDING APPLICATIONS:

• Milk bottles
• Pharmaceutical bottles
• Antifreeze bottles
• One piece chair
• Ice chest and coolers
• Garbage cans
• Drums
• Fuel tanks
• Polypropylene bottles