Types of Blow Molding

BLOW MOLDING:

Plastic processing technique in which air is blown in heated plastic until it fills a mold to produce a required hollow shape is called Blow Molding. Glass bottles also formed by this technique.

PROCEDURE OF BLOW MOLDING:

The basic procedure of Blow Molding includes:

• Melting the thermoplastic resin by extruder .
• Forming molten resin into the parison .
• The parison is placed inside a mold .The air is inflated plastic that push outward against the cavity wall.
• The formed is then cooled & ejected from the mold.

TYPES OF BLOW MOLDING:

Following are the main types of Blow Molding.

Injection Blow Molding.

Extrusion Blow Molding.

Injection Stretch Blow

Molding.

1. INJECTION MOLDING:

In this type of Blow Molding. We required a blow or core rod throughout the process. Process starts with the injection of parison in to a split mold cavity around the rod. The parison that is to be shaped looks like a test tube. The parison is transferred by core rod to the blow mold machine. where air is forced to create the desire shape. The rod then transfers and extrudes the finished product from the machine.

2. EXTRUSION MOLDING:

Extrusion molding can be classified as Continuous Extrusion Blow molding and Intermittent

Extrusion Blow Molding.

CONTINUOUS EXTRUSION BLOW MOLDING:

In continuous extrusion blow molding, a parison will be constantly fed into the mold and each form will be cut off with a blade as it forms.

INTERMITTENT EXTRUSION BLOW MOLDING:

Intermittent extrusion blow molding expels each new plastic from the metal mold when it is cooled and the parison is fed into the mold only after the preceding parison is expelled.

Extrusion blow molds are normally cheaper than injection blow molds and can be formed quickly as compare to the others.

Advantages include cost savings on tooling and shorter production time while disadvantages usually include lesser control of wall thickness and greater amount of scrap material.

3. INJECTION STRETCH MOLDING:

Injection stretch blow molding is the combine form of injection and molding and blow molding processes. In this process solid preform is made by molded plastic to create a threaded bottle neck.

After the preform cools down it is then fed into stretch blow mold. An infrared heater is used to reheat the preform and then blown into a plastic bottle with forced compressed air.

FACTORS AFFECTING BLOW MOLDING:

• Parison characteristics: Size, shape ,straightness, wall thickness, mechanical strength.
• Inflation pressure: pressure will be set according to the process. Here, stretch blow molding pressure is less needed .
• Mold design

ADVANTAGES OF BLOW MOLDING:

• Low tooling cost
• Fast production rate.
• Ability to mold complex.
• Little scrap generated.
• Recycling.
• Large hollow parts.

DISADVANTAGES OF BLOW MOLDING:

• Only for hollow parts .
• Defect may be seen .
• Thick parts can not be manufactured.