The process of Extrusion Blow Moulding Machine » Central Machinery & Plastic Products

Extrusion Blow Molding is the simplest type of blow moulding. A hot tube of plastic material, called a parison, is dropped from an extruder and captured in a water-cooled mould. Once the moulds are closed, the air blown through the top of the neck of the container. When the hot plastic material is blown up and touches the walls of the mould, the material freezes, the container now maintains its rigid shape. 

We at CMP, believe that Extrusion Blow Moulding is looking forward to converting parts/ products, having two components assembling into one Extrusion Blow Moulded part. Because Extrusion Blow Molding is a hollow part process, both sides of a product could mould together.

For coloured bottles, we often fed colourant into the extruder at a controlled rate and mixed it with the resin while being melted. If barrier and adhesive layers are required, they are added separately and combined in a co-extrusion head.

Different industry segments use EBM machines such as packaging (bottles), Pharma industries, Food grade industries, Cosmetic industries etc. Our products range from 50ml to 5000 ltr.

Following are details of the Blow Moulding Process:

1. The Process

• The process starts with the formation of a hollow tube of plastic, called a parison. The tube is extruded downward until it extends past the bottom of the mould. The mould then closes on the parison.
• A mould is used to make the part shape you desire. The mould has two halves that are closed around the molten parison.
• Air is introduced into the parison via a blow pin at the top of the part of a needle in the middle of the part, inflating the plastic and pushing it against the mould sides.
• Then part cools in the mould.
• Then the part is ejected from the mould.

2. The Excess

• When a bottle is produced using this blow moulding method, excess material is created when the mould closes around the parison. 
• The ‘flash’ must be removed to complete a finished bottle or jar. 
• Flash at the bottom (called the tail), the top (the moil), and for handled ware – a “handle slug” needs to be trimmed.
• Typically, the flash is removed upon mould release (trimmed in mould). 
• For bottles with handles (handle ware), offset neck and special circumstances, flash is extracted via a secondary operation downstream.

3. Secondary Operations

Every blow moulded product will require some degree of additional processing after it leaves the blow moulding machine. These secondary processes are used to remove unwanted materials, add features, and improve functionality. 

• Flash removal 
• Plastic welding 
• Riveting and staking 
• Foam pad assembly 
• Acoustic pad assembly 
• Blow mould assembly 

In addition to removing the flash, secondary (downstream) operations include flame treatment, leak detection, and post-mould decorating. Flame treatment is sometimes used before bottle decorating to improve ink adhesion. Leak detection, on the other hand, is always required to ensure the stability of the bottle.

Whether routine flash removal or something more advanced such as welding and assembly, designers should consider which secondary processes will be critical in finishing their blow-moulded product. 

4. Materials

Materials with High Melt Strength are needed in Extrusion Blow Molding to reduce the amount of Sag (and excess thinning) in the Parison. Wide Spec/Higher Molecular Weight grades are used to give the parison more strength to hang without tearing or excessive sagging.

• Olefins (Polyethylene, Polypropylene)
• Thermoplastic Elastomers (TPEs)
• Polycarbonate
• Polyvinyl chloride (PVC)

 5. Key Processing of EBM

• Melt Temperature – Changes the viscosity of the material.
• Extruder Speed – Determines the speed that the parison is made.
• Blow Time – Although blowing forms the product, holding the pressure on the product keeps it in contact with the mould and increases the cooling.
• Blow Pressure – Helps to pick up surface detail in the mould.
• Parison Drop Time – How long the parison hangs and stretches before the mould closes.
• Parison Programming – Creates local thickness changes in the parison.
• Mould In-Out Time – How fast the mould can collect the parison.
• Mould Open-Close Time – Creates an impact on mould cutting edges to deflash a component.

6. Process Advantages

• Moulds are inexpensive. Since moulding pressures are much lower, tooling can be produced in aluminium.
• Irregular geometry is easy to mould in the mould shape without destroying the part.
• There is the ability to combine several components into one part.
• By using specialized polymers, there are better barrier properties.
• Recycled materials could be layered in the middle.
• Less costly materials could be used in a layer to reduce the part’s cost

We, at CMP, have always moved forward with one motto ‘Quality over Quantity’ and with this same motto we have come this far and gave our best to our customers.