What is Blow Moulding?

The blow moulding is works as its name stated. The molten material known as parison or preform placing it in the mould and inflate with compressed air till it cover the mould and cool down before the mould is removed. Any hollow plastic product can be made with blow moulding. There are wide ranges of hollow plastic products around us and we use it in our daily routine life. Here are some products that are made with blow moulding plastic bottle making machine.


  • Medical supplies
  • Household items
  • Industry products
  • Toys
  • Plastic bottles
  • Automotive parts

The blow moulding process is similar to glassblowing process. The first production machines and products are developed in 1930 to manufacture blow moulded bottles. After the introducing of low and high density polyethylene which is suitable for blow moulding the market is hiked for blow moulding products.

The blow moulding process can be done with three different method according to product. Which are

  • Extrusion blow moulding
  • Injection blow moulding
  • Injection stretch blow moulding

The main difference between these processes is forming the parison.

Now start with Extrusion Blow moulding. In this process the polymer is melted and it is extruded from a die to make a parison or hollow tube. The moulds covered the parison and with the pressurised air blows through the needle and it inflate the shape of mould. After this the cool air is blown and moulds are opened and eject the complete product. The extrusion blow moulding there are two methods for extrusion which are continuous and intermittent. In continuous method the parison is extruded continuously and mould open and close to complete the process. In the intermittent the plastic is collected by extruder and then push it to die to make parison. The products made with this process are bottles, toys, appliances and automotive parts etc.

Let’s discuss Injection Blow moulding. In this process the polymer is injected into a core to from hollow tube known as preform. Then the preforms are rotate on a core rod to blow mould and is inflated and cooled at blowing station. The injection blow process is suitable for small bottles. The process has three steps namely injection, blow moulding and ejection and all this action done in single machine. The products like medical supplies, product packages etc hdpe blow moulding machine.

Next is Injection Stretch Blow moulding. This process is quite similar to injection blow moulding. In this process the moulded preform is stretched up to decided length to get better strength and is light in weight. The raw material is used for this process is PET or PP and they are stretched for better physical characteristic. The wall thickness of final product is high than extrusion and injection blow moulding. The injection stretch blow moulding is divided in one step and two step process.

The One Step process the preforms and blowing in the same machine. This process is completed in three or four station machines. At different stations there is different action performs namely Injection, Conditioning, Blowing and Ejection.  This process is suitable for small to high capacity with different shapes and various size plastic bottles.

In the Two Step process first the preform is made with injection moulding. The preforms have necks and threads on the top. These preforms are cooled and stored for re-heat blow moulding. The preforms are heated generally with infrared heaters and then stretched and blow using high pressure air in the mould.  The Two Step process is suitable for 1 litre bottles and under plastic blow moulding machine.

There materials used for blow moulding are High Density Polyethylene, Low Density Polyethylene, PET, PVC, Polycarbonate etc.


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