The blow moulding is worked as its name stated. The molten material is known as parison or preform placing it in the mould and inflate with compressed air until it covers the mould and cools 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.
- Medical supplies
- Household items
- Industry products
- Plastic bottles
- Automotive parts
The blow moulding process is similar to glass blowing process. The first production machines and products are developed in 1930 to manufacture blow moulded bottles. After the introducing of low and high-density polyethene which is suitable for blow moulding, the market is hiked for blow moulding products.
The blow moulding process can be done with three different methods according to a product. Which are
- Extrusion blow moulding
- Injection blow moulding
- Injection stretch blow moulding
The main difference between these processes is forming the prison.
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 prison and with the pressurised air blows through the needle and it inflates the shape of a 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 of extrusion which are continuous and intermittent. In the continuous method, the parison is extruded continuously and mould open and close to complete the process. In the intermittent, the plastic is collected by an 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 form a hollow tube known as a preform. Then the preforms are rotated on a core rod to blow mould and are 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 the single machine. The products like medical supplies, product packages etc.
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 a better physical characteristic. The wall thickness of the 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.
Their materials used for blow moulding are High-Density Polyethylene, Low-Density Polyethylene, PET, PVC, Polycarbonate etc.