Blow Molding Process Explained

Hey friends, ever wondered how the bottles are produced? Well they are actually produced by the ‘balloon way’. I remember it that way. It is actually an easy process and a little common sense is needed. Now you must be wondering how a balloon which is spherical in shape can be converted to a bottle which is a hollow cylinder?
Blow molding is a process of producing hollow cylinders using a plastic molding technique. You must be remembering that 19th century saw the advent of industrial revolution and this made it necessary to produce various components at a faster rate. Well the answer was blow molding in some cases. Blow Molding is actually a highly developed molding technology developed back in the late 1800's to produce celluloid baby rattles. (The ‘baby rattles’ is no scientific term please mind it serious engineers!). It is just a toy which new born babies chew!

A typical apparatus consists of following major components i.e. blow pin, plunger, accumulator and lastly a mold.
Actually the process utilizes air pressure to inflate softened thermoplastic tube which is sealed at one end (also called as parision). This parision is constantly inflated and extruded. Then later on it is cut according to required dimensions. The temperature in Accumulator is maintained around 400 degree Celsius or so.

The mold consists of two split parts which have a semi-circular cross-section. Usually the air pressure which is applied in low pressure molding is about 50 to 250 psi.
Various forms of blow molding used in industry today on a wide scale are Injection Blow Molding. Injection Blow Molding though not used in industry, has very limited and specific applications like making small medicine plastic bottles etc. The next is of course Extrusion Blow Molding.
Extrusion blow molding is the simplest form of blow molding. A tube of plastic material which is generally maintained hot, is dropped from an extruder only to be captured in a water cooled mold. Once the molds are closed, air is injected through the top or the neck of the container and the tube is inflated just like a balloon. When the hot plastic material is blown up and touches the walls of the mold the material is cooled and the container now maintains a solid, rigid shape.
Now Stretch blow molding, this process requires the raw material to be formed in a preform using injection molding and later on stretch blow molding process can be applied.

The product range varies from various cylindrical components like bottles, cans, floats heater ducts in automobile parts and various small pipe fittings and hollow cylindrical parts can be produced in mass production.

The advantages are many like the tooling costs are very less as compared to injection molding, the part performance is excellent under pressure. Then the products have excellent environmental stress crack resistance. The products also perform excellently in high speed impact strength than even the metal components the process can be automated and used in mass production.

The disadvantages mainly raise environmental concerns. It depends on petroleum industry as any plastic industry depends. Also the cylindrical shapes are delicate so if the dimensions are not accurate then they result in scrap.

So it is our own decision which matters in selection of a process as to what can be more economical wise and eco-friendly.