What is Blow Molding? | Guide to Blow Molding Process | Blow Molding Advantages | Blow Molding Disadvantages

Blow Molding

Hello guys, in this article, I will share some detailed information about the Blow molding process, construction, and advantages.

What is Blow Molding?

Blow Molding is an efficient way to manufacture hollow plastic parts. The method is mostly used to produce plastic bottles and containers. The working process of blow molding is relatively simple compared to injection molding.

It all began when molten plastic material poured through Parison. Parison is a tube-shaped piece of plastic with a hole to pass compressed air through it. Parison is formed when a molten plastic material is pushed through an extruder.

Mainly there are three main types of blow molding methods –  1. Extrusion blow molding, 2. injection blow molding, 3. injection stretch blow molding.

Blow Molding Process – 

As mentioned earlier, molten material is formed through parison, which is clamped with the mold, and the air is blown through it. With the help of air pressure, plastic is pushed at the front to match with the mold.

When the parison reached the desired length, the two halves of the mold combine around the parison, locking it at the bottom.

After some time, when the article is cooled and solidified, the mold opens up, and the part is removed. 

After discussing the process, let’s discuss different types of blow molding processes.

Also Read – Compression Molding Process – A Detailed Guide 

Types Of Blow Molding – 

  • Extrusion Blow Molding 
  • Injection Blow Molding 
  • Injection Strech Blow Molding

Extrusion Blow Molding – 

Extrusion Blow Molding

Extrusion blow molding is the most widely used blow molding method. In extrusion blow molding, the molten plastic material is extruded into a parison.

This parison is locked by closing it between the two sides of the cooled mold, and then air is blown into the parison transforming it into the shape of the final product.

Once the article is cooled enough, the mold is opened up, and the component is ejected.

The two variations in extrusion blow molding are namely continuous blow molding and intermittent blow molding.

The parisons are extruded continuously in continuous extrusion blow molding, and the individual parts are cut separately using a fitting knife.

Talking about intermittent extrusion molding, which mainly falls into two variations, namely straight method, and accumulator method.

The straight method is quite similar to the injection molding method, using a screw to turn and stop to push the material out.

In the accumulator method, the material is gathered until the previous mold is properly cooled and enough material has been collected. Then, a rod pushes the molten material and propels the parison.

Injection Blow Molding – 

injection blow molding

The injection blow molding method is mainly used for large-scale manufacturing of hollow glass and plastic products. In this method, the core pin plays a key role as it rotates to a blow molding station to be stretched and cooled.

The injection blow molding method is widely used to manufacture small medical and single-serve bottles.

The primary process cycle of injection blow molding is the screw assembly and extruder cycle, which melts the material.

The molten material is poured into a hot barrel manifold running through different nozzles into a heated cavity and core pin.

The cavity mold clamped with a core rod will create an external shape, resulting in the preform’s internal condition. The preform comes with a fully formed jar neck with some material stuck to it.

The mold will open, and the core rod will rotate and be clamped into a hollow, cold blow mold. An opening at the rod’s core allows compressed air to be filled in the preform, expanding it to a finished product.

Injection Stretch Blow Molding – 

injection stretch blow molding

The injection stretch blow molding method is divided into two different single and double stages.

Talking about the single-stage method, it uses the same machine for preform manufacturing and bottle blowing. The single-stage method is also divided into two processes called 3-station and 4-station.

The 4-stage method is expensive compared to the 3-stage way as it goes like injection, reheat, stretch blow, and ejection.

The latter process eliminates the reheating part and uses latent heat in the preform, resulting in a substantial decrease in heating and tooling costs. As a result, the process is quintessential for filling carbonated drinks.

Coming to the two-stage process, it molds the material into ‘preform’ using injection molding. These preforms are produced using threads on the other end. Finally, these preforms are wrapped up and fed after cooling into a heating stretch blow molding machine.

The process uses heated preforms, usually above the glass transition temperature. Then, high-pressured air is blown into bottles using metal blow molds.

Also Read – Extrusion Molding Process – Detailed Guide | Applications of Extrusion Molding | Advantages of Extrusion Molding | Disadvantages of Extrusion Molding

Blow Molding Pressure Distribution – 

Knowing how the low molding pressure distribution takes place is a vital part of the process.

Water Bottles –  P<1 bar

Plastic Buckets –  P= 1-2 bar

Large Liquid Containers – P= 2-5 bar

Advantages of Blow Molding Process – 

advantages of blow molding

  • The processing cost of die and tools is meager.
  • Ability to manufacture complicated parts and designs.
  • Production time is also fast, depending on the product being manufactured.
  • It offers the benefits of automation. With automation, the speed of manufacturing can be ramped up significantly.
  • The versatility is another key advantage for blow molding. A significant number of customizations are possible with products like plastic bottles, containers, jars, etc. That makes blow molding quite lucrative for the pharmaceutical and food industries.
  • The external thread can be added without any difficulty.

Disadvantages of Blow Molding process – 

disadvantages of Blow molding

  • It is heavily dependent on petroleum. However, as the world’s oil supply is diminishing, the heavy dependence on oil is seen as a drawback for the process.
  • It comes with minimal applications.
  • Parts with complex geometries are difficult to manufacture.
  • If the mold has a complex shape, it can result in non-uniform distribution, non-uniform compaction of the film, and overall low dimensional accuracy.

Defects of Blow Molding – 

  • The thickness of too much brimming of components.
  • High fluctuation can be noticed in the quality of blow molding components
  • Blow molding cannot produce in mass volume like injection molding
  • Deep vertical stripes
  • Non-uniform wall thickness

Applications of Blow Molding – 

The following are the most popular blow molding applications:

  • Plastic buckets
  • Water bottles
  • Plastic cups
  • Mugs 
  • Liquid containers, etc.

The Future of Blow Molding Industry – 

According to research conducted by Grandwireresearch, the global blow molded plastics market was USD 75.7 billion in 2020, and it is anticipated to grow at a CAGR of 3.3 % from 2021 to 2028. The key applications verticals such as automotive, construction, and packaging are expected to drive the growth in the forecast period.

Most future growth should come from BRICS countries (Brazil, Russia, India, China, South Africa). Contrary to conventional wisdom, the COVID-19 pandemic has turned out to be a good opportunity for blow molded parts as there is an increased demand for various pharmaceutical products, disinfectants, and sanitizers. As a result, the segment is expected to witness massive growth in the near future piping consumables & electronics and building & construction segments.

Over the last few years, there has been an increase in capacity addition in high-growth regions such as Asia-Pacific and the Middle East. As a result, countries in both regions have been creating consistent demand for these plastic parts.

Talking about applications, the packaging applications segment was the leader in the market with more than 39% share in global revenue owing to increased adoption of packaging products in emerging economies. The products responsible for increasing packaging demand are face masks, protective kits, and face shields.


1. Which are the most suitable material for blow molding?

Ans. The most suitable and utilized material for blow molding are Polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET).

2. Why is blow molding cheaper than injection molding?

Ans. Blow molding is cheaper than injection molding, and there are several reasons for that. However, the most important factor affecting the cost is the difference in pressure usage; blow molding utilizes less pressure than injection molding, thereby reducing the overall production costs.

Apart from that, blow molding machinery is cheaper than injection molding, contributing significantly to reducing production expenditure.

3. What is parison programming?

Ans. Parison programming means programming the geometry to specify the mandrel movement. Through a “pegboard” system of inserting pins in holes on a grid. Nowadays, most extrusion blow molding machines are equipped with a parison programming system. Parison programming makes the manufacturer’s job easier by setting pressure, sizing, and dimensional accuracy.

4. Which is the most common type of blow molding technique?

Ans. The most common type of blow molding technique undoubtedly is extrusion blow molding with more than 37% revenue share.

5. What are the types of molding?

Ans. The popular and widely utilized molding techniques include blow molding, injection molding, compression molding, extrusion, and sintering.

Final Thoughts – 

I tried my best to share my knowledge about the blow molding process in a brief manner. Blow molding is a fantastic technique for making hollow parts and can be a great way to make money compared to injection molding where initial investments can make a deep hole in your pocket.

So, I tell you guys that if you’re looking to set a blow molding business, you’re on the right track.

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