The appearance of the liquid is enhanced by the shape of a bottle. The quantity of the liquid that needs to be filled in the bottle helps in deciding its size and shape. The hollow in a bottle plays a significant role that may not receive the attention of the user immediately. The designs, the structure, and the external features are responsible to provide a user with the utility of a bottled product. All the visible, as well as the features that are not noticed, in a plastic bottle, are resultant of the blow moulding process.

Plastic bottles come in various shapes and sizes depending on the products they contain. Every product has a different utility to offer to the customers, which impacts the bottle’s profile. The pivotal factors to decide upon the design of a bottle are-

  • The usability of the product
  • The quantity that would go inside the bottle
  • Feasibility of handling for the users.

The blow moulding process is the technique that is used by manufacturers to endow a shape and outline to the bottles.

Blow Moulding in the Industry

Blow moulding takes up an immense share of the global market with an estimate of $78 billion, in the year 2019. Besides, the projected growth is 2.8%, per year, from 2020 to 2027. The computed global share of blow moulding is 49% approximately. One can understand the importance of the blow moulding process as well as the evolving technology around the same, across the world.

Understanding Blow Moulding

The blow moulding process is used for creating the hollow in the plastic bottles. The process requires a moulding machine and several various steps that shape a plastic bottle. Blow moulding involves heating parison (the molten plastic that is left for moulding after heating) and giving it a desired form. It could be understood better with a quick peek at the steps involved in the moulding cycle.

  • Heating of the medium (plastic or glass) that would be used for making a bottle.
  • The molten medium or plastic is infused in the dies to allow moulding.
  • The molten plastic is trapped in between the two dies or moulds.
  • The moulds shape the plastic in the given shape.
  • Air is applied to the moulds ensuring that the walls of the bottle become leaner.
  • The air pressure, thus, makes sure that the bottle is completely aligned with the shape of the mould.

After the moulding of the product, the process of cooling takes place. It further solidifies the product. Once the process of trimming is done, the product is sent for further processing.

Blow Moulding – Getting to the Crux

Now, the blow moulding process does not appear as simple as it sounds. It takes place in diverse phases at a regulated pace to make sure that firm products are made. The various stages include heating, melting, homogenizing, extrusion, blow moulding, solidifying, and product discharge. To get to the core of manufacturing plastic bottles, the blow moulding process has to be understood step by step.

Preparation of Mixture

Plastic Feeding: It is the first step in the process of blow moulding. The raw material or plastic pellets are introduced into the extruder hopper. The vacuum pumps take out the pallets from the huge containers. After that, the content is transferred into hoppers or silos.
The rate at which the material is fed to the extruder is regulated by the rotary feeder. It is installed at the bottom of the hopper. The kind of systems that are used by different manufacturers can vary. Some systems may not require separate conveying air systems.

Melting: The process is also called plasticizing. For melting, the plastic granules are added to an extrusion machine. Electric heating bands are placed in the extruder barrel to scatter heat through the granules. By employing continuous heating and folding, the granules are melted to the required consistency.
Moreover, there are separate sections dedicated to diverse purposes in the extruder screw. Feeding, compression, and metering are the functions integrated into the screw. The main purpose of these diverse operations in the extruder screw is to prepare a homogenized material. It is achieved by providing the required shearing as well as sufficient compression to the material.

Getting into Moulding

The Extrusion or Injection: The next step is to get the parison ready for inflation, which is a significant part of the blow moulding. In a preform mould, the plastic is injected. It is the beginning of those specific steps in which the plastic is started to be shaped. Here, the liquid is extruded into the cavity of the moulds for initiating the process of moulding.

Clamping: Also known as sealing, the process of clamping involves the capturing of the preform in between the split moulding dies. The preform is sealed from top to bottom leaving the opening of the bottle. The exposed part or opening is going to be used for inflation.
The moulds are specific to the process in use i.e. the moulds have to support the method being used for manufacturing. For example, ISBM molds are specific to injection stretch blow moulding.

Inflation: Now, the compressed air is introduced from the exposed part. The compressed air blows the bottle to the point where it starts to conform to the shape of the die. The infusion of air, thus, makes sure that the plastic aligns well with the mould.

The Ejection: Without cooling, proper ejection of the inserted object is not easy. Therefore, the process of cooling takes place within the dies where the plastic is held in shape. As soon as the plastic aligns with the shape of the mould, a predefined rate of cooling ensures that the dimension of the product is intact. Once the dimension stabilizes, the plastic bottle will be extruded from the dies.

Finishing Off and Quality Control

De-Flashing: To offer the proper appearance and shape to the product, removing the excess material from the bottle is crucial. It is the part that takes place in between the dies before ejection. As the dies clamp the product intact, it removes any material that is not required in the product. It is, thus, an important phase of removing the undesired material from the bottle.

Trimming: In the blow moulding process, flash is found around the bottle, often. It is the excess material that dries out around the moulded product. The plastic bottle is not complete with these glitches in the product.

There are rotating knives that help in removing the flashes from the moulded product. Some modern equipment addresses the concern of environmental friendliness. Therefore, they utilize the excess material by collecting them and reusing them for processing.

Test for Leakage: Since the bottles are remarkable packaging products. Therefore, leakage is not acceptable. This part comes in the process of quality check. Here, the vacuum is created inside the final product to monitor whether it has any leakage or not.

The product goes through a monitoring process. If leakage is found in a product, it would be removed from the rest of the products.
Besides, all the processes mentioned above, there is a procedure for labeling and marking. However, that varies from manufacturer to manufacturer.

Different Types of Blow Moulding Methods

The two major sets of blow moulding processes are injection moulding and extrusion moulding. The other types that are used are the modified versions of these two. Here are the different types of blow moulding processes discussed, briefly.

Extrusion Blow moulding

The extrusion process of blow moulding includes the introduction of molten liquid between the two dies that shape the object. The dies are open from one end and closed from another end. The closed part helps in holding the object together while the open end is used for introducing the compressed air. As the dies are cold, they firm up the object into a defined shape. Afterward, the bottle is ejected from the moulds.

The extrusion moulding process is further divided into two types. These are-

  • Continuous Extrusion Blow Moulding
  • Intermittent Extrusion Blow Moulding.

Injection Blow Moulding

The process of moulding differs from the extrusion blow moulding process. In the preform mould, there is a metallic rod at the center. Generally, a table of metallic rods is present in the process holding different phases of the moulding cycle. The usage of a preform mould enclosing a metal rod in the center diversifies the process of injection blow moulding. The moulds that shape and stiffen the plastic bottle differ in this case as well.
The secondary phase includes transferring the moulded container into a different mould for the final shape of the container. Thereafter, the final product is released.


The upshot, here, is to decode the method of blow moulding that is used for moulding a large number of containers every year. With this write-up, one can understand that-

There is a variety of plastic containers used for different products.
The diverse shapes are given to these containers with the help of the moulding process.
The various factors that decide the shape of a bottle are usability, quantity, and handling.
The blow moulding process is used for giving the desired shape to the containers.
Blow moulding can be used for shaping plastic as well as glass bottles.
Two major processes of blow moulding are injection blow moulding and extrusion blow moulding.
The injection moulding process differs from the extrusion moulding as it contains separate moulds for shaping and conforming.

Acme Drinktec Solutions is one of the leading single stage molds manufacturers in India. With a remarkable experience of over 20 years, the company has excelled in the domain of ASB moulds.