Blow Molding; Process, Types, Materials…

4 min reading time..

Blow molding is actually used in the glass industry to produce different types of glass containers. But also, blow molding processes are used for thermoplastic materials to produce different types of containers, bottles, drums, etc. For plastic blow molding processes, the production rate is very high. Because of this demand, automated blow molding machines are developed. In here;

  • You can find general information on the blow molding process of plastics,
  • Types of plastic blow molding processes, advantages and disadvantages of them,
  • Materials and products of blow molding processes.

What Is Blow Molding Process?

Injection type blow molding process illustration.

Blow molding is the production method to produce hollow plastic containers in a serial production manner. The general principle of the blow molding process is; with special tooling, a piece of hollow and semi-molten thermoplastic material is provided. And with the application of blow inside this piece of material, which is also called a parison, hollow shaped parts in a specific size is produced.

The swelling of the parison is controlled by special molds. Parison is provided inside these molds, and blowing is applied. Parison takes the shape of this mold by swelling.

In general, there are two types of blow molding processes available.

Injection Type Blow Molding

In injection type blow molding, the parison is provided by injection of thermoplastic polymer inside parison mold. A special rod which is called a blowing rod is submerged inside this parison mold. Then parison mold is opened, inside this parison mold, the parison is obtained around the blowing rod.

This blowing rod with parison is submerged inside the mold, then blowing air is given to parison to swell inside the mold. Then parison takes the shape of the mold. So, a container or hollow part is obtained.

Advantages of injection type blow molding: In injection type blow molding processes, waste material is much less and the production rate is bigger than the other one. Better accuracies and dimensional tolerances can be obtained. But, for large products, injection type blow molding can be expensive.

Extrusion Type Blow Molding

Extrusion type blow molding processes.

In the extrusion type blow molding process, the parison is obtained with extrusion of plastic from tube die. When the required length parison is extruded, two-part mold is closed, and the upper side of the parison is squeezed to close by mold halves. The bottom side of the parison is assembled with a blow pin.

From the blow pin, the air is blown inside parison and parison takes the shape of the mold. Then the mold is opened to detach the hollow plastic part from it.

Thickness In Blow Molding Processes

Obtaining the required thicknesses in blow molding processes is a very important parameter. Calculation of the thickness of the produced product is a very simple thing.

In the extrusion blow molding process, die swell must be considered in the extrusion process of the parison. The obtained parison is then blown to obtain the final shape. So, some parameters must be used to calculate the final thickness of the plastic hollow bottle or shape. You can use the calculator below to calculate the blown plastic product’s thickness.

Thickness Of Blown Product Calculator

















The use of the calculator above is very easy to use. Enter the required parameters inside boxes then click on ‘Calculate!’ to see the thickness of the final product of the extrusion blow molding process.

If you want to do another calculation, just click on the ‘Reset’ button then re-enter the whole values again.

In here;

  • The thickness of the parison die is the thickness of the parison hole.
  • Thickness after extrusion is the parison’s thickness. The parison’s thickness will be bigger than the thickness of the die because of the die swell effect.
  • The diameter of the die is the diameter of the parison die hole that material is being extruded.
  • The diameter of the parison is the produced parison’s diameter which is bigger than the diameter of the die because of the die swell effects again.
  • The diameter of the final shape is actually the diameter of the mold that shapes the final hollow part.

Your units must be the same length unit which can be both millimeters or inches.

If you want to convert your units, you can use the MB-Unit Converter tool for it.

Which Materials Are Used In Blow Molding Processes?

Blow molding processes are only applied to thermoplastic materials. In general in bottle production, HDPE is used. Also, PET is very common for small water bottles. PVC and polypropylene are used in blow molding operations.

Conclusion For Blow Molding Processes

Information here can be a good guide for the selection of proper blow molding process and blow molding process design for starting.

Mechanical Base does not accept any responsibility for any calculations done in calculators by users. A good engineer every time checks the results of calculations again and again.

Also, you can take a look at the other engineering calculators available in Mechanical Base!

Do not forget to leave your comments and questions below about the blow molding processes for plastics below.

Your precious feedbacks are very important to us.

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