Single Vs. Two Stage Blow Molding Machine

Single Vs. Two Stage Blow Molding Machine

The hype about the blow molding machine is worth it; the precision that is achieved through the use of this machine in each and every part of any shape, be it complex or simple. The blow molding machine is used to carry out the blow molding of hollow parts. There are a total of three methods for manufacturing hollow parts by blow molding. All these methods take on the blow molding process differently.

Therefore, all these methods use different blow molding machines to execute the specific blow molding processes correctly. Whatever machine is used with whichever process, as far as the single and double stage blow molding machine is concerned, it is used for injection stretch blow molding process. The three types of blow molding methods are:

•Injection stretch blow molding

•Injection blow molding

•Extrusion blow molding

What Is Injection Stretch Blow Molding?

It is a blow molding process in which specifically PET bottles that are polyethylene terephthalate or, you can say, plastic bottles are manufactured. This process involves single- and double-stage blow molding using single and double-stage blow molding machines. Let’s discuss the two processes to understand their differences better and choose the right method that suits your needs. 

•Single Stage Injection Stretch Blow Molding Process

In this process, everything is done in one go, all in one go. The raw material is melted and injected into the machine, where a preform is formed. This preform is then cooled and sent to a stretch blow molding station, which is reheated and blown into its final shape. All this is done in one go on the same machine. Therefore, this method is called the single-stage injection stretch blow molding process. There are some pros and cons of going with this method; let us be aware of them all so that you can choose accordingly.


The pros of going with this method are that it is suitable for mass production of PET bottles in no time. It is very cost-effective as everything is being done by one machine only. It is a very compact, flexible, and convenient method for manufacturing PET bottles. The technical advantages of opting for this method are that the transferring is optimal, bottles are blemish-free, produces control over perform production, and thread starts to align.


This method has inevitable setbacks, like its long cycles and changeover times. There are certain restrictions in methods like in the bottle design. The wall distribution in this method is often uneven. 

•Double Stage Injection Stretch Blow Molding Process

This method is different from the single-stage method in this way that it does the same thing but in two stages with the use of two different machines. In its first stage, an injection blow molding machine is used in which the melted raw material is poured, and a preform is obtained. This is where the first stage ends and the second stage begins.

Once the preform cools, it goes into that stretch blow molding machine, where it is reheated and stretched to its final shape. Although this process is almost the same as the single-stage process, it has some advantages that the single-stage method cannot provide.


The first most wanted advantage is a faster cycle and changeover times; this process is twofold faster than the single-stage method. Hence, it helps to mass-produce plastic parts in much less time than the single-stage method. There are no restrictions when it comes to designing your bottle; you can design it in any way by using this method, unlike the single-stage method. The wall distribution that is achieved in this process is always even. One can even sell the perform without having to process them any further. 


It requires a lot of floor space to carry out this process, which is a disadvantage often when one doesn’t have enough space. The bottles that come out of the machine might have scratches on them. Its capital is very high to maintain, and there are chances of potential damage to the preform in this method. 

Final Word

This is what the single and double-stage methods of blow molding are; when choosing one of the two methods, you need to make a wise decision. Both the methods have their own advantages and disadvantages. It is evident that where one fails, the other succeeds. Therefore, consider all these aspects and choose one method best suits your task. Only then will you be able to achieve what you have in your mind exactly as it is with proper wall distribution, threads, and more.