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Between single and two-stage PET blow molding machine, which one is better?

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Between single and two-stage PET blow molding machine, which one is better?


The use of PET molding machine requires you to follow either the injection or extrusion molding process for realization of quality bottles. These processes usually entail molding of the preform and stretching it before it is finally blown into bottles. However, these processes can either be integrated into one single stage or two-stage process. Both of these processes have pros and cons. As a buyer, it is usually good to understand each operation of the machine before you get one for your applications.

The advantages of the single-stage process are:

  •    It produces blemish-free PET bottles
  •    There is no need of transferring the ring
  •    You have control over the preform production
  •    There is the possibility of good conditioning
  •    You can choose the thread start to coincide with the shape of the bottle
  •    It is compact and flexible


  •    It takes time to complete one cycle
  •    Changeover time is long
  •    Wall distribution is normally uneven
  •    When thermal-gated runners are used, there is the production of low-quality products
  •    You have to run these machines all the time to avoid scrap percentage getting high.
  •    For operators, it has a longer learning curve
  •    There is an inefficient blow station

The latter disadvantage is a result of the injection station getting precedence over the long cycle time.

Advantages of two-stage

  •    More production of bottles in every hour, about 1000 bottles to 72000 bottles every hour.
  •    The is faster cycle times compared to that of single-stage
  •    The preform can be made anywhere hence flexible
  •    For round bottles, uniform wall distribution is achieved
  •    The process can be stopped anytime


  •    In two-stage, preforms can get damaged when they tumble into a storage container or a conveyor belt or dumped in the hoppers.
  •    When high ratios are used, scratches and nicks can be developed.
  •    When low-cavitation machines such as indexing machines are used, heat can be different in each preform. Sometimes about 4 or 6 preforms are loaded and blown.
  •    Sometimes there is the difference in temperatures between the cooling air and the lamp output.

In modern society, about 80% of the PET bottles are produced using the two-stage processes. The decisions of buying these tools are determined by the price and the application. To make the right decision, you have to be familiar with the particulars of your application and whether there are in line with the molding machine.

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