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Comparison between Direct Blow and Stretch Blow

Aug. 26, 2022
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Beverage industries have two pressing concerns when it comes to bottle molding equipment, one being the constant increase in plastic material costs, so beverage enterprises are always thinking of ways to cut packaging costs to maximize profits, thus advanced bottle molding equipment is required to produce bottles of lighter weight. 

The second concern is that due to the constant ever-changing market, beverage industries have to adapt flexibly to the shortening lifecycles of beverages. 

Corresponding to this issue, the industries have to reduce the time for mold replacement to minimum to keep up with the increasingly fast product replacement in PET bottle production. These two pressing issues have posed a significant challenge for bottle molding equipment suppliers.

Generally, there are two types of PET bottle molding methods,
“Direct Blow Molding Method” and “Stretch Blow Molding Method”:

 

Comparison between Direct Blow and Stretch Blow

Automatic PET Bottle Injection Stretch Blow Molding Machine

 

Direct Blow

Molding Method: In this method, the molten preform is first injected by the Injection Stretch Blow Molding Machine, after which it is stretch blown in the hollow mold. As the formation of the preform and the stretch blow molding take place in the same machine, it is called the “One-Stage Method”. In addition, as the preform is stretch blown using the remaining heat of the preform before cooling, it is also known as the “Hot Preform Method”.
*The processing procedure is as follows: PET raw materials are dehumidified and dried. > The raw materials are melted and injected into the preform mold through the injection nozzle. > The molten PET materials are cooled to 120 degree Celsius in the preform mold. > The hot preform is then placed in the bottle mold to begin the Dual Axis Stretch Blow Molding.

 

Stretch Blow

Molding Method: In this method, the preform is first injected by the Injection Machine, after which the cooled preform is then heated up in the PET Stretch Blow Molding Machine and stretch blown in the hollow mold. As this method involves two processing steps in the Injection Machine and Stretch Blow Molding Machine, it is known as the “Two-Stage Method”. In addition, as the preform is re-heated and stretch blown after cooling, it is also known as the “Cold Preform Method”.
*The processing procedure is as follows: PET raw materials are dehumidified and dried. > The Injection Machine is used to inject the molten materials into the preform mold. > The PET preform formed is allowed to cool down to room temperature. > The preform is processed by a finishing machine before delivered to the Stretch Blow Molding Machine for heating and Dual Axis Stretch Blow Molding.
Note: The “Dual Axis Stretch Blow Molding” refers to the use of extendable rod for vertical extensions and high-pressure air for lateral extensions.

 

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