For turning soft plastic into a molded cavity, a manufacturing process known as stretch blow molding is used. This process, which is also known as plastic blow molding, produces a broad range of plastic bottles. Extrusion blow molding products include hollow bottles used for shampoo, creams, pop, milk, water, and so on.
Blow Molding Process Step by Step
Using the appropriate blow molding machine, a tube of molten plastic is created, followed by it being inflated into the shape required by the customer. With the injection stretch blow molding process, a part with a biaxial molecular alignment is produced. In this case, a preform is elongated via a mechanical process in a mold. Next, the preform is significantly expanded during the blowing process. Compared to the other blow molding methods, the stretch process uses a lower temperature to achieve the required molecular orientation. This makes it somewhat more challenging.
Once the molecular orientation is achieved, the material is extremely strong. A huge advantage of the injection stretch blow molding process for plastic bottles is that less material is required compared to other molding processes. Although various types of bottles are produced with this method, it is most commonly used for manufacturing PET bottles.
Because these bottles are made of polyethylene terephthalate, the material can be recycled for reuse. This dramatically reduces the amount of waste that goes into landfills and helps with other environmental issues.
The stretch blow molding process can be either single or double stage, each with distinct advantages.
Single Stage (injection stretch blow molding)
- Plastic bottles are virtually blemish free.
- No transfer ring is required.
- Good conditioning for oblong bottles
- Good control over preform production
- Flexible and compact
- Thread start can be selected according to the shape of the bottle.
Even with these advantages, you have to consider that with single stage, cycle times are generally longer, as are changeover times. In addition, there is some risk of uneven wall distribution and a greater learning curve for operators.
Two Stage (reheat stretch blow molding)
- Extremely fast cycle times and changeovers
- Scalable from 1,000 to 72,000 bottles per hour
- Great wall distribution when manufacturing round bottles
- Good flexibility
- Process can be stopped as needed.
- Lower gram weights are possible for round bottles for the most part.
The primary drawback is that the preforms can be damaged when tumbling onto the conveyor belt, going into a storage container, or dumped into hoppers.
When it comes to blow molding machine suppliers, Pet All Manufacturing ranks among the best. You can visit our website to learn more about our company or contact us by phone.