Because there are several kinds of HDPE blow molding machine used in the production of PET (polyethylene terephthalate) bottles, producers must choose the best injection stretch blow molding technique for making plastic bottles.
The benefits of selecting the appropriate approach include boosting output, cutting expenses, and limiting the number of cycles needed to create these materials.
However, you must choose between single-stage and two-stage molding procedures due to their notable variances.
HDPE Blow Molding Machines: What Are They?
One piece of machinery used in the production of glass and plastic bottles is the blow molding machine. It makes use of a number of techniques to create hollow plastic sections before joining them to create a bottle.
Three main procedures are used to try to make this possible:
- Stretch blow molding by injection
- Blow molding by injection
- Blow molding by extrusion
Although a bottle can be produced using any of these methods, PET or plastic bottles must be made using the injection stretch blow molding technique.
The single-stage blow molding process: what is it?
Because preforms are made, stretched, and blown on the same machine before cooling, a single-stage method gets its name.
Thus, it is also possible to say that single-stage PET blow molding machines use a direct process.
The fact that the blow molding station and injection molding system are integrated into a single machine accounts for this degree of versatility.
The HDPE blow molding machine can also be a 4-station system or a 3-station system.
Injection, stretch blow, and expulsion are the three steps of a three-station single-stage machine. Additionally, it employs latent heat, which eliminates the need for reheating and lowers tooling heat by 25%.
In contrast, the 4-station has an extra warming stage in addition to these three stages.
Procedures Used in the One-Stage Approach
The steps listed below are used to convert the raw components into a bottle using the single-stage method:
- Drying and dehumidifying PET materials
- The raw components are melted and then injected via the injection nozzle into the preform mold.
- The molten material in the preform mold is cooled to 120 °C.
- To start the stretch molding process, move the heated preform mold to a bottle mold.
A two-stage blow molding process: what is it?
Two machines are utilized in the two-stage injection stretch blow molding process. These are the stretch blow molding machine and the injection molding system.
Here, the plastic is sent to the second machine after being formed into a completely cooled preform in the first machine.
The preform can be sold to a third party before it is blown using the second machine, and it often includes the bottle's thread and neck.
The latter receives them, unscrambles them, reheats them with infrared radiation, and conditions them before molding.
The "cool preform method" gets its name from the necessity of cooling the preform before stretching and reheating it.
Procedures Used in the Two-Stage Approach
- Drying and dehumidifying PET materials
- Melted raw materials are injected by the injection machine into the preform mold.
- Melted PET is cooled to room temperature.
- Processing of preform with a finishing machine
- Preform transfer to stretch blow molding machines that are reheated
- Using metal blow molds to force high-pressure air into bottles
Which Is Better, a Single-Stage or Two-Stage Process?
It is clear from comparing the single-stage and two-stage HDPE blow molding machine processes that when one fails, the other compensates.
Because of this, it is very important to be very careful before choosing one.
Single-Stage Blow Molding
Consider the single-stage approach, where the inability to check the preform before molding in the direct step must be taken into account.
Operators must be well-versed in injection and blow molding to identify any flaws that may have occurred during the preform's formation.
Two-Stage Blow Molding
Many people share this opinion of the cool preform process, which has the drawback of making bottles more prone to scratches. The latter is due to the necessity of aligning, storing, and moving the preform from one machine to another.
The preform falling onto the conveyor belt before it enters the storage containers is one example of this. Additionally, the HDPE blow molding machine may contain preforms, which might cause imperfections on the bottle.
It is important to remember that these scratches may not be very obvious because some businesses go to great lengths to hide them by labeling their bottles.
However, scratches can be the least concerning issue because these preforms might not be the correct size if they are bought from a third party or dealer.
As a result, issues like determining the bottle's appropriate neck and weight may come up.
Conclusion
After understanding the advantages and disadvantages of single-stage and two-stage HDPE blow molding machines, your decision will be based on your priorities.
Do you desire a bottle with no flaws, a fixed thread, an exact oblong form, and a reasonable initial cost? In that case, the single-thread option is preferable.
Because of its high scalability per hour, the two-stage technique is an alternative if you're looking for something more cost-effective, efficient, and technically straightforward.