Method for producing large-diameter plastic bottle

Most of the PET bottles (soft drinks and water) that we often encounter on the shelves of supermarkets have a diameter of 28-33 mm, and the juice bottle diameter is generally 43 mm. Bottles larger than 43 mm are considered wide mouth containers. Wide-mouth plastic packaging containers are more humanized to a certain extent, so they have been widely used in the packaging market in recent years.

The question faced by manufacturers is whether they can produce wide-mouth containers without using too much input on existing equipment.

The increase in the size of the plastic bottle's caliber causes the multiple parameters in the process to change. Whether it is a one-step injection blow molding process or a two-step injection-blow process, when a conventional mold is used to produce plastic bottles on an injection molding machine using a new mold, a few new molds are suitable for existing machine structures. In small-caliber products, large-diameter products have to use larger machines to obtain the same number of preformed parisons. (Most machines can produce a maximum diameter of 30 mm).

Figure 1: In the traditional process, the preform's caliber determines the caliber of the final product

Large machines are relatively slow to operate, which adds cycle time to processing. Wide-mouth plastic bottles are usually preferred for one-step production because the preforms are tightly held together with the caliber section. When the injection mold clamping force and blow molding equipment are large enough, the wide mouth container is relatively easy to process. Disadvantages Higher volume machines become very large and difficult to operate, while no standard machine can reach a production capacity of 30 million containers/year.

The two-step processing situation, which is based on higher output, is even more difficult.

Many wide-mouth preforms use a large taper from the neck to the bottom. This tends to create undesirable "set-up" behavior in which the preform bases nest together, making it more difficult to separate preforms into reheated blow molding equipment.

Another problem with the two-step method of starting the heating process is that the infrared heater in the caliber section needs to be protected from the blow molding equipment, because once it approaches or exceeds the glass transition temperature, the caliber portion itself will be deformed. The usual measure of protection is to place the shield along the edges of the preform just above the bottleneck support ring (also known as the clamp ring). When the bottleneck size increases, the bottleneck that can be protected by the shielding bar is smaller. In addition, the circumferential pressure of the bottleneck in the blow mold increases with the quadratic increase of the diameter, so that the 56 mm bottleneck has to withstand 4 times the circumferential pressure of the 28 mm bottleneck. This has prompted equipment manufacturers to develop new large-bottleneck methods that protect and cool the rotation in front of infrared heaters. Needless to say, they increase the cost of processing and increase the difficulty. In addition, the typical 50 mm roll gap between the pivots of the two blow molding equipment does not appear to be large enough for any size greater than 43 mm, requiring the use of special and more expensive equipment.

Figure 2: Infrared heating process is a constraint on different caliber preforms

All in all, on a stretch-blow moulding plant for secondary processing, a bottleneck of more than 43 mm is of course possible, but it is expensive and complicated. Wide-mouth containers are expensive to produce.
The blow-blown process can solve these problems and add some of its own elements.

The main feature of this technique is that the large diameter is produced during the blow molding process rather than during the injection process. Since preformed preforms must be sealed by the environment and pressed against a rotating rod, the bottleneck can only be formed by adding a dome structure that is larger than the bottleneck. They are cut by special dome cutting machines in the auxiliary process.

In this process of producing large calibers, a large number of flashes that need to be reprocessed are created. Moreover, when these comminuted sheets are conveyed from the drying apparatus to the feed port of the mechanical extruder, more than 20% of the amount tends to adhere due to static electricity and other reasons. Selling these crushed regrinds is not an economical method. Two solutions can be considered for this problem. Vibrating equipment can be used to directly add vibration to the crushed material, thus avoiding overhead and adhesion. Another solution is to recycle pellets and then add them proportionally to increase the cost.

Figure 3: Replacing different molds is a test of the original injection molding equipment

There are many aspects to be considered in the blow-punching process:

For preform injection molding, longer dimensions are required than conventional molds. Can it be produced directly from existing preformed preforms? When the large-diameter part has no complicated design and is very easy to produce, can it make the processing cost even lower. How to heat larger preformed preforms in standard reheat blow molding equipment. How to make the standard blow molding process not complicated. How to save resin consumption through design.

In short, the blow-and-flare flaring process can save a lot of dollars, which gives the plastic bottle manufacturer an extremely wide appeal.

Figure 4: The picture shows the gradual evolution from the prefabricated preform (pictured left) to the blown container and completed container. The front is two flash pieces, the right is the final packaged product

Of course, there are some issues that need to be carefully considered before you plan to design a blow-and-flare flaring project.

Large-scale processing companies use this process to produce multi-layer containers, only to find out the edge of the cut bottleneck after cutting. These could have been avoided.

Scrap and debris from the cutting process are often scattered within the container. A vault cutting machine is a difficult technique that plant employees may need to learn. High-speed equipment is more expensive and trimming is too sharp to allow consumers to drink directly through them

If manufacturers expect to benefit from this technology, they will need their experienced engineers to communicate with all parties involved in the value chain, so that the blow-and-flare flaring process can be applied effectively while achieving the best possible cost savings. .

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