How does a PET blowing machine work?

Of the many different machines used for manufacturing products, the blow molding machine is one of the most fascinating and useful. Known as extrusion blow molding, the simple explanation as to how this blow mold design works is that air is blown into a parison, shaping the hollow bottle as it inflates. However, there is much more to the plastic extrusion blow molding process.

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The Blow Molding Process

The extrusion blow molding process produces plastic bottles of various sizes and shapes. Millions of people use these bottles daily for soda, water, cleaning products, food, and more. With this process, low-pressure air of around 25 to 150 psi is forced into a parison. Multiple materials are used, including Low-Density Polypropylene (LDPE), High-Density Polyethylene (HDPE), Polyvinyl Chloride (PVC), Polyethylene Terephthalate (PET), and Polypropylene (PP).

• A parison with a conventional downward extrusion is inserted into the mold cavity until reaching the required length.
• The neck ending catches and holds while the bottom end pinches closed as the tube closes.
• A blow-pin

  is interested into the neck end of the hot parison while compressed air inflates it to the shape of the mold cavity. Simultaneously, the process creates the threaded opening.

• Once the mold sufficiently cools, it opens, ejecting the finished bottle along with excess plastic that was trimmed off from around the neck and bottom portions.

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The principle of the bottle blowing machine

The blowing process of the bottle blowing machine is divided into two parts.

1. Warm-up

An infrared high-temperature lamp irradiates the preform to heat and soften the preform. To maintain the shape of the bottle mouth, the preform mouth does not need to be heated, so a particular cooling device is required to cool it. 

2. Blow moulding

The preheated preform is placed in the blow mould, and the inside is inflated with high pressure to blow the preform into the required bottle. The automatic bottle blowing machine combines the two operations of bottle blowing through the operation of the manipulator, eliminating the need for the manual process of putting the preheated preform into the blowing mould. Significantly accelerate the rate of production. 

The process flow of the bottle blowing machine

The blow moulding machine process of the bottle blowing machine is a two-way stretching process. In this process, the PET chain is extended, oriented and arranged in two directions, which increases the mechanical properties of the bottle wall. It improves the tensile, tensile, and impact strength. It has good airtightness.

Although stretching helps to increase strength, it should not be overstretched. It is necessary to control the stretch-inflation ratio:

Do not exceed 3.5-4.2 in the radial direction and 2.8-3.1 in the axial direction. The wall thickness of the preform should not exceed 4.5mm.

Blowing is carried out between the glass transition temperature and the crystallization temperature, generally controlled between 90 and 120 degrees. The PET exhibits a highly elastic state in this interval and becomes a transparent bottle after rapid blow moulding and cooling, and setting.

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This temperature is determined by the length of the cooling time during the injection moulding process (such as the Aoki bottle blowing machine), so the relationship between the injection and blowing stations must connect.

The blowing process includes stretching-blowing once-blowing twice. The three actions are concise, but they must be well-coordinated, especially the first two steps to determine the overall distribution of the material and the blowing quality.

Therefore, it is necessary to adjust: stretching start timing, stretching speed, pre-blowing start and end timing, pre-blowing pressure, pre-blowing flow, etc.; if possible, it is better to control the overall temperature distribution of the preform, bottle The temperature gradient of the inner and outer walls of the blank. In the process of rapid blow moulding and cooling, induced stress is generated in the bottle wall. For gas-filled beverage bottles, it can resist internal pressure, which is beneficial. Still, hot-filled bottles must ensure that it is fully released above the glass transition temperature.

Common problems and solutions in the blowing process of the bottle blowing machine

1. What should I do with the bottom of the bottle blown by the bottle blowing machine?

The common factor for bottle accumulation is that the stretching rod is not adjusted in place. It is recommended that the stretching ratio between the preform and the bottle body is preferably 1:2.5 (excluding the mouth part), and at the same time adjust the heating temperature to extend the pre-blowing.

2. What should I do if the bottle&#;s mouth-blown by the bottle blowing machine is deformed?

Bottle mouth deformation Generally, during the heating process of the preform, the transmission chain drives the bottle base to transfer the temperature to the preform mouth. During the heating process, the temperature continues to accumulate, and the bottle mouth bulges and deforms. It only needs to increase the air-cooling or water-cooling of the bottle mouth. If the customer&#;s conditions permit, you can refer to the imported machine to install central air-conditioning in the production workshop to keep the ambient temperature of the workshop at an average temperature.

3. How can the bottle-blowing machine be operated, and which accessories should be checked?

As long as the equipment is controlled strictly following the method in the instruction manual and the performance of each safety door is checked regularly, the equipment as a whole is safe. However, the most significant hidden danger of the equipment is mainly on the seals of the water jacket and air jacket. For example, the water and air jacket are damaged, and the maintenance works are more troublesome.

4. How much chiller is needed for the carbonated beverage bottle blowing machine to blow the bottle?

The chiller for the carbonated bottle is about five times larger than the chiller for the water bottle. A simpler algorithm can be calculated at bottles/hp; for example, bottles/hour can equip with a 30-hp chiller. To ensure the stress requirements of the carbonate bottle bottom, the cooling time is generally 1.2 seconds, and the bottom mould temperature is 11 degrees. The number of lamp zones in the heating furnace can refer to the configuration of the hot filling machine, and the adequate heating time of the preform should be no less than 33 seconds.

5. What is the highest temperature resistance of the non-crystalline bottle mouth of the hot-filling bottle blowing machine? How many grams of preforms are needed?

At present, the preform mouths used in the production of hot-filled bottles in the industry are generally divided into crystalline mouths and non-crystalline mouths, and non-crystalline mouths are divided into 28 months and 38 months.

As far as the bottle mouth is concerned, the crystalline mouth can withstand 100 degrees without deformation, but the upper limit of heat resistance of the non-crystal mouth is only 92 degrees.

The preform and grammage used for blowing the medium-temperature bottle are best selected according to the requirements of hot filling. Suppose it is designed according to the single-mode bottles/hour. In that case, the single-mode cycle is 2.1 seconds, of which 1/4 of the time is the time to unlock the mould, and the remaining 3/4 of the time is the processing time, minus the balance; sealing, stretching, and pre-blowing is 0.2 seconds. The time for high-pressure forming and pressure-holding crystallization is only 1 second, the time for cold blowing and setting is 0.3 seconds, and the time for closing and closing is 0.1 seconds.

The time allocation mentioned here is only a reference value, and the specific time should be adjusted and guaranteed in real-time through the control panel during production.

Strictly speaking, compressed air must be processed by a freeze dryer before it can be used for high blowing and cold blowing. Because the pipeline between the air compressor and the bottle-blowing machine is long, to avoid the pipeline from being exposed to the sun, The compressed air pipeline used for cold blowing and shaping must be covered with thermal insulation cotton to ensure that the temperature of the air source is not affected.

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Summary: The above are the most common problems in the use of the bottle blowing machine. The bottle blowing machine causes different bottle problems during the blowing process. On the one hand, it is related to the structure of the bottle blowing machine itself, and on the other hand, it is the problem of debugging and use. , Most of the faults are caused by improper use of human factors. When you encounter problems, don&#;t worry; carefully analyze the problematic points of the blow moulding machine fault, carry out troubleshooting one by one or consult the sales service engineer of the blow moulding machine manufacturer.

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