PET blow-moulded bottles are divided into two types: pressure bottles, which are filled with carbonated beverages, and non-pressure bottles, which are filled with water, tea, edible oil, and other liquids.
The tea beverage bottle is either a modified PET bottle blended with polyethylene naphthalate (PEN) or a PET/thermoplastic polyacrylate composite bottle. It is classified as a hot bottle and can withstand temperatures of up to 85°C.
Heat resistance is not required for water bottles because they are cold bottles.
The hot bottle is similar to the cold bottle in terms of forming.
Blow Mould Equipment
At present, the manufacturers of PET automatic blow molding machines (blow moulder) mainly import from France SIDEL, Germany KRONES, and the domestic ones include Shenzhen iBottling.
Although the manufacturers differ, the basic principles of their equipment are the same, and they typically consist of five components: a preform supply system, a heating system, a blowing system, a control system, and auxiliary equipment.
Blow moulding process
PET bottle blow moulding process.
Preforms, heating, pre-blowing, moulds, and the production environment are all critical factors in the blow moulder’s PET bottle blow moulding process.
The PET chip is first injection moulded into a preform when making a blow-moulded bottle. It calls for low molecular weight and viscosity (molecular weight 31000-50000, intrinsic viscosity 0.78-0.85cm3/g) and a low proportion of secondary recycled materials (less than 5%).
According to China’s National Food Safety Law, secondary recycled materials are not allowed for food and medical packaging.
Before being used, the injection-moulded preform must be stored for at least 24 hours.
Preforms that have not been used after heating must be stored for at least 48 hours before being reheated.
Preforms should not be kept for longer than six months.
The advantages and disadvantages of preforms are primarily determined by the advantages and disadvantages of PET materials.
Materials that are simple to inflate and shape should be chosen, as should a good preform moulding process.
Experiments show that the imported raw materials are more accessible to blow-moulded than domestically produced preforms made of PET materials with the same viscosity;
And the same batch of preforms, but with a different production date and possibly a different blow moulding process.
The blow moulding process’ difficulty is determined by the preform’s quality.
Pure, transparent, free of impurities, no different colours, and suitable for the length of the spot and surrounding spots are the requirements for the preform.
A heating oven completes the preform heating process.The temperature is manually set and automatically adjusted.
The far-infrared lamp emits far-infrared rays to radiate and heat the preform in the oven.
The fan at the bottom of the oven circulates air to maintain a consistent temperature in the oven.
As the preform moves forward in the oven, it rotates, evenly heating the preform wall.
The lamp tube is arranged in an “X” shape in the oven from top to bottom, with more at ends and less in the middle.
The number of lamps turned on, the overall temperature setting, the oven’s power, and the heating ratio of each section all affect the oven’s heat.
The lamp tube opening should be adjusted in tandem with the pre-blowing.
The height, cooling plate, and other aspects of the oven must all be adjusted to function correctly.
If the adjustment is improper, defects such as swelling of the bottleneck (the bottle’s neck becoming larger) and hard bottleneck (the neck material cannot be pulled apart) are likely to occur during blow moulding.
Pre-blowing is a crucial step in the two-step blowing method.
It means that during the blow moulding process, the pre-blowing is started while the stretching rod is lowered so that the preform will take shape.
Three essential process variables are the pre-blowing position, pre-blowing pressure, and blowing flow.
The difficulty of the blow moulding process and the bottle’s performance are determined by the shape of the pre-blow bottle.
The pre-blowing bottle’s standard shape is a spindle shape, while the abnormal shapes are a bell and a handle shape.
Improper local heating, insufficient pre-blowing pressure, and insufficient blowing airflow are among the abnormal shape causes. The pre-blowing bottle size is determined by the pre-blowing pressure and position.
The size and shape of all pre-blowing bottles in the entire equipment should be maintained during production. If there are any discrepancies, specific reasons must be discovered. The heating or pre-blowing process can be adjusted depending on the pre-blowing situation.
The size of the pre-blowing pressure varies depending on the bottle specifications and the equipment’s capabilities. The capacity is generally large, and the pre-blowing pressure is small; the equipment’s production capacity is high, and the pre-blowing pressure is also high.
Auxiliary machine and mould
Auxiliary equipment primarily refers to keeping the mold at a constant temperature.
The mould’s constant temperature is crucial in maintaining the product’s stability.
The temperature of the bottle body is typically high, while the temperature of the bottle bottom is generally low.
Because the degree of molecular orientation in cold bottles is determined by the cooling effect at the bottom, it’s best to keep the temperature between 5-8°C.
The temperature at the bottom of the thermo flask is much higher.
The quality of the production environment has a more significant impact on process adjustment, and maintaining constant temperature conditions can keep the process and the product stable.
The best conditions for PET bottle blow molding are room temperature and low humidity.
The pressure bottle must pass both the stress test and the pressure test simultaneously.
The stress test is internal quality control to prevent molecular chain degradation, cracking, and leakage. The PET bottle is filled with a beverage and the bottom of the bottle comes into contact with the lubricant (alkaline).
The pressure test is quality control to prevent the bottle from bursting after being filled with specific gas pressure.
The thickness of the centre point must be controlled within a specific range to meet these two requirements.
The withstand voltage is generally poor; the centre point is thin, the stress test is better, and the centre point is thin.
The stress test is generally poor, the centre point is thick, the withstand voltage test is better, and the withstand voltage test is better.
The accumulation of materials in the transition zone around the centre point has a lot to do with the stress test results, which should be adjusted based on actual experience.
The PET bottle blowing process is adjusted for the appropriate material.
If the material is poor, the process’ requirements are incredibly stringent, and blowing out qualified bottles is even more difficult.
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