In the modern packaging industry, PET (polyethylene terephthalate) materials have become the preferred packaging material for beverage, food, cosmetics and other industries due to their excellent transparency, light weight and recyclability. As the core equipment for producing PET containers, the working principle of PET blow molding machine is directly related to product quality and production efficiency. This article will analyze in detail the three key steps of PET blow molding machine from preform to bottle, to help readers fully understand this important production process.
Step 1: Preform injection molding
Raw material pretreatment
The PET blowing process begins with high-quality raw material preparation. First, PET granules need to undergo strict drying treatment, usually at a temperature of 150-170℃ for 4-6 hours, and the water content is controlled below 0.005%. This step is very important because trace moisture will cause defects such as bubbles and atomization in the final product.
Injection molding process
The dried PET granules are fed into the injection molding machine and melted at a high temperature of 260-285℃. The molten PET material is injected into the precision-designed preform mold under a high pressure of 60-100MPa. The mold temperature is usually controlled at 10-30℃ to ensure that the preform can be quickly cooled and formed.
Preform quality control
The molded preform needs to meet strict size and appearance standards. Key parameters include:
Weight deviation: ±0.1g
Wall thickness uniformity: deviation does not exceed 5%
Appearance: no bubbles, no impurities, no scratches
Modern injection molding machines are usually equipped with visual inspection systems that can automatically remove unqualified preforms to ensure the quality of subsequent processes.
Step 2: Preform heating and temperature adjustment
Step 1: Preform injection molding
Raw material pretreatment
The PET blowing process begins with high-quality raw material preparation. First, PET granules need to undergo strict drying treatment, usually at a temperature of 150-170℃ for 4-6 hours, and the water content is controlled below 0.005%. This step is very important because trace moisture will cause defects such as bubbles and atomization in the final product.
Injection molding process
The dried PET granules are fed into the injection molding machine and melted at a high temperature of 260-285℃. The molten PET material is injected into the precision-designed preform mold under a high pressure of 60-100MPa. The mold temperature is usually controlled at 10-30℃ to ensure that the preform can be quickly cooled and formed.
Preform quality control
The molded preform needs to meet strict size and appearance standards. Key parameters include:
Weight deviation: ±0.1g
Wall thickness uniformity: deviation does not exceed 5%
Appearance: no bubbles, no impurities, no scratches
Modern injection molding machines are usually equipped with visual inspection systems that can automatically remove unqualified preforms to ensure the quality of subsequent processes.
Step 2: Preform heating and temperature adjustment
Infrared heating principle
The preform needs to be precisely heated before entering the blow molding process. The heating furnace usually uses infrared heating to heat the preform in sections through 8-12 independent temperature zones. The temperature of each temperature zone can be controlled independently to achieve the best temperature distribution in each part of the preform.
Temperature control technology
Typical heating temperature curve is as follows:
Bottle mouth: 100-110℃ (maintain rigidity)
Bottle body: 110-120℃ (optimal blow molding temperature)
Bottle bottom: 105-115℃ (ensure strength)
Modern heating system adopts PID closed-loop control, and temperature fluctuation can be controlled within ±1℃ to ensure heating uniformity.
Heating process optimization
To improve energy efficiency and production speed, the advanced heating system uses the following technologies:
Heat recovery device: Use the heat of exhaust gas to preheat the newly entered preform
Rotary heating: Ensure that the preform is heated evenly
Adaptive control: Automatically adjust the heating parameters according to the ambient temperature
Step 3: Stretch blow molding
Biaxial stretching process
The heated preform is transferred to the blow molding mold for biaxial stretch blow molding:
Axial stretching: The metal stretching rod stretches the preform longitudinally at a speed of 0.8-1.2m/s
Radial blow molding: High-pressure air of 25-40Bar is introduced at the same time to make the preform expand radially to fit the mold
Pressure control technology
The blow molding process is usually divided into three stages:
Pre-blowing stage: Low pressure (about 5Bar) for initial molding
Main blowing stage: High pressure (25-40Bar) for complete molding
Pressure holding stage: Maintain pressure to ensure shaping
Mold cooling system
Blow molding molds are equipped with an efficient cooling system, usually using 5-15℃ cooling water circulation to ensure that the bottle body is quickly cooled and shaped. The cooling time is usually controlled at 2-4 seconds, which directly affects the production cycle and product quality.
Quality control and innovative technology
1. Online detection system
Modern PET blow molding machines are equipped with a variety of detection devices:
Visual inspection: Check bottle mouth defects, black spots, etc.
Wall thickness detection: Ultrasonic or X-ray measurement
Leak test: Air pressure detection of sealing
2. Latest technological developments
Energy-saving technology: servo motor drive saves 40-60% energy compared to traditional hydraulic systems
Intelligent control: Automatic optimization of process parameters based on AI
Lightweight: Optimize bottle design through finite element analysis to reduce material consumption
Conclusion
The three key steps of PET blow molding machines from preform to bottle - injection molding, heating and temperature adjustment, stretch blow molding, each link requires precise control and advanced technical support. As the packaging industry continues to improve its requirements for production efficiency, energy conservation and environmental protection, PET bottle blowing technology is also continuing to innovate. Understanding these basic principles will help manufacturers optimize processes, improve product quality, and gain an advantage in the fierce market competition.
For readers who want to learn more about PET bottle blowing technology, we recommend:
Visit the equipment production site to intuitively understand the work process
Participate in professional technical training to master process optimization methods
Pay attention to industry exhibitions to learn about the latest technological developments
For more technical information or equipment consultation, please feel free to contact us.
Email：sales@longthinmachinery.com