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By Jason Jiang, General Manager, Guangdong DMG Compressor Co., Ltd
In the PET blow molding process, compressed air serves as more than just a source of power—it is a critical medium that comes into direct contact with the product. Its quality dictates the final bottle's aesthetic clarity, hygienic safety, and structural integrity. Substandard compressed air doesn't just lower quality; it triggers a cascade of production failures and significant economic losses.
I. Common issues and root cause analysis
- Insufficient pressure (<2.0 MPa): When the blowing pressure is too low, the PET material fails to fully expand against the mold walls. This results in blurred bottle contours, inaccurate internal volumes, and poor formation of the base.
- Excessive pressure (>4.0 MPa): Overly high pressure can cause the preform to over-stretch or even burst, leading to material waste, increased energy consumption, and accelerated equipment wear.
- Particulate and oil contamination: Microscopic particles or oil mist can adhere to the inner walls of the preform, creating visible spots and compromising the visual appeal and transparency required for premium packaging.
- Excessive moisture content: Moisture is a primary cause of "blooming" or "whitening" (atomization) of the bottle wall and can facilitate microbial growth inside the container.
II. Stringent quantitative standards
To comply with the rigorous hygiene and safety mandates of the food and beverage industry, compressed air must meet the following classifications:
|
Parameter |
Technical Requirement |
ISO 8573.1 Class |
|
Pressure Range |
Stable between 2.3 MPa and 3.5 MPa. (Up to 4.0 MPa for complex designs) |
N/A |
|
Solid Particles |
Particle size ≤ 1 µm |
Class 2–3 |
|
Moisture (Dew Point) |
Pressure Dew Point (PDP) at 2°C to 10°C |
Class 4 |
|
Oil Content |
≤ 0.01 mg/m³ |
Class 1 |
III. Essential post-treatment system configuration
- Multi-stage filtration: A hierarchical filtering approach is mandatory: C-level→ T-level → A Level→ AA-level. This ensures residual oil content drops below 0.01 ppm.
2. Advanced drying systems: Refrigerated dryers must consistently achieve a dew point of 2°C to 10°C to effectively remove water vapor before reaching the blowing nozzles.
In conclusion, by treating compressed air as a "raw material" rather than just a utility, manufacturers can ensure a stable production environment and minimize scrap rates.