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In bottle production, air pressure is one of the most important factors that directly influences product quality, production stability, and overall efficiency of your Bottle Blowing Machine. The term air pressure refers to the force with which compressed air is delivered into the preform during the blow Molding process. This pressure must be sufficient to stretch and expand the heated preform uniformly against the mold walls to form a consistent bottle shape with proper wall thickness and surface finish. Understanding the required air pressure helps you choose the right compressor, optimize energy use, and reduce defects in your production line.
PET bottles are formed through a stretch-blow molding process. After the preform is heated to the correct temperature, compressed air is injected at high pressure into the parison. This force expands the plastic into the contours of the mold. The blowing step demands a robust and consistent high-pressure air source to ensure the preform fully conforms to mold geometry without sagging or uneven thickness. If the air pressure is too low, bottles may be under-formed or warped. If it is excessively high, energy waste and undue stress on machine components may result.
Air pressure requirements vary depending on bottle size, material, and machine type. Below is a general reference range that applies to many industrial systems:
| Pressure Unit | Typical Working Range | Description |
|---|---|---|
| bar | 25 – 40 bar | Common operating pressure range for blow molding units in PET bottle production. |
| MPa | 2.5 – 4.0 MPa | Equivalent to 25 – 40 bar, representing high-pressure compressed air required for effective blow molding. |
| psi | ~360 – 580 psi | Alternative measurement equivalent to bar/MPa ranges, used in some systems. |
These values reflect the pressure needed at the blow head to ensure complete expansion of the preform within the shortest cycle time possible. Machines designed for larger bottles or complex shapes typically demand pressures on the upper end of this range.
In many modern blow molding applications, the recommended minimum pressure to initiate and maintain proper bottle formation is around 1.0 MPa (10 bar), with maximum requirements reaching up to 3.0 MPa (30 bar) for routine operations. This variation depends on the bottle’s final use, required production speed, and resin specifications.
Proper pressure ensures the preform material stretches evenly. Variations in pressure during the blowing cycle may cause wall thickness inconsistencies — thin sections where pressure is insufficient, and material concentration where pressure spikes. Consistent air pressure produces bottles with uniform strength and aesthetics.
Stable high pressure shortens the blowing phase of the production cycle, allowing faster throughput and reducing bottlenecks. Conversely, an unstable or inadequate pressure supply can slow cycles, lower output, and raise defect rates.
A well-sized air compressor and distribution system that delivers proper pressure will reduce the wear on pneumatic components, valves, and regulators. Poor pressure profiles can cause frequent maintenance, longer machine downtime, and higher operational costs.
To meet these pressure requirements reliably, it’s essential to design an air supply system that includes:
High-capacity compressors suitable for continuous duty at the required pressure range.
Air dryers and filters to maintain air quality and reduce moisture or contaminants that impact pneumatic components.
Air tanks and receivers to stabilize pressure delivery during peak demand.
Ensuring these elements are matched to your machine’s capacity will help maintain stable blowing conditions and lower rejection rates.
When investing in a blow molding system, consider models that support optimized air pathways, reliable high-pressure delivery, and efficient energy use. BOHANG bottle blowing machines are known for their robust pneumatic design and stable production performance. These machines integrate efficient high-pressure air systems to support consistent output and reduced downtime, making them suitable for a wide range of PET bottle production requirements.
The air pressure required in a bottle blowing machine is a fundamental parameter that dictates production quality, speed, and efficiency. Industrial blow molding systems typically operate with compressed air in the range of 25 – 40 bar (2.5 – 4.0 MPa) to ensure smooth stretching and shaping of PET preforms. Accurate pressure management, combined with a well-designed compressor and delivery system, is the key to achieving high-quality bottles with minimal defects. Choosing a reliable machine like those from BOHANG supports stable air pressure delivery and enhances long-term production outcomes.
