Let you learn more about screw air compressor

A Screw Air Compressor is a positive displacement air compressor that continuously compresses air using a pair of intermeshing helical rotors (male and female screws). It is the most popular compressed air supply device in modern industry. Its core function is to convert electrical energy into high-pressure, clean, and stable compressed air, providing energy support for various equipment and processes.

I. Basic Structure of a Screw Air Compressor

A Screw Air Compressor consists of the following core components:

1. Main Unit (Head)

- Male and Female Rotors: The core compression element, a pair of precisely meshed helical rotors (typically a male rotor with 4-6 teeth and a female rotor with 6-8 teeth).

- Casing: The sealed cavity surrounding the rotors, forming the compression chamber.

- Bearing System: Supports the rotors' high-speed rotation.

2. Drive System

- Electric Motor: Provides power (typically 7.5kW to 500kW).

- Transmission: Coupling or belt drive.

3. Lubrication and Cooling System

- Lubricating Oil: Serves as a seal, coolant, and lubricant.

- Oil Filter/Oil Separator: Filters impurities and separates oil from compressed air (oil-air separation efficiency >99.9%).

- Cooler: Air or water cooling to reduce oil and air temperatures.

4. Control System

- PLC/Microcomputer Controller: Monitors pressure, temperature, and operating status.

- Sensors: Pressure sensor, temperature sensor, etc.

5. Auxiliary Systems

- Inlet Valve: Regulates air intake.

- Minimum Pressure Valve: Maintains minimum system pressure (usually ≥4 bar).

- Safety Valve: Overpressure protection.

II. Operating Principle of a Screw Air Compressor (Taking an Oil-Injected Screw Compressor as an Example)

1. Intake Phase

- Air passes through the filter and enters the intake valve, filling the volume between the rotor teeth.

2. Compression Phase

- The male and female rotors mesh and rotate, gradually reducing the volume between the teeth and compressing the air.

- Oil injection: Lubricating oil is sprayed into the compression chamber to seal the gap, absorb heat, and lubricate the rotor.

3. Exhaust stage

After the compressed air and oil mixture reaches the set pressure, it enters the oil-gas separation barrel through the exhaust port.

4. Oil-gas separation

The mixed gas is centrifugally separated in the separation barrel, and then the remaining oil mist is filtered out by the oil separator to output clean compressed air.

- The lubricating oil is recycled after cooling and filtering.

> Oil-free screw: Synchronous gear transmission is used to avoid rotor contact, and no oil injection is required, but the structure is more complex and the cost is higher.

III. Core advantages

(1) Efficient and continuous operation: 24/7 continuous operation, no reciprocating parts, low vibration, and long life (usually >60,000 hours).

(2) Smooth output: The compressed air flow is pulsating, and the pressure fluctuation is <±0.1bar, suitable for precision equipment.

(3) Low maintenance cost: There are few moving parts, and maintenance is concentrated on oil/filter replacement (every 2000-8000 hours), with a low failure rate.

(4) High energy efficiency ratio: The variable frequency model can adjust the speed to match the load, saving 20%~40% energy compared to the piston machine.

(5) Compact structure: The volume is 30%~50% smaller than the piston machine under the same air volume, saving space.

(6) Low noise: The noise value is 70~85dB(A), which is lower than the piston machine (＞90dB(A)), suitable for indoor installation.

IV. Application industries and specific functions

1. Manufacturing

- Function:

- Drive pneumatic tools (tightening guns, grinders), cylinders of automated production lines, and mold opening and closing of injection molding machines.

- Provide clean air for product purging and parts drying (such as drying automobile parts after cleaning).

- Case: The welding workshop of an automobile factory uses 0.7MPa compressed air to drive the robot welding gun.

2. Chemical/Pharmaceutical

- Function:

- Transport powder (such as PVC particles) and stir reactors.

- Oil-free models: Provide sterile air for fermentation tanks or for tablet coating spraying.

- Key requirement: ISO 8573-1 Class 0 oil-free certification to prevent product contamination.

3. Food and Beverage

- Applications:

- Bottle drying in fillers and positioning in labelers.

- Pneumatic control of packaging equipment (such as can capping).

- Special design: Food-grade lubricant (NSF H1 certified), stainless steel piping for corrosion protection.

4. Textile Industry

- Applications:

- Driving air-jet looms (compressed air weft insertion, speeds > 1000 m/min).

- Air supply for yarn humidification and finishing equipment.

- Required features: High flow rate (1.5-2 m³/min per loom) and stable pressure.

5. Energy/Mining

- Applications:

- Power source for mining drills (replacing hydraulic systems). - Gas turbine startup and power plant instrumentation control gas source.

- Special models: Explosion-proof design (e.g., Screw Compressors for coal mines comply with ATEX standards).

6. Medical Industry

- Applications:

- Hospital centralized air supply systems (operating rooms, ICU ventilators).

- Dental equipment drives (drills, saliva extractors).

- Core requirements: 100% oil-free, silent (<60dB), and continuous, reliable air supply.

7. Construction Engineering

- Applications:

- Drive shield machine hydraulic systems and shotcrete equipment.

- Bridge prestressed grouting.

- Features: Mobile diesel-driven Screw Compressor (displacement 10-30 m³/min), suitable for field operations.

V. Selection Considerations

1. Gas Volume Matching: Select based on actual peak gas volume multiplied by 1.2 to avoid "a large horse pulling a small cart." 2. Pressure Requirement: Common pressures range from 0.7 to 1.0 MPa; ultra-high pressures require specialized models (>1.6 MPa).

3. Air Quality: Select the dryer (refrigerated/adsorption) and filter grade based on the process.

4. Variable Frequency Drive vs. Power Frequency Drive: Choose variable frequency drive for fluctuating loads (saving 20%-35%), and power frequency drive for stable loads.

Screw Air Compressors, with their high efficiency, stability, and long life, have become core power equipment in the industrial sector. Their applications range from small dental clinics to 10,000-ton shipbuilding operations, encompassing virtually every industry requiring compressed air. Proper selection and maintenance can significantly reduce a company's energy costs (compressed air accounts for 10%-30% of industrial electricity consumption), making them the indispensable "power heart" of the Industry 4.0 era.