Definition
A screw oil-free air compressor is a positive displacement compressor whose core working components consist of a pair of yin and yang rotors that engage with each other. During operation, the equipment does not need to add any lubricating oil to the compression chamber, resulting in oil-free compressed air. This type of compressor is usually divided into main technical types such as dry and water lubrication according to whether the compression medium is isolated from the lubricating oil to meet the air quality requirements of different industries.
Principle
The working principle of a screw oil-free air compressor is based on volume changes and gas dynamics. A pair of precision-machined spiral rotors rotate in the casing with a high-precision gap. As the rotor rotates, the interdental volume moves from the suction end to the exhaust end, and its sealing volume gradually decreases, so as to realize the continuous inhalation, compression and discharge of gas. In the dry oil-free design, there is a very small non-contact gap between the rotors and between the rotor and the housing, relying on synchronous gears to ensure precise transmission and avoid metal contact. In water lubrication design, water is used as a sealing, cooling, and lubrication medium to replace traditional lubricating oils. The heat generated throughout the compression process is typically efficiently exchanged through air or water cooling systems.
Performance measurement method
The evaluation of the performance of screw type oil-free air compressors should be carried out according to relevant national standards or international standards. The main measurement parameters include exhaust volume, working pressure, specific power, exhaust temperature and air quality.
The measurement of exhaust volume (usually refers to volumetric flow) can be carried out by nozzle method or orifice flow meter, which can be calculated by reference to the formula: Q = k * √ (ΔP / ρ), where Q is the actual volumetric flow, k is the instrument coefficient, ΔP is the differential pressure, and ρ is the air density. The working pressure is measured directly at the exhaust port by means of a calibrated pressure sensor. Specific power is a key measure of energy efficiency, which is the ratio of the input power of a compressor to the output exhaust. Exhaust temperature is measured in the exhaust duct using a thermocouple or thermal resistor. Air quality needs to be tested for solid particulate matter content, pressure dew point and oil vapor content (to ensure oil-free), and particle counters, dew point meters and total hydrocarbon analyzers are often used.
Performance Factors
The operating performance of a screw oil-free air compressor is affected by multiple factors. Intake ambient conditions, such as ambient temperature, humidity, and air filter status, directly affect intake density and final exhaust volume. The efficiency of the cooling system determines the temperature rise of the rotor and compressed gas, which affects the operating reliability and life of the machine. The shape design, machining accuracy and meshing gap control of the rotor are the core of the impact on volumetric efficiency, leakage and mechanical efficiency. The arrangement and pressure loss of the system pipeline, as well as the resistance of the post-treatment equipment, will also affect the output pressure of the whole machine. In addition, the rationality of the control logic has a significant effect on the energy efficiency performance under partial load.
Main application areas:
With their ability to produce clean compressed air, screw oil-free air compressors have critical applications in several industries with stringent air quality requirements. In the food and beverage industry, it is used for raw material conveying, packaging and bottle purging to avoid the risk of oil contamination. In electronic semiconductor manufacturing, it provides air supply for pneumatic tools in clean workshops, chip drying and other processes. In the chemical and textile fields, it is used for instrument control, material mixing and air-jet looms to ensure the purity of the process medium. In the laboratory, it provides a stable and reliable drying gas source for various analytical instruments. In addition, it is also one of the important power sources in the braking system of public transportation such as subway and high-speed rail.
Key points to consider in selection
When selecting a screw oil-free air compressor for a specific application, a systematic evaluation is required. First, the quality level of the required compressed air, including pressure dew point, particulate matter and oil content requirements, should be determined, which determines the type of compressor and the configuration of the necessary aftertreatment equipment. Secondly, the actual average air consumption and maximum working pressure of the system should be accurately calculated, and the rated exhaust volume of the compressor should have a moderate margin, but it should not be too large to avoid low load operation efficiency. In terms of energy efficiency, it is possible to compare the specific power values of different models under typical loads. The installation environment of the equipment, including ventilation conditions, ambient temperature, and power configuration, also needs to meet manufacturer requirements. At the same time, the ease of maintenance of the equipment throughout its life cycle, the availability of commonly used spare parts, and whether the operating noise level meets the site regulations should be considered.