ROTARY SCREW AIR COMPRESSOR
rotary screw air compressors are equipped with two spindle shaped mutually engaging rotors. As a rule, the main rotor is made with four, the auxiliary rotor with six lobes, where the main rotor transforms about 85-90% of the energy received at the coupling from the drive motor into pressure and heat energy. Injection technology led to the development of the rotary screw air compressor without synchronous transmission but with oil injection cooling, where the rotors could counter rotate in a non-contacting manner because of the lubrication provided by the injected oil.
The principle of the rotary screw air compressor was first patented by Heinrich Krigar of Hannover, Germany in March 1878.[2] He improved his designs later that year and lodged a second patent in August 1878. Both of these patents are amongst the earliest on record. However, the manufacturing capabilities available at that time prevented the commercial development of his designs. Half a century later, a Swedish steam air turbine manufacturer called Ljungstroms Angturbin AB appointed a new Chief Engineer, his name was Alf Lysholm and he was to be the rotary in the development of the modern rotary screw air compressor. At that time, Lysholm was looking into light weight compressors for gas and steam turbine use.
In a rotary screw air compressor, some air will slip back through the small gaps which exist between the screw air compressor rotors. This loss is called slippage. In an oil-free compressor (screw compressor), the air is compressed entirely through the action of the screws, without the assistance of an oil seal. They usually have lower maximum discharge pressure capability as a result. However, multi-stage oil-free compressors, where the air is compressed by several sets of screws, can achieve pressures of over 150 psig, and output volume of over 2000 cubic feet per minute (measured at 60 °C and atmospheric pressure). rotary screw air compressors are used in applications where entrained oil carry-over is not acceptable, such as medicial research and semiconductor manufacturing.
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