Oil-Free Screw Compressor or Oil-Injected Screw Compressor?

Atlas Copco China 1HK Ltd. has taken the biggest one in the Chinese compressor market shares. 1. The description of two types of screw compressor 2. The main applications of air compressor in China 3. Chinese customers' choices mainly upon air quality requirement 4. We promote oil-free compressor for customer's economy 5. Unique attraction of oil-injected compressor As we know, compressors may be simply classified as dynamic compressor and displacement compressor, the displacement compressors confine successive volumes of gas within a closed space and increase the pressure by reducing the volume of the space. The displacement compressors are also classified as two types: rotary compressor and reciprocating compressor. As a major type of rotary and positive displacement compressor, the screw compressor has been playing more and more important role in the applications of compressors. 1. TilE DESCRIPTION OF TWO TYPES OF SCREW COMPRESSOR The beginning of screw compressors concept was with a design of the Swedish inventor Alf Lysholm, who had patented, when its practical application had not yet to be seen. The complex screws were difficult to manufacture with sufficient precision,. avoiding deformation, breakage and leakage. In 1954 Atlas Copco acquired the rights to manufacture and sell screw compressors made according to the Lysholm principle, and in 1955 the first compressor was delivered to a mine of the Swedish company LKAB. After several years' innovative research, .the first oil-injected screw compressor by simply using screw element was brought onto the market by Atlas Copco in 1958. In 1967 Atlas Copco presented oilfree compressor, it met the requirement of textile, food and pharmaceutical industries because no oil is Fifteenth International Compressor Engineering Conference at Purdue University, West Lafayette, IN, USAJuly 25-28, 2000 885 injected in the compression chamber, no oil is stayed in the compressed arr at all. With oil-free compressor Atlas Copco broadened its market further. Compressors Dynamic Displacement Ejector Radial Axial Rotary Reciprocating one rotor two rotors Vane Liquid ring Screw Screw Roots Fig 1: Basic compressor types There are no inlet and outlet valves and no unbalanced mechanical forces, the screw compressor operates at high shaft-speeds. Consequently it combines high flow rates with small exterior dimensions. To maintain compressor efficiency at low flow rates calls for high shaft-speed, oil-free screw compressors use external timing-gears to synchronize the counter-rotating male and female rotors. As the rotors touch neither each other nor the casing, lubrication is not required within the compression space, so the compressed air discharged from compression chamber is absolutely oil-free. WIS Water-injected screw compressor sometimes is considered as oil-free screw compressor because there is not oil but water injected in compression chamber, and no oil stayed in the discharged compressed air though injected process is happened during compression. It is the new version in recent years, but its fatal weakness is the interior rusty problem. So water-injected screw compressor has not been the mature technology until now. In China, A Joint-venture beer plant in Shanghai who bought 3 sets of water-injected screw compressor has fallen in trouble with serious rusty problem, and stopped operating them for years. However, due to oil injected in the compression chamber, three functions: • to seal the internal clearances • to cool the air during compression • to lubricate the rotor, Oil-injected screw compressors operates at lower shaft-speeds. Male and female rotors are engaged just like two gears, so the timing-gear is not required in oil-injected screw compressor. The injected oil is reclaimed and re-circulated after compression. Oil-separator is required to separate oil Fifteenth International Compressor Engineering Conference at Purdue University, West Lafayette, IN, USAJuly 25-28, 2000 886 from compressed air. Through after-filters, there is still a little oil stayed in the compressed air, it is not absolutely oil-free compressed air. It should be called oil-less compressed air, 2. THE MAIN APPLICATIONS OF AIR COMPRESSOR IN CHINA In China, compressors are used at many industry sectors, such as Textile, Electronic, Automotive, Iron and Steel, Food and Beverage, Tobacco, Petroleum & Petrochemical, Pharmaceutical, Power station, Chemical and Machinery sectors and etc. The demands for compressors from all industry sectors have been changing much recently owing to the rapid development of Chinese Economy.