英文原文Screw Machine Design Holmes, 1999 reported that even higher accuracy was achieved on the new Holroyd vitrifying thread-grinding machine, thus keeping the manufacturing tolerances within 3 m even in large batch production. This means that, as far as rotor production alone is concerned, clearances between the rotors can be as small as 12 m. Screw machines are used today for different applications both as compressors and expanders. Fig. 1.4. Screw compressor mechanical partsFig. 1.5. Cross section of a screw compressor with gear boxFor optimum performance from them a specific design and operating mode is needed for each application. Hence, it is not possible to produce efficient machines by the specification of a universal rotor configuration or set of working parameters, even for a restricted class of machines. Industrial compressors are required to compress air, refrigerants and process gases. For each application their design must differ to obtain the most desirable result. Typically, refrigeration and process gas compressors, which operate for long periods, must have a high efficiency. In the case of air compressors, especially for mobile applications, efficiency may be less important than size and cost. Oil free compressed air is delivered almost exclusively by screw compressors. The situation is becoming similar for the case of process gas compression. In the field of refrigeration, reciprocating and vane compressors are continuously being replaced by screw and a dramatic increase in the needs for refrigeration compressors is expected in the next few years. The range of screw compressors sizes currently manufactured is covered by male rotor diameters of 75 to 620mm and this permits the delivery of compressed gas flow rates of 0.6m3/min to 600m3/min. A pressure ratio of 3.5 is attainable in them from a single stage for dry compressors and up to 15 for oil flooded ones. Normal pressure differences are up to 15 bars, but maximum pressure differences sometimes exceed 40 bars. Typically, for oil flooded air compression applications, the volumetric efficiency of these machines now exceeds 90% and the specific power input has been reduced to values which were regarded as unattainable only a few years ago.1.1 Screw Compressor Practice The Swedish company SRM was a pioneer and they are still leaders in the field of screw compressor practice. Other companies, like Compair U.K., Atlas- Copco in Belgium, Ingersol-Rand and Gardner Denver in the USA and GHH in Germany follow them closely. York, Trane and Carrier lead in screw compressor applications for refrigeration and air conditioning. Japanese screw compressor manufacturers, like Hitachi, Mycom and Kobe-Steel are also well known. Many relatively new screw compressor companies have been founded in the Middle and Far East. New markets in China and India and in other developing countries open new screw compressor factories. Although not directly involved in compressor production the British company, Holroyd, are the largest screw rotor manufacturer, they are world leaders in tool designand tool machine production for screw compressor rotors. Despite the increasing popularity of screw compressors, public knowledge and understanding of them is still limited. Three screw compressor textbooks were published in Russian in the early nineteen sixties. Sakun, 1960 gives a full description of circular, elliptic and cycloidal profile generation and a reproducible presentation of a Russian asymmetric profile named SKBK. Theprofile generation in his book was based on an envelope approach. Andreev, 1961 repeats the theory of screw profiles and makes a contribution to rotor tool profile generation theory. Golovintsovs textbook, 1964, is more general but its section on screw compressors is both interesting and informative. Asomov, 1977, also in Russian, gave a reproducible presentation of the SRM asymmetric profile, five years after it was patented, together with the classic Lysholm Profile. Two textbooks have been published in German. Rinder, 1979, presented a profile generation method based on gear theory to reconstruct the SRM asymmetric profile, seven years after it was patented. Konka, 1988, published some engineering aspects of screw compressors. Only recently a number of textbooks have been published in English, which deal with screw compressors. ONeill, 1993, on industrial compressors and Arbon, 1994, on rotary twin shaft compressors. There are a few compressor manufacturers handbooks on screw compressors and a number of brochures giving useful information on them, but these are either classified or not in the public domain. Some of them, like the SRM Data Book, although available only to SRM licensees, are cited in literature on screw compressors. There is an extraordinarily large number of patents on screw compressors. Literally thousands have appeared in the past thirty years, of which SRM, alone, h