The scroll compressor comprises a fixed scroll and an orbiting scroll each equipped with a mirror plate member and an involute spiral member (called scroll lap) perpendicular to said mirror plate member, the respective laps being interleaved in such a manner that one is fixed with the other free to orbit without spinning about its own axis so as to cause a closed space defined by and between the scroll laps to be shifted and diminished in the direction from the outer circumference to the inner circumference to thereby compress a gas such as Freon gas.
Heretofore, all the fixed scroll and orbiting scroll of the scroll compressor and the drive shaft (called rotor shaft) for driving the orbiting scroll have been made of cast iron. However, the scroll laps, the mirror surface of the mirror plate member and the surface of the rotor shaft which demand a precision of the order of microns must be subjected to both rough grinding and finishing which are time-consuming and extremely poor in production efficiency. In addition, the tools are subject to wear and require a very complicated tool control for maintaining the required processing accuracy. Therefore, an attempt was made to use cast aluminum which is easier to process in lieu of cast iron. However, in this case, the large centrifugal force accompanying a high speed gyration causes a large deformation and there is also a constant risk of general destruction due to an impact caused by local contact, thus requiring sufficient oil lubrication not only from the standpoint of wear resistance but also for circumventing the above-mentioned risk. The need for oil lubrication means that there must be a mechanism for pumping the lubricating oil, which would add to the complexity of the structure, thus imposing limitations on the reduction of cost, size and weight of parts. Furthermore, the metal rotor shaft of cast iron or cast aluminum has the disadvantage that the transmission magnetic sound (i.e. noise) from the motor rotor is high and that it is of large weight.