Abstract: A method of producing an oil-free screw compressor has the following steps: preparing a semi-finished metallic female rotor which has a spiral profile, and a semi-finished metallic male rotor which has a spiral profile; forming a metallic coating film containing particles of grinding material on the surface of the semi-finished female rotor; forming, on the surface of the semi-finished male rotor, a coating film of a material softer than the metallic coating film on the female rotor; grinding the surfaces of the semi-finished rotors into predetermined configurations; mounting the ground rotors on bearings so that the rotors are assembled in a rotor casing with a substantially constant spacing held between the axes of the semi-finished rotors; mounting timing gears on the rotors so as to drivingly connect the rotors each other; and driving the rotors by driving means while restraining the back lash in the rotating direction by means of the timing gears and applying a compression load to the rotors so that the

Abstract: A rotary fluid machine such as, for example, a screw compressor, a centrifugal compressor, or a pump, is provided with a thrust bearing mounting unit adapted to maintain natural frequencies of bending vibrations of rotors thereof within ranges of permissible values. The axial rigidity of the mounting unit is at least as high as that of the thrust bearings and the radial rigidity thereof is made to be not more than half that thereof. When a radial load is applied to the thrust bearings, the bearing mounting unit is deformed solely substantially in the radial direction and the thrust bearings bear substantially no radial load.

Abstract: Rotor tooth forms for a pair of screw rotors in the form of a female rotor and a male rotor, wherein the female rotor has a rotor tooth form including a flank of a surface of advance constituted by an arc and a second order curve, and a flank of a surface of retrocession constituted by a curve generated by an arc of a forward end portion of a lobe on the male rotor and an arc, and the male rotor has a rotor tooth form essentially formed by generating loci of the flank of the surface of advance of the female rotor and the flank of the surface of retrocession thereof.

Abstract: An oil-free rotary displacement compressor including a casing having a main casing defining a compression space, a pair of rotors housed in the compression space and each having a screw thread portion and shaft portions, radial bearings and thrust bearings for journalling the rotors, shaft sealing means for sealing the shaft portions to avoid gas leaks from the compression space to outside and entry of oil into the compression space from the bearings. Floating type screw seal rings, each formed on the inner surface with a spiral screw thread and a root of thread, are each fitted over one of the suction-side shaft portions and supported by the casing in such a manner as to be movable in both the radial and the axial directions with respect to the casing.

Abstract: A screw compressor including a female rotor and a male rotor rotating while meshing with each other, with the rotor tooth form of one of the female and male rotors meshing with each other without any clearance therebetween in normal temperature condition being used as a basic tooth form for obtaining a rotor tooth form produced by deformation on account of thermal expansion during operation. The basic tooth form and the tooth form thus obtained are employed in the assembled compressor. The rotors with these teeth form, when brought together in meshing engagement, have a clearance at start-up which allows for their expansion. This clearance is maintained at a minimum during operation of the compressor.

Abstract: In a compressor unit of a type wherein the ratio of delivery pressure relative to intake pressure, i.e., pressure ratio, is required to be as uniform as possible during unloaded and loaded operating conditions, as is in screw compressors of dry type, solenoids are used to drive an intake throttle valve and a pressure relief valve in such a manner that, when the throttle valve is closed, the pressure relief valve is opened to avoid an increase of the pressure ratio. When signals are produced to close the throttle valve and open the pressure relief valve, the solenoids are instantanously operative to close the throttle valve and open the pressure relief valve.

Abstract: Screw fluid machines are for use as a compressor for generating high pressure gas, a cooling-medium-compressing compressor for use in a refrigerator or an air conditioner. The fluid machine includes a rotor casing, two side-casings, a pair of screw rotors, and accessories such as silencer, a gas cooler, an oil cooler, and an oil tank. The rotor casing includes an outer wall, an inner wall and interconnecting members or ribs which interconnect the outer wall and the inner wall, with a space being provided between the outer wall and the inner wall. This space is partitioned into two or more spaces by means of the aforesaid interconnecting members. A working chamber or space is provided inwardly of the inner wall and has an inlet port and a discharge port. Both side-casings are secured to the opposite end faces of a rotor casing through the medium of flanges and are provided with a passage adapted to bring two or more spaces thus partitioned, into communication with each other.