Abstract:
A gas bearing for textile machine applications includes a rotor having a bearing surface shaped to define a truncated conical bearing surface and a foil shell having a corresponding truncated conical shape. This gas bearing supports both radial and axial loads, and two such bearings may be combined to support axial loads in two directions as well as radial loads.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to gas bearings for rapidly rotating parts on textile machines such as spinning and twisting machines, and, in particular, to gas bearings for spinning rotors, spinning rings and spinning spindles. 
     Many gas bearings having thin foils as bearing elements have in the past been ill suited to support axial loads. For optimum stability, such gas bearings often require at least one radial foil bearing to support radial loads and two axial bearings to support axial loads. Here each axial bearing supports axial loads in one direction, one axial bearing serving to absorb the weight of the spinning rotor during standstill and during startup. 
     During the spinning operation when a textile machine is operating at speed the moving thread may often exert axial forces on the rotor in an upward direction, which forces may exceed the weight of the rotor by a considerable amount. In this case, a second axial bearing surface is necessary to bear these upward forces. The carrying capacity of this second axial bearing surface is, however, limited by the oblique position of the rotor, i.e., the axial rotor surface and the axial stator surface at times are not oriented parallel to one another. This oblique positioning of the rotor with respect to the axial stator is often caused by dynamic imbalance of the ring rotor even in the case of an optimally balanced rotor. With conventional gas bearings of the prior art this second axial bearing could be eliminated only if the weight of the rotor could be made greater than the upward-acting axial forces of the thread; in many cases, however, it is not practical to make the rotor so heavy. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a gas bearing for rapidly rotating parts on spinning or twisting machines, which bearing is capable of supporting axial loads in at least one direction. In this way at least one axial bearing may be eliminated. According to this invention a gas bearing is provided with a foil bearing having at least one foil curved to define a portion of a truncated conical shell. 
     An important advantage of this invention is that both axial and radial loads can be supported by the conical foil bearing of this invention. Thus, with a single conical foil bearing one axial bearing can be eliminated and with two conical foil bearings both axial bearings can be eliminated. Furthermore, the conical foil bearing of this invention will support axial loads even when the rotor tilts from its nominal axis of rotation. In that axial loads can be easily supported, the mass of the rotor can be kept small. This use of a lightweight rotor brings the additional advantage that the rotor may often be started without supplying compressed feed air. Lightweight rotors also make possible rapid acceleration and synchronization of the gas bearing. Furthermore, the low frictional moment makes possible a low thread tension. Through these measures there is provided a particularly simple and economical, long life gas bearing. 
     The invention, together with further objects and attendant advantages, will best be understood by reference to the following description taken in conjunction with the appended drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1a is a cross sectional view of a first preferred embodiment of the gas bearing of this invention. 
     FIG. 1b is a plan view from below of the gas bearing of FIG. 1, showing the rotor removed. 
     FIG. 2 is a cross sectional view of a second preferred embodiment of the gas bearing of this invention. 
     FIG. 3 is a plan view of a foil for the gas bearing of either FIG. 1a or FIG. 2. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the drawings, FIGS. 1a and 1b show a first preferred embodiment of the gas bearing of the present invention including a conical foil bearing and a single axial bearing. This bearing includes a base plate 1 to which is fastened a stator 2. Three foils 4 are symmetrically mounted to the stator 2 by means of fastening elements 3 so as to define a downwardly opening truncated conical shell 5. The stator 2 defines an axial bearing surface 6 above the conical shell 5. Nozzles 7 are provided in the stator 2 through which compressed air is fed during the starting phase. On this bearing surface 6 of the stator 2 there is borne an axial bearing surface 8 of a rotor 9, the bearing surfaces 6 and 8 together forming an axial bearing. The axial bearing surface 8 of the rotor 9 includes spiral grooves (not shown) for the aerodynamic formation of an air cushion during operation. Underneath the axial bearing surface 8 the rotor 9, internally hollow, has a downward-opening truncated conical shell surface 10. The three foils 4 are placed against the surface 10 without bias tension, forming the truncated conical shell 5. The base plate 1 is mounted by means of a damping element 11 to a casing 12. 
     During startup compressed air is introduced via the nozzles 7 between the bearing surface 8 and the bearing surface 6 of the stator 2. This compressed air builds up an aerostatic gas cushion to reduce startup friction. Preferably, the flow of compressed air is terminated when the rotor 9 reaches a predetermined speed, for at that point the spiral grooves in the bearing surface 8 of the rotor 9 will have built up an aerodynamic gas cushion between the bearing surface 6 of the stator 2 and the bearing surface 8 of the rotor 9. 
     Similarly, at a certain speed of the rotor 9 an aerodynamic gas cushion will be formed between the truncated conical shell 5 of the stator 2 and the truncated conical shell surface 10 of the rotor 9. This gas cushion acts to provide a low friction bearing for the upwardly directed axial forces applied to the rotor 9 by the spinning thread (not shown). Of course, the truncated conical foil bearing formed by the truncated conical shell 5 of the stator 2 and the truncated conical shell surface 10 of the rotor 9 also acts to absorb radial forces applied to the rotor 9 by both the tension of the thread and the imbalance of a ring rotor (not shown). Furthermore, the foil bearing of FIGS. 1a, 1b absorbs upwardly-directed axial forces even when the rotor 9 is tilted from its nominal axis of rotation. 
     A second preferred embodiment of the gas bearing of this invention is represented in cross section in FIG. 2. This embodiment includes two opposed truncated conical foil bearings. Referring to FIG. 2, an upper stator 22 is mounted to a base plate 21. Three fastening elements 23 serve to mount three symetrically arranged foils 24 to the stator 22. These foils 24 define a downwardly-opening truncated conical shell 25. To the upper stator 22 there is attached a lower stator 26, on which, by means of three fastening elements 27, three foils 28 are symmetrically arranged, which foils define an upward-opening truncated conical shell 29. The foils 24,28 serve to define two opposed truncated conical shells 25,29 having adjacent base openings. These shells 25,29 surround two truncated conical shell surfaces 30,31 of an internally hollow rotor 32 substantially without bias tension. The base plate 21 is mounted by means of a damping element 33 to a casing 34. The embodiment of FIG. 2 is well suited for use with a lightweight rotor 32. To facilitate starting of the rotor 32 the foils 28 forming the lower truncated conical shell 29 preferably define fine bores 35, through which compressed air is supplied to the foils 28 by means of hoses 36 glued to the foils 28. Preferably, the supply of compressed air is shut off at a certain speed of the rotor 32, for then an aerodynamic gas cushion will have formed between the truncated conical shell 29 of the lower stator and the truncated conical shell surface 31 of the rotor 32. 
     The foils 4,24,28 may be formed of any suitable material, such as metal or plastic, for example. These foils may be formed either as straight strips or, as shown in FIG. 3, as flattened strips taken from the truncated conical shells 5,25,29 which correspond to the truncated conical shell surfaces 10,30,31 of the rotor 9,32. Notches 37 are formed at both ends of the foils 4,24,28 to create weak places at which rotation is possible. These notches 37 enable the foils 4,24,28 to conform themselves more closely to the truncated conical shell surfaces 10,30,31 of the rotor as the rotor tumbles so that a uniform air gap and thereby a uniformly carrying gas cushion is created between the foils 4,24,28 and the truncated conical shell surfaces 10,30,31 of the rotor 9,32. 
     An important advantage of this invention is that only two bearing surfaces are required to support axial loads, even during tumbling of the rotor 9,32. Since the mass of the rotor 9,32 can be small, the rotor 9,32 can generally be started without supplying compressed air. The low mass of the rotor 9,32 further makes possible a rapid acceleration to full speed and synchronization of the rotor 9,32 and the low frictional moment results in a low thread tension. Thus, the present invention provides an especially simple, economical, and long life gas bearing. 
     Of course, it should be understood that various changes and modifications to the preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the invention, and without diminishing its attendant advantages. It is, therefore, intended that such changes and modifications be covered by the following claims.