Abstract:
A hoop including a cylinder which, so that the hoop can be mounted around a shaft, is formed by multiple parts that are assembled together using steps that can produce an assembly without deformation of an external surface of the cylinder. A ring, of which an external surface forms the internal surface of a bearing and which, so that it can be secured to the external wall of the cylinder, is formed by multiple elements that are secured to the cylinder by securing devices that can maintain a machining tolerance of the external surface of the ring.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to PCT/EP2013/057663 filed Apr. 12, 2013, which claims priority to FR Application 1253442 filed Apr. 13, 2012 both of which are hereby incorporated in their entireties. 
     TECHNICAL FIELD 
     The invention relates to a hoop intended to be mounted on the shaft of a turning machine to form an inner surface of a hydrostatic or hydrodynamic bearing. 
     BACKGROUND 
     The advantages of water bearings in relation to oil bearings are known, in particular in terms of pollution. In fact the function and maintenance of an oil bearing inevitably causes some of the oil used to be released into the environment. 
     However production of a water bearing is particularly difficult. The radial play between the inner and outer surfaces of the bearing is reduced to the order of 0.1 mm, which in particular requires the inner surface of the bearing to be machined with a tolerance of less than or equal to 5 hundredths or a millimeter, preferably 3 hundredths of a millimeter. The best tools currently available allow such machining precision. 
     There is also a need to overhaul existing machines by replacing their oil bearings with water bearings. 
     Currently this overhaul consists of grinding the surface of the shaft forming the inner surface of the bearing, to change from the tolerance required for an oil bearing (typically 50 hundredths of a millimeter) to that required for a water bearing (typically 5 hundredths of a millimeters). For this the shaft must be removed from the machine to transport it from the operating site of the machine to a workshop for grinding the surface with a suitable tool. Then once ground, the shaft is transported from the factory to the operating site before being refitted, whereupon the machine can resume its operation. 
     As well as the risks linked to transport of the shaft and problems linked to a fitting and refitting the shaft, the time during which the machine is not in operation is particularly long (of the order of several months). This represents a high cost for the operator which often prevents him from proceeding with such an overhaul. 
     To reduce the lost operating time, document FR-A-2938616 proposes a hoop intended for mounting on the shaft, preferably in situ, the outer radial surface of the hoop constituting the inner surface of the bearing. 
     However mechanical constraints resulting from clamping of such a hoop have the effect of deforming the geometry of the outer surface of the hoop, such that the machining tolerance of the outer surface of the hoop obtained in the workshop is lost. Furthermore since the shaft surface is machined to the tolerance required for an oil bearing, after clamping of the hoop on the shaft surface, the tolerance of the outer surface of the mounted hoop corresponds to the tolerance of the shaft surface i.e. 50 hundredths of the millimeter. 
     SUMMARY 
     The aim of the invention is therefore to solve this problem by proposing in particular a hoop and a method for mounting this hoop which retains the machining tolerance of the outer surface of the hoop. 
     For this the object of the invention is a hoop intended to be mounted on a shaft of a turning machine to form an inner surface of a hydrostatic or hydrodynamic bearing, characterized in that it comprises:
         a cylinder which, in order to be able to be mounted around the shaft, is composed of multiple parts that are joined together by assembly means able to produce an assembly without deformation of an outer surface of the cylinder;   a ring, an outer surface of which constitutes the inner surface of the bearing and which, in order to be able to be fixed to the outer wall of the cylinder, is composed of multiple elements fixed to the cylinder by fixing means able to retain a machining tolerance of said outer surface of the ring.       

     According to advantageous but non-obligatory aspects of the invention, a hoop as mentioned above may incorporate one or more of the following characteristics, taken in all technically possible combinations:
         the cylinder is fitted with adjustment means, preferably consisting of a plurality of button-head screws which are arranged radially and can come to rest on the shaft, to allow balancing of the assembly formed by the shaft and cylinder while maintaining a space between the shaft and the cylinder;   the cylinder is composed of a first part and a second part, each part being semi-circular;   an outer surface of the cylinder comprises an annular collar extending radially towards the outside, and the ring comprises an annular groove constituting a housing adapted to the collar, for receiving this during fixing of the ring to the cylinder;   the collar comprises a plurality of axial through channels and the ring comprises a plurality of axial channels connecting a transverse face and the groove of the ring, said fixing means comprising a plurality of conical studs, each stud being adapted to be inserted in a passage formed by the alignment of an axial channel of the ring with an axial channel of the cylinder collar;   the outer surface of the ring is composed, at least partly in the axial direction, of a layer of a ceramic material;   the ring is composed of a first element and a second element, each element being semi-circular;   a yoke is mounted clamped on the shaft and fixed to a transverse face of the cylinder by fixing means preferably consisting of a plurality of stepped studs;   the fixing means also comprise a plurality of radial bolts, each bolt being inserted in a radially oriented opening arranged on an edge of the ring, and being screwed into a radially oriented threaded bore arranged in the cylinder;   the machining tolerance of the outer surface of the ring is 5 hundredths of a millimeter, preferably 4 hundredths of a millimeter, preferably 3 hundredths of a millimeter.       

     The object of the invention is also an assembly consisting of a shaft and a hoop, characterized in that the hoop corresponds to the abovementioned hoop, the hoop being fixed to the shaft by a cushioning layer made of a cushioning material adapted to and situated in a gap between the shaft and the cylinder. 
     According to advantageous but non-obligatory aspects of the invention, the assembly as described above may incorporate one or more of the following characteristics, taken in all technically possible combinations:
         the cushioning material is a non-shrinking fluid resin, preferably an epoxy resin.       

     The object of the invention is also a method for mounting a hoop corresponding to the abovementioned hoop on a shaft of a turning machine to form an inner surface of a hydrostatic or hydrodynamic bearing, characterized in that it comprises the steps consisting of:
         mounting the cylinder of the hoop around the shaft by assembling the various constituent parts of the cylinder;   fixing the cylinder to the shaft by producing a cushioning layer between the cylinder and the shaft;   mounting the ring on the cylinder by fixing the various constituent elements of the ring on the cylinder.       

     According to advantageous but non-obligatory aspects of the invention, the method may incorporate one or more of the following characteristics, taken in all technically possible combinations:
         the step of mounting the cylinder is followed by a step of adjustment, consisting of balancing the assembly formed by the shaft and the cylinder;   the step of fixing consists of injecting a non-shrinking fluid resin into a gap between the cylinder and the shaft, and waiting for the resin to dry.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood and further advantages will appear more clearly in the light of the description below of a particular embodiment of a hoop, an assembly and a method according to the invention, which is given purely as illustration and with reference to the attached drawings in which: 
         FIG. 1  is an overview of the turning machine integrating the hoop according to the invention mounted on a shaft; 
         FIG. 2  is an exploded view of the hoop according to the invention; 
         FIG. 3  is a section in an axial plane of the assembly formed by the hoop and the shaft; 
         FIG. 4  is a cross-section of the assembly formed by the hoop and the shaft; and 
         FIG. 5  is a depiction in the form of a block diagram of the method of mounting the hoop on the shaft. 
     
    
    
     DESCRIPTION 
     The installation shown in  FIG. 1  comprises a Francis water turbine  2 , the impeller  3  of which is supplied from a housing  4  into which a forced conduit  5  opens. 
     The turbine  2  also comprises a shaft  6  on which the impeller  3  is mounted and which rotates with this about an axis X 6  which in the present embodiment is vertical, this axis also being a longitudinal axis of the shaft  6 . The shaft  6  is rotationally fixed to another shaft  7  forming a drive element of an alternator  8 . 
     A series of pre-guide vanes  9  and guide vanes  10  is provided between the housing  4  and the impeller  3 , the function of which is to guide a flow E from the conduit  5  and the housing  4 , which flow is intended to pass through the impeller  3  in the direction of the suction pipe  11 . 
     The impeller  3  comprises vanes  31  which extend between a ceiling  32  and a belt  33 . 
     The impeller  3  is fixed to the lower end  61  of the shaft  6 , sometimes called the shaft foot. The shaft foot  61  may be integral with the remainder of the shaft  6  or attached thereto. The impeller  3  is mounted on the shaft foot  61  by means known in themselves, such as bolts (not shown). 
     A hydrostatic bearing  100  is formed around the shaft  6  above the shaft foot  61 , in order to absorb the forces exerted on the shaft  6  during rotation of the mobile parts  3  and  6  of the turbine  2  about axis X 6 . 
     As a variant, the bearing  100  may be a hydrodynamic bearing. 
     This bearing  100  is defined between a fixed lining  110  and a hoop  120  integral with the shaft  6 . The lining  110  is fixed in that it does not rotate about axis X 6  when the impeller  3  and the shaft  6  are turning. The lining  110  is therefore immobile in relation to the structure of the turbine  2 , which in particular comprises elements  4  and  5 . 
     The bearing  100  is delimited between the inner radial surface  111  of the lining  110  and the outer radial surface  121  of the hoop  120 , these surfaces being both cylindrical, circular and centered on axis X 6  when the turbine  2  is in the mounted configuration. 
     A supply line  160  allows a supply of clear pressurized water to the gap corresponding to bearing  100  between the surfaces  111  and  121  through the lining  110 . 
     In view of the rotation movement between the surface  121  and the surface  111 , it is important that surface  121  is as continuous as possible and free from roughness and irregularities. 
     The structure of the hoop  120  is shown in  FIGS. 2 to 4 . 
     The hoop  120  is composite. It comprises a cylinder  200  situated radially on the inside of the hoop  120  and surrounding the shaft  6 , a ring  300  situated radially on the outside of the hoop  120  and surrounding the cylinder  200 , fixing means for the ring  300  on the cylinder  200 , lower and upper yokes  500  and  600  on either side of the cylinder  200 , and means of fixing the yokes  500  and  600  to the cylinder  200 . 
     In order to be able to be mounted around the shaft  6 , the cylinder  200  is composed of a first part  202  and a second part  203 . The parts  202  and  203  are identical and joined together by assembly means. 
     Parts  202  and  203  are semi-circular. Each has a radial inner surface  210 , an outer surface  212 , flat lower and upper transverse faces  214  and  216  which join the surfaces  210  and  212  on a plane transverse to axis X 6 , and first and second flat sections  218  and  220  which join the surfaces  210  and  212  on an axial plane containing axis X 6 . 
     The contour of the outer surface  212  has lips protruding radially towards the outside: annular lower and upper lips  222  and  224 , and first and second rectilinear lips  226  and  228  ( FIG. 3 ). 
     The lower annular lip  222  carries an annular flange  230  protruding radially towards the outside so as to form with the lip  222  a shoulder  232  for the ring  300 . 
     The first section  218  and the second section  220  are formed on the first rectilinear lip  226  and the second rectilinear lip  228  respectively, while the lower transverse face  214  and upper transverse face  216  are formed on the flange  230  and the upper lip  222  respectively. 
     At mid-height, the outer surface  212  has a collar  234  protruding radially towards the outside. This extends radially beyond the lips  222  to  224  without extending beyond the flange  230 . 
     In the assembled position of the two parts  202  and  203 , the first section  218  of the first part  202  rests on the second section  220  of the second part  203 , while the second section  220  of the first part  202  rests on the first section  218  of the second part  203 . 
     Each rectilinear lip  226  and  228  comprises a plurality of through drillings  240  opening orthogonally onto its section. Each drilling of the first section of a part is aligned with a corresponding drilling of the second section of the other part. 
     The first and second parts  202  and  203  are joined together by bolts  242 . Each bolt is inserted in a drilling of one part and the corresponding drilling of the other part, then screwed down to apply the mutually facing rectilinear lips in pairs against each other. 
     Such assembly means allow the joining of the two parts  202  and  203  without deforming their geometry. 
     Once the two parts  202  and  203  have been joined, the meeting of the lower surfaces  210  constitutes the inner surface  122  of the hoop  120 . Surfaces  210  each have a radius slightly larger than the radius of the shaft  6 , at least in the portion of the shaft  6  around which the hoop  120  is mounted. More precisely, the radius of surfaces  210  is equal to the radius of shaft  6  plus a predefined play, preferably equal to 1 millimeter. This play is greater than the tolerance of 50 hundredths of a millimeter on the radius of the outer surface of the shaft  6 , so as to guarantee the presence of a gap  124  between the inner surface  122  of the hoop  120  and the shaft  6 . 
     This gap  124  is filled with a cushioning layer  126  allowing fixing of the cylinder  200  to the shaft  6 . The layer  126  is made from a cushioning resin, preferably an epoxy resin, linking the cylinder to the shaft so as to absorb the radial forces, the tangential forces being absorbed by the yokes  500  and  600 . 
     The cylinder  200  is fitted with adjustment means consisting of a plurality of button-head screws  260  held in radial threaded through holes  262  provided in the lower and upper lips  222  to  225  of parts  202  and  203 . When a button-head screw is screwed in, the distal end of the screw comes into contact with the shaft  6  such that by reaction, the position of the axis of cylinder  200  is modified in relation to that of axis X 6  of the shaft  6 . On mounting of the cylinder  200  on the shaft  6 , the adjustment of the various button-head screws  260  allows balancing of the assembly formed by the shaft  6  and cylinder  200  to avoid any imbalance phenomena around axis X 6  while maintaining the gap  124  between the shaft  6  and the cylinder  200 . 
     To fix the ring  300  to the cylinder  200 , the upper and lower lips  222  to and  224  of parts  202  and  203  are fitted with radial threaded blind bores  207  intended to cooperate with radial fixing screws of the ring  300  on the cylinder  200 , as will be described below. 
     Furthermore collars  234  and  235  of parts  202  and  203  comprise a plurality of axial through channels  208  distributed in a regular annular pattern. They are intended to receive the conical fixing studs of the ring  300  on the cylinder  200 , as will be described below. 
     Finally the upper and lower faces  214  and  216  of parts  202  and  203  are fitted with axial blind bores  209  to receive the stepped studs fixing the upper yoke  600  and lower yoke  500  to the cylinder  200  as will be described below. 
     In order to be able to be easily mounted on the outer surfaces  212  of cylinder  200 , the ring  300  is composed of a first element  302  and a second element  303  fixed to cylinder  200  by fixing means. 
     Elements  302  and  303  are semi-circular. Each comprise an inner face  310 , an outer radial face  312 , flat lower and upper transverse faces  314  and  316  which join surfaces  310  and  312  on a transverse plane, and first and second flat sections  318  and  320  which join surfaces  310  and  312  on an axial plane. 
     Preferably, the outer surfaces  312  of element  302  and  303  comprises lower and upper edges  323  and  325 , and a median portion  324 . This consists of a layer of a ceramic material forming an over-thickness and which has been machined when ring  300  is mounted on the cylinder  300 , such that in the median portion, the radius of the outer surfaces  312  have the required tolerance to constitute the inner surface of a water bearing. 
     Once the two elements  302  and  303  have been fixed to the cylinder  200  to form the ring  300 , the meeting of the outer surfaces  312  constitutes the outer radial surface  121  of the hoop  120 . The dimensions of elements  302  and  303  are adapted such that the outer surfaces  312  are tangential to each other at the junction between the first and second elements  302  and  303 , and form a substantially continuous surface. 
     At mid-height, the inner surfaces  310  of elements  302  or  303  respectively comprise an annular groove  330 , the axial dimensions of which are adapted to receive the collar  234  in an adjusted manner. 
     Element  302  or  303  respectively comprises a plurality of axial channels  308  extending from the upper face  316  to the lower part of element  302 ,  303 , passing through the groove  330 . In the position in which the ring  300  is fixed to the cylinder  200 , each channel  308  of the ring is precisely aligned with a corresponding channel  208  of the collars  234  of the cylinder ( FIG. 3 ). 
     Furthermore the upper and lower edges of the outer surfaces  312  respectively of elements  302 ,  303  have radial through openings  307  comprising an inner shoulder able to receive a headed fixing bolt of element  302 ,  303  on the cylinder. When the ring is fixed to the cylinder, each opening  307  is precisely aligned with a threaded bore  207  ( FIG. 4 ). 
     For fixing the ring to the cylinder, the fixing means comprise axial fixing means and radial fixing means. 
     The axial fixing means consist of conical tapered studs  410  inserted through passages which are formed by a channel  308  on the ring  300  and a corresponding channel  208  in the cylinder  200 . These conical studs  410  have a geometry able to ensure fixing without play but without stress on the ring  300  to the cylinder  200 . They are held in position by locking screws  412  screwed into the upper portion of the channel  308  situated next to the upper face  316 ,  317  of the ring. 
     The radial fixing means consist of radial hexagonal head bolts  414  inserted through openings  307  of the ring  300  and screwed into threaded bores  207  of cylinder  200 . The head of the bolt comes to rest on the shoulder of the opening so as to hold the ring  300  radially against the cylinder  200 . 
     Thus using these fixing means, the radius of the outer surface  121  of the hoop  120  retains after mounting the tolerance it had on machining. 
     The lower collar  500 , in order to be able to be mounted easily around the shaft  6 , is composed of a first segment  502  and a second segment  503  assembled around the shaft  6 . 
     Segment  502  is semi-circular and has an inner radial surface  510 , and outer radial surface  512 , flat lower and upper transverse faces  514  and  516  which join surfaces  510  and  512  on a transverse plane, and flat first and second flat sections  518  and  520  which join surfaces  510  and  512  on an axial plane. 
     Similarly, segment  503  is semi-circular and comprises a radial inner surface  511 , a radial outer surface  513 , flat lower and upper transverse faces  515  and  517 , and flat first and second sections  519  and  521 . 
     The inner surfaces  510  and  511  have a radius equal to or slightly less than the radius of the shaft  6 , or at least in the portion around which the hoop  120  is mounted. 
     Each segment  502  or  503  has a threaded bore  522  which opens orthogonally onto the second section  520 ,  521 . 
     Also the outer surface  512  and  513  respectively of each segment  502 ,  503  has a housing  526 , through the base of which passes an opening  528  which opens orthogonally onto the first section  518 ,  519  of segment  502 ,  503 . 
     A pin  506  is inserted tangentially inside the housing  526  then through the opening  528  in the first section of a segment, so that its rod is screwed into the threaded bore  522  of the second section of the other segment. Suitable screwing allows clamping of the collar on the shaft  6  in order to avoid a relative movement between the hoop and the shaft. This clamping is sufficient to absorb the tangential forces and in particular the seizing torque in the case of damage to the bearing. 
     The lower collar  500  also comprises a plurality of axial through holes  509  connecting the lower faces  514 ,  515  and upper faces  516 ,  517  of the collar  500 . Each hole  509  is intended to come into precise alignment with one of the holes  209  on the lower face  214 ,  215  of the cylinder  200  against which the lower collar  500  is placed. 
     The fixing means consists of a plurality of stepped studs  710 . Each stud  710  is housed in a hole  509  so as to protrude into the corresponding hole  209 . The studs  710  are dimensioned to allow the absorption of forces between the cylinder  200  and the collar  500 . 
     A similar description may be given to present the structure of the upper collar  600 . 
     The method for mounting the hoop  120  is as follows. 
     In a preceding step  1000  of machining the outer surface  121  of the hoop  120  while the ring  300  is mounted on the cylinder  200 , the ceramic layer forming the median portion of the outer faces  312  and  313  of elements  302  and  303  constituting the ring is machined. The outer surface  121  obtained has a radius characterized by a tolerance which is less than or equal to the tolerance required for the inner surface of the water bearing. 
     On site, when replacing an oil bearing by a water bearing, the oil bearing is removed and the hoop  120  described above is mounted directly on the shaft  6 . 
     In a step  1100  of mounting the lower collar  500 , the two segments  502  and  503  are brought to the shaft and joined together by the insertion of button-head screws  506 . Then the pins are screwed together to clamp the collar  500  to the shaft. 
     In a step  1200  of mounting the cylinder  200  around the shaft  6 , the first and second parts  202  and  203  are brought to either side of the shaft  6 . The first section  218 ,  219  of one part is brought to rest on the second section  220 ,  221  of the other part such that each drilling  240  of the first section is in alignment with corresponding drillings  240  of a second section. The two parts  202  and  203  are then assembled by placing the bolts  242  in the different pairs of drillings  240 , then tightening the bolts  242 . This assembly is then lowered vertically to rest on the upper face  516  of the lower collar  500 . The cylinder is rotated around axis X 6  such that the blind axial holes  209  of cylinder  200  are in alignment with the holes  509  of the lower collar  500 . The stepped studs  710  are screwed into holes  509  to protrude vertically beyond the upper transverse face  516  of collar  500  into the blind axial holes  209  of cylinder  200 . 
     In a step  1300  of adjusting the relative position of cylinder  200  in relation to axis X 6  of shaft  6 , an operator tightens or loosens the button-head screws  260  such that they come to rest on the shaft  6 . On each modification of the distance over which a button-head screw  260  protrudes radially in relation to the inner surface  210 ,  211  of cylinder  200 , the assembly formed by the shaft and the cylinder is set in rotation to determine whether the assembly is correctly balanced around rotation axis X 6 . After this step, a gap  124  is created between the cylinder  200  and the surface of the shaft  6 . 
     In a step  1400  of fixing the cylinder to the shaft  6 , a cushioning layer  126  is produced between the inner surfaces  210 ,  211  of cylinder  200  and the shaft surface. A cushioning resin with a suitable fluidity is injected into the gap  124 . The cushioning resin is selected such that it does not shrink during setting. After polymerization of the resin, cylinder  200  is fixed to the shaft  6  at least with regard to absorption of radial stresses, the tangential stresses being absorbed by collars  500  and  600 . 
     In a step  1500  of fixing the ring  300  to the cylinder  200 , the first element  302  is arranged on the cylinder such that its lower face  514  sits in the shoulder  232 ,  234  formed between the lower lip  222 ,  223  and the yoke  230 ,  231  of the cylinder, and that collar  234 ,  235  of the cylinder is received in the groove  330 . The first element  302  is moved radially to align each axial channel  308  with a corresponding axial channel  208  in the collar  234 ,  235  of the cylinder, and each radial opening  307  is aligned with a corresponding threaded bore  207  on the lower and upper lips of the cylinder. Conical studs  410  are inserted in the passages formed by the axial channels in the ring and cylinder, and are locked in position by tightening the locking screws  412 . Radial bolts  414  are screwed through openings  307  into bores  207 . The ring is thus fixed to the shaft  6  via the cylinder  300 . 
     In a step  1600  of mounting the upper yoke  600 , the two segments  602  and  603  are brought to the shaft and joined together by insertion of pins  506 . Before definitive tightening of the yoke  600  on the shaft  6 , the yoke  600  is applied against the upper transverse face  216  of cylinder  200  and oriented radially such that the axial through holes  609  align with the axial blind holes  209  of cylinder  200 . Once this relative position is obtained, the stepped studs  710  are inserted in holes  609  and  209 . Studs  710  are held in position by the fitting of locking screws  712 . Thus the lower yoke  600  is attached to cylinder  200 . 
     After mounting the hoop  120  on the shaft  6 , the lining  110  is fitted and other reassembly steps carried out allowing the machine to be recommissioned. 
     The hoop according to the invention and its mounting method guarantee that the inner surface of the bearing has the required tolerance. 
     The production of a cushioning layer means there is no need to machine the shaft surface to give it a tolerance compatible with a tolerance required on a surface constituting the inner surface of a water bearing. 
     The cylinder is fixed to the shaft without clamping and consequently without deforming its geometry, at least the geometry of its outer surfaces on which the constituent elements of the ring are positioned and fixed. 
     Furthermore, because the hoop consists of a cylinder and a ring, the ring can to be fixed to the shaft using axial and optionally radial fixing means. Thus the geometry of the outer surface of the ring is not deformed once fixed to the cylinder, which allows the tolerance achieved during machining to be retained.