Abstract:
An impeller fixing mechanism is provided in a centrifugal pump for immobilizing the impeller, relative to the pump shaft and drive shaft of the pump, while effecting repairs to the pump, thereby eliminating much of the labor-intensive need for realigning the pump shaft and drive shaft and assuring accurate positioning of the impeller relative to the pump shaft. A method for effecting repairs of centrifugal pumps employs use of the impeller fixing mechanism of the invention to immobilize the impeller relative to the pump shaft, thereby facilitating the repair.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates generally to pumps such as, for example, centrifugal pumps of the slurry processing type, and specifically relates to a method for handling components of the pump to facilitate repair of pumps in a more efficient and cost-effective manner. 
         [0003]    2. Description of Related Art 
         [0004]    Centrifugal slurry pumps are used in a large variety of industrial processes, especially in the grinding and grading stage of ore during mineral processing. Ore slurries are highly abrasive causing great wear and tear to those parts of the pump in contact with the slurry, which requires slurry pumps to undergo frequent servicing. 
         [0005]    In the processing of copper ore, a slurry pump typically processes approximately 2,000 tonnes of ore per hour, including about 20 tonnes of copper content. Depending on the slurry pump size and weight, which may range from 12 to 30 tonnes, replacement of a worn pump or its parts takes from eight to sixteen hours, and each replacement therefore causes a production loss of at least 150 to 300 tonnes of copper. 
         [0006]    For that reason there have been advances in the design and development of slurry pumps to extend the pump operating time between services. One of the typical solutions is to protect the pump casing with metallic or elastomeric sacrificial internal liners. However, in the state of the art, there is no technical solution to reduce the period of time it takes to change out a slurry pump, this being the technical problem that the present invention addresses. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    In accordance with the present invention, an impeller fixing mechanism is provided for immobilizing and fixing the impeller in a centralized position during a procedure for effecting pump repairs which eliminates much of the cost and time expenditure that is normally encountered in effecting pump repairs. Also disclosed is a method for effecting centrifugal pump repair in a cost-effective manner. 
         [0008]    Centrifugal pumps typically comprise a base, a casing or “wet end” as it may be referred to in the art, and a rotating impeller connected to a drive shaft. The wet end has a casing formed by two bolted halves with faces or surfaces inside the casing, and the two bolted halves form a housing in which an impeller, secured to the drive shaft, rotates. Sacrificial liners may also be used on the inside surfaces of the casing halves to protect the casing. 
         [0009]    Wet end liner and impeller replacement is normally carried out by changing the complete pump or by dismantling the pump wet end in situ and removing the wet end liners and impeller component by component. To avoid vibration and prevent damage to the pump a precise realignment of the impeller and the drive shaft is necessary as part of the repair. Such a procedure during wet end liner and impeller replacement takes in excess of eight hours. This long period of time is the technical problem that is resolved by the present invention which incorporates an impeller fixing device that allows removal of the pump casing or wet end without disengaging the pump shaft from the coupling device which couples it to the drive shaft. Therefore it does not require shaft realignment or wet end dismantling in situ. 
         [0010]    The impeller fixing mechanism of the present invention is comprised of two elements, each concentric with the pump shaft and positioned to abut against the inside surface of the casing faces. Preferably the fixing elements are annular in shape, having a diameter between 0.95D and 1D, where D is the impeller diameter. The two fixing elements each comprise a flexible elastomeric member and a stiff backing member. The stiff backing member incorporates a mechanism for loosening the mounting bolts and nuts to enable axial movement of the fixing elements toward the impeller to immobilize the impeller during repairs. 
         [0011]    Preferably, the thickness of the elastomeric members is about 10 mm to about 25 mm. Each elastomeric member, however, can have a different thickness relative to each other. Preferably, the diameter of the stiff backing member is the same as that of the elastomeric members to be radially co-extensive therewith, and is formed by a flat annular plate having ribs. The flat plate thickness may be between about 10 mm and about 30 mm and the height of the ribs may be between 20 to 50 mm. 
         [0012]    Preferably, the fixing mechanism tightening system comprises tightening bolts, which are screwed to the casing faces and abut against the rib or ribs of the stiff backing member, and the loosening system comprises loosening bolts, with nuts and washers. The loosening bolts freely pass through the casing holes and the bolts are jointly attached to the stiff backing member on the same rib where the tightening bolts are positioned to contact the fixing element. Preferably, the tightening bolts and loosening bolts are inserted therebetween and evenly spaced apart in a circumference concentric to the pump shaft. 
         [0013]    According to another aspect of the present invention there is provided a procedure for replacement of the liners and impeller in a centrifugal pump which presents a savings of time and cost in effecting repairs to the pump. These and other features of the present invention are described more fully below. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0014]    In the drawings, which currently illustrate the best mode for carrying out the invention: 
           [0015]      FIG. 1  is a cutaway view in elevation of a slurry pump without a sacrificial liner, shown for comparative purposes; 
           [0016]      FIG. 2  is a view in elevation of the front face (i.e., suction side) of the pump shown in  FIG. 1 ; 
           [0017]      FIG. 3  is a cutaway view in elevation of a slurry pump with sacrificial liners, shown for comparative purposes; 
           [0018]      FIG. 4  is a view in elevation of the front face (i.e., suction side) of the pump shown in  FIG. 3 ; 
           [0019]      FIG. 5  is a cutaway view in elevation of a slurry pump in a preferred embodiment of the invention; 
           [0020]      FIG. 6  is a view in elevation of the pump of  FIG. 5  showing the front face (i.e., suction side); 
           [0021]      FIG. 7  is an enlarged cutaway view in elevation of a preferred embodiment of the impeller fixing mechanism of the present invention; 
           [0022]      FIG. 8  is a perspective view of a portion of the impeller fixing mechanism corresponding to the front face or suction side of the pump; and 
           [0023]      FIG. 9  is a perspective view of a portion of the impeller fixing mechanism corresponding to the rear face or drive side of the pump. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]      FIG. 1  shows, for comparison purposes, a slurry pump assembly without liners. The pump assembly generally comprises a base  2  that is connected to subbase  1  by means of bolts  17 . Subbase  1  is anchored to the ground. Base  2  supports the slurry pump  30 , which consists of a casing  3 , otherwise referred to herein as the “wet end” in accordance with the term used in the art, and a rotating pump shaft  14  with a torque release mechanism  27 . The pump shaft  14  is connected by means of coupling  15  to the drive shaft  16 . Wet end  3  further comprises a metallic casing formed by two members, the casing frontal face  4   a  and the casing rear face  4   b , corresponding to the suction side and drive side of the pump, respectively. The frontal face  4   a  and rear face  4   b  are connected to each other by bolts  10 . Frontal face  4   a  is connected to the inlet or suction pipe  6  by means of bolts  8 . 
         [0025]    The casing, or wet end  3 , is fixed to base  2  by bolts  13  that are located in the rear face  4   b . On the inside of the wet end is impeller  5  which is secured to the pump shaft  14  for rotation thereby. The slurry enters through inlet pipe  6  under the suction produced by the rotating impeller  5  and is propelled from the pump via outlet pipe  7 , which is connected to the slurry pump  30  by bolts  9 . 
         [0026]    A slurry pump with sacrificial liners, as shown in  FIG. 3 , differs from the pump illustrated in  FIG. 1  in that the inner surfaces of the casing frontal face  4   a  and casing rear face  4   b  have a covering or lining  18   a  and  18   b , respectively, as shown in  FIG. 3 . The pump weight may vary between 12 to 30 tonnes depending on the pump size, and including the base  2 . Consequently, handling (i.e., raising or moving) the pump requires the use of chain blocks or cranes, for which purpose the wet end comprises flanges  11  having apertures  12  that are located at the outer side of casing frontal face  4   a  and casing rear face  4   b.    
         [0027]    The high rotation speed of the pump demands that there be a precise alignment between the pump shaft  14 , the drive shaft  16  and the impeller  5 . Thus, when the internal parts or elements of the pump become worn, the servicing of centrifugal pumps in presently and conventionally performed in one of two ways. Repairs are effected either by totally replacing the pump or by replacement of the pump liners and impeller through dismantling the pump in situ. 
         [0028]    Total replacement of the pump requires the following procedure, in connection with which reference is made to  FIG. 1 :
       1. Disconnect suction pipe  6  and discharge pipe  7  from the pump casing by removing bolts  8  and  9 , respectively;   2. Disconnect coupling  15  to disengage pump shaft  14  from drive shaft  16 ;   3. Remove bolts  17  which connect the complete pump assembly from its subbase  1 ;   4. Remove the complete pump assembly from the pump location by means of a chain block or crane and transport the complete pump assembly to repair facility for maintenance;   5. Transport to the pump location a new complete pump assembly by means of chain block or crane;   6. Connect the complete pump assembly to subbase  1  by means of bolts  17 ;   7. Connect coupling  15  which joins pump shaft  14  and drive shaft  16 ;   8. Perform precision alignment of pump shaft  14  and drive shaft  16 ; and   9. Connect suction pipe  6  and discharge pipe  7  to pump by means of bolts  8  and  9 , respectively.       
 
         [0038]    The foregoing procedure for replacement of the total pump presents certain disadvantages, namely the fact that it requires costly replacement of the entire pump assembly, including the entire mechanical system, bearing housing, packing gland, lubricating assemblies (not shown in the figures) and the pump shaft  14 , resulting in a greater investment cost; the weight to be handled, considering the complete pump assembly, is about twelve to thirty tonnes of which four to ten tonnes corresponds to the weight of base; alignment of the pump shaft to the drive shaft must be extremely accurate to avoid vibration and to prevent equipment damage, and the realignment procedure is an arduous task that requires considerable time; and, the pump replacement procedure takes over eight hours. 
         [0039]    Replacement of the worn pump parts with new elastomeric liners and/or a new impeller by dismantling the pump in situ requires the following steps, in connection with which reference is made to  FIG. 3 :
       1. Disconnect suction pipe  6  and discharge pipe  7  from the pump by removing bolts  8  and  9 , respectively;   2. Place lifting slings on the pump casing frontal face  4   a;      3. Open wet end  3  (i.e., disconnect casing frontal face  4   a  from casing rear face  4   b ) by removing bolts  10 ;   4. Remove casing frontal face  4   a  and store temporarily;   5. Disengage torque release mechanism  27 ;   6. Secure old impeller  5  with a special lifting device that maintains impeller  5  in a vertical position while allowing rotation of pump shaft  14  to reverse direction for disconnection of the impeller  5  from the pump shaft  14  and to permit removal of the impeller  5 ;   7. Place lifting slings on the casing rear face  4   b;      8. Remove bolts  13  which join the casing rear face  4   b  to the pump base  2 ;   9. Remove the casing rear face  4   b  and store temporarily for removal and replacement of liner  18   b  in casing rear face  4   b;      10. Reinstall the casing rear face  4   b , which has been outfitted with a new liner  18   b , and secure to pump base  2  by means of bolts  13 ;   11. Install the new impeller  5  by using the special device that keeps the impeller  5  in a centralized vertical position;   12. Re-engage the torque release mechanism  27 ;   13. Rotate pump shaft  14  in its normal rotational direction for connection of the new impeller  5 ; and   14. Install the casing frontal face  4   a  in which a new liner  18   a  has been installed, and close the pump (i.e., attach casing frontal face  4   a  to casing rear face  14   b ) by fastening bolts  10 .       
 
         [0054]    The foregoing procedure does not require the re-alignment of the pump shaft and drive shaft as required with the total pump replacement procedure; however, it presents the following disadvantages: 1) It requires many steps that take much working time, especially steps 3 and 11; 2) it requires using a special lifting device mounted on a chain block which keeps the impeller in a centralized vertical position for both disconnection and re-connection to the pump shaft; and 3) the total pump wet end liner and impeller replacement procedure takes over eight hours. 
         [0055]    The main problem encountered with the conventional procedures of pump replacement or repair, as outlined above, is the time it takes, which causes a drop in production rate or output. Due to the large mineral processing through-put, reduction in the amount of time the pump is off-line has a great impact in the plant productivity and profitability. In the current state of the art there is no procedure to replace slurry pump liners in less than eight hours. This is the technical problem that is solved by the present invention. 
         [0056]      FIGS. 5 and 6  illustrate a centrifugal pump having the impeller fixing mechanism of the present invention installed in the pump. Like parts of the centrifugal pump illustrated in  FIGS. 5 and 6  are denoted with the same reference numerals as shown in  FIGS. 1-4 . The present invention comprises an impeller fixing mechanism  40  (best seen in  FIGS. 8 and 9 ) that temporarily fixes the impeller  5  to the casing frontal face  4   a  and casing rear face  4   b  in such a way that the impeller  5  remains immobilized and perfectly centered in the wet end  3 , thereby enabling the impeller to be connected to pump shaft  14  without the need for realignment. In other words, the impeller fixing mechanism allows removal of the entire pump wet end assembly  3  from the slurry pump base  2  without the impeller  5  losing its position relative to the pump shaft  14 , and no realignment of the impeller  5  to the pump shaft  14  is required, nor is the slurry pump required to be dismantled in situ. 
         [0057]    When impeller  5  is fixed and immobilized, the wet end  3  can be removed by removing bolts  13  only, without the need of disconnecting pump shaft  14  from drive shaft  16  (i.e., through disconnection of coupling  15 ). Consequently, no realignment between the shafts is needed as is the case in the event of total replacement of the pump as previously described. Nor is it necessary to open the slurry pump wet end  3 , as required in the case of dismantling the pump in situ as previously described. 
         [0058]    One suitable embodiment of the impeller fixing mechanism of the present invention is shown in  FIGS. 5-9 .  FIG. 5  is a cross section view of a centrifugal pump in which is installed the impeller fixing mechanism  40 . In a preferred embodiment, the impeller fixing mechanism comprises two elements concentric with the pump shaft  14 , the first fixing element  19   a  being attached to the casing frontal face  4   a  on an inside surface thereof, and the second fixing element  19   b  being attached to the casing rear face  4   b  on an inside surface thereof. 
         [0059]    First fixing element  19   a  and second fixing element  19   b , as better seen in  FIGS. 7 ,  8  and  9 , are both annular members that are positioned in the pump concentric to the pump shaft  14 . Therefore, there will be a simultaneous and common description of structure of the two fixing elements  19   a  and  19   b . First fixing element  19   a  and second fixing element  19   b  each comprises a flexible elastomeric member  20   a  and  20   b , respectively, having a diameter 0.95D to 1.0D, where D is the diameter of the impeller  5 . The flexible elastomeric members  20   a  and  20   b  each have a thickness  25   a  and  25   b , respectively, that may range from about 10 mm to about 25 mm depending on the size of the pump. The thickness  25   a  and  25   b  of the respective elastomeric members  20   a  and  20   b  may be the same or may differ within the specified range. 
         [0060]    Each fixing element  19   a  and  19   b  further comprises a stiff backing member  21   a  and  21   b , respectively, the diameter of which is essentially radially co-extensive with the elastomeric member  20   a  and  20   b , respectively. The thickness of each stiff backing member  21   a  and  21   b  may range from between about 10 mm to about 30 mm. It should be noted that first fixing element  19   a , which is positioned in the pump against the casing frontal face  4   a , as shown in  FIG. 7 , is configured with an upstanding collar portion  27   a  in the elastomeric member  20   a  and a similar upstanding collar portion  27   b  in the stiff backing member  21   a . The upstanding collar portion  27   a  and  27   b  is configured to be received in the suction inlet of the pump. 
         [0061]    The stiff backing members  21   a  and  21   b  each are configured with axially extending, concentric ribs  28   a  and  28   b , as shown in  FIGS. 8 and 9 . The thickness, or axially extended height, of the ribs may range from between about 20 mm to about 50 mm. Therefore, the overall axial thickness of the stiff backing members  21   a ,  21   b  may range from between about 30 mm to about 80 mm. 
         [0062]    Tightening bolts  22   a  and  22   b  are provided for positioning through the respective casing faces  4   a  and  4   b  and are screwed into the casing faces  4   a  and  4   b  as shown in  FIG. 7 . The respective terminal ends of the tightening bolts  22   a  and  22   b  are positioned to contact the rib  28   a , and  28   b  of the respective stiff backing members  21   a  and  21   b.    
         [0063]    Each of the stiff backing members  21   a  and  21   b  further includes a loosening system consisting of loosening bolts  23   a  and  23   b , nuts  24   a  and  24   b , and washers  25   a  and  25   b . Bolts  23   a  and  23   b  are integrally connected or formed to the stiff backing members  21   a  and  21   b , respectively, and freely pass through the holes  26   a  and  26   b  in the respective casing faces  4   a  and  4   b  as illustrated in  FIG. 7 .  FIGS. 8 and 9  show the distribution of tightening bolts  22   a ,  22   b  and loosening bolts  23   a ,  23   b , which are inserted and evenly spaced apart in a concentric circumference about the fixing elements  19   a  and  19   b , and concentric with the pump shaft  14 . 
         [0064]    To fix the impeller  5  for effecting a repair of the pump, nuts  24   a  and  24   b  are first loosened, which allows free movement of loosening bolts  23   a  and  23   b . The tightening bolts  22   a  and  22   b  may then be turned to cause first fixing element  19   a  and second fixing element  19   b  to move, respectively, axially toward impeller  5  until the fixing elements  19   a  and  19   b  have each made contact with and are pressing on the impeller  5  surfaces to “sandwich” the impeller  5  between the fixing elements  19   a ,  19   b , immobilizing and keeping impeller  5  fixed in a centered position with respect to pump shaft  14 . 
         [0065]    To unlock or free the impeller  5  again, tightening bolts  22   a  and  22   b  are loosened and nuts  24   a  and  24   b  of loosening bolts  23   a  and  23   b  are rotated to urge the fixing element  19   a ,  19   b  away from the impeller. The tightening bolts  22   a ,  22   b  are then tightened to retain the fixing elements  19   a ,  19   b  in adjoining proximity to the respective casing face  4   a ,  4   b.    
         [0066]    By use of the impeller fixing mechanism of the present invention, the complete pump wet end replacement procedure comprises the following steps:
       1. Disconnect suction pipe  6  and discharge pipe  7  from the pump by removing bolts  8  and  9 , respectively;   2. Place lifting slings on the entire pump wet end  3 ;   3. Loosen nuts  25   a  and  25   b  to allow displacement of members  19   a  and  19   b  by tightening bolts  22   a  and  22   b  until members  19   a  and  19   b  make contact with and press on the impeller  5  front and rear faces;   4. Remove bolts  13  that fasten the casing rear face  4   b  to the pump base  2 ;   5. Disengage the torque release mechanism  27 ;   6. Rotate pump shaft  14  in its normal reverse rotation direction for disconnection from impeller  5 ;   7. Remove the wet end  3  and transport it to a repair facility;   8. Position the new wet end furnished with the impeller  5  assembled and restrained in the centralized position by an impeller fixing mechanism  40  and fasten it to base  2  by means of bolts  13 ;   9. Engage the torque release mechanism  27 ;   10. Rotate shaft  14  in its normal rotational direction for reconnection to impeller  5 ; and   11. Release bolts  22   a  and  22   b  to allow movement of members  19   a  and  19   b  away from the impeller  5  by rotating nuts  24   a  and  24   b , until members  19   a  and  19   b  make contact with faces  4   a  and  4   b.          
 
         [0078]    The advantages of this procedure which makes use of the impeller fixing mechanism of the present invention preferred over known procedures are
       a. There is a maximum of plant operating down-time of less than two hours;   b. It does not require disconnection of the pump shaft and drive shaft coupling; and   c. There is no need for realignment of the pump shafts.       
 
         [0082]    The impeller fixing mechanism of the present invention is directed to facilitating repairs to centrifugal pumps and may be adapted to use in any number or variety of pumps. Hence, reference herein to specific details or embodiments of the invention are by way of illustration only and not by way of limitation.