Abstract:
A bearing that is used in a motor pump in which a liquid is, not only pumped by means of an impeller driven by the pump, but also is used to lubricate components of the motor pump including the motor pump shaft. The bearing is for supporting the shaft at at least one location of the shaft. The bearing is constructed of a bronze material having added thereto a small amount of graphite, preferably around 2.5%.

Description:
RELATED APPLICATION 
       [0001]    This application is a continuation-in-part of application Ser. No. 12/136,851 filed on Jun. 11, 2008. This application also relates to an application in the name of the same inventors entitled “IMPROVED MOTOR PUMP”, and assigned Ser. No. 12/136,873 filed Jun. 11, 2008, now U.S. Pat. No. 8,083,500, the contents of which is hereby incorporated by reference herein in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates in general to an improved bearing for use with a motor driven pump. The present invention is directed to an improved bearing material that can be particularly used in constructing bearings for a canned motor pump. 
       BACKGROUND OF THE INVENTION 
       [0003]    Canned motor pumps are widely used to circulate water in heating and plumbing systems. Examples of canned motor pumps are found in U.S. Pat. Nos. 4,990,068 and 5,549,459. Canned motor pumps are lubricated by the fluid being pumped which typically is water. These pumps are commonly referred to as water lubricated pumps. The pumps are typically driven by an electric motor and the rotor of the motor, as well as the pump impeller, are mounted on a common shaft. 
         [0004]    An inherent feature of canned motor pumps is that all rotating parts are immersed in the fluid being pumped. Because of that they generally do not require any dynamic seals such as packings or mechanical seals. Since the shaft is immersed in the fluid being pumped, it follows that the bearings supporting the shaft are also immersed in the fluid, usually water. It is a common practice to use sleeve bearings, as opposed to ball bearings, in canned motor pumps. 
         [0005]    When constructing sleeve bearings, it is desired to achieve a hydrodynamic operating condition, i.e., complete separation of the shaft and the bearing by a fluid film. From a practical point, this is not consistently possible, particularly with small bearings and a lubricant of very low viscosity, such as water. Therefore, what actually occurs is so-called mixed-film lubrication where some contact between shaft and bearing remains and thus some rubbing is constantly present. For this reason, it is important that shaft and bearing materials are carefully selected so that they are compatible and do not undergo excessive wear. 
         [0006]    Early pumps used in heating systems utilized shafts made of hardened stainless steel and bearings made of bronze (either solid or sintered). This combination worked well as long as the water (and thus the bearing lubricant) was clean. However, many heating systems suffer from galvanic corrosion due to the presence of copper (in pipes) and iron (in the boiler). The galvanic corrosion product is magnetite (chemical formula Fe 3 O 4 ) which is very hard and abrasive. It precipitates out in the form of very fine particles which easily find their way into the bearing clearance where they have often caused severe wear of the stainless steel shaft. Even when hardened to the maximum possible extent, stainless steel is still softer than magnetite. To overcome this problem, shafts made of very hard ceramics such as alumina ceramic (chemical formula Al 2 O 3 ) have been used. Unfortunately, the combinations of a bronze bearing and a ceramic shaft resulted in so-called “galling,” i.e., the transfer of bronze from the bearing to the shaft, thus destroying the bearing. In the past the bronze of the bearing has been replaced by carbon-graphite (i.e. the bearing system then includes a ceramic shaft and carbon-graphite bearing). An example of the use of carbon-graphite at a bearing surface is found in U.S. Pat. No. 5,549,459. This arrangement provided an improved bearing system. However, carbon-graphite bearings are very expensive. 
         [0007]    Accordingly, it is an object of the present invention to provide an improved bearing system that provides a more durable bearing surface, while at the same time providing a bearing system that is relatively inexpensive, particularly in comparison to carbon-graphite bearings. 
         [0008]    Another object of the present invention is to provide an improved bearing that is particularly adapted for use in a canned motor pump. 
       SUMMARY OF THE INVENTION 
       [0009]    To accomplish the foregoing and other objects, features and advantages of the present invention there is provided a bearing that is used in a motor pump in which a liquid is not only pumped by means of an impeller driven by the motor, but also is used to lubricate components of the motor pump including the motor pump shaft. The bearing is for supporting the shaft at at least one location of the shaft. The bearing constructed of a bronze material having added thereto a small amount of graphite. 
         [0010]    In accordance with other aspects of the present invention the small amount of graphite is in a range of 1% to 10% of the total material comprising the bearing; alternatively the small amount of graphite is in a preferred range of 2.5% to 5% of the total material comprising the bearing; the bearing is constructed using a sintering technique that defines a porosity of the bearing; the graphite is mixed as a powder with a bronze powder prior to sintering or the graphite is impregnated into the bronze after sintering; the motor pump is a canned motor pump and the liquid is the fluid being pumped. 
         [0011]    In accordance with another embodiment of the present invention there is provided a method of forming a sleeve type bearing for use in a motor pump in which a liquid is not only pumped by means of an impeller driven by the pump, but also is used to lubricate components of the motor pump including the motor pump shaft. The method comprises the steps of: providing a main bearing component as a bronze powder; providing a small amount of an additive as a graphite powder; wherein the small amount of the additive is less than 10% of the total material of the combined powders; mixing the bronze and graphite powders together to form a composite material; and heating the mixed composite material to form the sleeve type bearing. 
         [0012]    In accordance with still other aspects of the present invention the heating step includes sintering the powder mixture; the small amount of graphite is in a range of 1% to 10% of the total material comprising the bearing; the small amount of graphite is in a range of 2.5% to 5% of the total material comprising the bearing; the motor pump is a canned motor pump and the liquid is the fluid being pumped. 
         [0013]    In accordance with still a further embodiment of the present invention there is provided a method of forming a sleeve type bearing for use in a motor pump in which a liquid is not only pumped by means of an impeller driven by the pump, but also is used to lubricate components of the motor pump including the motor pump shaft. The method comprises the steps of: providing a main bearing component as a bronze powder; providing a small amount of an additive as a graphite powder; wherein the small amount of the additive is less than 10% of the total material of the combined powders; heating the bronze powder to form the sleeve type bearing; and adding the small amount of graphite to the formed sleeve type bearing. 
         [0014]    In accordance with other aspects of the present invention the heating step includes sintering the bronze powder; the graphite is added by impregnating the graphite into the bronze bearing; the small amount of graphite is in a range of 1% to 10% of the total material comprising the bearing; the small amount of graphite is in a range of 2.5% to 5% of the total material comprising the bearing; the motor pump is a canned motor pump and the liquid is the fluid being pumped. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0015]    Numerous other objects, features and advantages of the present invention should now become apparent upon a reading of the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0016]      FIG. 1  is a cross sectional view through a canned motor pump that uses the improved bearing of the present invention; 
           [0017]      FIG. 2  is an axial cross-sectional view of the cartridge assembly in  FIG. 1 ; and 
           [0018]      FIG. 3  is a cross-sectional view taken along line  3 - 3  of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Reference is now made to the cross-sectional views shown in  FIGS. 1 and 2 .  FIG. 1  is a cross sectional view taken through a canned motor pump, and that uses the improved bearing of the present invention.  FIG. 2  is an axial cross-sectional view of the cartridge assembly in  FIG. 1 . It is to be understood that this particular canned motor pump is only shown by way of illustration, and that other canned motor pump structures, or any other motor pump structures may also use the bearing described herein. Furthermore, the principles of the present invention may also apply to other motor and/or pump constructions, and may apply to different locations therein where the improved bearing of the present invention can be used. 
         [0020]    The pump illustrated in  FIGS. 1 and 2  has been covered in the co-pending application.  FIG. 1  is a cross sectional view of a motor pump which is characterized by excellent alignment and field serviceability.  FIGS. 1 and 2  show further details of this pump including the pump housing  38 , the motor housing  40 , the front bearing support  42 , as well as sleeve bearings  44 A and  44 B. Within the motor housing  40  is disposed the stator  46  and adjacent thereto the rotor  48 . A sleeve  50  is shown supported between the rotor and stator. The support plate  52  secures the assembly to the pump housing. An O-ring  53  or other elastomeric member is provided between the shaft  54  and the bearing support  42 . The shaft  54  holds the rotor and is supported by the two bearings  44 A,  44 B. The front end of the shaft  54  supports the pump impeller  56 . A thrust washer  45  is preferably provided between bearing  44 A and the rotor assembly. The rear bearing  44 B is mounted in the sleeve  50  and the bearing support  42 , to which front bearing  44 A is mounted, is fitted to the sleeve  50 . Refer to  FIG. 2 . In the disclosed pump structure the liquid is illustrated at  36  (see  FIG. 1 ), flowing through the pump itself. 
         [0021]    In  FIG. 2  it is also noted that the bearing support member is preferably constructed with a reverse bend as at  39  in  FIG. 2  where, at one side the bearing  44 A is mounted, while the opposite side forms the pilot section  42 A. Both of these sides are preferably cylindrical. The pilot section  42 A is adapted for insertion into the corresponding pilot section  50 A of the sleeve  50 . There is thus formed an interface surface between the respective pilot sections  42 A,  50 A extending along dimension L in  FIG. 2 . 
         [0022]    In accordance with the present invention, rather than providing a press-fit between the bearing support  42  and the sleeve  50 , there is provided a pilot section P of the sleeve (see  FIG. 2 ) that has an undulating, wavy shape, instead of a plain circular or cylindrical shape. In this regard refer to the cross-sectional view of  FIG. 3  for an illustration of the shape of the sleeve along the length  50 A corresponding to the pilot section P. The undulating shape is dimensioned so that a diameter touching the inside low points K (six of them in  FIG. 3 ) of the sleeve length  50 A in  FIG. 3  is smaller than the outside diameter D of the pilot section L (see  FIG. 2 ) of the bearing support  42 . In this way, when pushing the rotor sub-assembly into the sleeve assembly in order to obtain the cartridge illustrated in  FIG. 2 , the waves or undulations are caused to flatten out to conform to the pilot diameter D of the bearing support  42 . The section P preferably extends beyond the section L to assure that there is proper contact between the components. Although reference has been made to contact points, as at K in  FIG. 3 , because this wave pattern extends along the entire length of the pilot section P ( 50 A) the contact is actually along a line that runs parallel to the shaft axis. 
         [0023]    This combination of the wavy or undulating surface of the sleeve with the cylindrical nature of the bearing support thus provides essentially a clearance-less assembly. The wavy shape of the length  51 A of the sleeve  50  functions as a radial spring. The sleeve length  50 A preferably has a wall thickness in a range on the order of 0.006 to 0.020 inch. Because of the relative thinness of the sleeve wall, particularly along the section  50 A, the spring forces are relatively small, allowing ready insertion and removal of the assembly by hand. 
         [0024]    The discovery of the present invention is that the addition of a relatively small amount of graphite to a bronze bearing results in a bearing structure that is characterized by improved durability and essentially an elimination of the afore-mentioned “galling”. This provides an improved bearing structure at relatively low cost. It has been discovered that by mixing a certain amount of graphite powder with bronze powder and then using the sintering process, bearings can be produced which have proven to work successfully with ceramic shafts, i.e., ceramic shafts are not abraded by magnetite and the addition of graphite to the bronze inhibits the transfer of bronze material to the shaft. 
         [0025]    It has been discovered that the addition of as little as 1.0% graphite is sufficient to provide the desired effect. The upper limit on the percentage is at the point where the strength of the bronze matrix of the mix is sufficiently lowered to become a problem. Too much graphite makes the bearing too brittle. The preferred range of percentage of graphite is 1.0% to 10%, and most preferred range is of 2.5% to 5%. 
         [0026]    The graphite may be combined with the bronze in basically two different ways. Both techniques include a sintering process. First, a graphite powder may be mixed with a bronze powder in the amounts indicated above, followed by the sintering (heating) process. In addition to mixing graphite with the bronze powder prior to sintering, bearings can be impregnated with graphite after the sintering process has been completed. It should be noted that sintered materials are porous and it is thus possible to impregnate the plain bronze material even after it has been sintered. 
         [0027]    Thus, in accordance with the present invention there is the discovery that one can use the combination of graphite and bronze to produce sintered bearings, either by pre-mixing graphite and bronze prior to the sintering process or by impregnation of porous sintered bronze bearings with graphite subsequent to the sintering process. The sintered bronze material is commercially available from Keystone Carbon Company. The material is designated C-62. 
         [0028]    The bearing of the present invention is for use with a canned motor pump in which, preferably, ends of the shaft of the motor pump are supported in respective bearings. The canned motor pump is for use in connection with circulating water in a water-filled system. Accordingly, oil impregnated bearings are not suitable for use. The water consumption system that the canned motor is used with is typically used for circulating drinkable water and as such, an oil impregnated bearing is not useable. 
         [0029]    Moreover, it has been found that with the bearing structure described herein, it is possible to have the canned motor operate effectively even under the conditions wherein the pump is run “dry.” One drawback to some existing canned motor pump constructions is that they are not capable of running in a “dry” condition which may be necessary, particularly for testing purposes. 
         [0030]    Having now described a limited number of embodiments of the present invention it should now be apparent to one skilled in the art that numerous other embodiments and modifications thereof are contemplated a falling within the scope of the present invention. For example, in the embodiment that is disclosed, such as in  FIG. 3 , there are six valleys (point K). However, greater than or fewer than six may be used. The preferred number of points K is three. The disclosed embodiment also has the undulations on the outer sleeve. However, in an alternate embodiment of the invention the undulations may be in the bearing support member such as along the length L shown in  FIG. 2 . The material of the sleeve and bearing support is preferably metal, and can be of any number of types of metals.