Patent Document

[0001]     This application claims the benefit of U.S. Provisional Patent Application No. 60/526,382, filed Dec. 2, 2003, under 35 U.S.C. 119(e). 
     
    
     TECHNICAL FIELD  
       [0002]     This invention relates in general to motors and more specifically to an insert molded end bell for motors, such as submersible motors, and method of manufacture thereof.  
       BACKGROUND  
       [0003]     Submersible motors are known. The motors typically have a housing, and end bell and bearing assemblies. The integrity of the housing, end bells and bearing assemblies is crucial to the life of such motors. Imperfections, damage due to impacts, and housing corrosion that allow moisture to penetrate the housing can dramatically shorten the life of the motor. Many submersible motor applications are in remote or other difficult to service environments where the cost of replacement may be more than the motor itself, placing a premium on quality and durability.  
         [0004]     Stamped end bells require multiple components and expensive assembly operations. Cast end bells require expensive secondary machining operations to achieve the tolerances required. Each such secondary operation is another point where a defect in the integrity of the motor may be introduced. All-metal construction increases the opportunity for corrosion. High quality stainless steel reduces the risk of failure due to corrosion but is expensive and adds weight to the motor. All-plastic end bells have good corrosion characteristics but often lack structural integrity of their metal counterparts and may also require expensive post-molding manufacturing steps to place and secure bearings.  
       SUMMARY  
       [0005]     An end bell for a motor has a metal base plate, a molded insert and a bearing. The operation forming the molded insert couples the bearing to the end bell. Structural elements of the end bell as well as the coupling of the bearing are formed in the molding operation. A secondary machining operation can correct for placement variations when molding the bearing. Features on the base plate, for example, a burr, can be used to retain the molded insert. The molded insert can provide improved corrosion characteristics over prior art end bells without molded inserts. The base plate and the bearing may be inserted into a mold and the molded insert formed using the base plate and bearing as mold elements. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention.  
         [0007]      FIG. 1  is a sectional view of a motor having an insert molded end bell.  
         [0008]      FIG. 2  is a perspective view of the top of the insert molded end bell of  FIG. 1 .  
         [0009]      FIG. 3  is a perspective view of the bottom of the insert molded end bell of  FIG. 1 .  
         [0010]      FIG. 4A-4C  shows top, bottom and sectional views of the insert molded end bell of  FIG. 1 .  
         [0011]      FIG. 5A-5C  shows several methods for securing the molded insert to the base plate of  FIG. 1 .  
         [0012]      FIG. 6  shows the mounting hole detail for the insert molded end bell of  FIG. 1 .  
         [0013]      FIG. 7  is a sectional view of the insert molded end bell of  FIG. 1  showing a tubular steel support molded therein; and  
         [0014]      FIG. 8  is a perspective view of the bottom of the end bell of  FIG. 1  showing an alternate method of fastening for the wiring connector. 
     
    
     DETAILED DESCRIPTION  
       [0015]     A motor  100  having an insert molded end bell  102  is illustrated in  FIG. 1 . The motor  100  described is a submersible motor, but the present invention is applicable to other motors, as well. The end bell  102  has a base plate  104  with a rim  106 . The end bell  102  also has a molded insert  108  coupling a bearing  110  to the base plate  104 . A motor shaft  112  protrudes through the end bell  102 . The end bell  102  is held to a housing  114  with fasteners, such as mounting screws  116 . The motor  100  also comprises a conventional motor apparatus  118 . Electrical connections to the motor apparatus  118  are made through an electrical connector  120 .  
         [0016]     More specifically and referring to  FIGS. 1-3 , the base plate  104  has a plurality of mounting holes  122 . The base plate  104  and the housing  114  may be metal, particularly stainless steel. The base plate  104  may be formed in any of several ways, but stamping is used in one embodiment. The rim  106  is substantially normal to the plane of the base plate  104 .  
         [0017]     The bearing  110  is preferably a conventional hydrodynamic bushing-type bearing, often used in vertically mounted motors, but may also be a ball-bearing, needle bearing or other known bearing. The molded insert  108  couples the bearing  110  to the base plate  104 . In forming the end bell  102 , the base plate  104  and the bearing  110  are aligned and held in place in a molding apparatus (not shown).  
         [0018]     The molding compound is injected to substantially fill in the shape of the end bell  102 , and in the process fully or partially encapsulates the outer surface of the bearing  110 . The molded insert  108  may include other features such as mounting cavities, splines, alignment guides, mounting holes  122 ,  124  and the like. The bearing  110  may be fabricated to have a slightly smaller inner diameter than desired for the final application. The bearing  110  may then be machined to the correct diameter for accepting the motor shaft  112 . Additionally, while machining the bearing  110  to the correct size, variations of the final placement of the bearing that occur in the molding process can be corrected by machining the inner diameter of the bearing to have a predetermined spatial relationship with the motor apparatus  118  and its shaft  112 . This may be accomplished by machining the bearing  110  in relationship to a feature of merit, for example, a base plate rim  106 , a base plate surface  138 , a mounting hole  122 , or a molded insert surface  140 .  
         [0019]     The mounting screws  116  that connect through the mounting holes  122  in the end bell  102  to the housing  114  may cause mechanical strain on the molded insert  108  and lead to a malfunction unless supported. To provide support, one or more bushings  132 , such as steel bushings, shown in  FIG. 6 , may be inserted to contact the base plate  104  at the mounting holes  122 . The bushings may be present at the time of molding or inserted after molding. Alternately, the bushings  132  may be a part of, or mounted to, the base plate  102 . When the bushing is inserted post-molding, a mold feature (not shown) approximately equal to the outer diameter of the bushing  132  may be incorporated in the mold to both create the hole for the bushing  132  and to hold the base plate  104  in position during the molding process. The inside diameter of the bushings  132  may be equal to the diameter of the mounting hole  122 .  
         [0020]     Mounting holes  124  can be used for attaching an external wiring connector  134 . The mounting holes  124  may use molded-in or pressed-in fasteners, such as nuts  142  or threaded inserts (not depicted). Alternately, the external wiring connector  134  can be mounted with screws that extend through the mounting holes  124  and attach to the stator end of the motor, as is known in the art. In another embodiment, a jam nut on the outside of the base plate  104  can secure the external wiring connector  134 . The threads coupling the jam nut may be formed in the molded insert  108  or in the base plate  104 . When the connector  134  is mounted from the inside of the end bell  102 , the threads for the jam nut may be on the external wiring connector  134  itself.  
         [0021]     Referring to FIGS.  5 A-C, when forming the end bell  102  it may be desired to secure the molded insert to the base plate  104 . Ultimately, when finally assembled, the force applied by the mounting screws  116  between the base plate  104  and the housing  114  will provide the retaining force for the assembly. However, before final assembly, securing the molded insert  108  to the base plate  104  may be accomplished in several ways. One method is to deform the rim  106  of the base plate  104  prior to filling the molding apparatus (not shown) with the molding compound.  FIG. 5A  shows how the rim  106  may be plastically deformed toward the centerline of the base plate  104 . When the molding compound is injected, the inwardly bent rim  126  will retain the molded insert  108  and any other parts captured by the molded insert.  
         [0022]      FIG. 5B  shows another mechanism for retaining the molded insert  108 . The rim  106  is bent parallel to a plane formed by the base plate  104  toward its centerline to form a cup-shape  128 . The molded insert  108  is retained by the cup-shaped portion  128  of the rim  106 .  
         [0023]      FIG. 5C  shows another embodiment wherein burrs  130  are intentionally formed on the rim  106  or other surface of the base plate  104  in contact with the molded insert  108 . Similar to the other embodiments, the burrs  130  serve as retention points for securing the base plate  104  to the molded insert  108 , for example, until final assembly or during servicing.  
         [0024]     After the base plate  104  is prepared, for example, in one of the manners above, the bearing  110  and the base plate  104  are arranged in a conventional and well known molding apparatus (not shown). As discussed above, features of the mold may be used to hold and align the base plate  104  in the molding apparatus. The mold is then filled with a molding compound to connectively couple the bearing  110  to the base plate  104  while forming the end bell  102 .  
         [0025]     Finally, the bushings  132  and/or fasteners, such as nuts  142  or threaded inserts may be disposed in holes provided, such as holes  122  and  124  respectively.  FIG. 8  shows a hex nut  142  disposed in hexagonal-shaped holes  124  for securing the external wiring connector  134 . The hex nut  142  can be pressed into the hole  124  or molded in the molded insert  108 . The hex nuts  142  may provide a more cost effective alternative to other threaded inserts.  
         [0026]     Referring to  FIG. 7 , a steel insert  136 , in one embodiment having a flared-shape, can be disposed circumferentially within the molded insert  108  for additional support, particularly to reduce deflections in the end bell  102  when used in large motors  100 . The steel insert  136  preferably has perforations (not shown) for molding compound flow in the manufacturing process and support in operation. The optimum number and placement of perforations is application specific and determined by the composition of the molded insert  108 , mold temperature and pressure. The thickness of the steel insert  136  may vary by application. The steel insert  136  may be formed as part of the base plate  104 , may be welded to the base plate  104  or may be disposed proximately to the base plate  104 . A conventional check valve (not depicted) for releasing moisture from the motor  100  may be incorporated into the base plate  104  or molded insert  108 .  
         [0027]     While the base plate  104  may be a metal stamping, it may be cast, for example of aluminum or made using a powdered metal process. The bearing  110  may be a known hydrodynamic bearing, that is, when spinning, the shaft  112  is supported by a hydraulic layer and is ideally not in contact with the bearing  110 . The bearing  110  may be polyphenlyene sulfide (PPS), brass or other suitable material. The molded insert  108  may be any suitable moldable plastic, such as Rynite 545™ (a trademark of DuPont), a thermoplastic polyester resin, specifically, a glass-reinforced polyethylene terephthalate (PET).  
         [0028]     In one embodiment, the entire molded insert  108  can be formed from polyphenlyene sulfide, or other suitable bearing material, eliminating the need for a separate bearing. In that case, a mold component (not shown), with suitable draft for removal of the molded insert, can be used to rough form the bearing inner diameter during the molding operation. As above when using a separate bearing, the final inner diameter of the shaft opening is machined to its final diameter in relationship to one or more features of the base plate  104 . By doing so, the shaft opening is both given a final diameter suitable for the corresponding shaft and aligned for accepting the motor shaft  112 .  
         [0029]     In another embodiment, the molded insert  108  can have a shaft hole formed or bored and a conventional bearing  110  press-fit into the molded insert  108  of the end bell  102 . The process for press-fit insertion of a bearing is known.  
         [0030]     In yet another embodiment, the molded insert may incorporate an upthrust bearing (not depicted), known in the art, for accommodating situations when the motor rotor (not depicted) pushes against the end bell  102 . The upthrust bearing may incorporate a separate plastic disk, but such a surface may be molded into the molded insert  108  or the bearing  110 .  
         [0031]     Various embodiments of methods and apparatus for manufacturing and using insert molded end bells have been discussed and described. It is expected that these embodiments or others in accordance with the principles of the present invention will have application to many rotating machinery applications. The disclosure extends to the constituent elements or equipment comprising such systems and specifically the methods employed thereby and therein.

Technology Category: 5