Abstract:
A molded wheel and bearing assembly includes two bearings in a molded housing forming a bearing assembly. The bearing assembly is molded into the hub of a caster wheel. The caster wheel is made by molding a hub around the bearing assembly, then molding a tread around the hub. No assembly of individual elements into the wheel is necessary.

Description:
MOLDED WHEEL AND BEARING ASSEMBLY 
     This application is a continuation-in-part of application Ser. No. 09/591,203, filed Jun. 9, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the field of wheels and, in particular, to caster wheels. 
     2. Description of Prior Art 
     For many years, most high quality wheels for casters such as shopping carts have utilized bearings that include a pair of steel races and steel ball bearings, where each piece is assembled separately into the wheel. Because each part of this bearing assembly is assembled separately, the system relies on the precision of the interlocking structural parts to control the tightness of the bearing. Due to the inherent problems of mass-producing caster wheels with such precision, this method of production results in many caster wheels having less than the required tolerances to ensure a consistent smooth operation. This characteristic can frequently cause the well known “wobble wheel”. Additionally, the cost and inefficiency in manufacturing the assembly is high, and thereby translates to higher consumer pricing. 
     High strength polymer resin compounds have been used extensively for making wheels. More recently, the use of bearing components that molded in the hubs of such wheels has been suggested to absorb shock loads and to lower the cost of the wheel and bearing assemblies. But these assemblies are still complex to manufacture since the bearing parts must still be accurately placed within the mold. To ensure precision of the molded in bearing, the wheel hub must be precisely formed as well. 
     Representative of this method is U.S. Pat. No. 5,871,286 issued Feb. 16, 1999, which discloses a molded wheel having a bearing assembly molded into the wheel hub. The device includes a synthetic resin outer bearing race element embedded in the hub of the molded wheel and having a cylindrical inner sliding, journal type bearing surface. An inner bearing assembly includes two molded synthetic resin bearing halves having continuous cylindrical outer bearing surfaces disposed within the outer bearing race in sliding engagement with the inner bearing surface of the outer race. The bearing halves of the inner bearing assembly abut each other at their inner ends and may include interlocking structural features at their inner ends that enable securing of the bearing halves together at their inner ends while presenting a continuous outer cylindrical bearing sliding surface that cooperates with the adjacent surface of the outer race. A wheel axle extends through the inner bearing assembly and supports the wheel and bearing assembly for rotation relative to a wheel support. 
     Although the above invention overcomes some disadvantages of wheel bearings, there are still many disadvantages. First, the outer race is the only bearing element molded into the wheel hub. This leaves the bearing susceptible to the “wobble wheel” phenomenon due to uncontrollable looseness. This effect translates to bearing assemblies having inconsistent tolerances. Second, although this invention attempts to control potential looseness using an interlocking structure between the bearing halves, this means will suffer natural mechanical wear and tear resulting in the “wobble wheel” effect. Finally, although the process of making this invention lowers the cost of wheel and bearing assemblies, only the outer race is added to the wheel at the time of molding and the remainder of the bearing must be assembled at a later time, increasing the overall cost. 
     Therefore, there is a need for a molded wheel and bearing assembly and method of making the same, wherein the molded wheel can use a pre-assembled bearing assembly having high tolerances such that the tolerances of the molded wheel itself does not substantial adversely effect the overall performance of the finished wheel and, wherein the wheel can be incorporated into a caster support or other support well known in the art and, wherein the wheel can be produced faster and less expensively that wheels made using present manufacturing techniques. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an aspect of the present invention to provide a molded wheel that can be produced less expensively than using present wheel construction methods. 
     It is another aspect of the invention to provide a molded wheel that is made using pre-assembled bearings having high tolerances. 
     Another aspect of the invention is to provide a molded wheel that uses butt out type bearing as the pre-assembled bearings. 
     Still another aspect of the invention is to provide a method of making a molded wheel using an easily fabricated housing to hold the pre-assembled bearings wherein the housing can be molded to high tolerances. 
     It is a further aspect of this invention to provide a simple method of molding a bearing assembly into a wheel suitable for use in a caster. 
     Another aspect of the invention is to provide a method of making a molded wheel that eliminates much of the assembly costs. 
     It is still another aspect of the invention to provide a method of making a molded wheel such that the hub of the wheel can be inexpensively molded yet the molded wheel will have high precision to ensure smooth operating of the wheel bearing assemblies. 
     Another aspect of the invention is to provide a method of making a molded wheel such that molding the hub can be accomplished with having substantially less scrap using prior art techniques. 
     It is still another aspect of the invention to provide a method of making a molded wheel where the need for much of the assembly equipment such as the machinery for making the bearing, assembly of the bearings into the hub, etc. can be eliminated. 
     Finally, it is an aspect of the invention to provide a method of making a molded wheel that can accomplished in a two step process and wherein the finished wheel is obtainable off the assembly line after the completion of the second step in the process. 
     The present invention provides a bearing assembly molded into a wheel. The bearing assembly includes two precision bearings, which are commercially available, and a molded housing, which can be easily manufactured. One bearing is positioned in each end of the housing. The complete bearing assembly is located in the center of the wheel surrounded by a molded hub. The molded tread is then placed on the molded hub to complete the wheel. The wheel can then be part of caster or other support structure. 
     The invention also provides a method of making a molded wheel and bearing assembly. A bearing assembly, including two butt-out bearings in a molded housing, is placed in the center of a wheel mold. The hub is molded around the assembly. A tread is then molded around the hub. A completed molded caster wheel can then be removed from the mold. Assembly of individual elements into the wheel is unnecessary. 
     These aspects of the invention are not meant to be exclusive. Other features, aspects, and advantages of the present invention will be readily apparent to those of ordinary skill in the art when read in conjunction with the following description, appended claims, and accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a detailed cross-sectional view of typical bearing used in the present invention. 
     FIG. 2 is a cross-sectional view of the butt-out bearings of FIG. 1 positioned within the molded housing in accordance with the invention. 
     FIG. 3 is an illustration of an alternative bearing, tube bearings, one having a male end and one having a female end, positioned within the molded housing in accordance with the invention. 
     FIG. 4 is an illustration of a male half of the tube bearings used in FIG.  3 . 
     FIG. 5 is an illustration of a female half of the tube bearings used in FIG.  3 . 
     FIG. 6 is a cross-sectional view of the completed wheel with the molded hub and tread in place. 
     FIG. 7 is a cross-sectional view of the hub mold in which the hub is molded around housing containing the two pre-assembled bearings. 
     FIG. 8 is an isometric view of the completed wheel in a typical caster mechanism. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, an element of the preferred embodiment of the invention is shown. Bearing  10  includes spindle  12  and casing  14 . Spindle  12  is hollow and extends through casing  14 . Casing  14  includes ball bearings and races to allow spindle  12  to rotate. An axle (not shown) can be inserted through spindle  12  so that completed wheel can be utilized as a caster or in any other similar situation well-known in the art. Bearing  10  is preferably a butt-out type of bearing which is commercially available as pre-assembled unit well known in the art. This type of bearing is available in many different sizes and provides precise fit between the components thus eliminates the need to attempt to precisely assembly the individual bearing parts within the wheel. Further, by utilizing a completed bearing  10 , the cost for assembling the bearing is also eliminated. 
     FIG. 2 is a cross-sectional view of the butt-out bearings  10 ,  20  positioned within the molded housing  18  in accordance with the invention to form bearing assembly  16 . Bearing assembly  16  includes housing  18 , bearing  10 , and second bearing  20 . Bearings  10 ,  20  are substantially identical to one another when used in a typical caster wheel, however, this is not essential. Some applications might require a longer spindle  12  for the bearings than the other. While butt-out type of precision bearings are used in the preferred embodiment of the invention, this is not critical. Any pre-assembled bearing assembly well known in the art would be suitable. Housing  18  is hollow, open ended, and substantially cylindrical. Housing  18  is preferably made of a moldable plastic, such as DELRIN. However, any plastic such polypropylene, polycarbonate, urethane, etc. could be utilized as long as the plastic can be molded accurately to required tolerances and has sufficient strength to hold press-fitted bearings  10  and  20  in place within housing  18 . Additionally, metal parts may be substituted so long as the parts meet the required tolerances of the invention. 
     As shown in FIG. 2, bearings  10  and  20  fit into interior  22  of the housing. End  24  of bearing  10  and end  26  of bearing  20  abut each other in interior  22  of housing  18 . The opposite ends, end  28  on bearing  10  and end  30  on bearing  20 , extend through the open ends of housing  18 . Casing  14  rests in relived area  32  of the housing, and casing  34  rests in relieved area  36 . When fitted to precise dimensions, the casings are held in the relieved areas inside the housing, while the spindles of bearings  10  and  20  are free to rotate. 
     Housing  18  may also include support ribs  38  along the exterior. Support ribs  38  extend longitudinally along the housing between relieved areas  32  and  36 . The use of support ribs  38  provides additional support and further ensures that the bearings are precisely aligned with the housing so that an accurately running wheel is obtained. 
     FIG. 3 illustrates an alternative embodiment of bearing assembly  16 . Tube bearings  11  and  21  fit into housing  18 . The tube bearings are fitted together inside housing  18  rather than abut each other. Tube bearing  11  includes male spindle half  13 , and tube bearing  21  includes female spindle half  23 . As shown in FIG. 4, spindle half  13  includes male end  15  and central bore  17 . FIG. 5 illustrates spindle half  23 , including female end  25  and central bore  27 . Female end  25  is dimensioned to receive male end  15 , while bores  17  and  27  are dimensioned to receive an axle of a wheel (not shown). 
     FIG. 6 is a cross-sectional view of the completed wheel  40  with the molded hub  42  and tread  44  in place. This is the preferred embodiment for wheel  40  when used as a caster wheel, especially suitable for use with shopping carts. However, this method of construction can be utilized wherever a mass produced wheel having substantially precise bearings is required. The pre-assembled bearings are available in a variety of sizes and spindles diameters so that wheels of various diameters and axle dimensions can be easily made. 
     Wheel  40  includes molded hub  42  which molded around bearing assembly  16  and molded tread  44 , which is, in turn, molded around hub  42 . Hub  42  and tread  44  are molded around the bearing assembly using injection molding techniques that are well known in the art. 
     As shown in FIG. 7, completed bearing assembly  16 , including bearings  10  and  20  which have been press fitted into housing  18 , are placed in the center of the bottom portion  50  on pin  48  of mold  51 . Top section  52  of mold  51  is then placed onto bottom section  50  of mold  51  so that mold  51  is closed and ready for injection of the plastic material to form hub  42 . The completed hub  42  with bearing assembly  16  molded therein is then removed and placed into another mold (not shown) wherein tread is then molded around hub  42  containing bearing assembly  16  to form a complete wheel. Those of ordinary skill in the art will appreciate that the molds can be provided so that many wheels are molded simultaneously or so that hub and tread may also be molded during the same process, again using techniques well known in the art. 
     As shown in FIG. 8, wheel  40  can be attached in a caster mechanism  60  via axle  62 , which is fed through spindles  12  of bearing assemblies  10 ,  20  (shown in FIGS.  1  and  2 ). 
     The illustrated embodiments of the invention are intended to be illustrative only, recognizing that persons having ordinary skill in the art may construct different forms of the invention that fully fall within the scope of the subject matter appearing in the following claims.