Abstract:
A caster has a horn of semi-circular configuration about an axle receiving apertured boss, a web extending radially outwardly from the boss to a semi-cylindrical flange and a pair of wheels, one on each side of the horn, the tread of the wheels being flush with the outer cylindrical surface of the flange. Hub shields are mounted on the wheels in such manner as to avoid load transmission to the shields, yet accommodating a variety of appearance features, ease of installation and reliable retention of the shields in place of the wheels.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to casters, and more particularly to casters of the type useful on carpeted surfaces and yet having decorative features. 
     2. Description of the Prior Art 
     The need for casters for carpeted surfaces has increased significantly in recent years. Typically a caster for use on carpeted surfaces may be a large ball-type caster but, for design, performance and economical consideration, other approaches have been attempted. One approach is to provide a two wheeled caster. An example is shown and described in U.S. Pat. No. 3,894,310 issued July 15, 1975 and one or more of the references cited therein. The difficulty in prior art carpet casters has been that of obtaining good performance characteristics, appearance, and yet doing so economically. The present invention is an answer to the problem of prior art casters. 
     SUMMARY OF THE INVENTION 
     Described briefly, in a typical embodiment of the present invention, a dual wheel caster has a pair of wheels on each side of a horn, and snap-in hub shields which are so-mounted as to avoid transmission of wheel loads to the hub shields. The horn structure enables utilization of wheels of the maximum diameter, while providing adequate structural strength and good appearance. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view of a dual wheeled caster assembly according to a typical embodiment of the present invention. 
     FIG. 2 is a front view thereof. 
     FIG. 3 is a top plan view thereof. 
     FIG. 4 is a section therethrough taken at line 4--4 in FIG. 3 and viewed in the direction of the arrows. 
     FIG. 5 is a section therethrough taken at line 5--5 in FIG. 4 and viewed in the direction of the arrows. 
     FIG. 6 is a view similar to FIG. 1 but showing a caster wheel with the hub shield removed. 
     FIG. 7 is an enlarged section showing details of the mounting of the hub shield in the wheel rim. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings in detail, the caster assembly 11 includes a stem 12, horn 13, and wheels 14. Each of the wheels has a hub shield 16 thereon. 
     Comparison of FIGS. 3, 4, and 5 shows the horn includes an axle boss 17 with center at 18, a semi-cylindrical flange 19 centered at 18, and a web 21 extending from the boss 17 to the flange 19. The axle 22 is received through the bore 23 in the axle boss and has wheels 14 mounted thereto, the axle actually being a rivet with the head 24 at the hub of one wheel, and the other end being swaged at 26 to retain the other wheel in place. The horn is typically die-cast metal, while the wheels are nylon. Other materials also may be used. Circularly spaced ribs or spokes 25 extend from the wheel hubs to the rims, with wheel webs 30 between the spokes providing a uniform smooth inside face of each wheel from its hub to its tread. 
     The treads 27 of the wheels are flush with the outer cylindrical surface 28 of the flange and thereby can be made the maximum diameter for the greatest facility of rolling on a carpeted surface. Also the surface of the flange can be made of a texture and material or color compatible with that of the wheels if desired to provide a unitary and homogeneous appearance as is apparent in FIG. 3, for example. 
     The caster stem is received in the stem socket and the lower end 29 thereof is supported by a ball 31 disposed in the bottom of the socket and which trasmits the vertical thrust load between the caster horn and the stem. The stem is retained in the bore by a friction ring 33 in a groove in the stem, and a similar friction ring 34 is provided in a groove near the upper end of the stem for reception in a socket on a piece of furniture or the like. The flange 36 immediately above the caster horn does not transmit any thrust loads as they are taken entirely on the ball at the bottom, and thus free swiveling is provided. 
     As can be seen by reference to FIGS. 4 and 5, the cross section thickness of the web from the stem socket rearward to the lines 37 and 38 is greater than elsewhere in the caster horn web to provide a sort of gusset portion 39, this thickness being approximately 1/4 inch in contrast to the normal thickness elsewhere in the web which is approximately 1/16 inch. The thickness of the boss at surface 17 of the boss is approximately 5/16 inch. These deimensions are given as examples to show differences in material thickness in different areas, to maximize strength, yet minimize use of material in the horn. 
     According to an important feature of the invention, the caster wheels are provided with shields for the hubs. An example is best shown in FIGS. 5 and 7, where the hub shield 41 is shown as a generally spherical shell received in a circumferential groove 42 in the wheel rim. The groove diameter at its maximum point 43, for example, is typically slightly greater than the free maximum diameter of the shield itself to the outer edge 44 thereof. However, the diameter of the entrance to the groove 43 at the edge 46 of the rim of the wheel is slightly less than the maximum diameter of the free, unloaded hub shield. The reason for this is the fact that it is desirable, according to one of the features of this invention, to avoid loading the hub shield by normal deformation of the wheel of the caster under load as it rolls. In this way, the hub shield can be made of a comparatively fragile material or have a finish thereon which is somewhat brittle but desirable for particular esthetic effect, and yet have it avoid destruction or damage during the use of the caster. The other particular advantage of this type of construction is the fact that a variety of different kinds and designs of hub shields can be employed with the caster to provide any particular contour or surface finish desired, without detracting from the basic structural design of the caster assembly. Thus it is preferable that the hub shield be of sufficient durability to be snapped into place in the groove 42 and yet float in the groove so it is not thereafter loaded by slight normal deformations of the wheel as it rolls. Of course, where the structure and materials and finish as employed in a particular hub shield are not sensitive to destruction or deterioration due to wheel deformaton, a snug fit of the shield in groove 42 could be employed. An additional feature of the construction according to the invention is the fact that hub shields can readily be assembled to the caster wheels at the point of purchase, in accordance with a particular customer&#39;s desires for appearance and color of the hub shield, for example, without the necessity of any special fastening or installation tools and without any visible fastening devices after the asembly is completed. 
     While the invention has been disclosed as employing a friction ring on the caster stem, it could also be retained in the stem socket by other means, such as staking, for example. Also, other variations will be recognized within the scope of the invention. By way of further example, the overall width of the flange at its surface 28 may be five eighths of an inch. The overall width of the tread of the 21/2  inch diameter wheel may be 1/2 inches, with a portion from the center of the tread outward being curved at a 2 inch radius from points in a circle about the axis 18 in a plane bisecting the tread, such as point 47 in plane 48 in FIG. 5, for example. 
     From the foregoing description, it should be apparent that the present invention provides a number of advantages, including the utilization of minimal material requirements in the horn, while maintaining structural and functional integrity. In addition, the features of the horn, shaft and wheel combination, permit easy assembly. Also the design of the wheel and associated shield permits easy assembly while eliminating any visual display of fastening devices. In addition, the hub shield as employed according to the present invention, permits ready variation of the esthetic quality of the caster, including various surface textures and contours, finishes and materials. One such finish could be a brittle lacquer or a ceramic. In addition, the complete caster, except for the hub shield, can be assembled in the factory and retained in inventory at the factory or point of sale, for ready assembly of the individual hub shield desired, for quick delivery from the factory, distributor or retailer. The combination also accommodates not only a wide variety of wheel and hub shield esthetic configurations but also will accommodate a wide variety of functional requirements including hard tread on carpet, soft tread on hard floors, or an all purpose tread, without sacrificing esthetic qualities. As mentioned above, the attachment of the hub shield to the wheel is such as to permit quick and easy assembly without special tools and yet allow the hub shield to float within the wheel and avoid transmission of load deflection of the wheel from the wheel into the hub, thereby eliminating the possibility of resultant loading from damaging the hub shield in such instances where the hub shield is made of a material or finishes which are particularly pleasing esthetically, but have little structural strength.