GB1603178A

GB1603178A - Trolley wheels

Info

Publication number: GB1603178A
Application number: GB1868678A
Authority: GB
Original assignee: Frost & Son Inc C L; CL Frost and Son Inc
Current assignee: Frost & Son Inc C L; CL Frost and Son Inc
Priority date: 1978-05-10
Filing date: 1978-05-10
Publication date: 1981-11-18

Description

(54) TROLLEY WHEELS (71) We, C.L. FROST & SON, INC., a Corporation organised under the laws of the State of Michigan, United States of America, of 2020 Bristol, N.W., Grand Rapids, Michigan, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to trolley wheel assemblies and to methods of manufacturing trolley wheel assemblies.

The invention is defined in the appended claims but various features and advantages of certain of the claims though not necessarily of all will now be discussed together with certain disadvantages of the prior art which will be overcome by the invention of certain of the claims though not necessarily of all.

Trolley wheels have long been used in many industries, especially in overhead and other conveyors. Such wheels typically support suspended brackets which transport goods through various processes. For many years, metal trolley wheels were used and were subject to wear, corrosion and deterioration and were also noisy in operation.

More recently, combination metal and plastics trolley wheel assemblies have been devised which have greatly advanced the industry because of their many advantages.

One such trolley wheel assembly is described in our copending Patent Application No. 49529/75 (Serial No. 1513269). This trolley wheel assembly essentially utilises a pair of metallic outer bearing race rings fitted adjacent a central opening in a plastics trolley wheel with an inner race assembly extending through the opening and a pair of full complement rows of ball bearings between the inner and outer races. The outer race rings are spaced apart in a predetermined spacing by a portion of the plastics wheel.

A difficulty which has been encountered with such prior wheel assemblies is that the portion of the wheel which spaces the outer race rings apart is critical to the spacing of the bearings and thus the proper functioning of the trolley wheel assembly. Because of material shrinkage during manufacture of the wheels, it has been difficult to obtain the critical dimensioning necessary for the wheel assemblies, and especially the portion of the wheel intermediate the outer races, prior to insertion of the outer race rings therein.

Another difficulty encountered during use was that of the rotation of the outer metallic bearing race rings with respect to the plastics wheel. Such rings were also difficult to maintain in axial alignment with the wheel. Rotation of the rings with respect to the wheel causes heat buildup and wear reducing the life of the wheel. Excessive wear throws the bearings out of alignment.

Also, prior outer race ring configurations have required drawing of a portion of the rings meaning that the material used had to be sufficiently ductile to allow that drawing.

Incorporation of sufficient ductility in the metallic material prevented the use of harder, longer-wearing materials and limited the load capabilities of the assembly.

Therefore, a need has existed for an improved trolley wheel assembly which maintains the advantages of the more recently designed metal-plastics trolley wheel assemblies useful in sanitary, overhead conveyor applications and yet overcomes the above-mentioned problems of manufacture, maintenance, and use.

The invention is extremely useful in conveyor applications, especially those applications requiring sanitary conditions and frequent steam cleaning or the like such as in the food processing industry where the assemblies must be subjected to high heat and moisture conditions and sustained use without corrosion, deterioration, or breakdown.

In one of its aspects, the invention may be seen to reside in a trolley wheel assembly comprising a plastics trolley wheel having a central opening with an axis therethrough; a pair of annular, metallic outer bearing races positioned back to back in abutment with one another in the central opening, the outer bearing races each including a contoured portion shaped to receive rolling contact bearing elements for rotational support of the wheel and outer bearing races, and recessed means for preventing rotation of the outer bearing race with respect to wheel; the wheel including engaging means engaging the recessed means of each of the outer bearing races to prevent such rotation as well as to prevent axial movement of the outer races away from the back-to-back position. Axially extending means may be provided in the central opening having a pair of inner raceways in registry with the contoured portions of the outer bearing races and rolling contact bearing elements disposed between each of the outer bearing races and respective inner raceway for rotationally supporting the wheel and the outer races.

In another of its aspects, the invention may be seen to reside in a trolley wheel assembly comprising a plastics trolley wheel having a central opening with an axis therethrough; a pair of annular, metallic, outer bearing races each including an annular, radially extending flange, an annular axially extending flange, and a curved transition area between the said flanges and forming a contoured area for receiving rolling contact bearing elements; the outer races being positioned back to back in the central opening with the radial flanges being parallel to and abutting one another and the axial flanges extending away from each other; the outer races each further including recessed means for preventing rotation of the outer bearing race with respect to the wheel; the wheel including engaging means engaging the recessed means of each of the outer bearing races to prevent such rotation as well as to prevent axial movement of the outer races away from the said back-to-back position; axially extending means in the central opening having a pair of inner raceways in registry with the contoured portions of the outer bearing races; and rolling contact bearing elements disposed between each of the outer bearing races and inner raceways for rotationally supporting the wheel and outer races.

In another aspect the invention provides a method of manufacturing a trolley wheel assembly comprising the steps of providing a pair of annular, metallic, outer rolling element bearing race rings, each ring having inner and outer surfaces, a flange which will extend generally in the radial direction in the completed wheel assembly, a flange which will extend generally in the axial direction in the completed assembly and recessed means for preventing rotation of the outer bearing race ring within the wheel assembly; supporting the rings back to back and in axial alignment with one another within a mould cavity with the outer surfaces of the radial flanges being parallel to and engaging one another, and the axial flanges extending away from one another; moulding a plastics wheel around the positioned rings by introducing a flowable plastics material into the mould cavity and around the outer surfaces of the rings and allowing the plastics material to set up and solidify around the rings while holding the rings in engagement with one another to prevent separation during such moulding such that the plastics fills in any spaces between but does not separate the rings from the back-to-back relationship and extends over the axial end surfaces of the axial flanges and into the recessed means to positions flush with the inner surfaces of the rings so that engagement of the plastics material in the said recessed means prevents relative rotation of the rings and the wheel constituted by the moulded plastics material, the back-to-back race rings avoiding the necessity for critical dimensioning of any wheel portion therebetween.

In a further aspect, the invention provides a method of manufacturing a trolley wheel assembly comprising the steps of: providing a pair of annular, metallic, outer bearing races, each race including a contoured portion adapted to receive rolling contact bearing elements for rotational support of the wheel assembly and recessed means for preventing rotation of the outer bearing race within the wheel assembly; positioning the races in engagement and in axial alignment with one another on a support in a mould cavity with the contoured portions facing away from one another, and moulding a plastics wheel around the races by introducing a flowable plastics material into the mould cavity and around the outer surfaces of the races and allowing the plastics material to set up and solidify around the races while holding the races in engagement with one another to prevent separation such that the wheel contacts the radially outermost surfaces of the races for support, fills any gaps or spaces therebetween but does not separate the races from their engaged positions, contacts the recessed means to prevent rotation between the races and the wheel, and extends axially beyond at least portions of the races to positions flush with the interior surfaces of the races to retain them in their engaged, axially aligned positions whereby the wheel maintains the races in axial and radial alignment.

Because the race rings are prepositioned in engagement with one another and the plastics wheel is actually moulded around the positioned rings there is no requirement for accurately forming those parts of the wheel which are to contact the race rings to critical dimensions. Moreover, the assembly is very durable and long wearing because rotation between the outer race rings and plastics wheel is prevented by the recessed means while the proper alignment of the bearings is ensured because of the axial retention of the races in engagement with one another by portions of the plastics moulded wheel. A higher load capacity is obtained in the assembly because the configuration of the outer bearing races eliminates the need for drawing during manufacture allowing the use of hardened materials.

In addition to all the above advantages, the assembly maintains the other advantages of usefulness in sanitary conveyor applications such as the food processing industry where the assemblies must be steam cleaned frequently and thus subjected to a high heat and moisture all without corroding, flaking, or chipping or other deterioration which could contaminate food bearing carried by such assemblies.

The invention may be carried into practice in various ways but one trolley wheel assembly, several modifications thereof, and its method of manufacture will now be described by way of example with reference to the accompanying drawings, in which: 1. Figure 1 is a fragmentary, sectional view of a trolley wheel assembly embodying the present invention secured to the upper end of a typical overhead conveyor trolley bracket; Figure 2 is an exploded, perspective view of the trolley wheel assembly shown in Figure 1; Figure 3 is an end view of the trolley wheel assembly shown in Figures 1 and 2; Figure 4 is a sectional view of the trolley wheel and outer race rings, without the remainder of the assembly, illustrating the positions of the outer race rings in the plastics wheel; Figure 5 is a sectional view of the trolley wheel without the remainder of the assembly taken along line V-V of Figure 3; Figure 6 is a fragmentary, sectional view of the axial end surface of one of the outer race rings and the interengagement of the wheel and outer bearing race taken along the plane VI-VI of Figure 4; Figure 7 is a sectional view of the trolley wheel assembled with another axial inner race assembly; Figure 8 is a sectional view of the trolley wheel assembled with yet another axial inner race assembly; Figure 9 is a sectional view of the trolley wheel assembled with a fourth axial inner race assembly; Figure 10 is a sectional view of injection moulding apparatus preferably used to manufacture the trolley wheel assembly; and Figure 11 is a plan view of the lower half of the injection moulding apparatus taken along the parting line and plane XI-XI of Figure 10.

Referring now to the drawings in greater detail, Figures 1 to 3 illustrate a trolley wheel assembly which is the preferred embodiment 10 of the present invention and includes a pair of identical, annular, metallic rings 12 constituting outer bearing races, a plastics trolley wheel 30 positioned about the rings 12, and an axially extending, multipiece inner race assembly 40 extending through the wheel-outer race combination.

A pair of full complement rows of ball bearings 80 is positioned between the axially and radially aligned outer races and inner raceways to rotationally support the wheel and outer race unit about the multipiece inner race assembly.

As shown in Figure 1, the wheel assembly 10 is designed for incorporation in and support on a trolley bracket 11 at its upper end such that the bracket is suspended from the wheel assembly. The wheel 30 itself includes a sloped or angled outer circumferential surface in order to accommodate the sloped surfaces of the lower flange of a conventional I-beam which is commonly used in overhead conveyor applications.

The bracket 11 extends on one open side of the I-beam with another bracket 11 and wheel assembly on the opposite side of the I-beam. The two brackets are secured together to hold the wheel assemblies in alignment with the beam for movement therealong.

As is best seen in Figures 1 and 2, the annular, metallic, outer bearing race rings 12 are utilized in pairs within a single wheel 30. Each of the rings 12 is preferably stamped from precipitation hardened, stainless steel to provide a durable, long-lasting support surface for the rows of ball bearings 80. Each race ring 12 includes a radially extending annular flange 14 having a circular central opening or aperture 16 therethrough. The radial flange 14 merges integrally through a curved transition area 18 into an axially extending, annular flange 20 having an axially outermost radially directed end surface 22 lying in one plane. The curved transition area 18 has the crosssectional shape of a portion of a circle to match the spherical contour of the ball bearings 80 which are received therein as shown in Figure 1. The outer axial edge 22 of the axially extending flange 20 of each ring also includes preferably four equally spaced, curved or arcuate scallops or recesses 24 extending thereinto. The recesses or scallops 24 mate with and are tightly engaged by correspondingly shaped portions of the plastics wheel 30 to prevent rotation between the race rings 12 and wheel 30 as well as to prevent axial movement and/or separation of rings 12 when in place within the wheel.

As shown in Figures 1 to 3, the plastics trolley wheel 30 receives the rings 12 in an engaged, back-to-back relationship within a central opening 32. The radial flanges 14 engage one another while the axial flanges 20 extend away from one another. Although the wheel 30 is shown as a separately manufactured part in Figure 2, in actual manufacture the wheel 30 is injection moulded about a pair of the aligned, prepositioned rings 12 in the manner shown in Figures 10 and 11.

The wheel 30 includes an annular, generally V-shaped cross-sectional portion 34 which fits between the contoured backs 28 of the engaged rings 12 to fully support those rings without separating them. Also included on either side of the central portion 34 are contoured areas 36 matching the curvature of the outside radially outermost surfaces of the rings 12 as well as radially extending annular flanges 37, 38 on either axial end of the wheel 30. The radial flanges 37, 38 extend over the axial end surfaces 22 of the rings 12 to tightly engage them to maintain the axial positions of the rings and include axially extending, curved protrusions 39 which are generally parallel to the axis of the wheel 30 as are the recesses 24 and mate with the recesses 24 to prevent rotation between the wheel and rings. The radially innermost surfaces of the flanges 37, 38 and protrusions 39 are coterminous and flush with the inner surface of the axial flanges 20 of the rings 12 to prevent any interference with the bearings 80 (Figures 1, 4 and 6).

Preferably, the wheel or tyre 30 is formed from a thermoplastic material such as an acetal resin sold under the trade mark "Delrin" by E.I. du Pont de Nemours and Company. This material may be easily injection moulded as will be hereinafter described and cools to form a durable, wear-resistant, high load bearing wheel which is friction resistant and easily movable especially in conveyor applications. The material has sufficient strength to hold the race rings 12 in their proper engaged position and is virtually noiseless in operation when in contact with a conventional metallic I-beam.

As is best seen in Figures 1 to 3, the axially extending inner race assembly 40, which is preferably entirely formed from stainless steel, includes a solid shaft 42 having an enlarged outer head portion 44 which tapers inwardly at section 46 to a generally constant diameter cylindrical shank portion 48. The outer free end of the shaft 48 is threaded at 50 for receipt of a nut to secure the shaft, and thus the entire wheel assembly, to the bracket 11 (Figure 1).

Received over the shaft 48 and in abutment with the head 44 and the tapered section 46 is a hollow, inner race member 52 including a first, enlarged outer diameter portion 54 and a curved, concave surface 56 forming an inner raceway which is complementary to the contour of the spherical ball bearings 80 and has the same radius of curvature as the contoured section 18 of the outer race rings 12. The raceway 56 merges with a constant diameter cylindrical portion 58 ending in a radial end surface 60. The member 52 has an inside diameter 53 which matches the outside diameter of the shaft 48 and includes an enlarged, tapered opening 55 abutting and engaging the correspondingly shaped enlarged head 44 to prevent movement of the member 52 past the head 44.

A second hollow, generally cylindrically shaped member 62 includes an enlarged outer diameter portion 64 curving inwardly in a contoured raceway 66 matched to ball bearings 80 to a reduced diameter portion 66 ending in a radially directed shoulder or end surface 70. The member 62 is fitted over the shaft 48 into abutment with the end surface 60 of the member 52 and has an inner diameter 72 matched to the shaft 48.

The inner race members 52, 62 are retained on the shaft 42 by a retainer assembly including a split, resilient retainer clip 74 fitted in registering grooves 75, 76 formed respectively on the outside and inside diameters of the shaft 42 and the inner race member 62. One of the grooves 75, 76 is slightly wider than the clip 74 such that slight axial movement may be obtained between the member 62 and the shaft 42 to allow the member 62 to be tightened securely against the shoulder 60 which, in turn, forces the member 52 against the head 44 such that the inner race members function together as a unit without rotation therebetween. The width of the member 62 is sufficient to project beyond the outer surface or axial side of the wheel 30 when assembled in the wheel (Figure 1). This allows the bracket 11 or another abutment to engage the member 62 to force it tightly against the shoulder 60 of the member 52. In addition, at least one of the grooves 75, 76 is sufficiently deep to receive the entirety of the resilient clip 65 after the member 52 is on the shaft 42 and as the member 62 is forced over the clip 65 on the shaft 48.

Referring now to Figures 7 to 9, alternative embodiments of the axially extending inner race assembly are illustrated which may all be substituted in the trolley wheel assembly shown in Figures 1 to 6. All of the alternative inner race assemblies are preferably formed from stainless steel and utilize split, resilient, retainer clips 74 seated in grooves having dimensional characteristics allowing assembly with the clip in place on one of the members and slight axial movement of the inner race pieces with respect to one another after assembly to ensure proper tightening of the members to function as a unit.

In Figure 7, a solid shaft 85 having an enlarged head 86 curving through a contoured, inner raceway section 87 matched to the spherical shape of the balls 80 to a constant diameter section 88 is inserted through the opening 16 of the bearing ring 12. A coaxial cylindrical extension 89 extends from the end surface of the cylinder 88 and is threaded at 90. A second inner race member exactly similar to the member 62 described above is fitted over the shaft 89 into abutment with the axial end surface 91 of the cylinder section 88 and is retained on the shaft 89 by a resilient clip 74 in the manner described above.

In Figure 8, the inner race assembly includes a bushing 95 having an outer surface having the same shape and contour as the solid stud 85 shown in Figure 7 except that the bushing 95 is hollow and adapted to receive a stud or shaft such as 42 shown in Figure 2. The bushing 95 includes a reduced diameter, cylindrical surface 96 which receives an inner race member 62 as described in connection with Figures 7 and 2. The member 62 is retained on the surface 96 by a resilient spring clip 74 in the manner described above while the member 62 projects slightly beyond the end of the member 95 and the side of the wheel 30 to allow the two members to be forced tightly together by an abutment or bracket.

In Figure 9, a three-piece inner race assembly extends through the opening 16 of the rings 12. This assembly is similar to that shown in Figure 8 except that two headed bushings 98,99 are used in place of the single bushing 95 shown in Figure 8. The member 62 abuts the end surface of the first bushing 98 and forces the same against the headed end of the second bushing 99 to retain all members tightly together when the resilient spring clip 74 is engaged between members 99 and 62 to retain the assembly together. In either Figure 8 or Figure 9, a separate axle or support shaft may be inserted through the inner diameter of the inner bushing for support of the assembly in the desired fashion.

Referring now to Figures 10 and 11, the preferred method and apparatus for making the trolley wheel assembly shown and described in Figures 1 to 9 is illustrated. The wheel is injection moulded in a mould apparatus 100 which includes an upper movable mould section 102 and a lower fixed mould section 140. Sections 102, 140 meet and engage one another along a parting line P as shown in Figure 10. The upper mould section 102 includes an upper plate 104 secured by conventional securing means or welding to a lower plate 106.

Received within the lower plate 106 is a central cavity plate or block 108 held against the upper plate 104 by shoulders 110.

Received within a pair of central openings 112 in the cavity block 108 are reciprocatable cylindrical mould projections or members 114 having a hollow, cylindrical, contoured end portion 116 and a central, cylindrical recess 118 therewithin. The reciprocatable moulding members 114 are biased downwardly by springs 122 which are seated in the upper plate 104 and which engage the upper surfaces of members 114, these members being limited in downward movement by shoulders 120. The upper portion of the contoured mould cavity C is formed in the central plate or block 108 with reciprocatable members 114 being moved downwardly therethrough to help form the mould cavity and preposition the outer race rings 12 as will be described below.

The lower mould section 140 includes a base plate 142 secured against a central plate 144 which in turn is secured to an upper plate 146 having a central opening 147 therewithin receiving a lower cavity block 148 secured against the plate 144 by means of shoulders 150. The cavity block 148 includes the lower portions of the mould cavities C formed therein and upstanding cylindrical posts 152 in the centre of each of the lower mould portions. The posts 152 include contoured shoulders 154 which match the contour of contoured portions 18 of outer race rings 12 which will be fitted thereover during the manufacture method.

The upper end of each post 152 matches the diameter of the recess 118 in the corresponding reciprocatable, biased, mould member 114.

A plurality of ejection rods 156 secured to a reciprocatable ejection plate 158 are inserted through aligned passageways or apertures extending through plates 144 and blocks 148 into the cavities C. The ends of the rods 156 are flush with the bottoms of the cavities when withdrawn but may be reciprocated upwardly by the plate 158 to eject the moulded wheel assembly out of the cavity C after the moulding process.

To form the wheels, the upper mould portion 102 is withdrawn from the lower portion 140 along the parting line. A pair of outer race rings 12 is inserted over each post 152 axially aligned, back-to-back fashion such that the contoured portion 18 of the lowermost ring engages the shoulders 154 of the post. Thereafter, the upper mould portion 102 is lowered into alignment and engagement with the lower mould portion 140 such that contoured portions 116 are received in the contoured portions 18 of the uppermost outer race ring seated on the posts 152. The posts 152 engage the recesses 118 to axially align the posts and the reciprocatable mould members 114. The springs 122 bias the members 114 downwardly to hold the race rings tightly together during moulding. Thereafter, molten plastics, preferably acetal resin as described above, in a flowable, heated condition is injected under pressure through a nozzle 160 and sprue passageways 162, 164 (Figure 11) into each of the mould cavities until the same are filled. The injected, molten plastics is allowed to cool, set up and solidify to retain the rings in their prepositioned locations before the ejection rods 156 are reciprocated by the plate 158 to eject the formed wheels when the mould top portion 102 is raised.

As will be seen in Figure 10, the plastics is tightly moulded about the rings 12 to form the portions 34 generally intermediate the backs of the rings for firm support as well as the flanges 37, 38 which are flush with the inside ball bearing contacting surfaces of the rings in the manner described above. This method eliminates the necessity for critically dimensioning any central portion of a wheel prior to assembly of the rings thereto and also tightly secures the rings against one another such that they are retained in proper axial and radial alignment and engagement throughout the life of the wheel.

Of course, it is possible to mould a wheel from a flexible, resilient plastics, rubber or other material.

WHAT WE CLAIM IS: 1. A trolley wheel assembly comprising plastics trolley wheel having a central open ing with an axis therethrough; a pair of annular, metallic outer bearing races posi tioned back to back in abutment with one another in the central opening, the outer bearing races each including a contoured portion shaped to receive rolling contact bearing elements for rotational support of the wheel and outer bearing races, and recessed means for preventing rotation of the outer bearing race with respect to the wheel; the wheel including engaging means engaging the recessed means of each of the outer bearing races to prevent such rotation as well as to prevent axial movement of the outer races away from the back-to-back position.

2. A trolley wheel assembly comprising plastics trolley wheel having a central opening with an axis therethrough; a pair of annular metallic outer bearing races positioned in back to back abutment with one another in the said central opening, the outer bearing races each including a contoured portion adapted to receive rolling contact bearing elements for rotational support of the wheel and outer races, and recessed means for preventing rotation of the outer bearing race with respect to the wheel; the wheel including engaging means engaging the recessed means of each of the said outer bearing races to prevent such rotation as well as to prevent axial movement of the outer races away from the said back-to-back position; axially extending means in the said central opening having a pair of inner raceways in registry with the contoured portions of the outer bearing races; and rolling contact bearing elements disposed between each of the outer bearing races and a respective inner raceway for rotationally supporting the wheel and the outer races.

3. A trolley wheel assembly as claimed in Claim 2 in which the recessed means on the outer bearing races and the engaging means extend parallel to the said axis.

4. A trolley wheel assembly as claimed in Claim 2 or Claim 3 which includes an axially extending flange on each of the outer bearing races, the said flanges extending away from one another; the engaging means including a radially extending flange abutting the end surface of each of the said axial outer race flanges.

5. A trolley wheel assembly as claimed in Claim 4 in which the outer races each include an annular, radially extending flange integral with and generally at right angles to the said axial flanges which are also annular, the radial outer race flanges being generally parallel to and abutting one another back to back, the contoured portions of the outer races each including portions of said annular radial and axial flanges and a curved, annular transition area therebetween.

6. A trolley wheel assembly as claimed in Claim 5 in which the contoured portions of the outer races include inside surface

Claims

**WARNING** start of CLMS field may overlap end of DESC **. A plurality of ejection rods 156 secured to a reciprocatable ejection plate 158 are inserted through aligned passageways or apertures extending through plates 144 and blocks 148 into the cavities C. The ends of the rods 156 are flush with the bottoms of the cavities when withdrawn but may be reciprocated upwardly by the plate 158 to eject the moulded wheel assembly out of the cavity C after the moulding process. To form the wheels, the upper mould portion 102 is withdrawn from the lower portion 140 along the parting line. A pair of outer race rings 12 is inserted over each post 152 axially aligned, back-to-back fashion such that the contoured portion 18 of the lowermost ring engages the shoulders 154 of the post. Thereafter, the upper mould portion 102 is lowered into alignment and engagement with the lower mould portion 140 such that contoured portions 116 are received in the contoured portions 18 of the uppermost outer race ring seated on the posts 152. The posts 152 engage the recesses 118 to axially align the posts and the reciprocatable mould members 114. The springs 122 bias the members 114 downwardly to hold the race rings tightly together during moulding. Thereafter, molten plastics, preferably acetal resin as described above, in a flowable, heated condition is injected under pressure through a nozzle 160 and sprue passageways 162, 164 (Figure 11) into each of the mould cavities until the same are filled. The injected, molten plastics is allowed to cool, set up and solidify to retain the rings in their prepositioned locations before the ejection rods 156 are reciprocated by the plate 158 to eject the formed wheels when the mould top portion 102 is raised. As will be seen in Figure 10, the plastics is tightly moulded about the rings 12 to form the portions 34 generally intermediate the backs of the rings for firm support as well as the flanges 37, 38 which are flush with the inside ball bearing contacting surfaces of the rings in the manner described above. This method eliminates the necessity for critically dimensioning any central portion of a wheel prior to assembly of the rings thereto and also tightly secures the rings against one another such that they are retained in proper axial and radial alignment and engagement throughout the life of the wheel. Of course, it is possible to mould a wheel from a flexible, resilient plastics, rubber or other material. WHAT WE CLAIM IS:

1. A trolley wheel assembly comprising plastics trolley wheel having a central open ing with an axis therethrough; a pair of annular, metallic outer bearing races posi tioned back to back in abutment with one another in the central opening, the outer bearing races each including a contoured portion shaped to receive rolling contact bearing elements for rotational support of the wheel and outer bearing races, and recessed means for preventing rotation of the outer bearing race with respect to the wheel; the wheel including engaging means engaging the recessed means of each of the outer bearing races to prevent such rotation as well as to prevent axial movement of the outer races away from the back-to-back position.

6. A trolley wheel assembly as claimed in Claim 5 in which the contoured portions of the outer races include inside surfaces

engaging the rolling contact bearing elements; the radially extending flanges of the engaging means being coterminous and flush with the said inside surfaces of the axially extending outer race flanges.

7. A trolley wheel assembly as claimed in Claim 6 in which the recessed means include at least one scallop recessed in the edge of each of the axially extending flanges of the outer bearing races; the radially extending flanges of the engaging means each including an axially extending protrusion extending into and mating with the scallop.

8. A trolley wheel assembly as claimed in Claim 2 in which the recessed means includes an axially extending recess in each of the outer bearing races; the engaging means including axial protrusions extending into and mating with recesses in the outer races.

9. A trolley wheel assembly as claimed in Claim 8 in which the engaging means also includes radially extending flanges engaging the axially outermost, radially extending portions of the outer races, the axial protrusions and radially extending flanges being flush with the surfaces of the outer races which engage the rolling contact bearing elements.

10. A trolley wheel assembly as claimed in Claim 2 in which the wheel is moulded about the outer bearing races which are prepositioned in the back-to-back relationship, the wheel including a central portion having a V-like cross-sectional shape engaging the radially outermost surfaces of the outer races while the engaging means extend into engagement with the axially outermost radial surfaces of the outer races.

11. A trolley wheel assembly as claimed in Claim 10 in which the recessed means includes an axially extending recess in each of the outer bearing races; the engaging means including axial protrusions extending into and mating with the recesses in the outer races.

12. A trolley wheel assembly as claimed in any of claims 2 to 11, in which the axially extending means includes a multipiece inner race assembly having separate, contoured, inner race means for forming the inner raceways in registry with the contoured outer race portions.

13. A trolley wheel assembly as claimed in Claim 12 which includes retaining means for retaining the inner race means together including means allowing axial movement therebetween whereby the inner race means may be tightened together.

14. A trolley wheel assembly comprising plastics trolley wheel having a central opening with an axis therethrough; a pair of annular, metallic, outer bearing races each including an annular radially extending flange, an annular axially extending flange, and a curved transition area between the said flanges and forming a contoured area for receiving rolling contact bearing elements; the outer races being positioned back to back in the central opening with the radial flanges being parallel to and abutting one another and the axial flanges extending away from each other; the outer races each further including recessed means for preventing rotation of the outer bearing race with respect to the wheel; the wheel including engaging means engaging the recessed means of each of the outer bearing races to prevent such rotation as well as to prevent axial movement of the outer races away from the said back-to-back position; axially extending means in the central opening having a pair of inner raceways in registry with the contoured portions of the outer bearing races; and rolling contact bearing elements disposed between each of the outer bearing races and inner raceways for rotationally supporting the wheel and outer races.

15. A trolley wheel assembly as claimed in Claim 14 in which the recesses means are formed in the axially extending flanges of the outer races, the engaging means including radially extending flanges abutting the ends of the axially extending outer race flanges.

16. A trolley wheel assembly as claimed in Claim 15 in which the recessed means include at least one scallop recessed in the edge of each of the axially extending flanges of the outer bearing races; the radially extending flanges of the engaging means each including an axially extending protrusion extending into and mating with the respective scallop.

17. A trolley wheel assembly as claimed in Claim 16 in which the axially extending protrusions and radially extending flanges of the engaging means are coterminous and flush with the inside surfaces of the outer bearing races which engage the rolling contact bearing elements.

18. A trolley wheel assembly as claimed in Claim 16 in which the plastics wheel is moulded about the outer bearing races which are prepositioned and held in the said back-to-back position during moulding.

19. A trolley wheel assembly as claimed in Claim 18 in which the plastics wheel is formed from a thermoplastic material, the outer races and the inner raceways being formed from stainless steel.

20. A method of manufacturing a trolley wheel assembly comprising the steps of providing a pair of annular, metallic, outer rolling element bearing race rings, each ring having inner and outer surfaces, a flange which will extend generally in the radial direction in the completed assembly and recessed means for preventing rotation of the outer bearing race ring within the wheel assembly; supporting the rings back to back and in axial alignment with one another within a mould cavity with the outer surfaces of the radial flanges being parallel to and engaging one another, and the axial flanges extending away from one another; moulding a plastics wheel around the positioned rings by introducing a flowable plastics material into the mould cavity and around the outer surfaces of the rings and allowing the plastics material to set up and solidify around the rings while holding the rings in engagement with one another to prevent separation during such moulding such that the plastics fills in any spaces between but does not separate the rings from the back-to-back relationship and extends over the axial end surfaces of the axial flanges and into the recessed means to positions flush with the inner surfaces of the rings so that engagement of the plastics material in the said recessed means prevents relative rotation of the rings and the wheel constituted by the moulded plastics material, the back-to-back race rings avoiding the necessity for critical dimensioning of any wheel portion therebetween.

21. A method as claimed in Claim 20 which includes positioning the outer race rings on an upstanding, central support in the mould cavity and engaging a holding member against the rings to hold them against the central support during moulding.

22. A method as claimed in Claim 21 in which portions of the holding member and central support are positioned flush with the radial innermost surfaces of the axially extending outer race flanges and are used as a portion of the mould cavity.

23. A method as claimed in Claim 21 or Claim 22 in which the holding member is biased into engagement with the rings to hold them against the central support.

24. A method of manufacturing a trolley wheel assembly comprising the steps of: providing a pair of annular, metallic, outer bearing races, each race including a contoured portion adapted to receive rolling contact bearing elements for rotational support of the wheel assembly and recessed means for preventing rotation of the outer bearing race within the wheel assembly: positioning the races in engagement and in axial alignment with one another on a support in a mould cavity with the contoured portions facing away from one andther, and moulding a plastics wheel around the races by introducing a flowable plastics material into the mould cavity and around the outer surfaces of the races and allowing the plastics material to set up and solidify around the races while holding the races in engagement with one another to prevent separation such that the wheel contacts the radially outermost surfaces of the races for support, fills any gaps or spaces therebetween but does not separate the races from their engaged positions, contacts the recessed means to prevent rotation between the races and the wheel, and extends axially beyond at least portions of the races to positions flush with the interior surfaces of the races to retain them in their engaged, axially aligned positions whereby the wheel maintains the races in axial and radial alignment.

25. A trolley wheel assembly substantially as described herein with reference to Figures 1 to 6 of the accompanying draw ings.

26. A trolley wheel assembly as claimed in Claim 25 modified substantially as described herein with reference to Figure 7 or Figure 8 or Figure 9 of the accompanying drawings.

27. A method of manufacturing a trolley wheel assembly substantially as described herein with reference to Figures 10 and 11 of the accompanying drawings.