SHELF STRUCTURE AND METHOD OF MAKING SAME

Abstract: A shelf 10, particularly for use in super­ markets, and having high load bearing capacity, has a shelf body member 14 and stiffening members 22,24 secured to the underside of the body member by stud rivets 34. In manufacture, the shelf body member is precoated on its upper load bearing surface with a wipe-clean plastics material. The stud rivets are subsequently electrically welded to the underside of the pre-coated body member under conditions such that no significant damage to the surface finish of the plastics material occurs. The stud rivets are received in apertures in the stiffening members and subsequently formed with smooth heads.

Description: This invention relates to techniques for for fabricating metal structures, and is concerned specifically with the relatively narrow field of fabricated shelf structures. The applicants have considerable experience in the field of fabricated metal structures, such as sheet metal fabrications with which this application is principally concerned, and the techniques of sheet metal fabrication and the associated questions of the strength of fabricated structures and the suitability for such structures of the wide range of fastening techniques available for use are matters of everyday experience to the applicants. Nevertheless, the specific field of shelving with which this application is concerned, and in particular the requirements of shelving for use in supermarkets, turns out to have rather specific and demanding technical parameters. The structures and method of the present invention are applicable particularly, but not exclusively to shelving for use in supermarkets. In the case of supermarket shelves, there is a formidable list of technical requirements, amongst which are the following. Firstly, there is the requirement for strength. For example, in the case of a shelf of length in the region of 1200 millimetres, it is necessary for the shelf to be able to carry a load of 300 kilograms. Such a load might arise when the shelf is stacked high with bags of sugar or tins of food. As a result of this requirement, some form of stiffening is needed for the basic sheet metal body structure of the shelf. However, although the concept of stiffening such a shelf by fastening to it one or more stiffeners appears to be a relatively straightforward matter, it does raise technical difficulties. Thus, for example, there is an interaction between the hygiene and strength requirements of a supermarket shelf which raises great difficulties in relation to the methods of construction and surface finishes which can be adopted. As regards the hygiene requirements, it is of course vital in the case of a supermarket shelf that it can be frequently and easily cleaned, so that the food displayed is in a suitable environment. Such cleaning involves wiping the shelf surfaces with a suitably treated cloth or the like. This must be done at short intervals of time. Moreover, it is important that during the wiping operation, articles of dirt or food etc can be completely removed and do not become lodged in surface irregularities, edges, projections etc. Thus, the surface finish of the shelf must be durable and wipe-clean and, even on the underside, the surfaces must be relatively smooth and free of dirt entrapment zones. As regards the durability of the surface finishes, we have discovered that a surface layer of a plastics material is particularly suitable. However, although no doubt it would be technically feasible to plastic coat the product after fabrication, this is a relatively complex operation and the associated cost would be prohibitive for a product of this sort which is to used in high volume. We therefore perceived that in order to take advantage of the good hygienic qualities of plastics-coated materials, it would be necessary to pre-coat those materials in an economic manner before the fabrication process is commenced. This however raises technical problems in relation to securing the stiffeners to the shelf structure as mentioned above. For example, the obvious and well known techniques for securing together sheet metal structures in a fabrication process, such as spot welding or mechanical rivetting are obviously unacceptable. Spot welding would obviously involve making electrical contact on both sides of the assembly to be fabricated and this would produce serious surface damage in the plastic-coated upper surface of the shelf. This objection applies of course whether the shelf material is coated only on its upper side or on both sides. Likewise, simple mechanical rivetting would result in, at the very least, the presence of rivet heads at intervals along the plastic coated upper surface of the shelf. During the course of an extended development programme we investigated the possibilities of employing a welding technique on the underside only of a shelf structure which is plastic-coated on its upper side. We discovered that it is possible to electrically weld to one side of a plastic-coated sheet without unduly damaging the plastic coating. However, the only immediately suitable technique for such welding, namely projection welding, proved technically inadequate. In short, under the conditions of loading mentioned above, it was found that a significant proportion of the projection weld-joints failed when the shelf was loaded up to 300 kilograms. The prior art includes many proposals for systems of mechanically securing together structures, and techniques for welding, together with details of how such welds may be employed for securing together various mechanical structures. For example, GB1593508 (=FR-A-2373712) contains much general disclosure relating to techniques of stud welding. However the specification contains no guidance as to how such techniques can be applied to structural members such as shelves formed of relatively thin metallic material and having a preformed plastics coating or the like thereon, so as to preserve a blemish-free appearance on the upper and exposed plastics surface thereof. Equally, the disclosure contains little if anything to suggest how the technique could be applied for securing together a relatively lightweight pressed metal shelf structure and a similarly constructed stiffener, these two structures being formed in metal of comparable thicknesses, and the joint so-formed not having awkwardly shaped zones and recesses likely to form food traps, as would occur in the embodiments shown in the latter of the drawings in this prior specification. The prior art also includes disclosures relating to the use of welding techniques for composite structures. For example GB1267943 discloses in Figs 9 to 17, a wide variety of methods of attaching structures to a composite assembly of urethane foam and metal walls, such structures as hinges, refrigeration equipment, lifting rings etc. These techniques include stud welding. There is no disclosure as to how these techniques can be applied to the specific problem of strongly structurally securing together shelves and their stiffeners while maintaining ablemishfree surface on the exposed plastic upper coating on the shelf itself. Where the prior art proposes to weld a stud or the like to a composite panel having urethane foam on one side, it cannot be determined whether the welding operation will produce substantial melting and distortion of the urethane foam. However, whether such occurs is of little significance, since it is within the interior structure of the composite wall of a refrigeration vessel. Somewhat nearer to the technical field of the present invention is the disclosure in GB2065011A where it is disclosed that stud welding can be used to produce a blemish-free result for securing structures to composite panels. There is proposed a particular form of stud for this purpose. However, the composite panels concerned comprise a plastics core with metal cover sheets. In the example, a polyethylene core is 3 mm thick and metal cladding on each side is of 0.5 mm thickness. The stud is welded to one of these extremely lightweight aluminium/magnesium cover sheets, and the joint so produced is stated to have a certain adequate strength. However, this disclosure is of little relevance to the heavy duty shelving situation with which the present invention is concerned, as indicated above. Moreover, for all that the panel of this prior art specification is a composite panel, the plastics material is located within the sandwich of the two metal sheets and although the latter may be blemish-free even when illuminated by inclined lighting, it can be expected that the plastics material itself within the core of the sandwich is most unlikely to be blemish-free, which is a pre-requisite for the plastics material on the external and upper shelf surface of a product according to the present invention. There is disclosed in GB1490793 (=FR-A-2258151) a proposal relating to shelving and stiffeners therefor, including a disclosure of the pre-characterising features of claims 1 and 9 hereof. This proposal concerns itself with the need for adequate strength in a shelving system and for the desirability to be able to employ a sheet metal shelf coated on its upper side with plastics material, without visably impairing the plastics coating on the upper side during the welding procedure. According to the proposal in this prior specification, the problem is to be solved by employing a spot welding technique for a very short duration, thereby to secure the stiffeners to the shelves themselves. However, the main strength of the shelf and stiffener assembly is derived from the stiffeners alone, and not from the stiffener/shelf assembly. The stiffeners themselves directly rest on the shelf supports. The shelves merely rest on the stiffeners and serve to provide an area on which a load can rest. The shelves do not co-operate with the stiffeners to form a unified structural assembly. The specification contains a full disclosure of the problems of obtaining satisfactory weld strength in the high load situation with which the present invention is concerned. An object of the present invention is to provide a shelf structure and a method of making same offering improvements in relation to one or more of the matters discussed above, or generally. According to the invention, there is provided a method of making a load-bearing shelf structure, together with a load-bearing shelf structure itself, as defined in the accompanying claims. The invention also provides such a method and article not limited by all features of any particular claim herein, but comprising any novel feature or any novel combination of features disclosed herein. An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Fig 1 shows a section through a shelf structure, the section being taken at right angles to the longitudinal direction of the shelf; Fig 2 show a section through a second embodiment, the section being similar to Fig 1; and Fig 3 shows a side elevation view of an end portion of the shelves of Figs 1 and 2, the direction of viewing being shown by arrow III in Figs 1 and 2. As shown in the drawings, there is provided a shelf structure 10 for use in a supermarket. The shelf is a fabrication formed from mild steel and, in this embodiment, is of length approximately 1200 millimetres and of width approximately 400 millimetres and has a load bearing capacity in excess of 300 kilograms. The shelf is formed with downwardly turned end flanges 12, one at each end of the shelf and extending across the full width of the shelf, for load-bearing engagement with suitable shelf support brackets (not shown). Shelf 10 comprises a shelf body member 14 having an upper load support surface 16. Body member 14 has side flanges 18 formed with inturned edges 20. Secured to the underside of body member 14 are two stiffening members. In the embodiment of Fig 1, the stiffening members 22, 24 are of V-section. In the embodiment of Fig 2 the stiffening members 26, 28 are of so-called 'top hat' section ie of rectangular channel section. In both the embodiments of Figs 1 and 2, the stiffening members have flanges 30, 32 extending lengthwise of the stiffening member and laterally outwardly from its edges and formed with spaced apertures in which fasteners 34 are affixed. In use, the hollow section stiffening members 22 to 28 are securely held in position by fasteners 34 against the substantial bending loads imposed thereon by merchandise carried on the shelves. The structure and method of making the shelves 10 will now be considered in more detail. Shelf body member 10 is formed from a length of mild steel section having a coating of a plastics material on its upper surface 16 and on the outer surfaces of side flanges 18 and inturned edges 20. The inner surfaces of shelf body member 14 are coated with a weldable colour wash. Steel sections coated in this manner are obtainable from British Steel under the trade mark Stelvetite. Many other plastic coated steel and other materials may well be suitable for the purpose of the invention. As regards the structure of the body member, a variety of ferrous or other weldable materials may be employed. As regards the plastics material, the main criterion is the possession of a durable wipe-clean surface which meets hygiene requirements and adheres satisfactorily to the material of the body member. Possible examples are PVC, polypropylene, and many other synthetic polymers and copolymers. Stiffening members 22, 24, 26 and 28 are likewise plastic coated on their outer surfaces in the same manner as the shelf body member 14, and are mild steel sections. Details of the manner of securing fasteners 34 to the assembly will now be considered. Fasteners 34 are in fact stud rivets which are electrically resistance welded to the underside 36 of the pre-coated body member 14 at spaced intervals. During welding, electrical connections to the shelf body member, for welding purposes, are made solely to the underside 36 or the underside and the end 38 or side edges 40 of the body member. As welding proceeds, the conditions employed with respect to the time and temperature required for achieving a satisfactory weld are chosen so as not to significantly damage the plastic upper surface finish of the shelf body member 14. We have found that it is possible to achieve this desirable result without impairing the mechanical strength of the resulting weld joint. With the studs extending through the apertures formed in the flanges 30, 32 of the stiffening members, all that remains is to complete the fastening operation by provision of an end on the fasteners so as to secure the stiffeners in position. We discovered, however, that conventional securing means for stud fasteners such as plastic caps and nuts were not capable of meeting hygiene requirements and the ends of the stud fasteners were instead formed with smooth domed heads 42 by a peening operation as a result of which the smooth slightly domed heads present a smooth surface for wipe-clean purposes and free of any significant dirt entrapment zones. In the drawings, the heads of the fasteners are in some cases shown by way of illustration, in a condition before completion of the peening operation. After securing the stiffeners in position, all that remains is to surface treat the underside of the shelf assembly as necessary. In the case where the stiffeners are themselves coated with plastics material, such surface treatment is only needed between the stiffeners and between them and the edge of the shelf assembly. Such surface treatment can, for example, be by means of painting. This underside, not being exposed to the abrasion and wear which occurs on the upperside of a shelf, does not necessarily require the plastics surface coating of the latter. Among modifications which could be made in the above embodiment while remaining within the scope of the invention are the following: 1 The use for the shelf body member of a section which is pre-coated on both sides. 2 The use of alternative stiffening member sections. These need not necessarily be hollow sections. 3 The stud rivets may have tubular instead of solid shanks. This may require some modification of the end forming operation. 4 The sequence of operations need not necessarily be as described above. For example, the welding of the studs could be performed through the apertures in the stiffening members if necessary. 5 A variety of weldable structural materials may be employed together with a variety of plastics materials, as discussed above. It will now be appreciated that amongst the other advantages provided by the embodiments described above is the simple fact of providing a heavy duty shelf with a wipe-clean plastic surface. There has been a longfelt need for such an article in supermarkets despite the existence for many years of all the materials needed for the construction of such an article. We believe that we have explained above the reasons why conventional techniques have not hitherto produced a fabricated reinforced shelf structure having suitable wipe-clean characteristics. We also believe that the above embodiments represent a significant step forward in the art. In this specification and claims the term 'stud' may be used instead of 'stud rivet' since any suitable form of stud may be employed.

Claims: A method of making a load-bearing shelf structure (10) comprising : providing a shelf body member (14) having an upper load support surface (16) ; providing a stiffening member (22,24;26,28) for the shelf body member ; and securing the stiffening member to the underside of the shelf body member by a method comprising a welding step so that the stiffening member extends lengthwise of the body member, the conditions with respect to welding time and temperature employed in said welding step being such as not to significantly damage the surface finish of the plastics material on the load bearing surface of the shelf body member ; and ; providing load transfer means (12) at each end of said shelf structure for load-bearing engagement with shelf support means, in use ; the shelf body member being precoated on its upper load bearing surface with a wipe-clean plastics material ; characterised in that said step of welding comprises electrically welding stud rivets (34) to the underside of the pre-coated shelf body member (14) at spaced intervals ; the electrical connections to the shelf body member for welding purposes being made solely to the underside of the shelf body member or the underside and edges thereof ; the method further comprising the step of forming apertures in the stiffening member at intervals to receive the studs , and assembling the apertured stiffening member on the studs ; forming the ends of each stud so as to produce a smooth head (42) thereon, which is domed or convex or level or flat or concave ; and said load transfer means (12) being provided on said shelf body member (14) whereby said stud rivets serve to transmit substantial loads between said shelf body member and said stiffening member in use. A method according to claim 1 characterise in that said stiffening member (22,24;26,28) is of hollow section. A method according to claim 2 characterised in that said hollow section is top hat section . A method according to any one of the preceding claims characterised in that said stiffening member (22,24;26,28) is itself precoated with a plastics material. A method according to any one of the preceding claims characterised in that said stud rivets (34) are solid stud rivets. A method according to any one of the preceding claims characterised in that the step of forming the ends of the studs comprises forming the studs with domed or slightly domed heads (42). A method according to any one of the preceding claims characterised in that said shelf member (14) is precoated on its upper load bearing surface only , the method comprising the further step of surface treating the underside (36) of the shelf member after assembly with the stiffening member . A method according to any one of the preceding claims characterised in that the shelf member (14) has integral lengthwise side flanges (18) which are plastic-coated. A shelf structure (10) comprising a shelf body member (14) having an upper load support surface and a stiffening member (22,24;26,28) secured by a method comprising a welding step to the underside of the shelf body member and extending lengthwise thereof and load transfer means (12) being provided at each end of said shelf structure for load-bearing engagement with shelf support means, in use ; , the shelf member being coated on its upper load bearing surface (16) with a wipe clean plastics material , characterised by said stiffening member being secured to the underside of the shelf body member by said welding step in which stud rivets (34) are electrically welded to the underside of the shelf body member at spaced intervals and extending through apertures formed in the stiffening member , the ends of the studs being formed so as to produce a smooth head, said load transfer means (12) being provided on said shelf body member whereby said stud rivets serve to transmit substantial loads between said shelf body members and said stiffening member, in use. A shelf structure (10) according to claim 9 characterised in that said stiffening member (22, 24; 26, 28) is of hollow section. A shelf structure (10) according to claim 10 characterised in that said hollow section is top hat section. A shelf structure (10) according to any one of claims 9 to 11 characterised in that said stiffening member (22, 24; 26, 28) is itself pre-coated with a plastics material. A shelf structure (10) according to any one of claims 9 to 12 characterised in that said stud rivets (34) are solid stud rivets. A shelf structure (10) according to any one of claims 9 to 13 characterised in that said studs are formed with domed or slightly domed heads (42). A shelf structure (10) according to any one of claims 9 to 14 characterised in that the shelf member (14) has integral lengthwise side flanges (18) which are plastic-coated.

Inventors: GOLBY, JOHN BARRY, MOSS, HENRY TEBBUTT
Applicants: PAUL FABRICATIONS LIMITED
Application year: 1987
Main classification: A47B96
IPC codes: A47B96