Ladder

Abstract: A structural component (11) subject to bending or other stress in use, comprises two generally parallel elongate hollow bodies (13, 14) joined along their length by a web (12). The structural component may be used as a ladder stile or any other load-bearing member resisting both bending stress and torsional stress 1

Description: The present invention relates generally to a ladder structure which is particularly suitable for resisting the bending stress to which ladders are subjectable. Conventionally metal ladders are made with a construction utilising an I-section main structural member or stile at each side. The use of I-section member s imposes certain limits, however, on the strength of the ladder, especially against lateral forces, that is forces exerted parallel to the length of the rungs, as well as torsional stresses. Torsional stiffness is, in fact, becoming increasingly important as a criterion for judging the suitability of a section for use as a ladder stile, because it affects the security of the rung fixing when using the known double clenching technique, by which rungs may be secured to the web of the stile. In this fixing technique the stile is pierced with an opening to receive the end of the rung and this is secured in place by two perimetral beads formed successively one on either side of the web to lock the rung firmly against the web. Any tendency for the ladder stile to flex under torsional stress can unacceptably influence the security of fixing of the rungs, especially by loosening the clenching and thereby, over the passage of time, allowing the ladder which is originally a tight rigid structure to become slack and thereby more readily subject to flex laterally. The objectives of the present invention, therefore, are to provide a ladder structure capable of resisting bending and other stress in use. It is important in this respect for the increased strength to be achieved if possible without the use of more material than has hithertofore been used in providing conventional ladder stiles, or at least with a minimum extra material. According to one aspect of the present invention, therefore, there is provided a ladder having two stiles each comprising two generally parallel elongate hollow bodies having a closed cross-section, joined together along their length by a web, and a plurality rungs the opposite ends of which are attached to the webs of respective stiles. Such a ladder is known from DE-U-7704088. In order to achieve the above-mentioned objective, said bodies project to either side of the plane of the web in such a way that the extent of projection of the bodies in a direction away from the opposite stile is greater than the extent of projection thereof towards the opposite stile such that the webs of the two stiles are closer to one another than are the median planes of the two stiles parallel to the web. In a preferred embodiment the said rungs are attached to only the webs of the respective stiles and do not interrupt the continuity of the said hollow bodies. Preferably, the two hollow bodies and the web are formed integrally as a unitary element. The said unitary element may be formed by extrusion or other techniques. For example, the said unitary element may be formed by deforming a box-section element such that two opposite walls thereof are brought into contact with one another to form the said web. In this case, of course, the web will have two layers or, alternatively, may be considered as two separate parallel webs. In this case the two webs may be fixed together at one or a plurality of points along their length. Alternatively, the two webs may be joined over the whole of there area in face-to-face contact. In a preferred embodiment of the invention the said two hollow bodies each have at least one generally planar wall portion parallel to but offset from the plane of the web. Likewise, it is preferred that the said two hollow bodies each have at least one major wall portion extending generally transversely of the plane of the web. Furthermore, the said two hollow bodies may have a cross-section or shape which tapers from a broader part adjacent the web to a narrower part space from web. It is preferred that the cross-section is symmetrical about a median transverse plane passing through the web, in which case the said two hollow bodies will have respective cross-sectional shapes which are specular images of one another across the median plane. It is, however, by no means essential that the two hollow bodies should be of the same or similar shape, and in certain specialist applications it is envisaged that the hollow bodies may be dissimilar. The web thickness may be greater than the wall thickness of the two hollow bodies (regardless of whether the section is made by extrusion, by roll forming a box section or any of the other techniques which will be described herein below. In addition to the basic form comprising two closed hollow bodies joined by a web, the ladder of the present invention may have stiles which include other features. For example, at least one of the said hollow bodies may have a reinforcing flange projecting therefrom. This reinforcing flange may project from the hollow body in a direction other than parallel to the plan of the web although a flange projecting in a direction parallel to the plan of the web may be provided or may also be provided. Such a reinforcing flange may be of particular value for a member adapted for use as a ladder stile, in which case the reinforcing flange may project from the said hollow body in a direction substantially perpendicular to the plan of the web. Of course, only one of the said hollow bodies may be provided with such a reinforcing flange, or both said hollow bodies may be so provided. One or both said hollow bodies may, likewise, further be provided with more than one such projecting flange. This will allow particular stresses to be accommodated when such stresses are foreseen, thereby minimising the mass of material which may be required in the element. When forming an element with such reinforcing flanges these may be substantially co-planer with one of the walls of the said hollow body from which it projects or may project in a direction transverse such wall. A ladder formed as an embodiment of the present invention may have stiles so shaped that the web is offset towards one side of the said two hollow bodies. This has a number of advantages, especially in simplifying the tools used for fitting the rungs and in reducing the actual length of each rung for a finer effective length. A ladder formed as an embodiment of the present invention may be provided with rungs formed as hollow metal tubular elements secured to the web by crimping or clinching at the ends thereof. Various embodiments of the invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which; Figure 1 is a cross-sectional view taken through an extruded section forming a ladder stile comprised in a first embodiment of the present invention; Figure 2 is a cross-sectional view through a ladder stile in a second embodiment of the invention; Figure 3a, 3b and 3c are schematic sectional views illustrating the formation of a further embodiment of the ladder stile of the invention from the box section element; Figures 4a, 4b and 4c illustrate schematically the formation of an alternative embodiment from a channel section blank element; Figure 5a and 5b illustrate schematically an alternative forming method for producing an embodiment of a ladder stile of the present invention starting from a channel section such as that illustrated in Figure 4; Figures 6a, 6b, 6c, 6d, 6e, 6f, 6g and 6h show schematically the formation of different ladder stiles of the present invention starting from I-section, H-section or specially shaped sections; Figure 7 is a schematic view illustrating a portion of a ladder formed as an embodiment of the present invention utilising the section of figure 1. Referring now to the drawings, the ladder stile shown comprises an integral, unitary extruded section, in this case of aluminium although other materials may be used (especially when utilising other forming techniques as will be described below) generally indicated with the reference numeral 11. The stile 11 comprises a planar web portion 12 of indefinite length joined along the entirety of each edge to a respective closed elongate hollow body 13, 14. The two hollow bodies are specularly symmetrical about a median plan X-X and therefore only a body 14 will be described in detail. This comprises two planar major wall portions 15, 16 which converge towards a connecting bight portion 17 of part-circular shape which is tangential to the plan of the walls 15, 16. From the bight portion 17 the two walls 15, 16 diverge to a transverse edge wall 18 which is joined to the planar major wall 15 by a part-circular section portion 19 which, again, is tangential to the walls 15 and 18 which is joined. Along its opposite edge the wall 18 is joined by a small inclined fillet 20 connecting the wall 18 to the web 12 at the edge thereof. At the junction of the faces of the web 12 with the fillet 20 and the wall 16 these are formed with a smooth radius as is the junction between the face of the wall 16 within the hollow body and the adjacent face, also within the hollow body of the fillet 20. The thickness of the web 12 is slightly greater than that of the walls 15, 16, 18 and, in specific embodiment illustrated, the web thickness is 1.65mm whilst the wall thickness of the hollow bodies is 1.35mm. These dimensions are given by way of example only, however, an embodiments having different ratios and different wall thicknesses as well as different overall dimensions may be formed. The ladder stile section illustrated in Figure 1 is particularly suitable to be formed by extrusion of metal alloy such as aluminium alloy. Referring now to Figure 2, a different section embodying the principles of the present invention is illustrated. This is also a ladder stile. In the embodiment of Figure 2 a planar web 22 joins to hollow elongate bodies 23, 24 along each opposite edge. Again, each of the hollow bodies 23, 24 is specularly symmetrical about a median plan Z-Z perpendicular to the plan of the web 22 and extending parallel to the length thereof. Accordingly only the body 24 will be described hereinbelow in detail. This body comprises two planar inclined walls 25, 26 converging along one edge to a junction 27 and spanned at their opposite edge by a transverse wall 28 joined to the planar wall 25 by an arcuate tangential curved section 29. A fillet 30 joins the wall 28 to the web 22. This embodiment differs from the embodiment of Figure 1, however, in that the planar wall 25 has a projection flange portion 31 extending beyond the junction 27 with the inclined wall 26, and terminating with a transverse rib 32 extending along the length of the flange 31 and projecting towards the hollow body 23. As with the embodiment of Figure 1, this embodiment is particularly suitable for production using extrusion techniques. A ladder stile member having a web joining to elongate hollow bodies may be formed in other ways, however, and various alternatives as illustrated in Figures 3 to 6. In Figure 3 there is shown a rectangular box section generally indicated 33 (3a) having to parallel sides 34, 35 joined by two parallel sides 36, 37 which are perpendicular to the major sides, 34, 35. Figure 3b shows this box section partially deformed by passing between two appropriately formed rollers to initiate the formation of two opposite hollow bodies 38, 39, and Figure 3c shows the finished shape in which the two walls 34, 35 have been brought together to form a composite central web 40 joining the two hollow bodies 38, 39. These bodies have been shown as symmetrical, segmental bodies although by suitable role-forming techniques bodies of any cross-sectional shape may be formed. Figure 4a illustrates a channel section of malleable metal, for example steel having a base 41 and two opposite parallel transverse flanges 42, 43. Figure 4b illustrates these flanges partially deformed towards one another to commence the formation of two opposite hollow bodies 44, 45 which are shown completed in figure 4c. The hollow bodies 44, 45 may be joined to the web 41 along the junction lines of the three edges of the deformed flanges 42, 43 for example by welding, to form a strong rigid structure. Figure 5 illustrates an alternative role-forming technique starting from the channel section such as that illustrated in Figure 4, in which the flanges 42, 43 are deformed outwardly away from one another to form the hollow bodies 44, 45. Figures 6a and 6b show the deformation of an H-section element generally indicated 46 having transverse flanges 47, 48 projecting on both sides of a central web 49. The basic section is illustrated in Figure 6a and the finished structural section illustrated in Figure 6b. The two opposite sides of each flange 47, 48 shown curved round to form a semi-circular (or rather semicylindrical) part of a respective hollow body 50, 51. The two free edges of the opposite parts of the flanges 47, 48 may be left butting or may be joined such as by welding along seem lines 52, 53 to form sealed bodies. Similar roll forming operations may be performed to generate the sections shown in figures 6c and 6d; 6e and 6f; 6g and 6h. As will be seen from these drawings, differently shaped finished structural components are achieved by starting from differently shaped initial sections. Fig. 5a, 5b and 6a to 6f show only the principle of forming a ladder stile; contrary to the present invention the illustrated stiles are symmetrical. Finally, Figure 7 illustrates a portion of a ladder formed using the structural component of Figure 1 as a stile. In the ladder illustrated in Figure 7 to opposite webs 60, 61 of two identical sections are joined by a plurality of rungs 62, 63 which are fitted into apertures (not shown) pre-formed into the webs 60, 61 and perimetral beads 66, 67 on the "outside" faces of the webs 60,61. As will be appreciated from Figure 7, the assymmetrical shape of the sections forming the stiles of the ladder offers the advantage that by positioning the webs 60, 61 closer to one another for a given overall width W of the ladder it is possible for each of the rungs 62, 63 to be shorter than would be the case if each web 60, 61 was symmetrical within the boundary of the section. This at the same time economises on the material used on the rungs since, as will be appreciated the effective available space for the user's feet is defined by the distance F between the walls 18 of the opposite hollow bodies. At the same time the lobe shape defined by the two converging side walls 15, 16 provides increased rigidity both against flexing in a transverse sense, that is bending about a line Y-Y of Figure 7 as well as increased torsional rigidity of the stile section as a whole thereby increasing the security of the clenched connection between the rungs 62, 63 and the webs 60, 61. A further advantage of the asymmetric section for use as a ladder stile lies in the simplification of rung assembling tools which can be shaped such that a simple closing action is sufficient to grip the rung and form the shoulder against which the bead for retaining the rung in position against the web is formed. This simplification also leads to considerable economy as there are no longer required means to make the clamping tools follow a complex path to complete their operation. The advantages of the structural component as a ladder stile does not reside solely in the increased structural stiffness and other mechanical attributes described above, but also offers an improved aesthetic appearance in that the bight portions 17 joining the planar inclined walls 15, 16 offer an extended rounded surface for the user's hands to grip the ladder whilst climbing, which compares favourably with the rather sharp corners presented by the edges of the transverse flanges of the I-sections hithertofore used for this purpose.

Claims: A ladder having two stiles (11) each comprising two generally parallel elongate hollow bodies (13, 14; 23, 24) having a closed cross-section, joined together along their length by a web (12, 22), and a plurality of rungs (62, 63) the opposite ends of which are attached to the webs (12; 22) of respective stiles (11), characterised in that the said bodies (13, 14; 23, 24) project to either side of the plane of the web (12; 22) in such a way that the extent of projection of the bodies (13, 14; 23, 24) in a direction away from the opposite stile (11) is greater than the extent of projection thereof towards the opposite stile (11) such that the webs of the two stiles are offset towards one side of the said two hollow bodies (13, 14; 23, 24) such as to be closer to one another than are the median planes of the two stiles parallel to the web (12; 22). A ladder according to Claim 1, characterised in that the said rungs (62, 63) are attached to only the webs (12; 22) of the respective stiles (11) and do not interrupt the continuity of the said hollow bodies (13, 14). A ladder according to Claim 1 or Claim 2, characterised in that the said two hollow bodies (13, 14; 23, 24) have respective cross-sectional shapes which are specular images of one another across a median plane perpendicular to the plane of the web (12; 22). A ladder according to in any of Claims 1 to 3, characterised in that each hollow body (13, 14; 23, 24) has a cross-sectional shape in which the maximum dimension transverse the plane of the web (12; 22) is greater than the maximum dimension parallel to the plane of the web (12;22). A ladder according to any preceding claim, characterised in that the two hollow bodies (13, 14; 23, 24) and the web (12; 22) of each stile (11) are formed integrally as a unitary element. A ladder according to Claim 5, characterised in that the said unitary element (11) is formed by extrusion. A ladder according to Claim 5, characterised in that the said unitary element is formed by deforming a box-section element (33) such that two opposite walls (34, 35) thereof are brought into contact with one another to form a web (40) having two layers. A ladder according to any preceding claim, characterised in that the wall thickness of the said two hollow bodies (13, 14; 23, 24) of each stile (11) is less than that of the web (12;22). A ladder according to any of the preceding claims, characterised in that the said two hollow bodies (13, 14; 23, 24) each have at least one generally planar wall portion (18; 28) parallel to but offset from the plane of the said web (12; 22). A ladder according to any preceding claim, characterised in that the said hollow bodies (13, 14; 23, 25) each have at least one major wall portion (15, 16; 25) extending generally transversely of the plane of the web (12;22). A ladder according to any preceding claim, characterised in that the said two hollow bodies (13, 14; 23, 25) have a cross-sectional shape which tapers from a broader part adjacent the web (12; 22) to a narrower part spaced from the web. A ladder according to any preceding claim, characterised in that at least one of the said hollow bodies (23, 24) has a reinforcing flange (31) projecting therefrom. A ladder according to Claim 12, characterised in that the said reinforcing flange (31) projects from the said hollow body (24) in a direction other than parallel to the plane of the web (22). A ladder according to Claim 13, characterised in that the said reinforcing flange (31) projects from the said hollow body (24) in a direction substantially perpendicular to the plane of the web (22). A ladder according to any one of Claims 12 to 14, characterised in that both said hollow bodies (23, 24) of each stile (11) have at least one said reinforcing flange (31) projecting therefrom. A ladder according to any one of Claims 12 to 15, characterised in that the or a said reinforcing flange (31) is substantially coplanar with one of the walls (25) of the said hollow body (24) from which it projects. A ladder according to any preceding claim, in which the rungs (62, 63) are formed as hollow metal tubular elements secured to the webs (12, 22) of the stiles (11) at the ends thereof.

Inventors: OLIVER DAVID P, REDSELL MARK, OLIVER, DAVID P., REDSELL, MARK
Applicants: ABRU ALUMINIUM LTD, ABRU ALUMINIUM LIMITED
Application year: 1992
Main classification: E06C7
IPC codes: E06C7, E04C3