EP0000344B1

EP0000344B1 - Improvements in or relating to ladders

Info

Publication number: EP0000344B1
Application number: EP78100247A
Authority: EP
Inventors: Edwin John Bruton
Original assignee: Abru Aluminium Ltd
Current assignee: Abru Aluminium Ltd
Priority date: 1977-07-06
Filing date: 1978-06-27
Publication date: 1981-04-15
Also published as: FI782172A; EP0000344A1; ES471508A1; NO782223L; DE2860615D1; AR219759A1; IT7853480V0; CA1094028A; IT1172892B; DK305678A; BR7804218A; JPS5418362A; IT7868578A0; AU3774078A; ZA783722B; GB1595202A

Description

The present invention relates to stiles and other components of ladders, as well as to ladders, especially extension ladders.
As is well known, aluminium has become very expensive and alternative materials, particularly for extension ladders, are urgently being sought. Plastics material with a foam filling has been suggested as an alternative in DE―A 24 15 441, but this specification does not teach how to manufacture a ladder of conventional shape, rather a continuous sandwich of two layers of plastics material or light alloy with a foam filling, small openings through the sandwich forming foot holds.
According to a first aspect of the present invention there is provided a stile for a ladder, extension ladder, steps or the like, which stile comprises a hollow box section, characterised in that the hollow section comprises two interlocked elongate sections of steel of a thickness in the range of from 0:5 to 0.8 mm, which elongate sections are interlocked by having been longitudinally slid one inside the other and the hollow being filled with a synthetic plastics material foam.
According to a second aspect of the present invention, there is provided a ladder, extension ladder, steps or the like, which comprises one or more stite(s) in accordance with the first aspect of the present invention.
According to a third aspect of the present invention, there is provided an extension ladder component which comprises two stiles, each stile comprising a hollow box section, characterised in that the hollow section comprising two interlocked elongate sections of steel of thickness in the range of from 0.5 to 0.8 mm, which elongate sections (2 and 3) are interlocked by having been longitudinally slid one inside the other and the hollow being filled with a synthetic plastics material foam.
According to a fourth aspect of the present invention, there is.provided an extension ladder which comprises two components, each component comprising two stiles and a multiplicity of rungs, each of which stiles comprises a hollow box section characterised in that the hollow section comprising two interlocked elongate sections of steel of a thickness in the range of from 0.5 to 0;8 mm coated with polyvinyl chloride, which elongate sections (2 and 3) are interlocked by having been slid one inside the other and the hollow being filled with polyurethane foam.
The term "tadder" as used herein is a generic term that includes extension ladders, ladders, steps and the like.
The hollow section is formed from two separate sections which, when slid together, form the hollow section. The two separate sections are made of steel generally having a wall thickness in the range of from 0.5 to 0.8 mm.
The formed hollow section will have good strength in pure bending about either the X―X or Y-Y axes, the strength naturally being dependent on the size of section, wall thickness of the material: and the material itself. However, such a hollow section will have little or no "torsional rigidity" because both sections are "open" sections.
To obtain good torsional rigidity, it has been found possible to restrain each face of the section from moving relative to the other face by filling the section with a synthetic plastics material foam, especially a low density polyurethane foam. Whilst one could use a foam other than a low density foam, this is not advantageous from a cost or weight point of view. The filling of the section serves not only the purpose of giving good torsional rigidity to the section but it also stiffens the thin walls of the section.
Normally, the sections of steel will be made of strip steel coated with P.V.C. Of course, the steel will normally be treated against rusting prior to coating with P.V.C.
The forming of the hollow by using two sections is provided for two basic reasons, namely to allow the use of P.V.C. coated steel or similar material that cannot be welded into a hollow section and to allow the rungs of the ladder to be fitted with no external protrusions.
The basic advantages of a ladder, particularly applicable to extension ladders, with stiles made of foam filled steel is that, especially when a low density polyurethane foam is used, the ladder is considerably lighter than an equivalent wooden ladder, it is very little heavier than an equivalent aluminium ladder, it is very much cheaper, at least at the present time, than an equivalent aluminium ladder and the price is comparable, at least at the present time, with an equivalent wooden ladder.
The preferred low density polyurethane foam has a density of about 3 lb. per cubic foot.
For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:-

Figure 1 shows a perspective view of part of an assembled extension ladder, and
Figure 2 shows a series of plan/sectional views showing how a tread is fastened to stiles.

Figure 1 of the drawings shows stiles 1 made up of sections 2 and 3, connected by treads 4, with the stiles being filled with foam 5.
Referring now to Figure 2 of the drawings, an aluminium section of ribbed tube 6, preferably of generally circular cross-section, has two ribs 7 formed thereabout, in the aluminium, spaced at the distance apart that the stiles are to be positioned, which strengthened tube is to form a rung or tread for the extension ladder. Two inner hollow section members 2 with appropriately dimensioned holes therein have the ends of the requisite number of treads inserted therein and then an additional rib 8 is formed at each end of each tread, so that each tread is securely fastened to each inner hollow section member 2. Caps (not shown) of steel for example are then generally fitted to the ends of the tube 6 to prevent ingress of foam thereinto in the later stages of manufacture (for economy of foam). A second hollow seetion member 3 is then slid onto each :of the hollow section members 2 having treads 6 fastened thereto and the formed hollow section is then filled with low density polyurethane foam which is allowed to cure therein. The end product is an extension ladder section. The hollow section members 2 and 3 are advantageously made of P.V.C. coated steel.
The tube 6 forming the .tread can of course be any convenient shape, for example of "D" shape or be rectangular in cross section.
Of course, the present invention could be used in the manufacture of ladders other than extension ladders, if so desired.

Claims

1. A stile (1) for a ladder, extension ladder, steps or the like, which stile comprises a hollow box section, characterised in that the hollow section comprising two interlocked elongate sections (2 and 3) of steet of a thickness in the range of from 0.5 to 0.8 mm, which elongate sections are interlocked by having been longitudinally slid one inside the other and the hollow being filled with a synthetic plastics material foam (5).

2. A stile according to Claim 1, wherein the steel is plastics material coated.

3. A ladder, extension ladder, steps or the like, which comprises one or more stile(s) (1) in accordance with any one of the preceding claims.

4. An extension ladder component which comprises two stiles, each stile (1) comprising a hollow box section, characterised in that the hollow section comprising two interlocked elongate sections (2 and 3) of steel of a thickness in the range of from 0.5 to 0.8 mm which elongate sections (2 and 3) are interlocked by having been longitudinally slid one inside the other and the hollow being filled with a synthetic plastics material foam (5).

5. An extension ladder which comprises two components, each component comprising two stiles (1) and a multiplicity of rungs (4), each of which stiles comprises a hollow box section, characterised in that the hollow section comprising two interlocked elongate sections (2 and 3) of steel of a thickness in the range of from 0.5 to 0.8 mm coated with polyvinyl chloride, which elongate sections (2 and 3) are interlocked by havang been slid one inside the other and the hollow being filled with polyurethane foam.

6. An extension ladder according to Claim 5, wherein the rungs (4) are locked to a respective one section (2) of each hollow section, so that the end of each rung.(4) is within the respective stile (1) and capped prior to the infill of foam (5) into the stiles (1).