EP0000344A1

EP0000344A1 - Improvements in or relating to ladders

Info

Publication number: EP0000344A1
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: 1979-01-24
Also published as: FI782172A; ES471508A1; NO782223L; DE2860615D1; AR219759A1; IT7853480V0; CA1094028A; IT1172892B; DK305678A; EP0000344B1; BR7804218A; JPS5418362A; IT7868578A0; AU3774078A; ZA783722B; GB1595202A

Abstract

A component for a ladder which comprises a thin hollow section of metallic material (2, 3) filled with a synthetic plastics material foam (5), such as polyurethane foam, with the section preferably made from thin sheet steel with a coating of plastics material thereon. There is also provided a ladder, especially an extension ladder, comprising one or more such components.

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.
According to the first aspect of the present invention, there is provided a component for a ladder (as hereinafter defined), which comprises a thin hollow section of metallic material with the hollow being filled with a synthetic plastics material foam, such as polyurethane foam, the thin hollow section preferably being a stile for or of an extension ladder.
According to the second aspect of the present invention, there is provided a ladder (as hereinafter defined), which comprises one or more components in accordance with the first aspect.
According to the third aspect of the present invention, there is provided an extension ladder component which comprises two stiles formed of thin hollow sections of metallic material with the hollow being filled with a synthetic plastics material foam. The invention further provides an extension ladder which comprises two components, each comprising two stiles and a multiplicity of rungs, the stiles being formed of thin hollow sections of polyvinylchloride coated steel, each hollow section being formed of two sections interlocked by being slid one inside the other and polyurethane foam filled therein.
The term "ladder" as used herein is a generic term that includes extension ladders, ladders, steps and the like.
Whilst there are obviously many ways of forming a hollow section, the hollow section is preferably formed from two separate sections which, when slid together, form the hollow section. The two separate sections are preferably made of very thin steel (generally having a wall thickness in the range of from 0.5 to 0.8 mm when using the steel). Of course, the section could be made of aluminium but the wall thickness will naturally be greater than the corresponding necessary thickness for steel.
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 when made of steel will be made of very thin wall 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 preferred 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 or similar thin walled material is that, especially when a low density polyurethane foam is used, the ladder is considerably lighter than an eauivalent 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 section 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 of thickness in the range of from 0.5 to 0.8 mm.
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 component for a ladder (as hereinbefore defined), which comprises a thin hollow section of metallic material with the hollow being filled with a synthetic plastics material foam.

2. A component according to Claim 1, which comprises a stile.

3. A component according to Claim 2, which comprises an extension ladder stile.

4. A component according to Claim 2 or 3, wherein the hollow section comprises two sections interlocked by being slid one inside the other and foam filled therein.

5. A component according to any one of the preceding claims, wherein the section(s) is/are formed of very thin steel.

6. A component according to Claim 5, wherein the steel is plastics material coated.

7. A ladder (as hereinbefore defined), which comprises one or more components in accordance with any one of the preceding claims.

8. An extension ladder component which comprises two stiles formed of thin hollow sections of metallic material with the hollow being filled with a synthetic plastics material foam.

9. An extension ladder which comprises two components, each comprising two stiles and a multiplicity of rungs, the stiles being formed of thin hollow sections of polyvinyl chloride coated steel, each hollow section being formed of two sections interlocked by being slid one inside the other and polyurethane foam filled therein.

10. An extension ladder according to Claim 9, wherein the rungs are locked to a respective one section of each hollow section, so that the end of the rungs are within the respective stile and capped prior to infill of foam into the stiles.