GB2255126A

GB2255126A - Ladder stile.

Info

Publication number: GB2255126A
Application number: GB9204313A
Authority: GB
Inventors: James Brian Clarke
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-04-25
Filing date: 1992-02-28
Publication date: 1992-10-28
Anticipated expiration: 2012-02-28
Also published as: GB2255126B; GB9204313D0

Abstract

A ladder having rungs (2) has two channel shaped stiles (1), each of which comprises a web (3) to which the rung are fixed. The stile (1) extends beyond each edge of the web (3) progressively into first (4), second (5) and third (6) portions. Each first portion (4) extends from the web (3) in the direction away from the rung (2). Each second portion (5) extends from the first portions (4) towards the other second portion (5). The third portion (6) provides an effective increase in the thickness of the edge of the second portion (5) remote from the first portion (4). <IMAGE>

Description

LADDER The stiles of a lean-to ladders need to be stiff, strong and lightweight.

Conventionally ladders have stiles with an I-shape cross-section. These sections are poor at resisting bending about the neutral axis (hereafter referred to as the Y axis) perpendicular both to the longitudinal axis of the stile and the axis of a rung fixed to the stile. This disadvantage arises because the Y axis lies in the web of the I section.

According to the present invention a ladder has rungs extending between two channel-shaped stiles, each of which comprises a web, to which the rungs are fixed, and the stile extending beyond each edge of the web progressively into first, second and third portions, of which each first portion extends from the web in the direction away from the rung, each second portion extends from the first portion towards the other second portion, and the third portion provides an effective increase in the thickness of the edge of each second portion remote from the first portion.

This provides a ladder with a substantially C shape cross-section which has the advantage over the I section that the web is now spaced apart from the Y axis and thus its resistance to bending about the Y axis is improved. If the C shape section consisted simply of a web with a flange at each edge, the deflection of the free edges of each flange would be considerably worse than an I section having a web and flanges of the same dimensions and would have a tendency to buckle. The flanges of the I section are supported along their centre lines and thus the distance from the line of support to the free edge is half that of the corresponding C section. For this reason, the invention provides the second portions which effectively stiffen the first portions and shift the neutral axis further from the web to provide an improved section modulus.Further, the first portions are less likely to deform if they receive a localised knock when they are stiffened by the second portions.

The longer the second portions become, the closer they approach to an axis parallel to the direction of a rung and passing through the centre of the stile (hereafter referred to as the X axis) and therefore the worse the ability of the stile to resist bending about this axis becomes. The ladder will tend to bend about this axis when it leans against a wall and is loaded by a person standing on a rung. To improve the performance about the X axis, the third portions are provided to provide an increase in the thickness of the edge of the second portion. This keeps material away from the X axis and therefore improves the stiles strength and stiffness about that axis.

Furthermore, the third portions tend to stiffen the first and second portions.

The ladder of the present invention demands less overall rung length for a given usable length of rung than an I section or box section of similar dimensions. In an I section the part of the rung adjacent to the web is obstructed by the flanges and in a conventional box section the rung is fitted to both sides of the box and the portion of the rung inside the box is unusable. The ladder can therefore be remade lighter than a ladder with an I shape or box shape cross-section or alternatively the material sas d can be used elsewhere on the ladder to improve its performance.

Each first portion preferably comprises a flange extending substantially perpendicularly to the web. Each second portion is preferably a flange extending substantially perpendicularly to the respective first portion. Each third portion is preferably a flange extending from the second portion towards the web. Such a section is easy to manufacturing by extrusion.

An example of the present invention will now be described with reference to the accompanying figure which is a cross-section through a stile and rung in a plane perpendicular to the longitudinal axis of the stile.

The ladder comprises a pair of stiles 1 interconnected by a plurality of rungs 2, one of each being shown in figure 1. The stile comprises a web 3 into which the rung 2 is fitted and fixed by conventional swaging, welding or bonding. Two plates 4, forming the first portions, extend from respective edges of the web 1 in a direction perpendicular to the web and away from the rung 2. Two flanges 5 forming the second portions extend perpendicularly from respective plates 4 towards one another. Two flanges 6 extend from respectively edges of the flange 5 in a direction perpendicular to the flanges 5 and towards the web 3.

The broken line 7 represents surplus rung material which would be necessary in a conventional I section. As can be seen the saving of material is considerable. This surplus material can be distributed to other parts of the ladder which require stiffening.

The stile may be provided with extra reinforcing flanges 8 shown by broken lines in figure 1. A stile having these flanges cannot be rolled, but can be extruded.

Calculations have shown that for a given weight of ladder the moment of inertia which is representative of stiffness and the elastic section modulus which is representative of strength are considerably improved about both X and Y axes as compared to an I section and a box section.

Claims

:LAIMS

1. A ladder having rungs extending between two channelshaped stiles, each of which comprises a web, to which the rungs are fixed, and the stile extending beyond each edge of the web progressively into first, second and third portions, of which each first portion extends from the web in the direction away from the rung, each second portion extends from the first portion towards the other second portion, and the third portion provides an effective increase in the thickness of the edge of each second portion remote from the first portion.

2. A ladder according to claim 1, in which the third portion is a flange extending from the second portion towards the web.

3. A ladder according to claim 1 or claim 2, in which each first portion comprises a flange extending substantially perpendicularly to the web.

4. A ladder according to claim 3, in which each second portion is a flange extending substantially perpendicularly to the respective first portion.

5. A ladder substantially as described with reference to the accompanying drawing.