GB2443453A

GB2443453A - Cable support ladder

Info

Publication number: GB2443453A
Application number: GB0621448A
Authority: GB
Inventors: Paul Nash
Original assignee: PHILIP GRAHAME INTERNAT Ltd
Current assignee: PHILIP GRAHAME INTERNAT Ltd
Priority date: 2006-10-30
Filing date: 2006-10-30
Publication date: 2008-05-07
Also published as: GB0621448D0

Abstract

A ladder for supporting a cable comprises two elongate sheet metal side rails 20 and rungs 24 of sheet metal extending transversely between and secured to the side rails 20. Each rung 24 is formed at each of its ends with a pair of flanges 40 projecting laterally in a plane normal to the longitudinal axis of the rung 24, and the flanges 40 at each end of each rung 24 are secured to a respective one of the two side rails 20.

Description

CABLE SUPPORT LADDER

Field of the invention

The present invention relates to a cable support ladder.

Background of the invention

When wiring an industrial building, it is necessary to provide some form of trunking which is secured to a wall or suspended from a ceiling of the building to support the weight of the cables. For lighter cables, it may suffice to use support trays formed of sheet metal that. is bent into a s channel sect.ion. Such trays would however collapse on themselves under the weight of heavier cables, and for these it is necessary to use a cable support ladder.

A partial perspective view of a currently commercially available cable support ladder is shown in Figure 1 of the accompanying drawings. The ladder is formed of a pair of parallel side rails 10, 12 each formed of sheet metal bent into a channel of Cshaped cross section. Rungs 14 (only one being shown in Figure 1) extend between the two side rails 10 and 12 to support the weight of cables resting on the ladder. The rungs 14 are likewise made of sheet metal bent into a channel section. A long length of trunking is formed by securing individual ladders to each other end to end using connecting pieces (not shown) that plug into he ends of the side rails 10 and 12. The connecting pieces are fixed to the side rails 10 and 12 by means of bolts passing through holes 16 in the side rails. The holes 16 can also be used to receive cable ties for holding cables in place on the ladder. In conventional cable support ladders, the rungs are welded to the side rails around their entire periphery, where they abut the side rails, in order to be able to achieve the desired strength.

Though the rails and the rungs can be manufactured inexpensively by bending and punching holes in sheet metal material, the welding of the rungs to the side rails requires skilled labour and is time consuming, these two factors adding considerabiy to the cost of the ladders.

Object of the invention The present invention seeks therefore to provide a cable support ladder that can he manufactured quickly and inexpensively without requiring skilled labour.

Summary of the invention

According to the present invention, there is provided a ladder for supporting a cable, comprising two elongate sheet metal side rails and rungs of sheet metal extending transversely between and secured to the side rails, characterised in that each rung is formed at each of its ends with a pair of flanges projecting laterally in a plane normal to the longitudinal axis of the rung, and in that the flanges at each end of each rung are secured to a respective one of the two side rails.

By providing flanges on the ends of the rungs, the invention simplifies the manner in which the ends of the rungs are secured to the side rails. Instead of needing to connect the edge of one metal sheet to the flat surface of another metal sheet, a task that can only be achieved satisfactorily by welding, the present invention only requires two parallel flat surfaces to be secured to one another, a task that can readily be achieved using mechanical fixings.

In the preferred embodiment of the invention, each side rail is formed with inwardly embossed pockets for receiving the flanges of the rungs such that the rungs and side rails are mechanically interlocked with one another prior to being secured to one another by mechanical fixings. In this case, it is further preferred for the embossed pockets to be rectangular and to have open slits along only two edges.

Preferably, the side rails and the rungs are formed of a mild steel to which a corrosion resistant coating is applied prior to the rungs and side rails being secured to one another, and mechanical fixings that do not destroy the integrity of the corrosion resistant coatings are used to secure the rungs to the side rails.

The rungs and side rails may suitably be formed of galvanised steel, the corrosion resistant coating being of zinc.

Advantageously, the mechanical fixings are produced by clinching the flanges of the rungs and the side rails to one another.

Brief description of the drawings

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which:-Figure 1 is, as earlier described, a partial perspective view of a known cable support ladder, Figure 2 is a partial exploded view of a side rail and a rung of a ladder of the present invention, prior to being assembled to one another, and Figure 3 is a section through ladder of the invention passing through one of the rungs.

Detailed description of the preferred embodiment

The side rail 20 shown in Figures 2 and 3 is generally similar to the side rail 10 of the prior art ladder shown in S Figure 1 and is once again formed of sheet metal bent into a channel of C-shaped cross section and has holes 26 punched into it to receive cable ties and to enable ladders to the secured end to end to one another. Likewise, the rung 24 is similar to the rungs 14 of prior art ladders. The essential difference resides in features of both the side rails 20 and the rungs 26 which allow them to be secured to one another by mechanical fixings instead of welding.

In addition to the holes 26, the side rails 20 have pairs of pockets 30 that are termed "embossed" because they are punched out of the plane of the sheet metal and protrude on the inner face of each side rail. The pockets 30 have open slits 32 and 34 along two sides. The vertical slits 32 of each pocket in a pair face towards one another while the horizontal slits 34 both face upwards. The pockets are however closed along their lower sides 36 and along their sides 38 facing away from one another.

Each rung 24 has at each end two laterally extending flanges 40. The separation of the pockets 30 in each pair corresponds to the width of each rung 24 and the pockets 30 are slightly larger than the flanges 40 projecting from the sides of the rung 24.

To assemble a ladder, two side rails 20 are positioned parallel to one another in a jig, with the distance between them set to be equal to the length of the rungs 24. The rungs 24 are simply positioned with their flanges 40 against the inner faces of the side rails and then dropped into the inwardly projecting pockets 30 through the open horizontal slits 34. The vertical slits 32 allow the rungs 24 to slide down all the way to the bottom of each pocket 30 at which point their movement is arrested by abutment with the closed lower sides 36 of the pockets 30.

In this position, Lhe rungs are interlocked with the S side rails. In particular, they cannot be pulled away out of the planes of the side rails 20 and in the plane of the side rails he engagement of Lhe flanges 40 in the pockets prevents sideways and downward movement of the rungs 24.

The rungs can therefore can only be disengaged by lifting them out of the pockets 30 and in use, the weight of the supported cables itself prevents the rungs from being moved in this manner. The mechanical interlock of the flanges 40 in the pockets 30 therefore ot itself provides a connection between the rungs 24 and the side rails 20 that is is sufficient to withstand all the forces acting on the ladder when it is in use. Additional fixings are only needed to the rungs and side rails together prior to their installation in a building, and to fulfil this function do not need to be extremely robust.

Because of this, it would suffice, to use a rivet or a spot weld to secure the flanges 40 in the embossed pockets 30. Both riveting and spot welding can be carried out without requiring skilled labour. However, both these methods have their own disadvantages and it is preferred to resort to a process known as clinching.

It is desirable for the sheet metal of the side rails and the rungs to be of galvanised mild steel. Galvanising the ladders after they have been assembled adds to their cost and it is preferred to assemble the ladders from steel that has been pre-galvanised. In this case, it is important that the method used to fix the flanges of the rungs to the side rails should not interfere with the integrity of the protective coating of zinc.

A rivet requires a hole to be formed in the zinc coating and welding also destroys the surface zinc coating.

This is the primary reason why button cJinching is preferred. To form a clinch as shown at 50 in Figure 3, a high pressure tool is used to deform two layers of sheet metal, namely a flange 40 and a pocket 30, into a die. This is done without breaking the corrosion resistant surface of either sheet. The die has an enlarged foot so that the deformations of the two sheets lock into one another and cannot readily be separated. If desired, the hole in the middle of a clinch can be filled by forcing a plug into it and either form of clinch (filled and unfilled) may be used without damaging the corrosion resistant coating on the mild steel.

Clinching is further preferred because it does not require additional components, it does not rely on skilled labour and is generally less hazardous and more environmentally friendly than spot welding. A clinch is at its weakest when resisting forces normal to the two joined surfaces and acting parallel to the clinch axis to pull the two surfaces apart. In the present invention, however, the only forces that the clinch is called upon to withstand are small forces acting at right angles to the clinch axis to slide the rung out of the embossed pockets of the side rail.

The rung 24 and the rung 14 are both shown with their channel facing upwards but this not necessarily be the case.

The rungs may be mounted facing upward or downwards and the oo conventional layout is for their orientation to alternate along the length of the ladder.

Figure 3 shows the clinches 50 as protruding from the outer sides of the side rails 20 but they may of course alternatively protrude from their inner sides and this would be preferable to maintain clear the channels for receiving the connecting pieces used to secure ladders to one another.

It will also be clear that various other modifications may be made to the illustrated ladder without departing from the scope of the invention as set out in the appended claims. For example, while the side rails and the rungs normally have an open C-shaped channel cross section, they may alternatively have a box section.

Claims

1. A ladder for supporting a cable, comprising two elongate sheet metal side rails and rungs of sheet metal extending transversely between and secured to the side rails, characterised in that each rung is formed at each of its ends with a pair of flanges projecting laterally in a plane normal to the longitudinal axis of the rung, and in that the flanges at each end of each rung are secured to a respective one of the two side rails.

2. A ladder as claimed in claim 1, wherein each side rail is formed with inwardly embossed pockets for receiving t.he flanges of the rungs such that the rungs and side rails are mechanically interlocked with one another.

3. A ladder as claimed in claim 2, wherein the embossed pockets are rectangular and have open slits along only two edges.

4. A ladder as claimed in any preceding claim, wherein the side rails and the rungs are formed of a mild steel to which a corrosion resistant coating is applied prior to the rungs and side rails being secured to one another, and mechanical fixings that do not destroy the integrity of the corrosion resistant coatings are used to secure the rungs to the side rails.

5. A ladder as claimed in claim 4, wherein the rungs :30 and side rails are formed of galvanised steel, the corrosion resistant coating being of zinc.

6. A ladder as claimed in claim 4 or 5, wherein the mechanical fixings are produced by clinching the flanges of the rungs and the side rails to one another.

7. A ladder for supporting a cable, constructed substantially as hereThbefore described with reference to arid as illustrated in Figures 2 and 3 of the accompanying drawings.