Note: Descriptions are shown in the official language in which they were submitted.
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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 alterna-
tive materials, particularly for extension ladders, are urgently being sought.
According to an aspect of the invention, there is provided a stile
for a ladder, extension ladder, steps or the like, said stile comprising a
hollow box section, the hollow box section comprising two interlocked elongate
sections of steel of a thickness in the range of from 0.5 to 0.8 mm, said
elongate sections being interlocked by having been longitudinally slid one in-
side the other, and the hollow being filled with a synthetic plastics materialfoam. The steel may be coated with plastic material.
According to another aspect of the invention, there is provided an
extension ladder component which comprises two stiles, each stile comprising a
hollow box section, each hollow section comprising two interlocked elongate
sections of steel of a thickness in the range of from 0.5 to 0.8 mm, said two
elongate sections being interlocked by having been longitudinally slid one in-
side the other, and the hollow being filled with a synthetic foam plastic
material.
According to a further aspect of the invention, there is provided an
extension ladder which comprises two components, each component comprising two
stiles and a multiplicity of rungs, each stile comprising a hollow box section,
the hollow section comprising two interlocked elongate sections of steel of a
thickness in the range of from D.5 to 0.8 mm coated with polyvinyl chloride,
said elongate sections being interlocked by having been slid one inside the
other and the hollow being filled with polyurethane foam. The rungs may be
locked to a respective one section of each hollow section, so that the end of
each rung is within the respective stile and capped prior to the infill of
foam into the stiles.
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The term "ladder" as used herein is a generic term that includes
extension ladders, ladders, steps and the
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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 prefer-
ably made of very thin steel (generPlly having a wall
thickness in the range of from 0.5 to 0.8 m~ 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 thic~ness of the material and the material itself.
However~ such a hollow section will have little or no
~torsional rigidity~ because both sections are "open" sec-
tions.
To obtain good torsional rigidity, it has been found
pos~ible to restrain each face of the section from moving
relative to the other face by filling the section with a
synthetic pla~tics 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 rigi-
dit~ 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 9 the steel will normally be treated against rusting
prior to coating with P.V.C.
The forming of the hollow by using two sect~ons is
preferred for two basic reasons, namely to allow t~e use
of P.V.~. coated steel or similar material that cannot b~
3~ welded into a hollow section and to allow the rungs of the
ladder to b8 fitted with no external protrusions.
The basic advantages of a ladder, particularly appli-
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cable to extension ladders, with stiles made of foam filledsteel or similar thin walled material 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 equiva-
lent wooden ladder.
The preferred low density polyurethane foam has a
density of about 3 lb. per cubic foot.
For a better underst~nding of the present invention
and to show how the same may be carried into effect, ref-
erence will now be made, by way of example, to the accom-
panying drawings, in whichs-
Figure 1 shows a perspective view of part of an assem-
bled extension ladder, and
Figure 2 shows a series of plan/sectional views showing
how a tread is fastened to stiles.
~igure 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 alumin-
ium section of ribbed tube 6, preferably of generally cir-
cular 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 exten~ion 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 cxample are then gener~ ly f;tted to
the en~s of the tube 6 to prevent ingress of foam there-
into in the later stages of manufacture (for economy of
foam). A second hollow section member 3 is then slid
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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 advanta-
geously made of P.V.C. coated steel of thickness ~n the
range of from 0.5 to 0.8 mm.
The tube 6 forming the tread can of course be any
convenient shape~ for exsmple of "D" shape or be rectangu-
lar in cros~ section.
Of course, the present invention could be used in the
manufacture of ladders other than e2tension ladders~ if so
desired.
