Note: Descriptions are shown in the official language in which they were submitted.
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METAL SHEETING
This invention relates to metal sheeting.
Metal profiled sheets are frequently used as roof panels
and for other building cladding purposes. It is well
known to provide a metal sheet which is pre-formed with
integral ribbing so that it may readily be interlocked
at adjoining edges with a similar sheet and which may be
fastened to a support without the fastening means being
exposed to the environment or being on the visible side
of the sheet. These products may include separate
fixing clips and involve on site roll forming to close
the interlocking seams. All such products are usually
referred to as "raised seam cladding". Many examples of
such profiled sheets are known and they are frequently
roll-formed from an aluminium alloy as well as other
metallic materials. ~sually each sheet has a first
upstanding hook formation along one edge and a second
upstanding formation along an opposite edge of the sheet
with a hook receiving part and a valley in the plane of
the sheet through which fasteners can be passed. When
the sheets are interlocked the first formation of one
sheet hooks on to the hook receiving part of an
adjoining sheet and covers the valley and its
fasteners. From their outer surfaces the sheets then
present a generally flat appearance having spaced apart
upstanding ribs with no fasteners visible. These ribs
are usually referred to as "raised seams".
In general, when used as roof panels, the sheets need to
be fully supported on a pre-prepared flat surface and
are not strong enough to span any worthwhile distance
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between supporting purlins. It is however clearly
desirable to provide sheets that can be supported at
intervals, as between spaced apart purlins, and it is
further desirable that the sheet should be wider so that
the spacing between the raised seams is increased. In
addition the sheets should be strong enough to support
snow loads, wind loads both in pressure and suction and
so that, for example, operatives can walk on them.
.
We have found that there are conflicting factors
between, on the one hand, increasing the strength and
stiffness of the sheet and, on the other hand, ensuring
adequate locking against suction forces under high wind
conditions.
It is therefore an object of the present invention to
provide an improved interlocking metal sheet which has
good strength characteristics and improved interlocking
formations.
According to the present invention there is provided a
metal sheet having a first upstanding hook formation
along one edge and a second, upstanding hook receiving
formation and a valley along an opposite edge the
arrangement being such that the sheet can be fastened
directly to a support without the interposition of
separate clips and so that the first formation of one
sheet can hook over the second formation of an adjoining
sheet and cover its valley characterised by latching
means acting between the formations so that after
interlocking the sheets said one sheet can be rotated
about the hook receiving formation of the other sheet
through at least 25 before the formations can be
disengaged.
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The rotation preferably occurs wi-thout significant
distortion of the material of either sheet.
Preferably upon said relative rotation the latching
action ceases to function, and further rotation through
at least 10 is required before the formations can be
disengaged.
The above and other aspects of the present invention
will now be described with reference to the accompanying
drawing in which:-
Fig. 1 is a transverse section through a metal
sheet,
Fig. 2 is a view similar to Fig. 1 showing part
of two sheets distorted by suction forces, and
Fig. 3 is a similar section, to a larger scale,
of an interconnection between two metal sheets.
~eferring to Fig. 1 a roll-formed aluminium alloy sheet
1 has along one side edge 2 a first, hook, formation
indicated generally at 3 which is upstanding from the
outer surface 4 of the sheet. At its other side edge 5
the sheet has a second, hook receiving, formation
indicated generally at 6 and a valley 7. The
formations 3 and 6 are separated by a web 8 which is
coplanar with the floor 9 of the valley 7. A number of
stiffening ribs 8b may be formed in the sheet.
The hook formation 3 comprises a sloping part 10, a wall
11 approximately at right angles to the web 8, a flat 12
and downwardly and inwardly projecting parts 13 and 14
constituting a hpok having a curved part 15. As shown
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the outer end of the part 14 is curved to be
approximately parallel with the wall 11 and to allow
run-out on the edge of the sheet material on roll
forming.
The hook receiving formation 6 comprises a sloping part
16 the upper end 16b of which is approximately at right
angles to the web 8 and is then folded at a part 17
which, together with the wall 16b defines a hook
receiving formation as will be described later. The
lower end of the folded part 17 is formed as a hollow
bead 18 and the rolled material of the sheet is then
formed as a platform 19 with a recess 20, a side wall 21
approximately at right angles to the web 8 leading to
the valley 7, the floor 9 of which has an upwardly
turned part 22 and a lip 23 at the same angle to the web
8 as the sloping part 10. The lip 23 allows run out of
the edge of the sheet material on roll forming.
Fig. 3 shows how the hook formation 3 engages over the
hook receiving part 6 of an adjoining sheet. In Fig. 3
the same reference numerals have been used except that
for the "adjoining" sheet suffixes "a" have been added
to each reference numeral.
It will be assumed that the sheet la is already mounted
on suitably spaced-apart purlins ~not shown) and secured
thereto through the valley floor 9a. The fixings used
can be conventional and may be arranged to accommodate
longitudinal expansion of the sheet la. The sheet 1 is
then held with its web 8 approximately vertically and
its hook formation 3 engaged around the bead 18a. The
sheet 1 is then pivoted to the position shown in cross-
hatched lines in Fig. 3 and secured to the purlins. In
this position the sloping part 10 engages with the lip
23_ and the wall 11, the flat 12, the part 13 and the
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curved part 15 respectively embrace the upper part of
the side wall 21_, the platform 19_, the part 17a and
the curved part 15a. Sealing material (not shown) may
be disposed in the recess 20a. The dimensions of the
formations 3 and 6 are such that the upper part of the
formation 3 is a "latching fit" over the upper part of
the formation 6.
As mentioned above we have found that conflicting
requirements exist in increasing the strength of the
sheets without at the same time increasing the risk that
suction forces under high wind conditions will tear off
one of the sheets. When the sheets are mounted on
spaced-apart purlins this reduces the number of edge
fastenings that can be used.
Although innately higher strength aluminium alloys than
are usually employed can be used this does not, of
itself, increase the strength of the sheets
sufficiently. Increasing the height of the "raised
seams" constituted by the formations 3 and 6 does
significantly increase the strength of the sheets and
enables them to be unsupported across suitably spaced
purlins. However such a change significantly alters the
pattern of distortion of the "other" sheet 1_ raised by
suction forces on the web 8a resulting from wind flow
across the outer surfaces 4 and 4a of the sheets. This
change tends to make easier the lateral separation of
the formations.
As shown in Fig. 2, wind flow across the outer surfaces
4 and 4a can cause high suction forces to be applied to
the webs of the sheets and lift these webs so that their
formations 3 and 6 distort and move laterally to
disengage the formations 3 and 6.
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With the present invention the close, "latching fit",
engagement between the upper parts of the formations
ensures that the wall 11 constitutes latching means for
the hook by its close fit against the upper part of the
side wall 21a. As shown in Fig. 3 the edge of the sheet
1 can rotate about the bead 18a through successive
positions indicated at A, B, C and D before reaching the
position E shown as a solid line. During the movement
A to approximately C the wall 11 rides up the side wall
21a and retains its latching action. At the
approximate position C the corner between the sloping
part 10 and the wall 11 rides over the corner between
the side wall 21a and the platform l9a. As a result of
the "latching fit" referred to above this transition
occurs suddenly. In positions D and E the hook still
remains engaged since the outer end of the part 14
remains in engagement with a part of the bead 18a which
extends parallel with the upper end of the sloping part
16. Once a sheet has been distorted to the extent
represented in position E the strains to which it is
subjected are extremely complex and not readily
predictable. However it would be expected that
position E represents the point at which the edge of the
sheet 1 will move laterally and the formations will
disengage.
In position C the chain line 25 represents the angle
between the edge of the web 8 and the line of the web
8a. The angle defined is G.
In position E the chain line 24 represents the angle
between the edge of the web 8 and the line of the web
8a. ' The angle defined is F. The precise angle F
reached for position E is determined by the detailed
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dimensions of the upper parts of the formations 3 and 6,
the width of the web 8 and the thickness of the sheet.
We have found the following criteria achieve good
results:-
Height of the formations 3 and 6 a minimum of 10%(preferably 12.5%) of the total sheet width. This is to
achieve a basic stiffness to the whole profile so as to
allow it to support the imposed loads.
Length of the vertical wall ll between 20% to 30%
(preferably 24%) of the height of the rib formation 3
and 6.
Centre of radius of tip of the hook receiving formation
in the range 10 to 20% (preferably 14%) below the top of
the rib formation 6.
Distance of centre of radius of tip of hook receiving
formation to vertical wall 11 when assembled in the
range 3.75% to 6.25% (preferably 5%) of the t;otal
formation width.
Sheet thickness lies in the range 0.15% to 0.25% of the
total formation width.
The angle G is in the range 25 to 30 (preferably 28).
The angle F is in the range 10 to 35 greater than
angle G (preferably 30).
By using a high strength aluminium alloy such as 3105 or
3004 in standard roofing sheet thicknesses and tempers
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and by increasing the height of the raised seams the
basic strength of sheets 500 mm wide can be increased
sufficiently to enable the sheets to span purlins with
spacings in excess of 2.0 m and still readily support
snow and wind loads both in pressure and suction and
carry the weight of an operative between the purlins.
By utilising the latching feature of the present
invention the disadvantages of increasing the height of
the seams can be obviated and increased protection
given against suction induced by wind force.
It will be understood that with the interlocking
formations described above then should the sheet 1 be
rotated through an angle significantly greater than the
angle F ~position E) the sheets will again interlock as
the part 14 extends upwardly behind ~the folded part 17.
Depending upon the dimensions of these parts this re-
engagement is likely to occur with an angle F of about
75-.
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