Note: Descriptions are shown in the official language in which they were submitted.
g ~ ~2~52
Element for securing metal plates and composi-te panels from
one slde only
. . ~
The inven-tion rela-tes to an element for securing metal panels in
place from one side only, in particular composite panels.
Composite panels, especially these with a core sheet and two cover
sheets, are often mounted and secured in place from one side only.
Especially when these panels are used as curtain walls there
should be no deformation or features on the decorative, -visible
side due to the means of securing on the o-ther side i.e. nothing
causing shadows or pa-tterns which would detract from the esthetic
effect, in particular when -the panel is illumina-ted by inclined
lighting.
However, also when composite panels are used as room dividers or
the like where the means of securing from one side are employed
on each of the two sides, the means of fixing the panels in place
should not detract in any way from the appearance of the panel
on the other side.
The use of elements which secure cover panels of any kind from
one side only is in most cases preferred, especially when the
visible side may not in any way be affected by the securing
element.
Elements for securing composite panels in place from one side
only are already known. However, these suffer from the disadvant-
age that they can not guarantee a blemish free appearance on the
visible side, or -they can be attached to the panel only by using
uneconomic methods, or are such that the strength of at-tachment
ls 1~ 58 than satisFactory.
l~iZ2S~! ~
Therefore, e.g. when using the expandable claw according to
German utility model 74 42 107 or the fric-tion welding method
accordiny to the Swiss patent 583 833, a hole must first be bored
in the cover sheet. This markedly limits the load which can be
borne by the joint and the plate; it also makes the method of
mounting more expensive.
There has been no lack of efforts to make a device for securing
composite panels in place with the help of condenser discharge
welding equipment. Up to now this method has brought no success
in connection with the above mentioned purpose as the resultant
strength was too 1Ow, especially when the connection was subjec-t~
ed to torsional forces. This was due to the use of the normal
bolts with concentric, slightly conical contact surface ~ith
centra] shaft discharge point. Only with sheet thicknesses of
larger than approximately 1 mm was it possible to achieve re-
sults of even paxtial success. However, the cover sheets used
are normally thinner than 1 mm. Neither condenser discharge weld-
ing nor any other method available up to now has provided a satis-
factory method for mounting the commercially available composite
panels.
The object of the present invention is therefore to develop an
element for mounting and securing in place metal panels, in
particular composite panels with a core of, for example, thermo-
plastic material and metal cover sheets, whereby the said element
does not feature the above mentioned handicaps.
In their efforts to achieve the above objec-tive the inventors
started from the observation that, in the case of bolts which are
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welded to the cover sheet, the deformation of the cover sheet
depends basically on the size of the stresses applied to the
bolt. When screwing on nuts the tightening torque, in which
tension and torsion act simultaneously, is of great
importance. When mounted e.g. as facade panels, there are
additional shear stresses which change depending on the
weight or size of the composite panel and the number of
supporting bolts Also, thermal s-tresses due to changes in
the ambient temperature act on the weld. It is therefore
revealing that the manner in which the -force is applied and
the place where peak stresses occur are of decisive
importance for the means used to secure the panel in place.
In accordance with the invention a special design
of securing element is joined to the metal cover sheet
using the condenser discharge method.
In one aspect of the invention there is provided
a bolt as an element for securing metal sheets and com-
posite panels with metal cover sheets from one side only
using condenser discharge welding to attach the bolt to the
~0 said sheets or panels wherein the metal bolt comprises a
shaft and a head integral therewith, wherein the head
includes a ring-shaped welding surface having the shape
inside and outside of a closed cone section on which a
ring-shaped arcing ring is provided.
3 -
~ 1 6~252
Surprisingly, it turns out that by changing the
geometric form of the securing element which up to now is
normally used for this purpose all the above mentioned
handicaps can be eliminated.
The invention is described in greater detail in
the following with the help of the schematic drawings
viz .,
FIGS. 1-5: Plan views of various versions
of the bolt according to the
invention.
FIGS. 6-9: End views of various versions
of the bolt according to the
invention.
".~
il 1 6;~252
The securing elf~ment according to the invention is a me-tallic
bolt which as shown in figs 1-5 comprises a shaft 10 and a head
20 provided at one end. The shaft can, for other connections, be
provided with inner or outer threads using generally known methods
for this, or can feature some other means of securing. Unlike the
conventional heads with an approximately 180C conical weld sur-
face and central arc tip, the head 20 is provided with a welding
surface 26 which is ring-shaped and the inner and outer limit-
ations of which are characterised ~y a closed cone section shape.
An arcing ring 28 is provided on the welding face 26 of the bolt
according to the invention.
The pot-like shape oE the head represents a simple version of
the invention. This exemplified embodiment of the invention is
explained in greater detail in the following with the help of
fig~ 1. The head 20 of the bolt comprises a circular base 22 on
which a hollow, cylindrical-shaped ring 2~ is mounted. The surface
26 to be welded to the sheet is ring-shaped and lies on a plane
approximately vertical to the longitudinal axis of the shaft 10.
The contact element to initiate the welding arc is a, preferably
circular, arcing ring 28 approximately in the middle of the sur-
face 26 to be welded to the sheet.
An advantage of ~his arxangement is that the welding does not
or ~i~ o~,e Gll'r~Ct~'Vr1,~
proceed radially on one side~as with the bol-ts used up to now,
but simultaneously inwards to smaller diameters and outwards to
larger diameters.
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In the course of development of the invention it was found that
the ring 24 need not necessarily be c~lindrical in shape. For
example blunted cone shapes or rounded versions such as are shown
in figs 2 and 3 also provea effective. With elliptical welding
surfaces 26 it is advantageous for the ratio of the elipse axes
not to exceed about 3. Usually it is ln the region of 1. It also
turns out that the base 22 can be omitted and the ring 24, as
shown for example in fig. 4, joins up directly to the shaft 10.
As shown by way of example in fig. 5, the modification of the
design of the bolt can be taken so far that the result is a tub-
ular bolt 40 in which the head 20 and shaft 10 form a unit and
can no longer be separately identified, and a hole penetrating
the whole length of the bolt forms the inner limit of the weld-
ing surface 26. With such a bolt an outer or inner thread for
example can serve to provide further means of attachment. As
shown in figs 8 and 9, according to a special embodiment of the
invention, the welding surface 26 or the ring 24 and/or the arc-
ing ring 2~ can be provided with one or more slits 30 running
approximately parallel to the shaft axis.
In a special version of the bolt the base 22 and the ring 24 are
circular, and their contact surfaces have the same size of outer
diameter, whereby this is 1 to 4 times, preferably 2 to 4 times,
as large as the diameter of the shaft 10. Also preferred is that
the thickness of the base 22 is 1 to 2 times the wall thickness
of the ring 24, and the height of the ring 24 is about the same
s the thickness of the b.lse 22. The diameter of the ~rcing ring
1~2252
28 is preferably half of the sum of the outer and inner diameters
of the ring 24, measured at the place where the welding surface
26 is, and the arcing ring 28 forms an isosceles to equilateral
triangle - as viewed in cross section - whereby the shorter side
lies in the plane of the welding surface 26 and the height is
about one tenth of the diameter of the shaft 10.
With the shape of bolt according to the invention much higher
strength can be achieved than with the bolts used up to now for
this purpose. mls can e.g. be seen veryclearly in the following
table.
Crack formation or fracture of different types of bolt subjected
to different kinds of loading
, ........ . . ~ . .................. ..
Type of bolt Shear load Tensile load Torsion moment
a 766 N 455 N 27 cm/kp
b 1455 N 1028 N 57,5 cm/]cp
The above values are the average values from 10 tests of each
kind. The panel used was one which is commercially available, viz.
4 mm thick and made up of a 3 mm thick polyethylene core with a
metal cladding of 0.5 mm thick, ~4 hard alloy AlMgl on each side.
The ultimate -tensile strength of the cover sheet ~B was 15 kp/~m .
Both bolts were made of alloy AlMg3 and had a shaft diameter of
6 mm. Bolt type a represents the conven-tional bol-t with an 3 mm
diameter welding surface. Bolt type b represents the bolt accord-
1 ~62~52
ing -to the invention and in the following preferred form: hollow~
cylindrical ring 24 with an outer diameter of 12 mm and height
3 mm, whereby the wall thickness of the ring 24 was dimensioned
such that the area of -the circular ring of the welding surface
26 corresponded exactly to the area of the we:Lding surface on bolt
type a. The arcing ring 28 constituted in cross section an isos-
celes triangle which has an angle of ~0 at the tip and has a
height of 0.6 mm.
In the case of bolt type a the weld spreads out from a central
arcing point where the first meltiny of the aluminum ta]ces place.
With this arrangement it is possible to achieve connections where
75 to 85~ of the total surface is welded. As soon as the arcing
ring 28 of bolt type b touches the cover sheet of the composite,
it is melted and the welding spreads, unlike with bolt a, radial-
ly on both sides of the arcing ring 28. The result is a homogene-
ous weld connection with 100% of the total available surface weld-
ed.
The high strength of the weld achieved with the bolt according to
the invention is presumably due to the fact that during welding,
because of the short distance over which the weld spreads across
the welding surface 26 according to the invention, the weld dross
and other impurities can be driven radially inwards and outwards
completely out of the weld zone so that the resultant weld formed
is free of dross and/or inclusions of impurities.
B~25~
The type of bolt according to the invention overcomes the disad-
vantages experienced up to now viz., the low tightening torque
and the permanent deformation of the sheet on the exposed side
Q f the panel.
An additional advantage is the better distribution of localised
heating over a larger area of sheet, which with composite panels
prevents the partial, local separation of the cover from the core
caused by the high concentration of heat on one spot by the bolts
normally employed up to now.
