Flanged joint for two sheet material air channel sections of rectangular cross section

A flanged joint for connecting sheet material air channel sections of essentially rectangular cross section to one another has flanges made of hollow sheet material shapes and steel angle pieces. Each of the hollow sheet material shapes is provided with projections and/or depressions in one or more of the walls which entirely or partially surround a leg of a respective steel angle piece. Each leg of a steel angle piece, in turn, is provided with projections and/or depressions which are disposed at the periphery of the leg and are adjusted to the positions of the projections and/or depressions in the hollow sheet material shapes. At least one of the projections then catches in at least one of the depressions upon pushing a leg of a steel angle piece into a hollow sheet material shape.

The invention relates to a flanged joint for two sheet material air channel 
sections of rectangular cross section. 
Flanged air channel joints having flanges which are formed from hollow 
sheet material shapes and steel angle pieces are state of the art. A 
device for joining air channel elements is known from the West German 
patent No. 32 03 204 and, at its abutting edges, is provided with 
receptacles for flanged shapes which define corners. The flanges shapes 
are constituted by double-walled shapes of essentially L-shaped cross 
section made of bent sheet material. On the one hand, this enables the 
flanged shapes to grip the walls of the air channel elements from above 
and below while, on the other hand, this enables the flanged shapes to 
define the receiving regions for the corners. The walls of the individual 
regions of the shapes are spaced from, and are substantially parallel to, 
one another. 
These known flanged joints have the drawback that, after insertion of the 
angle pieces in the hollow sheet material shapes, the angle pieces must be 
secured in the direction of insertion by grinding or spot welding. This 
prevents the frame-like flange consisting of four hollow sheet material 
shapes and four angle pieces from falling apart upon being drawn onto the 
air channel section. 
In view of this drawback, the West German Offenlegungsschrift No. 26 27 515 
proposes to produce flanges from hollow shapes and angle pieces with the 
angle pieces having more than two holes the centers of which are equally 
spaced from one another. The hollow shapes are formed in such a manner 
that cups having the same diameter and spacing as the holes in the angle 
piece are produced on the hollow shape. After the angle pieces are driven 
in, the cups of the hollow shapes are supposed to be received in the holes 
of the angle pieces. This flanged joint has been found to be unusable in 
practice. 
The hollow shapes are cut to length in accordance with the desired size of 
the air channel section. The cut may pass through a cup but can also lie 
somewhere between two cups. If the angle pieces are now driven in, either 
all or none of the cups on the hollow shape catch in the holes of the 
angle piece. Due to the predetermined, technically attainable diameter of 
the cups and holes, and due also to their uniform spacing, the tolerance 
for the length of a hollow shape with locked cups and two driven in angle 
pieces is at most twice the distance between neighboring cups and 
neighboring holes. For a proposed distance of 1 cm--a smaller distance is 
virtually unobtainable technically--the length tolerance would be about 19 
mm. In practice, however, at most 2 mm is acceptable. 
It is not only for this reason, however, that the flanged joint of the West 
German Offenlegungsschrift No. 26 27 515 cannot be used in practice. If a 
flange of hollow sheet material shapes and angle pieces is mounted on the 
ends of the air channel sections without further mechanical processing or 
spot welding to secure the angle pieces in the hollow sheet material 
shapes, a large force of engagement must exist between each hollow sheet 
material shape and angle piece because the flange is driven onto the air 
channel section with a hammer. Since the force of engagement for the 
proposed solution with cups and holes is equal to the force required for 
insertion, production of a flange by driving the angle pieces into the 
hollow shape with a large force is too time-consuming, wastes too much 
force and creates too great a danger of injury for the worker. 
Another flanged joint in which the angle pieces lock in the hollow shape is 
known from the West German Offenlegungsschrift No. 24 34 160. Here, a 
rectangular recess is stamped in the angle piece and a similarly 
rectangular tongue stamped out of the hollow shape catches therein. While 
the flanged frame produced in this manner cannot fall apart after the 
angle pieces are pushed into the hollow sheet material shapes, it is 
nevertheless unstable because of the required air gap between the tongue 
of the hollow sheet material shape and the recess in the angle piece. 
This flanges joint exhibits further serious drawbacks. The tongue in the 
hollow sheet material shape, which is necessary for locking, can be 
stamped only after the individual shaped hollow sheet material sections 
required for production of the flanged frame have been cut to length. This 
constitutes an additional processing operation which can be carried out 
only with a complicated, that is, expensive, stamping tool since the 
cutting plate of the stamping tool must be inserted in the hollow sheet 
material shape for the stamping procedure. Moreover, the galvanized 
surface of the hollow sheet material shape is ruined during the stamping 
procedure. 
It is, therefore, the object of the invention to provide a solution which 
allows flanged joints constituted by hollow sheet material shapes and 
angle pieces of steel to be produced in a time-saving, and thus 
economical, manner without additional fixing of the angle pieces in the 
direction of insertion by grinding or spot welding. At the same time, it 
is necessary to ensure that the shaped hollow sheet material sections need 
not be further processed after being cut into arbitrary lengths, that the 
assembled flanged area is stable and retains its dimensions, and that the 
force of engagement between the hollow sheet material shapes and the angle 
pieces is greater than that to be used in pushing or driving the angle 
pieces into the hollow sheet material shapes. 
According to the invention, the hollow sheet material shape is provided, in 
the region of insertion of the leg of the angle piece, and preferably in 
the wall remote from the front face of the channel, with a rack-like 
pattern perpendicular to the direction of insertion. This can be 
accomplished by an embossing roller during rolling of the hollow sheet 
material shape. 
The leg of the angle piece to be inserted is provided with several 
projections in the direction of insertion. The projections have different 
spacings which are to be selected in such a manner that, upon insertion of 
the angle piece in the desired final position, at least one projection of 
the leg of the angle piece engages in a depression of the rack-like 
pattern of the hollow sheet material shape. 
If the projections on the leg of the angle piece are, for example, 
triangular longitudinally of the leg with the apex of the triangular 
pointing in the direction of insertion of the angle piece and the triangle 
sloping from the base to the apex, the angle piece can be pushed to the 
final position in the hollow sheet material shape by hand without the 
exertion of great force. The protuberances in the rack-like pattern of the 
hollow sheet material shape slide over the inclined planes of the 
projections on the leg of the angle piece. As desired, however, a release 
of the angle piece from the hollow sheet material shape is no longer 
possible since the raised base of at least one triangular projection on 
the leg of the angle piece catches in a depression of the rack-like 
pattern. 
In the known hollow shapes, those wall areas of the hollow sheet material 
shape which surround the leg of the angle piece extend essentially 
perpendicular to the surface of the channel, and the moment of resistance 
of the hollow sheet material shape with respect to the axis extending 
normal to the surface of the channel is small. The moment of resistance of 
the hollow sheet material shape in the region of insertion of the angle 
piece and with respect to the axis extending normal to the surface of the 
channel is increased considerably relative to the known hollow sheet 
material shapes. This is achieved by designing that wall of the hollow 
sheet material shape which is remote from the front face of the channel 
with a slightly dovetailed groove in such a manner that, beginning from 
the open side of the groove, those regions of the wall adjacent to the 
groove are inclined upwards and downwards in a direction away from the 
front face of the channel. 
The form here disclosed for the projections on the leg of the angle piece 
is only one of many which are possible. The disclosed design also allows 
for recesses in the area of the leg of the angle piece. It is only 
necessary to take care that the form of the hollow sheet material shape is 
selected in such a manner that the hollow sheet material shape and the 
angle piece lock to one another as desired in the final position. 
Due to the structure of the projections and depressions in accordance with 
the invention, an arbitrarily small grid dimension may be achieved for the 
flange frame. After cutting the hollow sheet material shape to length, no 
further processing operation, as in the West German Offenlegungsschrift 
No. 24 34 160, is required. The force of engagement between the leg of the 
angle piece and the hollow sheet material shape is substantially greater 
than the force of insertion in contrast to the teaching of the West German 
Offenlegungsschrift No. 26 27 515 where the two forces are equal. It is 
true that the arrangement known from the West German Offenlegungsschrift 
No. 28 17 413 allows the grid dimension to be halved. However, no 
suggestion of an arbitrary reduction in the grid dimension is to be found 
in this publication.

FIG. 1 illustrates a hollow sheet material shape 1 consisting of the wall 3 
nearer to the front face of the channel, the wall 5 remote from the front 
face of the channel, a partially double-walled wall 4 bridging these two 
walls, and the walls 6 and 15 between which the channel wall of the air 
channel section 22 or 23 (see FIG. 7) is inserted. A slightly dovetailed 
groove 12 with protuberances 7 and depressions 8 extends parallel to the 
surface of the channel in the wall 5 remote from the front face of the 
channel. 
FIG. 2 illustrates an angle piece 2 with one of the legs 9 to be inserted. 
The second leg 9 is only partly shown. Triangular projections 10 are 
arranged in such a manner that they slope from the base 13 to the apex 14 
in the direction of insertion. In order that the angle piece 2 may be 
pushed to its final position in the hollow sheet material shape 1 
illustrated in FIG. 1, the ends of the legs 9 of the angle piece 2 are 
provided with shoulders 16 which abut the wall 4 of the hollow sheet 
material shape 1 in the final position. A bore 18 for bolting together a 
pair of assembled flanges is provided in the portion 17 of the angle piece 
2 which connects the two legs 9 of the angle piece 2 to one another. 
FIG. 3 illustrates a hollow sheet material shape 1 with a partially 
inserted angle piece 2. On the one hand, the inserted leg 9 is guided by 
the walls 3, 4 and 6. On the other hand, it is guided by means of the 
bases 13 of the triangular projections 10, along the walls of the groove 
12 which extend approximately parallel to the surface of the channel. 
FIG. 4 shows in section how the leg 9 of the angle piece 2 is arrested in 
the hollow sheet material shape 1 in the final position where the shoulder 
16 of the angle piece 2 bears against the wall 4 of the hollow sheet 
material shape 1. Due to the non-uniform spacings between the projections 
10 on the leg 9, one of the projections 10 lies in one of the depressions 
8 of the groove 12 with clearance, one of the projections 10 bears against 
one of the protuberances 7 of the groove 12, e.g., with its base 13, and 
thereby slightly deforms the wall of the groove 12, and one of the 
projections 10 of the leg 9 catches in one of the depressions 8 of the 
groove 12 with its base 13 and prevents a release of the angle piece 2 
from the hollow sheet material shape 1. 
In the embodiment illustrated in FIG. 5, protuberances 7a formed in the 
wall 4 define the rack-like pattern in the hollow sheet material shape. 
Accordingly, the projections 10a on the leg 9 of the angle piece are 
located on that portion of the periphery of the leg 9 which confronts the 
wall 4. 
In the embodiment shown in FIG. 6, the protuberances 7b are formed in the 
wall 5a while the corresponding recesses 11 in the leg 9 are constituted 
by bores.