Note: Descriptions are shown in the official language in which they were submitted.
2137879
~ADDER-TYPE CABLE TRAY
Background of the Invention
This invention relates generally to support
systems used in the construction industry, and more
particularly to ladder-type cable tray used to support
runs of cable, electrical wiring and the like.
Conventional ladder-type cable tray comprises a
pair of parallel side rails and a series of spaced-apart
rungs extending between the rails, the rails and rungs
typically being of extruded aluminum (although they may
also be steel parts). It has been the conventional
practi,ce in the industry to secure the rungs to the rails
by welding. Welding, however, has certain disadvantages,
including inconsistencies in the weld joints, the
creation of noxious fumes, the need for protective
equipment, high labor and capital costs, a relatively low
production rate, and the need to clean the parts after
the welding is complete.
Attempts have been made to fasten the rungs to
the rails by screw fasteners. These attempts have
involved fabricating the rungs with C-shaped or U-shaped
screw holes in the ends of the rungs, and driving self-
tapping screws through the side rails into these screw
holes to fasten the rungs to the rails. In these prior
designs, the screw holes are configured to be open along
one of their sides to permit expansion of the holes to
accommodate varying screw and rung tolerances. However,
this open design also reduces the extent to which the
screws may be tightened, which decreases the overall
mechanical strength of the cable tray. Further, when the
cable tray deflects under a load, the screws tend to pop
through the open sides of the screw holes, which reduces
the load-bearing capacity of the cable tray.
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There is a need, therefore, for ladder-type
cable tray which eliminates the problems associated with
welding the rungs to the side rails, but which has the
strength characteristics of welded cable tray.
Summary of the Invention
Among the several objects of this invention may
be noted the provision of improved ladder-type cable tray
wherein the rungs of the tray are attached to the side
rails by mechanical fasteners; the provision of such
cable tray which can be produced economically at high
production rates; the provision of such cable tray which
eliminates the noxious fumes, inconsistent weld joints,
high c~sts and other problems associated with welding;
the provision of such cable tray which has a load
capacity at least as great as conventional designs; the
provision of such cable tray which is safer to fabricate
than conventional designs; and the provision of such
cable tray which is designed to avoid snagging or damage
to items being carried by the tray.
In general, a cable tray of the present
invention comprises a pair of generally parallel spaced-
apart metal side rails and metal rungs extending between
the rails at intervals spaced along the rails. Each
metal rung has opposite ends generally abutting
respective side rails and a pair of preformed openings
extending inwardly from the opposite ends of the rung
lengthwise of the rung. A pair of metal mechanical
fasteners extend through the side rails and into
respective preformed openings in the rung to fasten the
rung to the side rails. Each of the openings is defined
by a rung structure which, as viewed in a cross section
taken transversely with respect to the rung, extends
completely around the perimeter of the opening so that
the perimeter of the opening is totally enclosed by the
rung structure. Each of the fasteners is engageable with
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the rung structure defining a respective opening for
securely holding the rung in fixed position with respect
to its respective side rail.
Other objects and features will be in part
apparent and in part pointed out hereinafter.
Brief Description of the Drawings
Fig. 1 is a perspective view of cable tray of
the present invention;
Fig. 2 is an enlarged exploded perspective view
of the cable tray of Fig. 1;
Fig. 3 is an end elevational view of the cable
tray of Fig. 1;
j' Fig. 4 is an enlarged sectional view taken
along the plane of line 4-4 of Fig. 3; and
Fig. 5 is a sectional view taken along the
plane of line 5-5 of Fig. 4.
Corresponding reference characters indicate
corresponding parts throughout the several views of the
drawings.
Description of the Preferred Embodiment
Referring now to the drawings, and first more
particularly to Figs. 1 and 2, a ladder-type cable tray
of the present invention is indicated in its entirety by
the reference numeral 20. The cable tray 20 comprises
first and second generally parallel spaced apart metal
side rails 22, 24 and a plurality of metal rungs, each
designated 26, extending between the rails at intervals
spaced along the rails. Each rung 26 has first and
second opposite ends 28, 30 abutting the first and second
side rails 22, 24, respectively. Mechanical fasteners,
such as self-tapping screws 32, extend through the side
rails 22, 24 and into the opposite ends 28, 30 of the
rungs 26 to fasten the rungs to the side rails.
CA 02137879 1998-07-17
.
The cable tray 20 is supported by a series of
support bars 34 (only one of which is shown in Fig. 1)
suspended at intervals spaced lengthwise of the cable
tray, the support bars extending generally crosswise
relative to the rails. Hold-down members 36 are provided
for securing the rails 22, 24 to the support bars 36.
As shown in Figs. 2-4, each rung 26 has
generally horizontal upper and lower flanges 38, 40 and a
generally vertical web 42 connecting the two flanges.
Electrical cable and wire placed in the cable tray 2Q is
adapted to rest on the upper flanges 38 of the rungs.
Each upper flange 38 has a smooth top surface with edge
margins 44 which curve downwardly to avoid snagging or
damage to the electrical cable and wire. The edge
margins 44 also have rounded edges 44a to avoid slicing
or snagging the electrical cable and wire. The web 42 of
the rung 26 lies in a central longitudinal vertical plane
(designated in Fig. 4 by the line Y-Y) of the rung and
the rung is symmetrical about this plane. The rung 26 is
also symmetrical about a central longitudinal horizontal
plane (designated in Fig. 4 by the line X-X) passing
through the rung midway between the upper and lower
flanges. Because of its symmetry, the rung is
reversible; in other words, the upper flange 38 of the
rung is identical to the lower flange 40 and the first
end 28 of the rung is identical to the second end. For
ease of manufacture, each rung 26 has a uniform cross
section throughout its entire length.
A generally rigid tubular rung structure 46 is
formed as an integral part of the web 42 of the rung 26
and extends continuously from one end of the rung to the
other end of the rung. The rung structure 46 has first
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and second preformed openings 48, 50 (Figs. 2 an~ 5~
extending inwardly from the opposite ends 28, 30 of the
rung lengthwise of the rung. Preferably, the first and
second openings 48, 50 combine to constitute a single
continuous hole 52 (Fig. 5) extending through the rung
structure 46 from the first end 28 of the rung to the
second end 30. As shown in Fig. 5, the diameter do of the
first and second openings 48, 50 (or hole 52) is somewhat
smaller than the diameter ds (i.e., the major diameter) of
the screw thread 32a of each screw 32. Since the screws
32 are self-tapping, the thread of each screw cuts into
the corresponding rung structure 46 when driven into the
opening 48, 50 to form an internal thread 54 in the rung
structjure. Although self-tapping screws are preferred,
machine screws, alternatively, may be used if internal
screw threads are tapped in the openings 48, 50 of the
rung. As shown in Fig. 4, the rung structure 46 extends
completely around the perimeter (circumference) of the
opening so that the perimeter of the opening is totally
enclosed by the rung structure to provide a strong
connection between the rung structure and the screws.
Preferably, the rung structure 46 and openings 48, 50 of
each rung 26 are circular in transverse cross section.
Alternatively, the rung structure 46 and/or openings 48,
50 may be square or polygonal in transverse cross
section, or have other suitable cross-sectional shapes.
In any event, the wall thickness of the tubular rung
structure 46 should be sufficient (e.g., 1/8 in.) to
prevent splitting of the structure in the event the fit
between the screws and the openings 48, 50 are somewhat
tighter than preferred due to tolerance variations. Each
rung is preferably aluminum and may be formed by
extrusion or other suitable method.
Each rung 26 is preferably I-shaped in
transverse cross section. However, it is to be
understood that, alternatively, the rung may be C-shaped,
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Z-shaped, or rectangular in transverse cross section, or
have other suitable cross-sectional shapes.
Referring to Figs. 2 and 3, the side rails 22,
24 are aluminum I-beams, preferably formed by extrusion.
Each side rail is formed with a vertical web 56, upper
and lower horizontal flanges 58, 60 extending laterally
from the web on opposite sides of the web, and a shoulder
62 projecting inwardly from the web. The shoulder 62
extends along the web 56 on its inside face 64 (Fig. 3)
at a location spaced above the lower flange 60 of the
rail. The spacing between the shoulder 62 and lower
flange 60 is selected to provide for a tight (snug) fit
of a respective end of each rung 26 between the shoulder
and lo~er flange of the rail. The shoulder 62 has a
lower face 62a opposing the upper flange 38 of each rung.
Each side rail 22, 24 has a plurality of holes 66 through
its web 56. The holes 66 are located generally midway
between the inwardly projecting shoulder 62 and lower
flange 60 of the rail and at intervals spaced along the
rail. The holes 66 through the webs 56 of the rails
align with the openings 48, 50 in opposite ends of the
rungs when the rungs are positioned with their ends
between the shoulders 62 and lower flanges 60 of the
rails. The screws 32 extend through the holes 66 in the
rails and into the openings 48, 50 in each rung to grip
the rung structure 46 and thereby secure the rung to the
rails. Preferably, the diameter of each rail hole 66
(Fig. 5) is greater than the diameter ds of the screw
thread 32a so that the screw thread clears the hole
during insertion of the screw. Since the screw thread
32a does not threadably engage the rail, the shank 32b of
the screw 32 is tensioned between the head 32c of the
screw and the rung structure 46 when the screw is tightly
turned in the corresponding opening of the rung structure
to firmly hold the rung 26 against the web 56 of the
rail.
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Preferably, the lower face 6Za of the shoulder
62 is horizontal. Alternatively, however, the lower face
62a may slope downwardly from the edge of the shoulder to
the web 56 of the rail, thereby forming a wedge which
pushes against the upper flange 38 of the rung to urge
the rung against the lower flange 60 of the rail when the
screw 32 is tightened in the corresponding opening of the
rung structure. If the lower face of the shoulder 62 is
sloped in this manner (as opposed to a horizontal lower
face) a slight gap is provided between a respective end
of the rung 26 and the web 56 of the rail. However, the
wedging of the rung 26 between the sloped lower face of
the shoulder and lower flange 60 firmly holds the rung
agains~ the rail.
Although each side rail 22, 24 is preferably I-
shaped in transverse cross section, it is to be
understood that, alternatively, the rails may be C-shaped
or Z-shaped in transverse cross section, or have other
suitable cross-sectional shapes. Also, although the
rails 22, 24 and rungs 26 are preferably of extruded
aluminum, the rails and rungs may be formed of other
metals or alloys or formed by other methods without
departing from the scope of this invention.
To assemble a cable tray of this invention, the
first end 28 of each rung 26 is placed against the inside
face 64 of the web 56 of the first rail 22 in a position
between shoulder 62 and lower flange 60, and the second
end 30 of each rung 26 is placed against the inside face
64 of the web 56 of the second rail 24 in a position
between shoulder 6~ and lower flange 60. Each rung 26 is
oriented relative to the rails 22, 24 such that the
flanges of the rungs and rails lie in planes generally
parallel to one another. In other words, the lower face
68 of the lower flange 40 of each rung 26 opposes the
lower flanges 60 of the side rails 22, 24, and the upper
flange 38 of each rung opposes the shoulders 62 of the
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rails. When the rungs and rails are in proper position
with respect to one another, i.e., when the openings 48,
50 in the rungs 26 are aligned with the corresponding
holes 66 through the webs 56 of the rails, the screws 32
are inserted through the holes 66 and threaded into the
openings 48, 50 in the rungs to firmly secure the rungs
against the rails. Since each rung 26 is symmetrical
about its central longitudinal vertical and horizontal
planes and is uniformly shaped throughout its length, the
first and second ends 28, 30 of the rung are identical
and the upper and lower flanges 38, 40 of the rung are
identical. Thus, the orientation of the rung 26 relative
to the rails 22, 40 is the same regardless of which end
of thel'rung is secured to which rail and regardless of
which flange of the rung opposes the shoulders 62 of the
rails. Since the rungs 26 are easily oriented relative
to the rails and secured to the rails by screws, cable
tray of the present invention can be produced
economically at high production rates.
A cable tray of the present invention has a
load capacity at least as great as conventional designs.
However, because the cable tray is assembled without the
need for welding, noxious fumes, inconsistent weld joints
and other problems associated with welding are
eliminated.
In view of the above, it will be seen that the
several objects of the invention are achieved and other
advantageous results attained.
As various changes could be made in the above
constructions without departing from the scope of the
invention, it is intended that all matter contained in
the above description or shown in the accompanying
drawings shall be interpreted as illustrative and not in
a limiting sense.
