CABLE CONDUIT WITH RIDGED INNER WALL

CANALISATION ELECTRIQUE A PAROIS INTERNES STRIEES

English Abstract

An electrical conduit is substantially circular and is
internally formed with zig-zag ridges. The ridges are angularly
equispaced and have portions of constant pitch a joined at corners, and
the ridges contact a cable in the conduit at regions K each defined by
the formula:
Ar = 0.16b2zL K,
where
A = the surface of area R, equal to between
4,5mm2 and 32mm2,
r = the radius of the conduit or D/2,
b = the width of the contact region K,
z = the number of ridges 1, and
L K = axial length of each ridge straight portion.
The straight-portion pitch g in radians is equal to:
g = r'al L K
and is between 0.0o1rad and 1.2rad, radius r being equal to between
12mm and 100mm and L K is between 500mm and 10,000mm, depending on the
diameter of the cable which can range from 5mm to 45mm.

French Abstract

La présente invention vise un conduit électrique de forme essentiellement circulaire dont l'intérieur présente des rainures en zigzag. Ces rainures sont façonnées à angle, à égale distance les unes des autres, et elles sont constituées de segments de même espacement réunis à leurs points de rencontre. Ces rainures sont en contact avec un câble, à l'intérieur du conduit, dans les zones K définies séparément par la formule Ar = 0.16b2zL K, où A = la surface de la région R dont la valeur se situe entre 4,5 et 32 mm2, r = au rayon du conduit ou à D/2, b = la largeur de la zone de contact K, z = le nombre de rainures l, et L K =la longueur axiale de chaque segment droit d'une rainure. L'espacement des segments droits exprimé en radians par la valeur g est égal à g =r'al L K et se situe entre 0.001 et 1.2 radian, le rayon r correspondant à une valeur se situant entre 12 et 100 mm, et la valeur L K se situant entre 500 et 10 000 mm, selon le diamètre du câble, qui être de 5 à 45 mm.

Claims

-8-
We Claim:
1. A cable routing device having at least one cable conduit which is made of
synthetic thermoplastic material and which comprises a cable routing duct having a duct
inner wall which is circular in cross-section and which has the conduit internal radius r
and having sliding ribs disposed on the duct inner wall which are integrally formed from
the synthetic thermoplastic material of the synthetic material conduit and which run at a
predetermined angle of rotation a with respect to the internal circumference, wherein, in
a cable conduit which is disposed in a straight line with a cable to be introduced, contact
areas of the rib contact width b are formed between the sliding ribs and the cable sheath
of the cable to be introduced, wherein the combination of the following features is put
into effect;
the sliding ribs run in the form of waves and form reversal regions between
sections with a constant angle of rotation;
the rib contact width b, the number z of sliding ribs distributed equidistantly
over the circumference of the duct inner wall, the conduit internal radius r, and a length,
which is denoted as L K, of the rib contact sections between the reversal regions satisfy
the equation
Ar = 0.16b2zL K,
where A defines the contact area of the cable sheath on the points of intersection with
the sliding ribs in the rib contact sections, and falls numerically within the range from
4.5 to 32 mm2;
the angle g, measured in radians, of the gradient of the sliding ribs measured at
the duct inner wall satisfies the equation
g = ra/L K
and falls numerically within the range from 0.001 to 1,2 radians;
wherein r is selected within the range from 12 to 100 mm and L K is selected
within the range from 500 to 10,000 mm, and wherein the cables to be introduced have
an external radius within the range from 5 to 45 mm.
2. A cable routing device according to claim 1, wherein the cable duct inner wall
between adjacent sliding ribs has the form of a channel which is concave towards the
cable duct and which extends on both sides into the ridge of the sliding ribs.
3. A cable routing device according to either one of claims 1 or 2, wherein the
angle of rotation a is selected within the range between 45° and 340°, and is preferably
about 180°.

-9-
4. A cable routing device according to any one of claims 1 to 3, wherein the
rib contact width b, the number z of the sliding ribs equidistantly distributed over
the circumference of the duct inner wall, the conduit internal radius r, the angle
of rotation a and the length L K of the rib contact sections between the reversal
regions satisfy the equation
Ar = 0.16b2z (0.0003 r2a2+ L K2)l/2
5. A cable routing device according to any one of claims 1 to 4, wherein
connecting sections of length L V are disposed between two sections with a
constant angle of rotation, in which connecting sections the sliding ribs continue
parallel to the conduit axis, and that the rib contact width b, the number z of the
sliding ribs equidistantly distributed over the circumference of the duct inner
wall, the conduit internal radius r, the angle of rotation a, the length L V of the
connecting sections satisfy the equation
Ar = 0.16b2z (0.0003 r2 + L K2)1/2+ 4L Vbr.
6. A method for pulling a cable into a cable conduit according to any one of
claims 1 to 5, whereby a pull-in speed of the cable to be fed is so selected that
contact faces are molten by friction heat, and a lubricant friction condition isprovided by the fused mass; whilst
a) the sliding ribs run in waveshape and form reversal zones between
sections with constant angle of rotation,
b) the rib contact width b, the number z of sliding ribs equidistantly
distributed over the circumference of the conduit inside wall, the tube
inside radius r, and a length or rib contact sections between reversal
zones, identified as L K, satisfy the equation
Ar = 0.16 b2z L K,
where A defines the contact face of the cable jacket at intersecting points
with sliding ribs in rib contact sections, and is numerically in the range
from 4.5 to 32 mm2, and
c) the angle g, measured in radians, of the sliding ribs' lead, measured on
the conduit inside wall, satisfies the equation
g = ra / L K

- 10 -
and ranges numerically from 0.001 to 1.2 rad, where r in the range from
12 and 100 mm and L K is in the range from 500 and 10,000 are selected,
and the cable to be fed has an outside radius in the range from 5 to 45
mm.

Description

2098219
CABLE CONDUIT WITH RIDGED INNEB WALL
Field of the Invention
The present invention relates to a cable conduit. More
particularly this invention concerns such a conduit which i8 typically
used underground to protect electrical wires and cables.
Back~round of the Invention
As described in German patent document 3,217,401 and in US
patent~ 5,069,254 and 4,036,891 all of H. Vogelsang conduit assemblies
are known comprising one or more tubes formed of a synthetic resin and
interconnected transversely by longitudinally extending webs. Thus the
tubes can be delivered rolled up on spools with the plurality of tubes
and their webs in a flat coil. For use they are unwound, cut to
length, and then bunched together to form the desired dense array of
~uxtaposed tubes through which electrical lines, e.g. wires or cables,
are pulled or pushed.
In order to facilitate insertion of the cables German patent
document 3,529,541 of H. Vogelsang proposes forming the inner wall of
each tube with longitud~n~lly extending ridges alternating with
longitnd~n~lly extending grooves. These longitud~n~lly continuous and
throughgoing formations reduce the contact area between the wires or
cables being inserted through them to facilitate such insertion.
A ma~or disadvantage of this arrangement is that the ridges
invariably run somewhat along a helix like a screwthread due to the
rotation of the worm in the extruder. These helically extending ridges
impart some torsion to the electrical lines being pushed or pulled
through the conduit. Hence these lines can twist up and get ~ammed, or
can ~ust wind about each other to form a bulky mass.
An electrical conduit for wires or cables has also been proposed
which is formed by a tube extending along a longitudinal axis and
having an inner wall formed with a plurality of longitudin~lly
throughgoing ridges each formed by a plurality of longitud~n~lly ~oined
portions with every other portion inclined oppositely relative to the
axis to the intervening portions. In other words the ridges run
alternately along a right-hand helix and then a left-hand helix. Thus
with this arrangement any torsion that the ridges apply to the wires or
cables being pulled or pushed through the conduit will be cancelled out

- 2 - 2~ ~ ~ 2 1~
from one portion to the next. In this manner there will be no twisting
and b~r~n~ of the cables. The portions may be of varying pitch and
may in fact be part circular. It is also possible for the portions to
be substantially identical in which case they are straight and meet at
corners. In this case the portions are all of the same pitch. German
utility model 9,014,571 published 21 March 1991 describes such an
arrangement where the portions meet at smoothly curved corners,
virtually having a sinusoidal shape.
The ridges of this system are of substantially triangular
cross-section. The tube has a predetermined wall thickness measured
radially and the ridges have a radial height above the inner wall that
is substantially less than the wall thickness. In addition the tube
has a predetermined wall thickness measured radially and the ridges
have an angular dimension that is substantially less than the wall
thickness. The inner wall is formed between the ridges with grooves
complementary to the ridges. It is possible for the ridges to be
unitary with the tubing. They can also be separate elements that are
applied in a separate stage so that the ridges are formed of a
synthetic resin having a lower coefficient of friction than the tube.
The conduit i8 made by forcing the tube longitu~1n~11y through
an ~nn~ r opening defined intern~lly by a mandrel or die itself formed
with peripheral grooves that form the ridges and alternately oppositely
rotating the inner tool. The rotation speed of the mandrel is varied
continuously to produce ridges of varying pitch. The inner tool itself
can operate without removal of material.
While these systems do offer various advantages, they still
present occasionally excessive resistance to lines being pushed or
pulled through them.
Sumrnary of the Invention
The present invention provides an improved ridged-wall cable conduit which
overcomes or at least mitigates the above-given disadvantages, that is which offers minim:~l
linear resistance to an electrical line being pulled or pushed through it.
B

- 3 - ~7 Q ~ ~ 2 1 ~
The invention defines ~e exact relationship of the various dimensions of the
conduit to reduce friction between it and the conduit to a minimum.
The invention also provides an improved method of feeding a cable through a
conduit acco.~ing to the invention.
In accordance with a particularly highly engineered embodiment
of the invention the conduit is substantially circ~lar, the ridges are
angularly eq~is~-~e~ and have portions of constant pitch a ~oined at
corners, and the ridges contact a cable in the conduit at regions K
each defined by the formula
Ar = 0.16b2z~ ,
where
A = the surface of area R, equal to between
4.5mm2 and 32mm2,
r = the radius of the conduit or D/2,
b = the width of the contact region K,
z = ~he number of ridges 3, and
~ = asial length of each ridge straight portion. In this
arrangement the straight-portion pitch g in radians is equal to:
g = ra/LK
and is between O.OOlrad and 1.2rad, radius r being equal to between
12mm and lOOmm and LR is between 500mm and lO,OOOmm, depending on the
diameter of the cable which can range from 5mm to 45mm.
According to the invention the inner wall is formed between
ad~acent ridges with concave inwardly open valleys that merge smoothly
with the respective ridges. Furthermore the diameter of the cable, the
radial height of the ridges, and the radial depth of the valleys are
such that the cable will not touch the tube inner wall between the~0 crests of ad~acent ridges.
Normally the pitch a is equal to between 45~ and 340~,
preferably about 180~. Furthermore the dimensions relative to a length
LK ~f the ridge~cable contact regions K satisfy the equation:
Ar = 0.16b2z (0.0003r2a2 ~ LK)~
and the dimensions relative to a length LV ~f the corners satisfy the
equation:
B

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_ 4 _ 2098219
Ar = 0.16b2z(0.0003r2a2 + LK)~ ~ 4 Lvbr.
The invention is based on the knowledge that a considerable
reduction of pulling forces can be achieved in the above defined and
dimensioned cable conduits and cables, provided that measures have been
taken to replace dry friction by a friction that approximates lubricant
friction, which, as is well known, has substantially lower friction
coefficients than dry friction, in case of occurrence of interferingly
high pulling forces during pulling work to be performed. To achieve
this, no special lubricant is required according to the invention.
It has been found that such a relationship between the
dimensions ensures very little friction. This is particularly true
when the ridges have a radial height of between 0.3mm and 0.5mm.
According to a further feature of this invention the inner wall
is formed between the ridges with grooves complementary to the ridges.
The wave length is about lOOcm and the amplitude is between one-eighth
and one-fourth of the inslde diameter. The inside diameter is between
30cm and 70cm, preferably about 50cm. Normally the amplitude is
between one-eighth and one-fourth of the inside diameter and the inside
diameter is between 30cm and 70cm.
The method according to the invention basically comprises the
step of feeding an electrical line through the conduit at such a
longitudinal speed that friction between the line and the ridges
partially melts the ridges so that the molten ridges act as a
lubricant. It has been found that while this is technically a dry-feed
system, it has less friction than the standard prior-art procedure of
coating the line with a lubricant, and is a great deal easier and less
messy.
Brief DescriPtion of the Drawin~s
The above and other ob~ects, features, and advantages will
become more readily apparent from the following, it being understood
that any feature described with reference to one embodiment of the
invention can be used where possible with any other embodiment and that
reference numerals or letters not specifically mentioned with reference
to one figure but identical to those of another refer to structure that
is functionally if not structurally identical. In the accompanying
drawings:

-
5 ~ 2098219
Fig. 1 is a perspective view of a conduit according to the
invention;
Fig. 2 is a diagrammatic view illustrating a region of contact
between a conduit ridge and an electrical line or cable in the conduit;
Fig. 3 is a side view of the inside of the conduit showing an
electrical line in the conduit;
Fig. 4 is a large-scale section taken along line IV--IV of Fig.
2 during feeding of the line through the conduit; and
Fig. 5 is a cross-section at very large scale illustrating a
conduit and cable according to the invention.
SDecific DescriDtion
As seen in Figs. 1 through 5, a conduit 2 according to the
invention is unitarily formed of a durable thermoplastic synthetic
resin with unillustrated webs or flanges that are connected to other
such conduits as described in the above-cited patent documents. This
conduit tube 2 is centered on a longitudinal axis A and has an inner
wall 1 that is cylindrical and also centered on the axis A and that is
formed with triangular-section ridges 3 separated by complementary
triangular-section grooves 9 (see Fig. 5). The ridges 3 are of
basically zig-zag shape (see Fig. 2).
Figs. 2 through 5 show how a cable 10 inserted through the
conduit 2 engages the ridges 3 along a strip 4 that intersects each of
these ridges 3 at a rhombic or diamond-shaped contact region K. In
this arrangement as seen in Fig. 3 the ridges 3 are each formed by
straight portions 6 of constant pitch a meeting at corners 8. The
straight portions 6 have an axial dimension LK.
According to the invention these dimensions follow the
relationship:
Ar = 0.16b2zLK,
where:
A = the surface of area K, equal to between
4.5mm2 and 32mm2;
r = the radius of the conduit or D/2;
b = the width of the contact region K; and
z = the number of ridges 3.
Furthermore the pitch 8 in radians is equal to:

-- 6 --
8 = ra ~OK ~ ~ 2 1 9
and is equal to between O.OOlrad and 1.2rad.
Normally radius r is equal to between 12mm and lOOmm and LK is
between 500mm and lO,OOOmm, depending on the diameter of the cable 10
which can range from 5mm to 45mm. In the illustrated embodiment the
pitch a is equal to about 180~.
According to a further feature of this invention as shown in
Fig. 5 the ridges 3 are spaced angularly apart by a spacing s and have
a radial height hR which is such that, with a cable of a given radius
rc of curvature, the cable only pro~ects into the valleys 9 by a
distance which comes short by a spacing Xf from the base of the valleys
9, not making contact therewith. Thus the cable 10 rides wholly on the
crests of the ridges 3.
Furthermore the following equation applies to the dimension LK:
Ar = 0.16b2z(0.0003r2a2 + LK2)~
Similarly, the dimension 1/2 satisfies the equation:
Ar = 0.16b2z(0.0003.r2a2 ~ LK)~ + 4Lvbr.
With the system of this invention it has been found extremely
advantageous to pull or push the cable through the conduit 2 at such a
speed as to heat and fuse the crests or outer edges of the ridges in
the contact zone K as shown at 8 in ~ig. 4. This produces a lubricant
effect that works so long as the cable is being pulled through the
conduit, but that disappears, leaving the conduit dry, once the cable
is in position. The lubricant effect of the fused film 8 in the
regions K is excellent, better in fact than the prior-art system of
squeezing a lubricant, typically a ~oap solution into the conduit. The
main advantage is that this lubricant effect is achieved all along the
cable, wherever it contacts the conduit so that the prior-art problems
of uniform distribution of the lubricant are wholly avoided.
Below is a Table that gives a sampling of conduits according to
the invention.

209~219
TABLE
5 Aspect Designation
of
Conduit 32 50 ~ 110 225
x3.0 x4.6x6.3 x12.8
~utside diameter (mm) 32.0 50.0110.0 225.0
Wall thickness t (mm) 3.0 4.6 6.3 12.8
Inside diameter D or 2r(mm) 26.0 40.8 97.4 199.4
Number z of ridges , 26 40 40 82
., ., . , .. .. ~ ..
Ridge spacing (mm) 3.14 3.207.65 7.65
~ ........ . . ..
Pitch angle a (~) 180 180 180 180
Ridge contact width b (mm) . 0.1 0.1 0.1 0.1
Length of ridge contact (mm) ; 1275 2000 4775 9775
Length LV ~f bights (mm) 2 2 2 2

Representative Drawing