PLASTIC CONDUIT WITH INTEGRAL PULL WIRE

CONDUIT DE PLASTIQUE A CABLE DE TRACTION INTEGRAL

English Abstract

ABSTRACT OF THE DISCLOSURE
A plastic conduit with an integral pull wire
avoids having to use a fish wire to pull electrical
conductors through the conduit. An improved process of
extruding plastic conduit comprises feeding a separate
flexible wire or cord element through an aperture at the
center of the plastic extruder die within the extruded
conduit in the same direction and speed as the extruded
conduit. An extrusion device has a plastic extrusion die
with a central mandrel supported on transverse webs
within the die exit, an aperture through one of the webs
having a bend therein so the aperture exits at the center
of the mandrel and in line with the die, feed rolls for
the flexible wire or cord and speed control for the feed
rolls to ensure the flexible wire or cord is fed at the
same speed as the conduit is extruded.

Claims

The embodiments of the invention in which an
exclusive property or privilege is claimed are defined as
follows.
1. A flexible plastic conduit for electrical
conductors having a separate flexible wire or cord
element extending through the center of the conduit for
at least the length of the conduit for attachment to
electrical conductors to be pulled through the conduit.
2. The flexible plastic conduit according to
Claim 1 wherein an additional length of flexible wire or
cord element is provided at each end of the conduit.
3. In a process of extruding a flexible plastic
conduit for electrical conductors from a plastic extruder
die, the improvement comprising the steps of, feeding a
separate flexible wire or cord element through an
aperture at the center of the plastic extruder die within
the extruded conduit in the same direction as the
extruded conduit at a feed speed corresponding to the
extrusion speed of the conduit.
4. The process according to Claim 3 wherein the
flexible plastic conduit has corrugations formed thereon
immediately after being extruded.
5. The process according to Claim 3 wherein
additional lengths of the separate flexible wire or cord
element are fed through the aperture at the center of the
plastic extrusion die prior to extruding the conduit and
after extruding the conduit.
6. A flexible plastic conduit for electrical
conductors having a separate flexible wire or cord
element extending through the centre of the conduit for
at least the length of the conduit, made by the process
according to Claim 3.
7. An extrusion device for flexible plastic conduit
comprising, an extruder having a plastic extrusion die
with a central mandrel supported on transverse webs
within the die exit, an aperture extending through one of
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the webs having a bend therein so the aperture exits at
the approximate center of the central mandrel, extending
in line with the extrusion die to feed a separate
flexible wire or cord element through the aperture inside
the extruded conduit, feed rolls for the flexible wire or
cord element, and speed control means for the feed rolls
to ensure the element is fed through the aperture at
substantially the same speed as the conduit is extruded.
8. The extrusion device according to Claim 7
including corrugation former means positioned after the
extrusion die.
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Description

~302310
PLASTIC CONDUIT WITES INTEGRAL PI~LL WIRE
The present invention relates to a plastic
conduit with an integral pull wire. More specifically
the present invention provides a plastic conduit for
electrical conductors which has a pull wire placed inside
the conduit during the manufacturing process to allow for
easy insertion of conductors into a conduit after
installation.
Flexible electrical conduits generally made of
plastic, and in some cases corrugated plastic, are cut to
size and fastened into place between junction and outlet
boxes that have already been positioned and located.
Once the conduit is in place, then a relatively stiff
wire called a fish wire, generally with a hook at the
end, is pushed through the conduit between adjacent
boxes. The electrical conductors or cables are then
attached to the hook at the end of the fish wire that has
been pushed through the conduit and the fish wire is then
pulled from the other end. The electrical conductors are
pulled by the fish wire and eased into the junction or
outlet box. The fish wire is then pulled right through
the conduit until the conductors emerge at the other
box. The conductors are then disconnected from the fish
wire and are ready for connection.
The pushing through of the fish wire is time
consuming and at times difficult as the fish wire has to
be fairly stiff in order to allow pushing it. At times
the wire gets stuck at conduit bends. Furthermore, a
fish wire is another piece of equipment which always has
to be available and if one is not available, then time is
wasted either to find a fish wire, or attempt to push
conductors through the conduit.
It is an aim of the present invention to provide
flexible plastic conduit which has a wire or cord in

1:~02310
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place, thus eliminating the need for a fish wire and
eliminating this step of inserting a fish wire through a
conduit after installation.
The present invention provides a flexible
plastic conduit for electrical conductors having a
separate flexible wire or cord element extending through
the center of the conduit for at least the length of the
conduit for attachment to electrical conductors to be
pulled through the conduit.
In another embodiment, there is provided in a
process of extruding a flexible plastic conduit for
electrical conductors from a plastic extruder die, the
improvement comprising the steps of feeding a separate
flexible wire or cord element through an aperture at the
center of the plastic extruder die within the extruded
conduit in the same direction as the extruding conduit at
a feed speed corresponding to the extrusion speed of the
conduit.
There is also provided an extrusion device for
flexible plastic conduit comprising an extruder having a
plastic extrusion die with a central mandrel supported on
transverse webs within the die exit, an aperture
extending through one of the webs and having a bend
therein so the aperture exits at the approximate center
of the central mandrel, extending in line with the
extrusion die to feed a separate flexible wire or cord
element through the aperture inside the extruded conduit r
feed rolls for the flexible wire or cord element, and
speed control means for the feed rolls to ensure the
element is fed through the aperture at substantially the
same speed as the conduit is extruded.
In a drawing which illustrates an embodiment of
the invention, a cross sectional side elevation shows
schematically an extruder die for extruding a plastic

1 30231~
conduit with feed rolls and an aperture in the central
mandrel of the die to feed a separate flexible wire or
cord element into the center of the conduit.
Referring now to the drawing, an extruder die 10
has an inlet 12 from the extruder which opens out to a
circular exit 14. A central mandrel 16 is supported on
at least two transverse webs 18. The central mandrel 16
forces the plastic to form a tube 19 when it leaves the
die 10. As shown in the drawing, the tube 19 passes
between two endless belts 20 which have semi-circular
ridges therein. Air pressure is applied within the tube
19 to form a conduit 22 with corrugations therein.
An aperture 24 is provided in the central
mandrel 16 extending through one of the transverse webs
18 and then having a bend therein so the aperture 24
exits at the center of the central mandrel 16 projecting
in line with the conduit 22 as it is extruded. A cord or
wire element 26 is passed through this aperture 24, the
element 26 is provided from a coil 28 or other suitable
storage means and passes through feed rolls 30 which feed
the element 26 through the aperture 24. The feed roll
speed is controlled to be the same speed as that of the
conduit 22 being extruded through the extruder die 10.
The element 26 can be made of wire or may be a
cord formed of nylon rope or other suitable material. It
must be strong enough to pull cables and wires through a
conduit. In one embodiment, the element is fed through
the aperture 24 for a short time before commencing
extrusion of the conduit 22 so that there is an extra
length of element and then is also fed for a short time
after the extrusion of the conduit ends, thus the element
extends from both sides of a conduit pipe. In another
embodiment the element extends for the length of the
conduit pipe and when an electrician is installing the

~30Z3~0
conduit pipe he merely cuts a short piece off each end of
the conduit to ensure that there is a sufficient length
of wire or cord to attach to the electrical conductors
and pull them through the conduit. Once the electrician
has attached one end of the element 26 to the electrical
conductors, he may then pull the other end and the
conductors move through the conduit. This avoids the
necessity of having to use a fish wire and makes the
installation of electrical conductors and cables in a
conduit a simpler matter that avoids the necessity of
initially inserting a fish wire.
Various changes may be made to the embodiments
described herein without departing from the scope of the
present invention which is limited only by the following
claims.

Representative Drawing