Stranded electric conductor manufacture

In a method of manufacturing a stranded conductor for use in an electric power cable, the cross-sectional shapes of wires being drawn towards or through a rotatably driven lay plate by which the wires are laid helically in a layer around the axis of the conductor are so modified that, on emerging from the lay plate and passing into at least one die downstream of the lay plate, the wires of modified cross-sectional shape fit tightly together and, if present, around a central wire or a preceding layer of helically applied wires. The wires of each layer preferably are initially of the same cross-sectional shape and size as one another, e.g. approximately circular, and, preferably, the modified cross-sectional shapes imparted to the wires of each layer are the same as one another, e.g. approximating to a sector of an annulus. No compacting of the wires is required in the die or dies and, as a consequence, a capstan drawing the wires through the die or dies is not subjected to a undesirable load.

In the manufacture of electric power cables comprising one or more than one 
cable conductor, with a view to ensuring that the cable is sufficiently 
flexible to enable it to be wound on and off a cable drum and to be 
readily installed, it is the general practice for the or each cable 
conductor to comprise a plurality of layers of wires or other elongate 
elements of metal or metal alloy, all hereinafter included in the generic 
term "wires", extending helically around the axis of the conductor, the 
lay of the wires of adjacent layers usually but not necessarily being of 
opposite hand. Such a cable conductor is generally, and hereinafter will 
be, referred to as a "stranded conductor". 
When manufacturing, for use in an electric power cable, a stranded 
conductor of a predetermined cross-sectional area of metal or metal alloy, 
unless the wires of the conductor are so compacted together that a 
stranded conductor is obtained whose diameter is not unnecessarily large, 
the overall diameter of the cable will be such that an unnecessary 
quantity of electrically insulating material and of other materials will 
be required in the cable manufacture and hence the cost of the cable will 
be unnecessarily high. 
With a view to limiting the diameter of a stranded conductor of a 
predetermined cross-sectional area of metal or metal alloy, during 
manufacture of the stranded conductor it is common practice for the 
partially-formed conductor and/or the wholly-formed conductor to be drawn 
through one or more than one die which compacts the wires of the conductor 
tightly together. This procedure has the serious disadvantage that the 
capstan drawing the conductor through the compacting die or dies is 
subjected to an undesirable high load. 
It has also been proposed to form each layer of preformed wires of such 
cross-sectional shapes that, when the wires are helically laid, they fit 
tightly together. This proposal has the disadvantage that a plurality of 
wires of cross-sectional shapes and sizes differing from one another are 
required for any one stranded conductor, thereby substantially adding to 
the cost of the cable of which the conductor is to form a part. 
It is an object of the present invention to provide an improved method of 
manufacturing a stranded conductor for use in an electric power cable by 
means of which the aforesaid disadvantages are avoided. 
According to the invention, in the improved method of manufacturing a 
stranded conductor, a plurality of wires being drawn towards or passing 
through a lay plate or other means by which the wires are laid helically 
in a layer around the axis of the conductor are each caused to pass 
through means by which the cross-sectional shape of the wire is so 
modified that, on emerging from the lay plate and passing into at least 
one die downstream of the lay plate, the wires of modified cross-sectional 
shape fit tightly together and, if present, around a central wire or a 
preceding layer of helically applied wires. 
Since the cross-sectional shapes of the wires emerging from the lay plate 
and entering said die or dies have been so modified that the wires will 
fit tightly together and, if present, around a central wire or a preceding 
layer of helically applied wires, no substantial compacting of the wires 
is effected by the die or dies and, as a consequence, the capstan drawing 
the wires through the die or dies is not subjected to an undesirable load. 
Preferably, the cross-sectional shapes of the wires of each layer of wires 
of the stranded conductor are so modified that, on emerging from the lay 
plate and passing into said die or dies, the wires of modified 
cross-sectional shape of said layer fit tightly together and around a 
central wire or a preceding layer of helically applied wires. 
The wires of the or a layer of wires being drawn towards or passing through 
the lay plate preferably are initially of the same cross-sectional shape 
and size as one another and, initially, may be of circular or non-circular 
cross-section. 
The modified cross-sectional shapes imparted to some of the wires of the or 
a layer may differ from the modified cross-sectional shapes imparted to 
other wires of said layer but, preferably, the modified cross-sectional 
shapes imparted to the wires of the or a layer are substantially the same 
as one another. For example, in one preferred embodiment, the modified 
cross-sectional shapes imparted to the wires of the or a layer each 
approximates to a sector of an annulus. 
The invention also includes improved apparatus for use in the improved 
method of manufacturing a stranded conductor as hereinbefore described, 
which improved apparatus comprises a lay plate or other means by which a 
plurality of wires travelling in the directions of their lengths can be 
laid helically in a layer around the axis of the conductor, at least one 
die disposed downstream of the lay plate for assembling the wires together 
and, disposed upstream of or on the lay plate. shaping means by which the 
cross-sectional shape of each wire can be so modified that, on emerging 
from the lay plate and passing through said die or dies, the wires of 
modified cross-sectional shape will fit tightly together. 
The shaping means by which the cross-sectional shape of each wire of the or 
a layer is modified may take any convenient form. In one preferred 
embodiment in which the shaping means are disposed upstream of the lay 
plate, each shaping means comprises a pair of freely rotatable rollers 
between which a wire is drawn, one or each roller being urged transversely 
towards the other roller and the circumferential surfaces of the rollers 
co-operating to define the cross-sectional shape into which the 
cross-section of the wire is to be modified. In a second preferred 
embodiment in which the shaping means are disposed on the lay plate, each 
shaping means comprises a bore extending through the lay plate, the 
cross-sectional shape of which bore over at least a part of its length 
changing smoothly and continuously from a substantially circular cross 
sectional shape at the upstream end of said part of said length to the 
required modified cross-sectional shape at the downstream end of said part 
of said length, the cross-sectional area of the bore over said part of 
said length being substantially constant. 
The invention is further illustrated by a description, by way of example, 
of a stranded electric conductor for use in an electric power cable, which 
conductor can be manufactured by the improved method of the invention, and 
of two preferred methods of and apparatus for forming one layer of wires 
of the stranded conductor, with reference to the accompanying drawings, in 
which:

The stranded conductor 1 shown in FIG. 1 comprises a central copper wire 2 
of circular cross-section, an inner layer 3 of copper wires 4 each of a 
cross-section approximating to a sector of an annulus extending helically 
around the central copper wire, and an outer layer 5 of copper wires 6 
each of another cross-section approximating to a sector of an annulus 
extending helically around the layer 3 with a direction of lay opposite to 
that of the wires 4 of layer 3. 
Referring to FIGS. 2 and 3, when forming the inner layer 3 of copper wires 
4 of the stranded conductor shown in FIG. 1 by the first preferred method, 
the central copper wire 2 is drawn along the axis of the stranded 
conductor to be formed through the center of a lay plate 7 rotating about 
the axis of the conductor and into a die 8 downstream of the lay plate. At 
the same time, six copper wires 4, each initially of the same 
approximately circular cross-section, are drawn through shaping means 9, 
one for each wire, upstream of the rotating lay plate 7 and through the 
lay plate into the die 8. As will be seen on referring to FIG. 3, each 
shaping means 9 comprises a pair of freely rotatable rollers 11 and 12, 
the roller 11 being fixed in space and the roller 12 being urged 
transversely towards the roller 11 by means of a hydraulically or 
pneumatically operated piston 14. The circumferential surfaces of the 
rollers 11 and 12 co-operate to define the cross-sectional shape of a 
sector of an annulus in accordance with each wire 4 as shown in FIG. 1. At 
each shaping means 9, the cross-sectional shape of the wire 4 passing 
therethrough is modified to a cross-sectional shape approximating to said 
sector of an annulus. At the rotating lay plate 7, the sector-shaped wires 
4 are laid helically around the advancing central copper wire 2 and, at 
the die 8, the helically extending sector shaped wires are caused to fit 
tightly together to form the layer 3 of approximately circular overall 
cross-section. 
Since no substantial compacting of the wires 4 is effected by the die 8, 
the capstan (not shown) drawing the wires through the die is not subjected 
to an undesirable load. 
Referring to FIGS. 4 and 5, when forming the inner layer 3 of copper wires 
4 of the stranded conductor shown in FIG. 1 by the second preferred 
method, the central copper wire 2 is drawn along the axis of the stranded 
conductor to be formed through the center of a lay plate 17 rotating about 
the axis of the conductor and into a die 18 downstream of the lay plate. 
At the same time, six copper wires 4, each initially of the same 
approximately circular cross-section, are drawn through shaping means 19 
disposed on the rotating lay plate 17, one shaping means for each wire, 
and beyond the lay plate into the die 18. As will be seen on referring to 
FIG. 5, each shaping means 19 comprises a bore 20 extending through the 
lay plate 17, the cross-sectional shape of which bore over a part of its 
length changing smoothly and continuously from a substantially circular 
cross-sectional shape 21 at the upstream end of said part of said length 
to a cross-sectional shape 22 at the downstream end of said part of said 
length approximating to a sector of an annulus in accordance with each 
wire 4 as shown in FIG. 1. The cross-sectional area of the bore 20 over 
said part of its length is substantially constant. At each shaping means 
19, the cross-sectional shape of the wire 4 passing therethrough is 
modified to the cross-sectional shape 22 approximating to a sector of an 
annulus and the sector-shaped wires are wound helically around the 
advancing central copper wire 2. At the die 18, the helically extending 
sector shaped wires 4 are caused to fit tightly together and around the 
central copper wire 2 to form the layer 3 of approximately circular 
overall cross-section. 
As in the case of the first preferred method described with reference to 
FIGS. 2 and 3, since no substantial compacting of the wires 4 is effected 
by the die 18, the capstan (not shown) drawing the wires through the die 
is not subjected to an undesirable load.