Concentric Compressed Unilay Stranded Conductors are formed of certain combinations of compressed wires, such as 1+7+12, 1+6+11 or 1+7+12+17, which have nominally equal diameters. The combinations of conductors or wires are selected so that the number of wires in any two adjacent layers, including a central layer, are not divisible by a common number with the exception of the integer one. The stranded conductors are optionally formed to have sectored cross-sectional configurations.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention generally relates to stranded cable manufacturing and more 
particularly to the manufacturing process for producing compressed 
concentric unilay stranded round, sectored and pre-spiraled sectored 
conductors with high speed single or double twist machinery, and cables 
and conductors produced thereby. 
2. Description of the Prior Art 
Compressed stranded cable conductors are well known in the art. Examples 
are disclosed in U.S. Pat. No. 4,473,995, 3,383,704 and 3,444,684. Such 
cables are preferred over uncompressed cables or compacted cables for 
several reasons. Compressed conductors typically have a nominal fill 
factor from about 81% to 84% Fill factor is defined as the ratio of the 
total cross-section of the wires in relation to the area of the circle 
that envelops the strand. 
Uncompressed cables require the maximum amount of insulation because the 
cable diameter is not reduced and because interstitial valleys or grooves 
between the outer strands are filled with insulation material. Typical 
fill factors for these conductors are about 76%. On the other hand, 
compact conductors, although eliminating the above-mentioned drawbacks, 
might have physical properties that are not desirable for specific 
applications. Typical fill factors for these constructions range from 91% 
to 94%. 
Multiwire compressed conductor strands are made in different configurations 
and by many different methods. Each method and configuration has 
advantages and disadvantages. One approach is to form the strand with a 
central wire surrounded by one or more helically layered wires. The strand 
is made by twisting the wires of each layer about the central wire with a 
wire twisting machine. A true concentric strand is one example of a strand 
made by this method. Each layer of a true concentric strand has a reverse 
lay and an increased length of lay with respect to the preceding layer. In 
case of a 19-wire conductor strand, two passes might be required through a 
wire twisting machine to make the strand. 
One example of a known strand involves one pass for a 6-wire layer having, 
for example, a Right Hand lay over the central wire and a second pass for 
a 12-wire layer having a Left Hand lay over the first six wire layer. The 
strand can also be made in one pass with machines having cages rotating in 
opposite directions applying both layers at the same time, but the 
productivity of such machines is very low. 
A unilay conductor is a second example of a conductor strand having 
helically laid layers disposed about the central wire. Each layer of a 
unilay strand has the same direction of lay and the same length of lay. 
Because each layer has the same lay length and same direction, the strand 
may be made in a single pass. As a result, productivity increases. 
Unilay strands are used in a variety of configurations and commonly for 
sizes up to and including 240 sq. mm. 
These strands can be manufactured either on a Single Twist machine or a 
Double Twist machine. The Single Twist machine has advantages over the 
Double Twist machine since strands made on such machines are generally 
more uniform than those used on Double Twist machines. This occurs because 
of the difficulty in a double twist machine of controlling the tension of 
the wire entering the closing die and because of the second twist that is 
applied to the wires after the cable has already been subjected to the 
first twist. 
However, Double Twist machines have the advantage of higher productivity 
than Single Twist machines because, by its configuration, a Double Twist 
machine imparts two twists for each revolution of the flyer. Moreover, 
because of differences in construction, Double Twist machines can easily 
operate at higher rotational speeds than single twist machines. 
As a result, the output of Double Twist machines is often more than three 
times the output of Single Twist machines for a similar strand. 
Referring to FIG. 1, one of the most commonly used unilay conductors is a 
conductor S.sub.1 formed with 19 wires of the same diameter D. In such a 
strand, the six wires 4 of the inner layer L.sub.1 and the twelve wires 6 
of the outer layer L.sub.2 are twisted about the central core wire 2 in 
the same way and in a concentric pattern. Normally a hexagonal pattern 
(dash outline H) is formed, and not the desired round configuration C. 
This hexagonal configuration presents many basic problems because the 
circumscribing circle C creates six voids V. These voids are filled with 
insulation requiring more insulation for a minimum insulation thickness as 
compared with a true concentric strand. 
Experience has also shown that the wires at the corners tend to change 
position and to back up during extrusion. 
As a result of this concern, engineers in the conductor wire industry have 
been seeking to develop conductor strands which maintain a circular 
cross-section and increase the uniformity of the conductor section. 
One approach is to try to position the outer twelve conductors in such a 
way as to have each two wires 6a, 6b at the second layer L.sub.2 perched 
on the surface of one of the six wires 4 of the first layer L.sub.1. Such 
conductor S.sub.2, shown in FIG. 2, is sometimes referred to as having a 
"smooth body" construction which avoids the problem mentioned above in 
connection with the conductor 2 in FIG. 1. 
However, the "smooth body" construction is not stable and cannot be easily 
achieved on a commercial basis without considerably reducing the lays and, 
therefore, the productivity of the machines. Furthermore, any variation in 
wire diameter or tension in the wires can cause the conductor strand to 
change into the hexagonal configuration shown in FIG. 1 which represents 
the stable, low energy construction. 
Another attempt to solve the problem has been to make a composite strand 
S.sub.3 in accordance with U.S. Pat. No. 4,471,161 and shown in FIG. 3. 
This last construction has the advantage of being stable, but the 
disadvantage of requiring wires 6c, 6d with different diameters D.sub.1, 
D.sub.2 in the second layer L.sub.2. However, in order to maintain a 
circular outer cross-section, the diameters D.sub.1, D.sub.2 which must be 
selected result in gaps or grooves G between the wires into which 
insulation can penetrate. A variation on this idea is represented in FIG. 
4 where the 7-wire core (1+6) is compressed, such compression allowing the 
smaller diameter wires 6d to move radially inwardly to a degree which 
substantially eliminates the tangential gaps in the 12-wire layer L.sub.2. 
Another solution has been to use a combination of formed or shaped and 
round elements or wires to assure that the desired fill factor is realized 
with a stable strand design minimizing the outer gap area and optimizing 
the use of the insulating material. One example of such a strand uses a 
combination of 7 "T" shaped elements with 12 round elements providing a 
stable strand design. Such constructions are shown in publication No. 
211091 published by Ceeco Machinery Manufacturing Limited, at page 537-7. 
In this construction, the outer 12 elements or wires are in contact with 
each other thereby minimizing the grooves or spaces and the fill factor is 
approximately 84%. In such a configuration, the outside wires abut against 
the flat surfaces of the inner layer and have no tendency to collapse into 
the minimal spaces or grooves therein. A modification of the 
aforementioned strand involves various degrees of compression of the outer 
round wires with the result that the range of fill factors can be 
increased from approximately 84 to 91%. Because the inner layer of the 7 
conductors is also compacted in the inner layer elements produce a 
substantially cylindrical outer surface with interstitial grooves 
minimized or substantially eliminated. While this eliminates the 
aforementioned problem of the outer layer collapsing into the grooves of 
the inner layer, such cables have fill factors that are too high for many 
applications. 
SUMMARY OF THE INVENTION 
According to the present invention, a multi-layer conductor can be 
manufactured in such a way as to eliminate the problems mentioned in the 
prior art while maintaining a high manufacturing efficiency. 
The strand will also have the physical characteristics that are desirable 
for a wide range of applications such as concentricity and a fill factor 
that will compare favorably with the traditional reverse lay concentric 
compressed strand. 
More specifically, a multi-wired strand of unilay construction in 
accordance with the present invention comprises a central layer consisting 
of at least one wire. At least one additional layer of wires is stranded 
about said central layer. Said wires in both said central layer and 
additional layers being such that the number of wires in adjacent layers 
are integers that are not divisible by a common number with the exception 
of the integer one. The wires of at least one of the layers are compressed 
to provide area reductions. The number of wires in each of the layers is 
selected such that adjacent wires in each of the layers, with appropriate 
area reductions, are substantially in contact with each other and the 
strand configuration has a stable substantially circular or sectored 
cross-section. The strand may be manufactured with wires having the same 
diameter, but the numbers of wires in the central layer and each 
additional layer will have the characteristics of not being divisible by 
any common number but the integer one. This will create a condition 
whereby the wires in each layer will not find more than one corresponding 
helical groove in the central layer or a previous layer to fall or 
collapse into. This may require area reductions in the wires in the 
central or in one or more additional layers so that with a number of wires 
selected in the central layer or in any given additional layer are 
substantially in contact or in very close proximity with each other. 
The invention also includes the method of forming a multi-wire strand of 
unilay construction. The method comprises the steps of stranding at least 
one additional layer of wires about a central layer consisting of at least 
one wire. The central layer may consist of a layer of wires that serves as 
the innermost layer. One or more additional layers of wires may be 
successively stranded about the central layer of wires. The number of 
wires in said central layer and additional layers being such that the 
number of wires in adjacent layers are integers that are not divisible by 
a common number with the exception of the integer one. The wires are 
compressed in at least one of the layers to provide area reductions 
therein. The number of wires in each of the layers is selected such that 
adjacent wires in each of the layers, with appropriate area reductions, 
are substantially in contact with each other and the strand configuration 
has a stable substantially circular or sectored cross-section.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now more specifically to the Figures, in which the identical or 
similar parts are designated by the same reference numerals throughout, 
and first referring to FIG. 5, a 20 wire concentric compressed unilay 
strand in accordance with the invention is illustrated, in cross-section, 
and designated by the reference designation S.sub.5. 
The strand S.sub.5 formed in accordance with the present invention includes 
a first or central layer or core wire 12 surrounded by a further or 
additional layer of intermediate conductors or wires 14. The conductors or 
wires 14 are initially nominally the same size as the central core wire 
12. One of the constructions in accordance with the present invention 
includes 7 wires in the intermediate layer L.sub.1. In order to achieve 
such a construction, it is necessary to compress the wires 14 of the 
intermediate layer L.sub.1 so as to squeeze or compress these wires 
together by applying radially inward forces, as by passage through a die. 
Once passed the die, the conductors 14 exhibit flattened radially outward 
surfaces 14a and interstitial grooves 14b. The compression of the wires 14 
through a die results in area reduction consistent with the standards for 
compressed wires. 
Wrapped about the intermediate or inner layer L.sub.1 is an outer layer 
L.sub.2 of wires 16, wound with the same lay as the intermediate layer. 
The wires 16 have the same nominal diameter as the wire 12 and the same as 
the initial diameters of the wires 14. Twelve such wires 16 are applied, 
forming interstitial grooves 16' between adjacent wires in the outer 
layer. 
The strand S.sub.5 in FIG. 5 represents a stable cable which cannot, due to 
movements, stresses, or the like, collapse into the hexagonal 
configuration illustrated in FIG. 1. Accordingly, the strand S.sub.5 
retains its circular external cross-section or cylindrical configuration. 
The strand S.sub.5 can be used without the insulation, although it can be 
passed through a sheathing device which extrudes a sheath or a layer 18 of 
insulation material. Because the 6 voids V shown in FIG. 1 are 
non-existent, the amount of insulation 18 applied to the strand S.sub.5 
will be minimized. 
In FIG. 6 a strand S.sub.6 is depicted, which is very similar to the strand 
S.sub.5 shown in FIG. 5, both strands consisting of 1+7+12 conductors 
formed of concentric compressed unilay wires. However, in the embodiment 
shown in FIG. 6 the strand is enhanced by being pulled through a sizing 
die in which the wires 16 in the outer layer L.sub.2 are compressed 
radially inwardly to form radially outwardly facing flattened surfaces 
16", this assuring the concentricity and dimensional integrity of the 
strand. 
An important feature of the present invention is that the number of wires 
in adjacent layers, including the central layer, are integers that are not 
divisible by a common number with the exception of the integer 1. Thus, in 
the embodiments shown in FIGS. 5 and 6, the numbers of wires in the 
central layer and layers L.sub.1, L.sub.2 are not divisible by any common 
denominator with the exception of the integer 1. This assures that a layer 
cannot collapse, with the exception of possibly one wire, into the 
interstitial grooves formed in the immediately adjacent radially inner 
layer in contact therewith. 
By selecting the appropriate number of conductors or wires, and compressing 
these layers within the range of approximately 0-20%, the number of wires 
in each of the layers, with appropriate area reductions, are in 
substantial contact with each other as shown, and the strand 
configurations have stable cross-sections. "Substantial contact" is 
defined as such contact between adjacent conductors that prevent pressure 
extrudate from penetrating gaps between the adjacent conductors. Area 
reductions, therefore, that may be appropriate are such area reductions 
that provide such substantial contact without exceeding the tensile 
strengths of the conductors that would result in breaking or damage to the 
conductors. The compression of the conductors will, therefore, vary from 
case to case and the aforementioned range of 0-20% is intended to cover 
the typical or normal applications. 
Referring to FIG. 7, another construction in accordance with the present 
invention is illustrated, formed of 1+6+11 wires. This strand S.sub.7 
includes a first or central layer in the nature of a circular core wire 
12. The subsequent layer L.sub.1 is formed of 6 wires which are radially 
inwardly compressed, by passage through a die, so as to flatten the outer 
cylindrical surfaces thereof as shown in FIG. 7. However, since only 6 
conductors 14 are used in the layer L.sub.1, and since the wires in that 
layer have an initial or nominal diameter which is the same as that of the 
core wire 12, it should be clear that the wires 12 must be compressed to a 
greater extent than those in the embodiments S.sub.5 and S.sub.6. The 11 
wires 16 forming on the outer layer L.sub.2 are circular in configuration, 
are not compressed and have the same nominal diameters as the other wires 
in the strand. Eleven wires 16 can be applied and adjacent wires touch 
each other when the intermediate layer L.sub.1 has been adequately 
compressed to reduce the outer diameter of the intermediate layer wires 
14, thereby forming a smaller circumference on which the 11 wires can be 
applied. The embodiment S.sub.8 shown in FIG. 8 is similar to that shown 
in FIG. 7, with the exception that the 11 wires formed in the outer layer 
L.sub.2 are compressed by passage through a sizing die to form flattened 
radially outward surfaces 16" as shown. 
Referring to FIG. 9, a further construction in accordance with the 
invention is shown, formed of 1+7+12+17 wires. This strand S.sub.9 is 
similar to the strand S.sub.6 shown in FIG. 6, in which the two layers 
L.sub.1 and L.sub.2 are both compressed. However, an additional layer 
L.sub.3 is wound over the layer L.sub.2 composed of non-compressed 
circular wires 20. As a result, interstitial grooves 20' are formed which 
are comparable in dimensions to those grooves 16' shown in FIG. 5. When 
the strand S.sub.9 is passed through a sizing die, the layer L.sub.3 is 
likewise compressed to form strand S.sub.10 shown in FIG. 10. As with the 
strand S.sub.6 in FIG. 6, the sizing results in flattened exterior 
surfaces 20", similar to surfaces 16" shown in FIG. 6. Thus the presently 
preferred embodiments of strands of the present invention are 
constructions which are formed of certain combinations of compressed 
wires, such as 1+7+12, 1+6+11 or 1+7+12+17, which have nominally equal 
input wire diameters for the same strand design. The 1+7+12 construction 
is presently preferred because it has a 81% fill factor, this being more 
consistent with existing cables in accordance with the North American 
Specifications. The embodiments which include 1+6+11 wires, as described, 
are also satisfactory, but with fill factors of approximately 83.3%. Fill 
factors of approximately 80-85% can be used, although the preferred range 
is 81-84%, particularly if the compressed conductors are again compressed 
or formed into strands having sector cross-sections as will be more fully 
discussed below. 
While FIGS. 5-8 show strands consisting of a central layer comprised of a 
single core wire enclosed by two outer multi-wire layers, and FIGS. 9 and 
10 show a central single wire layer or core surrounded by three outer 
layers, it is also possible to wind one or more outer layers about a first 
or central layer consisting of one or more wires, as suggested in FIG. 12. 
In FIG. 12 a 5+11 construction is shown wherein 11 wires are wound about a 
central layer consisting of 5 wires. 
Compressed strands have become important, and provide advantages over 
existing strand conductors. For one, such compressed strands exhibit 
smaller diameters. They require less insulation, as aforementioned. 
Additionally, because of the compression within dies, such strands become 
less sensitive to process errors and slight variations or deviations in 
the dimensions of the individual wires or strands. The sizing dies force 
the wires in a given layer together, thereby reducing the effect of 
tolerance variations. Compressed strands of the type described, which are 
formed by passage through a die, are less expensive to manufacture and can 
provide area reductions of 0-20%, which is typical or common for many 
conductor metals including copper, most aluminum and aluminum alloys. 
In some countries, sectored conductors find numerous applications. A 
sectored conductor is one in which the cross-section of the conductor is 
not circular but forms a sector of a circle or is pie-shaped. The size of 
the sector or the angle defined by its straight sides or flat surfaces may 
vary. Commonly, sectored conductors are bounded by a circular arc and two 
radial flat surfaces which are arranged 90.degree. to one another. The 
multi-wire compressed stranded conductors described above can be formed 
into sectored conductors when produced as interim steps in the manufacture 
of the sectored conductors. Thus, referring to FIG. 11, there is shown a 
1+7+12 sectored conductor in which the initial circular 1+7+12 conductor 
may be formed as previously described in order to compress the conductors. 
The round or circular assemblies of wires are then formed into a sector as 
shown by passing the assembly through a set or series of sets of sector 
rollers. In FIG. 12, a 5+11 compressed sectored conductor is shown which, 
again, is formed following the interim production of a 5+11 circular 
corresponding conductor. As indicated, the angle of the sector is not 
critical and may include angles of 60, 90, 120, 180 or, in fact, any 
number of degrees to suit the conductor design. 
Referring to FIG. 13, a schematic sketch is illustrated for a machine that 
includes a double twister for forming compressed cables in accordance with 
the present invention. Thus, in FIG. 2, there is shown a closing area 20 
which is arranged to close 1+7+12 conductors to form the arrangements 
illustrated in FIGS. 5-10. In the closing area 12, the cables are arranged 
in the desired orientations and compressed as needed. The strands at this 
point can have form factors of 80-85%, or preferably 81-84%, especially if 
the circular strand assemblies are further to be further compressed. The 
compressed circular cable is then advanced to the double twist machine 22 
which includes initial or input pulley 24, bow 26, and outlet or final 
pulley 28. Once inside the double twist machine, and after having been 
twisted to the extent desired, a takeup 30 is used to draw the wires which 
are then wound onto a spool or bobbin 32. 
When the stranded conductors are to be sectored, there is provided a sector 
rolling area 34 between the output or final pulley 28 and the takeup 30, 
the takeup 30 drawing the wires through the sectored rolling area for 
imparting the desired sectored configurations. 
When the strand reaches the region between the pulley 28 and the takeup 30 
it is possible to wind the wire on the takeup, die compact the wire to 
produce a circular compressed wire having fill factors of 84-99%, or 
sector the strand to compress it to fill factor levels of 84-99%. 
Typically, such fill factors at the rolling area 34 are increased to 
approximately 86-90%. As suggested, the wires can be formed into any 
desired sector configuration by passing the circular assemblies through a 
set or series of sets of sector rollers at the sector rolling area 34. 
This can be done in line (no separate process) in the preferred embodiment 
of the process (i.e. double twist machine). However, it should be clear 
that the process is not limited to such a process. The angle of the sector 
rolls could include 60, 90, 120, 180 or any other number of degrees to 
suit the conductor design. The approach can be equally applicable to 
pre-spiraled sectored conductors as well as to straight sectors. 
Although FIG. 13 illustrates a closing area which can be used to produce 
the compressed sectored conductor shown in FIG. 11, (e.g. 95 mm.sup.2 
90.degree. copper sector), the compressed sector conductor shown in FIG. 
12 may, for example, consist of a 35mm.sup.2 90.degree. straight sectored 
conductor. 
While this invention has been described in detail with particular reference 
to the preferred embodiments thereof, it will be understood that 
variations and modifications can be effective within the spirit and scope 
of the invention as described herein and as defined in the appendant 
claims.