Weld reinforcing member for strands in a cable

A stranded wire strength member (2, 3) has a cable locking element (4) lying in the interstice between adjacent wires of the strength member. The locking element is of mild steel and has a surface coating (4a) of carbide grit which locks the adjacent wires of the strength member together in the region of a welded joint, to improve the load sharing capacity of the wires of the strength member.

BACKGROUND OF THE INVENTION 
This invention relates to stranded wire strength members particularly but 
not exclusively such strength members used in submarine telecommunications 
cables. 
Tensile strength member wires are used in many applications from simple 
wire ropes to more complicated stranded strength member layers in 
submarine cables such as that shown somewhat schematically in FIG. 1 of 
the accompanying drawings. When a wire tensile strength member is laid up 
into a cable element or a strength member layer of a cable element, it is 
the normal practice when a wire supply bobbin becomes exhausted to weld 
the end of the wire from the bobbin onto the beginning of the wire of the 
next bobbin and to continue manufacture from the second bobbin. 
Where welds between butted ends of wires occur in a stranded wire strength 
member, the strength of the individual wire at the weld is not as great as 
the wire itself. Where these weld joints are randomly spread throughout a 
cable element, then this may not be of any great consequence, but where a 
stranded wire strength member is created from a plurality of wires of 
similar length from individual bobbins, then these bobbins tend to become 
exhausted at substantially the same place along the length of the cable 
being made. 
It is an object of the present invention to minimise if not eliminate any 
weakness of a welded joint creating a tensile weakness in the strength 
member so formed. 
SUMMARY OF THE INVENTION 
According to the present invention there is provided a wire tensile 
strength member comprising a plurality of wires assembled together and 
embracing each other and having interstices therebetween, at least one of 
the wires having a welded joint therein, and comprising a cable locking 
element arranged in the interstice between some of the wires and lying 
against the wire having the welded joint so that the locking element 
extends in both directions from the welded joint, said locking element 
comprising a roughened surface which thus locks the wire having the welded 
joint to at least one other adjacent wire over a longitudinal region 
extending on both sides of the welded joint. 
Preferably the locking element comprises a cross-sectionally round 
mild-steel wire coated with carbide grit bonded thereto by solder or braze 
or other adhesive. This wire when sized correctly can then deform to take 
up any desired cross-section to grip welded wires.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawing a submarine cable comprises an optical core 1 
which includes several optical fibres within a pressure-resistant and 
preferably conductive tube, as described in our earlier British patent 
1550588. 
Surrounding the optical core is a layer of high tensile strength wires 2 
which are stranded around the optical core 1. 
The single layer of wires 2 comprises the inner layer of a tensile strength 
member which includes also a second outer layer 3 of smaller diameter 
wires. For example the layer 2 comprises wires having a diameter of 2.64 
mm whereas the second outer layer each have a diameter of 1.19 mm. 
Where there is a weld in a wire of either the inner layer or the outer 
layer, then a cable locking element such as 4 shown in cross-section and 
on a larger scale in FIG. 2, is placed into the interstice between the 
inner and outer layers of wires. This wire has a diameter in this 
particular embodiment of 1.2 mm and is coated with carbide grit 4A having 
a sub- 125 um size bonded to the mild steel wire by a solder or braze 4B 
or by the use of other adhesive. A particularly suitable process is that 
used to make the "ABRAFILE" (registered trade mark) product in which we 
believe the metal surface is heated to about 1000.degree. Centrigrade and 
wetted with cobalt prior to bonding the carbide grit particles to the 
mild-steel by wetted surfaces. 
During manufacture the cable locking element 4 is inserted in between two 
adjacent inner strand wires 2 effectively acting as a filler wire. When 
the outer strand wires 3 are applied and the cable structure is drawn 
through a closing die, the cable locking element deforms and locks the 
inner and outer strand wires 2 and 3 together. A typical deformation of 
element 4 is shown in FIG. 3 which is a detail of the locking element 4 
and the immediately adjacent wires 2, 3 locked to it, including the wire 
with the weld. Thus the function of the locking element is to lock the 
inner and outer strand wires together and this alters the load sharing 
capacity of the cable. 
In the embodiment described the length of the cable locking element could 
be up to 12 meters long which means that 6 meters of cable will be gripped 
on either side of the welded region. 
The arrangement described allows a more advantageous load sharing capacity 
to be utilised in those regions of cable where welds are found in the 
outer strand wires. However the invention is applicable as described above 
to welded inner strand wires. Significant increases in cable loads before 
wire failures are expected and it may be possible to achieve 90% of the 
cable Ultimate Tensile Stress. 
We believe the cable locking element can be applied to lengths of cable 
without any major changes to the normal production line of the cable as 
there is adequate space between the strander which applies the inner layer 
2 and the strander which applies the outer layer 3, to allow a small 
single wire to be inserted before the outer strand wires are applied to 
the cable. The filler wire would only be applied to lengths of cable where 
welds are required. 
Although only one cable locking element is shown in the drawing, several 
such elements could be used and in fact we believe that one such element 
should be used for each welded wire in order to gain full advantage of the 
invention. 
In the embodiment described there are thirty-two outer wires in the layer 3 
and ten wires in the inner layer 2. The layers are wound in opposite 
directions to achieve a torque balance, although the invention is 
applicable to other wire sizes and configurations, not necessarily 
contra-wound. 
During manufacture of the cable where wires are to be welded, the locking 
element can be soldered or taped in place to hold it until the outer layer 
is stranded and laid up. 
The cable shown would be completed with an insulating sheath after the 
wires have been drawn down, and as described in the aforementioned patent. 
The strength member wires in this embodiment are of high tensile steel, 
which is hard in relation to the mild steel of the cable locking element, 
but not as hard as the roughened surface of the cable element formed by 
the carbide grit. Therefore although the locking element becomes deformed 
when the strength member is drawn down, the carbide grit becomes partially 
embedded both in the material of the cable locking element and in the high 
tensile steel wires adjacent to it. The locking elements therefore tend to 
prevent relative movement between the wires, so ensuring that tensile load 
on the strength member is evenly distributed throughout the wires.