[0001] The present invention relates to a cable jacket, especially a rubber jacket, to an
electric welding cable and is designed to enclose groups of electrical conductors
and coolant ducts for conducting pressurized medium for cooling the cable.
[0002] In modern automatic welding machines such as robot- type welders in which the length
of the welding cable is often very short, the welding cable must be quite flexible
both transversely to the longitudinal direction of the cable and about the central
axis, i.e. it must be both easily bendable and twistable. Furthermore, such cables
must be able to absorb the pressure stresses which are applied to the cable jacket
from the inside by the pressurized coolant, and by the repelling radial forces generated
by the cable cores every time the current through the cable is turned on or off.
[0003] The previously known welding cable jackets have not been able to fulfill all of these
requirements. Rather, the short cable lengths in question have been so rigid that
they have hampered the movement of the welding robot and have resulted in fatigue
failures at the bending points of the cable.
[0004] The primary purpose of the present invention is therefore to achieve a cable jacket
which, even with very short lengths, is sufficiently flexible with regard to both
bending and torsion, and is capable of absorbing the circumferential tensile forces
in the jacket arising due to the pressure exerted by the coolant in the cable and
the repelling radial forces generated by the cable cores every time the current through
the cable is turned on or off. To achieve this, the cable jacket described by way
of introduction is characterized, according to the invention, in that at least one
surrounding reinforcement layer of warp-knit type known per se is vulcanized into
the rubber jacket, and that radially outside said layer there are vulcanized one or
more unidirectionally, helically wound reinforcing cords, the spacing between the
adjacent cord windings measuring in the longitudinal direction of the jacket about
2-8 mm, preferably about 4 mm. To prevent the jacket with the warp-knit reinforcement
from expanding too much due to inner pressure and in order to provide good torsional
properties at the same time, it is thus necessary that the reinforcing cord(s) be
helically wound in the same direction and preferably lie in a single common cylinder
radially outside the warp-knit layer in the jacket. Suitably, each reinforcing cord
consists of a slightly twined polyester string. It is also suitable that the layers
of warp-knit reinforcement and reinforcing cords be separated radially by an intermediate
rubber layer.
[0005] The invention will be described below in mpre detail with reference to the accompanying
drawing.
Fig. 1 is a cross-sectional view of a welding cable with a jacket according to the
present invention, and
Fig. 2 is a cut-away perspective view showing the various layers in a cable jacket
according to the invention.
[0006] Fig. 1 shows according to scale a cross section of a welding cable 1, which has an
outer cable jacket 2 of rubber in accordance with the present invention. The jacket
2 encloses a group of electrical conductors in the form of copper cores 3 and 4 of
different polarity, the cores being placed in a ring and separated circumferentially
by rib- like walls 5 which project radially out from a central body 6 of rubber or
PVC. The central body 6 has a central coolant duct 7 and defines, between its outside
and the inside of the outer jacket 2, additional flow ducts 8 for a pressurized coolant,
e.g. water.
[0007] As indicated in Fig. 1, the jacket 2 comprises two reinforcement layers 9 of a warp-knit
fabric which is known per se and a cord helix 10 lying outside said two layers. Warp-knit
fabric refers in this context to a textile construction in which yarns, usually filament
yarns, are interlooped by knitting, with the yarn threads running essentially in the
longitudinal direction of the fabric.
[0008] Fig. 2 shows more clearly the structure of a jacket according to the invention, which
only shows one layer of warp-knit reinforcement 9. Starting from the inside, the jacket
2 has a rubber layer 11, a warp-knit reinforcement 9, a thin layer 12 of rubber, a
helically wound layer 10 e.g. of lightly twined polyester, and an outer layer 13 of
rubber. In order to obtain the desired flexibility both for bending and torsion, as
well as form strength, since the jacket is subjected to high inner pressure by the
coolant and radial repellant forces generated by the cable cores whenever the current
through the cable is turned on or off, it is essential that if a plurality of cords
10 are used that they run parallel to each other and be wound in the same direction,
i.e. not crossing each other. The cords should be wound leaving a gap of about 2-8
mm, preferably about 4 mm, between adjacent cord windings.
[0009] A cable jacket according to the invention is made preferably in finite lengths by
being built up on a mandrel, with one or two layers of warp-knit fabric being applied
around the inner rubber layer 11. If there is more than one layer, a thin layer of
rubber should be placed between the layers, and a thin layer 12 outside the outer
warp knit layer 9. Preferably a single cord 10 of previously described type is then
wound around the layer 12 helically with a pitch so that the distance between the
adjacent windings of the cord will be about 2-8 mm, preferably about 4 mm, at a normal
jacket diameter of about 5-6 cm. Although a single cord is preferable, two or even
more cords can be wound parallel in the same winding direction, maintaining said distance
between the cord windings, but this sacrifices some of the good torsional properties
of the jacket. An outer layer 13 of rubber is then applied outside the cord layer,
and the components of the jacket are then vulcanized together into an integrated unit.
The outside of the jacket is then given such a structure that its friction against
a surface is reduced to the required level.
1. Cable jacket, especially a rubber jacket (2) for a welding cable and designed to
enclose groups of electrical conductors (3,4) and coolant ducts (6,8} for conducting
pressurized medium for cooling the cable, characterized in that at least one surrounding
reinforcement layer (9) of warp-knit type is vulcanized into the rubber jacket (2),
and in that radially outside said reinforcement layer one or more unidirectionally
helically wound reinforcing cords (10) are vulcanized into the rubber jacket, the
spacing between adjacent cord windings measuring in the longitudinal direction of
the jacket about 2-8 mm, preferably about 4 mm.
2. Jacket according to Claim 1, characterized in that the cord(s) (10) forming the
cord reinforcing layer is/are disposed along the same cylinder in the jacket (2).
3. Jacket according to Claim 1 or 2, characterized in that each-reinforcing cord (10)
consists of a lightly twined polyester string.
4. Jacket according to any one of Claims 1-3, characterized in that the layers of
warp-knit reinforcement (9) and reinforcing cords (10) are separated radially by an
intermediate rubber layer (12).