Note: Descriptions are shown in the official language in which they were submitted.
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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.
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 :Elexible both transversely
to the longitudinal direction of the cable and about the central
axis, i.e. it must be both easily bendable and twistable. Further-
more, 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.
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
movemen-t of the welding robot and have resulted in fatigue failures
at the bending points of the cable.
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 invention provides a cable jacket, in particular
a rubber jacket for a welding cable and adapted -to enclose groups
of electrical conductors and coolant ducts for conducting pressur-
ized medium for cooling the cable, comprising a first inner rubber
layer, at least one reinforcement layer of warp-knit type radially
outwardly of said first layer, a second intermediate rubber layer
located radially outwardly of said reinorcement layer, at least
one cord helically wound radially outward said reinforcement layer,
sald cord consisting of a twined string, the spacing between adja-
cent cord windings measuring in the longitudinal direction of the
jacket about 2-8 mm, and an outer rubber layer radially outwardly
of said cord, the reinforcement warp-knit layer and the cord being
vulcanized into their respective adjacent rubber layers such that
in the finished ~acket a radial distance is maintained between the
warp-knit layer and the cord.
The cord is preferably a lightly twined polyester string,
the spacing between the adjacent cord windings preferably being
about 4 mm. To prevent the jacket with the warp-knit reinforcement
from expanding too much due to inner pressure and in order to pro-
vide 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 on a common cylindrical contour
radially outside the warp-knit layer in the jacket. Suitably, each
reinforcing cord consists o~ 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.
The invention will be described below in more detail with
reference to the accompanying drawing.
Figure 1 is a cross-sectional view of a welding cable
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2a
with a jacket according to the present invention, and
Figure 2 is a cut-away perspective view showing the
various layers in a cable jacket according to the invention.
Figure 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 sepa-
rated 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 pres-
surized coolant, e.g. water.
As indicated in Figure 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.
Fig. 2 shows more clearly the struct~re of a jacket
according to -the invention, which only shows one layer of
warp-knit reinforcement 9. Starting from the inside, ~he
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
l~ jacket is subjected to high inner press~re by the coolant
and radial repellant forces generated by the cable cores
whenever the current through the cabIe is turne~ on or off,
it is essential that if a plurality of cords lO 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 ~ap of about 2-8 mm, preferably
about 4 mm, between adjacent cord w;~ndings.
A cable jacket accord~ng 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 beiny
applied around the inner rubber layer 11. If there is more
than one layer~ a th~n layer of rubber should be placed be-
tween the layers, and a thin ~ayer 12 outsi~e the outer warp
knit layer 9. Preferably a single cord lO 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 d;ameter of about 5-6 cm. Althouyh
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.
