EP0109952B1

EP0109952B1 - Cable jacket

Info

Publication number: EP0109952B1
Application number: EP19830850303
Authority: EP
Inventors: Gunnar S. Friberg
Original assignee: Volvo AB
Current assignee: Volvo AB
Priority date: 1982-11-17
Filing date: 1983-11-10
Publication date: 1986-10-01
Also published as: SE450674B; DE3366628D1; ES285013U; SE8206551D0; EP0109952A2; ES285013Y; CA1204182A; EP0109952A3; JPS59103208A; SE8206551L

Description

The present invention relates to 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 a pressurized medium for cooling the cable, comprising a first, inner rubber layer, at least one reinforcement layer of warp-knit type radially outwardly of the first layer, at least one reinforcement cord helically wound radially outside the reinforcement layer, and an outer rubber layer radially outwardly of the cord.
In cable jackets of the type to which the present invention relates, namely welding cables, in particular welding cables for welding robots, in which the length of the welding cable is often very short and exposed to heavy loads in the form of torsion and pulsating radial loads, specific requirements must be fulfilled, such as flexibility both transversely to the longitudinal direction of the cable and about the central axis, i.e. the cable must be easily bendable as well as 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 repellant 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 movement of the welding robot and have resulted in fatigue failures at the bending points of the cable.
It is known per se from US-A-3,578,028 to use a warp-knit net fabric as a reinforcement layer in a hose intended for use in an automobile cooling system, and to provide a helically wound string in physical contact with the warp-knit fabric. If such a hose was used as a welding cable jacket, this would inevitably result in a rapid rupture of the warp-knit layer and/or the string and eventually of the jacket as a whole due to the strong repellant radial magnetic forces acting on the jacket.
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 the reinforcement layers of warp-knit type and of the cord are mutually radially spaced by an intermediate rubber layer, and in that the reinforcement cord consists of a twined multifilament string, the spacing between adjacent cord windings measuring in the longitudinal direction of the jacket about 2-8 mm, preferably 4 mm.
These features result in an enlarged cord binding area and an improved binding effect between the cord and the rubber layers enclosing it, and in a better overall strength of the cable jacket.
In case the cable jacket comprises two or more cords, it is suitable that the cords are unidirectionally wound in a common circumferential plane in order to prevent the jacket with the warp-knit reinforcement from expanding too much due to inner pressure and to provide good torsional properties at the same time.
The invention will be described below in more 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.
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 riblike 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.

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. 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 higher 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 to about 2-8 mm, preferably about 4 mm, between adjacent cord windings.
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.

Claims

1. Cable jacket, in particular a rubber jacket (2) for a welding cable and adapted to enclose groups of electrical conductors (3, 4) and coolant ducts (6, 8) for conducting a pressurized medium for cooling the cable, comprising a first, inner rubber layer (11), at least one reinforcement layer (9) of warp-knit type radially outwardly of the first layer (11), at least one reinforcement cord (10) helically wound radially outside the reinforcement layer (9), and an outer rubber layer (13) radially outwardly of the cord (10), characterized in that the reinforcement layers of warp-knit type (9) and of the cord (10) are mutually radially spaced by an intermediate rubber layer (12), and in that the reinforcement cord consists of a twined multifilament string (10), the spacing between adjacent cord windings measuring in the longitudinal direction of the jacket about 2-8 mm, preferably 4 mm.

2. Cable jacket according to Claim 1, comprising two or more cords, characterized in that the cords are unidirectionally wound in a common circumferential plane.