GB1576798A

GB1576798A - Method and apparatus for continuously manufacturing electric cables

Info

Publication number: GB1576798A
Application number: GB1748978A
Authority: GB
Original assignee: KM Kabelmetal AG
Current assignee: KM Kabelmetal AG
Priority date: 1978-05-03
Filing date: 1978-05-03
Publication date: 1980-10-15

Description

(54) METHOD AND APPARATUS FOR CONTINUOUSLY MANUFACTURING ELECTRIC CABLE (71) We, KABEL- UND METALLWERKE GUTEHOT;FNUNGSHiiTTE AKTIENGESELL- SCHAFT, a body corporate organised under the laws of Germany, of Postfach 260, Kabelkamp 20, 3000 Hannover 1, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method and apparatus for the continuous manufacturing of electric cables of the type comprising a cable core and a metallic sheath.

It is an object of the present invention to provide a method and apparatus for manufacturing electric cables of the type first mentioned, which method and apparatus are economical and give an electric cable with a mechanically protective sheath which is of great flexibility.

According to the present invention, we provide a method for the continuous manufacturing of electric cables having a metal sheath, in which, in a multi-step forming station, a thin metal strip is formed around a cable core into a tube of a greater diameter than the cable core, the strip forming this tube being guided in the last step of the forming station by a forming ring or a pair of concave rollers with vertical axes by which the edges of the metal strip are held abutting each other, and in which the edges of the metal strip are butt-welded by an electric arc welding apparatus under a protective gas atmosphere downstream of the said forming ring or pair of rollers, and in which the welded tube is drawn off by clamps of a split-clamp endless belt or chain draw-off device and conveyed thence to a corrugating device corrugating the welded tube annularly or helically, the corrugation being formed deep enough to grip the cable core.

Preferably the metal strip is cleaned and degreased in a continuous way by an organic solvent before entering the fdrming station, the solvent being preferably trichloroethylene or perchloroethylene. It is preferable to spray first a liquid solvent and then a solvent vapour against both sides of the metal strip.

This provides the advantage that there is neither dirt nor grease on the metal strip which may influence the welding seam in a negative way. The liquid solvent, which preferably has a temperature of nearly 50 C, removes the coarse dirt and dissolves the grease, while the solvent vapour condenses on the cool surface and rinses the dirt and grease and penetrates into the voids in the metal strip. It is advantageous to trim the metal strip at its edges before forming it into a tube. This trimming leads to oxide-free edges which can be welded without difficulty. The metal strip which is formed into a slit tube-the edges of which are welded together-forms the metallic sheath of the electric cable. It is therefore necessary to use a metal strip with a sufficient mechanical strength, e.g. copper, steel, aluminium.In order to have the edges of the metal strip in an abutting alignment during the welding, it is advantageous to deform, in the first forming step performed in the multi-step forming station, only the edges of the metal strip plastically, the radius of curvature of the edges of the metal strip corresponding to the radius of the curvature of the formed tube. Then the whole metal strip is continuously formed into a slit tube, and welded at the edges. The intensity of the welding current is preferably regulated in relationship to the tube speed. This prevents the welding beam from burning holes in the welding seam when the tube speed is reduced. After being welded, the tube is led to a split-clamp endless belt or chain drawoff device, which draws off the metal strip as well as the tube formed thereof.The split-clamp draw-off device preferably consists of a plurality of split clamps mounted on an endless chain and acting on the tube in order to draw it off with the help of guide rails. The contact area of the split clamps corresponds to the curvature of the tube.

Just before entering the split-clamp drawoff device, the tube is preferably calibrated.

This ensures that the tube diameter is always equal to the diameter of the area formed by the gripping jaws and that markings on the tube surface are avoided. This calibrating is preferably done with the help of concave calibrating rolls, though it can be done by a sinking die. Although the metal strip is formed around the cable core with a greater diameter, leaving an annulus, it is useful to take away the welding heat from the tube. Therefore the welded tube preferably has a lubricant (e.g. an emulsion) applied to it before corrugating. This serves as a lubricant during the corrugating. Preferably the welded tube with the lubricant applied to it is guided through à closely fitting sleeve immediately before corrugating.

As a corrugating disc-as described below- rotates eccentrically around the tube, the sleeve supports the tube against this movement and renders possible a satisfactory corrugation. The corrugating is preferably effected by a freely rotatable corrugator disc which is fixed eccentrically and inclined to the axis of the tube in a driven corrugator head and rolls on the surface of the welded tube, forming the corrugations. This corrugating method strains the material of the welded tube only a little, and allows a corrugation which is symmetrical even in the portion of the welding zone. For producing a helically corrugated cable sheath, an annular corrugator disc has to be used, while for producing a cable sheath with an annular corrugation a corrugator disc with a helical forming rib is necessary.

After being corrugated, the cable consisting of the cable core and the corrugated sheath is normally wound on a cable reel, and its density is checked. In order to render it possible for the electric cables to be buried, it is necessary to prevent corrosion.

It is therefore advantageous to treat the corrugated sheath first with a corrosion protective agent comprising bitumen, and to enclose this agent with a plastic foil, and then to extrude a plastic sheath onto the plastic foil.

The invention is preferably practised for the manufacturing of telephone cables. These telephone cables are usually sealed to prevent the penetration of moisture into the interior of the cable. The method according to the invention is of particular value for effecting this sealing in a continuous way.

A composition comprising petroleum jelly may be applied in successive portions onto the metal strip while this is being formed into a tube, the composition comprising petroleum jelly filling the whole space between the cable core and the welding tube during the corrugating; the said composition may also penetrate partly into the interstices between the conductors. Another way to form a telephone cable which will not suffer from the penetration of moisture into its interior is to fill the interstices of a cable core consisting of a plurality of insulated conductors with a composition comprising petroleum jelly, the composition being brought into the cable core by pressure, then to envelop the filled cable core by at least one foil, and then to form the metal strip around the cable core.

The invention also includes an apparatus for carrying out a method as described above, comprising: a degreasing station for the metal strip, a multi-step tube forming station, a stationary welding station, a split clamp endless belt or chain draw-off device, and a corrugating device, in tandem.

The invention is illustrated by way of example in the accompanying drawing, in which: Figure 1 shows diagrammatically the elements forming the cable manufacturing apparatus in the whole, Figure 2 shows in enlarged section the first step of the forming station, Figure 3 shows a section of the split clamp draw-off device, and Figure 4 shows a section of the corrugating device.

As shown in Figure 1, there is a reel 1 for the electric cable core 2 which is to be sheathed in accordance with the invention.

The core is fed by suitable guide means 3 to a multi-step forming station 4, to which is also fed, from a roll 5, a metal strip 6, for instance, a continuous strip of steel, aluminium or copper. The metal strip 6 is fed through a degreasing apparatus 7 in which it is at first sprayed from both sides with a liquid organic solvent and then with a solvent vapour in the same way. The metal strip 6 is fed through a pair of trimming rolls 8, to cut said strip 6 to precise width and to provide freshly cut strip edges.

The trimmed strip 6 then passes through the multi-step forming station 4, comprising pairs of forming rollers 9, 10, 11 and 12, which progressively convert the strip 6 into substantially tubular form. The last step of the station 4 emp]oys a pair of concave rollers, indicated at 12, with vertical axes, by which the edges of the strip 6 are held abutting each other. Rollers 12 may be replaced by a forming ring, however.

As shown in Fig. 2, the metal strip 6 is formed in the first step at its edges only, the radius df curvature being equal to that of the totally formed tube.

Back to Fig. 1: the strip edges are gradually brought into close contact. It is to be understood that the cable core 2 is being introduced into the sheath as the same is being formed at 4. At the distal end of the forming station 4, there is located a welding station 13, which comprises an electric arc welding machine working with a protective gas shield. The freshly welded tube passes from the welding station 13 to a corrugating device 15, wherein said sheath is corrugated transversely to produce a substantial degree of flexibility in the sheath. However, insofar as the operation of the device 15 may intro seduce torsional stresses in the sheath as it is being corrugated, we are concerned to avoid such stresses being transmitted back to the welding station 13 to adversely affect the welded joint.Accordingly, means is provided for smoothly gripping the freshly welded sheath while the same is moving from the welding station 13 to the corrugating device 15, vis. a split-clamp endless chain draw-off device 14. This comprises an elongated frame having a longitudinally extending, centrally located opening therethrough. Within the frame are arranged a pair of parallel, endless sprocket chains 16 entrained about sprocket wheels 17 and 18 at opposite ends of the frame. The chains 16 are driven through a motor not shown.

Mounted on said chains 16 are a series of longitudinally spaced, similar split clamps 19, which move longitudinally of the frame within the opening thereof.

The split clamps 19-as shown in -Fig.

3-are pushed against the tube by plates 20, which include convergent edge portions (not shown) at the proximal end thereof and divergent edge portions (not shown) at the distal end thereof, which move the clamps i 9 towards and away from the sheath. Before entering the device 14, the sheath or tube is calibrated and guided by a pair of rollers, not shown. The tube is fed then to the corrugating device 15, by means of the split clamp draw-off device 14.

As shown more clearly in Fig. 4, the tube, which is rinsed with an emulsion before entering the corrugating device 15, is guided by a sleeve 21. A tubular bushing 22 is secured to a corrugator head 23, and is mounted in rotatable and axially displaceable manner upon the stationary sleeve 21 by its inner surface. The tube which is to be corrugated is fed accurately to the cor ruator head 23.To this end, the sleeve 21, which is firmly connected to the machine housine, accommodates, 0'ia a fitting bush 21a, at its extremity facing the corrugator head 23, a sliding bushing 21b, the polished internal bore of which corresponds to the external diameter of the tube to be cor rugated. The bushings 21a and 21b are firmly connected to the sleeve 21 by means of the headless screw 24.

The corrugator disc 25 is secured, by means of a circlip 26, in an annular bushing 27, which is mounted rotatably in the cor rugator head 23 via the annular ball-bearing 28.

The corrugator disc 25 is mounted eccentrically and inclined in the annular bushing 27, impressing the corrugations 29 into the tube when being rotated.

The eccentricity of the corrugating disc 25 in respect of the annular bushing 27 is so adjusted that the troughs of the corrugations 29 engage the surface of the cable core 2. The metal sheathed cable 30 is then reeled on a cable drum 31, and can be checked for density.

In a subsequent operation-not shown the corrugated sheath can be treated with a corrosion protecting agent comprising bitumen, which is enveloped by a plastic foil.

Finally a plastic sheath is extruded on to the foil.

In the manufacturing of telephone cables, seals for preventing moisture penetration can be provided in two different ways.

In one way a composition comprising petroleum jelly is applied in successive portions on to the metal strip in the region of the forming station 4. During the corrugating, the composition is distributed in the whole space between the cable core 2 and the tube, forming seals which prevent water from spreading longitudinally.

Another way to seal the cable core is to fill the interstices between the conductors with a composition comprising petroleum jelly, under pressure. The filled cable core is then enveloped by a foil, particularly a plastic foil, and then sheathed by the metal strip 6. This can be done in a separate manufacturing operation or in tandem with the sheathing of the cable core.

WHAT WE CLAIM IS:- 1. A method for the continuous manufacturing of electric cables having a metal sheath, in which, in a multi-step forming station, a thin metal strip is formed around a cable core into a tube of a greater diameter than the cable core, the strip forming this tube being guided in the last step of the forming station by a forming ring or a pair of concave rollers with vertical axes by which the edges of the metal strip are held abutting each other, and in which the edges of the metal strip are butt-welded by an electric arc welding apparatus under a protective gas atmosphere downstream of the said forming ring or pair of rollers. and in which the welded tube is drawn off by clamps of a split-clamp endless belt or chain

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. radius df curvature being equal to that of the totally formed tube. Back to Fig. 1: the strip edges are gradually brought into close contact. It is to be understood that the cable core 2 is being introduced into the sheath as the same is being formed at 4. At the distal end of the forming station 4, there is located a welding station 13, which comprises an electric arc welding machine working with a protective gas shield. The freshly welded tube passes from the welding station 13 to a corrugating device 15, wherein said sheath is corrugated transversely to produce a substantial degree of flexibility in the sheath. However, insofar as the operation of the device 15 may intro seduce torsional stresses in the sheath as it is being corrugated, we are concerned to avoid such stresses being transmitted back to the welding station 13 to adversely affect the welded joint.Accordingly, means is provided for smoothly gripping the freshly welded sheath while the same is moving from the welding station 13 to the corrugating device 15, vis. a split-clamp endless chain draw-off device 14. This comprises an elongated frame having a longitudinally extending, centrally located opening therethrough. Within the frame are arranged a pair of parallel, endless sprocket chains 16 entrained about sprocket wheels 17 and 18 at opposite ends of the frame. The chains 16 are driven through a motor not shown. Mounted on said chains 16 are a series of longitudinally spaced, similar split clamps 19, which move longitudinally of the frame within the opening thereof. The split clamps 19-as shown in -Fig. 3-are pushed against the tube by plates 20, which include convergent edge portions (not shown) at the proximal end thereof and divergent edge portions (not shown) at the distal end thereof, which move the clamps i 9 towards and away from the sheath. Before entering the device 14, the sheath or tube is calibrated and guided by a pair of rollers, not shown. The tube is fed then to the corrugating device 15, by means of the split clamp draw-off device 14. As shown more clearly in Fig. 4, the tube, which is rinsed with an emulsion before entering the corrugating device 15, is guided by a sleeve 21. A tubular bushing 22 is secured to a corrugator head 23, and is mounted in rotatable and axially displaceable manner upon the stationary sleeve 21 by its inner surface. The tube which is to be corrugated is fed accurately to the cor ruator head 23.To this end, the sleeve 21, which is firmly connected to the machine housine, accommodates, 0'ia a fitting bush 21a, at its extremity facing the corrugator head 23, a sliding bushing 21b, the polished internal bore of which corresponds to the external diameter of the tube to be cor rugated. The bushings 21a and 21b are firmly connected to the sleeve 21 by means of the headless screw 24. The corrugator disc 25 is secured, by means of a circlip 26, in an annular bushing 27, which is mounted rotatably in the cor rugator head 23 via the annular ball-bearing 28. The corrugator disc 25 is mounted eccentrically and inclined in the annular bushing 27, impressing the corrugations 29 into the tube when being rotated. The eccentricity of the corrugating disc 25 in respect of the annular bushing 27 is so adjusted that the troughs of the corrugations 29 engage the surface of the cable core 2. The metal sheathed cable 30 is then reeled on a cable drum 31, and can be checked for density. In a subsequent operation-not shown the corrugated sheath can be treated with a corrosion protecting agent comprising bitumen, which is enveloped by a plastic foil. Finally a plastic sheath is extruded on to the foil. In the manufacturing of telephone cables, seals for preventing moisture penetration can be provided in two different ways. In one way a composition comprising petroleum jelly is applied in successive portions on to the metal strip in the region of the forming station 4. During the corrugating, the composition is distributed in the whole space between the cable core 2 and the tube, forming seals which prevent water from spreading longitudinally. Another way to seal the cable core is to fill the interstices between the conductors with a composition comprising petroleum jelly, under pressure. The filled cable core is then enveloped by a foil, particularly a plastic foil, and then sheathed by the metal strip 6. This can be done in a separate manufacturing operation or in tandem with the sheathing of the cable core. WHAT WE CLAIM IS:-

1. A method for the continuous manufacturing of electric cables having a metal sheath, in which, in a multi-step forming station, a thin metal strip is formed around a cable core into a tube of a greater diameter than the cable core, the strip forming this tube being guided in the last step of the forming station by a forming ring or a pair of concave rollers with vertical axes by which the edges of the metal strip are held abutting each other, and in which the edges of the metal strip are butt-welded by an electric arc welding apparatus under a protective gas atmosphere downstream of the said forming ring or pair of rollers. and in which the welded tube is drawn off by clamps of a split-clamp endless belt or chain

draw-off device and conveyed thence to a corrugating device corrugating the welded tube annularly or helically, the corrugations being formed deep enough to grip the cable core.

2. A method according to claim 1, in which the metal strip is cleaned and degreased in a continuous way by an organic solvent before entering the forming station, the solvent being preferably trichloroethylene or perchloroethylene.

3. A method according to claim 2 in which first a liquid solvent is sprayed against both sides of the metal strip and then a solvent vapour is sprayed against both sides of the metal strip.

4. A method according to any one of claims 1 to 3 in which the metal strip is trimmed at its edges before forming it into a tube.

5. A method according to any one of claims 1 to 4, in which, in the first forming step performed in the multi-step forming station, only the edges of the metal strip are deformed plastically, the radius of curvature of the edges of the metal strip corresponding to the radius of the curvature of the formed tube.

6. A method according to any one of claims 1 to 5, in which the intensity of the welding current is regulated in relationship to the speed of the tube.

7. A method according to any one of claims 1 to 6, in which the welded tube is calibrated just before entering the splitclamp draw-off device.

8. A method according to claim 7 in which the welded tube is calibrated with the help of concave calibrating rolls.

9. A method according to any one of the claims 1 to 8, in which the welded tube has a lubricant applied to it before corrugating.

10. A method according to claim 9, in which the welded tube with the lubricant applied to it is guided through a closely fitting sleeve immediately before corrugating.

11. A method according to claim 10, in which. downstream of the sleeve, a freely rotatable annular corrugator disc, which is fixed eccentrically and inclined to the axis of the tube in a rotatably driven corrugator head, rolls on the surface of the welded tube, forming thereby the corrugations.

12. A method according to any one of claims 1 to 11 in which the corrugated tube is treated first with a corrosion protective agent comprising bitumen, this corrosion protective agent being enclosed by a plastic foil, and then a plastic sheath is extruded on to the plastic foil.

13. A method according to any one of claims 1 to 12, in which a composition comprising petroleum jelly is applied in successive portions on to the metal strip while this is being formed into a tube, the composition comprising petroleum jelly filling the whole space between the cable core and the welded tube during the corrugating.

14. A method according to any one of claims 1 to 12, in which the interstices of a cable core consisting of a plurality of insulated conductors are filled with a composition comprising petroleum jelly, the composition being brought into the cable core by pressure, then the filled cable core is enveloped by at least one foil, and then the metal strip is formed around the cable core.

15. An apparatus for carrying out a method according to any one of claims 1 to 14 comprising a degreasing station for the metal strip, a multi-step tube forming station, a stationary welding station, a splitclamp endless belt or chain draw-off device, and a corrugating device, in tandem.

16. An electric cable manufactured by a method according to any of claims 1 to 14 or by means of an apparatus according to claim 15.

17. A method according to claim 1, substantially as described with reference to the accompanying drawings.

18. An apparatus according to claim 15, substantially as described with reference to the accompanying drawings.

19. An electric cable manufactured by a method according to claim 17 or by means of an apparatus according to claim 18.