GB1567342A

GB1567342A - Method of and apparatus for the insulation of cables

Info

Publication number: GB1567342A
Application number: GB24844/77A
Authority: GB
Original assignee: Nokia Oyj
Current assignee: Nokia Oyj
Priority date: 1977-06-14
Filing date: 1977-06-14
Publication date: 1980-05-14

Description

(54) METHOD OF AND APPARATUS FOR THE INSULATION OF CABLES (71) We, OY NOKIA AB, a Finnish body corporate, of P.O. Box 419, 00101 Helsinki 10, Finland, 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: The present invention relates to a method of providing, on an elongate doubled cable, an insulating sheath of vulcanised material, and to an apparatus for carrying out the method.

In known methods of providing such a cable with an insulating vulcanised sheath, the insulating material is extruded, in a molten or plasticised state, around the double cable, whereupon the cable is drawn through a vulcanisation tube and subjected to heating in a heating zone in said tube so as to heat the product to the vulcanisation temperature, and thereupon the product is, in a cooling zone in the tube, subjected to cooling so as to cool the vulcanised product.

A doubled cable comprises, as a rule, a plurality of individually insulated copper conductors doubled around one another in a certain way. The number of the conductors to be doubled and the mode of doubling are selected in accordance with the type of the cable. Conductors may also be doubled in several layers and their grouping and degree of twist are selected in accordance with the desired cable type.

In the known methods referred to, after the doubling step the cable is passed through an extruder, in which a plastics or rubber sheath is extruded onto the cable.

The insulated cable is then passed into a vulcanisation tube, in which the product is first subjected to heating so that the material of the sheath, containing a vulcanisation agent, reaches a temperature at which the vulcanisation reaction takes place, whereupon the vulcanised product -is cooled and passed out of the vulcanisation tube.

Various methods are previously known for performing the heating and cooling in the vulcanisation process. The heating can be performed by means of vapour or radiation heating, and the cooling by means of water or cooled gas.

In all known vulcanisation methods and forms of vulcanisation lines, the double cable is passed into the extrusion press and into the vulcanisation tube so that the doubled conductors and possible different layers are kept together at the tension that they obtained during the doubling process.

Various doubling processes produce internal tensions in the cable, which tensions attempt to straighten the twist produced in the conductors and to slacken the entire cable.

Two disadvantages may arise if the conductors of the cable are not firmly held together during extrusion and vulcanisation of the insulating sheath. Firstly, the plastics or the rubber extruded to form the sheath may penetrate unnecessarily into the conductor and increase the consumption of the material used to form the sheath.

Secondly, a loose layer hampers the passing of the cable through the plastics extruder die and may even result in blocking and rupture of the conductors.

For the above reasons, it is highly important that the doubled cable shall retain its tightness throughout the entire insulation and vulcanisation process. This requirement is also important in order that the cross-sectional area of the cable could be made as small as possible and that the so-called filling degree of the conductors should be good.

It is an object of the present invention to provide a method of providing, on an elongate doubled cable, an insulating sheath of vulcanised material, which method eliminates the above noted drawbacks.

According to one aspect of the invention there is provided a method of providing on an elongate doubled cable an insulating sheath of vulcanised material, and in which method the cable is passed longitudinally in succession, through an extrusion press, which provides the cable with the insulating sheath, and a vulcanisation tube in which the cable is first heated, to vulcanise said sheath, and is subsequently cooled, and in which method the cable is passed through the extrusion press and vulcanisation tube in a twisted condition, opposing twisting couples, in senses such as to maintain said twisted condition of the cable in the vulcanisation tube, being applied to the cable at two positions disposed respectively upstream of the extrusion press and downstream of the vulcanisation tube.

The method in accordance with the invention permits the insulating sheath to be applied and vulcanised, while the doubled conductors of the cable are very tightly pressed against each other.

According to another aspect of the invention there is provided apparatus for carrying out the above noted method, the apparatus comprising an extrusion press for extruding an insulating sheath around a cable passed therethrough, a vulcanising tube disposed downstream of said extrusion press and having associated therewith, means for heating in an upstream part of the tube, a cable passing through the tube, and means for cooling, in a downstream part of the tube, a cable passing through the tube, means for drawing a cable longitudinally through the extrusion press and sub sequently through the vulcanising tube and including twisting means disposed at a position downstream of the vulcanising tube for applying a twisting couple to a cable passing through the tube, upstream of said twisting means, and means disposed at a position upstream of the extrusion press for applying a counteracting twisting couple to a cable, whereby the -cable is twisted in passing the more upstream of said positions.

An embodiment of the invention is described below with reference to the attached drawings, in which: Figure 1 is a side view of a cable insulating and vulcanisation apparatus in which the vulcanisation line has the shape of a catenary curve, Figure 2 is a detailed side view to an enlarged scale as compared with Figure 1, of a cable twisting means forming part of the apparatus of Figure 1, Fiure 3 is a view from above, of the cable twisting means of Figure 2, and Figure 4 shows the formation of the twiting in the cable.

The apparatus shown in Figure 1 comprises a starting reel 1, from which a doubled cable 2 passes, as drawn by a con stant-sDeed pulling device 3, through an extrusion press 4, where the cable is coated with a sheath of plastics, rubber or equivalent. Hereupon the cable is passed into a vulcanisation tube 5, where it is heated by means of radiation heating (zone A), whereupon it is cooled by means of water (zone B). If it is desired that no microbubbles are formed in the product to be vulcanised, the cable is cooled in a completely waterfree space by means of cooled air. The end of the vulcanisation tube 5 is provided with a seal 6, through which the cable passes to a twisting means 7 through which, in turn, the cable passes into a pulling device 8, the speed of which is adjusted so that the cable passes along the tube 5 whilst freely hanging, without touching the wall of the tube. This is why the vulcanisation tube 5 has the shape of a catenary curve.

The vulcanised cable is reeled onto a receiving reel 9.

The twisting means 7 applies- to the cable a twisting couple, about the cable axis, which is opposed by a counteracting twisting couple, afforded by the reaction forces of the pulling device 3 and reel 1; As a result of these opposing twisting couples applied at positions respectively upstream of the extruder 4 and downstream of tube 5, the cable between these posi- tions, and thus whilst passing through extruder 4 and tube 5, is kept in a tightly twisted condition. In this way every point of the cable sheath moves along a helix in region between said two positions and, since the doubled cable is firmly bound, a dense tightening of the conductors of the doubled cable takes place at the pulling device 3.

Figures 2 and 3 illustrate a construction of the twisting means 7. It comprises two continuous belts 71 placed on opposite sides of the track of movement of the cable, which belts move over support reels 72.

The belts are pressed by means of flexible or flexibly mounted pressure rollers 73 against the cable so that no gliding occurs between the belts and the cable.

From Figure 3 it is seen that the belts are arranged crosswise in relation to each other and form an equal angle in relation to the -cable. Thus, the bolts engage the periphery of the cable along respective paths forming respective helices of the same hand and pitch. When the pulling device 8 now draws the cable through the twisting means 7, the cable has to be twisted around its axis, because, owing to their diagonal positions, the belts direct a twisting effect on the cable when the cable moves through the twisting means. Owing to its twisting rigiditv, the cable is correspondingly twisted over the entire length of the tube.

According to one embodiment, when the apparatus is set up initially prior to the provision, on a cable, of an insulating vulcanised sheath, the cable is passed into the twisting -means without initial-twisting, in which case the twisting means produces a twisting in the cable section between the pulling device 3 and the pulling. device 8, which twisting is gradually increased as the coating of the cable proceeds, until an equilibrium state is reached. Since in this case the cable during an initial period comes to the pulling device 8 as twisted, the pulling device must permit passage of the cable as twisted, or the pulling device 8 and the reel 9 must be rotated during this initial period so as to prevent twisting in the opposite direction downstream of the twisting means 7.

According to another embodiment, when the apparatus is set up initially a certain initial twisting is formed in the cable downstream of the pulling device 3 before the cable end is fed through the twisting device so that the cable enters the twisting device 7 as twisted. This situation is illustrated in Figure 4, wherein an imaginary sheath line is drawn onto the cable. It is noticed that the sheath line runs as a straight line D before the pulling device 3.

Since the cable has been provided with said initial twisting, the sheath line runs in the form of a helical line Dl after the pulling device. The twisting means 7 is arranged as twisting the cable in the direction of the helical line Dl, i.e. of the arrow C, around its axis. This is why the twisting device constantly attempts to tighten the initial twisting of the cable, but, since new cable keeps coming from the pulling device all the time, the twisting is shifted to this new portion so that the tightening of the twisting is compensated and the helical line Dl remains unchanged. Thus, the twisting means 7 in a way just shifts the initial twisting along the cable at the rate of movement of the cable. Under these circumstances, the twisting means 7 operates to maintain the twist in the cable portion upstream of the twisting means and to remove the twist from the cable portion downstream of the twisting means so that the sheath line passes, in the cable portion leaving the twisting means, as a straight line D1l into the pulling device 8.

The drawing and the related description are only intended to illustrate the idea of the invention. In its details the equipment in accordance with the invention may show consideration variation within the scope of the claims. Differing from the shape of a chain curve, the shape of the vulcanisation line may be, e.g. a vertical line.

WHAT WE CLAIM IS: 1. A method of providing on an elongate doubled cable an insulating sheath of vulcanised material, and in which method the cable is passed longitudinally in succession, through an extrusion press, which provides the cable with an insulating sheath, and a vulcanisation tube in which the cable is first heated, to vulcanise said sheath, and is subsequently cooled, and in which method the cable is passed through the extrusion press and vulcanisation tube in a twisted condition, opposing twisting couples in senses such as to maintain said twisted condition of the cable, in the vulcanisation tube, being applied to the cable at two positions disposed respectively upstream of the extrusion press and downstream of the vulcanisation tube.

2. A method as claimed in claim 1 in which at least some of the twist is removed from the cable in passing the more downstream of said two positions.

3. A method as claimed in claim 1 in which all of the twist is removed from the cable in passing the more downstream of said two positions, so that the cable, downstream of the more downstream of said two positions is in a completely untwisted condition.

4. Apparatus for carrying out the method of claim 1 comprising an extrusion press for extruding an insulating sheath around a cable passed therethrough, a vulcanising tube disposed downstream of said extrusion press and having associated therewith means for heating, in an upstream part of the tube, a cable passing through the tube, and means for cooling, in a downstream part of the tube, a cable passing through the tube, means for drawing a cable longitudinally through the extrusion press and subsequently through the vulcanising tube and including twisting means disposed at a position downstream of the vulcanising tube for applying a twisting couple to a cable passing through the tube, upstream of said twisting means, and means disposed at a position upstream of the extrusion press for applying a counteracting twisting couple to a cable, whereby the cable is twisted in passing the more upstream of said positions.

5. Apparatus according to claim 4 wherein said twisting means comprises two endless belts, placed crosswise in relation to each other and so arranged that, in use, a cable extended longitudinally through said extrusion press and vulcanisation tube can pass between said two belts, the belts being so disposed as to engage the periphery of such a cable along respective paths

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. twisting -means without initial-twisting, in which case the twisting means produces a twisting in the cable section between the pulling device 3 and the pulling. device 8, which twisting is gradually increased as the coating of the cable proceeds, until an equilibrium state is reached. Since in this case the cable during an initial period comes to the pulling device 8 as twisted, the pulling device must permit passage of the cable as twisted, or the pulling device 8 and the reel 9 must be rotated during this initial period so as to prevent twisting in the opposite direction downstream of the twisting means 7. According to another embodiment, when the apparatus is set up initially a certain initial twisting is formed in the cable downstream of the pulling device 3 before the cable end is fed through the twisting device so that the cable enters the twisting device 7 as twisted. This situation is illustrated in Figure 4, wherein an imaginary sheath line is drawn onto the cable. It is noticed that the sheath line runs as a straight line D before the pulling device 3. Since the cable has been provided with said initial twisting, the sheath line runs in the form of a helical line Dl after the pulling device. The twisting means 7 is arranged as twisting the cable in the direction of the helical line Dl, i.e. of the arrow C, around its axis. This is why the twisting device constantly attempts to tighten the initial twisting of the cable, but, since new cable keeps coming from the pulling device all the time, the twisting is shifted to this new portion so that the tightening of the twisting is compensated and the helical line Dl remains unchanged. Thus, the twisting means 7 in a way just shifts the initial twisting along the cable at the rate of movement of the cable. Under these circumstances, the twisting means 7 operates to maintain the twist in the cable portion upstream of the twisting means and to remove the twist from the cable portion downstream of the twisting means so that the sheath line passes, in the cable portion leaving the twisting means, as a straight line D1l into the pulling device 8. The drawing and the related description are only intended to illustrate the idea of the invention. In its details the equipment in accordance with the invention may show consideration variation within the scope of the claims. Differing from the shape of a chain curve, the shape of the vulcanisation line may be, e.g. a vertical line. WHAT WE CLAIM IS:

1. A method of providing on an elongate doubled cable an insulating sheath of vulcanised material, and in which method the cable is passed longitudinally in succession, through an extrusion press, which provides the cable with an insulating sheath, and a vulcanisation tube in which the cable is first heated, to vulcanise said sheath, and is subsequently cooled, and in which method the cable is passed through the extrusion press and vulcanisation tube in a twisted condition, opposing twisting couples in senses such as to maintain said twisted condition of the cable, in the vulcanisation tube, being applied to the cable at two positions disposed respectively upstream of the extrusion press and downstream of the vulcanisation tube.

forming respective helices of the same hand and pitch.

6. A method of providing, on an elongate doubled cable, an insulating sheath of vulcanised material, substantially as hereinbefore described with reference to the accompanying drawings.

7. Apparatus for providing, on an elongate doubled cable, an insulating sheath of vulcanised material, substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

8. A cable made by the method of any of claims 1, 2, 3 or 6 or by the apparatus of any of claims 4, 5 and 7.