Cables Having Non-metallic Cores

Abstract

A cable is provided with a solid core made of a relatively incompressible thermoplastic material.

Description

BACKGROUND OF THE INVENTION

Cables made from a plurality of metallic strands ordinarily comprise a core which may be either metallic or textile in nature. In the first case, this core consists of a central strand, or group of strands. In the second case, it is made from a synthetic filament or from natural or synthetic fibers which have been suitable twisted together and which may be considered to constitute a true axial core.

Those cables having textile cores have the disadvantage of being dimensionally unstable in both length and diameter. When the strands are wound upon the core, the core is strongly compressed. It is accordingly necessary to allow for this compression in determining the various parameters of the cable so that when it emerges from the cable-making machine there will be sufficient play between the metallic strands which encircle the central core. This is necessary to avoid excessive friction between the adjacent strands with all the disadvantages attendant thereon, such as wear, irregularity in tension, etc. When the cable is put in service, the strong tension applied to the cable abruptly increases the compression to which the textile core is subjected by the strands which are spirally wound about it. This produces additional compression of the core. Experience has shown that this compression does not subsequently stop, but increases more slowly, in an asymptotic manner, until the cable is worn out.

The phenomenon of compression is accompanied by elongation of the cable and a decrease in its diameter, as well as an increase in its hardness and stiffness. The metallic strands, which were initially separated by a certain amount of space for play, which was provided during the winding of the cable, then come more closely into contact with each other. This results in friction and wear, followed by abrasion of the wires which are in contact with each other. This results in indentations as well as contact corrosion, followed rapidly by breakage.

SUMMARY OF THE INVENTION

The present invention seeks to overcome the foregoing disadvantages and make it possible to provide cables having both a non-metallic core and an excellent dimensional stability.

Other objects of the invention include:

The avoidance of excessive compression of the core which occurs during the service of cables having textile cores of known types;

The avoidance of the appearance of substantial contact pressures between adjacent metallic strands of the cable or the provision of a certain permanent room for play therebetween, so as to make possible normal distribution of tensions along the length of these strands;

Permit the cable to work normally while avoiding the risk of friction between the strands which are in contact with each other throughout the life of the cable;

Avoid substantial variation in the length and/or the diameter of the cable while in use.

In accordance with the invention, the core of the cable consists of a synthetic material having good mechanical properties, such as polyethylene, polypropylene, a polyamide, or other analagous material, preferably of a thermoplastic nature. It conforms at least partially in shape to the inner contour of the assembly of strands which it supports.

In accordance with another characteristic of the invention, the core is solid. It should however be noted that it may also be made in the form of a strand if this is preferred.

In the preferred method of making the invention, the solid rod or filament which is to constitute the core of the cable is heated to its softening point. It is then introduced, while hot, into the cable-making machine so as to be compressed to a certain extent by the metallic strands which surround it and fill the interstices which exist inside the cable between the successive strands. The newly made cable is then subjected to compression by means such as a draw-plate, a set of shaped rollers, etc., so as to exactly calibrate the diameter in a manner which is impossible with cables of a known type having a textile core.

Of course, the diameter of the rod or filament used as the core must be sufficient to completely prevent the formation of open spaces inside the completed cable.

But it should be noted that there is no harm in selecting this diameter a little large. In that case, a certain amount of the material making up the softened core flows between the strands which are thus completely isolated from each other, and the rest of the excess of plastic material is absorbed by elongation of the rod as it enters the cable-making machine.

BRIEF DESCRIPTION OF THE DRAWINGS

The attached drawing, which is purely exemplary, makes it possible to better understand the invention, the characteristic features of the invention, and the advantages which it is adapted to provide. In this drawing:

FIG. 1 is a transverse section taken through a cable in accordance with the invention;

FIG. 2 is a schematic longitudinal view of a cable-making machine adapted to manufacture such a cable; and

FIG. 3 is a transverse section taken through a cable in which the core is made of a plurality of individual plastic filaments, shown before softening and twisting.

BRIEF DESCRIPTION OF THE DRAWINGS

The cable shown in FIG. 1 is made of a solid rod or filament of a plastic material having excellent mechanical qualities with respect to resistance to tension and with respect to elasticity.

This material is preferably thermoplastic. Polyethylene, polypropylene and polyamides are particularly suitable materials. The core 1 supports the metallic strands 2 which are spirally wound thereon in a conventional manner. As shown, the core 1 is shaped to conform to the inner contour of the group of strands 2 which are partially embedded therein. The core therefore comprises ridges 1a, which project to a greater or less extent between adjacent strands. In the example shown, the ridges 1a extend almost to the circle constituting the locus of the centers of the strands, but it will be appreciated that these ridges could be shorter or longer in certain cases.

The cable shown in FIG. 1 is quite stable as to both length and diameter. In effect, the core 1 is practically incompressible, so that the application of very great weight, and even suddenly applied tension, cannot crush this core, and consequently produce either a decrease in the exterior diameter of the cable, or an increase in its length, in contrast to what happens in the case of the conventional cables having a textile core. It will be further noted that the ridges 1a separate the strands 2 from each other and prevent all the phenomena of friction therebetween while permitting the free distribution of tension between the individual strands. It is, moreover, known that synthetic materials of the type indicated above, and more particularly the polyamides, have an extremely low coefficient of friction so that they permit small changes in position between the various strands without offering excessive resistance thereto.

Even if the ridges 1a have been made so short that the strands touch, the contact pressure is nevertheless reduced so that the strands will not abrade each other.

It should be added that the core 1 cannot retain humidity and is perfectly resistant to rotting and corrosion. FIG. 2 shows how a cable of the type illustrated in FIG. 1 may be made by adapting a cable-making machine of a conventional type.

In FIG. 2 reference numeral 3 indicates a support on which a reel 4 is rotatably mounted. This reel carries the rod or filament 5 which is to become the plastic core. The filament has at this point a perfectly circular section. The filament 5 passes from the reel 4 to a horizontal tube 6 having a double wall. The space between the double walls is supplied with steam through a duct 7 controlled by a valve 8. Means 9 are provided for evacuating the water of condensation. The tube 6 is axially mounted in the hollow shaft 10 of the cablemaking machine and supported by bearings 10a while being prevented from angular movement by the ducts 7 and 9 or in any other appropriate manner, for example by means of an arm such as 6a. Since the cable-making machine is of a conventional type, it will be described in only a summary manner. The shaft 10 supported by bearing means 11, carries supporting plates 12, 13, 14, on which the reels 15 carrying the strands 16 are mounted. These plates also support the guide rollers 17 which direct these strands toward the draw-plate.

The plate 14 turns in a cradle of rollers 18, in the usual way, to support the shaft 10. Guides 19 for the strands 16 are positioned at the downstream end of the shaft 10. Beyond the shaft 10 and its supports the machine comprises a table 20 carrying the winding head 21. This cable also carries, downstream of the winding head 21, a small auxiliary frame 22 carrying two pairs of rollers 23 and 24 which are designed to calibrate the cable 25 leaving the winding head 21.

The cable 25 itself is then wound around a capstan 26 from which it is directed to a suitable reel not shown.

The machine is driven through a pulley wheel 27 mounted on a lower longitudinal shaft 28. The shaft 28 is drivingly connected to the shaft 10 by a gear train 29, 30, 31. The end of the shaft 28 remote from the pulley 27 is itself drivingly connected by gearing 32 to the input of reduction gearing 33. This reduction gearing drives the capstan 26 through a variable speed transmission 34 adapted to permit the linear speed of the cable to be regulated so as to control the pitch of the strands. Reference numeral 35 indicates a transmission shaft for driving the receiving reel.

The temperature of the heating steam between the double walls of the tube 6 is so regulated as to just barely soften the rod or filament 5. Due to this softening, the wires 2 sink into this rod or filament, which thus becomes the core 1 shown in FIG. 1. It will be understood that the heating temperature and the tension imposed on the strands during the winding process may be regulated as desired.

At the output of the winding head 21 and while the core 1 is still deformable, the cable passes between the two pairs of rollers 23 and 24 which calibrate it exactly to the desired diameter. This diameter is rigorously maintained after hardening of the plastic material.

It should be noted that the diameter of the rod or filament 5 adapted to constitute the core 1 is not absolutely critical. It is preferably so selected that the section of this rod is greater than that of the core 1 in its final form. Under these conditions, the softened plastic material is pushed back a little at the entrance to the winding head. In other words, the rod elongates while decreasing in diameter so that its cross-section will correspond to that of the core. Looking at the matter from a different angle, the speed at which the rod 5 advances into the tube 6 is less than the linear speed imposed on the cable 25, so that the rod 5 is elongated.

It should of course be understood that the foregoing description has been given purely by way of example and that structural details thereof may be replaced by their mechanical equivalents without thereby departing from the basic principles of said invention. The number of strands may, of course, be varied. The specific details of the cable-making machine may be adapted to specific requirements. The rod 5 from which the core is formed may be heated in any suitable manner. In particular, the tube 6 may have a single wall into which steam is injected so long as means are provided for eliminating the residual water from between the strands. The core may also be electrically heated. On the other hand, while it is particularly advantageous to provide a one-piece core, it may consist of an assembly of filaments made of one of the synthetic materials indicated above, which assembly has been suitably twisted to keep it stiff. It will be appreciated that, after softening in the tube 6, such an assembly would also permit the strands to sink into its periphery. The compressive force applied to the plastic material while still soft would weld the elementary filaments together to produce a mass such that these threads could not shift relative to each other. A core made in this manner would obviously be less incompressible than that of FIG. 1, but would nevertheless be greatly more incompressible than the textile cores in present use.

Claims

What is claimed is:

1. Cable comprising a plurality of metallic strands wound on a core made of a strong, compression-resistant thermoplastic material, in which the external surface of said core is shaped to conform to the internal contour of the cylinder formed by said strands.

2. Cable as claimed in claim 1 in which said core is made of a material selected from the group consisting of poly-ethylene, polypropylene, and the polyamides.

3. Cable as claimed in claim 1 in which said core is solid.

4. Cable as claimed in claim 1 in which said core is made of a plurality of threads which are at least partly welded together.

5. Cable as claimed in claim 1 in which said core is provided with peripheral ridges which project between adjacent strands.