A method for manufacturing flexible wire-shaped elements, and flexible wire-shaped element obtainable thereby

Abstract

 A cable is formed comprising a filiform core (2) and at least one outer ring of wires (3, 4) arranged around the core in an array constituted, in alternating sequence, by first wires (3) and second wires (4) having a greater diameter than the first wires. The cable thus formed is then subjected to radial compression carried out, for example, by means of hammering, which causes plastic deformation of the second wires (4) until a cylindrical filiform element (1) of substantially constant diameter is obtained, from the cable.
The preferred application is in the manufacture of transmission elements for flexible control cables intended to operate in tension and, particularly, in compression.

Description

[0001] The present invention relates to the manufacture of flexible filiform wire-shaped elements.

[0002] It has been developed with particular attention to its possible application in the manufacture of transmission elements for flexible control cables, particularly flexible control cables which are able to transmit large forces when operating both in tension and in compression.

[0003] In view of this application, it is very important for the flexible filiform element to have very little, practically no tendency to expand diametrally - particularly where it travels round bends - to have a very smooth outer surface - so as to facilitate sliding within the guide sheath - and not to require - for its manufacture - the use of particularly complicated manufacturing methods.

[0004] The object of the present invention is to provide a method for the manufacture of a flexible filiform element which satisfies the requirements stated above very well.

[0005] According to the present invention, this object is achieved by virtue of a method for the manufacture of a flexible filiform element, characterised in that it includes the steps of:
    forming a cable including at least one outer ring of wires having a fixed radial dimension relative to the cable, and
    - exerting a radial compressive force on the cable so as to cause plastic deformation of at least some of the outer wires, until a cylindrical filiform element of substantially constant diameter is obtained from the cable.

[0006] The above radial compression of the cable is preferably carried out by means of a hammering operation.

[0007] A further subject of the invention is a flexible filiform element, characterised in that it includes at least one outer ring of wires arranged in an array of wires, extending with form coupling between adjacent wires, the filiform element having a substantially constant diameter.

[0008] The invention will now be described, purely by way of non-limiting example, with reference to the appended drawings, in which:

Figure 1 and Figure 2 show two stages of the method according to the invention,

Figure 3 shows a subsequent stage of the method according to the invention, and

Figure 4 shows the flexible filiform element produced by the method according to the invention.

[0009] In the drawings, reference numeral 1 generally indicates a flexible filiform element intended for use, for example, as an element for transmitting traction and thrust in a flexible control cable.
The element 1 consists essentially of two parts, that is to say:
    - a filiform core 2 constituted by a wire or a group of metal wires, for example steel wires, wound in a particular sense so as to constitute a cable, and
    - an outer ring of wires disposed around the core 2 in an array constituted, in alternating sequence, by first wires 3 and second wires 4; furthermore, in this case these are preferably metal wires which differ in hardness and/or strength, and are wound round the core 2, usually in the opposite sense from the sense of winding of the wires of the core 2.

[0010] With reference to the embodiment illustrated in Figure 1, the wires in the core 2 are wound in the dextrorotatory sense, while the wires 3 and 4 of the outer array are wound around the core 2 in the laevorotatory sense.

[0011] The second wires 4 in the outer ring are selected so as to have larger diametral or radial dimensions (measured relative to the axis of the cable obtained by winding these wires around the core 2) than the corresponding dimensions of the first wires 3.

[0012] Consequently, the cable obtained by winding the wires 3 and 4 around the core 2 has the appearance illustrated in Figure 2, in which the second wires 4 constitute, so to speak, ribs or lobes (from the generally helical shape) which project from the outer surface of the cable.

[0013] There are various possibilities for the selection of the materials constituting the core 2 and the wires 3 and 4 of the outer ring.

[0014] A first possibility is to make all the wires from the same metal, for example, steel, but with a difference in hardness between the wires 3 and the wires 4, the latter being more easily deformable than the former. Another possibility is to make the first wires 3 of the outer ring of a first material, such as steel, and the second wires 4 of a softer material, (for example brass), which can be deformed more easily and can retain the resultant shape (plastic deformation).

[0015] After its formation, obtained by winding the wires 3 and 4 of the outer ring around the wires of the core 2, the cable of Figure 2 is subjected to radial swaging carried out by passing the cable into a hammering machine M.

[0016] As shown schematically in Figure 3, the machine in question, of known type, consists essentially of two opposed anvils A which together define a cylindrical space traversed by the cable which moves within it in an axial direction. The two anvils A are rotated about the axis of the cylindrical space and are thus subjected, at their ends C, which are furthest away from each other, to a rhythmical percussive action caused by rollers (or hammers proper) R mounted on a fixed annular structure which surrounds the axis of rotation of the anvils A.

[0017] The effect of the radial hammering action exerted by the machine M is to cause radial compression of the cable 1 with the consequent plastic deformation of the second wires 4 into the configuration shown in Figure 4.

[0018] In other words, as a result of the radial hammering, the material constituting the second wires 4 is plastically deformed so that the wires extend with form coupling with the adjacent wires 3, that is, so that they fill the circumferential gaps or interstices between the first wires 3.

[0019] The deformation which the hammering operation causes in the latter wires, which project less from the outer surface of the cable of Figure 2, is, in fact, quite slight and actually limited to a certain squashing of the region of each wire 3 which faces outwardly of the cable, relative to the diameter of the cable 1 before the required diameter has been obtained by hammering.

[0020] The plastic deformation of the second wires 4, however, is quite marked, so that the material constituting the second wires reproduces, in a complementary manner, the outer surfaces of the first wires 3 and, to a certain extent, the surfaces of the wires of the core 2 facing outwardly of the core, as well.

[0021] As a result of this deformation, the second wires 4 form anchoring structures inside the flexible element 1 proper which (so to speak) lock the wires of the core 2 and the first wires 3 in place, opposing the tendency of the flexible element 1 to expand radially when it is subject to compression.

[0022] At the same time, the hammering operation leads to the formation of a cylindrical filiform element with a substantially constant outside diameter and with a very smooth outer surface which can slide easily within the guide sheath of the control. In practice, this outer surface is furrowed with shallow helical ribs in the regions where the outer surfaces of the first wires 3 and the outer surfaces of the deformed second wires 4 meet.

[0023] The flexible element produced according to the invention also has considerable resilience and flexibility and is able to slide well, even around very considerable curves in the guide sheath.

[0024] In particular, as far as its behaviour in the "free section", that is outside the guide sheath, is concerned, the fact that the larger-diameter, second wires 4 are deformed - by hammering - so as to form shapes which are complementary to those of the firs t wires 3 means that the combination of the wires 3, 4 in the outer ring achieves a circular-ring conformation in the finished element 1. This conformation has an appreciably greater moment of inertia about its axis of symmetry than that of a conventional cable structure with the same diameter.

[0025] It has also been observed that - according to the more general formulation of the present invention - if a radial swaging operation is carried out on a cable including at least one outer ring of wires until a cylindrical filiform element of substantially constant diameter is formed, the plastic deformation and consequent form coupling between adjacent wires thus produced enables filiform elements to be obtained which have a moment of inertia about the axis of symmetry - and hence a stability of shape - which is greater than those encountered in conventional cables with the same external diameter.

[0026] In general, the swaging operation improves the flexibility of the element, reduces the sliding friction and reduces the permanent deformations which are characteristic of single-wire elements used in flexible traction and compression transmissions.

[0027] The Applicant has been able to observe that particularly good results are obtained, as far as the dimensional stability of the final product is concerned, if the radial compression hammering is carried out in several successive stages, separated by intermediate stages. These intermediate stages serve to make the radial deformations stand out, which, in a subsequent hammering operation, come to obstruct any longitudinal, lengthening (or sliding) deformation.

Claims

1. A method for the manufacture of a flexible filiform element, characterised in that it includes steps of:
      - forming a cable (1) including at least one outer ring of wires (3, 4) having a fixed radial dimension relative to the cable (1), and
      - exerting a radial compressive force (M) on the cable (1) to cause plastic deformation of at least some (4) of the outer wires until a cylindrical filiform element, of substantially constant diameter, is obtained from the cable.

2. A method according to Claim 1, characterised in that the outer ring of wires (3, 4) is formed, in alternate sequence, of first wires (3) having a fixed radial dimension relative to the cable (1), and second wires (4) having a greater radial dimension, relative to the cable (1), than the fixed radial dimension, whereby the plastic deformation is produced mainly in the second wires (4).

3. A method according to Claim 1 or Claim 2, characterised in that it includes the step or effecting the radial compression of the cable by means of radial hammering (M).

4. A method according to any one of Claims 1 to 3, characterised in that the radial compression (M) is carried out in several successive stages.

5. A method according to any one of the preceding claims, characterised in that the at least one outer ring of wires (3, 4) is produced from metal wires.

6. A method according to Claim 2, characterised in that, in the ring of outer wires (3, 4), the material constituting the second wires (4) is more easily deformable than the material constituting the first wires (3).

7. A method according to any one of Claims 1 to 6, characterised in that it includes the step of forming a core (2) of the filiform element (1) in the form of a cable of respective wires wound in a predetermined sense and the step of winding the outer wires (3, 4) onto the core (2) in the opposite sense from the said predetermined sense.

8. A flexible filiform element, characterised in that it includes at least one outer ring of wires (3, 4) arranged in an array of wires (3, 4) extending with adjacent wires (3, 4) in form-coupling relationship, the filiform element (1) having a substantially constant diameter.

9. A filiform element according to Claim 8, character ised in that the outer ring of wires (3, 4) is constituted by first wires (3) which define circumferential spaces between them, and second wires (4) arranged in alternating sequence with the first wires (3) and extending so as to fill the circumferential spaces.

10. An element according to Claim 8 or claim 9, characterised in that the outer ring of wires (3, 4) is constituted by metal wires.

11. An element according to Claim 9, characterised in that the material constituting the second wires (4) of the outer ring of wires (3, 4) is a material which is more easily deformable than the material constituting the first wires (3).

12. A flexible element according to any one of Claims 8 to 11, characterised in that it includes a core (2), constituted by a cable of respective wires wound in a predetermined sense, and in that the outer ring of wires is constituted by wires (3, 4) which are wound on the filiform core (2) in the opposite sense from the said predetermined sense.

13. An element according to any one of Claims 8 to 12, as in the form of a transmission element for a flexible control cable.

Drawing