GB2093082A - Method of making flexible tubular guide sheaths for coaxial push-pull actuator cables and cable sheaths produced thereby - Google Patents

Abstract

A push-pull cable sheath is provided by swaging a plurality of round wires against a central cylindrical mandrel and circumferentially against each other so as to flatten their mutually abutting surfaces and to arcuately curve their inside surfaces in conformity with the mandrel. The abutting surfaces are radial and the outside wire surfaces are also curved. By starting with wires that are round, the resultant elements of the tubular array of sheath wall elements thus formed on the mandrel, though slightly wedge-shaped in cross section and tapered in width, approximate a square with rounded corners. The swaged wires are compressively wrapped with binder wire. This configuration is found to provide unique advantages in terms of low cost, flexibility and cable durability. <IMAGE>

Description

SPECIFICATION Method of making flexible tubular guide sheaths for coaxial push-pull actuator cables and cable sheaths produced thereby Background of the Invention This invention relates to flexible push-pull actuator cables and more particularly to a new and improved method and means for making the conduit or guide sheath of such cables of the type comprising a wire-wrapped tubular array of swaged elongated metal strips.

U.S. Patent No. 3,990,321 discloses an improved method and means for making up pushpull cable flexible guide conduits or sheaths.

Cross-sectionally flat metal strips were drawn from supply reels through a closing head that guides them into edge-abutted positions extending along a central swaging mandrel. From the closing head, the strips were drawn along the mandrel so as to pass through a surrounding swaging die. Compressed against the mandrel by the swaging die, the malleable strips were transversely bent about the mandrel and laterally expanded into wedge-shaped cross sections, together making up a multi-segment continuous tubular sheath. As the strips were being fed to the die and mandrel, the group of strip supply reels was rotated so as to impart a long pitch spiral to the strips making up the emerging sheath. The swaged strips making up the tubular sheath were next tightly bound together by a retainer wire swaged around them in a spiral wrap of opposite, shorter pitch.The resultant sheath was intended to present a smooth interior and to be capable of flexure by reason of the relative sliding action permitted between strips accompanying bending flexure of the sheath.

However, practical experience with push-pull actuator cables having sheaths made in the above-described manner revealed a certain limitation and one that was traced to the initial relatively wide and thin rectangular crosssectional form of the strips used in making up the sheath. Those strips in the sheath oriented in or near the plane of bending tended to distort, i.e., to spring out of the nominal smooth tubular contour of the composite sheath. In thus distorting, the strips presented corner edges to the interior of the sheath, edges that had a tendency to scour and scrape a sliding cable inner member and/or bearing elements interposed between the inner member and the sheath. Their circumferential width in the bending plane also added somewhat, undesirably, to bending stiffness of the sheath.

A main object of this invention is to overcome the aforementioned difficulty in such a cable sheath; more particularly, to provide an improved sheath that retains its interior smoothness in varying states of flexure and loading, and also one that is more flexible for a given wall thickness, hence for a given strength of the sheath in compression or tension.

Another object hereof is to provide an improved coaxial push-pull actuator cable sheath generally of the swaged multi-element type disclosed in the aforesaid patent improved in the respects mentioned and one that is manufactured more readily and at reduced manufacturing cost.

A further object hereof is to provide a push-pull cable sheath that can be produced from less expensive and more readily available wall material, in fact from common round wire of widespread availability and low cost.

Summary of the Invention In accordance with the present invention, sheaths of the type disclosed in the prior patent cited above are made not from edge-relieved flat strip material, but from plain circularly round wire.

In so doing, a special set of interrelated advantages accrue not heretofore recognized or expected. While a larger number of wires than flat strips are required to make up a tubular sheath of predetermined diameter and thickness, the cost of commonly available wire is still substantially less than the cost of flat ribbons or strips. The round wires present no lay-up orientation requirement (v.v. antitwist infeed guide requirements), whereas they swage as readily into the required wedgeshaped, mutually abutting cross sections of nearly square proportions. Perhaps of greater importance, a sheath of given wall thickness and diameter produced from swaged round wires is more flexible than one produced from flat strips, and when flexed in bending, retains the smoothness of its interior surface to a significantly higher degree than one made of flat rectangular strips.Consequently, the resultant sheath is capable of providing longer operating cable life due to reduced out-of-contour distortion of individual sheath elements with the cable bent, and thereby reduced abrasion-induced wear of the cable inner member, especially in a cable frequently operated when flexed. Yet, the concern about radial inward collapse that previously led to use of but few, relatively wide wall strips yielding relatively positive keying effect due to the steep wedge angles forming between opposite edge faces of each strip has proved not to be a problem with sheaths of the present invention despite the large number of relatively narrow wires used and their small wedging angle.

These and other features, objects and advantages of the invention will become more fully evident from the description that follows with reference to the accompanying drawings.

Brief Description of the Drawings FIGURE 1 is a block diagram, partially schematic, of a typical manufacturing line which may be used to produce push-pull cable sheathing according to the present invention, the drawing includes a series of cross-sectional showings designated A-A, B-B, C-C, D-D and E-E depicting progressive stages in the manufacture of the sheath.

FIGURE 2 is an isometric view of a completed sheath with portions broken away to reveal characterizing features of the improved sheath construction.

Detailed Description The system shown in FIGURE 1 for laying up and swaging the sheath array and the binder wire is or may be of the type now in use. Inasmuch as the longitudinal elements that form the sheath wall or conduit in this case are round wires instead of the flat strips used in prior practice, the swaging pressure required to swage the elements may differ from that required in the prior practice, although in some cases it may be the same, depending upon the diameter of the wire employed and also the malleability or softness characteristics of the wire making up the sheath wall elements.

In accordance with this invention, as illustrated, the wall or component elements of the sheath comprise a plurality of round wire strands W, in this case 1 6 in number, fed from a circular array of as many bobbins 10 0 carried on respective mounts 12. The bobbins are mounted at equal spacings on a rotary base 14 about central axis X-X. During sheath manufacturing operations, base 14 is turned unidirectionally by drive unit (gear reduction) unit 1 6 about axis X-X at a rotational speed bearing a fixed relationship to the lineal rate as wires W are drawn from bobbins 1 0. The motion ratio fixes the helical lay-up pitch of the wire elements making up the sheath.

From bobbins 10, wires W converge into a closing head 1 8 generally of the type now in use.

Centered on axis X-X, head 18 passes the coaxial rod-like swaging mandrel 20 centrally, as in past practice. The hardened, precision-ground elongated cylindrically round mandrel having a diameter equal to the desired sheath interior diameter is fixedly mounted at one end cantilevered from a suitable support 22. Before entering the closing head, the wires and mandrel appear cross-sectionally as in Subfigure A-A of FIGURE 1. After passing through the closing head, the wires and mandrel appear as in Subfigure B-B of FIGURE 1. Now the wires are tightly clustered around mandrel 20 abutted snugly against each other and slidably against the surface of the mandrel. They are given a slight helical twist about the mandrel in the laying-up process due to the slow progressive rotation of bobbin support spider 14.

From closing head 18, the wires are drawn slidably along stationary mandrel 20 through rotary swager 24 also of the type now in use. They emerge from the swager converted in form from their initial round cross section into a cross section which is approximately square but in fact is slightly arcuate and wedged-shaped. As a result of swaging pressure, the individual wires present opposite radially extending sides flattened against those of the adjacent wires and inside faces curved to the mandrel contour, with outside faces approximately of the same curvature but of somewhat larger radius. The flattened sides lying in substantially radial axial planes are left with slight rounding of the inside and outside corners.

The swaged wire cluster tightly enwrapping the mandrel as a multisegment tubular assembly next passes through a binder wire wrapper head 26 which applies a continuous enwrapment of round binder wire Y. The binder wire is applied under wrapping tension in the binder wire at a helical pitch distance which is small in relation to the helical pitch distance of the sheath wall elements and that is opposite to the direction of wall element twist. Typically, binder wire pitch distance will equal from one to two times the sheath diameter. In order to operate the wrapper 26, a drive unit (gear unit) 28 is employed which is also synchronized with the drive unit 1 6 as in past practice. Wrapping tension in the binder wire compresses the wall elements W against the mandrel as a means to insure accurate inside sheath diameter established by the mandrel.

From binder wire wrapper 26, the bound cluster of sheath element wires appears cross-sectionally as in Subfigure D-D of FIGURE 1, in which condition it passes next through a second rotary swager 30. The latter applies the usual light swaging pressure heretofore used which is sufficient to give the binder wire a substantially uniform tractional grip on the sheath wall element wires along the length of the binder wire, and thereby to impart uniform structural integrity to the assemblage along the length thereof while not materially or unduly impeding its flexibility. As an integral assemblage, the composite sheath can be cut into lengths and the lengths provided with terminal fittings in the usual manner to form individual push-pull cables of any selected lengths.

As shown, mandrel 20 terminates just beyond swager 30. This is depicted in Subfigure E-E of FIGURE 1 , wherein the completed assemblage of wires appears without the mandrel. In order to draw the sheath wire cluster progressively through the various stages of the manufacturing system, and from the bobbins, the prior practice is conveniently used here, that of employing a driven capstan 32 engaging to assembled sheath and a driven sheath take-up reel 34 turned synchronously by a drive unit (gear unit) 36. As shown, the driver units 1 6, 28 and 36 are preferably operatively connected to a common source of drive power 38, such as an electric motor unit.

The completed sheath is depicted in FIGURE 2.

In this figure, the sheath is shown covered by a sleeve of material such as a synthetic polymer that is extruded or heat shrunk or otherwise tightly bound around the sheath so as to keep out water and to further improve its structural integrity, yet permit it to undergo flexure in normal usage. The inside and outside corners of the sheath wires are left slightly rounded. This is accomplished by appropriately limiting the degree of swaging pressure applied in the initial swaging operation performed by swaging unit 24, an operation condition readily established and maintained in this art.This slight rounding of the corners of the sheath, particularly the inside corners, is desirable in order to avoid extrusion of burrs or the production of sharp edges that may thrust into the interior of the sheath, especially upon sheath flexure, and thereby scour and wear the slidable push-pull core member of the cable during cable operation.

It will thus be seen that the invention provides a durable, structurally integrated cable sheath made up of inexpensive readily available round wire, and that even though these wires when swaged are nearly square (i.e., their radial width approximates their median circumferential width), so as to require a relatively large number of them, there is nevertheless sufficient taper between the sides of each to prevent crushing under compressive force of the binder wire or that due to tension loading of the sheath during operation. Also, the bending flexibility is considerably improved over the prior form of device employing relatively few and wide wall elements. There is also a markedly reduced degree to which the individual wires are distorted by twisting under sheath flexure to present corner edges to the interior core member and that must slide in forced contact with those edges during cable push-pull operation. The latter advantage of reduced wear is aided by the convenience with which clearance is afforded in case of slight twisting of sheat elements during sheat flexure through leaving the inside corners of the initially round wire elements slightly rounded after swaging as a result of controlled limiting of the swaging pressure applied to the wires.

These and other advantages and the range of variations within the scope of the invention will be evident to those skilled in the art who will understand also that the claims that follow are intended to be construed in accordance with the illustrated embodiment and equivalents thereof.

Claims (11)

1. A push-pull cable sheath comprising a circular cluster of longitudinal wire-like sheath wall elements arranged around a longitudinal central sheath axis, with mutually adjacent sides of the elements abutting in radial longitudinal planes and with inside and outside faces circumferentially curved about said axis cooperatively defining inside and outside substantially cylindrical sheath wall faces, said elements having a median width circumferentially approximately the width of said sides radially, and binder means compressively enwrapping said cluster of elements along the common length thereof.

2. A sheath as defined in Claim 1 wherein the sheath wall elements are swaged in place from substantially round wires and at least the inside corner edges of said elements are slightly rounded.

3. A sheath as defined in Claim 2 wherein the side faces of said cluster of said elements have a relatively slow spiral twist in a first direction about said axis, and wherein the binder means comprises a binder wire spirally wrapped around the cluster with a relatively rapid opposite spiral twist.

4. A sheath as defined in Claim 3 wherein the binder wire is swaged in place.

5. A sheath as defined in Claim 4 wherein the binder means further comprises a synthetic jacketing sleeve compressively shrunk over the cluster and binder wire.

6. A method of manufacturing a flexible round tubular metal sheath, such as for a push-pull cable, comprising swaging a cluster of round wires layed longitudinally in circular series about and against an elongated round mandrel until concavely arcuate inside faces are formed against the mandrel adjoined by mutually abutted substantially radial faces, and enwrapping the swaged cluster by binder means compressively gripping the wires of the cluster.

7. A method as defined in Claim 6 wherein progression of the swaging is terminated with the inside corners of the swaged wires still slightly rounded.

8. A method as defined in Claim 7 wherein the cluster is wrapped by a binder wire at a predetermined pitch in a given direction around the cluster and swaged in place thereon.

9. A method as defined in Claim 8 wherein the wires of the cluster are layed around the mandrel with a spiral pitch that is high and opposite relative to that of the binder wire.

10. A push-pull cable sheath substantially as described hereinbefore with reference to and as illustrated in the accompanying drawings.

11. A method of manufacturing a flexible round tubular metal sheath substantially as described hereinbefore with reference to the accompanying drawings.

1 2. Any other novel feature or combination disclosed hereinbefore or in the accompanying drawings.