US 3193614 A
Description (OCR text may contain errors)
y 1965v J. M. RICHARDS 3,193,614
ELECTRIC CABLES Filed Aug. 3, 1962 3 Sheets-Sheet 1 y 1965 J. M. RICHARDS 3,193,614
ELECTRIC CABLES Filed Aug. 3, 1962 v 3 Sheets-Sheet 2 /24- ::I. I i 25 -a 3P FIG. 11. 4f
y 1965 J. M. RICHARDS 3,193,614
ELECTRIC CABLES Filed Aug. 3, 1962 3 Sheets-Sheet 5 United States Patent M 3,193,614 ELECTRIC CABLES Joseph M. Richards, Scdgley, England, assignor to The Wednesbury Tube Company Limited, Bilston, England, a British company Filed Aug. 3, 1952, Ser. No. 214,599 Claims priority, application Great Britain, Aug. 5, 1961, 28,521/61 8 Claims. (61. 174-412) This invention relates to electrical cables of the kind comprising a tubular metal sheath and two or more conductor cores extending through the sheath and separated from each other and from the sheath by a filling of powdered insulating material. Such cables are hereinafter referred to as being of the kind specified.
Cables of the kind specified are usually made by disposing the requisite number of conductor-cores within a tubular sheath to extend longitudinally thereof in at least approximately the positions which they are required to occupy in the finished cable, the sheath and the conductor cores being of cross-sectional dimensions larger than those which they are required finally to have, filling the space between the conductor cores and between the conductor cores and the sheath with powdered insulating material and compacting the latter, for example, by ramming the powdered material in the sheath in an endwise direction, and subjecting the filled sheath with the conductor cores therein to a drawing operation to reduce the cross-sectional dimensions of the sheath, conductor cores, and filling of insulating material. This method of manufacture is hereinafter referred to as being of the kind specified.
One of the requirements which arises in cables of the kind specified is to be able to identify an exposed conductor core at one end of the cable and an exposed conductor core at the other end of the cable as being parts of the same conductor core.
The object of the present invention is to provide a new or improved means for meeting this requirement.
From one aspect the present invention resides in the provision of a cable of the kind specified wherein one at least of the conductor cores has a longitudinally extending recessed formation in its surface. Preferably the recessed formation is filled with a material which presents a contrasting visual appearance in comparison with that presented by the surface of the conductor core itself.
Advantageously, but not essentially, the material with which the recess or each of same is filled may be the powdered insulating material incorporated in the cable;
The preferred form of recessed formation is a continuous groove which extends longitudinally of the conductor core concerned. 7
Ordinarily it is suificient for one only of the conductor cores to incorporate the recessed formation. Theremaining conductor cores are then identifiedby reference to their positions relatively to the conductor core which incorporates the recessed formation.
If it is required to identify by a specific marking more than one of the conductor cores the appropriate number of conductor cores, that is two or more, are then formed with respective longitudinally extending recessed forma tions differing from each other in appearance.
The sides of the groove may be convergent with respect to each other in a direction radially inwardly of the conductor core. The preferred cross-sectional shape .of the groove is V-shaped, the angle between the sides of the groove being large enough to permit filling material to be removed by scraping, abrasion or similar operations.
From a further aspect, the present invention resides in a method of manufacture of the kind specified wherein 3,193,614 Fatented July 6, 1965 a recessed formation is formed in one at least of the conductor cores of the cable prior to the operation of drawing the cable.
The recess or each of same then become filled with the powdered insulating material fed into the sheath, and during the drawing down of the cable with consequent reduction in the cross-sectional dimensions of the conductor core concerned the dimensions of the recess or each of same contract, so that the powdered material in the recess becomes compacted and is retained therein.
Where the recessed formation is in the form of a continuous groove this may be formed by subjecting ungrooved rod or wire stock to an operation which dis places the metal of the stock to change the cross-sectional shape and form the groove (as opposed to removing metal from the stock). One way in which this may be carried out is by subjecting the rod or wire stock to a drawing operation through a die shaped to conform to the grooved cross-sectional shape required. Alternatively, the rod or wire stock may be subjected to a rolling operation, the roller having a recess-forming part shaped in cross-section to conform to the crosssectional shape of the groove formed thereby.
The invention is illustrated in the accompanying drawings wherein:
FEGURE 1 is a View in cross-section of a conductor core of a cable of the kind specified, preparatory to insertion in the sheath of the cable and after a groove has been formed in this conductor core;
FIGURES 2 and 3 are respectively a longitudinally diametral cross-section and an end elevation of a die for forming the groove shown in FIGURE 1;
FIGURE 4 is a view in side elevation and partly in cross-section of a draw bench apparatus for subjecting thefilled cable to a drawing operation;
FIGURE 5 is a view in side elevation and partly in cross-section of an apparatus for filling the cable and compacting the insulating material;
FIGURE 6 is an enlarged fragmentary view on the line 66 of FIGURE 5;
FIGURE 7 is an enlarged cross-sectional view of the cable incorporating three conductor cores after the drawing operation;
FIGURE 8 is a view in side elevation and partly in cross-section of an alternative form of apparatus for drawing the cable;
FIGURE 9 is a view in side elevation and in vertical cross-section through the axis of a conductor core, and illustrating an alternative apparatus and method of producing a recessed formation in a conductor core;
FIGURE 10-isa View in end elevation of the parts shown in FIGURE 9; I
FIGURE 11 is a fragmentary view illustrating an end portion cable with protruding conductor cores incorporating respective recessed formations presenting different visual appearances; and
FEGURE 12 is a view similar to FIGURE 1 illustrating a modification wherein the groove is filled with another material, preparatory to insertion of the conductor core in the sheath of the cable.
Referring firstly to FIGURE 1 of the drawings wherein is shown in cross-section a piece of rod or wire stock =19 of a suitable electrically conductive material, such as copper, the rod or wire stock may have any suitable crosssectional shape initially, for example, circular as shown, and according to the size of the cable required to be manufactured may have an initial diameter ranging typically from about a quarter of an inch to about two inches.
The rod or wire stock is subjected to an operation to produce a recessed formation extending longitudinally of the stock. Such recessed formation may be a continuous groove 11. The cross-sectional area of the groove 11, rela- & tively to that of the rod or Wire stock as a whole, is not critical but should be such that it does not materially reduce the current carrying capacity of the conductor core after manufacture of the cable has been completed, whilst presenting a sufiiciently broad mouth to be readily visible for the purposes of identification of the conductor core.
In practice I found that a V-section groove, wherein the included angle between the side faces is approximately 100 and wherein the depth of the groove measured radially between its inner extremity and the mouth of the groove (as defined by a continuation of the outer boundary of the rod or wire stock in cross-section) of the order of one tenth of the diameter of the rod or wire stock, is satisfact-ory.
One of the reasons for preferring a relatively wide angle for the groove 11 is that powdered insulating material of the cable, which normally fills this groove and assists in identification of the conductor core by virtue of its contrasting visual appearance in relation to that afforded by the surface of the remaining part of the conductor core, can readily be removed by scraping with a knife or sharp pointed tool or by abrasion with a file or emery paper, and if need be a portion of the conductor core, which incorporates the groove, can thereafter be flattened with a file or similar tool so as to avoid any recessed or re-entrance formation. This may be important in certain cases where, having identified the conductor core, it is desired to fit a sealed termination to the cable which will prevent the ingress of liquid or moisture into the interior of the cable and thereby will maintain the insulation resistance afforded by the filling of the cable at a satisfactorily high value.
The groove 11 may be formed by drawing the rod or wire stock through a die of the form illustrated in FIG- URES 2 and 3 wherein it will be observed that the body 12 of the die affords a die opening 13 including convergent sections 14 and15 and a substantially parallel sided portion 16. Within the two latter portions 15 and 16 is'provided an inwardly projecting nib 17 which is shaped in cross-section to produce the groove 11.
Having formed the groove in the rod or wire stock a length of the rod or wire stock, together with an appropriate number of other conductor cores formed of similar rod or Wire stock, is assembled within a tubular sheath and the sheath is then filled with powdered insulating material, such as magnesium oxide, which is compacted.
These operations may be performed by an apparatus as illustrated generally in FIGURE 5, wherein the sheath tube 18 is accommodated mainly in a bore 19 in the floor 20 of the premises in which the apparatus is installed.
An upwardly projecting supporting structure or post 21 carries a reciprocating ram 22, guided intermediate its ends by a guide member 23, and supported and reciprocated by means of a carriage 24 which is moved upwardly along the post 21 in accordance with the level of the powdered content in the sheath tube and which has a driving unit 25 for reciprocating the ram.
Powder is delivered into the sheath tube 18 from a hopper 26 and passes down an interspace 27 between the outer face of the ram and the inner face of the sheath tube 18. The ram 22 is of hollow form to accommodate the rods or wires forming the conductor cores and is maintained in coaxial relation with the sheath tube by guide blocks or feathers 28.
After filling of the sheath tube and compaction of the powdered insulating material therein, the sheath tube, together with the rods or wires and the powdered insulating material, is subjected to a drawing operation to draw it down to the required size.
An apparatus for performing this operation is illustrated in FIGURE 4 wherein 29 designates a suitable drawing die through which the filled sheath tube is drawn by means of a carriage 30 including a means for gripping the leading end of the sheath tube 18 and conductor, and a coupling member 31 for releasable engagement with a draw chain 30 guided over sprockets, one of which is indi- =2 catcd at 32, driven in any suitable manner to advance the carriage 30 from left to right as seen in FIGURE 4.
An alternative form of apparatus for performing the drawing operation is illustrated in FIGURE 8 wherein the sheath tube 118 and a suitable die 129 are shown, the leading end portion of the sheath tube being held by a gripping dog member 13h provided on a Winding drum 131 rotated in the direction of the arrow 132 by any suitable drive means.
FIGURE 7 illustrates in cross-section the form of the cable produced as a result of the drawing operation.
Three conductor cores are illustrated, namely 33 (formed from the rod and wire stock 19 shown in FIG- URE 1), 34 and 35, of which the last two mentioned are not formed with any recessed formation. All these conductor cores are of single-strand or homogeneous form in cross-section.
The powdered insulating material 37, which mechanically separates and electrically insulates the con-ductor cores 33 to 35 from each other and from the sheath tube, fills the groove 36 in the conductor core 33 (such groove being in effect a reduction of the groove 11 in FIGURE 1). The powdered insulating material is normally retained in the groove 36 when the conductor cores are exposed by cutting away the sheath tube 18 and removing the insulating material, and since the latter is normally white in colour the marking produced by this filling of the groove 36 on the conductor core 33 is clearly apparent.
However, the filling of insulating material can be removed from the groove 36, as previously referred to, if desired.
The conductor cores do not become twisted or transposed within the sheath tube 18, so that ordinarily it is necessary only to identify one conductor core at each end of the cable where the conductor cores are normally exposed and then the other unrecessed conductors 34 and 35 by their positions relatively to the other recessed conductor core 33.
However, in cases where it is desired to provide for specific identification of each or more than one of the con ductor cores, these may be formed with respectively different recessed formations, as illustrated in FIGURE 11.
As seen therein, the conductor cores 233, 234 and 235 protrude from a filled sheath tube 218.
The conductor core 233 has a groove 236 which may be of V-shape similar to the groove 36 shown in FIGURE 7, whereas the conductor cores 234 and 235 have dis continuous recessed formations, in the former this consisting of a series of elongated recesses 237 and in the latter case a series of conical recesses 238, in both cases these recesses containing filling of the powdered insulating material.
The manner of forming recesses such as 237 and 238 is illustrated in FIGURES 9 and 10.
The rod or wire stock 310, from which the conductor cores are formed, may thus be passed between a pair of rolls 339 and 349, each formed with a peripheral groove of part-circular shape in cross-section to embrace and enclose the stock, as seen in FIGURE 10.
One of these rolls, for example 349, is formed in the base of this groove with a plurality of radial projections 350 which may be of conical form (for forming recesses such as 238), or possibly of elongated form were it desired to form recesses such as 237. The rolls 339 and 349, or at least one of them, preferably in this case that incorporating the projections 350, would be connected in any suitable manner to a drive motor, The apex angle of the conical recesses formed may be equal to that of the V-section groove, namely or thereabouts.
FIGURE 12 illustrates a further modification of rod or wire stock 410, wherein the recessed formation or groove 411 contains a filling 412 of a material other than the insulating material used to fill the sheath tube. This modification may be adopted in either of two cases. Firstly where it is desired that the conductor core as a whole shall be maintained to strictly circular shape in cross-section, thereby avoiding any difiiculty in achieving sealing at a cable termination, and secondly where it is desired that the current capacity of the conductor core shall not be diminished to any extent at all.
In the first case the filling material 412 may be either an insulating material or a metal, the surface of which presents a contrasting visual appearance with respect to that afforded by the remainder of the conductor cores.
In the second case the filling would be of an electrically conductive metal. Where the conductor core 410 is made of copper a suitable metal for this purpose would be tin or a tin lead alloy, or possibly aluminum.
In any case where this filling of the recessed formation is performed prior to the insertion of the rod or wire stock into the sheath tube and prior to the drawing down of the latter, the filler material should be selected so as to be capable of undergoing the drawing operation without breaking up into fragments and coming out of the recessed formation.
What I claim then is:
1. An electrical cable comprising a sheath, a plurality of conductor cores disposed in said sheath, at least one of said cores being initially provided with a wide-angled recess disposed in axial alignment therewith, and loose insulation material, said material being firmly packed within said sheath to space said conductor cores from each other and from said sheath, and said material being firmly packed into said recess to visually distinguish the filled recess cross-section of said one core from the integral cross-sections of said remaining cores.
2. An electrical cable having readily identifiable conductor cores therein, said cable comprising a tubular metal sheath, a plurality of conductor cores extending therethrough, insulating material disposed in said sheath spacing and electrically insulating said cores from each other and from said sheath, at least one of said cores having a longitudinally extending recessed formation in its surface, filling material disposed in said formation, said filling material having a contrasting visual appearance to that of said surface to identify said one core from the remaining cores in said sheath, said formation having a readily visible mouth defined by edges spaced apart at said surface in a direction circumferentially thereof.
3. An electrical cable having readily identifiable conductor cores therein, said cable comprising a tubular metal sheath, a plurality of conductor cores extending therethrough, insulating material disposed in said sheath spacing and electrically insulating said cores from each other and from said sheath, said insulation material presenting a different visual appearance from that of said cores, at least one of said cores having a continuous longitudinally extending groove in its outer surface, said groove being filled with said insulating material to distinguish it from the remainder of said cores.
4. An electrical cable according to claim 2 wherein at least one of said cores is provided with a longitudinally extending series of spaced recesses in said surface, each of said recesses being filled with said insulating material.
5. An electrical cable according to claim 2, wherein said conductors are single strand cores of substantially circular cross-section, said formation having a readily visible mouth defined by closely circumferentially spaced edges, said formation extending inwardly from said surface through a short distance relative to the cross-section radius of said core.
6. A method of making an electric cable having readily identifiable cores therein, said method comprising the steps of assembling lengths of elongated metal stock, forming conductor cores from said stock, forming a longitudinally extending recess in at least one of said cores, inserting a plurality of said cores including said recessed core through a sheath-forming tube, introducing powdered material through one end of said tube, packing said material within said tube to fill said recess and electrically insulate said cores from each other and said tube, and then reducing said tube to a predetermined crosssectional dimension.
7. The method according to claim 6, including the steps of drawing said one core through a die having a crosssectional shape complementary to said stock and forming a continuous groove therein.
8. The method according to claim 6, including the steps of forming substantially circular cores from said stock and then rolling said one core between rollers which in combination define an aperture of a cross-sectional shape complementary to that of said core while forming said recess with side faces which are convergent with respect to each other in a direction radially inwardly of said one core at an angle in a range exceeding a value of approximately degrees.
References Cited by the Examiner UNITED STATES PATENTS 689,615 12/01 Heyl-Dia 174-133 X 2,036,034 3/36 Fulmer et al. 29547 X 2,973,706 3/61 Kingsley.
3,136,054 6/64 Palmer et al. 29-547 FOREIGN PATENTS 573,607 4/59 Canada.
OTHER REFERENCES A.P.C. application of Beckett, Serial No. 218,848, published June 8, 1943.
JOHN F. BURNS, Primary Examiner.
JOHN P. WILDMAN, E. JAMES SAX, Examiners.