US2738910A - Electric cables or other insulated electric conductors - Google Patents

Description

March 1956 G. D. CLOTHIER 2,73

ELECTRIC CABLES OR OTHER INSULATED ELECTRIC CONDUCTORS Filed Aug. 17, 1950 4 Sheets-Sheet 1 A E r F F/G./. E F /G.2.

Inventor CmcLoTHiEA By WM, Lind L 91mm A tiomey:

March 20, 1956 G. D. CLOTHIER 2,738,910

ELECTRIC CABLES OR OTHER INSULATED ELECTRIC CON'DUCTORS Filed Aug. 17, 1950 4 Sheets-Sheet 2 I I l I I 2' Inventpr G. b- QLoTHiER y mummy mm? L Pwmh Ailorneys March 20, 1956 Filed Aug. 17, 1950 G. D. CLOTHIER ELECTRIC CABLES OR OTHER INSULATED ELECTRIC CONDUCTORS 4 Sheets-Sheet 3 Inventor C; h. QLOTHiE R A ilornew March 20, 1956 G. D. CLOTHIER 2,738,910

ELECTRIC CABLES OR OTHER INSULATED ELECTRIC CONDUCTORS Filed Aug. 17, 1950 4 Sheets-Sheet 4 Inventor 6'50 R as DONfll-D 62 a mi: R

WdVvM United States Patent ELECTRIC CABLES OROTHER INSULATED ELECTRIC CONDUCTGRS George Donald Clothier, Newcastle-on-Tyne, England Application August 17, 1950, Serial No. 179,999 Claims priority, application Great Britain August 19, 1949 19 Claims. (Cl. 226-'24) This invention relates to electric cables or other insulated conductors, for heating purposes, or for power conduction purposes, such as for lighting or control or low voltage power circuits, of the kind comprising a metal sheath separated from a conducting core or cores by pulverulent insulating material, such for example as magnesia, and to a process and apparatus for manufacturing such cables or conductors.

In theprocess according to the invention, the insulating material is fed in powder form to the interior of the sheath tube, and relative longitudinal movement between the sheath tube and a ram within it is effected to move the ram into contact with the column of insulating powder in the sheath tube, the ram or the sheath tube being subjected to one or more longitudinal blows or impacts after the said contact has been established and before the ram again leaves the surface of the powder column.

Preferably, the relative longitudinal movement between the ram and the sheath tube is effected at low frequency and high amplitude, and the longitudinal blows or impacts are applied to the ram or the sheath tube at relatively high frequency and low amplitude.

. A frictional device is preferably provided, which yields at a predetermined stage in the relative longitudinal movement between the ram and the sheath tube and thereby terminates such relative movement. Conveniently, such frictional device takes the form of a frictional abutment, which opposes the compressive thrust applied by the ram to the powder column in the sheath tube and yields when such thrust exceeds a predetermined value, thereby permitting the ram and sheath tube to move together under the thrust, in the manner which in itself forms the subject of the present applicants copending application, Serial No. 177,200, filed August 2, 1950.

The feeding of the powder to the sheath tube may be eifected in various ways, and in one convenient arrangement the ram is made hollow or tubular and the powder is fed to the sheath tube through the interior of the ram. The apparatus may be subjected to agitation or vibration to promote the flow of the powder. Thus, the percussion device for imparting the longitudinal blows or impacts may be caused to operate also before the ram has reached the powder column and after it has left the powder column, thereby producing the agitation for assisting the powder flow. The percussion device is conveniently separated from the ram or sheath tube. by a lost motion device which yields'to permit such blows or impacts to be effective on the ram or sheath tube only when a compressive thrust is being applied to the powder column.

Preferably, the insulating powder is fed to the sheath tube through one or more feed openings in the head of the ram and such feed opening .or openings are controlled by means of a valve, in the manner forming the subject of the present applicants .copending application, Serial No. 177,199, filed August 2, i950.

Conveniently, such valve is closed at or 'befor-ecommencement :of the compressive thrust on the powder column and is reopened when or shortly after the ram is retracted from the powder column. Thus, the valve may comprise a ,part carried :by the ram head and a cooperating relatively movable part so suspended from the ram or its head as to be free to move longitudinally relatively thereto.

After the filling process is completed, the workpiece, constituted by the sheath tube filled around the core rod or rods therein with powder compacted by the ram, may be subjected to one or more mechanical drawing stages, in order to elongatezit into the form of an :electric cable.

The inventionmay be carried into practice in various ways, but a convenient practical construction of cablemanufacturing apparatus according thereto, is illustrated by way of example in the accompanying drawings, in which Figures -1 and 2 respectively show the apparatus in front and side elevation,

Figure 3 is an enlarged view of the upper part 'ofFigure l in central vertical section, and

Figure 4 is a similar view of the lower part showing a preferred valveconstruction.

Figure 5 is a side view, partly in section and partly in elevation of the percussion device of the invention.

In this construction, the apparatus :is arranged 'vertically and is carried by a tower or superstructure, which may take the form of :a suitably supported gallery .A above a well B in the ground, deep enough to take the length of the metal tube C, which will ultimately form the cable sheath, and of the conducting rod or rods 0 which will form the cable core or cores. In the example illustrated, two core rods C :are shown for the manufacture of a two-core cable.

Suspended from a bracket A on the gallery A, .and reaching nearly :to the ground surfacetBh-is a fixed shroud tube D, which is in alignment with the well l3 :and is likewise of a length to 'house thesheath tube C within it, a fixed eye B carried on a pillar B upstanding from the ground, being provided to ensure that the shroud itube remains in alignment with the well B. The samebracket A also serves to carry "upwardly projectingb'ars A for supporting a driving machine, which may consist for instance of an electricmotor or (as shown) of a doubleacting pneumatic cylinder E fed at its ends through two flexible pipes E E connected through a valve indicated at E to a main supply :pipe E rfedfrom asource :of compressed air (not shown). The valve E is driven through reduction gearing E from a small electric motor mounted on the gallery A, the arrangement being such that the two .pipes 151, E :are connected alternatively :to the main supply pipe E through the valve, the pipe E or E not connected at :a particular moment to the pipe B being opened by the valve E to exhaust into the atmosphere. The piston l5. (see Figure 39 :in the cylinder E is carried by a rod E fixed to a crossbar A on the two vertical supporting bars A so that the cylinder E is :caused to reciprocate up and down .in accordance with the supply of compressed air 1 through the pipes E and E the .cylinder'being guided by means of arms E whose lower ends cooperate with a spindle 5 which runs in vertical slots A in the supporting bars A and is connected to atubularram 'F. This ram F extends downwardly within the sheath tube C around the core rods C and by its reciprocation serves to tamp the insulating powder in the sheath tube.

Connected to the base of the cylinder E is a percussion device, which operates at a frequency materially higher than that of the reciprocations of the cylinder E. Such device may takevariious :forms but in the example illustrated consists of a pneumatic hammer Lsupplied with compressed air through a pipe 1L controlled by avalve L The striker L of the percussion device acts, when required, on the upper end of the ram F through shock absorbing pads F which serve to deaden the shock and thereby to reduce fatigue stresses in the ram. A spring L is provided between the percussion device L and the ram F, of strength great enough to hold the two apart during the main reciprocating movement of the ram so that the striker L will not impinge on the ram, this spring however yielding when the ram applies a compressive thrust to the powder column in the sheath tube (in the manner to be described later), whereby the striker L imparts its blows or impacts to the ram only when such compressive thrust is being applied to the powder. The arms B have a lost-motion connection at F to the spindle F to permit compression of the spring L The insulating powder, which may consist for example of magnesia, is fed to the sheath tube C through the interior of the ram P, which is provided at its upper end with a feed opening F for this purpose.

The powder feed mechanism may take various forms,

but in the example illustrated it is itself carried by the ram and consists of a hopper G, into which the powder can be fed, by hand, or otherwise, and a reciprocating plunger G below the hopper for pushing the powder through the feed opening F in the ram F. The plunger G is reciprocated in synchronism with the ram drive by means of a rope or chain G passing over a pulley G carried by the casing of the powder feed mechanism, one end of the rope G being attached to the bracket A whilst the other is secured to the end of a rod G fixed to the plunger G Thus whilst the ram F is moving upwards, the rope G causes the plunger G to advance to force powder into the ram, whilst on the downward stroke of the ram a spring G pulls the plunger G back again in readiness for the next feed stroke. A skirt F iscarried by the ram beneath the feed opening F to prevent any ingress of dust from the powder into the shroud tube D.

It will be appreciated that other forms of powder feed mechanism may be used.

At its lower end (see Figure 4) the tubular ram F is provided with a preferably detachable head H having ports H in its wall, through which the powder can escape from the interior of the ram through a feed opening C which may consist of a continuous annular opening surrounding the operative lower end of the ram head within the sheath tube C or may be divided into a number of separate arcuate openings. The lower end of the ram head is closed by a plate having apertures through which the core rods C can pass freely, and a disc H is clamped beneath such plate by a clamping ring H This disc H is provided with guide apertures closely fitting the core rods C and is made of a material to which the core rods will not adhere or seize as they slide through the guide apertures.

Suspended by hooks K which engage into the lateral ports H in the wall of the ram head H so as to hang on the apertured plate closing the lower end of the head, is a valve ring K, which fits within the sheath tube C with slight clearance. The valve ring K is thus free to move up or down to close or to open the annular feed opening C around the ram head. The inner surface of the valve ring K is formed with a pair of opposed conical surfaces K K of which the upper K serves as a guide surface to direct the powder from the feed opening C in a downward and inward direction and also as a valve seating for engagement with the peripheral edge of the clamping ring H on the ram head, such edge preferably being given a slight chamfer so as to engage properly with the conical surface K but only over a small area. The shape of the cooperating parts of the valve is such as to minimise risk of jamming of the valve by a coarse particle of the powder and also to assist in the proper centering of the parts, as more fully described in the specification of the copending application Serial No.

4 177,199, filed August 2, 1950, above mentioned, which also describes various alternative valve arrangements.

The lower end of the shroud tube D is cut with slits D to give it slight flexibility, and a liner D of friction material, which may be similar to that commonly used for friction brake linings, is fitted in segments within the split end of the shroud tube D to fit closely around the sheath tube C. The pressure exerted by this liner D on the surface of the sheath tube C is controlled by means of a ring I surrounding the shroud tube D and having internal studs 1 engaging with the surface of the shroud tube. One of such studs J is adjustably mounted in the ring I and can be screwed in or out by means of a handwheel 1 so as to clamp more tightly or to loosen the grip of the liner D on the sheath tube C.

In operation, when it is desired to insert a new length of sheath tube for filling, this tube, after thorough cleaning of its inner and outer surfaces, is let down into the well B until its upper end is below the lower end of the shroud tube D and the ram F. The sheath tube C is then slipped over the end of the ram within the liner D and raised (the friction grip at this stage having been loosened), until the lower end of the sheath tube is only a short distance below the lower end of the ram. The core rods C after thorough cleaning, are then pushed up through the guide apertures in the disc H (after fitting the valve ring K in position on the ram head), their lower ends being firmly secured to an anchoring plug C which fits over the lower end of the sheath tube C and is clamped thereto at C. This plug C thus seals the lower end of the sheath tube C, and it will usually be convenient to provide a packing wad C of asbestos or other suitable material against the inside of the plug C around the core rods C The friction grip handwheel J is now operated to tighten the grip and clamp the sheath tube firmly, and the pneumatic driving device and the percussion device are set into operation, insulating powder having been poured into the hopper G. At first the ram reciprocates idly, while a small quantity of powder is being fed into the sheath tube C. During each upward stroke of the ram, the plunger G pushes a charge of powder into the interior of the ram, and the powder falls down the ram and out therefrom through the ports H and the feed opening C into the bottom of the sheath tube. The percussion device L is meanwhile vibrating idly, but imparts a degree of vibration to the whole apparatus, which materially assists the downward flow of the powder. The powder thus gradually builds up on the packing wad C in the bottom of the sheath, tube until it comes in contact with the ram face at the bottom of the downward stroke thereof. The friction grip is then gradually slackened off to give the desired resistance value, while the ram compresses the small quantity of powder already in the sheath tube.

The valve will be open during the upward stroke of the ram, since the friction of the powder with the wall of the sheath tube just above the valve will be amply sufficient to open the valve, and in fact this frictional force will tend to pull the powder through the valve and thereby ensure good flow of the powder. During the downward stroke of the ram, the valve will close, probably at a fairly early stage in the downstroke owing to friction with the sheath tube, but in any event not later than the first engagement of the valve with the powder column in the sheath tube. The compressive thrust on the powder will then commence, and it should be mentioned that, although the valve ring projects beyond the central portion of the operative face of the ram head, the compressive thrust will be exerted, since in practice the powder flows fairly readily, not only by the valve ring in the peripheral region but by the whole end of the ram and valve unit, notwithstanding its irregular shape.

Thus, near the end of each downward stroke of the ram,

arsenic a compressive thrust is applied to the powder column in the sheath tube, and this exerts a resistance to the ram movement as the result of which the spring L yields and causes the percussion dev ice L to impart a succession of blows or impacts to the upper end of the ram, while the ram head remains in contact with the powder column. These hammer blows increase the compressive thrust on the powder and have the elfect of compacting it uniformly to a much higher degree of density than would be obtained by simple reciprocation of the ram at either high or low frequency. As the powder becomes more tightly packed, the compressive thrust increases until it finally exceeds the resistance of the friction grip, which will then yield to allow the sheath tube and core rods to slip and move with the ram to the end of the downward stroke thereof. The sheath tube is thus driven downwards a short distance at the end of each downward stroke of the ram, in a step-by-step movement into the well B. The hammer blows on the ram of course cease immediately the ram commences each upward stroke.

By suitably dimensioning the powder feed mechanism, the rate of powder supply can be so controlled that the sheath and the core rods are displaced downwardly through approximately the same distance during each downward stroke of the ram, the amount of slip being determined by the amount of powder compressed. In this way, a uniformly compacted column of powder is gradually built up in the sheath tube around the core rods.

Owing to the provisionof the valve, the amount of powder compressed during each downward stroke is properly controlled even if the feed into the top of the ram is uneven or not properly matched with the outflow at the bottom of the ram. The valve thus contributes materially towards ensuring a very even compression of the powder in the sheath tube.

When the sheath tube has been filled nearly to the top with powder and has therefore been moved down into the well nearly to its lowest position, the driving mechanism is stopped, and the friction grip is loosened toal'low the sheath tube to be pulled down clear of the lower end of the ram. The upper end of the sheath tube is then at once sealed, and the filled workpiece thus formed is withdrawn from the well B in readiness for its further treatment. This further treatment consists of one or more stages of mechanical drawing, with such intermediate annealing as may be necessary, until the sheath tube, core rods and insulation have been sufficiently elongated and reduced in cross-section to produce the final sheathed cable. The mechanical drawing, of course, also assists in the consolidation and compacting of the insulating powder and, following the initial compacting by the ram, ensures a very high and uniform density to the powder filling throughout the finished cable.

It will be understood that the foregoing arrangement has been described by way of example only and may be modified in various ways within the scope of the invention.

Thus, for instance, it is not essential to the invention for the apparatus to be mounted vertically provided that, if not suitable arrangements are made to ensure proper flow of the powder. Again, it is not essential for the powder to be fed to the sheath tube through the interior of the ram.

Further, the reciprocating drive and the hammer blows may both be applied in an alternative way, for example one may be applied to the sheath tube and the other to the ram as shown in Figure 5. It is not essential to the invention that there should be more than a single hammer blow during each reciprocation, provided the amount of powder fed to the sheath tube during each stroke is kept small.

What I claim as my invention and declare to secure by Letters Patent is:

1. The process of manufacturing an electric cable or other insulated conductor of the kind comprising a metal sheath separated from a conducting core or cores within it by pulverulent insulating material, which comprises the steps of feeding the insulating material in powder form to the interior of a sheath tube which will ultimately constitute the :said metal sheath, ramming the column of powder within the sheath tube by a relative reciprocating movement 'of two member-s constituted by the sheath tube and a ram within it, and superimposing on the reciprocating ramming movement at least one longitudinal impact applied to one of the two relatively reciprocating members during the period in each reciprocation when the ram is actually in contact with'thepowder column.

2. The process as claimed in claim 1 including the step of agitating the apparatus to promote the flow of powder to the sheath tube by maintaining the means for applying the said longitudinal impact in operation not only when such impact is operative but also during the period in each reciprocation when the ram is out of contact with the powder column.

' 3. The process as claimed in claim 1, including the step of causing step-by-step separating movement between the sheath tube and the ram within it to take place as the compressed powder column builds up within a sheath tube, one step of such movement taking place at each reciprocation.

4. The process of manufacuring an electric cable or other insulated conductor of the kind comprising a metal sheath separated from a conducting core or cores within it by pulverulent insulating material, which comprises the steps of feeding the insulating material in powder form to the interior of a sheath tube, and ramming the column of powder within the sheath tube by two superimposed relative reciprocating movements of the sheath tube and the ram within it, one of such movements having relatively low frequency and high amplitude and the other relatively high frequency and low amplitude.

5. The process as claimed in claim 4, including the step of causing step-by-step separating movement between the sheath tube and the ram within it to take place as the compressed powder column builds up within the sheath tube, one step of such movement taking place during each cycle of the relatively low frequency reciprocation.

6. The process as claimed in claim 4, including providing lost motion in the relatively high frequency reciprocation whereby it is effective for ramming only during those parts of the relatively low frequency reciprocations wherein a compressive thrust is being applied to the powder column in the sheath tube, the remaining parts of the high frequency reciprocation alfording agitation to promote the flow of powder into the sheath tube.

7. Apparatus for manufacturing an electric cable or other insulated conductor of the kind in which a metal sheath is separated from a conducting core or cores within it by pulverulent insulation, comprising means for feeding the insulating material in powder form to the interior of a sheath tube, a ram within the sheath tube, driving means for imparting relative longitudinal reciprocating movement to the ram and the sheath tube whereby the ram is caused to apply a compressive thrust to the column of insulating powder in the sheath tube during part of the reciprocating movement, and a percussion device operatively connected to one of the two elements comprising the ram and the sheath tube for subjecting said element to at least one longitudinal impact during each period when the ram is actually in contact with the powder column in the sheath tube.

8. Apparatus as claimed in claim 7, including a frictional device which yields at a predetermined stage in the relative longitudinal movement between the ram and the sheath tube and thereby terminates such relative movement.

9. Apparatus for manufacturing an electric cable or other insulated conductor of the kind in which a metal sheath is separated from a conducting core or cores with- 7 in it by pulverulent insulation, comprising a ram within the sheath tube having at least one feed opening in its head, means for feeding the insulating material in powder form into the interior of the sheath tube through said opening, a valve controlling the flow of the powder through said opening, driving means for imparting relative longitudinal reciprocating movement to the ram and the sheath tube whereby the ram is caused to apply a compressive thrust to the column of insulating powder in the sheath tube during part of the reciprocating movement. and a percussion device operatively connected to one of the two elements comprising the ram and the sheath tube for subjecting said element to at least one longitudinal impact during each period when the ram is actually incontact with the powder column in the sheath tube. r

10. Apparatus as claimed in claim 9, wherein the valve comprises a part carried by the ram head, and a cooperating relatively movable part so suspended from one of the two elements comprising the ram and the ram head as to be free to move longitudinally relatively thereto.

11. Apparatus as claimed in claim 9, including a frictional device which yields at a predetermined stage in the elative longitudinal movement between the ram and the sheath tube and thereby terminates such relative movement.

12. Apparatus for manufacturing an electric cable or other insulated conductor of the kind in which a metal sheath is separated from a conducting core or cores within it by pulverulent insulation, comprising means for feeding the insulating material in powder form to the interior of a sheath tube which will ultimately constitute the said metal sheath, a ram within the sheath tube, driving means for imparting longitudinal reciproeating movement to the ram whereby the ram is caused to apply a compressive thrust to the column of insulating powder in the sheath tube during part of the reciprocating movement, and a percussion device operatively connected to the ram for subjecting the ram to at least one longitudinal impact during each period when the ram is actually in contact with the powder column in the sheath tube.

13. Apparatus as claimed in claim 12, wherein the ram has at least one feed opening in its head, including means for feeding the powder into the interior of the sheath tube through said opening, and a valve controlling the flow of the powder through said opening.

14. Apparatus as claimed in claim 13, wherein the valve comprises a part carried by the ram head. and a cooperating relatively movable part so suspended from one of the two elements comprising the ram and the ram head as to be free to move longitudinally relativcly thereto.

15. Apparatus for manufacturing an electric cable or other insulated conductor of the kind in which a metal sheath is separated from a conducting core or cores within it by pulverulent insulation, comprising means for feeding the insulating material in powder form to the interior of a sheath tube, a ram within the sheath tube, driving means for imparting relative longitudinal movement to the ram and the sheath tube whereby the ram is caused to apply a compressive thrust to the column of insulating powder in the sheath tube, a lost motion device, a compression spring and a percussion device operatively connected through the lost motion device and the compression spring to one of the two elements comprising the ram and the sheath tube, the

compression spring yielding to permit the percussion device to deliver at least one longitudinal impact to the said element only when a compressive thrust is being applied to the powder column.

16. Apparatus as claimed in claim 15, including a frictional abutment which opposes the compressive thrust exerted by the ram on the column of insulating powder and yields when such thrust exceeds a predetermined value to permit the ram and the sheath tube to move together under the thrust.

17. Apparatus for manufacturing an electric cable or other insulated conductor of the kind in which a metal sheath is separated from a conducting core or cores within it by pulverulent insulation, comprising means for feeding the insulating material in powder form to ti: interior of a sheath tube, a ram within the sheath tube, driving means for imparting relative longitudinal reciprocating movement to the ram and the sheath tube at low frequency and high amplitude whereby the ram is moved into contact with the column of insulating powder in the sheath tube, and a percussion device operatively connected to one of the two elements comprising the ram and the sheath tube for subjecting said element to longitudinal impacts at relatively high frequency and low amplitude during the periods when the ram is actually in contact with the powder column.

18. Apparatus as claimed in claim 17, including a frictional abutment which opposes the compressive thrust exerted by the ram on the column of insulating powder and yields when such thrust exceeds a predetermined value to permit the ram and the sheath tube to move together under the thrust.

19. Apparatus for manufacturing an electric cable or other insulated conductor of the kind in which a metal sheath is separated from a conducting core or cores within it by pulverulent insulation, comprising means for feeding the insulating material in powder form to the interior of a sheath tube, a ram within the sheath tube, driving means for imparting relative longitudinal reciprocating movement to the ram and the sheath tube whereby the ram is caused to apply a compressive thrust to the column of insulating powder in the sheath tube during part of the reciprocating movement, a percussion device operatively connected to one of the two elements comprising the ram and the sheath tube for subjecting said element to at least one longitudinal impact during each period when the ram is actually in contact with the powder column in the sheath tube, and means whereby the successive compressive thrusts applied to the powder column cause step-by-step relative separating movement between the ram and that sheath tube to take place as the powder column compressed by the ram builds up within the sheath tube.

References Cited in the file of this patent UNITED STATES PATENTS 1,547,336 Lightfoot et al July 23, 1925 l,897,6l2 Helfrecht Feb. 14, 1933 2,033,735 Pack Mar. 10, 1936 2,277,321 Harris Mar. 24, 1942 2,445,035 Munger July 13, 1948 FOREIGN PATENTS 456,323 Great Britain Nov. 6, 1936

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