US2884660A - Manufacture of electric cables or other insulated electric conductors - Google Patents

Description

May '5, 1959 Filed March 19, 1956 5 Sheets-Sheet 1 Inven'tbr JAMES A. AUS TIN W, Attorneys y 1959 J. A. AUSTIN 2,884,660

MANUFACTURE OF ELECTRIC CABLES OR OTHER INSULATED ELECTRIC CONDUCTORS 5 Sheets-Sheet 2 Filed March 19', 1956 W Attorneys May 1959 J., A. AUSTIN I 2,884,660

MANUFACTURE OF ELECTRIC CABLES OR OTHER INSULATED ELECTRIC CONDUCTORS Filed March 19, 1956 5 Sheets-Sheet 3' Inventor JAMES A. AUS TIN y I M W X Att0mey5 May 5, 1959 J. A. AUSTIN 2,884,660

MANUFACTURE OF ELECTRIC CABLES OR OTHER INSULATED ELECTRIC CONDUCTORSY Filed March 19, 1956 5 Shets-Sheet 4 lnven tor JAMES A. AUSTIN y WM, d/M Attorney:

May 5, 1959 J. A. AUSTIN MANUFACTURE OF ELECTRIC CABLES OR OTHER INSULATED ELECTRIC. CONDUCTORS 5 Sheets-Sheet 5 Filed March 19, 1956 lnvento r JAMES A. AUSTIN WM, Attorneys United States Patent MANUFACTURE OF ELECTRIC CABLES OR OTHER INSULATED ELECTRIC CONDUC- TORS James Alexander Austin, Whitley Bay, England, assiguor, by mesne assignments, to Association en Participation pour le Developpement du Pyrotenax Aux U.S.A., Paris, France, a French company Application March 19, 1956, Serial No. 572,316 Claims priority, application Great Britain March 12, 1956 12 Claims. (Cl. 185) This in vention relates to apparatus for manufacturing an electric cable or other insulated conductor of the kind comprising a metal sheath separated from a conducting core or cores by pulverulent insulating material, such for example as magnesia, and in particular to apparatus 0 The present invention has for its object to effect im- 4 provements in such apparatus and more especially in the control of the powder feed into the sheath tube.

The apparatus, according to the present invention, includes a powder-feeding appliance comprising a valve device for controlling the feed of powder into the sheath tube, and a relay device operated in accordance with the relative reciprocations of the sheath tube and the ram, such relay device acting to control the valve device so that the feed of powder is substantially prevented during that portion of the period of the cycle of reciprocation during which powder is being compressed.

Preferably, the valve device controls an opening through which powder can be fedfrom a powder supply into a chamber from which it is fed into the sheath tube by forward movement of a plunger, and such plunger may itself constitute the movable member of the valve device. The action of the relay device may be such that, during the major portion of each cycle of reciprocation, the plunger is maintained substantially in its foremost position, thus substantially closing the powder feed opening.

The plunger may be driven by means of a double-acting cylinder and piston, the relay device acting to control the fluid supply to such cylinder. Thus, the relay device may include a control valve wherein the fluid flow is controlled by means of a pivoted arm operated in accordance with the relative reciprocations of the sheath tube and the ram.

The powder-feeding appliance preferably includes a hand-operated adjustment device for controlling the movement of the plunger, whereby the quantity of powder permitted to enter the chamber, and fed into the sheath tube by each forward stroke of the plunger, can be varied. Means may be provided whereby such adjustment device can be locked in a chosen position of adjustment. The adjustment device may conveniently comprise a movable part for varying the axial position of the end wall at the rear end of the cylinder, whereby the terminal position of the plunger at the end of each backward stroke can be varied.

A further double-acting piston and cylinder are preferably provided for causing the relative reciprocations of the sheath tube and the ram, together with valve gear operated by the relative movements of the piston and cylinder for alternately connecting the fluid supply to the 2,884,660 Patented May 5, 1959 ice two ends of such cylinder. Such valve gear may control the fluid supply to the cylinder and piston driving the plunger.

The invention may be carried into practice in various ways, but two alternative constructions of cable manufacturing apparatus according thereto will now be described with reference to the accompanying drawings, in which Figure 1 is a front view of the main parts of the apparatus, to which the alternative constructions of powderfeeding appliance are applied,

Figure 2 is a side view of the apparatus showing part of one construction of powder-feeding appliance,

Figure 3 is an enlarged view, in axial section, of the lower part of the apparatus of Figure 1,

Figure 4 is an enlarged view, in axial section, of the upper part of the apparatus showing one construction of powder-feeding appliance, and

Figure 5 is a view corresponding to that of Figure 4 and showing a modified construction of powder-feeding appliance.

Referring to the construction of Figures 1 to 4, 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 C 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 surface B is a fixed shroud tube D, which is in alignment with the well B and is likewise of a length to house the sheath tube C within it, a fixed eye B carried on a pillar B upstanding from the ground, being provided to ensure that the shroud tube remains in alignment with the well B. The same bracket A also serves to carry upwardly projecting bars A for supporting a driving machine, which may consist for instance of an electric motor or (as shown) of a double acting 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 fed from a source of compressed air (not shown). The valve E is driven through reduction gearing E from a small electric motor E mounted on the gallery A, the arrangement being such that the two pipes E 13 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 E being opened by the valve E to exhaust into the atmosphere. The piston E 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 through the pipes E and E the cylinder being guided by means of arms E whose lower ends cooperate with a spindle F which runs in vertical slots A in the supporting bars A and is connected to a tubular ram 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 take various forms but in the example illustrated consists of a pneumatic hammer L supplied with compressed air through a pipe L controlled by a valve 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 E 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 F, which is provided at itsupper end with a pair of feed openings F for this purpose. The powder is fed intothe ram by means of a powder-feeding appliance to be described later.

Conveniently, as shown in Figure 3, the ram head at the lower end of the ram H is detachable and has 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.

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 J 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 J so as to clamp more tightly or to loosen the grip of the liner D on the sheath tube C.

One construction of appliance for feeding powder into the openings F in the ram F is shown in Figure 4.

The powder is stored in two similar sealed hoppers M, on opposite sides of the main apparatus, each hopper opening into a downwardly extending supply passage M formed in a hopper block M carrying the hopper, the two hopper blocks M being mounted on opposite sides of a collar M on the upper end of the ram F. Each supply passage M opens into a chamber M formed within the hopper block M such chamber extending transversely across the block towards the ram F to permit the passage of a plunger N which, on its forward stroke, pushes powder out of the chamber on the side adjacent to the ram into a short passage M through the collar M connecting with one of the openings F in the wall of the ram. Each plunger N fits fairly closely within its chamber M so that the chamber is completely emptied of powder by each forward stroke of the plunger, and in its foremost position, the plunger completely shuts off the flow of powder from the hopper by blocking the opening M from the passage M into the chamber M so that the cooperation of such opening and such plunger constitute in effect a valve controlling the powder feed.

In its rearmost position, i.e. its position at the commencement of a forward stroke, the plunger N may leave such opening M partially or completely clear, so that the quantity of powder entering the chamber M and fed into the sheath tube by the next forward stroke, is determined by such rearmost position of the plunger.

Each plunger N is driven by a piston N and cylinder N the latter of which is fixed relatively to the adjacent hopper block M so that the pistons and cylinders, together with the hoppers M and the hopper blocks, all reciprocate with the ram F. The piston N is coupled to the plunger by a .piston rod N passing through the front end wall of the cylinder, and the fluid supply to such cylinder N is controlled by means of a relay device which consists of a piston valve P operated in a manner to be described later.

At its rear end the cylinder N is closed by a plug N movable axially therein by means of a tubular cap N which fits over this end of the cylinder in screwthreaded engagement therewith, so that by rotating the cap, the rear end Wall of the cylinder constituted by the plug N can be moved along the axis of the cylinder. The position of the rear end wall of the cylinder N determines the terminal position of the piston N at the end of each backward stroke, and thus the position of the plunger N at the end of each backward stroke, whereby, since the latter determines the quantity of powder entering the hopper block chamber M in the manner previously described, the movable cap member N provides a convenient adjustment device for varying the quantity of powder fed into the interior of the ram F by each plunger stroke. The tubular cap N is provided with a spoke handle N for rotating the cap by hand, and a forked lever arm N", pivoted on a bracket N carried by the front end of the cylinder N is arranged so that its forked end can be swung over the spoke handle to lock the tubular cap in a chosen position of adjustment.

The piston valve P comprises a piston P sliding within a casing P having an inlet port P connected through a pipe P to a fluid supply such as a compressed air source, and two exhaust ports P Two further ports P and P", respectively connected through pipes P and P to the rear ends and to the front ends of the plunger cylinders N are also provided in the casing P and the piston P has internal passages controlling the connections of these ports to the inlet port P and the exhaust ports P the arrangements being such that in each operative position of the piston one of the ports P P is connected to the inlet port and the other to an exhaust port. The piston P is operated by a trip arm Q pivoted to the valve casing P and actuated by a projecting lug Q on the reciprocating ram cylinder E, a spring Q being provided to bias the piston P normally into the position in which the port P communicating with the rear ends of the plunger cylinders N is connected to the inlet port P and the port P communicating with the front ends of such cylinders is connected to exhaust.

Thus, normally the feed plungers N occupy their most forward positions in Which the feed of powder from the hoppers M is prevented. During the downstroke of the ram, the lug Q strikes the trip arm Q in a direction which has no efiect on the valve piston P and moves past the trip arm, which at once drops back to its normal position. At an appropriate point during the upstroke of the ram, however, the lug Q strikes the trip arm Q in the opposite direction and thereby forces the piston P into its other operative position, in which compressed air is supplied through the pipe P to the front ends of the plunger cylinders N the rear ends thereof being connected to exhaust. The feed plungers N are therefore withdrawn to their rearmost positions and powder is fed through from the hoppers M into the chambers M When the lug Q has moved past the trip arm Q, the piston P is released and moves back to its normal position under the action of the spring Q This again reverses the air supply to the plunger cylinders N so that the plungers N are moved forward to drive the charge of powder into the ram and again to cut off powder feed from the hoppers. Thus, at a chosen point during each upstroke of the ram, powder is fed into the ram, but at all other times, including the whole of each downstroke of the ram, the powder feed is positively prevented.

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 ramv 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 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 hoppers M. 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 plungers N push 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.

Thereafter, the apparatus will operate in the following continuous and uniform manner. During each upstroke of the ram F, the valve in the ram head H will open to permit the flow of powder into the sheath tube from the interior of the ram. Also during the upstroke, the powder feed plungers N will complete, in comparatively quick succession, a backward and then a forward stroke, the latter of which will feed the powder which has entered the chamber M into the ram F through the openings F such powder thereafter falling down the ram and passing through the ports H of the ram head H. During each downward stroke, and before the ram head H first comes into contact with the powder in the sheath tube C, the valve in the ram head H will close and thereafter the compressive thrust on the powder in the sheath tube will commence. It is important that, as described earlier, no powder is fed into the ram F during the downstroke, or more particularly, during the period during which the powder is being compressed, since such powder may itself tend to become compacted above the ram [head H and cause jamming of powder. Again, such powder may tend to escape upwards between the ram F and the sheath tube C, and cause the ram to jam during a later downstroke. However, it will be appreciated that, with the powderfeeding appliance previously described, should the ram become jammed in this or any other manner, further powder feed will be positively prevented since the powder feed openings M will remain completely shut off by the plungers N.

Thus, near the end of each downstroke of the ram, a compressive thrust is applied to the powder column in the sheath tube, and this exerts a resistance to the rain movement as the result of which the spring L yields and causes the percussion device L to impart a succession of blows or impacts to the upper end of the ram, while the ram head remains in contact wtih the powder column. These hammer blows increase the compressive thrust on the powder and have the effect 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 stepby-step movement into the well B. The hammer blows on the ram of course cease immediately the ram commences each upward stroke.

The hand control adjustment device is adjusted to control the amount of powder fed into the ram, this amount being chosen in accordance with the diameter of the sheath tube and the number of core rods. Since the amount of powder fed into the ram openings F by each forward stroke of the plunger N remains constant after such adjustment has been effected, and substantially the whole of such amount fed passes through the ram head H during each upward stroke of the ram, the sheath and core rods are displaced downwardly by the same distance during each downward stroke of the ram, the amount of slip being determined by such amount of powder fed. The degree of compactness of the powder in the sheath tube is determined by the adjustment of the friction grip, and it will often be convenient to provide a remote control for the friction grip for operation from the gallery A so that the same operator can control both the grip and the powder feed in order to suit them one to the other.

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 to allow 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 work piece thus formed 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 sufiiciently 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.

An alternative construction of powder-feeding appliance is shown in Figure 5. The arrangement of hoppers M, hopper blocks M plungers N and pistons N and cylinders N for driving such plungers is similar to that described previously, but the fluid supply for "such powder feed cylinders N is controlled by valve gear which is also the valve gear controlling the fluid circuit of the reciprocating ram cylinder C, and for simplicity, this circuit will be first described.

The main fluid supply for the ram cylinder E is fed to a follower valve R, through which the direction of fluid flow is controlled by the rocking of a centrally pivoted member R in a chamber R in the lower part of the valve. The connections to the ram cylinder E are made through flexible pipes R since such cylinder is a reciprocating member. The ram cylinder E is provided with two spring tappets S adjustably mounted on two brackets S respectively near the upper end and the lower end of the cylinder so that, as the cylinder reciprocates, the tappets S alternately elevate and depress the end of a rocker arm T pivoted on a control valve T, and determining the direction of fluid flow in such control valve. The control valve T has an inlet port T from a control fluid supply, an exhaust port T and two further ports-T connecting to two top ports R in the follower valve R, each such top port controlling the movement of one of two small piston rods R in the follower valve. The rocking of the arm T of the control valve T causes the top ports R of the follower valve R to be alternately opened to the control fluid supply, and alternately opened to exhaust, so that the piston rods R in the follower valve reciprocate in opposite phase. The piston rods R are arranged one on each side of the follower valve R, and extend into the chamber R in its lower part so that their ends alternately depress opposite sides of the centrally pivoted member R thereby causing its rocking action. The main fluid supply is connected to this chamber R in the follower valve R through a flexible pipe R and by means of the rocking member R the chamber is divided into two sections such that, while the member is depressed one way, one end of the ram cylinder E is connected to the main fluid supply and the other end of the ram cylinder is connected to exhaust, and while the member is depressed the other way, the opposite connections are elfected. The length or position of the reciprocating cylinder movement can be adjusted by moving one or both of the tappets S in a direction parallel to the cylinder axis on sleeves S provided on the cylinder brackets S for this purpose.

. As before, each powder feed cylinder N has two ports, one at the fixed front end, and one in the movable rear end wall, and flexible pipe connections are made to the ram cylinder fluid circuit so as to effect the reciprocations of the plungers in accordance with the ram movement. Thus, the front end port of one cylinder is connected to the pipe R supplying one end of the ram cylinder, while the rear end port of the other is connected to the pipe R supplying the other end of the ram cylinder. The other two ports of powder feed cylinders are connected to the two ports T of the control valve T, such connections being effected so that while the front end port of each powder feed cylinder N is connected to the fluid supply (one is connected to the control fluid supply and one is connected to the main fluid supply), the rear end port of each such cylinder is connected to exhaust, and while each rear end port is connected to the fluid supply, each front end port is connected to exhaust. Fluid flow conditions in the system may not be such that the powder feed plungers reciprocate in phase with the ram and preferably conditions are arranged so that each plunger N starts a backward stroke immediately after the completion of each compressive thrust of the ram F, in which case powder is fed down the ram at the beginning of each downstroke of the ram F, While the valve in the ram head H is still open to permit powder to flow into the sheath tube, whereby, since the time taken by the plunger N substantially to complete its stroke is much less than that taken by the ram F, very little powder will be left above the ram head H after the valve in such head has closed, and no powder will be fed into the'ram thereafter during the compression stroke, so that the risk of powder being compacted above such ram head H is minimised, .as in the previous arrangement.

It is to be appreciated that the constructions of apparatus above described are by way of example only, and the various modifications are possible, both to the powder-feeding appliance and to the other apparatus therein, with the scope of the invention. Thus, in the powder-feeding appliance, the valve device controlling the feed of powder may include a movable member other than the plunger for shutting 01f the powder supply passage, such member being controlled by the relay device, which may be operated for example electromagnetically instead of pneumatically. Again, the hand control adjustment of the amount of powder feed may be effected in other ways, such for example as moving each plunger cylinder bodily with respect to the plunger chamber. In respect of the rest of the apparatus used in the manufacture, such apparatus may be mounted horizontally or inclined at an angle, suitable arrangements being made to ensure proper flow of the powder. Again, the reciprocating drive may be applied to the ram, the friction grip then being applied to the ram instead of the sheath tube. Furthermore, the powder may be fed into the sheath tube down the outside of the ram and within the sheath tube, in which case the powder feeding appliance can be carried by a fixed framework mounted on the supporting superstructure.

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

1. Apparatus for manufacturing an electric cable or other insulated conductor of the kind in which a metal sheath is separated from a core or cores within it by insulating powder, comprising a sheath tube sealed at its lower end, a ram passing through the upper end of the sheath tube and having a head within the sheath tube, means for imparting relative longitudinal reciprocating movement to the sheath tube and the ram, the length of stroke of such reciprocating movement being small in comparison with the length of the sheath tube, a powder feeding appliance comprising a valve device for controlling the feed of powder to the upper end of the sheath tube above the ram head, means in the ram head for permitting such powder to flow past the ram head into the lower end of the sheath tube wherein it is compressed by the relative reciprocations of the sheath tube and the ram, a relay device, means for causing such relay device to operate in accordance with the relative reciprocations of the sheath tube and the ram, and means for operating the relay device to cause the valve device substantially to prevent the feed of powder into the upper end of the sheath tube during that portion of each cycle of reciprocation during which the powder in the lower end of the sheath tube is being compressed.

2. Apparatus as claimed in claim 1, in which the powder feeding appliance includes a powder chamber, a passage having an opening into such chamber through which powder is fed into the chamber, a plunger cooperating with such opening to constitute the valve device, and means for causing reciprocation of the plunger whereby, on the forward stroke thereof, powder is fed from the chamber into the upper end of the sheath tube.

3. Apparatus as claimed in claim 2 having a hand operated adjustment device and means whereby such adjustment device acts to control the stroke of the plunger, whereby the quantity of powder permitted to enter the plunger chamber, and fed into the upper end of the sheath tube by each forward stroke of the plunger, can be varied.

4. Apparatus as claimed in claim 3 having means whereby the hand operated adjustment device can be locked in a chosen position of adjustment.

5. Apparatus as claimed in claim 2, in which the means for causing the reciprocation of the plunger comprise a cylinder, a piston within the cylinder, means connecting the piston with the plunger, a fluid supply source, and means whereby the relay device connects such source alternately to opposite ends of the cylinder.

6. Apparatus as claimed in claim 2, in which the means for causing reciprocation of the plunger comprise a cylinder, a piston within the cylinder, means connecting the piston with the plunger, and a fluid supply source, and the relay device includes a control valve, a pivoted arm operated in accordance with the relative reciprocations of the sheath tube and the ram, and means whereby the movements of the pivoted arm cause the control valve to connect the fluid supply alternately to opposite ends of the cylinder.

7. Apparatus as claimed in claim 1, in which the means for imparting relative longitudinal,reciprocations to the sheath tube and the ram comprise a cylinder, a piston within the cylinder, a fluid supply source, a follower valve acting to connect such fluid supply alternately to opposite ends of such cylinder, and means whereby the operation of the follower valve is controlled by the relay device.

8. Apparatus for manufacturing an electric cable or other insulated conductor of the kind in which a metal sheath is separated from a core or cores within it by insulating powder, comprising a sheath tube sealed at its lower end, a ram passing through the upper end of the sheath tube and having a head within the sheath tube, means for imparting relative longitudinal reciprocating movement to the sheath tube and the ram, the length of stroke of such reciprocating movement being small in comparison with the length of the sheath tube, a powder feeding appliance comprising a powder chamber, a passage having an opening into such chamber through which powder is fed into the chamber, a plunger controlling the powder feed through such opening, means for causing reciprocation of the plunger whereby, on the forward stroke thereof, powder is fed from the chamber into the upper end of the sheath tube above the ram head, means in the ram head for permitting such powder to flow past the ram head into the lower end of the sheath tube wherein it is compressed by the relative reciprocations of the sheath tube and the ram, a relay device, means for causing such relay device to operate in accordance with the relative reciprocations of the sheath tube and the ram, and means for operating the relay device to maintain the plunger in a position in which it cuts oflf the powder feed into the upper end of the sheath tube during the major portion of each cycle of reciprocation including that portion in which the powder in the lower end of the sheath tube is being compresed.

9. Apparatus as claimed in claim 8, in which the means for causing reciprocation of the plunger comprise a cylinder, a piston within such cylinder, means connecting the piston with the plunger, a fluid supply source, and means whereby the relay device connects such source alternately to opposite ends of such cylinder.

10. Apparatus as claimed in claim 9, in which the relay device includes a control valve, a pivoted arm operated in accordance with the relative reciprocations of the sheath tube and the ram, and means whereby the movements of the pivoted arm cause the control valve to connect the fluid supply source alternately to opposite ends of the cylinder.

11. Apparatus as claimed in claim 8 having a hand operated adjustment device and means whereby such hand operated adjustment device acts to control the stroke of the plunger, whereby the quantity of powder permitted to enter the chamber and fed into the upper end of the sheath tube by each forward stroke of the plunger can be varied.

12. Apparatus as claimed in claim 8, in which the means for causing reciprocation of the plunger comprise a cylinder, 3. piston within such cylinder, means connecting the piston with the plunger, a fluid supply source, means whereby the relay device connects such source alternately to opposite ends of such cylinder, and means for adjusting the axial position of the rear end wall of the cylinder whereby the terminal position of the plunger at the end of each backward stroke can be varied.

References Cited in the file of this patent UNITED STATES PATENTS 2,404,559 Ashbaugh July 23, 1946 2,431,843 Swoger Dec. 2, 1947 2,738,910 Clothier Mar. 20, 1956 FOREIGN PATENTS 165,579 Austria Oct. 12, 1955

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