US2947652A - Electric cables - Google Patents

Description

Aug. 2, 1960 H. BURR 2,947,652

ELECTRIC CABLES Original Filed Dec. 18, 1950 3 Sheets-Sheet 1 INVENTOR. H. BUB/P Aug. 2, 1960 H. BURR 2,947,652 ELECTRIC CABLES Original Filed Dec. 18, 1950 3 Sheets-Sheet 2 FIG. 3.

IN V EN TOR.

ATTORNEY H. BURR ELECTRIC CABLES Aug. 2, 1960 3 Sheets-Sheet 3 Original Filed Dec. 18, 1950 FIG. 6.

FIG. 7.

INVENTOR. H. BU/PE ATTORNEY Ute iateg P ELECTRIC CABLES Harvey Burr, London, England, assignor to International Standard Electric Corporation, New York, N.Y., a corporation of Delaware Original application Dec. 18, 1950, Ser. No. 201,348,

now Patent No. 2,810,011, dated Oct. 15, 1957. Divided and this application Mar. 8, 1957, Ser. No. 646,188

Claims priority, application Great Britain Dec. 23, 1949 3 Claims. (Cl. 154'2.24)

, This invention relates to the manufacture of electric cables and has particular reference to multi-conductor telephone cables.

This application is a division of my copending application, Serial No. 201,348, filed December 18, 1950, for Electric Cables, now Patent No. 2,810,011. a

The basic unit of one form of conventional telephone cable is usually the twisted pair of paper insulated conductors. Such twisted pairs are usually made by first applying a helical lapping of paper tape to each Wire and then twisting the insulated wires together. This process involves two separate operations and moreover the speed is limited by the fact that there is a limit to the speed at which the paper insulation can be applied without breaking. Careful handling is necessary to avoid stripping off the insulation.

Numerous attempts have been made to avoid applying the paper as a helical lapping but they have notbeen found completely satisfactory.

It is also known to insulate a pair of wires simultaneously by passing the wires and an insulating tape through a bath of molten insulating compound while the tape is being folded around the wires. This wrapping holds the wires in position as it passes into a cooling bath where the insulating compound solidifies. This is essentially a very low speed process, slower than the conventional method of lapping a tape helically around each wire individually. Moreover the thickness of insulation around the wires is considerable and the presence of the insulating compound renders the wire unsuitable for use in telephone cable.

There is also known a process of applying an insulating strip in the form of an 8 about a pair of conductors leaving air space between each conductor and surrounding strip. In this type of process the insulating strip is necessarily made of stiff insulating material because the material retains its S-fold without requiring heat or adhesives to fix the fold. This type of insulation about a pair of wires is unsatisfactory because the wires are unsupported in the surrounding airspace and the electrical characteristics of the pair Varies to such anextent along the length of the pair that a cable made up of a piurality of such pairs would be completely unsatisfactory for telephone purposes. In addition, each pair occupies a greater space than a pair in the normal type of cable and thus, the construction would lead to an increase in cable diameter which is costly, as well as, space consuming.

An object of the present invention is to provide means by which two wires forming a pair can be simultaneously insulated to form a compact pair useful in multi-conductor telephone type cable. Another object is to provide such means which enables the two wires to be simultaneously insulated and to be twisted immediately thereafter.

According to a feature of the present invention the two wires to form the pair are passed through a die through which there is also passed a strip of insulating 2,947,652 Patented Aug. 2, 1960 ice material wide enough to provide at least one turn round each wire, the die being so shaped that the Wires are gradually brought closer together and the said strip is rolled around the two wires. The invention will be understood from the following description taken in conjunction with the accompanying drawings from which it will be appreciated that the invention comprises an improved process and apparatus for insulating electrical conductors particularly for the manufacture of communication cables.

in the drawings:

Fig. 1 is a purely diagrammatic representation of the apparatus for carrying out the process according to the invention.

Fig. 2 illustrates diagrammatically a portion of one form of insulated pair cable according to the invention.

Fig. 3 represents a detail of the apparatus.

Fig. 4 represents in simplified form the insulating die for carrying out the process.

Fig. 5 represents in perspective a practical form of die.

Fig. 6 shows in greater detail one construction of die.

-Fig. 7 shows in detail another construction of die.

In Fig. 1 conductor wires 1, 2 are supplied from reels not shown and passed around two pulleys 3, 4 which are braked by means of friction belts 5, 6 the tension of which is controlled by weights 7, 8. The two wires then pass through a guide member 9 through which there are two channeis guiding the wires so that they will approach the insulating die 10 at the correct angle. The strip of paper 11 is supplied from a reel, not shown, and passes directly into the guide member 9 which ensures that it is fed into the insulating die 10 correctly.

The only function of guide member 9 is to assemble the paper strip and the wires correctly for feeding into the insulating die. In Fig. 3 there is shown a cross section of the guide member 9 which will be referred to later.

Fig. 2 shows on an enlarged scale a portion of an insulated pair of wires produced by the process. The two wires 1 and 2 are insulated by an S shaped Wrapping of paper 12 of which one side carries distinguishing marks as shown. It can be seen that the wires are insulated from one another and that the inner edges of the insulating paper are held down by the outer turn of paper so that the two wires are completely covered. Returning now to Fig. l. After the two wires and the strip of paper have passed through the guide member 9 they pass to the insulating die 10 which will be described in more detail below. In this die the paper is wrapped round the two wires in the 8 formation shown in Fig. 2. It is to be mentioned that if desired more turns can be wrapped around the wires than the one and a half turns shown in Fig. 2.

The die 10 is heated as is conventionally indicated in Fig. 1, by a Bunsen burner 13. As explained earlier this heating facilitates the passage of the paper through the die. The paper, which is somewhat hygroscopic, is passed in an undried condition and therefore contains considerable moisture. It is believed that the evaporation of the moisture from the pores of the paper results in the production of a vapour cushion which enables the paper to be drawn through a well shaped die at high speed. In practice the'temperature of the die is fairly accurately controlled according to the conditions obtaining by means of a thermostat, but a temperature of 220 C. represents an average value which has been found satisfactory. The presence of the water vapour also produces an ironing effect so that the coating of insulation is smooth and retains its shape. After the insulated pair emerges from the die 10 it passes round the draw ofi capstan 14 which is suitably mounted on a supclear.

port 15 and driven by a motor, not shown. It can be seen that the tension on the wires between the pulleys 3, 4 and the capstan 14 is determined by the friction exerted by the belts 5, 6 and can'therefore be controlled by the correct selection of the weights 7, 8.

This tension is important as it is desirable to apply the insulation while the wire is slightly extended so that after the insulated pair leaves the capstan 14 the wires will contract slightly with the result that the paper insulation will not be under tension. This provides a margin so that the paper will not be so taut that it is liable to break if the insulated pair is bent or stretched during the subsequent operations involved in twisting and laying the insulated pairs up intocable form. After the insulated pair leaves the capstan 14 it passes round a tensioningdevice before being wound onto the take up drum 17. The obiect of the tensioning device is simply to ensure that there is enough tension on the pair to cause the pair to wind correctly on 'the drum. It is important that the tension on the pair after it leaves the capstan should be less than that on the pair before it reaches the capstan as explained above. The form of tensioning device 16 shown is suitable because it does not allow the tension to increase suddenly owing to any irregularities in the rotation of the take up drum 17.

It is usually desirable to twist the pair before it is laid up into a cable both for electrical reasons such as the reduction of cross talk and also to eliminate any tendency for the wires to roll against and unwind the insulation. For this purpose the take up drum 17 is mounted in a twisting yoke 18 which can be rotated about an axis coinciding with the line of approach of the insulated pair.

This twisting yoke 18 is geared to the drive of the capstan 1 and the gearing can be set to provide the precise twist length required.

Referring to Fig. 3 the guide member 9 consists of two metal blocks 1?, 20 provided with grooves 21, 22 through which the wires 1, 2 (see Fig. 1) pass. These grooves 21, 22 which are also indicated in Fig. 1, lead the wires along approaching paths while a strip of paper 11 passes through a rectangular channel 23 formed by the shaping of the metal blocks 19 and 26. The channel 23 is in practice only a narrow slit accommodating a strip of thin insulating paper 11 but it has been shown on a rather exaggerated scale to make the arrangements The slit is however appreciably wider than the thickness of the paper to allow for irregularities. The blocks 19, 20 are held together by screws 24, 25. After the wires and paper have passed through the guide member 9 they next enter the insulating die 10 where the.

process of wrapping the paper longitudinally about the wires takes place.

Fig. '4 illustrates diagrammatically the principle of the insulating die. In Fig. 4(a) there is shown the intake end of the die there being two apertures 26 connected by a narrow slit 27. At the output end of the die shown in Fig. 4(b) the two aperatures 26 are so close together that the slit has virtually vanished. Fig. 4(c) is a plan view of the die showing the two channels 26 converging. The diameter of the channels 26 is gradually slightly increased as they come closer together since a little more space is required as the paper is wrapped round the wires.

In Fig. there is shown an exploded view of a prac- The blocks 28 and 29' have arcuate grooves.

30 and 31 have grooves 34 and 35 cut along their appropriate edges. 7 7

It is to be noted that none of the blocks 28, 29, 30, 31 have the general form of rectangular'parallelepipeds. Block 28 is wider at its distant end (as shown) than at its near end, and this is also true of block 31. Blocks 29 and 39 are wider at their near ends than at their distant ends. When these two parts, Figs. 5(a) and (b) are brought together the grooves 32 and 33 form with grooves 34 and 35 respectively the channels 26 shown in Fig. 4 and the slit 27 is the space between surface 36 of block 29 and the under surface 37 of block 30 which surfaces it will be seen have been slightly cut away at 38 and 39 from the general level of the mating surfaces of the blocks 28, 29 and 3t 31 respectively. When the two parts of the die shown in Figs. 5(a) and (b) are brought together the actual die passage will be as shown in Fig. 4 and the external shape of the die will be, as drawn, a rectangular parallelepiped. The outer shape of the die is however of no importance in connection with the invention.

There are inevitably some irregularities in the paper and at times it will be necessary to make a join in the paper as for example when a supply reel is exhausted. It is necessary therefore to arrange the blocks forming the die in such a Way that they can separate slightly to allow a thickened portion of the paper to pass, and such an adjustment has to be rather delicate since the paper is fragile.

In Fig. 6 there is shown in more detail a die constructed with the general design described immediately above and illustrated in Fig. 5.

Blocks 28 and 29 are shown mounted on a base plate 40 and rigidly fixed together and to the base plate by a screw 41. Blocks 30 and 31 are rigidly fixed together by screw 42, but are slidable on the base plate. A spring 43 acting between a stop member 44 and the top of the unit formed of blocks 30 and 31 keep the unit pressed against the base plate. Another spring 45 acting between a stop member 46 and the side of the unit formed of blocks 30 and 31 keep the unit pressed up against the unit formed of blocks 28 and 29. The stop members 44 and 46 are made adjustable so that the pressure exerted by the springs can be controlled.

It can be seen that if a place where the paper strip is thicker or wider than usual passes into the slit 27 the unit formed of blocks 30 and 31 can move upwards or sideways andthepaper will not be damaged. The entrance to the die may be slightly bell mouthed to enable the oversize paper to enter and cause the unit to move. The dieneed not however be built up of four blocks and in Fig. 7 there is shown a die formed of an upper block 47 mounted on a lower block 48. The passage through the die so formed may be of the same shape and proportions as that in the four block die of Figs. 5 and 6. It is however still desirable to allow for variations in the paper width and thickness and this necessitates designing the assembly so that the upper block 47 can move slightly with respect to the lower block 48 and this involves a somewhat different structure from that shown in Fig. 6.

I In Fig.7 the lower block 48 is rigidly fixed to a baseplate 49 which forms part of a rigid framework 50 by means of screws 51. The upper block 47 is slidably mounted on the block 48 as shown. It is held in position by a system of rods which allow it a limitedfreedom of movement.

7 Thus rods 52 are. rigidly held in the framework by engagement with the base plate 49 and the upper member of the frame 50 by the nuts 53.

Where the rods pass through block 47 however they are slightly smaller than the drillings through which they pass. Thus the upper block is only permitted a limited movementin the right and left direction as shown in the drawing. Similarly one or more rods 54 pass through one or more drillings in the block 47 which have a diameter slightly larger than that of rod 54. The rods are held firmly in position in the framework 50 by nuts 55. These rods 54 serve to limit the movement of block 47 in the up and down direction.

The upper block 47 is pressed down onto block 48 by means of spring 56 which is compressed between a plate 57 and the upper surface of block 47. The pressure can be controlled by means of hand screw 58. Block 47 is also pressed to the left as shown in the drawing by means of spring 59 which is compressed between plate 60 and the side of block 47.

The pressure can be controlled by the handscrew 61.

It is to be understood that the particular constructions for the die and its assembly illustrated in Figs. 6 and 7 are only examples and providing the fundamental shape and proportions of the passage through the die are maintained any method of mounting the components which is found suitable may be adopted.

It will be seen that with the process according to this invention where the wires issue from the machine they are close together and half the width of the paper strip is wrapped around one wire and the other half around the other wire, the edges of the strip being on the inside of the two lappings so that there is no tendency for the paper to unwrap itself. The paper strip is so wrapped around the wires that one side is exposed around one wire and the other around the other wire, the wrapping is in fact in the shape of a letter S. This has the advantage that if paper is printed in colour or otherwise marked on one side it is always possible to identify the wires of a pair.

It has been found advantageous to heat the die when applying paper insulation as this greatly facilitates the passage and folding of the strip and also results in the insulation being as it were baked in position on the wires. A temperature of220 C. has been found satisfactory.

It can be seen that this process lends itself to the very rapid production of twisted pair as there are no high speed rotating parts. It also has the advantage that a thinner and/or narrower paper can be used since there is less danger of breaking. The insulation on the finished product can be more closely packed than with helical lapping and this means that a given number of pairs can be accommodated in a smaller cable thus saving some of the expensive sheathing material.

If thought desirable a line of perforations can be provided down the middle of the original paper strip. These would then appear in the membrane between the insulated wires and would facilitate their separation for jointing purposes.

Although the invention has been described in connection with paper insulation it is not limited thereto. Amongst other applications there may be mentioned the possibility of using textile tapes, or plastic fihns of rubber strip.

While the principles of the invention have been described above in connection with specific embodiments, and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the in vention.

What I claim is:

1. Apparatus for insulating two conductors one from the other, comprising an elongated die having an input end and an output end, said die having first and second channels of substantially circular cross section extending longitudinally through the die, said first and second channels being parallel to a plane extending through said die, said first channel having its center displaced from one side of said plane, said second channel having its center displaced from the other side of said plane, a third channel of rectangular cross section having its central plane lying on said first mentioned plane and having its sides tangential to the lower portion of said first channel and to the upper portion of said second channel at said input end, said first and second channels converging front said input end so that continuous portions of said first and second channels tangential with said third channel at its input end overlap at said output end of said die, said third channel having the cross section of its longitudinal sides decreasing until said third channel disappears at the point of overlap of said first and second channels, means for traversing a strip of insulating material and said two separated conductors through respective channels, and means for heating the die during said traversing.

2. Apparatus as claimed in claim 1, and further comprising means for applying greater tension to said Wires than to said strip during their passage through said die.

3. Apparatus as claimed in claim 1 in which said die is divided into two separate portions, and spring pressure holding said two portions together.

Barrett Sept. 19, 1893 Barrett Sept. 19, 1893

Claims (1)

1. APPARATUS FOR INSULATILNG TWO CONDUCTORS ONE FROM THE OTHER, COMPRISING AN ELONGATED DIE HAVILNG AN INPUT END AND AN OUTPUT END, SAID DIE HAVING FIRST AND SECOND CHANNELS OF SUBSTANTIALLY CIRCULAR CROSS SECTION EXTENDING LONGITUDINALLY THROUGH THE DIE, SAID FILRST AND SECOND CHANNELS BEING PARALLEL TO A PLANE EXTENDING THROUGH SAID DIE, SAID FIRST CHANNEL HAVING ITS CENTER DISPLACED FROM ONE SIDE OF SAID PLANE, SAID SECOND CHANNEL HAVING ITS CENTER DISPLACED FROM THE OTHER SIDE OF SAID PLANE, A THIRD CHANNEL OF RECTANGULAR CROSS SECTION HAVING ITS CENTRAL PLANE LYING ON SAID FIRST MENTIONED PLANE AND HAVING ITS SIDE TANGENTIAL TO THE LOWER PORTION OF SAID FIRST CHANNEL AND TO THE UPPER PORTION OF SAID SECOND CHANNEL AT SAID INPUT END, SAID FIRST AND SECOND CHANNELS CONVERGING FROM SAID INPUT END SO THAT CONTINUOUS PORTIONS OF SAID FIRST AND SECOND CHANNELS TANGENTIAL WITH SAID THIRD CHANNEL AT ITS INPUT END OVERLAP AT SAID OUTPUT END OF SAID DIE, SAID THIRD CHANNELS TANGENTIAL WITH SAID OF ITS LONGITUDINAL SIDES DECREASING UNTIL SAID THIRD CHANNEL DISAPPEARS AT THE POINT OF OVERLAP OF SAID FIRST AND SECOND CHANNELS, MEANS FOR TRAVERSING A STRIP OF INSULATING MATERIAL AND SAID TWO SEPARATED CONDUCTORS THROUGH RESPECTIVE CHANNELS, AND MEANS FOR HEATING THE DIE DURING SAID TRAVERSING.

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