US3610814A

US3610814A - Spiral-four quad structure

Info

Publication number: US3610814A
Application number: US883222A
Authority: US
Inventors: John M Peacock
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1969-12-08
Filing date: 1969-12-08
Publication date: 1971-10-05
Anticipated expiration: 1988-10-05

Abstract

This application discloses a spiral-four quad conductor structure in which a desired square geometry is maintained by a thermoplastic filler. Four conductors are drawn through a filler bath and thereafter, through a circular die. Cooling of the filler assures maintenance of the quad into its desired geometry, as well as providing waterproofing for the quad.

Description

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OTHER REFERENCES Biskeborn et al. Jelly Blend Waterproof Cable in Bell Lab. Records, March 1969, pp. 71- 75 Primary Examiner-E. A. Goldberg [54] SPIRAL-FOUR QUAD STRUCTURE 6 Claims, 8 Drawing Figs.

Attorneys-R. J. Guenther and Edwin B. Cave ABSTRACT: This application discloses a spiral-four quad conductor structure in which a desired square geometry is maintained by a thermoplastic filler. Four conductors are EMM M P/Z 3 7 0 0 4i lib- /.ll.l 4/0 3 74" In m3 m "2 n a m u u u S .1 o M mm al Q U h 1 ll. 2 0 5 55 .l. [l

[56] References Cited UNITED STATES PATENTS 1/1968 327,459 9/1885 Spalding.......................

drawn through a filler bath and thereafter, through a circular die. Cooling of the tiller assures maintenance of the quad into l74/l l3 X its desired geometry, as well as providing waterproofing for 174/113 X the quad.

PATENTED nm 5 IBYI SHEET 1 BF 2 /Nl ENTO/? By J M. PEACOCK A @M. 8. 1M

ATTORNEK SPIRAL-FOUR QUAD STRUCTURE FIELD OF THE INVENTION This invention relates to multiconductor telephone cable and more specifically to a spiral-four quad structure and its related manufacturing methodology.

BACKGROUND OF THE INVENTION As an alternative to the widely used twisted pair in multipair telephone cable, the so-called spiral-four quad has in theory many advantages. It is, for example, much less susceptible to twist length distortion since the four wires are nested in a square geometry rather than lying flat as do pairs. Also, crosstalk-causing electric fields have less influence on a quad than on a twisted pair. The quad additionally provides a significant space saving per circuit as compared to twisted pairs. Even beyond this, it is possible by the use of the phantom circuit to provide still further increase in circuit capacity.

The widespread use of spiral-four quads in the United States has, however, been impeded by the extreme difficulty in achieving the desired low side-to-side capacitance unbalance within the quad. This problem traces to the tendency of quads with handling or usage to assume geometries other than the required square configuration. The typical solution heretofore has been to incorporate a properly sized filer such as a string in the center of quad structure or, as disclosed in US. Pat. No. 3,364,305, incorporate a webbing between opposite conductors in the structure.

The present invention addresses the problem of providing a highly stable square configuration in a spiral-four quad while reserving full freedom to apply shielding. Additionally the invention involves concurrently supplying the basic building block for a cable which is waterproof.

The principal inventive objects are:

to enhance the long-term geometric stability and hence the transmission performance of the spiral-four quad conductor;

to accomplish the above objects without sacrifice of useful shielding configurations; and

at the same time, to utilize the stabilizing medium as the vehicle for cable waterproofing.

SUMMARY OF THE INVENTION The desired square geometry of a spiral-four quad is maintained, pursuant to the broad inventive teaching, by the presence of a tacky, thermoplastic material completely filling the interstitial space between four polyethylene insulated conductors arranged in square configuration, and the presence of sufiicient inwardly directed binding forces on the conductors to prevent their spreading outwardly in later use and handling.

Any departure from the square configuration requires either a reduction in the interstitial cross section area or a spreading outwardly of at least one of the conductors. Preventing the latter substantially prevents the former in the instant invention since the area reduction cannot occur without expulsion of the filler material therefrom. The interstitial material is, however, too tacky at normal operating temperatures to flow. The area accordingly does not contract, and the insulated conductors therefore retain their original square geometry.

Numerous expedients, singly or in suitable combinations, can provide the requisite inwardly directed forces on the insulated conductors of each spiral-four quad. The same thermoplastic material, for example, is in one embodiment applied to surround the exterior of the quad in a circular geometry. For further example, a shielding tape or binder applied around the quad supplies the retaining force. Further still, numerous such quads can be assembled in a unit, the interstices of which in turn are similarly filled, with the entire unit then jacketed.

An example of suitable filler material is a 3:1 by weight mixture of petroleum jelly and a thermoplastic polymer of high average molecular weight. Numerous examples of such material are disclosed in the copending application of M. C. Biskeborn et al. Ser. No. 780,314 filed Dec. 2, 1968 and assigned to applicant's assignee; and this disclosure to the extent pertinent is hereby incorporated by reference into the instant specification. These materials when used pursuant to the present teachings supply the added advantage of waterproofing to the end of stabilizing the quads transmission performance.

In a particular inventive embodiment embracing methodology, four polyethylene-insulated conductors are drawn through a bath of thermoplastic filler and, thereafter, through a properly sized circular polishing die whose diameter is chosen to just pass the four conductors. The conductors thus are forced into a symmetrical square geometry, with the filler flooded into the configurations interior as well as in the exterior interstices. On emerging from the polishing die, the filler solidifies, freezing the quad into its desired geometry.

Shielding in the form, for example, of a longitudinally applied metallic tape advantageously is formed over the quad, for example afterthe above-mentioned cooling stage. Thereafter, a suitable number of such quads are combined as piece parts to form a multipair-communications cable.

The filler used in constructing the spiral-four quad is characterized, pursuant to the invention, by a low dielectric constant, low moisture permeability, adequate body and tack at the range of temperatures to be encountered in service so as to hold the quad in position and flexibility at reduced tempera tures.

The invention and its further objects, features, and advantages will be more fully apprehended from a reading of the following detailed descriptions embracing illustrative embodiments.

THE DRAWING FIGS. 5A, 5B, and 5C depict sectional views through the bath at three points.

lLLUSTRATIVE EMBODIMENT FIG. 1A shows in broad schematic form the essential elements for the manufacture of a spiral-four quad pursuantto the present invention. For illustration's sake, the making of but a single quad is described, it being understood that manufacture of numerous such quads concurrently is both feasible and desirable.

As shown in FIGS. 1A and 1B, polyethylene-insulated conductors 2, 4, 5, 6 are supplied from sources such as reel 1 to a filler bath 3. All conductor sources are similar to reel 1. Advantageously, each is rotated in the direction of arrow 7 while paying out their conductor. The amount of rotation can, for example, be one turn for each 15 diameters of advance. In this fashion, possible eccentricities of the insulation of each of the conductors 2, 4, 5, and 6 with respect to the center wire are averaged out and thus compensated for, to avoid capacitance unbalances that might otherwise result. Another way of avoiding diameter differences and eccentricities is to use on all reels insulated conductor from contiguous section of the output of a given extruder. This is generally termed matched-insulated conductor. Preferably also, the wire from which the conductors are made is matched in the same sense. I

The bath 3 consists of an end plate 8, internal guide rings such as 9, and 10, and a circular die 11, which, for example, can be a properly sized orifice in the end 12 of bath 3. Heatedtherrnoplastic filler is introduced into the interior of bath 3 through

pipes

13a, 13b, 13c, 13d, 13e, 13], 133 from

suitable sources

40, 41. The filler when used with polyethylene-insulated wire should have a dielectric constant in the range of 2.2 to 2.4. It should be readily flowable at temperatures of, say. C. to facilitate its application to and around the conductors in bath 3 while they are moving at a rate of about a foot per second. The adherence to the insulation must be firm at all temperatures below 120 C. particularly those in the usual operation range from 50 C. to C. or less. Material rigidity and techniques in this range must be sufficient to prevent oozing or flowing of the material from between the contacting-insulated conductors once they are held in a square geometry. At low temperatures, the material must remain flexible.

The end plate 8 in bath 3 receives the conductors 2, 4, 5, and 6 through ports 14, l5, l6, and 17 respectively. The orifices are of a diameter to pass the conductors without allowing filler inside to escape. Entrance ports 14-17 are separated sufficiently to space the conductors 2, 4, 5, 6 as they enter the bath 3. In FIG. 1B, because of the perspective, only orifices I5, 17 and insulated conductors 4, 6 are shown.

The filler is, for example, a blend of 80 to 89 percent petroleum jelly and 1 l to 20 percent of crystalline-olefin polymer having an average molecular weight greater than 20,000 and a dielectric constant of from 2.2 to 2.4 at room temperature. The olefin polymer is one of a group consisting of ethylene and a-olefins, for example, polyethylene, polybutene, or polypropylene. The filler temperature in the bath is about 120 C., but on exiting is rapidly cooled.

The guides 9, within bath 3 are, for example, circular rings mounted on legs such as 18. The guide diameters are chosen to coerce the conductors 2, 4, 5, 6 in stages toward each other as they are drawn through the viscous filler, so that ultimately at forming die 1 1 the conductors will have assumed a symmetrical square configuration. Typical of the stages through which the conductors 2, 4, 5, 6 pass are the configurations of FIGS. 5A, 5B, and 5C. In FIG. 5C, it is seen that the conductors, by virtue of their closely controlled insulationouter diameter interacting with the appropriately sized form ing die 11, are necessarily forced into the desired square contacting geometry, in which the conductor centers from the comers of a square and the insulation surfaces are in contact.

On exiting from bath 3, the now-formed quad, designated 20, is enveloped internally and externally in the filler compound and has a circular cross section. Now, the requisite spiral in either direction such as denoted by the arrow 21 in FIG. 2 is applied to the quad. This is achieved through a conventional expedient such as rotating the takeup reel 22 in the direction of arrow 23 in FIG. 1A. The reel 22 itself is driven in the direction of arrow 24 for takeup purposes by a suitable motor, not shown. Reel 22 is mounted in the reel fork assembly 25 that in turn is fastened to shaft 26, the latter being rotated to produce the desired quad twist.

In the instant embodiment, longitudinal shielding tape 29 is applied to quad after the filler is applied and while the quad is being twisted and taken up. The tape apparatus as shown FIG. 1 consists of a shielding tape supply reel 27 suitably mounted in rigid fashion by arms 28 upon fork 25. The tape 29 and quad 20 pass in unison through a conventional shoehom forming die 30 which is also rigidly supported from fork by arms a.

It can be advantageous to supply filler into bath 3 from an additional entrance port 13g located in the region of end plate 8 between the entering conductors 2, 4, 5, 6. This location supplied filler to facilitate complete filling of the interstitial region between the conductors. Entrance port 13g can also be used to supply a different filler material from that destined for the quad s outer surface. For example, a less viscous or harder filler in the interstitial region between conductors may be desired to provide added rigidity and security to the square geometry.

Filling is further enhanced by coercing the wires together in stages through

guides

9 and 10. In this way, as the conductors draw together, the filler in the interstitial region is compacted and forced outwardly into the main body of filer in the bath. Then, as the quad passes through the polishing die 11, the filler in the inner region undergoes a slight amount of final compacting. The filler remaining in the interstitial region is the maximum amount compactible into that region.

Shleldmg tape incorporated into the process may be as exemplified in FIG. 18. There, the tape results in a quad having the configuration illustrated in FIG. 2. FIGS. 3 and 4 illustrate two further possible shielded structures. In FIG. 3 a shielding tape 29a has been applied as a loop around the diametrically

opposite conductors

14, 17. In FIG. 4 a shielding tape 29b has been applied in figure-eight fashion around opposed conductors l4, 17. In each case, the

tapes

29a and 29b are applied by machinery advantageously located (but now shown) within the bath 3. In this fashion, the interstitial area between the conductors continues to be occupied by the filler, with both the

shielding tapes

29a or 29b and the conductors surrounded with the filler.

The shielding tape 29 of FIG. 3 also supplies inwardly directed force upon the conductors 2, 4, 5, 6. Other tapes, such as plastic ribbon binders, are also capable of providing this force. The binding force must be sufiicient in all cases to prevent separation of the insulated conductors 2, 4, 5, 6that is, to prevent any two which are in contact with each other from losing that contact.

The second important aspect of the thermoplastic filler, as taught generally in the aforementioned Biskeborn at al. application, is as a waterproofing agent for each of the quads 20. Reference to the structures of FIGS. 3 and 4 reveals that the filler 32 sufficiently envelops the conductors to render impossible the intrusion of any water within the structure. This then assures the stable performance of the quad in its application as a transmission line. Additionally, by a further filler flooding operation during a subsequent step (not shown) of assembling a multiquad cable from numerous such quads, the waterproofing of the cable itself is assured. This is of advantage to enhance the long-term maintainability of the cable, particularly when buried in the ground, or in an underground conduit.

The spirit of the invention is embraced in the scope of the claims to follow.

What is claimed is:

l. A spiral-four quad comprising:

four matched insulated conductors arrayed in square, contacting configuration;

a thermoplastic, waterproof, tacky material completely filling the space between said conductors; and

means binding said insulated conductors together with a force sufficient to prevent their separating outwardly.

2. A spiral-four quad comprising:

four matched, insulated conductors arrayed in square, contacting configuration;

a thermoplastic, waterproof, tacky material filling the space between said conductors, said material also completely covering the exterior surfaces and completely filling the exterior interstices of said four conductors; and

3. A spiral-four quad pursuant to claim 2 wherein the outer surface of said material covering said exterior interstices is circular in cross section.

4. A spiral-four quad in accordance with claim 3, further comprising a tape binder applied directly over said outer surface.

5. A quad in accordance with claim 2 in which said insulation is polyethylene and said material is further characterized by a dielectric constant of from 2.2 to 2.4 low viscosity at temperatures of about 120 C., tackiness at temperatures below about 50 C. and flexibility at temperatures below freezing.

6. A quad in accordance with claim 2 in which said material comprises a blend of to 89 percent petroleum jelly and I l to 20 percent of crystalline olefin polymer having a weight average molecular weight greater than 20,000 and a dielectric constant .less than 2.4 at room temperature, wherein said polymer is one of a group consisting of ethylene and a-olefins.

Claims

1. A spiral-four quad comprising: four matched insulated conductors arrayed in square, contacting configuration; a thermoplastic, waterproof, tacky material completely filling the space between said conductors; and means binding said insulated conductors together with a force sufficient to prevent their separating outwardly.

2. A spiral-four quad comprising: four matched, insulated conductors arrayed in square, contacting configuratiOn; a thermoplastic, waterproof, tacky material filling the space between said conductors, said material also completely covering the exterior surfaces and completely filling the exterior interstices of said four conductors; and means binding said insulated conductors together with a force sufficient to prevent their separating outwardly.

5. A quad in accordance with claim 2 in which said insulation is polyethylene and said material is further characterized by a dielectric constant of from 2.2 to 2.4 low viscosity at temperatures of about 120* C., tackiness at temperatures below about 50* C. and flexibility at temperatures below freezing.

6. A quad in accordance with claim 2 in which said material comprises a blend of 80 to 89 percent petroleum jelly and 11 to 20 percent of crystalline olefin polymer having a weight average molecular weight greater than 20,000 and a dielectric constant less than 2.4 at room temperature, wherein said polymer is one of a group consisting of ethylene and Alpha -olefins.