United States Patent (19)
`Broreira
`
`54 FLAME RETARDANT INSIDE WIRING
`CABLE WITH AN ANNEALED METAL
`SHEATH
`75) Inventor:
`73 Assignee:
`
`William J. Brorein, Whippany, N.J.
`General Cable Corporation,
`Greenwich, Conn.
`21 Appl. No.: 959,904
`22 Filed:
`Nov. 13, 1978
`
`63
`
`Related U.S. Application Data
`Continuation-in-part of Ser. No. 845,874, Oct. 25, 1977,
`Pat. No. 4,154,976.
`int. Cl. ...................... H01B 13/26; H01B 13/06
`51
`52 U.S. C. ........................................ 156/55; 156/56;
`156/250; 156/324; 156/304.5; 29/871
`53 Field of Search ....................... 156/56, 55, 54, 53,
`156/47, 304, 324; 29/624
`References Cited
`U.S. PATENT DOCUMENTS
`9/1970 Polizzano et al. ..................... 29/234
`3,529,340
`3,614,299 10/1971
`Grail .................................. 156/56 X
`3,964,945
`6/1976 Everhart et al. .................. 156/56 X
`4,100,002
`7/1978 Woytiuk et al. ................... 156/56 X
`4,113,534 9/1978 Pound et al. ........................... 156/56
`
`56
`
`11
`45
`
`4,253,890
`Mar. 3, 1981
`
`1/1979 Dembiak et al. .................. 156/56X
`4,134,953
`Primary Examiner-George F. Lesmes
`Assistant Examiner-Alexander S. Thomas
`Attorney, Agent, or Firm-Roy C. Hopgood; John M.
`Calimafde; Charles W. Neill
`(57)
`ABSTRACT
`This specification describes an improved method for
`making fire-resistant communication cables that have a
`core which includes a multitude of individual conduc
`tors or pairs with insulation surrounding some or all of
`the conductors. The conductors are enclosed in a metal
`sheath that has a welded seam and that is annealed to
`maintain the flexibility of the cable. The sheath is of
`larger diameter of the core when welded, but is drawn
`down to a reduced diameter that hugs the core prior to
`the annealing. Heat insulation is wrapped around the
`core to protect the insulation on the conductors from
`the heat that is used to anneal the sheath. The purpose
`of the construction is to provide indoor cable that does
`not propagate flames from a burning area in a building
`into adjacent non-burning areas. The cable sheath is
`purposely not bonded to the core to facilitate sheath
`removal for ease of terminating the cable.
`
`9 Claims, 5 Drawing Figures
`
`
`
`ANNEALED
`FLEX BLE
`ALUMNUM
`TUBE-8
`
`
`
`HEAT
`BARRER
`TAPES
`
`

`

`U.S. Patent
`
`Mar. 3, 1981
`
`4,253,890
`
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`U.S. Patent
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`Mar. 3, 1981
`
`4,253,890
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`

`1.
`
`FLAME RETARDANT INSIDE WRNG CABLE
`WITH AN ANNEALED METAL SHEATH
`
`PRIORAPPLICATION
`This case is a continuation-in-part of my application
`Ser. No. 845,874, filed Oct. 25, 1977, now U.S. Pat. No.
`4,154,976.
`
`15
`
`4,253,890
`2
`A still further advantage is that the lightweight flexi
`ble annealed aluminum sheath cables are easy to install
`and such an installation is far more economical than
`placing plastic sheath cables in metal conduits.
`Other objects, features and advantages of the inven
`tion will appear or be pointed out as the description
`proceeds.
`BRIEF DESCRIPTION OF DRAWINGS
`In the drawing, forming a part hereof, in which like
`reference characters indicate corresponding parts in all
`the views:
`FIG. 1 is a diagrammatic showing of apparatus for
`making cable by the method of this invention;
`FIG. 2 is a sectional view of a flame-retardant inside
`wiring cable made by the method of this invention;
`FIG. 3 is a diagrammatic showing of an intermixture
`of cables having outer plastic jackets and aluminum
`sheaths, and
`FIGS. 4 and 5 are diagrammatic views showing the
`removal of the sheath to facilitate splicing.
`DESCRIPTION OF PREFERRED EMBODIMENT
`FIG. 1 is a diagrammatic showing of one way in
`which the metal sheath inside wiring cable of this inven
`tion can be made. A cable core 10 is guided to a clad
`ding station 12 by rollers 13. Metal tape is withdrawn
`from a roll 14 of such tape and is advanced through
`forming rolls 16 of the cladding station 12 where it is
`longitudinally foided around the cable core with the
`inside diameter of the tubular sheath somewhat larger
`than the outside diameter of the cable core i0. The
`sheath, as it comes from the cladding station 12, is indi
`cated by the reference character 18 in FIG. i.
`The manufacture of the cable core 10 may be by
`conventional means, and the construction of the core
`will be described in connection with FIG. 2.
`The edges of the metal sheath are held in abutting
`relation by guiding rollers 16 or forming dies with the
`longitudinal abutting edges of the metal in contact with
`one another as they pass through a welding station 22
`which welds the abutting edges of the seam together.
`Welding by the tungsten insert gas (TIF) process is
`typical.
`The larger diameter of the sheath 18 provides spacing
`of the seam from the core, which protects the core from
`damage by the welding heat; and the heat in the seam is
`dissipated rapidly by a lubricant spray 23 and by con
`duction into the cooler portions of the sheath 18. The
`sheath 18 then passes through a reducing die 24 or rolls
`which reduces the diameter of the sheath so that its
`inside diameter is substantially equal to the outside di
`ameter of the core 10, and the metal provides a continu
`ous fire-retardant protective jacket around the core.
`Beyond the reducing die 24, the sheathed cable passes
`through an annealing zone 26 which supplies sufficient
`heat, by induction coil 27, to anneal the metal, followed
`by cooling sprays 28 to quickly quench the metal of the
`sheath. The cable is advanced through the successive
`operating stations by one or more pullers, which are
`shown diagrammatically in FIG. 1 and indicated by the
`reference characters 29 and 29'.
`FIG. 2 shows the cable core 10 formed with a plural
`ity of conductors 30, each of which is surrounded by a
`layer of insulation, preferably a semi-rigid polyvinyl
`chloride insulation. The insulation on the conductors 30
`preferably contains some 5 to 40 parts of inorganic filler
`
`O
`
`PRIOR ART
`U.S. patents that seem pertinent to part of this inven
`tion are as follows: U.S. Pat. Nos. 3,529,340; 3,567,846;
`and 3,693,250.
`BACKGROUND AND SUMMARY OF THE
`INVENTION
`The object of this invention is to make a more flame
`retardant flexible cable for use inside buildings for inter
`connecting telephone and other low voltage communi
`20
`cation or signal circuits.
`Basically to accomplish this objective, the usual PVC
`plastic jacket over the cable core has been replaced
`with an annealed flexible aluminum or copper tube that
`is made from a longitudinal strip that is formed into a
`25
`tube over the core, continuously welded, drawn down
`snugly onto the core and annealed in a continuous oper
`ation.
`The cable core, consisting of a number of insulated
`single or paired conductors, is wrapped with heat bar
`30
`rier tapes to protect the core during manufacture and
`subsequent use in the field. These tapes may consist of
`one or more layers of asbestos, paper, fiberglass, heat
`resistant plastic or the like; however, paper tapes either
`helically or longitudinally applied are the most econom
`35
`ical at this time; and crepe paper is advantageous for
`lower heat conduction.
`-
`The conductor insulator is a specially formulated
`semi-rigid PVC that is self-extinguishing and it emits
`minimum smoke fumes when exposed to fire due to the
`40
`use of relatively large amounts of inorganic materials in
`its composition.
`Some of the advantages of this invention over con
`ventional polyvinyl chloride plastic jacketed cables are
`that the non-combustible metal sheath of the invention
`45
`replaces a plastic jacket which comprises more than half
`of the combustible material weight in the conventional
`cable. For example, a popular size of conventional cable
`containing 25 pairs of No. 24 AWG wire contains 27
`lbs. of PVC jacket material per thousand feet and 24 lbs.
`50
`of PVC conductor insulation. Also, the non-combusti
`ble metal sheath greatly reduces flame spread in the
`event of a fire and also prevents afterburn in the cable of
`the present invention.
`Elaborate tests prescribed by the Underwriters Labo
`55
`ratories' showed that aluminum sheathed cables of this
`invention had negligible flame travel or spread beyond
`the point of direct flame application, while all compara
`ble plastic sheathed cables had flame spread the entire
`length of the cable in vertical flame tests and for 10 to 15
`60
`feet in horizontal flame tests.
`*U.L. 1277; ASTM-E 84 (modified for cable)
`it was also discovered that the intermixing of alumi
`nun sheath cables among plastic sheath cables, which
`might be cables already installed, had the effect of re
`65
`ducing flame spread among all of the cables, as was
`demonstrated by tests. The metal sheath is easily re
`moved from the core to facilitate terminating the cable.
`
`

`

`5
`
`20
`
`25
`
`4,253,890
`3.
`gi,
`material including antimony trioxide. A typical formu
`of this invention, the sheath 8 can be easily aid quickly
`removed from the end portion of the cable without risk
`ation would be:
`of damaging the insulation of any of the conductors 30.
`PVC resin: 100 parts
`A tool 42, having a handle 34, is used to for in a circum
`Plasticizer: 20 to 40 parts
`Filler: 5 to 40 parts
`ferential score 436 in the sheath 8. This circumferential
`scroe 46 preferably extends only part way through the
`Stabilizers & Lubricants: 1 to 10 parts
`sheath 3, and the sheath can be easily broken at the
`The conductors 30 are approximately 0.015 to 0.020
`score 46 by flexing the cable slightly first one way and
`inches with insulation thereon of approximately 0.007 to
`D.OO inches.
`then the other.
`One or more layers of heat-resistant materiai is ap
`When the cable sheath i3 is severed at the score of
`indentation 46, the length of sheath beyond the score 46
`plied over the conductors 30 to complete the construc
`can be displaced toward the right in FiG. 4, as indicated
`cion of the cable core 10. FIG. 2 shows two such layers,
`including an inner layer 32 and an outer layer 34. These
`by the reference character i8 with the dotted leader
`tayers are preferably tapes applied either helically or
`line. This is easily done by hoiding the sheath 8 at
`opposite sides of the score at £5 and sliding the portion
`longitudinally and they can be made of heat-resistant
`material such as asbestos, paper, fiberglass, or heat
`of the sheath to the right of score 46 until it is com
`pletely clear of the end portion of the cable.
`(esistant plastic. Where more than one layer is used,
`ihey can be made of different kinds of material from one
`The sheath 18 is drawn down over the cabie core in
`another. Ordinary kraft paper is quite suitable, but crepe
`the die 24 (FIG. i.), but the draw down causes the
`sheath to hug the core without setting up sufficient
`paper can be used for greater heat insulation of the core.
`pressure to cause excessive friction to movement of the
`Foam heat-resistant plastic tapes, rubber tapes, rubber
`polyester laminated tapes, or silicone rubber are desir
`severed end of the sheath, as illustrated in FiG. 4. Also,
`able where high dielectric strength is needed between
`the tape 34, which contacts with the sheath, has a low
`friction surface to facilitate the sliding off of the end of
`he sheath and the cable core. Intumescent tapes, such
`as made by Avco Systems and others are useful for
`the sheath fron the core of the cable.
`elaying damage to the core and to prolong the cable
`FIG. 5 is a view similar to FIG. 4, but with oniy the
`integrity when exposed to flame.
`sheath 8 shown in section. The tapes 32 and 34 are not
`The expression "heat-resistant plastic' is used herein
`cut off by the tooi (32, and it is preferable that they
`to designate plastic that does not melt and stick to adja
`should not be, because if the tool 42 cut through the
`tapes, it might also damage the insulation on the con
`cent material such as the sheath 18, when exposed to the
`neat used to anneal the sheat 18 at the annealing zone
`ductors 30. Also, if the break in the sheath at the depres
`sion 46 leaves a rough inner edge on the cut-off portion
`26.
`of the sheath, the tapes 32 and 34 will protect the insu
`For minimum fuel contribution, where the cable may
`pe melted and entirely destroyed by flames, fiberglass
`lated conductors of the core from damage by the rough
`edge as the end of the sheath is moved longitudinally to
`and asbestos tapes are most desirable.
`Where paper tapes are used, each layer may be 0.005'
`the right in FIGS. 4 and 5 to completely remove it from
`hick, while rubber laminated with polyester (polyeth
`the cable.
`yiene terephthalate) may be 0.015' thick. These are
`While the tapes 32 and 34 may be unwound and torn
`off at the shoulder 45", it is preferable to apply a layer of
`preferred dimensions, and it will be understood that the
`thickness of the heat-insulating tapes and the combina
`adhesive tape 43 over tapes 32 and 34 adjacent to the
`shoulder 46" to protect the conductors from the possibil
`ions of different materials that may be used will depend
`ity of damage from the sheath edge 46". The insulated
`upon the amount of heat insulation desired and other
`able requirements.
`conductors 30 can be spread, as indicated in F.G. 5; and
`The thickness of the metal tape 14 when aluminum is
`they can be connected to connectors, terminal strips or
`used depends upon the size of the cable. Experience has
`the next length of cable from which the sheath has been
`45
`shown that a wall thickness of an aluminum sheath of
`removed in the same manner as described in FIG. 4.
`about 0.020 inches or less is satisfactory for a 0.250'
`The purpose of this invention is to provide a cable of
`D.D. cable; and that this thickness should be increased
`moderate cost that is easy to install and connect; and
`which contributes, when exposed to flanes from exter
`o about 0.040' for a 0.750' O.D. cable. These values
`are given by way of illustration.
`nal sources, a minimum of smoke and fuel to the existing
`While aluminum is the preferred material for the
`flames, and which does not spread the flames from one
`metal sheath of this invention, other metals can be used
`area to another.
`such as copper.
`The preferred embodiment of the invention has been
`illustrated and described, but changes and modifications
`FIG. 4 shows the cable 10 with the tube 18 in contact
`with heat barrier tapes 32 and 34 with the inner taper 32
`can be made and some features can be used in different
`55
`combinations without departing from the invention as
`in contact with the conductors 30 of the core and with
`he outer tape 34 supported by the inner tape 32. The
`defined in the claims.
`puter surface of the tape 34 contacts with the inside
`What is claimed is:
`i. The method of making a communication cable
`urface of the sheath 18 but is not adhered thereto.
`from a multitude of similar individual pre-insulated
`FIG. 4 shows an end 40 at which the core 10 and the
`conductors, and with the conductors brought together
`netal sheath 18 both terminate. In order to continue the
`zircuits of the conductors 30, it is necessary to splice the
`to form a core surrounded by heat-insulating tapes
`espective conductors 30 to corresponding, similarly
`which method comprises advancing the cable core,
`:olor-coded conductors of another length of cable or to
`folding around the advancing core a metal sheath of
`:onnect them to a connector, terminal strip or piece of 65
`greater inside diameter than the outside diameter of the
`multi-conductor core, welding together the edge por
`pparatus.
`in order to make such connections, it is necessary to
`tions of a seam of the sheath, drawing the welded sheath
`emove the metal sheath 18; and with the construction
`down to a Snug fit around the multi-conductor core,
`
`60
`
`35
`
`SO
`
`

`

`4,253,890
`6
`5
`an end of the cable, breaking off the sheath at the cut,
`annealing the metal of the sheath to increase the flexibil
`sliding the severed sheath longitudinally over the end of
`ity of the cable, and protecting the insulation on the
`the cable while the tape that surrounds the conductors
`conductors of the core that are near the periphery of the
`core by using the layer of tape as a heat barrier to pro
`of the core protects the insulated conductors from dam
`age by contact with the severed edge of the sheath as
`vide protection from the heat that anneals the metal
`sheath by making the layer of tape of a material that
`the sheath slides from the region of severance to the
`does not melt or burn when exposed to the annealing
`ends of the insulated conductors, and removing the
`tape, after removal of the sheath, to expose the conduc
`heat that flows through the metal shield during the
`annealing operation, and making the heat barrier layer
`tors of the core for making electrical and mechanical
`of a thickness much less than the radius of the core, and
`connections.
`crowding the insulated conductors together in contact
`6. The method described in claim 1 characterized by
`making the conductors of the cable core of wires of
`with one another in the core, and leaving the sheath as
`approximately 0.015 to 0.020 inches and with insulation
`the outside surface of the cable for fire protection, and
`thereon having a thickness of approximately 0.007 to
`free to slide longitudinally on the surface of the core
`when the sheath is severed circumferentially at a loca
`0.010 inches.
`tion longitudinally spaced back from an end of the cable
`7. The method described in claim 1 characterized by
`to expose the conductors of the core for making electri
`making the conductors of the core of metal wires hav
`ing insulation thereon and a thickness less than the di
`cal and mechanical connections.
`ameter of the wires to which the insulation is applied.
`2. The method described in claim 1 characterized by
`8. The method described in claim 1 characterized by
`the insulation on the insulated conductors of the core
`20
`advancing the cable core with continuous motion, ap
`being color coded, and the heat barrier layer that en
`closes the core being made of paper which confronts
`plying the sheath to the core while the core advances,
`the sheath and which is free of any surface-to-surface
`and with the sheath formed into a tube around the core
`and of substantially larger inside diameter than the out
`connection with the sheath.
`side diameter of the core, welding a seam of the sheath
`3. The method described in claim 1 characterized by
`25
`applying a plurality of layers of tape to enclose the core,
`as it advances with the core, passing the sheath through
`and superimposing one tape upon an underlying tape
`apparatus that reduces the diameter of the sheath to a
`with the outer tape free of any surface-to-surface con
`size that hugs the core, and with the sheath in contact
`with the circumference of the core, heating the sheath
`nection with the sheath.
`to a temperature high enough to anneal the sheath, and
`4. The method described in claim 1 characterized by
`30
`cooling the sheath before the annealing heat damages
`supplying tape between the core and the metal sheath,
`with the surface of the tape free to slide with respect to
`the sheath and the conductors near the outside of the
`the sheath both before and after being subjected to the
`CO
`9. The method described in claim 1 characterized by
`heat that anneals the metal of the sheath.
`making the tape heat barrier of material from the group
`5. The method described in claim 1 characterized by
`35
`forming the metal sheath preparing one end of the cable
`consisting of asbestos, paper, fiberglass, rubber, solid
`for splicing by cutting part way through the metal
`and foamed plastics.
`sheath circumferentially at a location spaced back from
`
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