US2536885A

US2536885A - Method of making multiconductor cables

Info

Publication number: US2536885A
Application number: US22269A
Authority: US
Inventors: John W Olson
Original assignee: Anaconda Wire and Cable Co
Current assignee: Anaconda Wire and Cable Co
Priority date: 1948-04-21
Filing date: 1948-04-21
Publication date: 1951-01-02
Anticipated expiration: 1968-01-02

Description

Jan. 2, 1951 J. w. OLSON METHOD 0F MAKING MULTICONDUCTOR CABLES Filed April 2l 1948 .M1 Q M.

Q awww@ INVENTOR fa/n /4/ 015m BY P am@ tu Patented Jan. 2, 1951 METHOD F MAKING MULTICONDUCTOR CABLES John W. Olson, Ardsley on Hudson, N. Y., assignor to Anaconda Wire and Cable Company, a coi'- poration of Delaware Application April 21, 1948, Serial No. 22,269

7 Claims.

This invention relates to insulated electrical cables, and is particularly concerned with the provision of an improved method of making multiconductor cables of the type known as nonmetallic sheathed cables commonly used i'or building wiring. In accordance with the invention, the conductors are enclosed in a sheath made up of (l) a wrapping of fibrous material (preferably paper) which is precoated (but only on the side facing away from the conductors) with a thermoplastic composition, and (2) an overlying brous jacket impregnated with a thermoplastic composition under conditions that substantially prevent penetration of the thermoplastic material through the wrapping. The method of the invention leads to the production of a multiconductor cable of improved character, and such improved cables also come within the scope of this invention. This application is a continuation-impart of my prior application Serial No. 542,720, filed June 29, 1944, entitled Insulated Electrical Conductor, now abandoned.

`Non-metallic sheathed cable usually comprises two or more wires each insulated with rubber and a bitumen-impregnated fibrous braid, and each wrapped with a folded-paper tape. The wires are enclosed in a sheath of fibrous material, generally in the form of a braided cotton jacket, with or without an underlying wrapping of paper. This sheath is impregnated with a bituminous saturant by immersing the sheathed cable in a heated molten bath of the saturant for a long enough period of time to saturate the jacket. The length of time required for saturation of the jacket, however, is necessarily also long enough for a substantial amount of the saturant to penetrate completely through the sheath (even when it includes a layer of paper immediately surrounding the insulated conductors), and cause the sheath to stick to the individual wires. This is a source of considerable annoyance and trouble to electricians who install the cable because it makes it diiiicult to separate and bare the conductors, without injuring the cable, for the purpose of making electrical connections. It also sometimes results in injury by overheating to wax ilnishers with which the paper tape wrappings about the individual conductors sometimes are impregnated, and even to the rubber insulation of the individual wires.

The improved method of the invention for manufacturing non-metallic sheathed cable and like multiconductor cables overcomes the foregoing disadvantages of the method heretofore used, and leads to the production of an improved cable. In accordance with the invention, the

individually insulated conductors are assembledtogether and a sheet of fibrous material such as paper, that has been precoated on one side only with a thermoplastic material, is wrapped about them. The wrapping is applied with its precoated side facing away from the conductors. A jacket of fibrous material, such as a cotton braid, is next applied over the wrapped assembly. Then the jacket is impregnated by immersing it in a thermoplastic material heated to a high enough temperature to be fluid. The duration of the impregnating operation is made long enough to eiTect saturation of the jacket, but is too short for any substantial amount of the thermoplastic material to penetrate through the wrapping. The precoating of the wrapping enables this control over the duration of the impregnating operation to be quite readily effected: the fibrous jacket in effect receives thermoplastic saturant from both sides, so that it becomes thoroughly saturated much more rapidly than by the method heretofore employed. The completed cable is characterized by having a Well-impregnated jacket, but with the precoated wrapping free of any thermoplastic material on the side toward the conductors, so that the sheath is not stuck to the individual wires or to the paper tapes with which they are wrapped.

The thermoplastic material used in making multiconductor cables in accordance with the invention is preferably a bituminous composition having an A. s. T. M. ring and ball softening point above. F. and which is non-flowing at room temperature. The same composition may be used both for precoating the paper wrapping and for saturating the fibrous jacket, but better results can be obtained if the composition used for impregnating the jacket has a higher (by 50 F. or so) softening point than the material with which the wrapping is precoated. The actual duration of the impregnating operation is very short-not more than about five seconds and sometimes as short as one second or so when a bitumen having a softening point above F. and heated to above 300 F. in the saturating bath is used for saturating the jacket.

The invention is described in greater detaii' below with reference to the accompanying drawing, the single ilgure of which shows a nonmetallic sheathed cable made in accordance with the invention.

The cable shown in the drawing comprises a pair of metallic conductors l and 2, each having rubber I and a covering of cotton braid I which is saturated with a thermoplastic material such as an asphaltic bitumen 5. The exterior of the insulation about one or both wires may be painted for purposes of circuit identification. Each of the insulated wires is provided with a spiral wrapping l of folded paper which serves to keep the wires out of contact with each other, and which makes the wires more readily accessible to electricians when the cable is installed. The individual wires are assembled side by side, and

-a nller of jute cord is laid in the valley spaces it may be in the form of a strip wrapped lengthwise around the assembled wires. In either case it is best applied with edges overlapping somewhat. The side of the wrapping to which the coating of bituminous material has ilrst been applied faces away from the wires. and care should be taken to avoid crumpling the wrappingor otherwise deforming it in any manner that will bring its coated side into contact with the wires.

The precoating of bitumen or other thermoplastic material may be applied in any desired manner, using conventional paper-coating apparatus. An asphaltic bituminous coating may be applied either while heated to a thinly fluid condition, or in the form `of a iluid emulsion. The coating should be dry and reasonably hard before the wrapping is applied about the assembled wires, in order to facilitate wrapping it in place.

An outer fibrous jacket I2 is applied over the wrapping I0. A cotton braid forms a particul'aly satisfactory outer jacket, but otheriibrous V..

materials such as spun glass, asbestos, or mixtures of these materials with each other or with cotton. may also be used.

After the outer jacket i2 has been applied, it is impregnated with an asphaltic bituminous composition or other thermoplastic material.

impregnation is accomplished most advanta.

geously by immersing the jacketed assembly in a bath of the composition heated to a high enough temperature to be quite thinly iluid. It is characteristic of the method of the invention that the duration of the operation is very short-.ordinarily not over about five seconds (in contrast to the time of five minutes or so required for c'mplete saturation by methods heretofore employed). Five seconds or less has been found to be sumcient timev to effect saturation of the jacket when the underlying paper wrapping has been precoated with an asphaltic bitumen, because the jacket in effect becomes impregnated from both sides at the same time. The jacket is not so thick but that the bituminous precoating on the wrapping Ill-'becomesI softened enough to penetrate between the fibers of the jacket when the cable is immersed in a hot jacket saturant even for the short period of time the invention con- 4 individual wires enclosed thereby. Hence these wires do not become stuck to the jacket, and the jacket is very readily removed wherever necessary for making electrical connections when the cable is installed. Furthermore, the very short impregnation period insures against any damage to the rubber and other materials forming parts of the insulation about the individual conductors I and Z--they do not become heated to any deleterious extent in so short a period of time. If, as is sometimes the practice, a coating templates. As a result of the extremely short impregnation period, there is substantially no penetration of the bituminous composition through the paper wrapping and into contact with the of paraiiln wax is applied to the insulated wires or to the folded-paper wrappings 1 thereabout, it comes through the impregnation step completely undamaged either in consequence of being overheated or by being fiuxed with the bituminous material. v

I prefer to employ a llame-resistant bituminous composition of the character described in the applications of John W. Olson and Charles W. Bechle Serial Nos. 415,144 (now U. S. Patent No. 2,442,706) and 415,145,A (now U. S. Patent No. 2,442,707) illed October l5, 1941,-both as the material with which the paper wrapping i0 is precoated and as the material with which the jacket i2 is saturated. Any bitumen used, however, should have a softening point above F. Best results are secured when the bituminous material with which the jacket l2 is saturatedzhas a higher softening point (preferably above'175F.) than the coating il on the wrapping. IU. As a. specic v example, very good results are obtained `when using a flame-resistant asphaltic composition having a softening point of about F. for precoating the wrapping I0, and a flame-resistant asphaltic composition having a softening pointof about 225 F. for impregnating the jacket.A Ihe latter composition is heated to about 325 F. to render it adequately iluid for impregnation of the jacket, and the actual time of immersion of the jacketed cable in this hot saturating composition is only about a second or so.

Multiconductor cables having sheaths made i accordance with the invention are substantially as resistant to moisture absorption as similar cables made by the methods heretofore employed. They are superior to cables made by heretofore known methods in that the short period of inimersion in the jacket-saturating bitumen insures against any damage to the vulcanized rubber or other components of the insulation about the individual wires, and in that the-'sheath is readily separated from the wires, withoutv damage to the cable structure, wherever electrical concable, involving assemblingv two;- or.Y more wires within a common sheath, the improvement which comprises coating one side only of a sheet of brous material withl a thermoplastic material, applying said vcoated sheetasawrapping about an assembly of .individually insulated: wires with the coated surface of thesheetiacingaway from the wires, enclosing thethus-wrapped assembly; in a fibrous jacket, and' impregnating` the jacket' with a thermoplastic materialf'heat'edhto a highl enough temperature to be.,uid,-the;duration off the impregnating operationabeingflong enough. to eilect saturation of' thezisaid-jacketwith'the'I thermoplastic material but too-shortfor any substantial amount of thermoplastic material penetrate through said wrapping.

2. In the manufacture of a multiconductor.- cable, involving assembling twoforfmore wires' within a common sheath, the improvement which comprises coating one side only of a sheet of fibrous material with a thermoplastic bituminous material that is non-flowing at 'room temperature, applying said coated sheet as a wrapping about an assembly of individually insulated wires with the coated surface of the sheet facing away from the wires, enclosing the thus-wrapped assembly in a fibrous jacket, and impregnating the jacket with a thermoplastic bituminous material heated to a high enough temperature to be fluid, the duration of said impregnating operation being long enough to soften the bituminous coating on the, wrapping and effect saturation of the jacket with the bituminousv material but too short for any substantial amount of the bituminous coating on the wrapping to penetrate therethrough.

3. In the manufacture of a multiconductor cable, involving assembling two or more wires within a common sheath, the improvement which comprises forming said sheath by applying about an assembly of individually insulated wires a wrapping of fibrous sheet material that has been precoated on one side only with a bituminous material having a softening point above 125 F., said wrapping being applied with its coated side facing away from the wires, applying a jacket of fibrous material about the thus-wrapped assembly, and impregnating the jacket with a bituminous material having a softening point above 125 F. and heated to above said softening point, the duration of the impregnating operation being long enough to soften the bituminous coating on the wrapping and effect saturation of the jacket with the bituminous material but too short for any substantial amount of the bituminous material to penetrate through the wrapping.

4. In the manufacture of a multiconductor cable, involving assembling two or more wires within a common sheath, the improvement which comprises forming said sheath by applying about an assembly of individually insulated wires a wrapping of paper that has been precoated on one side only with a bituminous material having a softening point above 125 F., said paper being applied with its coated side facing away from the wires, applying a jacket of fibrous material about the thus-Wrapped assembly, and immersing the jacketed assembly in a bituminous material havinga softening point above 125 F. and heated t0 above said softening point for -a period of time long enough to soften the bituminous coating on the paper wrapping and effect saturation of the fibrous jacket with the bituminous material but too short for any substantial amount of the bituminous material to penetrate through the paper wrapping.

5. In the manufacture of a multiconductor cable, involving assembling two or more wires within a common sheath, the improvement which comprises forming said sheath by applying about an assembly of individually insulated wires a wrapping of paper that has been precoated on one side only with a bituminous material having a softening point above 125 F., said paper being applied with its coated side facing away from the wires, applying a jacket of fibrous material about the thus-wrapped assembly, and immersing the Jacketed assembly in a bituminous material having a softening point above F. and heated to above 300 F. for a period of time not longer than about flve seconds, whereby the coating on the paper is softened and the brous jacket is impregnated with the bituminous material but no substantial amount of the bituminous material penetrates through the paper.

6. In the manufacture of a multiconductor cablel involving assembling two or more wires within a common sheath, the improvement which comprises forming said sheath by applying about an assembly of individually insulated wires a wrapping of fibrous material that has been precoated on one side only with a first thermoplastic material, said wrapping being applied with its coated side facing away from the wires, applying a jacket of fibrous material about the thuswrapped assembly, and impregnating the jacket with a second thermoplastic material having a softening point higher than that of said first thermoplastic material and heated to a temperature above its softening point, the duration of the impregnating operation being long enough to soften the first thermoplastic material coating the wrapping and effect saturation of the jacket with the thermoplasie materials but too short for any substantial amount of bituminous material to penetrate through the fibrous wrapping.

7. In the manufacture of a multiconductor cable involving assembling two or more wires within a common sheath, the improvement which comprises forming said sheath by applying about an assembly of individually insulated wires a wrapping of paper that has been precoated on one side only with a, first bituminous material having a softening point above 125 F., said wrapping being applied with its coated side facing away from the wires, applying a jacket of fibrous material about the thus-wrapped assembly, and impregnating the jacket with a second bituminous material having a softening point higher than said first bituminous material and above F. by immersing the ja'cketed assembly for a period not longer than about five seconds in a bath of said second bituminous material that is heated to a temperature above 300 F., whereby the coating on the paper Wrapping is softened and the jacket is thoroughly saturated with bituminous material but no substantial amount of the bituminous material penetrates through the paper wrapping into contact with the individual insulaed wires.

JOHN W. OLSON.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 809,312 Lougee Jan. 9, 1906 1,890,253 Frederickson Dec. 6, 1932 1,905,789 Benner et al Apr. 25, 1933 2,090,510 Bower Aug. 17, 1937 2,093,411 Bowden et al. Sept. 21, 1937 2,222,638 Szilard Nov. 26, 1940 2,281,111 Robinson et al Apr. 28, 1942 2,426,413 Pollett Aug. 26. 1947