US2697740A - Wire insulation - Google Patents

Description

Dec. 21, 1954 J NOVAK 2,697,740

WIRE INSULATION Filed April 2, 1949 1721/2 11 for: .[Zadm' J,//0 W&Z

(2% orneg United States Patent WIRE INSULATION lzador J. Novak, Trumbull, Conn., assignor to Raybestos- Manhattan, Inc., Passaic, N. L, a corporation of New Jersey Application April 2, 1949, Serial No. 85,187

Claims. (Cl. 174-110) This invention relates to electrical conductors or other wire provided with an insulating wall or walls of novel character, and to a novel method for the manufacture thereof.

It is an object of the present invention to coat wire, such as electrical conductors, welding wire, wire reinforced asbestos for packing, wire for heat insulation, and the like with fibrous asbestos, but without requirement for such procedures as carding, spinning or weaving the asbestos fibers.

It is a further object to coat wire with asbestos in a rapid, economical, highly efiicient and efiFective manner, so as to provide the electrical conductors. with a unitary insulating wall of fibrous asbestos of high thermal resistance and dielectric strength.

In general, the objects of the present invention are accomplished by extruding, in a continuous manner, an aqueous, plastic, self-sustaining mass of individualized and dispersed, i. e. non-clotted, asbestos fibers composed of single fibers or fascicular fiber bundles instead of the predominantly clotted and tangled multiple fiber groups known to wet or dry asbestos practice, and wherein the fibers are in a lubricated, slippery and relatively slidable condition, and which may be prepared in accordance with the general teachings of the ctr-pending application of I. J. Novak, Serial No. 66,552, filed December 21, 1948, now Patent No. 2,626,213, the present application being a continuation-in-part thereof.

The dispersed asbestos employed in the practice of the present invention, and as further described in said application, is composed predominantly of Chrysotile asbestos fibers of unit diameter, that is of a diameter of from about 200 to about 500 Angstrom units, the fibers having organic surface-active agent adsorbed thereon, the aqueous phase of the. plastic mass, as presently employed, containing an additional relatively small amount of free surface-active agent. As further described and claimed in said application, the asbestos mass herein employed is prepared by mixing Chrysotile asbestos agglomerates with an aqueous liquid containing organic surface-active detergent adsorbable on the asbestos and capable of forming n alkaline dispersion therewith. the amount of detergent being in excess of that adsorbed on the asbestos and sufficient to form and preserve the dispersion. One highly suitable example of such detergent is Aerosol OT (dioctyl sodium sulfosuccinate).

By first preparing such dispersion in highly dilute condition, say 0.1% to 1% asbestos content it is possible to remove by, for example, slotted screen plates such as employed in paper making, associated impurities, such as serpentine fragments, magnetite inclusions or other clots which do not open, or are not adequately opened, portions of original rock, and altered asbestos which is not amenable to fiberization. This results in a refined asbestos and, when ultimately applied to the wire. provides a covering of a fine uniform character with attendant advantages which will be readily apparent as to uniformity of insulating character, dielectric value, strength, etc., and allows extrusion of thin walls of asbestos without the defects which might be caused by oversize fragments or clots of fiber.

For use in accordance with the present invention, the asbestos dispersion should have a high enough concentration or asbestos content so as to beof a plastic, selfsupporting nature so that it will hold its position and shape when applied to the wire and not drip or drop ofi 2,697,740 Patented Dec. 21,. 1954 between the period of application and drying thereof. A dispersion of about 25% to 60% by weight of asbestos has been found to meet this requirement where no additional viscosity builders are added. By the use of viscosity builders such as glue, alginates, polyvinyl alcohol, bentonite, etc., the self-supporting character may be obtained at lower asbestos concentrations. The maximum asbestos concentrations which can be employed is one which still has adequate plastic flow and which will not clog the extrusion orifice, and both the minimum and maximum concentrations will be related to the thickness of the extruded coating.

If the dispersion is originally prepared in dilute form, it may be concentrated to the desired extent by removal of dispersing fluid by such means as filtration or centrifuging. Thus, an asbestos dispersion of about 30% fiber content prepared with Aerosol OT will be stable with a total Aerosol OT content of about 4% by weight of the asbestos, but, as: actually employed, will preferably contain about 6% thereof. With higher concentrations, the amount of dispersing agent will be some what reduced, since although there is a minimum requirement for adsorption on and opening of the asbestos, an additional amount is required to maintain the dispersion and which is proportional to the amount of the aqueous phase of the dispersion.

In one specific embodiment, and for the insulation of electrical conductor wires, particularly when little or no added binders are employed, the present invention is further characterized by the employment of asbestos fibers of spinning grade length which provides good strength to the applied insulating wall and resistance to rupture and deformation thereof in use and on fiexing, particularly when the fiber formation is arranged in helical fashion about the conductor, as will be hereinafter more fully set forth. Fibers of spinning grade length are those known as #1 and #2 crude, and the group of #3 grades of mill fibers, in accordance with Canadian Chrysotile Classification, and as set forth on page 70 in Bulletin 403 of the U. S. Department of interior, Bureau of Mines, entitled Asbestos." The #3R grade has been found particularly suitable for the present purpose.

The invention will be further explained in connection with the accompanying drawings, wherein:

Fig. 1 diagrammatically illustrates an arrangement of apparatus for extruding a plastic mass of dispersed asbestos upon an electrical conductor or other wire;

Fig. 2 is a view on the line 22 of Pig. 1; and

Fig. 3 is an illustration of a length of conductor, coated in accordance with the present invention.

Referring to the drawings, the reference numeral 10 illustrates a hopper for reception of a supply of a plastic mass of dispersed asbestos 11 which is fed to the cham ber of the extruder 12 under pressure by means of the mechanical feed screw 13. The dispersed asbestos mass may include plastic binders in emulsion or in dissolved form, such as, for example, the binders previously indicated, rubber, silicone resins, or other insulating binders, compounding agents, fillers and the like, and which do not affect or upset the stability of the asbestos dispersion. These may be added by direct addition to the plastic asbestos mass in a suitable mixer, such as a dough mixer, Banbury mixer, cake mixer, or the like, as emulsions or cements, or even as undiluted oils or monomers, since the plastic asbestos mass has high emulsifying properties. The electrical conductor 14, which may be composed of one or more strands of wire, is drawn from the reel 15 into the extrusion chamber 12, through the mandrel 16 and its wire aligning cone 17. Although not essential, if desired, the wire 14 may be preheated or pre-coated with an adhesive of either a water-aetivatable nature, such as glue, or heat-activatable nature, such as styrene polymer, for the purpose of providing better bond of the asbestos to the wire. Although not shown, the extruder may be provided with conventional means for heating the wire in its path to or at the extruding die 18 if the wire is to be pre-heated or provided with a heat-activatable binder coating as previously indicated. As the wire is drawn through the orifice 19 of the extruding die 18, it becomes surrounded with a layer of dispersed asbestos 11 which, due to the dispersed, individualized nature of the fibers thereof and due to the extruding action, takes on a fiber formation which is substantially parallel in the longitudinal direction to the wire 14. Immediately upon issuance of the wire with its extruded wall of dispersed asbestos, it is passed through the revolving head, generally indicated at 20, and which comprises a rotatable disc 21 provided with a plurality of radially adjustable arms 22 having rounded terminal ends for smoothing the coating upon emergence from the extruder. tive rotary motion to the conductor and its coating, further serve to arrange the fibers of the asbestos coating in a helical direction as indicated at 23 of Fig. 3 instead of permitting the fibers to remain directionalized in the direction of the wire travel, so that the flexing of the covered conductor will not tend to open up a path between the fibers to the conductor. For some uses, however, it may not be necessary or desirable to rearrange the fibers, and in such event the revolving head 20 may be by-passed. The covered conductor next passes through a suitable drying and curing chamber 24 which may be electrically or otherwise heated, and is thereafter reeled up on the reel 25. The curing chamber serves to evaporate the moisture, and auxiliary solvent or other dispersing agent when present, from the dis-- persed asbestos coating and further serves to modify the character of the organic dispersing agent employed, and to reduce the unctuous or slippery and lubricated nature of the asbestos dispersion to a firm bonded character and to enhance the strength thereof. The drying or curing chamber 24 may further serve to heat-cure admixed bonding agents when employed as previously indicated. The temperature and time of curing should be correlated and controlled so as to avoid steam blisters which might loosen the coating on the wire or distort the coating within itself, and to dry or cure any of the aforementioned additives if employed, and activate a heat sensitive adhesive on the wire if this is employed, as will be understood by those skilled in this art.

Although not illustrated, it will be apparent that a plurality of successive extrusion and curing means may be employed before reeling up the coated wire on the reel 25, to coat the wire with a plurality of layers of dispersed asbestos or other insulating or coating compositions. In similar manner, there may be interposed before final reeling up of the wire, means for impregnating the asbestos coatingthe coating being amenable to such treatment, it being of a finely porous nature. Means may similarly be interposed or added, such as rolls or condensing tubes, not shown, for densifying the dried or cured asbestos coating, either as an intermediate step when successive layers are applied, or as a final step.

Due to the nature of the asbestos dispersion employed, and the great number of fibers of extremely small diameter, which predominate and characterize the material, the resulting coating is of high density and of high dielectric strength and yet withal may be composed substantially entirely of asbestos fibers, with the exception of the small residue of organic material which may be as low as 1-2% after cure where no organic binder has been added. Further, due to the employment of and the ability to employ fibers of the spinning grade length, and the helicalization thereof after extrusion, the resulting coating wall retains its unitary or continuous The rotating arms 22, by their relaone-piece nature and strongly clings to the wire upon repeated rough usage and flexing to provide and maintain a highly effective insulating wall of a character heretofore not obtainable.

In another, non-fully equivalent embodiment of my invention, I may employ shorter grade of asbestos, such as from the paper making grades down to dust for the coating of such wires as welding wire. With these shorter fibers, however, a flexible or elastomeric heat resisting binder must be incorporated, and I have found that I may employ such binders in the amount up to 40% by weight of the short fiber asbestos, in which event the properties of the coating become predominantly the properties of the binder, rather than the properties of the asbestos. Such binders as silicone binders, poly-fluoro ethylenes, or poly-chloro-fluoro-ethylene may be used as binders. Since it is essential that the coating be of such a character that it resists fracture at the knee on bending the covered wire, the flexible heat resistant binders should be incorporated in suflicient amount to overcome any tendency of short fiber asbestos to crack or break on bending to avoid exposure of the covered wire.

I claim as my invention:

1. The combination with a wire of a continuous surrounding layer of a dried residue of a plastic mass comprised of an alkaline, gelatinous, stable, aqueous dispersion of individualized Chrysotile asbestos fibers predominantly of a diameter of from about 200 to about 500 Angstrom units and containing organic surface-active agent adsorbable by and adsorbed on the fibers and a free excess in the aqueous phase maintaining the dispersion.

2. The combination with a wire of a continuous flex-.

ible surrounding layer comprised of the dried residue of a colloidal dispersion os asbestos fibers.

3. The combination with an electrical conductor of a continuous, flexible, plastic surrounding layer comprised of the dried residue of a colloidal dispersion of asbestos fibers and a plastic binder.

4. The combination with an electrical conductor of a continuous, flexible surrounding layer comprised of the dried residue of a colloidal dispersion of asbestos fibers and an elastomeric binder.

5. An insulated conductor including a coating of asbestos which is the residue of a dispersion of finely divided asbestos fibers in a liquid.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 290,121 Shaw Dec. 11, 1883 1,370,800 Egerton Mar. 8, 1921 1,907,616 Tucker May 9, 1933 1,946,331 Reeves Feb. 6, 1934 2,138,378 Johnson Nov. 29, 1938 2,258,219 Rochow Oct. 7, 1941 2,308,638 Balthis Jan. 19, 1943 2,332,535 Smith Oct. 26, 1943 FOREIGN PATENTS Number Country Date 544,681 Great Britain Apr. 23, 1942

Claims (1)

1. 5. AN INSULATED CONDUCTOR INCLUDING A COATING OF ASBESTOS WHICH IS THE RESIDUE OF A DISPERSION OF FINELY DIVIDED ASBESTOS FIBERS IN A LIQUID.

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