US2103841A - Method of insulating conductors - Google Patents

Description

De-c.'28, 1937. J. F. CALVERT 2,103,841

METHOD OF INSULATING CONDUCTORS Filed Jan. 50, 1957 WlTNESSES: INVENTOR Job/7 Ca/l/erz Patented Dec. 28, .1937

UNITED STATES PATENT OFFICE John F. Calvert, Ames, Iowa, assignor to Westinghouse Electric 8: Manufacturing Company,

syl

East Pittsburgh, Pa., a corporation of Pennvania Application January 30, 1937, Serial No. 123,243

' 8 Claims.

o the insulating material, a part of the bonding material is lost in the form of a vapor before the material is suiiiciently polymerized to the nonvolatile state. The escaping vapor tends to leave voids in the insulation. Such non-uniformly in-' sulated conductors .are dangerous.

An object of. this invention is to provide a method of insulating electric conductors whereby the conductors will have a uniform insulating coating.

A further object of this invention is to provide a method for preventing loss of insulating material by vaporization while insulating an electrical conductor.

Other objects of this invention will become apparent from the following description when taken in conjunction with the accompanying drawing, in which the single figure, partly in section and partly in side elevation, illustrates a conductor which is insulated in accordance with the teachings of this invention.

According to this invention, tape coverings or wrappings for electrical conductors are impregmated with self-polymerizing material and the covered conductors are subjected to a treatment for polymerizing the material in the tape whereby a uniform insulating coating is provided for the conductor.

In order to secure a satisfactory impregnation of the tape usually employed in the insulating conductors, it has been found to be desirable to thoroughly cleanse the tape of resin and deleterious material before the self-polymerizing material is applied. In practice, tape comprising papenmica flakes and asphaltic sticking varnish may be cleansed by treating the tape with benzol to extract the asphaltic varnish. Since benzol is quite volatile, it is easily removed by drying the tape.

The cleansed mica tape is impregnated with an insulating medium of the self-polymerizing tape which may be satisfactorily hardened. Selfpolymerizing materials which may be satisfactorily employed as the insulating medium comprise styrol, such as monostyrene or a low viscosity or fluid product of styrol such as a mixture of polymerized products of styrene in liquid styrene. Other self-polymerizing materials which may also be employed are derivatives of acrylic acid or alpha methyl acrylic acid or derivatives of acrylic acid or alpha methyl acrylic acid which are only slightly polymerized and fluid or have a low viscosity.

In preparing the conductor to be insulated, the tape is impregnated in any suitable manner such as dipping or brushing with one of the selfpolymerizing materials hereinbefore mentioned. In order to stabilize the impregnant and to prevent the polymerization of the material until desired, an inhibitor such as hydroquinone is mixed in the self-polymerizing material. As illustrated in the drawing, tape impregnated with the selfpolymerizing material containing the inhibitor is wrapped around the conductor 10 constituting an inner layenor covering l2, the reason of which will be explained more fully hereinafter.

Since the impregnant is volatile and it is desired to prevent loss of the insulating materialby vaporization, additional tape is impregnated with the self-polymerizing material to form an outer layer or covering 14 when wrapped on the conductor ID, as illustrated in the drawing. In order to accelerate the polymerization of the insulating material in the outer layer H to obtain the polymerization thereof without excessive losses by. volatilization of the material, a catalyst such as benzoyl peroxide is added to the self-polymerizing material before the tape is impregnated.

In order to harden the outer layer [4, to prevent losses of the impregnant of the layer I2 when heat treated, as described hereinafter, the tape wrapped conductor is heated to a sufficient temperature to cause the polymerization of the impregnant containing the catalyst in the outer layer It. Through experience, it is found that Where the tape wrapped conductor is exposed to room temperature for a period of time of a few hours, the self-polymerizing material in the outer layer It becomes hardened. The polymerization of the insulating material in the outer layer l4 may be further accelerated by heating briefly at slightly higher temperatures than room temperature.

In order to protect the wrappings of tape around the conductor II) when subjected to heat and pressure to cause the polymerization of the insulating material of the inner layer of tape, a protective covering [8 of some suitable material such as cotton tape or cotton tape with a clay or powder on the surface adjacent the outer layer ll of tape iswrapped around the exposed surface Gil or the hardened outer layer 14. Other soft and pliable sheet material which may be easily wrapped around the conductor or applied to the conductor surface and held in place may be employed as the protective covering.

In order to polymerize and harden the insulating material containing the inhibitor in the inner layer of tape, the wrapped conductor in its protective covering is immersed in hot asphalt orvother hot fluid in an autoclave and then sub- 'jected to heat and pressure for a predetermined period of time sumcient to polymerize the impregnant. As a result of hardening the outer layer of the tape around the conductor before immersing the conductor in the hot asphalt and subjecting it to heat and pressure, the full hydrostatic pressure developed in the autoclave is exerted with equal force throughout the entire outer surface of the windings of the conductor, producing a dense and uniform insulating struc-. ture around the conductor, When removed from the autoclave, the protective covering may be removed from the insulated conductor where desired.

In practicing this invention, the tape comprising the different layers around the conductor may be thoroughly impregnated with the sellpolymerizing materials containing the inhibitor or catalyst as hereinbeiore described and then wound around the conductor. Instead.- of impregnating the tape prior to winding the conductor, the conductor may be wound with an unimpregnated layer oi tape and then the taped conductor may be brushed with or dipped into the sell-polymerizing material containing the in hibitor to thoroughly-impregnate it. An outer layer of unimpregnated tape ,may then be wrapped around the impregnated layer, after which the wrapped conductor maybe brushed with or dipped into the self-polymerizing mate rial containing the catalyst impregnate the outer layer of tape.

m practicing this method, it is iound that there is very little loss oi the volatile seli-poly=' merining material by vaporization during the polymerization process. This is because the hardened outer layer oi the tape prevents the escape of the impregnating material in the inner layer oi the tape when heat and pressure are applied thereto. Conductors which have been wrapped with tape impregnated with self-polymerizlng materials containing inhibitors and catalysts and polymerized, as hereinbeiore described, have been found to be uniformly insu= lated. h'nrther, this type of insulation has been found to have a very low power factor and to be quite hard at temperatures ranging between 90 C. and 12d (G.

While a specific method has been described embodying this invention, it is to be understood that this invention is not to be limited thereto except as is necessitated by the prior art and the scope oi the appended claims.

I claim-as my invention:

1-. In the method of insulating conductors, in

combination, covering the conductor with a lay-.

er of self-polymerizing materialcontaining an inhibitor, covering the layer of sell-polymerizing opposing the covered conductor to sumcient heat to cause the layer of material containing the catalyst to harden without causing polymerization of the material containing the inhibitor, and

pressure to cause the material containing the inhibitor to hardemthe layer of material hardened before the polymerization of the material containing the inhibitor preventing vaporization of the materal polymerized under the heat and pressure.

2. In the method of insulating conductors, in combination, covering the conductor with a plurality of layers of self-polymerizing material, theinner layer of the self-polymerizing material containing an inhibitor and the outer layer containing a catalyst, exposing the covered conductor to suficient heat to harden the'outerlayer of matetaining an inhibitor associated therewith and the outer layer of the tape having a self-polymerizing? material containing a catalyst associated therewith, subjecting the wrapped conductor to a temperature of at least room temperature to harden the material containing the catalyst in the outer layer of tape without causing polymerization oi the material containing the inhibitor in the inner layer of the tape, and subjecting the conductor I in the hardened outer layer of tape to heat and pressure to cause the polymerization of the material containing the inhibitor, the outer layer of tape and its associated hardened material preventing loss of the material containing the inhibitor by vaporization during its polymerization.

imthe method of insulating conductors, in combination, wrapping a layer of tape on the conductor, impregnating the tape with a selfpolymerizlng material containing an inhibitor,

wrapping an outer layer of tape on the tape impregnated with the self-polymerizing material containing the inhibitor, impregnating the outer layer of tape with a self-polymerizing material containing a catalyst, subjecting the wrapped conductor to'a temperature of at least room temperature to harden the material containing the catalyst in the outer layer of tape without causing polymerization of the material contain-= ing the inhibitor in the inner layer of the tape. and subjecting the conductor wrapped in the hardened outer layeroi tape to heat and pres sure to cause the polymerization of the material containing the inhibitor, the hardened outer layer or tape preventing loss or the material containing the inhibitor by vaporization during its poly-= merization.

5. In the method of insulating conductors, inv

combination, wrapping the conductor with a plurality of layers oitape, the inner layer of the tape having a self-polymerizing material containing an inhibitor associated therewith and the outer layer or the tape having a. sell-polymerinng material containing a, catalyst asso= elated therewith, subjecting the wrapped conductor to a temperature of at least room ternperature to harden the material containing the catalyst in the outer layer of tape without caus ing polymerization of the material containing the inhibitor in' the inner layer or the tape,

wrapping aprotective covering over the hardened outer layer of tape, immersing the conductor in the protective wrapping in a-hotresin and applying pressure thereto to cause the polymerization of the material containing the inhibitor, the hardened outer layer .of tape preventing loss of the material containing the inhibitor by vaporization during its ,polymerization, removing the conductor from the hot resin when the material containing the inhibitor is polymerized, and removing the protectivecovering from the insulated conductor.

6. In the method of insulating conductors, in combination-wrapping .a layer 01 tape on the conductor, impregnating the tape with a selfpolymerizing material containing an inhibitor,

wrapping an outer layer of tape on the tape impregnated with the self-polymerizing material containing the inhibitor, impregnating the outer layer oi tape. with a self-polymerizing material containing a catalyst, subjectingthe wrapped conductor to a temperature of at least room temperature to harden the material containing the catalyst in the outer layer of tape without causing polymerization of the material containing the inhibitorin the inner layer of the tape, wrapping a protective covering over the hard ened outer layer of tape, immersing the conductor in the protective wrapping in a hot resin andcombination, impregnating tape with a selfpolymerizing material containing an inhibitor,

wrapping the impregnated tape on the conductor. covering the wrapped conductor with an outer layer of self-polymerizing material containing a catalyst, subjecting the covered conductorto a temperature of at least room temperature for a period oi time sufflcient to harden the outer layer of self-polymerizing material without causing polymerization of the selfpolymerizing material in the tape wrapping, and subjecting the conductor in the hardened cover'to heat and pressure to cause the polymerization of the material containing the inhibitor in the tape, the hardened outer covering on the conductor preventing loss of the impregnating material of the tape by vaporization during its polymerization.

8. In the method of insulating conductors, in

combination, impregnating tape with a selfpolymerizing material containing an inhibitor,

wrapping the impregnated tape on the conductor, covering the wrapped conductor with an outer layer of self-polymerizing material containing a catalyst, subjecting the covered conductor to a temperature of at-leastro'om ternperature for a period of time suflicient to harden the outer layer of self-polymerizing material without causing polymerization of the selfpolymerizing material in the tape wrapping, wrapping a protective covering over the hardened outenlayer to protect it, immersing the conductor wrapped in the protective covering in a hot resin and applying pressure thereto to cause the polymerization of the material containing the inhibitor in the tape, the hardened outerlayer of material preventing loss or the impregnating material of the tape by vaporization during its polymerization, removing. the conductor from the hot resin when the impregnant oi the tape is polymerized, and removing the protective covering from the insulated conductor.

' JOHN F. CALVERT.

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