US2190711A - Sheet insulation material - Google Patents

Description

Feb. 20, 1940. Q F HANSQN 2,190,711

SHEET INSULATION MATERIAL Filed- March 16, 1958 INVENTOR BY 627k? 6'0/I/, W

AT TORNEY Patented Feb. 20, 1940 UNITED STATES PATENT OFFICE SHEET INSULATION MATERIAL Application March 16, 1938, Serial No. 196,146

4 Claims.

This invention relates to improvements in flexible electrical-insulation spacing, binding and wrapping material in the form of coated or impregnated sheet material; and the invention has reference, more particularly, to a novel material of high normal dielectric properties which is capable of maximum stretch, especially under conditions of use requiring lapped winding thereof, without risk of reducing or impairing its dielectric properties sufliciently to render it either inefficient or unsafe.

Coated or impregnated sheet material for electrical insulating functions have heretofore been available. These heretofore known materials have included varnished kraft and bond papers, as well as varnished straight out and bias cut textile fabrics, such as cotton cloth.

Varnished kraft and bond papers have been successfully employed as spacing insulation between windings of electrical coils of various kinds, and can be used as an insulating wrapping around electrical conductors when no lapping of the helices of the wrapping is required. When, however, lapping of the windings of such varnished papers about a conductor is attempted its use for such purpose is very unsatisfactory and in the majority of instances a failure. The reason for this lies in the fact that such varnished papers cannot be lapped in winding since the paper body does not possess sufficient strength or extensibility to permit the over-lapped marginal edge portion of a succeeding winding of the tape thereof to elongate where engaged. over and around the underlying marginal edge portion of the preceding winding thereof.

Varnished cloth of the straight out type may be employed in the form of tape for winding around a conductor, provided the winding is done by machine, but even then only very narrow laps are possible, since this material does not permit of enough stretch or extensibility to allow a wide overlap of one winding thereof upon another.

Neither the varnished papers nor the straight out varnished cloth above referred to can be satisfactorily applied to electrical conductors by hand overlap, since material of this type is easily stretched or extended. In applying this type of material by hand, as a spirally wound wrapping about a conductor, if too much pull is exerted during the winding application thereof, there is considerable risk of rupture and consequent impairment of its dielectric strength. This tendency to rupture is the cause of constant apprehension among insulation engineers who are responsible for proper application of this type of tape in practice, and much damage can be done by a workman who applies this type of tape should he pull it excessively with consequent im pairment of its dielectric strength, and resultant condemnation of the finished work.

It is an object of this invention to provide a novel coated or impregnated sheet material for insulation purposes which overcomes the objections to the materials hereinabove referred to in that it possesses a considerable degree of elastic ity, extensibility or stretching ability, while at the same time being of such physical characteristics that it will resist stretch to an extent likely to dangerously impair the dielectric strength of the coating or impregnation forming part thereof and the invention has for another object to provide a novel sheet material so characterized which can be easily cut to or produced in tape form for use in wrapping conductors either by hand or machine, but being especially adapted for hand wrapping manipulation.

The invention has for another object to provide a novel coated or impregnated insulation tape capable of such extensible or stretched deformation as to permit attainment of smooth and tight overlapped windings thereof about a conductor to which it is applied; and whereby lapping thereof up to at least one-half its width is readily possible of attainment.

Other objects of this invention, not at this time more particularly enumerated, will be understood from the following description of the same.

Illustrative embodiments of this invention are shown in the accompanying drawing, in which:

Fig. 1 is a face view of sheet insulation material according to this invention, with parts broken away to show component parts thereof; and Fig. 2 is a sectional view of the material of Fig. 1, drawn on a greatly enlarged scale. Fig. 3 is a view similar to that of Fig. 1 but showing a modified form of the sheet insulation material according to this invention.

The novel sheet insulation material according to this invention comprises a basesheet of crepe paper It] which is characterized by the possession uct.

of a wrinkled or rugose grain. To the crepe paper body In is applied any suitable form of insulating varnish, such e. g. as those made from tung oil, linseed oil and resin combinations so formulated as to yield a somewhat elastic prod- The selected varnish may be either clear, black or pigmented as may be desired. The insulating varnish may be applied, as coatings II, to one or both faces of the crepe paper body or base so as to evenly film over said surfaces or impregnate the paper body to a desired degree.

The sheet insulation material, characterized as above described, will be found to be highly efiicient as to its dielectric properties, while at the same time possessing to a marked degree the physical properties of stretchability or elastic extensibility which is highly desirable, especially when using the material in a tape form for winding insulating wrappings about conductors and other electrically conductive elements.

In producing tapes from the material, the sheet material is cut into strips of suitable width in such manner that the rugose grain of the crepe paper body or base is disposed substantially transversely of the length of the strip or tape, i. e. the rugose grain may run symmetrically crosswise of the tape, as indicated in Fig. 1, or it may run diagonally or on the bias, as indicated in Fig. 3.

Owing to the rugose grain of the crepe paper body or base, as disposed to lie substantially transversely of the length of the tape, said tape is adapted to easily stretch lengthwise to a considerable degree by reason of the fact that rugosities of the crepe paper body or base tend, under. stretching effects, to flatten out thus yieldingly extending itself where subjected to pulling stresses. Since the insulating varnish coatings of the tape also conform more or less to the rugosities of the crepe paper base, while at the same. time the coating films per se are also possessed of more or less elasticity, when the crepe paper body or base is stretched or extended an accompanying and corresponding stretch or extension of the varnish films will also occur, and consequently the tape as a whole is adapted to stretch or extend to a considerable extent with minimum risk of fracturing or puncturing the varnish film or films with resultant impairment of the dielectric strength or efficiency thereof.

From the above it will be obvious that a highly efiicient varnished insulating tape is provided by the sheet material made according to this invention, which, especially when used to obtain a wound wrapping for envelopment of electrical conductors and the like, will easily stretch or elongate in the areas of the turns or windings thereof which overlap preceding turns or wind-' for use in hand wrapping electrical conductors,

cables and the like.

Tests of a sample run of the novel varnished crepe paper insulating tape have shown the following:

The dielectric strength of the tape in its initial non-stretched condition approximates 1540 volts per mil.

The dielectric strength of the tape, after average stretch or elongation, such as occurs when the same. is snugly and smoothly wrapped by overlapped windings about a conductor either by hand or machine, approximates 1360 volts per mil.

The dielectric strength of the tape after it has been pulled to rupture in a tensile testin machine approximates 1000 volts per mil.

From the standpoint of extensibility or elongation, the novel varnished crepe paper tape will elongate from 1 to 1.5% under a load of 6 pounds per inch width applied for 35 minutes at room temperature.

Comparing the dielectric properties and extensibility of the novel varnished crepe paper tape, as above indicated, with that of straight out varnished cloth tape, it is found that its dielectric strength, is substantially the same as that of said straight out cloth tape, but its extensibility is considerably more. To obtain the same amount of elongation in straight out varnished cloth would require application thereto of apvolts per mil. whereas, as above set forth, the

latter possesses, when pulling to rupture, a dielectric strength approximating .1000 volts per mil; -it is therefore obvious that, under such conditions, the varnished crepe paper tape possesses a dielectric strength about seven times greater than that possessed by bias cut'vamished cloth.

The results of the tests of a sample run of the tape above quoted are indications of the superiority thereof with respect to dielectric strength and extensibility which have been obtained by laboratory tests; for application of the tape in use, however, it is believed the following specifications can be assured:

A dielectric strength in initial condition of 1100 volts per mil.

A dielectric strength, after elongation resulting from application of a load of six pounds per inch width for thirty-five minutes, of 900 volts per mil.

A dielectric strength, after rupture in a tensile test, of 800 volts per mil.

Having described my invention, I claim:

1. Flexible insulation material for the purposes described which is capable of local stretching in areas thereof subjected to excess stress comprising, a sheet of'asymmetrically crinkled paper providing a multiplicity of discretive sinuosities forming a rug ulose grain, and a coating film of elastic insulating varnish adhered to' at 3. A flexible insulating tape capable of local stretching in areas subjected to excess stress comprising, asymmetrically crinkled paper procomprising, asymmetrically crinkled paper providing a multiplicity of discretive sinuosities forming a, rugulose grain which runs substantially transverse to the length of the tape, and coating films of elastic insulating varnish united with 5 and covering the opposite faces thereof.

CARL F. HANSON.

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