US1982179A - Inorganic insulation for electrical sheets - Google Patents

Description

Patented Nov. 27, 1934 1,982,179 INORGANIC INSULATION FOR ELECTRICAL SHEETS Charles A. Scharschu, Brackenridge, Pa., assignor to Allegheny Steel Company, a corporation of Pennsylvania No Drawing. Application June 8, 1931, Serial No. 543,003

3 Claims. (01. 15443) This invention relates to inorganic enamels for electrical sheets and to a method of applying the same to such sheets.

Hitherto organic enamels or varnishes have been used to coat electrical sheets for the purpose of insulating one sheet from another in electrical apparatus, thus cutting down the eddy loss. There are, however, many applications for which this type of coating is objectionable, such as in those cases where it is desired to anneal the punching after the enamel has been applied.

For producing porcelainic enamels, silicates are generally used, but these enamels, on account of the properties desired, are more complex than is preferred in an enamel for electrical sheets and these enamels are, moreover, of such a composition and fired at such temperatures as to cause the enamel to melt and flow. Enamels of this nature consequently are not suitable for electrical sheets as such enamels would cause the individual sheets to stick together when annealed in stacks. Again, these enamels are much heavier and more continuous than is necessary for the insulation of electrical sheets.-

Inorganic enamels when properly made and applied have excellent electrical resistance and. may be used to coat electrical sheets. When inorganic enamels are used the electrical sheet may be enameled before it is punched or cut into parts for electrical apparatus and these punchings may be subsequently annealed to produce better electrical qualities without destroying the enamel.

One of the objects of this invention is the provision of an inorganic insulation which will adhere to electrical sheets and which can be uniformly deposited thereupon.

Another object is to provide an inorganic insulation which can be subjected to an anneal without detriment to the enamel.

A further object is the production of an inorganic enamel of certain composition which not only has the desired electrical properties but which acts as a protective coating for the sheets to prevent rusting of the same.

A still further object is the provision of a meth- -od of applying an inorganic insulating material so as to produce an even adherent coating having the desired characteristics.

Other and further objects and advantages will be understood by those skilled in this art or will be pointed out hereinafter.

I have found that very simple enamelsare satisfactory for coating electrical sheets. For instance, water glass may be used as the source of 59 silicate although finely ground silica may also be used. To either of these there is added lime and another metallic oxide such as iron oxide, the proportions depending upon the properties desired in the enamel.

For example, these three constituents are used in the following proportions for certain applications:---

Water 200 cc.

Lime 15 grams Iron oxide 28 grams Water glass '70 grams It is understood that magnesium oxide may be substituted for the lime or both may be used and that silica, preferably in a finely ground condition, may be substituted for the water glass and the iron oxide may or may not be used depending upon the properties desired in the enamel.

The sheets of material destined for electrical uses are passed singly through a bath of the liquid enamel, then through a set of rolls and through a drying oven to drive off the water. The rolls cause an even distribution of the liquid enamel on the surfaces of the sheets and remove excess enamel and may be of any suitable type. If desired, or found necessary glue or. an excess of water glass'may be added to the bath to make the enamel adhere more tightly to the sheet before the sheets are heated.

The drying oven is kept at a suitable temperature, for example, about 600 Fahrenheit, and the coated sheets are passed therethrough at a suitable rate such that the coating is subjected to the heat for about two minutes. The coating is iinally baked on in the anneal which is carried out at about 1450 Fahrenheit. The temperature of the drying oven may vary considerably but in such cases the time of exposure thereto is suitably varied in inverse relationship thereto; that is, the hotter the oven the less the time of exposure and the cooler the oven the greater the time of exposure.

I may vary the constituents over wide limits to produce enamels having different properties, which when baked at the proper temperature form an insulating enamel suitable for electrical sheets. This enamel, especially when applied to pickled sheets, also acts as a protective coating preventing the sheets from rusting.

What I claim as new and desire to secure by Letters Patent is:

1. Steel elements for electrical apparatus coated with an inorganic electrical insulating enamel consisting substantially entirely of an insoluble complex silicate unaffected by conditions encountered in annealing such sheets according to commercial practice.

2. Steel elements for electrical apparatus coated with an inorganic electrical insulation consisting chiefly of silica, iron oxide and an oxide of the alkaline earth metals converted by heat, prior to annealing the elements, into a complex silicate which is un'afiected by moisture and by conditions of annealing encountered in the processing of such elements.

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