US1996840A - Process of enameling metal articles - Google Patents

Description

Patented Apr. 9, 1935 1 UNITED STATES PATENT OFFICE PROCESS OF E Homer F. Staley,

This invention relates to 1,996,040 museum rmrsr. narrows Warren Township, somerset County, N. J.

No. Drawinl. Appli cation May a, 1932,

Serial no. 613,271

. 5 Claimsprocesses of enameling metal articles; and it comprises heating an article in a non-oxidizing atmosphere in a furnace to an enamel-fusing temperatm'e and applying one or more coatings of dry powdered vitriflable enamel material, by means of a Jet, to

the article in the furnace,

the temperature remaining at an enamel-fusing point throughout the process; all as more forth andasclaimed.

fully hereinafter set In enameling metal articles, it is customary to apply a coating of afusible enameling composition to the metal, at atmospheric temperatures,

and then place the article in a furnace and heat it until the coating fuses; this operation forming what is called a ground coat. The coating may be applied either as a dry powder or in liquid suspension. If additional coatings are desired, the article is removed from the furnace afterthecoatingisfusedin place, and, in the dry powdering process, a powderis sifted on to the hot surface, and

the article is then returned to the furnace and heated until the second coatfuses. This operation can be repeated to obtain the desired number of coatings. where the wet used, the ground-coated article coming process is from the furnace is allowed to cool to atmospheric temperature, then a in a liquid vehicle, generally water,

suspension of enamel is sprayed or spread over the surface, after which the article isreturnedtothefurnace and heated until the second coat fuses. This procedure also can be repeated to obtain the desired number of coatinss.

The presence of a ground coat on a metal surface to be enameled has been considered necessary. to protect the surface from oxidation during the heating to an enamel-fusing temperature. In the furnace after application.

art all coatings are heated in the I have now discovered that if metals are heated to enamel-fusing temperatures in furnaces in which the atmosphere is kept neutral or reducmg, i. e. non-oxidizing, the

use of such a ground coat is not necessary. -The untreated or naked heated surface is in satisfactory'condition for directly receiving a coating of vitriflable enamel.

I have found that enamel can be applied to these naked heated surfaces while still in the furnace, and can be fused to produce an adherent and satisfactory coating. I have also found that after this coating has fused, as many additional successive coatings as are desired the dry powder method without removal article from the furnace.

may be applied by Or, alternatively, the

of the 1 article may be removed from the furnace and additional coats applied by either the dry powder or the wet process in the customary ways.

I have found it advantageous not to subject the enameled object subsequently to higher temperatures than those used in the first coating operation, as certain defects, such as hairlines, bubbles, blisters, and pinholes, due to changes in temperature during enameling, are thereby avoided.

My invention has many advantages over the old art, where the ware must be removed from the furnace between each successive coating, since I eliminate frequent reheating of the ware, there'- by saving fuel; and-frequent handling, thereby 15 saving labor. Moreover, as I keep the temperature constant, the occurrence of several common defects is prevented. Hairlineawhich are cracks in the first coating occurring when the cooled article is reheated, do not occur. Bubbles, formed 2 by gases entrapped in the powdered enamel, are obviated, since the. enamel is not applied until an enamel-fusing temperature is reached. Bub}- bles are not retained .in the molten coating.

ture of bubbles, do not occur.

In a specific embodiment of my process, an iron casting to be enameled with two coats of dark blue enamel, was placed in a furnace in which the furnace gases were neutral or slightly o reducing. The temperature of the casting was allowed to reach that of the furnace atmosphere; approximately l600 F. In the meantime, a

* batch of dry. powdered enamel of the following composition has been prepared (all parts being by weight): Silica 49.0 Alumina 6.5 Boric oxide 14.0 Alkalies 20.0 ll'iuorspar 1 7.5 Cobalt oxide 3.0

Whenthe casting reached thetemperature of the furnace, a sui'flcient amount of this dry, powdered enamel was deposited in an even layer over the surface to be enameled, by means of an air-jet and suitable piping. The coating means was then withdrawn from theflfurnace and the enamel coating exposed to heat for about two minutes, care having been taken tbat'the temperature of the furnace remained the same as it was upon the completion ofthe coating process.

Blisters and pinholes, being defects due to rup- 25 This sufficed to produce an even homogeneous coat. The second coat was then applied in the same manner but as a somewhat thinner layer.

and allowed to .stand under substantially the same heatfor'about one and three-quarters minutes. Ihecasting was then removed from the furnace and allowedtocool. It then carrieda satisfactory two-layer coating.

My process may be combined with other enameling processes. For instance, the firstcoating may be applied by my method and then other methods may be used foriapplying and heating subsequent coats. Also, enamel may be' applied to substances other than metal by my process.

The. present process may be operated in any of the usual furnaces employed for enameling metalware, the only difference being that the atmosphere is maintained neutral or slightly reducing. It is-advantageous to have as much reduction as is consistent with avoiding the danger of sooting or reduction of delicate oxides in the.

enamel. Too much C0 in-the furnace atmosphere is not desirable, Where enamels of different fusing points are employed, corresponding temperatures may-be employed, but it is desirable that no succeeding coating be applied at a higher temperature than that used with the precoating to a greater extent than may he necessary to secure union. The second temperature should, of course, be high enough to fuse the glaze applied at that temperature.

What I claim is:

1. In the enameling of metal articles, heating L the naked article to enamel-fusing temperature in a furnace having a non-oxidizing atmosphere and applying to the heated naked article in the furnace a coating of vitriflable dry enamel powder. while keeping the furnace at said temperature and maintaining the non-oxidizing atmosphere.

2. In enameling metal articles with a plurality of successive layers, the process which comprises heating a naked metal article in a furnace hats; ing a non-oxidizing atmosphere and at an enameli'using temperature, applying to the naked heated article while in the furnace and while maintaining the non-oxidizing atmosphere a. coating of enamel material in powdered form, allowing the coating to fusein place and then applying another coating of enamel material to the coated surface.

3. In the process of claim 2, fusing the successive coating layers without elevation of temperature. 7

4. In the process of claim 2, fusing the successive coating layers at progressively decreasing temperatures.

110m Ff STALEY.