US2101616A - Vitreous enameling process - Google Patents

Description

Dec. '7, 1937. H, F G|LBERT 2,101,616

vVITREOUS ENAMELING PROCESS Original Filed Aug. 3, 1933 Patented Dec. 7, 1937 PATENT OFFICE VITREOUS ENAMELING PROCESS Herman F. Gilbert, Greenville, Mich., signor to Gibson Electric Refrigerator Corporation, a corporation of Michigan Substitute for application Serial No. l683,457, August 3, 1933. This application February Z3, 1937, Serial N0. 127,284

^ 4 Claims.

This invention relates to porcelain enamel processes, and is particularly directed to overcoming certain dimculties which have in pastpracticed methods of applying such enamels prevented attainmentof uniform results, and frequently caused spoilage of large quantities of work. Avoidance of such spoilage in processes involving the application of vitreous enamels by dipping was regarded as unavoidable, inasmuch as its causes were unknown.

In some enameling plants these diiliculties seemed to vary with the seasons and weather, and' in some plants also they were more serious than in others. In many enamellng establishments it was found, for example, that at timesI perfect work could be turned out consistently and over considerable periods, while at other times, or after a sudden and inexplicable, apparently causeless change, without variance by the persons in charge of the process or materials used, the frit would tend to 'separate from the setting up agents in the enamel too quickly, and the resultant work would become too thin in some areas and too thick in others, rough and orange peeled. Frequently such enamel was then thrown away, which is of course wasteful and expensive, or additional setting-up agent was added to lthe mixture. The latter expedient is a very poor and hazardous practice, however, asideirom introducing additional expense and delay. `In any event, redraining of the imperfect work was frequently necessitated, causing further delay and expense, or the work was delivered imperfect, or scrapped or sold a't a lowprice because of the defective finish. Such elements of uncertainty and waste, heretofore regarded as unavoidable in the art, it is the primary object of this invention to overcome.

Other objects and advantages will be apparent from the following description, wherein reference is made to the accompanying drawing illustrating a preferred embodiment of my invention and wherein similar reference numerals designate similar parts in the drawing.

The single gure of drawing shows in perspective and partly broken away a waterjacketed dip tank constituting asuitable receptacle for and means for controlling the temperature of the enamel.

In carrying out my improved process the general4 order of procedure now in use may be iollowed insofar as the sequence and nature of the several steps are concerned. I introduce as an additional element, however, a continuous and (Cl. Sil-72) careful control of the temperature of the enamel throughout the entire period of its use.

Ordinarily the enamel is first ground with water in a pebble mill or the like, and its consistency and color modied by the addition of 5 clay, borax or other setting-up agents, and a suitable oxide pigment, to the constituents of the enamel itself, commonly termed frit, which may comprise such substances as silica, feldspar, magnesia, quartz, sand and cobalt, although these l0 are merely exemplary and other materials may be used. The milling operation heats the mixture considerably, and the heat in turn has the effect of thickening the enamel. Immediately after `milling, the complete enamel, comprising the 15 frit, setting-up and opacifying agents, would accordingly be too thick to be used without the addition of water, while if water were to'be added at that time to reduce it to the proper'consistency, it would become too thin upon cooling, as 20 a result of which the coating which adhered to the ware dipped therein would also be too thin. The milling also charges the enamel with considerable air. As a result of these considerations it is the practice to allow the enamel to age 25 from twenty-four to forty-eight hours after milling, during which time the air escapes and the enamel cools to a point where its consistency is suitable to permit it to be worked with.

I have found, however, that after the aging s0 process is completed and the enamel has once cooled, an increase in temperature has a reverse effect, and results in thinning the enamel, causing the frit particles and setting-up agents to separate prematurely, thus weakening its suspending strength and allowing the enamel to slip too freely, and making the coating which adheres to articles dipped therein much too thin and very irregular. This effect is seen4 also in a tendency of the enamel to Wash itself off the ware as it drains downward therefrom, leaving the coating uneven from top to bottom as Well as rough and orange peeled by reason of the weakening of the floating agentia,A I have further found thatany temperature materially over seventy degrees Fahrenheit is sumcient to produce this highly yundesirable effect,` upon vthe enamel after its aging is once completed. Thus as it cools down during the aging process after milling, no matter what the temperature may be inthe plant or other establishment where the work is being doneeven though the air temperature may be over eighty, asit frequently is-the enamel will inevitably at some time reach the proper consistency. It is this fact which has doubtless misled prior workers in the art, for if the temperature is too high, that proper consistency cannot long be maintained, and the enamel particles begin to separate and the mixture to thin in the well known and objectionable manner above referred to,-because of the aforementioned reverse eiect of heat after the aging process is complete. If after aging, however, the temperature of the enamel is controlled and prevented from rising above approximately seventy degrees, being preferably prevented from fluctuating more than a few degrees and held at a temperature between sixty-five and seventy degrees, it will maintain its specific gravity indefinitely without tending to separate and thin out. It thus becomes possible to set up the constituents in the mill studiedly, and with the knowledge that the finished enamel can be held at the calculated specific gravity; and the coating which adheres to ware dipped in enamel whose temperature has been so controlled is remarkably smooth and uniform. Spoilage because of failure of the enamel itself becomes literally unknown, and after the subsequent drying and firing operations perfect finish is invariably secured. 'I'he temperature of the enamel can be allowed to rise as high as 85 F. and fluctuation only restricted against variations of more than twenty or twenty-five degrees, and such control will have beneficial results, although the specic gravity of the mix cannot be maintained as well or as permanently in such manner as if the preferred temperatures previously noted are held.

Inasmuch as in most enameling plants tanks are used for holding the enamel in which the ware is dipped, and as the temperatures in the plants themselves fluctuate widely, not only because of climatic conditions but because of the proximity, of firing furnaces and other apparatus and machinery, it is necessary in order to attain the disclosed advantages of temperature control of the enamel, to provide practically constant temperature controlling means. I have found that a very satisfactory method of holding the temperature of the enamel within the desired limits is to provide the dip tank with a water jacket, connected to a source of water supply whose temperature is held within the desired limits. Other temperature controlling agents may of course be used, the important` consideration being, as above stated, the proper i control of the temperature of the enamel in the disclosed manner.

As shown in the drawing, a suitable watercooled dip tank may comprise inner and outer box-like receptacles, designated I, 2 respectively, between which sealed water Jacket space 3 is left. lA water inlet 4 is provided near the top of the tank upon one side, opening into the jacket space, and a similarly connected outlet 5 upon the other. The inlet may be connected to a suitable supply of water at proper temperature (not shown) and the outlet run to a drain or applied to any suitable use. A drain 6 for the enamel is sealed in the inner receptacle and extends through the jacket to permit drawing olf the enamel when desired, and the tank assembly may if desired be mounted on a suitable support las 1.

By controlling the temperature of the enamel in the disclosed or other suitable manner during the stated portions of the enameling process, and preferably within the specified limits, the percentage of perfect work which may be turned out uninterruptedly with a single outlay of enameling equipment is greatly increased, and losses because of the previously uncontrollable failures of the enamel, which developed heretofore with costly frequency, are completely eliminated.

While it will be apparent that the illustrated embodiment of my invention herein disclosed is well calculated to adequately fulill the objects and advantages primarily stated, it is to be understood that the invention is susceptible to variation, modification and change within the spirit and scope of the subjoined claims.

This application is a substitute for application Ser. No. 683,457, filed August 3, 1933.

I claim:

1. '111e process of vitreous enameling which comprises milling a mass of enamel frit, opacifying agent, setting up agent and water, whereby the mass becomes heated and aerated, aging the resulting mixture for an extended period to cool the same and remove air, thus producing an enamel slip of a predetermined viscosity, dipping articles to be coated into the slip, the temperature of the slip being directly controlled throughout the active life thereof to prevent a temperature change after the completion of the aging operation of more than 25 F., and maintaining the temperature thereof after aging below a maximum of 85 F. whereby the predetermined viscosity is maintained substantially constant.

2. 'I'he process as set forth in claim 1, in which the mass is maintained in an enclosed zone during the dipping operation, and a fluid is mechanically circulated about said zone to maintain the specified temperature of the mass.

3. The process of vitreous enameling which comprises milling a mass of enamel frit, opacifying agent, setting up agent and water,wh erebythe mass becomes heated and aerated, aging the resulting mixture for an extended period to cool the same and remove air, thus producing an enamel slip of a predetermined viscosity, dipping articles to be coated into the slip, the temperature of the slip being directly controlled by a mechanically circulated liq'uid throughout the active life thereof to prevent a temperature change after the completion of the aging operation of more than 25 F., whereby the predetermined viscosity is maintained substantially constant.

4. The process of vitreous enameling which comprises milling a mass of enamel frit, opacifying agent, setting up agent and water, whereby the mass becomes heated and aerated, aging the resulting mixture for an extended period to cool the same and remove air, thus producing an enamel slip of a predetermined viscosity, dipping articles to be coated into the slip, the temperature of the slip being directly controlled throughout the active life thereof to prevent a temperature change after thev completion of the aging operation of more than 10 F., and maintaining the temperature thereof after aging below a maximum of 75 F., whereby the predetermined viscosity is maintained substantially constant.

HERMAN F. GnriBEaT.

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