US3120458A

US3120458A - Process for the enameling of articles made of iron with vitreous enamels

Info

Publication number: US3120458A
Application number: US133310A
Authority: US
Inventors: Evelbauer Karl
Original assignee: Rickmann & Rappe Fa Dr
Current assignee: Dr Rickmann & Rappe Firma; Rickmann & Rappe Fa Dr
Priority date: 1960-10-15
Filing date: 1961-08-23
Publication date: 1964-02-04
Anticipated expiration: 1981-02-04
Also published as: DE1135264B; NL122247C; NL269606A; CH378124A; GB963547A; DE1796295B1

Description

Feb. 4, 1964 K EVELBAUER 3,120,458

PROCESS-FOR TI-IE ENAMELING OF ARTICLES MADE OF IRON WITH VITREOUS ENAMELS Filed Aug. 25, 1961 SHEET IRON,DEGREASED IN THE CUSTOMARY MANNER IN AN ALKALINE SOLUTION RINSE, COLD WATER ETCHING BATH, 5" 30 MIN. AT ROOM TEMP. HYDROCHLORIC ACID= 50% BY VOLUME NITRIC ACID 2 BY VOLUME CHROMIC ACID 0.2% BY VOLUME WATER BALANCE I RINSE, COLD WATER PICKLING BATH TO FORM THE BLACK LAYER 0,3 I5 MIN. AT ROOM TEMP NITRIC ACID 5% BY VOLUME COPPER SULFATE O.l% BY VOLUME WATER BALANCE RINSE, COLD WATER FIXING BATH,O.5 3 MIN., 50-80C INHIBITED PHOSPHORIC ACID 2 BY VOLUME NICKEL SULFATE 3% BY VOLUME BORAX I% BY VOLUME WATER BALANCE BOILING WEAKLY-ALKALINE BATH,O,5-IO MIN.

SODIUM NITRITE 0.5 BY VOLUME ENAMELING WITH A WHITE COVERING ENAMEL IN THE CONVENTIONAL MANNER II II II INVENTOR.

KARL EVELBAUER United States The invention relates to a process for the enameling of articles made of iron with vitreous enamels, and, more particularly, to the preparation of said iron articles for the application of such enamels and to a process whereby a covering coat of said vitreous enamel can be applied without using a prime coat.

The drawing is a flow diagram illustrating an embodiment of the invention.

For the enameling of iron goods with vitreous enamels, it has hitherto been the common practice to degrease these iron goods, to etch or pickle them, to wash and to dry them preparatory to spraying them with the enameling mass or applying the same by powdering, allowing these masses to dry, and firing them. As a general rule, the iron goods, such as kitchen utensils, etc., are provided with a prime glaze, onto which one or more cover glazes are laid. However, the prime glaze frequently is omitted, and a covering glaze is applied directly to the surface of the iron vessel, it being feasible to lay on a number of further covering glazes, if desired. For the direct enameling of the iron surface, it is necessary to use an enamel'of a particular composition and/or to subject the iron to a special surface treatment.

Upon etching or pickling the iron goods, preparatory to enameling in the manner described above, the phenomenon frequently occurs whereby a black layer covers a portion or even the entirety of the iron surface. Heretofore, it had been assumed that this black layer, during the ensuing enameling process, exhibits disadvantageous actions and/or flaws in the enamel glaze. In particular, thedetrimental occurrence known as a boil-up of the enamel during firing of the glaze has been ascribed to these black layers. Also, the local scorching of the base or prime enamel upon firing of the iron goods coated with a prime enamel has been believed to be caused by these black layers. Hence, it has always been endeavored to avoid the formation of such black spots or layers during etching or pickling of the iron articles preparatory to enameling of the same. When these black spots or layers did form, the iron goods were subjected to a special treat ment in order to eifect their removal.

The instant invention is based on the surprising discovery that a black layer formation on pickled iron goods, contrary to previous contentions, not only is not detrimental to the glazing of these articles, but actually has a favorable influence upon the enameling process, such as a smooth glazing and an adhesion of the enamel to the iron which is considerably stronger than normally attained. Especially, it has been established that iron articles having the black layer on their surface can be coated immediately with a covering enamel without first applying a primer or base enamel.

On the basis of this discovery, the process for the enameling of iron goods according to the invention consists in forming the black layer on the degreased iron surfaces, said black layer covering these surfaces. The black layer then is fixed on the iron surfaces by immersion in a nickel plating bath, whereafter the iron goods are passivated and subsequently enameled in the conventional manner.

A single etching or picking sufiices to produce the black layers. However, it is of distinct advantage to etch the iron articles in a first step with a known etching agent in aqueous solution, such as hydrochloric acid, nitric acid, or chromic acid, to rinse them thereafter in water, and subsequently to pickle them as a second step, in order to produce the black layer, in an oxidizing pickling bath, such as an aqueous solution of nitric acid and copper sulfate. In all instances, it is important that the black layer thus formed is continuous and uninterrupted.

To the step wherein the black layer is produced according to the invention, a fixing step, for instance in a nickel plating bath, is to be added, followed by passivation. As the nickel plating bath, opportunely an aqueous solution of phosphoric acid, nickel sulfate, and borax is used, whereas the passivation can be carried out, in a manner known per se, in an aqueous solution of sodium nitrite and borax, to which advantageously phosphates may be added. It is preferred to passivate the goods treated without rinsing after the fixing step, whereas a rinsing with water is hardly avoidable subsequent to the pickling steps.

The first etching step and the pickling step wherein the black layer is produced advantageously are carried out cold, i.e. at room temperature. The fixing step opportunely is effected at approximately 5080 C., whereas it is recommended to passivate in a boiling bath. The first etching step, depending upon the bath concentration, advantageously is carried out within approximately 5-30 minutes, the second pickling step, also in dependence on the bath concentration, within approximately 0.3 to 15 minutes, and the fixing step within 0.5 to 3 minutes.

Albeit the process according to the invention is designed primarily for a single-layer enameling of alloyed or unalloyed sheet iron, especially for the application of white glazes, it goes without saying that it is applicable to any and all other kinds of enameling of iron goods.

The process according to the invention now will be further illustrated by the following example. However, it should be' understood that this is given merely by way of explanation, not of limitation, and that numerous changes may be made in the details without departing from the spirit and the scope of the invention as hereinafter claimed.

I Example A cold-rolled sheet iron, having the following analysis was used:

This sheet iron was degreased in the customary manner in an alkaline solution which may contain detergents and emulsifiers, as commercially available for degreasing of metal articles, It was then rinsed with cold water. The

degreased sheet was subjected to the first etching step within approximately 5 to 30 minutes at room temperature. The etching bath had the following composition:

Percent by volume Hydrochloric acid 50 Nitric acid 2 Chromic acid 0.2 Water Balance The sheet thus etched was rinsed with water and then immersed in the pickling bath to form the black layer, as the second step, at room temperature for approximately 0.3 to 15 minutes, whereby the black 'layer formed. The bath had the following composition:

Percent by volume Nitric acid 5 Copper sulfate 0.1 Water Balance Percent by volume Inhibited phosphoric acid 2 Nickel sulfate 3 Borax 1 Water Balance After that, the sheet, without rinsing, was passivated in a boiling weakly-alkaline bath for approximately 0.5 to minutes. The bath was an aqueous solution containing a mixture of sodium nitrite (0.5 percent by volume), and borax (0.5 percent by volume), to which, if desired, phosphates could be added in the customary manner.

The sheet iron thus provided with a fixed continuous black surface layer was then coated with a White covering enamel in the conventional manner, and then was fired, also conventionally.

What is claimed is:

1. In a process for the enameling of degreased iron articles with vitreous enamel, the steps comprising producing a pickling residue in the form of a continuous black layer on the surfaces of said articles by pickling in an oxidizing solution substantially at room temperature for approximately 0.3 to minutes, fixing said black layer in a nickel plating bath at temperatures of approximately 50-80 C. for approximately 0.5 to 3 minutes, passivating them in a boiling, weakly alkaline, solution for approximately 0.5 to 10 minutes, and enameling the articles thus treated.

2. A process for the enameling of degreased iron articles with a single covering vitreous enamel glaze, obviating the need for applying a prime enamel coat, which comprises producing a pickling residue in the form of a continuous black layer on the surface of said articles by pickling in an oxidizing solution substantially at room temperature for approximately 0.3 to 15 minutes, lfixing said black layer in a nickel plating bath at approximately 50- 80 C. for approximately 0.5 to 3 minutes, passivating the same in a boiling, Weakly-alkaline, solution for approximately 0.5 to 10 minutes, applying a covering vitreous enamel {glaze to the articles thus treated, and firing said glaze.

3. In a process for the enameling of degreased iron articles with vitreous enamel, the steps which comprise etching said articles in an acid bath substantially at room temperature for approximately 5 to minutes, rinsing them with water, pickling them in an oxidizing solution substantially at room temperature for approximately 0.3 to 15 minutes, thus forming a pickling residue in the form of a continuous black layer on the surfaces of said iron ar i l i ing aid articles with water, fixing said black layer in a nickel plating bath at a temperature of approximately 50-80 C. for approximately 0.5 to 3 minutes, passivating said articles in a weakly alkaline, boiling bath, for approximately 0.5 to 10 minutes, and then enameling the articles thus treated.

4. A process for the enameling of degreased iron articles with a single covering vitreous enamel glaze, obviating the need for applying a prime enamel coat, which comprises etching said articles in an acid bath substantially at room temperature for approximately 5 to 30 minutes, rinsing them with water, pickling them in an oxidizing solution substantially at room temperature for approximately 0.3 to 15 minutes, thus forming a pickling residue in the form of a continuous black layer on the surfaces of said articles, rinsing said articles with water, fixing said black layer in a nickel plating bath for approximately 0.5 to 3 minutes at approximately 50-80 C., passivating said articles in a weakly-alkaline boiling bath for approximately 0.5 to 10 minutes, applying a covering vitreous enamel glaze to said articles thus treated, and firing said glaze.

5. In a process for the enameling of degreased iron articles with vitreous enamel, the steps which comprise etching said articles substantially at room temperature for approximately 5 to 30 minutes in a bath consisting substantially of Percent by volume Nitric acid 2 Hydrochloric acid 5O Chromic acid 0.2 Water Balance rinsing acid articles with water, pickling them, substantially at room temperature, for approximately 0.3 to 15 minutes in a bath consisting substantially of Percent by volume Nitric acid 5 Copper sulfate 0.1 Water Balance thus forming a pickling residue in the form of a continuous black layer on the surfaces of said articles, rinsing the same with water, fixing said black layer by immersing said articles at a temperature of approximately 50-80 C. for approximately 0.5 to 3 minutes, in a bath consisting substantially of Percent by volume Inhibited phosphoric acid 2 Nickel sulfate 2 Borax 3 Water Balance passivating said articles immediately after the fixing operation in a boiling bath for approximately 0.5-l0 minutes, consisting essentially of Percent by volume Sodium nitrite 0.5 Borax 0.5 Water Balance Percent by volume Nitric acid 2 Hydrochloric acid 50 Chromic acid 0.2 Water Balance rinsing said articles with water, pickling them substantially at room temperature for approximately 0.3 to 15 minutes in a bath consisting essentially of Percent by volume Nitric acid 5 Copper sulfate 0.1 Water Balance Percent by volume Inhibited phosphoric acid 2 Nickel sulfate 2 Borax 3 Water Balance passivating said articles immediately after the fixing operation in a boiling bath for approximately 0.5 to 10 minutes, consisting essentially of Percent by volume Sodium nitrite 0.5 Borax 0.5 Water Balance applying a covering vitroeous enamel glaze to said articles thus treated, and firing said glaze,

References Cited in the file of this patent UNITED STATES PATENTS 1,779,273 Hommel Oct. 21, 1930 2,772,183 Talmey et a1. Nov. 27, 1956 2,817,610 Newell et al Dec. 24, 1957 2,961,337 Bryant et al. Nov. 22, 1960

Claims

1. IN A PROCESS FOR THE ENAMELING OF DEGREASED IRON ARTICLES WITH VITREOUS ENAMEL, THE STEPS COMPRISING PRODUCING A PICKLING RESIDUE IN THE FORM OF A CONTINUOUS BLACK LAYER ON THE SURFACES OF SAID ARTICLES BY PICKLING IN AN OXIDIZING SOLUTION SUBSTANTIALLY AT ROOM TEMPERATURE FOR APPROXIMATELY 0.3 TO 15 MINUTES, FIXING SAID BLACK LAYER IN A NICKEL PLATING BATH AT TEMPERATURES OF APPROXIMATELY 50-80*C. FOR APPROXIMATELY 0.5 TO 3 MINUTES, PASSIVATING THEM IN A BOILING, WEAKLY ALKALINE, SOLUTION FOR APPROXIMATELY 0.5 TO 10 MINUTES, AND ENAMELING THE ARTICLES THUS TREATED.