US2473004A - Galvanizing flux - Google Patents

Description

Patented June 14;, 1949 UNITED STATES PATENT OFFICE GALVANIZING FLUX ration of Delaware No Drawing. Application June 2, 1945, Serial No. 597,382

4 Claims. 1

This invention relates to ammonium chloride fluxes for galvanizing and is more particularly directed to ammonium chloride fluxes which contain small amounts of alkali metal chlorides, and which may additionally contain small amounts of calcium chloride.

In the galvanizing of metal articles by dipping them in a bath of molten metal it is frequently the practice to provide a flux coating on top of the galvanizing bath to clean articles to be galvanized as they are lowered thru the flux layer into the molten metal. The best of these fluxes are ammonium chloride, zinc ammonium chloride, or ammoniumchloride mixed with zinc chloride, but even when newly applied to a galvanizing pot these fluxes do not have sufficient activity in cleaning articles to be galvanized and they do not have sufficient fluidity to meet the needs of modern galvanizing processes. Worse yet, these fluxes become inactive, viscous, and high melting after a period of use. Consequently, it has been diificult consistently to produce smooth, uniform, and adherent metal coatings free from blemishes and this difiiculty has increased When attempts were made to operate galvanizing processes at high speed.

The required characteristicsof a galvanizing flux may be tabulated:

1. A low melting point which permits the flux to become liquid when it comes into contact with the molten metal bath with which it will be used. The freezing point should be as low as possible so that cold metal articles may pass thru the flux without deleterious solidification which would result in the flux adhering to the article. The melting point should be low and should remain low during use of the flux.

2. Low viscosity so that the flux will flow readily around an article passed thru it so that it may quickly react and so that it will allow the article to be withdrawn without dragging flux along with it. The viscosity should remain low.

3. High chemical activity so that rust or other impurities which may be present on the surface of the article to be galvanized may quickly and effectively be removed. The activity should continue at a high level during use of the flux.

It is particularly to be observed that for continuous strip galvanizing in which the article being galvanized passes rather rapidly thru the flux and thruthe galvanizing bath, an emphasis must be placed on high activity, high fluidity, and low melting point.

It is an object oi this invention to provide flux compositions and processes which possessthe above tabulated characteristics and which are particularly characterized by high activity, high fluidity, and low melting point so that they are particularly well adapted for continuous strip galvanizing. It is a further object of this invention to provide flux compositions which have high activity to a steel surface and low activity to the galvanizing bath whereby less zinc is consumed by the flux to produce skimmings. It is a further object of this invention to provide galvanizing fluxes which in use continue to have the above-tabulated advantages. It is a further object of this invention to provide galvanizing fluxes and galvanizing processes which in large measure overcome the disadvantages experienced by the prior art. It is a still further object to provide galvanizing fluxes and galvanizing processes which are simple and inexpensive. It is a still further object to provide galvanizing fluxes and galvanizing processes by the use of which galvanizing may be effected rapidly, uniformly, and satisfactorily. Other objects will become apparent hereinafter.

The foregoing and other objects are attained by the inclusion in an ammonium chloride fiux of a minor amount of a mixture of sodium and potassium chloride which may additionally contain calcium chloride.

An ammonium chloride flux, according to the present invention, will ordinarily contain from about to of ammonium chloride, from about '7 to 15% of a mixture of sodium and p0- tassium chlorides, and from about 3 to 5% of calcium chloride. The sodium and potassium chlorides will usually be used in about equal amount the generally there may be used from about 70 to 30 parts by weight of potassium chloride.

While reference is made herein to the use of sodium chloride, potassium chloride, and calcium chloride, it will be understood that equivalents may be used.

It will be understood, for instance, that there may be used either a metal chloride or a compound which under the conditions of use will be converted to a chloride. Thus, there may be used such compounds as form a chloride by reacting with ammonium chloride in an aqueous pre-flux or by reacting under the conditions existing when brought into contact with a galvanizing bath in the presence of ammonium chloride. Numerous compounds thus suitable will readily suggest themselves to those skilled in the art and as examples there may be suggested carbonates, acetates, hydroxides, or oxides of sodium, potassium, and calcium. Accordingly it will be understood that when reference is made to the use of a chloride of one of these metals an equivalent compound may be used instead of the chloride without departing from the spirit of this invention.

Flux compositions of the invention may contain various minor additions in accordance with practices already set out in the art. They may, for instance, contain foaming agents as set out in U. S. Patents 1,965,759, 1, 965, 760, 2,106,982, and 2,123,949. It is to be observed that such additions are very minor in their amount, not ever. say, about 1 to 2%, and the flux compositions still are comprised essentially of ammonium chloride and the sodium, potassium, and calcium chlorides as set out above.

While it is preferred, as above indicated, to prepare compositions comprising a mixture of ammonium chloride, sodium chloride, potassium chloride, and calcium chloride, the components may be added separately to the molten flux on a molten metal bath, though it will be evident that such a procedure is not convenient. Alternativeif desired, the added metal chlorides either with or without the other flux constituents may be dissolved in water thru which articles to be galvanized are passed, and thus carried on the articles to the molten metal bath. It will also be apparent that compositions of the invention can be applied as a top-flux to a galvanizing bath; they can be dissolved in water as a pre-dip, or they can even be dusted on the surface of an article to be galvanized.

It will be understood that flux compositions according to the present invention whether added directly to the bath or added indirectly through the use of a flux wash should contain no deleterious materials. Fluorides, sulfates, and compounds of aluminum and of magnesium should in general be avoided. The presence of excessive a amounts of acids or acidulous salts should similarly be avoided and the compositions should not be so constituted as to have an acidity equivalent to substantially less than about pH 3. In other words the flux compositions of the present inventions when dissolved in water should have an acidity of about pH 3 or more,

In order that the invention may be better understood reference should be had to the followin illustrative examples:

Example I A flux consisting of the following was made up and used as pre-flux:

Per cent Ammonium chloride 85 Sodium chloride 7.5 Potassium chloride 7.5

A solution consisting of 25 per cent by weight of the above mixture was held at 160 F. while sheets of mild steel were dipped in them. When the sheets dried at room temperature, they tended to rust less than sheets dipped in a 25 per cent solution of plain ammonium chloride. The sheets were then galvanized by dipping them into molten zinc. Subsequent analysis of the zinc indicated that the sheets dipped in the solution containing ammonium chloride with sodium and potassium chlorides formed less dross than the sheets dipped in the ammonium chloride solution. The flux of this example is particularly well adapted for use in continuous strip galvanizing and it may be employed as a top flux in such use with excellent results.

4 Example II A flux was made up as follows:

Per cent Sodium chloride 5 Potassium chloride 5 Calcium chloride 4 Ammonium chloride 86 The flux thus prepared was found to have high activity, high fluidity, and low melting point and was well suited for use as a top-flux for continuous strip galvanizing. The addition of about one per cent of tallow, or about one-half of one per cent of glycerol was .sufilcient to make the flux form a stable foam.

Example III A flux of the invention was made up as follows:

Per cent Ammonium chloride 89 Sodium chloride 35 Potassium chloride 3.5

Calcium chloride 4 The flux thus prepared was used on a zinc galvanizing pot and it was found to have a low melting point, a low viscosity, and high activity. The properties of the flux were excellent after nine hours of use while a flux made up similarly but omitting the sodium, potassium, and calcium 1. chlorides had become no longer usable by reason of an increase in viscosity and melting point.

The flux was particularly well adapted for use on continuous strip galvanizing. It is also to be observed that when 1.10% of tallow was used, in accordance with customary practices, the flux composition foamed in a most satisfactory manner.

While we have shown certain illustrative compositions and processes it will be understood that one skilled in the art may readily devise numerous similar compositions and processes without departing from the spirit of this invention. This application is a continuation-in-part of our copending application Serial Number 437,032 filed March 31, 1942, now abandoned.

We claim:

1. A galvanizing flux for continuous strip galvanizing consisting essentially 7 to 15% of a mixture of sodium and potassium chlorides, and the balance ammonium chloride, the mixture of sodium and potassium chlorides containing '70 to 30 per cent by Weight of potassium chloride and the balance being sodium chloride.

2. A galvanizing flux for continuous strip galvanizing consisting essentially 7 to 15% of a mixture of sodium and potassium chlorides, 3 to 5% calcium chloride, and the balance ammonium chloride, the mixture of sodium and potassium chlorides containing '70 to 30 per cent by weight of potassium chloride and the balance being sodium chloride.

3. In a galvanizing process the step comprising contacting an article prior to galvanizing with a flux consisting essentially '7 to 15% of a mixture of sodium and potassium chlorides, and the balance ammonium chloride, the mixture of sodium and potassium chlorides containing '70 to '30 per cent by weight of potassium chloride and the balance being sodium chloride.

l. In a galvanizing process the step comprising contacting the article prior to galvanizing with a flux consisting essentially 7 to 15% of a mixture of sodium and potassium chlorides, 3 to 5% calcium chloride, and the balance ammonium chloride, the mixture of sodium and potassium 5 6 chlorides containing 70 to 30 per cent by weight UNITED STATES PA'I'ENTS of potassium chloride and the balance being Number I Name Date $dmm chlmde- 92,998 Peake July 27, 1869 ERNEST R. BOLLER. 1,941,750 Johansson Jan. 2, 1934 LOWELL D. EUBANK. 5 2,040,283 Swartz May 12, 1936 RAYMOND J. KEPFER.

OTHER REFERENCES REFERENCES CITED International Critical Tables, Vol. IV, pages 45 The following references are of record in the m and 81, McGraw-Hill, New York (1928). file of this patent: