US3740275A - Galvanizing preflux wash composition - Google Patents

Abstract

AN AQUEOUS PREFLUX WASH HAVING THE PURPOSE OF WETTING A FERROUS METAL WITH A FILM TO CONDITION THE SURFACE IN FINAL PREPARATION FOR NON-FUMING GALVANIZING IN A MOLTEN ZINC BATH USING A SMOKELESS BLANKET FLUX ACCORDING TO MY PAT. NO. 3,244,551. THE PURPOSE OF THIS PREFLUX IS NOT ONLY TO REPLACE THE CONVENTIONAL ZINC AMMONIUM CHLORIDE CONTAINING PREFLUX MATERIAL, WHICH IS FUMING, BUT TO ELIMINATE ALL FACTORS CONTRIBUTING TO AIR POLLUTION.

Description

Uni'ted States Patent "ice 3,740,275 GALVANIZING PREFLUX WASH COMPOSITION Sidney M. Heins, Chicago, Ill., assignor to Thiem Corporation, Milwaukee, Wis.

No Drawing. Continuation-impart of application Ser. No. 128,551, Mar. 26, 1971. This application Aug. 6, 1971, Ser. No. 169,846

Int. Cl. B23r 35/34; C2211 9/10; B32b 15/18 U.S. Cl. 148-26 Claims ABSTRACT OF THE DISCLOSURE An aqueous preflux wash having the purpose of wetting a ferrous metal with a film to condition the surface in final preparation for non-fuming galvanizing in a molten zinc bath using a smokeless blanket flux according to my Pat. No. 3,244,551. The purpose of this preflux is not only to replace the conventional zinc ammonium chloride containing preflux material, which is fuming, but to eliminate all factors contributing to air pollution.

RELATED APPLICATION The related application pertaining to this invention is Ser. No. 128,551, field Mar. 26, 1971, of which the instant application is a continuation-in-part.

BACKGROUND OF THE INVENTION In the galvanizing of ferrous base metal, the essential function of a blanket flux is to prepare the surface of the metal by cleansing it of rust and other corrosion products by chemical means. Only metallically bright surfaces, i.e., those free from all non-metallic substances, can react with each other. The base metal presumably has already been degreased and pickled removing dirt, grease, scale layers and iron salt residues by conventional means. The main task of the blanket flux is to remove all impurities from the iron surface, as well as to keep free from oxides that part of the zinc bath surface at which the steel is immersed into the bath. The impurities on the steel surfaces are partly those scale components which have not been dissolved by the acid of the pickling bath, such as complex iron oxides, or inclusions in the iron, sparingly soluble in acid, such as Fe C and partly the reaction products of the pickling process, i.e., aqueous solutions of iron chlorides or iron sulphates. One source of these surface impurities occurs while the articles to be galvanized are being taken from the pickling bath to the galvanizing bath, wherein iron surfaces are exposed to the action of the atmosphere, and these iron salts become oxidized. The purpose of the blanket flux is not only to remove these actual iron salts from the ferrous metal surface itself but also the water adhering to the articles. On the zinc bath surface itself, it is also necessary for the blanket flux to take up the oxides of the zinc bath formed by the action of oxygen, the flux being required to shield the place of immersion in such a manner that during the first reaction between iron and zinc, all oxygen is kept away from the two reactants.

It is, therefore, necessary for the flux to be able to wet the two metallic surfaces satisfactorily and remove everything that may find its way in between them. By removing all foreign bodies from between the two metals, these 3,740,275 Patented June 19, 1973 can be brought so close to each other that they can approach within reach of their metallic active forces. In the process known as wet-galvanizing, the flux is placed as a blanket onto the zinc bath so that the wet iron objects from a prewash procedure are immersed into the molten metal bath through the melted flux blanket. In the process referred to as drygalvanizing, a preflux material is first applied to the galvanzing articles as an aqueous solution after which it is allowed to dry before immersion of the articles through a flux blanket into the zinc bath as before.

It is a common practice in preparation for galvanizing that after pickling, the articles are washed in cold for warm water. 'On the Way to the galvanizing tank, these moist surfaces, which have become very active by pickling, are exposed to the air. However carefully washed, some iron salts still remain behind in the aqueous washing material and on the iron surface where they are rapidly converted by air into basic iron salts. In recent years, a liquid preflux wash has been used to detach these basic iron salts from the iron surface and simultaneously to act as a flux in the manner described for dry-galvanizing. By thus being covered, the iron surface is protected against oxidation on the way to galvanizing without attack on the iron base and the amount of dross formed in the galvanizing bath is reduced.

At the present time, the galvanizing trade is using a mixture of zinc chloride (ZnCl and ammonium chloride (NH Cl), or zinc ammonium chloride (ZnCl -2NH Cl or ZnCl -3NH Cl) as a preflux wash for the purpose of wetting the ferrous base metal with a film to condition the surface in preparation for galvanizing in the molten metal bath. This perflux wash causes visible smoke-like fumes to develop when carried over in the bath in a manner characteristic of all ammoniacal salt fluxes.

Because all ammoniacal salt preflux washes cause visible smoke fumes to develop even when carried over into a molten zinc bath using a smokeless blanket flux according to my Pat. No. 3,244,551, there is a standing need for a preflux wash which is non-fuming when used in conjunction with my smokeless blanket flux.

SUMMARY OF THE INVENTION The primary object of this invention is air pollution control. The emission of fumes and visible smoke from the zinc pots of galvanizing baths has always contributed to undesirable pollution of air in shop and factory. It is the purpose of this invention to render the whole galvanizing process completely free of such obnoxious smoke and fumes.

While a smokeless galvanizing flux such as described in my Pat. No. 3,244,551, used as a blanket flux in the wet process, does not emit any fumes, it is a contributing object of this invention to provide a non-fuming preflux wash which, if used in connection with a dry-galvanizing" application, also results in a non-fuming operation. Such preflux washes are in general made smokeless by replacing the conventional ammoniacal fluxes used in the galvanizing trade with a non-ammoniacal flux which does not fume.

The preflux wash composition of this invention is comprised basically of a mixture of about 60% zinc chloride, about 15% borax or boric acid, about 5% potassium aluminum fluoride, about 10% sodium chloride and about 10% of either barium chloride crystals or calcium chloride pellets. Normally these preflux washes are of a sufficient strength when dissolved in water to provide a solution of about 15 to 50 B. and are used at a temperature of around 150 to 180 F.

The non-fuming preflux wash process used in preparation of the iron or steel surfaces after pickling comprises the steps of washingthe surfaces in cold or warm water and then immediately immersing these surfaces in the preflux Wash composition of this invention and Withdrawing the same after said surfaces have been fully wetted with the said composition and a film of the composition is firmly attached thereto.

DESCRIPTION OF THE INVENTION Broadly the preflux composition of this invention is comprised of the following ingredients in terms of percentages by weight:

Ingredients: Percent by weight (range) Zinc chloride 35-75 Borax or boric acid 5-l5 Potassium aluminum fluoride 510 Sodium chloride 20 Barium chloride, calcium chloride 10-20 The borax and the boric acid are interchangeable With each other. The boric acid with a more acid bath gives slightly better results. The barium chloride and the calcium chloride are interchangeable with each other or alternately may be mixtures of any one or both of these salts.

Any preflux wash composition within the above specified proportional limits and having a solubility strength in Water of about to B. and when used at a temperature of around 150 to 180 F. for light gauge articles will produce excellent fluxing properties when used in conjunction with smokeless blanket flux pursuant to the disclosure of my Pat. No. 3,244,551. However, heavy gauge articles require a somewhat higher B.

The function of each of the above mentioned ingredients other than to provide a non-fuming or non-smoking preflux Wash composition is not too well understood. It is believed, however, that the zinc chloride acts as a cleansing agent while the borax or boric acid will absorb the iron oxides. The potassium aluminum fluoride improves fluidity or lowers the viscosity of the molten flux composition. The fluoride salt is also believed to assist in preventing the zinc chloride from decomposing or converting to other zinc compounds (e.g., hydrate or oxide) such as, for example, by reaction with atmospheric constituents. In addition, the fluoride salt is believed to act between the base metal and the molten metal of the galvanizing bath to result in a more firm adherence of a uniform metallic coating; and to prevent oxidation of aluminum metal, if any, in the molten zinc metal bath. The sodium chloride and the alternates, barium chloride and calcium chloride, are believed to assist in the obtaining of a true solution of the composition in the molten state or liquid phase.

The above mentioned proportional limits should be substantially adhered to because compositions outside these ranges have solubilities in water outside the range of 15 to 50 B. resulting in a deficiency of one or more of the above discussed functions of the specific ingredients. Thus, in order to obtain satisfactory results, the proportional limits of each ingredient should be adhered to in accordance with the above stated limits.

From my experiments, it appears that the presence of potassium and fluorine are essential in this invention and may not be substituted. Apparently the combination of elements present produces a synergistic effect in improved fluxing properties while fluoride emission was kept below 28 parts per million.

The preferred composition of the preflux wash of this invention is in accordance with the following proportions of ingredients in terms of percentages by Weight:

Ingredients: Percent by weight Zinc chloride 6-0 Borax or boric acid 15 Potassium aluminum fluoride 5 Sodium chloride 10 Barium chloride, calcium chloride 10 The above ingredients dissolved in water in the stated proportions give a preflux wash solution having a strength of 18 B. When heated to F. producing satisfactory results in a typical smokeless galvanizing operation on thin gauge steel.

The ingredients of a composition of the smokeless blanket flux according to my Pat. No. 3,244,551 separately mixed together and heated establish a liquid phase state. This molten flux is then placed on the surface of a molten galvanizing bath forming What is commonly known as a flux blanket in a galvanizing pot of the kind described in that patent. A brightener addition to the galvanizing bath metal consists of an aluminum-zinc alloy, comprising about 93% by weight of zinc metal with the balance being substantially aluminum metal. The galvanizing bath is maintained at an operating temperature of about 840 F.

This gauge steel sheet as a base metal article is passed through the preflux wash solution. Before the wash dries, the sheet is fed through the flux blanket of the above patented composition into the molten metal galvanizing bath from whence it emerges through the clear metal. The sheet steel, as a result thereof, is uniformly coated with the galvanizing metal and the coating, which is extremely bright and smooth and firmly bonded, is acomplished without the occurrence of any visible fumes emanating from the bath and with minimum dross formation. Whether barium chloride or calcium chloride is used makes no difference in the final result.

Having now described the invention, it must be understood that changes and modifications may be made which do not depart from the spirit of the invention nor from the scope thereof as defined in the appended claims.

I claim:

1. A non-ammoniacal preflux wash composition for preparing the surface of ferrous metal articles for galrvanizing completely free of smoke and fumes which consists of about 35% to about 70% by weight of zinc chloride, about 5% to about 15% by weight of a material selected from the group consisting of boric acid and borax, about 5% to about 10% by weight of potassium aluminum fluoride, about 10% to about 20% by weight of sodium chloride, and about 10% to about 20% by Weight 01fY barium chloride or calcium chloride or a mixture there- 0 2. A non-ammoniacal preflux wash as in claim 1 wherein the composition consists of 60% by weight of zinc chloride, 15% by weight of borax, 5% by weight of potassium aluminum fluoride, 10% by weight of sodium chloride, and 10% by weight of barium chloride or calcium chloride or a mixture thereof.

3. A non-ammoniacal preflux Wash as in claim 1 wherein the composition consists of 60% by weight of zinc chloride, 15% by weight of boric acid, 5% by weight of potassium aluminum fluoride, 10% by weight of sodium chloride, and 10% by weight of barium chloride or calcium chloride or a mixture thereof.

4. An aqueous solution of the preflux wash composition as in claim 1 with a strength of about 15 to 50 B. at a temperature of around 150 to 180 F.

5. An aqueous solution of the preflux Wash composition as in claim 2 with a strength of about 15 to 50 B. at a temperature of around 150 to 180 F.

(References on following page) 6 References Cited 2,817,894 12/1957 Steinberg 148--26 2,867,037 1/ 1959 Lawton 148-26 UNITED STATES PATENTS 2 4 Zg L. DEWAYNE RUTLEDGE, Primary Examiner g i fgg 75:94 5 P. D. ROSENBERG, Assistant Examiner Peake 75-94 U-Sl C l XvRl Wasserman 14826 7594; 11713(); 13442; 252-432