US2112468A - Process for the production of galvanized sheets and the like - Google Patents

Description

or less mill Famed Moi-.29, i938 PROCESS FOR PRODUCTION OF GAL- VANIZED SHEETS AND THE LIKE lhleohn E. Morgan.

meme alignments, flol, Cleveland, Ohio, Jersey No Drawing. A

My invention relates to an existing methods employed in the production of galvanized sheets and the like, wherein the rolled sheets are first box annealed and then pickled to 5 prepare them forilnal treatment in a spelter bath for galvanizing, or in any like bath for the application of a protective surface coating to the sheets. 7

The finished rolled sheet stock, bearing more scale, is usually cold rolled to flatten the sheets so they will pile compactly for the. box annealing step. As this annealim step proceeds, the mill scale, due to the chemical reaction of its oxygenand the carbon in the sheets, becomes ll reduced to a residue, in the form of an iron sponge comprising some pure iron and some unreduced oxide of no which generally appears in spots on the sheets and, in mill parlance, is referred to as white oxide. It is resistant to the attack of the so pickling solution, and unless removed in the pickling bath, will produce sheets that are graded seconds" or "rejects". 'Ijherefore, it is the practice, in. the effort to maintain the gradeof the sheets, to glve'them' a longer pickling treatment to eiiectively clean them and to apply a heavier spelter coat than would otherwise be necemary. As a result, a reduction in productlon occurs and there is an increase in acid and spelter consumption per ton of sheets.

I have conceived that if the surface elements ofthe sheet, which during the annealing step would become reduced to iron oxide or white oxide", could instead be converted into mainly sulphide ofiron,theywould thenbeinaform 35 that is readily removable by the pickle liquor,

as a result I could eliminate the white oxid reduce the pickling time required for cleaning sheets,attainmaterialsavingsofmaterialsin both the pickling and galvanizing step and,

40 what is of greatest importance, produce a superior grade of sheets practically free of sec-' onds" or "rejects".

Broadly expressed, my invention contemplates annealing the sheets in the presence of an agent 45 whichwillcausethemill scaleorothersurface portion of the sheet, heretofore reduced to white oxide", to become converted into mainly sulphide-of iron. Such an agent may be a copperas solution with which the sheets are treated before improvement in the sulphur gases are aid in cleaning the sheet surface when the sheets 55 arepickled. Otherugentsoftheorder ofthose mercial iron sulphate to spelter coat.

that I can effectively ing of materials running as high-as pounds Ala assi n, y

Gadsden.

to Republic Steel corpora a corporation or New thin March 9, 1936,

po Serial No. 61,91! '1 Claims. (Cl. 14H) above specified may be employed with similar results.

I prefer to prevent the objectionable reducing action on the surface of the sheets during the box annealing step by wetting the sheet surfaces 5 in any suitable. manner, either in whole or in part, with a solution of sulphate of iron or copperas containing two to three pounds of comthe gallon of water. Ihave put my invention into practice by pass- 10 a ing the sheets from the cold rolls through a bath of, or otherwise wetting their surfaces in whole or in part with, B. copperas solution, then heat drying the sheets and stacking them preparatory" for the box annealing step which pro- 5 seeds as usual,.the annealed sheets being then passed through the pickle bath to clean them before they enter the spelter bath for galvaninng.

I have also successfully practiced my invention by the use of an acid treatment in which about ten pounds of commercial 6 0 B. sulphuric acid is placed in an iron pot under the cover with the sheets during box annealing.

I am also of opinion that like results can be obtained by spraying the copperas solution or pickle liquor on the outer edges of the sheets in the pack ready for the box annealing step.

While the chemical reactions upon which my present method is based are probably compli- I cated, I am of opinion that they proceed in gen I eral as follows. In the copperassolution treatment, the copperas disassociates, at box/annealing temperatures, into sulphur gases SO: and SOawhich, in the presence of a reducing atmosphere react with themill scale so that it is readily 5 removable in the acid pickling bath;

In the acid treatment, the acid evaporates and decomposes into S02, 80:, water and oxygen in the annealing box changing the gases therein so that-the same reactions occur as when the sheets 40 are dipped. This may be said to produce a preliminary pickling of the sheets prior to annealing, which prepares them for a quicker and more eflective cleaning in the final pickle bath that immediately precedes the application of the 4 I-ilnd that by the use of my process I can reduce the pickling time I can lower the acidity of the pickling bath from 7% at the start to around 5% and eiiect an acid saving up to 30%; and the sheets come so uniformly gray and clean and free of "white oxide from the pickling bath galvanize them with a say-J of spelter and 3 pounds of sal ammoniac per ton 01' sheets. 7

Having thus described my invention and the preferred methods by which it may beg practiced, what I claim as new is:

1. The herein described step in the. method of preparing cold rolled scale bearing finished stock for a galvanizing or like coating step, which con-' sist in wetting the sheet surfaces with a solution of copperas, and then box annealing the treated stock.

2. The herein described steps in the method of preparing cold rolled scale bearing stock for a ing, which consists in annealing the unpickled stock in an atmosphere containing sulphur dioxide and sulphur tri-oxide.

5. In a process for the production of galvanized 'ferrous metal sheets, the steps, for the prevention of defects due to the effect of box annealing on mill scale on the sheets, which consist, first, in taking the sheets as they come from the mill .and box annealing them in an atmosphere containing a decomposed sulphate in vapor form to react on the mill scale to convert same into a form of iron which is more readily soluble in -pickle liquor, and then pickling the annealed sheets.

6. The herein described steps in the method of alvanizingcold-rolled ferrous metal sheets bearing mill scale, which consists in annealing such sheets before they have been pickled in an atmosphere containing sulphuric acid fumes to react with. the mill scale during the annealing step, and then pickling the treated sheets.

7. The herein described method for reducing the pickling time required for galvanizing ferrous metal sheets and for reducing the consumption of spelter and pickling acidgwhich consists in box annealing the unpickled sheets in the presence of vaporized sulphuric acid;

Mamom E. MORGAN.