US1572155A - Pickling - Google Patents

Description

Patented Feb. 9, 1926.

' UNITED STATES PATENT OFFICE.

HENRY S. MARSH AND HALF S. COCHRAN, OF YOUNGSTOWN, OHIO, ASSIGNORS TO DELAWARE.

No Drawing.

To all whom it may concern:

Be it known that we, HENRY S. Mlansu and RALF S. CooHRAN, residing at Youngstown, in the county of Mahoning and State of Ohio, both citizens of the United States, have invented or discovered certain ,new and useful Improvements in Pickling, of which improvements the following is a specification. f

Our invention relates to improvements in the method of pickling ferrous articles, particularly rolled steel sheets and plates, and its objects are the production of clean surfaces, and also the overcoming of ditions which tend to delay and prolong the normal operation of pickling.

In the practice of pickling rolled steel sheets and plates, the articles are apt [to come from the pickling vat, not bright and white, as they should be, but clouded and mottled and streaked with dull brown. A sheet or plate so discolored is, because of its very appearance, less acceptable to the customer, and, furthermore, it is in some respects inferior in utility and serviceability. For instance, the scrap cut from the sheets or plates in their further fabrication, is commonly fashioned to other articles. The articles so produced are sometimes found to be defective, in that they are not responsive to the case-hardening operation.

\l/Ve have investigated, and have discovered that the mottled and darkened appearance upon the surfaces of the sheets and plates, is due to the presence of other metals, chiefly copper, and, in less degree, arsenic and lead, electroplated upon or otherwise oleposited upon the steel surfaces while in the picklingbath.

Copper has of late years been increasing- 1y used as an alloy of iron, and this, together with the circumstances that steel parts are in industry enerally, often provided with copper fittings of one sort and another, results in this: that steel scrap contains a very appreciable, though very un-- certain, copper content. In steel-making steel 'scrap'is charged together with pig iron into the refining furnace, and in consequence copper appears as an appreciable ingredient of the newly produced steel. In the preparation of the pickling bath, too, and in the reclaiming of spent pickling so+ lutions, the dilute acid which constitutes BICKLING.

I Application filed November 14, 1924. Serial No. 749,981.

operation is performed upon steel sheets and plates, two undeslrable circumstances appear: first, the sheets and plates are apt to come from the bath mottled and dirty in appearance, as has been said. This we impute primarily to the presence of cop per, and in less degree to lead and arsenlc. In the second place, the operation of pickling is retarded, and this we impute primarily to the -presence of lead and arsenic,

which act as inhibitors, and in less degree to copper.

The pickling solution, attacking the surface of the sheet, tends to eat away the cop-' per as well as the iron, but there is a countervailing tendency of the copper salt in solution sulphate, ordinarily) (c pp OHIO, A CORPORATION OF whether initially present in the bath, or

derived from thematerial under treatment, to break up; the phenomenon of electrolysis appears, and metallic copper is deposited' electrolytically upon the surface of the steel sheet or plate. The dull and dirty appearance of this deposit is due to the condition of the electrolyte, and particularly to the presence of other metals or metalloids, deposited with the copper."

We have discovered, and herein lies our invention, that by generating in the pickling bath and in sufficient quantities, sulphu- -retted hydrogen, the copper present in the nated, the electrolytic deposits will not occur, nor will the normal pickling operation be retarded.

In the practice of our invention we preferably begin with the pickling liquid reclaimed from previous service. We bring" this pickling liquid into a suitable tank or container, where we introduce into it iron sulphide. The acid reacts upon the iron gen; the sulphuretted hydrogen reacts upon the salts of the undesired etals and forms separation by increasing the temperature of the liquid to approximately120 F. vAnd this We conveniently-acc0mplish by the injection of s'team'into the liquid.

' 'Pro'ce'eding to the pickling operation itself, we introduce iron sulphide into the pickling vat also. And there also the acid reacting upon the iron sulphide releases sub phuretted hydrogen; And the sulphuretted hydrogen in turn, reacting with the copper as it is eaten by the acid from the sheets or plates under treatment, forms copper sulphide, and in that ultimate form the copper a the bath with the desired 1 is eliminated from the further reactions, and.

held from electrolytic deposition. Similarly there is no deposit of other undesired metal, and the sheets and plates go from bright and clean surfaces.

In order to make our invention elfective to the fullestextent, it is desirable that the pickling bath be at all times saturated with sulphuretted hydrogen. This is a condition which in practice is not diificult to main- I tain; all'that'is requisite is that the iron;

sulphide be supplied in such quantity that the bath smells of sulphuretted hydrogen.

The relatively high temperature normally maintained in pickling tends of course to re lease whatever sulphuretted hydrogen may be present in solution. In, order therefore to insure the presence of the sulphuretted hydrogen in suflicient quantities, we maintain within the pickling vat good-sized I lumps of iron sulphide. From. these the sulphuretted hydrogen is enerated gradually, and as itis generated it is taken up found the difiiculty less, to the correction of which our invention is addressed. But in the case of heavier sheets and plates, and 1n case the coatings of oxide are continuous and heavy, we are able in the practice of our invention to overcome a difiiculty'of sub-- stantial magnitude and achieve a substantial gain. i

. lVe claim' as our invention 1. The method herein described oi pickling metallic objects which consists in con-' ducting the pickling operation in a pickling solution burdened with sulphuretted hydrogen.

2. The method herein described of producing bright-surfaced pickled articlesof adulterated iron which consists in conducting the picklingv operation in a pickling bath saturated with sulphuretted hydrogen.

3. The method herein described of conducting the pickling operation upon metallicobJects which consists in causing reclaimed pickling solution at elevated temperature to react upon iron sulphide, allowing the precipitate to settle, and introducing the articles to' be pickled into the solution so previously treated.

4. A pickling bath consisting of a body of dilutesulphuric acid, having immersed in it lumps of iron sulphide.

In testimony whereof we have hereunto set our hands.

HENRY s. MAR-SH- RALF s. COCHRAN.