US2860092A - Electropickling process - Google Patents

Description

United States Pater G ELECTROPICKLING PROCESS Arthur L. Hart, Cary, and Gilbert G. Kamm, Barrington, 11]., assignors to American Can Company, New York, N. Y., a corporation of New Jersey No Drawing. Application December 31, 1957 Serial No. 706,291

4 Claims. (Cl. 204-143) phosphate, chromate, etc., and other undesirable materials from a black iron surface using electrical energy to speed up the heating and pickling operations of the process.

The instant invention will be described in relation to treating the margins of black iron can body blanks. However, it is to be understood that the invention is limited only by the scope of the claims since modifications will be readily apparent to those skilled in the art whereby other shapes may be treated Without departing from the spirit of the invention.

Before the longitudinal margins of a black iron, i. e. untinned, low carbon steel, can be bonded such as by soldering or welding to form a tubular can body, it is necessary that any coating such as iron oxidation products, grease, dirt and other foreign matter be removed from the surface of these margins. Since commercial practice demands that can bodies be made at a speed of 400 per minute or higher, very little time is available to accomplish the necessary cleaning operation.

It is, therefore, an object of the present invention to provide a process for the removal of oxidation products of iron, dirt, grease and other foreign matter from the surface of a ferrous metal object at high speed.

It is also an object of the invention to provide a process of the character described which is well suited to cleaning the longitudinal margins of a black iron can body blank at commercially acceptable speeds.

Numerous other objects and advantages of the invention will be apparent as it is better understood from the following description which is of a preferred embodiment thereof.

The present invention achieves the above objects by first inductively heating the surface to be cleaned to a temperature within a critical range, then immersing the heated, surface in an aqueous solution of a strong acid fora brief time interval, the concentration of the acid and the temperature of the solution being within a critical range, and passing an alternating current having a density within a critical range through the solution while the surface, which is one electrode in the electrochemical circuit, is immersed therein. Thereafter, the cleaned surface is washed free of the pickling solution and dried. As a result of this procedure, involving merely a matter of seconds, subsequent operations such as tinning, soldering or welding, may be readily and efficiently performed upon the treated surface.

The induction heating step is especially necessary and critical to obtain the desired results of the instant invention. After extensive experimentation, it was determined that to obtain rapid and efficient cleaning of a black plate surface in the electropickling operation, the surface must be heated to a temperature of from 450 F. to 550 F. and preferably 525 F. before immersion in the Patented Nov. 11, 1958 ice pickling solution. It was found that the only means of raising the surface to the necessary temperature in a commercially feasible time interval is by inductively heating the surface using an induction frequency of from 10 kilocycles to l megacycle per second, and preferably from to 500 kilocycles. The lower induction frequencies are preferred so that lower voltagesprevail at the coil surrounding the work thereby reducing the danger of arcing between this work coil and the work. With the induction heating step of the present invention, a time interval of only .25 to 1 second, and more particularly only .4 second, is required to raise the margins of a black iron can body blank to the necessary temperature.

An additional advantage obtained by use of induction heating over other forms of heating such as gas flames and infra red, is that the heat is confined to the work being treated and does not heat adjacent machinery. The value of this advantage in preventing wasting of energy and detriment to the adjacent machinery is ob VlOUS.

Induction coils for preforming induction heating are Well known in the art and, therefore, deemed unnecessary of description. These coils may take various shapes depending upon the shape of the work being treated. United States Patent No. 2,647,981 discloses various shapes and positioning of induction coils for the heating of a metal surface, including a flat surface- I The strong acid in the aqueous pickling solution is hydrochloric acid. It is present in a weight concentration, at least initially, of about 15% to 20% and preferably about 18%. The pickling bath may also contain other optional ingredients in small amounts such as: a non-foaming wetting agent, for example, 0.1% of a polyethylene glycol alkyl and ether (Triton X400).

The pickling bath must be maintained at a temperature of about F. to 150 F. and preferably about F. to preform the rapid and eflicient cleaning of the instant invention. The necessary heat may be im parted to the bath by means of gas burners, electric resistance heaters or the like. However, it has been found that after a relatively short interval of initial operation, the hot body blanks as they are immersed in the pickling bath supply sufficient heat to the bath to maintain it at the necessary temperature thereby obviating the need for auxiliary heating. If desired, the initial warm-up period can be shortened by heating the bath such as by gas burners until the desired temperature is obtained.

In the electropickling process, the work constitutes one electrode and the other electrode is formed from an inert, electrically conductive material, preferably carbon. The best arrangement for carrying out this process is to have a pair of carbon electrodes connected in parallel spaced 2 to 3 inches apart with the work, i. e. the marginal edge portion of the can body blank, perpendicular to a line between the carbon electrodes and centered between them. The 2 inch minimum is necessary to minimize resistance differences between the Work and its opposed carbon electrodes caused by slight variations in the position of the work relative to its opposed carbon electrodes. Substantial differences in resistance between each side of the work in relation to its adjacent carbon electrode prevents even distribution of the current, thereby causing uneven cleaning of one side of the work relative to its opposite side. Spacing of the carbon electrodes greater than 3 inches apart, although operable, is commercially impracticable because of equipment limitations and the greater power consumption occasioned thereby.

As is well known, the polarity of the work and carbon electrodes reverses cycylically due to the use of alternating current in the electropickling operation. The chemical reactions at each of the electrodes is well known in the art.. Suflice it to say that when the work is the anode,

metal e. g. iron if the work is composed of steel, is

dissolved from its submerged surface; and when the work is the cathode, hydrogen is liberated at its surface.

'These reactions on the surface of the work greatly facilitate the pickling or cleaning operation in that the dissolution of the base metal tends to loosen or undermine any surface film while the hydrogen gas formed performs, in effect, a scrubbing action whereby the .loosened surface film is removed.

. The current density used in the present invention is from 500 to 2000 amperes per square foot, and preferably about 1500 amperes per square foot of work surface to I "2,860,092 V T V between induction coils, heating said surface to a temperature of about 500 F. to 550 F. in about .25 to 1 second by means of said coils, immersing the thus heated surface in an aqueous HCl solution for about from 2 to 4 seconds, said solution containing 15% to 20% by weight of HCl and being maintained at a temperature of from 110 F. to 150 F., making said surface one electrode in an electrochemical circuit, and passing an alternating current having a current density of from 500 to 2000 amperes per square foot through said solution whereby said surface is cleaned and deoxidized by an electropickling action.

2. The method set forth in claim 1 wherein said surface is the marginal edge portion of a can body blank.

3. The method set forth in claim 1 wherein the induction frequency in said induction heating coils is from 10 kilocycles to one megacycle.

4. A method of high speed cleaning and deoxidizing the marginal edge portion of a ferrous can body blank, comprising passing said portion between induction heating coils having an induction frequency of from 100 to 500 kilocycles, heating said portion to a temperature of an air knife, followed by washing of the surface by spraying or flooding with water and thereafter dried such as by a squeegee or air knife. The cleaned surface is then in condition for a desired subsequent operation such as tinning, soldering or welding.

It is thought that the invention and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes may be made in the steps of the process described and their order of accomplishment without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the process hereinbefore described being merely a preferred embodiment thereof.

We claim:

1. A method of high speed cleaning and deoxidizing a ferrous metal surface, comprising passing said surface about 525 F. in about 0.4 second by means of said coils, immersing the thus heated portion in an aqueous HCl solution for about 3 seconds, said solution containing about 18% by weight HCl and being maintained at a temperature of about F., making said can body blank one electrode in an electrochemical circuit, and

passing an alternating current having a current density of about 1500 amperes per square foot through said solution whereby said portion is cleaned and deoxidized by an electropickling action.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. 4. A METHOD OF HIGH SPEED CLEANING AND DEOXIDIZING THE MARGINAL EDGE PORTION OF A FERROUS CAN BODY BLANK, COMPRISING PASSING SAID PORTION BETWEEN INDUCTION HEATING COILS HAVING AN INDUCTION FREQUENCY OF FROM 100 TO 500 KILOCYCLES, HEATING SAID PORTION TO A TEMPERATURE OF ABOUT 525*F. IN ABOUT 0.4 SECOND BY MEANS OF SAID COILS, IMMERSING THE THUS HEATED PORTION IN AN AQUEOUS HCI SOLUTION FOR ABOUT 3 SECONDS, SAID SOLUTION CONTAINING ABOUT 18% BY WEIGHT HCI AND BEING MAINTAINED AT A TEMPERATURE OF ABOUT 120*F., MAKING SAID CAN BODY BLANK ONE ELECTRODE IN AN ELECTROCHEMICAL CIRCUIT, AND PASSING AN ALTERNATING CURRENT HAVING A CURRENT DENSITY OF ABOUT 1500 AMPERES PER SQUARE FOOT THROUGH SAID SOLUTION WHEREBY SAID PORTION IS CLEANED AND DEOXIDIZED BY AN ELECTROPICKLING ACTION.