US2697673A

US2697673A - Method of cleansing metal

Info

Publication number: US2697673A
Application number: US216125A
Authority: US
Inventors: James K Rice
Original assignee: Cyrus Wm Rice & Co Inc
Current assignee: Cyrus Wm Rice & Co Inc; Cyrus Wm Rice & Company Inc
Priority date: 1951-03-17
Filing date: 1951-03-17
Publication date: 1954-12-21
Anticipated expiration: 1971-12-21

Description

Dec. 21, J, K

METHOD OF CLEANSING METAL 2 Sheets-Sheet 1 Filed March 17, 1951 l l 0 IO 20 3040 50607060 9010010 20 5040 506070 80 m H m.

James itjce Dec. 21, 1954 J, K,-

I METHOD OF CLEANSING METAL 2 Sheets-Sheet 2 Filed March 17, 1951 O 5 ICE! 354045 50 5560657075 [NI/ENTOQ James like i9! 2% 416 aFvr fi 7 United States Patent METHOD OF CLEANSING METAL James K. Rice, Crafton, Pa., assignor to Cyrus Wm. Rice & Company, Inc., Pittsburgh, Pa., a corporation of Pennsylvania Application March 17, 1951, Serial No. 216,125

4 Claims. (Cl. 134-15) This invention relates to the testing of solutions for pickling metals such as the ferrous metals, for the removal of inorganic coatings such as rust and scale from the surface of the metal subjected to pickling.

In the pickling of metals by means of pickling solutions containing either one or a plurality of active ingredients, the pickling solution becomes gradually exhausted and loses its effectiveness by repeated pickling operations. Such exhaustion leads to imperfect cleaning of metal from the surface of which inorganic coating is to be removed, to the necessity of subjecting the metal to a bath of the pickling solution for an unreasonable length of time or to loss of time by subjecting the metal to the intended action of an exhausted pickling solution for an extended period of time without adequate removal of the inorganic coating from the surface of the metal. Common practice has been merely a visual inspection of the metal discharged from the pickling solution with respect to the time during which it has been subjected to the pickling solution. Such inspection is insufficiently accurate to serve as a guide for the addition of an active ingredient or ingredients to the pickling solution adequate to restore the effectiveness of the solution, with consequent waste of time and material and with inadequate pickling or over-pickling as result of the attempted restoration of the solution. Proposed methods of testing pickling solutions by passing an electric current through a path including the metal having an inorganic surface coating have proven inaccurate, because the conductivity of the pickling solution varies under conditions not directly related to its effectiveness in removing the coating.

A generic object of my invention is to provide a simple and accurate method of testing the effectiveness of a pickling solution in removing an inorganic coating from the surfaces of metals which are to be cleaned.

One more specific object of my invention is to provide a method of making a determination of the above-noted sort by means of a spot test, or sequence of spot tests performed from time to time, the spot test being made typically outside the pickling assembly the solution of which is the subject of the test.

Another more specific object of my invention is to provide a method of making such test in a continuous pickling operation of the sort in which a continuous body of metal, such as a steel strip or wire, moves through a pickling bath the solution of which is the subiect matter of the test, such test being performed typically within the pickling assembly.

Primarily my invention resides in determining the effectiveness of a pickling solution by measuring the time rate of drop in the potential-developing properties of a metal initially carrying an inorganic coating as that coating is removed by the action of the pickling solution. This I do by making the initially coated metal an electrode of a cell in which the pickling solution is the electrolyte. In one adaptation of this principle the other electrode of the cell is to be considered as reference electrode and may be composed of any material capable of creating a potential in cooperation with the metal the surface of which initially carries an inorganic coating. For simplicity of calculation. such reference electrode desirably is of constant potential in the pickling solution and conveniently can be a like metal to the one subjected to pickling but having a surface which initially is clean. By connecting both electrodes with a millivoltmeter the drop in the potential-developed in the cell indicates the removal of inorganic coating from the surface 2,697,673 Patented Dec. 21, 1954 of the metal being cleaned, the potential dropping to an approximate zero value with complete removal if the reference electrode is of like metal with the initially coated electrode or to a constant predetermined value if the reference electrode is unlike.

In another analogous adaptation of the principle involved, two bodies, or regions, of the same metal one coated and one uncoated provide the electrodes of two electrically connected cells the other electrode of each of which is composed of material of constant potential in the pickling solution. The two cells thus formed are connected to the same millivoltmeter, which shows as a potential the difference between the potentials developed by the two connected cells.

In the accompanying drawings illustrating the embodiment of my invention, all views being schematic or diagrammatic in nature:

Fig. I is a vertical sectional view of a single cell outside the pickling assembly organized for testing a pickling solution in accordance with the method of my invention.

Fig. II is a similar view showing the condition of the cell at the conclusion of a test.

Fig. III is a graph illustrating by means of stylized curves indications obtained from the cell when it includes fresh and active pickling solution, when the pickling solution becomes exhausted from use and when the effectiveness of the solution has been restored by the addition of an active ingredient.

Fig. IV is a vertical sectional view illustrating the practice of my method by means of two electrically connected cells and a millivoltmeter connected with both.

Fig. V is a similar view showing the further adaptation of the two-cell idea to testing a pickling solution used in cleaning a continuous body of metal passing continuously through a pickling bath.

Fig. Va is a fragmentary view on an enlarged scale showing the electrodes which form the two cells indicated in Fig. V.

Fig. VI is a diagram illustrating the positioning of electrodes at various points along a pickling tank through which a continuous body of metal is passed continuously.

Fig. VII is av graph illustrating by means of stylized curves the time rate of potential drop on the associated millivoltmeter in practicing the adaptation of my method shown in Figs. V and VI.

Referring initially to Figs. I, II and III of the drawings and the adaptation of my method therein illustrated, reference numeral 1 designates a container set apart from a pickling tank and containing the pickling solution 2 which is subjected to test. The test place 3 of metal carrying on its surface an inorganic coating 3:: and a reference electrode 4 of constant potential which may be a cleaned sample of the same metal as the test piece, or electrode 3, are immersed in pickling solution 2 and are connected by wires 5 and 6 respectively with a millivoltmeter 7 which indicates the potential-developing prop erties of the coated electrode 3 with respect to the reference electrode 4. Fig. II of the drawings shows the test electrode 3 freed of its inorganic coating 311 by the action of pickling solution 2 which serves as electrolyte. As electrode 3 gives up coating 3a from its surface, the potential-developing properties of the electrode drop, such drop in potential being shown by millivoltmeter 7. The magnitude of this potential drop and the time rate of the drop indicate the effectiveness of the pickling solution. This shows the progress of the pickling and the time required to bring the coated electrode 3 to or approximately to the condition shown in Fig. II of the drawings.

The diagram of Fig. III shows graphically the difference in the eifect of a fresh and spent pickling solution and the result of restoring the solution to effectiveness by the addition of an active ingredient. It may be ex plained that the pickling solution used in plott ng the curves of Fig. III is a pickling solution comprising two active ingredients, nitric acid and hydrofluoric acid. In the graph of Fig. III the ordinate is laid off in potential by millivolts and the abscissa in terms of time by seconds. In Fig. III the curve A is plotted to follow the indicated potential resulting when a sample of fresh pickling solution is taken. It will be noted that this curve shows a relatively abrupt drop in potential falling to approxi mately zero value in a period of about 70 seconds before levelling off. Curve B shows a condition in which the pickling solution has become inadequate, the action being incomplete and apparently terminated after 160 seconds. Curve C shows the action after the pickling solution has been renovated by substantial addition of both its active ingredients. This graph illustrates clearly how observation of the millivoltmeter with respect to time provides a guide for renovation or replacement of the pickling solution.

Fig. IV of the drawings shows an adaptation o f my method which permits its employment under conditions in which it is of particularly great utility. As shown,

the apparatus used in this adaptation of my method cornboth of which contain identical samples of the pickling solution 11 which is to be tested. In vessel 9 there are immersed an electrode 12 which is a sample of the metal subjected to pickl ng and which carries on its surface an inorganic coating 12a and a second electrode 13 which is of constant potential in the pickling solution and which is most desirably composed of platinum. In vessel 10 there is immersed an electrode 14 which may be considered as a reference electrode and which desirably is a sample of the same metal as that of which electrode 12 is composed but having an initially clean surface. In any event this electrode should be of constant potential in the pickling solution being tested. In vessel 10 there is also immersed a second electrode 15 which like electrode 13 is desirably composed of platinum.

Electrodes

12 and 14 are interconnected by conductor wire 16 and

electrodes

13 and 15 are connected by conductor wires 17 and 18 respectively with a millivoltmeter 19. This arrangement gives two interconnected cells in a potential-developing circuit which includes a millivoltmeter.

As in the simplest adaptation of my method illustrated in Figs. I and II of the drawings, the test of the pickling solution in the adaptation of Fig. IV is based ori the drop in the potential-developing properties of the initially coated metal used as an electrode as the action of the pickling solution in the surface of that metal proceeds. In this adaptation of my method the two unlike

electrodes

12 and 13 in vessel 9 tend to set up a potential and the two unlike

electrodes

14 and 15 in vessel 10 containing as electrolyte an identical sample of pickling solution 11 tend to set up a differential potential. The difference between the two, or potential between the two cells, is indicated in millivolts by millivoltmeter 19. This differential potential thus is based primarily on the potential-developing properties of electrode 12 carrying on its surface inorganic coating 12a with respect to reference electrode 14, the

electrodes

12 and 14 acting respectively in conjunction with

electrodes

13 and 15. The drop in indicated differential potential with respect to time shows the effectiveness of the pickling solution.

This latter adaptation of my testing method is carried forward as illustrated in the succeeding figures of the drawings to give an accurate test of the effectiveness of a pickling solution used in a continuous pickling process practised on a continuous body of metal passing at constant speed through a pickling bath. In this latter and highly practical variant of my method the principle is identical with that of the adaptations previously described, although the result is arrived at by somewhat different mental processes.

As shown in Fig. V, a continuous elongated body of metal designated by reference numeral 20 is passed at a constant rate of travel through a bath 21 of pickling solution in a pickling tank 22, the pickling solution 21 serving as electrolyte in testing its own effectiveness. In the organization of Fig. V the effect of two cells P and P is obtained by placing one electrode 23 of constant potential in the pickling solution in proximity to the moving body of metal 20 in a region adjacent its point of entry into the pickling solution and a second like electrode 24 in proximity to the continuous body of metal adjacent its point of exit from the solution. These two electrodes are both connected with millivoltmeter 25 by

conductor wires

26 and 27 respectively.

Electrodes

23 and 24 desirably are composed of platimum and being constantly immersed in the pickling solution are mounted each in an insulating shoe 28 to direct their coaction specifically to the adjacent region of continuous metal body 20. That body being continuous, its reach 20a between the regions which constitute cells prises two vessels 9 and 10 P and P acts conductively to take the place of conductor wire 16 of Fig. IV.

Primarily the effect is like that of the arrangement shown in Fig. IV, the difference between the potential developed at cell P and the potential developed at cell P being indicated on millivoltmeter 25. Likewise it is the drop in the potential developed at one of the separated points forming these cells which gives the required indication. Here there is, however, an inversion in the interpretation of that indication. We may take the potential-developing effect reflected at cell P as being zero value if the pickling solution is at its maximum effectiveness and that maximum potential-developing properties exist at the cell P at which point the surface of the metal carries a maximum of inorganic coating. The metal at these points is, however, a part of a single continuous metal body, and the potential developed at cell P where the coating on the surface of the metal is maximum is approximately constant. The variable quantity which indicates the effectiveness of the pickling solution is therefore at cell P, a falling-off in the effectiveness of the pickling solution causes increase in the potential developed at cell P, this increase being evidenced bya drop in the differential potential shown by millivoltmeter 25. Such drop in differential indicates that the pickling solution has fallen below its maximum effectiveness and should be renovated or replaced. In this adaptation of the method the region of metal in the continuous body 20 which is cooperative with electrode 24 to form cell P is in effect the electrode of variable potential-developing properties. The region of the metal which is cooperative with electrode 23 to form cell P being constantly coated is in effect the reference electrode of constant potential-developing properties in the pickling solution.

In conducting a test of the pickling solution in situ in accordance with this adaptation of my method it is to be assumed that the continuous body of metal has a constant rate of travel through the pickling solution, so that the distance between the two

platinum electrodes

23 and 24 is translatable into time of pickling. The use of various positions for the electrode is shown diagrammatically in Fig. VI, which serves in conjunction with the graph of Fig. VII and the accompanying explanation to clarify procedure in accordance with this adaptation of my method. Referring to Fig. VI of the drawings and taking as exemplary a rate of travel of one foot per second of the metal body 20 through pickling solution 21 in tank 22, the distance between the electrodes 23 and 2 4 to form cells P and P is readily translatable into time of immersion of the metal in the pickling solution. It is, of course, most desirable to place the electrode which forms cell P with the portion of the continuous metal body which has been subjected to pickling reasonably close to the exit point of the metal from the pickling solution, as shown in Fig. V, to indicate the complete action of the pickling solution on the metal. For purposes of illustration in the form of hypothetical curves to illustrate the testing of the solution I have, however, shown various positions for the placing of electrode 24 in Fig. VI of the drawings.

In Fig. VI reference letter a shows the position of elec trode 23 to form cell P. Reference letters b, c and d illustrate alternative positions of electrode 24 to form cell P short of the exit point of the metal from the pickling bath. If we assume that position b is spaced 12.5 feet from the position a the metal at its constant rate of travel will have been immersed 12.5 seconds at the point b. This point b is shown in the curve x of Fig. VII, which curve represents the effect of fresh pickling solution. Point b therefore indicates the difference in potential developed by the cells P and P after the metal has been immersed for the stated period of 12.5 seconds. If we assume the initially developed potential at cell P at position a to be 640 millivolts and the potential developed in cell P at point b to be 550 millivolts, the difference of millivolts will be indicated on millivoltmeter 25.

If the second electrode 24 is located at a position a 25 feet from position a then the metal when it reaches the cell P formed by the continuous body of metal and electrode 24 has been immersed in the pickling solution for 25 seconds. As marked on the curve x of Fig. VII the potential as measured between the electrodes of cell P and P will be the difference between the potential at position-a or at Zero seconds, which is 640 millivolts and the potential after seconds of immersion which is 320 millivolts. The potential of 320 millivolts is shown at point c on curve x and the difference between this potential and the potential of 640 millivolts, or 320 millivolts, is indicated on the millivoltmeter.

If the second electrode 24 is located at position d which position is 42.5 feet from position a, that position represents a time of immersion of 42.5 seconds. On the curve x of Fig. VII the point d is shown as indicating a complete cleansing of the metal by its immersion in a fresh pickling solution of high efiectiveness. At this point d, the indicated potential is zero and the millivoltmeter, therefore, would indicate the maximum potential difference between the cells P and P, or 640 millivolts, and complete removal of inorganic coating from the metal is thus indicated. It may be understood that this indication may represent some overpickling of the metal by an abnormal effectiveness of the pickling solution, because point d is substantially removed from the exit point of the metal from the bath. It is to be understood, therefore, that the showing of Figs. VI and VII merely represents the testing of the pickling solution under one hypothetical set of conditions for purposes of illustration and does not necessarily represent a test made under ideal pickling conditions.

Referring still to Fig. VII, curve y reflects the results of test on the basis of Fig. VI when the pickling solution has lost effectiveness. Thus in the curve y the points a and d represent the potential difference between the

electrodes

23 and 24 spaced apart 42.5 feet so that there is a period of 42.5 seconds treatment between the metal apposed to electrode 23 and the metal apposed to electrode 24. This is indicated by a potential of 760 at position a and a potential of 670 at position d, or a potential difference of only 90 millivolts after a relatively long pickling period. Also with electrode 24 disposed at position b of electrode 24, after a pickling period of 12.5 seconds the differential potential is negligible as shown at point b and at position 0 after a pickling period of 25 seconds the potential difference between calls P and P is only between and 40 millivolts as indicated at point 0', both points b and c being included in curve y. It will thus be seen that there is a wide diversity between the indication exhibited when the pickling solution is effective and when the solution becomes ineffective.

In addition to the advantage of accuracy and simplicity inherent in my method of testing pickling solutions, that method possesses a further outstanding advantage related directly, however, to accuracy of indication. Thus Whether the existence of a drop in potential-developing properties between the pickled and unpickled metal is indicated directly or is indicated indirectly as a potential differential, it is possible to read indications as to the effectiveness of the pickling solution as the pickling operation proceeds. This is of course based on the time element which is a feature of my testing method. Thus in the use of the spot check, the indication that the potential between the coated and uncoated electrodes is not dropping with sufficient rapidity allows the pickling solution to be renovated soon after the beginning of the pickling operation, and thus to minimize the additional time during which the stationary work must be subjected to the action of the pickling solution in order that it be adequately cleansed. In testing the effectiveness of the pickling solution used in a continuous pickling process the same advantage appears. If an early indication does not indicate adequate drop in the potential-developing properties in the metal which nears the exit end of the tank, the progress of the metal can be stopped while the pickling solution is renovated. In either case it is the drop in the potential-developing properties of the metal as its inorganic coating is removed which indicates the order of effectiveness of the pickling solution.

Having described and illustrated one embodiment of my invention, I call attention to the fact that numerous variations in the apparatus used and procedure which is followed may be made while adhering to the essence of the invention so embodied, and that the scope of the invention is therefore to be restricted only by the statement of the claims appended hereto.

I claim as my invention:

1. The method of removing an inorganic coating from a metallic surface and simultaneously testing the effectiveness of a pickling solution, said method comprising the steps of immersing a member having at least a portion of its surface bearing a substantial coating of the type to be removed by said pickling solution and defining first electrode means; immersing substantially uncoated second electrode means into said pickling solution; said pickling solution acting as an electrolyte and defining with said electrode means at least one cell; linking said electrode means solely to themselves by current conductive means and a potential measuring device to define at least one closed circuit cell; and measuring with respect to time the drop in potential as the coating is removed from said first electrode means.

2. The method of removing an inorganic coating from a metallic surface and simultaneously testing the effectiveness of a pickling solution, said method comprising the steps of immersing a metallic member into said pickling solution, bearing on at least a portion of its surface a substantial coating of the type to be removed, to define at least one electrode means at its coated surface; immersing at least one substantially uncoated second metallic member into said pickling solution to form another electrode means in adjacent spaced relation to said coated portion of said first member; linking said electrodes solely to themselves by current conductive means, and a potential measuring device, and said pickling solution, acting as an electrolyte, to define at least one closed circuit cell; and measuring with respect to time the drop in potential as the coating is removed from the coated surface of said first member.

3. The method of removing an inorganic coating from a metallic surface and simultaneously testing the effectiveness of a pickling solution, said method comprising the steps of passing an elongated body continuously at constant speed through a pickling solution having a substantial coating as it enters said solution and which is essentially uncoated as said body leaves said pickling solution; said coated and uncoated portions of said body defining at least a pair of electrodes in said solution; immersing at least a pair of substantially uncoated metallic members defining a pair of other electrodes adjacent said coated and uncoated portions of said body; linking said other electrodes solely to each other by current conductive means and a potential measuring device, and said first electrodes by means of said body to define at least a pair of spaced cells with said solution as an electrolyte; and measuring with respect to time the differential drop in potential between said cells to indicate the effectiveness of said pickling solution in removing coating from said body.

4. The method of removing an inorganic coating from a metallic surface and simultaneously testing the effectiveness of a pickling solution, said method comprising the steps of immersing a metallic member, bearing a substantial coating of the type to be removed into a sample of said pickling solution to be tested, to define a first electrode; immersing a substantially uncoated second metallic member into said pickling solution to be tested to define another electrode; linking said first and second electrodes solely to each other by current conductive means, and a potential measuring device, and said pickling solution, acting as an electrolyte, to define a closed circuit cell; and measuring with respect to time the drop in potential as the coating is removed from the coated surface of said first electrode.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Jour., Instit. of Metals, vol. 40, 1928, pages 148-159.