US 2560966 A
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y 1951 H. J. LEE 2,560,966
METHOD OF ELECTROPLAT'ING COPPER CLAD TAINLESS STEEL COOKING VESSELS 2 Sheets-Sheet 1 Filed July 31, 1947 mm V WYH IYMQ I nUefii/ m? raid JLee.
Ha mud Isl. J. LEE
Jul 17, 1951 4 2,560,966
METHOD OF ELE TROPLATING COPPER CLAD STAINLESS STEEL COOKING VESSELS 2 Sheets-Sheet 2 Filed July 31, 1947 6mm 0 v In?) I 1 3273%: 3d 3142a, 35%27M? Patented July 17, 1951 METHOD OF ELECTROPLATING COPPER CLAD STAINLESS STEEL COOKING VES- SELS .Harold J. Lee, Rome, N. Y., assignor to Revere Copper and Brass Inco a corporation of Maryla Application July 31, 1947, Serial No. 764,956
Claims. 1 My invention relates to methods of cladding stainless steel cooking vessels with .an electrodeposited layer of copper. r The invention constitutes an improvement in the method and apparatus disclosed in Kennedy,
Knight and Lee United States Patent 2,363,973 issued November 28, 1944 to the assignee of this application, and in respect to the embodiment of the invention illustrated in the application drawings is particularly useful in claddin stainless steel cooking vessels by employment of apparatus of the general type disclosed in pending Kennedy, Knight and Lee application" Serial Number 630,266, filed November 23, 1945, now Patent 2,506,794, dated May 9, 1950.
As disclosed by the patents above referred to, before electrodepositing on the stainless steel cooking vessel a cladding layer of copper the vessel is first treated for preparing it to receive such layer and cause the latter firmly to adhere thereto. Briefly, as described by said patents, such preliminary treatment consists in cleaning the surfaces of the vessel, when necessary, to remove grease, dirt and the like, then preferably roughening the cleaned surfaces, and treating them with electrolytically released hydrogen While the surfaces are made a cathode in a dilute sulphuric acid bath. As further described by'said patents, upon competition of this preliminary treatment said surfaces are substantially immediately immersed in a copper plating bath in spaced opposed relation to a soluble copper electrode, the latter being made an anode and the vessel a cathode when said surfaces are so immersed for substantially immediately initiating deposition of the copper.
The surfaces of the vessel on which the layer of copper is to be electrodeposited may be roughened by chemically etching them or by sand blasting. Best results, however, it has been found will be secured by etching them anodically. For etching them anodically the surfaces of the vessel on which the copper layer is to be subsequently electrodeposited may be immersed inan electrolytic bath consisting of water containing from about 8.5 to 62%, preferably about 30%, by weight of sulphuric acid. The bottom portion of the vessel immersed in this electrolyte with its bottom surface in spaced relation to an insoluble electrode such as lead, the electrode being made a cathode and the vessel an anode so as to plate off the exterior surface of the immersed portion of the vessel when current is passed. Best results will be secured with: current densities of from 300 to 350 amperesper square foot of anode will be electrolyzed rporated, Rome, N. Y., nd
surface, although smaller and larger densities, say from to 550 amperes per square foot, may be employed. The current is passed until the surface is suificiently etched to begin to show a socalled satin surface.
Preferably just as soon as the vessel begins to show the satin surface above referred to it is removed from the electrolyte, immediately rinsed with water, and its roughened surfaces placed in a second electrolyte of, the same composition above referred to with its bottom surface in spaced relation to an insoluble electrode such as lead, this electrode being made an anode and the vessel a cathode. When current is passed the electrolyte to liberate nascent hydrogen which is plated on the roughened surfaces of the vessel, whereupon the vessel is removed from the electrolyte and immediately rinsed with water and placed in the copper plating bath in spaced opposed relation to the soluble copper electrode and electrodeposition of copper immediately initiated by making the electrode an anode and the vessel a cathode as above described. If the surfaces of the vessel'are roughened by sand blasting or chemical etching they are preferably immediately rinsed with .water, and. placed in the electrolyte for treating them cathodically with electrolytically released hydrogen, as just explained. Preferably much lower current densities are employed when the vessel is made a oath ode as compared to when 'it is made an anode. When it is a cathode current densities of from 40 to 400 amperes per square foot of cathode surface may be employed. g
The same electrolyte may be employed for treating the vessel cathodically as that employed for treating it anodically, in which case the vessel will be first/treated anodically and then the polarity of the electrical connections to the vessel and electrode will be reversed to make the vessel a cathode and the electrode an anode. For reversing the polarity there may be employed the familiar double-throw two-pole switch, aresistance being thrown into circuit with the vessel when it is the cathode for reducing the current density to the desired value. Preferably, however, to prevent undue contamination of the electrolyte which treats the vessel cathodically, sepa-. rate electrolytes are employed for the anodic and cathodic treatments. 6 In the apparatus disclosed by Patent 2,363,973 above referred to the bottom and adjacent side wall portions of the vessel are immersed in the electrolyte and the vessel axially rotated with the bottom in spaced coaxial relation to a fiat electrode. Applicant has found that with such an arrangement the times of both the anodic and cathodic treatments to secure satisfactory results are unduly prolonged, and that as a result of the cathodic treatment with such an arrangement poor adherence of the subsequently electrodeposited copper layer is liable to result particularly when high current densities are employed for speeding up the cathodic treatment. He has however found that these defects may be eliminated by employing for the electrode one having a convex surface which is substantially a surface of revolution, and placing the vessel in coaxial relation therewith with the bottom of the vessel opposed to said surface.
Applicant believes that with the flat electrode the current passing between it and the vessel is non-uniformly distributed, the minimum current being at the center of the bottom of the vessel and the maximum current being at the edge portions of said bottom and adjacent side walls of the vessel, while with the electrode having the convex surface the current density is approximately uniform over the entire immersed portion of the vessel. For example, he believes that with a flat electrode, when the total current flowing is say 250 amperes, there may be a current density of say only 100 amperes per suqare foot at the center portion of the bottom of the vessel and a current density of say 900 amperes per square foot at the extreme edge portions of said bottom. The time necessary to treat any portion of the immersed surfaces of the vessel satisfactorily will depend upon the current density at that portion, the greater the current density the less the time. Consequently when a flat electrode is employed, and the current density is a minimum at the center portion of the bottom of the vessel, the time for treating the vessel satisfactorily will depend upon the time it takes to treat that portion satisfactorily. When the convex electrode is employed this time will be much reduced, because for any total current flowing the current density at the center portion of the vessel is increased at the expense of the current density at the edge portions, making the current density approximately uniform over the entire surface of the, bottom of the vessel, as above explained. Applicant has found that to some extent a uniform distribution of the current over the immersed portions of the vessel may be secured by using a flat electrode with an annular shield interposed between the edge portions of the vessel and the electrode. However, such a shield will be suitable for but one diameter of vessel, and a shield of different size must be substituted for each diameter of vessel. However, the electrode having the convex surface is adapted for use with any diameter of vessel, because the greater the diameter of the vessel the farther are its edge portions away from the surface portion of the electrode immediately below it.
In respect to improved adherence of the electrodeposited layer of copper on the stainless steel surfaces treated cathodically by use of the convex electrode, applicant believes that when av fiat electrode is employed, and the acid electrolyte is contaminated with even minute traces of a heavy metal, minute practically microscopic quantities of such metal are electrodeposited on the edge portions of the immersed surfaces of the vessel when it is being treated cathodically with electrolytically released hydrogen, this resulting because of the high current density at said portions and the relatively prolonged time necessary for treating the immersed surfaces as above described, this deposit of metal because of the high current density being spongy so that it prevents the subsequently electrodeposited layer of copper from satisfactorily adhering to thestainless'steel. When the electrode having the convex surface is employed, however, the current at the edge portions of the immersed surfaces of the vessel and the time necessary to treat those surfaces are reduced as above explained, with the result that no appreciable quantities of heavy metal will be deposited on the surfaces, or, even assuming they were deposited, would not be spongy.
Suitable apparatus according to the invention for performing the above method is shown in the accompanying drawings, in which:
Fig. 1'is a transverse section of apparatus for treating the vessel either cathodically or anodically;
Figs. 2, 3 and 4 are, respectively, sections on the lines 2-2, 3--3 and 4-4 of Fig. l, with parts omitted and parts broken away, Fig. 4 being on a reduced scale;
Fig. 5 is a plan of the apparatus according to Fig. l; r
Fig. 6 is a section on the line 66 of Fig. 1, with parts omitted and parts broken away; and
Figs. 7, 8 and 9 are, respectively, sections on the lines 1-'I, 8-8 and 9-9 of Fig. 5, with parts omitted and parts broken away.
Referring to the drawings, the electrolyte is contained in an open top tank having a bottom I, side walls 3 and end walls 5, this tank being preferably formed of steel and interiorly coated, as indicated at I, with lead, rubber, or other material inert with respect to the electrolyte.
Interiorly of the tankis positioned a flat horizontal bar 9 of copper extending in spaced relation to the bottom of the tank'from adjacent one end wall 5 thereof to the other. At each of opposite ends this bar is shown as supported in an adjacent block ll of insulating material, the blocks resting upon and being secured by bolts It. to the lower portion [5 of an inverted U-shaped bracket. As shown, H of the bracket have end flanges I9 resting upon the outwardly projecting flanges 2| of the adjacent side walls of the tank, to which flanges 2| said flanges is are secured by bolts 23. The U-shaped bracket, like the tank, also is preferably coated with lead, rubber, or the like.
At one end the bar 9 is provided with an upwardly extending portion 25, which portion at its upper end is bent outwardly, as shown at 21, and rests upon and is brazed to a bar 29 of conductive material such as copper. Brazed to the bar 29 adjacent one of its ends is a connector 31 for a cable 33. The bar 29, as shown, rests upon a strip 35 of insulating material, and is secured to the outwardly extending; flange 31 of the adjacent end wall of the tank by bolts 39 extending through said flange and. strip and tapped into the bar, a flanged bushing 4| surrounding, the bolt insulating it from the flange.
As shown, carried by the bar 9 are upwardly projecting, brackets 43 having lower flanges 45 brazed to the upper surface of the bar. At their upper ends each bracket has a flange 41 to pairs of which are brazed, soldered or welded the edge portions of disk-like electrodes 49. Each elec-' trode is in the form of a sheet oflead, or other conductive material insoluble in the electrolyte; shapedto present an upper surface it whicnis the opposite legs approximately a segment of a sphere. As shown, each electrode is formed with perforations 53 distributed 'thereover in relatively closely adjacent relation. When the cooking vessels are placed above the electrodes and rotated as hereinafter described electrolyte is drawn through the perforations from beneath the electrodes and forced radially outwardly through the spaces between the electrodes and bottoms of the vessels, the rapid circulation of the electrolyte thus .caused permitting the use of high current densities without burning of the immersed surfaces, of the vessels. Preferably the bar 9, the
.upwardly extendin portion 25 of that bar, and
the brackets 43 have a coating 55 of lead to .protect them from the corrosive action of the electrolyte, or, if desired, may be coated with rubber for that purpose and for insulating them from the electrolyte.
At the opposite end of the tank from the bar 29 the'outwardly projecting upper flange 51 of the tank end wall carries a second bar 59 of copper to which is brazed a connector SI for the cable 63. Interposed between the bar 59 and the flange 51 is a strip 65 of insulating material, the bar 59 being secured to the flange by bolts 61 extending through the flange and strip and tapped into the bar. For insulating the bolt from the flange is provided a flanged insulating bushing 69 through which the bolt extends.
Supported in the tank above each electrode 49 in coaxial relation therewith is shown a cooking vessel V having a flat bottom Wall II and side walls 13, the latter includin the rounded portions I5 at the corner between the side walls and the bottom. In practice the tank ordinarily will be filled with electrolyte to about a level L, and with a smaller cooking vessel as, for example, that illustrated at 22, the tank will be filled with electrolyte to about a level Z, in each case to cause the lower portion of the vessel to be immersed to just above the top of its rounded corner portion I5. It will be understood, however, that the vessel may have a square corner,
and that whether the corner is square or rounded the depth of immersion of the vessel will depend upon the portion thereof to be clad with copper after it is removed from the tank. Satisfactory results, it has been found, will be secured by having minimum spacing between the bottom of the vessel and the electrode about three-quarters of an inch and the depth of immersion of the vessel not exceeding two and one-half times that distance, although such spacing and the depth of immersion are not I critical. Satisfactory results will be secured in treating vessels having diameters of from 4 to 15 Inches with electrodes 18 inches in diameter, the upper surface of the electrode being a segment of asphere of about 21 inches radius resulting in the circumferential edge of the top surface of the electrode being about 2 inches below its center portion. With such radius of curvature the current density, it has been found, is approximately uniform over the entire surface of the vessel. However, the radius of curvature is not critical, as a marked improvement in current density distribution is noted with other radii causing the upper surface of the electrode to be convex. In fact such improvement will be secured when its convexity is presented by a conical surface of the same ratio of diameter to altitude as the spherical surface, and a conical surface will for some reason give even better results than will a spherical surface with vessels depending portions 83 screw 9I.
of from 4 to '7 inches in diameter. the diameter of the electrode should not be less than about 1 to 1 inches greater than the diameter of the vessel, and having the electrode radius not less than the radius of the vessel plus the depth of immersion of the vessel will satisfy this condition.
As shown, the vessels V are supported by a carrier comprising the spaced bars 11 which are preferably formed of metal such as brass and are integrally connected at their ends by cross-bars 19. As shown, at the intermediate portion of the carrier are cross-bars BI integrally formed with the side bars TI. These cross-bars BI have which are perforated for fixedly carrying elongated vertical sleeves 85, in which latter are rotatably mounted vertical shafts 81. As shown, carried by the lower end of each shaft 8? is a sleeve '89 (Fig. 7) secured thereto by a set screw 9I, the sleeve projecting beyond the lower end of the shaft 31 for receiving the upper end of a, shaft 93, the latter being removably secured to the sleeve by a second set Carried by the lower end of each shaft 93 is a chuck for supporting the cooking vessel. This chuck, which is preferably formed of resilient sheet copper, has a bottom 95 to which the shaft 93 is joined, as by welding, and has side walls formed with V-shaped splits 91 to form a circular series of spaced resilient prongs 99, the latter for engaging the lower portions of the inher side wall surfaces of the vessel for supporting it and detachably connecting it to the shaft .33.
As shown, each shaft 81 is provided at its upper end with a bevel gear IllI meshing with a bevel gear I 93 on a horizontal shaft l rotatably supported in bearing-s I01 on the carrier crossbars 8|. For driving the shaft I05 it is shown as connected by an insulating coupling I09 to the driven shaft I m of an electric motor, I I I, the mo- In general tor being supported on a plate M3 of insulating ing upon and secured by rivets or the like I23 (Fig. 3) to an insulating strip I25, the bars adjacent one end being connected by leads I21 to a source of current supply. As shown, the strip I25 at opposite ends is secured to and supported on brackets I29 carried by the adjacent end wall 5 of the tank. These brushes are of a known type in which the contact portions I Iii are yieldingly extensible relative to the bodies of the brushes so as to make good contact with the bars I2I when the carrier for the vessels is placed in position.
As shown, when the carrier is placed on the tank the lower contact portion I 3i (Fig. 8) of the cross-bar I33, which latter is formed integrally with the side bars 'I! of the carrier, rests upon the bar 59 connected to one side of the line by the cable 63. This will place the vessels in electrical communication with the cable 63 by way of the connector 6|, cross-bar I33, side bars I'!, cross-bars 8|, depending portions 83 of the latter, sleeves 85, shafts 87, sleeves '89, shafts '93, and the chuck-s having the portions 99 which engage the vessel. At the same time the electrodes 49 will be placed in communication with the cable 33 connected, as above explained, to the opposite side of the line. For supporting the end of the carthe copper on them.
escapee electrodes 59 are cathodes, and that when the roughened surfaces of the vessel are treated with electrolytically released hydrogen the cables are rier opposite the cross-oar I33, when the carrier "is placed on the tank, the cross-bar is at that end so connected that the vessels are cathodes and the electrodes are anodes. As above explained,
the vessels are preferably treated anodicall and catho'dically in separate tanks. In practicethe vessels will be placed on the chucks'before the carrier is placed on the tank, the carrier preferably being supported on a suitable rack forcthat purpose, then by use of a suitable conveyor, preferably one of the swinging arm type of known construction, the carrier is removed from the rack and placed on the tank for treating the vessel anodically, then, at the end of the anodic treatment, by use of a second conveyer, preferably of the same type, the carrier is lifted and immediately placed on the tank for treating the vessel cathodically, and at the completion of the cathodic treatment the carrier is lifted by a conveyer of the same type and placed on the tank for electrodepositing copper on the c'athodically treated portion of the vessel, which last men tioned tank may be of the type described in the above mentioned Patent 2,506,794 according to which the tank has soluble copper anode elec trodes immersed in the electrolyte, in spaced opposed relation to which electrodes the bottoms of the cathodically treated vessels are placed and the vessels made cathodes for electrodepositing For permitting such movement of the carrier from tank to tank the carrier is shown as provided at each of opposite ends with a projection 54! for engagement by the conv'eyer, suitable provision being made, for example having the projection of insulating material, to prevent grounding of the vessel during its travel from the tank in which it is treated cathodically to the tank in which the copper is electrodeposited, as grounding of the vessel apparently acts to dissipate the film of hydrogen placed on the surfaces of the vessel during the cathodic treatment, or acts to destroy the efliciency of that film if not dissipated.
It will be understood that within the scope of the appended claims wide deviations may be made from the method described without departing from the spirit of the invention.
1. In a method of coating the substantially flat bottom and adjacent side wall surfaces of revolution of a stainless steel cooking vessel with a strongly adhering layer of electrodeposited copper, the steps of immersing said surfaces ina dilute sulphuric acid bath with said bottom surface in opposed spaced substantially coaxial relation to the convex surface of revolution of an insoluble electrode of greater diameter than the diameter of the vessel and of material altitude, making said vessel a cathode and said electrode an anode while immersed in said bath for treating said surfaces of the vessel with electrolyticall'y released hydrogen, and upon cessation of such treatment removing said vessel from said bath and substantially immediately immersing said surfaces thereof in a copper plating bath in opposed spaced relation to a soluble copper electrode and. making the latter an anode and the vessel a cathode.
2. In the method according to claim 1 axially rotating the vessel while it is a cathode in both instances.
3. In the method according to claim 1 the step of roughening the said surfaces of the vessel prior to treating them with the electrolytically released hydrogen.
4. In the method according to claim 1 the steps of roughening the said surfaces of the vessel, prior to treating them with the electrolytically released hydrogen, by immersing said surfaces in a dilute sulphuric acid bath with the bottom surface of the vessel in opposed spaced substantially coaxial relation to the convex surface of revolution of an insoluble electrode of greater diameter than the vessel and of material altitude, and making the vessel an anode and said electrode a cathode while immersed in said bath.
5. In the method according to claim 1 the steps of roughening the said surfaces of the vessel, prior to treating them with the electrolytically released hydrogen, by immersing said surfaces in a dilute sulphuric acid bath with the bottom surface of the vessel in opposed spaced substantially coaxial relation to the convex surface of revolu tion of an insoluble electrode of greater diameter than the vessel and of material altitude, making the vessel an anode and said electrode a cathode while immersed in said bath, and axially rotating the vessel both when it is an anode for toughening it and when it is a cathode for treating it with hydrogen.
l-IAROLD J. LEE.
REFERENCES CITED The followingreferences are of record in the file of this patent:
UNITED STATES PATENTS OTHER REFERENCES The Metal Industry, London, April 28, .1944; pages 266-367, an article by Leadbeater.