US2363973A - Method of copper plating stainless steel cooking vessels - Google Patents

Description

Nov. 28, 1944. J. M. KENNEDY ET AL 2,363,973

METHOD OF COPPER PLATING STAINLESS STEEL COOKING VESSELS Filed July 8, 1939 7 Sheets-Sheet 1 Fig 171/1249 ni/ a rs James M'Kenzwd y. flr'ifhwz'fli'n Ha 2'0 Ed J L ee,

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Nov 28, 194 J. M. KENNEDY ET AL. METHOD OF COPPER PLATING STAINLESS STEEL COOKING VESSELS I Filed July 8, 1939 '7 Sheets-Sheet 2 3221/7 M MWvZ%/ NOV. 1944- J. M. KENNEDY ET AL I 2,363,973

METHOD OF COPPER PLATI'NG STAINLESS STEEL COOKING VESSELS Filed Jul 8, 1939 '7 Sheets-Sheet 3 Invenfiors: JamsMKezz nedy, girihwioglgfnzlghi az'o e Qy M -W ww- Nov. 28, 1944.

METHOD OF'COPPER PLATING STAINLESS STEEL COOKING VESSELS J. M; KENNEDY ETAL 2,363,973

Filed July 8, 1939 7 Sheets-Sheet 4 Nov. 28, 1944.

J. M. KENNEDY ET AL METHOD OF COPPER PLATING STAINLESS STEEL COOKING VESSELS Filed July 8, 1939 7 SheetsSheet'5 (iii/i398.

Nov. 28, 1944. J. M. KENNEDY ET AL 2,363,973

METHOD OF COPPER PLATING STAINLESS STEEL COOKING VESSELS 7 Sheets-Sheet 6 Filed July 8, 1939 I 71220 n 70 ms.- Jam as MIIZWTMEd y. dz ihwrfllfnighi,

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Patented Nov. 1944 UNITED STATES PATENT oar-Ica- I I Q James M. Kennedy, Arthur P. Knight, and Haroldv J. Lee, Rome, N. Y., assignors to Revere Copper andBrass Incorporated, Rome, N. Y., a corporation of Maryland Application July 8,1939, Serial No. 283,432

15 Claims. (c1. eon-s4 This application is a continuation-in-part of our co-pending application Serial Number 240,060, filed November 12, 1938, now Patent No. 2,272,609, which isa continuation-in-part of our co-pending application Serial Number 182,482, filed December'30, 1937, now abandoned.

,Our invention relates to methodsof making plated stainless 'steel articles, particularly but not exclusively to stainless steel cooking utensils having an electro-deposited coating of copper for distributingthe heat.

The invention will bebest understood from the following description of methods of making a- "cooking vessel,

paratus 'for-usedn practice of the methods, the" 7 scope of the invention being more particularly pointed-out in the appended claims. 1

' In the drawings w Fig. 1- is an elevation, with parts in section, of -.apparatus for use in preparing the surface of a stainless steel article for electro-depositing thereon a layer of copper or other metal;

Fig. 2 is a plan of the apparatus according to Fig. 1 with the motor omitted;

Fig. 3 is a section on the line 3-3.of Fig. 2

with parts omitted;

. Fig. 4 is an elevation, with parts in section, of apparatus for use in electro-depositing a coating of copper or other metal on the article;

Fig. 5 is a plan of a fragment of the apparatus according to Fig. 4 with the motor and article, and support therefor, omitted;

Fig. 6 is a schematic diagram of electrical connections employed in connection with the apparatus according to Figs. 1 and 2;

' Fig. 7 is a vertical diametric section of the bottom portion of the finished article, the thickness of the metals being exaggerated;

Fig. 8 .is ail-elevation, with parts in section and "parts omitted. of a modified form of apparatus for in preparing the surface of a stainless 5 steel article for electro depositing thereon a layer :of copper or other metal;

Fig. 9 isanelevation, with parts in section ahd parts omitted, of amodified form of apparatus.

- for u'se'in electro-depositing a coating of copper or other metal on 'the article;

Fig. 10 is a more or less diagrammatic representation, on an enlarged scale, of a fragment of the support and shield of Fig. 9; Fig. 11 isa. plan, with parts omitted, of a fragment of the apparatus according to Fig. 9;

' F a.- 2 ls' pl m an enlarged scal with broken away, of the nozzle of the apparatus according to Figs. 9, 10 and 11; and

Fig. 13 is a section on the line 13-43 of Fig. 12.

The apparatus illustrated is particularly adapted for electro-depositlng a copp r layer on the bottom surface of cooking vessels made of stainless steel, that is to say, iron, or iron-nickel alloy, containing sufficient chromium,- say 6 to 25%, to make it stainless and corrosion resistant, and commonly [small amounts of other metals present as impurities or added for improving the chemical and physical properties of the alloy. Although not limited thereto, an alloy containing 18% chromium and 8% nickel is very satisfactory for use in making coolnng vessels according to the present invention.

It will'be understood that'stainless steel, although presenting'a desirable material in respect to its resistance to the corrosive action of foods, is unsatisfactory for cooldng vessels such as frying pans, pots, and the like, for the reason that it is not only a relatively poor conductor of it is attempted to cook batter in a. stainless steelfrying pm to produce a pancake," no matter what cooking temperature is employed, the pancake will burn in spots before the portions between these spots will show any particular evidence of being cooked. To overcome this difficulty it has been proposed to provide the under side of the bottom of a cooking vessel with a layer of copper or other material of high heat conductivity so as to distribute. the heat over the surface of that bottom. The apparatus and methods herein described are particularly useful in forming such a layer by electro-deposition on the bottom of a cooking vessel. It will be understood, however, that the apparatus and methods described are not limited to main con- 7 nection with pooking vessels, but may be em-' ployed in connection with electro-depositing copper on any sort of stainless steel article.

In the practice of the method the surface to be plated is preferably first treated to clean it of grease. .As suitable for this purpose applicants have found as satisfactory a solution which. contains for each gallon of water 0.5 ounce sodium hydroxide, 1.5 ounces sodium carbonate, and 4 ounces sodium silicate. The article may be val-- lowed to stand in this alkaline solution for a short time until by observation. or trial the grease is removed, after which it maybe rinsed in water to remove all traces of the-treating solution and plating methods.

products of the reaction. However, if desired, any other known way and compound for "degreasing-metal surfaces ordinarily may be emcants have found that in both the anodic and cathodic treatments best results will be secured by employing an electrolyte consisting of water containing about 30% by weight of sulphuric acid,

to which solution preferably, but not necessarily, is added about by weight of anhydrous sodium sulphate, and, for the electrolyte used for the cathodic treatment, preferably .also suflicien't substance such as sodium chloride to cause the electrolyte to contain about 0.05% by weight of chloride radical.

Either or both the sodium sulphate and chloride radical may be omitted. It has been found,

however. that sodium sulphate improves the conductivityv of the sulphuric acid electrolyte and also is electrolyzed to liberate sodium at the cathode when the article is made the cathode.

This sodium reacts with the water to increase the amount of hydrogen liberated at the cathode, and .thusfcuts down the time necessary for c'athodically treating the article. The chloride radical, it has been found, acts in the nature of a catalyst in respect to the effects produced when the article is a cathode, and when employed also acts to decrease the time necessary for cathodic treatment of the article. In practice theamount of sodium sulphate may be from J about 5 to of the electrolyte, and the range of the chloride radical from about 0.01 to 0.5% of the electrolyte.

The concentration of the sulphuric acid of the electrolyte employed in these preliminary treatments may vary from about 8.5 to 62% by weight. However, it has-been found that the time necessary for treating the article for a given current density decreases as the concentration of sulphuric acid is increased from about 8.5 to 30% by weight, but no substantial decrease in time has been observed by increasing the sulphuric acid concentration above about 30% by weight.

When the article is made the anode it has been found that best results will be secured with current densities of frdm 300 to 350 amperes per square foot, although smaller and larger densities. say from 40 to 550 amperes per square foot of anode surface, may be employed. The total time of treating the article as an anode decreases as the current density is increased. This total time is such that the article is treated until etching of the'surfa-ce begins, as shown by a satin surface" just beginning to form on the article. Ordinarily the total time of this treatment will be from 30 to 45 seconds depending upon the current density employed within the range of from 40 to 550 amperes per square foot of anode surface.

Preferably much lower current densities are employed when the article is made the cathode. Preferablya current density of from 40 to 400 amperes per square foot of cathode surface is employed. The necessary time of treatme t creaseswith the current density, and ordinarily satisfactory results will be secured with a treatment of 1 to 3' minutes depending upon the current density. However, longer times of treatment are not precluded.

In treating the article anodically, as above described, platingolf of its surface occurs slightly to roughen it, as evidenced by the production of a satin surface as above explained. This anodic treatment in some instances may be omitted, but without assurance of obtaining an adhering coating. If this omission is made, the surface may be roughened prior to cathodic treatment by other means, say by sand blasting, chemical etching, or the like.

When the article is made a cathode, hydrogen is evolved at its surface, which hydrogen acts as a deoxidizer and is believed also to form a film of hydrogen on said surface, protecting the surface while the article is being transferred to the plating bath and causing the plating to adhere to the surface. The time of this transfer and that which elapses before the platingoperation is initiated should be kept at-a; minimum lest the hydrogen film be dissipated before the plating operation is initiated. It is necessary. so far as has been observed, to make the article a cathode to secure satisfactory results. and to make it a cathode last in respect to it being made the anode no matter how many times it may be made acathode and ail-anode. r I

Electrolyteof thesame composition preferably is employed'when the article is both an anode and a cathode. Best results are secured when; the

electrolyte is kept at about room temperature when it is a cathode so as to minimize heating of the article and consequent dissipation of the hydrogen film. Preferably, to prevent the possibility of the article being treated cathodically in an electrolyte which has been deleteriously contaminated by employing it for treating the article anodically, these operations" are performed in separate baths. After-the satin surface forms when the article is treated anodically itmay be immediately rinsed with water and placed in a second bath in which it is made the cathode. In such case only the bath in which the article is made the cathode need contain either the sodium sul hate or the chloride radical.

If the same bath is employed for both the anodic and cathodic treatments, alternations in the current may be made byuse of a suitable pole changing device as, for example, the familiar double-throw two-pole switch, a resistance being, thrown into circuit with the article when it is the cathode for reducing the current density to the desired value. Ordinarily but one alternation need be made, the article first being made an anode until the satin surface begins to form, and then made a cathode. v

The article after being cathodlcally treated as above described, is removed from the acid bath and placed in a "plating bath. Prefer- '-ably, so as not to increase the, acidity of the plating bath, the treated surfaces of the article before being placed in the plating bath are washed with water, preferably at about room temperature, to free the surfaces of acid, and the article is placed in the plating bath before it dries. This washing operation may be performed by subjecting the article to a water spray or by immersing it in water. Preferably the article, if its shape permits. as would be the case with a cooking vessel, is axially rotated while bein washed to subject all parts of its treated surfaces to water, and is axially rotated when the washing is discontinued to throw off the excess water from its surfaces.

As above explained, the time which elapses between the cessation of the cathodic treatment of the article and the initiation of the plating operation on its treated surfaces should not be so prolonged as to permit material dissipation of the hydrogen him on the treated surfaces, and particularly the time the treated surfaces are exposed to the drying action of the air when wet with acid or water should be kept at a minimum to avoid dissipation of this films Ordinarily to insure satisfactory results the total time which elapses should not exceed about half the necessary time of cathodic treatment,-that is to say, if the article is treated cathodically for 1 minute should not exceed 30 seconds, or if treatedcathodically for 10 minutes should not exceed 5 minutes. although minutes treatment in any ordinary case would be far in excess of that which is necessary. Further, it has been found that when the cathodically treated surfaces are placed in the plating electrolyte the latter acts to destroy the hydrogen film during the time which elapses before the plating. current is established toinitiate deposition. Therefore, ths electrolyte to which the treated surfaces are exposed preferably is kept at about room temrperature, say not over about 80 F. for an acid copper sulphate electrolyte. and the-plating current established immediately upon the article being immersed in the electrolyte. Somewhat higher electrolyte temperatures, however. are not precluded, but the permissible elapsed-time for establishing the plating current rapidly diminishes with the rise in temperainre with .de-

creased assurance of securing a strongly adhering electro-deposit, unidl with temperatures oi about 140 F. the permissible time does. not ex ceed about 20 seconds. It will therefore be understood that, in the sense the total time which may elapse between the cessation of the oathodic treatment and the initiation of electrodeposition, including the time for transferring the article and washing its cathodically treated surfaces, is limited to that which will not cause the electro-deposited coating to be non-adhering on account'of dissipation of the hydrogen film or for other causes which would occur if 1 electrolyte maintained at a relatively high tem-- perature and with use of a plating current of relativel high density. The first step is employed preferably to lay a thin, dense, strongly adhering layer or strike coating, andthe second step to build up that coating to the desired thickness. Ordinarily, to make a coating'that is bonded to the base metal strongly enough" to withstand high temperatures and stresses to which a cooking vessel is subjected in use, the first coating preferably is just slight y more than a' socalled flas coating. With the ordinary cooking vessel the total thickness of the coating, after the second coating is laid, will be -at least 0.02 inch to secure satisfactory results.

For vessels with thicker walls, say those exceeding 0.05 inch in thickness, the thickness of the copper coating ordinarily should be increased proportionally to secure best results.

As a suitable example of the plating method, but without limitation thereto, the thin preliminary coating may be electro-deposited employing a 20% (by weight) sulphuric acid electrolyte containing about 10% (by weight) copper sulphate. However, from 5 to 40% (by weight) sulphuric acid may be employed with 5 to 20% (by weight) copper sulphate, the amount of copper sulphate varying inversely with the amount of acid. Preferably, in laying this coating, the article is rotated, or motion between it and the electrolyte otherwise caused.

With these electrolytes for the preliminary copper layer a current density of up'to amperes per square foot of cathode surface may be employed, the anode preferably being soluble as. for example, being formed of copper. I Higher current densities, say up to 300 ampere per square foot of cathode surface, and high percentage copper sulphate electrolytes, could be employed, but it would be necessary under such conditions strongly to agitate the electrolyte to keepdown burn- -ing of the copper layer,- andsuch agitation would be liable to'admlt air and destroy that property of the stainless steel surface which enables the coating to be placed upon it.

Under the above conditions the preliminary coating'is formed in from 20 seconds to 3 minutes depending upon the current density and the copper sulphate concentration of the electrolyte. The coating is dense and of fine grain, and strongly adheres to the stainless steel so as to be in substance integral therewith in the finished article.

Although it is preferred to employ an acid copper sulphate electrolyte for the preliminary strike coating, other suitable electrolyte may be employed as, for example. an aqueous copper cyanide electrolyte,say one containing 3 ounces (by weight) of copper per gallon in the form of cop- .per sodium cyanide, with 0.5 to 3 ounces (by weight) of free sodium cyanide per gallon to increase the conductivity of the electrolyte and provide anode corrosion. With the copper cyanide electrolytes a slightly higher temperature, not

less than F., must be employed.

The preliminary step of electro-plating could be continued to lay a coating of the desired thickness in the finished article, but would involve such time as to be economically prohibitive. Consequently, for laying the remainder of the coat lng, preferably the article is transferred from the bath just mentioned to a second bath without permitting it'to dry, or without rinsing it if the preliminary coating is deposited from a copper ulphate electrolyte. It has been found that, to secure good results, if the article is accidentally permitted to dry at this stage of the process it cathodically treated 4 4 ounces per gallon'of aluminum sulphate to give a smoother surface to the 'flnished copper coating.

The above mentioned electrolyte employed for laying the flnal copper coating is maintained preferably at a temperature of about 130 F. to increase the rate of deposition. Temperatures up to 150 F. may be employed, but preferably the temperature is not raised to above 130 F. to prevent the plating from becoming too coarse.

Current densities up to about 500- arnperes per square foot may be employed, and for the higher ranges of current density preferably not only is the work rotated, or motion between it and the electrolyte otherwise-caused, but the electrolyte is strongly agitated as, for example, by introducing into it a jet of air, or by pumping electrolyte even when plated on sheets and the same are bent back and forth'at right angles untilthey fracture. 'In this connectlonit will belunderstood that severe flexing occurs in a cooking vessel when the bottom is heated and permitted to cool. Further, up to ordinary cooking temperatures, say 650" F., it has-.been'iound that the coating in respect to'its bond'with the stainless steel is strongly resistant to heat, and will not loosen under such conditions. It is dense and hard, and admirably withstands thorough treatment to which it is subjected when scoured by the housewifeto clean it. r

It is possible to place the article after bein cathodically treated in the cell having the anode and plating bath for performing the final plating operation described above, and omit the operation of forming the flash coating as a preliimnary step, but only with some sacrifice of the excellence of. the results secured and with less assurance of uniformly satisfactory results being obtained. In such case the coating will be much coarser, and less assurance will be had that the coating will adhere. Further, in such case, extreme care must -be taken that on account of the rather high temperature of the electrolyteJzhe plating current is established without delay when the cathodically treated article is immersed in it, and an attempt to avoid this difllculty by lowering the temperature of the electrolyte will result in materially decreasing the rate of deposition. Still further. on account of the high current densities that would be employed in this case it would be necessary strongly to agitate the electrolyte to prevent burning of the copper, and such agitation would result in the possibility of admitting air against the surface, thus reducing the assurance that a good adherence of the coating would be obtained. In these connections it will be understood that preliminary rather slowly layins a strike coating with an electrolyte of low temperature and concentration by use of a plating current of low density not only insures strong adherence of the coating because of these factors but lays a dense smooth coating, which smoothagainst. either or both the anode and cathode. It

ness, it will be understood by those skilled in the art, is imparted to the exposed surface of the final coating when it is deposited at a more rapid rate.

Figs. 1 and 2 illustrate one form of apparatus for use in anodically and cathodically treating the surface of a stainless steel cooking vessel on the bottom and adjacent portions of which is to be electro-deposited the layer of copper or other good heat conductive material.

Referring to Figs. 1 and 2, the body of electrolyte is contained in a suitable receptacle 3 as, for example, a lead pot, herein shown as supported by a table top 5 of wood, the table top having an opening I through which the pot extends for allowing the circumferential flange 9 at the top of the pot to rest upon the top of the table.

-As shown in Figs. 1 and 2, supported in the not 3 is a cup-shaped electrode, preferably of insoluble material such as lead, having the bottom wall H- and side walls l3, the bottom wall being provided with a plurality of spaced perforations i5 distributed thereover, and the side walls being provided with a lower circumferential row of perforations and'an upperrow of perforations i9, the bottomof the perforations l9 being at about the level of the electrolyte. As shown, the electrade is supported by a plurality of straps, made for example of lead, having the vertical portions 2| joined to the upper edge of the electrode and horizontal portions 23 which rest upon the flange 9 of the pot. Conveniently, one or more of these straps is connected to a lead 25- from one terminal of the source of plating electromotive force.

As illustrated, atone side of the pot the table top 5 supports a vertical standard 21 on which is slidably mounted an arm 29 adapted to be secured to the standard in adjusted positions vertically thereof by a set screw indicated at 3|. At one end this am 29 carries the vertical post 33, preferably of insulating material, to which is detachably secured the casing 35 of an electric motor, the rotary metal shaft 31 of the motor projecting vertically downward from the motor casing. This shaft extends through an elongated stationary metal sleeve 39 in' contacting relation with the walls thereof, the sleeve being carried by a metal arm 4| in electrical communication therewith.- As shown, the arm 4| has a vertical portion 43 which is rigidly joined to the arm 29 in insulated relation thereto and is placed in electrical communication with the other terminal of the source of plating electro-motive force by a lead 45 so that the shaft 31 of the motor serves as part of the conductor leading to the cooking vessel V being treated.

As shown (Figs. 2 and 3) ,for joining the vertical portion 43 of the arm 4| to the arm 29, the portion 43 is provided at opposite sides thereof at its upper end with a pair of projections 41 embracing the arm 29. A pair of bolts 49, extending through aligned openings in the projections vertical portion 43 of the arm 4| in assembled relation, the two being insulated from each other and from the bolts by suitable insulation 5| and 53. These bolts are employed also to secure the bases'o'i of the terminal lugs 51 on the end of the lead 45 in electrical communication with the vertical portion 43 of the arm 4|, as will be clear from Fig. 3.

As illustrated, detachably joined to the end of the .metal shaft 31 oi the motor, by means of the metal sleeve 59 and set screws ,BI, is a second aseam'e metal shaft as. This latter shaft-carries at its lower end, in electrical communication therewith.

a chuck for supporting the cooking vessel V. As

shown, the chuck, which preferably is formed of resilient sheet copper, has a bottom 65, to which the shaft 83 is joined, and has side walls formed with V-shaped splits 61 to form a circumferential give a linear speed at the outer periphery of the vessel corresponding to 150 to 300 R. P. M, for a ever, are not precluded.

- The bottomoi the vessel, which in practice vessel 7 inches in diameter. Other speeds, howy be spacedirom the bottom of the cup-shaped electrode a distance of from about 3Q to =54, inches, when rotated, forms with that electrode a centriiugal pump which draws the electrolyte through the perforations l5 atithe center; portions of the cup-shaped. electrode,.:and.- forces it out of the perforations II and out .offtheperforations .l 5 adjacent the periphery of theelectroda-thus cirm ing the the-bottom of the vesse1..;.A certainsportion-ot-the electrolyte. flows upward :l'D' discharge 1 through the perforations B, which latter serve as an'overflow to maintain'approx'imatelyconstant the level oi the electrolyte. ingthe annular space between the vertical walls of the vessel and thef'cup-shaped "electrode. Bythls, for a purpose hereinafter described, portions.of:.-the' sidewalls of the vessel adjacent itsbottom treated; if?

The circuit arrangement used-4n 1 connection h t e p a u l t d msv e mov d for treating the vessel-asbotha cathode and an anode, is schematically illustratedin ig. 6. Reterring. to Fig. 6,. the leads I'll from a'source of plating electromotive force are connected to the center terminals of. a double throw two-pole switch schematically indicated at 13. The upper terminals of this switch are-connected by leads 15 and 11 to the cup-shaped electrode II, l3 and the vessel V respectively. The lower right hand terminal of the switch is connected by a leadlfl to the lead 15, and the lower left hand terminal to the lead 11 through a variable ohmic resistance 8!. By'this arrangement, when the'switch 13 is thrown to connect the leads II to the upper terminals of the switch, a high plating'currentwill 1 be throughthe bath, under whichconditions the vessel Via the anode." When-"the switch. is thrown to connect the leads II to the lower terminals otthe switch tomake the vessel V the cathode the resistance." isthrown 'into circuit as cut down the plating current below-that which it was when the vessel was the anode.

The depth the cooking vessel v is immersed in 'theelectrolytecanbereadilyadjustedbymoving the arm 28 upjand down the standard 21. 'Preierably a stop collar 83,-which may be secured to thestandard 21 in'adjusted positions by use of a set screw 85, is provided, so that by causing the arm 28 to test against the collar when the arm is in its lower position all vessels V of similar size will be iminer'sedin the the same depth At thecompletlon or the operation the] set screw 3! may be loosened and the arm 28 40 and {mm plating ofi of its surface.

thus permitting the vessel to be readily slipped out of engagement with the clutch on the end of the shaft 63.

Another form of apparatus for use in the pre- 5 liminary treatment of the stainless steel vessel is shown in Fig. 8. This apparatus is exactly like that illustrated in Figs. 1, 2 and 3, except that a flat anode i3 9 having the perforations i5 is employed instead of a cup-shaped anode, the

anode being supported by straps i4! similar to the straps 2i hereinbeiore mentioned. Except that in some instances a slightly greater time is required for the treatment when employing the flat electrode, equally eificacious results will be secured with it as compared to those obtained with the cup-shaped electrode, with the advantake that by making .the flat electrode of large diameter it is adaptable for use with a wider range of diameters of vessels than is the cupshaped electrode.

One form of apparatus for electro-depositing the copper is illustrated by Figs. 4 and 5. This apparatus is similar to that heretofore described in respect to the support for the motor and ves- 25,sel V, and the description of that part of the apparatus need not therefore be repeated.

As shown (Figs. 4 and 5), this last mentioned apparatus comprises a tank 81 formed, for example', of iron lined with insulating material 89 3o suchas rubber. Along one edge of the tank, in

insulated relation thereto, is shown a. bus-bar 9! serving as one terminal of the sourc of plating electromotive force, the other terminal of which is constituted by the lead 45 in electrical communication with the vessel V.

Connected to the bus-bar, in electrical oom- I munication therewith, is an anode support, preferably in the form of a copper casting having a coating 93 of lead to protect it from corrosion As shown, this support comprises a horizontal portion 95 which rests upon and is bolted by means of bolts 91 to the bus-bar 9| in electrical communication therewith. Connected to the horizontal portion is a vertical portion 89 which projects downward into the electrolyte tank and carries a horizontal portion QM to the outer end of which is secured a soluble anode N3 of copper or other metal to be plated on the vessel V. As shown, a disk I05,

of relatively strong metal such as copper, has

soldered thereto a disk- I B! of lead which is burned to the lead lining 93 of the anode support. The soluble anode Hi3- on its lower side is provided with a recess I09 which receives the disk I135 to which it is detachably secured in electrical communication therewith by screws Ill.

As illustrated, the anode I03 is provided with a plurality of spaced perforations H3 through 69 which electrolyte is drawn into the space between the anode and vessel V when the latter is rotated.

The anode inland its supporting disks I05 and [01 as shown in Figs. 4 and 5 are provided with aligned central perforations H4 into which ex- 5 tends the end of a vertical pipe H5 formed of 70 or othermaterial inert with respect to the electrolyte, the amount of air admitted to the box being controlled, and when desired the air being cut ofi, by a valve not shown. The box, as shown,

H is supported by a bracket I2l of lead or other raised to move the vessel out of the electrolyte, materialinert with respect to the electrolyte carrled by the tank preferably in insulated relation thereto. At the top of the pipe H is a small I hole I25, say one about 1*; of an inch in diam- I eter, which discharges the air in an upward direction toward the vessel V. This air causes agi tation of the electrolyte and eliminates the possibility of the existence of quiescent spots in the electrolyte adjacent the center of the bottom of the rotating vessel, which spots, if they existed, might cause burning" of the copper being deposited. Further agitation of the electrolyte is caused by the same being drawn through the perforations H3 and Ill of the anode when the vessel is rotated, and being discharged outward from the space between the anode and the vessel at the periphery of the anode. Still further agitation of the electrolyte is caused by providing the top of the box In with line holes I21, say about or an inch in diameter, through which air is discharged.

It will further be unerstood that the temperature of the electrolyte may be controlled by varying the amount 0! air admitted. It will also be understood that by moving the electrolyte and vessel relative to each other a scouring effect is 3 produced which improves'the Physical properties of copper by making it or fln'e grain. In laying the preliminary fatrike coating of copper in the above described method it will be understood that the air supply is interrupted to prevent'oxidization of the heatedstainless steel surface and thus cause the copper to adhere as hereinbefore explained. Y

It will be observed ,from Fig, 1 that the extremelowermost portions of the-side walls I29, and curved corner portions I which Join the side walls to thejbottom 133 of the cooking vessel V, are treated by the preliminary operation to permittheir being electro-plated with copper. As will be clear from Fig. 4, the corner as may be subjected to deposition, until the coat- 8 merges at I31 with the stainless steel surface preferably. at about where the corner portions merge into the side walls, as is illustrated in Fig. 7, or slightly above or below it, the rate of diminution of thickness for different increment of length .on the profile oi the vessel being ro hly the rate of decrease in current density for those increments as influenced by the rate of increase in the distance oi. those increments from the anode. As shown, however, Fig. 7 is moreor less approximate, and in practice the edge of the coating may be positioned somewhat diflerently from there shown, as desired and depending upon the depth of immersion of .the article and its speed of rotation during the plating operations. The coating described provides the'vessel with -a copper coating. on its lower exterior surface portions, the edges of which coating are free from projecting corners,

and thus not only improves the appearance of the article but eliminates any shoulders or cracks-at which peeling of! oi the copper might start by mechanical action, or at which grease and dirt might accumulate or enter to start peeling by corrosive action or the copper. Any slight irregularities which may exist at the edges of the copper layer as a result of the plating op- Iii ' ing a symmetrical relation with each other, and

that as a consequence the coating, in respect to thickness, and at its edges, is laid substantially symmetrically with respect to the vessel.

Conveniently the article is immersed in the sulphuric acid electrolyte during the preliminary treatment a slightly greater distance than in the copper bearing electrolytes so as to insure that no untreated surfaces willbe subjected to deposition. In depositing the copper, the electrolyte tends slightly to creep up the walls of the rotating vessel, say about of an inch above the normal electrolyte level, in the form of a rather attenuated film of thickness as it extend above that level, which film also aids in causing the copper deposit to merge into the surface of the stainless steel because the rate of deposition in this film is very small.-

If desired, the copper deposit may be coated with a. thin-electro-deposit of nickel, chromium or other tarnish and corrosion resistant metal to protect the copper against corrosion and pitting. This final coating may be applied in the usual manner employed in the art.

Another form of apparatus for plating the copper is shown in Figs. .9 to 13. Inthis-latter form of apparatus the anode takes the form of a flat. copper disk- I43 opposed to the bottom sur face of the vessel V in coaxial relation therewith. As illustrated, the anode isformed with a center opening I45 which receives a boss I4! projecting upwardly from the upper side or the terminal portion I49 of a support, this terminal portion having a flat upper surface in which the bottom side of the anode rests.

As shown, the anode I43 is secured to the support by means of the nozzle illustrated in Figs..

12 and 13. This nozzle, which is formed ofhard rubber or other suitable insulating material, 'as shown comprises a flat head I 5| and an exteriorly screw-threaded shank I53, the latter being screwed into a screw-threaded perforation I (Fig. 9) which extends through the boss I" and terminal portion I49 of the support, a suitable washer or Washers I51 of metal such as lead being interposed between the head I6! and the upper surface of the anode. By reason of this construction no plating oil of the anode beneath the head I5I can occur, and that portion of the anode therefore remains of the same thickness as the plating operations continue and the anode therefore will not become loose but will always remain firmly clamped to and in electrical contact with the upper surface of the terminal portion I49 of the support. Also the head Iil being of insulatin material causes the plating current to follow a longer path from the anode to the axial portions of the cathode surface than aseaavs the head. The opening IBI also communicates with a plurality of small diameter openings I55 opening on the upper side of the head. As a result of this construction'electrolyte supplied to the nozzle will be discharged radially from the passages I68 through the space between the anode and bottom surface of the cooking vessel in substantially all directions, and from the openings I65 upwardly against said surface adjacent its axial portion.

In-this modification, for supplying the nozzle with electrolyte, screw-threaded into the lower end of the opening I 55 of the terminal portion 90f the'support is an elbow I61 (Fig. 9) to which is secured the end of a rubber hose I69 supplied with electrolyte from a manifold III at the exterior of the tank 89, this manifold having an outlet nipple I13 to which the opposite end of the hose is secured. Convenientlythe hose is provided with a. pinch cock I15, or other suitable valve is provided for regulating the flow of electrolyte through the hose so that theamount thereof which discharges from the nozzle may be readily controlled. As shown in Fig. 11, electrolyte is drawn from one'en'd of the tank 89 through a pipe I" by means of a suitably driven pump I19. This pump, by way of the pipe connection I80, forces the electrolyte through a suitable filter BI, and

from the latter into the communicating manifold III, the manifold extending lengthwise of the tank and being provided with an outlet nipple I13 for each of the units for plating the vessels V. In practice the pinch cocks may be set to discharge in.,the order of-five gallons of electronozzle cause agitation. of the electrolyte to prevent, in conjunction with the rotation of the vessel, burning" of the copper when the high current density is employed. It will be understood, however, that ordinarily it will be unnecessary to supply electrolyte through the nozzlewhen the preliminary strike coating is being deposited on account of the low current density employed for that operation.

As illustrated in Figs. 9, and 11, there is interposed between the anode I83 and the oathode constituted by the vessel V a shield indicated in its entirety at I33. This shield is of annular shape having a. central opening I85 coaxial with the axis of rotation of the vessel. The shield conveniently may be formed of a flat steel plate l8'l'covered with a layer I89 of rubber or other compound inert with respect to the electrolyte. The shield as shown is supported by a ring I9I formed with a plurality of integrally projecting lugs I93 on which 'the shield removably rests,

. the outer periphery of the shield preferably the collar and hence the shield may be adjusted into difierent vertical positions. Preferably the rod, ringand lugs are coated with a layer 203 of rubberor other compound inert with respect to the electrolyte.

By use of the shield, which may also be employed in situations where air is admitted through the anode into the space between-the latter and the bottom surface of the vessel, as in the apparatus illustrated in Fig. 4, the path of travel of the plating current from the anode to the cathode constituted by the vessel progressively increases from points opposite the inner peripheral edge of the annular shield to the edges of the surface being plated. Hence, as the ohmic resistance lncreaseswith the length of path of travel of the current, the value of the current and consequent rate of deposition progressively diminish from points opposite the inner peripheral edge of the shield to the edges of the surfaces being plated as compared to what they would be were the shield omitted. It has been found that'when the'anode is not of materially smaller diameter than the surface being plated the deposit in absence of the shield tends to be heaviest at the edge or corner of the cathode. cathode and anode are as shown in Fig. 9, in absence of the shield the deposit at the rounded corners of the bottom of the vessel would'be' of greater thiclmess than at adjacent portions of the bottom. The shield by din'iinishing the-rate of plating at the comers eliminates this fe'fie'ct' and permits various sizediameter vesslsto be plated with the same large diameter catliode. by substituting different shields'and to'a'lesser the corner, and therefore by properly'positioning the shield the thickness of the deposit at the comer may be regulated.- The shield also a causes the deposit atthe rounded c'orner to be of decreasing thickness as the edge of the-depositv is approached, and by its use the deposit at the edge thereof can be made approximately a feather edge merging into the side wallof the vessel. To secure this effect without the presence of the shield the anode must be of proper smaller diameter than the vessel.

It has also been found that the head I5I which holds the anode in place acts todiminish the plating current and consequent rate of deposition at the axial portion of the bottom of the vessel. If the cathode extended over the space occupied by the head it has been found-that the deposit would tend to be somewhat thicker-than at the intermediate portions of the radii of the bottom surface of the vessel. The head there: fore acts to increase the length of path of the plating current from the anode to points opposite the head, and in this respect acts like shield. i

It will be understood that within the scope of the appended claims wide deviations may be made from the forms of the invention herein described without departing from the spirit of the invention.

We claim: 1

1. The method of coating the bottom. and adjacent side wall surfaces of a stainless steel cooking vessel with a strongly adhering layer of cop-v I For example, if'the diameters of the acid and while axially rotating the vessel making it a cathode; removing the vessel from said acid at the completion of the cathodic treatment and substantially immediately immersing said bottom 1 portions in an aqueous sulphuric, acid copper bearing electrolyte and initiating electro-deposl tion of copper thereon by making the vessel a cathode and while axially rotating said vessel electro-depositing on the cathodically treated surfaces a strike coating of copper with a plating current not exceeding 100 amperes per square foot of cathode surface; and then transferring said vessel to and immersing said bottom portions in a high copper content aqueous sulphuric acid electrolyte and while axially rotating said mersing the bottom portions only of the vessel in anon-metal bearing dilute aqueous sulphuric acid and while axially rotating the vessel making it a cathode; removing the vessel from said acid at the completion of the cathodic treatment and substantially immediately immersing said bottom portions in an aqueous copper bearingv electrolyte and initiating electro-deposition of copperthereon by making the vessel a cathode, and while rapidly axially rotating said vessel electro-depositing on the cathodically treated surfaces a strike coating of copper with a plating current not exceeding 100 amperes per square foot of cathode surface; and while rapidly axially rotating the vessel. with said bottom portions immersed in a high copper content aqueous sulphuric acid electrolyte electro-depositing on said strike coating a relatively thick layer of copper by use of a plating current of greater density than the first mentioned plating current.

3. The method of coating the bottom and adjacent side wall surfaces of a stainless steel cooking vessel with a strongly adhering layer of. copper which comprises preliminarily treating said surfaces to roughen them, subjecting the roughened surfaces to electrolytically released hydrogen without depositing metal on them by immersing the bottom portions only of the vessel in a non-metal bearing dilute aqueous sulphuric acid and while axially rotating the vessel making it a cathode; removing the vessel from said acid at the completion of the cathodic treatment and substantially immediately immersing said bottom portions in an aqueous copper bearing electrolyte to a lesser depth than they were immersed to treat them cathodically in said acid and initiating electro-deposition of copper thereon by making the vessel a cathode, and while rapidly axially rotating said vessel electro-depositing on the cathodically treated surfaces a strike coating of copper with a plating current not exceeding 100 amperes per square foot of cathodesurface; and while rapidly axially rotating the vessel with said bottom portions immersed in a high copper content aqueous sulphuric acid electrolyte electr'o-depositing on said strike coating a relatlvely thick layer of copper by use of a plating current of greater density than the first mentioned plating current, in which latter electrolyte said strike coating is immersed to no greater metal on them by maldng them a cathode in a non-metal bearing aqueous sulphuric acid electrolyte, substantially immediately upon completion of such cathodic treatment subjecting said surface portions to electro-deposition of the copv per layer, the electro-deposition of said layer comprising making the vessel a cathode with the axis of said surface portions positioned vertically and with said lower surface portions partially immersed in an aqueous sulphuric acid copper I bearing electrolyte in spaced relation to an anode from which the current travels along longer paths to the edge portions of said surface portions than to intermediate portions thereof, thelengthsof said paths at said edgeportions. progressively increasing as the outer. edges thereof are ap -proached,- and relatively rapidly rotating said vessel about said axis while depositing-thereon a copper coating and at suchspeed 8 8170 draw an attenuated fllm .ofelectrolyte up the edge portions of the vessel above the normal electrolyte" level, whereby said coating is symmetrically deposited with relation to said axis and at said edge portions is of gradually: decreasing thickness as the edges of said coating are'approachedand'said' of a stainless steel cooking vessel with a strongly Y adhering layer of .copper which comprises preliminarily roughening said-surface, making the roughened surface a cathode in a non-metal hearing aqueous sulphuric acid'electrolyte to subject it to electrolytically released hydrogen without depositing metal thereon, and removing it from said acid electrolyte upon the completion of the cathodic treatment and substantially immediately immersing it in an aqueous copper bearing electrolyte and initiating electro-de'position of copper thereon. I

6. Themethod of coating the bottom surface of a stainless steel cooking vessel with a strongly adhering layerof copper which comprises etching said surface by making-it an anode in a. non-v metal bearing aqueous'sulphurlc acid electrolyte, afterward making the'etched surface a cathode in a non-metal bearing'aqueous sulphuric acid electrolyte to subject it to electrolytically released,

etching it in the same non-metal bearing aqueous sulphuric acid electrolyte as that in which it is made a cathode for subjecting it to hydrogen.

8. The method of coating the bottom surface of a stainless steel cooking vessel with a strongly adhering layer of copper which comprises etching rinsing it with water and immersing it in an aqueous copper bearing sulphuric acid electrolyte, and when so immersed substantially immediately making it a cathode to initiate electro-deposltion of copper thereon.

9. The method of coating 2. stainless steel sur-.

'face of a cooking vessel wltih a strongly adherlng layer of copper which comprises roughening said surface, making the roughened surface a cathode in a non-metal bearing aqueous sulphuric acid electrolyte to subject it to electrolytically released hydrogen without depositing metal thereon, removing the vessel from said acid electrolyte upon the completion of the cathodic treatment and substantially immediately immersing it in an aqueous sulphuric acid copper sulphate electrolyte having, by weight, 10 to 40% sulphuric acid and to 20% copper sulphate with the amount of sulphuric acid greater thanthe amount of copper sulphate and initiating electrodeposition of copper-thereon by use of a plating current not exceeding 100 ampercs per square foot of cathode surface; and, after deposition, of a strike coating of copper thereon, electro-depositing a relatively thick layer of copper on said strike coating by use of an aqueous sulphuric acid copper sulphate electrolyte having, by weight, 5 to 15% sulphuric'acid and 15 to 25% copper sulphate but with the amount of sulphuric acid less than the amount of copper sulphate and a plating current of greater density than the first mentioned plating current but not exceeding 500 amperes per square foot of cathode surface.

10. The method of coating a stainless steel surface of a cooking vessel with a strongly adhering layer of copper which comprises roughening said surface, making the roughened surface a cathode in a non-metal bearing aqueous sulphuric acid electrolyte to subject it to electrolytically released hydrogen without depositing metal thereon, removing the vessel from said acid electrolyte upon the completion of the cathodic treatment and substantially immediately immersing it in an aqueous sulphuric acid copper .sulphate electrolyte not materially above room temperature and having, by weight, to 49% sulphuric acid and 5 to 20% copper sulphate with the amount of sulphuric acid greater than the amount of copper sulphate and initiating electrodeposition of copper thereon by use of 'a plating current not exceeding 100 amperes per square foot of cathode surface; and, after deposition of a strike coating of copper thereon,,electrodepositing a relatively thick layer of copper on said strike coating by use of an aqueous sulphuric acid copper sulphate electrolyte having, by

weight, 5 to sulphuric acid and 15 to 25% copper sulphate but with the amount of sulphuric acid less than the amount of copper sulphate and a plating current of greater density than the first mentioned plating current but not exceeding 500 amperes per square toot of cathode surface.

11. The method of coating a stainless steel surface of a cooking vessel with a strongly adhering layer of. copper which comprises etching said surface by making it an anode in an aqueous sulphuric acid electrolyte, making the etched surface a cathode in a non-metal bearing aqueous sulphuric acid electrolyte to subject it to electroiyticauy released hydrogen without depositing metal thereon, removing the vessel from the last mentioned acid electrolyte upon the completion or the cathodic treatment and substantially immediately immersing it in an aqueous sulphuric acid copper sulphate electrolyte not materially above room -temperattn'e and having, by weight, 10 to 40% sulphuric acid and 5 to 20% copper sulphate with the amount of sulphuric acid greater than the amount of copper sulphate and initiating electro-depositlon of copper thereon by use of a plating current not exceeding 100 amperes per square foot of cathode surface; and, after deposition of a strike coating of copper thereon, electro-depositing a relatively thick layer 01 copper on said strike coating by use of a second aqueous sulphuric acid copper sulphate electrolyte and a surface of a cooking vessel for receiving a relatlvely thick, strongly adhering layer of electrodeposited copper which comprises roughening said surface, making the roughened surface a cathode in a non-metal bearing aqueous sulphuric acid electrolyte to subject it to electrolytically released hydrogen without depositing metalthereon, and removing the vessel from said electrolyte upon the completion'of the cathodic treatment and substantially immediately immersing it in an aqueous copper bearing electrolyte and initiating electro-deposition of copper thereon by use Of a plating current not exceeding amperes per square foot of cathode surface.

13. The method of preparing a stainless steel surface of a cooking vessel for receiving a relatively thick, strongly adhering layer of electrodeposited copper which comprises roughening said surface, making the roughened surface a cathode in a non-metal bearing aqueous sulphuric acid electrolyte to subject it to'electrolytically released hydrogen without depositing metal thereon, and removingthe vessel from said electrolyte upon the completion of the cathodic treatment and substantially immediately immersing it in an aqueous sulphuricacid copper sulphate electrolyte-having, by weight, 5 to 15% sulphuri'c acid and 15 to 25% copper sulphate with the amount of sulphuric acid greater than the amount of copper sulphate and initiating electrodeposition of copper thereon by use of a plating current not exceeding 100 amperes per square foot of cathode surface. a

14. The method of coating a stainless steel surface of a cooking vessel with a strongly adhering layer of copper which comprises preparing the surface for receiving such coating by roughening it and making the roughened surface a cathode in a non-metal bearing aqueous sulphuric acid bath to treat it with electrolytically released hydrogen without depositing metal on it: and forming the copper layer by first electro-depositing a strike coating of copper on the roughened, ca-

thodically treated surface, and then depositing the a n-Wm...

ing by use of a plating current not exceeding 100 amperes per square foot of cathode surface: the forming or the remainder oi the copper layer comprising electrmdepositing a. relatively thick layer of copper on the strike coating by use of an aqueous sulphuric acid copper sulphate electrolyte having, by weight, 5 to 15% sulphuric acid and 15 to 25% copper sulphate. with the amount of sulphuric acid less than the animmt of copper Sm hate nu 'e plating current or greater density than the first mentioned plating current but not exceeding 500 amperes per square foot of cathode surface.

15. The method according to claim 14 in which the vessel is axially rotated during the plating of both the strike coating and the thick layer, and at such speed during at least the plating of said layer as to draw an attenuated film of electrolyte 10 up the adjacent side walls Of the vessel above the normal level of the electrolyte.

' JAMES M. KENNEDY.

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