US2451341A - Electroplating - Google Patents

Description

Oct. 12, 1948. G. w. JERNs'rEDT 2,451,341

ELECTROPLATING Filed Aug. 10, 1945 32 0 .Bun-32 Serate/1 34 Pore 36 34' 3 36 Direcl Current ,D/afyy lterna'ny 'ul'em P/af'ny Fiyi F290.

WITNEssEs: l v l INVENTOR @mi MWL 637%: w. emsfedf. Wy@ I BY l Patented Oct. l2, 1948 vuNiTEo sTATEs PATENT or-rlcE 2,451,341 v a applicati Anm 1o, 1945. serai No. alcuni This invention relates to electroplating and,

the

possible with as high equality as is reasonably 1o claims., A'lettini-44) In' electroplating a member from any givenv solution 4of electrolyte, the limitation on the cur- -rentdensitylfwhich may be employed to deposit metal occurs when the lelectrolyte immediately adjacent the base member becomes depleted of suincient metal ions to plate out inv accordance v with theelectric'al current applied. Thereafter attainable.- Quality is so much-more .important a factorl in electroplating thatspeed is. almostA invariably sacriilced ii required to' produce a good grade of'eiectrodeposit. In actual pra.ctice,itggisI f well known to those skilled inthe electroplating art that it requires the highest degree of skill,

and unremitting care and attention in order .to produce consistently good high-grade electrodeposits. ,l j

Commercially' acceptable electroplating requires a homogeneous uniformly thick f andA smooth plate. In many cases-the plate must be as bright as possible to avoid excessive subsequent buillng and polishing treatment. Industry often accepts relatively non-uniform and unattractively rough, unhomogeneous plating because i-t either is too costly to secure better work,4

or, as is often the case, better plating Vcannot be produced. Mechanical bumng is then relied upon tobring the plated metalto a better condition. Usually electroplating must be conducted at a'certain amount o! the water in the electrolyte vbeginsgto decompose and hydrogen is formed on :the surface-oi the bas'emexnber.` This reduces the VVplaing c fllciency. Hydrogen tends to blanket theV suria'ceof the base member and .thereby greatly diminishes the plating. 'I'his phenomenon lis known as polarization. -.Plating is ordinarily relatively low current densities in order vto besureV to secure a satisfactory metal deposit'.` VLikewise'.

the electrodeposition of metal requires a consid? erable amount of skill as developed byexperience in order to satisfactorily electroplate irregularly shaped objects as by proper disposition oifano'des,` A

selecting proper current densities and electrolyte quality. As more and more irregular shapes are subjected to electroplating, many problems begin to present themselves, and vit becomes progressively more difficult to secure a uniform and homogeneous electrodeposit. A square sheet is much harder to electroplate successfully than a cylinder while a member having projections, recesses and cavities requires specialized conditions to secure a good plating job.

Particularly great dimculties are encountered in electroplating on base members thick deposits of metal of the order of 10 mils (0.010 inch),` thickness and greater. The electrodeposits tend to become progressively more nodular, rough, non-uniform in thickness, and often occur as course crystalline or dendritic coatings. It has been recognized that electroplating tends initi- ,35 composition. For instance, a cylindrical member such as a tube or a wire can be 'electroplated atv relatively high currentdenslties with the elecv tropiated metal usually being of a fairly high' conducted at such a rate as to prevent polarization from occurring,'atleast to a substantial extent. Some polarization appears to occur even inthe vmostcarei'ully conducted plating operations, but ordinarily may be kept within reasonable limits. --Polarization causes ineiliciency and non-uniformity in plating.

The present invention is` directed to the application of a predetermined alternating or reversed current cycle to the base .member being plated. the current being so applied that at predetermined intervals a given vthickness of metal is electrodeposited on-the base member and then reversed sol that the given thickness of the electrodeposlt .is partially-.depleted whereby unsound andvinieriormetalis removed. In this manner, '1v 'the base'member is plated so that it acquires a funiiorm deposit composed of a great number of '.vel-'ythiir hornogen'eously bonded increments of metal..l Numerousfadvantages have been toundrtofollow theelectroplating of members by meansfofithe'currentcycle ol! this invention.

inwhich at intervalsV plating is vinterrupted by ally to deposit sound metal, b ut that the deposit becomes disproportionately poorer in structure and smoothness as more and more metal is electrodeposited continuously over the initial deposit.

brieilyyreversing-,the current for a small fraction of'asecond for the purpose of depolarization only of the plated surfaces and then resuming plating. This procedure has'been tried but it does not produce any improvement in the plated metal. By contrast, as disclosed herelnby applying a suiclent reverse current for a suiiicient period oi time to deplate unsound and inferior metal, highly. unexpected and desirable results in plating are secured.

The object of this invention is to provide for electrodepositing on a base member a sound and homogeneous electroplat-e.

A further object of the invention is to electrodeposit on a base member a metal plate by a periodic alternating current process to build up a predetermined electrodeposit from which all .un-sound and inferior metal has been removed as 3 rent applied to -a member during the process of plating metal thereon in order to remove unsound or inferior metal, thereby to improve the quality of the plated metal and to impart greater speed and eiiiciency to the plating operation.

Other dbiects of the invention will, in part. be obvious and will. in part. appear hereinafter.

For a better understanding of the nature and objects of the invention. reference should be had to the following detailed description and drawing. in which:

Figure 1 is a view in elevation in section through an electroplating system:

Fig. 2 is a graph plotting time against current employed in .the plating cycle;

Fig. 3 is a fragmentary greatly enlarged crosssection through a. base member and the electroplate deposited thereon by conventional methods;

Fig. 4 is a greatly enlarged fragmentary crosssection of 'a base member and an electrodeposit produced thereon according to the present invention:

'Fig. 5 is a perspective view of an electromagnet; and

Fig. 6 is a perspective through a rectangular frame.

According to my invention, electroplating may be accomplished not only at greater speeds than are ordinarily possible, but more important still, the quality of the electrodeposits produced may be so controlled that they are superior to any attained heretofore in the plating art.

A Briey. it has been discovered that the electroplating process and the eleotrodeposits produced may be greatly improved by applying to the base member being electropl'ated an alternating current in which the base member is alternately cathodic for a period of time from about2to 40 seconds and is anod-ic for a period of time from about one-half to 10 seconds, respectively. 'I'he anodic phase portion of the current cycle should be of suilicient current density and applied for a suflicient length of time to deplate unsound and inferior metal plated during the preceding cathodic phase portion of the cycle. In particular, the anodic or deplating portion of the cycle should apply at least 10% of the coulombs of current applied to the base member during the c'athodic portion of the cycle. For plating nearly all metals, the best results have been obtained where the anodic current phase applies to the base member from to 40% of the coulombs of current applied during the cathodic phase portion of the cycle.

The cathodic portion of the current-plating cycle may be of a current density many times greater than the current dens-ity that may be applied to a base member using conventional direct current. Since lthe plating portion of the cycle only operates from about 2 to 40 seconds. polarization is negligible and it does not build up to as Ihigh a degree as would occur if the same current density were employed using direct current. When the current is reversed and the base member 'is rendered anodic, it frequently is desirable to impart a current density somewhat larger than the plating or cathodic current phase of the cycle. In many cases, excellent results were attained where the anodic current density has been 50% to 100% greater than the oathodic current density.

Many desirable and unexpected results have lbeen obtained by electrodepositing on a base member a` metal from an electrolyte using the alternating-current cycle which is the feature of same electrolyte in from to 20% of the time required using only'direct current. However, the outstanding advantage is the remarkable quality of the electrodeposited metal produced by lthe Process of this invention. The surfaces of the electrodepos-its are much brighter. In many cases, the electrodeposits produced by the practice of the present invention are so highly smooth and polished that nothing comparable has ever been previously secured in any electroplating process. In nearly all cases, with the exception of chromium, as will be explained hereinafter, the smoothness, hardness. uniformity, color, and corrosion-resistance of the metal electrodeposited by the process of 'this invention are deiin-itely superior to the same metals deposited from the same electrolyte using direct current. Other advantages of the invention will be disclosed hereinafter as the process is described in detail.

Referring to Fig. 1 of the drawing, there is shown an electroplating tank i0 provided lwith a chemically resistant liner I2 in which is located the electrolyte I4 of a suitable composition to electroplate the desired metal. The conducting bars i6 and I0 are each provided with current from the source 2l of alternating or periodically reversed current meeting the requirements herein set forth. The source of alternating current 20 may be an alternatingcurrent generator designed to generate current acording to the desired cycle set forth. In other cases, the source of alternating current 20 may Y be a direct-current source, such as a battery,

generator, or rectiiler combined with suitable relays, reversing switches andv resistances operated by a timing mechanism to reverse the current at predetermined times in accordance with the requirements of the invention. In other cases, other suitable mechanisms may be de- -vised to produce the desired current cycle. The

conductor bar i6 carries a hanger 22 on which there is supported the base member 24 to be electroplated. The hanger 26 supported by the conductor bar I8 carries a suitable anode electrode 28. Y

By referring to Fig. 2 of the drawing, there is illustrated the alternating-current cycle applied to the member 24 by the current source 20. At the point O-A, the base member 2l becomes cathodic and metal is plated thereon. ,For most purposes, the current density at A will be higher than that ordinarily employed, everything else being equal. using only direct current. However, it should be understood that it is not necessary to employ greater currents than arenormally employed using only direct current. Excellent plating will be secured on the base member even though the current density at A is a value which is less than that normally used.V

The present invention allows a wider latitude ,of current densities than previously possible. '.Ihe only limitation is that the current density at A should not be of such a high value that the electroplated metal is burned or excessive gassing or other undesirable effects occur in the short time that the member is cathodic. The time from A to B may be from about 2 to 40 seconds. The time which is selected will depend on the electrolyte in which the process is being carried out, the shape of the member being plated, and other conditions. The cathodic current from A -any predetermined manner.

-At the point B, the current is suddenly reversed to the value C andthe member 2l is made anodic.

As shown, the anodic current density at C is` greater than the cathodic current density. In most cases, it will be found that a higher anodic current density is required. tov secure the desired results of the invention. However, l in many cases, it has been found that the-anodic current density may be the same as the cathodic current density. The significant criterion ofthe anodic or reverse current at C Ais that it beso correlated to the electrolyte that the plated member b e deplated to the extent-of removing a substantial amount of plated metal. applied for a period of time of from about onehalf to ten seconds based on the corresponding plating or. cathodic current. The product of time and the anodic current should have a value in coulombs equal to at least and prefer'- ably 20% to 40%, of the coulombs applied during the cathodic portion of the cycle. 'I'he cur-w rent from C to D need not be uniform as shown, but may be rippled or pulsating or may vary in y At D, the current is again reversed and the base member is made cathodic and the cycle repeated. In all cases, the cycle will benen-symmetrical. The cycle O-A-B-QC-D-E is repeated until suitable thickness of metal has been plated on the base member. moved from the electrolyte il between the portions C and D of the cycle when the member is anodic since the polish of the plated metal is at an optimum at this point.

As the member 24 is subjected to the current cycle shown in Fig. 2, it will be found that metal is plated from the electrolyte I4 at a high rate of speed between the points A and B for from about 2 to 40, seconds. Experience shows that the metal plated during this time is not of a uniform quality but varies. The metal first The anodic current is The base member is preferably re-` v trodeposit of metal tends to greatly accelerate its growth atr the burr I2 in accordance with well known phenomenon. A nodule 3l. accordingly, is produced over the burr 32. particularly' if the plating is of any appreciable thickness. At the scratch il. the electrodeposlted metal form an exaggerated valley Il which comprises relatively sharp ridges thicker than the main portion of the electrodeposited metal and a lesser thickness of metalis deposited in the valley of the scratch than the main portion -of the electrodeposited metal.v At the pore n. the electrodeposited v metal forms a slightly thicker lip surrounding the'pore with substantially no metal deposited over the relatively non-conducting inclusion. It.

will be apparent that the surface of the plated member Il in Pig. 3 becomes progressively rougher as plating is carried on. With respect to corrosion resistance, the plated metal is unsatisfactory since there are portions much thinner than the average. thickness of the platedmetal.

' jected to plating by the alternating current plated has been found to be of a higher quality and more sound than the subsequent metal, deposited toward the end of the cathodic period, in particular the later plated metal becomes coarser in structure and less dense with an inferior polish and smoothness. Sharp projections, high spots and corners tend to build up plated metal faster than nat areas or recesses. When subjected to the anodic portion of the cycle at point C to D, the unsound and inferior metal is deplated, leaving an electrodeposit of very high quality metal. The deplating portion of the cycle does more than deplate unsound metal. Experience shows that the previously plated metal is preferentially dissolved in such a manner as to remove more metal from the corners, edges and rough projections, such as high spots, nodules, and similar elevated portions from a microscopic standpoint where it was previously plated in excess, than from flat areas and the' general surfaces.

Scratches, pores, and other discontinuities and imperfections of the surface of a base member are likewise unusually affected by plating with the alternating current cycle. Referring to Figs. 3

cycle, there is produced upon the burr I2 a corresponding plated projection with, however, a greater radius and much less difference in height with respect to the main body of the metal adjacent thereto than would occur in ldirect current plating. No nodules are formed. Over the scratch 34, it will be found that the metal is plated in such a manner as to ll in most of the scratch. Therefore, the scratch is rendered less prominent. Greater protection as well as a smoother surface actually results. The inclusion 38 is soon completely plated over by the process of the present invention. It will bev apparent that the surfaces produced by plating according to my invention are smoother than the original base metal surface itself. The uniformity of the plated metal is far superior to any electrodeposit produced heretofore by conventional methods. 0f course, it willbe understood that only minor or microscopic irregularities are smoothed over. The main contours of the base member are faithfully followed and conformed to by the plated metal.

As an explanation of the unexpected results such as are shown in Fig. 4, the following is offered. but Ido not wish to be bound strictly to such explanation. Following the plating of metal upon the base member 24 for about 2 to 40 seconds, during the subsequent anodic portion oi the cycle unsound and inferior metal is removed and put back into solution immediately adjacent the base member. Any elevations, corners or projections are deplated at a greater rate than the main flat areas of the electrodeposit. Thus the burr metal 44 deplates more than the rest of the plate. The metal in the scratch 46 is removed at a lesser rate than the lips of the scratch or the plating elsewhere. portion of the plating cycle is again applied to the base member, the metal concentration adjacent the base member is abnormally high, and thereby plating starts and is maintained for part of the period at approximately 100% eillciency in many electrolytes. The metal concentration within and near the scratch 34 is high enough to plate rapidly on .both sides of the scratch, and the scratch is filled up from its bottom at a greater rate than the main body of metal is being built up. However, the projections such as M do not build up a much greater thickness of metal than does the main body of the plate. There fore, no nodular or treeing eiiects are secured. On being repeated, the anodic portion of the cycle again reduces the projections in preference to the scratches or other microscopic depressions and thereby a progressively more uniform surface is secured. It will be apparent that the anodic portion in combination with the cathodic portion of the current cycle imparts new and unexpected characteristics to the plated metal.

Other benecial effects secured by the anodic portion of the cycle are the replenishing of the metal ions adjacent the base member by deplating inferior and unsound metal. Therefore, the anodic portion of the cycle does not represent wasted energy since plating during the subsequent cathodic portion of the cycle is expedited and is more eflicient due to the replenishment of the metal in the closely adjacent electrolyte.

In practicing the invention, exceptionally good results have been obtained in electrodepositing copper, brass, and silver. Electrodeposits of zinc, tin, cadmium, and gold have been produced superior in manyrespects to those obtained by any conventional plating method. In all these cases, the electrolytes used were those employed in conventional plating practice. No substantial changes in composition are necessary in order to secure the benefits oi' the present invention. The alternating-current cycle of this invention has been found to give good results not only with Conventional plating electrolytes but with electrolytes modified to provide for a better cooperation between the current and the metal being plated. The only exception was encountered in plating chromium; when the reverse or deplating current was applied-the base metal deplated instead of the chromium plate.

As examples of various electrolytes and metals that have been plated with the alternating-current cycle of this invention, the following are typical:

Example I An electrolyte was prepared containing:

Copper '.-ounces per gallon-- 7.35 Free potassium cyanide ..do 1.50 Potassium hydroxide d 2.48 Addition agent; Ml. per gallon-- 8 The complex -shaped -base member 50 shown in Fig. of the drawing was electroplated in a bath as shown in Figure 1. The member 50 is a cobalt ferrous alloy electromagnet having approximately Il; square foot of surface area. The requirements called for electroplating a thickness of approximately 0.018 to 0.020 inch of copper having a total weight between 28 and 33 grams. It will be readily recognized that plating the member 50 would be quite dfllcult if a reasonably smooth.

When the cathodic uniform plate were required. The temperature of the electrolyte was varied from 140 F. to 210 F. The pH was maintained at 12 and higher.A

The electrode 28 was a copper anode. The member 60 was plated in the copper electrolyte according to the following alternating-current cycle:

Time Current Amper" r .Sfeco'nds Square Fm Cathode 15 65 Anode 3 100 available to the trade using direct-current, thel plating of the electromagnets has required from 9 to 11 hours to secure the same weight of copper thereon. Apart from the faster plating by thev process of this invention, the copper plate deposited on the 'member 50 was brighter and smoother than any copper plate heretofore known. It was extremely adherent.

Samples of the copper plate produced by the process' of this invention were removed from the magnet 50, and the density thereof was found to 'be approximately 25% to 50% greater than the density of as good a copper plate as could be produced to an equivalent thickness from a directcurrent bath of about the same composition. The copper metal produced by the practice of this invention was springy and much harder than conventionally plated copper. The latter, when flexed in the finger, broke, readily and had a 4rough crystalline structure, while the copper plate of this invention when ilexed in the hand, did not break but showed considerable elasticity. Upon breaking the copper plate of this invention, the structure was observed to be much ilner than the best direct current plated copper.

Various base members plated with the copper plate using the alternating-current cycle of this invention were far more corrosion-resisting than conventional copper plate. For example, 0.0005 inch of direct-current plated copper on steel plates had less corrosion resistance in a salt spray than did 0.00035 inch thickness of copper plate produced by the process of this invention.

Example II Time Current Amper-es per Seconds Square Foot Cathode 15 90 Anode 5 90 The effective current density was 45 amperes per square foot. In 31/2 hours 30.37 grams of copper of a thickness of 0.012 inch were deposited on the member. The copper plate was very smooth and shiny in appearance. Electrical tests for the resistance of the copper plate indicated that it lwas as conducting as 31 grams (thickness 0.018 inch) of copper applied from the same bath over a period of from 11 to 12 hours using direct current.

9 Example!!! The following Rochelle copper electrolyte Vwas prepared:

Ounces per gallon Copper cyanide 4 Sodium cyanide 5.1 Sodium carbonate 2 Rochelle saim 5 The temperature of the electrolyte 160 F. The following alternating-current cycle was applied to the complex surface member of Fig. 5:

'rims current ma gaat Fad cathode 14 oo Anode 3.5 120 The eifective current density was 48 amperes per square foot. 'I'he electrodeposit produced was polished and smooth. The copper appeared to be as high a quality as that produced with` the straight cyanide electrolyte of Examples I and II.

Example 1V An electrolyte for plating brass was prepared as follows:

v Grams per liter Copper cyanide 30 Zinc cyanide 9.49 Sodium cyanide 56 The temperature of the electrolyte was 100 F. Rectangular steel plates of an area of one-tenth The eilective current density was 45 amperes per square foot. A smooth uniform deposit of zinc was produced by the electroplating cycle of this.. example. The zinc had a surface brightness `equal A-steel mcmbercomprising a rectangular sheet of one-tenth `square foot area was .immersed in the electrolyte and plated with the following current.

'rime current Seconds ASquafmMuFoot (inimm- 15 e 40 .snode z v co The effective current density was 28 amperes per square foot. The plate of cadmium producedwas markedly improved over any direct-current plated cadmium known. The coatings were unusually smooth and had a bright, polished appearance.

In another case, samples of steel were .plated in the cadmium electrolyte under the following square foot flashed with copper were plated in` conditions:

the brass electrolyte using the following dimin- -The eifective current density was amperes per square foot. An unexpected result was that the electrodeposit was a very bright brass. As far as known, it has been desirable to secure a bright brass directly by plating, but this has not hitherto been commercially possible by any known plating process. The tests of the brass plate indicated that it was smoother and more homogeneous than ordinary brass plate as well as being more tenaciously adherent and much more rcorrosion-resistant. The brass was denser than brass secured by direct current plating.

Example V A zinc-plating electrolyte was prepared withv the following constituents:

Ounces per gallon Zinc cyanide-- -8 Sodium cyanide 5Y Sodium hydroxide 11- Rectangular sheets having a surface area of onetenth square foot were plated in the zinc electrolyte under the following conditions: v

Time Current 'squarefoot The cadmium plating secured by following this cycle was of as high a vquality as that produced by following thel current cycle immediately preceding. l Y l Y Example V!! A silver electrolyteewas prepared with the following composition:

. A(iramsper liter Silver cyanide 40 -Potas'sium cyanide 62.5 Free potassium cyanide -1.... 40 Potassium carbonate 1... 50 Potassium hydroxide 10 The bath temperature was 80 C. The following alternating-current cycle was employed:

' 'rms current Ampmr canoa v "no E" ,"f' .inode 4 121 lAvenge. l l Y The effective current density was 8 amperes per square foot. The silver electrodeposited from this electrolyte using the current cycle `indicated was of an extraordinary polished brilliancy. No mechanical' bumngi or polishing. wasA necessary since it was as bright as could be secured by any mechanical treatment. By comparison ordinary direct-current electroplated silver has an inferior, unattractive and dull appearance. The silver plate produced by the present invention was unusually homogeneous, smooth and uniform. Plated silver; using the alternate current of this invention would be 'completely satisfactory for immediate use. Household silver andany other silver plating that would ordinarily be employed in industry or commerce could be successfully plated by the present process and used.v

without any mechanical bulng or other treatment.

Numerous other plating cycles for plating silver were employed with equally good results. For example, with a cathodic current density of amperes per square foot, the time was varied from 10 to 30 seconds. The anode current densities varied from 50 to 150 amperes per square foot maximum for periods of time from 21/2 to 9 seconds. The anodic current densities with silver tended to drop toward the end of the periods. Silver plating may be accomplished using cathode current densities of as high as 100 amperes per square foot.

Example VIII An aqueous solution for plating-gold was prepared with essential ingredients as follows:

Ounces per gallon The effective current density was 3 amperes per square foot. The gold was electroplated upon a rectangular steel .base member. 'The gold was far better both in smoothness and color than any direct-current gold plate known.

The electrolytes of the preceding examples are not exhaustive but are only exemplary of the present invention. 'In 'many cases the electrode 28 employed in each of the solutions Was ofthe same metal as that being deposited. However, in plating gold, the electrode was an inert member. The plating can be accomplished satisfactorily according to this invention regardless ofthe nature of the anodes.Y

Illustrative of a further advantage of the process of this invention, reference should be had to Fig. 6 of the drawing showing a rectangular open ended casing member 52. The member 52 is a common form of casing for enclosing apparatus and instruments. Hitherto in plating members corresponding to or similar to the member 52, it was necessary to employ an anode inside the frame of member 52 as well as anodes about the exterior of the frame. Even then uneven electroplated deposits often occurred. By using the alternating-current cycle of this invention, it has been found possible to electroplate both the inner and outer surfaces of the frame member 52 quite uniformly without using any-internally located anodes or resorting to other time-consuming expedients. The plating of copper on a steel casing corresponding to member 52 resulted in asmooth bright coating over both the interior and exterior surfaces of the member using only The better distribution of plated metal secured bythe alternating-current cycle cf this invention as exemplified by the plating of the members of Figs. 5 and 6 constitutes an important feature of the invention. The plating current densities; practicable even .with the complex surface mem-` bers are far higher than would be possible using direct-current plating.'

The eltrodeposits produced by the invention are superior in both mechanical and chemical properties to plating produced by conventional processes and, therefore, are advantageous for numerous applications requiring the best attainable properties of electroplated metal. Automobile hardware Which is subject to abrasion and exposure to moisture and deleterious gases may be advantageously plated with a more durable and corrosion-resistant plating by the process of the present invention. Household appliances subject to heating, food acids, Iand other corrosive influences will be found to be capable of lasting longer and with better results if produced as herein disclosed.' In many eases, particularly in plating copper, silver, and brass electrodeposits, mechan- `ical buifing or polishing may be entirely eliminated since the plated member will be as bright as can be secured by any mechanical polishing operation. Engraving dies, electrotypes, plastic` molds and similar members of complex' shape may be prepared by electroplating metal base members, graphitic or carbon bodies, wax or resin master patterns dusted with a conducting surface coating of metal powder or graphite in accordance With the present invention to produce a much more durable and wear-resisting plating than can be secured by any known process of plating. The plated metal will be found to be much harder and more corrosion-resistant to conditions encountered in service than ordinary plated metal. The pattern will be followed faithfully without excessive plating on corners and projections. Accordingly, longer wearing dies and printing vplates will be attained. l

All plating operations regardless of the shape= size or use of the member being plated should be benefited by being conducted with alternating or periodic reverse current in accordance with the teachings of the present invention.

The alternating current plating of the present invention may be carried out in anyV type of systeni or apparatus commonly employed for plating. Rubber-covered steel tanks will generally be found to give good results, though wood, glass, or other materials may be employed. The work may be hung on a stationary holder or on a moving conveyor. The size of the apparatus has not introduced any dilculties. Plating with the alternating-current cycle has been carried out as effectively in small glass beakers as well as in large tanks having a capacity of several hundred gallons of electrolyte.

It will be appreciated that alloys as Well as single metals may be electrodeposited bythe present alternating current process. Several successive deposits of metal in any desirable proportions may be plated on a single member.

The electrolyte may be agitated or distributed in accordance with well known practices in plating. It has been found desirable to maintain a clean electrolyte, for example, by filtering or the like, since the electrodeposits have such a highly polished surface that any solid impurities 13 from the electrolyte deposited on the plated work are much more apparent than in ordinary electroplating. The temperature of the electrolyte may be varied to suit the plating requirements. The current cycle works aswell at temperatures of boiling water as at temperatures below room temperature.

It is intended that all'matter contained in the above description or in the accompanying drawing shall be taken as illustrative and not in a limiting sense.

I claim as my invention:

1., The process oi' electropiatlng metal from the group consisting of copper, brass, silver, zinc, tin, cadmium and gold on a base member from an electroplating electrolyte in which the deposited metal is readily soluble on the passage ot electric current when thev base member is the anode, comprising the steps of connecting the base member to be plated into an electroplating circuit including the electrolyte, causing electric current to now in the plating circuit while the base member is in contact with the electrolyte,

the electric current flowing in-the plating cir/cyste@ being periodically reversed so as alternatelyA electroplate metal on and then deplate metal from the base member, the current for plating metal on the base member being caused to flow for a period of time of not over 40 seconds until a layer oi! metal is deposited when the currentis reversed in direction for a period of time oi not over l seconds to deplate metal from the base member to remove a portion of the layer of plated metal, the deplating current being of a magnitude and applied for a sufilcient period of time to deliver at least of the coulombs delivered during the preceding platin-g,period so that a substantial amount of the plated metal is removed, and repeating the cycle of plating and deplating to cooperate in building up on the base member an electrodeposit in small increments to produce a smooth, sound, homogeneous plate.

2. The process of electroplating metal from the group consisting of copper, brass, silver, zinc, tin, cadmium and gold on a base member from an electroplating electrolyte, the plated metal being one that is readily soluble in the electrolyte upon the passage of an electric current when the base member is the anode, comprising the steps of applying the electrolyte to the base member, passing an electric current through the base member and the electrolyte in a direction to make the base member cathodic for a period oi time of not over seconds to electroplate metal on the base member, then reversing the direction of ilow of the electric current to make the base member anodic for a sufilcient period of time to deliver to the base member at least 10 per cent of the coulombs that were delivered during the preceding cathodic time period to deplate metal which would result in an inferior deposit, and continuing to make the base member successively cathodic and anodic until a desired thickness of metal has been electroplated on the base member.

3. The process of electroplating metal from the group consisting of copper, brass, silver, zinc, tin, cadmium and gold on a base member from an electroplating electrolyte in which the electro' plated metal is readily soluble on the passage of an electric current making the base member an anode, comprising the steps of causing electric current to flow through the electrolyte to the base member for not less than 2 seconds and not more than 40 seconds in a direction to make the base member a cathode to plate metal on the base member and then reversing the ow of current for a lesser period of not less than l/, second and not more than 10 seconds, respectively, to make the base member anV anode to partially deplate the metal plated on the base member, the period and density of reverse ilow of current being such as to'apply to the base member from 20% to 40% of the coulombs that were applied while the base member was a cathode. and repeating the steps of causing electric current to ilow in a direction to plate metal and reversing the direction of flow to deplate part of the metal plated until a desired thicknesspr metal has been plated on the base member. i v

4. The process of electroplating metal from the group consisting of copper, brass, silver, zinc, tin, cadmium and gold on a-base member from an electroplating electrolyte, the plated metal being one that is readily soluble in the electrolyte on the passage of a current making the base member anodic, comprising the steps ot applying the electrolyte to the base member, passing an electric currentv of predetermined density through the base member and the electrolyte in a direction to make the base member cathodic for a period of time of from 2 to 40 seconds to electroplate metal on the base member, then making the base member anodic and applying a higher anodic current density than the immediately preceding cathodic current density for aperiod of time suiiicient.

to deliver to the base member at least 10% of the coulombs that were delivered during the preceding cathodic period to deplate metal which would result in an inferior deposit, and continuing to make the base member successively cathodic and anodic until a desired thickness of metal has been deposited on the base member.

5. The process o! electroplating sound metal from the group consisting of copper, brass, silver, zinc, tin, cadmium and gold from an electroplating electrolyte having the metal dissolved vtherein upon a base member immersed therein at an increased rate as compared to continuous direct current plating from the same electroplating electrolyte, the plated metal deposited on the base member being one that is readily soluble in the electrolyte upon the passage of a current making the member anodic, comprising the steps of applying to the base member successive cycles of current veach cycle composed of a cathodic portion and an anodic portion to deliver to the base member for a period of time of from about 2 to 40 seconds a cathodic plating current at a density substantially higher than can be effectively applied as continuous direct current to plate the same metal thereon, and then to deliver to the base member an anodic current of a suiilcient current density and for a suillcient period 'of -time to deliver to the base'member at least 10 per cent of the coulombs delivered during the preceding cathodic portion of the cycle to remove metal plated during the preceding cathodic period which would result in an inferior electroplate, whereby the plated metal is rendered brighter and more homogeneous and has a smoother surface than is obtainable by means of continuous direct current' at said cathodic current density from the same electrolyte.

6. The process ofv electroplatlng metal' from the group consisting of copper, brass, silver, zinc, tin, cadmium and` gold on a base member from an electroplating electrolyte, the deposited lmetal being one that is readily soluble in the electrolyte on the passage of a current making the base member anodic, comprising the steps of applyto apply a given cathodic current `density thereto e Y for a period of. time of -from 2 to 40 seconds to electroplate metal on the base member, then making the base member anodic for a time period whichis about one-quarter the preceding cathodic period to apply an anodic current at a suiilcient current density to deliver to the base member during said anodic period from about 20 to 40 per cent of the coulombs that were delivered during the preceding cathodic period to deplate metal which would result in an inferior deposit, and continuing to make the member successively cathodic and anodic until a desired thickness of metal has been plated on the base member.

7. In the method of electroplating metal from the group consisting of copper, brass, silver, zinc, tin, cadmium and gold on a base member from an electroplating electrolyte in which the plated metal deposited on the base member is readily soluble on the passage of a current when the base member is the anode, the steps comprising passing a plating electric current through the base member while it is in contact with the electrolyte, the plating current being applied for a period of time not less than 2 seconds and not more than 40 seconds to electroplate an increment of the metal, then applying a deplating electric current to the base member to deplate a substantial portion of the preceding increment, the deplating current being of a magnitude and applied for a sufcient period ot time to deliver at least of the coulombs delivered during the preceding plating period to eiect removal of a part of the previously plated increment, and continuing the alternate plating and deplating until a desired thickness of metal has been applied to the base member.

8. In the method of electroplating a metal from the group consisting of copper, brass, silver, zinc, tin, cadmium and gold on a base member from 16 ing the metal to be plated dissolved therein and in which the base member and an anode of the metal to be plated are immersed, the steps com-'- prising applying a plating electric current to the base member for not less than 2 seconds and not more than 40 seconds to electroplate an increment of the metal, then applying a deplating electric current for a period of from 1/2 to 10 seconds to the base member to deplate a substantial portion of the preceding increment, the deplating current being of a magnitude and applied for a suillcient period of time todeliver at Y least 10% of the coulombs delivered during the Cil an aqueous electroplating electrolyte having the metal to be plated dissolved therein and in which the base member is immersed, the steps comprising applying a plating electric current to the base member for not less than 2 seconds and not more than 40 seconds to electroplate an increment of the metal, then applying a deplating electric current for a period of from 1/2 to 10 seconds to the base member 4to deplate a substantial portion of the preceding increment, the deplating current being of a magnitude and applied for a suiiicient period of time to deliver at least 10% of the coulombs delivered during the preceding plating period to effect removal of a part of the previously plated increment, and continuing the alternate plating and deplating until a desired thickness of metal is applied to the base member.

9. In the method of electroplating a metal from the group consisting of copper, brass, silver, zinc, tin, cadmium and gold on a base member from an aqueous cyanide electroplating electrolyte havpreceding plating period to eiect removal of a part of the previously plated increment, and continuing the alternate plating and deplating until a desired thickness of metal is applied to the base member.

10. In the method of electroplating a metal from the group c isting of copper, silver, zinc, cadmium, and golxson a. base member from an aqueous electroplating electrolyte having the metal to be plated -dissolved therein and in which the base member is immersed, the steps comprising applying a plating electric current to the base member for not less than about 3 seconds and not more than about 30 seconds to electroplate an-increment of the metal, then applying a deplating electric current for a period of from about Vg second to about 3 seconds to the base member to deplate a substantial portion of the preceding increment, the deplating current being of a magnitude and applied for a suiiicient period of time to deliver at least 10% of the coulomb. delivered during the vpreceding plating period to effect removal of a part of the previously plated increment, and continuing alternate plating and deplating until a desired thickness of metal is applied to the base member.

- GEORGE W. JERNSTEDT. l

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATS PATENTS OTHER REFERENCES Transactions Electrochemical Society, preprint 81-20, Apr. 20,-1942, pages 312-315. Electroplating, Freeman and Hoppe, 1930, page -102. l y

Principles of Electroplating and Electroforming, Blum and Hogaboom, 2d edition, 1930, pages 89, 90, 108, 109, 215-217.

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