US2558090A

US2558090A - Periodic reverse current electroplating apparatus

Info

Publication number: US2558090A
Application number: US791027A
Authority: US
Inventors: George W Jernstedt
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1947-12-11
Filing date: 1947-12-11
Publication date: 1951-06-26
Anticipated expiration: 1968-06-26
Also published as: FR976409A

Description

June 26, 1951 G. w. JERNSTEDT 0 9 0 8 5 5 S 2 U T W P P A G .m T A L P m m L E T W C E s R E V E R C I D O I R E P 2 Sheets-Sheet 1 Filed Dec. ll, 1947 INVENTOR George W'Jernsed.

June 26, 1951 G. w. JERNsTDT 2558,090

PERIODIC REVERSE CURRENT ELECTROPLATING APPARATUS Filed Dec. ll, 1947 w 2 Sheets-Sheet 2 WITNESSES:

` lNvENToR W i George' W Jernsedf.

Patentted June 26, 1951 UNITED S'TATES PATENT. OFFICE 'I'ERIODIC REVERSE vCURRENT'ELECTRO- PLATIN G APPARATUS George W. Jernstedt, Pittsburgh, Pa., assignor to Westinghousc Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application December 11, 1947, serial No. 791,027

5 Clams. 1

This invention relates to .anxelectroplating conveyor apparatus, and in particularto apparatus constructed to function automatically to lelectrodeposit metal on members by applying thereto a periodic reverse current.

There is disclosed in my copending patent application SerialNo. 610,107, filed August 10, 1945, now Patent 2,451,341, that metal'may be electrodeposited with. considerable improvement in quality and speed of plating by employing a periodically reversed current. While the use of special current reversing mechanisms, such vasv reversing switches or'specially Wound generators, may be resorted to in order to secure a periodically reversed current, the initial cost and maintenance are often high. Furthermore, there are many conventional conveyorized electroplating installations that Would require considerable additional equipment and rebuilding to convert them to periodic reverse current plating. It is desirable .to employ conventional apparatus as far as possible in any electroplating apparatus and to convertA it to a reverse current plating set up with the minimum of alteration or change. In particular, it would be desirable to employ conventional sources of continuous direct current, such, for example, as a direct-current generator or a rectifier, and to make a relatively simple alteration to produce a reverse current plating installation therefrom.

According to -the present invention, it has been found possible by a relatively simple change in conventional electroplating systems employing conveyors to enable them to `electroplate members with a periodic reverse current and certain exceptional advantages have been found to follow.

The object of the present invention is to provde an electroplating conveyor apparatus for automatically periodically r-eversing the current applied to members being plated during the operation thereof.

Another object of the invention is to provide an electroplating conveyor apparatus with an electrical conductor provided With alternate anodic and cathodic current Sections whereby work being plated has applied thereto periodically reversed current.

Other objects of the invention will in part appear 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 vdescription and drawings, in which:

Figure 1 is a plan view of an electroplating conveyor apparatus constructed in accordance with the invention;

Fig. 2 is a fragmentary view partlyin section of the conveyor of Fig. 1';

- Fig. '3 is a view in perspective, partly insection, showing details;

Fig. 4 is a 'schematic view of'a modified form of the invention;

Fig. 5 is a side elevation, 'partly broken of a modified form of conveyor apparatus; and

Fig. 6 is a schematic view of another modification of the invention.

As disclosed in my copending Patent 2,451,341, the electroplating process and electrodeposits produced may be greatly improved by applying'to base members beingelectroplated a periodically reversed current in 'which thebase member is subj'ected to aseries of alternate cathodic and anodic current pulses, each extending over a predetermined short' interval of' time. In partie'- ular, the cathodic currentinterval should be for a time of not over v4b seconds whereby an increment of metal is i'deposited on the base member. The 'cathodic current is succeeded by an anodic current which is' of a su'fiicient current density and is applied for a period of time sufiicient to deplate unsound and inferiozmetal from the increment plated duringthel preceding cathodic portion of the cycle. After the 'preceding increment is preferenti'ally partially deplated, by the anodic current, thereby leaving smooth, sound metal, a second pulse of cathodic current is 'applied to deposit more metal and, in turn, is followed by a succeedingvanodic current Vpulse to deplate unsound `and inferior metal from this latter increment. This cathodic-anodic current cycle is repe'ated until the required amount of metal has been'plated. i In particular, the anodic portion of the cycle should be at such a current density and for a s'ufficient period of time to apply at least 4% of the coulombs'applied to the base member during the cathodic or'plating portion of the cycle but not exceeding approximately of the coulombs applied during the rcathodic portion of the cycle. For plating mostv metals, the best results are'se'cured from' vthe standpoint of total metal plated'and quality of metal plated where the anodic current` portion applies to the base member from '20% to40% of the coulombs applied during the cathodic portion of the cycle. Usually the current density during the'cathodic and anodic pulse is the" same and the time intervals lare adjusted' to secure the proper ratio of eoulombs.

The periodic reverse' current cycle hasv given good results when v'em'ploy'ed for'plating copper, brass, zinc, cadmium, silver, gold, nickel, iron,

cobalt and various alloys of these metals. Electrodeposits are produced with periodic reverse current that are smoother, brighter and Sounder than produced by conventional continuous direct current, also the speed of plating can be greatly increased. The cycles which have given good results in practice will vary to some extent with the metal being plated and the nature of the electrolyte. Periodic reverse current plating has been found to have the following advantages over con'- tinuous direct-current plating with regard to the following factors:

1. An increase in the rate of metal deposited per unit time.

2. An increase in the density of electrodeposited metal.

3. Increased surface brightness of the electrodeposit.

4. Plating of metal smoother and sounder than the base member. z

5. Heavier deposits of acceptable quality.

6. A decreased porosity.

7. Better metal distribution over base member.

The periodic reverse current process is fiexible and may be so carried out by varying the proportion of the anodic and cathodic current cycles to greatly emphasize one or more of the above '7 features.

More specifically, for plating copper, brass and silver from aqueous cyanide solutions, it has been found that the Optimum results are secured with a current cycle having a cathodic interval of from 2 to 40 seconds, and an anodic interval of from 1/!2 to 10 seconds, wherein the anodic' current applies from 10% to 50% of the coulombs applied during the cathodic interval. For plating nickel and cobalt, as disclosed in the copending application 759,796, filed July 9, 21947, now Patent 2,470,775, the cathodic interval should be less than 2 seconds, and preferably from 1/2 to one hundredth of a second. while the anodic interval is approximately 1/2 to 1/25 of the cathodic period, the coulombs during the anodic portion of the cycles varying from 4% to 60% of the coulombs during the cathodic portion.

According to the present invention, conveyorized electroplating apparatus is so constructed and arranged that it automatically applies a periodically reverse current to members being plated during the operation thereof. The conveyorized electroplating apparatus is supplied with conventional continuous direct-current from a suitable source, such as a generator, rectifier, battery or the like.

Referring to Fig. 1 of the drawings, there is illustrated a conveyorized electroplating machine which consists of a tank of glass, rubber covered metal, Wood or other material unaffected by an electrolyte l2 from which metal is to be plated contained therein. Anode conductor bars |4 are disposed at the outer side walls and at the inner portions of the tank for Supporting a plurality of anodes Hi of the metal to be electrodeposited on base members being processed. The number and spacing of the anodes are in accordance with well known practice. The conveyor mechanism includes two sprocket Wheels 4 23 may be supplied with insulating bushings to prevent fiow of current to them or they may be oomposed entirely of a resin laminate which is electrically non-conductive. The links 24 each carry a movable support 26 from which there hangs a work holding rack 28 having a plurality of arms 30 on which base members 32 may be hung. A great variety of racks are employed in the industry and the illustration in the drawings is only exemplary. In general, electrical current passes from the Support 26 to the rack 28, thence to the arms 30 and thence to the base members 32 which, when thus electried while in contact .with the electrolyte will be subject to electrolytic action. A guide and support rail 34 assists the supports 26 to carry the load of the electroplated work without irnposing an undue strain on the p cham 22.

IB and 20 disposed one at each end of the tank The movable supportsoB are disposed to move in slidable contact with'a conductor bar 38. The body of the conductor bar 38 carries continuous direct current and is maintained at a negative or cathodic potential. At spaced intervals the conductor bar 38 is recessed thereby leaving raised Sections 39, and Sections or portions 40 electrically insulated by insulation 42 are disposed in the recesses. The surface of the conductor bar therefore presents

alternate Sections

39 and 40. Both the conductor bar 38 and the Sections or portions 40 may be oomposed of copper or other good conductor material. The Sections 40 are each connected to the positive terminal of a continuous direct-current source whereby they are kept anodic. Any Supports 26 in contact with the surface of a section 39 receive cathodic current and members 32 supported therefrom will have metal deposited thereon from the electrolyte |2. When a movable support 26 comes into slidable engagement with one of the Sections 40, the current in the support becomes anodic and metal plated on the members 32 will be deplated until the support 26 moves out of engagement with the section 40.

The spacing between the supports 28 is so adjusted with relation to the spacing and dimensions of the cathodic Sections 39 and the anodic Sections 40 that at any given time over the entire length of the conductor bar 38 a relatively constant number of the supports are in contact With the Sections 40 and the remainder, except for a very small proportion riding on the insulation 42, are in contact with the cathodic portion 38. This feature can be Secured by spacing the supports 25 by a distance which is not a multiple of the total distance of an anodic section 40 plus a oathodic section 39. In this manner, there is obtained a relatively constant anodic and cathodic current fiow without substantial fiuctuations during the operation of the apparatus. The Sections 40 are of lesser length in the direction of travel of themovable supports 26, than the cathodic Sections 39 therebetween, the lengths being proportioned to the desired ratio of cathodic current to the anodic current in the periodic reverse current cycle. In general, less than half of the supports 23 are in contact with the Sections 40 and more than half are in` contact with the Sections 39. Thus it will be apparent that during movement of the conveyor, each support 26 Will become alternately energized With cathodic and'anodic current whereby on contacting section 39, an increment of metal is plated on a base member 32 for a period of time depending on the speed of movement of the chain 22 and the. length of a Section 39 and then on passing into slidable contact with a section 40, the support and base member is rendered anodic to deplate a portion of the metal plated thereon during the preceding cathodic interval. In this manner, the members 32 are plated with a periodic reverse current with all the advantages ensuing therefrom as previously set forth.

While supports 26 carry racks, it is feasible to mount a rotating plating barrel on the support for plating small articles in bulk.

Referring to Fig. 3 of the drawings, there is illustrated in detail a modified form of a conductor bar for supplying reversed current. The movable support 26 is operated for slidable movement. Paralleling the direction of such slidable movement is a cathodic conductor bar mounted on an insulating support 102, and having recesses in the upper surface therein at spaced intervals with insulating material |06 disposed in the recesses fiush With the upper surface' The conductor bar li therefore has a series of exposed conducting sections 504. The insulating material 106 may be a resinous material, such as phenol formaldehyde resin laminate or other suitable substance. Also mounted on the insulating support 02 and paralleling the bar |00 is an anodic conductor bar |l0 also having recesses therein but at staggered alternating intervals with respect to the recess in the bar 100, the recesses being filled with an insulating material I 08. The conductor bar presents a series of exposed conducting Sections I i I. The upper surfaces of the bars il and U0 therefore, present a series of alternating conducting Sections 101i and HI in the lengthwise direction. The support 26 is provided with a box VI |2 having two brushes lli and HB, which may be carbon brushes. Springs 116 and l20 urge the brushes IM and M8 into engagement with the' conductor bars i IB and E00, respectively. A source of direct current 522 is suitably connected to the two conductor bars M0' and 100 to render them, respectively, anodic and cathodic. During movement of the support 26, it Will be clear that the brushes ll and |l8 will be alternately and periodically energized With anodic and cathodic current, respectively, by contact With the sections IH and 104 of the conductor bars ll and l00, and a periodically reversed current will be conducted to the base members 32 on the rack 28, whereby reverse current plating is carried out.

The insulation 4.2 shown in Fig. 2 of the drawings should have a thickness sufiicient that the contact area of the support 26 does not exceed such thickness, otherwise shorting of current beu tween the

Sections

39 and 40 Will take place. For a similar reason, the insulated segments m0 and 108 in Fig. 3 should overlap in .the lengthwise direction by an amount equal to at least the thiclrness of the brushes.

While carbon brushes have been shown in Fig. 3 of the drawings, metallio contact members of various kinds may be employed. Since considerable amperage must flow from the conductor bars to the supports, the contact area of the brushes, contacts or the like and the contact pressures employed. should be designed to take this fact into account.

The following is an example of a plating conveyor embodying the features of the invention. The total length of a conductor bar, similar to the bar 38 in Fig. l of the drawings, is 60 feet and it is divided into a series of 60 Sections, each approximately 10 inches long, with another series of 60 portions, each approximately 2 inches in length, a :2 inch portion being. inserted between each 10 inch section. The 2 inch portions are connected to a bus bar which is attached to the positive terminal ofV direct-current generator. The conveyor comprises 24 movable work supports spaced approximately 2' 7 apart. Approximately 12,000 amperes of cathodic current are passed ,to the cathodic portion of the conductor bar. The anodicV current flows in the proportion of approximately 10,000 amperes to ipermanent anodes o f copper similar to the anodes |6, and 2,000 amperes to the anodic 2 inch portions inserted in the bus bar. The conveyor moves at a speed of 5 feet a minute, whereby base members are plated in approximately 12 minutes during w'hich approximately 60 pulses of cathodic current deposit respective increments of copper.

Each cathodic pulse lasts 10 seconds whilethe anodic current pulse deplates unsound and inferior metal for 2 seconds. Due to the fact that the conveyor speed is variable, the cycle may be varied to provide for shorter or longer cathodic and anodic perods. However, the ratio of cathodic to anodic pulses is fixed by the particular conductor bar structure.

In some cases it may be desirable to apply a materially increased current density to the anodic Sections or portions of the conductor bar in order to deplate a larger proportion of the previusly plated increment without however changing or unduly increasing the length of the conveyor. This may be accomplished conveniently by including an additional source of direct current in the circuit in the manner illustrated in Fig. 4 of the drawings. As illustrated, a main direct-current generator 50 has its negative terminal 52` elcctrically connected by a bus 56 to the cathodic segments 39 of the conductor bar. The vpositive terminal 54 of the generator 50 is connected by a bus 58 to the permanent anodes [6 of the metal being plated. An auxiliary direct-current generator 64 of much smaller capacity than the generator 50, for instance a generator having 20% of the output of the generator 50, has its negative terminal 66 connected to the bus 56. An increase in the cathodic current is thus applied to the cathodic Sections '30, of the conductor. The positive terminal 68 of the auxiliary generator 64 is connected to a conductor 10 which is connected to the anodic Sections 40. Anodic current flows from bus 58 through the conductor 60 to the conductor 10. In order to prevent anodic current from generator 64 passing to the bus 58, a unidirectional valve or rectifier 62 is placed in the circuit formed by conductor 60. By regulating the output of the direct-current generator 64, there accordingly may be secured a predetermined variable proportionality between the coulombs in anodic and cathodic pulses applied to the supports 26 and the work thereon during their re- `spective times of contact with the Sections 39 |2 has disposed on each side thereof a pair of driving Wheels 132 moving in counterclockwise direction an endless belt |34 to which are afiixed lugs I 36 at predetermined intervals. 134. move loose copper support bars [46 from The vlugs v right to left as seen in Figure 5. The copper bars 146 are supported on the conductor bar 138 supported on insulating brackets 144 having alternate cathodic Sections 139 and anodic sections 140 constructed and functioning as described previously With respect to

Sections

39 and 40. At the start, each copper bar 143 is carried manually or by appropriate mechanism and laid on an insulated end section 142 of the conductor bar 138. As the endless belt 134 moves the next lug 136 into engagement With the copper bar, it moves Slidably along the length of the conductor bar 138 until the bar 146 reaches a terminal insulated section 143 when the lug 136 moves out of engagement with the copper bar. The copper bar carries racks 148 which support base members 32 for electroplating. During the travel of the copper bar 146 the length of the conductor bar 138 the base members 32 are subjected to alternate cathodic and anodic current pulses as the

bar contacts sections

139 and 140 successively Whereby the base members are plated by periodic reverse current. At the end of the tank 130, the loose copper bars 136 are lifted by hand or by a suitable lifting mecham'sm for washing or other further processing of the plated base members.

For some purposes the lengths of each of the

respective Sections

39 and 40, or 139 and 140, need not be constant throughout the entire length of the conductor bars. It may be found desirable to vary the lengths of the Sections, as well as the ratios of the coulombs of anodic and cathodic current supplied, as more metal is plated on the base members in order to secure predetermined surface characteristics.

In some cases it may be desirable to provide an electrical circuit supplied With electrical current from a single source of energy so that the current supplied the anodic Sections 40 may be varied in order to modify the plating operation. Referring to Fig. 6 of the drawings, there is'illustrated electrical members connected in electrical circui-t relation to a single source 200 of continuous direct current such as a generator. The negative lead from the source 200 is connected by conductor 202 to the cathodic Sections 3-9. The positive lead from the source 200 is connected by the conductor 204 to conductor 206 leading to the anodio Sections 40 and conductor 210, in parallel therewith, to the anodes 15. The variable resistance 208 in conductor 206 and a second variable resistance 212 in conductor 210 enable the proportioning of the total anodic ampere output of the source 200 between the anodes 16 and anodic Sections within a predetermined range of values. The source 200 ordinarily will operate at 'from 3 to 12 volts, and the

resistances

208 and 212 may 1be so constructed and operated to introduce a maximum resistance in each case of from about 1/0,000 to 1/100 of an ohm. However, the voltage and resistance may be varied in aocordance with the size of the :plating installation, the metal being plated and other factors.

The advantages of the automatic electroplating conveyor arrangement disclosed herein are several. They include a rapid reversal of current from anodic to cathodic and vice versa with a minimum of time lost. It has been found that generators Operating on field reversal have a substantial time lag in changing from maximum anodic to maximum cathodic current output. Another advantage is that timing mechanisms and. contactors with their associated mainte- 8 1 nance problems are eliminated. The relatively' simple structures required for the conductor bars and slidable contacts as disclosed herein are such as will operate indefinitely 'With good results with a minimum of maintenance. Furthermore, substantially constant current conditions are realized, thus avoiding the violent current fluotuations which are met with When the entire work in a tank is made Simultaneously anodic or cathodic. The throwing power of the electrolyte in the present invention is improved, since the work being plated is Surrounded on all sides with anodes during the cathodic portion of the cycle.

Since certain obvious changes may be made in the above and different embodiments of the invention may be constructed without departing from the scope thereof, it is intended that all the matter contained in the above description and drawings be interpreted as illustrative and not in a limiting Sense. i

I claim as my invention:

1. In a conveyor electroplating machine for plating members with metal from anodes of the metal, in combination, a tank containing an electrolyte, a plurality of Spaced movable supports having means thereon for supporting members to be immersed in the electrolyte for electroplating, means for moving the supports in one direction at a predetermined speed, contact means carried by each Support for supplying electrical current to members thereon, a relatively stationary conductor means supported by the tank and disposed for Slidable contact with the contact means on each support, the conductor means comprising a series of alternate electrically conducting surface Sections electrically insulated from each other, the Sections being so disposed and proportioned that every second one is shorter than the preceding section along the direction of travel of the contact means with respect thereto, the series of shorter Sections having means for connecting them to the anodic terminal of a source of continuous direct current, the series of longer Sections having means for connecting them to the cathodic terminal of a source of direct current, and the spacing between the movable supports being substantially uniform and So proportioned to the dimensions of the Sections that a relatively constant number of all the contact means is in sliding contact With the shorter sections, whereby, in operation, a relatively constant anodic current is being supplied to less than half the supports and members being carried thereon and a relatively constant cathodic current is being supplied to more than half the supports and members being carried thereon, and, during movement of a movable Support, any members supported thereon receive a successive and alternating series of cathodic and anodic current pulses.

2. In an electroplating apparatus for plating members, a tank containing an electrolyte, a Support disposed above the tank having means thereon for supporting the members, the Support being composed of an electrically conducting metal, a bar carried by the tank upon which the support rests for slidable movement thereon, means for slidably moving the Support along the bar, the bar comprising a plurality of insulated electrically conducting surface portions of unequal length arranged to present alternate short and long Sections in contact With the support in its sliding movement, means for connecting the short sections to a source of continuous anodic auuaooo direct current and the long sections to a source of continuous cathodic current, whereby on movement of the support and its members on the bar it is subjected to a series of alternating anodic current pulses for a short period of time and cathodic current for a longer period of time, and means attached to the tank for supporting a plurality of anodes of the metal to be plated on the members.

3. In an electroplatng conveyor for plating members with metal from an electrolyte in which is disposed an anode of the metal, in combination, a plurality of movable supports for supporting members to be electroplated and for conducting electrical current to the members, each support including an arm, suspending means on the arm for suspending in the electrolyte the members being plated, means for conducting current to the suspending means on the arm, and electrical insulation between each arm and its neigh- `bors, means for moving the supports substantially continuously in a given path, a contact means associated and movable with each support to supply the electrical current to the movable support, the contact means comprising a contact member on the arm connected in circuit relation with the means for conducting ourrent to the suspending means on the arm, a con- ,ductor bar located along the path of movement,

of the movable support and positioned so as to be slidably contacted by the contact means, the entire length of the conductor bar comprising a plurality of alternate electrically conducting cathodic and anodic surface portions with insulation separating the portions, and means connecting a source of electrical current to the surface portions of the bar to render them anodic and cathodic respectively, whereby each movable support is rendered successively cathodic and anodic as its associated contact member passes over the alternate portions of the conductor bar during its movement.

4. In an electroplating conveyor for plating members with metal from an electrolyte in which is disposed an anode of the metal, in combination, a plurality of movable supports for supporting members to be electroplated and for conducting electrical current to the members, each support including an arm, suspending means on the arm for suspending in Vthe electrolyte the members being plated, means for conducting current to the suspending means on the arm, and electrical insulation between each arm and its neighbors, means for moving the supports substantially continuously in a given path, a contact means associated and movable with each support to supply the electrical current to the movable support, the contact means comprising a contact member on the arm connected in circuit relation with the means for conducting current to the suspending means on the arm, a conductor bar located along the path of movement of the 10 movable support and positioned so as to be slidably contacted by the contact means, the entire conductor bar comprising a plurality of alternate electrically conducting cathodic and anodic surface portions with insulation separating the portions, and means connecting a source of electrical current to the surface portions of the bar to render them anodic and cathodic respectively, Whereby each movable support is rendered successively cathodic and anodic as its associated contact member passes over the alternate portions of the conductor bar during its movement.

5. In a conveyor plating machine for plating members with metal from an electrolyte in which is disposed an anode of the metal, in combination, a plurality of spaced movable supports for supporting members to be electroplated, each support including an arm, suspending means on the arm for suspending in the electrolyte the members being plated, means for conducting current to the suspending means on the arm and its neighbors, and electrical insulation between each arm, means for moving the support substantially continuously in a given path, contact means on each support for supplying electrical current to the members thereon being plated, a relatively stationary conductor located along the path of movement of the movable supports to be slidably contacted by the contact means on each support, the stationary conductor having a plurality of electrically conducting cathodic and anodic surface portions disposed in alternate spaced arrangement with insulation separating the portions for successive contact by each contact means, and means connecting a source of electrical current to the portions of the bar to render them anodic and cathodic respectively, whereby the members on each support are rendered alternately cathodic and anodic during movement of the movable supports, the spacing between the supports being greater than and proportioned in relation to the dimensions of successive anodic and cathodic portions so that a substantially Constant number of all the contact means are in contact with the anodic portions, the anodic portions being shorter than the cathodic portions along the .direction of travel of the contact means.

GEORGE W. JERNSTEDT.

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

UNITED STATES PATENTS Number Name Date 1,574,055 Pedersen Feb. 23, 1926 1,769,188 Rabezzana July 1, 1930 1,809,139 Miller June 9, 1931 2,085,730 Cox July 6, 1937 2,237,103 Lex Apr. 1, 1941