US2438885A - Apparatus for electroplating rings and discs - Google Patents

Description

Ap 6, 1948. H. M. BELL, 3D

APPARATUS FOR ELEC'J.R OPJ'.|ATING' RINGS AND- DISCS Filed Oct. 16, 1943 2 Sheets-Sheet l awe Mm;

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April 1943- H. M. BELL, 3D 2,438,885

, APPARATUS FOR ELECTROPLATING RINGS AND DISCS Filed Oct. 16, 1943 2 Sheets-Sheet 2 Patented Apr. 6,1948

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APPARATUS FOR ELECTROPLATING RINGS AND DISCS Henderson M. Bell, III, Cleveland, Ohio, assignmto Chromium Corporation of America, New York, N. Y., a corporation of Delaware Application ()ctober 16, 1943, Serial No. 506,546

1 Claim. 1

This invention relates to method of electroplatingrings and discs and apparatus therefor; and it comprises a method of electroplating rings, annular discs and otherldisc-shaped articles wherein a plurality of such articles are mounted on a rotatable shaft in spaced parallel arrangement with only their lower portions dipping into an electrolytic plating bath and. are. slowly rotated between circular segmental anodes which are mounted in said bath in between said discs, current being passed from said anodes through said bath to said discs serving as cathodes. The invention also includes an apparatus for conducting the. said process, said apparatus comprising in combination. a tank containing an electrolytic plating bath, a rotatable shaft mounted above said bath, a plurality of abutting hubs removably mounted on and adapted to rotate with said shaft, a plurality of annular articles to be plated, means for mounting said articles on said hubs in such manner that they ar spaced parallel with only their lower portions dipping into said bath; said mounting means usually consisting of a plurality of spokes radiating from said hubs, at least one of said spokes being sufiiciently resilient to provide for the rapid mounting and dismounting ofsaid discs on said hubs; a plurality of anodes substantially conforming in shape to the submerged portions of said articles and mountedin said bath intermediate said articles, means for rotating said shaft and articles, and means for passing an electric current through said bath from said anodes to saidarticles; all as more fully hereinafter set forth and as. claimed.

Electroplating operations can usually be classifled into two general types. In what is known as decorative plating, the purpose is to cover the work with a film of metal of uniform appearance, provided only that the coating in its thinnest portion has sufficient corrosion or abrasion resistance to perform the service for which it is intended. Such deposits are often exceedingly thin, and even thethickest portion of the deposit is still quite thin, so thatv lack of uniformity in thickness means very little actual difference in the weight of coating applied from one area to another. this reason, so long as all significant areas are covered with the minimum permissible thickness of coating, special precautions to prevent excessive deposition of metal on some portions of the work are rarely justified.

In. industrial" plating, however,, deposits of notably greater thickness are required, for mechanical or chemical resistance, and in this case the difiererrce in thickness of 1 deposit from one For area to another may be of considerable importance. Thus, for example chromium when applied for decorative purposes, need oftenbe only 0.00001 inch thick, and, if the thickest deposit is three times as thick as the thinnest, this thickest deposit is still only 0.00003 inch thick, a waste, of 0.00002 inch, which is insignificant. For industrial purposes, however, the coating of chromium required may have a minimum thickness of 0.005 inch, and, if the same ratio holds, thethickest deposit will be'0.015 inch. The excessive deposit of 0.010 inch not only represents a notable waste of metal, but might constitute an impermissible alteration in the dimensions of the object, necessitating an expensive grinding operation to remove the superfiuous metal. If nickel or copper are the metals deposited, the variations in thickness over the piece will generally be less than is the case with chromium, owing. to the better throwing power of nickel and copper baths, but variations still exist and still constitute a source of waste of metal as well as frequently a cause for a grinding or machining operation. For this reason, it isgenerally of importance, in industrial plating, to insure a uniform deposition of metal, and elaborate precautions for this purpose are often thoroughly justified.

Of the various methods known in the art of plating for obtaining uniform deposits, the best, when it is applicable, is to so shape and position the anode with respect to the work that the resultant pattern of current densities and interelectrode distances causes the metal to deposit evenly. For some types of work this is simple; for others very difficult. For example, in. the plating of a flat ring on both sides, it is necessary to arrange circular anodes opposite each face of the ring, concentric with it, and of smaller section. The designand construction of a plating rack for this-purpose, combining cathode holder and anode rings insulated from it, .but in definite relation to the position of the rings, is a matter of considerable difficulty. Such arack is moreover hard to keep in shape; there is continual danger of failure of the insulation with consequent shortcircuiting, and it is troublesome to insert the rings to be plated between the anodes without dislodging them from their correct locations.

In the art of electro-winni'ng or electro-refining of metals, it is common practiceto set up a series of alternating anodes and cathodes to save space. Theseare generally fiat and stationary, and the cathodes are removed when the deposits thereon are sufficiently thick. Sometimes, the cathodes have. been mounted on a rotatingshaft, in order to agitate the solution, or to more thoroughly extract all the metal from it. Occasionally the shaft has been set up above the solution line to permit removal of the deposit as it is formed; In these cases, however, it is unnecessary to remove the cathode discs and a uniform deposit is of no importance. Such constructions are not adaptable to the plating of rings, because of the irregularity of the deposit obtained, and the difiiculty, amounting sometimes to impossibility, of

replacing plated cathodes with unplated ones,

and inserting them in the correct locations with respect to the anodes.

By means of my invention, I am able, through the use of a comparatively simple construction, to avoid the above difficulties, and to obtain always a uniform deposition of metal on the rings. This invention can be explained more accurately by reference to the accompanying drawing which shows, more or less diagrammatically, several illustrative embodiments of apparatus within my invention which are useful in conducting my process. In this showing,

. Fig. 1 is a longitudinal elevation of my plating rack, partly in section, showing it installed in a plating tank, the tank being in section,

Fig. 2 is a vertical section of the apparatus shown in Fig. 1, taken along the line 2-2 of Fig 1,

Fig. 3 is an enlarged vertical section taken through one of the hubs of the plating rack and showing the spokes for holding the work to be plated,

Fig. 4 is a similar partial view of a modified hub and spoke,

Fig. 5 is a similar partial showing of a second modification having a resilient spoke of rectangular cross section,

Fig. 6 is a longitudinal enlarged section through one of the hubs of the plating rack,

Fig. 7 is a similar view of a modified hub,

Fig. 8 is a partial view, similar to that of Fig.

'2 but showing a different form of anode,

Fig. 9 is a partial elevational view of the plating rack showing cathodes and disc anodes in position to produce a heavier coating on one side than on the other of the discs, while Fig. 10 is a diagrammatic showing of a driving mechanism adapted to produce a non-uniform deposit on the cathodes.

In the various figures like parts are designated by like reference numerals. Referring to Figs. 1 and 2, my plating rack comprises a cathode shaft I4 journaled in open bearings I I which are mounted on the tops of opposite walls of a plating tank I2 made of electrically non-conductive material containing plating solution 13. The bearings employed are adapted to permit ready removal of the cathode shaft from the tank. The shaft is provided with shoulders l5 which engage the ends of one of the bearings in order to prevent endwise motion of the shaft. The shaft is driven by a system of gearing from which it can be readily disengaged, such as jack shaft I6 and bevel gears l1 and H. The jack shaft can be driven. by any suitable means, such as the chain drive shown in Fig. 10, for example. The shaft i4 is provided with a series of removable hubs l8 having a sliding fit on the shaft, which abut each other and which are used for mounting and spacing the rings or annular discs 23 to be plated. Details of these hubs are shown best in Figs. 3 to 7.

The hubs are held in place on shaft M by means of set-screws I 9 and are definitely positioned with place by lock nuts 29.

respect to the anodes by means of their length and of the shoulder 20 on the shaft. These hubs are each provided with two fixed but adjustable spokes or arms 2| and with one arm 22 which is usually resilient in order to permit quick mounting and removal of the rings or discs to be plated. These arms engage the inner rims as of the rings or discs.

. Secured to the tops of the longitudinal tank walls on either side of the shaft M are bus bars 24 to which conducting arms 25 are rigidly fastened on either side at fixed distances apart, as shown in Fig. 2. From these arms the U-shaped anodes 26 depend. It will be noted that in Fig. 1 the two anodes normally positioned at the left of the figure have been removed in order to show thearrangement of the hubs [8. These anodes are so shaped that, below the solution line 27, they are semicircular. In cross section these anodes may be rectangular, square, circular, elliptical or of any other desired shape. They are concentric with and conform substantially in contour and/or shape to the submerged portions of the work to be plated. Bus bars 24 and bearings l l are connected to the positive and negative sides, respectively, of a source of plating current.

Fig. 3 shows in more detail the construction of the hub I8 and arms 2! and 22 which support the rings or discs to be plated. To the sleeve portion of the hub are welded or otherwise rigidly fastened small sleeves 28 and 36. Sleeves 28 are internally threaded to engage the threaded ends of rods or spokes 2!, which are firmly held in Arm 22 has a sliding fit in sleeve 39 and is resiliently held against the inner rim 40 of the ring or disc by means of the spring 3!. Alternatively, as shown in Fig. 4, arm 22 may have its inner end threaded to engage an interior thread provided in sleeve 32. This construction gives a firmer but less easily manipulated contact than does the structure of Fig. 3. A further modification is shown in Fig. 5. In this case the spokes are fiat bars and arm 22 is replaced by a fiat spring 33, the long cross sectional dimension of which is parallel to the axis of the hub, so that its end 34 will have a large area of contact with the work pieces. This spring has sufficient resilience so that the rings or discs can be readily mounted or removed from the plating rack.

The hubs used in my platin rack may be of any desired length and configuration and each hub can be provided with several sets of spokes if desired. These hubs have the additional function of protecting the shaft M from fumes and splashing from the plating bath. Further pro tection is provided if the hubs are constructed in the manners shown in Figs. 6 and 7. The hub of Fig. 6 is provided with a beveled edge 35 at one end and a correspondingly tapered socket 35' at the other end. When these hubs are abutted the beveled ends fit into the tapered sockets of adjacent hubs forming relatively tight joints therebetween. The hub of Fig. 7 is provided with an external thread 36 at one end and a correspondingly internally threaded socket 37 at the other end. When mounted on the shaft the threaded ends are screwed into the sockets of adjacent hubs forming in efiect a long sleeve bearing a plurality of sets of spokes. The shoulders 38 at each end provide a definite stop for the threads and hence a definite spacing of the work to be plated.

It will be noted that the sleeves 28 and 30 (or 32) of my hubs it do not enter the plating bath in several other ways.

'hence they are not plated and the threads remain tree from metal. The cniy parts which enter the plating bath, aside irom the work to be plated and the anodes, are the outer ends of the spokes 2i and 22. These can be made small in diameter to reduce the metal st in their plating but preferably they are covered with a suitable insulating varnish or resist so that all the current passes to the pieces being plated. It is particularly important that the hubs and the shaft 14 remain above the plating solution, since otherwise the loss of metal would be serious and the method would soon become inoperative due to the building up of metal on the bearings, on the joints between hubs and on the shaft itself.

It will be noted that in each of the modifications described two of the spokes or arms 2? of the :hubs F3 are fixed .in length So that t ir ends are the same distance from the center.

This means that, when the :rings or discs are mounted, pressure from the .moveable arms :22

will hold the work'ti'ghtly against the fixed arms thus centering the work and providing good electrical contact, while preventing the work from becoming eccentric with respect to the hubs and shaft 1'4. The adjustable feature of fixed arms :21 is important for the reason that, if the apparatus should be used to plate rings or discs having a diiferent inner diameter, this can be accomplished by suitable adjustment of the length of these arms. The provision of threaded sleeves 28 and lock nuts 12% make exact adjustment of length an easy matter. Moreover, if it should be desired to plate one portion of the rings or discs more heavily than another portion, this can be accomplished by the simple expedient of adjusting the fixed arms in such fashion that the work is held on the spokes eccentrically with respect to the shaft. When the arms are adjusted in this fashion one portion of the work dips into the bath more deeply and hence for an increased period of time and thus acquires a relatively heavier coating.

Another method of producing a heavier coating on predetermined radial sectors of rings or discs to be plated is to employ an irregular drive for shaft I 4. This can be accomplished, for example, by the drive shown in Fig. 10. In this figure jack shaft i6 is driven by :a 'chain 4'! and sprocket wheels #4 and #46, sprocket it being secured to shaft 16. Sprocket is a disc having an eccentric bore adapted to receive shaft 35 of a motor, reducing gear for the like. As this latter shaft is rotated the eccentric motion of sprocket produces an alternating fast and slow rotation of sprocket M and hence of shafts i6 and M. During the slow portion of the cycle the discs are plated more heavily on the radial segments then immersed in the plating bath than on the non-immersed segments. Whatever the irregularity in coating produced by this means, this irregularity is reproduced on all of the discs plated both in the first and in succeedin operations. Accurately reproducible results are therefore possible. Other Well known expedients can, of course, be employed to produce substantially the same result.

It is possible to vary the thickness of the plating If it is desirable to plate the discs more heavily on their inner margins than on their outer edges, for example, this can be accomplished by suitable changes in the disposition of the anodes, as shown in Fig. 8. In this figure it will be noted that the inner edges If it is desired to plate the discs more heavily on one side than on the other, this can be accomplished as shown in Fig. 9. In this figure the shoulder 2%, which determines the positions oi t e discs with respect to the anodes, is at the -e point but a short collar M has been laced on shaft id adjacent this shoulder. This displaces the positions of the'hubs uniformly and to such extent that the distances 82 between the left sides of the discs to the adjacent anodes are approximately one-third the distances 43 between the right sides of the discs to the adjacent anodes. This means that the discs will acquire coating on their left sides which is roughly three times as heavy as that on their right sides. This will be true with respect to ail discs plated as spokes by weaving and twisting them slightly, the hubs ail he slid on'zand their set screws id ti htened before the discs are mounted. The fir t hub brought up tightly against the shoulder ii-ii and locked in place by tightening its set screw, the second is brought up tightly against the first and on. The number of hubs "to be desired to plate at one time. After the hubs and the discs are mounted on the shaft it :is then only necessary to insert the shaft in its bearings ll, thereby engaging the gears ll, ll to start the shaft rotating and then to turn on the plating current.

It will be noted that each disc, when mounted as described, is definitely located in the tank at a predetermined point-and at a predetermined distance from adjacent anodes. When the discs are mounted concentric with the shaft 14 and when the drive is uniform, each successive portion of the surface of each of the discs follows'inexactly the same path, occupies exactly the same position and receives the same treatment as every preceding portion. Since the anodes 25 are rigidly fixed to the arms 25, which are secured to the bus bar 2 5, the position of the anodes in the bath is likewise fixed. By making the submerged portions of the anodes concentric with the discs and somewhat narrower, it is easy to insure a uniform deposition of metal. On the other hand, if it is desired to produce a predetermined irregularity of deposit on the discs, this can be conveniently accomplished by alteration of the shape of the anodes, by changing the distances from the discs to the anodes in various ways, by varying the shaft speed in a, regularly repeated manner, by mounting th discs eccentrically on the hubs orby a combination of any or all of these expedients. In all of these cases, owing to the use of shoulders and hubs on the shaft l4, it is since it is relatively easy to slip the discs over the.

used corresponds to the number of discs fit is possible to obtain accurately reproducible results due to the facts that all inter-cathode spacings are fixed by these shoulders and hubs and that the positions of the anodes are likewise fixed in the plating bath and need not be disturbed when the shaft M holding the work to be plated is introduced into or removed from its bearings. Thus, while my device is capable of highly reproducible and accurate plating results, suflicient flexibility is provided so that discs of different sizes and proportions can be plated and so that either uniform or non-uniform plating can be secured all on the same apparatus. Because of the resilient third spoke on the hubs, the work can be quickly mounted and dismounted on the cathode shaft, while the exact relationship between anodes and cathodes is automatically maintained. If desired, a second shaft carrying new work to be plated may be introduced in the bearings as soon as a shaft carrying plated work is removed therefrom.

While I have described the most important embodiments of this invention it is evident that various modifications can be made in the specific procedures and apparatus described without departing from the purview of this invention. It is evident from the preceding description that the more important features of my invention include the use of a rotatable shaft removably mounted above a, plating bath, said shaft being provided with shoulders to prevent longitudinal movement thereof and a shoulder to serve as a stop for a plurality of work-holding hubs of uniform length adapted to be mounted in predetermined relationship on the shaft, said hubs being usually provided with spokes adapted to hold disc-shaped articles to be plated in spaced parallel relationshi with annular anodes. While the apparatus described is particularly adapted to the plating of rings and annular disc's, it is evident, of course, that some features of this invention are applicable to the plating of other types of work. While the drawing shows the cathode shaft mounted in bearings on top of the tank walls, any suitable mounting for this shaft may be employed which is adapted to hold the work suspended in the plating bath in the manner described. And,

-while the anodes in the drawing are shown mounted on the edges of the tank, it is possible to mount anodes, cathode shaft, bearings and drive mechanism on a single frame which can be moved from one plating tank to another. .It is also possible to employ various mechanisms for periodically interrupting the rotation of the cathode shaft in order to produce variations in the thickness, of the plating, as well as mechanisms 8 other than those which have been described for periodically changing the rate of rotation of this shaft. Additional modifications of this invention which fall within the scope of the following claim will be immediately evident to those skilled in this art.

What I claim is:

An apparatus for plating annular articles which comprises in combination a plating tank holding an electrolytic plating bath, open bearings mounted on top of opposite walls of said tank, a work-holding cathode shaft journaled in said bearings, means for rotating said shaft; said bearings and said rotating means permitting the lifting of the shaft and the work bodily out of said bearings and said tank; a plurality of workholding hubs having elongated sleeve portions adapted to be slipped on said shaft in abutting relationship in such manner that the length of the sleeve portions determines the spacing of said articles and the shaft is protected from the plating bath, three annularly spaced spokes mounted on and radiating from each of said hubs, two of said spokes being of fixed and equal length while the third is adjustable in length, said spokes having outer ends adapted to engage the inner rims of said annular articles in order to support and hold said articles concentrically and in predetermined positions about said hubs, a plurality of anodes mounted in the tank inbetween and in spaced relationship with said articles, a shoulder on said shaft forming a stop against which said hubs are abutted to determine their spacing from said anodes, and means for supplying plating current to said shaft and said anodes.

HENDERSON M. BELL, III.

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

UNITED STATES PATENTS Great Britain Feb. 18, 193

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