US 2500206 A
Description (OCR text may contain errors)
March 14, 1950 R. AfSCHAEFER ET AL APPARATUS FOR PLATING 2 Sheets-Sheet 1 Filed June 29 1946 VINVENTORSQ EAL/w A. Scmmre Jam; 6. M /L M if mi m x i P i Armelms 0 I R. A. SYCHAEFER ETAL 2,500,206
March 14, 1950 APPARATUS FOR PLATING 2 sheets-sheet? Filed June 29, 1946 Patented Mar. 14, 1950 UNITED STATES PATENT OFFICE.
APPARATUS FOR PLATING Ohio Application June 29, 1946, Serial No. 680,380
The present invention relating, as indicated, to an apparatus for plating, is more particularly directed to the electrodepositing of a layer of metal or metallic alloy onto the concave surfaces of either a plurality of semi-cylindrical articles or to a single semi-cylindrical article of great axial length with relation to the diameter and to maintaining a uniform thickness of deposited metal both circumferentially around the inner surface of the article and axially thereof. In a ccpending application, Serial No. 587,964, filed April 11, 1945, there is describeda method and apparatus for electrodepositing a uniform layer of metal upon the concave surface of a semi-cylindrical article in which the article has a relatively short axial length and the present application describes a method and apparatus for adopting the method of the above-named application to the roduction of electroplating of either multiple articles of the type shown in the above named application or of a single relatively long article having an axial dimension substantially much greater than its diameter.
Specifically the invention relates to the electrodeposition of a layer of metal onto a plurality of semi-cylindrical metal articles and to the maintenance during the plating operation of a uniform thickness, both axially throughout the column of stacked articles and axially from lateral edge to lateral edge of each cylindrical article. The term lateral edges, employed above, denotes the straight parallel edges of the semi-cylindrical object, the inner or concave surface of which is to be plated. The term uniform, used above and as used'herein, denotes that degree of uniformity in which no portion of the electrode posited layer departs from the average by more than in thickness.
In the plating of any semi-cylindrical article which has a length several times its diameter mounted vertically in a plating bath in the conventional manner, it is a well known fact that more metal will be deposited on the lower portion of the article than on the upper, and also if plating is conducted in the conventional way there will be heavier deposit adjacent to the lateral edges than in the center of the concave portion of the'article. Ordinary plating racks and practices have heretofore made it impossible to plate either a long semicylindrical article or the equivalent thereof, such as a column of stacked semi-cylindrical articles so that a uniform thickness was deposited axially and circumferentially. This in turn has made it impossible to carry out high production plating of semi-cylindrical articles in those instances where it was necessary to have a uniform thickness of deposited metal upon the base metal. By virtue of the present invention, consisting of a simple plating rack or box' it is now possible to greatly reduce or entirely eliminate subsequent machining operations, resulting in a very considerable saving in the cost of applying a uniform layer of electrodeposited metal to a base metal.
The present invention is further concerned with method and apparatus for electrodepositing a uniform layer of metal on a multiplicity of stacked or aligned semi-cylindrical articles or upon a single long tubular article placed in a tank in vertical position.
To the accomplishment of the foregoing and related ends, said invention, then, consists of the means hereinafter fully described and particu larly pointed out in the claims; the annexed drawings and the following description setting forth in detail certain means and one mode of carrying out the invention, such disclosed means and mode illustrating, however, but one of various ways in which the principle of the invention may be used.
In said annexed drawings:
Fig. 1 is a plan view of a semi-cylindrical article which is electroplated on its concave face;
Fig. 2 is an elevational View of the article shown in Fig. 1;
Fig. 3 is a plan view of a plating rack embodying the features of the invention;
Fig. 4 is a sectional view taken along the line 4--"., of Fig. 3;
Fig. 5 is a view of a section of the plating rack showing the bottom of the slot;
Fig. 6 is a sectional view partially diagram-' matic of the slot showing the construction at the top;
Fig. 7 is a view partly in perspective and partly in section "of one form of our plating rack or box embodying the present invention; and
Fig. 8 is a partial view showing the contact plate in the box of Fig. '7.
The articles, which it is desired to plate, are composed of any suitable base metal. These articles are shaped to finished semi-cylindrical conformity prior to the plating operation. It is desired to hold the tolerance of the finished plated surfaces as close as possible and to obtain the same thickness of plate on each article. The ordinary thickness, which it is desired to plate, is in the neighborhood of .001 inch to .005 inch on concave surface, with or without an electroplated layer on the convex surface.
In Fig. 1 is shown a semi-cylindrical article with a base metal l and a plated layer of metal 3. In 2 is shown an elevational view of the same article. The rack as illustrated in Fig. 3 produces a plated surface which is uniform on the article both circumferentially and laterally across the faces. The rack l is constructed of an insulating material such as hard rubber or the like and may be completely sealed electrically except for the slot opening 8 in the face 9. The most important I features of this rack dimensionally are the slot opening 8 and the lips 2|) which are on the inner face of the rack. As will be explained later, the dimensions A, B and C are critical and must be held to a certain ratio to the diameter for a uniform deposit circumferentially upon the articles. Other critical factors are the construction of the slot at either end of the plating column. The cross-section of the vertically constructed slot controls the uniformity of thickness laterally across the face of the article or articles being plated. It will be understood that where the term semi-cylindrical article is used herein it refers either to a multiplicity of relatively small semi-cylindrical articles having axial lengths ap proximating or less than their diameter, or to a single semi-cylindrical article having an axial length ranging from two to many times its diameter. In operation then such an article is mounted with its concave face adjacent the slot 6. The article is held in position by a suitable clamping device, and electrical contact is made with the article near the top of the rack. Access to the interior of the rack is gained by raising the sliding member 8 when loading or unloading the article therefrom and by means of this constrution a controlled thickness can be plated on the concave surface of the article and also, if desired, on the convex surface thereof. This latter thickness is controlled by the fitting of the panel 8 in the grooves It and I! (Fig. 4). With a loosely fitting panel 8 current follows the electrolyte around the edge of the panel and distributes itself through the solution within the box, plating against and on the back of the semi-cylindrical bearings mounted therein. If the fitting of the panel 8 in the grooves is sufficiently tight there will be approximately no plating on the back of the bearing and the condition of the fit therefore controls the quantity of plate deposited on the convex side of the bearings. Another method of either controlling or preventing plate on the convex surface is by inserting an electrical robber element 6! between the cover and the outside of the convex surface as shown in Fig. '7. In mountv ing the article in the rack it is necessary to center it with respect to the slot to obtain proper uniformity of deposit and the edges 1 2 and i3 should be firmly pressed against the inside surface [4 or should be otherwise insulated to avoid plating on these edges and also to prevent current from passing to the back of the article and causing a deposit thereon when not desired.
In order to prevent a heavier deposit on the lower area of the plated article it becomes necessary because of metal ion depletion to increase the resistance in the plating circuit in the lower portion of the rack. The amount of this additional resistance decreases in a regular manner vertically up the rack. After a distance of 4% inches from the bottom has been reached the column will be plated uniformly regardless of its lensth. Ordinary convection currents cause the metal ion de letion factor to approach equilibrium which requires no further correction in the rack for uniform deposits. This change and effect can be accomplished in various ways which will be explained hereinafter.
Another factor which is necessary in order to properly plate the bottom shell in the rack is a slight ledge [8 on the bottom of the slot. This is shown in Fig. 5 which is a section 5-5 taken in Fig. 3 and shows that the slot must be stopped just short of the end of the bottom shell. This ledge should be from 2 to 8% of the width of the slot A, preventing what is commonly known as end effect in the plating industry.
Uniformity on the top shell in the rack is maintained by having the slot at the top of the rack flush with the upper edge of the top shell or by having an insulator plate H! which extends through the slot and in the box as shown in Fig. 6. This plate may be constructed of any insulating material, such as hard rubber, resin, etc.
We have found. that the dimensions of the slot 6 and the lips 2.". are critical in order to obtain a 5% variation in thickness circumferentially around the shell 16 and the following dimensions have been found satisfactory as expressed percentages of shell diameters.
A=22% to 38% B: 3% to 4% C: 6% to 10% The above figures are for conventional plating voltages. Similar accuracy can be obtained by decreasing the above values which increases the total resistance in the plating circuit with a corresponding increase in the plating voltage. Nor- .ial voltages are in the range of 6 to 12.
To prevent a heavier deposit on the lower 4% inches of the plating column a shadow is inserted in the lower 4% inches of the slot A. This shadow may be in the form of a right triangle on either side of the slot A with the right angle in the lower corner of the ledge l3 and vertical slot 6. The one leg of the right triangle being 4% inches and the other leg of a length sufficient so that the area of each of the two right triangles is 5% of the open slot 6 area. The total restriction of area being 10% of the opening in the lower portion. This is one form of shadow although others may be used. At a point 4% inches above the bottom of the rack the opening is A inches wide. The right triangles are such that a shadowing effect of 10 per cent will be obtained with the maximum shadowing at the bottom of the slot.
A convenient apparatus for plating multiple semi-cylindrical shells is illustrated in Fig. 7. The apparatus consists of a box 50 of generally rectangular form provided with end and side walls 2! and 22, respectively, and a removable cover 24. The shells are stacked within the box in vertical alignment and with their open faces pressed against the bottom of the box, that is, against the inside of the back of the box proper and with their convex exterior toward the cover of the box and are maintained in that relationship by means of a spring pressed contact 26, (Fig. 8) which is brought into position against an insulated plate 35 mounted on top of the colum of shells to be plated after the latter have been assembled in proper relation in the box. The clamping device consists of the plate 26 which is raised and lowered by means of the supporting stud 5| which has attached thereto a bracket 52 having extended lugs which contact the lever 53. In the position shown in Fig. 7 the spring 55 is compressed and the plate 26 is raised. After the shells have been assembled in the box the lever 53 is raised and slipped out of place, thus releasing the spring 55 and allowing the plate 26. to contact the shells l and hold them in Vertical position on the stack I. Current is brought to the contact plate by means of a conductor '21 extending through an opening in the top of the box and connected to a source of current externally. The top of the box is provided with an arm 30 extending upwardly and terminating in a downwardly pointing conical hook 32 adapted to rest in a suitable conveyor arm in a conveyor for operation in a continuous system of tank plating.
The cover of the box 24 forms with the box proper a complete enclosure for the row of vertically stacked bearings and the two together serve to substantially electrically insulate the semi-cylindrical article except as current is brought through the conductor already referred to and carried directly to the article. The cover may be held in place by any suitable means, such for example as a ring 29 engaging an extending arm portion at the bottom and releasing cam 3|, as shown at the top.
As an example of the application of the invention, a rack similar to that shown in Fig. 7 was made up of hard rubber molded to shape and having a molded hard rubber cover. The inside length of the rack was approximately 21 inches. the width about 5 inches and the depth about 2 inches. The thickness of the rubber was about inch. A slot and lip were molded in the face of the rack, the dimensions of which were determined from the diameter of shells which it was desired to plate. In order to plate a shell, having a diameter of 2.75 inches, the slot was constructed with the A dimension .690 inch; B, .090 inch; and C, .220 inch. In the bottom of the slot, as already explained, the slot area is diminished by 10% in the portion already explained. There was also a ledge at the bottom of the slot about .024 inch high. Inside the rack and extending through the slot at the top was an insulating member made up of hard rubber. Shells were placed inside the rack with the concave faces adjacent the slot and centered with respect to the slot. They were held in place with a clamping device and a connection was made to the top of the shells for an electrical circuit. The back was placed on the rack and was tightly sealed to keep the convex surfaces from plating. The rack was provided with a hook 3! for suspending in a plating bath and the assembly was processed through the precleaning and etching solutions and Was then suspended vertically in a bath consisting of Grams per liter Lead 100 to 110 Hydrofluoboric acid 40 to 50 Total tin 8 to 12' Resorcinal 1 to 5 Gelatin minimum .1 Copper 1 t 3 The anodes were composed of 10% tin, balance lead and placed around the periphery of the plating tank in a vertical position but in no particular relationship with the rack. The copper is added in the form of soluble salts. The rack remained in the electrolyte for approximately 21 minutes with a current density of 20 am'peres per square foot and between 4 and 6 volts. Upon removal from the electrolyte, the shells were carefully measured and were found to have a thickness of .001 inch, the variation in thickness in any direction being no greater than It will be understood, of course, that there may be some electrodeposition on the back or convex surfaces of the bearings, but this, if not desired, can be avoided by any one of several known methods, although in practice a light deposition of the nature of a flash coating is not detrimental since it will serve to prevent rusting of the backs of the bearings during subsequent operations and shipment.
We claim: 1. A plating device comprising an elongated box of insulating material adapted to receive a series of semi-cylindrical articles to be plated mounted in registering endwise relation and having the inner aligned surfaces thereof facing toward one wall of said box, said box being provided with a longitudinal slot extending for a distance in the wall in which it is formed sub,- stantially equal to the aggregate length of the registering semi-cylindrical articles mountedin said box and such slot being disposed parallel to'the axis of said articles and having a width of substantially 22 to 38% of the diameter of each of said articles, said articles being arranged symmetrically with respect to such slot, and the wall of said box having inwardly projecting lips at each side of such slot with the inward projection of such lips being approximately 3 to 4% of the diameter of said articles and the width of such lips being approximately 6 to 10% of the diameter of said articles, retaining means for maintaining said articles in such position and with their edges against the inner face of said wall of said box having the slot therein and with the articles in close contact edgewise with each other, a removable member constituting the wall of said box opposite to that wall provided with such slot, said removable member when in position being adapted to substantially seal the box electrically except for such slot, and current conducting means passing through said box and engaging with one of said members to be plated.
2. A plating device comprising an elongated box of insulating material adapted to receive a series of semi-cylindrical articles to be plated mounted in registering endwise relation and having the inner aligned surfaces thereof facing toward one wall of said box, said box being provided with a longitudinal slot extending for a distance in the wall in which it is formed substantially equal to the aggregate length of the registering semi-cylindrical articles mounted in said box and such slot being disposed parallel to the axis of said articles and having a width of substantially 22 to 38% of the diameter of each of said articles, said articles being arranged symmetrically with respect to such slot and such slot being slightly tapered at its vertically lower end for a distance approximating twenty percent of its length, retaining means for maintaining said articles in such position and with their edges against the inner face of said wall of said box having the slot therein and with the articles in close contact edgewise with each other, a removable member constituting the wall of said box opposite to that wall provided with such slot, said removable member when in position being adapted to substantially seal the box electrically except for such slot, and current conducting means passing through said box and engaging with one of said members to be plated.
3. A plating device comprising an elongated box of insulating material adapted to receive a series of semi-cylindrical articles to be plated mounted in registering endwise relation and having the inner aligned surfaces thereof facing toward one wall of said box, said box being provided with a longitudinal slot extending for a distance in the wall in which it is formed substantially equal to the aggregate length of the registering semi-cylindrical articles mounted in said box and such slot being disposed parallel to the axis of said articles and having a width of substantially 22 to 38% of the diameter of each of said articles, said articles being arranged symmetrically with respect to such slot, and the wall of said box having inwardly projecting lips at each side of such slot with the inward projection of such lips being approximately 3 to 4% of the diameter of said articles and the width of such lips being approximately 6 to 10% of the diameter of said articles, said slot being slightly tapered at its vertically lower end for a distance approximately 20% of its length, retaining means for maintaining said articles in such position with their edges against the inner face of said wall of said box having the slot therein and with the articles in close contact edgewise with each other, a removable member constituting the wall REFERENCES CITED The following references are of record in the file of this patent:
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