US2721834A - Electroplating method and apparatus - Google Patents

Description

Oct. 25, 1955 F. KOURY ELECTROPLATING METHOD AND APPARATUS 2 Sheets-Sheet 1 Filed May 23 1951 F I l I l |l R O T N E v m FREDERIC KOURY ATTORNEY United States Patent fiice 2,721,834 Patented Oct. 25, 1955 ELECTROPLATING METHOD AND APPARATUS Frederic Koury, Lexington, ldass assiguor to Syivania Electric Products Inc, a corporation of Massachusetts Application May 23, 1951, Serial No. 227,843

6 Claims. (Cl. 204-23) The present invention relates to methods and apparatus for electroprocessing large numbers of small metal parts.

Numerous techniques have been used heretofore in order to handle small metal parts while using these parts as terminals in an electroprocessing bath, more specifically as cathodes in an electroplating bath.

In one common practice, termed barrel plating, a drum of insulating material containing the parts to be plated and having numerous small perforations is rotated about a horizontal axis while submerging the parts in the electrolyte. The cathode connection to the parts is often made by discrete metal structures carried by the barrel or otherwise projecting into the barrel so as to contact the parts periodically; and only during such haphazard contact, current flows through the part and to the negative connections in the plating circuit. The barrel plating apparatus and method is of characteristically limited efficiency in respect to the time required for depositing a given thickness of plating. In addition, it is found that the proportion of plated metal that appears on the articles in relation to the metal deposited on the negative returncircuit connections is relatively low. These effects may be explained by the observation that, while the negative connections are constantly exposed and act as a cathode to receive a plating deposit, it is only at more or less random moments during the rotation of the barrel that any article is in engagement with the return circuit connections so as to receive a share of the deposited metal.

Barrel plating as frequently practiced involves an anode outside the barrel; and when this is the case only a limitedportion of the anode area is effectively projected to the articles to be plated. This is true because of the limitation of the size of holes in the barrel that can be tolerated when handling small parts.

As an improvement over barrel plating the present invention aims at increasing the time-rate of electrodeposition, considering equal plating current. The present invention also aims at increasing the ratio of metal deposited on the articles to be plated in contrast to the metal inherently deposited on the cathode connection. Phrased otherwise, the invention aims at improving the efliciency of plating of small parts.

In another practice, small articles have been plated by mounting them individually in a large rack or in multiple large racks. For example, many nail-like elements have been hung in a rack of wire mesh during electroplating, with reasonable spacing allowed between the several elements. Such arrangement inherently is extravagant as to the handling effort lavished on the individual parts. Furthermore, where any large number of parts is carried by the rack, certain of these act as electrical shields shadowing others, resulting in variations in plating thicknesses, for equal periods of time. In contrast to such method and apparatus, the present invention aims at improving uniformity in electroplating large numbers of small parts simultaneously; and a further object is to save substantially in the handling required preparatory to plating.

In the illustrative practice of the invention described below, parts to be plated are merely deposited in a tray supported for largely vertical but none-the-less complex vibration, using a short stroke and at high frequency while submerged in electrolyte. The numerous parts evidently remain in contact With each other and with the tray substantially continuously and thus there is rapidly changing yet substantially sustained circuit connection through the mass of parts to the tray. When the vibration is suitably adjusted it is possible to produce migration of the parts. The mass of parts then appears to churn and simulate kneading, and, in the case of rod-like parts, rotation of such parts about their axes is observed. The net effect is to expose all portions of all the parts to remarkably uniform electrochemical treatment, and to sustain depolarization mechanically. The invention in its illustrative form is described in connection with copper and tin plating, but it will be evident that other operations can be effectively carried out through application of the novel features. Furthermore, while the invention is particularly effective in the plating of rod-like objects, its application to articles of other form will be apparent to those skilled in the art. The nature of the invention will be more fully appreciated and various additional features of novelty will become apparent from the following detailed disclosure of an illustrative embodiment thereof in which reference is made to the accompanying drawings. In these drawings:

Figure l is a vertical view of apparatus embodying features of the invention, in which certain parts are shown in cross section and Figure 2 is a fragmentary plan view along the line II--II in Figure 1;

Figure 3 is a view in larger scale of a portion of the structure appearing in Figure 2; and

Figure 4 is a graph demonstrating a typical range of plated thicknesses produced in a known method and in accordance with the present invention.

Referring now to Figure l, a ceramic tank 10 is shown containing electrolyte 16 and supporting a number of anodes 12 which in this example are of tin having terminals 14 to be connected in common to the positive terminal of a suitable direct current supply. During the plating operation a metal pan or tray 18 supporting large numbers of articles to be plated is immersed in the electrolyte. This tray is carried by three rods 20, 22 and 24 which grip the edges of the tray and are in turn suspended, rods 20 and 22 being carried by a horizontal shaft 25 and shaft 25 being in turn carried with rod 24 by a further horizontal shaft 26. Three resilient cords 28, 30 and 32,

as of nylon, yieldably and somewhat resiliently support shafts 25 and 26 and the depending rods, these cords being carried by a rigid frame 27 above tank 10. Fixed to shaft 26 through rods 34 is a short-stroke vibrator, including a and connected to opposite ends of cylinder 46 can be selectively coupled through rotary valve 52 to source 54 of compressed air.

The mechanism including cradle 40 and the air cylinder and its compressed air system is provided for raising and lowering the vibrator and the framework which carries pan 18 out of solution 16 for loading and unloading charges of articles to be electroprocessed. Valve 52 is connected to the compressed air source and to line 50 for raising the structure, and to line 48 for lowering the structure into the solution. As illustrated in Figure 1, cradle 40 has dropped the tray and its supporting structure so that that structure is suspended by cords 28, 30 and 32. Cradle 40 is lowered somewhat further so as to be out of contact with the vibrator. During the lifting operation it will be understood that cradle 40 first engages the vibrator and lifts the depending mechanism so that cords 28, 30 and 32 no longer provide support.

During operation of the mechanism described above, the air cylinder is so operated as to elevate tray or pan 18 into a position of clearance well above the electrolyte and a large number of small parts are deposited in this tray. Next the pan and its supporting mechanism are lowered by the pneumatic elevator system into the elec trolyte. It is desirable that the pan be submerged substantially in order that the parts may have an ample volume of electrolyte exposing them to current directly from the anodes. Also, a damping effect on the parts is produced by the liquid above the pans during vibration. In the illustration the anodes are in a position of clearance mechanically for unobstructed vertical travel of the tray. In the lowermost position of the tray, the total area of the anodes above the tray in the electrolyte should be ample. Twice the anode area in relation to the upper tray surface is recommended. The arrangement of anodes shown is preferred to a possible alternative in which a movable anode can be positioned vertically above the tray, because the handling is simplified with the arrangement shown and because the horizontally disposed anode would require special casting to provide holes for escape of accumulated gas produced in the plating operation.

When tray 18 has been immersed to the extent that cradle 40 releases the vibrator and the entire immersed structure is supported by cords 28, 30, 32, alternating current of power frequency, 60 cycles per second for example, is connected to the electromagnet which then vibrates shafts 20, 22 and 24 with vertical stroke of reciprocation. Because of the arrangement of the supporting framework 25, 26 and 34, the mechanical phase of reciprocation of shaft 24 is somewhat different from that of shafts 20 and 22, attributable to differences in resilient mechanical coupling between those shafts and the vibrating armature. Moreover, shaft 24 is seen to be disposed somewhat skew in relation to shafts 20 and 22. Shafts 20, 22 and 24 grip pan 18 at points representing an equilateral triangle whereas at the points where they are coupled to shafts 25 and 26 they are not disposed in an equilateral triangle. The result of this support is to cause the parts in the tray when submerged to act as though they were being churned or kneaded during the vibration, and they migrate and form a pattern as represented in Figure 3. The action is particularly prominent with long and slender rod-like parts small in comparison to the tray size. Parts which are figures of revolution when handled in this apparatus are observed to rotate about their axis more or less continuously so as to expose all surfaces to electrochemical action with a high degree of uniformity. The kneading and mixing of the parts produced by the vibration provides assurance that none of the parts will remain concealed by others for an unequal part of the plating cycle. Each of the parts statistically is exposed to the direct action of the plating currents while other parts are being somewhat shielded or shadowed from such direct plating action. The sloping surface 13a and its smoothly curved contour also contribute significantly to the mixing and the kneading character of the parts movement. Finally, as observed with the aid of a stroboscope, a high-frequency synchronized source of short duration light flashes, the isolated points of support at which pan 18 is gripped for positive application of vibrating forces produce a kind of mechanical standing Waves in different parts of the pan. In an example, a pan of ten inch diameter and of approximately .005 inch thickness of steel produced effective migration of the parts, and mixing and rotating of the parts about their axes with a vibration of 120 cycles-per-second and of amplitude at the shaft 25 of approximately inch (as adjusted by controlling the voltage applied to the electromagnet).

It will be recognized, of course, that during the electroplating operation a substantial amount of metal is deposited on the pan which is part of the cathode structure in the electroplating circuit and that therefore, the mechanical mass of the tray increases during plating. For effective operation it has been found advantageous to discard a pan 18 after its thickness has increased by plating to four or five times its original weight. In example, a charge of 2000 pins of approximately two inch length and different cross sections at their ends of .030 inch diameter for three-fourths their length and .070 inch diameter for the remainder were variously plated, first for depositing copper plate and then for adding tin plate; with the result that after a suitable plating interval, two minutes for the copper and twenty minutes for the tin, a variation in diameters was realized as shown by the solid lines in Figure 4. The relative heights of the graph for different pin diameters represents relative numbers of pins. A portion of this spread is chargeable to original differences in pin diameter. In contrast, in this same figure, 400 pins were plated by supporting them vertically in a wire mesh rack, manually loaded, with a much wider spread of plating thicknesses resulting, as shown in the dotted lines. The high degree of uniformity of plating thicknesses throughoutthe quantity of pins and the larger number of pins that can be conveniently handled is notable.

While the method and apparatus is not dependent in its novel aspects on the plating involved, the following examples of plating are given. For electroplating copper, an electrolyte consisting of the following may be used:

Grams per liter Sodium cyanide 34 Cuprous cyanide 26 Rochelle salts 30 For electroplating tin an electrolyte of the following proportions is effective:

Sodium hydroxide Sodium acetate The plating current for a ten-inch pan with a load of approximately two thousand units is approximately 45 to amps. and approximately 4 /2 to 6 volts is suitable for both copper and tin at to C., although substantial latitude of current densities is permissible. Parts of entirely different shape and ratio of surface to mass have been successfully plated in the method and with the apparatus described such, for example, as machined frustoconical solids, cylindrical sheet metal cups, and metal spheres of greater weight than the pins described above but nonetheless small relative to the supporting tray or pan.

Computation based on plating current density, plating time, and weight of deposited metal, allowing for the shadowing effect of one volume of parts which at any one moment electrically shields the other parts from effective plating deposition, shows that the parts remain in the electric circuit virtually continuously, a factor that.

vastly reduces the required plating time in comparison, for example, to the barrel plating described above. It would seem that although some of the parts shield others from the direct plating currents, nevertheless some of the parts maintain a continuous circuit between the pan and others of the parts that are momentarily lifted by vibration of contact with the pan. In other words, some of the parts which are kicked up from the pan are nev ertheless in the electric circuit to the cathode connec.

tion by virtue of their contact with others of the parts which at that moment are in contact with the pan.

The round pan with sloping edges shown has been found very effective for the purposes described, contributing measurably to the parts migration and mixing. The three-point support has been replaced, resulting in somewhat inferior kneading action, by symmetrical four-point support. Replacing the sloping rim and rounded contour of the pan with vertical-side, straight-walled pans, however, substantially reduces the eflectivc mixing of the parts during vibration plating and consequently the parts tend to be less equally exposed to the plating current than in the arrangement described.

It has been said above that the sloping edge portions of pan or tray 18 contribute to the mixing and migration of the parts and thus contribute significantly to the uniformity of the electroprocessing effected, and that the mechanical standing waves that are established throughout the pan contribute to the same result. These factors may be regarded in broader aspect as constituting a sloping supporting surface that is vibrated vertically through a stroke small relative to the pan itself and to the largest dimension of the parts, for the purpose of rotating the parts individually and causing mixing and migration of the parts.

In the preferred embodiment, pan 18 is made of sheet metal, largely imperforate. A limited number of holes 18b, small relative to the size of the parts to be contained, are formed in the pan for draining the electrolyte as the pan is lifted from the bath at the end of the plating cycle. The holes may, to a minor extent, affect the physical coupling between the bottom of the pan and the fluid, so as to modify the action of the fluid in damping the motion of the parts being vibrated; but this effect can be compensated by appropriate adjustment of the vibration amplitude.

It will be recognized that the foregoing embodiment of the invention as described is subject to a latitude of modification and to varied application as will be apparent to those skilled in the art, and, therefore, the appended claims should be accorded the proper latitude of interpretation consistent with the spirit and scope of the invention.

What is claimed is:

1. Apparatus for electroplating a large number of small parts concurrently, including an open-top container for electrolyte, an anode carried on the side wall thereof and being vertically disposed, a metal pan having resilient supporting means and having a vertical-stroke vibrator connected thereto as a unitary assembly, and an elevator mechanism for raising and lowering said unitary assembly including said pan and its vibrator between the electrolyte and a position of clearance for loading the parts into the pan and immersing the parts in the electrolyte without obstruction by the anode.

2. The method of electroplating a large number of small parts simultaneously, which includes the steps of supporting the parts in a pan of circular edge contour, a flat bottom and sloping edge portions, energizing the pan as the cathode in an electroplating circuit and during such energization vibrating the pan by engagement at discrete edge points thereof through a stroke of approximately th inch and approximately cycles per second.

3. In the process of electroplating a large number of small parts simultaneously, the steps of rotating the parts individually and churning the aggregation of parts by supporting the parts in a flexible pan immersed in an electrolyte and vibrating discrete edge portions of the pan through short strokes and at high frequency in such manner as to establish standing mechanical Waves in the pan and vibration of the parts, and passing current from an anode through the electrolyte to the parts and said pan.

4. Apparatus for electroprocessing numerous small parts simultaneously, including a vessel for containing an r electrolyte, anode and cathode structures supported in said vessel, spaced from each other and having terminals for connection to positive and negative terminals of a direct current supply, one of said structures including a pan for containing the parts to be electroprocessed, a magnetic armature mechanically joined to said pan and a solenoid disposed adjacent said armature and having terminals for connection to a commercial frequency alternating current power supply.

5. Apparatus for electroplating a large number of small parts simultaneously, including a vessel for containing an electrolyte, a pan of thin resilient metal having a con tinuously curved periphery and inwardly sloping edge portions and a vertical-stroke vibrator connected to said pan at plural discrete peripheral points, said vibrator having an armature and a coil having terminals for direct connection to a commercial alternating current power supply, said pan having a terminal for connection to the negative terminal of an electroplating circuit, and electroplating anodes in said container having terminals for connection in the electroplating circuit during operation.

6. Apparatus for electroprocessing numerous small parts simultaneously, including a vessel for containing an electrolyte, anode and cathode structures supported in said vessel, spaced from each other and having terminals for connection to positive and negative terminals of a direct current supply, one of said structures including a pan for containing the parts to be electroprocessed, and a short-stroke, high-frequency vibrator mechanically connected to said pan for vertical vibration thereof, said pan having a fiat bottom with sloping edge portions, the mechanical connection of the vibrator in the pan including a plurality of substantially vertically disposed rods engaging said pan at discrete edge portions, one of said rogs being somewhat skew relative to another of said re s.

References Cited in the file of this patent UNITED STATES PATENTS 615,699 Hartley Dec. 13, 1898 1,376,379 North Apr. 26, 1921 1,865,767 Kirchner July 5, 1932 2,071,260 Holden Feb. 16, 1937 2,470,741 Gordon May 17, 1949

Claims (1)

1. APPARATUS FOR ELECTROPLATING A LARGE NUMBER OF SMALL PARTS CONCURRENTLY, INCLUDING AN OPEN-TOP CONTAINER FOR ELECTROLYTE, AN ANODE CARRIED ON THE SIDE WALL THEREOF AND BEING VERTICALLY DISPOSED, A METAL PAN HAVING RESILIENT SUPPORTING MEANS AND HAVING A VERTICAL-STROKE VIBRATOR CONNECTED THERETO AS A UNITARY ASSEMBLY, AND AN ELEVATOR MECHANISM FOR RAISING AND LOWERING SAID UNITARY ASSEMBLY INCLUDING SAID PAN AND ITS VIBRATOR BETWEEN THE ELECTRO-

Images