US2285553A

US2285553A - Method and apparatus for electroplating magnetizable articles in bulk

Info

Publication number: US2285553A
Authority: US
Publication date: 1942-06-09
Anticipated expiration: 1959-06-09

Description

June 9, 1942. T 2,285,553

METHOD AND APPARATUS FOR ELECTROPLATING MAGNETIZABLE ARTICLESIN BULK Filed Jan. 10, 1939 2 heets-Sheet 1 INVE/QTOR H. a. ARLT A T7 'ORNE Y H. ARLT June 9, 194 2.

METHOD AND APPARATUS FOR ELEGTROPLATING MAGNETIZABLE ARTICLES IN BULK Filed Jan. 10, 1959 2 Sheets-Sheet 2 FIGS INVENTOR By H. G. ARLT nnnnn 00 ATTORNEY Patented June 9, 1942 METEGD AND APPARATUS FOR WCTRO- PLATHNG MAGNETEWLE ARTICHIES IN span Herbert G. 'Arlt, Teancck, N. 3., asslgnor to Bell Telephone laboratories, Incorporated, New York, N. Y., a corporation of New York assistants January it, 1939, Serial No. seams 9 Claims.

The present invention relates to methods and apparatus for electroplating metallic articles. More particularly it relates to methods and ap= paratus for the chromium plating in built of articles formed of a magnetizable material, such as iron or steel.

It is an object of the present invention to improve the deposit formed in the plating of magnetizable articles with various metals by the barrel-plating method.

It is a further object to effect a suitable chromium plating of magnetizable articles by the barrel-plating method.

In the past it has been the practice to carry out the chromium plating of small parts, such as screws, by racking each of the parts individually and then suspending them in the plating bath. This procedure involves considerable expense due to the time and labor necessary for the individual handling of each piece. Barrel-plating methods, in which the pieces are handled in bulk with consequent reduction in handling expense, have been successfully applied to plating with other metals, but their application to chromium plating has met with little success because of the unusual characteristics of chromium plating baths.

One disadvantageous characteristic of chromic acid baths is their low throwing power. For this reason when a large mass of articles is packed together, only a relatively small number of them will receive a coating of metal in a given time. However, in view of the passivating action of the bath, which renders the bare metal surfaces unable to receive a plate, it is necessary to have the metal surface covered with chromium as soon as possible after immersion in the bath. Obviously, it is dimcult to cover the entire sur-= face of a closely packed mass in a short time due to the low throwing power of the bath.

A second disadvantageous characteristic is the narrow range of current density which is capable of depositing a bright chromium plate on the metal surface. If the current density is too low, the plate is dull or absent and passivatlon may occur. It it is too high, the plate has a burned appearance. When articles are loosely tumbled in a barrel they will rarely make such contact with the cathode that the current density at the surface of the parts will be within the critical range. The situation is further aggravated by the fact that a very high current density is necessary'in order for any deposit at all to be formed. Even where parts are separately racked, it is necessary to take precautions to insure a willciently firm contact to permit the required current density at the plating surface. Therefore obviously when the articles lie loosely in contact with the cathode in a barrel, they will rarely carry sufllcient current to permit plating unless an excessive voltage is employed.

A further dimculty arises from the fact that if a suflicient voltage is not continuously maintained on each part, a gray plate will appear and blistering will often result.- Contacts between the cathode and the article being plated must necessarily be broken many times'if the articles are loosely tumbled in a barrel.

To overcome this inherent looseness of contact in barrel plating it has been proposed in U. S. Patent 1,873,826 to M. Devecis, in connection with the plating of various articles in an inclined barrel, to place an electromagnet or permanent magnet below the bottom of the barrel so that the articles are attracted toward and held rigidly against a cathode plate in the bottom of the barrel. Periodically the magnetic force is removed so that the articles may be tumbled freely in the barrel for a short period of time in order to expose new surfaces for plating. Alternatively, magnets of opposite polarity may be placed beneath different portions of the floor of the barrel so that the articles will turn them selves without interruption of the magnetic force as soon as possible since the articles are heldrigidly in a single position for a long period of time. When the magnetic force is interrupted to permit tumbling, contact will be broken for a considerable period of time. Both these conditions will tend to cause passivation and the formation of a blistered gray plate. Although in the second-mentioned procedure these dimculties are somewhat overcome, operation is limited to the plating of a small number of articles of a particular shape. If a mass of articles is treated in this manner, the individual articles will not be free to turn and expose new surfaces for plating.

According to the present invention it has been found that a mass of magnetic parts may be given a bright and uniform chromium plate in bulk if the parts are agitated in a plating bath in a magnetic field under certain conditions. The critical condition is that the strength of the magnetic field be so regulated that the parts are held in firm and substantially continuous electrical as they pass from a magnet of one polarity to a contact with the cathode but that they are not held so rigidly that they are prevented from moving freely over one another under the influence of the agitating force, so as to expose new surfaces continually.

A second condition which facilitates the establishment of the above-mentioned critical condition, lies in the use of a magnetic fieldwhich has a substantially uniform fiux distribution in the region normally occupied by the parts being plated. In such a field, magnetic parts are subjected to no substantial magnetically generated force other than mutual attraction.

A third condition lies in the use of a cathode formed of magnetizable material. This expedient also facilitates the establishment of the critical field strength. In the presence of such a cathode the articles to be plated are attracted to I the cathode by mutual attraction so that the application of an extraneous force as employed in U. S. Patent 1,873,826 is unnecessary to hold the articles in contact with the cathode.

Although the econd and third conditions are not as essential as the first condition, it is however true that the best result is obtained, particularly in the case of chromium plating, when all three conditions are present.

The invention may best be understood by reference to the accompanying drawings in which:

Fig. 1 is an isometric view, partly in section, of a plating barrel which is the preferred embodiment of the apparatus of the present invention Fig. 2 is a sectional view of the device of Fig. 1;

Fig. 3 is a detailed view of the shaft carrying the plating barrel viewed from the line 3--3 of Fig. 2;

Fig. 4 is a front elevation, partly in section, of an apparatus similar to that of Fig. 1 but having a modified form of cathode;

Fig. 5 is a front elevation partly in section of the same apparatus having still another modified form of cathode; and

Fig. 6 is a front elevation partly in section of the same apparatus having still another modified form of cathode.

In the form of apparatus illustrated in Figs. 1 and 2, a barrel l which is formed of any suitable material, such as a rubber-covered nonmagnetic metal, is mounted on a shaft 2 supported on an inclined base 3 and rotated by a suitable power source 4. The barrel is inclined at any suitable angle, such as about 45 degrees. The barrel is surrounded at its lower end by a suitable electromagnetic winding 5. This winding is made up of a sufficient number of turns to give the required strength of field within the barrel when it is carrying the desired amount of current. A perforated basket 6 formed of an insulating material, such as hard rubber, is fitted within the barrel, resting upon the bottom and held firmly in place by the clips I, which engage the top of the barrel. This basket is preferably of polygonal cross-section so as to cause a greater agitation of the articles being plated as the barrel rotates.

A stationary anode member 8 and stationary cathode rod 9 project into the barrel to within a short distance from the bottom. The cathode 9 is formed of a magnetic material, such as soft iron. It is insulated to within a short distance of its lower end by means of the insulating cover l0 made of any suitable material, such as rubber. The insulating cover prevent excessive deposi tion of chromium on the cathode rod. The cathode rod is so situated that it will extend into the mass of parts being plated when the barrel is rotated. Thus it is situated somewhat below the plane of the axis of rotation of the barrel, and for counter-clockwise rotation of the barrel as illustrated, it is situated omewhat to the right of the vertical plane through the axis of rotation. The anode 8 is formed of any suitable and preferably inert metal, such as lead. At its lower end the anode is preferably curved so as to approximately parallel the surface formed by the mass of parts lying in the barrel during plating. The anode and cathode are held in place in any suitable manner, as for instance by means of the support H, from which they are insulated. The anode and cathode are connected to a suitable current source by means of the leads l2 and I3.

The electromagnetic winding 5 is supplied with current by means of the leads l4 which are fastened to the slip rings l5 mounted on the shaft 2. The slip rings are insulated from the shaft by means of the insulating sleeve IS. The slip rings are supplied with current by means of the brushes I! (Fig. 3), which are connected to a suitable current source.

The embodiments shown in Figs. 4, 5 'and 6 differ from that shown in Figs. 1 and 2 in that the cathode 9 is replaced by cathodes I8, l9 and 20, respectively. In Fig. 4 the cathode consists of a rod N3 of magnetizable material fixed to the center of the barrel and rotating therewith. In Fig. 5 the cathode consists of a flat plate I9 of magnetizable material covering the entire bottom of the perforated basket. In Fig. 6 the cathode consists of an annular ring 20 of magnetizable material mounted in the bottom of the perforated basket symmetrically about the axis of rotation.

In each case suitable means is provided for supplying plating current to the cathode while permitting the ready removal of the perforated basket from the barrel. One method of accomplishing this result is illustrated in Fig. 6, in which it can be seen that the cathode 20 is electrically connected by means of the conducting bolts or rivets 2| to a conducting plate 22 mounted on the bottom of the perforated basket. A conducting member 23 is rigidly fastened to the bottom of the basket at its center and is electrically connected to plate 22. The member 23 is free to slide within the hollow sleeve 24, which is formed of an insulating material of suitable mechanical strength such as a fibrous material impregnated with a resin. The member 23 is keyed to conducting member 25, which is held rigidly in place within the sleeve 24, by means of the pin 26. Member 25 is supplied with plating current by means of conductor 21, which is electrically connected to slip ring 28. The plate 22 is kept out of contact with the bottom of the barrel by means of the resilient bushing 29, which may be formed of sponge rubber or other suitable material. The basket is held firmly, but removably, in place by means of the spring ball-bearing device 30 which cooperates with the groove 3| on the member 23. The weight of the barrel may be removed partly from the insulating sleeve 24 by allowing the barrel to rest on suitable sliding or rolling supports (not shown) at its upper end.

In the operation of the device illustrated in Figs. 1 and 2 a mass of suitable magnetic parts is placed in the perforated basket in the barrel to about the level indicated by the line A-A in Fig. 2. In order to prevent the solution of the iron in the plating bath and to prevent passivation, the magnetic winding is preferably energized, the plating potential is preferably applied and the rotation of the barrel is preferably begun before the plating bath is introduced into the barrel. The barrel is rotated at any suitable rate, as for instance about three revolutions per minute, depending upon the size, shape and number of articles being plated. Any suitable chromium plating bath may be employed. The amount of current supplied to the electromagnetic winding is regulated so that the magnetic parts tend to form a. cohesive mass which adheres to the lower portion of the cathode rod. However, the field is maintained sumciently weak so that the parts are freedom of motion of the parts permits new surfaces to be continually exposed for plating and insures a relatively rapid initial coating of all surfaces, even those initially buried in the bottom of the mass. Since the parts are substantially continuously in electrical contact with the plating potential, there is no tendency toward passivation, blistering or the formation of a gray plate.

Because of the fact that the electromagnetic winding surrounds the portion of the barrel occupied by the ferrous parts, there is no substan tial magnetic force acting on these parts other than the forces of mutual attraction between the parts and the cathode rod. When neither the rod nor the ferrous parts are present in the barrel, there is a substantially uniform fiux distribution within the coil. In a field of this type it is much simpler to cause the proper balance between free tumbling and goodelectrical contact between each of the parts and the cathode rod than when there is an extraneous attractive force, such as exists when the electromagnetic winding is situated. in some other position than about the region being occupied by the parts being plated. When there is such an extraneous force, the parts being plated are held more rigidly against the walls or the bottom of the barrel and the resultant friction impedes free tumbling.

The use of a magnetic cathode member also aids in establishing a good electrical contact without the use of a magnetic field so strong as to prevent the tumbling of the articles being plated, since the parts closest to the cathode are held in contact therewith by the strongest magnetic force and the parts remote from the cathode are not greatly ailected thereby.

The strength of the magnetic field and the plating potential suitable for each particular apparatus and each particular plating job may readily be determined by one skilled in the art. When the plating operation is completed, the magnetizing and plating currents are interrupted and the cathode and anode members are removed from the bath. The perforated basket may then be withdrawn from the barrel and the parts removed.

modifications shown in Figs. 4, 5 and 6 are essentially the same as those described above. In each case the articles being plated are held in contact with the magnetic cathode by a mutual attractive force.

Obviously many modifications may be made in the apparatus. Although plating in a barrel has been particularly described, it is apparent that any other device producing a similar agitating or tumbling motion may be employed. Thus a horizontal barrel could be substituted for theim clined barrel shown in the drawings. Similarly an inclined upwardly moving belt, particularly one the slope of which increases as it moves upwardly, could be employed. The-type of magnetic field may also be varied. Although a field having a substantially uniform fiux distribution in the region occupied by the parts being plated is highly desirable, it is not absolutely necessary, provided the strength oi the field is so regulated that the articles being plated are free to tumble and are maintained in firm and substantially continuous electrical contact with the cathode. It is more difficult, however, to maintain this condition when the forces 01 mutual attraction are I not the predominant, magnetic forces acting on the articles being plated. Thus the magnetic member may be placed below or to one side, or above the plating zone. Obviously the magnetic member, wherever situated. may be fixed to the barrel or may be stationary.

It is not absolutely essential that the cathode member be formed of magnetic material although it is more difficult to maintain the condition of firm and substantially continuous electrical conward attractive force.

The plating procedure has been described in connection with chromium plating. However, continuous electrical contact with the cathode is of obvious advantage in connection with plating with other metals, such as nickel, copper, silver, zinc.

The parts to be plated may be prepared for plating in any customary manner. An initial plate of copper and/or nickel may be applied before chromium plating. if desired.

Although the invention has been described in the terms of specific embodiments, it should be understood that it is of general application and is to be limited in scope only by the terms of the appended claims.

What is claimed is:

1. Apparatus for electroplating magnetizable articles in bulk which comprises means for supporting a mass of said articles while they are being plated; means for agitating said articles to expose different surfaces thereof for plating; and, associated with said supporting means. an electromagnetic winding which substantially surrounds said articles while they are being plated and which is adapted to produce a continuous magnetic field which induces in said articles suificient magnetism substantially to I maintain electrical contact between said articles The plating operations in connection with the while they move relatively to each other during agitation, but which winding is so disposed that it does not produce magnetic forces, tending to urge said articles against said supporting means, which are sufiicient to impede the relative movement of said articles with respect to each other and to said supporting means during agitation.

2. Apparatus for electroplating magnetizable articles in bulk which comprises means for supporting a mass of said articles while they are plated having a supporting surface capable of moving upward at an. angle to the horizontal to cause said articles to tumble under the influence of gravity and expose different surfaces thereof for plating; means for continuously so moving said surface; and, associated with said supporting means, an electromagnetic winding which substantially surrounds said articles while they are being plated and which is adapted to produce a continuous magnetic field which induces in said articles sufiicient magnetism substantially to maintain electrical contact between said articles while they move relatively to each other during tumbling, but which winding is so disposed that it does not produce magnetic forces, tending to urge said articles against said supporting means, which are suflicient to prevent said articles from tumbling under the influence of gravity.

3. Apparatus for electroplating'magnetizable articles in bulk which comprises means for supporting a mass of said articles'while they are plated; means for agitating said articles to expose difierent surfaces thereof for plating; a cathode formed of magnetizable material disposed so that at least a portion thereof extends into the region occupied by and adapted, to be contacted by said articles while they are being plated; and, associated with said supporting means, an electromagnetic winding which substantiallyv surrounds said articles and said cathode while said articles are being plated and which is adapted to produce a magnetic field which induces in said cathode and said articles sufficient magnetism substantially to maintain electrical contact between said articles and between said articles and said cathode while said articles move relatively to each other and to said cathode during agitation, but which winding is so disposed th t it does not produce magnetic forces, tending urge said articles against said supporting means, which are sufiicient to impede movement of said articles during agitation.

4. Apparatus for electroplating magnetizable articles in bulk which comprises a plating barrel adapted to contain a mass of said articles while they are being plated and which is rotatable about an upright inclined axis so that the articles therein tend to. tumble under the influence of gravity during rotation of said barrel and expose different surfaces of said articles for plating; means for rotating said barrel about said upright inclined axis; and, associated with said barrel, an electromagnetic winding which substantially surrounds the region normally occupied by said articles while they are being plated and which is adapted to produce a magnetic field which induces in said articles sufiicient magnetism substantially to maintain electrical contact between said articles while they move relatively to each other during said tumbling, but which winding is so disposed that it does not produce magnetic forces, tending to urge said articles against said barrel, which are sufficient to prevent said articles from tumbling under the influence of gravity.

5. Apparatus for electroplating articles in bulk which comprises a plating barrel adapted to contain a mass of said articles while they are being plated and which is rotatable about an upright inclined axis so that the articles therein tend to tumble during rotation of said barrel and expose different surfaces of said articles for plating; a cathode formed of magnetizable material and positioned to contact said articles while they are being plated in said barrel; and, associated with said barrel, an electromagnetic winding which substantially surrounds the region normally occupied by said articles while they are being plated, and which is adapted to produce a magnetic field which induces in said articles and in said cathode sufficient magnetism substantially to maintain electrical contact between said articles and between said articles and said cathode even though said articles move relatively to each other and to said cathode during said tumbling, but which winding is so disposed that it does not produce magnetic forces, tending to urge said articles against said barrel, which are suflicient to prevent said articles from tumbling and moving relatively to each. other under the influence of gravity.

6. Apparatus for electroplating articles in bulk which comprises a rotatable plating barrel adapted to contain a mass of said articles while they are being plated; means for agitating said articles in said barrel during said rotation to expose diflerent surfaces of said articles for plating; and, associated with said barrel, an electromagnetic winding which substantially surrounds the region normally occupied by the articles while they are being plated.

7. The method of electroplating magnetizable articles in bulk which comprises subjecting a mass of said articles to an electroplating operation while carried by supporting means within the space bounded by an electromagnetic winding, agitating said articles during said electroplating operation so as to expose different surfaces for plating, and passing an electrical current through said winding to produce a continuous electromagnetic field which induces suiiicient magnetism in said articles substantially to maintain electrical contact between said articles while they move relatively to each other during agitation, but which provides no magnetic forces, tending to urge. said articles against said supporting means, sufficient to impede agitation of said articles.

8. The method of chromium plating magnetizable articles in bulk which comprises subjecting a mass of said articles to a chromium plating operation while carried by supporting means within the space bounded by an electromagnetic winding, agitating said articles during said chromium plating operation so as to expose different surfaces for plating, and passing an electrical current through said winding to produce a continuous electromagnetic field which induces sufficient magnetism in said articles substantially to maintain electrical contact between said articles while they move relatively to each other during agitation, but which provides no magnetic forces, tending to urge said articles against said supporting means, sufficient to impede agitation of said articles.

9. The method of chromium plating magnetizable articles in bulk which comprises subjecting a mass of said articles to a chromium plating operation while they are contained within the space boundedby an electromagnetic winding and in a plating barrel rotating about an upright stantially to maintain electrical contact between said articles while they move relatively to each other while they tumble, but which produces no magnetic forces, tending to urge said articles against said plating barrel, sufllcient to impede agitation of said articles.

. HERBERT G. ARLT.