US1772074A - Method of producing galvanic coatings - Google Patents

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Aug. 5, 1930. v. ENGELHARDT ET AL METHOD OF PRODUCING GALVANIC COATINGS Filed Feb. 9, 1926 ILVCIIZZEI'S" 15 WW Attorn/qys.

Patented Aug. 5, 1930 UNITED STATES PATENT OFFICE VICTOR ENGELHABDT, OF IBEBLIN-CHARLOTTENBEBG, AND KURT ILLIG, OF BERLIN- WILMERSDORF, GERMANY, ASSIGNOBS TO SIEMENS a HALSKE, AKTIENGESELL- SCHAFT, OF SIEHENSSTADT, NEAR BERLIN, GERMANY, A CORPORATION or GED- MANY METHOD OF PRODUCING GALVANIO COATINGS Application filed February 9, 1926, Serial No. 87,020, and in Germany October 17, 1925.

The present invention relates to the production of galvanic coatings on bodies, es e- (ciall on narrow tubes. In obtaining dura le coatings it is often necessary--for example when producing a chromium coat1ngto work with an electrolyte which attacks nearly a1 substances, especially metals in the unpolarized condition, giving rise to 1111 purities in the electrolyte. In such case 1t 1s therefore necessary to use the hollow body as the cathode and, furthermore, when making internal coatings, to use it as electrolyzer. Again, in the case of the production of coatings on comparatively narrow tubes,-there is present in the internal hollow space of the tube only a small quantity of the electrolyte which, on the passage of the electric current, is liable to become heated to boiling point by the J oules heat developed. The whirling of the liquid resulting in this case and the rising gas bubbles then make the production of a satisfactory inner coating for the tube impossible.

The invention relates to a process for ob- 2 viating the disadvantages mentioned and to an apparatus that is es ecially advantageous for the carrying out 0 this process, particularly for producing chromium coatings, but is also applicable to other electroplating processes in which difiiculties similar to those set forth above are experienced.

In carrying out the new method for producing galvanic coatings on bodies, the body to be coated is used as the cathode and brought into an electrolyzer. According to the invention an anode arrangement continuously dipping into the electrolyte is moved with relation to the cathode body along those parts of the surface which are to be coated. The velocity of this movement is so chosen that the resulting coating is of the desired thickness at every point. It is immaterial to the invention whether only the body or only the anode arrangement or both parts be moved as long as there is a relative motion. The essential advantage of the new method with regard to other well-known methods consists in the fact that the newmethod may be employed for producing outer or inner galvanic coatings on bodies of any form, and especially on narrow tubes.

In the drawings there is shown an example of an apparatus for carrying out the new process. Figure 1 is a longitudinal section through the apparatus and Figure 2 is a section on the line AB of Figure 1. i

In an electrolyzgr orvelectrolytic vessel 1 that contains the electrol te 2 a hollow body 3 is arranged so as to be xed in position, for example by being suspended by means of a wire 18, and is connected in such'a manner that it will become the cathode. For instance, the suspension wire 18 may be employed as a conductor connected to the negative wire of a direct current line 14, 15. The anode is constituted by the bodies 4 and 5 which are movably arranged, by means of suspension wires 9 and 10 passing over rollers 6, 7 and 8, in the interior and on the exterior respec- 7 tively of the hollow body 3. The anode 4 is I shown as a continuous unitary solid body, but may if desired also be in the form of a hollow body-for example, a'hollow cylinder. The wires 9 and 10 can likewise serve as current conductors by connecting them to the positive wire of the line 14, 15. On the anodes 4 and 5, the length of which is preferably about one-tenth of that of the hollow body, there are arranged projections 11 and 12 of insulating material for the purpose of obviating short-circuiting between the electrodes. Instead. of the lug-like projections shown, centeringbeads of insulating material may be provided on the anodes. These insulators also serve the purpose of guiding the anodes with relation to the cathodes and have the effect of maintaining a nearly constant spacing between the anodes and cathode, and consequently of maintaining a nearly constant current density at the cathode, this being of great importance inplating with chromium from chromic acid solutions. A cock 13 arranged on the vessel 1 serves for the introduction of fresh electrolyte. The apparatus is preferably employed in the following manner First, the anodes 4 and 5 are let down until their lower edges are approximately on a level with that of the hollow body 3. The level of the electrolyte is then preferably so chosen that it is only at a small distance above the upper edges of the anodes. Thereupon the current is switched on by means of the switch 17 and the anodes 4 and 5 are gradually raised by means of the wires 9 and 10 by a handle 16, connected to the wires 9, 10. Instead of the handle 16 any suitable automatically working machinefor example a clockworkmay be used for the same purpose. The cock 13 is at the same time opened to such an extent that the level of the electrolyte 1s always maintained a little-for example, a few centimetres-*above the upper edges of the anodes 4 and 5. The movement of the anodes preferably takes place at a uniform velocity which is so chosen that the coating produced is of the desired thickness.

The insulating centering pieces, which may also be secured to the upper and the lower ends of the anodes 4 and 5 (for instance 1n the form of tooth-like discs), prevent the anodes 4 and 5 as they move vertically in a straight path, from striking against the cathode 3.

In this way, the whole hollow body becomes gradually coated. It is self-evident that if a galvanic coating is to be produced only on the interior or only on the exterior surface of a body, the particular anode which at the time being is not to be used, is removed from the bath.

In the new process a slight dispersion up wardly and downwardly from the edges of the anode generally takes place which results even before the actual galvanization, in the production of a coating similar to that produced by breathing on a surface on the parts of, the body that are encountered by the dispersed substance. The advantage of this is that the body is not attacked by the electrolyte and, in addition, the main coating produced on direct juxtaposition of anode and cathode adheres with extraordinary'firmness. It will be noted that both the inner and the outer surfaces of the hollow body 3 are in contact with the electrolyte, and that the liquid in the two annular zones through which the current passes from the anodes 4' and 5 to the cathode formed by the body 3, is in communication with a much larger body of liquid. In the deposition of chromium and of some other metals, considerable heat is developed. This heat, which is liable to interfere with the success of the plating operation, is readily absorbed'by, and dissipated in, the large body of electrolyte in which the body 3 and both anodes 4, 5 are immersed.

The new process is therefore especially advantageously applicable in the case of the production of chromiumcoatings; it can, however, be employed for the production of any other desired coatings, especially in the case of oxidizin electrolytes and hollow bodies of easily attac able metal.

body, passing an electric current from said anode throughthe electrolyte to said body, the latter serving as a cathode, and effecting relative movement of anode and cathode lengthwise of said hollow body, the anode, at the beginnin of such movement, being adjacent to the lbwer end of said body, and adding quantities of the electrolyte to keep the level of theelectrolyte a small distance above the upper edge of said anode.

2. The method of producing a galvanic chromium coating on a hollow body, which consists in dipping the hollow body into an electrolyte suitable for chromium deposition, in such a manner that said electrolyte will be in contact with the inner surface and with the lower end of the said hollow body, placing within said body an anode which is a small fraction of the length of said hollow body, passing an electric current from said anode through the electrolyte to said body, the latter serving as a cathode, efi'ecting rel ative movement of anode and cathode lengthwise of said body, in a vertical direction, and adding such quantities of electrolyte that the level of the electrolyte will be ke t a small distance above the upper edge 0 the said anode.

3. The method of producing a galvanic chromium coating on a hollow body, which consists in dipping the hollow body into an electrolyte suitable for chromium deposition, in such a maner that said electrolyte will be in contact with the outer surface and with the lower end of the said hollow body as well as with the inner surface thereof, placing an anode exteriorly of said body and an anode within such body, each of said anodes being a small fraction of the length of said hollow body, passing an electric current through said electrolyte from said anodes to said body, the latter serving as a cathode, and moving said anodes lengthwise of said hollow body from the bottom thereof to the top, and adding quantities of the electrolyte to keep the level of the electrolyte a small distance above the upper edges of said anvanic chromium coating on a tubular body,.

comprising in combination a vessel adapted to contain an electrolyte suitable for chromium deposition and the tubular body to be coated, a wire for connecting the said tubular body with the negative pole of a source of electric current, means for suspending the said tubular body stationary in the said vessel at adistance above the bottom of the said vessel, an anode suspended within said body, said anode being a small fraction of the length of said hollow body, insulating means to guide and to keep said anode out of contact with said tubular body, means for moving the said anode along the inner surface of the said tubular body from the bottom to the top, and a device for introducing such quantities of electrolyte intothe said vessel that the level of the electrolyte in the said vessel both within and without the said tubular body will be kept a small distance above the upper end of the said anode.

6. Apparatus for producing a chromium coating on both the outer and the inner surfaces of a tube, comprising in combination, a vessel adapted to contain an electrolyte suitable for chromium deposition and the tube to be coated, means for suspending the said tube in a vertical position in the said vessel and for connecting the said tube with the negative pole of a source of electric current, an anode suspended within the said tube, insulating means for guiding and for keeping said anode out of contact with said tube, a wire connected to said anode, an annular anode exteriorly of the said tube, each of said anodes being a small fraction of the len h of-said hollow body, insulating means or guiding and for keeping said second anode out of contact with said tube, another wire connected to said second anode, and means adapted to move the said anodes lon 'tudinally along the spectively. 4

7. The method of electroplating a conducting hollow bod on both its outer and its inner surfaces, w ich consists in dipping it into an electrolyte in such a manner is said surfaces of the body will be in contact with the electrolyte, placlng two anodes each of relativelly small length com ared with that of said bo adjacent to said ody, one interiorly and other exteriorly thereof, efiectinner and the outer sur aces of the tube reat both of ing relative movement between said anodes and said body, and passing an electric current through the electrolyte from said anodes to said body, the latter serving as a cathode.

8. Apparatus for electroplating conducting hollow bodies both on their inner and on their outer surfaces, comprising a vessel adapted to contain an electrolyte and the body to be plated, two spaced anodes so located that the article to be coated may be placed between them, said anodes each being of a length which is relatively small as compared with the height of said vessel, connections for causing an electric current to pass through the electrolyte from said anodes to said body, and means for effecting relative longitudinal movement between said anodes and said body.

9. Apparatus for electroplating conductinghollow bodies both on their inner and on their outer surfaces, comprising a vessel adapted to contain an electrolyte and the body to be plated, two spaced anodes so located that the article to be coated may be placed between them, said anodeseachbeingofalen'gth which is relatively small as compared with the height of aid vessel, connections for causingan electric current to pass through the electrolyte from said anodes to said body, and insulating means carried by each anode and projecting therefrom toward the other anode to prevent contact of said body with either anode, and to guide the latter.

tures.

VICTOR ENGELHARDT. KURT ILLIG.

In testimony whereof we aflix our signa-

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