US 3622284 A
Description (OCR text may contain errors)
United States Patent  inventor Siegfried G. Bart Montclair, NJ.
 Appl. No. 709,354
 Filed Feb. 29, 1968  Patented Nov. 23, 1971 l 73] Assignee Bart Manufacturing Corporation Newark, NJ.
I54] ELECTRODEPOSITION OF METAL OVER LARGE NONCONDUCTING SURFACES 15 Claims, 9 Drawing Figs.
 U.S.Cl 29/19L4, 204/9, 204/1 1, 204/12, 204/20, 204/25, 204/281 [51 Int. Cl 823p 3/20, C23b 7/02. C23b 5/60  Field of Search 204/2025, 281,11,6,3,4,l2;29/191.4
 References Cited UNITED STATES PATENTS 1,589,564 6/1926 Robinson 204/12 3,230,163 1/1966 Dreyfus 204/281 2,632,722 3/1953 Libberton 204/6 2,637,404 5/1953 Bart 204/20 2,776,253 1/1957 Scho1l.. 204/20 2,826,143 3/1958 Muse 204/6 FOREIGN PATENTS 281,819 8/1965 Australia 363,432 9/1931 Great Britain 204/20 481,785 3/1938 Great Britain 204/11 Primary Examiner-John H. Mack Assistant Examiner-T. Tufariello Allorney-Lane, Aitken, Dunner & Ziems ABSTRACT: A method of electrodepositing metal on a large nonconducting surface involving the use of nonconductive surface having an exposed network of interconnecting electrical conductors. Methods of electroforming and electroplating involving the use of such a surface. A method of making an electroforming mold and an electrodeposition form with such a surface. An electroforming mold and an electrodeposition form with such a surface. An electroplated article having a base containing such a surface. A method of making a foraminous metal article utilizing such a surface.
ELECTRODEIOSIT ION OF METAL OVER LARGE NONCONDUCTING SURFACES BACKGROUND OF THE INVENTION a cathode in a electrolytic cell is used as a mold. When metal is electrodeposited on the conducting for the electrolysis, and it is made conducting by applying an electrically conducting coating to the surface. This process, prior to the present invention, was a long, tedious and questionable operation. Because the current had to flow through the thin conducting coating, which was not without significant resistance, electrodeposition began at the edge of the coating where connection was made to the coating high current to be transmitted through a relatively thin conductive coating,
BRIEF SUMMARY OF THE INVENTION The system of the present invention overcomes these problems of the prior art by providing an electrically interconnected network of electrical conductors Within and adjacent the surface of the nonconducting portion of the cathodic mold. Prior to the application of a conductive coating, the surface of the cathodic mold is lightly abraded to expose portions of the conductors in the nonconductive surface. An electrically conducting coating is then applied to the surface. This coating will contact the exposed conductor portions at a large number of points uniformly distributed over the entire surface on which electrodeposition is to take place. When the resulting cathodic mold is placed in the electrolytic bath for electrodeposition on the conducting surface of the mold, electrical connection to the mold is made through the conductors. As a result of the conductivity provided by such conductors, the electrodeposition will take place at a uniform rate over the entire surface and high current concentration points on the conducting surface will be eliminated. Because of the uniform the time for depositing a given overall thickness is greatly reduced.
Accordingly, an object of the present invention is to provide an improved method of electrodeposition over large nonconducting surfaces.
Another object of the present invention is to provide an improved method of electroforming large articles.
A further object of the present invention is to facilitate electrodeposition at a uniform rate over a large nonconducting surface.
A still further object of the present invention is to eliminate the problem of high current concentrations in the electrodeposition of metal over large nonconducting surfaces.
A still further object of the present invention is to decrease the time to electrodeposit a layer of metal to a given thickness over a large nonconducting surface.
A still further object of the present invention is to provide an improved mold for electrofonning.
A still further object of the present invention is to provide improved electrodeposited products.
A still further object of the present invention is to provide an improved method of electrofonning a foraminous article such as a screen and to provide an improved cathode for electroforming said article.
become readily apparent as the following detailed description of the invention unfolds, the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a plaster form used in one embodiment of the present invention;
FIG. 2 is an enlarged detailed sectional view illustrating a portion of a cathodic mold of the present invention being manufactured on the plaster form of FIG. I;
FIG. 3 is an enlarged detailed view of a portion of the surface of the cathodic mold before it is coated with an electrically conducting film;
FIG. 4 is an enlarged detailed sectional view of a portion of the cathodic mold with a layer of metal electroformed on the mold;
FIG. 5 is a perspective view illustrating the part electroformed on the mold of FIGS. 2-4 after it is removed from the mold;
FIG. 6 is a sectional view of an article of manufacture made by the electroplating process of the present invention;
FIG. 7 illustrates a cathode made in accordance with a different embodiment of the invention for electroforming a metal screen;
FIG. 8 is a sectional view of the cathode of FIG. 7 with the screen electroformed on the cathode; and
FIG. 9 illustrates an enlarged view of a portion of a screen electroformed by the cathode illustrated in FIGS. 7 and 8.
DETAILED DESCRIPTION OF THE INVENTION As shown in FIG. 1, a plaster form designated by the reference number 11 is made of the shape in which the part is desired to electroformed. In the specific example illustrated, the part to be electroformed is an aircraft nose section approximately parabolic in shape and forming half of an aircraft nose. This part might be for example 10 feet long and measure 8 feet along the surface from side to side. The surface 13 of the plaster form 11 is formed into the desired shape of the part to be manufactured. This surface I3 is then coated with a parting compound, which is preferably silicone oil and is designated by the reference number 14 in FIG. 2. A wire mesh or screen 15 is then positioned overlying the entire surface 13. In this example, the screen is 54-inch mesh of 23 gage copper wire. Instead, fly screen, expanded metal mesh, or an interconnecting network of metal ribbons could be used. The mesh is carefully set in place very close to the surface 13 of the plaster form and may be impressed right to the surface 13. A conventional epoxy mixture is then applied to the back of the screen 15 filling in the interstices of the screen and any spaces which exist between the screen and the surface 13, care being taken not to displace the screen. A fiberglass cloth 16 is then placed over the screen and an additional epoxy mixture is applied to the back of the fiberglass cloth coating and filling in the interstices of the cloth. This process is repeated with addi tional alternate layers of fiberglass cloth and epoxy until the structure is built up to the desired thickness, which in the preferred embodiment is about a quarter of an inch. A tubular metallic or plastic structure may be added between or in back of the fiberglass layers in this process to rigidize and strengthen the shape of the epoxy structure to facilitate its handling.
After the structure is built up to its desired thickness, it is cured in a conventional manner. The structure comprising the screen and the laminated fiberglass bonded together by the epoxy resin is then removed from the plaster form 11 and will form the base of the cathodic mold over which the parts to be electroformed are electrodeposited. After the mold has been removed from the plaster form fill, the surface of the mold which conforms to the surface 13 of the plaster form Ill and adjacent which the screen 15 is positioned is lightly abraded (as by sanding) to expose portions of the screen H. The sanding is conducted until at least one half of the perimeter of each square of the screen 15 is exposed and preferably until three quarters of the perimeter of each screen square is exposed.
FIG. 3 illustrates the surface of the mold after the sanding of the surface has been carried out. The exposed portions of the screen are designated by the reference number 17 The resulting structure, after sanding, is then cleaned and the surface containing the exposed portions 17 is coated with an electrically conducting thin film, which may be a silver, copper or other conductive paint. Preferably, however, a silver reduction process is used. A solution of silver nitrate and formaldehyde is mixed together (in a ratio of approximately 200 g. of silver nitrate for each 200 cc. of formaldehyde) and sprayed over the surface. The mixing process is carried out in a nozzle just prior to the spraying to give a bright silver coating to the mold. This silver film is made very thin, just thick enough to entirely cover the surface of the mold. The surface coated with this film will be the surface on which the electroforming is carried out and accordingly is referred to as the electroforming surface.
Electrodeposition of metal is carried out by immersing the electroforming surface in an electroforming bath, and conmeeting the screen 15 to the negative side of a DC power source to render the mold cathodic. When these steps have been carried out and the anodes of the bath are connected to the positive side of the power source, metal will be electrodeposited on the electrically conducting film. This electrodeposition is continued until a layer of metal of the desired thickness (which commonly will be at least one quarter of an inch or more) is formed on the electrically conducting film. in the sectional view in FIG, 4, the electrodeposited layer of metal is designated by the reference number 2i and the thin electrically conducting film is designated by the reference number 22. During this electrodeposition, current will be carried uniformly to all parts of the electroforming surface of the mold by the screen 15 so the layer 2B of metal will grow uniformly over the entire surface of the mold and high current densities in the conducting film of silver will be eliminated. In addition, the electroformed layer 21 will grow to the desired thickness much more quickly than the systems of the prior art. Because the screen 15 carries the current, the thickness of the conducting film 22 can be reduced to a minimum measuring in microinches, thereby making possible a high fidelity of duplication.
One example of the electroforming bath to be used in this electroforming process and which provides copper electrodeposits is an aqueous solution of about 25 to 100 (preferably 50) grams per liter of sulfuric acid and about 100 to 300 (preferably 200) grams per liter of copper sulfate. In this example, the electroforming is carried out at room temperature or in the range of about 7590 F. and preferably at 80 F. The current density at the surface of the anode should be in the range of to 40 amperes per square foot and is preferably 30 amperes per square foot. At 20 amperes per square foot, the electroformed layer 21 will grow uniformly over the entire electroforming surface of the mold at a rate of about one-thousandths of an inch per hour. The anodes used in this example are soluble copper anodes.
In another specific example adapted to provide a nickel electro-deposit, the electrolytic bath is an aqueous solution of 300 grams per liter of nickel sulfate and 50 grams per liter of boric acid with a pH of about 4.2. The nickel sulfate may range between about 200-800 grams per liter and the boric acid may range between about 35-75 grams per liter with the pH ranging from about 3 to 4.5. The electrodeposition in this example is carried out preferably at a temperature of 120 F. but may range from 100 to 150 F. in this example, the
preferred current density over the cathode surface is 30 amperes per square foot and may rangefrom 5-800 amperes per square foot. The anodes used are SD nickel chips in anode baskets. SD nickel chips are manufactured by lntemational Nickel Company and are sulfur-containing nickel. The sulfur is added to the nickel to make the nickel more soluble. Alternatively, cast carbon nickel anodes or depolarized nickel anodes could be used. The cast carbon nickel anodes contain carbon to increase the solubility of the anodes and the depolarized anodes contain oxygen to increase their solubility.
After the electroformed layer 21 has been built up to the desired thickness, it is stripped from the mold and the thin silver film 22 operates as a parting compound in the stripping operation. FIG. 5 illustrates the aircraft nose section, electroforrned by the process illustrated in FIGS. 1-4.
The above described process may be also used with the same advantages to electroplate large nonconducting surfaces in which the finished product comprises the base of nonconducting material as well as the electrodeposited layer. In the electroplating embodiment, the screen i5 is embedded in the nonconducting surface to be electroplated and the surface is lightly sanded to expose the nodes of the screen in the same manner as described above. Also, as described above, a thin conductive film is applied to the surface to be electroplated. Then metal is electrodeposited in an electrolytic bath on this electrically conducting surface. FIG. 6 is a sectional view of a product made by this electroplating process. Typical applications of this process would be fiberglass rotor blades, fiberglass propeller blades and fiberglass boats.
FIGS. 7 and 8 illustrate a method of electroforming a foraminous article such as a screen in accordance with the present invention. As shown in the figures, a stamped screen 25 is embedded in a nonconducting slab of material 27. This slab of nonconducting material may be laminated fiberglass layers bound together and to the stamped screen 25 by an epoxy resin and may be formed in the same manner as the mold described with reference to FIGS. 1 and 2. The surface to which the screen 25 is adjacent is sanded to expose the entire outer surface of the screen in the slab 27. The slab 27 is then placed in electrolytic bath, and an electrical connection is made to the screen 25 connecting it as a cathode so as to electrodeposit metal on the exposed conducting surfaces. As a result, electrodeposition will take place in the form of the pattern of the electrically conducting portion in the surface of the member 27, in this case forming a screen. When the strands of the screen have built up to the desired thickness, the slab 27 is removed from the electrolytic bath and the electroformed screen is stripped away. FIG. is an enlarged fragmented view of the resulting electrodeposited screen.
It is to be noted that in the production of a forarninous article such as a screen, where the entire outer conductor surface of the screen is exposed, it is not necessary as in the case of the other embodiments to coat the conductors with an electrically conductive coating.
The above description is of preferred embodiments of the present invention and may modifications may be made thereof without departing from the spirit and scope of the invention which is defined in the appended claims.
What is claimed is:
l. A method of forming a layer of metal over a large nonconducting surface comprising the steps of embedding a network of interconnecting electrical conductors in said surface in a manner so that portions of said conductors are exposed on said surface, coating said surface with an electrically conducting film whereby said film is in electrical contact with said exposed portions of said conductors and electrodepositing a layer of metal on said film.
2. A method of forming a layer of metal over a large nonconducting surface as recited in claim 1 wherein said portions of said conductors in said surface are exposed prior to the coating of said surface with a conducting film by abrading said surface.
3. A method of forming a layer of metal over a large nonconducting surface as recited in claim 1 wherein said interconnecting conductors comprise a screen.
4. A method of electroforming comprising the steps of making a mold of nonconducting material defining a surface in the shape of the part to be electroformed and having a network of interconnecting electrical conductors embedded in said surface with portions of said conductors distributed over said surface exposed on said surface, coating said surface with a film of electrically conducting parting compound, electrodepositing metal on said film, and recovering said electrodeposited metal from said mold.
S. A method of electroforming as recited in claim 4 wherein the exposed portions of said conductors in said nonconducting surface are made flush with said surface prior to the coating of said surface with said film.
6. A method of electroforming as recited in claim 5 wherein said portions of said conductors are exposed and made flush with said surface by abrading said surface.
7. A method of electroforming as recited in claim 4 wherein said network of interconnecting conductors comprises a screen.
8. A method electroforming as recited in claim 4 wherein said step of making said mold comprises setting said network of electrical conductors adjacent to a surface defining the shape of the form of the part to be electroformed, and then filling the interstices of said network of electrical conductors with a nonconducting material,
9. A method of electroforming as recited in claim 8 wherein said step of making said mold further includes embedding a fiberglass cloth in said nonconducting material behind said network of interconnecting electrical conductors.
10. A method of electrodepositing a layer of metal in a contoured shape comprising making a base of nonconducting material defining a surface in the form of said contoured shape and having a network of interconnecting electrical conductors embedded in said surface with portions of said conductors distributed over said surface exposed on said surface, coating said surface with an electrically conducting film and electrodepositing metal on said film.
H. A method of electrodeposition as recited in claim 10 wherein said step of making said base comprises setting said network of electrical conductors adjacent to a surface defining said contoured shape and then filling the interstices of said network of electrical conductors with a nonconducting material.
112. A method of electrodeposition as recited in claim 11 wherein said step of making said base further includes embedding a fiberglass cloth in said nonconducting material behind said network of interconnecting electrical conductors.
13. An electroplated article of manufacture comprising a base of nonconducting material defining a molded surface, a network of interconnecting electrical conductors which are in physical and electrical contact with each other and embedded in and distributed over said surface, and having portions thereof exposed in said surface, a layer of conducting material covering said molded surface, and an electrodeposited layer of metal covering the layer of conducting material which is in electrical contact with said network of electrical conductors.
M. An electroplated article as recited in claim 13 wherein said network of electrical conductors comprises a screen.
15. An electroplated article as recited in claim 13 wherein a film of electrically conducting material is sandwiched between said layer of metal and said network of conductors providing electrical connection between said layer and said conductors.