US 3450625 A
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7 June 1'], 1969 Filed Sept. 7, 1965 K. c. RAMSEY ETAI- ELECTROLYTIC PLATING TANK Sheet of 4 Me F162 2 Zhaz/ M June 17,
1969 K. c. RAMSEY ET AL v ELECTROLYTIC PLATING' TANK Sheet INPUT VOLTAGE FIG.3
OLTAGE AMPERAGE I RELATION For TYPE 5.0. ELECTRONICKEL June 17, 1969 K. RAMSEY ET AL 3,450,625
ELECTROLYTIC PLATING TANK Filed Sept. 7, 1965 Sheet uOm 00h.
dd 2.3. l v 0.2.5 d 2: I n 01:0 2305 0 o 5u 02005 I 2C cow- United States Patent 9 Int. Cl. C23h 5/70 5/08; B01k 3/04 US. Cl. 204-237 8 Claims ABSTRACT OF THE DISCLOSURE An electroplating apparatus wherein a foraminous screen separates a tank into anode and cathode compartments, the anode compartment being filled with particulate anode material. The tank itself may be of a metal such as titanium which carries electric current to the anode material through one of the tank walls in direct electrical contact therewith. The tank walls are protected from corrosion by oxide formed as result of the anodic charge and the cathode compartment tank walls are coated with an insulator to prevent stray currents. A fabric sheet adjacent to the foraminous screen prevents particulate material from passing into the cathodic compartment.
This invention relates to a new and improved electroplating tank and more specifically to an electroplating tank provided with a new retaining means for plating particles.
It is common practice in the electroplating industry to employ individually suspended rolled or cast pieces of anode metal or large metallic baskets as containers for the electroplating anode material. When baskets are used they are constructed of materials that are chemically inert, electrically conductive and possess a high tensile strength. The baskets or anodes are hung in the tank from an electrical current input bar which is connected to the positive terminal of a DC. power source while being externally located and insulated from the tank containing the plating solution. There are various difficulties associated with the use such as cost of fabrication, inefficient use of tank space, and loading and handling difliculties. When the baskets are cleaned of sludge, dirt, etc., the tank operation must be shut down and the process therefore cannot be made completely continuous. Individually suspended anodes of the metal being plated out give similar problems and are also a more expensive type of material than that which is normally used in the metallic baskets.
Conventional plating tanks are normally made from materials which must be protected from corrosion by a plastic or rubber lining which completely covers any surfaces in contact with the plating solution. In addition, they must be electrically insulated from the plating currents to insure that they will not suffer an electrochemical corrosion attack.
It is an object of this invention to provide a new and improved electroplating tank in which the electroplating material is loaded into means associated with the tank surface, thereby eliminating the container basket.
Other objects of the invention will become apparent from the description to follow.
The objects of this invention are attained in an electroplating apparatus comprising a tank having one or more conductive sidewalls and bottom surfaces, and a foraminous screen positioned inwardly from a said conductive surface to form a space between the surface and screen, the said space adapted to contain electroplating particles.
3,450,625 Patented June 17, 1969 In the diagrams:
FIG.1 represents a perspective View of one embodiment of the electroplating tank;
FIG. 2 is a diagrammatic and sectional view showing a filter recirculation system for the tank; and
FIGS. 3-5 represent efliciency curves when plating with electrolytic and SD. nickel.
The tank 1 is shown with sidewalls 2, end walls 3 and bottom 4 constructed of a metal suitable for an electroplating operation such as titanium, zirconium, etc. Such a metal is protected from corrosion because of its properties when imparted with an anodic electric charge. These properties include the formation of a non-porous metallic oxide on the surface of the metal which is strong- 1y adherent, electrically conductive and corrosion resistant.
Positioned inwardly from one of the side walls is a metal screen 5 which is of a mesh or similar porous construction to allow the electrolyte to enter the space 9 and dissolve the plating material 7 which may be nickel.
The screen may be perforated or constructed of an expanded or woven material and is usually of the same material as the side walls. However, an electrically nonconducting substance such as a glass or plastic may be used as the screen material in place of a metal. It is also possible to construct the tank of an electrically nonconductive material, and have the screen a conductor. However, this variation is less eflicient. A sheet of cloth or similar fabric may be positioned near the screen to prevent plating particles and sludge from entering the plating area of the tank, and its design can be such that it may be continuously unwound into and removed from the tank to maintain its efliciency by exposing a fresh surface. For commercial operations a space similar to 9 is provided along wall 21 to plate simultaneously and on both sides of the workpiece 14.
Objects 14 to be plated in solution 17 are suspended from cathodic conducting bar 15 which is connected to a negative D.C. supply (not shown) while a series of connections 16 from the tank wall 2 are made to the positive side of the DC. supply. The metal screen may be fastened to the tank wall with the same connection 16. To prevent stray currents affecting the migration of plating ions, the end walls 3, 3 side wall 21 and bottom 4 of the tank are coated with a suitable inert insulator 20 such as rigid PVC.
The space 9 formed between the sidewall 2 and screen 5 is filled with plating material 7 and it will be observed that no great restriction on particle size is necessary since the length of the tank can accommodate lengths of plating particles far beyond the capacity provided by the usual baskets.
FIG. 2 illustrates a filtering and recirculation system for the metal ions and it will be observed that although the current i proceeds through the screen, the direction of pumping is such as to remove metal plating ions from the space 9, through the pump 10', filter 11 and into the plating area of the tank 12. The liquid pressure differential produced by the direction of pumping will cause a difference in liquid levels 13, 17 respectively between the main tank through the external pumping and filtering circuit rather than through the screen. This eliminates contamination of the solution and provides a more uniform supply of plating ions.
A sludge accumulator 18 is positioned below the tank level. Sludge formed by the electrolysis reaction falls through the porous screen 6 placed at the bottom of the tank wall in space 9 and enters the accumulator which runs the length of the tank. A pipe connector 19 links the accumulator to the pump line.
'It will thus be seen that the tank wall itself is the anode connector obviating the need for a separate external insulated positively charged current input bar and because of this an electroplating apparatus is supplied in which the current can spread uniformly along the tank wall, into the nickel anode and then uniformly through the porous screen. With this method of imparting a uniform electrical current to the anode metal in the plating area the system will produce more eilicient and uniform plating action to the objects 14. This etficiency is particularly noticeable when operating at temperatures exceeding the 140 F.165 F. range presently used in the electroplating industry. This invention enables plating operations to be carried out at temperatures of 185 F. and higher. Since plating efiiciencies, such as the rate of metal deposition, improve with temperature increase of the plating solution, this of course is highly desirable.
FIGS. 3, 4 and 5 illustrate plating efiiciency in terms of amperage, voltage and temperature and it will be observed that an increase in solution temperature enables a higher electrical current flow to be achieved in the solution for a given voltage. Consequently there will be an increase in the transport number of the plating ions and a corresponding improvement in plating speeds.
1. In an electroplating apparatus comprising a tank, a rigid foraminous screen spaced from one of the walls of said tank to provide an anodic compartment for the accommodation of particulate material to be deposited and a cathodic compartment for the accommodation of an article to be plated as cathode, the improvement of which at least one of the side and bottom walls of said tank is electrically conductive in that portion forming the anodic compartment, said walls being electrically nonconductive in that portion forming the cathodic compartment and a fabric sheet is provided adjacent to and contiguous with said foraminous screen adapted to prevent particulate material from passing from the anodic compartment to the cathodic compartment.
2. An apparatus as claimed in claim 1 in Which a second rigid toraminous screen and fabric sheet are located 4 in the tank spaced from the wall opposite to said one wall of said tank to provide a similar second anodic compartment.
3. An apparatus as claimed in claim 1 in which the screen is a metallic screen.
4. An apparatus as claimed in claim 1 in which the fabric sheet is adapted for continuous unwinding.
5. An apparatus as claimed in claim 1 in which the tank is formed from titanium, the walls of the tank forming the cathodic compartment being electrically insulated.
6. An apparatus as claimed in claim 5 in which the screen is a titanium screen.
7. An apparatus as claimed in claim 1 in which each anodic compartment is provided with a horizontal screen spaced from the bottom wall of the tank to provide a sludge accumulator to receive sludge formed in the electrolytic process.
8. An apparatus as claimed in claim 7 in which means are provided to circulate the electrolyte in the anodic compartment through a filter system to the cathodic compartment.
References Cited UNITED STATES PATENTS 82,877 10/1868 Remington 204285 XR 494,232 3/ 1893 Schoenmehl 204237 578,171 3/1897 Turner 204285 XR 969,921 9/1910 Thum 204283 XR 1,062,966 5/1913 Guiterman 20414 1,449,462 3/1923 Van Arsdale 204285 XR 1,734,909 5/1929 Jones 204242 2,771,415 11/1956 Ross 204238 2,984,081 5/1961 Hahn 204239 XR JOHN H. MACK, Primary Examiner.
D. R. VALENTINE, Assistant Examiner.
Us. 01. X.R. 204442, 287