US2751344A - Electropolisher - Google Patents

Description

ELECTROPOLISHER Charles A. Kienberger, Ralph E. Greene, Irving C. "Flanders, and Arville R. Flynn, ak'-Ridge,-Tenn., as-

signors to the United States of America as represented by the United- States. Atomic Energy Commission Application June 21, 1949, Serial No. 100,358

4 Claims. (Cl. 204-225) This invention relates to the "art of the preparation of highly accurate or perfect surfaces on a material such as metal, the metal to be used as a sample upon-which another metal such as uranium is plated for purposes of scientific analysis of the uranium or other metal for determining its isotopic content. The scientific analysis may be a fission process of analysis. The sample upon which the metal to be analyzed 'is plated is usually in the form of a disc and may be made of nickel for example. it has been found that the degree of perfectuessof the surface of the metal disc, uponwhich the metal, such as, uranium is plated for scientific analysis,'hasa-direct efiect upon the precision and accuracy of-the scientific analysis. it has been found that there are verypronounced variations in the surfaces-of nickeldiscs obtainedifrom commercial'sources. Inorder to achievelhighly accurateresults intheanalysis for isotopic content f such material as uranium, it is necessary to minimizeor eliminate the variation in degree of perfection of the surfaces of sample discs used.

This invention utilizes a process of electropolishingthe sample discs for obtaining a uniformly reproduciblesurface on large quantities of discs. Electropolishing is the reverse of electroplating, since the metal being polished is the anode and rapidly goes into solution. On the surface or" the metal being polished, the highest current densities occur at the peaks and projections'and. sharp edges and, therefore, these have a tendency to. go into solution before the remainder of the surface. This causes asmoothing of the surface and, with the appropriate combination of electrolyte and current density,.a mirror-like surface can be produced.

The primary objectofthe present invention is to, provide a simple, convenient, and effective device for electropolishing sample discs using the above describedprocess, rapidly, effectively, and uniformly. H v

Another object of the invention is toprovidea device as referred to above, capable of withstanding the electrochemical action of the electrolyte and the high current involved.

Another object of the invention is to provide an electropolisher for sample discs comprising an electrolyte container having a fiat anode therein, a vertically reciprocable cathode holder 'irnmersable in the electrolyte, the cathode embodying a shoe for carrying the sample disc and the cathode holder being reciprocable into a position wherein the sample disc is broughtintopressure contact with the anode.

Another object of the invention is to provide an electropolishing device comprising a containerof electrolyte,-a horizontal anode-forming surface immersed in said electrolyte, a vertically reciprocable cathode aligned with said anode surface and said cathode embodying a holder for samples to be electroplated, the cathode holder being movable in a direction to bringfthe sample intopres'sure contact with the anode surface. Further objects and numerous other advantages of our invention will become 2 apparent from the following detailed'description and annexed drawings, wherein- Figure'l is a'perspective view, partly cut away, of one formof our invention.

Figure 2 is a sectional view of the cathode and sample holder.

Figure? is a cross sec'tional view of the anode member.

Referring to Figureil of the'drawings, there is shown a frame consistingof an h-shaped supporting arm 1 rigidly attached at -its' lowerend to a current-conducting base plate 2 andat its upper end'to-a vertical, slotted, tubular holder 3. iSlidably' mounted in this tubular holder 3 is a cylindrical support 4 made of a current-insulating material (such as plastic). Ri'gidly-attachedto the support 4 is an insulated handlle 5 which projects through'a slot 3a in the tubular holder 3. The slot 3a is of approximately the'same-width'throughout as the diameter of the handle '5, thus preventing play'of the handle 5 between the sides ofthe slot 3a;such play would be particularly objectionable when the handle 5 is in the lower, substantially lateral, part of the'slotfia. The lateral part of slot 3a has a slight downward'slant forpurposes which will presently become apparent.

The center of the support 4 is hollowed'to permit the passage-of a current-conducting rod 6, about which the suppo'rt'4' can turn freely. 'Both ends of the rod 6 are threaded. The topend of the rod-6-extends out of the support 4 and through, respectively, a metal protector cap '7, a supporting "nut (indicatedat 8),-'a lug 9 connected to the. negative terminal of a directcurrent power supply (not shown), anda unt l-0 for clamping the lug 9 in place. The lower: end of the rod 6 is threaded into a tapped extension lla "of a 'current-conducting circular electrode 11 forming a cathode as will be described. The extension lla fits into'a recess provided in the lower end of the support=4; the'diameter of the'recess permits free turning ofthesupriorbdabout the extension 11a.

The circular base .of .the electrode 11 has a diameter slightlylarger'than' that-of the nickel discs to be polished. Rigidly'attached to the underside of this base by three screws 12 tis aidiscsholding assembly composed of two aligned rings 13 and 14 made of current-insulating material such as 'fluorothene an'd held firmly together by two screws 15 as shown. "Passages for liquid and gas are provided'in this assembly through the openings formed by-cut-away portions'at the top edge of-the ring 13. A portion'of the lower edge of the top ring 13 is cut away was to form a slit 13a through which specimen nickel discs -may beinserted into the disc-holding assembly 13, Bland-'15. The internal diameter ofthe assembly is such that the rim'of a completely-inserted disc iseverywhere supported :bythe ibottom ring 14, as'shown in Fig. 2. The-lower-inner edge of ring-13- is bevelled as shown at 1315. The hole 16 provides easy'access for a tool used to insert and remove the disc.

Beneath the disc- holding assembly 13, 14 and 15 is a container 17 madeofcurrent-insulating material and containingan iacid solutionconstituting anelectrolyte. In this container:17,and'centered beneath the disc-holding assembly 13, .14 and .15, :is a cylindrical electrode assern bly, :thediameterof whichpermits the ring 14 to fit around the 'assemblys -top "edge-whenthe disc-holding assemblyis lowered over it. As shownin'detail' in Fig. 3, tthe assembly consists of :a eurrent conducting electrode 18 .(Fig. 3) clampedto.acurrentdnsulating circular support 19 by a nut 26 screwed on a threaded extension 18a of the electrode 18 (Fig. 3).

-Thesu'rface of the electrode :18 (Fig. 3 which would be exposed .tozthe acid solution in the container 17 is covered with a protectingsheet 21 ofacurrent-conducting material (like platinum) which is resistant to electrolytic decomposition. This protecting sheet 21 is softice soldered to the under-edge of the electrode 18 (Fig. 3). A circular depression 21a is provided to take up slack in the sheet 21, permitting a wrinkle-free surface on which the nickel discs rest. The remainder of the electrode 18 (Fig. 3) is protected from inleakage of solution by two rubber gaskets-one'(22) placed between the edge of the protecting sheet 21 and theelectrode support 19, and the other gasket 23 placed between the electrode support 19 and the container 17. The entire electrode assembly (shown in detail in Fig. 3) is clamped to the container 17 and the base plate 2 by a nut 24 screwed on the threaded extension 18a. Also bolted to the base plate 2 is a cable 25 connected to the positive terminal of the direct current power supply previously mentioned herein. The electrode assembly shown in Fig. 3 is thus an anode.

Owing to the corrosive nature of the electrolytic solution, the electropolisher is preferably constructed throughout of materials resistant to acid corrosion. In a desired construction of the electropolisher, the negative cable, which is connected to lug 9 is anchored at some point near connection of the lug to the rod 6; this prevents rotation of the rod 6, permitting the disc- holding assembly 13, 14 and 15 to remain in one predetermined position during operation. Preferably, the supporting nut 8 is screwed down far enough on the rod 6 to allow only a slight vertical play of the rod 6 in the support 4.

In a preferred use of the electropolisher, a solution of approximately 70% sulphuric acid and 30% water (by weight) is placed in the container 17, where it is cooled by water flowing through glass tubing 27. Then, after the electropolisher power supply is energized, a nickel disc is fitted into the disc- holding assembly 13, 14 and 15, and the handle 5 is moved to the bottom of the vertical section of the slot 311. and the parts attached to it, as described, fitting the nickel disc against the upper surface of the protecting sheet 21 with sufficient pressure to force the nickel disc upward against the previously described bevelled edge 13b (Fig. 2) of the top ring 13. The bevelled edge 13b (Fig. 2) acts to center the nickel disc and to prevent its sliding out of the slit 13a. The handle 5 then is moved into the lateral portion of the bottom of the slot 3a and to the end thereof. The slightly downward inclination of this lateral part of the slot 3a places a predetermined, additional pressure on the nickel disc to prevent arcing between the disc and the protecting sheet 21. In practice this pressure has been as much as several hundred pounds.

The lateral movement of the handle 5 moves only the v free-turning support 4 and results in no twisting or wearing action on the nickel disc or the protecting sheet 21. With the nickel disc thus positioned, it thus becomes the anode in the electrolytic circuit, its upper surface being uniformly spaced from the cathode 11. The handle 5 is allowed to remain in the lower, lateral position in the slot 3a for approximately two minutes, during which This lowers the support 4 r i 4 piece composed of chemically resistant conducting material. Again, the cable 25 could be connected directly to the threaded extension 18a, eliminating the necessity of making the base plate 2 of current-conducting material. It is intended that all such equivalents and such variations and alternatives as may occur to those skilled in the art shall fall within the spirit and scope of the claims appended hereto.

We claim:

1. An electropolisher for polishing one side of a substantially fiat metal disc comprising a frame, a cathode support slidably mounted in said frame, an electrolyte container placed in juxtaposition to said support, an anode mounted in said container, a cathode having a substantially fiat surface mounted on said support so that its surface is essentially parallel to the surface of said anode and in alignment therewith, means for holding a metal disc at a fixed distance from said cathode, said support, anode, cathode, and disc-holding members having a common vertical axis, and means for bringing said cathode within said container and for contacting the upper surface of said anode in pressure relation with the lower surface of said disc.

2. A metal polishing apparatus comprising a tank containing an electrolyte, an electrode immersed therein, a second electrode mounted in juxtaposition with said tank, an electrical insulator forming specimen disc-supporting means and carried by said second electrode, means for simultaneously contacting said first electrode with said specimen and positioning said second electrode in said electrolyte in proper operative relation with said first electrode, and means connecting said first electrode to the positive side of a source of power and said second electrode to the negative side whereby said second electrode becomes a cathode and said specimen becomes an anode and by electrolytic action a polishing effect is exerted on said specimen.

3. An electropolisher for metal discs comprising a slotted frame, a support member slidably mounted in said frame, a handle rigidly fixed to said member and extending through an U-shaped slot in said frame, a conductor carried by said support, a cathode plate carried by said conductor, a slotted hollow cylindrical insulator having side ports for ingress and egress of electrolyte forming a disc holder and fixed to said cathode plate, an electrolyte container, an anode assembly including a conductive, electrolyte-resistant sheet forming a wrinklefree surface over a support member having a central depression, said assembly being disposed within said container and aligned with said cathode and said disc holder, said handle and said slot being so arranged as to allow said support to move said holder and cathode into juxtatime the nickel disc is subjected to an electrolytic polishk ing current of approximately 36 amperes at a voltage of 12 to 15 volts. At the expiration of this polishing time, the handle 5 is raised to the position shown in Fig. l and the polished nickel disc is removed. This procedure is repeated for each disc polished. During operations, heat generated is carried away by cooling coil 27.

With the above procedure discs of mirror-like quality and good uniformity have been produced at the rate of about twenty-five discs per hour. The amperage and time interval may of course be considerably varied; the

position with said anode and to contact one surface of a disc held in said holder in pressure relation with said anode sheet.

4. The structure of claim 2 wherein said disc-supporting means comprises a pair of aligned insulating rings containing cut away portions forming fluid ports and a slit adapted to receive a disk specimen.

References Cited in the file of this patent UNITED STATES PATENTS 1,747,165 Eaton Feb. 18, 1930 2,323,952 Wick July 13, 1943 2,349,908 La Motte May 30, 1944 2,372,567 Graham et al Mar. 27, 1945 2,378,002 Drummond et al June 12, 1945 2,399,254, Rieger Apr. 30, 1946 2,475,586 Bartlett July 12, 1949 FOREIGN PATENTS 350,658 Great Britain June 18, 1931

Claims (1)

1. AN ELECTROPOLISHER FOR POLISHING ONE SIDE OF A SUBSTANTIALLY FLAT METAL DISC COMPRISING A FRAME, A CATHODE SUPPORT SLIDABLY MOUNTED IN SAID FRAME, AN ELECTROLYTE CONTAINER PLACED IN JUXTAPOSITION OF SAID SUPPORT, AN ANODE MOUNDTED IN SAID CONTAINER, A CATHODE HAVING A SUBSTANTIALLY FLAT SURFACE MOUNTED ON SAID SUPPORT SO THAT ITS SURFACE IS ESSENTIALLY PARALLEL TO THE SURFACE OF SAID ANODE AND IN ALIGNMENT THEREWITH, MEANS FOR HOLDING A METAL

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