US3635805A

US3635805A - Working of metal bodies

Info

Publication number: US3635805A
Application number: US751925A
Authority: US
Inventors: Samuel Raviv; Elsa Rabinovitz; Shimon Malkiely
Original assignee: Israel Atomic Energy Commission
Current assignee: Israel Atomic Energy Commission
Priority date: 1968-02-29
Filing date: 1968-08-12
Publication date: 1972-01-18
Anticipated expiration: 1989-01-18
Also published as: CH508054A; FR1586334A; GB1234463A; DE1790053A1; BE722485A; NL6815325A

Abstract

Electrolytic working of metal or mineral bodies. An electrolytic circuit is established using nitric acid as electrolyte and cathodes which are inert to the electrolyte under the operating conditions and the body to be worked is immersed into the electrolyte and brought into direct contact with, or close proximity to, the cathode. A current is flown through the circuit and by this the body is bored, cut or the like according to the specific arrangement.

Description

United States Patent Raviv et al.

[451 Jan. 18, 1972 [54] WORKING OF METAL BODIES [72] Inventors: Samuel Raviv, Beer-Sheva; Elsa Rabinovitz, Dimona; Shimon Malkiely, Beer-Sheva, all of Israel [73] Assignee: The State of Israel, Atomic Energy Commission, Beer-Sheva, Israel [22] Filed: Aug.tl2, 1968 [21] Appl.No.: 751,925

[30] I Foreign Application Priority Data Feb. 29, 1968 Israel ..29,547

[5 6] References Cited UNITED STATES PATENTS 2,990,282 6/1961 Wicke ..204/143 X 3,139,394 6/1964 0elgoetz.... ..204/143 3,485,731 12/1969 Yokozawa et al ..204/143 X Primary Examiner-Daniel E. Wyman Assistant Examiner-C. F. Dees Attorney-Browdy and Niemark [57] ABSTRACT 9 Claims, 1 Drawing Figure WORKING or METAL BODIES The present invention concerns a method for working metals, metal alloys and minerals.

In the context of the present specification, the term working is used in a general way and is meant to imply various kinds of shaping operations that are conventionally brought about by mechanical means such as boring, cutting, reaming, engraving and the like.

Working of metals, especially hard metals, such as various nonofidable steels, various nickel alloys, uranium and the like, as well as of hard minerals, requires cumbersome equipment with special hard-tipped tools which, in view of the high abrasion and wear and tear, have to be replaced frequently. Moreover, the energetic requirements for working hard metals and minerals are high.

It is the object of the present invention to provide simpler and cheaper means for working metals and minerals.

Recent work by the same inventors on certain electrolytic phenomena has led to some surprising discoveries. Thus, in Belgian Pat. No. 704.471 of the 29th Sept., 1967, there is described a method of separating the core of a uranium fuel element from its cladding which comprises inserting the element into a nitric acid bath whose concentration is within the range of from 7 to 12 N, connecting the uranium core, while the element is so immersed, as cathode into an electrolytic circuit, allowing electric current to flow in the electric circuit until the core is sufficiently loosened from the cladding and then extracting the core. The possibility to extract the uranium core from its metal cladding in such a manner was completely unexpected since the measures employed, i.e., immersion into nitric acid and connection of the uranium core as cathode into an electrolytic circuit, are known each by themselves to cause passivation, a phenomenon which is antagonistic to dissolution. Yet by proceeding in the above manner dissolution of uranium occurs, in particular at the uranium-cladding interphase.

In Belgian Pat. No. 704.472, of the 29th Sept., 1967, there is described a method for the dissolution of electronegative metals and metal alloys that normally are either not attacked at all or attacked only very slowly by nitric acid. This method comprises the immersion of the metal into nitric acid, connecting it while so immersed as cathode into an'electrolytic circuit and allowing an electric current to flow in the circuit until the desired degree of dissolution has occurred. Here again, the possibility to dissolve in this manner an electronegative metal of the kind specified was surprising, again for the reason that each expedient by itself, that is treatment with nitric acid and cathodic treatment, leads to passivation, that is to a phenomenon antagonistic to dissolution.

In Belgian Pat. No. 703.419, of the 4th Sept., 1967, there is described a process for the production of nitrous oxide comprising establishing an electrolytic circuit in which the elec' trolyte is nitric acid, one electrode is of an electronegative metal or metal alloy, which is not attacked at all or attacked only very slowly by nitric acid, and the other is of a conductive material inert to nitric acid under operational conditions, and flowing an electric current through this circuit under conditions which do not cause dissolution of the electronegative electrode. Under these conditions a nitrous oxide containing gas mixture evolves near the cathode and can be withdrawn therefrom.

All the above unexpected phenomena led to the assumption that they were due to certain electric surface phenomena occurring at the interphase between metal bodies and nitric acid and that these phenomena can be influenced in a desired direction by an imposed electric current. This recognition has then led to further investigations and surprising discoveries which underlie the present invention.

The present invention consists in a method for working a metal or mineral body, comprising establishing an electrolytic circuit in which the electrolyte is nitric acid and the electrodes are inert to the electrolyte-under the operational conditions, provided that the cathode is of a different material than said body, introducing said body into the electrolyte in a proximity relationship with the cathode, flowing a unidirectional electric current through the circuit thereby to bring about local dis solution of the body, maintaining the proximityrelationship of the body with the cathode until the desired degree of local dissolution is achieved, and then withdrawing the body from the electrolyte.

If desired, the system may comprise two or more cathodes connected in parallel.

The term proximity relationship" is used herein to describe the distance between the worked body and the cathode and is meant to imply either direct physical contact or a spaced relationship not exceeding 10 millimeters. The description local dissolution" implies dissolution within the zone, that is, in proximity relationship with a cathode.

Within the scope of the above general method many different embodiments are conceivable. Thus, in accordance with one embodiment, the body is bored by placing one or more oblong cathodes each in proximity relationship to said body. In accordance with this embodiment it may be necessary to move gradually the body and the cathode towards each other as the boring proceeds.

In accordance with another embodiment of the invention, the diameter of an existing bore is widened by placing an oblong cathode so as to extend therethrough in axial direction and the electric current is made to flow until the bore is widened to the desired diameter.

In accordance with yet another embodiment of the invention, a metal or mineral body is cut or engraved by bringing one or more cathodes into a proximity relationship with the body along a predetermined cutting line or lines. In carrying out this embodiment it is possible to move a pointed cathode along the cutting line or to wind a flexible cathode on the body along the line. Also in this embodiment a gradual movement of the body and each cathode towards each other as the operation proceeds may be necessary.

Many other embodiments are conceivable within the scopeof the present invention, all being variations within the frame of the above general principle.

The electrodes used in carrying out the method according to the invention may be of any suitable material provided they are not chemically attacked by the nitric acid under the operating conditions.

There are no critical limitations for the temperature of the nitric acid bath that is used in carrying out the method according to the invention and any temperature between the freezing and boiling points may be employed. Wherever possible it will be preferable to operate at room or only slightly elevated temperature.

Likewise, there are also no critical limitations for the concentration of the nitric acid and/or the current intensity. Both parameters have to be selected in accordance with the properties of the body to be worked, taking, however, into consideration that both the body and the electrodes must not be attacked chemically.

The method according to the invention differs basically from all hitherto known electrolytic processes. In known electrolytic processes the system comprises only a cathode, an anode and an electrolytic bath. Where in such a process a body has to be worked in any way, electroplated, passivated or dissolved, e.g., in accordance with the above-mentioned Belgian Pat. No. 704.472, the body itself forms one of the electrodes, e.g., the cathode. In consequence, where a body is worked in accordance with any known method and thus serves as an electrode in the system, this electrode, i.e., the body, changes in the course of the treatment. In distinction therefrom, in the method according to the invention, three elements are present in the electrolytic bath, to wit, an anode, a cathode and the body that is being worked. The body, which is thus neither cathode nor anode, will for the reason of its proximity relationship with the cathode, be termed hereinafter as anticathode." In a system according to the invention only the anticathode changes in accordance with the treatment whereas cathodes and anodes remain substantially unaffected.

It is a characteristic feature of the present invention that the treatment is completely topical and only a zone of the anticathode tat is in proximity relationship with the cathode is dissolved whereas the remaining part of the anticathode remains unaffected. It is due to this feature that a complete control of the process is possible and the anticathode may in accordance with the invention be shaped in any desired way.

It is believed that the method according to the invention is based on local modifications of the electric surface properties of the anticathode, which modifications occur in the zone of close proximity to the cathode. As a consequence of these modifications a zone of the anticathode that is in proximity relationship with a cathode is depassivated to such an extent that it can be attacked chemically by nitric acid.

The invention is illustrated, by way of example only, in the accompanying drawing which is a wiring diagram of an electrolytic system for carrying out the method according to the invention.

As shown in the drawing, an electrolytic system in accordance with the invention comprises a vessel 1 holding a nitric acid bath 2. Into vessel 1 dips a cathode 3 and an anode 4 and immersed in the bath and positioned in proximity relationship with the tip of cathode 3 is an anticathode 5 which is the body to be worked in accordance with the invention. As can be seen, contrary to common anodic dissolution systems, the anode 4 is not electrically connected to the work body 5. Cathode 3 is connected to the negative terminal and anode 4 to the positive terminal of a battery 6. An ammeter A serves for measuring the current intensity and a voltmeter V for voltage determination. The system further comprises switching means as well as voltage and current intensity controlling means which are all known per se and not illustrated in the wiring diagram.

Where it is desired, for example, to bore a hole in anticathode 5 the DC is switched on and the anticathode 5 and cathode 3 are gradually moved towards each other as the boring proceeds. The operation continues as long as desired and is interrupted by switching off the current. The so-processed anticathode is then removed from the bath.

The invention is further illustrated by the following examples to which it is not limited. In all the examples the electric current was DC.

EXAMPLE 1 A cylindrical uranium rod of 35-millimeter diameter and 80-mm. long was cut across. For this purpose a platinum wire was wound around the circumferential line along which the cut was intended. The body was placed horizontally into a 1.5- liter bath of 4N HNO at 25 C. and the anode, equally a platinum wire, was so placed that its lower tip was 2 cms. above the uranium rodv An electric current of 12 volts and amperes was applied for 30 hours after which the rod was fully cut. During this operation the cathode, which formed a loop around the uranium rod, was permanently tensioned.

EXAMPLE 2 A uranium rod of the same dimension as that used in example l was bored across. To this end the loop-shaped cathode used in example 1 was replaced by a straight, pointed cathode whose lower tip was directed in direction of the intended bore. The bath was again 1.5 liter of 4N HNO solution, the voltage applied was from 10 to 12 volts, the current intensity from 5 to 8 amperes, and the temperature varied between and C. After 8.55 hours a diametrical bore was achieved whose inner diameter was 4 mm.

The same procedure was repeated for boring an axial bore into the rod (80 mm. length) and this was achieved after 26.30 hours. The bore obtained in this way had an inner diameter of 2 mm.

EXAMPLE 3 A l-mm. thick wall of nonoxidizable steel pipe was bored. A

l-liter bath of a 7N HNO solution was employed, the voltage was 15 volts, the current intensity 20 amperes and the tem- EXAMPLE 4 A nonoxidizable steel pipe measuring mm. in length and whose wall was 0.5 mm. thick was cut in axial direction. For this purpose two cathodes connected in parallel to the same DC source were used and applied at two diametrically opposed points on the pipe. The cathode and anode were both of platinum. The electrolytic bath was 8N HNO, solution, the voltage was 5 volts, the current intensity l0 amperes and the temperature around 30 C. The two cathodes were gradually moved in axial direction along the pipe and after a period of 45 minutes an axial cut of 35 mm. was produced.

EXAMPLE 5 The experiments of examples 3 and 4 were repeated with Inconnel pipes (Inconnel is a trade name for an alloy containing approximately 78 percent of nickel, 15 percent of chromium and 7 percent of iron) having the same respective dimensions. Similar results were obtained.

EXAMPLE 6 A uranium rod measuring 35 mm. in diameter and 80 mm. in length was bored using an aluminum cathode and platinum anode, a 4N HNO solution, a current intensity of 4 amperes at a voltage of 10 volts. The operational temperature was 60 C. and after 6 hours a l2-mm. long bore was produced.

We claim:

1. A method for working a metal body which is chemically inert to nitric acid, comprising establishing an electrolytic circuit in which the electrolyte is nitric acid and the electrodes are inert to the electrolyte under the operating conditions provided that the cathode is of a different material than said body, introducing said body into the electrolyte in a proximity relationship with the cathode and not electrically connected to the anode, flowing a unidirectional electric current through the circuit thereby to bring about local dissolution of the body, maintaining the proximity relationship of the body with the cathode until the desired degree of local dissolution is achieved, and then withdrawing the body from the electrolyte.

2. A method according to claim 1, wherein at least two cathodes are applied to said body.

3. A method according to claim 1, wherein said body is bored by placing at least one oblong cathode in proximity relationship thereto.

4. A method according to claim 1, wherein an existing bore in said body is widened by placing an oblong cathode so as to extend therethrough in axial direction and the electric current is made to flow until the bore is widened to the desired diameter.

5. A method according to claim 1, wherein said body is cut or engraved by bringing at least one cathode into proximity relationship with said body along a predetermined line.

6. A method according to claim 5, wherein a pointed cathode is used and is moved along said line.

7. A method according to claim 5, wherein a flexible cathode is wound around said line or part thereof.

8. A method according to claim 1, wherein said body and each cathode are gradually moved towards each other.

9. A method according to claim 7, wherein a cathode is wound on said body and is gradually tightened as the cutting proceeds.

Claims

2. A method according to claim 1, wherein at least two cathodes are applied to said body.
3. A method according to claim 1, wherein said body is bored by placing at least one oblong cathode in proximity relationship thereto.
4. A method according to claim 1, wherein an existing bore in said body is widened by placing an oblong cathode so as to extend therethrough in axial direction and the electric current is made to flow until the bore is widened to the desired diameter.
5. A method according to claim 1, wherein said body is cut or engraved by bringing at least one cathode into proximity relationship with said body along a predetermined line.
6. A method according to claim 5, wherein a pointed cathode is used and is moved along said line.
7. A method according to claim 5, wherein a flexible cathode is wound around said line or part thereof.
8. A method according to claim 1, wherein said body and each cathode are gradually moved towards each other.
9. A method according to claim 7, wherein a cathode is wound on said body and is gradually tightened as the cutting proceeds.