US2150470A - Process of producing metallic articles substantially free from impurities - Google Patents

Description

Patented Mar. 14, 1939 UNITED STATES PROCESS OF PRODUCING METALLIC ARTI- CLES SUBSTANTIALLY FREE FROM IM- PURITIES John Tyssowski, Dobbs Ferry, N. Y.

- No Drawing. Application April 28, 1937,

Serial No. 139,503

2 Claims.

This application is a continuation in part of my copending application, Serial No. 68,689, filed March 13, 1936.

The invention relates to the art of refining metal and plastically converting it into articles that are substantially free from impurities.

The principal object of the invention is to improve the process of producing so-called brittle cathodes and subsequently coalescing them and plastically transforming them, as by extrusion, into merchantable shapes without melting the metal.

The invention is particularly applicable to the refining of copper, and the plastic transformation of it into substantially pure articles, and the invention will be described in its application to that I metal.

The various steps of the process upon which this invention is an improvement are disclosed in the patent to Stout No. 1,822,939 and the patents to Stout and Osborn Nos. 1,846,697 and 1,938,608. Briefly the steps are as follows:

1) The electrolytic production of a metal cathode having special characteristics which distinguish it from the tough, dense cathodes made by the usual electrolytic process and which are intended for subsequent melting prior to further treatment. The special characteristics of the cathode are its coarse crystalline structure, its porosity, its brittleness, it frangibility, its ability to be readily stripped from the starting blank or starting cathode, and its very rough and ragged exterior surface. Cathodes having these special characteristics are called brittle cathodes and are produced by coating a suitable blank, used as the starting cathode in the electrolytic cell, with asphalt, or the like, having the requisite prop-' order to increase their life it is customary to treat the moulds with a mould wash before each casting operation. The mould wash also prevents sticking of the castings in the moulds and thereby facilitates their removal. In casting copper anodes the mould wash usually employed comprises an emulsion of silica or silicates.

(2) Stripping the deposited brittle cathode from the starting blank, breaking it into small pieces, and compressing the pieces into billets,

(3) Subjecting the billets to a fluid cleansing treatment at an elevated temperature below the melting point of the metal. The cleansing fluid penetrates the interstices of the billet and substantially reduces such impurities as sulfur from any sulfate entrained from the electrolytic bath,

oxygen which may be present in the sulfates and oxygen which may be due to oxidation of the metal from exposure to the air, carbonaceous material from the coating compound used on the starting cathode, arsenic and antimony from any electrolyte that might adhere to the brittle oaths ode when it is removed from the electrolytic cell, and perhaps other impurities. This cleansing process is supposed to leave all surfaces of the metal particles clean and pure so that the particles will properly coalesce in the subsequent step.

(4) subjecting the cleansed billets to pressure to coalesce them and extrude the billets in the form of bars, rods, etc. The coalescence and extrusion of the metal is effected at an elevated temperature below the melting point of the metal. The metal is maintained in a neutral or noninjurious atmosphere from the time it is cleansed of its impurities to the time the metal has been extruded. The extrusion of the billet under pressure coalesces the metal particles into a homogeneous mass and causes new crystal grain growth throughout the mass.

In practicing the complete coalescence process outlined above, in the production of extruded copper articles it was found that while the cleansing step (step No. 3 above) was intended to remove all objectionable impurities, there were certain substances in the form of discrete particles that resisted removal by the treatment and found their way into the extruded articles. Their presence in the extruded articles was highly objectionable especially when the extruded articles were further fabricated into articles of small cross section, particularly fine wire. I discovered that these substances were particles of silica or silicates and I traced them to the silica or silicates contained in the anode mould wash. I found that when the anode castings were removed from the moulds, some of the mould wash unavoidably adhered to the surfaces of the castings. During the subsequent dissolution of the anode in the electrolyte, the adhering mould wash particles were released, and while most of them settled to the bottom of the tank where they could be removed along with other sediment beforethe next charge of anodes was placed in the tank, some of them found their way over to the cathodes and became attached to them as an impurity. The

rough surface of the brittle cathode, and the numerous pores throughout its mass, afforded abundant lodgment" places for the silica and silicate particles, thus making the brittle cathode more subject to contamination by these impurities than would be the case with the usual dense cathode having a relatively smooth surface. Inasmuch as the brittle cathodes are converted by the coalescence process directly into extruded articles without melting, no opportunity was afforded for slagging off the silica or silicate particles.

Having thus ascertained the nature-and cause of the objectionable discrete particles in the extruded articles I thereupon improved the complete coalescence process outlined above for refining and plastically transforming copper and other metals into merchantable articles, by eliminating, or materially reducing, the possibility of the mould wash particles finding their way into the end products.

In accordance with my invention, substantially all mould Wash particles which happen to adhere to the anodes are prevented from reaching the brittle cathodes, thus keeping them out of the coalesced finished articles.

I accomplish this by the use of a mould wash for the anode moulds which is chosen not only from the standpoint of its ability to perform its usual functions of protecting the moulds and facilitating removal of the castings, but also with due regard to how any particles of the mould wash which adhere to the anodes are going to behave in the subsequent formation of the brittle cathodes in the electrolytic refining step. The mould wash, to be satisfactory for my purpose, should not only fulfill its usual purposes but it should also be capable of dissolving in the electrolyte used in the refining step, and it should not form insoluble compounds with the electrolyte. Substantially all of the mould wash particles adhering to the anodes will then be dissolved in the electrolyte during the refining step and will remain in solution and few, if any, will reach the cathodes to contaminate them. The mould wash should have a melting point above the temperature of the molten metal being cast in the mould and it should not form compounds or liquid solution with the molten metal being cast. Nor should it form compounds with the metal of the mould or otherwise detrimentally affect it. I have found that zinc oxide answers all of these requirements.

The moulds in which the copper anodes are cast may be of any appropriate metal but they are preferably made of refined copper. Unless the moulds are treated with a mould wash there would be a slight but accumulative corrosive and erosive action on the surface of the copper moulds due to the impingement of, and contact with, the molten copper being cast. To prolong their life, and to facilitate removal of the cast anodes from the moulds, the copper moulds are cooled by any suitable means between casts and the surface of each mould is treated before the next cast with a zinc oxide mould wash. The zinc oxide may be mixed with a suitable liquid, preferably water, and may be applied in the usual way as by spraying or brushing it on the surface of the mould. The copper to be refined, and converted into a brittle cathode, is cast into anodes in the moulds thus treated, and then the cast anodes are removed from the moulds and assembled in the electrolytic tank with the starting blanks or starting cathodes. The electrolyte may be a dilute solution of sulfuric acid. The refining operation is now started by passing an electric current through the electrolytic cell. Any mould wash particles which adhere to the copper anodes when they are removed from their moulds are dissolved in the electrolyte, at least to a substantial extent and remain in solution and very few, if any, of them ever reach the brittle cathodes to contaminate them. At the end of the refining operation, and before the next charge of anodes is placed in the electrolytic tank, any sediment in the bottom of the tank may be removed in the usual manner, together with any mould wash particles which may not have been dissolved and which have settled to the bottom of the tank.

The dissolving of the mould wash particles in the electrolyte before they have a chance to be caught by the numerous ledges and interstices of the rough brittle cathode, and their continuance in solution, prevents the cathode from being contaminated by them, or'by insoluble compounds formed from them, and the extruded articles will therefore be practically free from contamination either by particles of the mould wash, or particles of insoluble compounds. If the cathodes were of the usual tough dense type, and subsequently melted for further treatment, an opportunity would be afforded for slagging off in the melting furnace any insoluble mould wash particles that happen to reach the cathode and consequently would not appear in the cast articles to any large extent. However, in the process of making brittle cathodes. and converting them directly into articles by coalescence and extrusion no such opportunity is afforded as the metal is not melted at any stage of the process. It is, therefore, important in that type of process to provide for the elimination of the mould wash particles in some other way.

It will now be seen that my invention makes it possible to produce substantially pure brittle cathodes so far as contamination by mould wash particles is concerned. The other impurities are satisfactorily removed by the cleansing step which precedes the coalescence, and therefore the elimination of both sets of impurities makes it possible to produce substantially pure end products containing no mould Wash particles which, as above stated, are particularly objectionable where the brittle cathodes are coalesced and extruded into bars, rods or any shapes subsequently tobe fabricated into articles of small cross section, particularly into fine wire.

I claim:

1. A process of producing a metallic article which comprises treating a' mould with a zinc oxide mould wash, casting the metal from which L the article is to be formed into anode form in said treated mould, electrolytically producing a refined brittle cathode from the anode, and coalescing the brittle cathode and transforming it without melting into a merchantable shape by pressure, whereby the final article is substantially uncontaminated by impurities from the casting operation.

2. A process of producing a copper article which comp-rises treating a copper mould with a zinc oxide mould wash, casting copper from which the article is to be formed into anode form in said treated mould, electrolytically producing a refined brittle cathode from the anode, and coalescing the brittle cathode and transforming it without melting into a .merchantable shape by pressure, whereby the final article is substan tially uncontaminated by impurities from the casting operation.

JOHN TYSSOWSKI.