US 3300298 A
Description (OCR text may contain errors)
United States Patent 3,300,298 TRANSFER OF MOLTEN MAGNESIUM ALONG FERROUS METAL SURFACE WITHOUT HA- LIDE FLUX CREEPAGE John N. Reeling, Jr., Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Filed Jan. 9, 1963, Ser. No. 250,212
' 8 Claims. (Cl. 75-67) This invention relates to wetting of metal surfaces and more particularly concerns a method of rendering ferrous metal surfaces 'wettable by molten magnesium.
Ordinary nominally clean ferrous metal surfaces when placed in contact with molten magnesium are not wetted by the molten metal, that is, substanially no adhesion occurs between the magnesium and the ferrous surface. Further. when such as ferrous surface is in contact with both molten magnesium and molten flux it is preferentially wetted by the latter; a thin layer of the flux will, in a remarkably short time, creep along the entire ferrous surface completely covering it or that portion which is at a temperature above the melting point of the magnesium. Thus, if ferrous metal melt transferring devices such as, for example, dipping ladles, pumps and pipe lines, or open troughs are used to transfer molten magnesium, from a flux protected body thereof, and if the surfaces of said devices are only nominally clean, the surfaces which are in contact with the magnesium will become covered with flux, some of which will separate therefrom to contaminate the molten magnesium being transferred.
On the other hand, a clean oxide-free ferrous surface is preferentially wetted, either in or out of the presence of flux, by molten magnesium. However, even where the ferrous surface is initially clean, it oxidizes fairly rapidly when exposed to the atmosphere, and further, the heat of the molten magnesium body and preheating of the transfer device appreciably increases the rate of oxidation making it heretofore practically impossible to retain an oxide-free ferrous surface immediately preceding immersion of the ferrous article in the bath or the bringing together of the molten magnesium and the ferrous metal.
Reference throughout this specification to the term magnesium means magnesium in all commercial grades and the alloys thereof containing 50 percent or more magnesium. The term nominally clean as used herein refers to ferrous metal surfaces which are free from gross foreign matter such as mill scale, grease, oil and dirt but covered at least partially with an oxide, hydroxide, or other ferrous product of reaction with air (and other surrounding media). Also, reference to flux is to fusible halide salt mixtures commonly used in the operations of melting and refining magnesium.
An object of the invention is to provide a method of transferring molten magnesium free of flux contamination through creepage from a supply of said metal which is in contact with the flux.
Other objects and advantages of the invention will become apparent from the detailed description presented hereinafter.
In practicing the method of this invention, the ferrous metal device Which is intended to be used and whose surfaces, or a portion thereof, have been previously cleaned and adherently coated, such as, for example, by galvanizing or electroplating with a metal which is readily soluble in molten magnesium, for example, cadmium, copper, nickel, tin, or zinc is contacted with molten magnesium for a sufiiciently long duration to allow dissolution of the said coating metal so that 3,300,298 Patented Jan. 24, 1967 the underlying clean oxide-free 'ferrous surface is thereby exposed directly to the molten magnesium before the intervention of air, flux, or other contaminants. Dissolution of the coating metal'usually takes place within from about 5 to about 20 minutes after immersion. Initial wetting by magnesium of the coating metal is thereby accomplished, with continued preferential wetting on the exposed ferrous metal surface after dissolution of the coating metal. Since both the initial coated surface and the subsequently exposed ferrous surface are preferentially wetted by the molten magnesium, flux contamination through creepage along the interface between the molten magnesium and the adjacent ferrous metal surface is completely eliminated. When the ferrous metal device is removed from the molten magnesium, a wetting film of molten magnesium remains on the ferrous surface. On cooling, the magnesium film solidifies on the surface thereof providing a wettable and protective surface over the ferrous metal for subsequent use as in repeated exposure in molten magnesium.
It is understood that in certain cases, depending on the nature of the operation, such as, for example, transferring molten magnesium from a melting pot wherein the magnesium is covered with molten flux, using for example, a ferrous metal pipe to affect the transfer, not all of the ferrous metal surface which is intended to contact molten magnesium need be initially coated with one of the aforesaid metals in order to stop flux creepage along the ferrous surface at the interface between it and the molten magnesium; but rather, only a portion of such surface over which the molten magnesium may pass need be coated; for example, a portion as a band from about 3 inches to about 3 feet wide, said coated portion being located at a point between the supply reservoir containing molten magnesium and molten flux and the destination of the molten magnesium. The socoated portion provides a preferentially wettable surface by molten magnesium, with continued preferential wetting on the resulting clean exposed underlying ferrous surface after dissolution of the coating by the molten magnesium to form an interface of molten magnesium and the ferrous surface. Both the initial and final interface portion thus provided effectively act as a barrier to flux creepage due to preferential wetting thereon by magnesium rather than flux, thereby eliminating flux contamination in the molten magnesium being transferred.
Any ferrous metal device can be treated to accomplish preferential wetting by initially coating the suitably cleaned surface, or a selected portion thereof, with either cadmium, copper, nickel, tin, or zinc using a method such as, for example, galvanizing or electrodeposition whereby all or substantially all the iron oxides and other foreign material normally present on ferrous metal surfaces will be removed from said surfaces either before or during the coating operation such that no intermediate layer of oxide or other foreign material exists between the coating metal and ferrous metal in a quantity sufficient to prevent adherence of the coating metal. Of the coating metals set forth, zinc is to be preferred.
Preferential wetting by magnesium of zinc-coated surfaces, for example, rather than nominallyclean ferrous surfaces can be clearly illustrated by immersing two pieces of steel pipe, one having been galvanized, the other uncoated, but nominally clean, into a molten magnesium bath covered with a layer of flux. Upon withdrawing the two pieces, visual examination shows the galvanized piece to be covered with a film of magnesium, whereas the uncoated piece is covered with a layer of flux. A close study of the microstructure of the galvanized piece after an immersion of several minutes revealed no significant trace of zinc nor any flux.
The followin example further illustrates the application of the present invention.
Example A steel pipe galvanized both inside and out was, in conjunction with a pump, used to transfer molten magnesium from a melting pot in which the molten ma gnesiurn was covered with molten flux. The input end of the pipe when introduced into the metal was preferentially wetted by the molten magnesium and the magnesium transferred therethrough from the melting pot was found to be free of flux. Upon subsequent sectioning and eX- ami-nation of said so used pipe it was found to be free of flux illustrating that flux did not creep along any surfaces wetted by the magnesium.
In addition, an adherent, solidified wettable coating of magnesium was formed on both the inside and outside surface of the pipe which was in contact with the molten magnesium.
1. A method of preventing halide flux creepage along the interface between a ferrous metal surface and molten magnesium maintained under the protection of a molten halide flux which comprises, adherently coating :1 portion of said ferrous metal surface with a metal selected from a group consisting of cadmium, copper, nickel, tin and zinc, contacting the said molten magnesium with the so-coated portion of the ferrous metal surface, continuing said contact for a sufficient duration to dissolve the metallic coating on the so-coated portion thereby allowing the molten magnesium to make direct contact with the clean ferrous metal thereby establishing an interface along which the passage of flux is thereby prevented.
2. The method of claim 1 wherein the minimum distance across the coated portion of the ferrous metal surface is from 3 inches to about 3 feet.
3. A method of transferring molten magnesium from a halide flux protected body thereof contained in ferrous metal equipment without flux contamination through creepage along a ferrous metal surface of a melt-transferring device at the interface between it and the molten magnesium which comprises, contacting the molten magnesium of the flux protected body with the ferrous metal melt-transferring device, a portion of Whose surface, which is intended to form an interface with the molten magnesium having been initially adherently coated with a coating metal selected from the group consisting of cadmium, copper, nickel, tin and zinc, said coated portion being located between the supply of molten magnesium and the destination thereof so that all the magnesium passing from the flux protected body to the destination must traverse the coated portion, and continuing the contact of the molten magnesium with the said portion for a sufiicient duration to dissolve the adherent coating by moving the molten magnesium past the said portion toward its destination thereby allowing direct contact of molten magnesium with clean ferrous metal thereby exposed to the magnesium as the molten magnesium dissolves the coating metal, the direct contact so obtained preventing flux creepage and resulting contamination in the molten magnesium transferred.
4. The method of claim 3 wherein the ferrous metal melt-transferring device is a pipe.
5. The method of claim 4 wherein, the length of the coated portion of the ferrous metal pipe is from about 3 inches to about 3 feet.
6. The method of claim 3 wherein said portion of the ferrous metal melt-transferring device is initially coated with zinc.
7. The method of claim 3 wherein said portion of the ferrous metal melt-transferring devioe is initially coated with cadmium.
8. The method of claim 3 wherein said portion of the ferrous metal melt-transferring device is initially coated with tin.
References Cited by the Examiner UNITED STATES PATENTS 1,165,920 12/1915 Uyeno 11751 2,550,709 5/1951 Moe et al. 11752 2,912,346 11/1959 Kanter 1l751 2,935,421 5/1960 Chisholm 11752 ALFRED L. LEAVITT, Primary Exaimner.
JOSEPH B. SPENCER, RICHARD D. NEVIUS, I. R,
BATTEN, JR., Assistant Examiners.