US2378699A - Protection of molten magnesium and magnesium-base alloys - Google Patents

Description

Patented June 19, 1945 UNITED STATES.

PATENT OFFICE 2,378,699 PROTECTION OF MOLTEN MAGNESIUM AND MAGNESIUM-BASE armors George F. Gunn, Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich, a corporation of Michigan No Drawing. Application January is, 1941,

Serial No. 374,769

Claims. 21. 22-200) ml is disadvantageous, however, in that frequently violent chemical reaction occurs between the metal and the sulfur, with consequent sputter-- the'metal-for a long period of time. I e protective layer is mobile, and may be parted for stirring or pouring, and then moved back into position after such operation is completed.

as stated, the heat-insulating substance which constitutes the major proportion of the composition should be a loose mass of sigh divided material which does not tend to stick together or form a,

crust on heating, and is preferably in fibrous or granular form. (In general. siliceous materials, themagnesium.

.. especially fibrous siliceous minerals, are the most satisfactory, asbestos, preferably when fiuil'y, rock wool, glass wool, and exploded mica being commonly used.' The gas-forming protective substance in the composition is usually a solid in finely-divided form, powdered sulfur being ordinarily employed, although boric acid .or borates, and borofluorides, or mixtures thereof with sulfur are likewise operable. Certain liquids, such as glycerin and other polyhydric alcohols, which liberate protective vapors on heating, may also be used.

In practice the heat-insulating substance and a minor proportion of the protective material,

ing, minor flames, and loss. An alternative procommonly 3 to 10 per cent by weight, are mixed cedure has'been to cover the metal with a protogether, either by hand or by machinery, orditective crust, such as a metal fluoride, and then ly l t P i to se, and he r sulting mass is to strew sulfur on the c t. This method likespread on the metal to be protected, usually as wise is not overly satis tory from a practical a layer or mat one-half to one-and one-half viewpoint, in that two procedural steps are ininches thick. If desired, further gas-forming provolved instead of one, and in that the crust, once tective material may later be sprinkled upon the broken, as by stirring, pouring, or shrinking of insulating layer to replace that consumed during the metal, cannot easily be repaired, but must be use. V wholly replaced. The composition of the invention is particu- An object of the present invention, then, is to l ly nvenient for use in preparing castings provide an effective means for protecting readily from l ic m n i m and m nesiumse oxidizable metals against atmospheric attack alloys. In this case, the air in the casting mold which is extremely simple and yet which avoids is first displaced with a gas nod-oxidizing t the difficulties mentioned. v nesium, and the molten metal is poured into the These objects are attained in the composition mold. All exposed surfaces of the metal in the of th invention, whic consists ntiall f a, filled mold are then covered with a layer of the loose mass ofa subdivided noncohesible thermocomposition, e. g. a mixture of loose flufly asbesstable heat-insulating substance, such as asbestos, his and sulfur. The sulfur burns slowly to sulfur which has an apparent specific gravity lower than dioxide which protects the metal against oxidathat of the metal to b protected a i uh ta tion, while the asbestos prevents too rapid cooltially inert chemically thereto, and having adm of the top of the vcasting. th acting s a mixed therewith a minor proportion of a prohot top" and minimizing piping. If desired, tective substance, such as sulfur, which when after cooling, the asbestos layer may be parted, heated in air liberates a gas non-oxidizing toward and additional molten ma nesium poured into the metal. In use, the composition is strewed on 40 the mold to fill Shrinkage IOSSeS-v Wh n fully top of the molten metal in such manner as to solidified, the casting is removed'from the mold, cover the exposed surfaces thereof.' The asbestos y asbestos lin ing thereto bein brushed oil or like material serves as thermal-insulation, and and saved for re-use. x 'the sulfur or other agent evolves-a protective gas I claim:

at low rate, efl'ectlvely preventing oxidation of 1. A composition for protecting surfaces of molten magnesium and magesium-base. alloys against burning which consists essentially of a loose mass of a subdivided noncohesjrble thermostable heat insulating siliceous material which has an apparent speciflcgravitylower than that of the metal and is substantially inert chemically thereto, having admixed therewith a minor proportion of a finely-divided substance which when heated in air liberates a gas non-oxidizing toward 2. A composition according to claim 1 wherein the siliceous material is a fibrous mineral.

3. A composition according to claim 1 wherein the siliceous material is asbestos.

4. A composition according to claim 1 wherein the siliceous material is rock wool. N 5. a composition according to claim 1 wherein the siliceous material is eiploded iiiioa.

6. Afcomposition ior protecting surfaces oi --molten magnesium and magnesium-base alloys against burning which consists essentially oi loose fiufly asbestos having admixed therewith a small proportion '01 finely-divided sulfur.

7. A method of protecting the surfaces of molten bodies of masn'esiu'm and magesium-base alloys which comprises covering the surface with a protective layer consisting essentially-oi a loose mass of a subdivided noncohesible thermostable heat-insulating siliceous substance having an apparent specific gravity lower than thesaid metal, and being substantially inert chemically thereto, having admixed therewith a minor proportion oi a finely-divided substance which when heated iriair-liberates a gas non-oxidizing toward the metal. Y

a; A method or motectins the surfaces or metal and being substantially inert checally thereto, and having admixed therewith a minor Proportion of finely-divided suliur.

" eixmetnoaofpro'tectingi e p swam-oi molten magnesium and magesium-base alloys against oxidation which comprises covering the surface with protective layer consisting essentially of loose flufly; asbestos having aueol "therewith aminor proportion of finely-divided sulfur.

10. In amethod of preparing case from the steps which comprise: displacing the air in a casting mold with a gas non-oxidizing to magnesium, pouring the molten metal into the mold, covering the exposed surfaces or the metal in the filled mold with a protective layer consisting essentially oi! a mixture of loose flufly astos molten bodies or magsium and masesium-base alloys which comprises eoverins the surface with andca small proportion of finely-divided sulfur, allowing the metal to solidify while thus covered, and removing the casting so formed from the mold. v

' GEORGE F. G,