US2208242A - Method of melting magnesium and magnesium base alloys in induction furnaces - Google Patents

Description

Q Patented July 16, 1940? METHOD OF MELTING MAGNESIUM AND MAGNESIUMBASE ALLOYS IN INDUCTION FURNACES Adolf Beck, Herman Schunck, and Giinther Ostermann, Bitterfeld, Germany, anignors, by memo assignments, to Magnesium Development FFICE' Corporation, a corporation of Delaware No Drawing.

Ap lloation April 18, 1989, Serial Germany April 21, 1988 3 Claims. (CL 75-10) This invention relates to the melting of magnesium and magnesium base alloys in induction furnaces.

When using induction furnaces for meltin g metals and alloys, the composition of the lining of the furnace should be such that the constituents of the lining do not react with the metals and alloys and thus contaminate the latter.

, Moreover, since the dimensions of the lining genm orally render it impracticable to bake the lining before putting the furnace into operation, it is usual to bake or sinter the linings in situ by the actual melting of the metal in the furnace. In

order to be able to do this it is impracticable to lb provide a lining consisting of pure oxides such as al or magnesia which only sinter at very high temperatures, but a lining of the kind comprising mixtures of these oxides with silica maybe used, these mixtures baking or sinterm ing at the usual melting temperature of the metals or in the case of relatively low melting aluminium, only moderately above the melting point. If desired. such mixtures may also contain oxides of the alkali metals or of the heavy metals.

Hitherto it was considered impossible to use lining compositions which can be baked or sintered in situ at low temperatures in induction furnaces for melting magnesium and magnesium a. base alloys. since experience has taught that molten magnesium reacts violently with the silica of the lining. even when it is present in the form of silicate. This reaction leads to rapid destruction of the lining, despite the relatively short a duration of the melting operation, and considerable quantities of silica are taken up by the metal and adversely afiectJts mechanical properties.

It has now been ascertained that when melt- 50 section of the lining in course of time and that the depth of that portion of the lining which is practically free from silica canrwith sumcient duration of treatment. attain about 8 cms. In this manner a lining is formed which comprises an outer portion which has not been aflected by ing aluminium or aluminium base alloys in inthe foregoing reaction and thus still contains the original quantity of silica and which has become sintered to a rigid mass, and an inner portion which is practically free from silica, which latter has been replaced by alumina. 6

Based onthe foregoing observations the present invention provides a method of melting magnesium and magnesium base alloys in induction furnaces lined with a siliceous lining of the kind hereinbefore set forth. which consists in previ- 1 ously conditioning the lining of the induction furnaces by subjecting that portion of the lining which is liable to react with the magnesium or magnesium base alloy to a treatment with molten aluminium or aluminium base alloy for the purpose of removing silica from said portion and thereafter melting the magnesium or magnesium base alloy in the thus conditioned furnace.

By virtue of this conditioning of the furnace lining by the removal of the silica from that portion of the lining which comes into contact with the molten magnesium or magnesium base alloy, any reaction between the magnesium and the lining is precluded. 5

Since the replacement of silica by alumina 'in the lining can be considerably accelerated by the use of high temperatures, it is preferable to prepare the induction furnace for the subsequent melting of magnesium or magnesium base alloy by melting a single charge of aluminium or aluminium base alloy at a temperature substantially above the otherwise usual temperature and maintaining said charge at that temperature in the furnace until the portion of lining poor in silica i has reached the desired depth. For example, in the base of a furnace having a capacity of about 1000 kgs. of aluminium. corresponding to approximately 660 kgs. of magnesium, and a lining of a. total thickness of 15 cms.. a charge consisting of 1000kgs. of aluminium is maintained in the furnace at a temperature of about 1000 C. for a period of about 24 hours in order to produce a zone of lining poor in silica of an average depth of 6 cm. I

It is also possible to condition the furnace for the melting of magnesium and magnesium base alloys by treating a succession of charges of aluminiumor aluminium alloys therein for the 60 usual melting period and at the usual melting temperatures, in which case of course, the percentsge silicon content of the aluminium established by absorption from the lining. is correspondingly reduced. amounting to the order of u silica, which consists in first conditioning the lining of the induction furnaces by exposing that portion of the lining which is liable to react with the magnesium, to contact with molten aluminium in such a manner as to remove the silica from said portion, and thereafter melting magnesium in the thus conditioned furnace.

2. A method of melting magnesium in induction furnaces provided with a lining containing silica which consists in first conditioning the lining of the induction furnaces by maintaining molten aluminium in contact with the inner furnace walls for such periods of time and at 'such temperatures as are required to remove .silica from that portion of the furnace lining which is liable to react with magnesium, the heat for maintaining such aluminium at the proper temperatures being supplied by induction, and thereafter melting magnesium in the thus conditioned furnace.

3. A method of melting magnesium in induction furnaces provided with a lining containing silica, which consists in melting a batch of aluminium in the furnace and maintaining such batch at a temperature of about 1000 C. until the silica is removed from that portion of the furnace lining which is liable to react with magnesium, thereafter discharging the aluminium from the furnace, and melting magnesium in the thus conditioned furnace.

ADOLF BECK. HERMAN SCHUNCK. GUNTHER OSTERMANN.