US1220839A - Method of making furnace-hearths. - Google Patents

Description

J. H. GRAY.

METHOD OF MAKING FURNACE HEARTHS. APPLICATION HLED JAN-23.1914.

1,220,839 Patented Mar. 27, 1917. 1M1.

INVENTOI? Arm/awn UNITED s'ra'rns PATENT OFFICE.

JAMES H. GRAY, OF NEW YORK, NI Y.

METHOD OF'MAKING rnnnaon-nnanrns.

To all whom it may concern:

Be it known that 1, JAMES H. GRAY, a citizen of the United States, residing in the city, county, and State of New York, have invented certain new and useful improvements in Methods of Making Furnace- Hearths, of which the following is a specification.

This invention relates to the making of liearths or bottoms ofiametallurgical furnace, and especially of an are electric furnace of the type used in making and. refining steel, such for example as the Heroult arc furnace. The invention is especiallyapplicable to electric furnaces because such furnaces are provided with the necessary electrical equipment. But it will be understood that non-electric furnaces may be provided with bottoms or hearths in accordance with this invention by providinga special electrical equipment for the purpose.

- The customary method of maki'ng the hearths of electric furnaces at present is to ram in cold a complete bottom of magnesia upon themetal shell of the furnace, with tar or pitch as a binder, to introduce a layer of coke upon the rammed layer of magnesia and to lower the electrodes to the bed of coke and start the current. The current flows through the coke and brings the latter to incandescence and brings the inside of the furnace to a white heat. This accomplishes the burning in or fritting of the hearth.

But the high temperature necessary for such fritting penetrates to a depth bf only a few inches, leaving the lower part of the magnesia bottom still in granular condition so that when the furnace is operated and the molten-material wears or breaks through the fritted surface it works into the granular material and destroys the hearth.

By the present invention 1 secure a hearth which is practically monolithic, and which is thoroughly burned in or fritted throughout its depth and which can be made quickly and economically. By my improved method the material is introduced into place in a molten or semi-molten, condition progressively and continuously from the bottom to the top. I have found that magnesia and similar materials used for the making of furnace hearths are pyro-conductors,that is they are good conductors of electricity at high temperatures, above a red heat for example, and I utilize this property of the Specification of Letters Patent.

Patented Mar. 27, 31917.

Application filed January 23, 1914. Serial No. 813,894.

material to pass a current of electricity through it and to bring it to a molten or semi-molten condition, in which condition it is shaped and built up to the desired depth,

after which upon a slight lowering of the temperature it becomes solid.

An example of my process is as follows, supposing it desired .to make a hearth of magnesia or calcined magnesite in a Heroult electric furnace. This type of furnace comprises two or more electrodes which are lowcred nearly to the surface of the steel or 7 other bath and the current passes from one. electrode into the steel bath and thence to the other electrode. I first place a layer of magnesia bricks on the bottom of the shell of thefurnace and then place a layer 'of granular magnesia one or two inches thick on the bricks. I then heat the furnace and the magnesia to such a temperature that the latter becomes a good conductor of elec tricity.

This may be done in any one of severalways. For example, a flame furnished by fuel oil may be introduced into the furnace, or a bed of coke may be laid on the magnesia and the electric current passed through the coke from the electrodes in the, manner above described-to heatl the same to incandescence, or lengths of electrodes may be laid on the bottom;- and the regular electrodes lowered to strike arcs therewith and to pass'an incandescing current through these special lengths. Any one of these methods will bring themainelectrodes to a White heat and will furnish sufficient heat in the furnace to bring the magnesia to a temperature at which it becomes a sufficiently good conductor of electricity.

hen this temperature is reached the electrodes are lowered to the bottom of the furnace (removing any coke or similar material which may have been introduced for the initial heating) and arcs are struck between the electrodes and'the now conductive magnesia. The arcs and the current passing through the magnesia increase its temperature until it becomes molten or semi-molten or pasty. When this condition has beemobtained more magnesia in granular form is introduced about the electrodes and this in turn becomes conductive as it receives heat both from the electric arcs and from the heated walls and atmosphere of the furnace.

As the material banked about the electrodes 110 becomes conductive the electrodes are gradually raised so as to maintain the necessary resistance at the arcs for the desired number of amperes of current to flow through the electrodes, the raising of the electrodes being accomplished either by hand or by automatic' regulators such as are now generally employed for regulating the height of electrodes in such furnaces. The hearth is thus built. up to the desired depth and shape in a sound and reliable monolith, by throwing in new material progressively at such points as may need building up.

Certain forms of magnesia, on account of their extreme purity, may be more refractory than is desired. Tn such ease I mix with the magnesia one or more less refractory materials, such for example as dolomite, basic openhearth slag, blast furnace slag, etc. These materials facilitate the bringing of the magnesia to a pasty condition, but do not detract from the serviceability of the hearth at the temperatures at which it is used. For furnaces intended to be used with lower.temperatures materials or mixtures may be used for the hearth which are more easily fusible or reducible to a pasty condition than for furnaces which are to be used at higher temperatures.

The hearths of metallurgical furnaces, and especially electric furnaces used in metallurgy, are nearly always made of magnesia or of mixtures containing a large percentage of magnesia, and the present'invention is aimed chiefly at the making of hearths of this material quickly, cheaply and of the best quality.

i The previous process above described of making hearths of electric furnaces pro- .duces an inferior hearth as compared with my invention, costs very much more and requires forty-eight or more hours where my process requires only ten or twelve hours. Tn open-hearth furnaces the hearths are sometimes made by laying in successive thin layers ofmagnesia and fritting them in succession by a flame. \Vhile this produces a good hearth it requires from one to two Weeks depending upon the size of the furnace, Where the same hearth could be put in by my process in about twelve hours, and

the cost in each case is proportional to the. length of time required.

lln certain are electric furnaces, of the Heroult type for example. the current passes through one electrode into the bath or mass of conductive material and out through another electrode, the two electrodes or various groups of electrodes being in series. lln certain other are electric furnaces the current passes from the electrodes through the naaoeee furnace in which the current can be passed through the mate ial of which the hearth is to be formed in sufficient intensity and volume to reduce it to a condition in which it can be moldedto the desired shape.

The accompanying drawings illustrate the )rocess dia rannnaticall Fi ures 1. 2 and Z7 7 D I this base to form a path for the current at starting, its ends coming under the electrodes F so that when the current is switched on arcs G are formed by the current passing from ,one. vertical electrode to the other through the intermediate path E. This condition is maintained until the interior of the furnace is at a white hot temperature. The operators then, with shovels, throw in the magnesia through doors H, placing it first in the corners to form fillets J. The heat is so great that this magnesia, as well as the layer D, is softened to a pasty condition and welded into an integral mass. The operators soon become expert in placing it so as to build the hearth up to the desired shape. When the condition of Fig. 1 is reached the current is turned oil and the carbon rod E with its supporting blocks are removed and the elec trodes lowered to strike arcs directlywith the molded mass of magnesia, which is now so hot that it furnishes a good conductor from one arc over to the other. Further material is thrown in as before and built I up 'iirthe manner of Fig. 2. As the material is built up sufficiently to shorten the arcs tegral hearth K, Fig. 2. The heat immediately adjacent to. the arcs is sufficient to form small pools L of magnesite in liquid condition, but it isso refractory that the liquid condition does not extend far from the arc. Fresh granular magnesite is thrown in around the arcs as indicated roughly at M. These, being comparatively cold, are nonconductive and do not at first affect the operation. But as they become heated and conductive the automatic regulating mechanism lifts the electrodes farther; and so the process continues. Finally the operators cease to throw fresh magnesia about the electrodes and the electrod s remain stationary with arcs G between their lower ends and a completely formed hearth N (Fig. 8). Holes or superficial irregularities are remedied by the operators throwing loose magnesia on them, which becomes pasty and suf- 13o ficiently smooth so that in the end a practically perfect hearth is obtained.

Though I have described with great particularity of detail certain specific embodiments of my invention, yet it is not to be understood therefrom that the invention is limited to the particular embodiments disclosed. Various modifications thereof may be made by those skilled in the art without departing from the invention.

What I claim is:

1. The method of making furnace hearths of pyro-conductive material which consists in introducing the material into place, heating the same to the temperature at which it becomes conductive, forming an electric are from an electrode to said material, heating the same by said are to the necessary pasty Copies of this patent may be obtained for condition and building up the same in plac while in such pasty condition.

2. The method of making furnace hearths of magnesia or the like, which consists in introducing the material into place, heating the same to the temperature at which it becomes conductive, forming an electric are from an electrode to said material, heating the same by said are to the necessary pasty condition and building up the same in place while in such pasty condition.

In witness. whereof, I have hereunto signed my name in the presence of two subscribing witnesses,

JAMES H. GRAY. Witnesses D. -ANTHONY Usma, LULU STUBENVOLL.

five cents each, by addressing the Commissioner of Patents. wuhingtolm. G."

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