US1226122A - Electric furnace and method of producing molten magnetite therein. - Google Patents

Description

A. P. SCOTT.

E LECTRIC FURNACE AND METHUD 0F PRODUCING MOLTEN MAGNETITE THEHEIN.

vAPPLICATION FILED NDV.` 17.19l5.

Patented May15,r1917.

IN VEN TOR A TTORNEYS ARTHUR P. SCOTT, OF CHICAGO, ILLINOIS, ASSIGNOR To CHILE ExrLonArIoN com- .'PANY, 0F NEW YORK, N. Y., A CORPORATION O F NEW JERSEY.

ELECTRIC FUBNACE AND METHOD OF PRODUCING MOLTEN MAGNETITE THEBEIN.

Specioation of Letters Patent.

Patented May 15, 191'?.

Application led November 17, 1915. Serial No. 61,905.

To all whom z't may concern.'

Be it known that I, ARTHUR P. Soo'rr, a subject ofthe King of Great Britain, residing at Chicago, county of Cook= and State of Illinois, have invented certain new and useful Improvements in Electric Furnaces and Methods ,of Producing Molten Magnetite Therein; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same. l

This invention relates to improvements in single phase alternating current electric furnaces of the direct are type, and particularly to furnaces for the melting of iron ore and the production of molten magnetite therefrom; and to methods of producing a protective layer of magnetite, and molten magnetite, therein.

In furnaces of this type, whenI utilized for melting ore, (purple ore or leached Rio Tinto cinder), it has been found that the arc tends to melt principally downward and with very little lateral fusion, and that the bath thus tends to assume the form of a deep well of small cross section instead of the usual shallow basin. Inorder toprotect the bottom contact from overheating and injury during this melting process, the *furnace bottom is provided, according'to the present invention, lwith a protective layer of solid magnetite above the bottom contact. While the ore itself is a non-conductor, it

becomes a good conductor when molten andV cast, so that the protective layer itself forms the bottom electrode.

A furnace embodying the invention and illustrative thereof is shown in the .accompanylng drawings in central vertical sectlon.

The furnace illustrated is of lthe tilting type and is provided withsuitable means (not shown) for rocking or tilting it into the position shown in dotted lines. The furnace is constructed of appropriate refractory materiali within an outer casing and is provided with a top 2, and bottomrocker supports 8 mounted upon the foundation 4.

The upper graphite electrode is indicated at 5, carriedby an arm 6. This arm is adjustable in the vertical support 7 by means of suitable adjusting or operating mechanism 8. The bottom contact is indicated at 10 and the lateral opening in the furnace, by means of which access to, at 1l. Above the bottom steel contact, and formmg a bottom protective layer, is the cast layer ofmagnetite 9. v

In the production of. molten is essential that the furnace lining be of a basic nature. In practice this lining is made of magnesite. A mixture of the magnesite with pitchis tamped into the shell around a wooden form. After removing the form, the pitch is removed,'as by a slow coke fire, and the furnace is ready for operation.

In starting the furnace and producing the layer of magnetite, the ore (e. g. purple ore or leached Rio Tinto cinder) in suitableamount is piled up around the sides of the hearth to allow the upper graphite electrode to pass through and make contact with the bottom steel electrode. This is necessary because of the non-conducting character of the raw ore. After the electric current has been turned on, the upper' graphite electrode is lowered into contact with the bottom to make the arc and-then gradually raised.

As fast as the material below the arc is melted, fresh ore is rabbled down from the sides with a Wooden pole to prevent the bottom contact frombeing eaten away b the molten magnetite. As soon as a su cient quantity of pasty material has accumulated below rabbling is stopped and the current left. on for five or ten minutes to allow the melt to become fluid and clear. cut oil and the furnace allowed to cool for arsuitable period of time g. three or four hours) to permit the bottom to set. The operation is repeated until the magnetite bot.-

may be had theremagnetite ity The current is thenl the arc (e. gfabout half an hour), the l tom has attained a suiiicient thickness for use in the normal melting operation, and the furnace is then allowed to remain inactive for a further period of time, say over night. f

Because of the tendency of the arc to melt principally downward, and with little lateral fusion, and of the-resultin tendency of the bath to assume the form o a deep well of small cross section instead of the usual shallow basin, it has been found that the magnetite bottom immediately below the electrode was frequently penetrated, making it necessary to suspend o erations or even to build up an entire new Aottom.

It has been found, however, that this diiiculty can be readily overcome by the addition of broken magnetite electrode scrap. This scrap, when added to the bath, is but slowly absorbed, the raw ore going into solution, or becoming molten, much more readily. This scrap settles to the bottom of the bath, and where raw ore is added from time to time remains practically unattacked.

Accordingly, when the magnetite bottom has become penetrated and needs repairing, or to prevent danger-:of such penetra-tion,

the magnetite scrap is added. It .may thus form a layer at the bottom of the molten ore and above the protective laver of'magnetite, `or it maybe or become 'incorporated in this protective layer itself.

The roof of the furnace can be made of.

basic material, or even of silica brick, the silica remaining practically unaffected. It tends to.sla with the"'ore whenthe latter is accidenta y brought into contact. with it,-

but as this can readily be avoided the'tend enc isvnegligiblel A fter the protective layer of magnetite has been formed the furnace Vis ready for use inthe normal operation of melting the ore for the production of magnetite suitable for casting purposes, 4e.' g. for casting electrodes.

.In the normalv meltm operation, the graphite electrode Vis first owered into contact with themagnetite bottom, a suitable charge of the ore isV thrown in around the electrode, and the electrode gradually raised as fast as the ore near the arc is melted and becomes conducting. At the same time the i bath of suiiicient outlying portions of the charge around the periphery of the hearth are gradually poled down into the zone of4 fusion. When the bath has become .clear and fluid and of a pro er temperature, it is ready for pourin efore pouring, and after the clear uigd guantity has accumulated, lit is -in practice a vantageous to add a further small portion of the ore and to pour the molten ore as soon as this added portion has been absorbed. This final addition serves both as a temperature check and to limit the formation of an excess of ferrous oxid. The temperature of the ore when cast is about 1590 C.

The method of casting the electrodos after a suitable bath has been produced forms the subject-matter of a companion application, Serial No. 61,904, filed November 17, 1915. lFrom the above description it will be seen that the magnetite bottom not only protects the magnesite lining from the dlrect heat of the arc, but it takes the place of the steel bottom contact preventin excessive corrosion at this point and itse f forming the lower electrode. It will further be seen that by the simple expedient of adding cast magnetite electrode scrap to the bath, or incorporating it in the bottom protective layer, the magnetite layer is itself preserved and protected from overheating and penetration. I

What I claim is:

1. An electric furnace of the direct arc type provided with a bottom protective conducting layer of mhgnetite; substantially as described.

'2. An electric furnace of the direct are type provided with a lower xed contact and an upper movable electrode, and with a protective conducting layer of magnet-ite overlying said bottom contact and forming the bottom electrode; substantially as described.

3. An electric furnace of the direct `arc type provided with a bottom protective conducting layer of magnetite with which cast magnetite scrap is incorporated; substanti ally as described.

4.-- An electric furnace of the direct arc type provided. with a lower fixed contact and an upper movable electrode, and with a protective conducting layer of magnetite Aoverlying said bottom contact and forming lthe bottom electrode, said layer of. magnetite having cast magneti-te scrap incorporated therewith.; substantially as described.

-5. A single phase alternating current electric furnace ofthe direct arc type provided with aflower fixed electrode and an upper movable electrode, and with a protectivevconducting layer of magnetite overlying electric'arc furnace to produce a duid body of the magnetite, allowingl said body to set to form a bottom protective layer, and pro tecting the bottom contact by such protective layer during the subsequent melting of further portions of ore; substantially as described. y n

'8. In a method of producing molten magnetite, melting the ore between the up er and lower electrodes of an electric arc urnace'to produce a fluid bodyr of magnetite,' allowing such body to set, and melting fur.

ther amount of ore above said protective l layer of magnetite to produce further amounts of fluid magnetite, and permitting said further amounts of magnetite to 'set to form a" bottom protective layer of suitable thickness substantially as described.

ture. 4

ARTHUR P. SCOTT.

In testlmony whereof I aix my signan

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