US2459256A - Desulfurizing molten ferrous metal - Google Patents

Description

Jan. 18, 1949. F. w. WHITE ET AL DESULFURIZING MOLTEN FERROUS METAL Filed Jan. 11, 1947 Patented Jan. 18, 1949 UNITED STATES PATENT OFFICE 2,659,258 DESULFURIZING MOLTEN FERROUS METAL Application January 11, 1947, Serial No. 721,659

4 Claims. 1

This invention relates to desulphurizing molten ferrous metal. It relates particularly to the desulphurizing of molten ferrous metal when it is desired that the desulphurized metal shall be uniform as to sulphur content and that the sulphur content shall be relatively low.

Desulphurized molten ferrous metal which is uniform as to sulphur content and in which the sulphur content is quite low is in demand for various uses. One such use is the admixture of the desulphurized molten ferrous metal with molten iron silicate slag to form by the Aston process wrought iron sponge balls which are ultimately worked into wrought iron products. If the metal is not uniform as to sulphur content the resultant wrought iron is non-uniform and in particular cases may not meet specifications or may be unsuited for the use for which it is intended. If the sulphur content is not uniformly desirably low in metal for use in the manufacture of wrought iron by the Aston process which is to be used for certain purposes, as, for example, stay bolts, the wrought iron may not meet specifications and may be otherwise unsatisfactory.

The sulphur content of the metal also constitutes a limiting factor with respect to the temperature at which wrought iron made by use of the metal may be rolled. For reasons well known to those skilled in the art it is desirable to effect at least part of the rolling at relatively low tem- 30 perature. If the rolling procedure is established for a certain desirably low finishing temperature and particular billets of wrought iron have a sulphur content higher than the sulphur content compatible with the particular finishing temperature being employed defective rolling may and probably will result.

Heretofore it has not always been possible to produce molten ferrous metal for use in the manufacture of wrought iron by the Aston process which had desirably low sulphur content. Very low sulphur ferrous metal could not be obtained when the sulphur content of the metal prior to 'desulphurizing and refining was higher than usual. It is customary in" producing molten fer-' rous metal for the manufacture of wrought iron by the Aston process to melt the metal in cupolas. When the sulphur content of the molten metal as tapped from the cupolas was unusually high this relatively high sulphur content carried through the desulphurization step and the refining (e. g., Bessemerizing) step, the result being wrought iron of undesirably high sulphur content which might not meet specifications or be suited to particular intended uses or which might not roll satisfactorily at particular rolling temperatures being employ It is common to desulphurizemolten ferrous metal by admixing the molten ferrous metal with a molten desulphurizer, such, for example, as caustic soda or soda ash. The admixing is customarily effected by pouring the molten metal into the molten desulphurizer which is maintained in a receptacle. The sulphur in the metal and the desulphurizer react in known manner so that the sulphur content of the metal is reduced, the desulphurizer, being of relatively low specific gravityas compared with the metal, forming as a slag on top of the metal and carrying with it the sulphur extracted from the metal. The metal and the slag are separated either by decanting oil the slag or by withdrawing the metal from beneath the slag.

It has heretofore been proposed to maintain a quantity of molten desulphurizer or desulphurizing slag and successively pour batches of molten ferrous metal to be desulphurized into the slag, replenishing the slag from time to time with new desulphurizer in solid form. The introduction into the ladle containing the molten desulphurizer of replenishing desulphurizer in solid form results in foaming of the slag. Sometimes the slag eflervesces so that it overflows the receptacle. It has not been possible by the procedure mentioned to obtain uniformly desirably low sulphur content in batches of molten ferrous metal.

We have discovered that eflicient desulphurization is interfered with by foam in the desulphurizing ladle. when the metal is poured into and through a foamy desulphurizing slag the slag apparently does not have suilicient body to cause the metal as it strikes and passes through the slag to break up into relatively small particles which can efl'ectively react with the slag. The desul- '40 phurizing reaction is an interface reaction and its --eiiiciency is dependent upon intimate contact small particles of metal with the slag. We have found that desirably intimate contact does not take place when the desulphurizing slag is foamy.

The principal cause of foam in the desulphurizin'g slag is the driving oi! of water of crystalliza- A tion in the replenishing desulphurizer which is introduced in solid form. The water of crystallization forms steam which creates an ebullience in the slag resulting in the undesirable foamy condition above described.

We have discovered that if the addition of solid replenishing desulphurizer to the molten desulphurizer in the desulphurizing ladle is avoided the 5 undesirable foamy condition of the molten desulphurizing slag is likewise avoided. By avoidin adding solid replenishing desulphurizer to the molten desulphurizer in the desulphuriaing ladle we can maintain a relatively thick homogeneous slag of relatively high specific gravity which very effectively and uniformly desulphurizes the metal. bringing about results not previously obtainable.

We obviate undesirable foaming of the desulphurlzing slag by melting the replenishing desulphurizer before it is introduced into the dean!- phurizing ladle. If the water of crystallization has been driven ofi by melting of the replenishing desulphurizer before it meets the main body of molten desulphurizer in the desulphurizlng ladle there is very little ebullience or foaming and the slag possesses the desirable characteristics above mentioned.

The replenishing desulphurizer may be premelted in various ways, for example, in a separate furnace provided for that purpose or by the heat of the molten ferrous metal which is to be desulphurized. In one manner of procedure the replenishing desulphurizer may be admixed with the molten ferrous metal which is to be desulphurized before that molten ferrous metal has been admixed with the main body of molten desulphurizing slag. A limited amount of foaming occurs when the solid replenishing desulphurizer is admixed with the molten ferrous metal but the foaming is not excessive because the replenishing desulphurizer is of relatively limited mass and is segregated from the main body of molten desulphurizer in the desulphurizing ladle.

We preferably melt ferrous metal in cupolas and tap the cupolas into a tapping ladle. At the beginning of tapping the tapping ladle is preferably empty. During tapping the solid replenishing desulphurizer may be thrown into the tapping ladle where it is melted by the heat of the molten metal. The quantity of replenishing desulphurizer is small compared with the quantity of desulphurizer in the main body of molten desulphurizer in the desulphurizing ladle. For example, for each heat of 27,000 pounds of molten ferrous metal from one hundred to four hundred pounds of solid replenishing desulphurizer may be thrown into the tapping ladle during tapping of the metal from the cupolas.

When the replenishing desulphurizer is all or substantially all melted in the tapping ladle and the tapping for that heat has been concluded the contents of the tapping ladle are poured into the desulphurizing ladle which contains the main body of molten desulphurizing slag which is maintained in the desulphurizing ladle. The contents of the tapping ladle are poured into the desulphurizing ladle slowly and preferably in a stream which has considerable area so that an opportunity for the metal to break up into small particles as it passes into and through the dew]- phurizing slag is afforded. The desulphurizing slag is desirably of considerable depth, as, for example, 12 to 18 inches. The desulphurizlng ladle is preferably a ladle of the hooded type having 'a pouring orifice below its top.

As each batch of molten metal with the relatively small amount of replenishing desulphurizer admixed with it is poured into the desulphurizing ladle the level of the molten contents of the desulphurizing ladle rises until some of the slas. which because of its lower specific gravity rises to the top, may pass out or be discharged through the pouring orifice of the ladle. Preferably the mass of the thus discharged slag is substantially equal to the mass of the replenishing desulphurizer which is thrown into the tapping ladle as above described. Thus at each heat a predetermined mass, say 300 pounds, of replenishin desulphurizer may be added in the tappin ladle and a substantially equal mass of spent desulphurlzin slag discharged through the pouring orifice of the desulphul'izing ladle while the contents of the tapping ladle are being poured into the desulphurizing ladle. The discharge of the spent slag in this manner of procedure is autm matic and the mass of slag discharged will always be substantially the same as the mass of the replenishing desulphurizer added in the tapping ladle since the mass of molten metal poured out of the desulphurizlng ladle after desulphurization therein is substantially equal to the mass of metal poured into that ladle.

As an alternative procedure, instead of causing a portion of the spent desulphurizing slag to be discharged through the pouring orifice of the desulphurizing ladle in each cycle of operation as above described, the surface of the desulphurizing slag may be maintained normally well below the pouring orifice of the desulphurizing ladle so that spent desulphurizing slag will not be automatically discharged through the pouring orifice. At desired intervals spent desulphurizing slag may be discharged from the pouring orifice of the desulphurizing ladle by tilting the desulphurizin ladle to pour out a desired quantity of spent desulphurizing slag. This may be done in each cycle of operation or it may be done less often than in each cycle of operation, as, for example, in each third or fourth cycle.

After the contents of the tappin ladle have been poured into the desulphurizlng ladle as above explained the desulphurizing ladle is picked up by an overhead crane, moved to a position above a transfer ladle and tilted to pour out the desulphurized metal into the transfer ladle, the desulphurizing slag being retained in the desul' phurizing ladle. This is accomplished by initially rapidly tilting the desulphurizing ladle so that the slag which floats on top of the metal passes quickly past the pouring orifice of the ladle so that a negligible amount of slag passes out through the pouring orifice before pouring of the desulphurized metal begins. Desirably the mass of metal poured into the desulphurlzing ladle has previously been ascertained and the transfer ladle is disposed on a scale and the pouring is stopped when the mass of desulphurizing metal poured out of the desulphurizing ladle into the transfer ladle substantially equals the mass of metal poured from the tapping ladle into the desulphurizing ladle. A small amount of metal may be and desirably is left in the desulphurizing ladle to avoid pouring out any substantial amount of slag when the metal is poured into the transfer ladle. If all the metal were poured out it would be difficult to avoid pouring out some slag with it at the end of the pour.

The desulphurized metal in the transfer ladle may be poured into a Bessemer converter and refined by Bessemerizing. The molten Bessemerized metal may then be admixed with molten iron silicate slag to make a wrought iron sponge ball by the Aston process. This is preferably done by pouring the molten metal into and through the iron silicate slag as is now well known.

Our desulphurizing process may be employed in desulphurizing molten ferrous metal tapped from a blast furnace or melted in a cupola, air furnace or other melting furnace.

Other details, objects and advantages of the practicing the same an prese apparatus for thepractice re'ot rproc d In the accompanying, drawinggf} have lll sr trated a present preirrfedmeth oiiprdotihlflk the invention and have shownbrese ntlpreieri-ed apparatus for use in tlie .in which the figure is a plan xylem; largely diagr mmatic, of a portion er'spl ni: rcr thernanuiactdrc of 8 i by e Ast n 1mm I Referring now more particularlyto thedraw ing, there is provided a batteryoi n1 being shown and being desigriatedfbfr erence numeral 2. The cupolas havellillnl il Iconnected by a trough 0 having a deliv'ejry portion 5 disposed at a tanning sta i -y .32 the an" ment shown any one or more urnle'cupussmay be tapped at one time and the inolten metal tapped therefrom is' delivered at the tannin! station. There is provided a straightjh'aci I which extends past the cupolas and" pest a'battery of Bessemer converters I, We beaverters being shown. Disposed odtheftrack l are three cars l! ahd'lll. 'l he 'oars" I I and II are releasablycoupledtogether. Any source or motive Water is provided for the cars I. I and Ill along the track. iii 7 a cable Ida may have its' ends conj edtcdijwlth the car and may pass, abouts. winding I-Iband ashe'a've lie. 7 As the ears are i ieasably coupled together the car I 0' maybe in oved alone or the cars a and 'Iii may be moved without the car I, or all three cars ay be moved together.

A tapping ladle H is mounted on the car I. A desulphurizlng ladle II is mounted on the car I. A transfer ladle it is mounted on. the car N. The ladies 'II and II are or the open top lip pour type. The ladle I2 is of the hooded type having a pouring orifice below the top tun-ear.

A hooded type ladle is "shown in; Patent No. 2,241,434. All three ladies are removably mount: ed upon their respective cars so that they can be picked up by an overhead crane II. moved tram" one position to another and tiltedto pour out their contents.

Two scales are provided, one being designated It and being disposed at the tapping station and" theother being desginated l1 andbel generally beneath the runway forth A preferred method or operation willinow sees.

scribed. At the beginning oi" operation all three ladles H, II and II will be'empli y, hill nfterd a few heats have been tapped from the cupolas a substantial volume of molten desulphurizer'or during operation and when the ladle it contains itsfnbrmal quant desulphurizing slag. The desulphurlie'r' needle 7 preferably caustic soda although soda ashj 'orj other suitable desulphurizer may be employed.

Caustic soda is supplied mj solid form and'has to be renderedmolten mr'taejaesnpsunzinc or molten ferrous metal. "During normal With a quantity of mblten und rtones orde sulphuriz'lng slag being melamine in denflplmrizing ladle II and withtapping' 'ladle II and the transfer ladle" empty, more smart as desulphurizing slag will be maintalned' as thei desulphurizing ladle it. We shall describe the treatment of a heat of molten ierrous metal? 1-" r L Z f-l ladle down r; s s d at t e lam a station n the scale i 'Ine welsht ptmclten Ierrous m le n r m t r s-.0 Q lw ss utotha tapping ladle il" isdetermined-bg the scale it. In the normaloperation at the. Ambridge plant oi A -M. Byers qompany about 2?,000mnds of molten ierrous metal is tapped irom the cupol s at each During the time when the .molten ferrous metai being tapped irom the cupolasls flowing into the tapping ladle N; there isintroduced into the tannin ladle ii a replenishins quantity of caustic soda which mayhave a mass of the order of 300 pounds for a 27,000 poundheat oi molten i'errous metal. Preierably ll A small amountfloi molten metal is first allowed to run into the tanning ladle whem pim the solid caustic soda is thrown into the ladle. o The solid caustic, soda may be thrown in in portions at spaeed intcrvalss d A V heat 01' the molten metal melts. the caustic. soda and drives oi! the water oi cyrstallization which forms steam and causes some amount ot ioaming in the tappins ladle. While a ioamy desulphurizing slag in the desulphurie zlng. ladle is. undesirable ior reasons above enplained' the presence of some loam in the tapping ladle is not serious inasmuch as the desulphurizlngf action of the desulphurizer in the tapping ladle is only partly relied on. The purp se of. et s ucin the repl g q an ty 1 des'ulphun zer in the tapping ladle is to melt that desulphurizer beioreintroducing it lnto the desulphurizing ladle. The premeitiug of the replenishing desulphurizer before it is introduced into the desulphurizing ladle obviates objectionclip sothat the stream issuing therefrom may easily break up into small particles as it enters and'passes through the molten desulphurizing slag in the desulphurizing ladle l2. explained above thlswpromotes effective desulphurlzation.

During pouring of the contents of the tapping ladle ll into the desulphurizlng ladle i2 slag will issue from the pouring orifice oi the desulphurizlag ladle. This is because thevolume of metal and slag whichv would be contained in the desulphurizlng ladle I! it the pouring orifice were plugged issuch that it would extend above the level of the pouring orifice sufllciently that about 800 pounds of slag would be above that level, i. e., a mass '01 slag equal to the replenishing mass of aesmphunm [introduced into the tapping ladle II as above explained; Consequently upon each heat there is a discharge through th pouri s oriflce orthe desulphurizing ladle l2 oi a mass of spent desulphurizing slag substantially equal to the 'otrreplenishing desulphurizer added di iring tllit heat; In this way a constant volume oi 'de'sulphuilzlng slag is maintained and contincev vm A After the; contents oi the tapping ladle II have been poured into the desulphurlzing ladle I: as above explained the desulphurizing ladle is picked up by theoverhead crane and the train oi cars is moyedito the right, viewing the drawing, in positionthe'car II on the scale l|.j The desulphurrising ladle I! is positioned over transfer ladle oi the cupolas I isor' '75 i8 is tilted to pour outa"portion of its contents through the pouring orifice. The desulphurizing ladle is initially tilted very rapidly so that the slag therein which because of its lower specific gravity floats upon the metal will rise above the level of the pouring orifice without a substantial portion of the slag passing through the pouring orifice. The desulphurized metal is poured out of the desulphurizing ladle l2 into the transfer ladle ll until 27,000 pounds of molten metal, 1. e., the same mass as was tapped from the cupolas in the same heat, is in the transfer ladle Ii. Then the desulphurizing ladle I2 is quickly tilted back to upright position.

After the operation just described the desulphurizing ladle I: will contain the same mass of desulphurizing slag and metal as at the beginning of the heat because 27,000 pounds of metal and 300 pounds of desulphurizer were introduced into the ladle II from the ladle ll, 27,000 pounds of metal were poured from the ladle I2 into the ladle I3 and 300 pounds of slag issued from the pouring orifice of the ladle if. A small amount of metal remains in the ladle I! with the slag to obviate pouring out of slag near the end of the pour when metal is poured from the ladle i2 into the ladle II, which would be likely to occur if an effort were made to pour out all of the metal.

There will be some slag on top of the metal in the transfer ladle l3. That slag is raked oil, whereupon the car if! is moved to a position opposite one of the Bessemer converters I where the desulphurized metal is poured from the transfer ladle I3 into the converter. That metal is refined in the converter in the usual way after which it is delivered from the converter in a ladle mounted on a car movable on a track il below the level of the track 8 to a processing station l9 where it is poured into a bath of molten iron silicate slag maintained in a ladle to form a wrought iron sponge ball by the Aston process as known in the art.

When the plant is being started up there will be no molten desulphurizing slag in the desulphurizing ladle II. In other words, as mentioned above, all three of the ladies ii, I! and II will be empty. The cupolas are tapped into the ladle II but in the first heat instead of tapping only 27,000 pounds, which is a normal heat, a somewhat greater mass of metal will be tapped into the ladle ii, for example, 29,000 to 30,000 pounds. About 300 or possibly about 400 pounds of caustic soda is thrown into the ladle ii. The contents of the ladle II are poured into the ladle if. The 300 or 400 pounds of fresh caustic soda is sufficient to desulphurize the 29,000 to 30,000 pounds of metal in the desulphurizing ladle but since there was no substantial quantity of slag in that ladle at the time the contents of the ladle II were poured in no slag will issue from the pouring orilice during that heat. After desulphurizing 27,000 pounds of metal will be poured from the ladle l2 into the ladle l3, leaving in the ladle l2 2,000 to 3,000 pounds of metal and 300 or 400 pounds of slag. Thereafter 27,000 pounds of metal is tapped at each heat and 300 pounds of caustic soda is introduced into the ladle II at each heat and the normal procedure as first explained above is followed. No substantial amount of slag will issue from the pouring orifice of the ladle l2 until after several heats when the volume of slag in the ladle l2 has been built up to the point where the slag will rise above the pouring orifice upon introduction into the ladle I! of the contents of the ladle Ii.

Not only do we obtain a vastly more satiafactory and uniform desulphurlzing of the metal than has heretofore been obtainable but we efl'ect a remarkable economy of desulphurizer, which is expensive. The key to the improvement is in the rendering molten oi the replenishing desulphurizer before introducing it into the desulphurizing ladle. While in the preferred method above described the replenishing desulphurizer is melted by the heat of the metal in the ladle ii it may be melted in a separate furnace provided for that purpose and delivered from that furnace either into the ladle ii or directly into the ladle it.

While we have shown and described a present preferred method of practicing the invention it is to be understood that the invention is not limited thereto but may be otherwise variously practiced within the scope of the following claims.

We claim:

1. A method of desulphurizing molten ferrous metal comprising heating to a temperature about that of the molten ferrous metal to be desulphurized a quantity of previously unused desulphurizer which gasifles upon being heated to melt and decompose the desulphurizer to drive oil substantially all gaseous matter formed and, after thus preparing the desulphurized, intimately associating the desulphurizer and the molten ferrous metal to effect desulphurization of the molten ferrous metal by pouring the molten ferrous metal and desulphurizer into a single chamber receptacle wherein throughout the pour all molten ferrous metal in the receptacle forms a single pool all portions of which are in mixable contact with the desulphurizer, the desulphurizetion in said receptacle being characterized by minimization of foaming which would be caused by release of gaseous matter and by enhancement of interface reaction between the desulphurizer and all portions of the metal.

2. A method of desulphurizing molten ferrous metal comprising introducing into molten ferrous metal to be desulphurized desulphurizer in unmelted form which gasifles upon being heated and by the molten ferrous metal heating the desulphurizer to a temperature about that of the molten ferrous metal to melt and decompose the desulphurizer to drive oi! substantially all gaseous matter formed and. after the desulphurizer has been thus prepared, intimately associating the desulphurizer and the molten ferrous metal to effect desulphurizatlon of the molten ferrous metal by pouring the desulphurizer and molten ferrous metal into a single chamber receptacle wherein throughout the pour all molten ferrous metal in the receptacle forms a single pool all portion of which are in mixable contact with the desulphurizer, the desulphuriaation in said receptacle being characterized by minimization of foaming which would be caused by release of gaseous matter and by enhancement of interface reaction between the desulphurizer and all portions of the metal.

3. A method of desulphurizing molten ferrous metal comprising forming a bath of molten ferrous metal and previously unused desulphurizer which gaslfles upon being heated which has been heated to a temperature about that of the molten ferrous metal to melt and decompose the desulphurizer to drive or! substantially all gaseous k matter formed and thereafter intimately associstantial portion of the desulphurlzer enters the receptacle at least as early as during the early part of the pour and wherein throughout the pour all molten ferrous metal in the receptacle forms a single pool all portions of which are in mixable contact with the desulphurizer, the desulphurization in said receptacle being characterized by minimization of foaming which would be caused by release of gaseous matter and by enhancement of interface reaction between the desulphurizer and all portions of the metal.

4. A method of desulphurizing molten ferrous metal comprising maintaining in a single chamber receptacle a quantity of molten desulphurizer, simultaneously introducing into the receptacle molten ferrous metal to be desulphurized and additional desulphurlzer which gasifles upon being heated which has been heated to a temperature about that of the molten ferrous metal to melt and decompose the desulphurizer to drive 08 substantially all gaseous matter formed, the molten ferrous metal in the receptacle forming throughout the pour a single pool all portions of which are in mixable contact with the desulphuriner, the desulphurization in said receptacle being characterized by minimization of foaming which would be caused by release of gaseous matter and by enhancement of interface reaction between the desulphurizer and all portions of the metal,

10 sulphurized molten ferrous metal from the molten desulphurilter.

FREDERICK W. WHITE. EDWARD B. STORY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,532,072 Parsons et ai Mar. 21, 1925 1,590,739 Evans June 29, 1026 1,646,728 Evans Oct. 25, 1927 2,015,692 Perrin Oct. 1, 1935 2,110,066 Heuer Mar. 1, 1938 2,204,813 Muskat June 18, 1940 FOREIGN PATENTS Number Country Date 481,878 Great Britain Mar. 14, 1938 OTHER REFERENCES Refining Iron in Mixing Ladies, published in "The Foundry," August 1937, page 72.

"Recent Developments in Pig Iron Manufacture," published in Foundry Trade Journal (British), Jan. 9, 1941, pages 21, 22.

"Desulphurization of Molten Iron," published the additional desuiphurizer replenishing the first in proceedings of A. I. M. E. Blast Furnace Commentionod desulphurizer, and separating the demittee 1941, P ges 68-91.

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