US1590731A - Refining of iron - Google Patents

Description

June 29 1926. 1,590,731

, G. S. EVANS I REFINING OF IRON Filed May 1925 /y Q /3 j a INVENTOR O BY ATTOR N EYJ' is gradually burned and is replenished by r I so Patented June 29, 1926.

UNITED STATES PATENT OFFICE.

REFINING OF IROIiI.

Application filed May 9,

This invention relates to improvements in the operation of foundry cupolas whereby the molten iron is obtained in a clean and refined state and whereby improved melting and fluxing conditions are maintained during the cupola operation. I

In the operation of foundry cupolas it is customary to use limenone as a flux to combine with the siliceous material formed from the coke ash and with impurities contained in the cupola charge so as to form' a fluid slag which can be tapped from the cupola and removed so that the impurities will not interfere with the operation of the cupola. Sometimes fiuorspar is added in small amount to the cupola charge to give a more fluid slag.

When a cupola is started in operation a' deep layer of coke is firstcharged and then alternate layers of iron and coke, together with suitable additions of ing the operation of the cupola and the melt-I ing of the iron therein, the iron is supported on a column of coke which extends to the bottom of the cupola. The iron, as fast as it melts, trickles down over the column ofcoke to the bottom of the cupola. The coke successive layers of coke which serve to support and by their combustion to liquef the alternating layers of iron. As the iron drops down over the coke it absorbs sulfur, the amount absorbedvarying with the relative amount of coke and iron used and the per cent of sulfur in the coke. To avoid or minimize this absorption of sulfur, care is taken to obtain and use a coke as low in sulfur as possible; anoL high sulfur cokes, although obtainable at lowerprices, are objectionable and are commonly considered unsuitable for foundry use.

Furthermore, in ordinary cupola operations, there is sometimes a tendency for the charge to bridge over, particularly during the latter part of therun. This bridging interferes with the free settling of the charge in the cupola, and, if the bridge or shelving gives way, it permits an excess of the charge to fall into the tuyere or melting zone; while any such bridging requires removal from the cupola at the end of the run and before the next run is begun.

The present invention provides an improved process in which objectionable bridging is avoided, in which .a thinly fluid slag is insured, in which the avoidance of increase form, such as limestone. .Dur-

the melting zone.

1925. Serial No. 29,053.

in sulfur in the iron is made possible, and even reduction inthe sulfur content of the iron charged, in which a hot, clean iron is readily obtainable, in which improved fluxlngand melting conditions are maintained, and in which the cupola operation is otherwise benefited. The invention makes possible the use of high sulfur coke, higher in sulfur than now commonly considered available for foundry practice. It also makes possible the use of high sulfur pig iron, which is refined to a greater or less extent and lowered in its sulfur content by the remelting and refining process of the present invention.

According to the present invention, there is included in the cupola charge a regulated amount of soda ash in a dense aggregated fused lump ash, fused ash molded into blocks or bricks, or pressed bricks consolidated to a sufficient density to withstand impacts of the, charging process, weight of the overlaying charges and the abrasion with the descent of the charges to A convenient form, and

one which is recommended, is fused soda ash molded in the form of bricks of about two pounds each. These bricks are-of convenient size for handling'and they enable the quantity used per ton of metal charged to be regulated by the-number of bricks added per charge, so that separate weighing is avoided and the use of the materialso simplified that it can be handled by the regular charging gang. Soda ash in this form is not injurious to the skinland may be safely handled with the bare hands and may be stored under ordinary dry shelter without deterioration.

' ere limestone is used as the fluxing material in the cupola charge, the fused soda ash may be charged with it and may be added either upon the coke or metalcharge in accordance with the practice followed with limestone. It can be charged in the form of whole bricks, e. g. of two pounds each, or in the form of half bricks of about one pound each.

The amount of soda ash used is sufficient to produce a strongly alkaline and fluid slag which Willrea'ct with the impurities 1n the iron as melted and with the impurities of the coke over which the molten soda' ash trickles, and which will form a good the bath of iron in the hearth Somewhat increased amounts ash are used at the outset of the process in of the cuplola.

of fused soda order to insure the desiredresult. Where from thirty to fifty pounds of limestone are used per ton of metal charged, the amount of the dense aggregated sodium carbonate may vary from one to four pounds or somewhat more. With cupolas using twothousand to three thousand pound charges. two bricks or four pounds of the fused sodium carbonate may be added upon the bed charge and one brick or two pounds upon the following charges. With heavierflc harges, the quantity of the fused sodium carbonate may be proportionally increased. This amount, however, may be insufficient, in which case asomewhat larger amount may be more advantageous, for example, two or more of the bricks (four pounds or more) may be added on the regular charges. In general. the amount used on the bed charge should be twice as much. or somewhat more than that, as compared with the amount used with each of the regular charges.

In using the dense aggregated sodium carbonate, it is added to the charge near the center of the cupola'stock and away from the cupola lining. By adding it in this way, it passes down into the melting zone with the charge and is there melted. For example, when bricks are used, these reach the melting zone intact and fuse just ahead of the metal. The melted soda ash trickles down over the coke and combines with the slag layer in the hearth of the cupola. Sodium carbonate tends to attack the lining more rapidly while melting. but by charging the dense soda ash in the center of the charge, it is kept awayfrom the lining both during melting and while it is trickling down over' the coke so that the lining is protected from objectionable corrosion or attack; The sodium carbonate thus melted increases thealkalinity and fluidity of the slag just. prior to and during the melting of each metal charge. Some volatilization of the sodium carbonate doubtless takes place and its action is such that objectionable bridging is prevented, while at the sametime objectionable attacking of thelining is also prevented.

Y The use ofthe sodium carbonate in a dense aggregated form prevents it from being blown from the cupola by the blast, except for such small amounts as may be volatilized and may escape. condensation and deposit in the upper portion of the charge. The'use of the sodium carbonate in dense aggregated form also insures that it will reach the melting zone and will there be melted and caused to .trickle down over the coke, where it comes in contact with impurities such as sulfur and apparently. combines therewith or converts the sulfur into a form such that the molten iron doesnot absorb any apreclable amount of sulfur from the coke. vhile I do not wish to limit myself by any theoretical explanation of the action which takes place, yet the action of the sodium carbonate is apparently a protective action such that the sulfur whichwould otherwise combine with and enter the molten iron trickling down over the coke will instead combine with the alkali of the sodium carbonate and will be converted into a form such that i the sulfur will not enter the molten iron. The iron which is progressively melted and which trickles down over the coke will thus plex character with the lime, silica etc., and

gives an alkaline and thinly fluid slag which collects in the bottom of'the coupla upon-the molten iron.

Enough of the'dense sodium carbonate is used so that theslag' layer .so formed in the bottom of the cupola will have a sufiicient alkaline character to exert a desulfurizing and refining action upon the molten iron.

.This action may begin before the iron reaches the molten bath at the bottom of the cupola. It may begin during the melting operation while the iron is being progressively melted and whileit is trickling down over-the coke and through the layer of basic slag to the pool of iron at the bottom. Such purification may take place even though the layer or bed of slag is not of any considerable thickness or of any high alkalinity; but a further and improved result is obtained when a substantial layerof slag.is maintained with a sufficient alkalinity to make it thinly fluid and to cause it to have a' further desulfurizing and refining action upon the molten iron. Inorder to promote this action, the iron notch is advantageously arranged so as to" maintain an appreciable ibody of molten iron in the cupolawhich may be tapped periodically or which may be permitted to runcontinuously from the iron notch as the iron is melted-in the cupola. With an iron notch which iskept open to permitcontinuous tapping, the slag notch is advantageously-also kept open, and

is arranged at a sufficient height above the iron notch to provide a substantial body of slag continuously above the layer of molten 'excessfslag will be tapped 'ofi through the slag notch and the iron will be tapped through the iron notch during the continuation of the operation of the upola The presence of the sodium carbonate, when used in the manner above described, improves the fiuxing of the impurities, and improves the melting conditions, while it also absorbs sulfur and has a deoxidizing effect upon the metal; The molten iron is thus deoxidized and freed from occluded gases and from entrained slag particles. The elimination of these impurities reduces segregation, blowholes and other imperfections in' the finished castings. The removal of sulfur, and the prevention of the pick-up of additional sulfur from the fuel by the molten iron, avoids cold shortness and sluggish- I ness in the iron and the presence of undesirable and excessive quantities of sulfur in the iron and resulting impairment of the quality of the finished castings. A reduction in sulfur content of the molten iron from 10 to per cent or more of the normal sulfur ordinarily obtained fromthe same mixture can be obtained by the use of a regulated amount of the dense aggregated sodium carbonate.

The molten ,iron tapped from the cupola is thus a more or less refined iron, while it is also a hot, clean iron. This hot fluid metal can be used for light section castings, even from lower silicon irons, producing a more uniform structure casting with greater strength and density. The castings are also produced with reduced losses resulting from shrinkage ordraws and from segregation of impurities. The deox-idized metal, and the removal of slag inclusions and other impurities, results in castings of improved machining quality.

The addition of the dense sodium carbonate also permits a reduction inthe amount of limestone required in the charge. When from four to eight pounds of fused sodium carbonate bricks are added per ton of metal, the quantity of limestone commonly used may be materially reduced, e. g., by about one third that required when used by itself, with a resulting saving'in fuel for melting the flux, and with relief of the cupola from the added burden of slag.

The invention also makes possible the use of high ash cokes and dirty charges. In such cases. the amount .of sodium carbonate used may be somewhat increased. The slag will nevertheless be a fluid alkaline slag which keeps the melting zone of the cupola open for proper combustion, which will prevent bridging, and give a clean cupola drop at the finish of the heat. A fluid slag is obtainable which is highly active even when the cupola'is running cold or when a fluid slag is most needed. The chipping which is required in preparation for the next days heat is materially reduced and to this extent small plants, with the lining is saved. Corrosion to a greater or less extent may take place, particularly where the alkaline slag comes in contact with the fireclay lining; but such corrosion is readily taken care of by luting or repairing of the lining; and the cost of such re pairs is small as compared with the advan- I tage otherwise obtainable in the carrying out of the process of the invention.

In ordinary foundry practice, limestone is used as a flux to form a slag with the silica and other impurities of the coke. In some cases no limestone is used. The process of the invention can advantageously be applied in such cases, and even where the impurities are not slagged off during the run. The addition of a small and regulated amout ofthe dense sodium carbonate, added to the charge' near the center of the furnace, will take care of the impurities going in with the charge and with the products of combustion. with the resulting production of a minimum volume of slag of a thinly fluid character, and with the resulting advantages of purification of the molten iron, improvements in melt ing of the charge, etc. For example, in short heats, where no fluxing material is now used, the addition of a small amount of the dense sodium carbonate will materially improve the operation of the cupola and the properties of the molten iron tapped therefrom.

The present invention makes possible the use of an increased amount of scrap iron and a reduced amount of pig iron in the foundry charge. It also makes possible the use of iron of higher sulfur content, which does not increase in sulfur content in the cupola, but which may even be materially reduced in sulfur content therein, and may otherwise be obtained in a refined and deoxidized state. J

The invention is applicable, as above pointed out, both when the iron is tapped intermittently, and when it is tapped continuously, from the cupola, In carrying out long runs, the tapping is advantageously made continuous through an iron notch which is sealed to prevent the tapping of slag therethrough. A suitable construction for this purpose is illustrated conventionally in the accompanying drawing, which shows the lower part of a foundry cupola of conventional construction in central vertical section.

The cupola illustrated has the outer shell 1 with the usual firebricklining 2, and a bottom lining 3, supported by the drop members 4. The cupola as a whole is supported on suitable supports 5. The drop members 5are supported by one or more supports 6. The usual tuyeres 7 and bustle pipe 8' are provided. 1 I v The slag notch 9 with slag spout 10 is arranged at a-distance from the bottom of Hit the cupola so that a substantial depth of slag will be maintained above the molten iron at the bottom of the cupola. The irori notch 11 has a'spout 12 with raised portion or dam therein to seal the notch so as to prevent the escape of slag therefrom and so as to maintain a body of molten iron in the bottom of the cupola in contact with the superposed layer of alkaline slag.

' maintain a predetermined. depth of molten iron in the cupola. As fresh amounts of iron are melted and trickle down over the coke, they are protected from contamination by increased amounts of sulfur, and they are then caused to pass down through the alkaline slag into the bath of molten iron. The provision of an alkaline slag in contact with the molten iron, where both the molten iron and slag are of a hot thinly fluid character, permits 0 portunity for further refining of the iron rom sulfur and by deoxidizfoundry cupolas wh1ch comprises adding to ing so that the iron tapped from the cupola .is of reduced sulfur content, is deoxidlzed and refined, and substantially freed from impurities such as occluded gases and en trained slag particles which, if present, would tend to segregate and form blow-holes and other imperfections in the finished castings. Other advantages will be obtained in the foundry voperation, such as improved melting and fluxing conditions, above re ferred to.

It will thus be seen that the presentinvention provides an improved method of cupola operation in which a regulated amount of dense aggregated sodium car bonate or soda ash is supplied to vthe cupola" charge, near the center of the, cupola and away from the lining,;and.in which materialimprovements in theroperation oftheoupola are effected. Among theseimprovements are included the following :-An improved fluxing of the impurities of'the coke and introduced with the charge with the resulting formation of a thin fillld and alkaline slag; the removal of the impurities from the melt- ,ing zone of the cupola as formed so as not.

to=interfere with or prevent proper combustion; the prevention of the absorption of impurities bythe iron during themelting operation and while it is trickling down over the coke; the washing out of entrained particles of foreign substances picked up from the coke or contained in the iron, such as sulfur, oxides, etc.; the formation and maintenance of a covering layer of alkaline slag over the bath of iron as a protection i -from the blast; the avoidance of bridg and the production of a fluid slag even when the cupola is running cold, giving a clean cupola drop at the end of the run; the provision of a basic slag which has a refining action upon the metal bath 'and upon the iron ventering it; etc. The invention also presents the advantages, above mentioned, of permitting the use of cheaper high sulfur coke and of scrap and pig iron higher in impurities, while nevertheless giving a satisfactory refined molten iron.

4 It willaccordingly be seen that the inven- 'tion provides a materially improved process of cupola operation in which a very fluid slag or an alkaline character is produced, in which sulfur pick-up from the fuel by the. iron during the melting process is' prevented or minimized, and in which moreover sulfur is removedfrom the iron together with entrained slag particles, and in which the iron is refined and deoxidized so that niolten iron of superior casting qualities is obtained, from which castingscan be produced which are free or substantially free from segregation, blow-holes and other imperfections.

I claim 1.'The improvement in the operation of dium carbonate, such sodium carbonate be-' ing added near the center of the charge, and carrying out the melting operation w1th the resulting production of a thinly fluid slag.

2. The further improvement in the procless of claim, 1, in which a substantial body of molten metal is maintained in the bottom of--the cu 01a and in which asubstantial la er of t inly fluid alkaline slag is maintamed thereupon. a

3. The improvementin the operation of foundry cu olas without the slagging off of impurities uring a short heat, which comprises addin to the charge a regulated amount of ense aggregated sodium carbonate. v

4. The improvement in the operation of foundry cupolas which comprises melting iron therein for the combustion of coke, supplying to the foundry charge sodium carbonate in amount suflicient to form and maintain a thinly fluid alkaline slag, and maintaining a substantial body of such slag in contact with molten metal in the hearthof the cupola durin the cupola operation.

5. he improvement in the operation of foundry cupolas which comprises adding to the char e a regulated amount of fused sodium cai bonate in the form of unit masses of definite weight, such sodium carbonate being added near the center of the charge, and a uniform number of such masses bein added with successive charges of metal an coke whereby a definite and predetermined content of alkali ismaintained in the cupola ation.

6. The improvement in the operation of foundry cupolas which comprises adding to the charge of metal coke and limestone a regulated amount of dense aggregated so dium carbonate an increased amount of such sodium carbonate. being added with the bed charge and asomewhat decreased but uniform amount being added with successive uniform charges of metal, coke and lime stone.

7. The improvement in the operation of foundry cupolas which comprises maintainmg a substantial body of thinly fluid alkaline slag in the bottom of the cupola upon the molten metal contained therein and supplying sodium carbonate in a dense aggregated form with successive charges of metal, coke and limestone to maintain the thinly fluid alkaline character of the slag.

-8. The improvement in the operation of foundry cupolas which comprises maintaining a substantial body of molten iron in the bottom of the cupola and a substantial body of thinly fluid alkaline slag thereabove, and maintaining the thinly fluid alkaline character of such slag by further additions of dense aggregated sodium carbonate with successive charges of metal, coke and limestone.

9. The improvement in'the. operation of foundry cupolas which comprises maintainmg the bottom of the cupola, tapping the metal therefrom continuously as additional metal is melted in the cupola, maintaining on such molten metal a bed of substantial depth of a thinly fluid alkaline slag, and supplying sodium carbonate in a dense aggregated form with successive charges of metal, coke and limestone, such sodium carbonate being added near the center of the charge and being regulated in amount to maintaln the thinly fluid alkaline slag.

In testimony whereof I aflix my signature.

GEORGE SEPTIMUS EVANS.

30 a substantial body of molten metal in

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