US2600575A - Treatment of molten metal - Google Patents

Description

J1me 1952 F. REINARTZ ETAL 2,600,575

' TREATMENT OF MOLTEN METAL F91 Filed March 17, 1945 Patented June 17, 1952 UNITED STATES PATENT OFFICE TREATMENT OF MOLTEN METAL Leo F. Reinartz and Charles R. Fon Dersmith, Middletown, Ohio, assignors to Armco Steel Corporation, a corporation of Ohio Application March 17, 1945, Serial No. 583,350

3 Claims. 1

This application is a continuation in part of our copending application of the same title, Serial No. 393,424 filed May 14, 1941, now abandoned.

It has been understood that where molten metal is to be introduced into an open hearth furnace or equivalent refining device, theoretical advantages could be obtained by pretreating the molten metal with mill scale or other forms of iron oxide. These advantages include an immediate and valuable reduction in the silicon and manganese contents of the molten metal and, under some circumstances, reductions in the content of phosphorus, sulphur, and other impurities. The use of mill scale or other waste oxides would be valuable from the standpoint of utilization of waste materials; and a successful treatment would result in the realization of iron values from such materials.

Hitherto, in all attempts to treat molten blast furnace metal with iron oxide, the oxide was either added to the ladle in which the pig metal is tapped, or to the molten metal as it flows through the blast furnace runner, so that it will be carried by the metal into the ladle, or both; but the known procedures involve such serious difficulties that in all instances in which they have been tried, they have had to be abandoned.

The reaction between the metal and the oxide is exothermic and may become violent and explosive, so that the danger to workmen is excessive.

The preferred way of getting metal from the blast furnace to the open hearth is to collect the metal from the blast furnace runner in mixer cars, e. g. Pugh ladles, whence it is poured as required into open hearth ladles for charging. The Pugh ladles make the use of mixers unnecessary, and permit the holding of metal in molten form for as long as may be necessary.

But when iron oxide is added to the blast furnace metal as described, it can no longer be collected in a Pugh ladle. The reaction produces an acid slag of high melting point which builds up in Pugh ladles, attacking their linings and ultimately rendering them useless. Hence the metal must first be run and treated in an open top blast furnace ladle, from which, when the reaction is completed, it must be tapped into a Pugh ladle with removal of the slag. This involves extra equipment, labor and time delay, as Well as substantial heat loss in the metal.

The treatment as hitherto known was incapable of chemical control. There is no way of ascertaining exactly the chemical content of a batch of blast furnace metal in advance of tapping the furnace; but once the furnace is tapped, it is necessary to take the metal. Hence if it is to be treated with iron oxide, the oxide must be added by judgment or guess based upon observation of the action of the furnace.

The chief objects of our invention are the provision of a treatment method and apparatus whereby these disadvantages are all eliminated, and whereby the theoretical advantages of a prepurification of the metal with iron oxide can be attained in practice.

It is an object of our invention to avoid the safety hazards involved in the former known treatment.

It is an object of our invention to provide a process in which blast furnace metal can be collected, handled, held and dispensed to the open hearth furnaces in the manner and by the means heretofore found most advantageous, but in which the metal may nevertheless be treated with iron oxide.

It is an object of our invention to provide a process of treating molten blast furnace metal with iron oxide in which any re-ladling for slagging purposes is eliminated entirely.

It is an object of our invention to provide a process of treating molten blast furnace metal with iron oxide in accordance with the principles of exact chemical control, and based upon the known content of the metal of the impurities to be removed.

It is an object of our invention to provide a process of treating molten blast furnace metal with iron oxide which requires no containers for molten metal other than those customarily used for untreated metal and which requires additional apparatus of negligible cost only. I We accomplish these objects, and others which will be pointed out herein or will be apparent to one skilled in the art upon reading this specification, by that certain construction and arrangement of parts and in that procedure, of which We shall now describe an exemplary embodiment. Reference is made to the drawings wherein:

Figure 1 is a plan view of an exemplary treatment apparatus according to our invention. 1

Figure 2 is a side elevation'thereof. Our invention is based upon a concept of treating the molten metal very rapidly and in theincrements desired for charging into the open hearth furnace, as against treating the whole fashion control may be exercised-as hereinafter We shall use the term blast furnace to indi-- cate generally the point of origin of the molten metal; and we shall use the term -open hearthfurnace" as indicative of the means for refin ing the molten metal.

In our practice the pig metal from'the' blast furnace is tapped therefrom and run into mixer cars or Pugh ladles, as in the accepted practice for non-treated metal. In these ladles the molten metal. can beheld without .losingits molten charactersfor such-.periods of time. as to permit convenient charging of the open .hearth furnaces in accordance with their requirements.

No' attempt is made .atfthis stage to treat '.the

metal; but during the holding period an analysis ismadeof the metal to. determine its content of impurities; e. g. of silicon and manganese; On this analysisa calculationis made of the quantityof: iron oxide requiredziperunit quantity of the molten metal to reduce its content Sci impurities to a desired value in thelightof advantageous; open hearth. practice.

lniordin'ary practice for. charging the open hearth furnaces, the metal is poured asrequired fromithePugh ladle'into open hearth ladles. The apparatusv departure we'make in .accordance withathis invention'involves the provisionof a runner toreceiveithe metal from the Pugh ladle antdiiieliizer. it 'ito'the openhearthladle, together with aiameans ifo'rffeedingiron oxide into the runner.

The'rmoltenrmetal is poured into the runner under: conditions'in which the volume of f the streanr'can'be icontrolled. Increments .of 1 oxide are introduced'intothe:runner.along with the molten ";metal..- The increments .so added total thecquantityof ironv oxide shown to be required b-yrthefanalysis for the particular quantity of metal ltoibe poured .throughthe runner into the desired'batch. receiving vessel.

The molten metal, having been'treated with thelronoxide is delivered at the end of the runnerrinto aladle-suitable for charging the metal intoitheopen hearth. The pouring is discontinuedeassoon as the desired quantity of metal has been introduced into the ladle.- The process does not delay the transier'of themetal from the Pugh ladleto the furnace.

Itwill now beevident that the success of our process involves carrying on-the reaction in a very rapid and controlled manner so that it will becompleted or substantially completed 7 during the short time required to fill an open hearth ladle-from a Pugh ladle (or as hereinafter set forth,- from: two Pugh ladles pouring simultaneously-and-rapidly). We have found that this can be done if the followingconditions are met:

1; Itsis essential not only that the iron oxide be-added to the molten metal in the runner but also that it be mixed with the molten metal in the v:runner. If'iron oxide be added to molten metal- 'in'a-blast furnace-runner it tends to float uponthesurfaiceof the metal and is carried therebyinto the -ladle'. In'this event, as also in the case where the oxide is added directly to the ladle, whatever mixing there is occurs primarily in the ladle. This will not serve our purpose; and we can neither add all our oxide to the ladle nor can we allow it to be floated into the ladle substantially unmixed. In either event the reaction is incomplete and uncontrollable.

2; We provide a runnerso' constructed as to have an enfolding function for the iron oxide. Our runner has a receiving head or hopper into which we pour the metal in one or more streams and into which We also introduce the oxide. Mixing occurs at this point. Again the open runnerleading from this head or hopper is not straightbutts-tortuous in the sense that it has 3.- The iron oxide must beadded gradually and substantiallyuniformly to the -molten metal. This is-done-by a mechanically actuatedfeed hopper located above the-receiving head. During the greater portion'of the pouring, and-pref erablyduring-all of it, equal :increments ofthe oxide are added to equal increments ofthe molten. The metal is poured rapidly from: one

metal. or two Pugh ladles-into the receiving head or hopper of the runner, but evenly, and the oxide is thus evenly-and fairly uniformly associa-ted' with themetal, quantity for quantity, beforethe metal enters the open hearth ladle. Theraterofpour from the Pugh ladle or ladles-isof course.

controlled by the 'motors tilting the ladles, and

the rate-of feeding of theoxide is controlled by a" motoron or in connectionwith the "oxide hopper:

4; Nevertheless, the type of treatment reagent must'be one very rapid-in its action. Not every form of iron oxide can be used; Iron-ores of various types, oxide bearingflue dusts and the like; available in the former processes; are-not sufficiently rapid nor'sufiiciently easily'miscible with the *molterrmetal for our procedure. We

have found that mill scale-is, howevensufiicientlyactive and sufl'iciently heavy to enable us to: treat metal in the way herein described, and this-isjthe oxide whichwe use.

When these conditions are takesplacein substantial measurein the runner and alsocontinues for ashort period in the ladle. It is strongly exothermiciandtvery active. The metal .in'the runner givescff a shower of sparks, but there is little likelihood of explosion-if "pre cautions are taken to assure a. dry condition of the. mill scale. The reaction is largely controlled by' the continuous proportioning of the mill scale to the molten metal. The circumstances are suchthat the operators may be adequately shielded and protected; They are not-required to Work in exposed positions about an open runner asat'theblast furnace. The now of metal from the Pugh ladles may, of course, be cut off atany time.

The metal collecting in the open hearth ladle is also active; but less violently so. If, as the ladle becomes nearly full, a tendency toboil'over appears, the metal may be quieted by the addition of a smaller quantity of salt to the ladle:

met, .the' reaction This is not usually necessary; the reaction rapidly spends itself, and the high-melting point acid slag formed by the reaction begins to congeal on the top of the molten metal,"

The ladle is then carried directly to the open hearth and the hotmetal charged into it. This may, if desired, be done by tapping the ladle so as to separate the slag. In the majority of instances nearly all the slag will have formed a stiif crust on the metal, so that it is possible to pour the metal from the ladle into the open hearth by tilting the ladle in the usual way, the bulk of slag remaining in the ladle. Afterward the slag may be removed fromthe ladle by up-ending it over a thimble or the like.

Since the metal is treated as desired for charging, and since the treated metal is charged at once into the open hearth without re-ladling for slag removal, the heat generated by the exothermic reaction is no longer lost; but the charged metal is hotter than the metal .in the Pugh ladles. This is not only important in the matter of open hearth efliciency, but is especially valuable when it has been necessary for any reason to hold the metal in the Pugh ladles until its temperature has become too low.

The distance of the blast furnace from the open hearth is not in any sense determinative of the utility of our process. The Pugh ladle, as in ordinary practice, permits holding the molten metal until required for charging, and also permits its interim transportation should that be necessary. For reasons which will now be clear, however, our treatment of the molten metal with mill scale, to realize all of its advantages, must be carried on so close to the open hearth that the treated metal may be collected in an open hearth charging ladle and charged directly into the furnace.

All of these factors permit us to introduce into our open hearth furnaces charges of molten metal of enhanced iron value and at higher temperatures than would be possible otherwise. There molten metal charges, together with charges of scrap and the like, and charges of treatment reagents, permit us to operate the open hearth furnaces under improved conditions. The treated metal may be introduced without that slag which results from the treatment with the mill scale. The added heat enables us to shorten the cycles in the open hearth furnace, and the pre-reduction of the silicon and manganese contents of the molten metal reduces the slagging problem in the furnace.

In the drawings of our exemplary apparatus, we have indicated at l a framework or housing, and at 2 and 3 mixer cars of the Pugh type. These cars move on tracks 4 and 5 at a high level on the framework and interspaced, so that the mixers of one or both mixer cars may be simultaneously rotated on their axes to pour the molten metal into the head 6 of the runner which is located between the two tracks. The hopper for the mill scale is indicated at B. This hopper is mechanically actuated to deliver a controlled stream or controlled increments of the mill scale into the head of the runner, as required by a controlled rate of pour from the Pugh cars.

The runner proper is a refractory lined structure of tortuous character to assist in the mixing and comprises angularly related straight sections 'l' and corner boxes 'la wherein the overfolding action of the molten metal takes place. It may also have, if desired, one or more vertical drops in it to enhance the mixing action. It is located between the tracks and at a lower level in furnace or furnaces (not shown). a

the framework i as shown. This permits us to fence or housethe runner, as indicated at. 9, l0 and I whereby the workmenare protected'from the violence of the reaction occurring therein. The "operator who controls the rate of pouring of the hot metal and the addition of the scale may be conveniently and safely located in a control house provided with a safety glass window located immediately behind and below the scale hopper. The runner, near the end remote from the head, passees under one of the tracks "as shown and delivers the molten metal into a ladle [2 located at a still lower level. When the ladle is full or has received the total quantity of molten metal intended for. it, itis picked. up by a crane and tapped or poured into the open hearth It will have been noted that We preferably provide two tracks and two mixer cars for reasons already given. But we may thus, if desired, pour metals of dissimilar analysessimultaneously into the runner for treatment. This practice improves uniformity of the addition of hot metal in the open hearth practice, andenables us to make minimum additions of scale in our treatment. In regular practice, by mixing metal from two ladles, or by pouring single ladles, as the analysis may indicate, we are enabled to work closer to a common end point, say 0.35 to 0.45% silicon, which will allow the use of a maximum ratio of hot metal to scrap in the open hearth, without charge ore additions or permit a still higher hot metal ratio with only small charge ore additions. Charge ore additions are likely to cause serious foaming of the metal bath in the open hearth furnace. We secure a greater uniformity of our metal because of close control of the silicon in the hot metal, in addition to the other advantages of our process,

It is not outside the purview of our invention to use other treatment reagents along with mill scale for special purposes. In some operations, finely crushed manganese ore may be used like mill scale to reduce silicon, while preserving manganese in the molten metal. Manganese ore likewise has an exothermic reaction with molten iron.

Other treatment agents may also be employed. Soda ash, barium oxide or other alkali compounds may be added to reduce sulphur. These do not have a significant exothermic efiect, but may be addedalong with mill scale or manganese ore. The very corrosive slag they produce can, in our process, be kept out of the open hearth furnace or other refining means.

Modifications may be made in our invention without departing from the spirit of it. Having thus described our invention, what we claim as new and desire to secure as Letters Patent is:

1. Apparatus for the treatment of molten pig iron metal comprising interspaced tracks upon which carriers for molten metal may be run, means for supporting said tracks at an elevated level, a runner located between said tracks, adapted to receive molten metal from said carriers simultaneously and located at a lower level, a hopper adapted to deliver mill scale into said runner, and a ladle located at a still lower level, and housing means surrounding said runner.

2. Apparatus as claimed in claim 1 in which said ladle is located at the side of one of said tracks remote from the interspace between the said tracks, and wherein an end of said runner passes through one of said housing means.

3. A process of supplying improved molten blastfurnace iron to an open hearth furnace, whichioomprises tapping the molten metal from the blastiurnacezinto a refractory lined vessel, and .at a pointadjacent an open hearth furnace, pouring it rapidly from said vessel into a tortuous runneryadding mill scale to it in the said runner in increments. proportioned to the rate of flow therethrough, adding equal increments of mill scale to the runner along with equal increments of molten metal during a por-tionat least of the pouring, the mill scale mixedwith the molten metal being proportioned to the known content of silicon and manganese in" the molten metal, the-molten metal poured into the runner being simultaneously derived from sources of difierent analyses, delivering it from the runner into a ladle in quantity suitable for charging it into the open hearth, discontinuing the said pouring upon the-accumulation of a charge in said ladle, and promptly transferring the metal from said ladle into said open hearth furnace.

LEO F. REINARTZ. CHARLES R 'FGN DERSMITH.

8 REFERENCES CITED The" following references are of record in th file of this patent:

UNITED STATES PATENTS Number Name 7 Date 843,582 Campbell Feb. 12, 1907 374,391 Chute Dec. 24, 1907 1,863,686 Corsalli June 21, 1932 2,302,999 OBrien Nov. 24, 1942 FOREIGN PATENTS Number Country Date 16,601 Great Britain of 1911 OTHER REFERENCES

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