US2151360A - Method for treating molten metal - Google Patents

Description

March 21,' 1939.

T. TAFEL, JR METHOD FOR TREATING MOLTN METALl 2 Sheets-Sheet l Filed Jan. 14,' 1937 l 75m/E NTOR vanua.

lnaenooa T. TAFEL, JR

March 21, 1939.

METHOD FOR TREA'IING MOLTEN METAL .2 sheets-sheet 2 Filed Jan. 14, 1937 INVENTOR 721i@ @www l, am

Patented Mar. 21, 1939 PATENT OFFICE METHOD FOR TREATING MOLTEN METAL Theodore Tafel,

Jr., Forest Hill Village, Toronto Ontario, Canada Application January 14, 1937, Serial No. 120,516

2 Claims. (Cl. 'l5-61) This invention relates to the art of commercial iasting and more particularly to a method for treating molten ferrous metal after'the withdrawal thereof from a bath of such metal and 5 prior to the casting thereof in which a composition changing material is added to the molten metal during such interval and the analysis changed without reheatinghe molten metal or subjecting it to a source of auxiliary heat.

One object of this invention is to provide a method for treating molten ferrous metal in which the metal is ysubjected to a violent stirring and agitating force immediately upon leaving the cupola while such ingredients as Will produce 15 the desired analysis are being added thereto.

Another object of this invention is to provide a method for simultaneously increasing the carbon content and decreasing the sulphur content of -molten ferrous metal to produce a metal suitable for making commercial castings and in which a carbonaceous materialY and a desulphurizing agent are added to and thoroughly mixed with the molten metal withdrawn from the cupola or melting furnace prior to the casting thereof.

Another object of my invention is to provide a mixing ladle which will not only stir the material being mixed with the molten ferrous metal but which will also lift and break up the lighter material and force it toward the bottom of the ladle whereby it is prevented from oating on the surface of the heavier ferrous metal.

A further object is to provide a method of preparing ferrous metals for casting in which a quantity of molten metal is withdrawn from a bath and subjected to violent stirring and agitating force while a composition completing material is being added thereto and in which the metal so treated is poured into the moulds without being necessarily subjected to any auxiliary o heat during or after the time that the composition is being changed.

A still further object is to provide means forY mixing carbonaceous material with molten ferrous metal to increase the carbon content thereof without appreciably lowering the temperature of the metal during the mixing operation.

A" still further object is to provide a mixing ladle having lifting members projected thereinto so that the material being stirred will be lifted and movedtoward the bottom of the ladle and thus prevent the lighter composition changing materials from floatingl on the surface of the molten metal. L

A still further object is to provide a mixing ladle which may be continuously revolved at a ered to a ladle or container revolving at a relarelatively high peripheral speed and is provided with means for subjecting thematerial to be mixed to a violent stirring and agitating action whereby two or more materials suitable for use in producing special objects may be properly 6 united or alloyed together.

These and other objects which will be hereinafter made apparent to those skilled in this par-v ticular art are accomplished by means of thisv l invention, one embodiment of which is described 10 in the following specification and illustrated in the accompanying drawings, wherein:

Figure 1 is a .view in elevation showing a mixing ladle made-in accordance with my invention and positioned in front of a cupola;

Fig. 2 is a view in elevation with the ladle in upright position 'and having portions thereof broken away and other portions in section for convenience of illustration;

Fig. 3 is a perspective View of the ladle turned to its pouring position and having the top thereof removed for convenience of illustration; and

Fig. 4 is a sectional view taken on line IV-IV of Fig. 1 showing the ladle in its pouring position.

Broadly, in the practice of my invention, a quota of molten ferrous metal is withdrawn from a bath maintained at the desired temperature ,in a suitable cupola or melting furnace and delivtively high peripheral speed and having inwardly projecting members which violently agitate and stir the molten metal delivered thereto.

While the molten metal is in the container or ladle a composition changing material of a character and amount suicient to produce an iron of the desired analysis is introduced into the ladle which, as the ladle continues to rotate, is mixed thoroughly with the molten iron by the violent agitation and stirring action which results from the speed of rotation of the ladle in combination with the action of the projecting members on the inner surface. After the mixing operation, the molten metal is withdrawn from the ladle and poured to produce castings.

For example, to increase the carbon content of molten iron, a carbonaceous material such as graphite, charcoal, or the like, in an amount suitable to raise the carbon content of the iron to the desired percentage is poured into the ladle inthe i presence of a suitable desulphurizing agent such as sodium carbonateA or sodium nitrate. The carbonaceous material and the desulphurizing agent are then thoroughly mixed with the molten ferrous metal in the ladle and the carbon content and sulphur content of the molten metal are sibstantially and instantaneously increased and decreased respectively, and this is accomplished in such a relatively short time that the metal does not need to be reheated or subjected to' a source of auxiliary heat during the mixing of these ma-` teiials therewith but may be withdrawn from the ladle and poured directly into the moulds for producing commercial castings.

Alloying materials such as copper, nickel, magnesium, and the like, may also be introduced into the ladle to further change or vary the analysis of the molten iron to produce a ferrous alloy having an analysis suitable for producing any commercial type of special casting.

Referring to the drawings, III indicates the pouring spout of a suitable cupola or melting furnace in which the ferrous metal to be treated is melted and maintained/in a molten state at the desired temperature. From the bath in the cupola a quota of molten metal is withdrawn and delivered to a revolving mixing ladle or container II where a suitable compositionchanging material is mixed with the molten metal. 'I'he ladle II which is positioned below the spout I0 comprises a cylindrically shaped metallic shell IIa lined `with a suitable insulating material IIb which supports a heat resisting member. llc formed preferably of refractory material.' The upper end of the ladle Il is tapered inwardly to provide a pouring spout having a relatively small pouring opening I2 through which the molten metal is rst introduced into the ladle and is then poured from the ladle into a container suitable forconveying the molten metal to the moulds to be poured.

The ladle I I is mounted to rotate about its vertical axis and has a centrally disposed shaft I4 depending from the bottom thereof Iwhich'. is journalled in a bearing I5 carried by the base of a U-shaped yoke I6 depending from annular trunnion rings I'l-IB which surround the ladle Il. -To prevent lateral movement of the ladle relative to the rings II-I8 and the shaft I4 on the ladle from being )pulled out of the bearing I5 when the ladle is tilted, as will be hereafter' explained, a series of grooved rollers I9 are moimted between the rings I1-l8 at spaced intervals which engage theilange of an annular track 20 that is secured to the outer surface of the shell Ila of the ladle II. Each of the'rollers I9 is carried on a vertical shaft 2l which eulone to another of a series or bank of cupolas along a track 28.

In order to tilt the ladle Il to turn the ladle from a metal receiving position underneath the cupola spout I0 to a mixing position and then to a pouring position, the trunnion 22 has a worm wheel 29 secured thereto which meshes with a worm. 30 on a shaft 3| and which is rotated in either direction by turning a hand wheel 32 on a shaft 33 that is geared to the shaft 3| through f worm and wheel elements 34-35.

The ladle II may be continuously rotated at a relatively high peripheral speed during the ,periods of receiving the molten metal, mixing bearing for the shaft. The shaft sa is connected to and is driven by a suitable motor 4|! through speed reduction gears tlg-42. 'Ihe motor 40 is also carried by the frame 26. i

In order to increase the carbon content of the molten metal in the mixing ladle and to simultaneously decrease the sulphur content, a` carbonaceous material such as graphite, charcoal,

' or the like, and a suitable desulphurizing agent,

such as sodium carbonate or sodium nitrate, in such quantities as will produce the desired carbon and sulphur content, are introduced into the ladle and mixed with the molten metal therein. The proportion of carbonaceous material in relation to the vdesulphurizing agent, and the amount of both added to the iron are preferably as set forth in United States letters Patent No. 2,021,159 issued to me on November 19, 1935. To insure the complete mixing of the carbonaceous material and the desulphurizing agent with the molten iron and toi prevent the lighten carbonaceous material from iioating on the surface of the heavier molten iron, stirring members 44 of refractory material are mounted on the inner surface of ythe heat resisting shell IIc and project into the ladle so that as the ladle revolves these inwardly projecting members 444 tend to lift the materials therein and direct them toward the "bottom of the ladle. The members 44 and material, and consequently the carbon pick up and the decrease in sulphur, takes place almost immediately due to violent stirring and agitating action in the ladle, and after the materials have been mixed for a short period, the ladle is tilted to its pouring position and the treated metal is withdrawn therefrom and poured into the mould for the castings after which the ladle is again tilted to its metal receiving position with the opening I2 underneath the spout I0 and another quota of molten metal is delivered from thebath to the ladle and mixed with the vdesired composition changing material.

From the foregoing description of my invention it is apparent that as the ladle revolves, the materials contained therein, i. e., the molten metal and the composition completing material, are violently agitated and stirred due to the lifting and directing forces set up bythe projecting members 44, and the composition completing material is forced violently into intimate contact with the molten metal. As a result of this violent stirring and agitating action of the materials in the ladle the desired changes in the analysis of the molten metal are secured within a relathe lining IIc may be formed of any suitable tively short period; and since the ladle is insu- ,iated, there is 1itt1e,if any, heat ioss in the molten metal during the time it is being stirred in the ladle, and consequently it is unnecessary to subject the-treated molten metal to any auxiliary source of heat prior to the casting thereof.

I have found that when the ladle is being used to mix a carbonaceous material with molten iron that the desired ,carbon pick up and sulphur reductions occur in the iron almost instantaneously when the ladle is being revolved at a peripheral speed of at least feet per minute, and since this recarbonization and desulphurlzing of the iron takes place almost instantaneously it is apparent that my process and apparatus can be readily used to treat molten iron after it has been withdrawn from the cupola and before it is cast with little or no heat loss occurring in the metal during the time that the carbonaceous material and the desulphurizing agent are being added thereto.

With my method and apparatus I have found that I can get both the carbon pick up and the V sulphur reduction in the same ladle by using sodium carbonate or sodium nitrate in conjunc- `tion with the carbonaceous material and without the use of any other oxidizing agent, since by having a large volume of material in the mixing ladle the heat content of thematerial isalways maintained at a sufficiently high temperature to insure the carbon pick up under the violent agitation in the ladle `without the necessity of using any additional oxidizing agent. l

With my improved process and apparatus I have found that I can melt scrap iron or other forms of iron having a low carbon content (for example, 2.80%) and a high sulphur content (e. g., .20%) and practically instantaneously increase the carbon content. to any desired figure (e. g., 3.50%) and, at the same time, reduce the sulphur to any desired content (e. g., .04% or less), and I secure these results without reheating orholding up shop production, and I have produced good commercial castings from treating in this manner melted scrap mixtures of all types and descriptions in which all parts of the mix were of iron scrap material. y

While I have described my process in connection with a tilting ladle, itis to be understood that the same results can be obtained where the ladle is maintained in a horizontal. position with the iron running in at one end and coming out at the other end without departing from the spiritv of my invention.

Further, itis to be understood that my invention is not to be limited to the recarbonization of the molten iron but may be used as well to alloy ferrous metal with other metals such as copper, nickel, magnesium, and the like, which can be added to the mixing ladle, and since the metal in the ladle is violently agitated and periodically lifted and folded it is apparent that a complete alloying will take place and that an alloy metal suitable for pouring any commercial type of special casting can be readily produced. Since the ladle is well insulated by the lining lI I b it is obvious that this result can be obtained without any appreciable loss in temperature of the molten metal. Consequently, alloys can be produced in my mixing ladle from iron melted in a cupola without the so-calied duplexing process which is usually necessary in the production of special castings.

Further, it is to be understood that my invention is not to be limited to the recarbonization of molten iron but may be used as well to burn out excess carbon when certain types of steel or malleable castings are desired. In order to decrease the carbon content, an oxidizing agent such as sodium nitrate is added to the molten metal in the ladle while the ladle is being revolved at a high peripheral speed and the metal therein is being stirred and agitated which not only reduces the carbon and sulphur contents but also materially increases the temperature of the molten iron. When malleable castings are to be produced, a mixture of sodium nitrate and an alloying material is added to the molten iron in the revolving. ladle and the increased temperature of the molten iron occasioned by the sodium nitrate and the mixing resulting from the revolving of the ladle occasion a complete alloying of the material added with the sodium nitrate and the g molten iron in the ladle.

While I have described one embodiment of my invention it is apparent that I am not limited to the type of mixing ladle therein disclosed but that any type of mixing ladle which violently agitates and stirs the metal will suiilce to carry out my process and that other changes, modifications, additions, and subtractions may be made therein without departing from the spirit of my invention or the scope of the following claims.

What I claim as new and desire to secure by Letters Patent is:

1. A method of effecting a change' in the composition of ferrous metal which comprises charging a quota of molten ferrous metal and composition changing materials into the top of a container'which is rotating at a relatively high peripheral speed about a substantially vertical axis and while such rotation continues in tilting the container from such position of charging to pouring position whereby the composition of such metal is changed without an appreciabletemperature drop therein.

2. A method of effecting a change in the composition of ferrous metal which comprises charga

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