US3575230A - Method of making steel - Google Patents

Abstract

This disclosure proposes an improved method of continuous casting of steel or the like metals, especially with respect to the tapping temperatures, the initiation and the maintenance of casting operations. One aspect of such improved method resides in being able to successfully cast with furnace tapping temperatures which are substantially lower than the temperatures required to continuously cast conventionally. This is accomplished by pouring metal directly into a relatively small composite refractory reservoir having a chilling mold in close proximity thereof and whose refractory portions are intensely preheated to prevent premature solidification of molten metal in the refractory portions particularly in the area adjoining said chilling mold. It is essential that the heat-sensitive chilling mold not be subjected to the intense heat necessary for preheating the refractory. Specific procedures are set forth to protect the chilling mold, e.g. by cooling within defined temperature limits. Another aspect of the instant method resides in controlling the point at which the initial skin formation occurs, thereby preventing solidification of molten metal in the refractory portions of the apparatus. This is accomplished by determining the location of initial shell formation with the confines of the chilling mold and varying the speed at which the solidified shape is withdrawn from the chilling mold to retain the location of initial shell formation within the chilling mold.

Description

[lll 3,575,230

United States Patent ['72] Inventor Albert Calderon Primary Examiner-1. Spencer Overholser Assistant Examiner-R. Spencer Annear 7732 Ragall Parkway, Cleveland, Ohio 44130 Attorney-Settle, Batchelder and Oltman Continuation-impart of application Ser. No. 494,017, Oct. 8, 1965, now abandoned.

ABSTRACT: This disclosure proposes an improved method of continuous casting of steel or the like metals, especially with respect to the tapping temperatures, the initiation and the maintenance of casting operations. One aspect of such improved method resides in being able to successfully cast with furnace tapping temperatures which are substantially lower than the temperatures required to continuousl conventionally. This is accom directly into a relativel having a chilling mold in close refractory portions are intensely premature solidification of molten portions particularly in the area ad is essential that the heat-sensitive chillin subjected to the intense heat necessar refractory. Specific procedures are set chilling mold limits. Another aspect of the instant method the solidified shape is withdrawn retain the location of initial shell mold.

c.2, pps. 431- 435.

BLS-75,230

PAENTED APR2 o mn SHEET l F 3 I NVENTOR.

ALBERT CALDERON.

SE TTLE, BATCHELDER 8 OLTMAN.

ATT'YS.

SHEET 2 UF 3 INVENTOR. ALBERT CALDERON.

m m 8 m H m v E n S ATTl YS.

PATENTE@ ma@ @n SHEET 3 UF 3 V44 s 8,6. BN)

(OUT) INVENTOR. ALBERT CALDEON.

FIG. 6

SE TTLE BTCHELDER OLTMAN.

Il/IIETIHIOD OIF llfllNG STEEL CROSS REFERENCES TO RELATED APPLICATIONS This application is a continuation-in-part of the copending application of Albert Calderon, Ser. No. 494,017 filed in the U.S. Patent Office on Oct. 8, 1965, and assigned to the assignee of the present invention, now abandoned.

BACKGROUND OF THE INVENTION The continuous casting of steel and similar metals has been commercially accomplished for some time. However, it has been found that certain types and grades of steel cannot be continuously cast successfully, and that continuously cast steel necessarily suffers fromv various quality defects, such asv segregation of components of the steel composition, internal cracking of the continuously cast shape, poor external surface characteristics, and the occurence of pin holes" or porosity internally of the cast shape. Further the tapping temperatures of heats destined for conventional continuous casting must be very high approaching and even exceeding 3000 F. depending upon the carbon analysis and the heat size. The smaller the heat the higher the tapping temperature.

It has now been found by actual operations at the Duluth works of United States Steel Corporation that superior steels can be made by horizontal continuous casting asset forth in the above-identified earlier applicationof Albert Calderon, and that the tapping temperatures range from 2800 F. to a maximum of 2900" F. depending upon the carbon analysis, the heat size being l65 tons. Specifically, it has been found that the following tapping temperatures depending upon the carbon analysis are adequate to give a successful cast. For example, a steel containing 0.03 percent carbon which is real low requires a fumace tapping temperature of 2895 F. and a steel containing 0.80 percentcarbon which is fairly high, requires a tapping temperature of 2800 F. The tapping temperatures of the steels having a carbon analysis between 0.03` percent and 0.80 percent fall between 2895 F. and 2800" F. accordingly. As is evident to anyone skilled in the art of continuous casting, this range of temperatures is substantially lower and falls within the normal range of casting into regular ingots.

The success in casting higher quality steels generally at lower furnace tapping temperatures, is attributable to several factors present in the casting concept herein set forth. For example, a horizontal casting operation utilizing a mold of inverted T-shape or of L-shape does not require any increase in vertical height to obtain a correspondingly greater casting speed thus making possible very rapid and controlled cooling which also avoids segregation and improves surface quality. In the event a deoxidizer is used such as aluminum, segregation of aluminum oxide or other components does occur, but the segregated material merely floats to the surface of the vertical reservoir portion of the oscillating mold. The addition of aluminum as a deoxidizer tends to remove oxygen and reduces the tendency for the formation of internal cracks by increasing the ductility of the steel as cast. Further, the cast shape can be cooled more slowly horizontally than vertically, while the addition of aluminum increases the thermal diffusion rate. The addition of aluminum to increase the ductility of the cast metal and the faster movement of the initially formed skin through the chilling mold gives a better surface on the cast shape, while the casting from the quiescent pool provided by the vertical reservoir prevents the inclusion of air and reduces the formation of pinholes or the appearance of porosity in the center of the cast shape.

The heat losses necessarily incurred in present vertical casting (i.e. through the employment of tundish and the tundish nozzles, and through the free fall from the tundish into the water cooled copper mold) result in forcing the steelmaker to increase his furnace tapping temperatures which in turn causes higher fuel consumption, lower productivity and shorter refractory life.

It has not been found that in order to keep tapping temperatures-low and successfully initiate the casting process, it is critical to preheat the refractory portions of the mold to prevent initial chilling of the steel to such an extent that skin formation occurs in the refractory. This is one aspect of the present invention. Secondly, it has been found necessary (particularly during the initial stages of continuous casting) to positively prevent the formation of a solidified skin in the refractory and to form the skin only within the confines of the chilling mold. Otherwise, the skin will be formed against the refractory and will not strip from the mold, causing breakouts, inside as well as outside the mold. Breakouts inside the chilling mold cause defects to the surface while breakouts outside it force the shutting down of the process.

SUMMARY OF THE INVENTION As above explained, the present invention is concerned with continuous casting of steel or the like metals in an oscillatable mold. Such a mold comprises a composite refractory portion and'a chilling portion. In the case of a vertical oscillatable mold the refractory portion is mounted on top of the chilling portion, whereas in the case of the horizontal oscillatable mold, the mold comprises an upright or vertical reservoir section into which molten steel flows downwardly to a chilling portion of the mold. Whether the mold is of inverted T-shape or of L-shape, the flow of molten metal must be deflected from the downward vertical flow through the reservoir to horizontal flow through the horizontal chilling mold. This change in direction is accomplished by a joining portion which confines the molten steel from the vertical reservoir to the horizontal chilling mold. The reservoir and the joining portion are refractory lined, the chilling mold is nonrefractory lined. The chilling mold is cooled with water or other liquid coolant, and the chilling surfaces contracting the molten metal are preferably formed of a metal, such as copper, or graphite, or ofother heat conductive material. Of course, it is the function ofthe reservoir and the joining portion to feed molten metal to the chilling mold under a ferrostatic head which is not necessarily critical to be maintained constant. It is the function of the chilling mold to peripherally chill the molten metal passing through it to an extent such that a peripheral skin is formed which is self-supporting by the time the still partially molten shape issues from the open end of the mold.

lt is critical however to keep the refractory reservoir relatively small particularly said joining portion and also to keep the chilling portion in close proximity to said reservoir in order to effectively preheat the refractories and to keep the amount of superheat to a bare minimum. Further it is critical to eliminate all possible surfaces that cause skin formation on an inner face in order to prevent skin to cling and hang thereto. In fact, it is preferred to have said joining portion to diverge towards said chilling portion when casting bigger shapes to facilitate extraction of any premature4 skin i molten metal entering the reservoir and the attainable casting speed. Since it is necessary to take out only a minimum amount of heat in this way, the lower the tapping temperature, the better. The exact relationship is not yet known between temperature and speed. The carbon content of the steel also has an e`ect on speed, in that the higher the carbon content, the lower the tapping temperature and the faster the `casting speed. The addition of aluminum demands the increase of casting speed since it hastens freezing.

Of course, the lower the temperature the more likelihood there is that some skin formation will occur within the reservoir portion of the mold. To prevent any such possibility ofskin formation, the refractory portions of the mold are preheated in accordance with the present invention. Desirably, the preheating is accomplished by directing a combustion burner downwardly into the vertical reservoir portion of the mold and exhausting the combustion products through the mold joining portion and the mold chilling portion.

Since the preheating is done to appreciable temperatures, the chilling walls of the chilling portion of the mold may well be damaged by their exposure to the combustion gases, and the chilling walls must be protected. Such protection can be accomplished by either circulating coolant liquid through the chilling portion of the mold or by blocking the flow of combustion gases prior to entry into the chilling mold. Since one of the products of combustion, when a hydrocarbon fuel is utilized, is water, condensation occurs on the chill walls if the chill walls are excessively cooled. Thus, the chill walls are cooled to an extent such that their temperature is less than that of the deformation point of the chill walls themselves and greater than the dew point of the combustion products. The elimination of condensation is of utmost importance in order to prevent explosions. As is known in the art of steelmaking molten steel and moisture should never come in contact, and as a note of interest, an explosion did occur in Duluth on the 7th day of Feb. 1968 because of moisture in the composite mold. The operator failed to keep close control of chilling mold temperature and the amount of water circulating therethrough.

Further, in the lower tapping temperatures contemplated by this invention, there is a decided danger that the high heat extraction rates at the chilling mold may cause initial solidification or skin formation to occur in the refractory lined portions of the mold, i.e. particularly in the joining portion where the molten metal flows from the reservoir into the chill mold portions. In the event such skin fonnation should occur prematurely, it is extremely difficult to strip any such skin from the mold, because of the necessary surface irregularities in the refractory and because of the angularly related or arcuate walls in the joining portion. Of course, if an adequate skin is not built up interiorly of the chill mold portion, the cast shape issuing from the mold will not be selfsustaining and breakout" will occur.

Any such premature skin formation or the possibility of "breakout" is positively prevented by (l) determining the location of the point of initial skin formation within the chill mold proper, and (2) adjusting the speed of the withdrawal or takeout rolls to effect initial skin formation at their location or at another desired location. Other methods of controlling skin formation location might be considered such as the varying of the amount and/or speed of water flowing through said chill mold. To determine the location of the point of skin formation, the present invention proposes the provision of temperature sensing elements, e.g. thermocouples, preferably in the upper chilling surface of the mold, since the temperature of a portion of the chilling surface not in contact with the formed skin will be lower by virtue of thermal shrinkage of the formed skin away from the upper chilled surface. However, other means of determining the exact point of skin formation may be utilized, if desired.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is a side elevational view of the casting apparatus of the present invention illustrating an oscillating mold of inverted T-shape, a cooling mechanism and a withdrawal mechanism located exteriorly of the mold and a ladle for supplying molten metal to the mold;

FIG. 2 is a perspective view, with parts broken away and in section, illustrating specifically the mold of FIG. l;

FIG. 3 is a vertical sectional view, with parts shown in elevation;

FIG. 4 is an enlarged perspective view of a dummy bar head utilized for extracting cast steel from the apparatus of FIG. l;

FIG. 5 is an enlarged, fragmentary, sectional view illustrating the skin sensing and withdrawal speed control mechanism of the present invention; and

FIG. 6 is a vertical sectional view of a modified form of mold of the present invention of L-shaped configuration.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, reference numeral 10 refers generally to a continuous casting apparatus of the present invention, comprising generally a centrally located mold 1l which is horizontally oscillated by suitable means, such as an electric motor I2 and a crank I3, the mold being supported for such horizontal oscillation on wheels 14 running a horizontally extending track 15.

As illustrated in FIG. 2, the mold I1 is of inverted T-shape and partially solidified steel shapes I6 issue horizontally therefrom to be supported on support rollers I7 while a coolant, such as water, is sprayed thereon from sprinklers 18. Overhead hoods 20 are provided to convey away the steam evolved due to the spraying of the water on the still-hot, partially molten steel shapes 16. Power-driven withdrawal rolls 22 engage the steel shapes 16 only after the shapes have been mostly or completely solidified.

The mold Il receives molten steel from a ladle 25 supported over the mold by suitable means, as by cranehook 26, or transfer car (not shown), the ladle being positioned so that molten steel issuing from the ladle nozzle 27 enters directly into the vertical reservoir section of the mold ll without passing through an intermediate means such as a "tundish or pony ladle as used in the present art of continuous casting. The ladle 25 is provided with a conventional internal stopper 28 controllable from a conventional exterior mechanism 29 for opening and closing the nozzle 27. Preferably, the molten steel is issued from the ladle 25 into the mold 1l in accurately controlled, intermittent spurts" rather than as a continuous thin stream to lessen heat losses from the molten steel during pouring.

The apparatus l0 generally shown in FIG. l of the drawings is substantially the same as that disclosed in the aboveidentified copending application and the detailed operation thereof, which is also set forth in this copending application, need not be repeated here.

Turning now to FIG. 2 of the drawings, the mold 11 is illustrated in detail therein. Generally, the reservoir portion of the mold assembly ll comprises an exterior metal support skin 30 of rectangular cross section in a horizontal plane lined with a vertically arranged series of refractory bricks 31 inside which is a cast or rammed refractory core 32. The inner walls of the core 32 define the reservoir consisting. of an upward outwardly flared entry portion 33 and a central reservoir portion 34 merging through lower inwardly inclined wall portions 35 into a lower joining portion 36 surrounding a center opening or passage 37 which, at its lower ends, blends through straight or arcuate walls 38 into horizontal, oppositely directed passages 39 having outwardly facing openings 40. Passages 39, preferably are made to diverge towards openings 40 in order to provide a draft to facilitate stripping of prematurely formed skin, if any, and also enhance drainage.

Water cooled mounting plates 41 surround the refractory openings 40 and mounted on these mounting plates and projecting horizontally outwardly therefrom are the chill mold portions 42 of the mold Il'. Plates 41 also serve to cool the ends of chill mold portions 42 which abut against openings 40 in order to eliminate overheating of said ends to prevent the portions 42 from drooping and thus disturb their alignment. These chill mold portions consist of interior chill wall surfaces 43 which are generally planar in configuration and which, in combination, define the shape to be cast (FIG. 3). These surfaces 43 are actually the inner surfaces of the walls 44, these walls being surrounded by exterior metal walls 45 spaced therefrom, as through gap 46, this gap 46 completely surrounding the walls 44 and serving for the circulation of coolant liquid.

This liquid coolant is supplied to the gaps 46 through coolant conduits 50 communicating with a suitable source of coolant under pressure, such as water supplied by a pump, into vertical header boxes 5I positioned on either side of the outer extremities of the walls 44. The coolant flows, as per the directional arrows of FIG. 2, through joining conduits 52 into upper and lower distribution boxes S3 and through side distribution boxes 54 for flow into the gaps 46 and inwardly through the gaps 4o to upper and lower exit boxes 57 and side exit boxes 58 to vertically extending exit headers S9 from which the coolant circulates through exit conduit 60 to the drain.

lt will readily be appreciated that, as described in my earlier application, molten steel in the vertical reservoir 30 will flow downwardly through the joining portion 36 to exit horizontally through the chill molds 42 with the liquid coolantflowing through the gaps 46 chilling the molten metal sufficiently to form an exterior skin thereon which is self-sustaining by the time the cast shape leaves the chill mold portions.

In accordance with the present invention, and for thc reasons hereinbefore explained, it is necessary to preheat the reservoir passages 34 and 35 and the joining passages 37, the joining portion 33 and the outlet passages 39 prior to the introduction of molten metal, as from the ladle 25, into the mold llll. This preheating is accomplished as illustrated in FIG. 2 of the drawings by lowering atmovable combustion burner b into the upper inclined portion 33 of the mold Ill and directing a combustion gas and the products of combustion downwardly directly into the reservoir portion to preheat the refractory passages 34, 35, 37, 33 and 39 to elevated temperatures as to reduce to a minimum freezing of molten metal prematurely. The combustion products preferably are exhausted outwardly through the chill molds 42. However, since the chill walls 44 are formed of copper or similar heat conductive surfaces, the inner surfaces 43 of these walls may well be damaged when subjected to the intense heat of the combustion products.

If one were merely to circulate coolant liquid through the circulation system heretofore described, moisture would condense on the surfaces 43, since one of the primary combustion products of any combustible hydrocarbon gas is water. Upon subsequent introduction of molten metal into the mold, any contact between such condensed moisture and thc molten metal will immediately tum the moisture into steam and an explosion will result.

Thus, the circulation of moisture must be controlled to maintain the surfaces 43 at a temperature below the wai-page point of the walls 44 and yet above the dew point of the combustion gases. To ascertain such temperature, thermocouples, schematically illustrated at 66, and embedded in the walls 44 with their temperature responsive elements as close as possible to the interior wall surfaces 43, such thermocouples giving an accurate temperature of the surfaces 43 to avoid damage thereto or condensation thereon. lf desired, the thermocouples may be utilized to control the flow of liquid coolant through the coolant system to automatically maintain a temperature within the indicated extremes.

Another method of preventing damage to the surfaces 43 is the utilization of the dummy bar structure 70 illustrated schematically in FIG. 2 and in detail in FIG. 4 of the drawings. The dummy bar 70, of course, is utilized to pull initially formed steel shapes from the chill molds 42 in the manner described in detail by my earlier filed application. Such a dummy bar 70 has its free end 71 contoured and sized to be insertable into the chill mold passage defined by the walls 43, the front face of the dummy bar carrying an angle iron end 72 to which a head 73 is connected for relative swiveling movement by means of an eyebolt 74 and attaching bolt 75.

The head 73 may assume any suitable shape but by way of example is of the configuration illustrated in FIG. 4 of the drawings and includes a transverse block 77 of a size substantially smaller than, but of the same general configuration as, the mold space defined by the mold surfaces 43 and a longitudinal extension 73 having a transverse aperture 79 therein. Prior to insertion of the head 73 between the surfaces 43, a resilient, heat-resistant packing is applied to the transverse and longitudinal edges of the head 73. Such material may suitably be a resilient asbestos packing or fabric indication of the` 80 which if folded upon itself to provide a cushion of such thickness that the head will snuggly fit between the surfaces 43, and this packing then is secured to the head by suitable means, such as a reinforced adhesive tape 8l. Additionally, the head 73 and particularly the extension 73 thereof may be provided with an internal coolant passage 32 communicating with coolant conduits 83 by means of which a liquid coolant is circulated therethrough.

Upon insertion of the packed head 73 into the mold passage defined by the walls 43 (for example as illustrated in FIG. 6 of the drawings) the flow of combustion products into the chill mold area is prohibited or blocked and damage to the walls 44 is prevented. The packing of the head 73 not only insures the insulation of the heated combustion products from the chill mold chambers, it also serves to accommodate the expansion of the head after the head is contacted by the molten steel flowing from the reservoir and the joining portions. If the head were to fit snuggly into the chill mold passages, any thermal expansion of the head due to its contact with the hot molten metal would bind the head into the passage. If the head were made undersized and not packed, the molten steel would run past the head and out of the chill mold passages. By utilizing the resilient packing the expansion of the head is accommodated without jamming the head in the cooled passages. Thermal expansion of the head is also inhibited and rapid chilling of the molten steel in contact with the head is accommodated by the flow of circulating coolant through coolant passage 82, while the presence of solidified steel in the hold 79 of the head provides a mechanical means interlocking the steel and the head itself. Thus, the dummy bar and the at least partially solidified steel are interconnected for subsequent extraction of the cast shape from the chill mold passage by means of the withdrawal rolls engaging the rear end ofthe dummy bar 71.

Of course, if desired, other heating means may be substituted for the combustion burner 65. For example, an electric induction coil 35a (FIG. 2) may be embedded in the cast refractory 32 defining the reservoir and the joining portions. However, a metallic core must be utilized to accommodate preheating by means of an induction coil. Embedded heating cores of the electrical type also may be utilized, but such heaters are much less efficient than the combustion heater illustrated in FlG. 2, and are difficult to maintain.

One particularly useful combination of heating means incorporates the combustion burner 65 of FIG. 2 for initial preheating and an embedded induction coil which is energized only after the reservoir is filled with molten metal, the molten metal then acting as the core. The induction heating coil thus heats the reservoir and joining portion after the molten metal has been introduced thereinto during the crucial initial operating period, i.e. before a great deal of heat has been imparted to the reservoir and joining portion refractory walls by heat flow from the molten metal.

Another facet of the present invention, as above-described, resides in the control of the location of the initial skin formed in the chilled mold portions of the mold ll. This portion of the invention is illustrated in FIG. 5 of the drawings. In this FIG., the various mold elements are schematically represented, and the mold is illustrated during the actual casting process.

A plurality of thermocouples Tll through T7 are illustrated as being embedded in the upper chilling mold portion wall 44 with the heat sensitive elements thereof as close 'as possible to the undersurface 43 of this wall. These thermocouples each give an accurate indication of the temperature of that portion of the surface 43 immediately adjacent thereto.

Because of the circulation of the liquid coolant through the chill mold as indicated by directional arrows 35, a solidified skin will be formed on the molten metal, this skin being indicated at 36 and the molten interior of the shape to be cast by being indicated schematically by the broken line 87.

' Assuming that the initial skin formation occurs at the location of the line 38, the upper surface of the skin will thermally shrink away from the undersurface 43 of the wall 44. Since molten metal is no longer in direct, surface-to-surface contact with the undersurface of the wall 44 to the right of the location of the line 88, there will be a substantial difference in temperature reading between the thermocouple T1 and the thermocoupler T3. This difference will indicate the fact that the skin formed somewhere between these two locations.

Assuming that this is the place at which the desired skin formation is located, any more rapid formation of this skin will move the line 88 to the left. When this line becomes located between thermocouples T1 and T2 a temperature difference will exist therebetween. lf the skin forms more slowly, the line 88 moves to the right and the difference in temperature reading between any two thermocouples, such as T4 and T5 will indicate that the point of skin formation is intermediate these two points.

By connecting the thermocouples Tl through T7 in a desired pattern and into an appropriate circuit indicated schematically at 90, the difference in reading between successive thermocouples can be utilized to speed up or slow down the rotational speed of the withdrawal rolls 22 with compensation to the oscillatory motion of mold 11, to position the line 88 at any desired location along the surface 43. Thus, by determining the location of the point of initial skin formation along the surface 43 and then varying the speed of the withdrawal rolls in accordance with the location of this initial skin formation, premature skin formation against the refractory walls of the reservoir or joining portions of the mold can be readily avoided. ln operation it has been found that in order to eliminate freezing up in said refractory portions, it is imperative to immediately start withdrawal as soon as molten metal is poured into said reservoir. Also it is very important to keep the withdrawal continuous as the molten metal must always be kept in a dynamic state. ln conventional casting, feeding from a tundish or pony ladle, this is not the case; in fact in many instances the flow and/or mold are completely stopped during casting. ln the case of a composite reservoir and chill mold, skin tends to creep from the chill mold into the refractory portions if the speed is too slow or if there is an interruption of withdrawal, causing freezeups which result in starving the flow of molten metal into the chill mold which eventually shuts the system or which result in clinging or hanging in said refractory portions causing breakouts which often occur externally forcing the immediate cessation of operations and also causing damage to the equipment adjacent to the exit end of said chill mold.

That embodiment of the invention illustrated in FIG. 6 of the drawings is substantially the same as that illustrated in FlG. 2, with the exception that the mold is L-shaped rather than of inverted T-shape. The same reference numerals refer to like parts of both embodiments of the invention.

lt will be understood that the preheating can also be utilized in connection with vertical continuous casting apparatus. In this event, the mold and the reservoir are vertically aligned so that the at least partially solidified shape issues vertically from the chilling mold. The problem of protecting the chill mold from the intense heat of the preheating, is the same as heretofore described, and the chill mold is protected in the same manner as above set forth in detail. Thus, it is not deemed necessary to illustrate or describe in detail the adaption of the method of the present invention to this specific apparatus. However, the great advantages obtained in eliminating the need for the conventional tundish by preheating will be apparent to those skilled in the art.

For purposes of clarity, the details of the dummy bar withdrawal means, the mechanism for shearing the cast shape to length and the other handling mechanism are also deleted from this disclosure. The above-identified, earlier filed, copending application sets forth such mechanisms and can be referred to for specific disclosures of these parts if necessary.

Also set forth in the earlier application is the specific lubrication of the chilling mold wall surfaces. Such lubrication can be utilized herein if desired or necessary.

Iclaim:

l. ln the tapping of furnaces making metals destined for continuous casting, the method of continuously casting metals by the steps of tapping the heat of molten metal in the aforementioned range into a ladle, transporting the ladle to an oscillatable mold which is adapted for the flow of molten metal therethrough and having a reservoir portion and a chill portion said portions encompassing interior metal receiving open-ended passages communicating with each other through a joining passage, the reservoir passage and the joining passage being defined by refractory walls, and said chilling passage being defined by nonrefractory walls cooled sufficiently to partially solidify the molten metal passing therethrough thereby forming a solidified peripheral shell of the shape to be cast, which shape is further solidified by secondary cooling means, withdrawn by withdrawal means and cut by cutting means, said secondary cooling means, withdrawal means and cutting means being located exteriorly of said mold; the improvements employing the same range 0f tapping temperatures as those employed in the casting into ingots but which temperatures are substantially lower than the temperatures required by conventional continuous casting comprising the steps of applying directly intense heat to the refractory walls of the reservoir passage and the joining passage to preheat them to an extent sufficient to prevent chilling and consequent freezing of the molten metal initially introduced in said refractory passages; concurrently protecting the nonrefractory walls of said chilling passage from the intense heat applied by cooling said chilling passage walls and by inserting into said chilling passage a dummy bar having its one end engageable with said withdrawal means and its other end provided with a head interposed between said refractory and nonrefractory walls; pouring molten metal directly from said ladle into said reservoir; the application of said intense heat taking place prior to the introduction of the molten metal and for an adequate period of time to sufficiently preheat said reservoir and joining passage; and activating said withdrawal means at the introduction of molten metal into said reservoir to withdraw without delay the dummy bar and the skin being instantaneously formed away from said reservoir joining passage in order to prevent solidified skin from creeping and building up inside said refractory passages.

2. ln a method as set forth in claim l, the improvement of the nonrefractory walls of the chilling passage being metallic and water cooled.

3. ln a method as defined in claim l, the further improvement wherein the step of preheating is accomplished by a combustion heating means positioned vertically adjacent the reservoir portion of the mold.

4. ln a method as set forth in claim l, the further improvement wherein the preheating is accomplished by electrical heating means.

5. ln a method as set forth in claim 4, the further improvement wherein said heating is accomplished by a combination of combustion heating means and electric heating means, said combustion heating means being turned off just prior to the feed of molten metal into the vertical portion and the electrical heating means being utilized after introduction of molten metal into the reservoir portion.

6. In a method as defined in claim l, the further improvement of accomplishing the step of protecting the walls of the chilling passage by circulating controlled amounts of water in heat exchange relation to said walls.

7. In a method as set forth in claim 1, the further improvement wherein the protection of said walls of said chilling passage is accomplished by locating a heat shield at the juncture of the joining passage and said chilling passage.

8. The method as set forth in claim 6 wherein sufficient amount of coolant is circulated to maintain the chilling walls at a temperature below the warpage point thereof and above the dew point of the combustion gases coming in contact therewith to prevent condensation of moisture on said walls.

9. ln a method as set forth in claim 1 wherein the casting is applicable to steelmaking, the further improvement resides in tapping the furnace between 2800 F. and 2900 F. depending upon the carbon analysis of the heat, the lower the carbon the higher the tapping temperature.

l0, In a method as set forth in claim l, the further improvement wherein the activation of said withdrawal means is followed by variation of speed thereof to insure that no skin forms inside said refractory passages nor the partially solidified shell leaves the chilling passage with too thin a shell.

lll. In a method as set forth in claim l, the further improvement wherein the withdrawal of said shape is always kept in a dynamic state to prevent skin formation and ultimate freeze up in said refractory passages.

l2. ln a method as set forth in claim l, the further improvement wherein the pouring of molten metal into said reservoir is performed in spurts rather than dribbles in order to minimize heat losses as the metal passes from said ladle into said reservoir.

i3. The method as set forth in claim l, the further improvement wherein the initial stripping of the partially solidified shape from said chilling lportion is aided by an articulated joint located between the head and the dummy bar to compensate for misalignment.

la. ln a method of casting steel utilizing a continuous casting apparatus including (l) an oscillating mold adapted for the flow of molten steel therethrough and having a vertical reservoir portion and at least one horizontal chilling portion, said portions encompassing interior metal-receiving, openended passages communicating with one another through a joining passage, the reservoir passage and the joining passage being defined by refractory walls land said chilling passage being defined by nonrefractory walls cooled sufficiently to at least partially solidify the molten metal passing therethrough, thereby forming a solidified peripheral shell of the shape to be cast, and (2) cooling means, variable speed withdrawal means and cutting means located exteriorly of the mold for forming fully solidified steel shapes of discrete length from the partially solidified shape continuously issuing from the mold; the improvement insuring initial shell formation within the confines of said chilling passage and comprising the steps of determining the location'of initial shell formation within the confines of said chilling passage, and varying the speed of said withdrawal means to retain said location of initial shell fonnation within said chilling passage.

l. ln a method as defined in claim i4, further improvement of determining the location of initial shell formation Vby measuring the gradient of temperature along said chilling passage.

lb. ln a method as defined in claim i4, the further improvement of determining the location of initial shell formation by the difference in temperature between a pair of thermocouples responsive to a temperature gradient in an upper, liquid cooled wall of said chilling passage.

i7. ln a method of casting steel continuously in a horizontally reciprocable mold of inverted T-shape and wherein a central open-topped vertical reservoir receives molten metal which flows downwardly and laterally outwardly through transition passages into oppositely directed, openended, molds from which at least partially solidified shapes issue, the reservoir and transition passages being provided with refractory nonchilling molten metal contacting surfaces and said molds having chilling surfaces for contacting the molten metal and means for circulating a fluid coolant through said molds to cool said chilling surfaces, the improvements residing in the steps performed prior to initial introduction of molten metal into said mold of (l) injecting and burning a combustible fuel vin said reservoir and said transition passages, (2) exhausting the combustion products ,Y

l@ the refractory linings of said reservoir and said transition passages are preheated to an extent sufficient to prevent any substantial surface chilling effect on molten steel subsequently introduced into contact therewith.

i8. ln a method of casting steel wherein molten steel is introduced into a vertical, open-topped refractory lined reservoir for flow through a refractory-lined joining passage into and through a horizontal, open-ended, metal-lined mold in which the molten steel is chilled sufficiently to form a peripheral skin which is self-sustaining by the time the metal issues from the mold, the reservoir, joining passage and mold being jointly reciprocable in a horizontal plane and wherein withdrawal rolls exterior to the mold engage the skin to continuously withdraw at least partially solidified steel from the mold, the improvement facilitating initiation of casting operations and residing in the steps of (l) positioning a combustion burner adjacent the open top of said reservoir, (2) injecting a combustible fuel through said burner, (3) burning said fuel in said reservoir, (4) exhausting the combustion products from said reservoir by flowing the same downwardly through said joining portion and outwardly through said metal-lined mold, (5) circulating a coolant fluid through said metal-lined mold to maintain the metal lining thereof at a temperature between the warpage point of the metal lining and the dew point of the combustion products, (6) continuing steps (l) through (5) until the refractory lining of said reservoir and said joining passage are at an elevated temperature adequate to prevent sufficient chilling of the molten steel flowing therethrough to solidify molten metal after the initiation of casting operations, and (7) initiating continuous casting operations only after said refractory lining attains said elevated temperature.

19. ln a method as set forth in claim l, the further improvement wherein the end of said chill portion next to said joining passage is effectively kept cool by a water cooled plate means in order to maintain the alignment of said chill portion.

20. ln a method as set forth in claim 14, the further improvement wherein the adjustment of the cooling capacity of said cooling means is effected to correspond to the varying speed of said withdrawal means, said varying of speed being employed to insure the location of initial skin formation within said chilling passage and also the prevention of skin creepage from said chilling passage into said refractory passage.

.21. ln a method as set forth in claim l5, the further improvement of applying heat to said molten metal in atleast one of said reservoir and said joining passage in the event the speed of said withdrawal means drops below a critical level in order to insure the prevention of skin formation which would creep from said chilling passage into said reservoir passage.

22, ln the tapping of fumaces making metals destined for continuous casting by the steps of tapping the heat of molten metal into a ladle; transporting the ladle to a mold which is adapted for the flow of molten metal therethrough and having a reservoir portion and a chill portion, said portions encompassing interior metal receiving open-ended passages communicating with each other through a joining passage, the reservoir passage and the joining passages being defined by refractory walls, said chilling passage being defined by nonrefractory walls cooled sufficiently to partially solidify the molten metal passing therethrough thereby forming a solidified peripheral shell of the shape to be cast which shape is further solidified vby secondary cooling means, withdrawn by withdrawal means and cut by cutting means, said secondary cooling means, withdrawal means and cutting means being located exteriorly of said mold; the improvement comprising: the steps of cooling said chilling passage and inserting into said chilling passage a dummy bar having its one end engageable with said withdrawal means and its other end provided with a head located at the juncture of said refractory and nonrefractory walls to aid in initially stripping the solidified metal from said chilling portion; pouring molten metal from said ladle into said reservoir; applying sufficient heat by means of an electrical heating unit at the time of the introduction of the molten metal and thereafter for an adequate period of time to suiciently heat said reservoir and joining passage to insure the prevention of solidification of metal in said refractory walls and thereby make possible the tapping of the metal at lower furnace temperatures and with minimum superheat; starting said withdrawal means at the introduction of molten metal into said reservoir to withdraw without delay the dummy bar and the skin being instantaneously formed away from said reservoir joining passage in order to prevent solidified skin from creeping and building up inside said refractory passages; deactivating said heating unit once said refractory walls have been soaked with heat; and reactivating said heat unit if there is a slowdown in the speed of said withdrawal means in order to prevent solidified skin from creeping into said reservoir portion from said chilling portion.

23. ln a method as set forth in claim 22, the improvement of tapering the refractory joining passage divergently towards said chilling passage in order to facilitate the stripping of solidified skin in the event such skin should form within said joining passage.

24. ln a method of casting steel utilizing a continuous casting apparatus including a mold adapted for the flow of molten steel therethrough and having a vertical reservoir portion for receiving molten steel from a ladle or the like and at least one horizontal chilling portion, said portions encompassing interior metal-receiving, open-ended passages communicating with one another through an arcuate joining passage, the reservoir passage and the joining passage being defined by refractory walls and said chilling passage being defined by metal walls cooled sufficiently to at least partially solidify the molten metal passing therethrough, thereby forming therein a solidified peripheral shell having the shape of said passage and cooling means, withdrawal means and cutting means located exteriorly of the mold for forming fully solidified steel shapes of discrete length from the partially solidified shape continuously issuing from the mold; the improvementaiding in starting continuous casting operation and accommodating the casting of molten steel at temperatures substantially lower than those necessary in vertical continuous casting comprising the steps of l directly applying intense heat to the refractory walls of the reservoir passage and the joining passage prior to the introduction of the molten metal thereinto to preheat said passages to an extent sufficient to inhibit chilling and consequent freezing of that molten metal initially introduced into said passages, and (2) concurrently cooling said metallic walls to protect the metallic walls of said chilling passage from the intense heat applied to said reservoir and joining passages.

25. ln a method as defined in claim 24, the further improvements insuring initial shell formation within the confines of said chilling passage and comprising the steps of determining the location of initial shell formation, and adjusting the speed of said withdrawal means to retain said location.

Claims (24)

1. 2. In a method as set forth in claim 1, the improvement of the nonrefractory walls of the chilling passage being metallic and water cooled.
2. 3. In a method as defined in claim 1, the further improvement wherein the step of preheating is accomplished by a combustion heating means positioned vertically adjacent the reservoir portion of the mold.
3. 4. In a method as set forth in claim 1, the further improvement wherein the preheating is accomplished by electrical heating means.
4. 5. In a method as set forth in claim 4, the further improvement wherein said heating is accomplished by a combination of combustion heating means and electric heating means, said combustion heating means being turned off just prior to the feed of molten metal into the vertical portion and the electrical heating means being utilized after introduction of molten metal into the reservoir portion.
5. 6. In a method as defined in claim 1, the further improvement of accomplishing the step of protecting the walls of the chilling passage by circulating controlled amounts of water in heat exchange relation to said walls.
6. 7. In a method as set forth in claim 1, the further improvement wherein the protection of said walls of said chilling passage is accomplished by locating a heat shield at the juncture of the joining passage and said chilling passage.
7. 8. The method as set forth in claim 6 wherein sufficient amount of coolant is circulated to maintain the chilling walls at a temperature below the warpage point thereof and above the dew point of the combustion gases coming in contact therewith to prevent condensation of moisture on said walls.
8. 9. In a method as set foRth in claim 1 wherein the casting is applicable to steelmaking, the further improvement resides in tapping the furnace between 2800* F. and 2900* F. depending upon the carbon analysis of the heat, the lower the carbon the higher the tapping temperature.
9. 10. In a method as set forth in claim 1, the further improvement wherein the activation of said withdrawal means is followed by variation of speed thereof to insure that no skin forms inside said refractory passages nor the partially solidified shell leaves the chilling passage with too thin a shell.
10. 11. In a method as set forth in claim 1, the further improvement wherein the withdrawal of said shape is always kept in a dynamic state to prevent skin formation and ultimate freeze up in said refractory passages.
11. 12. In a method as set forth in claim 1, the further improvement wherein the pouring of molten metal into said reservoir is performed in spurts rather than dribbles in order to minimize heat losses as the metal passes from said ladle into said reservoir.
12. 13. The method as set forth in claim 1, the further improvement wherein the initial stripping of the partially solidified shape from said chilling portion is aided by an articulated joint located between the head and the dummy bar to compensate for misalignment.
13. 14. In a method of casting steel utilizing a continuous casting apparatus including (1) an oscillating mold adapted for the flow of molten steel therethrough and having a vertical reservoir portion and at least one horizontal chilling portion, said portions encompassing interior metal-receiving, open-ended passages communicating with one another through a joining passage, the reservoir passage and the joining passage being defined by refractory walls and said chilling passage being defined by nonrefractory walls cooled sufficiently to at least partially solidify the molten metal passing therethrough, thereby forming a solidified peripheral shell of the shape to be cast, and (2) cooling means, variable speed withdrawal means and cutting means located exteriorly of the mold for forming fully solidified steel shapes of discrete length from the partially solidified shape continuously issuing from the mold; the improvement insuring initial shell formation within the confines of said chilling passage and comprising the steps of determining the location of initial shell formation within the confines of said chilling passage, and varying the speed of said withdrawal means to retain said location of initial shell formation within said chilling passage.
14. 15. In a method as defined in claim 14, further improvement of determining the location of initial shell formation by measuring the gradient of temperature along said chilling passage.
15. 16. In a method as defined in claim 14, the further improvement of determining the location of initial shell formation by the difference in temperature between a pair of thermocouples responsive to a temperature gradient in an upper, liquid cooled wall of said chilling passage.
16. 17. In a method of casting steel continuously in a horizontally reciprocable mold of inverted T-shape and wherein a central open-topped vertical reservoir receives molten metal which flows downwardly and laterally outwardly through transition passages into oppositely directed, open-ended, molds from which at least partially solidified shapes issue, the reservoir and transition passages being provided with refractory nonchilling molten metal contacting surfaces and said molds having chilling surfaces for contacting the molten metal and means for circulating a fluid coolant through said molds to cool said chilling surfaces, the improvements residing in the steps performed prior to initial introduction of molten metal into said mold of (1) injecting and burning a combustible fuel in said reservoir and said transition passages, (2) exhausting the combustion products of said fuel through said molds, (3) circulating said fluid coolant Through said molds to an extent sufficient to retain the temperature of said mold chilling surfaces (a) below that temperature at which said surfaces will be damaged and (b) above the dew point of the combustion products flowing therethrough and, (4) continuing steps (1) through (3) until the refractory linings of said reservoir and said transition passages are preheated to an extent sufficient to prevent any substantial surface chilling effect on molten steel subsequently introduced into contact therewith.
17. 18. In a method of casting steel wherein molten steel is introduced into a vertical, open-topped refractory lined reservoir for flow through a refractory-lined joining passage into and through a horizontal, open-ended, metal-lined mold in which the molten steel is chilled sufficiently to form a peripheral skin which is self-sustaining by the time the metal issues from the mold, the reservoir, joining passage and mold being jointly reciprocable in a horizontal plane and wherein withdrawal rolls exterior to the mold engage the skin to continuously withdraw at least partially solidified steel from the mold, the improvement facilitating initiation of casting operations and residing in the steps of (1) positioning a combustion burner adjacent the open top of said reservoir, (2) injecting a combustible fuel through said burner, (3) burning said fuel in said reservoir, (4) exhausting the combustion products from said reservoir by flowing the same downwardly through said joining portion and outwardly through said metal-lined mold, (5) circulating a coolant fluid through said metal-lined mold to maintain the metal lining thereof at a temperature between the warpage point of the metal lining and the dew point of the combustion products, (6) continuing steps (1) through (5) until the refractory lining of said reservoir and said joining passage are at an elevated temperature adequate to prevent sufficient chilling of the molten steel flowing therethrough to solidify molten metal after the initiation of casting operations, and (7) initiating continuous casting operations only after said refractory lining attains said elevated temperature.
18. 19. In a method as set forth in claim 1, the further improvement wherein the end of said chill portion next to said joining passage is effectively kept cool by a water cooled plate means in order to maintain the alignment of said chill portion.
19. 20. In a method as set forth in claim 14, the further improvement wherein the adjustment of the cooling capacity of said cooling means is effected to correspond to the varying speed of said withdrawal means, said varying of speed being employed to insure the location of initial skin formation within said chilling passage and also the prevention of skin creepage from said chilling passage into said refractory passage.
20. 21. In a method as set forth in claim 15, the further improvement of applying heat to said molten metal in at least one of said reservoir and said joining passage in the event the speed of said withdrawal means drops below a critical level in order to insure the prevention of skin formation which would creep from said chilling passage into said reservoir passage.
21. 22. In the tapping of furnaces making metals destined for continuous casting by the steps of tapping the heat of molten metal into a ladle; transporting the ladle to a mold which is adapted for the flow of molten metal therethrough and having a reservoir portion and a chill portion, said portions encompassing interior metal receiving open-ended passages communicating with each other through a joining passage, the reservoir passage and the joining passages being defined by refractory walls, said chilling passage being defined by nonrefractory walls cooled sufficiently to partially solidify the molten metal passing therethrough thereby forming a solidified peripheral shell of the shape to be cast which shape is further solidified by secondary coolIng means, withdrawn by withdrawal means and cut by cutting means, said secondary cooling means, withdrawal means and cutting means being located exteriorly of said mold; the improvement comprising: the steps of cooling said chilling passage and inserting into said chilling passage a dummy bar having its one end engageable with said withdrawal means and its other end provided with a head located at the juncture of said refractory and nonrefractory walls to aid in initially stripping the solidified metal from said chilling portion; pouring molten metal from said ladle into said reservoir; applying sufficient heat by means of an electrical heating unit at the time of the introduction of the molten metal and thereafter for an adequate period of time to sufficiently heat said reservoir and joining passage to insure the prevention of solidification of metal in said refractory walls and thereby make possible the tapping of the metal at lower furnace temperatures and with minimum superheat; starting said withdrawal means at the introduction of molten metal into said reservoir to withdraw without delay the dummy bar and the skin being instantaneously formed away from said reservoir joining passage in order to prevent solidified skin from creeping and building up inside said refractory passages; deactivating said heating unit once said refractory walls have been soaked with heat; and reactivating said heat unit if there is a slowdown in the speed of said withdrawal means in order to prevent solidified skin from creeping into said reservoir portion from said chilling portion.
22. 23. In a method as set forth in claim 22, the improvement of tapering the refractory joining passage divergently towards said chilling passage in order to facilitate the stripping of solidified skin in the event such skin should form within said joining passage.
23. 24. In a method of casting steel utilizing a continuous casting apparatus including a mold adapted for the flow of molten steel therethrough and having a vertical reservoir portion for receiving molten steel from a ladle or the like and at least one horizontal chilling portion, said portions encompassing interior metal-receiving, open-ended passages communicating with one another through an arcuate joining passage, the reservoir passage and the joining passage being defined by refractory walls and said chilling passage being defined by metal walls cooled sufficiently to at least partially solidify the molten metal passing therethrough, thereby forming therein a solidified peripheral shell having the shape of said passage and cooling means, withdrawal means and cutting means located exteriorly of the mold for forming fully solidified steel shapes of discrete length from the partially solidified shape continuously issuing from the mold; the improvement aiding in starting continuous casting operation and accommodating the casting of molten steel at temperatures substantially lower than those necessary in vertical continuous casting comprising the steps of (1) directly applying intense heat to the refractory walls of the reservoir passage and the joining passage prior to the introduction of the molten metal thereinto to preheat said passages to an extent sufficient to inhibit chilling and consequent freezing of that molten metal initially introduced into said passages, and (2) concurrently cooling said metallic walls to protect the metallic walls of said chilling passage from the intense heat applied to said reservoir and joining passages.
24. 25. In a method as defined in claim 24, the further improvements insuring initial shell formation within the confines of said chilling passage and comprising the steps of determining the location of initial shell formation, and adjusting the speed of said withdrawal means to retain said location.

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