US3517726A - Method of introducing molten metal into a continuous casting mold - Google Patents

Description

N. T. MILLS ET AL METHOD OF INTRODUCING MOLTEN METAL INTO June 30, 1970 A CONTINUOUS CASTING MOLD Filed Aug. 4, 1969 2 Sheets-Sheet 1 H1 H11 )ull "HIH HH 115 II iii Inventors Norman. T. Mills Charles R.JackSon. James Inhi'falleqk fl-H-orneg June 30, 1970 M s ET AL 3,517,726

METHOD OF INTRODUCING MOLTEN METAL INTO A CONTINUOUS CASTING MOLD Filed Aug. 4, 1969 2 Sheets-Sheet 3 WIIIVII1II.,-,

WIIIIIIIIIIIIIIA Inventors Norman. T. Mills Char-[es R.J acl son mes m. Hfaller s mmww kasww rHzorriegs United States Patent 3,517,726 METHOD OF INTRODUCING MOLTEN METAL INTO A CONTINUOUS CASTING MOLD Norman Thomas Mills, Highland, Charles Richard Jackson, Hammond, and James Wood Halley, Chesterton, Ind., assignors to Inland Steel Company, Chicago, Ill., a corporation of Delaware Continuation-impart of application Ser. No. 779,088,

Nov. 26, 1968. This application Aug. 4, 1969, Ser.

Int. Cl. B22d 11/10 US. Cl. 164-82 14 Claims ABSTRACT OF THE DISCLOSURE A continuous casting process whereby objectionable surface inclusions are substantially eliminated from the continuous casting and wherein molten steel is introduced into a continuous casting mold by an injection means which discharges the molten metal into the mold below the surface of the molten metal pool maintained in the mold through controlled streams having an upwardly and outwardly flowing component which contact the solidifying casting surfaces to wash away objectionable inclusion materials normally frozen into the casting and deliver the objectionable inclusion material to the surface of the molten metal pool where they can be readily removed.

Injection nozzles adapted for use with continuous casting molds are disclosed which comprise tubular sections having circumferentially spaced lateral discharge openings for introducing the molten metal into the mold.

This application is a continuation-in-part application of copending U.S. application Ser. No. 779,088, filed Nov. 26', 1968.

The present invention relates generally to an improved continuous casting method and apparatus, and more particularly to an improved method of continuously introducing molten metal into an open ended continuous casting mold and to submergible injection nozzles used for introducing molten metal into a continuous casting mold.

In the continuous casting of molten metals and particularly molten steel, non-metallic inclusion materials, such as aluminum oxide and aluminum silicon oxide and gaseous bubbles of carbon oxides frequently cause surface defects in the rolled steel because the inclusion materials tend to become trapped in or near the surface portion of the casting adjacent the mold wall. The inclusion materials are particularly objectionable, for example, when entrapped in the wider sides of a rectangular casting, such as a steel slab, where after rolling into finished steel, the wider sides form the fiat surfaces of the rolled steel. Problems of a generally similar nature are encountered in the continuous casting of steel billets and blooms.

'Bifurcated submerged injection nozzles have heretofore been used which direct the incoming molten metal in streams flowing in diametrically opposite directions toward the narrower end walls of a mold having an elongated rectangular cross-section, but such nozzles do not prevent trapping the oxide and other objectionable inclusion materials in the wider lateral surfaces of such a continuous casting. As a result, the rolled sheets produced from such castings frequently have objectionable defects along the fiat surface thereof which reduce the value and usefulness of the sheet product.

Molten metal has also been introduced into a continuous casting mold through nozzles having a plurality of submerged outlets which are designed to impart to the molten metal within the mold a rotating or circular motion concentric with the longitudinal axis of the inice jection nozzle and mold to obtain more effective mixing of additives (see U.S. Pat. No. 2,224,414 and No. 2,290,- 083) or to prevent coarse grain crystallization (see US. Pat. No. 3,050,793). Others have attempted to reduce the surface imperfections in continuous 'bastings by minimizing the contact between the inflowing molten metal and the solidifying metal skin and by avoiding creating significant currents in the molten metal in the mold (see French Pat. No. 1,492,871 and U.S. Pat. No. 3,371,- 704). Such efforts, however, have not solved the major problem of preventing the trapping of oxides and other objectionable inclusion materials near the surface of the casting, particularly along the longer casting surfaces and edges adjacent the corners of a continuous casting having an elongated rectangular cross-section, and the products made from such castings contain objectionable surface imperfections and are, therefore, less valuable and useful.

It is, therefore, an object of the present invention to provide an improved method and apparatus for continuously casting molten metal in a continuous casting mold which substantially avoids trapping oxides and other objectionable matter in or near the lateral surfaces of a continuous casting, particularly in the wider faces of a continuous casting when the mold has an elongated rectangular form.

It is a further object of the present invention toprovide an improved submergible injection nozzle for introducing molten metal into a continuous casting mold which reduces the likelihood of entrapping inclusion materials in the lateral surfaces of a continuous casting, such as in the wider lateral surfaces of the casting when the continuous casting mold has an elongated rectangular shape.

Other objects of the invention will be apparent to those skilled in the art from the following detailed description and claims when read in conjunction with the accompanying drawing wherein:

FIG. 1 is a fragmentary schematic perspective view of the upper section of a continuous casting mold which shows a continuous casting being produced in accordance with the present invention (the submerged lower end of the axially disposed injection nozzle being omitted for clarity).

FIG. 1A is a vertical sectional view taken along the line 1A1A of FIG. 1;

FIG. 1B is a vertical sectional view taken along the line 1B-1B of FIG. 1;

FIG. 2 is a fragmentary schematic side elevational view partially in vertical section of an injection nozzle embodying the present invention and which is operatively disposed in an elongated rectangular continuous casting mo d;

FIG. 2A is a fragmentary schematic vertical sectional view taken along the line 2A2A of FIG. 2;

FIG. 2B is a schematic horizontal sectional view taken along the line 2B-2B of FIG. 2;

FIG. 3 is a fragmentary schematic side elevational View partially in vertical section of a modified form of injection nozzle operatively disposed in an elongated rectangular continuous casting mold;

FIG. 3A is a horizontal sectional view taken along the line 3A3A of FIG. 3;

FIG. 3B is a horizontal sectional view showing the injection nozzle of FIGS. 3 and 3A disposed in an alternate operative position with an elongated rectangular continuous casting mold.

FIG. 4 is a fragmentary schematic side elevational view partially in vertical section of a further modified form of injection nozzle operatively disposed in an elongated rectangular continuous casting mold;

FIG. 4A is a horizontal sectional view taken along the line 4A-4A of FIG. 4;

FIG. 5 is a fragmentary schematic side elevational view partially in vertical section of a still further modified form of injection nozzle operatively disposed in an elongated rectangular continuous casting mold;

FIG. 5A is a horizontal sectional view taken along the line SA-SA of FIG. 5;

FIG. 6 is a fragmentary schematic side elevational view partially in vertical section of another modified form of injection nozzle operatively disposed in a square continuous casting mold; and

FIG. 6A is a horizontal sectional view taken along the line 6A6A of FIG. 6.

It has been found that the foregoing and other objects of the present invention can be achieved by introducing molten metal into a continuous casting mold with a generally vertically disposed mold wall in a manner which establishes a novel dynamic fluid flow pattern of molten metal within the pool of molten metal maintained in the upper portion of the mold. In the preferred embodiment the novel flow pattern is established by forming in the pool a plurality of streams of molten metal horizontally spaced less than 180 degrees apart which flow toward the mold and have at the point of introduction into the mold a fixed directional orientation with the axis of each of the streams lying substantially in the same plane and with each of the streams having an upwardly flowing component of sufficient velocity to contact and wash the surface of the solidifying casting supported by the mold wall where the metal is initially solidifying at a very high freezing rate and effectively carry away from the solidifying wall surface of the casting objectional inclusion materials. The several streams of molten metal flowing upwardly in a generally axial direction carrying the objectionable inclusion materials preferably substantially merge to form a substantially uniform front so that the molten metal is substantially uniformly distributed over the surface of the solidifying casting. The upwardly flowing streams travel with sufiicient dynamic energy that upon reaching the upper surface of the molten metal, they form a standing wave on the surface of the pool of molten metal adjacent the mold wall and then flow inwardly away from the wall toward the axis of the casting forming a central depressed zone or trough.

The invention will initially be described in connection with the continuous casting of slabs in an elongated rectangular mold having a pair of wider opposed side walls and a pair of narrow opposed end walls.

FIG. 1 of the drawing illustrating a process of continuous casting in a generally vertically disposed elongated rectangular mold (but which is typical of continuous casting in a mold of any configuration) schematically shows the flow pattern of the molten metal ideally established in a pool of molten metal maintained in the upper end portion of a continuous casting mold 10 and a continuous casting 11 in accordance with the present invention. The novel flow pattern established is such that it effects removal from the initially solidifying walls of the casting the objectional inclusion materials which normally are frozen into the surface of the continuous casting and thereby facilitates forming continuous castings having a substantially inclusion-free surface, particularly in the wider lateral surfaces 12, 12 of an elongated rectangular casting which corresponds to the exposed flat surfaces of a rolled steel sheet formed therefrom. The objectionable inclusion materials which are swept away from the rapidly freezing face of the continuous casting preferably collect on the surface of the central depressed zone or trough 1! formed in the upper molten metal surface 13 of the casting where they agglomerate to form a slag 14. Because of the low density of the agglomerated slag 14, the slag floats on the surface of the molten metal and is not incorporated in the casting. The slag that accumulates can be removed by skimming or can be dis- 4 solved in a fluid artificial slag which can be provided on the surface of the molten metal.

In accordance with one preferred method of establishing the novel dynamic fluid flow pattern in the pool of molten metal, the infiowing molten metal is introduced into the continuous casting mold at a point proximate the longitudinal axis of the mold below the surface of the pool of molten metal in such a manner that a plurality of streams of molten metal are formed which are disposed in angularly spaced relationship in a single horizontal plane and have a fixed directional orientation at the point of introduction into the mold so that the flow of molten metal is substantially uniformly distributed over the initially solidifying surfaces of at least the two wider lateral Walls of the elongated rectangular continuous casting before the streams reach the upper surface of the pool of molten metal in the mold. It is important that the streams of molten metal travel with suflicient dynamic energy so that a substantial proportion of each of the streams flows outwardly until contacting the surface of the solidifying casting below the surface of the pool of molten metal in the mold, then flows generally upwardly in contact with the solidifying casting surfaces, and before reaching the upper surface of the molten metal the streams form a substantially uniform front of flowing metal which at the upper surface of the molten metal rolls inwardly away from the walls of the mold. The foregoing substantially uniform outwardly, upwardly and inwardly continuous dynamic flow of molten metal within the pool of molten metal in the mold produces a pronounced standing wave or roll on the surface of the molten steel, as indicated at w (see FIGS. 1-1B), which extends from the mold walls inwardly at the upper end of the casting and forms a relatively elongated axial depression or trough t in the upper surface of the pool of molten metal between the lateral walls of the casting generally in accordance with the idealized flow pattern shown diagrammatically in FIGS. 1, 1A and 1B of the drawing. The objectionable inclusion materials carried upwardly and inwardly by the flowing molten metal from the solidifying casting surfaces are concentrated in the upper surface of the trough t.

In carrying out the continuous casting process of the present invention, it has been found that highly satisfactory results are obtained by introducing molten metal into a continuous casting mold through a tubular injection nozzle or snorkel having formed in the lateral Wall surface adjacent the lower end thereof a plurality of lateral discharge passages with all having their longitudinal axes lying in substantially the same plane and with the spacing between the said passages being less than degrees. The discharge passages or outlet means are preferably symmetrically arranged with respect to a plane passing through the longitudinal axis of the nozzle; whereby streams of molten metal are initially directionally oriented in pairs which flow in diametrically opposite directions. The nozzle si adapted to discharge the molten metal through the pas sages below the surface of the pool of molten metal in a plurality of streams which initially have a fixed directional orientation, and the molten metal is discharged through the passages at a rate which causes the stream to flow with suflicient dynamic energy that a substantial portion of the molten metal in each stream flows upwardly, preferably uniformly contacting the walls of the solidifying casting, and then rolls or flows inwardly to form the desired standing wave along the edge of the mold wall and the axial depression or trough in the upper surface of the pool of molten metal between the mold walls, as previously described.

The injection nozzle which has been found best suited for continuously transferring the molten metal from a supply source, such as a tundish, to the interior of an elongated rectangular continuous casting mold in accordance with the present invention is a cylindrical tubular injection nozzle closed by a lower end wall and provided with a plurality of discharge openings, preferably providing a plurality of pairs of diametrically oppositely disposed discharge passages, formed in the lateral surface of the injection nozzle and lying in substantially the same conical or horizontal plane passing through the cylindrical tubular injection nozzle.

The size and the cross-sectional form of the tubular injection nozzle and the size, the cross-sectional form and the circumferential arrangement of the discharge openings in the nozzle can be varied without departing from the inventive concept of the present invention with the only limitation being that the injection nozzle must establish in the upper portion of the pool of molten metal of the mold a dynamic flow pattern of the type herein described. Thus, for example, the tubular injection nozzle and the discharge openings therein do not have to be circular and can have an oval, rectangular or other shape, if desired. And, although not essential to this invention, the dynamic energy delivered in an upward direction by the stream flowing upwardly in contact with the solidifying casting surface can be increased by inclining the longitudinal axis of each of the discharge openings upwardly from the horizontal where the nozzle in use is disposed vertically with its longitudinal axis parallel to the longitudinal axis of the mold. The metal streams which flow from these upwardly inclined discharge openings or passages will have a more definite upward angle of inclination from the horizontal than streams flowing from horizontally disposed nozzle openings. With a nozzle having discharge openings inclined upwardly from the horizontal, however, it is important that the upwardly inclined streams of molten metal, preferably originating at about the axis of the mold, contact the lateral walls of the solidifying casting before contacting the upper surface of the molten metal in the mold in order to eifect the desired washing action on the wall surfaces of the casting and establish the herein described required dynamic flow pattern within the upper portion of the molten metal pool.

When forming a continuous casting having an elongated rectangular cross-section (i.e. a so-called sla where it is of paramount importance to avoid surface imperfections in the wide faces of the slab, best results are obtained when the discharge passages of the injection nozzle are positioned with respect to the walls of the mold so that none of the molten metal streams flow directly toward the narrow walls of the elongated rectangular mold, as shown in FIGS. 2, 2A, 3, 3A, 4, 4A, 4, 5A. The nozzle should also be positioned so that the molten metal streams wash as much of the wide face as possible by maintaining as uniform a flow condition as possible across each of the wide faces of the casting. To maintain substantially uniform molten metal fluid flow conditions across the wide face of an elongated rectangular or slabcasting, it is helpful, but not necessary, to make the crosssectional area of each molten metal discharge openings proportional to the axial distance each stream must travel before contacting and washing the solidifying face of the casting in order to equalize the distribution of the kinetic energy of the flowing metal over the surface of the wider walls of the casting.

The discharge openings in the injection nozzle are preferably circular in form to minimize the frictional resistance to the flow of molten metal for an opening of a given cross-sectional area. However, all the openings do not have to be the same size and discharge openings having oval or elongated cross-sections can be used, if it is desirable to have the streams of metal spread or fanned out, as shown in FIGS. 4 and 5 of the drawing. Also, if desired, a plurality of single-holed or multi-holed nozzles can be used in place of a single nozzle to provide the desired herein described dynamic flow and uniform distribution of the molten metal within the continuous casting mold.

The injection nozzle 20 shown in FIGS. 2, 2A and 2B of the drawing specifically illustrates a preferred embodiment of the present invention, and the nozzle 20 comprises a suitable refractory cylindrical tubular section 21 having its extreme lower end closed and its upper end connected with a reservoir of molten metal, such as a tundish (not shown), which has a means for regulating the flow of molten metal to the injection nozzle 20. The discharge passages or openings 23, 23A and 23B are formed in the lateral wall of the tubular section 21 at or adjacent the inner surface of the lower end wall 22 which closes the lower end of the nozzle 20 and comprise six cylindrical passages which have their axis lying substantially in a conical plane having the apex thereof coinciding with the longitudinal axis of the nozzle 20. The discharge passages 23, 23A and 23B are equally spaced about the circumference of the nozzle (i.e. spaced 60 apart) with the midpoint of each outlet opening spaced axially a short distance from the lower end of the nozzle 20. The openings 23A and 23B are of equal size and have about half the cross-sectional area of the remaining openings 23 so that the streams of molten metal which travel a greater distance have a larger cross sectional area. Each of the discharge openings 23, 23A and 23B has its axis inclined upwardly at an angle of about fifteen degrees from the horizontal plane when the nozzle 20 is operatively disposed in the mold 24. The axis of each of the discharge openings intersects the longitudinal axis of the nozzle 20 below the midpoint of the discharge openings. It will thus be evident that the molten metal flowing from each of the openings 23, 23A and 23B will initially form a stream having a small upward inclination relative to the horizontal but nevertheless travel generally transversely toward the mold substantially in the same conical or tranverse plane.

The nozzle 20 is immersed in the pool of molten metal which is maintained within the open ended continuous casting mold 24 so that the lateral discharge openings 23, 23A and 23B are below the upper surface of the molten metal midway between the wide faces 26 and narrow end faces 27. with the axes of the openings 23A and 23B lying in a vertical plane perpendicular to the vertical planes of the wide mold faces 26, as best shown in FIG. 2B. The nozzle is disposed so that the smaller openings 23A and 23B are directed perpendicularly at the midpoints of the long side walls 26 of the mold, while the larger openings 23 are directed obliquely towards the opposite end portions of the wide side walls 26, with the result that the wide sides of the casting are washed by the metal emerging from the nozzle and inclusion materials are not trapped therein.

As a specific example of the invention applied to the continuous casting of steel in a continuous casting mold having a cross sectional dimension of 37 inches by 8 inches, a fused silica nozzle having the general configuration shown in FIGS. 2, 2A and 2B was used for casting low-carbon aluminum-killed slabs for rolling to drawingquality cold-rolled sheet product having a chemical specification of 0.06% C maximum, 0.28-0.35% Mn, 0.010% P maximum, 0.030% S maximum and 0.020- 0.060% A1. The nozzle had an internal diameter of 2 /2 inches, the discharge openings 23 hada diameter of 1% inches spaced 60 from openings 23A and 23B which had a diameter of inch. The bottom edge of the discharge openings coincided with the inner bottom of nozzle 20 and the openings were inclined upwardly forming an angle of 15 with the horizontal plane. The nozzle Was disposed with the openings oriented as shown in FIG. 2B and located about 6 inches below the surface of the molten metal in the mold. The flow rate of molten steel through the nozzle was between 2 /2 and 3 /3 tons per minute and the linear casting speed of the slab strand was 60 to inches per minute. A typical 450-ton sample of slabs cast with this procedure and processed into cold-rolled sheet product was subjected to standard methods of surface inspection practiced in sheet mills. Over of the sheet product was acceptable for application on exposed automobile body parts (hoods, roofs, doors, deck lids, fenders) which require superior surface quality.

The flow pattern of the molten metal in the mold 24 and the casting 29 which is established by the nozzle 20 under the specified operating conditions is best shown in FIGS. 2A and 2B, and the standing wave or rolP (w) which surrounds the axial trough (t) is best shown in FIGS. 2 and 2A of the drawing. The flow pattern of the molten metal is generally similar to the idealized pattern shown in FIGS. 1, 1A and 1B, and the objectionable inclusion materials commonly present in the mold are effectively concentrated on the surface of the molten metal in the axial trough, so that inclusions which normally cause surface steelmaking defects are substantially eliminated, particularly from the wider faces 26 of the elongated rectangular continuous casting.

The modified form of injection nozzle 30 shown in FIGS. 3 and 3A of the drawing comprises a cylindrical tubular section 31, of a suitable refractory material, having its lower end closed and its upper end connected with a tundish (not shown) which is provided with a means for controlling the flow of molten metal to the injection nozzle 30. The lateral discharge passages or openings 33 comprise six equally spaced, equal diameter radially extending cylindrical passages. The axes of the openings 33 are disposed in a single plane extending transversely of the nozzle 30 and the lower edges of the openings 33 are at or spaced a short distance above the inner surface of the lower end wall 34 of the nozzle 30. In use, the nozzle 30 is immersed in the pool of molten metal within the continuous casting mold 35 so that the lateral discharge openings 33 are below the surface of the metal and are directed toward the mold walls in the manner best shown in FIG. 3A. Thus, the nozzle 30 is placed midway between the wide faces 36 and narrow faces 37 of the mold 35 with four of the openings 33 symmetrically and obliquely disposed with respent to the wide faces 36 and two of the openings 33 disposed with their axes perpendicular to the wide faces 36.

The streams of molten metal flowing from the discharge openings 33 have a substantial upwardly flowing component, and the flow pattern established by the nozzle 30 is generally similar to the flow pattern described in connection with FIGS. 2, 2A and 2B. The streams of flowing metal eifect the desired removal of objectionable inclusion materials from the surfaces of the casting, particularly from the wider faces of the casting.

In FIG. 3B the nozzle 30B having the same configuration as nozzle 30 described in connection with FIGS. 3 and 3A is shown positioned in the upper end of an elongated rectangular continuous casting mold 35B midway between the wide faces 36' and narrow faces 37' with one of the diametrically opposed lateral discharge passages or openings 33a perpendicularly facing the midpoint of each of the narrow faces 37' and having the remaining discharge passages 33b directed obliquely toward the wide faces 36', with the axis of each forming an angle of about 30 with the perpendicular through the midpoint of the wide faces 36' so that the outflowing molten metal is substantially uniformly distributed over the wide faces 36'. While the results obtained with the latter arrangement of the nozzle 30B in the mold 35B are not as good as with the nozzle arrangement of FIGS. 3 and 3A, there is still a marked improvement over the results produced by the prior art continuous casting nozzles.

As a further specific example of the invention applied to the continuous casting of steel in an elongated rec tangular mold having a cross sectional dimension of 37 inches by 8 inches, a fused silica nozzle having the general configuration described in connection with FIGS. 3 and 3A was used as shown in FIG. 3B for casting lowcarbon aluminum-killed slabs for rolling to drawingquality cold-rolled sheet product having a chemical specification of 0.06% C maximum, 0.280.35% Mn, 0.010% P maximum, 0.030% S maximum and 0.0200.060% Al.

The nozzle had an internal diameter of 2 /2 inches, the horizontally disposed openings 33a had a diameter of 1 inches spaced 60 from the horizontally disposed openings 33b which also had a diameter of 1 inches. The bottom edge of the openings coincided with the inner bottom of nozzle 30B. With the nozzle 30B positioned in the mold 35B as shown in FIG. 3B, the discharge openings were located about 6 inches below the surface of the molten metal in the mold. The flow rate of molten steel through the nozzle was between 2 /2 and 3 /3 tons per minute and the linear casting speed of the slab strand was 60 to inches per minute. A typical 400 ton sample of slabs cast in the foregoing manner and processed into cold-rolled sheet product was subjected to standard methods of surface inspection practiced in sheet mills. About of the sheet product was acceptable for application on exposed automobile body parts.

In order to provide a basis for comparing the quality of the rolled sheets obtained from castings produced by the nozzles and process of the present invention with castings produced by the prior art submergible bifurcated nozzles (i.e. nozzles having all the discharge openings in the lateral wall surface lying in a single vertical plane extending through the longitudinal axis of the nozzle) and straight bore injection nozzles, low-carbon aluminumkilled steel slabs of the same composition used with the nozzles of the present invention were cast using various submergible bifurcated and straight bore nozzles. The several bifurcated nozzles which were used had an internal diameter range between 2% and 2 /2 inches with dis charge passages between 1 /2 and 2% inches in diameter, and the discharge openings were disposed at angles ranging from horizontal to 30 below the horizontal. In all cases the nozzles were oriented in the mold so that the diametrically opposed openings were directed toward the narrower end walls of the mold in accordance with the prior art teaching. The flow rate of the molten steel through the nozzle ranged from 2 /2 to 3 /3 tons per minute, and the linear casting speed of the slab strand ranged from 60* to 80 inches per minute. Using many combinations of casting speed, nozzle dimensions and port angularity, a 700 ton lot of cast slabs was processed into cold-rolled sheet product. None of the nozzle combinations tested produced a satisfactory proportion of acceptable sheet product. For the total sample, only 50% of the sheet product was acceptable for application on exposed automobile body parts.

The straight bore nozzles used had an internal diam eter of 1% inches, molten metal flowed through the nozzle at a rate between 1 and 1 /3 tons per minute, and the linear casting speed ranged from 25 to 40 inches per minute. Over 4000 tons of slabs were cast using the straight bore nozzles and only a small portion was suit able for processing to sheet product, and of all the sheet product made less than 10% was suitable for application to exposed automobile body parts.

In processing low-carbon aluminum-killed slabs to hot or cold-rolled sheet product from either conventional cast ingots or continuous castings, it has heretofore been customary to recondition the slabs by removing the entire surface or skin of the casting through the use of manually operated or mechanized oxy-acetylene torches (i.e. skin scarfing). The objective of skin scarfing is to remove visible undesirable surface blemishes, such as cracks and scabs, and also subsurface inclusions, since both types of inclusions can cause objectionable surface imperfections in the finished rolled sheet product. When using the preferred nozzle shown in FIGS. 2, 2A and 2B and the modified nozzle in FIGS. 3, 3A and 3B as disclosed herein it was found unnecessary to remove the entire surface of the slab (i.e. skin scarfing). Only the occasional visible surface blemishes on the slab had to be removed (i.e. spot scarfing). The spot scarfing of the test lots of the present invention which were processed and examined for surface defects as previously described involved reconditioning only about of the slab surface, whereas skin scarfing requires reconditioning 100% of the slab surface. Even with the sharply reduced amount of surface reconditioned employed on slabs produced in accordance with the present invention, over 95% of cold-rolled sheet produced from slabs made using the preferred nozzle of FIGS. 2, 2A and 2B was suitable for application on exposed automobile body parts and 90% of the sheet product made using the modified nozzle as shown in FIG. 3B was suitable for application on the same class of parts. By making it possible to substitute spot scarfing for skin scarfing, the present invention substantially reduces the cost of reconditioning slabs preparatory to rolling.

It was found necessary to employ skin scarfing (i.e. 100% surface skinning) in processing the slabs which were cast using the several bifurcated nozzles and straight bore nozzles heretofore described in order to upgrade the surface quality of the finished sheets produced therefrom. Even with 100% surface reconditioning through skin scarfing, however, only 50% of the cold rolled sheets made from slabs cast with the bifurcated nozzles had surface quality suitable for application on exposed automobile parts, and the sheet product made with the straight bore nozzles yielded less than cold rolled sheets suitable for exposed automobile parts.

The modified form of nozzle in FIGS. 4 and 4A shows that the cross-sectional shape of the nozzle and the discharge ports need not be circular as in FIG. 1 through FIG. 3B but can be any shape as long as the herein described flow pattern is established in the mold. The tubular nozzle 40 in FIGS. 4 and 4A has a generally oblong or eliptical cross-section and is provided with four oblong or generally elliptically shaped discharge openings 41 spaced symmetrically on opposite sides of the minor axis of the elliptical nozzle 40. In use the nozzle 40 is positioned within the mold 45 with its minor axis pointing toward the midpoints of the wider sides-43 of the mold 45 so that none of the discharge openings 41 point directly toward the narrow sides 44 of the mold 45.

The modified form of nozzle shown in FIGS. 5 and 5A illustrates a further possible configuration and arrangement of the lateral discharge ports or passages of a submergihle nozzle capable of providing a substantially uniform flow of molten metal over the wide face of an elongated rectangular continuous casting. The cylindrical tubular immersion nozzle 50 of FIGS. 5 and 5A is provided with only two diametrically opposed symmetrical openings 52, 52' which have the shape of a generally elongated slot the midpoints 53 of which has a lesser vertical height than the ends and resembles a bow tie. In use, the nozzle 50 is disposed in the mold 55 with the openings 52, 52' directly facing the wider sides 56, 56' of the mold so that the streams flowing from the openings 52, 52' will cover substantially the entire wider sides 56, 56' of the mold or casting formed therein.

While the foregoing specific embodiments of the invention have related to continuous casting in an elongated rectangular mold designed for casting slabs, the modified form of nozzle shown in FIG. 6 and FIG. 6A illustrates the application of the present invention to continuous casting in a generally square mold for casting billets or blooms and wherein the inflowing molten metal is distributed substantially uniformly over the surface of the solidifying casting by flowing outwardly toward the solidifying casting walls with suflicient dynamic energy to form upwardly flowing streams which wash the solidifying casting walls to remove objectionable inclusion materials therefrom before the inclusion material is frozen into the casting in substantially the same manner described in connection with continuous casting in the elongated rectangular molds. The cylidrical tubular injection nozzle 60 of FIGS. 6 and 6A is preferably provided with four equally spaced circular discharge openings or passages 62 of equal size with the axes thereof lying in a single horizontal plane extending transversely through the nozzle 60. In use the nozzle 60 is disposed axially within the square mold 63 with each of the discharge openings 62 disposed below the surface of the molten metal and directly facing the midpoint of a wall 64 of the mold 63 with the axis of each opening being perpendicular to the mold wall 64.

If desired, the discharge openings or passages 62 in the nozzle 60 for casting in a square or billet mold can be modified with regards to the shape, number and arrangement as described in connection with the discharge open ings of the nozzle used with a rectangular mold (see FIGS. 1-5). Thus, it will be evident that the openings 62 can have an upward inclination relative to a horizontal plane extending perpendicularly through the longitudinal axis of the nozzle 60, provided, however, the upwards and outwardly flow of the streams of molten metal does not intersect the surface of the pool of molten metal maintained within the upper portion of the casting mold before contact is made with the rapidly solidifying surface of the casting. And, as when casting in a rectangular mold, the degree of upward inclination should preferably be as large as possible without causing an appreciable amount of the infiowing molten metal to intersect the surface of the pool before contacting the solidifying casting surface.

The present invention is applicable to continuous casting in molds having shapes other than the elongated rectangular slab and square billet molds specifically illustrated herein, including circular and I-shaped continuous castings, if desired. Other submergible means for introducing molten metal into the continuous casting mold can also be used, since the present invention is not limited to using the herein disclosed nozzles and discharge passages. In each of the applications of the present invention, regardless of the shape of the mold or the configuration and positioning of the means for introducing the molten metal into the continuous casting mold below the surface of the pool of molten metal in the upper end of the casting, the submerged nozzle or other submergible means for introducing the molten metal should substantially uniformly distribute the molten metal over at least one of the rapidly solidifying surfaces and preferably over all the surfaces of the casting which should be free of surface defects with the molten metal flowing upwardly along the surface or skin of the solidifying casting and wiping the solidifying casting surface from a point below the upper surface of the pool of molten metal and the upper edge of the solidifying casting to the uppermost edge of the solidifying casting, and the upwardly flowing molten metal should have sufiicient dynamic energy to cause the infiowing molten metal being continually introduced into the continuous casting mold to wash the solidifying casting surface or skin of the casting with an upwardly axially flowing stream to effect removal of objectionable inclusion materials from the casting surface before the inclusion materials become frozen into the surface of the solidifying casting or in the immediate subsurface portion of the casting contiguous with the wall surface in contact with the mold. The desired dynamic molten metal flow pattern which effects the desired washing of the solidifying casting surface is evidenced within the mold by the formation of a standing wave along the edge of the pool of molten metal which on reaching the surface of the pool flows or rolls inwardly from the mold wall preferably forming a trough on the surface of the pool between the mold walls. In the preferred embodiment of the present invention the nozzle means employed for introducing the molten metal into the continuous casting mold have the lateral discharge passages circumferentially spaced less than degrees with the outlets of all the discharge passages lying substantially in the same transverse plane through the nozzle means and with the longitudinal axes of all the passages having an upward inclination relative to the transverse plane through the nozzle means forming substantially the same angle with the longitudinal axis of the nozzle means.

While the specific embodiments illustrating the present invention relate to the casting of steel, the invention can be used in the continuous casting of any metal or alloy, including copper, aluminum, magnesium and brass.

We claim:

1. A process for the continuous casting of a molten metal comprising; introducing a stream of a molten metal into an open ended continuous casting mold having a substantially vertically disposed mold wall at a fixed point below the upper surface of a pool of molten metal maintained in said mold, the said stream being directionally oriented at the point of introduction into said pool with a major proportion thereof comprising an outwardly and upwardly flowing component contacting a continuous casting surface supported by said mold wall before contacting said upper surface of said pool, and providing said stream with sufficientdynamic energy to effect after said component has contacted said casting surface a continuously upwardly flow of said stream comprising a substantial proportion of said molten metal in a generally axial direction which contacts at least the said area where said casting is initially solidifying and upon reaching said upper surface of said pool having said stream effecting an inwardly flow away from said mold wall; whereby said solidifying casting surface at least in the area where said casting is initially solidifying is contacted with molten metal flowing in a generally upwardly axial direction to effect removal of objectionable inclusion material therefrom before said inclusion material is frozen into the solidifying casting surface and then carry said inclusion material away from said mold wall and to the central zone of said upper surface of said pool.

2. A process for the continuous casting of a molten metal comprising: introducing a plurality of streams of a molten metal into an open ended continuous casting mold having a substantially vertically disposed mold wall below the upper surface of a pool of molten metal maintained in said mold with said streams being horizontally spaced and having a fixed directional orientation at the point of introduction into said mold and the axes of all of said streams lying substantially in the same plane whereby a major proportion of each said streams has an outwardly and upwardly flowing component which contacts a solidifying casting surface supported by said mold wall before contacting said upper surface of said pool, and imparting to said streams sufficient dynamic energy to cause each said component after contacting said casting surface to flow continuously upwardly in a generally axial direction in contact with said solidifying casting surface at least in the area where said casting is initially solidifying and upon reaching said upper surface of said pool to flow inwardly away from said mold wall establishing a dynamic flow of molten metal within said pool which forms a standing wave on the surface of said pool along said mold wall and which extends inwardly from said mold wall; whereby said solidifying casting surface is contacted with molten metal flowing in a generally upwardly axial direction which removes from said initially solidifying casting surface objectionable inclusion material before said inclusion material is frozen into the solidifying casting surface and carries said inclusion material away from said mold wall.

3. A process as in claim 2, wherein said molten metal is substantially uniformly distributed over said solidifying casting surface.

4. A process as in claim 2, wherein objectionable inclusion material contained in said molten metal which is normally frozen into the surface of said casting is carried by said upwardly flowing stream of molten metal from said solidifying casting surface and concentrated on the surface of said pool spaced inwardly from said mold wall and solidifying casting surface.

5. A process as in claim 2, wherein said mold is an elongated rectangular continuous casting mold.

6. A process for the continuous casting of a molten metal comprising; introducing a plurality of pairs of streams of molten metal directionally oriented at the point of introduction into an open ended elongated rectangular continuous casting mold having oppositely disposed narrow end walls and wide side walls, said streams being introduced adjacent the longitudinal axis of said mold and below the upper surface of a pool of molten metal maintained in said mold, each of said streams of molten metal being symmetrically disposed with respect to a plane through the longitudinal axis of said mold and flowing substantially linearly outwardly from adjacent said axis in pairs which flow in diametrically opposite directions toward the said side walls of said mold, and each of said streams being so directionally oriented and provided with sufficient dynamic energy to produce a continuously upwardly flowing component comprising a major proportion of said stream having suflicient velocity to contact an initially solidifying casting surface supported by one of said side walls before contacting said upper surface and flowing upwardly in a generally axial direction in contact with said solidifying casting surface and upon reaching said upper surface of said pool flowing inwardly from said side walls to establish a dynamic flow of molten metal within said upper end of said pool which forms a standing wave along said side walls and extending inwardly from said side walls and forms a centrally located trough between said side walls with objectionable inclusion materials being carried by said flow of molten metal from said solidifying casting surfaces and being concentrated on the surface of said trough.

7. A process for continuous casting as in claim 6, wherein one of said pairs of streams is directionally oriented so that the longitudinal axes thereof are perpendicular to said wide side walls of said mold and at least two other of said pairs of said streams have their longitudinal axes obliquely disposed relative to the said wide side walls.

8. A process of continuous casting as in claim 6, wherein one of said pairs of said streams is directionally oriented so that the longitudinal axes thereof are perpendicular to said narrow end walls of said mold with at least two others of said pairs being directionally oriented so that their longitudinal axes are obliquely disposed relative to the said wide side walls.

9. A process for continuous casting as in claim 6, wherein each of said streams which flow outwardly toward said solidifying continuous casting surfaces has the cross-sectional area thereof directly proportioned to the distance each said stream must travel before striking a solidifying casting surface in the path of said stream with the streams which travel the greater distance having the larger cross-sectional area.

10. A process for continuous casting as in claim 6, wherein at least one of said streams at the point of introduction into said mold has the longitudinal axis thereof forming an upwardly inclined angle with a horizontal plane.

11. A process of continuous casting as in claim 6, wherein at least one of said streams at the point of introduction into said mold has a circular cross-section.

12. A process of continuous casting as in claim 6, wherein at least one of said streams at the point of introduction into said mold has a cross-section whose width is greater than the vertical height thereof.

13. A process of continuous casting as in claim 2, wherein at least one of said streams at the point of introduction into said mold has a cross-section in the general shape of an elongated horizontal slot with the midpoint thereof having the narrowest dimension which gradually increases in size toward the opposite ends thereof.

14. A process as in claim 2, wherein said mold is a continuous casting mold having four lateral walls of about equal width.

(References on following page) References Cited UNITED STATES PATENTS Junghans. Junghans. Webster. Gunn et a1. Tarmann. Tragner et a1. Astrov et a1.

FOREIGN PATENTS France. France. France.

OTHER REFERENCES Applicants Non-Pat. Citations, Concast News, vol. 7, February 1968, TN1C8, pp. 1, 5 and 6.

10 J. SPENCER OVERHOLSER, Primary Examiner R. S. ANNEAR, Assistant Examiner U.S. cl. X.R. 15 164-134, 135, 281

Images