US3799239A

US3799239A - Method for continuous casting of metal

Info

Publication number: US3799239A
Application number: US00230496A
Authority: US
Inventors: Fillon J Dumont; L Vedda
Original assignee: Institut de Recherches de la Siderurgie Francaise IRSID
Current assignee: Institut de Recherches de la Siderurgie Francaise IRSID
Priority date: 1968-11-26
Filing date: 1972-02-29
Publication date: 1974-03-26
Anticipated expiration: 1991-03-26

Abstract

Continuous casting method wherein molten metal is poured into a vertical passage bounded by the inner stretches of four endless metallic bands which travel downwardly at the speed of metal flow. The inner stretches are cooled by liquid coolant which is admitted into upper ends and is discharged at the lower ends of narrow chambers each adjacent to and extending along the full width and length of a stretch. The inlets and outlets of the chambers are bounded by arcuate surfaces which insure that the coolant enters and leaves the chambers without appreciable turbulence. Each inlet receives fresh coolant from a first compartment and each outlet admits spent coolant into a second compartment.

Description

United States Patent 1 1 3,799,239

Dumont-Fillon et al. Mar. 26, 1974 [54] METHOD FOR CONTINUOUS CASTING OF 2,767,448 10/1956 Harter et a1. 164/283 METAL 3,321,008 5/1967 164/2s3'x In s: J q m ll n, Saint 2,867,018 1/1959 Harter et a1. 164/283 x Germain-en-Laye; Louis Vedda, Metz, both of France [73] Assignee: lnstitut De Recherches De La Siderurgie F rancaise, Saint Germain-en-Laye, France [22] Filed: Feb. 29, 1972 [21] Appl. No.: 230,496 [57] ABSTRACT Application Data Continuous casting method wherein molten metal is [63] Commuano" of 87918611 1969* poured into a vertical passage bounded by the inner Primary Examiner.l. Spencer Overholser Assistant ExaminerJohn E. Roethel Attorney, Agent, or Firm-Michael S. Striker abandoned stretches of four endless metallic bands which travel downwardl at the speed of metal flow. The inner [30] Forelgn Apphcanon Pnomy Data stretches a e cooled by liquid coolant which is admit- NOV. 26, 1968 France [ed into upper ends and is discharged at the lower ends of narrow chambers each adjacent to and extend- U.S-

6 ing along the and length of a tretch The 164/283 inlets and outlets of the chambers are bounded by ar- [51] Int. Cl 822d 11/06 cuate surfaCes which insure that the coolant enters 1 Field of Search 164/87, 88, 1 1 and leaves the chambers without appreciable turbu- 164/283 lence. Each inlet receives fresh coolant from a first compartment and each outlet admits spent coolant Reiei'ences Cited into a second compartment.

UNITED STATES PATENTS 3,452,809 7/1969 Dumont-Fillon 164/278 7 Claims, 6 Drawing Figures A ZIa Ill/716171711 METHOD FOR CONTINUOUS CASTING F METAL CROSS-REFERENCE TO RELATED APPLICATIONS The casting method of the present invention constitutes an improvement over and a further development of apparatus which are disclosed in French Pat. No. 1,481,252, U.S. Pat. No. 3,452,809 granted July 28, 1969 to Jacques Dumont-Fillon and application Ser. No. 628,444 filed Apr. 4, 1967 by Jacques Dumont- Fillon, now U.S. Pat. No. 3,482,620 all assigned to the same assignee.

BACKGROUND OF THE INVENTION The present invention relates to continuous casting apparatus in general, and more particularly to improvements in casting apparatus of the type wherein the mold through which molten metal passes during solidification includes several endless bands or belts which confine the molten metal and travel in the direction Of metal flow. Still more particularly, the invention relates to improvements in cooling systems for continuous casting apparatus which are especially suited for the production of continuous steel slabs, billets or blooms.

An advantage of continuous casting apparatus wherein molten metal is converted into a continuous solid product between traveling bands is that the bands can be driven at the exact speed of material flow so that the friction between the bands and the metallic material is reduced to zero with the result that the solidified product exhibits a highly satisfactory surface finish. Another advantage of such casting apparatus is that the bands can be readily mounted with a view to insure continuous contact with metallic material in the passage despite the fact that the cross-sectional area of such material decreases as a result of cooling.

Serious problems arise in connection with the cooling of traveling bands. Such cooling is necessary in order to remove heat and to prevent damage to the bands. The problems are aggravated by the fact that the bands must consist of very thin metallic material; this is necessary to insure satisfactory transfer of heat and ready deformability in regions where the bands travel over driven and idler rollers. As a rule, the bands consist of steel whose thermal conductivity is less satisfactory than that of copper but which exhibits a satisfactory tensile strength even if its thickness is greatly reduced to thus enhance the withdrawal of heat from molten metal. Improper cooling of a small portion of a thin steel band suffices to cause localized Overheating and the formation of holes so that the apparatus must be brought to a standstill in order to replace the defective band or bands. This causes substantial losses in output. The just mentioned problems in connection with proper cooling of relatively thin bands render presently known continuous casting apparatus suitable for the production of relatively thin metallic slabs or sheets but not for the production of billets or blooms with a substantially rectangular cross-sectional outline.

The cooling systems of presently known casting apparatus ofthe above Outlined character normally utilize nozzles which spray a liquid collant against the outer sides of traveling bands along the passage for molten metal. Such cooling systems cannot insure uniform cooling of an entire band, i.e., of that stretch which is adjacent to and in contact with the metal. Moreover, it is difficult to properly confine liquid coolant which is being sprayed by nozzles and to eventually recirculate such coolant into renewed contact with the traveling bands. Also, it is not possible to efficiently recover heat from liquid which is directed against the traveling bands in the form of discrete jets or sprays.

SUMMARY OF THE INVENTION An object of the present invention is to provide a continuous casting apparatus which utilizes traveling bands of steel or the like and wherein the bands are cooled in a novel and improved way so that they are cooled uniformly in all zones which come into contact with molten metal.

Another object of the invention is to provide a cooling system for use in the just outlined casting apparatus and to construct and assemble the cooling system in such a way that the traveling bands are less likely to undergo localized overheating during contact with molten metal, that such bands are cooled uniformly by resorting to a relatively small number of simple and compact parts, and that the bands are cooled by a fluid which is circulated at a substantial rate of speed and in large quantities to insure uniform withdrawal of large amount of heat.

A further object of the invention is to provide a casting apparatus wherein the molten metal can be converted in continuous slabs, billets, blooms or like bodies of rectangular or other polygonal outline.

An additional object of the invention is to provide a casting apparatus wherein the fluid which cools the traveling bands is confined and recirculated in a novel and improved way.

It is also an object of the invention to provide for a method casting continuous billets in the casting apparatus in which ferrostatic pressure of the molten metal acting on the traveling bands is substantially compensated by the cooling fluid.

The invention is embodied in a casting apparatus for the production of continuous billets or like products from molten metal. The apparatus comprises a mold defining a substantially vertical passage for metal and including wall means surrounding the passage and having at least one pair of endless metallic bands located opposite each other and having inner stretches extending downwardly along the passage, and drive means for moving the stretches downwardly, preferably at the exact speed of metal flow. In accordance with a feature of the invention, at least one of the stretches is cooled by a cooling means including panel means outwardly adjacent to and defining with the one stretch a narrow or shallow chamber extending substantially along the full width and length of the one stretch and having inlet means at the upper end and outlet means at the lower end thereof, and means for circulating a fluid coolant through the chamber including a first compartment containing fresh coolant and communicating with the inlet means and a second compartment communicating with the outlet means to receive spent coolant. One or more pumps are used to continuously circulate the coolant, preferably at the speed of travel of the one stretch. The inlet and outlet means are preferably bounced by arcuate surfaces to insure that the coolant enters and leaves the chamber without any appreciable turbulence.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved casting apparatus itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic plan view of a casting apparatus which embodies the invention;

FIG. 2 is an enlarged schematic vertical sectional view as seen in the direction of arrows from the line 11-11 of FIG. 1;

FIG. 3 is an enlarged view of a detail in the structure of FIG. 3;

FIG. 4 is an enlarged view of a detail in the structure of FIG. 2;

FIG. 5 is a view as seen in the direction of arrow V in FIG. 4, with certain parts removed; and

FIG. 6 is a horizontal sectional view as seen in the direction of arrows from the line VI-VI of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1, there is shown a continuous casting apparatus which comprises an ingot mold open at its top and bottom and having wall means formed by substantially vertical inner stretches of four endless bands 1, 1a, 1b, 1c. These vertical stretches define a preferably vertical passage into which molten metal is poured to form a continuous billet or bloom 4. A somewhat similar apparatus is disclosed in US. Pat. No. 3,452,809 granted July 28, 1968 to Jacques Dumont- Fillon and assigned to the same assignee. It will be noted that the pairs of opposed bands 1, lb and la, 1c are laterally offset with reference to each other so that the passage for the billet or bloom 4 is surrounded by vertically extending portions of the inner stretches of such bands. An advantage of such mounting of the bands l-lc is that they can be readily shifted in directions indicated by double-headed arrows 2a, 3a to either enlarge or reduce the cross-sectional area of the passage or to form a rather flat passage for the production of slabs or like bodies wherein the width exceeds the depth or vice versa.

As described in the aforementioned US. Pat. No. 3,452,809, the passage between the inner stretches of the bands l-lc preferably resembles a truncated pyramid whose base is located at the metal-receiving end of the apparatus. Thus, the mold including the bands l-lc is a big-end-up mold. The rate at which the passage tapers downwardly is rather small but it suffices to insure proper compensation for shrinkage due to cooling of metal during travel through the mold so that the inner stretches of the bands l-lc remain in continuous contact with the adjacent sides of the product. This also contributes to satisfactory cooling of the product by exchange of heat with the bands at least one of which is cooled in accordance with the present invention. The taper of the passage between the bands 1-1c is so small that it is not noticeable in the drawing.

Referring to FIG. 2, there is shown a portion of the casting apparatus, namely, the band 1, a frame 12 which supports the band 1, the drive means and guide means for band 1, and a novel cooling or heat withdrawing system which is used to continuously remove heat from the metal-contacting inner stretch 1A of the band 1. The apparatus of FIG. 1 preferably comprises at least two bands (e.g., the bands 1, 1b) which are mounted, driven and cooled in a manner as shown for the band 1 of FIG. 2. For example, the band 1 may consist of a strip or tape having a thickness of 0.5 millimeter and a width of 200 millimeters. The material of the band 1 is preferably very soft carbon steel having a carbon content of about 0.35 percent. The ends of the tape which is employed to form the band 1 are welded to each other end-to-end to form an endless flexible e]- ement. The other three bands la-lc are preferably constructed and dimensioned in the same way as the band 1. As stated above, the inner stretch 1A of the band 1 is substantially vertical; it is inclined downwardly and to the right, as viewed in FIG. 2, to compensate for shrinkage of the material which passes therealong. The direction in which molten metal is poured into the mold is indicated by arrows 7.

The band 1 is trained over five rollers including two guide rollers or supporting

rollers

5, 6 which are respectively adjacent to the upper and lower ends of the inner stretch 1A, a driven roller 8 which is rotated by a suitable motor, preferably through the intermediary of a variable-speed transmission (not shown), a tensioning roller 9 which is movable up and down by a jack or analogous displacing means, and a deflecting roller 11 which is located upstream of the guide roller 5 and serves to guide the portion 18 of the band 1 at the intake end of the passage between the inner stretches of the bands l-lc. The novel cooling system for the stretch 1A is disposed between the

guide rollers

5, 6. At least the upper guide roller 5 is formed with circumferential grooves or flutes (see the flutes 5a in FIG. 5) which are bounded by concave surfaces having preferably a semicircular cross-sectional outline. Such constr-uction reduces frictional engagement between the band- 1 and the roller 5 and further permits effective cooling of the roller in a manner to be described later. Furthermore, the flutes or grooves in the roller 6 and- /or 5 facilitate cooling of the band 1 upstream and downstream of the respective guide roller.

The diameter of the driven'roller 8 exceeds the diameters of the

guide rollers

5, 6. This roller 8 is rotated in a clockwise direction, as viewed in FIG. 2, at a speed of 2.5 meters per minute which is the speed at which the continuous product is being withdrawn from the lower end of the passage between the bands 1lc. Such selection of the speedof the band 1 is desirable and advantageous because the inner stretch 1A need not move with reference to the descending product during solidification or molten metal in the vertical passage, i.e., there is practically no friction between the product and the stretch 1A. Absence of friction between the bands and the product enables the apparatus to produce a continuous billet, bloom or slab with a highly satisfactory surface finish.

The aforementioned displacing jack 10 causes the tensioning roller 9 to exert on the band 1 a pressure in the range of 1,000 kg; this produces in the band a tension in the range of kg/mm which is clearly below the elastic limit of the band material and insures that the band can remain in use for long periods of time. As stated before, the deflecting roller 11 merely serves to maintain in rather strongly inclined positions those increments of the band 1 which advance toward the periphery of the upper guide roller 5. The shafts of the

rollers

5, 6, 8, 9 and 11 are mounted in a frame 12 which is supported on a horizontal rod or bar 13 permitting a shifting of the frame at right angles to the iongitudinal direction of the passage for the purposes which were explained in connection with FIG. 1. The driven roller 8 is preferably mounted on a bearing (not shown) which can be displaced by a suitable eccentric or the like in order to change the inclination of the axis of the roller 8 and to thus insure that the periphery of the roller engages the band 1 along its full width. The mechanism which can change the inclination of the axis of the roller 8 is preferably automatic and can be designed to respond to lateral movements of the band with reference to the passage for molten metal.

FIG. 2 further shows certain essential and important elements of the improved cooling system for the stretch 1A. This cooling system includes a fixed wall or panel which is located behind the defines with the stretch 1A a narrow chamber 14 wherein a continuous sheet of coolant (preferably water) descends in the direction of travel of the stretch 1A. The chamber 14 is of generally rectangular outline and extends substantially along the full width of the band 1 as well as close to the

guide rollers

5, 6. The panel 15 is parallel or substantially parallel to the stretch 1A so that the depth of the chamber 14 varies very little or not at all. The marginal portions of the chamber 14 along the vertical edges of the stretch 1A are sealed by elastically deformable sealing elements in the form of strips 40 shown in FIGS. 5 and 6. The depth of the chamber 14 is selected in such a way that the liquid coolant forms a sheet which descends along the outer side of the stretch 1A and withdraws heat from the band to permit continuous casting of molten metal into the passage between the belts l-lc. The chamber 14 has a specially configurated inlet 16 directly below or close to the upper guide roller 5 and an outlet 18 located directly above or at least close to the lower guide roller 6. The cooling system further comprises an upper compartment 17 which contains a supply of cool liquid and communicates with the inlet 16, and a lower compartment 19 which communicates with the outlet 18. The configuration of the outlet 18 may but need not be identical with that of the inlet 16. The configuration of the inlet 16 and outlet 18 is such that liquid enters the chamber 14 along its full width by flowing in substantial parallelism with the outer side and in the direction of travel of the stretch 1A, and that spent liquid leaves the chamber in a similar way. This will be described in detail in connection with FIG. 4. The upper compartment 17 receives fresh liquid coolant by way ofa supply conduit 20. A second conduit 21 serves to evacuate spend coolant from the lower compartment 19. If desired, coolant leaving the compartment 19 may be recirculated through a heat recuperating system, thereupon through a cooling system and, if necessary, through one or more filters prior to being reintroduced into the supply conduit 20. The pumping means which causes the coolant to flow from the supply conduit 20, through the compartment 17, inlet 16, chamber 14, outlet 18, compartment 19 and discharged conduit 21 is of conventional design and is not shown in the drawing.

The upper and lower portions 15a, 15b of the panel 15 are respectively adjacent to the

compartments

17, 19 and constitute a pair of baffles or barriers which confine the descending sheet of liquid coolant to flow along the outer side of the stretch 1A. Moreover, the upper portion of the panel 15 prevents coolant which is admitted into the compartment 17 from impinging or striking against the upper part of the stretch 1A with a force which could cause a flexing of the band away from the panel 15; this could cause undesirable deformation of the product in the passage between the bands l-lc, i.e., the billet or bloom would be bounded by concave surfaces. The only way for the coolant to leave the compartment 17 is through the inlet 16 which is designed to control the entry of coolant into the upper part of the chamber 14 in the aforedescribed manner, namely, that the liquid flows in parallel with the outer side and in the direction of travel of the stretch 1A. This prevents the formation of turbulence at the inlet 16 and insures the formation of a homogeneous sheet of coolant which effects uniform withdrawal of heat from the entire stretch 1A. For example, the length of the stretch lAmay be about 700 milimeters. The outlet 18 is also designed with a view to reduce the likelihood of turbulence at the lower end of the chamber 14.

The cooling system for the stretch 1A of the band 1 is shown on a larger scale and is greater detail in FIG. 3. The compartments l7, 19 are bounded in part by a metallic casing 22 which constitutes the main part of the panel 15. The portion 15a, 15b are respectively secured to the casing 22 by screws 23a, 24a and 24b. The

conduits

20, 21 are respectively secured to flanges 20a, 21a by

screws

20b, 20c and 21b, 21c, and these flanges are welded to the casing 22.

The casing 22 is adjustably secured to the frame 12 by fastener

means including bolts

25, 26. Such adjustability enables the persons in charge to change the distance between said frame and said casing. As shown in the lower part of FIG. 3, the bolt 26 meshes with an internally threaded sleeve 27 which is coupled to the frame 12. The head of the bolt 26 engages the inner side of the flange 21a. A lock nut 28 surrounds the stem of the bolt 26 and has a threaded portion 29 which extends into a complementary portion 30 of the sleeve 27. It will be readily understood that rotation of the nut 28 causes the panel 15 to move toward or away from the stretch 1A. Also, the nut 28 serves to prevent uncontrolled changes in the position of the panel 15. The upper bolt 25 is coupled with the frame 12 in similar fashion.

FIG. 3 further shows that the discharge conduit 21 conveys spent coolant into a further conduit 31a which communicates with a conduit 31b. The latter can convey the coolant to aforementioned regenerating, cooling and filtering means. A flexible sleeve 32 of synthetic rubber or like elastomeric material couples the conduit 21 with the conduit 31a and permits necessary adjustments in the position of the panel 15 with reference to the stretch 1A. The supply conduit 20 is preferably connected with one or more additional conduits (not shown) in the same way as described for the conduits 21, 3111,3112.

FIG. 4 illustrates in full detail the construction of the upper part of the cooling system, particularly of the compartment 17 and inlet 16 to the upper part of the chamber 14. The inlet 16 comprises a slightly convergent first section 33 which receives coolant from the compartment 17 and a curved second section 34 of substantially constant cross-sectional area. The second section 34 is bounded from below by a rounded top edge 36 of the panel portion 15a and from above by a concave surface provided on an upwardly inclined wall member 35 secured to the flange 200 by screws 39. The concave surface above the second section 34 of the inlet 16 is curved in such a way that it guides the incoming coolant gradually into substantial parallelism with the outer side of the stretch 1A. This prevents turbulence at the inlet 16 and insures homogeneous distribution of coolant along the full width of the chamber 14. The speed of each portion of the downwardly flowing sheet of coolant in the chamber 14 is at least nearly the same which insures uniform withdrawal of heat from the band 1. It was found that the speed of the sheet of coolant along the edges of the stretch 1A is almost identical with the speed of the central portion of such sheet. In the cooling system which is shown in FIG. 4, the speed of coolant in the chamber 14 is about 7 meters per second and the rate of coolant circulation is 20 cubic meters per hour. The depth of chamber 14 (i.e., the thickness of the sheet of coolant therein) is millimeters. Due to the fact that the first section 33 of the inlet 16 converges slightly toward the second section 34, the pressure of coolant in the upper part of the chamber 14 is slightly less than the pressure of coolant in the compartment 17. In the illustrated embodiment, the width of the section 33 at the compartment 17 is assumed to be 8 millimeters and such width decreases to 5 millimeters at the point where the section 33 merges into the second section 34. The inclination of the center line of the section 33 with reference to the plane of the stretch 1A is about 45.

The outlet 18 is configurated substantially in the same way as the inlet 16. However, it is presently preferred to employ an outlet whose width is uniform substantially all the way from the lower end of the chamber 14 to the compartment 19; such width may be about millimeters. With the above-given dimensions and speeds in mind, the pressure in the compartment 17 may be maintained at 0.8 bar and the pressure of coolant in the sheet of liquid filling the chamber 14 is then 0.62 bar. Thus, the pressure loss during flow of coolant from the compartment 17 into the chamber 14 is rather low. This permits for circulation of large quantities of coolant per unit of time and the coolant need not be maintained at an elevated pressure. The circulation of coolant at relatively low pressures is desirable because such coolant does not exhibit the tendency to shift the stretch 1A of the band 1 away from the adjacent side of the panel 15, i.e., the billet or bloom in the passage between the bands l-lc will be formed with surfaces of predictable outline. The aforementioned pressure in the chamber 14 suffices to at least substantially compensate for ferrostatic pressure (hydraulic pressure exerted by liquid metal due to gravity), mainly in the lower part of the passage for metal. Ferrostatic pressure of liquid steel having a density of about 7.2 and flowing in a passage with a height of 700 millimeters is about 0.5 bar.

The just described cooling system was found to be capable of withdrawing a flux of about 200 calories per cm per second. The temperature of fresh coolant at the inlet 16 was about 20 C. and the temperature of spent coolant at the outlet 18 was about 40 C. There was no danger of overheating at the point where fresh liquid coolant impinges against the stretch 1A and each portion of the stretch 1A was cooled with a high degree of uniformity. The cooling system is capable of effectively preventing piercing or other damage to the band, such as is often due to localized overheating of bands in presently known continuous casting apparatus.

Referring again to FIG. 4 it will be seen that the wall 35 has a front face which is adjacent to the stretch 1A and is formed with vertically extending grooves or flutes 38 bounded by preferably concave surfaces of substantially semicircular outline. The wall member 35 is further provided with upwardly inclined bores or orifices 37 which communicate with the inlet 16 and grooves 38 to admit fresh coolant which is effective in the region immediately below the guide roller 5. Furthermore, the grooves 38 admit coolant into the circumferential flutes or grooves 5a of the roller 5 (see also FIG. 5) so that the roller 5 is properly cooled without necessitating the provision of a separate cooling system therefor. The wall member 35 constitutes the roof of the upper compartment 17. The aforementioned pressure in the compartment 17 suffices to cause penetration of fresh coolant into the grooves 38 and flutes 50, at least into those portions of the flutes 5a which are outwardly adjacent to the band 1 so that the latter is cooled even before it reaches the inlet 16. The coolant which penetrates into the flutes 5a removes heat which is transmitted to the roller 5 by conduction through the band 1 and by radiation of heat from molten metal in the zone above the intake end of the passage between the bands 1-lc.

The casting apparatus of FIG. 1 preferably comprises four independent cooling systems, one for each of the bands l-lc. The cooling liquid is preferably water.

FIG. 5 shows that the cooling system may comprise several supply conduits 20 (and preferably an equal number of discharge conduits 21, not shown in FIG. 5). The upper portion 15a of the panel 15 has been removed in this illustration to expose the parts in the compartment 17. It will be seen that the means for adjusting the distance between the panel 15 and the stretch 1A may include several bolts 25 (and preferably an equal number of bolts 26). The arrows indicate the direction of coolant flow in the grooves 38 of the wall member 35. The open sides of these grooves 38 are sealed by the adjacent portions of the band 1 so that such grooves form channels in which the coolant can rise to enter the flutes 5a of the upper guide roller 5.

FIG. 5 further shows one of the lateral sealing elements 40 which prevent escape of coolant from the chamber 14 in a direction laterally and beyond the adjacent edges of the stretch 1A. The sealing elements 40 are strips of elastomeric material having beads which are received in enlarged portions of grooves 41 (see FIG. 6) defined by the frame 12 and battens or retaining members 42 secured to the frame by screws 43. The battens 42 preferably consist of aluminum bronze. The material of the sealing elements 40 is preferably a synthetic rubber containing fluorine to enhance its resistance to heat. The temperature along the edges of the stretch 1A may rise to about 200 C. The exposed portions of the sealing elements 40 are preferably bevelled or chamfered to enhance their sealing action along the edges of the stretch 1A. The liquid coolant in the chamber 14 exerts on the elements 40 a certain pressure which urges the bevelled edges into more satisfactory sealing engagement with the band 1. The pressure of coolant in the chamber 14 suffices to prevent the stretch 1A from yielding to the pressure of liquid metal in the passage between the bands l-lc so that such stretch need not be engaged by rollers or other conventional devices which could interfere with proper distribution, flow and other characteristics of coolant in the chamber 14. I

An important advantage of the improved cooling system is that it causes the formation of a homogeneous sheet of liquid coolant which flowsdownwardly in the chamber 14 without any appreciable turbulence. Such homogeneous flow of coolant cannot be achieved with cooling systems which employ nozzles or like means for spraying the coolant onto the traveling bands. Liquid coolant which is sprayed in the form of jets forms an irregular sheet wherein different zones contain liquid flowing at different velocities. As a rule, the velocity is lower along the edges of the band and is highest in the median zone between the edges. This prevents uniform cooling of the bands because the liquid along the edges is evacuated at a lower rate. Also, the jets cannot admit liquid coolant at a rate which insures withdrawal of heat necessary to avoid localized or complete overheating of bands during extended periods of use. The inlet 16 and the outlet 18 preferably extend along the full width of the chamber 14 to thus further enhance the uniformity and homogeneousness of liquid flow along the stretch 1A.

Satisfactory cooling of molten material is desirable for the following reasons: If the bands 1-10 are properly cooled, the molten metal in the passage between the inner stretches of these bands develops a skin which is sufficiently thick when it moves beyond the passage to permit convenient withdrawal and further treatment of the metallic product. Thus, proper cooling 'of the bands allows for the use of withdrawing means which transports the product away from the mold at a speed which exceeds the speed of withdrawal in presently known continuous casting apparatus, i.e., the output can be raised without affecting the quality of the product. Thus, it takes less time to convert the liquid contents of a converter into a continuous metallic bar, slab or the like.

As stated before, the pressure of liquid coolant in the chamber 14 is preferably selected with a view to insure that such pressure compensates, at least substantially, for ferrostatic pressure in the passage between the bands l-lc, particularly for ferrostatic pressure in the lower portion of the passage. This, in turn, enables the casting apparatus to produce bars, billets, slabs or like products with a predictable configuration of their sur' faces, i.e., with surfaces which are free of bulges, valleys and other irregularities and whose finish is much more satisfactory than the finish of surfaces in products which are obtained in presently known continuous casting apparatus. It was found that the cooling system of the present invention can properly compensate for ferrostatic pressures even if the bands are made of extremely thin metallic sheet material.

It is clear that the cooling system which is illustrated in FIGS. 2 to 6 is susceptible of many additional modifications without departing from the spirit of the present invention. It is also clear that the aforementioned dimensions, pressures and other specific data were given in a limitative sense.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of our contribution to the art and, therefore, such adapatations should and are intended to be comprehended within the meaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

We claim:

1. A method of casting a continuous billet in a mold having a substantially vertical passage defined by wall means including at least one pair of endless, thin, flexible metallic bands located opposite each other and having inner stretches extending downwardly along said passage, said method comprising the steps of continuously casting molten metal into the upper end of the vertical passage so that the metal fills and flows downwardly in said passage; simultaneously moving said inner stretches of said flexible metal bands in downward direction; circulating about the outer surfaces of said inner stretches of said flexible metal bands a cooling fluid to cool the bands and the metal passing through the passage; and maintaining the pressure of the circulating cooling fluid at a minimum value corresponding at least to the maximum value of ferrostatic pressure of molten metal in said passage so as to obtain at least substantial compensation of the ferrostatic pressure exerted by the molten metal on the bands to prevent outward deflection of said inner stretches solely by the pressure of the cooling fluid on the outer surfaces of said inner stretches of said bands.

2. A method as defined in claim 1, wherein said inner stretches of said flexible metal bands are moved in downward direction at a speed which is substantially equal to the speed at which the cast molten metal moves downwardly in said passage.

3. A method as defined in claim 1, wherein the step of circulating a cooling fluid about the outer surfaces of said inner stretches of said flexible metal bands comprises the step of maintaining a continuous sheet of cooling fluid flowing in downward direction along said outer surfaces of said inner stretches so as to uniformly cool said bands along said inner stretches over the whole width thereof.

4. A method as defined in claim 3, wherein the step of maintaining an downwardly flowing sheet of cooling fluid along said outer surfaces of said inner stretches comprises the step of arranging a stationary guide face outwardly spaced from the outer surface of each stretch and extending substantially parallel thereto and continuously feeding a cooling fluid into the upper end of the space between said guide face and said outer surface and continuously discharging cooling fluid from the lower end of said space.

5. A method as defined in claim 4, wherein said cooling fluid is fed at the upper end and discharged from the lower end of said space in such a manner so as to avoid turbulence of the cooling water in said space.

6. A method as defined in claim 5, wherein said cooling fluid is fed into said space substantially parallel to the direction of movement of the respective flexible band.

7. A method as defined in claim 3, wherein said sheet of cooling fluid is maintained at a depth of about 5 millimeters.

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