US3794108A

US3794108A - High speed continuous casting system

Info

Publication number: US3794108A
Application number: US00365071A
Authority: US
Inventors: V Koump
Original assignee: Urban Reclamation Technologies Inc
Current assignee: URBAN RECLAMATION TECHNOLOGIES INC US; Urban Reclamation Technologies Inc
Priority date: 1973-05-30
Filing date: 1973-05-30
Publication date: 1974-02-26
Anticipated expiration: 1991-02-26

Abstract

A continuous casting system for molten steel involving (1) a high cooling capacity, low friction mold characterized by a reticulated skirt and liquid sprays for heat removal from the lower portion of the mold, (2) an intermediate pressure chamber over the spray-cooled part of the mold, (3) an underground structure that defines a pressure chamber, (4) a sequence of idler and pinch rolls therewithin defining a path for a continuously advancing billet that solidifies within the underground pressure chamber, and (5) a gaseous medium within the upper and lower pressure chambers at greater than atmospheric pressure. The high cooling capacity, low friction mold and higher than atmospheric pressure of the gaseous medium in the upper and lower chambers increase frozen skin strength and decrease stresses in the frozen skin, by reducing frictional forces and neutralizing the metallostatic pressure of the molten steel within the billet and hence permit casting of billets and slabs at unusually high casting speeds.

Description

nited States Patent [1 1 Koump [451 Feb. 26, 1974 HIGH SPEED CONTINUOUS CASTING [73] Assignee: Urban Reclamation Technologies,

Inc., Waltham, Mass.

221 Filed: May 30,1973

21 Appl. No.: 365,071

Related US. Application Data [63] Continuation of Ser. No. 109,139, Jan. 25, 1971,

Primary E.\'aminer--R. Spencer Annear Attorney, Agent, or Firm-Morse, Altman, Oates &

Bello [57] ABSTRACT A continuous casting system for molten steel involving l) a high cooling capacity, low friction mold characterized by a reticulated skirt and liquid sprays for heat removal from the lower portion of the mold, (2) an intermediate pressure chamber over the spray-cooled part of the mold, (3) an underground structure that defines a pressure chamber, (4) a sequence of idler and pinch rolls therewithin defining a path for a continuously advancing billet that solidifies within the underground pressure chamber, and (5) a gaseous medium within the upper and lower pressure chambers at greater than atmospheric pressure. The high cooling capacity, low friction mold and higher than atmospheric pressure of the gaseous medium in the upper and lower chambers increase frozen skin strength and decrease stresses in the frozen skin, by reducing frictional forces and neutralizing the metallostatic pressure of the molten steel within the billet and hence permit casting of billets and slabs at unusually high casting speeds.

7 Claims, 8 Drawing Figures PATENTED'FEB26I974 $794,108

SHEET 1 OF 3 INVENTOR. VALENT/N KOUMP BY Wane wa y 6 A T.TORN E YS PATENIED $794,108

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INVENTOR.

VALENTIN KOUMP ATTORNEYS HIGH SPEED CONTINUOUS CASTING SYSTEM RELATED APPLICATION The present application is a continuation of copending application Ser. No. 109,139, filed Jan. 25, 1971, now abandoned.

BACKGROUND AND SUMMARY The present invention relates to the metallurgy of iron ans steel and, more particularly, to a high speed continuous casting technique that is designed for incorporation into an integrated high speed, continuous steel making system and process involving supplying iron base solids, removing non-ferrous metals therefrom, delivering the iron base solids to a continuous electric melter for conversion to an iron base melt, successively transferring increments of the iron base melt to a series of discrete vessels, successively adjusting the chemical components and thermal energies of the iron base melt increments to produce steel meeting predetermined specifications, continuously casting the steel melt to form a continuous billet, and continuously conditioning and working the continuous billet on line to produce a finished steel shape.

In a continuous steel making system, in which the individual processes (such as melting, refining, casting and rolling) are of inherently matched capacity, are coupled and are operated as integrated components, productivity of the system is limited by the-output of a continuous casting machine. For example, using a conventional continuous casting machine, a 4 X 4 inch cross-section billet can be cast at approximately 150 inches per minute. On the other hand, a 4 X 4 inch cross-section billet typically enters the first stand of a rolling mill at approximately 300 to 400 inches per minute. Thus if the casting machine and the rolling mill were coupled, the rolling mill, a heavy capital investment, would be operated at less than 50 percent capac ity. Accordingly, there exists a need for a continuous casting technique that can operate at speeds substantially higher than those presently available.

The primary object of the present invention is to provide a continuous casting system that can cast semifinished steel atspeeds two to three times the speed of prior systems. This system is particularly adapted for combination with continuous melting, refining, casting and rolling operations by which a fully integrated steel making system is provided and in which productivity is high and labor costs and capital investment are low.

More specifically, the continuous casting machine of the present invention comprises, as components, a mold with a reticulated skirt that initiates billet formation at high speed. A spray system, to remove the heat from the solidifying billet, around the reticulated skirt, an upper pressure chamber surrounding the skirt portion of the mold, an underground structure that defines a pressure chamber, a sequence of support and pinch rolls therewithin defining a path for a continuously advancing billet that solidifies within the chamber, water sprays within the underground pressure chamber to remove heat from the solidifying billet and a compressor for establishing elevated pressure within the upper and lower pressure chambers. The continuous casting process of the present invention comprises,-as steps, flowing molten steel through the die region of a mold to initiate a billet at high speed, cooling the billet intensively in the skirt region of the mold by sprays, advancing the billet through a curved path defined by a series of support and pinch roll pairs, applying an inert gas to the billet within the upper and lower pressure chambers at greater than atmospheric pressure in order to compensate for the metallostatic pressure of molten steel, i.e., to prevent bulging of frozen skin between the supports, and break-outs, and cooling the billet as it advances through the path in order to solidify the surface of the billet as a skin about a molten core and to increase the thickness of the skin until the billet is completely solidi- Other objects of the present invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the devices and processes, together with their components, steps and interrelationships, which are exemplified in the present disclosure, the scope of which will be indicated in the appended claims.

DETAILED DESCRIPTION OF DRAWINGS For a fuller understanding of the nature and objects of the present invention reference is made to the following detailed specification, taken in connection with the accompanying drawings, wherein:

FIG. 1 is a cross-sectional elevation illustrating a conventional continuous casting machine and process;

FIG. 2 is a cross-sectional elevation illustrating a high speed continuous casting machine and process of the present invention;

FIG. 3 is a cross-sectional elevation illustrating a continuous casting system and process of the present invention;

FIG. 4A is an enlarged detail view, partly in cross section, of a component of the system of FIG. 3;

FIG. 4B is a side view, partly in cross-section, of the component of FIG. 4A.

FIG. 4C is a cross-sectional view of FIG. 4A, taken along the line 4C-4C;

FIG. 4D is an enlarged cross-sectional view of FIG. 2, taken along the line 4D-4D; and

FIG. 5 is a top plan view of a compound system of the type shown in FIG. 3, illustrating the relationships between two mirror image systems of the type shown in FIG. 5.

DETAILED DESCRIPTION A schematic diagram of a conventional continuous casting machine is shown in FIG. 1 as follows. A stream of molten steel 11 enters a water cooled copper mold 13 and emerges as a partially frozen billet 15 having a molten interior 17 and a solid skin 19 that thickens as more heat is removed from the billet. The mold is oscillated in a vertical direction at a frequency of 2-5 cycles per second and an amplitude ranging between 0.1-0.75 inch to minimize sticking of the steel to the mold. Below the mold, the billet is supported by rolls 21 and is cooled by water sprays 23. The maximum speed of the process is determined by the strength of solid skin 19. At low casting speed, solid skin 19 thickens rapidly so that it can retain the column of molten steel at the center of the billet. As the speed of the process increases, the thickness of solid skin 19 decreases and its average temperature increases. Eventually, a speed is reached at which the solid skin is no longer capable of: (l) supporting the metallo-static pressure of the column of molten steel so that skin failure (breakout) oc- 3 curs either between the bottom of the mold and the first roll support or between subsequent roll supports; or (2) withstanding the axial force on the billet due to friction between the copper mold and the solid skin or tension generated in the billet due to bulging of the solid skin between roll supports in the roll rack.

The key factors related to mold performance that limits the casting speed in conventional continuous casting machines are: (1) a decrease on the heat flux in the mold, with distance from the liquid level, as a result of formation of the air gap between the mold wall and the surface of the billet (due to thermal shrinkage and shrinkage as a result of solidification); (2) variation of heat flux along the periphery of the mold as a result of variation of the air gap along the periphery of the mold, due to minor misalignments between the mold and the roll rack; and (3) frictional forces between the surface of the partially frozen billet and the mold walls, which when excessive, may tear the frozen skin in or below the mold.

' A schematic diagram of a high speed continuous casting machine embodying the present invention is shown in FIG. 2 as follows. Details are shown in FIGS. 4A, B, C and D. A stream of molten steel 25 enters a mold 27, which includes a water cooled upper die 29 and a lower skirt 31. This molten steel emerges from upper die 29 at high speed as a billet with a very thin skin. Lower skirt 31 is cage of the same inside dimensions as the mold, defined by a plurality of spaced ribs. The billet advances into the cage where it is cooled intensively by sprays of water or other cooling medium impinging on the steel billet directly between the ribs. One such other medium is a low melting point metal such as tin. The rate of heat removal from the billet in the cage by direct contact of sprays and hot billets is substantially higher than the rate of heat removal in the lower part of a conventional mold. As a result, the frozen shell of the billet, emerging from the cage, is thicker and at lower temperature (and therefore stronger) than in conventional continuous casting practice.

Furthermore, the minor misalignments between the mold and the roll rack no longer effect the rate of heat removal from the billet since the billet is cooled directly by the sprays. In consequence, substantially improved peripheral uniformity of the thickness of the frozen skin is achieved by the preceeding method. Below the mold, the billet is supported by rolls 33 and is cooled by water sprays 35. As will be explained below, the shape of the rapidly advancing billet is maintained in part by a high pressure atmosphere. This atmosphere is retained by seal rolls 37 to be described more fully below. An intermediate pressure chamber 39 is positioned about skirt 31 to receive gases escaping from the main pressure chamber and to provide partial support to the frozen skirt in the space between the ribs.

Since the area of contact between the billet and the skirt of the present mold is smaller than the conventional mold, and a portion of the'normal force (due to metallostatic pressure) is relieved by ambient pressure, the total frictional force transmitted by the mold to the billet is substantially reduced. Because the pressure in the underground chamber reduces bulging between the rolls, net frictional force in the roll rack is reduced, thereby decreasing stresses in the frozen skin. In turn, higher casting velocity can be achieved. The higher than normal rate of heat removal in the mold, a more uniform peripheral distribution of heat flux in the mold, lower friction, small spacing between the ribs of the cage and higher than atmospheric ambient pressure of gas around the cage and in the underground pressure chamber, in the present system, permit casting of steel at substantially higher casting velocity than is possible in conventional casting machines.

A general schematic view of a continuous casting system of the present invention, FIG. 3, includes a holding vessel 10 and a tundish vessel 12, which receives the contents of holding vessel 10 continuously for the maintanance of substantially predetermined weight. Vessel 10 is shown as having a cover 14, in which are electric heaters to compensate for heat loss. Vessel 10 is mounted for rocking motion under the control of a hydraulic drive (not shown). Holding vessel 10 is supported on a car 20, which rides by flanged wheels 22 on suitable rails. Molten steel 24 is poured through a spout 26 from holding vessel 10 into a tundish vessel 12. Tundish vessel 12 is provided at its floor with a sequence of nozzels 30, which successively can be moved into operating position automatically as operating nozzels of the sequence become eroded. Tundish vessel 12 is supported on a car (not shown), which rides by flanged wheels on suitable rails (not shown). The metallostatic head in tundish vessel 12 is maintained by controlling its tilt about a pivot by a hydraulic drive (not shown).

In accordance with the present invention, the molten stream 36 from tundish vessel 12, after passing through a high speed mold of the type shown in FIG. 2, is converted into a solid billet within a pressure chamber 38, enclosing all of the operating components of the continuous casting system. Molten stream 36 advances from the mold into a roll rack 42. Roll rack 42 includes driven rolls 43, idler rolls 45 and water sprays 47. The initial thin solid skin is thickened in roll rack 42. From roll rack 42 the billet, the core of which is solidifying, advances in an arcuate path between the nips of pairs of bending rolls and pinch rolls 44, 46, idler rolls 49 and straightening rolls 48. The pinch rolls are driven. Cooling sprays extend throughout the length of the billet in the underground chamber.

As shown in FIG. 5, chamber 38 is defined underground by a steel reinforced, concrete casting. As shown in FIG. 5 chamber 38 is one of a pair of like chambers, the other of which is designated 54. Each of

chambers

38, 54 is an independent heremetically isolated pressure chamber that selectively is supplied with inert gas from a pump and gas supply 56 through a valve 60. Two chambers are provided so that when the components of one are under repair,the other is operating on line with the remainder of the continuous steel making system. When chamber 38 is in operation, tundish vessel 12 is positioned above die opening 40 so as to produce the billet shown at 62. When chamber 54 is in operation, tundish vessel 12 is positioned above a die opening 64 so as to produce the billet shown at 66. Once advanced out of its chamber either billet is advanced into a forming station for processing in the remainder of the continuous steel system. A pair of

manholes

70, 72 are provided for entry into the underground chamber for repairs during down time. The gas in the underground chamber is permitted to escape from the chamber in the vicinity of mold 40 in order to provide pressurizing gas for the upper pressure chambe). The pressure in the upper chamber is controlled by a valve that regulates escape of steam and pressurizing gas to the atmosphere.

Preferably, the gas within the pressure chamber is inert, being selected from the class consisting of carbon dioxide, nitrogen, carbon monoxide and hydrocarbon gas. Preferably, the gas pressure ranges from 1/2 to 3 atmospheres. 1n alternative systems, air may be used instead of inert gas although, in this case, the steel must be such that the resulting increased rate of oxidation can be tolerated. in one specific example, the are through which a 2 inch billet advances is approximately 20 feet in diameter, the spacing between the ribs of the cage is 0.5-l inch, the gas is combustion products of natural gas, the gas pressure is approximately 1.2 to 1.3 atmospheres absolute (.2 to .3 above normal) in the upper pressure chamber and is approximately 2 atmospheres absolute (1 atmosphere above normal) the underground chamber and the speed of the billet is approximately 60 feet per minute, which is more than twice the conventional speed of a billetin a continuous casting machine.

Since certain changes may be made in the present disclosure without departing from the scope of the present invention, it is intended that all matter shown in the accompanying drawings and described in 'the foregoing specification be interpreted in an illustrative and not in a limiting scope.

What is claimed is:

l. A system including an upper mold and a lower structure defining a plurality of pressure chambers communicating for continuous casting of steel, said upper mold comprising an upper portion extending along part of the total length of said upper mold and a lower portion in the form of a reticulated skirt extending along the remaining part of the length of said upper mold, said remaining part involving a plurality of ribs spaced apart from 0.2 to 1.0 inch, high volume liquid sprays for heat removal in said remaining part of the length of said upper mold, said lower part being surrounded by one of said pressure chambers, said lower structure encompassing said other of said pressure chambers, the pressure in said one of said pressure chambers being maintained at 0.1 to 0.5 atmospheres above atmospheric pressure depending on the level of molten steel in said one of said pressure chambers, said structure being composed of concrete and being situated underground, a series of rolls at least in part in said other of said pressure chambers defining a loop through which a continuous length of cast steel is advanced, said pressure in said one of said pressure chambers being established by a gas flowing from said other of said pressure chambers, said pressure partially supporting the surface of said length of cast steel which constitutes partially solidified skin, said gas being substantially inert with respect to said continuous length.

within said pressure chamber.

Claims

1. A system including an upper mold and a lower structure defining a plurality of pressure chambers communicating for continuous casting of steel, said upper mold comprising an upper portion extending along part of the total length of said upper mold and a lower portion in the form of a reticulated skirt extending along the remaining part of the length of said upper mold, said remaining part involving a plurality of ribs spaced apart from 0.2 to 1.0 inch, high volume liquid sprays for heat removal in said remaining part of the length of said upper mold, said lower part being surrounded by one of said pressure chambers, said lower structure encompassing said other of said pressure chambers, the pressure in said one of said pressure chambers being maintained at 0.1 to 0.5 atmospheres above atmospheric pressure depending on the level of molten steel in said one of said pressure chambers, said structure being composed of concrete and being situated underground, a series of rolls at least in part in said other of said pressure chambers defining a loop through which a continuous length of cast steel is advanced, said pressure in said one of said pressure chambers being established by a gas flowing from said other of said pressure chambers, said pressure partially supporting the surface of said length of cast steel which constitutes partially solidified skin, said gas being substantially inert with respect to said continuous length.

2. The system of claim 1 wherein said liquid is water.

3. The system of claim 1 wherein said liquid is molten metal.

4. The system of claim 1 wherein said gas is selected from the class consisting of nitrogen, carbon dioxide and combustion products of hydrocarbon fuel.

5. The system of claim 1 wherein said length of cast steel is a billet.

6. The system of claim 1 wherein said length of cast steel is a slab.

7. The system of claim 1 wherein said loop is entirely within said pressure chamber.