Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/14—Plants for continuous casting
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
  • B21B1/46—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling metal immediately subsequent to continuous casting
  • B21B1/463—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling metal immediately subsequent to continuous casting in a continuous process, i.e. the cast not being cut before rolling
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B9/00—Measures for carrying out rolling operations under special conditions, e.g. in vacuum or inert atmosphere to prevent oxidation of work; Special measures for removing fumes from rolling mills
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/06—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
  • B22D11/0622—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars formed by two casting wheels
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/06—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
  • B22D11/0637—Accessories therefor
  • B22D11/0697—Accessories therefor for casting in a protected atmosphere
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
  • B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
  • B21B1/24—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length in a continuous or semi-continuous process
  • B21B1/26—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length in a continuous or semi-continuous process by hot-rolling, e.g. Steckel hot mill
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
  • B21B45/04—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills for de-scaling, e.g. by brushing
  • B21B45/08—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills for de-scaling, e.g. by brushing hydraulically

Definitions

• This invention relates to the production of thin steel strip. It has particular application to the production of steel strip by continuous casting and inline hot rolling of the strip to a final gauge or thickness.
• Steel strip produced by continuous thin slab casting or by twin roll strip casting may be subjected to inline hot rolling to reduce the strip to the final gauge.
• molten metal is introduced between a pair of contra-rotated horizontal casting rolls which are cooled so that metal shells solidify on the moving roll surfaces and are brought together at the nip between them to produce a solidified strip product delivered downwardly from the nip between the rolls.
• nip is used herein to refer to the general region at which the rolls are closest together.
• the molten metal may be poured from a ladle into a smaller vessel from which it flows through a metal delivery nozzle located above the nip so as to direct it into the nip between the rolls, so forming a casting pool of molten metal supported on the casting surfaces of the rolls immediately above the nip and extending along the length of the nip.
• This casting pool is usually confined between side plates or dams held in sliding engagement with end surfaces of the rolls so as to dam the two ends of the casting pool against outflow, although alternative means such as electromagnetic barriers have also been proposed.
• the strip leaving the hot rolling mill was subjected to water cooling and then coiled. With this procedure, the strip may need to be subsequently descaled or pickled prior to some end uses.
• the hot rolled strip is subjected to descaling prior to coiling at temperatures in the range 900°C to 600°C the rate of rescaling will be very low.
• the strip can be coiled with very low scale of the order of only 1 to 2 micron thick and there will be no further appreciable scale development.
• the resulting coils can be sent directly to end users for many applications such as in the production of drums and any painted strip products. In other applications, they will allow much faster pickling than the material not subjected to descaling immediately prior to coiling.
• a method of producing steel strip comprising: continuously casting a steel strip; guiding the strip through an enclosure containing an atmosphere which inhibits oxidation of the strip surface - 3 -
• the strip may be passed out of said enclosure prior to passing through the rolling mill.
• the rolling mill may be disposed within the enclosure so that the strip passes through the rolling mill before leaving the enclosure.
• the strip is continuously cast by supporting a casting pool of molten steel on a pair of chilled casting rolls forming a nip between them and the solidified strip is produced by rotating the rolls in mutually opposite directions such that the solidified strip moves downwardly from the nip.
• the atmosphere in said enclosure may be formed of inert or reducing gases or it may be an atmosphere containing oxygen at a level lower than the atmosphere surrounding the enclosure.
• the atmosphere in the enclosure is formed by sealing the enclosure to restrict ingress of oxygen containing atmosphere, causing oxidation of the strip within the enclosure during an initial phase of casting thereby to extract oxygen from the sealed enclosure and to cause the enclosure to have an oxygen content less than the atmosphere surrounding the enclosure, and thereafter maintaining the oxygen content in the sealed enclosure at less than that of the surrounding atmosphere by continuous oxidation of the strip passing through the sealed enclosure thereby to control the thickness of the resulting scale on the strip.
• the rolling mill hot rolls the strip at a temperature in the range of 750 to 1250°C. - 4 -
• the invention further provides apparatus for producing steel strip comprising: a continuous caster for continuously casting steel strip; strip guide means to guide the strip through a transit path away from the caster; an oxidation inhibiting enclosure to confine the strip throughout said transit path to control formation of scale on the strip; a rolling mill operable to roll the strip as it is produced; a descaler operable to descale the strip as it leaves the rolling mill; and a coiler to receive the rolled and descaled strip.
• the continuous caster includes: a pair of generally horizontal casting rolls forming a nip between them; metal delivery means to deliver molten steel into the nip between the casting rolls to form a casting pool of molten steel supported on the rolls; means to chill the casting rolls; and means to rotate the casting rolls in mutually opposite directions whereby to cast said strip and to deliver it downwardly from the nip.
• Figure 1 is a vertical cross-section through a steel strip casting and rolling installation constructed and operated in accordance with the present invention
• Figure 2 illustrates essential components of a twin roll caster incorporated in the installation
• Figure 3 is a vertical cross-section through part - 5 -
• Figure 4 is a cross-section through end parts of the caster.
• Figure 5 is a cross-section on the line 5-5 in Figure 4;
• Figure 6 is a view on the line 6-6 in Figure 4.
• Figure 7 is a diagrammatic view of part of a modified installation constructed and operated in accordance with the invention.
• the illustrated casting and rolling installation comprises a twin roll caster denoted generally as 11 which produces a cast steel strip 12 which passes in a transit path 10 across a guide table 13 to a pinch roll stand 14.
• the strip passes into a hot rolling mill 15 comprising roll stands 16 in which it is hot rolled to reduce its thickness.
• the thus rolled strip exits the rolling mill and passes to a run out table 17 on which it may be force cooled by water jets 18.
• the strip is then passed through a descaler 19 before passing between pinch rolls 20A of a pinch roll stand 20 to a coiler 50.
• Twin roll caster 11 comprises a main machine frame 21 which supports a pair of parallel casting rolls 22 having casting surfaces 22A.
• Molten metal is supplied during a casting operation from a ladle 23 through a refractory ladle outlet shroud 24 to a tundish 25 and thence through a metal delivery nozzle 26 into the nip 27 between the casting rolls 22.
• Hot metal thus delivered to the nip 27 forms a pool 30 above the nip and this pool is confined at the ends of the rolls by a pair of side closure dams or plates 28 which are applied to stepped ends of the rolls by a pair of thrusters 31 comprising hydraulic cylinder units 32 connected to side plate holders 28A.
• pool 30 (generally referred to as the "meniscus" level) may rise above the lower end of the delivery nozzle so that the lower end of the delivery nozzle is immersed within this pool.
• Casting rolls 22 are water cooled so that shells solidify on the moving roller surfaces and are brought together at the nip 27 between them to produce the solidified strip 12 which is delivered downwardly from the nip between the rolls.
• a short length of imperfect strip is produced as the casting conditions stabilise.
• the casting rolls are moved apart slightly and then brought together again to cause this leading end of the strip to break away in the manner described in
• twin roll caster may be of the kind which is illustrated and described in some detail in granted Australian Patents 631728 and 637548 and United States Patents 5,184,668 and 5,277,243 and reference may be made to those patents for appropriate constructional details which form no part of the present invention.
• the installation is manufactured and assembled to form a single very large scale enclosure denoted generally as 37 defining a sealed space 38 within which the steel strip 12 is confined throughout a transit path from the nip between the casting rolls to the entry nip 39 of the pinch - 7 -
• Enclosure 37 is formed by a number of separate wall sections which fit together at various seal connections to form a continuous enclosure wall. These comprise a wall section 41 which is formed at the twin roll caster to enclose the casting rolls and a wall section 42 which extends downwardly beneath wall section 41 to engage the upper edges of scrap box 33 when the scrap box is in its operative position so that the scrap box becomes part of the enclosure.
• the scrap box and enclosure wall section 42 may be connected by a seal 43 formed by a ceramic fibre rope fitted into a groove in the upper edge of the scrap box and engaging flat sealing gasket 44 fitted to the lower end of wall section 42.
• Scrap box 33 may be mounted on a carriage 45 fitted with wheels 46 which run on rails 47 whereby the scrap box can be moved after a casting operation to a scrap discharge position.
• Cylinder units 40 are operable to lift the scrap box from carriage 45 when it is in the operative position so that it is pushed upwardly against the enclosure wall section 42 and compresses the seal 43. After a casting operation the cylinder units 40 are released to lower the scrap box onto carriage 45 to enable it to be moved to scrap discharge position.
• Enclosure 37 further comprises a wall section 48 disposed about the guide table 13 and connected to the frame 49 of pinch roll stand 14 which includes a pair of pinch rolls 14A against which the enclosure is sealed by sliding seals 60. Accordingly, the strip exits the enclosure 38 by passing between the pair of pinch rolls 14A and it passes immediately into the hot rolling mill 15.
• the spacing between pinch rolls 14 and the entry to the rolling mill should be as small as possible so as to control the formation of scale prior to entry into the rolling mill.
• Most of the enclosure wall sections may be lined with fire brick and the scrap box 33 may be lined either with fire brick or with a castable refractory lining. - 8 -
• the enclosure wall section 41 which surrounds the casting rolls is formed with side plates 51 provided with notches 52 shaped to snugly receive the side dam plate holders 28A when the side dam plates 28 are pressed against the ends of the rolls by the cylinder units 32.
• the interfaces between the side plate holders 28A and the enclosure side wall sections 51 are sealed by sliding seals 53 to maintain sealing of the enclosure. Seals 53 may be formed of ceramic fibre rope.
• the cylinder units 32 extend outwardly through the enclosure wall section 41 and at these locations the enclosure is sealed by sealing plates 54 fitted to the cylinder units so as to engage with the enclosure wall section 41 when the cylinder units are actuated to press the side plates against the ends of the rolls.
• Thrusters 31 also move refractory slides 55 which are moved by the actuation of the cylinder units 32 to close slots 56 in the top of the enclosure through which the side plates are initially inserted into the enclosure and into the holders 28A for application to the rolls.
• the top of the enclosure is closed by the tundish, the side plate holders 28A and the slides 55 when the cylinder units are actuated to apply the side dam plates against the rolls.
• the complete enclosure 37 is sealed prior to a casting operation to establish the sealed space 38 whereby to limit the supply of oxygen to the strip 12 as it passes from the casting rolls to the pinch roll stand 14. Initially the strip will take up all of the oxygen from the enclosure space 38 to form heavy scale on the strip.
• the sealing of space 38 controls the ingress of oxygen containing atmosphere below the amount of oxygen that could be taken up by the strip.
• the oxygen content in the enclosure space 38 will remain depleted so limiting the availability of oxygen for oxidation of the strip.
• the formation of scale is controlled without the need to continuously feed a reducing or non-oxidising gas into the enclosure space 38.
• the enclosure space can be purged immediately prior to the commencement of casting so as to reduce the initial oxygen level within the enclosure and so reduce the time for the oxygen level to be stabilised as a result of the interaction of oxygen from the scaled enclosure due to oxidation of the strip passing through it.
• the enclosure may conveniently be purged with nitrogen gas. It has been found that reduction of the initial oxygen content to levels of between 5% to 10% will limit the scaling of the strip at the exit from the enclosure to about 10 microns to 17 microns even during the initial start-up phase.
• the temperature of the strip passing from the caster will be of the order of 1400°C and the temperature of the strip presented to the mill may be about 1200°C.
• the strip may have a width in the range 0.9 m to 2.0 m and a thickness in the range 0.7 mm to 2.0 mm.
• the strip speed may be of the order of 1.0 m/s. It has been found that with strip produced under these conditions it is quite possible to control the leakage of air into the enclosure space 38 to such a degree as to limit the growth of scale on the strip to a thickness of less than 5 microns at the exit from the enclosure space 38, which equates to an average oxygen level of 2% with that enclosure space.
• the volume of the enclosure space 38 is not particularly critical since all of the oxygen will rapidly be taken up by the strip during the initial start up phase of a casting operation and the subsequent formation of scale is determined solely by the rate of leakage of atmosphere into the enclosure space though the seals. It is preferred to control this leakage rate so that the thickness of the scale at the mill entry is in the range 1 micron to 5 microns.
• Experimental work has shown that the strip needs some scale on its surface to prevent welding and sticking during hot rolling. Specifically, this work suggests that a minimum thickness of the order of 0.5 to 1 micron is necessary to ensure satisfactory

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Metal Rolling (AREA)
• Continuous Casting (AREA)
• Heat Treatment Of Articles (AREA)
• Dry Formation Of Fiberboard And The Like (AREA)

Applications Claiming Priority (3)

Publications (1)

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• 1999
  • 1999-11-03 AU AUPQ3850A patent/AUPQ385099A0/en not_active Abandoned
• 2000
  • 2000-11-02 EP EP00972472A patent/EP1242204A1/en not_active Withdrawn
  • 2000-11-02 PE PE2000001170A patent/PE20010876A1/es not_active Application Discontinuation
  • 2000-11-02 WO PCT/AU2000/001344 patent/WO2001032335A1/en not_active Application Discontinuation
  • 2000-11-02 CN CN00815269A patent/CN1387467A/zh active Pending
  • 2000-11-02 JP JP2001534530A patent/JP2003512934A/ja active Pending
  • 2000-11-02 RU RU2002114358/02A patent/RU2002114358A/ru not_active Application Discontinuation
  • 2000-11-02 KR KR1020027005691A patent/KR20020063886A/ko not_active Application Discontinuation
  • 2000-11-02 CA CA002389288A patent/CA2389288A1/en not_active Abandoned
  • 2000-11-02 BR BR0015292-7A patent/BR0015292A/pt not_active Application Discontinuation
  • 2000-11-03 AR ARP000105797A patent/AR026348A1/es unknown
  • 2000-12-28 TW TW089123118A patent/TW499340B/zh not_active IP Right Cessation

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