US3848656A

US3848656A - Process for cooling and supporting a continuously cast metal bar

Info

Publication number: US3848656A
Application number: US00260733A
Authority: US
Inventors: J Meylan
Original assignee: Battelle Memorial Institute Inc
Current assignee: Battelle Memorial Institute Inc
Priority date: 1971-06-09
Filing date: 1972-06-08
Publication date: 1974-11-19
Anticipated expiration: 1991-11-19
Also published as: IT959069B; CH539474A; FR2140522B1; FR2140522A1; GB1398891A; BE792303A; DE2228317A1

Abstract

A process and apparatus for continuous casting of metal bars, in which the metal bar is formed in a cooled mould, extracted therefrom by roller trains, cooled during extraction and along its path of extraction the metal bar is subjected to the action of a fluid in an airtight chamber, the fluid having a pressure such as to compensate the hydrostatic internal pressure in the metal bar to reduce pressure and stress on the roller trains.

Description

United States Patent 1191 Meylan 1451 Nov. 19, 1974 PROCESS FOR COOLING AND 3,191,251 6/1965 OlSSOIl 164/283 s x SUPPORTING A CONTINUOUSLY CAST 3,358,744 12/1967 Rossi 164/283 S X 3,596,706 8/1971 Knorr et a1. 164/282 METAL BAR Jean-Luc Charles Meylan, Geneva, Switzerland Assignee: Battelle Memorial Institute, Carouge/Geneva, Germany Filed: June 8, 1972 Appl. No.: 260,733

Inventor:

Foreign Application Priority Data June 9, 1971 Switzerland... 8423/71 References Cited UNITED STATES PATENTS 7/1908 Trotz 164/283 R X Primary Examiner-R. Spencer Annear Attorney, Agent, or Firm-Waters, Roditi, Schwartz.& Nissen [57] ABSTRACT A process and apparatus for continuous casting of metal bars, in which the metal bar is formed in a cooled mould, extracted therefrom by roller trains. cooled during extraction and along its path of extraction the metal bar is subjected to the action of a fluid in an airtight chamber, the fluid having a pressure such as to compensate the hydrostatic internal pressure in the metal bar to reduce pressure and stress on the roller trains.

7 Claims, 13 Drawing Figures PATENIE new 1 9mm SHEET 1 0F 4 FIG FIG. BO

PROCESS FOR COOLING AND SUPPORTING A E CONTINUOUSLY CAST METAL BAR veying the steel strand thus obtained along and between two series of rollers while it is being cooled until it has completely solidified. The cooling is effected first by means of water jets and then by natural heat radiation and convection. The path of the steel rod, which initially is inclined and curved, is gradually diverted into a horizontal plane by the roller trains.

This process has, however, some disadvantages such 1 as it is necessary to use a great many heavily loaded rollers, the apparatus required for carrying out the process is heavy and bulky;

2. the life of the rollers is limited to but a few days;

3. the metal strand tends to bulge between the rollers due to the effect exerted by the hydrostatic (ferrostatic) internal pressure; the bulging brings about the well known metallurgical disadvantages such as fissures and cracks, etc; in order to reduce the bulging a great number of rollers is required; therefore, a great mechanical force is required to move the metal strand;

4. the surface available between the rollers for cooling the metal strand is limited;

5. the speed of movement of the metal strandis limited to about lm/min.

It is an object of the present invention to eliminate the aforementioned disadvantages in a process for continuous casting of metal strands, particularly steel slabs, in which the metal strand is formed in a cooled mould and extracted from the mould by roller trains, the metal strand being cooled during extraction until it has completely hardened. To achieve this object, the process according to the present invention comprises subjecting the surface of the metal strand, in the region of solidification of the metal strand, along its path of extraction, to the action of a gaseous medium having about the same pressure as the ferrostatic internal pressure of the meta] strandthat at the same time said metal strand being cooled by spraying liquid on its surface.

Thus, the process of the present invention consists in counterbalancing the hydrostatic pressure acting on the skin of the metal strand by the pressure of a gaseous medium located outwardly of the metal strand, instead of the rollers used for this purpose in the conventional processes. Consequently, the rollers in the process of the present invention only serve as guide rollers and therefore their number and size may be considerably reduced and they may be spaced further apart. The fluid pressure acting on the surface of the strand reduces the bulging between the rollers and therefore the force required for moving the strand can be considerably reduced, particularly since the rollers are no longer subjected to the hydrostatic internal pressure of the metal strand, acting perpendicularly to their axes. Thereby roller wear is considerably reduced and their life is extended. This further permits to increase their speed of rotation, resulting in an increase of the speed of movement of the metal strand and consequently in an increase of the production capacity.

Although various gaseous mediums may be used in the process of the present invention, steam is most advantageous as it can be produced at the desired pressure and at low cost by spraying water on the surface of the metal strand. Thus, for example, the heat emanated by a metal slabof 30 X 200 cm, moving at a speed of l m/min., permits to produce about 15 kg of steam per second.

Also air may be used as a gaseous medium although its use necessitates the employment of a compressor of a very high power. Also a mixture of air and steam may be used, but such a mixture is less advantageous than pure steam.

The process and apparatus of the present invention will now be described in detail with reference to the accompanying drawings which schematically show two embodiments of the apparatus with some variations thereof and in which:

FIG. 1 is a longitudinal sectional view of a first embodiment of the apparatus;

FIG. 2 is a section taken on the line Il-ll of FIG. 1;

FIG. 3 is an illustrative diagram;

FIG. 4 is a part perspective view of a variation of the apparatus shown in FIG. 1;

FIG. 5 is a schematic longitudinal section of a variation of the apparatus shown in FIG. 4;

FIG. 6 is a schematic longitudinal section of another variation of the apparatus shown in FIG. 4;

FIG. 7 is a schematic transverse section through a particular embodiment of the injection device;

FIG. 8 is a plan view showing the elements of the injection device of FIG. 7;

FIG. 9 is a sectional view, on a larger scale, showing a member of the injection device of FIG. 7;

FIGS. 10, 11 and 12 are part longitudinal sections through the apparatus of FIG. 1, illustrating its operation, and

FIG. 13 is a longitudinal section through a second embodiment of the apparatus comprising only a horizontal portion.

The apparatus shown in FIG. 1 together with a cast metal slab 11 comprises a conventional mould l of the type commonly used for continuous casting of steel slabs, a series of compartments 2a to 2g forming an inclined portion of the apparatus and separated from one another by parallel horizontal partitions, 3a to 3f, and a compartment 4'separated from the compartment 2g by a horizontal partition 3g and forming a horizontal portion of the apparatus. Approximately in their con tral portion the partitions 3a to 3g are provided with .an

aperture 33a to 33g-having the shape of the crosssection of the metal slab 11 cast and a size largerby a few millimetres than this cross-section so as to provide some limited play for the passage of metal slab. The compartment 4 is closed at .its free end by a wall 5 having an aperture provided with .an outlet seal 6 permitting the metal slab 11 to pass freely without any substantial leak of fluid from theinterior of the compartment 4 to the outside. The partitions 3a to 3g are spaced from one another by about 20 centimeters.

Rollers 9 are placed with their axes horizontally in the compartments 2a to 2g and the compartment 4 to guide and straighten the cast metal slab. The number of rollers 9 may obviously also be different from that shown in FIG. 1, and in particular it may be smaller than that shown, but at any rate it is smaller than the number of rollers in the conventional apparatus for continuous casting of steel slabs. Each of the compartments 2a to 2g is provided with at least two injection nozzles 10 arranged substantially opposite each other on two sides of the metal slab 11. The number of injection nozzles 10 in the compartment 4 depends on its length, in the illustrated embodiment there are twenty.

Each of the compartments 2a to 2g is connected to the adjacent one by a pressure control valve 14a to 14g. The compartment 2a is provided with a fluid outlet aperture 13 provided with a control valve 13a.

In the illustrated apparatus the fluid utilized is steam produced in situ by injection of hot water through the injection nozzles 10 into the compartments 2a to 2g and 4. The operation of the apparatus is as follows:

By means of a casting ladle not shown in the drawings a jet 12 of molten metal, for example, liquid steel having a temperature in the order of l,500 C, is cast into the mould 1. The steel slab flowing out of the mould 1 traverses the apparatus shown in FIG. 1 from top to bottom and from left to right, cooling on its way and solidifying progressively from outside toward its inside. When the steel slab leaves the mould 1 it is almost completely liquid apart from a thin deformable skin on its outer surface and when it leaves the apparatus at the outlet seal 6 it has completely solidified into an indeformable rigid block.

On the other hand, in the inclined portion of the apparatus the metal slab is mainly liquid. The portion of the metal bar located between the dash lines shown in FIG. 1 is the liquid pump inner portion of the metal slab.

In the compartments 2a to 2g and 4 the water injected through the injection nozzles 10 is vaporized on contact with the metal slab 11 and with the walls of these compartments to which some of the heat emitted by the metal slab is transmitted. In this manner in each of the compartments 2a to 2g and'4 a pressure is produced which is equivalent to the hydrostatic pressure of the portion of the metal slab traversing the respective compartment. The temperature of the metal slab in the compartment 2g is in the order of 1,000 C and its hydrostatic pressure is about 5 to bars. In the compartment 2a the hydrostatic pressure of the metal slab is of the order of 1 bar. The pressure of the vapour increases progressively from the compartment 2a to the compartment 2g so as to counterblanace the hydrostatic pressure of the metal slab along its path through said compartments. The temperature at which the water enters each of the compartments is adjusted to a value near the vapour saturation temperature corresponding to the pressure required to prevail in the respective compartment, i.e., a value between 100 and 180 C. In this manner any undesired vapour condensation is avoided which might occur if an amount of water much higher than the amount of produced vapour were injected.

The diagram of FIG. 3 illustrates the internal hydrostatic pressure PH of the metal slab and the pressures of the steam (fluid) PF acting on the metal bar in the various compartments 2a to 2g and 4 of the apparatus. As shown in FIG. 3, the steam pressure in each compartment is constant and its value corresponds to the medium value of the internal hydrostatic pressure of the portion of the metal slab in the respective compartment.

The part perspective view of FIG. 4 shows a variation of the apparatus of FIG. 1, in which the space of the compartment 4 which is not occupied by the metal slab 11 is longitudinally divided into two portions, i.e., an upper portion 4a and a lower portion 4b, by a pressure loss device or dynamic joint formed by a plurality of horizontal partitions 8 which in the illustrated embodiment are five in number and arranged around the metal slab 11 so as to form labyrinths 7. A by-pass pressure control valve 1411 (FIG. 5) connects the two portions 4a and 4b.

This variation permits to obtain below the metal slab a fluid pressure different from that above the metal slab. Thus, by producing, for example, below the metal slab 11 a pressure higher than that above the metal bar the latter is still better supported and guided and so the number of guide rollers can be further reduced.

The part view of FIG. 5 shows another variation of the apparatus without the metal strand. In addition to the pressure loss device of the variation described above, this variation comprises a steam recycling system including a condenser 15 provided with a cooling fluid circuit 16, a pump 17 and a conduit 18 for feeding the hot water produced by the condenser 15 to the injection nozzles 10 (not shown in FIG. 5). The arrows indicate the flow direction of the steam in the chamber and that of the water produced by condensation of the vapour. The temperature of this water is in the order of C at the outlet from the condenser 15 in which the pressure is therefore slightly higher than atmospheric.

The apparatus shown in FIG. 6 is similar to that of FIG. 5, but comprising additionally a second steam recycling system including a vapour condenser 19 provided with a cooling fluid circuit 20, a pump 21 and a conduit 22 for re-introduction of the hot water into the apparatus. A second control valve 23 permits vapour at high pressure to be removed from the compartment 2g and to be introduced into the condenser 19. The water at the outlet of the condenser 19 has a temperature of about C., whereas the temperature of the water at the outlet of the condenser 15 is again 105 C.

The transverse section of FIG. 7 shows a compart ment of the apparatus provided with a special type of water injection device formed by injection pots 24 containing injection nozzles 25 connected through a conduit 26 to the source of water under pressure. The arrows indicate the flow direction of the produced steam. The pressure of the vapour in the pots 24 is higher than the pressure in the rest of the compartment. This injection device permits to improve the supporting and guiding of the strand and can be used either in all or only some of the compartments of the apparatus. In the horizontal portion of the apparatus formed substantially by the compartment 4 this injection device may be used, for example, only below the strand.

FIG. 8 shows the arrangement of the injection pots 24 with respect to one another. This staggered arrangement avoids the formation of permanent deformations in the skin of the strand. The injection pots 24 may also have a different shape than that shown in FIG. 7, for example, a rectangular, oval or some other shape.

FIG. 9 shows an injection pot 24 provided with a rim 27 in the form of a labyrinth seal which permits to obtain a more progressive and regular distribution of the pressure exerted by the water vapour on the surface of the metal slab 11.

FIGS. 10, 11 and 12 show the means used for setting the apparatus of the present invention into operation. For this purpose an articulated dummy bar 28 is provided which at one end has a dummy bar head 29 with a surface corresponding to the cross section of the metal slab 11. Before starting operation of the apparatus, the head 29 closes the mould 1 as shown in FIG. 10. The other end of the articulated dummy bar 28 is connected to appropriate means, not shovm, permitting to exert a pulling force on the articulated dummy bar 28. In the lower portion of the apparatus, the articulated rod 28 passes along a channel provided in the interior of a rigid rod 30 of the same cross section and weight per unit of length as the metal slab 11. The rigid rod 30 is likewise connected to appropriate means, not shown, permitting to pull the rod 30 in the direction of movement of the metal slab 11.

The apparatus operates in the following manner: Initially the apparatus is in the position shown in FIG. 10. Then the mould 1 is filled with steel. The steel is allowed to form on its outer surface a skin which is thick enough to permit the slab 1 1 to be withdrawn. Then the slab 11 is pulled off while the mould 1 is supplied with a sufficient amount of liquid steel. The pressure in the compartments 2a to 2g and the compartments 4a and 4 l is adjusted to a value corresponding to that of the hydrostatic pressure of the head of the slab 11. Thus, in the position shown in FIG. 11, the hydrostatic pressure of the head of the slab 11 in the compartment 2a is about 1.2 bars and the pressure in the compartments 2a to 2g is adjusted to this same value of 1.2 bars. In the position shown in FIG. 12, the head of the slab 11 has reached the compartment 4a and pressure in the compartments 2a to 2g increases by successive increments so as to counterbalance the hydrostatic pressure of the slab 11, the values of this pressure being, for example, 1.2 bars, 1.4 bars, 1.6 bars, 1.8 bars, etc. Thus, the weight of the cast steel slab 11 in each compartment is compensated by the pressure of the fluid and the only force that need be applied is the force required to guide the slab 11 from one compartment to another. When the head of the slab ll arrives at the point of its path where the horizontal portion thereof meets the inclined portion,,the rigid rod 30 is moved which hitherto has remained stationary and a difference in pressure is produced between the compartment 4b and the compartment 4a, which difference is sufficient to lift the rigid rod 30 and thus the cast steel slab 11 and is produced by feeding into the compartment 4b a fluid under pressure, for example, air or steam supplied respectively by a compressor or an auxiliary boiler, not shown. When the head of the cast steel slab ll arrives in the vicinity of the outlet seal 6, water is introduced through the injection nozzles (FIG. 1) and the apparatus is operated in the usual manner.

The embodiment of the apparatus shown in FIG. 13 has no curved portion. Instead of the mould 1 of the conventional type this apparatus has a mould composed of a refractory ceramic portion 32 having no particular cooling means, and a portion 33 provided with cooling means. As a variation this embodiment of the apparatus may also comprise a pressure loss device of the type indicated by 7 and 8 in FIGS. 4 to 6. It may also be provided with a fluid injection device of the type shown in FIGS. 7 to 9 either on both sides of the cast metal slab 11 or only on its lower side.

The process and apparatus of the present invention may also be used either in only the inclined portion or the horizontal portion of the cast metal path with the other portion constructed in the conventional manner.

I claim:

1. A process for cooling and supporting a continuously cast metal strand, particularly a steel slab, in which the metal strand is formed in a cooled mould and extracted from the mould by roller trains, the metal strand being cooled during extraction until it has completely hardened, the improvement comprising subjecting the surface of the metal strand, in the region of solidification of the metal strand, along its path of extraction, to the action of a gaseous medium having about the same pressure as the ferrostatic internal pressure of the metal strand and, at the same time, cooling said metal strand by spraying liquid on its surface, the metal strand leaving the mould being guided first along an inclined and curved path and then along a substantially horizontal path, the surface of the metal strand being subjected to the pressure of the gaseous medium increasing by steps along the inclined path, the value of the pressure in each step being substantially constant and corresponding to the medium value of the ferrostatic internal pressure of the portion of the metal strand traversing said step.

2. A process for cooling and supporting a continuously cast metal strand, particularly a steel slab, in which the metal strand is formed in a cooled mould and extracted from the mould by roller trains, the metal strand being cooled during extraction until it has completely hardened, the improvement comprising subjecting the surface of the metal strand, in the region of solidification of the metal strand, along its path of extraction, to the action of a gaseous medium having about the same pressure as the ferrostatic internal pressure of the metal strand and, at the same time, cooling said metal strand by spraying liquid on the surface thereof and subjecting the lower surface of the metal strand to a higher pressure of the gaseous medium than the upper surface of the metal strand in a horizontal portion of the path thereof.

3. A process as claimed in claim 1 wherein said gaseous medium is steam.

4. A process as claimed in claim 2 wherein said gase ous medium is steam.

5. A process for cooling and supporting a continuously cast metal strand, particularly a steel slab, in which the metal strand is formed in a cooled mould and extracted from the mould by roller trains, the metal strand being cooled during extraction until it has completely hardened, the improvement comprising subjecting the surface of the metal strand, in the region of so lidification of the metal strand, along its path of extraction, to the action of a gaseous medium having about the same pressure as the ferrostatic internal pressure of the metal strand at various positions'along said strand and, at the same time, cooling said metal strand by spraying liquid on the surface thereof, said gaseous medium being steam produced by spraying hot water on the surface of the metal strand, the temperature of the sprayed water being near the vapour saturation temperature corresponding to the desired pressure.

6. A process as claimed in claim wherein the temperature of the sprayed water is between 100 and 180 C.

7. A process for cooling and supporting a continuously cast metal strand, particularly a steel slab, in which the metal strand is formed in a cooled mould and extracted from the mould by roller trains, the metal strand being cooled during extraction until it has completely hardened, the improvement comprising subjecting the surface of the metal strand, in the region of solidification of the metal strand, along its path of extraction, to the action of a gaseous medium having about the same pressure as the ferrostatic internal pressure of the metal strand and, at the same time, cooling said metal strand by spraying liquid on the surface thereof in a direction opposite to the direction of movement of the latter, said steam being condensed to form hot water, and the hot water being used to produce the vapor of the desired pressure.

Claims

3. A process as claimed in claim 1 wherein said gaseous medium is steam.

4. A process as claimed in claim 2 wherein said gaseous medium is steam.

5. A process for cooling and supporting a continuously cast metal strand, particularly a steel slab, in which the metal strand is formed in a cooled mould and extracted from the mould by roller trains, the metal strand being cooled during extraction until it has completely hardened, the improvement comprising subjecting the surface of the metal strand, in the region of solidification of the metal strand, along its path of extraction, to the action of a gaseous medium having about the same pressure as the ferrostatic internal pressure of the metal strand at various positions along said strand and, at the same time, cooling said metal strand by spraying liquid on the surface thereof, said gaseous medium being steam produced by spraying hot water on the surface of the metal strand, the temperature of the sprayed water being near the vapour saturation temperature corresponding to the desired pressure.

6. A process as claimed in claim 5 wherein the temperature of the sprayed water is between 100* and 180* C.

7. A process for cooling and supporting a continuously cast metal strand, particularly a steel slab, in which the metal strand is formed in a cooled mould and extracted from the mould by roller trains, the metal strand being cooled during extraction until it has completely hardened, the improvement comprising subjecting the surface of the metal strand, in the region of solidification of the metal strand, along its path of extraction, to the action of a gaseous medium having about the same pressure as the ferrostatic internal pressure of the metal strand and, at the same time, cooling said metal strand by spraying liquid on the surface thereof and in which the metal strand leaving the mould is guided first along an inclined and curved path and then along a substantially horizontal path, and whereby the surface of the metal strand is subjected to the pressure of the gaseous medium increasing by steps along the inclined path, the value of the pressure in each step being substantially constant and corresponding to the medium value of the ferrostatic internal pressure of the portion of the metal strand traversing said step and wherein the steam is conducted along the metal strand in a direction opposite to the direction of movement of the latter, said steam being condensed to form hot water, and the hot water being used to produce the vapor of the desired pressure.