DE2301783A1 - METHOD AND DEVICE FOR COOLING A METAL STRAND - Google Patents

Description

DK-tl? 0. E.

PATSNTAi -Ψ, Μλ

7 STUTTGART-! MSCHEiSTRASiS 19 TELEPHONE 242761/2

A 11 459

i - dm

2nd January 1973

INSTITUT DB BEOHEHCHES DE LA SIDERURGIE 185 “rue President Roosevelt, Saint öermain-en-Iiaye

(Yvelinea), France

Method and device for cooling a metal

strands

The invention relates to a method and an apparatus for the immediate cooling of a continuous casting process from a vertically arranged mold flowing from a strand of a high melting point

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send metal *

The one taking place in a continuously operating casting device A cast strand is generally cooled in two successive treatment stages> Xn one The first treatment stage is the continuous flow process in a mold that is open at its lower end, the inner walls of which are maintained by a circulating flow a coolant can be cooled. During this treatment, the heat is dissipated from the cast strand Thermal conduction due to direct contact of the (soot strand with the inner wall of the mold. The further the cast strand moves downwards in the mold and solidifies in the process, the surface of the cast strand moves away to » taking from the inner wall of the mold, so that the heat exchange between the cast strand and the inner wall of the mold is getting smaller «.

In order to increase the output of a continuously operating casting device, efforts are made to use the solidifying To cool the cast strand at the exit of the mold as sustainably and quickly as possible in order to increase the speed of the cast bar flowing through the mold.

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The cast strand is then generally a second Subject to cooling, in which the coolant, for example water «acts directly on the surface of the cast strand ·

It has already been proposed to effect this second cooling by acting on the Gußatrang from different sides a jet of water is directed. Since the surface of the cast = strange has a relatively high temperature, a vapor layer forms on this surface, which largely prevents heat transfer, completely prevents heat conduction and thus counteracts cooling by the water. In addition, it is difficult with this method to ensure uniform cooling over the entire surface of the GuB strand.

In FR-PS 1 280 293 a method is described in which a water layer in a cavity having a, at both ends of the open envelope of the greeting strand to be cooled flows downwards, with this on the inner wall Enclosure Over its entire length in the direction of the flowing water facing openings are provided to this Make out the space between the core and the wrapping

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To feed water »In this process, the water flows within the layer adjoining the surface of the cast strand at great speed, so that the heat transfer assumes a relatively high value. The flow velocity of the water within this layer is so large that the steam that forms on the surface of the cast strand is washed away and thus none of the Form the surface of the cast strand adhering vapor layer can. Nevertheless, even with this process, it is difficult to achieve a uniform and homogeneous process under atmospheric pressure to maintain a downward closing layer of water and to prevent the water layer from adhering detached individual points from the surface of the cast strand.

The invention is therefore based on the object in the above to avoid the disadvantages listed and in particular to develop a method in which the immediate Contact between the flowing water layer and the high temperature surface of the cast strand Is maintained to in this way an effective, uniform and rapid cooling of a cast strand at a To achieve casting method of the type mentioned.

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This is achieved in a method of the type mentioned according to the invention in that the cooling liquid continuously introduced into the lower region of the space surrounding the cast strand and flowing out at the upper end of this space flows upwards at such a speed that the strand surface has a temperature which does not cause the strand surface to dry out due to the boiling of the liquid _o

According to the invention, a device is used to carry out this method, in which the coolant flowing through the tree surrounding the cast strand has a constant cross-section over its entire length and with the lower At the end of the jacket delimiting the space through which a coaxially formed inflow head is connected, the one Annular channel with a supply line and a ring coaxial with the strand. Bores directed upwards at an angle has, which connect the annular channel with a coaxial recess, the inner diameter of which at the transition to the The jacket delimiting the space through which it flows is equal to the inner diameter of the coat is. The inclination of these holes is so dimensioned that the one flowing into the aforementioned recess Coolant forms an angle of at least 135 ° with the vertical.

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A centering element is advantageously provided with the inflow head connected, the one arranged at a distance from the strand to be cooled, provided with a movable supply line Has an annular channel which is provided with a ring of bores directed perpendicularly to the strand *

The device therefore advantageously has on upper end of the tree through which the cooling liquid flows an organ causing a pressure loss in the form of a ring with an outflow opening coaxially with the jacket for the coolant, its inner diameter is larger than the diameter of the strand and smaller than the inner diameter of the sheath «,

According to the method, the cooling of the erfindungagensäSen Gußstr & Ntot in direct contact takes place with a ringa with great speed ina the Guöstrang in a homogeneous layer upward ·, coolant flowing _a irrt'ße The speed kanr .. basis of known heat theoretical considerations are calculated. The minimum

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The value of this speed depends on the given casting conditions on the temperature of the cooling liquid fed into the device and the geometric dimensions the device, in particular the length of the jacket surrounding the cast strand and the degree of solidification of the Cast strand entering the cooling device,

The formation of the recesses provided in the inflow head and the resulting flow conditions favor the maintenance of a homogeneous upward flow flowing layer avoiding any local discontinuities in contact of the cooling liquid with the Surface of the cast strand.

In addition, the method according to the invention has the advantage that the phenomena which have an adverse effect on the degree and uniformity of the cooling are caused by an untimely formation of zones of local heating, caused by temporary changes in the casting conditions or any other changes, can be quickly eliminated or suppressed.

In the drawing is an embodiment of the invention

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according to the device shown in schexnatic "iron, based on which the advantages of the method according to the invention i ». should be explained below.

You drawing shows a vertical section through the Cooling device that carries out the second stage of cooling of a lic continuous casting process η produced Knüppels serves.

The device has an open at both ends, extending over a certain length of the GuQetranga, hollow cylindrical jacket 1, which is arranged coaxially to a cast strand 2 having a circular cross-section that between the cast strand 2 and the dumbbell 1 a ring-shaped Cross-section having intermediate 3 remains * The cast strand 2 is produced in a manner known per se and therefore not shown in the drawing. The vertical distance between the upper end of the dumbbell 1 and the mold can be determined according to the respective requirements. The hollow cylindrical dumbbell 1 can be arranged, for example, below the StUts rollers usually provided under the mold . The dumbbell 1 * we * Jecoo aa # e ~ be classified is allceseUen On an "oil · * * Ua in which the Gußetrang another schseleflüeei-

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has the core, ie that the jacket is arranged in the so-called second cooling zone. The cast strand can rotate around its axis as it moves downwards. At the lower end of the jacket 1 is connected to this a feed head 4, which has a coaxial Äuaeparung? ouch which has the same inner diameter at its upper end as the jacket 1. The head 4 has an annular channel 6 below the recess 5, which is connected via a flexible line 7 to a pressure fluid source and distributed evenly over the circumference and inclined upwards facing holes 8 is connected to the recess 5. The angle of these holes with the vertical is 165 °. The recess 5 has the 3-shape of a truncated cone, in the base of which the bores 8 open and the dumbbell-generating part of which runs essentially parallel to the axis of the bores 8. The upper clear cross section 9 of the recess 5 corresponds to the clear width of the hollow cylindrical jacket 1. At the upper free end of the jacket a ring 10 is inserted into this, which narrows the clear cross section of the jacket in such a way that a pressure jump is formed at this point. The jacket 1 is at its upper end of a frame, not shown, concentric to the cast strand ? held.

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The cardanic © provided at the upper end of the jacket 1 Bracket enables the device to be pivoted about its normal vertical position Swing horizontally arranged pins 17, which in turn are connected to an outer rim 16, which in turn designed to swing with respect to the frame and connected to this frame via two pins, not shown is, whose aligned horizontal axis is offset from the axis of the pin 17 by 90 ° = the inflow head 4 is also connected to a self-centering device, which is connected to the inflow head 4 Hing duct 11 connected via a pipe flange 12 is formed whose inner diameter is slightly larger than the outer diameter of the cast strand. The ring channel 11 is over a flexible conduit 13 with a source of pressurized fluid connected and has in its center plane arranged perpendicular to the axis of the annular channel, on the surface of the Cast strand directed bores 14, so that in this way the inflow head 4 is always in a coaxial to the cast strand Location is held. The annular channel 11 can also be acted upon with compressed air instead of a pressure fluid.

The mode of operation of this device according to the invention is

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the following

The hydraulic fluid, for example water, is via the Line 7 introduced into the hanging channel 6 of the inflow head 4, it reaches the recess via the inclined bores θ 5, the hydraulic fluid dividing into two streams, from one of which is directed essentially vertically upwards, so that the cooling liquid flows into the annular space 3, the constant change in direction of this Stroaes has a minor loss of pressure aur as a result, and ron which the other is directed downwards, this abrupt change of direction imposed on the coolant causing a large pressure loss.

The distribution of the seed flow through the holes θ of the inflow head 4 into the two aforementioned substreams depends on the value of the kinetic energy imposed on the hydraulic fluid for a given arrangement of the bores from, which in turn punctures the Gesaatdurohflusses and the dimensions of the holes 1st. Of course, these are · parameters depending on the length of the jacket «1 of the · type established, since £ the upward «flowing ·, the cooling & ·· il «aft» & · fts * »siM« «t« A * 41 · Bftk · f ·· et * »*»

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Reached the end of dumbbell 1 and flows out into the open. Of the The minimum value of the total liquid fed into the hanging channel that satisfies the aforementioned condition can be calculated and, if necessary, experimentally in individual pails yet to be corrected, although this condition is considered essential for the performance of the improper Procedure requires mentioning, this minimum value does not necessarily represent a critical one Value because the real minimum value of the flow rate due to the conditions of heat exchange between the Coolant and the cast strand is determined, as explained in the following »

For a billet manufactured using the continuous casting process, the effect of the cooling in the second stage can be estimated by determining the depth of the still liquid metal core inside the billet _a

It is known that the length of this core can be reduced considerably and can accelerate the cooling by increasing the flow rate of the cooling liquid. The heat exchange coefficient between the coolant and the

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The cast strand to be cooled assumes higher values with increasing flow velocity. The value of the minimum speed is calculated for a specific cast strand so that the surface temperature of the cast strand during of the cooling process is continuously maintained at a value that allows the cooling liquid to undergo such conditions causing the strand surface to dry out in places. (The basics of this calculation can be found in the book by W.H. McAdams "Heat Transmission" McGrawhil Publishing Company Ltd., New York.) From this so The calculated minimum value of the speed is derived from the corresponding minimum flow rate, whereby the geometric Dimensions of the device into account.

In order to meet the heat exchange conditions described above, it is necessary that the flow the cooling liquid remains homogeneous at least in the layer adjacent to the strand surface, i.e. the strand surface during the passage of the strand through the cooling device last in contact with the upward moving The liquid layer remains, which is to be understood by the expression "homogeneous flow". A detachment of the Cooling liquid from the surface of the strand to be cooled

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would result in a disruption of the cooling processes local heating causes disruption of the cooling process still enlarged. The upward flow of the cooling liquid within the jacket surrounding the strand ensures the permanent maintenance of contact between the coolant and the inside of the Cooling device located surface of the strand. The force of gravity acting on the cooling liquid in a direction opposite to the stoning is very beneficial maintaining this direct contact since the static pressure at every point of the jacket umechlos » This annulus permanently has a higher value than the atmospheric pressure arranged segment 10 caused pressure jump favors the formation of a homogeneous flow in particular in the upper area of the annulus, as this segment is the training favors a laminar flow. The use of such a pressure crack at the top The end of the ring roughness is an advantageous feature of the device according to the invention, however, aie is not an indispensable requirement for the implementation of the device according to the invention Procedure.

The downwardly deflected partial flow of the cooling liquid provides

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only a relatively small part of the total fed into the ring channel 6, the conditions of a sufficient Sufficient cooling. This partial flow points to the flow quantities in question as a result of the abrupt change of direction imposed on him and due to the static pressure acting on the flow in the same direction as the flow direction reducing gravity completely hetarcgenic flow properties on. The corresponding liquid flows relatively quickly into the free atmosphere and Xeietet practically no contribution to the cooling of the cast strand. This flow has an additional beneficial effect, when it counteracts the suction of air into the recess 5.

Should be at one point on the surface of the cast strand to be cooled heating due to a temporary change in one of the parameters determining the heat exchange occur, the steam that forms will occur as a result of the interaction the cooling liquid flowing at high speed and the different density caused buoyancy is torn upwards, where it escapes into the atmosphere

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Do not destroy the homogeneity of the upward flow of the cooling liquid, - The same is the case if air accidentally penetrates through the recess 5 into the ring gray through which the cooling liquid flows. The choice of the layer thickness of the upwardly flowing cooling liquid in the radial direction takes two aspects into account. Too little play between the surface of the cast strand and the casing bypassing the cast strand can be disadvantageous insofar as small particles that detach from the candy strand are jammed between the surface of the greetings strand and the casing. Small lateral displacements deo Gyßstranges other hand, can the throughput = flow of the cooling liquid ört! IAH complicate ₀ Me total amount of air flowing through the annular space cooling liquid, however, must be able to be kept for obvious reasons at an acceptable value * Depending on the type of G-ußstranges selects a value between 3 and 10 mmλ is used for the thickness of the cooling liquid layer

The centering element formed by the annular channel 11 and arranged below the inflow head 4 ensures any contact between the inflow head and the surface of the carbon black if it is displaced in relation to the MarrteX 1 _P during

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the position of the cast strand as it enters the cooling device is exactly defined by the support rollers, which are usually arranged below the mold, by the interaction the entirety of the individual jets of liquid emerging from the bores 14 of the annular channel 11 is in the In the event of a lateral displacement of the cast strand, the annular channel 11 is also displaced to a corresponding extent, so that the annular channel 11 is coaxial with respect to the cast strand Maintains location, Since the inflow head 4 with the annular channel 11 is rigidly connected, is a permanent automatic centering of the entire cooling device in relation to the cast strand,

Experiments turned out to be surprising to such an extent effective cooling achieved that it appeared appropriate in certain cases, the effects achieved, for example to be reduced by an appropriate choice of the length of the jacket and the position of the jacket with respect to the mold, whereby the position of the jacket determines the diameter of the still liquid core of the cast strandB at the beginning of the cooling process given cast strand and a given casting speed to avoid too rapid cooling, which is a disadvantageous Structure of the (usszeugniases. A such a controllable result could be achieved with

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the previously known process of cooling a billet made of high-melting metal, such as steel, produced in the continuous casting process is not expected »

In the following, the mode of action of a device according to the invention is described Device described for cooling a billet of ! 2O min diameter is used, that in the vertical continuous casting process was produced. The jacket of the cooling device had a length of 1.40 m and an inner diameter of 130 mm and was connected to an inflow head, the total Had 108 holes with a diameter of 2.8 mm, which had an angle of inclination of 170 ° to the vertical. The top of the jacket was 2.7 m below the lower end of the mold; the mean diameter of the still liquid core was at the upper end of the Sheath 70 mm, the billet being subjected to cooling by means of water jets at the exit of the mold in a known manner was «The minimum amount of the total in the tributary head injected cooling liquid, which was necessary to create a flow within the mantle with the speed of sight Zero to produce, in other words, the minimum amount of total coolant that was necessary to produce a to cause an ascending current within the mantle,

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was 14- m / η. The Gießtemepratur was maintained at a value of 154O ° ± 5 ⁰ O C, the metal was steel with a content of 0.18? GC and the casting speed was 2.3 m / min. With these values, the calculated value of the heat dissipating via the cooling liquid, taking into account a surface temperature of the cast strand of 10O ⁰ O at the level of the upper end of the jacket, i.e. at the beginning of the cooling process, was 630 W / cm and the calculated value on the Height of the bores of the inflow head 200 W / cm, the heat dissipation between these two levels decreased very quickly, to a value of 310 W / cm at a height of 20 cm below the upper end of the jacket, whereupon this value was essentially steady to on the aforementioned value

200 W / cm decreased »

These values allow using the approximate calculation a calculation of the speed that the cooling liquid flowing upwards must have, including fulfilling the condition au, that during the cooling process at no point a drying out caused by the boiling of the cooling liquid Strand surface occurs, this calculation shows the relationship takes into account the "between the coefficient for the heat exchange between the Kühlflüsaigkeit and the cast strand on the one hand and the speed of the coolant »

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on the other hand, there is a flow of power. In this way it has been determined by calculation that the aforementioned condition was fulfilled in the area of the upper end of the Hanteis, v / o this condition is the most critical? namely at a speed of 3.5 m / aec, which corresponds to an amount of liquid flowing upwards between the cast strand and the jacket of 25 m / h. The calculated value of the total amount of fed into the Zuflußkopf liquid, which called this ¹ pre ~ corresponding value was 32 m / h at the geometric dimensions of the apparatus used "This amount of liquid of 32 m / h was introduced into the Zufluflkopf.

When the cast strand is cooled, it is centered on the surface The water jets of the ixußstranges, directed essentially over its entire length, reached the depth of the still liquid Metal core up to 8 m. When using the device described above with a total amount of liquid from 32 m / h it was found that this depth extended to about 4 m, which means that the oussstrang when leaving the cooling device according to the invention completely solidified was. Although complete solidification is not necessarily a goal to be striven for in every pail, it shows This result clearly shows the extraordinary effectiveness this procedure.

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The method according to the invention can be carried out consequently, the take-off speed in the continuous casting process through the use of the erfindungsgeaäflen, the cooling in the second stage serving device due to the To increase the fact that the depth to which the liquid core of the cast strand extends with the aforementioned Withdrawal speed related. The output of a The system for carrying out the continuous casting process can thus be significantly increased while at the same time ensuring uniform cooling on the entire surface of the cast strand,

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Claims (1)

2nd January 1973 Patent claims 1, method of cooling a in the continuous casting process A metal strand drawn off a vertically arranged mold by means of a directly surrounding the strand, flowing parallel to the strand axis at high speed in a limited space surrounding the strand Cooling liquid, characterized in that the continuously introduced into the lower region of the limited space (3), and at the upper end of this tree outflowing cooling liquid with such a minimum speed upwards flows so that the strand surface has a temperature which does not cause the strand surface to dry out due to the boiling of the liquid » 2 »apparatus for carrying out the method according to claim dea ■ 1, characterized geke η η α β η 1 a h et that the flowed through by dor KühlflüaeigkeLt, the strand - 23 309830/0474 - there 2.1.1973 (2) surrounding tree (3) has a constant cross-section along its entire length and bit the lower end of the jacket (1) bounding the tree (3) through which it flows a coaxially designed inflow head (4) is connected, the hanging channel (6) with a feed device (7) and a bit of the strand (2) coaxial wreath of oblique has upwardly directed bores (8) which connect the annular channel (6) with a coaxial recess (5) » the inner diameter of which at the transition to the jacket (1) delimiting the space (3) through which it flows is equal to the inner diameter of the jacket (1), 3 · Door direction according to claim 2, characterized in that a centering member in the form of a the strand-directed bores (14) and a movable supply line (13) provided * at a distance from the xu cooling strand (2) arranged annular channel (11) ait the inflow head (4) is rigidly connected. 4 · Door direction according to claims 2 and 3, thereby characterized in that at the upper end of the space (3) through which the cooling liquid flows a single 309830/0474 - 24 - »Dia 2.1.1975 new pressure jump causing organ (10) in the form of a
with the dumbbell (1) coaxially arranged rings is provided, the inner diameter of which is greater than the diameter of the strand (2) and smaller than the inner diameter of the jacket (1). 5. The method according to claim 1 using a device device according to claims 2 and 3 »thereby marked ^ that the ring channel (11)
is acted upon with a hydraulic fluid. ο Method according to claim 1 using a device according to claims 2 and 3 »thereby
characterized in that the ring channel (11)
is acted upon with a pressurized gas. 7 »Device according to claim 2, characterized in that the jacket (T) on his
upper end is gimbaled » 309830/0474