US3856281A - Device for cooling hot rolled metallic strips - Google Patents

Abstract

Device for cooling hot-rolled metallic strips, by means of water directed against the rapidly moving strip, between the last finishing stand of the mill and the coiler, comprising: MEANS CAPABLE OF DELIVERING A CONTINUOUS WATER FILM, WITH VERY LOW TURBULENCE, LIMITED THICKNESS AND WITH A LENGTH EXCEEDING GREATLY THE SAID THICKNESS. MEANS CAPABLE OF CONTROLLING THE FLOW RATE OF THE SAID WATER FILM WITHIN A CONSIDERABLE RANGE. MEANS CAPABLE OF ORIENTING PROPERLY THE SAID WATER FILM AGAINST THE STRIP.

Description

United States Patent [191 Bertolotti et al.

[ Dec. 24, 1974 DEVICE FOR COOLING HOT ROLLED METALLIC STRIPS Inventors: Nino Bertolotti, Tirrenia; Bruno Sabatini; Giuseppe Mocci, both of Rome, all of Italy Centro Sperimentale Metallurgico S.p.A.

Filed: July 10, 1972 Appl. N0.: 270,292

Assignee:

Foreign Application Priority Data July 17,1971 Italy 51720/71 June 22, 1972 Italy U 51091/72 US. Cl 266/3 R, 134/64, 266/4 S, 266/6 S, 239/590 Int. Cl C21d l/62 Field of Search 266/3 R, 4 S, 6 R, 6 S; 134/64,122,198;l48/143,153,156; 239/590, 590.3, 590.5, 456, 597

References Cited UNITED STATES PATENTS 4/1921 Sundh 134/64 3,208,742 9/1965 Peretick 266/3 R X 3,554,513 l/l97l Chance 266/3 R 3,659,428 5/1972 Kunioka et al. 266/6 s UX FOREIGN PATENTS OR APPLICATIONS 272,433 3 1930 ltaly 266/6 s Primary Examiner-Roy Lake Assistant Examiner-Paul A. Bell Attorney, Agent, or FirmYoung and Thompson [57] ABSTRACT 18 Claims, 11 Drawing Figures Pmmwmw 3.856.281

sum 2 er 5 15 2o 20 20 F/G.4

PATENIEBHEBM H 3,856,281

SHEET 5 BF 5 FIG. I F/GJO DEVICE FOR COOLING HOT ROLLED METALLIC STRIPS The present invention relates to a device for cooling hot-rolled metallic strips, and more particularly to a device for conveying water under pressure onto the strip in the form of a continuous thin film at very low turbulence and at an optionally controllable flow rate, the said device being suitable for advantageous utilization as a component of the runout cooling table between the last finishing stand of the hot strip mill and the coiler.

As is known, in metal strip hot-rolling the apparent strip temperature emerging from the last rolling stand is quite high, (in the case of steel it ranges from 850 to 950C), and before being coiled the strip must be cooled down to a proper temperature according to its thickness and to the metal involved (in the case of steel the temperature after cooling ranges from 550 to 750C). This cooling is realized when the strip passes over the runout table, along which it is subjected to water sprays. The length of this cooling section depends, other conditions being equal, on three fundamental parameters: the strip speed, the cooling efficiency (Kcal/kg of H and the water flow rate, in the sense that for a given strip speed, which in general is a fixed parameter, and for each thickness of the strip to be processed and each thermal difference to be realized, the length of the table increases if the efficiency and/or the flow rate decrease.

The cooling devices known in the art are essentially of the following types:

a. Spray system. This consists of a number of manifolds from which some nozzles branch off to deliver water under pressure, atomized into more or less minute particles. Each one of the said nozzles diverges by a certain angle, which determines a well defined impact area of the sprays on the strip to be cooled. The specific flow rates of the various installations which are invariable for each installation range from 18 to 30 m /h.m with a cooling efficiency of about 20 Kcalories per kg of water used. The extent of the impact area of a single water spray and the required thermal drop, together with the amount of heat to be removed, the specific flow rates and the cooling efficiency, all determine the number of water sprays necessary and hence the length of the cooling section.

In this type of installation, the cooling efficiency is critically linked with the specific flow rate of the nozzles in that, outside of the optimal flow rates pertinent to the type of the nozzles used, the cooling efficiency diminishes very rapidly; it is necessary, therfore, in view of qualitative and quantitative variations of the product, to oversize the installation and then to use it partially when working. In this way the cooling section is very long and the installation is minimally flexible, if a good cooling efficiency has to be maintained.

b. Laminar flow system. Essentially it consists of a certain number of cylindrical tubes, set side by side and perpendicularly over the strip, and from which tubes, uniform cylindrical water streams flow with low turbulence. The specific flow rates that are invariable for every installation which this type of plant can deliver, are high (more than 90 m /h.m with a cooling efficiency, of about Kcal/kg of water. This system too has the drawback of low flexibility, whereby it is necessary to oversize and subsequently to use the installation partially when working.

The aforesaid drawbacks are serious because the frequent need of increasing the productivity of an existing line and of varying the product mix makes it desirable to have a system more efficient and flexible than the existing ones, because very often for economic reasons or owing to lack of space it is not possible to increase the length of the runout cooling table.

It is an object of the present invention to supply a device which eliminates the drawbacks of the cooling systems used hitherto.

Another object of the present invention is to supply a device for cooling hot-rolled metallic strips allowing high specific water flow rates and a good cooling efficiency, thus allowing for a reduced length of the cooling runout tables.

A further object of the present invention is to supply a device for cooling hot-rolled metallic strips capable of supplying water in the form of a film with limited thickness, very low turbulence, and at optionally and continuously controllable flow rates within a wide range, the said device allowing the delivery of even considerably different flow rates while maintaining an acceptable cooling efficiency.

Another object of the present invention is to supply a device for cooling of hot-rolled metallic strips, capable of effecting a cooling of said strip more rapid than what was possible hitherto and such as to establish a finer grain structure in the strip, thus reducing the duration of the subsequent thermal treatments and making the subsequent cold rolling easier.

However, it should be observed that the structural complexity and moreover, the overall dimensions and finally the greater cost of such a device, do not suggest its use whenever the cooling devices have to work for rather long periods, as happens most frequently, under constant operating conditions, that is, for the sheets or strip which do not present noticeable variations of dimensions during the same period.

Therefore, as it is not necessary, in this case, to regulate continuously and with sufficient rapidity the flow rate of the cooling fluid, it is possible and advisable to adopt a second, simpler, sturdier type of cooling device, with smaller overall dimensions, which, while guaranteeing a sufficiently rapid cooling needed to establish a fine grain structure in the strip, by reducing the time of the subsequent thermal treatments and by making the subsequent cold rolling easier nevertheless eliminates the drawbacks already mentioned in the case of the first type of the device.

Therefore, a specific object of the present invention is also a device for cooling hot-rolled metallic strips in mills operating at constant conditions, on a strip with substantially constant dimensions, by means of a water flow over the rapidly moving strip, between the last finishing stand of the hot rolling mill and the first coiler, which comprises: means suitable for delivery of a continuous film of water with low turbulence and limited thickness, the length of which exceeds greatly the said thickness. means suitable for orienting the said water film with respect to the strip.

The delivering means comprise a distributing box, without the regulation blade or septum, and defined in its inside by two longitudinal lateral walls with a profile symmetrical with respect to the median vertical plane of the outflow section, which compel the cooling water to follow a path with a gradually decreasing cross section. The solution suggested for effecting the said decreasing shape of the outflow section, consists in shaping directly the longitudinal lateral walls of the box, while avoiding thickenings or protrusions, by adopting for them a curvature defined by regular arcs of circle so that the plane tangential to the profile surface of the wall, at the edge of the outflow slit, forms an angle ranging from to 10 with the vertical plane of symmetry.

This solution does not preclude, in any event, the possibility of a regulation of the flow rate, in relation to the variations of the rolling schedules, because the device can be integrated with elements suitable to vary the section of the outflow, as it will be described hereinafter.

The present invention will not be described with reference to the drawings, which are herein attached only as an example and not in a limitative way, wherein:

FIG. 1 shows a distributing box;

FIG. 2 shows an inside view of the said distributing box, without the conveying blade or septum;

FIG. 3 shows a cross section of the said distributing box with the conveying septum;

FIG. 4 schematically shows a cooling runout table of a hot rolling mill, in order to indicate various possible arrangements of the said distributing boxes with respect to the vertical plane normal to the strip;

FIG. 5 gives a schematic view from the top, of a portion of the runout cooling table to show a possible angulation of the said distributing boxes;

FIG. 6 shows a section of a distributing box, with several internal septa, the end ones being in closing position;

FIG. 7 gives a schematic view from the top, of a portion of the runout cooling table in the case when the length of each single distributing box is inferior to the width of the strip;

FIG. 8 is an exploded view of a further embodiment of a distributing box, according to the invention;

FIG. 9 is an internal, partially sectioned, perspective view of a still further embodiment of distributing box;

FIG. 10 is a vertical section of a fragment of the box indicated in FIG. 8; and

FIG. 11 is a vertical section view of a second regulation member of the flow section of the box indicated in FIG. 8.

The device according to the present invention, comprises essentially means to deliver a low turbulence water film with controllable thickness and a length exceeding greatly its own thickness. (By length is herein intended the maximum dimension of the water film paralleling the strip). With the aforesaid means are included, cooperate means to control, within a considerable range, the flow rate of the said water film and means to orient properly the said water film with respect to the strip.

The said means, to deliver a water film comprise a distributing box 1, constituting a repetitive module for the whole width of the runout cooling table, supplied with piping for water inlet 2, a septum or blade 3 to control the flow rate of the said water film, with devices 4, known in the art, for the vertical displacement of the said septum or blade in the inside of the said distributing box 1, and with means 5, also already known, for properly orienting the said water film with respect to the strip to be cooled. According to the present invention, the said distributing box 1 is supplied on the wall 6 facing the strip with a longitudinal slit 7 wherein the said septum or blade 3 is inserted. The longitudinal edges 8 of the said slit are prolonged into the lateral walls 9 of the said box, by protrusions 10, having a transverse section departing from the junction of the said protrusions, to the lateral walls of the said box initially with a profile concave towards the inside of the said box, with a curvature increasing as far as the inflection point, located at about one third of the protrusion height from the wall 6 of the box facing the strip and, beyond an inflextion point, the said protrusions are terminated on the longitudinal edges 8 of the said slit 7 with a sharp edge, in such a way that the tangent to the profile of the said protrusion 10, at its intersection with the edge 8 of the said slit, forms an angle ranging from 65 to 88 with the wall 6 facing the strip.

The said protrusions can be inserted into the box and fixed to it, or they can be obtained from the box lateral walls 9 themselves, properly shaped for instance by forming or by other means suitable for this purpose.

The said box is orientable with respect to the strip, in such a way that the water film delivered by it can impinge on the strip at various angles with respect both to the vertical and to the width of the strip itself. The dimensions of the said box are such that its height and length ratio, and its width and the said height ratio, range from 1 to 0.1, these two ratios, however, being not equal in general to each other.

Also according to the present invention, the said protrusions are sized in such a way that their height, as measured along the lateral walls 9 of the said box, ranges from to l 15 percent of the width of the box itself, while their maximum width, as measured along the wall 6 of the said box, facing the strip, at the edge 8 of the longitudinal slit 7, ranges from 25 to 45 percent of the said width of the box. The said longitudinal slit 7 on the wall 6 facing the strip of the said box, has a length equal to that of the said wall 6, and has a width ranging from 10 to 50 percent of the width of the box itself.

In the said longitudinal slit 7 there is inserted a septum or blade 3 which is as long as the said slit and which defines, with the edges 8 of the same, two longitudinal openings 11 from which the cooling water flows as two slightly convergent streams which join at the outlet edge 12 of the said septum 3, producing a water film having the required characteristics (limited thickness and laminar flow). The said septum or blade is symmetrical with respect to its own longitudinal center plane, and presents a cross section departing from the leading or junction edge 13 with the fluid stream initially with a convex profile, with increasing curvature as far as a maximum located from one-third to one-fourth of the height of the same septum from its upper edge l3, which is the said junction edge of the fluid stream, and then with a decreasing curvature to an inflection point beyond which the profile is slightly concave.

The symmetrical profiles of the said septum or blade 3, are such that their upper edges meet at an angle ranging from 50 to and their lower or trailing or outlet edges 12 meet at an angle ranging from 4 to 20.

The said septum or blade, inside the said box, has its own longitudinal symmetry plane coinciding with the longitudinal center plane of the box, and it is movable, along the said longitudinal symmetry plane, in such a way as to vary, with a displacement ranging from to 100 mm, the cross section of the said openings 11 from the maximum to the minimum value at which the said openings are completely closed. In the maximum opening position, the total available cross section for the water outflow which is the sum of the existing spaces located between the said septum and the two longitudinal edges of the said slit ranges from 10 to 50 percent of the area of the said slit.

According to the present invention, the hereinbefore described device is advantageously utilized to convey over the hot strip, a water film of limited thickness with very low turbulence, and with a length to thickness ratio ranging from 10 to 500.

Furthermore, the said box may preferably cover the entire width of the cooling runout table, and in this case it protrudes from both edges of the strip by an extent ranging from 5 to 25 percent of the width of the strip itself. In case the rolling schedule calls for the cooling of strips with very different widths, it is clear that a distributing box, having adequate dimensions for the widest strip would be excessive for the most narrow strip, causing a considerable waste of water. This drawback can be advantageously eliminated by placing the said box in a sharply angulated position with respect to the width of the strip, or by dividing the septum or blade of the box into at least three smaller septa, 3,3',3" (see FIG. 6) in such a way as to close completely the delivery in the end zones of the box, or finally by placing a group of boxes, whose length is shorter than the width of the cooling bed, on the width of the bed itself, covering its entire width, the external boxes of the said group being positioned in such a way as to protrude beyond the edges of the wider strip to be rolled by a value ranging from 5 to 25 percent of the width of the said strip. The said group consists at least of three boxes which can be placed as shown in FIG. 7, wherein 24 indicates the group of such smaller boxes.

According to the present invention, a plurality of said water streams 23 are conveyed onto the moving strip, both from above and from below, as shown in FIG. 4, wherein the runout cooling table of a hot-rolling mill is shown schematically, and wherein the last finishing stand of the rolling mill is indicated by 14, the strip by 15, the rollers of the runout table where the said strip runs by 16, the coiler by 21, the series of boxes placed below the strip by 20, and the boxes placed above the strip by l7, l8 and 19. According to the present invention, the distributing boxes can be oriented properly, with respect to the strip, in such a way that the water films delivered by the boxes can impinge on the strip at various angles, both with respect to the vertical, (as shown in FIG. 4, details 18 and 19), and with respect to the width of the strip itself, (as shown in H0. 5, detail 22). The said water films 23, are delivered by the said distributing boxes at widely varying pressures, the most convenient minimum pressure ranging from 0.01 to 1 atmosphere gauge, and the maximum pressure ranging advantageously from 1 to 10 atmospheres gauge.

Some practical tests on the first type of the device, according to the present invention, have been performed on a steel strip 600 mm wide and 1.2 mm thick. The cooling bed consisted of 10 boxes, as described in the text of the present specification. From a statistical average of the results of these practical tests the following data have been obtained:

Specific flow rates m lhm 50 1 l0 18 230 Cooling efficiency Kcal/Kg H 0 14 16.2 l5 12 According to the aforementioned test results, the

cooling efficiency undergoes a decrement lower than 30 percent of the value of the optimal efficiency, for specific flow rates variations ranging from less than percent to more than 1 10 percent, with respect to the value of the specific flow rate corresponding to the said optimal cooling efficiency.

With particular reference to FIG. 8 of the attached drawings, there can be observed the distributing box 25, with length l, heigth h, and width b, which constitutes a repetitive module for the whole width of the cooling bed, wherein the water is introduced by piping 26, derived from the feeding manifold. The box 25 is provided, in this embodiment, in its lower portion, with a longitudinal slit 27, with a width a, defining the outflow cross section. The longitudinal edges 28 of the said slit 27 are prolonged into the lateral walls 29 of the box '26, by two stretches of wall 30 with a height 11,, which present a regular profile of two arcs of circle, symmetrical with respect to the vertical center plane of the slit 27. The said stretches of wall 30 end in the longitudinal edges of the outlet of slit 27, filleting in such a way that the tangent to the said shaped stretches of wall, at the intersection point with the said edges, forms with the horizontal base plane of the slit, an angle ranging from 80 to (O-l0 angle, with the vertical plane). The said stretches of wall 30, shaped as an arc of circle, can be manufactured in a simpler manner, for example by rolling, than the protrusions of the device before described.

The distributing box 25 is orientable with respect to the strip so that the angle of the water film with respect to it can be varied.

The dimensions of the box, very much reduced in comparison of that before described are such as to be able to define the following ratios:

h (height)/I (length) 0.05 l

b (width)/h (height) 0.1 l

h, (height of the shaped stretch wall)/b (width) 0.5 2

b (width)/a (outflow cross section) which the box has been built. The cooling water is compelled to penetrate into the downflow zone (defined by two septa or walls 33, tilted downwards, with height h of width 2a,, comprising an upper inlet zone ending downwardly in an outflow slit 34 with a width a. A blade 35, with a height h fixed to the upper wall of pipe 32, penetrates into the outflow zone for a certain distance (kg/2), creating a partition wall for the distribution of the flow of the liquid.

The dimensions of the box, are defined by the following ratios:

b/l=0.05 1; h /b 0.1 0.95

bla= 5 50; h /b= 0.8; 2a /a= l 15 In FIGS. 10 and 11 are shown, in the two preferred embodiments, the members for the variation of the area of the cross section of outflow from the longitudinal slit.

Means are shown which permit the rotation (FIG. 10) of the shaped wall 36 of the distributing box, or its translation (FIG. 11) perpendicularly to the symmetry plane of the shaped walls.

In FIG. 10, the profile 36 ends, on the upper part, in a curved portion 37 which is accomodated between two tightening surfaces, driven by the tightening pin 38 controlled by the tightening nuts 39, whereby it can be given different adjusted positions.

In FIG. 11, the profile 36 ends, on the upper part, in a stretch 40 at an angle which can adopt, horizontally, different positions under the control of the tightening group 41.

As an example and not as a limitation, the results of some experimental tests performed on a 500 X 20 mm steel strip are reported. The cooling unit consisted of boxes. A cooling of the strip surface from 950C to 550C has been obtained in the average time of 5-7 seconds, with an efficiency (degree of water utilization) of about 16 Kcal/kg of water. Summarizing, for the specific flow rates hereinbefore mentioned, the data reported in the following table have been obtained:

Specific flow rates [20 I50 240 300 (m lm Exchang e intensity 3200 3000 3400 2900 (Kcal/m h C) Coolinlg efficiency l7 l5 I4 12 (Kcal/ .H O)

The present invention has been described and illustrated with reference to various embodiments thereof, but it is intended that variations or modifications may be introduced therein, without departing from the scope of the appended claims.

Having thus described the present invention, what is claimed is:

1. A device for cooling hot rolled metallic strip by means of water directed against a strip moving rapidly between the last finishing stand of a strip mill and a coiler, comprising a cooling water distributing box having inner side walls that converge downwardly and terminate downwardly in a slit that extends generally transverse to the path of movement of the strip, said side walls having upper concave portions and lower convex portions adjacent said slit.

2. A device as claimed in claim 1, said concave portions being substantially taller than said convex portions. I

3.'A device as claimed in claim 1, said inner side walls forming an angle of 65 to 88 to the horizontal at said slit.

4. A device as claimed in claim 1, and means to adjust the position of said box vertically relative to a said path of movement of the strip.

5. A device as claimed in claim 1, and means to adjust the position of said box so that said slit forms an adjustable angle with said path of movement of the strip.

6. A device as claimed in claim 1, and means for controlling the flow rate of water through said slit, said means comprising a blade disposed in the distributing box and extending downwardly into said slit, and means for vertically adjusting the position of the blade relative to said side walls.

7. A device as claimed in claim 6, said blade having downwardly converging outer side walls.

8. A device as claimed in claim 7, said blade having a cross-sectional configuration which is symmetrical with respect to its vertical midplane.

9. A device as claimed in claim 8, said blade having a cross-sectional configuration which is substantially of tear-drop shape.

10. A device as claimed in claim 9, said tear-drop shape having a convex curvature that increases downwardly for a minor portion of the height of the blade and then decreases to an inflection point below which said outer side walls of said blade are concave.

11. A device as claimed in claim 6, said blade having upper edges disposed at an angle of 60 to 100 to each other and lower edges disposed at an angle of 4 to 20 to each other.

12. A device as claimed in claim 6, said blade occupying 50 to 90% of the width of said slit.

13. A device as claimed in claim 6, said blade being divided into at least three pieces disposed side-by-side and individually vertically movable independently of each other.

14. A device as claimed in claim 1, the upper portion of said box having a circular cross-sectional configuration.

15. A device as claimed in claim 1, and means mounting said inner side walls for adjustive movement toward and away from each other.

16. A device as claimed in claim 1, and means for adjusting the angle of said inner side walls relative to each other.

17. A device as claimed in claim 1, said box being elongated and having a generally rectangular configuration and said other side walls being defined by protrusions disposed in said box, said protrusions having substantially uniform cross-sectional configuration lengthwise of said box, said slit extending lengthwise of said box.

18. A device as claimed in claim 1, in which the water directed against the strip forms a continuous bandshaped flow having a width substantially corresponding to the width of said strip.

Claims (18)

1. A device for cooling hot rolled metallic strip by means of water directed against a strip moving rapidly between the last finishing stand of a strip mill and a coiler, comprising a cooling water distributing box having inner side walls that converge downwardly and terminate downwardly in a slit that extends generally transverse to the path of movement of the strip, said side walls having upper concave portions and lower convex portions adjacent said slit.

2. A device as claimed in claim 1, said concave portions being substantially taller than said convex portions.

3. A device as claimed in claim 1, said inner side walls forming an angle of 65* to 88* to the horizontal at said slit.

4. A device as claimed in claim 1, and means to adjust the position of said box vertically relative to a said path of movement of the strip.

5. A device as claimed in claim 1, and means to adjust the position of said box so that said slit forms an adjustable angle with said path of movement of the strip.

6. A device as claimed in claim 1, and means for controlling the flow rate of water through said slit, said means comprising a blade disposed in the distributing box and extending downwardly into said slit, and means for vertically adjusting the position of the blade relative to said side walls.

7. A device as claimed in claim 6, said blade having downwardly converging outer side walls.

8. A device as claimed in claim 7, said blade having a cross-sectional configuration which is symmetrical with respect to its vertical midplane.

9. A device as claimed in claim 8, said blade having a cross-sectional configuration which is substantially of tear-drop shape.

10. A device as claimed in claim 9, said tear-drop shape having a convex curvature that increases downwardly for a minor portion of the height of the blade and then decreases to an inflection point below which said outer side walls of said blade are concave.

11. A device as claimed in claim 6, said blade having upper edges disposed at an angle of 60* to 100* to each other and lower edges disposed at an angle of 4* to 20* to each other.

12. A device as claimed in claim 6, said blade occupying 50 to 90% of the width of said slit.

13. A device as claimed in claim 6, said blade being divided into at least three pieces disposed side-by-side and individually vertically movable independently of each other.

14. A device as claimed in claim 1, the upper portion of said box having a circular cross-sectional configuration.

15. A device as claimed in claim 1, and means mounting said inner side walls for adjustive movement toward and away from each other.

16. A device as claimed in claim 1, and means for adjusting the angle of said inner side walls relative to each other.

17. A device as claimed in claim 1, said box being elongated and having a generally rectangular configuration and said other side wAlls being defined by protrusions disposed in said box, said protrusions having substantially uniform cross-sectional configuration lengthwise of said box, said slit extending lengthwise of said box.

18. A device as claimed in claim 1, in which the water directed against the strip forms a continuous band-shaped flow having a width substantially corresponding to the width of said strip.

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