US3138200A - Cooling of moving metal strip - Google Patents

Description

June 23, 1964 Filed May 4, 1961 c. CONE COOLING OF MOVING METAL STRIP 2 Sheets-Sheet 1 D NVENTOR: T AHHULL ENE 15 fig; .2. m yi.

June 23, 1964 Filed May 4, 1961 C. CONE COOLING OF MOVING METAL STRIP 2 Sheets-Sheet 2 2/ 22 H g F16! FEA- . INVENTOR: E5RL7LL 501m.

United States Patent 3,138,200 COGLING OF MOVING METAL STRIP Carroll Cone, Toledo, Ohio, assignor to Midland-Ross Corporation, Toledo, Ohio, a corporation of Ohio Filed May 4, 1961, Ser. No. 107,783 3 Qlajms. (Cl. 165-420) tinplate has been characterized in recent years by a definite trend from batch type metallurgical heat treating processes to continuous processes especially in regard to annealing processes. In a continuous heat treating process, such as a process for annealing, a continuous strip of metal is passed in a plurality of passes or strands, usually vertical, through successive heating and cooling units to achieve heat treatment according to a predetermined time vs. temperature relationship.

The general trend to continuous annealing processes, with special reference to the production of tinplate, is discussed in a Symposium on Continuous Annealing of Steel Strip which was published in the February 1957 issue of Iron and Steel Engineer. As is pointed out in this article, the heating step in a continuous annealing cycle has posed few problems to prior artisans as compared to problems encountered in cooling the strip from annealing temperature at a desired cooling rate to a satisfactory handling temperature. The problem of cooling moving strip from a relatively high annealing temperature, say 1350 F., to a relatively low handling temperature, say 150 F., is inherently difficult because of the change in heat transfer rates of the common cooling techniques, radiation and forced convection, with respect to each other as the strip is progressively cooled. Thus, the rate of cooling by radiation is quite high when the strip is hot but decreases extremely rapidly as the strip is cooled. (It is noted here that the radiation heat transfer coefficient is a function of the ditference of the fourth powers of the absolute temperatures of the strip and the radiation heat sink whereas the rate of convection heat transfer is a function of the difference of the first powers of the temperatures of the strip and the convection heat sink.) Because of the change in the ratio of radiation heat transfer to forced convection heat transfer as the strip is cooled it is now the accepted practice in the art to cool the strip in a plurality of cooling stages, each stage utilizing the heat transfer process most suited for strip cooling over the strip temperatures encountered within the stage.

In cooling strip from one high temperature to another high temperature, say from an annealing temperature of about 1350" F. to about 800" F.-l100 F., the strip may be cooled very readily by direct thermal radiation to air cooled tubes within the cooling chamber, the radiation heat transfer coefficients at such temperatures being ample to provide the cooling rates desired commercially. Accordingly, it has been proposed to cool strip over such a temperature range by means of simple thermal radiation with no provision for forced convection cooling. Suitable apparatus for accomplishing this cooling step is illustrated in FIGS. 4-7 of co-pending application of E. A. Cook et a1. Serial Number 783,446, now United States Patent 3,033,539.

When cooling strip from a low temperature of say 200 3,138,200 Patented June 23, 1964 F. to 500 F. to a final temperature of F. to 200 F. the benefits of radiation heat transfer are negligible and therefore it is suggested that this cooling step be done entirely by means of forced convection heat transfer.

When cooling the strip over the intermediate temper a ture range of from 800 F.-ll00 F. to 200 F.500 F., it is advantageous to use both radiation and forced convection cooling since the rate of these heat transfer expediencies are substantial at the strip temperatures involved. Certain embodiments of apparatus for accomplishing the cooling of strip at such temperatures by means of both radiation and forced convection heat transfer are well known in the prior art.

In the art prior to this invention it was known to cool strip in a strip cooling chamber in which the strip was cooled by radiation to water cooled Walls erected between the vertical strands of strip, each wall serving, in effect, as a radiation heat sink. This radiation cooling effect was supplemented by forced convection cooling which was obtained by circulating protective atmosphere through the chamber. The circulating atmosphere itself was cooled by circulating it past the same water cooled walls which were erected between the strip. Thus, the water cooled walls served to cool the strip directly by receiving radiation from the strip and indirectly by convectively cooling the circulated atmosphere as it passed thereby.

The basic concept of cooling strip by radiation to water cooled elements between strip passes in combination with the circulation of atmosphere past the same walls has proven advantageous. However, there are certain inherent disadvantages which arise in connection with the structure utilized by prior artisans to accomplish this cooling step. One of the disadvantages of the prior art cooling chambers is found in the use of recirculating fans mounted externally to the chamber. One of the features of this construction is that the region of lowest pressure in the recirculating system, i.e., the region immediately upstream of the recirculating fan, is located externally to the cooling chamber. The pressure at this point will normally be subatmospheric which makes it possible for air to infiltrate and contaminate the special protective atmosphere being recirculated.

Another disadvantage of the prior art cooling chambers lies in the fact that no strip is passed through the a strand of strip can be passed through the return duct.

would permit each cooling element to receive radiation from two (2) strip passes and would therefore permit a very substantial reduction in the number of cooling elements required for a given installation.

It is, therefore, an object of this invention to provide improved apparatus to cool a continuously moving heated metal strip by means of radiation and forced convection heat transfer. It is a further object to provide a chamber for cooling a plurality of vertical passes of a metal strip, such chamber being equipped with not more than one vertical water cooled cooling element between two adjacent passes of strip. It is also an object of this invention to provide, in combination with such a chamber, improved means to recirculate atmosphere within such chamber.

For a further consideration of what I believe to be novel and my invention, attention is directed to the following portion of the specification, the drawing, and the appended claims.

In the drawing:

FIGURE 1 illustrates an elevational sectional view of an embodiment of apparatus constructed in accordance with this invention;

FIGURE 2 is a sectional view taken on line 2-2 of FIGURE 1.

FIGURE 3 illustrates a detail of construction of the cooling chamber.

FIGURE 4 illustrates a detail of construction taken on line 4-4 of FIGURE 1.

As illustrated in FIGURE 1, a strip of sheet metal S enters cooling chamber 11 through an inlet port 12 at the charging end thereof. Strip S will normally enter cooling chamber 11 from a first cooling chamber (not shown) where it will have been partially cooled from a higher temperature to which it had, in turn, been previously heated for metallurgical purposes.

Chamber 11 is defined by walls such as end wall 13. Each wall is formed, as is shown in FIGURE 3, of a metal plate 14. Heat transfer from chamber 11 through plate 14 may be retarded by lining the plate with a sheet of corrugated metal 15 clad with metal sheet 15a which acts as a radiation shield to block thermal radiation to the plate.

Strip S is advanced from the inlet port 12 of cooling chamber 11 to the outlet port 16 in a number of successive upwardly and downwardly traveling strands or passes, the strip being supported within chamber 11 by means of a number of turning rollers such as lower rollers numbered 53-56 and upper rollers 57-59, which will normally be driven at controlled speed by means not shown to facilitate strip advancement through the chamber.

Within chamber 11 are mounted a number of axial flow atmosphere recirculating fans such as fan 19 which is driven by motor unit 20 mounted in a recess 21 of cooling chamber roof 22. Each fan is suited to recirculate furnace atmosphere generally parallel to six (6) vertical strands of strip numbered 24-29. The re circulated atmosphere travels downwardly in two (2) streams, one path flowing past strands 24 and 25 and the other stream flowing past strands 28 and 29. As these two (2) streams near the bottom of the chamber they will divert towards each other and will return in a single stream to the fan inlet past strands 26 and 27.

Located within chamber 11 between successive strands of strip are a plurality of water cooled cooling elements such as cooling elements numbered 33-39 which are located between the strip passes. These cooling elements may be suspended from the sides of the chamber or retained in position by other suitable means. The construction of each cooling element, as is shown in FIG. 2 which illustrates cooling element 36, consists of a plurality of vertical cooling tubes 41 extending from a lower water inlet manifold 42 to an upper water outlet manifold 43. Cooling water under suitable pressure from a suitable supply source is added to cooling element 36 at inlet manifold 42 by means of inlet pipe 49. The cooling water thence flows upwardly through tubes 41 of element 36 from whence it is dischanged through outlet pipe 44 to a sewer or, when economics make it justifiable, to cooling equipment whereby it may be reused.

A plenum chamber 30 is located immediately subjacent fan 19 and is in fluid communication therewith. This plenum, which extends downwardly from fan 19 for a substantial distance thereby surrounding the last portion of the stream of recirculated atmosphere that is returning to the fan. The pressure which was imparted to this atmosphere when it originally was discharged by the fan will be spent by the time it has returned to the fan and, therefore, it is in the region immediately upstream of the fan that there will be the greatest danger of air infiltrating into the cooling chamber and contaminating the special recirculating atmosphere. Suspended plenum 30 4 combats this problem by physically isolating this region from the source of contamination.

In addition, plenum chamber 30 has skirt portions 31 and 32 and which extend downwardly therefrom to the tops of the immediately subjacent cooling elements 35 and 37. The purpose of these skirt portions is to physically prevent the relatively high pressure streams of atmosphere flowing downwardly past strands 24 and 25 and past strands 28 and 29 from short-circuiting into the relatively low pressure stream of atmosphere flowing upwardly past strands 26 and 27 into plenum chamber 30.

Intermingling of the atmosphere being recirculated by fan 19 with the atmosphere being circulated by adjacent fans 19a and 1% can be combatted by extending bafiles 61 and 62 respectively from roof 22 to the tops of cooling elements 33 and 39. Intermingling of the various upwardly and downwardly flowing streams of recirculated atmosphere in the regions subjacent skirts 31 and 32 and bafiies 41 and 42 can be prevented by constructing cooling elements 33, 35, 37 and 39 with baflles between the cooling tubes. This construction is shown in FIGURE 4 which illustrates a fragment of cooling element 37 having generally channel-shaped baflles 45 and 46 being inserted intermediate cooling tubes 41 and being retained in place by a nut and bolt assembly 47 and 48 spaced at periodic intervals.

Cooling of the strip according to the apparatus described is achieved in two (2) Ways. First, the strip is cooled by direct thermal radiation to the intermediate cooling elements which are kept at a relatively low temerature by virtue of the cooling water flowing therethrough. It is to be noted in this regard that each cooling element is adapted to receive thermal radiation from two (2) strands of strip (with the exception of cooling elements 51 and 52 at the extremities of the cooling chamber) thereby assuring full utiliaztion of the surface area of each element. This feature is to be contrasted with the prior art in which two (2) water cooled walls were erected between two (2) adjacent strands of strip. Such a construction permitted each cooling element to receive radiation from only one (1) strip pass thereby causing the potential heat transfer surface area to be wasted.

The second way in which the strip is cooled is by convective heat transfer to the forcibly recirculated cooling chamber atmosphere. This recirculated atmosphere, which flows generally parallel to the various passes of strip, is, in turn cooled by convection heat transfer to the water cooled cooling elements. In this way the cooling elements serve as heat sinks for both the heat transferred from the strip by thermal radiation and the heat transferred by forced convection.

The best mode known to me to carry out this invention has been described above in terms sufficiently full, clear and concise, and exact as to enable any person skilled in the art to make and use the same. However, certain modifications of the above described can be made by a skilled artisan without departing from the scope of the invention which is defined only by the appended claims.

I claim:

1. In a cooling zone for cooling strip an individual cooling unit comprising, in combination: three upper turning rollers and four lower turning rollers for passing strip to and fro therethrough in six vertical strands; seven watercooled cooling elements, each of said cooling units comprising a water inlet manifold, a water outlet manifold, and a plurality of water tubes extending therebetween and each of the second, third, fourth and fifth of said cooling elements being disposed respectively between the first and second, second and third, third and fourth, fourth and fifth, and fifth and sixth strands of strip and being adapted to receive thermal radiation from both strands between which it is disposed, the first and seventh cooling element being disposed outside of and adapted to receive thermal radiation from, respectively, the first and sixth strands of strip; an axial flow fan disposed on an axis intermediate the third and fourth strands of strip and located superjacent the second upper turning roller and being adapted to draw a main stream of atmosphere up through the cooling unit past the third, fourth, and fifth cooling elements and return the main stream toward the bottom of the cooling unit in two partial streams, the first partial stream flowing downwardly past the first, second, and third cooling elements and the second partial stream flowing downwardly past the fifth, sixth, and seventh cooling elements; a plenum chamber in fluid communication with the axial flow fan and extending therefrom substantially to the tops of the third, fourth, and fifth cooling elements, said plenum chamber circumposing at least a portion of the second upper turning roller and having side skirt portions in contact with the third and fifth cooling elements to prevent the first and second partial streams from short-circuiting into the main stream across the tops thereof; and baflle plates intermediate the water tubes of the third and fifth cooling elements to prevent the first and second partial streams from short-circuiting into the main stream therethrough.

2. A cooling zone for cooling a continuously moving metal strip comprising a plurality of individual cooling units with each cooling unt comprising, in combination: roller means for passing strip through said cooling unit in a plurality of vertical strands; a plurality of water-cooled cooling elements disposed successively between successive strands of strip with each of said elements being adapted to directly receive thermal radiation from the successive strands between which it is disposed; a fan disposed within said cooling unit superjacent said roller means, said strands, and said elements, said fan being adapted to recirculate atmosphere within said cooling unit in a direction upwardly past at least some of said elements and some of said strands and thence in a direction downwardly past others of said elements and others of said strands whereby the recirculating atmosphere is in contact both with cooling elements and with strands in both the upward and downward direction.

3. Apparatus according to claim 2 and further comprising a plenum chamber immediately upstream of said fan and in fluid communication therewith, said plenum chamber serving to combat the infiltration of contaminants into said chamber by physically isolating a region of low pressure.

References Cited in the file of this patent UNITED STATES PATENTS 2,101,301 Wellrnar Dec. 7, 1937 2,847,192 Smith et al Aug. 12, 1958 FOREIGN PATENTS 866,719 France May 31, 1941

Claims (1)

1. IN A COOLING ZONE FOR COOLING STRIP AN INDIVIDUAL COOLING UNIT COMPRISING, IN COMBINATION: THREE UPPER TURNING ROLLERS AND FOUR LOWER TURNING ROLLERS FOR PASSING STRIP TO AND FRO THERETHROUGH IN SIX VERTICAL STRANDS; SEVEN WATERCOOLED COOLING ELEMENTS, EACH OF SAID COOLING UNITS COMPRISING A WATER INLET MANIFOLD, A WATER OUTLET MANIFOLD, AND A PLURALITY OF WATER TUBES EXTENDING THEREBETWEEN AND EACH OF THE SECOND, THIRD, FOURTH AND FIFTH OF SAID COOLING ELEMENTS BEING DISPOSED RESPECTIVELY BETWEEN THE FIRST AND SECOND, SECOND AND THIRD, THIRD AND FOURTH, FOURTH AND FIFTH, AND FIFTH AND SIXTH STRANDS OF STRIP AND BEING ADAPTED TO RECEIVE THERMAL RADIATION FROM BOTH STRANDS BETWEEN WHICH IT IS DISPOSED, THE FIRST AND SEVENTH COOLING ELEMENT BEING DISPOSED OUTSIDE OF AND ADAPTED TO RECEIVE THERMAL RADIATION FROM, RESPECTIVELY, THE FIRST AND SIXTH STRANDS OF STRIP; AN AXIAL FLOW FAN DISPOSED ON AN AXIS INTERMEDIATE THE THIRD AND FOURTH STRANDS OF STRIP AND LOCATED SUPERJACENT THE SECOND UPPER TURNING ROLLER AND BEING ADAPTED TO DRAW A MAIN STREAM OF ATMOSPHERE UP THROUGH THE COOLING UNIT PAST THE THIRD, FOURTH, AND FIFTH COOLING ELEMENTS AND RETURN THE MAIN STREAM TOWARD THE BOTTOM OF THE COOLING UNIT IN TWO PARTIAL STREAMS, THE FIRST PARTIAL STREAM FLOWING DOWNWARDLY PAST THE FIRST, SECOND, AND THIRD COOLING ELEMENTS AND THE SECOND PARTIAL STREAM FLOWING DOWNWARDLY PAST THE FIFTH, SIXTH, AND SEVENTH COOLING ELEMENTS; A PLENUM CHAMBER IN FLUID COMMUNICATION WITH THE AXIAL FLOW FAN AND EXTENDING THEREFROM SUBSTANTIALLY TO THE TOPS OF THE THIRD, FOURTH, AND FIFTH COOLING ELEMENTS, SAID PLENUM CHAMBER CIRCUMPOSING AT LEAST A PORTION OF THE SECOND UPPER TURNING ROLLER AND HAVING SIDE SKIRT PORTIONS IN CONTACT WITH THE THIRD AND FIFTH COOLING ELEMENTS TO PREVENT THE FIRST AND SECOND PARTIAL STREAMS FROM SHORT-CIRCUITING INTO THE MAIN STREAM ACROSS THE TOPS THEREOF; AND BAFFLE PLATES INTERMEDIATE THE WATER TUBES OF THE THIRD AND FIFTH COOLING ELEMENTS TO PREVENT THE FIRST AND SECOND PARTIAL STREAMS FROM SHORT-CIRCUITING INTO THE MAIN STREAM THERETHROUGH.

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