EP0761829A1 - Cooling device for rolled products - Google Patents

Abstract

The device cools a rolled prod. (1), e.g. steel strip, defiling in front of the device, and comprises a device (4) for putting under gaseous pressure at least one caisson (10) which is made up of several thin strips forming a conduit (11). Each strip (11) incorporates at least one outlet orifice (12) for the gas in the direction of at least one of the surfaces of the rolled prod. (1), the orifices (12) of each strip (11) being aligned in the transverse direction to the rolled prod. (1). Each space (13) sepg. two adjacent strips (11) has a depth (P) in a direction perpendicular to the surface of the rolled prod. (1) and a width (L), in the direction longitudinal to the rolled prod. (1) that are sufficient to allow the evacuation of the gas (5) without disrupting the outlet of gas from the adjacent strips. The relationship of the gas (5) flow in m<3>/sec. at the outlet of the assembly of orifices (12) of a strip (11) on the section (S) in m<2> of the space (13) sepg. adjacent strips is less than 20, this section (S) corresp. to a section in a plane perpendicular to the rolled prod. (1) and parallel to the direction of defilement of the rolled prod.. The depth (P) of the space (13) between adjacent strips is greater than 200 mm and pref. 300 mm. The distance sepg. adjacent strips (11) is 0.8-5 times the distance sepg. each orifice (12) of the same strip (11). Also claimed is a cooling device incorporating at least one of these cooling devices.

Description

The present invention relates to a device for cooling a ferrous or non-ferrous laminated product, in particular a steel strip.

It is known to heat treat rolled products which pass vertically on rollers and pass through successive treatment chambers. In the manufacture of steel sheets for car bodies, continuous annealing or galvanizing lines are used in which the steel is brought to temperatures of up to 600-900 ° C. A rapid and uniform cooling of these products is then necessary in order to bring the temperature of the product to a temperature below 500 ° C. according to the desired quality.

Various cooling methods have been used so far. It is known for example to scroll the rolled product on cooled rollers or to dip it in a liquid or semi-liquid medium. These two-phase conduction or convection cooling methods achieve local heat transfer coefficients greater than 400 kCal / m ² .h. ° C, but for short drops in temperature. In addition, these methods have the drawback of generating problems of oxidation of the rolled product and contact of the rolled product with the cooling liquid or solid frequently causes flatness defects.

Another type of method, by spraying a gas, makes it possible to avoid the abovementioned drawbacks. US Patent 4,363,471 describes a steel annealing line in which the steel strip passes in front of a box comprising a series of gas blowing nozzles. However, these nozzles form only small projections on the surface of the box. Gas evacuation, after being in contact with the steel strip, is therefore hampered by the box: back-pressure zones then appear between the nozzles and the box, thus disturbing the projection of the cooling gas towards the steel strip . In addition, the gas can only escape laterally along the width of the rolled product, which causes preferential cooling of the edges of the rolled product and can lead to flatness defects. The heat transfer coefficients achieved by this type of device do not exceed 200 kCal / m ² .h. ° C for a gas composed of a mixture of hydrogen and nitrogen with a hydrogen level of 5%, and even less for air.

In an article by T. Kaihara et al entitled "New technology in KM-CAL for sheet gage" (New technology in multi-function continuous annealing lines for a laminated sample) and published in 1992 in "Developments in the annealing of rolled steel ", ed. Pradhan and Gupta, it is specified that a maximum rate of 50 ° C / s can be obtained for a laminated product with a thickness equal to 0.7 mm, which is equivalent to a transfer coefficient of approximately 175 kCal / m ² .h. ° C.

In the same publication, an article entitled "Recent developments in the Metallurgical Technology of Continuous Annealing for Cold-rolled and Surface-coated sheet steels" by Hiroshi Takechi describes that, even by positioning the gas outlet orifices at a distance of 50 mm from the rolled product, one can only obtain a cooling rate of 100 ° C / s for a plate of thickness less than 0 , 35 mm, i.e. corresponding to a transfer coefficient of 200 kCal / m ² .h. ° C.

WO 92/02316 describes a cooling device in which an extruded profile runs horizontally between blade-shaped conduits having gas outlet orifices extending in the transverse direction of the profile. Only the position of the upper and lower blades, staggered with respect to each other, is specified in order to obtain uniform cooling of the profile. However, in this document, the problem of the evacuation of the gas after its impact on the profile is not considered. The impact of the gas on the profile is then disturbed by the gases which stagnate between the blades.

The article "Heating and cooling technology in the continuous annealing" by IMOSE (Transactions ISIJ, Vol.25, 1985, 911-932) indicates that one can obtain a heat transfer coefficient equal to a maximum of 250 kCal / m ² .h. ° C by increasing the speed and the volume of projected gas, reducing the distance between the rolled product and the blowing nozzles and enriching the gas with hydrogen. This value of the heat transfer coefficient is however insufficient to obtain a really accelerated cooling of the rolled product.

In addition, all the processes consisting in increasing the hydrogen level in order to improve the transfer coefficient are difficult to comply with safety standards and present real dangers for operators.

The table below summarizes the various means proposed to date for cooling a steel strip from 600 ° C to 400 ° C.

Cooling methods Heat transfer coefficient (kCal / m ² .h. ° C) Cooling rate between 600 and 400 ° C for a 1 mm thick steel strip (° C / s) Remarks By gas jets -normal 100 17 too weak -extreme possible * (* according to IMOSE) 250 42 only for high hydrogen content By passing over cooled rollers 1000 160 serious flatness defects Soaking in hot water (≥90 ° C) 400 67 Product oxidation Soaking in cold water 6000 1000 Oxidation of the product and stop of cooling impossible By mist projection 600 100 Product oxidation

The object of the present invention is to provide a gas spray cooling device which allows a rolled product to be cooled with a heat transfer coefficient greater than 350 kcal / m ² .h. ° C, while using a harmless gas.

The cooling device targeted by the invention makes it possible to cool a rolled product, in particular a steel strip, passing in front of the device which comprises means for pressurizing gas of at least one box, the box comprising several blades forming a duct. , each blade comprising at least one gas outlet orifice in the direction of at least one of the surfaces of the laminated product, the orifices of each blade being aligned in the transverse direction of the laminated product.

According to the present invention, this cooling device is characterized in that each space separating two adjacent blades has a depth in a direction perpendicular to the surface of the rolled product and a width in the longitudinal direction of the rolled product sufficient to allow the evacuation of the gas without disturbing the gas outlet of the adjacent blades, the ratio of the gas flow rate in m ³ / s at the outlet of all the orifices of a blade on the section in m ² of the space separating this blade from one or other of the adjacent blades being less than 20, the section corresponding to a section in a plane perpendicular to the product laminated and parallel to the direction of travel of the laminated product.

Thanks to the spaces provided between each series of orifices, the evacuation of the gas after projection is facilitated. The emission of gas jets is therefore not hampered and the speed of the jets can reach 220 m / s.

By keeping the gas flow below a threshold fixed as a function of the section of the separation space, the circulation of the gas in the cooling device is regular, and the gas can be evacuated without generating preferential cooling of the edges. The cooling device of the invention is therefore perfectly suited to continuous heat treatment, such as that used in continuous steel treatment lines.

This results in much higher cooling rates than those obtained by conventional gas spraying devices. Transfer coefficients greater than 350 kcal / m ² .h. ° C are obtained.

According to an advantageous version of the invention, the depth of each space is greater than 200 mm, and preferably 300 mm.

The return of the gas, after its impact on the surface of the rolled product, is facilitated by this significant depth existing behind the outlet orifices up to the box. Accumulation of gas at The level of the outlet orifices is thus avoided: the projection of the cooling gas is therefore not disturbed by stagnant gas which escapes with difficulty between the outlet orifices.

According to a preferred version of the invention, the distance separating the adjacent blades is between 0.8 and 5 times the distance separating each orifice from the same blade.

In this way, the blades are sufficiently close to each other, at the height of their gas outlet orifices, to uniformly cool the entire surface of the laminated product moving past these outlet orifices.

According to another aspect of the invention, a cooling installation comprising at least one cooling device is characterized in that stabilizing rollers are arranged on either side of the cooling device (s), said rollers being capable of deflecting the rolled product with an angle of less than 7 °.

Very high cooling power can thus be obtained, the rollers preventing the rolled product from vibrating under the effect of the pressure of the projected cooling gas.

Other features and advantages of the invention will appear in the description below.

• La figure 1 est une vue de face du dispositif de refroidissement conforme à l'invention;
• La figure 2 est une vue de coté du dispositif de la figure 1;
• La figure 3 est un schéma illustrant la disposition du dispositif de refroidissement par rapport à un produit laminé;
• La figure 4 est un schéma illustrant la disposition respective des orifices de soufflage;
• La figure 5 est une vue schématique de lames du dispositif de refroidissement conforme à l'invention; et
• La figure 6 est vue d'une installation de refroidissement conforme à l'invention.

In the appended drawings, given by way of nonlimiting examples:

• Figure 1 is a front view of the cooling device according to the invention;
• Figure 2 is a side view of the device of Figure 1;
• Figure 3 is a diagram illustrating the arrangement of the cooling device with respect to a rolled product;
• Figure 4 is a diagram illustrating the respective arrangement of the blowing orifices;
• Figure 5 is a schematic view of blades of the cooling device according to the invention; and
• Figure 6 is a view of a cooling installation according to the invention.

The cooling device according to the invention is intended in particular to be integrated in a continuous annealing line such as that conventionally used for the treatment of steel strips.

These steel strips have a thickness of between 0.15 and 2.3 mm. Their width is of the order of 0.6 to 2 m.

During the heat treatment of the steel strips, it is necessary to cool the strips in a very short time, from a temperature close to 600-900 ° C to a temperature below 500 ° C.

In the case of cooling after coating or hot tempering of steel by immersion in a bath of molten metal, it is important to cool the strip very quickly after its hot coating to a temperature of 200 ° C to 300 ° C approx. This cooling is carried out using air.

With reference to FIGS. 1 and 2, the rolled product 1 passes by vertical passes in the direction of the arrow F between transport rollers 2.

The cooling device comprises means for pressurizing gas 4 of a box 1.

The box 1 extends parallel to the surface of the rolled product and is supplied by at least one fan 4 intended to introduce a high flow rate of cooling gas 5 under pressure into the box. Of course, several supply fans could be used and distributed evenly over the height of the cabinet. We could also replace the fan with a compressor.

For clarity, a single box 10 is shown in Figure 2, but preferably the device of the invention comprises a second box 10, positioned symmetrically with respect to the rolled product, so that the latter is cooled on these two faces opposite at the same time.

The box comprises several blades forming a duct 11, outlet orifices 12 for the gas 5 towards the surface of the laminated product 1 being provided at the end of these blades 11. The orifices 12 of each blade 11 are aligned in the transverse direction of the rolled product 1. As illustrated in FIGS. 3 and 4, each space 13 separating two adjacent blades has a depth P in a direction perpendicular to the surface of the rolled product 1 and a width L in the longitudinal direction of the rolled product 1 sufficient to allow gas evacuation 5.

Each orifice 12 opens at the end of a conduit formed by a blade 11 extending from the box 10 in the direction of the laminated product.

The gas 5 can escape backwards after its contact on the rolled product, between the different blades. In the case where, to avoid oxidizing the product, cooling must be carried out under a protective atmosphere, such as for example a mixture of nitrogen and hydrogen, the entire cooling device is surrounded in a known manner by 'A sealed envelope for recovering the sprayed gas in order to recycle it continuously in the gas pressurization means. Recycling includes a gas recovery step, a gas cooling step and a reinjection step.

The gas temperature in the box is less than 100 ° C.

The distance D existing between the adjacent blades 11 is between 0.8 and 5 times the distance d separating each orifice 12 of the same blade 11. This distance D corresponds to the distance separating the blades 11, in the direction F of travel , at the height of the outlet orifices 12.

The distance d separating each orifice 12 of the same series is uniform.

Preferably, the distance D between two adjacent blades is between 30 and 200 mm.

In addition, as illustrated in FIG. 4, the orifices can be aligned in the longitudinal direction of the rolled product so that they form the four corners of contiguous squares.

The orifices can also be arranged in staggered rows, as shown in FIG. 1 and thus form the corners of contiguous diamonds.

The distribution of the cooling gas jets is therefore uniform over the entire surface of the rolled product.

The holes are circular, rectangular, oblong, etc. holes, or small slots. Each blade may also have only one outlet opening forming a slit opposite the laminated product.

For proper operation of the device and rapid cooling of the rolled product, it is important that the depth of each separation space 13 is greater than 200 mm, and preferably greater than 300 mm.

The ratio of the gas flow rate 5 in m ³ / s at the outlet of all the orifices 12 of a blade 11 on the section S in m ² of the space 13 separating this strip 11 from the adjacent strips is less than 20. Section S corresponds to the section in a plane perpendicular to the rolled product and parallel to the direction of travel of this product.

The speed of the gas during its escape to the outlet or the suction, (depending on whether the gas is recycled or not), in the spaces 13 between the blades 11, is thus maintained under a critical value of 20 m / s in order to limit the phenomena of turbulence in these spaces 13 which would disturb the evacuation of the gas after its impact on the rolled product.

The equivalent diameter of the orifices 12 can be between 5 and 15 mm: the equivalent diameter corresponds to the diameter of the circle having an area equal to that of the section of the orifice.

In view of the above, it is advantageous to arrange the cooling device so that the outlet orifices 12 are at a distance 1 from the surface of the rolled product 1 of between five and twelve times the equivalent diameter of the orifice 12 , and preferably between six and eight times the equivalent diameter.

In order to be able to modify this distance 1, it is advantageous that the boxes 10 can be movable in a direction perpendicular to the rolled product 1, so as to be able to be brought close to or away from the rolled product.

As illustrated in FIG. 5, preferably each blade forming a conduit 11 has a section which decreases in the direction of passage of the gas, that is to say from the box to the outlet orifice 12. The height of the conduit inside of the blade 11, in the vertical direction F of travel of the laminated product 1, decreases continuously.

The outlet orifice 12 is profiled so that its section is substantially the same as the outlet section of the blade 11. This construction makes it possible to obtain a gas at high speed at the outlet while limiting parasitic pressure losses

The blades and the orifices can be manufactured indifferently by molding, forming, stamping, assembly and / or machining.

With reference to FIG. 6, a cooling installation according to the invention comprises at least one cooling device 21. Stabilizing rollers 20 are arranged on either side of the cooling device (s) 21, the rollers being adapted to cause deflection of 7 ° or less of the rolled product 1.

These rollers limit the vibration of the product, especially when the distance 1 between the orifices 12 of this product is small. These rollers are movable laterally, that is to say perpendicular to the rolled product, to align the latter and are motorized to drive the product in movement.

The distance separating in height two series of rollers 20 is less than or equal to 6 m and the height of a stack of conduits in the same device 21 is less than or equal to 5 m. This limits the vibrations of the product as well as possible while obtaining very high cooling power.

The cooling device preferably comprises a number of blades superimposed in the longitudinal direction of the rolled product and each blade has a number of orifices 12 such that the total section of openings of the device is between 1 and 5% of the covered area. by all of the blades, and preferably between 2 and 4% of this surface.

The cooling device comprises at least one box 10 disposed on each side of the rolled product. Preferably, it comprises several boxes 10a, 10b arranged on the same side of the rolled product 1. There is thus provided one to seven boxes positioned side by side in the width of the rolled product and the pressure of which is regulated independently so as to ensure the transverse homogeneity of the cooling. We can indeed adjust the cooling intensity over the width of the rolled product according to the desired thermal profile.

The gas used consists of a mixture of hydrogen and nitrogen, the proportion of hydrogen preferably being less than or equal to 5%. This gas can also be air or pure nitrogen.

Thanks to the cooling device according to the invention, it is possible to cool a steel strip with a thickness of 0.8 mm with a cooling rate greater than 80 ° C./s, that is to say corresponding to a transfer coefficient at least equal to 400kCal / m ² .h. ° C.

Of course, the invention is not limited to the embodiment described above, and many modifications can be made without departing from the scope of the invention.

Claims (11)

Device for cooling a rolled product (1), in particular a steel strip, running past said device, comprising means for pressurizing gas (4) of at least one box (10), said box ( 10) comprising several blades forming a duct (11), each blade (11) comprising at least one outlet orifice (12) for the gas in the direction of at least one of the surfaces of the laminated product (1), the orifices (12) of each blade (11) being aligned in the transverse direction of the laminated product (1), characterized in that each space (13) separating two adjacent blades (11) has a depth (P) in a direction perpendicular to the surface of the laminated product (1) and a width (L) in the longitudinal direction of the rolled product sufficient to allow the evacuation of the gas (5) without disturbing the gas outlet of the adjacent blades, the ratio of the gas flow rate (5) in m ³ / s at the outlet of all the orifices (12) of a blade (11) on the section (S) in m ² of l space (13) separating said blade (11) from one or other of the adjacent blades being less than 20, said section (S) corresponding to a section in a plane perpendicular to the rolled product (1) and parallel to the direction of travel of said laminated product. Cooling device according to claim 1, characterized in that the depth (P) of each space (13) is greater than 200 mm, preferably 300 mm. Cooling device according to one of claims 1 or 2, characterized in that the distance (D) separating the adjacent blades is between 0.8 and 5 times the distance (d) separating each orifice (12) from same blade (11). Cooling device according to one of claims 1 to 3, characterized in that the distance (D) separating the adjacent blades (11) is between 30 and 200 mm. Cooling device according to one of claims 1 to 4, characterized in that the distance (d) separating each orifice (12) of the same blade (11) is uniform. Cooling device according to one of claims 1 to 5, characterized in that the section of the blades (11) decreases from the box (10) towards the orifices (12). Cooling device according to one of claims 1 to 6, characterized in that it comprises several boxes (10a, 10b) arranged on the same side of the rolled product (1) and positioned side by side across the width of the rolled product , the pressure of each box (10a, 10b) being regulated independently. Cooling device according to one of Claims 1 to 7, characterized in that the distance (1) separating the orifices (12) from the surface of the laminated product (1) is between 5 and 12 times the equivalent diameter of the orifices (12). Cooling device according to one of claims 1 to 8, characterized in that the gas (5) consists of a mixture of hydrogen and nitrogen, said device being surrounded by a sealed enclosure and the gas ( 5) being continuously recycled. Cooling device according to one of claims 1 to 9, characterized in that the blades (11) and the orifices (12) are produced by molding, forming, stamping, assembly and / or machining. Cooling installation comprising at least one cooling device (21) conforming to one of claims 1 to 10, characterized in that stabilizing rollers (20) are arranged on either side of the cooling device (s) (21), said rollers being adapted to deflect the rolled product (1) d '' an angle less than 7 °.

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