EP0761829B1 - 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 of a ferrous or non-ferrous laminated product ferrous, especially a steel strip.

It is known to heat treat rolled products which travel vertically on rollers and pass through successive chambers of treatment. In the manufacture of steel sheets for car body, we use annealing lines or continuous galvanizing in which the steel is brought to temperatures up to 600-900 ° C. Rapid and uniform cooling of these products is then necessary in order to bring back the product 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. The evacuation of the gas, 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 of 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.

Document WO 92/02316 describes a device for cooling in which an extruded profile runs horizontally between blade-shaped conduits having gas outlet ports extending into the transverse direction of the profile. Only the position of upper and lower blades staggered compared to the others, is specified in order to obtain a uniform cooling of the profile. However, in this document, the problem of gas evacuation after its impact on the profile is not envisaged. The impact of 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 of the methods of increase the hydrogen level to improve the transfer coefficient are hardly compatible with safety standards and present real hazards 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, each space separating two adjacent blades to a depth in a direction perpendicular to the surface of the rolled product and a width in the longitudinal direction of the rolled product which define a section (S) in m ² in a plane perpendicular to the rolled product and parallel to the running direction of the rolled product. According to the present invention, this cooling device is characterized in that the section (S) is such that the ratio of the gas flow rate in m ³ / s at the outlet of all of the orifices of a blade on the section (S ) is always less than 20, in order to allow the evacuation of the gas without disturbing the gas outlet of the adjacent blades.

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

By keeping the gas flow below a fixed threshold depending on the section of the separation space, the gas circulation in the cooling device is regular, and the gas can be evacuated without generating preferential cooling of the banks. The device of the invention is therefore perfectly suitable for continuous heat treatment, such as that used in steel processing lines continuously.

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 more than 200 mm, and preferably 300 mm.

The return of gas, after its impact on the surface of the rolled product, is facilitated by this significant depth existing behind the orifices exit to the caisson. Accumulation of gas at level of the outlet orifices is thus avoided: the projection of the cooling gas is therefore not disturbed by stagnant and escaping gas difficult between the outlet ports.

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

This way the blades are sufficiently close to each other, at the height of their gas outlet ports, to cool evenly the entire surface of the rolled product moving in look at these outlet ports.

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 the side and other of the cooling device (s), said rollers being able to deflect the product laminated at an angle of less than 7 °.

We can thus obtain a very strong power cooling rollers preventing the product laminate to vibrate under the effect of gas pressure projected cooling.

Other features and advantages of the invention will appear further 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 into a continuous annealing line such as that used conventionally for the processing of tapes of steel.

These steel strips have a thickness comprised between 0.15 and 2.3 mm. Their width is around 0.6 at 2 m.

During the heat treatment of steel strips, it is necessary to cool these strips in a while very short, with a temperature close to 600-900 ° C up 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 very quickly the strip after hot coating up a temperature of 200 ° C to 300 ° C approximately. This cooling is achieved using air.

With reference to Figures 1 and 2, the product laminated 1 scrolls in vertical passes in the direction of arrow F between transport rollers 2.

The cooling device includes gas pressurization means 4 of a box 1.

Box 1 extends parallel to the surface rolled product and is supplied by at least one fan 4 intended to introduce at a high flow rate pressurized cooling gas 5 in the box. Of course, several fans of blowing could be used and spread 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 product laminated, so that the latter is cooled on these two opposite sides at the same time.

The box includes several blades forming conduit 11, outlet ports 12 for gas 5 in direction of the surface of the rolled 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 rolled product 1 sufficient to allow gas to escape 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 rolled product.

Gas 5 can escape backwards after its contact on the laminated product, between the different blades. In the event that, to avoid oxidizing the product, cooling should be done under a protective atmosphere, such as a mixture nitrogen and hydrogen, the entire system of cooling is surrounded in a known manner by a waterproof casing to recover the projected gas in order to recycle it continuously in the disposal means under gas pressure. Recycling includes a step gas recovery, a cooling step of this one and a reinjection step.

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

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

The distance d separating each orifice 12 from a same series is uniform.

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

In addition, as illustrated in FIG. 4, the holes 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 as shown in Figure 1 and formed thus the corners of contiguous diamonds.

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

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

For proper operation of the device and a rapid cooling of the rolled product, it is important that the depth of each space of separation 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 blade 11 from the adjacent blades 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 when it escapes to outlet or suction, (depending on whether the gas is recycled or not), in the spaces 13 between the blades 11, is thus kept below 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 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 equal surface to that of the orifice section.

In view of the above, it is advantageous to arrange the cooling device so that the outlet ports 12 are at a distance 1 of 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 diameter equivalent.

In order to modify this distance 1, it it is advantageous that the boxes 10 can be mobile in a direction perpendicular to the rolled product 1, so that they can be brought closer or further away from the laminated product.

As illustrated in Figure 5, preferably each duct blade 11 has a decreasing section in the direction of gas flow, i.e. from the box to outlet 12. The height of the duct inside of the blade 11, in the vertical direction F of the rolled product 1, decreases so keep on going.

The outlet orifice 12 is profiled so that its section is substantially the same as the section of exit of the blade 11. This construction allows obtain a gas at high speed by limiting parasitic pressure losses

Blades and holes can be made indifferently by molding, forming, stamping, assembly and / or machining.

Referring to Figure 6, an installation of cooling according to the invention comprises at least a cooling device 21. Rollers stabilizers 20 are arranged on either side of the or cooling devices 21, the rollers being adapted to cause lower deflection or equal to 7 ° 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 weak. These rollers are movable laterally, i.e. perpendicular to the rolled product, to align it and are motorized to drive the product scrolling.

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 5m. We thus limit at best the vibrations of the product while obtaining a power very important cooling.

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

The cooling device comprises at minus one box 10 placed on each side of the product the mine. Preferably, it includes several boxes 10a, 10b arranged on the same side of the rolled product 1. One to seven boxes are thus provided positioned side by side. side in the width of the rolled product and the pressure is independently regulated to ensure the transverse homogeneity of the cooling. We can indeed adjust the cooling intensity on the width of the rolled product depending on the profile desired thermal.

The gas used consists of a mixture of hydrogen and nitrogen, the proportion of hydrogen being preferably 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.

Claims (11)

1. Device for cooling a flat rolled product (1), especially a steel strip, running continuously past the said device, comprising means (4) for pressurizing the gas in at least one box (10), the said box (10) comprising several duct-forming blades (11), each blade (11) having at least one gas outlet orifice (12) facing at least one of the surfaces of the rolled product (1), the orifices (12) of each blade (11) being aligned in the transverse direction of the rolled product (1), each space (13) separating two adjacent blades (11) having 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 which define a section (S) in m² in a plane perpendicular to the rolled product (1) and parallel to the direction in which the said rolled product runs, characterized in that the said section (S) is such that the ratio of the flow rate of the gas (5) in m³/s leaving all of the orifices (12) of a blade (11) to the said section (S) in m² is always less than 20 so as to allow the gas (5) to escape without disturbing the gas leaving the adjacent blades.
2. Cooling device according to Claim 1, characterized in that the depth (P) of each space (13) is greater than 200 mm, preferably greater than 300 mm.
3. Cooling device according to either of Claims 1 and 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) of the same blade (11).
4. 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.
5. 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.
6. 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).
7. Cooling device according to one of Claims 1 to 6, characterized in that it comprises several boxes (10a, 10b) placed on the same side of the rolled product (1) and positioned side by side along the width of the rolled product, the pressure in each box (10a, 10b) being regulated independently.
8. 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 rolled product (1) is between 5 and 12 times the equivalent diameter of the orifices (12).
9. Cooling device according to one of Claims 1 to 8, characterized in that the gas (5) consists of a mixture of hydrogen and nitrogen, the said device being surrounded by a sealed enclosure and the gas (5) being continuously recycled.
10. Cooling device according to one of Claims 1 to 9, characterized in that the blades (11) and the orifices (12) are manufactured by moulding, forming, drawing, joining and/or machining.
11. Cooling plant comprising at least one cooling device (21) according to one of Claims 1 to 10, characterized in that stabilizer rollers (20) are placed on either side of the cooling device or devices (21), the said rollers being designed to deflect the rolled product (1) by an angle of less than 7°.

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