Section and method for cooling a continuous line combining dry cooling and wet cooling

Abstract

Cooling section for a steel strip continuous annealing or galvanizing line arranged to handle a metal strip (1), said section comprising at least one area (2) for dry cooling set up to project gas on said steel strip and at least one wet cooling area (5) set up to project a liquid or a mixture of gas and liquid on said steel strip.

Claims

1. Cooling section for a steel strip continuous annealing or galvanizing line arranged to handle a metal strip (1), said section comprising: at least one area (2) for dry cooling set up to project gas on said steel strip; at least one wet cooling area (5) set up to project a liquid or a mixture of gas and liquid on said steel strip; and an atmosphere separation seal (4) between the dry cooling area and the wet cooling area, the atmosphere separation seal (4) comprising: three pairs of rolls (8, 9, 10), each of the three pairs set transversely to the metal strip running direction, the three pairs of rolls creating between them two areas within the said seal, respectively a first area (11) between a first roll pair of the two pairs of rolls (8, 9) in the strip running direction and located on the dry cooling area (2) side with means of extraction (15), and respectively a second area (12) between a second roll pair of the two pairs of rolls (9,10) in the strip running direction and located on the wet cooling area (5) side with means (14) to inject an inert gas.

2. Cooling section as per claim 1, where the dry cooling area and wet cooling area are arranged in a vertical pass, the wet cooling area being located beneath the dry cooling area.

3. Cooling section as per claim 1, also including a drying and purging system (24, 25, 26, 27, 28, 29) of the wet cooling area.

4. Cooling section as per claim 3, where the drying and purging system of the wet cooling area includes equipment (27, 28) arranged to inject nitrogen.

5. Cooling section as per claim 3, where the drying and purging system of the wet cooling area includes equipment (25) arranged to heat the walls of said wet cooling area.

6. Cooling section as per claim 3, where the drying and purging system of the wet cooling area includes a system of nitrogen knives directed downwards in the wet cooling area and arranged to blow nitrogen at the interior walls of the wet cooling area.

Description

(1) The invention consists, besides the provisions described above, of a certain number of other provisions which will be more explicitly addressed hereafter, with reference to assembly examples described in relation to the attached drawings, but which are in no way limiting. On these drawings:

(2) FIG. 1 is a schematic view of a cooling section, in a first arrangement of the invention, from a continuous strip processing line.

(3) FIG. 2 is a schematic view of a cooling section, in a second arrangement of the invention, showing a drying and purging system for the wet cooling area.

(4) The attached FIG. 1 diagram shows a cooling section, as per the first arrangement, for a continuous annealing or galvanizing line for metal strips, set up to receive a metal strip 1 with a running direction S, successively combining, in the running direction, at least one dry cooling area 2 and one wet cooling area 5.

(5) In the example shown, the cooling section also includes an atmosphere separation seal 4, separating the dry cooling area 2 and the wet cooling area 5.

(6) The strip 1 enters the cooling section running downwards in the direction S. It passes first through the dry cooling area 2 where a mixture of nitrogen and hydrogen is projected on the strip using blowing boxes 3. The strip then passes through the atmosphere separation seal 4 before entering the wet cooling area 5.

(7) The wet cooling area 5 has nozzles 6 arranged to project a cooling fluid on the metal strip 1.

(8) The wet cooling area 5 includes vapor extraction 7, which in the example shown in the figure is located in the upper section of the wet cooling area 5.

(9) The atmosphere separation seal 4 located between the dry area 2 and the wet area 5 comprises three successive pairs 8, 9 and 10 of rolls, in the running direction S of the metal strip 1. Each of the pairs is set transversely to the running direction of the metal strip.

(10) Between them, the three pairs delimit two successive areas 11 and 12 of the seal, in the running direction of the strip. Area 11, delimited by roll pairs 8 and 9 is located on the side of the dry cooling area 2; area 12, delimited by roll pairs 9 and 10 is located on the wet cooling area side.

(11) The rolls rotate at the strip running speed. They are kept in contact with the strip, or in a position of immediate proximity to the strip.

(12) Behind and beside the rolls, a mechanism 13 limits the circulation of gas between the areas of the seal, particularly by limiting the space between fixed and moving parts.

(13) An injection of nitrogen is made into area 12 by means of a supply 14 that is a device arranged to inject inert gas. Extraction takes place in area 11 using an extraction device 15. The pressure and injection flow rate of the inert gas into area 12 and the extraction flow from area 11 are set so that the flow of gas between areas 11 and 12 takes place solely from area 12 towards area 11. This prevents wet atmosphere from the wet area 5 entering area 11 of the seal and any mixing with the dry atmosphere of area 2.

(14) In the example shown, at the exit of the wet cooling area 5, in the strip running direction, there is a set 16 of liquid knives for removing the majority of run-off liquid from the strip. The set 16 of liquid knives is followed by a set 17 of gas knives for removing the remainder of the liquid from the strip.

(15) Still referring to the first arrangement, the metal strip 1 then passes through a return tank 18 where the cooling liquid projected by the nozzles 6 and the liquid knives 16 is collected before being sent to a recirculation tank (not shown) via a duct 24.

(16) The return tank 18 includes a second set 19 of gas knives to remove any remaining liquid from the metal strip 1.

(17) In the example shown, the first set 17 and the second set 19 of gas knives are fed from supplies coming from the same supply duct (not numbered) shown with a vertical arrow.

(18) The metal strip 1 then passes through an area 20 where heating tubes 21 eliminate all traces of liquid on the strip. On leaving this area 20, the strip passes through an atmosphere separation seal 22 between wet areas 5, 18, 20 and areas 23 downstream in the strip running direction.

(19) For example, the strip is cooled in the dry area 2 from a temperature of 800° C. to a temperature of 700° C., and is then cooled in the wet area 5 from a temperature of 700° C. to temperature of 460° C.

(20) The cooling liquid is for example water, or an acid solution containing formic acid.

(21) The attached FIG. 2 diagram shows a second arrangement for a system as per the invention, described only for its differences from the first arrangement.

(22) The second arrangement also includes a drying and purging system for the inventions' wet cooling area.

(23) The drying and purging system for the wet cooling area comprises inert gas knives 27, of nitrogen for example, directed downwards and blowing on the interior walls of a casing within the wet cooling area, to help evacuate the liquid from the walls towards a recirculation duct 24 or a purge duct 26.

(24) As well as the inert gas introduced by the knives 27, the drying and purging system of the cooling area in the second arrangement includes inert gas injection points 28, for example nitrogen, and vents 29 for a rapid purge of the wet cooling area 5. The inert gas feeding the knives 27 and injection points 28 is heated in advance, for example to a temperature of around 50° C.

(25) A heating and thermal insulation system 25 of the casing walls for the wet cooling area is installed outside the walls of the wet cooling area.

(26) Advantageously, the liquid directed onto the strip is a solution of formic acid, with a concentration of between 0.1% and 5.5%, advantageously between 0.1% and 5%, advantageously between 0.1% and 4.5%, advantageously between 0.1% and 4%, advantageously between 0.1% and 3.5%, advantageously between 0.1% and 3%, advantageously between 0.1% and 2.5%, advantageously between 0.15% and 2.5%, advantageously between 0.2% and 2.5%, advantageously between 0.3% and 2%, advantageously between 0.35% and 2.5%, advantageously between 0.4% and 2.5%, advantageously between 0.45% and 2.5% by mass of the solution. More advantageously, the solution has a concentration of formic acid between 0.46% and 2.4%, advantageously between 0.47% and 2.3%, advantageously between 0.48% and 2.2%, advantageously between 0.49% and 2.1% by mass of the solution. Even more advantageously, the solution has a concentration of formic acid between 0.5% and 2% by mass of the solution.

(27) Of course, the invention is not limited to the examples described above and numerous adjustments can be made to these examples without moving outside the frame of the invention. Moreover, the invention's various characteristics, forms, variants and assembly methods can be linked to one another in different combinations to the extent that they remain compatible and do not exclude each other.