EP0731853B1 - Device for the accelerated cooling of a fast-moving continuous substrate in a vertical plane - Google Patents

Description

The present invention relates to an accelerated cooling device continuous substrate moving rapidly in a vertical plane, plus particularly a coated metal strip, for example a sheet hot dip galvanized.

The cooling device, object of the present invention, will intentionally described and to facilitate understanding in as part of its use during cooling, after treatment of galvannealing, of a strip of galvanized steel, but this description in no way prejudges that the device of the invention cannot apply in other circumstances requiring conditions similar cooling.

The heat treatment called "galvannealing" consists in subjecting a hot-dip galvanized steel sheet after heating, temperature maintenance then cooling.

This treatment aims to ensure the diffusion of iron from the sheet through the coating layer, usually zinc or zinc alloy, so to obtain iron contents between 7% and 13% in the layer of the aforementioned coating. This heat treatment operation has for effect of obtaining a coating having better stampability and weldability.

The classic galvannealing operation is carried out in an installation where the sheet describes at least two vertical passes namely a pass upward and downward pass.

Schematically, it will be said that the sheet leaves the bath vertically galvanizing to start its upward phase and enter, directly after the wringing device consisting of air knives, in a heating oven which brings the sheet to a temperature between 460 ° C and 600 ° C; the sheet then circulates in a holding oven at temperature. Above this oven is located at least one device for cooling intended to solidify the coating of the sheet metal, so as not to damage this coating on the rollers return ending the ascending phase and guiding the sheet towards the phase descending.

It turned out that the quality of the coating obtained, after the operation of galvannealing, is directly related to the diffusion of iron in the layer of zinc or zinc alloy and that this is favorably influenced by a sufficiently long temperature holding time, for example greater than 10 seconds.

However, the length of the ascending phase is limited by problems of mechanical construction and vibration control produced in the sheet metal at the level of the air knives.

To make the best use of the installation length available for perform the heating, holding and cooling operations before passage on the deflection rollers located above the ascending phase, the applicant has developed a process in which the heating power as cooling flows to limit the space necessary for these two operations and thereby preserve a sufficient length to obtain a passage time in the furnace of keeping as high a temperature as possible in order to obtain optimal conditions for iron diffusion in the coating layer; the cycle thus produced approaches the ideal cycle called "square".

Already known, in particular by publication EP-A-0 395 759, a double device jet to produce a steel strip coated with zinc by immersion, having a minimum flowering, which includes an enclosure equipped with water / air mist nozzles and having an inlet and an outlet for the steel strip.

US-A-3,428,023 also describes a device for depositing a coating of zinc on a moving steel strip, and to cool and solidify this coating by means of water spray jets.

The present invention relates to an accelerated cooling device of low length, particularly suitable for being used for cooling rapid by means of water / air mist nozzles of a coated substrate after leaving it last out of a temperature maintenance oven and before passing over rollers referral, particularly in the context of galvannealing treatment.

According to the present invention, an accelerated cooling device of a continuous substrate moving rapidly in a vertical plane, formed by an enclosure close with a lower inlet and an upper outlet for the passage of said substrate, in which said enclosure comprises a zone of so-called main cooling, provided with means for introducing the cooling in the form of water-air mist curtains on either side of said substrate, a so-called secondary cooling zone provided with means favoring the contact between the coolant and the substrate, and an extraction zone of the coolant, and wherein said inlet and outlet ports are provided means for retaining the coolant inside the enclosure, is characterized in that said fog curtains are arranged in space in forming an angle between 30 ° and 60 ° relative to the direction of movement of said substrate, and in that said means for retaining the coolant are consisting of compressed air jets arranged on either side of said substrate and directed towards it, to prevent any coolant from escaping from said enclosure.

According to a preferred embodiment of the cooling device, said angle is between 35 ° and 40 °.

According to another preferred embodiment of the cooling device of the invention, the means for forming one or more fog curtains comprise fog projection ramps, and said projection ramps consist of two tubes whose longitudinal axes are parallel to the plane of said substrate, one of the two tubes encompassing the other and one of the tubes being supplied with water while the other is supplied with air, as well as by sprinklers supplied with water and in air by the two aforementioned tubes so as to form said mist curtains.

According to another preferred embodiment of the device, object of the invention, it comprises suction and evacuation means coolant outside the closed enclosure of said device cooling and preferably said means are located near of the upper end of the aforementioned device.

According to yet another preferred embodiment of the device of the invention, the aforementioned evacuation means include fume extractor hoods used as cooling fluid.

The previous modality provides a very effective solution to the problems techniques posed respectively, on the one hand by the waterfall in the bath of molten zinc and secondly by entrainment of fluid cooling outside the enclosure and bringing it into contact with the upper idler rollers.

la figure 1

illustre le principe du traitement thermique de galvannealing;

la figure 2

représente une vue globale du dispositif de refroidissement de l'invention.

The description which follows relates to a particular embodiment and will be explained with reference to the appended drawings, in which

figure 1

illustrates the principle of galvannealing heat treatment;

figure 2

shows an overall view of the cooling device of the invention.

The above figures constitute schematic representations in which we have reproduced only the elements necessary for the proper understanding of the invention.

FIG. 1 shows that the substrate 1 passes through the bath 2 of zinc or zinc alloy contained in the galvanizing tank 3, leaves this last vertically after return around roller 4, goes through a roller guide system 5, spins at device level wringing 6, consisting of air knives intended to adjust the thickness of the coating layer on the substrate. This last then begins a vertical upward trajectory until the second deflection roller 7, follows a horizontal path up to third deflection roller 8, then descends in a trajectory vertical to a later operation.

During the upward path between the rollers 4 and 7, the substrate goes through a short rapid heater 9 and then a short temperature equalization device 10, a device much longer 11 holding temperature and finally in a short rapid cooling device 12 equipped with fog ramps water / air.

FIG. 2 illustrates a preferred embodiment of the device 12 for rapidly cooling a coated substrate.

We distinguish in this figure 2, the closed enclosure 13 including the rapid cooling device, the substrate to be cooled 1, the inlet 14 with compressed air barriers 141 preventing the coolant go down to the galvanizing bath, outlet 15 with air dams 151 preventing coolant from escaping towards the upper deflection rollers, the projection ramps 16 water / air mist, as well as devices 161, such as deflectors, intended to promote contact between the substrate and the fog and finally the hoods 17 for extracting the fog out of the enclosure defining the cooling device.

It goes without saying that the above description is voluntarily limited to a particular field such as galvannealing, but there is none left less true that the present patent application aims to cover any stake using the claimed cooling device independently application methods, such as the nature of the fluid used.

Claims (3)

1. Accelerated cooling device for a continuous quick-running substrate in a vertical plane, formed with a closed enclosure comprising a lower inlet orifice and an upper outlet orifice for the passage of said substrate, wherein said enclosure comprises a so-called primary cooling zone provided with cooling fluid introducing means as water-air mist curtains on either side of said substrate, a so-called secundary cooling zone provided with means favoring a contact between the cooling fluid and the substrate, and a cooling fluid extracting zone, and wherein said inlet and outlet orifices are provided with cooling fluid retaining means inside the enclosure, characterized in that said mist curtains are spatially arranged by forming an angle comprised between 30° and 60° with respect to the movement direction of said substrate, and in that said cooling fluid retaining means are formed by pressurized air jets arranged on either side of said substrate and oriented towards it, to prevent any output of cooling fluid out of said enclosure.
2. Cooling device according to claim 1, characterized in that said angle is comprised between 35° and 40°.
3. Cooling device according to claim 1 or 2, characterized in that the means to form one or more mist curtains comprise mist-projecting ramps and in that said projecting ramps are formed by two tubes the longitudinal axes of which are parallel to the plane of said substrate, one of the two tubes enclosing the other one and one of the tubes being fed with water, whereas the other one is fed with air, as well as by nozzles fed with water and air by both above-mentioned tubes so as to form, said mist curtains.

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