FR2527638A1 - METHOD FOR HEATING A COATED STRIP FOR TRANSFORMING THE COATING STRUCTURE, PARTICULARLY FOR PRODUCING SHEETS - Google Patents

Abstract

COATED STRIP HEATING PROCESS, FOR TRANSFORMATION OF THE COATING STRUCTURE, IN PARTICULAR FOR THE REALIZATION OF GALVANIZED SHEETS, CHARACTERIZED IN THAT IT USES EXCLUSIVELY CONVECTIVE EXCHANGES, THE HEATING BEING CARRIED OUT BY BLOWING A UNDERWATER TEMPERATURE 1000C, AND PREFERABLY BETWEEN ABOUT 800 AND 1000C.

Description

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  The present invention relates to the heating of coated strips

  for transformation of the structure of the coating We know that, in the

  in the manufacture of galvanized sheets, it is sought after, for certain

  applications, transforming the zinc coating into an iron-

  zinc. Furthermore, it is known that this transformation takes place thanks to a phenomenon of diffusion of iron, from the base metal, through the coating. The speed of diffusion of iron through the zinc coating depends on both the temperature of the metal and its coating, as well as the residence time at this temperature. It is generally sufficient to wear the coated strip from 450 to 550 ° C. about in a few seconds and then let it cool

  in the ambient air for a few more seconds, to achieve the diffusion

  iron in zinc in the desired proportions.

  In the processes currently implemented, the heating of the strip is generally carried out by means of burners with direct impact of the flame on the strip, this flame being able to be cylindrical or planar Taking into account, on the one hand, a temperature of high combustion, and, on the other hand,

  heating performed over a short length, the gases escaping from the

  heating plants are still very hot, and the thermal efficiency obtained is relatively low, between 10 and 20% This result can

  be improved by providing a heating zone in the heating system

  cuperation, which allows both to exhaust the fumes and to add a hand-

  after heating In these conditions, heating can be done at a

  slightly lower temperature.

  However, in these known installations, the mode

  main heat exchange is radiative, and, like the coefficients of ab-

  sorption of the coated sheet are very low, the thermal efficiency of

seems to be very poor.

  The invention proposes to provide a method of heating coated strips making it possible to increase this thermal efficiency, to a significant extent. To this end, the heating method according to the invention is characterized in that it exclusively uses convective exchanges, the heating being carried out by blowing a gas at a temperature below 10,000 C, of

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  preferably of the order of 800 to 10,000 C. According to a characteristic of this invention, the hot gas is blown

  perpendicular to the strip, over the entire height of the heating installation

  fage This produces orthogonal convection heating which ensures very high heat exchange homogeneity, unlike the results obtained with certain heating systems using burners

  direct impact of cylindrical flames.

  Operating at a relatively low temperature, of the order of 800 to 1000 C, allows thermal yields greater than 45% to be obtained, while carrying out intensive heat exchanges at all points.

of the installation.

  The method according to the invention also has the advantage of being able to operate in a closed neutral gas circuit, which makes it possible to implement it in galvanizing installations on one side without risk.

  oxidation of the uncoated side.

  According to the invention, blowing gas on the strip can advantageously-

  This is done through slots or sheets perforated with circular orifices.

  laires, or a combination of the two, placed at a short distance from the strip.

  According to another characteristic of the invention, the blown gas, after its exchange with the strip, is taken up by a recirculation fan at high temperature. In this recirculation circuit is placed a gas exchanger or heater, which can be supplied by energy from

  combustion or electrical energy.

  This exchanger provides the additional heat necessary to bring the temperature of the already hot return gas to that which it must have

blowing.

  Electric power can be supplied, for example, through

  resistances, or by a plasma torch.

  The combustion energy is released inside radiant tubes, swept externally by the recirculated gas These radiant tubes can be supplied with any fuel (gas or fuel) The recirculated gas can be air, but also a neutral gas , providing tape protection

against oxidation.

  It remains to be understood that this invention is not limited to the examples of implementation described here, but that it encompasses all variants thereof.

Claims (6)

  1 Process for heating a coated strip, for transforming the structure of the coating, in particular for producing galvanized sheets,   characterized in that it exclusively uses convective exchanges, the heating   fage being produced by blowing a gas at a temperature below 1000 ° C,   and preferably between approximately 800 and 10,000 C.   2 Method according to claim 1, characterized in that the hot gas is blown perpendicular to the coated strip, over the entire height   of the heating system, so as to obtain convective heating orthogonal tion.   3 Method according to one of claims 1 or 2, characterized in   that it operates in a closed neutral gas circuit.   4 Method according to any one of claims 1 to 3, character-   laughed in that the blown gas, after heat exchange with the strip, is   resumed to perform a recirculation at high temperature, the recirculation circuit   circulation comprising a gas exchanger or heater carrying the time   return gas temperature to the desired supply temperature.   Method according to claim 4, characterized in that the gas   recirculated is air or a neutral gas.   ZO 6 Method according to any one of the preceding claims,   characterized in that the heating is carried out using liquid fuels solid or gaseous.   7 Method according to any one of claims 1 to 5, character-   risé in that the heating is carried out using electric means.   8 Method according to any one of the preceding claims,   characterized in that the gas blowing on the strip is carried out through slots and / or sheets provided with circular perforations, the orifices of   blowing being placed at a short distance from the strip.