Process and installation for heating a metallic strip, notably for an annealing

Abstract

The invention pertains to the heating of a metal strip, and relates to equipment for heating a metal strip that comprises a pre-heating housing provided with a device for projecting hot gases towards the strip, a heating housing with regenerative burners, a duct for discharging the gases from the heating housing, a three-way adjustable valve and an adjustment device including a sensor for detecting the setpoint temperature of the metal strip and a member for adjusting the three-way valve so that it can adjust the amount of hot gases fed to the projection device. The invention can be used in equipment for heating narrow strips before annealing the same.

1 - 10 . (canceled) 
   
   
       11 . A process for heating a metallic strip to a set temperature needing the presence of a reducing combustion atmosphere, comprising the steps of:
 preheating the strip to an intermediary temperature needing not the presence of a protective atmosphere, by projecting hot gases towards at least one side of the strip, and   heating the strip in a reducing combustion atmosphere from the intermediary temperature to the set temperature,   with the control of the set temperature by varying the projection of hot gases for the preheating;   characterized in that   the heating in a reducing combustion atmosphere is carried out by means of regenerative open fire burners in a first phase which comprises, in at least one first burner, a combustion with the help of air that has absorbed heat from a first thermal absorption mass, and, in at least one other burner, a heat absorption regeneration of the combustion gases from the first burner by at least one different thermal absorption mass, and in a second phase in which the functions of at least the first burner and of at least the different burner on the one hand and the functions of the first thermal absorption mass and of the different thermal absorption mass on the other hand are reversed,   the heat absorption regeneration of the combustion gases is carried out in an operation which comprises, before the passage of the combustion gases through the regenerative mass, the mixing of these combustion gases to an additional quantity of post-combustion air,   the preheating by projection of hot gases comprises the use of at least a part of the gases evacuated from the heating by regenerative burners, and   the control of the set temperature comprises the adjustment of the quantity of hot gases for the projection preheating.   
   
   
       12 . A process according to  claim 11 , characterized in that the adjustment of the proportions of the hot gases transmitted to the projection step on the one hand and to the hot gas evacuation step on the other hand. 
   
   
       13 . A process according to  claim 11 , characterized in that the quantity of air introduced for the mixing to the combustion gases is sufficient for the evacuated gases to have no reducing power. 
   
   
       14 . A process according to  claim 11 , characterized in that the mixing of the combustion gases to the post-combustion air introduced before the passage of the combustion gases through the regenerative mass is adjusted according to the result of a measure of the reducing power of the combustion gases. 
   
   
       15 . A process according to  claim 11 , characterized in that it comprises the implement of a gas circulation directly from the heating step to the preheating step and the injection of post-combustion air between both these steps. 
   
   
       16 . An installation for heating a metallic strip to a set temperature needing the presence of a reducing combustion atmosphere, comprising:
 a preheating chamber provided with a projection device for projecting hot gases towards the strip,   a heating chamber provided with an open fire heating unit for heating in a reducing combustion atmosphere, the heating unit comprising at least two regenerative burners, working in tandem, at least one of the burners working in a combustion mode in which combustion air circulates through a regenerative mass before participating to a combustion, and at least another burner working in a heat recuperation mode in which the combustion gases from at least the first burner circulate through the regenerative mass of the other burner and heat it, the at least two burners exchanging theirs working modes, each burner comprising an air feeding device working in a regeneration mode, in order that this air mixes up to the combustion gases in the reducing state before they circulate through the regenerative mass,   a duct for evacuating the gases from the heating unit,   an adjustable three-way valve with an entry connected to the duct for evacuating the gases from the heating unit, an exit connected to the gas projection unit of the preheating chamber, and an exit connected to a duct for evacuating the gases outside the installation, and   a control device comprising a set temperature sensor for the metallic strip and an adjustment component for the three-way valve, in order that this valve controls the quantity of hot gases transmitted to the projection device.   
   
   
       17 . An installation according to  claim 16 , characterized in that the air feeding device working in a regeneration mode introduces an essentially constant quantity of air, which is at least sufficient for the evacuated gases to have always no reducing power. 
   
   
       18 . An installation according to  claim 16 , characterized in that it comprises a second control device which comprises a sensor for measuring the reducing power of the gases and an adjustment component for adjusting the introduced quantity of air according to the signal from the sensor for measuring the reducing power, and which is intended to control the quantity of air introduced by the air feeding device. 
   
   
       19 . An installation according to  claim 16 , characterized in that the preheating and heating chambers are adjacent and collinear. 
   
   
       20 . An installation according to  claim 16 , characterized in that it further comprises a device for introducing post-combustion air between the preheating and heating chambers, the quantity of air introduced by this device being sufficient for the preheating chamber to contain gases with no reducing power.