EP0971192B1 - Improvements in or relating to heating furnaces for iron and steel products - Google Patents

Abstract

A heating furnace reheats batches of iron steel products, which differ in their thermal state, introduced in succession into the furnace. The furnace has heating zones followed by at least two equalization zones, the products passing through at least one of these zones, at a speed different from that of the other zones. This speed can be adjusted depending on the thermal objective for the products to be reheated, and at least one of these zones is used as a heating zone.

Description

The present invention relates to a reheating of steel products to reduce or eliminate losses of production during reheating of batches of different products introduced successively in the oven.

US 3,304,210 relates to a method for reheating billets with limitation of their decarburization. This process consists of heating the billets at slow speed up to a temperature of the order of 600 ° C. then, above this temperature, the transfer of billets is accelerated in order to limit their residence time in a area where decarburization occurs. Reducing the residence time of the billets in the oven is provided to limit the chemical reactions taking place on the surface some products. This document does not discuss the problem of rolling after a reheating furnace and possible production losses when reheating lots of different products.

Indeed, we know that reheating ovens are intended to carry, to temperatures required for rolling, steel products such as slabs, blooms, billets, sketches or any other semi-finished steel product.

It is also known that rolling, depending on the nature of the process used or of the final thickness of the finished product to be obtained, requires heat treatment and precise hardness of the product to be laminated. This hardness depends, for a metal of given chemical composition, the temperature to which the product has been heated.

• la température moyenne du produit et,
• l'homogénéité de température du produit, par exemple entre sa face supérieure, son centre et sa face inférieure.

The product temperatures required by the rolling operations are characterized by:

• the average temperature of the product and,
• the temperature uniformity of the product, for example between its upper face, its center and its lower face.

The precision of the thermal state of the products (average temperature and homogeneity temperature) is imperative for the quality of the rolling of steels, in particular high carbon steels, stainless steels, ferritic steels and austenitics, silicon steels, etc.

The average temperature level is obtained by passing the products through so-called heating zones which are characterized by thermal input important which generates a large thermal heterogeneity in the products.

The temperature uniformity of the products reaches the desired levels thanks to the passage of said products, for a controlled period, in an equalization zone in which the heat input is very low, which makes it possible to obtain the homogenization of temperatures within the products.

• une inertie thermique importante du four qui limite les changements rapides de la température de ce dernier et,
• le nombre limité des zones de régulation du four qui, notamment pour des raisons de construction, ne permet pas un contrôle précis des températures sur toute la longueur du four.

At present, the known reheating furnaces for steel products, before rolling, are characterized by:

• a significant thermal inertia of the oven which limits rapid changes in the temperature of the latter and,
• the limited number of furnace control zones which, in particular for construction reasons, do not allow precise temperature control over the entire length of the furnace.

• température d'enfournement,
• dimensions ou formes et
• nuances d'acier, ou des lots de produits différents, en particulier pour leur objectif de thermique de réchauffage caractérisé par :

• leur température de défournement,
• l'homogénéité de la température de défournement,
• la présence de traces noires,
• les pertes au feu,
• le fluage,
• la décarburation,ou
• le traitement thermique.

These two characteristics of known reheating ovens limit the flexibility of these ovens as well as their capacity to heat, in an uninterrupted manner, batches of different products, in particular, for their physical characteristics of:

• charging temperature,
• dimensions or shapes and
• steel grades, or lots of different products, in particular for their thermal reheating objective characterized by:

• their charging temperature,
• homogeneity of the charging temperature,
• the presence of black marks,
• fire losses,
• creep,
• decarburization, or
• heat treatment.

Figure 1 of the accompanying drawings is a diagram illustrating an example of reheating of two batches of products with target temperatures different. This diagram represents the discharge temperatures as a function of the time.

As can be seen in this diagram, the products of the first batch must be reheated at a temperature T1 and the products of the second batch must be reheated to a temperature T2. Products 1 to 5 belonging to the first batch are sold to instants t1 to t5 after being heated to a temperature which is located in the temperature tolerance range T1. Likewise, products 8 to 13 forming part of the second batch are discharged at times t8 to t13, after having been heated to a temperature within the tolerance range of temperature T2.

Products 6 and 7, supplied in the time range between t5 and t8 have a temperature that is outside the tolerances of the temperatures T1 and T2 and therefore cannot be placed in the first batch, nor in the second batch and they must therefore be downgraded or discarded. In order to avoid such a loss of material, at the present time, the products 6 and 7, outside tolerances, when the oven is placed in the oven. As a result, the locations of these products constitute what should be called a "hole" in the oven load. The presence of this hole causes a discontinuity in the charging and in the feed rate of the rolling mill positioned downstream of the furnace, between instants t5 and t8, which results in a loss of production which corresponds to the time interval between two thermal products acceptable.

The principle set out above with reference to FIG. 1 for a temperature of T2 charging higher than the T1 charging temperature can be transposed in case the temperature T2 is lower than T1. During the passage time of the temperature T1 at temperature T2, it will be necessary to provide "holes" in the load so as to remove the products whose thermal situation does not correspond to the first batch, nor to the second batch.

The principle set out above for temperature changes between two batches of products can also be transposed to all adjustment changes of an oven resulting from a modification of one or more characteristics physical products from a first batch to a different second batch or a modification of their thermal objectives.

The "holes" constitute physical separations between the different lots. They allow time for the oven zones to pass from the one batch area at the next batch zone temperature.

• la différence entre les états thermiques du premier et du deuxième lot est grande,
• la précision de l'état thermique requise pour les produits de chaque lot au défournement est élevée,
• l'inertie du four est importante et,
• le mode de fonctionnement par lot est fréquent.

The holes have the drawback of causing significant production losses which are all the more significant as:

• the difference between the thermal states of the first and second batch is large,
• the accuracy of the thermal state required for the products in each batch when it is loaded is high,
• the inertia of the oven is important and,
• the batch mode of operation is frequent.

• l'une au moins pouvant être traversée par les produits à une vitesse différente de celle des autres zones, cette vitesse étant réglable en fonction de l'objectif thermique des produits à réchauffer,
• l'une au moins pouvant être utilisée comme zone de chauffage.

Starting from this state of the art, the invention proposes to make improvements to a furnace for reheating steel products making it possible to reduce or eliminate the losses of production during the reheating of batches of products whose thermal state is different , introduced successively into the oven, these improvements being characterized in that said oven comprises heating zones followed by at least two equalization zones:

• at least one which can be crossed by the products at a speed different from that of the other zones, this speed being adjustable as a function of the thermal objective of the products to be heated,
• at least one of which can be used as a heating zone.

The present invention applies more particularly to a furnace for reheating billets, blooms, slabs, blanks or any other semi-finished steel products.

According to a preferred embodiment of the invention, at least two zones are provided successive equalization at least one of which can be used to homogenization of product temperature.

Figure 2 of the accompanying drawings illustrates the operating principle of an oven provided improvements which are the subject of the present invention. This figure is a diagram on which the bed of products has been represented in the oven opposite the one or more heating zones and at least two designated equalization zones zone E1 and zone E2 respectively following the heating zone or zones. This diagram refers to an example of operation of the oven during a passage of a first batch of products designated by references 1 to 10 to a second batch of products referenced 11 to 23.

The difference in setting the oven zones for reheating the products of the first and second batch may be imposed by one or more differences between the physical characteristics of the products of these two lots, by a difference between the thermal objectives of the products or by a difference with regard to the needs of rolling equipment located downstream of the furnace.

The diagram in FIG. 2 refers to an example of operation of the oven relating to reheating two batches of products: the first batch being reheated to one temperature T1 and the second batch being heated to a temperature T2, the temperature T2 being higher than temperature T1. The skilled person will understand that this principle is easily transposable to the operation of the oven for any adjustment change related to the heating of products whose physical characteristics or thermal objectives are different.

As will be seen below, according to the present invention, the length is optimized "holes" in the loading of the oven between two batches of lens products different temperatures, depending on the characteristics of the oven, products and rate of delivery, without creating discontinuity of delivery of oven products, therefore loss of production.

la partie (1) se réfère à la configuration d'un lot de produits similaires introduits dans le four, tous les produits 1-10 se déplaçant à une vitesse identique et suivant une courbe de température similaire pendant leur traversée du four. Tous les produits du lot sont réchauffés jusqu'à la fin de la zone E1 et égalisés lors de leur traversée de la zone E2. La zone E1 se comporte donc comme une zone de chauffage pour les produits de ce lot.Le cadencement du défournement est constant pour alimenter le laminoir placé en aval du four : dans cet exemple, le produit désigné par la référence 10 est prêt à être défourné.

les parties (2) et (3) présentent l'instant du changement de lot de produits à l'enfournement. Une interruption du chargement des produits constitue un « trou » dans le chargement entre le dernier produit du premier lot désigné par la référence 1 et le premier produit du deuxième lot désigné par la référence 11. La longueur de ce « trou » parfaitement visible sur la figure 2, peut être supérieure ou inférieure à la longueur de la zone d'égalisation E2. Cette longueur est définie en fonction de la différence entre les objectifs thermiques des produits du premier lot et ceux du second lot et en fonction de l'inertie du four. Le cadencement du défournement des produits reste constant avec le défournement des produits désignés par les références 8 et 7 qui ont suivi une courbe de température adaptée à leur objectif thermique.

la partie (4) du schéma de la figure 2 montre comment s'effectue le déplacement du « trou » en fonction de l'avance du lit de produits dans le four. Le « trou » permet d'adapter les températures des zones du four aux objectifs thermiques des produits du premier et du second lot.

la partie (5) représente l'arrivée du premier produit du second lot désigné par la référence 11, à la fin de la zone de chauffage. Les consignes de la zone E1 sont alors modifiées afin de répondre au besoin thermique des produits du second lot.

la partie (6) représente la position du lit de produits dans le four lorsque les produits du deuxième lot pénètrent dans la zone E1 pour y être homogénéisés. L'état thermique de ces produits sera conforme à l'objectif thermique fixé à la fin de cette zone. Le cadencement du défournement des produits reste constant avec le défournement du dernier produit du premier lot, désigné par la référence 1, qui a suivi une courbe de température adaptée à son objectif thermique.

la partie (7) de la figure 2 illustre l'arrivée du premier produit du second lot, désigné par la référence 11, à la fin de la zone d'égalisation E1. Les produits du deuxième lot ont subi un réchauffage qui a amené les premiers produits de ce lot désignés par les références 11 et 12 dans un état proche de leur objectif thermique. La zone d'homogénéisation E2 est vide de tout produit et les consignes de cette zone E2 peuvent être modifiées de manière à répondre aux besoins thermiques des produits du deuxième lot.

la partie (8) représente la situation des produits du deuxième lot à l'extrémité de la zone E1. Pour conserver le cadencement de défournement des produits, il serait nécessaire d'avancer rapidement le lit de produits dans le four afin de placer le produit désigné par la référence 11 en position de défournement. Cette avance rapide des produits entraíne le déplacement des premiers produits du deuxième lot dans la zone E2 dont le réglage ne correspond pas à ces produits, ainsi que la diminution du temps de séjour des produits situés dans le four. L'avance rapide des produits dans le four entraíne une dégradation de l'état thermique des produits qui sont situés dans les zones de chauffage ou dans la zone d'égalisation E2. Afin d'éviter ce problème, l'invention prévoit d'utiliser des systèmes mécaniques assurant un transfert rapide des produits dans la ou les dernières zones du four, afin de contrôler l'incidence de cette zone sur l'état thermique du produit transféré, ou afin de limiter ou de supprimer les pertes de production malgré la présence des « trous » dans le chargement du four. De même, on prévoit des systèmes mécaniques permettant de défourner rapidement des produits afin de contrôler l'incidence de la ou des dernières zones du four sur l'état thermique du procédé. Dans l'exemple illustré par le schéma de la figure 2, de tels équipements thermiques de transfert rapide sont utilisés pour défourner le produit désigné par la référence 11, ce transfert rapide permettant de maintenir la cadence du défournement du four qui réchauffe les produits du deuxième lot, conformément à l'objectif thermique fixé.Selon la présente invention, ce transfert thermique rapide d'un ou de plusieur produits peut être obtenu grâce à :

• un dispositif de défournement à longue course qui vient saisir le produit à la jonction des zones E1 et E2 afin de l'extraire du four ;
• un équipement mécanique de transfert des produits dans le four dont le tronçon correspondant à la zone E2 est animé de mouvements indépendants des autres tronçons constituant les autres zones du four. Le tronçon de l'équipement mécanique de transfert de la zone E2 permet un déplacement rapide d'un produit à défourner sur toute la longueur de la zone E2 de manière à placer ce produit dans une position autorisant son évacuation par la machine de défournement. Le défournement du produit peut s'effectuer de façon frontale ou latérale par rapport au four.

Des exemples de réalisation non limitatifs de ces équipements mécaniques seront décrits ci-après en référence aux figures 4 et 5 des dessins annexés. Bien évidemment, on peut utiliser tout autre dispositif équivalent.

la partie (9) du schéma de la figure 2 illustre un exemple de fonctionnement du four durant toute la période où les conditions thermiques de la zone d'égalisation E2 sont incompatibles avec les objectifs des produits du deuxième lot. Durant cette période, les produits désignés par les références 12 et 13 sont rapidement défournés par les équipements mécaniques qui sont prévus dans ce but dans la zone E2, comme mentionné ci-dessus, afin d'alimenter le laminoir. Après chaque défournement de produit, les systèmes de supportage et de transfert des produits qui sont prévus dans la ou les zones de chauffage et dans la zone E1 (et qui seront décrits ci-après en référence aux figures 4 et 5) déplacent le lit de produits du four jusqu'à amener un produit en position d'attente en fin de zone E1. Dans cet exemple, le produit désigné par la référence 14 occupe cette position d'attente.

la partie (10) se réfère au fonctionnement du four lorsque les conditions thermiques de la zone d'égalisation E2 sont devenues compatibles avec les objectifs thermiques des produits du deuxième lot.

Still referring to Figure 2:

part (1) refers to the configuration of a batch of similar products introduced into the oven, all products 1-10 moving at an identical speed and following a similar temperature curve during their passage through the oven. All the products in the batch are reheated until the end of zone E1 and equalized when they cross zone E2. The E1 zone therefore behaves like a heating zone for the products in this batch. The timing of the discharge is constant to supply the rolling mill placed downstream of the oven: in this example, the product designated by the reference 10 is ready to be discharged .

parts (2) and (3) present the moment of the change of batch of products in the oven. An interruption in the loading of products constitutes a "hole" in the loading between the last product of the first batch designated by the reference 1 and the first product of the second batch designated by the reference 11. The length of this "hole" perfectly visible on the Figure 2, may be greater or less than the length of the equalization area E2. This length is defined according to the difference between the thermal objectives of the products of the first batch and those of the second batch and according to the inertia of the oven. The timing of the product discharge remains constant with the discharge of the products designated by the references 8 and 7 which have followed a temperature curve adapted to their thermal objective.

part (4) of the diagram in FIG. 2 shows how the "hole" is displaced as a function of the advance of the bed of products in the oven. The "hole" makes it possible to adapt the temperatures of the oven zones to the thermal objectives of the products of the first and second batch.

part (5) represents the arrival of the first product of the second batch designated by the reference 11, at the end of the heating zone. The instructions in zone E1 are then modified in order to meet the thermal requirement of the products of the second batch.

the part (6) represents the position of the bed of products in the oven when the products of the second batch enter the zone E1 to be homogenized there. The thermal state of these products will comply with the thermal objective set at the end of this zone. The timing of product discharge remains constant with the discharge of the last product in the first batch, designated by the reference 1, which has followed a temperature curve adapted to its thermal objective.

part (7) of FIG. 2 illustrates the arrival of the first product of the second batch, designated by the reference 11, at the end of the equalization zone E1. The products of the second batch underwent reheating which brought the first products of this batch designated by the references 11 and 12 in a state close to their thermal objective. The homogenization zone E2 is empty of any product and the instructions of this zone E2 can be modified so as to meet the thermal requirements of the products of the second batch.

the part (8) represents the situation of the products of the second batch at the end of the zone E1. To maintain the timing of product discharge, it would be necessary to rapidly advance the bed of products in the oven in order to place the product designated by the reference 11 in the discharge position. This rapid advance of the products causes the movement of the first products of the second batch in the E2 area whose setting does not correspond to these products, as well as the reduction of the residence time of the products located in the oven. The rapid advance of the products in the oven leads to a degradation of the thermal state of the products which are located in the heating zones or in the equalization zone E2. In order to avoid this problem, the invention provides for the use of mechanical systems ensuring rapid transfer of the products into the last zone or zones of the furnace, in order to control the impact of this zone on the thermal state of the transferred product, or in order to limit or eliminate production losses despite the presence of "holes" in the loading of the oven. Likewise, mechanical systems are provided for rapidly discharging products in order to control the impact of the last zone or zones of the furnace on the thermal state of the process. In the example illustrated by the diagram in FIG. 2, such rapid transfer thermal equipment is used to unload the product designated by the reference 11, this rapid transfer making it possible to maintain the rate of unloading of the oven which heats the products of the second batch, in accordance with the fixed thermal objective. According to the present invention, this rapid thermal transfer of one or more products can be obtained by:

• a long-stroke discharge device which grasps the product at the junction of zones E1 and E2 in order to extract it from the oven;
• mechanical equipment for transferring products into the oven, the section of which corresponds to zone E2 is driven by movements independent of the other sections constituting the other areas of the oven. The section of the mechanical transfer equipment of the zone E2 allows rapid movement of a product to be discharged over the entire length of the zone E2 so as to place this product in a position allowing its evacuation by the discharge machine. The product can be discharged frontally or sideways relative to the oven.

Non-limiting exemplary embodiments of this mechanical equipment will be described below with reference to Figures 4 and 5 of the accompanying drawings. Obviously, any other equivalent device can be used.

part (9) of the diagram in FIG. 2 illustrates an example of operation of the oven during the whole period when the thermal conditions of the equalization zone E2 are incompatible with the objectives of the products of the second batch. During this period, the products designated by the references 12 and 13 are quickly discharged by the mechanical equipment which is provided for this purpose in the zone E2, as mentioned above, in order to supply the rolling mill. After each product discharge, the support and product transfer systems which are provided in the heating zone (s) and in the zone E1 (and which will be described below with reference to FIGS. 4 and 5) move the bed of products from the oven until a product is brought to the standby position at the end of zone E1. In this example, the product designated by the reference 14 occupies this waiting position.

the part (10) refers to the operation of the oven when the thermal conditions of the equalization zone E2 have become compatible with the thermal objectives of the products of the second batch.

The equalization zone E2 is used for the homogenization of the temperatures of the products of the second batch, the equalization zone E1 being used, either for equalization, ie for the end of product heating.

The transfer of the products of the second batch in zone E2 is carried out in one or several times to ensure the maintenance of the thermal objective of the products of the second batch within the previously defined tolerances.

We now refer to Figures 3 to 5 illustrating exemplary embodiments of mechanical systems used to translate the products into the zone E2 of the oven.

La figure 3 est une vue schématique en élévation latérale d'un four conventionnel pour le réchauffage de produits sidérurgiques auquel s'applique la présente invention.

La figure 4 est une vue similaire à la figure 3 illustrant un système permettant de réaliser les fonctions de l'invention définie ci-dessus et,

la figure 5 est une vue similaire aux figures 3 et 4 illustrant un autre dispositif pour la réalisation des fonctions de l'invention.

In these figures:

Figure 3 is a schematic side elevational view of a conventional furnace for heating steel products to which the present invention applies.

FIG. 4 is a view similar to FIG. 3 illustrating a system making it possible to carry out the functions of the invention defined above and,

Figure 5 is a view similar to Figures 3 and 4 illustrating another device for performing the functions of the invention.

Referring to Figure 3 we see that in an oven according to the technique traditional, the products to be reheated designated by the reference 1 are treated in an insulated enclosure 2 using burners shown schematically in 3. The products are supported and transferred over the entire length of the oven using fixed and mobile beams designated by the reference 4. The mobile beams are integral with a frame 5 allowing their movement in horizontal translation, the whole resting on a system consisting of a beam 6 resting itself on rollers which can move on wedges in the form of an inclined plane, this system as being designed to allow lifting movement of mobile side rails. The translational movement of the products is obtained using a cylinder 7 acting on the chassis 5, while the lifting movement is obtained by means of a jack 8 moving the chassis 6 along planes inclined. In such an oven, the entire bed of products such as 1 rests on a unique support / transfer equipment, all bed products moving at the same speed and the same distance, with each movement of said equipment.

According to the present invention, the functions which have been mentioned in the description made above are carried out using mechanical systems which ensure rapid transfer of the products, in the last zone or zones of the oven, these mechanical systems being able moreover to ensure a rapid discharge of the produced by frontal or lateral evacuation.

We now refer to Figure 4 which illustrates a first embodiment a device for performing the functions of the invention. These measures essentially comprises arms designated by the reference 10 and actuated by a device 11 for entering the products. The arms such as 10 are therefore located substantially at the level of the side members supporting and transferring the products. In the example illustrated by the drawing, the product to be turned around designated by the reference 9 is located at the end of the equalization zone (E1) in FIG. 2 and it is grasped by the arms 10 of so as to be removed from the oven in a single operation in order to carry out the feeding of the rolling mill (not shown in the drawing). Thus, this system allows for a rapid transfer of the products to the last zone of the oven as well as their fast feed, in order to control the incidence of the last zone (s) of the oven on the thermal state of the product. Note that the charging system consisting of the arms 10 and their actuating device 11, can be arranged to so as to ensure a front or side discharge of the oven, of a product seized by said system inside the oven, at a given point in its thermal cycle in view its discharge outside the oven, for example to a rolling mill (not shown in the drawing).

We now refer to Figure 5 which illustrates another embodiment a mechanical device making it possible to carry out the functions of the invention.

In this embodiment, an independent supporting and supporting section is provided. transfer of products inside the oven, this section allowing movement of the or products supported at a speed independent of that of the products

Claims (8)

1. Furnace for heating iron and steel products with a view to reducing or elimination production losses during the heating of batches of products having a different thermal state and successively introduced into the furnace, characterized in that said furnace comprises heating zones followed by at least two equalizing zones (E1, E2) :

   where at least the first equalizing zone (E1) can be used as a heating zone,

   where at least the last equalizing zone (E2) can be traversed by the products at a speed different from that of the other zones, said speed being regulatable as a function of the thermal objective of the products to be heated.
2. Furnace according to claim 1, characterized in that said heating furnace is used for heating billets, blooms, slabs, blanks and other semifinished iron and steel products.
3. Furnace according to claim 1, characterized in that said furnace comprises at least two successive equalizing zones, at least one of which is used to ensure the homogenization of the temperature of the products.
4. Furnace according to any one of the preceding claims, characterized in that said furnace is equipped with mechanical systems (10, 11; 12, 15, 16) ensuring the rapid transfer of the products (9; 13) into the final zone or zones of the furnace.
5. Furnace according to claim 4, characterized in that said mechanical systems (10, 11; 12, 15) also ensure a rapid drawing of the products.
6. Furnace according to one of the claims 4 or 5, characterized in that said mechanical systems (10, 11; 12, 15) are implemented so as to ensure a front or side discharge of a product grasped within the furnace at a given point of its thermal cycle with a view to its discharge to the outside of the furnace.
7. Furnace according to any one of the claims 4 to 6, characterized in that said mechanical systems have arms (10) for gripping the products and means (11) for actuating said arms.
8. Furnace according to any one of the claims 4 to 6, characterized in that said mechanical systems are implemented in the form of an independent section (12) for supporting and transferring products within the furnace, said section ensuring a displacement of the products at a speed independent of that of the products supported and transferred by the other sections of the furnace.

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