EP0379104A1 - Process for annealing metal work pieces in a hydrogen-enriched protective atmosphere in a continuous furnace - Google Patents

Process for annealing metal work pieces in a hydrogen-enriched protective atmosphere in a continuous furnace Download PDF

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Publication number
EP0379104A1
EP0379104A1 EP90100679A EP90100679A EP0379104A1 EP 0379104 A1 EP0379104 A1 EP 0379104A1 EP 90100679 A EP90100679 A EP 90100679A EP 90100679 A EP90100679 A EP 90100679A EP 0379104 A1 EP0379104 A1 EP 0379104A1
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Prior art keywords
hydrogen
gas
furnace
protective gas
continuous furnace
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EP90100679A
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German (de)
French (fr)
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EP0379104B1 (en
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Reinhard Dipl.-Ing. Strigl
Alexander Dipl.-Ing. Jurmann
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Linde Gas AG
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Linde GmbH
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C21D9/54—Furnaces for treating strips or wire
    • C21D9/56—Continuous furnaces for strip or wire
    • C21D9/562—Details
    • C21D9/565—Sealing arrangements
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material

Definitions

  • the invention relates to a method for annealing metal parts under a hydrogen-rich protective gas in a continuous furnace.
  • the object of the present invention is therefore to design a method for annealing metal parts under hydrogen gas or hydrogen-rich protective gas in continuous furnaces so that the need for protective gas can be reduced as far as possible without other negative phenomena, such as air entry or the formation of white dust , to cause.
  • This object is achieved in that at the leakage openings of the continuous furnace, for example and in particular at the furnace inlet and outlet, gas with a higher density than hydrogen is blown in and thus admixed with the protective gas located there, while otherwise the hydrogen-rich atmosphere in the continuous furnace is carried out according to the Heat treatment is maintained.
  • the protective gas atmosphere is maintained in terms of composition and pressure by the fact that the addition of protective gas is regulated based on the measurement of the internal furnace pressure and in such a way that a defined pressure curve, for example a constant pressure value, for example between 3 - 5 mbar internal furnace pressure, is maintained.
  • the aim of saving shielding gas according to the invention is achieved in an automated manner, because, as already stated, the furnace pressure rises after the admixing gases have been supplied and the quantity of protective gas has remained constant. This supply quantity is now reduced due to the pressure-induced control and thus less protective gas is consumed.
  • the withdrawal of the shielding gas quantity may, however, only extend so far that other parameters important for the shielding gas atmosphere, e.g. the ratio H2 / H2O (oxidation equilibrium), should not be undercut. In critical cases, this can be monitored by another sensor and included in the control.
  • the addition of the admixing gases only in the vicinity of the leakage openings also means that practically no admixing gas, in particular no nitrogen, reaches the main areas of the continuous furnace, which limits the formation of white dust.
  • the admixing gases are blown into the leak cross sections with a higher density than hydrogen in the area of the leak openings in the direction of the furnace exterior. This ensures that a particularly efficient mixing of the admixing gases with the protective gas takes place and only a minimal proportion of the Additive gases are introduced into the main areas of the continuous furnace. This procedure could also be described as the supply of a mixed pulse towards the outside of the furnace.
  • Figure 1 shows a continuous furnace for annealing steel strips.
  • a steel strip 5 is guided through the furnace by means of rollers 6, which successively consists of an inlet area 1, an annealing area 2, a cooling area 3 and an outlet area 4.
  • a protective gas supply line 7 e.g. with a heat treatment with a pure H2 atmosphere, a hydrogen supply line.
  • devices 8, ⁇ ' for carrying out the method according to the invention.
  • nitrogen is blown in toward the exterior of the furnace in the area of the essential leak cross-sections through which the protective gas leaves the system.
  • nitrogen feeds 8, ⁇ 'are provided which are shown in detail in Figure 2, which represents a section along the line A-A of Figure 1.
  • Figure 2 shows the inlet area of the continuous furnace with the steel belt 5 schematically in cross section.
  • bores 10 are directed obliquely downwards with respect to the plane of the drawing, that is to say they are oriented towards the outside of the furnace into the entry gap of the steel strip 5, which represents an essential leak opening.
  • nitrogen is specifically introduced into the column to the side next to the running sheet metal strip 5 and on one side over the entire width of the inlet gap, and the effects desired according to the invention are thus achieved.
  • the entry or exit area of a strip annealing furnace can also be configured with guide rollers 21, 22.
  • the sheet metal strip 5 runs between the rollers 21, 22 into the continuous annealing furnace.
  • felt strips 25, 26 are provided between the outer walls 23, 24 and the rollers 21, 22 of this arrangement, and the rollers have end plates 27 on their faces, both in the gaps 28 formed next to the sheet metal strip and in the areas 29 outside of the end plates 27, admixing gas is blown into the leak cross sections via feed lines 30, 31.
  • the procedure according to the invention takes place as follows for the overall sequence with regard to the heat treatment to be carried out:
  • the furnace pressure is measured via a pressure sensor 35 installed in the continuous furnace.
  • the admixture of a certain amount of the admixing gas in the leak cross sections causes the pressure in the furnace to rise after the admixture has started.
  • This increase is determined by means of the pressure sensor and the protective gas addition is subsequently reduced by means of a suitably programmed control unit 36, which is coupled to a control valve 37 arranged in the protective gas supply line 7, and the pressure is maintained as desired.
  • the pressure is expediently set approximately constant at a level to be determined in the control loop method. This means that the amount of protective gas required for the heat treatment is significantly reduced.
  • the need for a hydrogen atmosphere can be reduced below the need for a process with NH3-cracked gas, in which one works without the inventive or other saving devices.
  • the formation of white dust is also reduced in the case of pure hydrogen atmospheres.
  • the pressure of the annealing process via the furnace pressure
  • the amount of admixing gas added is also another variable that can be varied when performing annealing processes.
  • the process according to the invention additionally increases the safety for processes with hydrogen-rich atmospheres, since the risk of ignition is reduced due to the reduced hydrogen content of the protective gas escaping.
  • the proposed method is therefore a particularly advantageous embodiment of a heat treatment with hydrogen-rich protective gas, in which substantial savings in treatment gas are achieved through the use of small amounts of a further gas.

Abstract

The invention relates to a process for annealing metal work pieces in a protective hydrogen gas in a furnace, wherein, to reduce the amount of protective gas required and as an additional process parameter, gas with a higher density than hydrogen is blown into the leakage openings of the continuous furnace, for example and in particular at the inlet (11) and outlet (4) of the furnace and is thus mixed with the protective gas situated there, whereas in the rest of the continuous furnace the hydrogen-enriched protective atmosphere is maintained in accordance with the heat treatment to be carried out. <IMAGE>

Description

Die Erfindung betrifft ein Verfahren zum Glühen von Metallteilen unter wasserstoffreichem Schutzgas in einem Durchlaufofen.The invention relates to a method for annealing metal parts under a hydrogen-rich protective gas in a continuous furnace.

In der DE 37 33 884 A1 ist ein Verfahren zum Glühen von Metallteilen unter einer im wesentlichen aus Wasserstoff bestehenden Schutzgasatmosphäre vorgeschlagen. Dabei besteht folgende Problematik: Das Glühen mit einer Wasserstoffatmosphäre in einem Durchlaufofen ist verhältnismäßig kostspielig, da Wasserstoff einerseits ein vergleichsweise teures Schutzgas darstellt und andererseits aufgrund des kontinuierlichen Verfahrens­ablaufs mit ständig oder periodisch geöffneten Austritts­möglichkeiten eine große Mengen davon aus dem Durchlaufofen verloren gehen.DE 37 33 884 A1 proposes a method for annealing metal parts under a protective gas atmosphere consisting essentially of hydrogen. The problem here is as follows: Annealing with a hydrogen atmosphere in a continuous furnace is relatively expensive, since hydrogen is a comparatively expensive shielding gas on the one hand, and on the other hand a large amount of it is lost from the continuous furnace due to the continuous process flow with continuously or periodically opened discharge options.

Diesbezüglich ist es bekannt, die Austrittsverluste von Schutzgas durch schleusenartige Vorrichtungen am Ofeneintritt und -austritt der Anlage zu verringern. In einer günstigen Variante geschieht dies beispielsweise derart, daß in die Schleusenkammern an Eintritt und Austritt des Durchlaufofens ständig Stickstoff eingeleitet wird und so die Austrittsverluste von Wasserstoff aus dem Ofen verringert werden.In this regard, it is known to reduce the leakage losses of protective gas by means of lock-type devices at the furnace inlet and outlet of the system. In In a favorable variant, this is done, for example, in such a way that nitrogen is continuously introduced into the lock chambers at the inlet and outlet of the continuous furnace, thus reducing the loss of hydrogen from the furnace.

Neben der jetzt beschriebenen Rein-Wasserstoff-Wärme­behandlung sind Wärmebehandlungen und Glühverfahren bekannt, die mit einer aus Ammoniak erzeugten Schutzgasatmosphäre arbeiten. Diese Atmosphäre wird durch Spaltung von Ammoniak (NH₃) erzeugt und enthält mit 75 Vol-% Wasserstoff und 25 Vol-% Stickstoff einen sehr hohen Wasserstoffanteil. Mit diesem Schutzgas und dieser Schutzgasherstellung werden auch viele Wärmebehandlungs­verfahren durchgeführt, wobei für diese in Durchlauföfen wiederum besonders hohe Gasmengen notwendig sind.In addition to the pure hydrogen heat treatment now described, heat treatments and annealing processes are known which work with a protective gas atmosphere generated from ammonia. This atmosphere is generated by cleavage of ammonia (NH₃) and contains a very high proportion of hydrogen with 75 vol% hydrogen and 25 vol% nitrogen. Many heat treatment processes are also carried out with this protective gas and this protective gas production, which in turn requires particularly high amounts of gas in continuous furnaces.

Darüber hinaus sind viele Wärmebehandlungen bekannt, die auf der Basis von getrennt vorhandenen Einzelgasen arbeiten und bei denen beim Anwender vor Ort beliebig zusammengesetzte, sogenannte synthetische Schutzgase hergestellt werden. Davon sind für die hier in Rede stehende Erfindung im wesentlichen die Wärmebehandlungs­verfahren mit mehr als 50 % Wasserstoffanteil im Schutzgas von Bedeutung. Diese Verfahren sind im vorliegenden Zusammenhang als Verfahren mit wasserstoffreichen Schutzgasatmosphären anzusehen und bei diesen besteht ebenfalls das Bestreben, die Verluste an Schutzgas so niedrig wie möglich zuhalten.In addition, many heat treatments are known that work on the basis of separate individual gases and in which the user can produce so-called synthetic protective gases of any composition on site. Of these, the heat treatment processes with more than 50% hydrogen content in the protective gas are essentially of importance for the invention in question. In the present context, these processes are to be regarded as processes with hydrogen-rich protective gas atmospheres, and there is also an attempt to keep the losses of protective gas as low as possible.

Insbesondere bei den Verfahren bei denen eine reine Wasserstoff-Atmosphäre angestrebt wird tritt noch ein weiteres Problem insbesondere dann wieder in den Vordergrund, wenn ein- und ausgangsseitig am Durchlaufofen Schleusen angeordnet sind und diese mit Stickstoff gespült werden, da dabei auch Stickstoff in die Hauptbereiche des Durchlaufofens eindringt. Das Eindringen von Stickstoff in besagte Zonen einer derartige Anlage bewirkt nämlich unter Umständen die Bildung eines sogenannten weißen Staubes, die im folgenden zur Verminderung der Abkühlleistung in der Kühlzone aufgrund der Verstopfung der dort befindlichen Wärmetauscher führt (diese Problematik siehe im Einzelnen in der obengenannten Patentanmeldung oder Stahl und Eisen/107, März 1987/Nr.6, Seiten 267 - 273, insbesondere Seite271, rechte Spalte, unten). Deshalb ergibt sich bei diesen Wasserstoff-Wärmebehandlungen die Problematik, entweder einen hohen Wasserstoffverbrauch ohne Stickstoffschleusen in Kauf zu nehmen oder die Bildung des weißen Staubes in verstärktem Maß zu akzeptieren.In particular in the case of processes in which a pure hydrogen atmosphere is sought, a further problem arises in particular again Foreground if locks are arranged on the inlet and outlet sides of the continuous furnace and these are flushed with nitrogen, since nitrogen also penetrates into the main areas of the continuous furnace. The penetration of nitrogen into said zones of such a system may cause the formation of a so-called white dust, which subsequently leads to a reduction in the cooling capacity in the cooling zone due to the blockage of the heat exchangers located there (for this problem, see in detail in the above-mentioned patent application or Stahl und Eisen / 107, March 1987 / No. 6, pages 267 - 273, especially page 271, right column, below). Therefore, with these hydrogen heat treatments there is the problem of either accepting high hydrogen consumption without nitrogen locks or accepting the formation of white dust to an increased extent.

Die Aufgabenstellung der vorliegenden Erfindung besteht deshalb darin, ein Verfahren zum Glühen von Metallteilen unter Wasserstoffgas oder wasserstoffreichem Schutzgas in Durchlauföfen so zu gestalten, daß der Bedarf an Schutzgas möglichst weit abgesenkt werden kann, ohne andere negative Erscheinungen, wie Lufteintritt oder die Bildung von weißem Staub, zu verursachen.The object of the present invention is therefore to design a method for annealing metal parts under hydrogen gas or hydrogen-rich protective gas in continuous furnaces so that the need for protective gas can be reduced as far as possible without other negative phenomena, such as air entry or the formation of white dust , to cause.

Diese Aufgabe wird erfindungsgemäß dadurch gelöst, daß bei den Lecköffnungen des Durchlaufofens, beispielsweise und insbesondere am Ofeneintritt und -austritt, Gas mit höherer Dichte als Wasserstoff eingeblasen wird und somit dem dort befindlichen Schutzgas zugemischt wird, während ansonsten im Durchlaufofen die wasserstoffreiche Atmosphäre gemäß der durchzuführenden Wärmebehandlung aufrecht erhalten wird.This object is achieved in that at the leakage openings of the continuous furnace, for example and in particular at the furnace inlet and outlet, gas with a higher density than hydrogen is blown in and thus admixed with the protective gas located there, while otherwise the hydrogen-rich atmosphere in the continuous furnace is carried out according to the Heat treatment is maintained.

Diese Vorgehensweise beruht auf der Erkenntnis, daß die Durchflußmenge Q eines Gases durch eine LeckÖffnung,aus einem mit Überdruck ΔP betriebenen Ofen, von der Dichte d des durchfließenden Gases wie folgt abhängt:
Q = f (d) = A *( 1/d * 2 Δp )1/2
(A = Ofenkonstante).This procedure is based on the knowledge that the flow rate Q of a gas through a leak opening from an oven operated with excess pressure ΔP depends on the density d of the gas flowing through as follows:
Q = f (d) = A * (1 / d * 2 Δp) 1/2
(A = furnace constant).

Da es sich bei wasserstoffreichen Atmosphären um Gase niedriger Dichte handelt, ergibt sich für Wasserstoff und wasserstoffreiche Gasgemische eine sehr große Durchflußmenge und deshalb im Fall von Wärmebehandlungen mit solchen Schutzgasen große Schutzgasverluste. Bringt man in die Umgebung solcher Lecköffnungen, beispielsweise in den Querschnitt der Lecköffnungen, im Sinne der Grundidee der vorliegenden Erfindung Gase höherer Dichte als Wasserstoff ein, z. B. Stickstoff, Argon oder auch SF₆ und andere, so wird das Schutzgas in diesem Bereich mit dem zugeführten Gas gemischt, wodurch sich die Dichte des entstehenden Gasgemisches erhöht und die Durchfluß­menge durch die Lecköffnung unter der Voraussetzung eines gleichbleibenden Ofendrucks entsprechend sinkt. Daraus resultiert, daß insgesamt weniger Schutzgas bei gleichen Druckverhältnissen die Wärmebehandlungsanlage verläßt oder sich bei gleichbleibender Schutzgasmengenzugabe ein Druckanstieg in der Wärmebehandlungsanlage ergibt.Since hydrogen-rich atmospheres are low-density gases, there is a very large flow rate for hydrogen and hydrogen-rich gas mixtures and therefore, in the case of heat treatments with such protective gases, large losses of protective gas. If one brings in the vicinity of such leak openings, for example in the cross section of the leak openings, in the sense of the basic idea of the present invention, gases of higher density than hydrogen, for. B. nitrogen, argon or SF₆ and others, the protective gas is mixed in this area with the supplied gas, which increases the density of the resulting gas mixture and the flow rate through the leakage opening correspondingly decreases provided a constant furnace pressure. The result of this is that overall less protective gas leaves the heat treatment system at the same pressure conditions, or there is an increase in pressure in the heat treatment system with the same amount of protective gas added.

Hiermit ergibt sich eine besonders vorteilhafte Ausgestaltung der vorliegenden Erfindung, nämlich daß die Aufrechterhaltung der Schutzgasatmosphäre im Hinblick auf Zusammensetzung und Druck dadurch erfolgt, daß die Zugabe an Schutzgas basierend auf der Messung des Ofeninnendrucks geregelt wird und zwar so, daß ein festgelegter Druckverlauf, z.B. ein konstanter Druckwert, etwa zwischen 3 - 5 mbar Ofeninnendruck, eingehalten wird.This results in a particularly advantageous embodiment of the present invention, namely that the protective gas atmosphere is maintained in terms of composition and pressure by the fact that the addition of protective gas is regulated based on the measurement of the internal furnace pressure and in such a way that a defined pressure curve, for example a constant pressure value, for example between 3 - 5 mbar internal furnace pressure, is maintained.

Mit dieser druckgesteuerten Schutzgas-Zufuhr wird das erfindungsgemäße Ziel der Schutzgaseinsparung in automatisierter Weise erreicht, denn, wie bereits festgestellt, steigt der Ofendruck nach Zufuhr der Zumischgase und gleichbleibender Zufuhrmenge von Schutzgas an. Diese Zufuhrmenge wird nun aufgrund der druckinduzier­ten Steuerung verringert und somit weniger Schutzgas verbraucht. Die Zurücknahme der Schutzgasmenge darf dabei jedoch höchstens soweit reichen, daß andere, für die Schutzgasatmosphäre wichtige Parameter, z.B. das Verhältnis H₂/H₂O (Oxidationsgleichgewicht), nicht unterschritten werden. Dies kann in kritischen Fällen durch einen weiteren Sensor überwacht und in die Steuerung und Regelung miteinbezogen werden.With this pressure-controlled shielding gas supply, the aim of saving shielding gas according to the invention is achieved in an automated manner, because, as already stated, the furnace pressure rises after the admixing gases have been supplied and the quantity of protective gas has remained constant. This supply quantity is now reduced due to the pressure-induced control and thus less protective gas is consumed. The withdrawal of the shielding gas quantity may, however, only extend so far that other parameters important for the shielding gas atmosphere, e.g. the ratio H₂ / H₂O (oxidation equilibrium), should not be undercut. In critical cases, this can be monitored by another sensor and included in the control.

Grundsätzlich wird durch die Zugabe der Zumischgase nur in der Umgebung der Lecköffnungen darüber hinaus erreicht, daß praktisch kein Zumischgas, insbesondere kein Stickstoff, in die Hauptbereiche des Durchlaufofens gelangt, was die Bildung von weißem Staub einschränkt.In principle, the addition of the admixing gases only in the vicinity of the leakage openings also means that practically no admixing gas, in particular no nitrogen, reaches the main areas of the continuous furnace, which limits the formation of white dust.

In einer besonders vorteilhaften Ausgestaltung werden die Zumischgase mit höherer Dichte als Wasserstoff im Bereich der Lecköffnungen mit Richtung zum Ofenäußeren hin in die Leckquerschnitte eingeblasen. Dadurch wird erreicht, daß eine besonders effiziente Mischung der Zumischgase mit dem Schutzgas stattfindet und nur ein minimaler Anteil der Zumischgase in die Hauptbereiche des Durchlaufofens eingeschleppt wird. Man könnte diese Vorgehensweise auch als die Zufuhr eines Mischimpulses mit Richtung zum Ofenäußeren bezeichnen.In a particularly advantageous embodiment, the admixing gases are blown into the leak cross sections with a higher density than hydrogen in the area of the leak openings in the direction of the furnace exterior. This ensures that a particularly efficient mixing of the admixing gases with the protective gas takes place and only a minimal proportion of the Additive gases are introduced into the main areas of the continuous furnace. This procedure could also be described as the supply of a mixed pulse towards the outside of the furnace.

Anhand der schematischen Zeichnungen soll das erfindungsgemäße Verfahren im folgenden beispielhaft näher erläutert werden.

  • Figur 1 zeigt das Schema eines Durchlaufofens zum Glühen von Stahlbändern mit erfindungsgemäßen Einrichtungen an Ofenein- und -austritt,
  • Figur 2 zeigt einen erfindungsgemäßen Ofeneintritt im Detail,
  • Figur 3 zeigt einen Ofeneintritt mit Führungsrollen.
The method according to the invention is to be explained in more detail below by way of example with reference to the schematic drawings.
  • FIG. 1 shows the diagram of a continuous furnace for annealing steel strips with devices according to the invention at the furnace inlet and outlet,
  • FIG. 2 shows a furnace inlet according to the invention in detail,
  • Figure 3 shows an oven inlet with guide rollers.

Figur 1 zeigt einen Durchlaufofen zum Glühen von Stahlbändern. Ein Stahlband 5 wird mittels Rollen 6 durch den Ofen geführt, der aufeinanderfolgend aus einem Einlaufbereich 1, einem Glühbereich 2, einem Abkühl­bereich 3 und einem Auslaufbereich 4 besteht. Zwischen Glühbereich 2 und Abkühlbereich 3 ist eine Schutzgas­zuleitung 7, also z.B. bei einer Wärmebehandlung mit reiner H₂-Atmosphäre eine Wasserstoffzuleitung, angeordnet. Im Eintrittsbereich 1 und Austrittsbereich 4 befinden sich Einrichtungen 8, ϑ′ zur Durchführung des erfindungsgemäßen Verfahrens.Figure 1 shows a continuous furnace for annealing steel strips. A steel strip 5 is guided through the furnace by means of rollers 6, which successively consists of an inlet area 1, an annealing area 2, a cooling area 3 and an outlet area 4. Between the annealing area 2 and the cooling area 3 there is a protective gas supply line 7, e.g. with a heat treatment with a pure H₂ atmosphere, a hydrogen supply line. In the entry area 1 and exit area 4 there are devices 8, ϑ 'for carrying out the method according to the invention.

Im Rein-Wasserstoff-Betrieb wird also über die Zuleitung 7 Wasserstoff in den Durchlaufofen eingeleitet. Im Vergleich zum Betrieb mit Ammoniakspaltgas oder einem entsprechenden synthetischen Gasgemisch aus 75 % Wasserstoff und 25 % Stickstoff erhöht sich allein durch den Einsatz reinen Wassersstoffs die benötigte, einzuleitende Menge Schutzgas bei ansonsten gleichen Bedingungen deutlich, da reiner Wasserstoff eine geringere Dichte als das eben genannte Gasgemisch besitzt. Insbesondere bei Reinwasserstoff­atmosphären jedoch auch bei wasserstoffreichen Atmosphären ist deshalb der Einsatz des vorliegenden Verfahrens vorteilhaft.In pure hydrogen operation, hydrogen is thus introduced into the continuous furnace via the feed line 7. Compared to operation with ammonia cracked gas or a corresponding synthetic gas mixture of 75% hydrogen and 25% Nitrogen increases the required amount of protective gas to be introduced under otherwise identical conditions solely through the use of pure hydrogen, since pure hydrogen has a lower density than the gas mixture just mentioned. The use of the present method is therefore advantageous in particular in pure hydrogen atmospheres, but also in hydrogen-rich atmospheres.

Erfindungsgemäß wird nun im Bereich der wesentlichen Leckquerschnitte, durch die Schutzgas die Anlage verläßt, Stickstoff in Richtung zum Ofenäußeren hin eingeblasen. Dazu sind Stickstoffzuführungen 8, ϑ′ vorgesehen, die in Figur 2, welche einen Schnitt entsprechend der Linie A-A aus Figur 1 darstellt, im Detail gezeigt sind. Die Figur 2 zeigt also den Einlaufbereich des Durchlaufofens mit dem Stahlband 5 schematisch im Querschnitt. Mit der Stickstoffzufuhreinrichtung 8 ist quer eine an beiden Enden verschlossene Röhre 9 verbunden, die auf ihrem Umfang etwa auf einer Längslinie mit Bohrungen 10 versehen ist (sogenannter Düsenstock). Diese Bohrungen 10 sind in Bezug zur Zeichenebene schräg nach unten gerichtet, also in Richtung zum Ofenäußeren in den Eintrittsspalt des Stahlbandes 5 hinein ausgerichtet, der ja eine wesentliche Lecköffnung darstellt. Es wird also gemäß Figur 2 speziell in die Spalte seitlich neben dem laufenden Blechband 5 und einseitig auf der gesamten Eintrittsspaltbreite Stickstoff eingeführt und somit die erfindungsgemäß erwünschten Effekte erreicht.According to the invention, nitrogen is blown in toward the exterior of the furnace in the area of the essential leak cross-sections through which the protective gas leaves the system. For this purpose, nitrogen feeds 8, ϑ 'are provided, which are shown in detail in Figure 2, which represents a section along the line A-A of Figure 1. Figure 2 shows the inlet area of the continuous furnace with the steel belt 5 schematically in cross section. A tube 9, which is closed at both ends and which is provided with holes 10 on its circumference approximately on a longitudinal line (so-called nozzle assembly), is connected transversely to the nitrogen supply device 8. These bores 10 are directed obliquely downwards with respect to the plane of the drawing, that is to say they are oriented towards the outside of the furnace into the entry gap of the steel strip 5, which represents an essential leak opening. According to FIG. 2, nitrogen is specifically introduced into the column to the side next to the running sheet metal strip 5 and on one side over the entire width of the inlet gap, and the effects desired according to the invention are thus achieved.

Insbesondere der Eintritts- oder auch der Austrittsbereich eines Bandglühofens kann auch mit Führungsrollen 21, 22 ausgestaltet sein. Dies ist in Figur 3 ebenfalls in einer Querschnittsdraufsicht dargestellt. Das Blechband 5 läuft zwischen den Rollen 21, 22 in den Durchlaufglühofen ein. Zur Abdichtung dieser Anordnung sind zwischen den Außenwänden 23, 24 und den Rollen 21, 22 dieser Anordnung Filzstreifen 25, 26 vorgesehen und die Rollen besitzen an ihren Stirnseiten Abschlußscheiben 27. Sowohl in die neben dem Blechband entstehenden Spalten 28 als auch in die Bereiche 29 außerhalb der Abschlußscheiben 27 wird Zumischgas über Zuleitungen 30, 31 in die Leckquerschnitte eingeblasen.In particular, the entry or exit area of a strip annealing furnace can also be configured with guide rollers 21, 22. This is also in one in FIG Cross-sectional top view shown. The sheet metal strip 5 runs between the rollers 21, 22 into the continuous annealing furnace. To seal this arrangement, felt strips 25, 26 are provided between the outer walls 23, 24 and the rollers 21, 22 of this arrangement, and the rollers have end plates 27 on their faces, both in the gaps 28 formed next to the sheet metal strip and in the areas 29 outside of the end plates 27, admixing gas is blown into the leak cross sections via feed lines 30, 31.

Vom Gesamtablauf im Hinblick auf die durchzuführende Wärmebehandlung erfolgt das erfindungsgemäße Vorgehen wie folgt: Über einen im Durchlaufofen angebrachten Drucksensor 35 wird der Ofendruck gemessen. Die Zumischung einer bestimmten Menge des Zumischgases in den Leckquer­schnitten bewirkt ein Ansteigen des Drucks im Ofen nach Beginn der Zumischung. Dieser Anstieg wird mittels des Drucksensors festgestellt und in der Folge wird die Schutzgaszugabe mittels einer entsprechend programmierten Regeleinheit 36, die mit einem in der Schutzgaszuleitung 7 angeordneten Regelventil 37 gekoppelt ist, vermindert und so der Druck wie gewünscht gehalten. Im Ganzen wird der Druck günstigerweise im Regelkreis-Verfahren etwa konstant auf einem festzulegenden Niveau eingestellt. Daraus ergibt sich, daß die für die Wärmebehandlung notwendige Schutzgasmenge deutlich verringert ist. Beispielsweise kann der Bedarf bei einer Wasserstoffatmosphäre unter den Bedarf bei einem Verfahren mit NH₃-Spaltgas gesenkt werden, bei dem ohne die erfindungsgemäße oder andere einsparende Einrichtungen gearbeitet wird. Ebenso wird im Falle von Rein-Wasserstoff-Atmosphären die Bildung von weißem Staub verringert.The procedure according to the invention takes place as follows for the overall sequence with regard to the heat treatment to be carried out: The furnace pressure is measured via a pressure sensor 35 installed in the continuous furnace. The admixture of a certain amount of the admixing gas in the leak cross sections causes the pressure in the furnace to rise after the admixture has started. This increase is determined by means of the pressure sensor and the protective gas addition is subsequently reduced by means of a suitably programmed control unit 36, which is coupled to a control valve 37 arranged in the protective gas supply line 7, and the pressure is maintained as desired. Overall, the pressure is expediently set approximately constant at a level to be determined in the control loop method. This means that the amount of protective gas required for the heat treatment is significantly reduced. For example, the need for a hydrogen atmosphere can be reduced below the need for a process with NH₃-cracked gas, in which one works without the inventive or other saving devices. The formation of white dust is also reduced in the case of pure hydrogen atmospheres.

Neben einer Drucksteuerung des Glühverfahrens über den Ofendruck, ist insbesondere auch eine Steuerung über den Wasserstoffgehalt im Austrittsgas oder die Austritts­geschwindigkeit des Austrittsgases aus der betreffenden Lecköffnung möglich. Die Zugabemenge an Zumischgas stellt darüber hinaus für sich selbst eine weitere regelbare Größe dar, die bei der Durchführung von Glühverfahren variiert werden kann.In addition to controlling the pressure of the annealing process via the furnace pressure, it is also possible in particular to control the hydrogen content in the exit gas or the exit speed of the exit gas from the leak opening in question. The amount of admixing gas added is also another variable that can be varied when performing annealing processes.

Aus dem erfindungsgemäßen Verfahren ergibt sich als Nebeneffekt zusätzlich eine Steigerung der Sicherheit für Verfahren mit wasserstoffreichen Atmosphären, da aufgrund des erniedrigten Wasserstoffgehalts des austretenden Schutzgases die Entzündungsgefahr vermindert ist.As a side effect, the process according to the invention additionally increases the safety for processes with hydrogen-rich atmospheres, since the risk of ignition is reduced due to the reduced hydrogen content of the protective gas escaping.

Das vorgeschlagene Verfahren ist also eine besonders vorteilhafte Ausgestaltung einer Wärmebehandlungen mit wasserstoffreichem Schutzgas, bei dem durch den Einsatz geringer Mengen eines weiteren Gases wesentliche Einsparungen an Behandlungsgas erreicht werden.The proposed method is therefore a particularly advantageous embodiment of a heat treatment with hydrogen-rich protective gas, in which substantial savings in treatment gas are achieved through the use of small amounts of a further gas.

Claims (4)

1. Verfahren zum Glühen von Metallteilen unter wasserstoffreichem Schutzgas in einem Durchlaufofen, dadurch gekennzeichnet, daß bei den Lecköffnungen des Durchlaufofens, beispielsweise und insbesondere am Ofeneintritt und -austritt, Gas mit höherer Dichte als Wasserstoff eingeblasen wird und somit dem dort befindlichen Schutzgas zugemischt wird, während im übrigen im Durchlaufofen die wasserstoffreiche Schutzgas-Atmosphäre gemäß der durchzuführenden Wärme­behandlung aufrecht erhalten wird.1. A process for the annealing of metal parts under hydrogen-rich protective gas in a continuous furnace, characterized in that gas with a higher density than hydrogen is blown in at the leakage openings of the continuous furnace, for example and in particular at the furnace inlet and outlet, and is thus admixed with the protective gas located there. while in the continuous furnace the hydrogen-rich protective gas atmosphere is maintained according to the heat treatment to be carried out. 2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die Aufrechterhaltung der Schutzgasatmosphäre dadurch erfolgt, daß die Zugabe an Schutzgas basierend auf der Messung des Ofeninnendrucks geregelt wird und zwar so, daß ein festgelegter Druckverlauf, der abhängig ist von Betriebsart und Produkt, eingehalten wird.2. The method according to claim 1, characterized in that the maintenance of the protective gas atmosphere takes place in that the addition of protective gas is regulated based on the measurement of the internal furnace pressure and in such a way that a predetermined pressure curve, which is dependent on the operating mode and product, is maintained . 3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß das Gas mit höherer Dichte als Wasserstoff mit Richtung zum Ofenäußeren hin in die jeweilige Lecköffnungen des Durchlaufofens eingeblasen wird.3. The method according to claim 1 or 2, characterized in that the gas is injected with higher density than hydrogen in the direction of the furnace exterior into the respective leak openings of the continuous furnace. 4. Verfahren nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß soviel Gas höherer Dichte eingeblasen wird, daß der Anteil dieses Gases im ausfließenden Gas mehr als 25% beträgt.4. The method according to any one of claims 1 to 3, characterized in that so much gas of higher density is blown in that the proportion of this gas in the outflowing gas is more than 25%.
EP90100679A 1989-01-17 1990-01-13 Process for annealing metal work pieces in a hydrogen-enriched protective atmosphere in a continuous furnace Expired - Lifetime EP0379104B1 (en)

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AT90100679T ATE96467T1 (en) 1989-01-17 1990-01-13 PROCESS FOR ANNEALING METAL PARTS UNDER HYDROGEN-RICH INert GAS IN A CONTINUOUS FURNACE.

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DE3901215 1989-01-17
DE3901215 1989-01-17
DE3926417A DE3926417A1 (en) 1989-01-17 1989-08-10 METHOD FOR GLOWING METAL PARTS UNDER HYDROGEN PROTECTIVE GAS IN A CONTINUOUS OVEN
DE3926417 1989-08-10

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JP2601378B2 (en) * 1991-03-13 1997-04-16 日新製鋼株式会社 Method and apparatus for recovering atmosphere gas of heat treatment furnace
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DE59003173D1 (en) 1993-12-02
JPH02228420A (en) 1990-09-11
DE3926417A1 (en) 1990-07-19

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