EP0632842A1 - Heat treatment process for metal articles. - Google Patents

Heat treatment process for metal articles.

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Publication number
EP0632842A1
EP0632842A1 EP93907835A EP93907835A EP0632842A1 EP 0632842 A1 EP0632842 A1 EP 0632842A1 EP 93907835 A EP93907835 A EP 93907835A EP 93907835 A EP93907835 A EP 93907835A EP 0632842 A1 EP0632842 A1 EP 0632842A1
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EP
European Patent Office
Prior art keywords
zone
heated
temperature zone
articles
burners
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP93907835A
Other languages
German (de)
French (fr)
Other versions
EP0632842B1 (en
Inventor
Hans-Georg Bittner
Hartmut Weber
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Heimsoth Verwaltungen & Co KG Beteiligungsge GmbH
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Heimsoth Verwaltungen GmbH and Co KG
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Publication of EP0632842A1 publication Critical patent/EP0632842A1/en
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Classifications

    • 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
    • C21D9/0056—Furnaces through which the charge is moved in a horizontal straight path
    • 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
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B9/00—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity
    • F27B9/02—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity of multiple-track type; of multiple-chamber type; Combinations of furnaces
    • F27B9/028—Multi-chamber type furnaces
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B9/00—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity
    • F27B9/30—Details, accessories, or equipment peculiar to furnaces of these types
    • F27B9/36—Arrangements of heating devices
    • F27B2009/3638—Heaters located above and under the track

Definitions

  • the invention relates to the heat treatment of metallic material in a roller furnace, in particular of relatively thin steel parts, such as ball bearing rings, sheet blanks, knives and the like, which warp easily when heated.
  • a device for heat treating metallic material (DE-PS 31 50 576) is known, in which annealing racks are arranged on a roller conveyor, which in turn have been fitted with the metallic parts in the individual compartments.
  • the glow racks equipped with the metallic material pass through an oven.
  • metal parts which have a longitudinal dimension in the cm range and a small thickness in the m range, have not distorted after the heat treatment.
  • the invention is concerned with the problem of enabling heat treatment of metal parts, in which the metal parts do not warp and only marginal edge decarburization phenomena and insignificant edge oxidation or scale formation phenomena occur.
  • the temperature gradient immediately above the roller conveyor is so small that the metal parts located there cannot warp.
  • a temperature distribution can only be achieved with a one heated directly with high-speed burners Roller furnace can be reached.
  • this cannot be achieved in a roller oven with sole upper heating or when using annealing aids or annealing racks.
  • ceramic and carbon-free rollers are advantageously used according to the invention, which have sufficient heat resistance.
  • pittings do not occur since no contact of hot metal with hot metal occurs during the annealing process, but rather the steel parts rest on the ceramic rollers.
  • metal rollers are predominantly used, which is only possible if a relatively great effort is made for the air or water cooling of the rollers.
  • the burners are operated in the high temperature range, for example during heat treatment for hardening steel, the so-called austenitizing range, without excess air.
  • the burners are set in such a way that a protective gas can indeed be dispensed with.
  • metal parts of this type are easily scaled on the surface, with a layer thickness in the range of approximately 0.01-0.03 mm.
  • This edge scaling has no influence on the product quality, on the contrary, the scaling prevents the metal parts from carburizing or decarburizing, so that a uniform structure is achieved after the heat treatment and only an edge decarburization of approx. 0.01 - 0.03 mm occurs.
  • This slight decarburization or scaling is common approved, since surface treatment must generally be carried out in subsequent work steps.
  • the metal parts are conveyed through the roller furnace at different speeds.
  • the speed depends on the thickness of the metal material to be heat-treated, and when a temperature of approximately 850 ° C. is reached, the parts to be heat-treated are transported at a higher speed.
  • the residence time of the metals in the region of higher temperatures can be limited to a time period which does not permit any noticeable carburization or decarburization processes.
  • the metal parts are finally transported at an even higher speed. After passing through the high temperature zone, the hot material is removed from the oven very quickly.
  • baffles In the roller furnace for carrying out the method according to the present invention, no doors are required in the inlet and outlet, instead so-called baffles can also be worked there, with one or more baffles being located one behind the other at the outlet.
  • the oven can be heated up and down in a short time. Since the temperature field directly above the rollers can be spatially constant in the method according to the invention, it is possible to treat metal parts with different dimensions at the same time, especially if the thickness of these parts is not significantly different.
  • the temperature can also be made more uniform by using pulse burners or high-speed burners which can be set with a constant gas-air mixture and can also be operated in a clocked manner.
  • the metal annealing furnace for carrying out the method according to the invention is divided into several zones which meet the following conditions:
  • the temperature of the goods should be brought as evenly as possible to approx. 800 - 850 ° C. Uniformity is important here, so this zone can also be divided into several areas, in each of which the temperature should be raised to a certain level.
  • the problem with thin and large round blanks is that the temperature outside takes on the temperature of the environment faster than inside. If the ambient temperature were now too high, this temperature would quickly set up on the outside, but this would not be the case on the inside and a considerable difference from inside to outside would result in the part being warped.
  • the slow increase in temperature also makes the structure of the metal part more uniform, so that a kind of stress relief annealing takes place.
  • the next step is to reach the final temperature, which can be up to 1200 ... 1250 ° C for steel. It is important that this temperature is maintained as precisely as possible, for example with +/- 1 K or at most +/- 5 K. Changes in this temperature, which should be kept as constant as possible, lead to changes in hardness and an undesired structure.
  • an atmosphere with free oxygen is used, whereas in the high-temperature zone there is no longer any free oxygen, but on the contrary, a reducing atmosphere, such as CO.
  • a scaling takes place in the oxygen-containing atmosphere.
  • steel is scaled in an oxygen-containing atmosphere, this leads to a scale layer that is very easy to remove from the surface, which can be easily removed or chipped.
  • a reducing atmosphere were present in the initial phase, a so-called layer of adhesive scale would form, which cannot be easily removed.
  • more complex mechanical processing operations have to be carried out and / or acids or alkalis have to be used, which is highly undesirable. Since the dwell time of the workpiece at high temperature is now very limited, i.e. much shorter than that at low temperatures in the preheating zone of the furnace, the scale layer can only increase slightly, especially because there is no free oxygen left , just the reducing atmosphere.
  • the temperature in the high temperature range can be kept constant with a small tolerance.
  • this arrangement of the rollers and roller baffles below the roller conveyor enables a higher temperature (e.g. 20 K more) to be regulated to +/- 1K than above.
  • the single figure shows a diagrammatic longitudinal view of a roller furnace for carrying out the method according to the invention.
  • a roller furnace is shown schematically, the roller conveyor being clearly visible through the cross-sectional representation of the rollers.
  • the inlet is on the left and the outlet on the right, the direction of transport for the parts to be treated is indicated by an arrow.
  • the furnace consists of three spatially separated zones I, II and III.
  • zone I the unheated preheating zone, here the furnace gas is taken up and discharged via a chimney 10.
  • air is blown in via inlet 11 to set the temperature curve.
  • the burners are above and below the
  • roller conveyor shown schematically. In zone III, the
  • a quick draw is located after the high temperature zone.
  • zone I the material to be heat-treated is warmed up - evenly from the inside out.
  • Zone II includes the further heating of the goods until the high temperature limit is reached.
  • zone III the metal parts finally reach the high-temperature range in which, for example, steel is subjected to austenitization.
  • the burners of zones II and III can be controlled in groups, above and below the roller conveyor, in order to obtain the desired temperature profile.
  • S is used to indicate height-adjustable baffles in order to separate the individual zones from each other in terms of heat.

Landscapes

  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Thermal Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • General Engineering & Computer Science (AREA)
  • Heat Treatment Of Articles (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)
  • Tunnel Furnaces (AREA)
  • Heat Treatments In General, Especially Conveying And Cooling (AREA)

Abstract

PCT No. PCT/EP93/00741 Sec. 371 Date Apr. 26, 1994 Sec. 102(e) Date Apr. 26, 1994 PCT Filed Mar. 26, 1993 PCT Pub. No. WO93/20248 PCT Pub. Date Oct. 14, 1993.A heat treatment process in a roll type furnace for metal articles, in which the articles are heated in stages up to 800 DEG -850 DEG C. in several pre-heating zones with atmospheres containing free oxygen; the articles are heated in a high temperature zone in a reducing atmosphere containing no free oxygen and run through this zone relatively quickly; the burners of the high temperature zone are timed with high and low power periods, depending on the quantity of articles supplied and the amount of heat to be transmitted; rolls of the furnace are set in the high temperature zone at a short distance from each other; and baffle plates between the zones are set at the smallest possible distance from the rolling track or the articles on the rolling track. The burners are located above and below the rolling track.

Description

Verfahren zur Wärmebehandlung von metallis chem Gut . Process for the heat treatment of metallic chemicals.
Die Erfindung bezieht sich auf die Wärmebehandlung von metallischem Gut in einem Rollenofen, insbesondere von relativ dünnen, sich bei Erwärmung leicht verziehenden Stahlteilen, wie beispielsweise Kugellagerringen, Blechronden , Messer und dergleichen .The invention relates to the heat treatment of metallic material in a roller furnace, in particular of relatively thin steel parts, such as ball bearing rings, sheet blanks, knives and the like, which warp easily when heated.
Es ist eine Vorrichtung zum Wärmebehandeln von metallischem Gut (DE-PS 31 50 576) bekannt , bei welcher auf einer Rollenbahn Glühgestelle angeordnet werden, die ihrerseits in den einzelnen Fächern mit den metallischen Teilen bestückt worden sind . Die mit dem metallischen Gut bestückten Glühgestelle durchlaufen einen Ofen . Es kann jedoch kaum erreicht werden, daß sich Metallteile, die eine Längsabmessung im cm-Bereich und eine geringe Dicke im m -Bereich haben, nach der Wärmebehandlung nicht bleibend verzogen haben .A device for heat treating metallic material (DE-PS 31 50 576) is known, in which annealing racks are arranged on a roller conveyor, which in turn have been fitted with the metallic parts in the individual compartments. The glow racks equipped with the metallic material pass through an oven. However, it can hardly be achieved that metal parts, which have a longitudinal dimension in the cm range and a small thickness in the m range, have not distorted after the heat treatment.
Darüber hinaus ist es bislang üblich im Zusammenhang mit der Wärmebehandlung von Metallteilen solche Öfen einzusetzen, die eine Schutzgasatmosphäre aufweisen und teilweise elektrisch beheizt sind, um zu verhindern, daß sich beispielsweise der Kohlenst o f f geha lt der Meta l lt e i le während de s Wärmebehandlungsvorganges ändert bzw . die Metallteile aufoxidieren. Bei den meisten Metallteilen ist jedoch weder die Aufkohlung noch die Entkohlung noch die Aufoxidation erwünscht.In addition, it has hitherto been customary in connection with the heat treatment of metal parts to use furnaces which have a protective gas atmosphere and are partially electrically heated in order to prevent, for example, the carbon content of the metal from changing during the heat treatment process respectively . the metal parts oxidize. For most metal parts, however, carburization, decarburization and oxidation are not desirable.
Die Erfindung befaßt sich mit dem Problem, eine Wärmebehandlung von Metallteilen zu ermöglichen, bei der die Metallteile sich nicht verziehen und lediglich unerhebliche Randauf- bzw. Randentkohlungserscheinungen sowie unbedeutende Randaufoxidations- bzw. Randzunderbildungserscheinungen auftreten.The invention is concerned with the problem of enabling heat treatment of metal parts, in which the metal parts do not warp and only marginal edge decarburization phenomena and insignificant edge oxidation or scale formation phenomena occur.
Erreicht wird dies durch ein Verfahren der eingangs genannten Art,* welches dadurch gekennzeichnet ist, daß das metallische Gut in mehreren Vorwärmzonen (I, II) mit Atmosphären mit freiem Sauerstoff stufenweise auf bis 800...850 °C erwärmt wird, danach das metallische Gut in einer Hochtemperaturzone (III) mit einer reduzierenden Atmosphäre, die keinen freien Sauerstoff enthält, erwärmt wird und diese Zone relativ schnell durchläuft, die Brenner der Hochtemperaturzone (III) je nach angelieferter Menge an metallischem Gut bzw. zu übertragener Wärmemenge kurz oder länger getaktet werden, und daß die Rollen in der Hochtemperaturzone (III) mit geringem Abstand zueinander und die Schikanen (S, US) zwischen den Zonen (I, II, III) auf möglichst kleine Abstände zur Rollenbahn bzw. dem Metallgut auf der Rollbahn eingestellt werden, wobei sich Brenner oberhalb und unterhalb der Rollenbahn befinden.This is achieved by a process of the type mentioned at the beginning, * which is characterized in that the metallic material is heated in several preheating zones (I, II) with atmospheres with free oxygen in stages to up to 800 ... 850 ° C, then the metallic Good in a high-temperature zone (III) with a reducing atmosphere that does not contain free oxygen, is heated and passes through this zone relatively quickly, the burners of the high-temperature zone (III) are cycled for a short or longer time depending on the amount of metallic material delivered or the amount of heat to be transferred and that the rollers in the high-temperature zone (III) are set close to each other and the baffles (S, US) between zones (I, II, III) are set as close as possible to the roller conveyor or the metal material on the roller conveyor, with burners located above and below the roller conveyor.
Bei dem Verfahren gemäß der Erfindung ist zunächst einmal der Temperaturgradient unmittelbar oberhalb der Rollenbahn so gering, daß die sich dort befindlichen Metallteile nicht verziehen können. Eine solche Temperaturverteilung kann aber nur mit einem direkt mit Hochgeschwindigkeitsbrennern beheizten Rollenofen erreicht werden. In einem Rollenofen mit alleiniger Oberbeheizung jedoch oder bei dem Einsatz von Glühhilfsmitteln oder Glühgestellen kann dies nicht erreicht werden.In the method according to the invention, the temperature gradient immediately above the roller conveyor is so small that the metal parts located there cannot warp. However, such a temperature distribution can only be achieved with a one heated directly with high-speed burners Roller furnace can be reached. However, this cannot be achieved in a roller oven with sole upper heating or when using annealing aids or annealing racks.
Im Zusammenhang mit der Glühbehandlung von Stahlteilen werden gemäß der Erfindung vorteilhafterweise keramische und kohlenstofffreie Rollen eingesetzt, die eine ausreichende Wärmestandfestigkeit haben. Darüber hinaus kann dadurch auch erreicht werden, daß die unter dem Ausdruck "pittings" bekannten Erscheinungen nicht auftreten, da keine Berührung von heißem Metall mit heißem Metall während des Glühvorganges auftritt, sondern die Stahlteile auf den Keramikrollen aufliegen. Bei bekannten Rollenöfen für die wärmebehandelnde Metallindustrie werden überwiegend Metallrollen eingesetzt, was nur möglich ist, wenn ein relativ großer Aufwand für die Luft¬ bzw. Wasserkühlung der Rollen getrieben wird.In connection with the annealing treatment of steel parts, ceramic and carbon-free rollers are advantageously used according to the invention, which have sufficient heat resistance. In addition, it can also be achieved that the phenomena known under the term "pittings" do not occur since no contact of hot metal with hot metal occurs during the annealing process, but rather the steel parts rest on the ceramic rollers. In the case of known roller furnaces for the heat-treating metal industry, metal rollers are predominantly used, which is only possible if a relatively great effort is made for the air or water cooling of the rollers.
Um den Sauerstoffgehalt im Ofen möglichst gering zu halten werden die Brenner im Hochtemperaturbereich, zum Beispiel beim Wärmebehandeln zum Härten von Stahl, dem sogenannten Austenitisierungsbereich, ohne Luftüberschuß betrieben. Beim Verfahren gemäß der vorliegenden Erfindung werden die Brenner also derartig eingestellt, daß in der Tat auf ein Schutzgas verzichtet werden kann. Dies liegt darin begründet, daß derartige Metallteile an der Oberfläche leicht verzundern, und zwar mit einer Schichtdicke im Bereich von ca. 0.01 - 0.03 mm. Diese Randverzunderung hat keinen Einfluß auf die Produktqualität, im Gegenteil wird durch die Verzunderung verhindert, daß die Metallteile auf- bzw. entkohlen, so daß ein gleichmäßiges Gefüge nach der Wärmebehandlung erzielt wird und lediglich eine Randentkohlung von ca. 0.01 - 0.03 mm auftritt. Diese leichte Randentkohlung bzw. Verzunderung wird häufig zugelas sen, da in der Regel in nachges chalteten Arbeitss chritten ohnehin eine Oberflächenbearbeitung durchgeführt werden muß .In order to keep the oxygen content in the furnace as low as possible, the burners are operated in the high temperature range, for example during heat treatment for hardening steel, the so-called austenitizing range, without excess air. In the method according to the present invention, the burners are set in such a way that a protective gas can indeed be dispensed with. The reason for this is that metal parts of this type are easily scaled on the surface, with a layer thickness in the range of approximately 0.01-0.03 mm. This edge scaling has no influence on the product quality, on the contrary, the scaling prevents the metal parts from carburizing or decarburizing, so that a uniform structure is achieved after the heat treatment and only an edge decarburization of approx. 0.01 - 0.03 mm occurs. This slight decarburization or scaling is common approved, since surface treatment must generally be carried out in subsequent work steps.
Bei dem Verfahren gemäß der Erfindung werden die Metallteile mit unterschiedlichen Geschwindigkeiten durch den Rollenofen gefördert . In den unbeheizten Aufheizzonen und der beheizten Aufheiz zone wird mit einer von der D icke des wäremzubehandelnden metallischen Gutes abhängigen Geschwindigkeit gefahren, und bei Erreichen einer Temperatur von ca. 850 °C, werden die mit Wärme zu behandelnden Teile mit einer höheren Geschwindigkeit transportiert . Hierdurch kann die Verweilzeit der Metalle im Bereich höherer Temperaturen auf eine solche Zeitspanne begrenzt werden, die keine merkliche Auf- oder Entkohlungs Vorgänge zuläßt . In der dritten Zone, bei Stahl beispielsweise bei Austenitisierungstemperatur, werden die Metallteile schließlich mit einer noch höheren Geschwindigkeit transportiert . Nach Durchlaufen der Hochtemperaturzone wird das heiße Gut sehr schnell dem Ofen entnommen .In the method according to the invention, the metal parts are conveyed through the roller furnace at different speeds. In the unheated heating zones and the heated heating zone, the speed depends on the thickness of the metal material to be heat-treated, and when a temperature of approximately 850 ° C. is reached, the parts to be heat-treated are transported at a higher speed. As a result, the residence time of the metals in the region of higher temperatures can be limited to a time period which does not permit any noticeable carburization or decarburization processes. In the third zone, for steel, for example, at the austenitizing temperature, the metal parts are finally transported at an even higher speed. After passing through the high temperature zone, the hot material is removed from the oven very quickly.
Bei dem Rollenofen zur Durchführung des Verfahrens gemäß der vorliegenden Erfindung sind keine Türen im Ein- und Auslauf erforderlich, stattdessen kann auch dort mit sogenannten Schikanen gearbeitet werden, wobei sich am Aus lauf eine dicke oder mehrere Schikanen hintereinander befinden.In the roller furnace for carrying out the method according to the present invention, no doors are required in the inlet and outlet, instead so-called baffles can also be worked there, with one or more baffles being located one behind the other at the outlet.
Wird bei der Durchführung des Verfahrens gemäß der Erfindung ein Ofen mit einer leichten feuerfesten Auskleidung, beispielsweise aus Fasermaterialien verwendet, so kann der Ofen in kurzer Zeit auf- und abgeheizt werden. Da das Temperaturfeld unmittelbar oberhalb der Rollen bei dem Verfahren gemäß der Erfindung räumlich konstant eingestellt werden kann, ist es möglich, gleichzeitig Metallteile mit unterschiedlichen Abmessungen zu behandeln, insbesondere wenn die Dicke dieser Teile nicht wesentlich unterschiedlich ist. Die Temperatur kann weiterhin dadurch vergleichmäßigt werden, daß Impulsbrenner oder Hochgeschwindigkeitsbrenner eingesetzt werden, die mit einem konstanten Gas-Luft-Gemisch eingestellt und auch taktend betrieben werden können.If an oven with a light refractory lining, for example made of fiber materials, is used in carrying out the method according to the invention, the oven can be heated up and down in a short time. Since the temperature field directly above the rollers can be spatially constant in the method according to the invention, it is possible to treat metal parts with different dimensions at the same time, especially if the thickness of these parts is not significantly different. The temperature can also be made more uniform by using pulse burners or high-speed burners which can be set with a constant gas-air mixture and can also be operated in a clocked manner.
Der Metallglühofen zur Durchführung des Verfahrens gemäß der Erfindung ist in mehrere Zonen unterteilt, die folgende Bedingungen erfüllen:The metal annealing furnace for carrying out the method according to the invention is divided into several zones which meet the following conditions:
In der ersten Zone, der unbeheizten Vorwärmzone, soll die Temperatur des Gutes möglichst gleichmäßig auf ca. 800 - 850°C gebracht werden. Hier kommt es auf die Gleichmäßigkeit darauf an, daher kann diese Zone auch in mehrere Bereiche unterteilt werden, in denen jeweils die Temperatur auf eine bestimmte Höhe angehoben werden soll. Problematisch ist nämlich bei dünnen und großflächigen Ronden, daß die Temperatur außen schneller die Temperatur der Umgebung als innen annimmt. Wäre nun die Umgebungstemperatur zu hoch, so würde sich zwar außen diese Temperatur schnell einstellen, während innen das jedoch nicht der Fall ist und eine erhebliche Differenz von innen nach außen würde zum Verziehen des Teils führen. Außerdem bewirkt das langsame Erhöhen der Temperatur auch eine Vergleichmäßigung der Struktur des Metallteiles, es findet also eine Art Spannungsfreiglühen statt. Es handelt sich hierbei um Spannungen, die aufgrund irgendeiner Vorbehandlung in dem Werkstück vorhanden ware . In der nachfolgenden Stufe geht es darum, die Endtemperatur zu erreichen, diese kann für Stahl bis zu 1200...1250 °C liegen. Hierbei ist wichtig, daß diese Temperatur möglichst genau eingehalten wird, also beispielsweise mit +/-1 K oder höchstens +/-5 K. Änderungen in dieser möglichst konstant zu haltenden Temperatur führen zu Härteänderungen und einem nicht erwünschten Gefüge.In the first zone, the unheated preheating zone, the temperature of the goods should be brought as evenly as possible to approx. 800 - 850 ° C. Uniformity is important here, so this zone can also be divided into several areas, in each of which the temperature should be raised to a certain level. The problem with thin and large round blanks is that the temperature outside takes on the temperature of the environment faster than inside. If the ambient temperature were now too high, this temperature would quickly set up on the outside, but this would not be the case on the inside and a considerable difference from inside to outside would result in the part being warped. In addition, the slow increase in temperature also makes the structure of the metal part more uniform, so that a kind of stress relief annealing takes place. These are tensions that would be present in the workpiece due to some pretreatment. The next step is to reach the final temperature, which can be up to 1200 ... 1250 ° C for steel. It is important that this temperature is maintained as precisely as possible, for example with +/- 1 K or at most +/- 5 K. Changes in this temperature, which should be kept as constant as possible, lead to changes in hardness and an undesired structure.
In der beheizten Vorwärmzone wird unter einer Atmosphäre mit freiem Sauerstoff gearbeitet, wohingegen in der Hochtemperaturzone kein freier Sauerstoff mehr vorhanden ist, sondern im Gegenteil eine reduzierende Atmosphäre, etwa CO.In the heated preheating zone, an atmosphere with free oxygen is used, whereas in the high-temperature zone there is no longer any free oxygen, but on the contrary, a reducing atmosphere, such as CO.
Hieraus resultieren wiederum folgende Vorteile:This results in the following advantages:
In der sauerstoffhaltigen Atmosphäre findet eine Verzunderung statt. Wenn jedoch Stahl in einer sauerstoffhaltigen Atmosphäre verzundert, so führt dies zu einer sich sehr leicht von der Oberfläche wieder lösenden Zunderschicht, die einfach entfernt werden kann oder absplittert. Wäre hingegen in der Anfangsphase eine reduzierende Atmosphäre vorhanden, so würde sich eine sogenannte Schicht aus Klebzunder bilden, die nicht ohne weiteres entfernt werden kann. Hierzu müssen aufwendigere mechanische Bearbeitungsvorgänge durchgeführt und/oder Säuren oder Laugen eingesetzt werden, was höchst unerwünscht ist. Da sich nun die Verweilzeit des Werkstücks auf hoher Temperatur sehr in Grenzen hält, also wesentlich kürzer ist als die bei niedrigen Temperaturen in der Vorwärmzone des Ofens, kann sich die Zunderschicht nur noch wenig vergrößern, insbesondere auch deshalb, weil kein freier Sauerstoff mehr vorhanden ist, sondern nur die reduzierende Atmosphäre. Das Ergebnis ist eine dünne Zunderschicht am Werkstück, die leicht abplatzt, so daß kein Nacharbeitsvorgang erforderlich ist. Darüber hinaus ergibt sich je nach Temperaturhöhe in der Hochtemperatur auch eine einstellbare und definierte sehr feine Kornverteilung, die ein sehr feines, gleichmäßig verteiltes Gefüge zeigt .A scaling takes place in the oxygen-containing atmosphere. However, if steel is scaled in an oxygen-containing atmosphere, this leads to a scale layer that is very easy to remove from the surface, which can be easily removed or chipped. If, on the other hand, a reducing atmosphere were present in the initial phase, a so-called layer of adhesive scale would form, which cannot be easily removed. For this purpose, more complex mechanical processing operations have to be carried out and / or acids or alkalis have to be used, which is highly undesirable. Since the dwell time of the workpiece at high temperature is now very limited, i.e. much shorter than that at low temperatures in the preheating zone of the furnace, the scale layer can only increase slightly, especially because there is no free oxygen left , just the reducing atmosphere. The result is a thin layer of scale on the workpiece that flakes off easily so that no reworking is required. In addition, depending on the temperature level in the high temperature, there is also an adjustable and defined very fine particle size distribution, which shows a very fine, evenly distributed structure.
Für die Erfindung ist die Unterteilung der beiden Zonen und deren Abgrenzung durch Schikanen von besonderer Bedeutung. Von unten her handelt es sich vorzugsweise um eine gemauerte Schikane, von oben her ist eine aus mehreren Keramikrohren gebildete Trennwand vorgesehen, die auf das gewünschte Abstandsmaß eingestellt werden kann. Schließlich befinden sich auch die einzelnen Rollen, zumindest in der Hochtemperaturzone in einem so geringen Abstand zueinander, daß auch eine Abtrennung des Ober- vom Unterofen realisiert wird. Diese räumliche Abtrennung, die quasi zu einer Art Wärmekammer führt, in die das zu erwärmende Gut eingegeben wird, hat auch noch ihre Bedeutung bei ungleichmäßiger Materialzufuhr. Bei Öfen muß nämlich sehr darauf geachtet werden, daß pro Zeiteinheit möglichst immer die gleiche Masse an Gut zugeführt wird, was man in der Praxis natürlich nicht einhalten kann. In der ersten beheizten Zone ist eine Ungleichmäßigkeit, die allein schon durch Übergang von einem Werkstück auf ein anderes entsteht, von untergeordneter Bedeutung, und in der ersten beheizten Zone des Ofens wird bei schnellen LeistungsSchwankungen ständig die gleiche Wärmemenge eingekoppelt . In der Hochtemperaturphase kann man diesen Weg nicht gehen, dort wird getaktet. Kommt nun viel Material, das erwärmt werden muß in die Hochtemperaturzone, so wird entsprechend länger getaktet. Ist gar kein Material vorhanden, so wird weniger häufig oder gar keine Wärme zugeführt. Diese Ungleichmäßigkeit mit der die Wärme in der Hochtemperaturzone zugegeben wird, könnte bei Öfen ohne Schikanen zu Schwingungsphänomenen führen. Bei dem gemäß der Erfindung verwendeten Ofen, bei dem die Hochtemperaturzone durch Schikanen von dem anderen Bereich des Ofens abgetrennt ist, treten keine solche Schwingungen ein. Vielmehr hat sich herausgestellt, daß die Temperatur im Hochtemperaturbereich mit einer geringen Toleranz konstant gehalten werden kann. Darüber hinaus kann durch diese Anordnung der Rollen und Rollenschikanen unterhalb der Rollenbahn eine höhere Temperatur (z. B. 20 K mehr) auf +/- 1K ausgeregelt gefahren werden als oberhalb.The subdivision of the two zones and their delimitation by chicanes is of particular importance for the invention. From the bottom it is preferably a brick chicane, from the top a partition made of several ceramic tubes is provided, which can be adjusted to the desired distance. Finally, the individual rolls, at least in the high-temperature zone, are located at such a small distance from one another that the upper furnace and the lower furnace are also separated. This spatial separation, which leads to a kind of heat chamber into which the material to be heated is fed, also has its meaning in the case of uneven material supply. In the case of ovens, great care must be taken to ensure that the same mass of goods is always supplied per unit of time, which of course cannot be observed in practice. In the first heated zone, an unevenness that arises simply from the transition from one workpiece to another is of minor importance, and in the first heated zone of the furnace, the same amount of heat is constantly injected in the event of rapid fluctuations in output. You cannot go this route in the high temperature phase, there is clocking. If a lot of material comes into the high-temperature zone that has to be heated, the cycle will be longer. If there is no material at all, heat is applied less frequently or not at all. This unevenness with the If heat is added in the high-temperature zone, this could lead to vibration phenomena in ovens without baffles. In the furnace used according to the invention, in which the high temperature zone is separated from the other region of the furnace by chicaning, no such vibrations occur. Rather, it has been found that the temperature in the high temperature range can be kept constant with a small tolerance. In addition, this arrangement of the rollers and roller baffles below the roller conveyor enables a higher temperature (e.g. 20 K more) to be regulated to +/- 1K than above.
Die Erfindung wird nachstehend anhand der Zeichnung beispielsweise erläutert:The invention is explained below with reference to the drawing, for example:
Die einzige Figur zeigt eine schaubildliche Längsansicht eines Rollenofens zur Durchführung des Verfahrens gemäß der Erfindung.The single figure shows a diagrammatic longitudinal view of a roller furnace for carrying out the method according to the invention.
In der Figur ist ein Rollenofen schematisch wiedergegeben, wobei die Rollenbahn durch die Querschnittsdarstelung der Rollen gut zu erkennen ist. Links befindet sich der Einlauf und rechts der Auslauf, wobei die Transportrichtung für die zu behandelnden Teile mit einem Pfeil angegeben ist.In the figure, a roller furnace is shown schematically, the roller conveyor being clearly visible through the cross-sectional representation of the rollers. The inlet is on the left and the outlet on the right, the direction of transport for the parts to be treated is indicated by an arrow.
Der Ofen besteht aus drei räumlich voneinander abgegrenzten Zonen I, II und III.The furnace consists of three spatially separated zones I, II and III.
In der Zone I, der unbeheizten Vorwärmzone, befinden sich keine Brenner, hier wird das Ofengas aufgenommen und über einen Kamin 10 abgeführt. Darüber hinaus wird zur Einstellung der Temperaturkurve Luft über Einlasse 11 eingeblasen. In der Figur sind die Brenner oberhalb und unterhalb derThere are no burners in zone I, the unheated preheating zone, here the furnace gas is taken up and discharged via a chimney 10. In addition, air is blown in via inlet 11 to set the temperature curve. In the figure, the burners are above and below the
Rollenbahn schematisch wiedergegeben. In der Zone III, derRoller conveyor shown schematically. In zone III, the
Hochtemperaturzone, sind mehr Brenner als in der Zone II, der beheizten Vorwärmzone, gezeigt.High temperature zone, more burners are shown than in zone II, the heated preheating zone.
Nach der Hochtemperaturzone ist ein Schnellabzug angeordnet.A quick draw is located after the high temperature zone.
In der Zone I wird das wärmezubehandelnde Gut - von innen nach außen gleichmäßig - aufgewärmt.In zone I, the material to be heat-treated is warmed up - evenly from the inside out.
Die Zone II beinhaltet die weitere Erwärmung des Gutes bis zum Erreichen der Hochtemperaturgrenze.Zone II includes the further heating of the goods until the high temperature limit is reached.
In der Zone III gelangen die Metallteile schließlich in den Hochtemperaturbereich, in welcher bei Stahl beispielsweise die Austenitisierung durchgeführt wird.In zone III, the metal parts finally reach the high-temperature range in which, for example, steel is subjected to austenitization.
Die Brenner der Zonen II und III können gruppenweise, und zwar ober- und unterhalb der Rollenbahn angesteuert werden, um das gewünschte Temperaturprofil zu erhalten.The burners of zones II and III can be controlled in groups, above and below the roller conveyor, in order to obtain the desired temperature profile.
Mit S sind höhenverstellbare Schikanen bezeichnet, um die einzelnen Zonen wärmemäßig voneinander zu trennen.S is used to indicate height-adjustable baffles in order to separate the individual zones from each other in terms of heat.
Mit US sind untere feste Schikanen bezeichnet.Lower fixed chicanes are denoted by US.
Es ist möglich, den Ofen vollautomatisch zu beschicken und vollautomatisch mit einem Quettensystem zu entladen. Das Wesentliche ist hierbei die Produktqualität gekoppelt mit dem Durchlauf der Ware, wobei die Ware nicht nur erwärmt, sondern auch gezielt abgekühlt wird. It is possible to load the furnace fully automatically and to unload it fully automatically using a squeeze system. The main thing here is the product quality coupled with the throughput of the goods, whereby the goods are not only heated, but also specifically cooled.

Claims

Patentanspruch Claim
Verfahren zur Wärmebehandlung von metallischem Gut in einem Rollenofen, insbesondere von relativ dünnen, sich bei Erwärmung leicht verziehenden Stahlteilen, wie beispielsweise Kugel lagerringen, Blechronden, Messer und dergleichen, dadurch gekennzeichnet, daß das metallische Gut in mehreren Vorwärmzonen (I, II) mit Atmosphären mit freiem Sauerstoff stufenweise auf bis 800 . . . 850°C erwärmt wird, danach das metallische Gut in einer Hochtemperaturzone (III) mit einer reduzierenden Atmosphäre, die keinen freien Sauerstoff enthält, erwärmt wird und diese Zone relativ schnell durchläuft, die Brenner der Hochtemperatur zone (III) je nach angelieferter Menge an metallischem Gut bzw. zu übertragener Wärmemenge kurz oder länger getaktet werden, und daß die Rollen in der Hochtemperaturzone (III) mit geringem Abstand zueinander und die Schikanen (S, US) zwischen den Zonen (I, II, III) auf möglichst kleine Abstände zur Rollenbahn bzw. dem Metallgut auf der Rollbahn eingestellt werden, wobei sich Brenner oberhalb und unterhalb der Rollenbahn befinden. Process for the heat treatment of metallic material in a roller furnace, in particular of relatively thin steel parts, such as ball bearing rings, sheet round blanks, knives and the like, which warp easily when heated, characterized in that the metallic material in several preheating zones (I, II) with atmospheres with free oxygen gradually up to 800. . . 850 ° C is heated, then the metallic material is heated in a high-temperature zone (III) with a reducing atmosphere, which contains no free oxygen, and passes through this zone relatively quickly, the burners of the high-temperature zone (III) depending on the amount of metallic delivered Good or transferred amount of heat are clocked short or longer, and that the rollers in the high temperature zone (III) with a small distance from each other and the baffles (S, US) between the zones (I, II, III) to the smallest possible distance from the roller conveyor or the metal material on the runway, with burners located above and below the runway.
EP93907835A 1992-03-27 1993-03-26 Heat treatment process for metal articles Expired - Lifetime EP0632842B1 (en)

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DE4209978 1992-03-27
PCT/EP1993/000741 WO1993020248A1 (en) 1992-03-27 1993-03-26 Heat treatment process for metal articles

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JP2771330B2 (en) 1998-07-02
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ATE129748T1 (en) 1995-11-15
ES2082641T3 (en) 1996-03-16

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