EP0206873B1 - Wärmebehandlungsverfahren, Gasabdichtungsvorrichtung und dessen Verwendung in Wärmebehandlungsöfen - Google Patents

Wärmebehandlungsverfahren, Gasabdichtungsvorrichtung und dessen Verwendung in Wärmebehandlungsöfen Download PDF

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Publication number
EP0206873B1
EP0206873B1 EP86401150A EP86401150A EP0206873B1 EP 0206873 B1 EP0206873 B1 EP 0206873B1 EP 86401150 A EP86401150 A EP 86401150A EP 86401150 A EP86401150 A EP 86401150A EP 0206873 B1 EP0206873 B1 EP 0206873B1
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Prior art keywords
gas
oven
inert
hood
intake chamber
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English (en)
French (fr)
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EP0206873B2 (de
EP0206873A1 (de
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Vincent Guillaume
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LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
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LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
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Application filed by LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude filed Critical LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority to AT86401150T priority Critical patent/ATE39501T1/de
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D99/00—Subject matter not provided for in other groups of this subclass
    • F27D99/0073—Seals
    • F27D99/0075—Gas curtain seals
    • 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
    • F27B9/04—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity adapted for treating the charge in vacuum or special atmosphere
    • F27B9/045—Furnaces with controlled atmosphere
    • 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
    • F27B9/14—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity characterised by the path of the charge during treatment; characterised by the means by which the charge is moved during treatment
    • 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
    • F27B9/14—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity characterised by the path of the charge during treatment; characterised by the means by which the charge is moved during treatment
    • F27B9/20—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity characterised by the path of the charge during treatment; characterised by the means by which the charge is moved during treatment the charge moving in a substantially straight path tunnel furnace
    • F27B9/24—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity characterised by the path of the charge during treatment; characterised by the means by which the charge is moved during treatment the charge moving in a substantially straight path tunnel furnace being carried by a conveyor
    • F27B9/243—Endless-strand conveyor

Definitions

  • the present invention relates to a method of heat treatment of objects in a continuous oven comprising at least one heat treatment zone, method in which an atmosphere of non-reactive gas is created under the treatment conditions, at at least one of the ends of said treatment area.
  • the ovens are generally continuous and open at their ends. They carry an entry zone for the objects to be heat treated, a heat treatment zone as well as generally a cooling zone, and an exit zone for the objects.
  • the oven has a system for advancing objects to the heat treatment zone, the temperature of the objects gradually increasing as they advance into the oven.
  • the object When the treatment is finished, the object generally crosses a cooling zone in which it is cooled to a temperature such that no oxidation of this object will occur in the ambient air.
  • the required heat treatment atmosphere is supplied to the furnace via endothermic or exothermic generators or by direct injection of suitable liquid-gas mixtures.
  • the injection of this atmosphere is generally carried out in or near the heat treatment zone. It is necessary to carry out an overpressure of the atmosphere-generating gas at its injection point in order to try to avoid the return in the furnace of the oxidizing species contained in the air.
  • the system described in this patent also makes it possible to avoid the gaseous atmosphere of the oven from being ejected from the oven and to mix with the ambient air, which leads, of course, to reducing the amount of gas injected into the treatment oven for a specified time interval.
  • the injection of inert gas through a perforated tube creates a vortex current in the chamber: for the perforations located on the same circumference of the tube, the geometry tends to create a first vortex zone around the tube. Furthermore, the supply of inert gas being carried out at one end of the perforated tube, the other end of which is closed, the gas will tend, with equal perforation diameter, to escape through the end situated at near the closed part and on the contrary create a suction through the perforations located near the arrival of the inert gas, thus creating a second vortex current in the chamber.
  • the suction system allows the air-inert gas mixture to be evacuated before it can enter the heat treatment zone of the oven.
  • the inlet and outlet zones of the furnace comprise a plurality of curtains arranged parallel to each other defining a plurality of chambers into which an inert gas such as nitrogen is injected.
  • This injection is carried out through a perforated wall situated above and / or below said chambers.
  • the nitrogen injection through these perforated walls is carried out using a conduit in front of which a deflector is placed, the gas bypassing the latter before entering through the perforations in said chambers.
  • the method according to the invention avoids this drawback.
  • said atmosphere of non-reactive gas is created by a substantially homogeneous curtain of gas, injected into a plane traversed by the direction of advance of the parts to be treated, the injection of non-reactive gas s performing under conditions such that a substantially laminar flow regime is maintained over the entire height of the non-reactive gas curtain.
  • the substantially homogeneous gas curtain is generated at each end of the furnace, the pressure losses induced by these being different from each other, so as to modify the relative value of the incoming gas flows and out of the oven.
  • the use of the method according to the invention allows in particular the zoning of heat treatment furnaces.
  • the presence of the homogeneous curtain of inert gas at one and / or the other end of the furnace makes it possible, depending on the modulation of the flows of neutral gas injected into each curtain, to modify in a distinct manner the conditions of exit of the gases at each end of the furnace, and this in a significant way compared to the pressure losses imposed on the moving gas inside the furnace.
  • this injection point When there is a gas injection point at a higher pressure than that of the gases injected at the other points, this injection point will make it possible to orient the gas flow rates in the furnace. If it is located towards the entrance of the oven, the gas flow will be the same as the direction of advance of the parts. Conversely, if it is located near the outlet of the oven, the gas flow will be in the opposite direction to the direction of advance of the parts in the oven.
  • the zone at maximum pressure of the furnace can be better located in the desired location, in the case of a plurality of injections at different points without thereby increasing the flow rates of the active gases.
  • non-reactive gas used in the present application naturally means an inert or non-reactive gas with respect to the other constituents of the atmosphere of the oven as well as the parts which must be treated in it.
  • nitrogen is used as the non-reactive gas, although in some cases it is preferable to use argon or possibly helium.
  • active gas designates the gas or gases from the heat treatment atmosphere.
  • heat treatment includes all the heat treatments that are usually subjected to metals, ceramics, etc., but is particularly intended for the annealing of metal parts such as stainless steel.
  • heat treatment zone means one or more parts of the oven in which heating means are optionally arranged, in which identical or different atmospheres are created, each atmosphere preferably being homogeneous. It also includes the case where the heat present in this zone comes from the part itself which enters the heat treatment zone to undergo a transformation such as hot rolling, etc.
  • the method according to the invention can be used in all continuous ovens of the horizontal or vertical type.
  • the conditions of homogeneity imposed on the inert gas curtains are such that the entry and / or exit zones provided with the homogeneous gas curtains according to the invention must be located in parts not vertical from the oven.
  • the non-reactive gases as well as the reactive gases intended for the heat treatment of the parts are injected directly into the heat treatment zone of the furnace, or in the vicinity thereof. It is however possible to introduce these gases into part of the cooling zone or possibly into or near the zone of entry into the furnace. In all cases, the use of the method according to the invention will make it possible to direct the flow of these gases towards the interior of the furnace and achieve zoning thereof.
  • the method according to the invention is characterized in that said atmosphere of inert or non-reactive gas is created by a stream of inert gas injected vertically at the inlet of the substantially homogeneous furnace, according to a laminar flow regime with a flow rate equal to the air flow entering the oven in the absence of injection of inert gas.
  • the air enters the oven, by natural convection phenomena, through the lower part of the inlet zone, because this air is much colder than the out of the oven.
  • the curtain of inert or non-reactive gas is injected from top to bottom, the presence of curtains, preferably refractory, on either side of the gas curtain, is necessary, these curtains are 'extend substantially to the conveyor belt of objects in the oven.
  • the use of the process according to the invention proves to be particularly effective when the continuous ovens have a short entry zone and / or a significant temperature difference between the gases leaving the oven and the ambient temperature (for example, a temperature difference greater than 300 ° C).
  • the homogeneous curtain of inert gas will be created using a hood making it possible to maintain the flow of non-reactive gas in laminar mode and substantially homogeneous at all points of the gas curtain.
  • the curtains used in this hood will preferably take the form of those described in the American patent cited above, this form of curtains made up of a plurality of elements of different lengths being better suited in particular to ovens in which objects of different forms are treated.
  • the material constituting said curtains must be on the one hand without action on the flow of non-reactive gas from the hood and on the other hand must resist the temperatures to which it is subjected.
  • sintered materials such as materials of the rock wool, quartz wool, or glass wool type, having a thickness of at least two centimeters , were particularly suitable in this application.
  • the inlet chamber of the inert or non-reactive gas generally has a rectangular shape, the base of which is formed by the perforated plate. It has been found that the best results of continuity and uniformity of the gas curtain were obtained when the height of this intake chamber was at least twice the thickness of the material permeable to neutral gas. In this way, the pressure gradients and therefore the turbulence inside this intake chamber are practically avoided.
  • the means for injecting the inert gas into the intake chamber will generally be in communication with the latter on the face opposite to its perforated face. It was found that it was preferable to have the arrival of neutral gas substantially in the center of this plate, so as to create symmetry in the injection of said neutral gas.
  • the inert gas supply channel is connected to the intake chamber by means of a pre-admission chamber which is substantially symmetrical about the axis of arrival of the inert gas.
  • the connection zone between this pre-admission chamber and the intake chamber will be constituted by means permeable to neutral gas identical in their nature and structure to those described above.
  • the invention also relates to the use of the method in a heat treatment oven, comprising a hood as defined above, at least at the inlet and / or the outlet thereof.
  • This hood will preferably be arranged with its intake chamber placed above the parts to be treated. it is also possible to place this hood in the lower part of the oven.
  • the perforated plate of the intake chamber will be opposite the passage of the objects to be treated, while the curtains which allow the confinement of the flow of homogeneous laminar gas will be suspended from the upper part of the oven.
  • a hood placed in the upper part of the oven and provided with its curtains, while a second intake chamber is placed in the lower part of the oven so as to that the flow of inert gas leaving the perforated plate of this second chamber is located between the curtains of the upper hood.
  • a hood at each end of the oven, the pressure of inert gas injected into each of the hoods being different, the pressure losses induced by each curtain of gas being different from each other, so as to modify the relative value of the gas flows entering and leaving the furnace. It is thus possible to orient the flow of said heat treatment gases in the desired direction relative to the direction of advance of the parts to be treated. In particular, it is possible to direct the flow of gases against the current in the direction of advance of the parts, according to the type of heat treatment to which said parts are subjected. In some cases, this pressure difference may result in the absence of injection of inert gas into one of the hoods.
  • a heat treatment furnace is shown diagrammatically comprising successively an inlet zone H i followed by the hot heat treatment zone HZ, followed by a cooling zone CZ at the end of which is the zone H 2 outlet.
  • the injection of heat treatment gas takes place at the point GI substantially in the zone of separation of the hot zone HZ and the cooling zone CZ.
  • the curves shown above the schematic view of this furnace show the pressure on the ordinate and the distance from the point considered with respect to the inlet zone of the furnace on the abscissa.
  • the curve Ci represents the pressure variations of the heat treatment gas injected at point GI for a conventional open oven according to the prior art.
  • the maximum pressure of the heat treatment gas is located in GI, point of injection of this gas, the pressure of the gas, which moves away on the one hand towards the hot zone and on the other hand in the direction of the cooling zone, being equal in the zones H 1 and H 2 to atmospheric pressure.
  • Curve C 3 shows the profile of the pressures in the oven after having placed a homogeneous gas curtain according to the invention at the ends thereof. The pressure is then maintained at a maximum at the gas injection points to decrease to a value which remains above atmospheric pressure in the vicinity of the inlet and / or outlet zones of the furnace.
  • Pt or max Pf max is in the order of 10 -1 to 10- 2 Pascal above atmospheric pressure.
  • FIG. 2 represents a schematic view of an open furnace with a stainless steel annealing mat, according to the invention.
  • this oven successively comprises an inlet hood Hi described in more detail below, a zone for introducing IZ of the parts to be treated, of length L 1 , a heat treatment zone HZ, of length L 2 , then a zone of cooling CZ, of length L 3 which ends in a hood H 2 identical to the hood H 1 .
  • Different gas injection points are provided in particular substantially in the middle of the cooling zone CZ, the injection point Gl i , at the limit of the cooling zones CZ and of the heat treatment HZ, the injection point G1 2 , at the entrance to the heat treatment zone HZ the injection point G1 3 and at the entrance to the zone IZ the injection point G1 4 .
  • Figure 3 shows on its part 3A a front view and on its part 3B a sectional view of a hood according to the invention. It consists of a supply channel 100 of inert gas connected to the inlet of the preadmission chamber 103.
  • the latter of substantially cylindrical shape, of diameter substantially equal to that of the height of the zone 107 of the chamber intake (see below) comprises two zones having substantially the same volume, a first zone 120, followed for a second zone delimited by two perforated plates 101, 102 between which is disposed a rock wool mattress 104.
  • the wall perforated 102 opens into the intake chamber 105 of substantially parallelepiped shape.
  • the intake chamber 105 is bordered laterally by walls 111 and 112 as well as 121 and 122. Towards the lower part of said walls 111 and 112 are located two fixing strips 115, 116 parallel to said walls to which are hung two refractory curtains 113, 114. The height of these curtains is such that those these come into contact with the advance conveyor of objects in the oven.
  • FIG. 4 represents different possibilities of fixing the hoods in an oven, the same elements as those of the preceding figures bearing the same references.
  • FIG. 4A schematically represents a hood fixed in the upper part of the oven
  • FIG. 4B represents a hood fixed in the lower part of the oven
  • FIG. 4C represents a variant with two diffusion chambers and a single pair of curtains.
  • 150 and 151 respectively represent the upper and lower walls of the furnace.
  • the refractory curtains 113 and 114 extend substantially to the bottom wall 151 of the oven.
  • the refractory curtains 113, 114 are fixed by their fixing strips 115, 116 to the upper wall 150 of the furnace, while the expansion chamber 205 (identical to the chamber 105 previously described) is fixed to the lower wall 151 of the oven, the perforated plate of said chamber 105 being oriented towards the upper wall 150 of the oven.
  • the gas is injected into the chamber 205 via the pipe 203, the ends of the curtains 113 and 114 arriving substantially at the level of the perforated wall of the chamber 205.
  • FIG. 4C shows a variant with a single pair of curtains and two intake chambers 105 and 205 respectively.
  • the relative arrangements of the two chambers 105 and 205, substantially identical to each other, are such that the refractory curtains 113 and 114 in a vertical position surround the intake chamber 205, so as to maintain the gas injected through the pipes 103 and 203 between said curtains 113 and 114.
  • the example below relates to a continuous open furnace for annealing steel pipe.
  • the atmosphere used in this annealing furnace has substantially the following composition: 10% of H 2 , 8% of CO, 4% of C0 2 , 78 of N 2 (by volume), dew point: approximately 0 ° C.
  • This oven has a P.H.Z. 3.50 meters in length followed by a heat treatment zone at around 900 ° C. In the preheating zone, the steel tubes are gradually brought to the temperature of the hot zone.
  • FIG. 5 illustrates, using the curves J 1 and J 2 respectively , the ratio of the concentrations of carbon dioxide and carbon monoxide as a function of the distance in the furnace relative to the inlet zone.
  • a hood having the structure shown in FIG. 3 with the dimensions given below had been installed at the inlet of the oven, the outlet of the latter taking place directly on the ambient atmosphere.
  • Curve J 1 represents the ratio of CO / CO 2 concentrations in the absence of a homogeneous laminar flow of nitrogen in the hood, while curve J 2 represents the same concentration ratio with a homogeneous and laminar flow of nitrogen between the refractory curtains of said hood.
  • the nitrogen flow in the hood was 10 Nm 3 per hour.
  • This example was carried out using the furnace shown in FIG. 2.
  • the oven is an open oven with stainless steel annealing mat.
  • the different atmospheres injected at points Gl 1 , G1 2 , G1 3 , G1 4 of the oven are shown in the table below:
  • Figure 6 shows the hydrogen concentrations in the furnace.
  • Curve D i represents the hydrogen concentration in the furnace in the absence of a hood
  • curve D 2 represents the hydrogen concentration in the furnace using the method according to the invention, summarized in the table above.
  • the injection point G1 2 is located at the limit of the heat treatment heating zone and the furnace cooling zone. According to the invention, the hydrogen is almost exclusively directed to the cooling zone of the furnace. The parts taken out of the oven show no trace of oxidation.
  • Curve D (oven without hood) shows that, practically over the entire length of the hot zone HZ of the treatment oven, (4 meters in this example), there is a significant concentration of hydrogen. This varies from approximately 25% at the injection point (7 meters from the inlet area) to approximately 1% at 3 meters from the oven inlet area. In the middle of this hot zone, there is a concentration of about 10% in hydrogen.
  • Curve D 2 (oven with hoods according to the invention) shows that the hydrogen concentration is of the order of 1% at about 6 meters from the inlet of the oven, 3/4 of the hot zone not having d 'hydrogen.
  • the hydrogen concentration profile with or without a hood in the CZ cooling zone is substantially identical.
  • This example shows the possibilities of precise zoning of heat treatment furnaces using the method according to the invention.
  • This example was carried out in the furnace of FIG. 1.
  • the heat treatment zone HZ was at a temperature of 800 ° C., with an injection of gas at the point GI at the limit between the hot zone HZ and the cooling zone CZ .
  • a hood was placed only at the inlet H 1 of the hot zone, no hood being arranged at the outlet.
  • the atmosphere injected is identical to that of Example 1, an atmosphere well known to those skilled in the art for the annealing of steel strips.
  • FIG. 7A represents the concentration of carbon dioxide in the atmosphere of the furnace respectively without hood (E1) and with hood (E2), as a function of the abscissa of the measurement point in the furnace relative to the inlet thereof. this.
  • the concentration of C0 2 is the same in both cases, while there is a decrease of half the concentration of C0 2 at 1 meter from the inlet, in the case of an oven provided with an inlet hood according to the invention.
  • the concentration of C0 2 at the inlet of the oven is substantially identical to that of the atmosphere injected into the oven, which shows the absence of entry of oxidizing species into the oven using the process according to the invention.
  • the curves F, and F 2 of FIG. 7B represent the variations of the dew point in ° C in an oven respectively without hood and with hood with respect to the abscissa of the measurement point thereof with respect to the input .
  • the dew point is significantly lowered, with a hood (curve F 2 ) which is substantially identical in both cases 8 meters from the entrance to the oven. Consequently, the concentration of H 2 0, oxidizing species, in the oven using the method according to the invention is also kept constant until the inlet of the oven.
  • the flow rate of neutral gas in the hoods was 2.5 m 3 / hour.
  • FIG. 8 illustrates a preferred embodiment of the method according to the invention, requiring at least two points for injecting gas into the treatment oven.
  • This variant is characterized by equal pressures at the injection points GI and G'.I '. from the oven.
  • this alternative embodiment is applied to the furnace of FIG. 2, choosing to inject GI 2 gas. and G.1 3 . only, that is to say at the entry and exit of the hot zone HZ, this will have the characteristics of the zone CD described above.
  • the following relationships concerning pressures are:
  • FIGS. 9A and 9B represent a preferred variant of the invention in which a curtain of inert or inactive gas (N 2 in the figure) is used at the entrance only to the oven.
  • the oven is shown diagrammatically, seen in section, only at its inlet 303 and its outlet 304.
  • a hood 305 provided with refractory curtains 306 and 307, such as 'illustrated in Figures 3 and 4, this hood being integral with the upper part 301 of the oven.
  • the refractory curtains have their lower end located near the lower part 302 of the oven, generally provided with a conveyor belt for advancing objects such as 308.
  • a distance of the order of a few centimeters between the lower end of the curtains 306 and 307 and the lower part 302 of the oven is well suited in practice. No particular device is placed at the outlet 304 of the oven.
  • inert or inactive gas generally nitrogen
  • measurements are made at the curtains 306 and 307, in the absence nitrogen injection, the air flow that enters the oven by natural convection phenomena. This measurement is carried out using a hot wire, in a manner known per se.
  • FIG. 9B the same elements as those in FIG. 9Aa have the same references.
  • the hood 305 is placed, in this variant, in the lower part of the oven, without refractory curtains.
  • the nitrogen flow is adjusted as described above. It is noted as above that the air arriving near the inlet of the oven does not penetrate into it but is entrained upwards by the atmospheric current leaving the upper part of the inlet of the oven.
  • the use of the method illustrated in FIG. 9 makes it possible to reduce the flow rates of atmosphere used in the heat treatment furnaces, whatever the number and the nature of the gas injection points therein, for its rate of oxygen determined in the hot zone of the oven.
  • a continuous oven having an inlet area of 2m, a hot area at 800 ° C of 5m and a water cooling area of 10m, as well as an inlet section of about 0.2 m 2 , consumed when its two ends were open 100 Nm 3 / h of nitrogen to achieve a protective atmosphere intended for the annealing of copper parts.
  • the air speed is measured at l entry of the oven, in the absence of nitrogen in the hood. This is 37 cm / s. Nitrogen is then injected at 37 cm / s into said hood, which corresponds to a flow rate of 30 Nm 3 / h of nitrogen. The nitrogen flow rate in the oven can then be reduced to 20 Nm 3 / h, for an identical quantity of the products leaving the oven. There is therefore an overall reduction of 50% in the nitrogen flow rates in this furnace.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Organic Chemistry (AREA)
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  • Metallurgy (AREA)
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  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatments In General, Especially Conveying And Cooling (AREA)
  • Furnace Details (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)
  • Powder Metallurgy (AREA)
  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
  • Tunnel Furnaces (AREA)
  • Drying Of Solid Materials (AREA)
  • Processing And Handling Of Plastics And Other Materials For Molding In General (AREA)
  • Waste-Gas Treatment And Other Accessory Devices For Furnaces (AREA)

Claims (18)

1. Verfahren zur Wärmebehandlung von Gegenständen in einem Durchlaufofen, in welchen die zu behandelnden Gegenstände nacheinander durch einen beweglichen Träger in den Durchlaufofen eingeführt werden, wobei der Ofen mindestens eine Wärmebehandlungszone (H.Z.) aufweist, in welche eine Atmosphäre bestimmter Zusammensetzung eingespritzt wird, wobei die Eingangs- und/oder Ausgangszonen des Durchlaufofens Mittel aufweisen, welche eine Atmosphäre inerten oder nichtreaktiven Gases unter den Behandlungsbedingungen derart erzeugen, dass der Eintritt von Luft in den Ofen im wesentlichen vermieden wird, dadurch gekennzeichnet, dass die Atmosphäre inerten oder nichtreaktiven Gases durch einen Vorhang von im wesentlichen homogenem Gas erzeugt wird, welches in eine Ebene eingespritzt wird quer zur Vorlaufrichtung der zu behandelnden Werkstücke und dass die Einspritzung des inerten oder nichtreaktiven Gases unter solchen Bedingungen erfolgt, dass ein im wesentlichen laminarer Fliesszustand auf der ganzen Höhe des Gasvorhanges aufrechterhalten wird.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass der Vorhang inerten oder nichtreaktiven Gases sich im wesentlichen über die ganze Höhe des Ofens erstreckt.
3. Verfahren nach Anspruch 2, dadurch gekennzeichnet, dass die Mittel, welche eine Atmosphäre inerten oder nichtreaktiven Gases erzeugen, zwei Vorhänge aus feuerfestem Material aufweisen, die sich im wesentlichen bis zu dem beweglichen Träger erstrecken, zwischen welchen der Vorhang inerten oder nichtreaktiven Gases von oben nach unten eingespritzt wird.
4. Verfahren nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, dass der im wesentlichen homogene Gasvorhang durch Einspritzen von inertem oder nichtreaktivem Gas von unten nach oben erfolgt.
5. Verfahren nach Anspruch 4, dadurch gekennzeichnet, dass das Einspritzen des inerten oder nichtreaktiven Gases in einer im wesentlichen vertikalen Ebene erfolgt.
6. Verfahren nach einem der Ansprüche 1 bis 5, bei welchem die Mittel, welche eine Atmosphäre inerten oder nichtreaktiven Gases erzeugen, mindestens am Eingang des Durchlaufofens angeordnet sind, dadurch gekennzeichnet, dass der Durchsatz von inertem oder nichtreaktivem Gas, welchen durch die Mittel eingespritzt wird, gleich dem Luftdurchsatz ist, der in den Ofen eintritt, gemessen in Abwesenheit des Durchsatzes von inertem oder nichtreaktivem Gas in den die besagte Gasatmosphäre erzeugenden Mitteln.
7. Verfahren nach einem der Ansprüche 1 bis 6, bei welchem der Wärmebehandlungsofen zwei Gaseinspritzstellen aufweist, dadurch gekennzeichnet, dass die Einspritzung des Gases unter gleichem Druck an diesen zwei Stellen derart erfolgt, dass eine Zone gleichen Druckes zwischen ihnen aufrechterhalten wird, und dass die eingespritzen Gase auf beiden Seiten dieser Zone fliessen.
8. Verfahren nach einem der Ansprüche 1 bis 7, dadurch gekennzeichnet, dass die Gasdrücke in dem Ofen durch eine der folgenden Beziehungen verbunden sind:
Figure imgb0009
oder
Figure imgb0010
wobei gilt
- Pa ist der Atmosphärendruck;
- Phmaxi ist der maximale Druck in der Abdichtung;
- Ptmaxi ist der maximale Druck in der Wärmebehandlungszone;
- Pfmaxi isr der maximale Druck in der Kühlzone des Ofens.
9. Abdichtung zur Durchführung des Verfahrens nach einem der Ansprüche 1 bis 8, bei welcher vorgesehen sind:
- Einspritzmittel für nichtreaktives Gas in eine Eintrittskammer (105), deren Boden (109) perforiert ist,
- mindestens ein feuerfester Vorhang (113, 114) auf beiden Seiten des Gasstromes, beweglich um eine Achse (115, 116), die in der Ebene des Vorhanges (113, 114) angeordnet ist, und derart ausgerichtet ist, dass er im Durchgang der zu behandelnden Werkstücke angeordnet ist, dadurch gekennzeichnet, dass sie auch aufweist:
- für nichtreaktives Gas durchlässige Mittel (110), die auf dem perforierten Boden (109) der Einlasskammer (105) angeordnet sind und die Möglichkeit vorsehen, dem Gasfluss am Ausgang der perforierten Platte (109) eine sehr kleine Geschwindigkeit zu geben, ohne in der Strömung erheblichen Beschickungsverlust hervorzurufen, derart, dass zwischen den feuerfesten Vorhängen (113, 114) ein Vorhang von im wesentlichen homogenem und laminarem Gas auf seiner ganzen Höhe erzeugt wird.
10. Abdichtung nach Anspruch 9, bei welcher die Einlasskammer (105) einen perforierten Boden (109) aufweist, der im wesentlichen rechteckig ist, dessen Länge gleich der Länge des Ofens ist, an welchem die Abdichtung angebracht werden soll, dadurch gekennzeichnet, dass die Geschwindigkeit des inerten, nichtreaktiven Gases im wesentlichen gänzlich der Durchquerung der perforierten Platte identisch ist und kleiner als:
Figure imgb0011
wobei
n = Viskosität des Neutralgases bei Umgebungstemperatur,
p = Volumenmasse des Neutralgases unter Normalbedingungen,
a = Breite des Ofens,
b = Tiefe der Diffusionsplatte.
11. Abdichtung nach einem der Ansprüche 9 oder 10, dadurch gekennzeichnet, dass die Einspritzung des Gases in die Einlasskammer (105) im wesentlichen symmetrisch zur Einlassrichtung des Gases in die Kammer (105) erfolgt.
12. Abdichtung nach einem der Ansprüche 9 oder 10, dadurch gekennzeichnet, dass die Einspritzung in die Eintrittskammer (105) mittels einer Voreintrittskammer (103) erfolgt, die von der Eintrittskammer (105) durch für das inerte Gas permeable Mittel (110) getrennt ist, wobei die Möglichkeit gegeben ist, dem Gas während seines Eintritts in die Eintrittskammer (105) eine sehr geringe Geschwindigkeit zu geben, ohne wesentlichen Beschickungsverlust in der Gasströmung hervorzurufen.
13. Abdichtung nach Anspruch 12, dadurch gekennzeichnet, dass die Voreintrittskammer (103) auch zwei perforierte Wände (120, 102) aufweist, zwischen denen für Gas permeable Mittel (104) angeordnet sind.
14. Abdichtung nach einem der Ansprüche 9 bis 13, dadurch gekennzeichnet, dass die Höhe der Eintrittskammer (105) wenigstens zweimal so gross ist wie die Dicke der für das Gas permeablen Mittel (110).
15. Abdichtung nach einem der Ansprüche 9 bis 14, dadurch gekennzeichnet, dass die für das Gas permeablen Mittel (110) unter den gesinterten Materialien, Gesteinsfaser, Glaswolle, Quarzfaser, ausgesucht sind.
16. Abdichtung nach einem der Ansprüche 9 bis 15, dadurch gekennzeichnet, dass die Dicke der für das Gas permeablen Mittel (110) im wesentlichen auf der ganzen Fläche des perforierten Bodens (109) der Eintrittskammer (105) identisch und nicht kleiner als 2 cm ist.
17. Abdichtung nach einem der Ansprüche 9 bis 16, dadurch gekennzeichnet, dass die Höhe der Eintrittskammer (105) im wesentlichen konstant ist.
18. Verwendung der Abdichtung nach einem der Ansprüche 9 bis 17 in Wärmebehandlungsöfen.
EP86401150A 1985-06-05 1986-05-30 Wärmebehandlungsverfahren, Gasabdichtungsvorrichtung und dessen Verwendung in Wärmebehandlungsöfen Expired - Lifetime EP0206873B2 (de)

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FR8508470A FR2583064B1 (fr) 1985-06-05 1985-06-05 Procede de traitement thermique, hotte pour la mise en oeuvre de ce procede et son utilisation dans les fours de traitement thermique
FR8508470 1985-06-05

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ZA864139B (en) 1987-02-25
CA1277214C (fr) 1990-12-04
KR870000438A (ko) 1987-02-18
ATE39501T1 (de) 1989-01-15
BR8602604A (pt) 1987-02-03
FR2583064B1 (fr) 1987-08-14
AU587256B2 (en) 1989-08-10
JP2665333B2 (ja) 1997-10-22
EP0206873B2 (de) 1992-07-08
ES557554A0 (es) 1987-10-16
US4746289A (en) 1988-05-24
AU5832786A (en) 1986-12-11
ES8708018A1 (es) 1987-09-01
DE3661542D1 (en) 1989-02-02
ES8800412A1 (es) 1987-10-16
JPS6237317A (ja) 1987-02-18
FR2583064A1 (fr) 1986-12-12
EP0206873A1 (de) 1986-12-30
ES555695A0 (es) 1987-09-01

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