JPH0617501B2 - Metal heat treatment method - Google Patents

Description

The present invention relates to a heat treatment method for metals.

Heat treatments of metals such as annealing, spheroidizing, sintering, brazing, malleable, and quenching are usually desirable in a furnace with a reducing or non-oxidizing atmosphere. The heat treatment can be batch or continuous. Continuous heat treatment furnaces are usually open at the ends. The furnaces have an inlet for the metal or workpiece to be heat treated, a heat treatment zone, a cooling zone, and an outlet for the workpiece. The work piece is fed through the furnace at a certain rate, heated in the heat treatment zone to the required treatment temperature, and then cooled in the cooling zone to a temperature that does not oxidize when exposed to the atmosphere. The required atmosphere is usually created, for example, by an exothermic or endothermic gas generator or an ammonia cracker. The atmosphere is fed to the heat treatment zone and expands to fill the gas space in the furnace. The atmosphere is particularly flammable and must usually be burned at both the inlet and outlet of the furnace. It was thus prior art that there were two directions of flow inside the furnace, with gas emanating from the heat treatment zone in both directions.

That is, the gas supplied to the heat treatment area contains a combustion gas such as hydrogen (or carbon monoxide in some cases). The gas emitted from the inlet and outlet of the furnace is burned because it causes danger. On the other hand, the lower limit of the combustible concentration of hydrogen gas is 4%, and the released gas containing hydrogen gas at a concentration lower than 4% cannot be burned. On the other hand, it is safe to release hydrogen gas with a concentration significantly lower than 4% as it is,
If hydrogen gas of a level slightly lower than 4% is released as it is, the hydrogen concentration in the released gas is relatively high, and as described above, there is a risk that the hydrogen gas will stay and cause an explosion or the like depending on the usage conditions. Therefore, in the prior art, in order to burn the released gas while maintaining the working conditions in the furnace, reducing gas such as hydrogen is introduced into the heat treatment furnace at a flow rate higher than the theoretically necessary amount for reducing or non-oxidizing conditions. It has been actually practiced to increase the concentration of a reducing gas such as hydrogen (which may be carbon monoxide) at the inlet and the outlet to reliably burn the reducing gas in the released gas. Therefore, the conventional technique has a drawback that the amount of gas used increases.

It is an object of the present invention to provide a heat treatment method which ameliorates the drawbacks of such conventionally practiced methods.

According to the invention, there are sequentially provided inlets, heat treatment zones,
In a method of heat treating a discontinuous metal work piece in a continuous furnace having a cooling zone and an outlet, substantially preventing air from entering the furnace through the inlet and the outlet, reducing gas and Introducing a non-reacting gas into the heat treatment zone, the non-reacting gas in one of the cooling zones to prevent gas from flowing out of the heat treatment zone through the cooling zone.
At one or more points to create a gas flow from the cooling zone through the heat treatment zone towards the inlet, the concentration of reducing gas in the heat treatment zone being higher than the concentration of reducing gas in the cooling zone. And a step of passing the metal part through the furnace from the inlet to the outlet.

The term "non-reactive gas" as used herein means a gas that does not react with other components of the atmosphere and the workpiece or metal to be heat treated. Nitrogen is generally used as the non-reacting gas, but in some cases argon may be used if nitrogen has any detrimental effect on the metal being heat treated.

The term "heat treatment of metal" used herein includes annealing (including spheroidizing), sintering (for example, powder including non-metal powder), plaging, quenching, and malleability. The method of the invention is particularly suitable for annealing and sintering.

The method of the invention is suitable for a horizontal continuous furnace (a furnace in which the workpieces are fed in a generally horizontal direction). Examples of horizontal continuous furnaces include continuous strip wire furnaces, mesh belt furnaces, roller bed furnaces, and pusher furnaces.

Typically, the non-reacting gas and the reducing gas are introduced directly into the heat treatment zone of the horizontal furnace. Alternatively, the gases are directed to one or more locations in the cooling zone near the heat treatment zone,
Alternatively or additionally, it is introduced at a location remote from the heat treatment zone, or both, where a substantial portion of the reducing gas is allowed to flow into the heat treatment zone. Usually, the non-reacting gas and the reducing gas are introduced into the furnace at the outside temperature, but the heat treatment area has a temperature of as high as 1100 ° C. depending on the type of heat treatment to be performed, so that the gas in the heat treatment area is substantially Expansion occurs. Thus, the gas will flow from the heat treatment zone both in the direction of the furnace inlet and in the direction of the cooling zone.
In the case of a horizontal furnace, the amount of gas leaving the heat treatment zone is preferably substantially higher at one end of the zone than at the other end. It is also desirable that the gas leaving both ends of the furnace be non-flammable, but the flaming gas is burned out only near one end of the furnace. Usually, the end where the gas is burned out is the furnace inlet and the flow of gas from the heat treatment zone to the cooling zone is blocked. In order to prevent the gas flow exiting the cooling zone through the furnace outlet, a device may be provided in the cooling zone of the furnace which physically blocks the gas flow. Preferably, a non-reacting gas having a horizontal velocity component in the direction of the heat treatment zone is supplied to one or more points of the cooling zone to further block the flow of gas from the heat treatment zone to the cooling zone. It This makes it possible to considerably reduce the amount of gas flowing from the heat treatment zone into the part of the cooling zone opposite this zone, and thus to reduce the total supply of non-reacted gas to the heat treatment zone. You can

With these devices, the amount of reducing gas reaching the exit of the furnace can be substantially reduced, so that it is generally not necessary to burn the gas at the exit of the furnace. Therefore, it is desirable to seal the flue or the flue at or near the outlet to prevent air from flowing into the furnace.

In order to create a positive flow of gas through the exit of the horizontal furnace which prevents or substantially limits the entry of air into the furnace from the exit of the horizontal furnace, the non-reacted gas is forced into the velocity component in the direction of the exit. It is therefore advisable to introduce them into the horizontal furnace at one or more points at or near the outlet. Typically, such non-reacting gas also serves the function described above to reduce the proportion of non-reacting gas in the atmosphere exiting the furnace exit. Preferably, a flow restrictor is provided to help prevent the ingress of air from the outlet of the furnace and thus prevent the flow of gas into the furnace without preventing the metal being processed from exiting the furnace. Typically, the device that physically obstructs the outflow of gas from the cooling zone also serves to prevent gas from flowing into the furnace from the outlet. A suitable flow restrictor is one that comprises one or more curtains with a plurality of generally vertically depending fibers or filaments. When the fibers or filaments are not moved, they close substantially the entire cross sectional area of the furnace at or near the outlet, but the metal passing through the furnace has its lower end moved laterally so that the metal Pass through. The combination of such a flow restricting device with a device for introducing non-reacting gas into the furnace at or near the flow restricting device generally prevents air from entering the furnace from the outlet. Especially effective for.

In a preferred embodiment of the method of the present invention, a spaced partition and / or curtain or the like defining at least one chamber into which nitrogen or other non-reacting gas is introduced in the portion of the cooling zone near the furnace exit. Is provided. The partitions are configured to allow the metal to be treated to pass through the chamber.

Such techniques would be commonly applied in heat treatment furnaces to reduce total gas consumption. For example, in sintering, it is known to provide a preheating zone between the sintering (or heat treatment) zone and the furnace inlet. Lubricants and the like are oxidized in the preheating zone. Therefore, it is permissible for a limited amount of air to enter through the inlet to create an oxidizing atmosphere.The present invention therefore also includes a sequentially provided inlet, heat treatment zone,
Both a spaced apart partition and a curtain (or the like) having a cooling zone and an outlet and defining at least one end or at least one chamber through which the metal to be treated can be passed. Or in a method of heat treating a metal in a continuous furnace comprising one of: introducing a suitable gas or gases into the heat treatment zone to create a suitable atmosphere for the heat treatment; Supplying unreacted gas to the chamber to substantially prevent entry through the chamber and into the furnace section between the chamber and the heat treatment zone, and from the inlet to the outlet in the furnace A method is provided that includes the steps of threading metal through.

Non-reacting gas is preferably introduced directly into the chamber.

The rate of introduction of non-reacted gas into the chamber and the physical obstruction of the partition to the gas flow is preferably such that the following conditions are met.

Pc> Pu and Pu> Pa where Pc is the pressure in the chamber, Pu is the pressure of the furnace atmosphere in the vicinity of the chamber and between the chamber and the heat treatment zone, and Pa is the atmospheric pressure. .

More preferably, the horizontal furnace is provided with at least two chambers and is as described below.

Pc> Pu> Pt> Pa where Pc is the pressure in the chamber closest to the heat treatment zone, Pu and Pa are the same as before, and Pt is the pressure in the heat treatment zone.

When the chamber is in the cooling zone near the exit end of the furnace and the pressure in the chamber is greater than ambient pressure, less air enters the cooling zone of the furnace from the furnace exit. If the pressure in the chamber is greater than the pressure in the rest of the cooling zone and in the heat treatment zone, the formation of the required flow in the furnace by the non-flaming gas mixture leaving the furnace outlet will be facilitated at the same time. The total demand for non-reacting and reducing gas can be reduced.

If more than one such chamber is used, they will typically be interconnected at substantially the same pressure.

Suitably at least two, usually three or more chambers are provided, each supplied with non-reacting gas directly. Particularly in such chamber configurations, if necessary, a relatively high hydrogen (or other reactive gas) concentration (eg, 50% by volume or more by volume) in the portion of the cooling zone between the heat treatment zone and the chambers. ) Can be maintained, and its concentration can be progressively reduced from the inner chamber to the outer chamber (the hydrogen concentration in the outermost chamber is such that the atmosphere therein is nonflammable). Since the specific heat of hydrogen is relatively high, increasing the hydrogen concentration in the cooling zone helps cool the metal. Such high hydrogen concentrations are desired when the furnace processes particularly large amounts of metal per hour. However, in other cases it is not necessary and instead, by introducing most of the hydrogen directly into the heat treatment zone or into the part of the cooling zone close to the heat treatment zone, It is desirable to maximize the hydrogen concentration.

The partition is hinged or pivotally attached to a suitable support at or near the ceiling of a conventional furnace. If the metal being treated is an elongated strip, each partition will be in the form of a flap that will substantially fluid tightly seal or engage the metal being treated and the sides of the furnace. If the metal being treated is a more bulky article (eg, a gear), each partition pivots or hinges a row of adjacent "finger" members to the top of the furnace, It will consist of a pendant down to the workpiece transfer surface. Such an arrangement allows the treated metal to pass through, but creates a physical barrier to the gas flow. Various materials may be used for the partition material. It can be, for example, a steel or ceramic material, or a suitable composite or laminate.

The reducing gas can be hydrogen, typically supplied from a high pressure vessel of commercial purity hydrogen, an ammonia cracker, or a hydrocarbon such as methane or propane. The reducing gas can also be a mixture of hydrogen and carbon monoxide produced in situ by the thermal decomposition of volatile organic compounds such as methanol. At a temperature of 700 ° C. or higher, 1 mol of methanol decomposes to form 1 mol of carbon monoxide and 2 mol of hydrogen. If the work piece to be heat treated is oily, methanol is a suitable source of hydrogen.
If grease is present on the work piece, water may be introduced into the treatment zone or preheat zone to remove soot on the work piece. This is after passing the non-reacted gas through the humidifier,
This may be done by placing the work piece in the treatment area. It is important that the metal itself is not oxidised, so that as far as the metal is concerned, non-oxidizing and reducing conditions are maintained substantially throughout the furnace.

In order to prevent or limit the entry of air into the furnace from the inlet, a non-reacting gas with a horizontal velocity component in the direction of the inlet is introduced into the furnace at one or more points between the heat treatment zone and the inlet. May be introduced into. One or more baffles, or a chamber fed with non-reacting gas such as used in the cooling zone could be provided at the inlet end of the furnace. The reducing gas in the gas mixture passing through the inlet is burned out as in normal operation of a continuous heat treatment furnace.

The composition of the atmosphere in the heat treatment zone of the furnace depends on the type of treatment performed, the composition of the metal to be treated, the dew point of the fluid forming the atmosphere, the oil on the surface of the metal to be treated entering the furnace during the heat treatment operation. It is selected according to whether it has arrived and the efficiency of regulating or excluding air from the furnace.

By substantially limiting the ingress of air into the furnace,
If necessary, the average concentration of reducing agent in the furnace atmosphere for a given process may be lower than in conventional furnace operation without substantially reducing the concentration of reducing gas obtained in the heat treatment zone. You can do the work. Further, for example, by using commercial purity hydrogen and nitrogen instead of decomposed ammonia, the dew point of the atmosphere in the furnace can be lowered, and therefore, the reducing gas lower than that when using decomposed ammonia as the reducing gas source is used. Can work at the level of. By blocking the flow of gas from the heat treatment zone to the cooling zone, the amount of reducing gas that must be supplied to the heat treatment zone can be reduced. That is, in many cases, the gas supply rate to conventional horizontal processing furnaces can be significantly reduced, thereby lowering their operating costs. That is, in the prior art, non-oxidizing gas containing reducing gas (hydrogen, carbon monoxide, etc.) is released from both the inlet and the outlet of the furnace, and from the viewpoint of ensuring safety, the released gas containing this reducing gas must be reliably In the state where the reducing gas concentration was made high for combustion (the combustible limit concentration of gas was about 4% for hydrogen and 12% for carbon monoxide), the mixed gas was released to both the inlet and outlet of the furnace and burned, In the present invention, it suffices to release the combustible reducing gas-containing mixed gas only from the inlet of the furnace and burn it, and at the outlet of the furnace, a gas that contains only a sufficiently low concentration of reducing gas that ensures safety (ie, Since most of them emit non-oxidizing gas), the reducing gas is more than the amount that makes the reducing gas in the mixed gas released from the furnace inlet combustible and metal working during heat treatment in the heat treatment area. Only supply an amount that does not oxidize things to the furnace Well, significantly reducing gas consumption compared to the prior art is lowered.

Typical atmospheres that can be created in the heat treatment zone for different heat treatments of different materials are shown in Tables 1 and 2 below (in some cases higher hydrogen concentrations may be used).

In the method of the present invention, the atmosphere in the heat treatment zone and the cooling zone of the furnace is not uniform. Usually, the proportion of reducing gas, such as hydrogen, contained in the atmosphere of the cooling zone is substantially lower than in the heat treatment zone.

The method of the present invention will become more apparent from the description of the examples with reference to the accompanying drawings.

This example relates to the annealing of ferrous metal parts in a standard Birlec 18 "mesh belt furnace.

As shown in FIG. 1, the mesh belt furnace, designated by the reference numeral 2, has an inlet 4 and an outlet 6 for the workpiece to be annealed. The furnace 2 comprises a heat treatment zone 8 provided near the inlet 4 and a cooling zone 10 provided between the outlet 6 and the heat treatment zone 8. Heat treatment area 8 is a "globar"
It is heated by a heating element (not shown).

The workpiece to be annealed is sent onto the endless mesh belt 11. The belt 11 is driven around an endless path extending through the furnace 2 from the inlet 4 to the outlet 6. Belt 11 is mounted on rollers 12 and at least one of these rollers is driven by a motor (not shown). In the operation, the workpiece to be annealed is located in the belt 1 just before the entrance 4.
1 is placed on the belt 1, is fed through the furnace at a predetermined speed, reaches the outlet 6, and is lifted from the belt 10.

Below the belt 11 in the heat treatment zone 8 there are two inlets 14 and 16 which can supply gas to the heat treatment zone 8.

Two coaxial nitrogen / methanol injectors 18 and 20 extend downwardly from the top of the furnace to the heat treatment zone. Injector 18
Is equipped with an outer pipe 22 for nitrogen and an inner pipe 26 for methanol coaxial with the outer pipe 22. The tip of the pipe 26 is
Placed slightly inside the exit of the above. The injector 20 is substantially the same as the injector 18, and includes an outer pipe 24 for nitrogen and an inner pipe 28 for methanol. Injectors 18 and 20
Is operated by causing a drop of methanol to be entrained in nitrogen, vaporizing it, and then hitting it against the annealed workpiece.

A directional nitrogen injector 30 comprising a pipe with perforations or holes oriented at an angle of 45 ° to the direction of the outlet 6 extends from the roof of the furnace 2 into the cooling zone 10. The position of the injector 30 in the cooling zone is relatively close to the outlet 6 of the furnace. Between the injector 30 and the outlet 6, four rows of curtains 34 hang from the ceiling of the furnace 2, the lower end of which extends a distance above the mesh belt 11 sufficient to allow the workpiece to pass. Each of the curtains typically consists of a plurality of vertically interlocking, generally vertically depending glass fibers which substantially close the furnace outlet when the curtain is "closed". But,
The metal passing through the furnace is pushed open allowing the metal to exit the furnace.

A directional nitrogen injector 32 having a perforation or holes oriented at an angle of 45 ° to the direction of the heat treatment zone 8 extends downwardly into the upper portion of the cooling zone 10. The injector 32 is located between the injector 30 and the heat treatment zone 8.

In the operation of furnace 2, nitrogen is typically used in injectors 30 and 3.
2 is introduced into the cooling zone 10 to expel air from the furnace. The device for heating the heat treatment zone 8 is then activated to raise the temperature therein to the required processing temperature. Nitrogen and methanol are then introduced into the heat treatment zone 8 to create the required atmosphere therein. Methanol enters the treatment zone 8 in liquid form, where it vaporizes due to its great expansion. Similarly, injectors 18 and 20 and inlet 14
Nitrogen introduced into the treatment zone 8 from 16 and 16 is heated from about ambient temperature to the treatment temperature and also expands.
The nitrogen introduced from the injector 32 into the cooling zone 10 has a velocity component in the direction of the heat treatment zone 8 and its flow is
Sufficient to substantially block the flow of gas that expands and exits within heat treatment zone 8 and enters cooling zone 10. Therefore, most of these gases flow in the direction of the inlet 4. The gases enter the flue 38 where the flammable components are burned out. A sliding plate 40 is provided to regulate the gas entering the flue 38.

In general, the gas flow below the plate 40 is sufficient to prevent a significant amount of air from entering the furnace through the inlet 4. However, if necessary, nitrogen may be introduced into the furnace between the treatment zone 8 and the inlet 4 by means of a nozzle or injector (not shown) having one or more outlets directed towards the inlet 4. May be introduced. This additional nitrogen flow helps prevent air from entering the inlet 4.

The structure of the injector 30 and the curtain 34 substantially regulates the entry of air from the outlet 6 into the furnace. If any flue, such as flue 38, is provided at the exit 6 to burn out the non-flammable gases, it is sealed to prevent air from flowing into the furnace therethrough. Must.

A nitrogen methanol supply suitable for use with the furnace of FIG. 1 is shown in FIG. The apparatus comprises a nitrogen supply pipeline 50 connected to a commercial purity nitrogen source (not shown). The nitrogen source is typically a vacuum-insulated bath containing liquid nitrogen, which is fitted with a vaporizer for vaporizing the liquid nitrogen. The feeder also comprises a pipeline 52 which connects to a tank (not shown) containing liquid methanol. The supply of methanol to the pipeline 52 may be done by a pump or by the pressure of nitrogen supplied to the dead space of the methanol tank.

An isolation or shut-off valve 54 is provided in the nitrogen pipeline 50 and includes inlets 14 and 16, injectors 18, 20, 30, 32.
To shut off the nitrogen source. Pipeline 5
A pressure regulator 56 is provided on the downstream side of the zero valve 54, and pipes 58 and 6 connected to the pipeline 50 on the downstream side thereof.
Adjust the pressure of nitrogen supplied to 0, 62, 64. The pipe 58 is connected to two branch pipes 72 and 74, which are connected to the injectors 30 and 3 respectively.
2 is supplied. Pipe 60 connects to inlets 14 and 16. Pipe 62 connects to nitrogen pipe 22 of injector 18 and pipe 64 connects to nitrogen pipe 24 of injector 20. The pipes 60, 62, 64 are provided with respective flow control valves 66. A flow meter 68 is provided downstream of these valves 66. In addition, the flow meter 6 is also attached to the pipe 58.
8 are provided. A pressure regulator 70 is provided on the downstream side of each flow meter 68 of the pipes 60, 62, 64.

Pipe 58 connects to pipes 72 and 74, and is equipped with flow control valves 76 and 78, respectively. The device shown in FIG. 2 comprises a device for humidifying the nitrogen supplied to the injector 20. The humidifier comprises a water containing drum 82 having an inlet 80 which is submerged under water. The inlet 80 connects to the pipeline 64 downstream of the valve 70. The drum 82 has an outlet that connects with a pipe 86 leading to the nitrogen pipe 24 of the injector 20. When the nitrogen flowing downstream of the connection point between the pipeline 64 and the inlet 80 is made dry, the valve 84 is opened, and all the nitrogen in the pipeline 64 flows through the valve 84 to the pipe 86. . When valve 84 is closed, all nitrogen in pipeline 64 passes through drum 82. The purpose of this humidifier will be described later.

The methanol pipeline 52 is the first insulation or shutoff valve 8
8 is provided. This valve 88 has a filter 90 on the downstream side to remove solids floating in methanol. A pipeline 96 is provided on the downstream side of the filter 90.
Connect to. The pipeline 96 connects to the methanol pipe 26 of the injector 18. Flow control valve 9 in pipe 96
8 is provided and a flow meter 100 is installed downstream of the valve 98. A flow control valve 92 is provided downstream of the connection point of the pipeline 52 with the pipeline 96, and a flow meter 94 is provided downstream of this valve. Downstream of the flow meter 94, the pipeline 52 connects to the methanol pipe 28 of the injector 20.

In order to actually show the difference between the present invention and the prior art, first the heat treatment in the prior art was actually carried out. That is, the ejector 1
Before making any modifications to install 8, 20, 30, 32 and curtain 34, and connecting inlets 14 and 16 to a nitrogen source (and closing any flue at the exit end of the furnace). Prior to performing, the furnace 2 is operated at
It was operated by directing 0 standard cubic feet (54 m ³ ) of concentrated exothermic gas into the heat treatment zone 8 from inlets 14 and 16. The resulting flammable gas mixture was burnt out at both ends of the furnace. Next, in this furnace, injectors 18, 2
No. 0, 30, 32 and the curtain 34 are attached to the furnace used in the present invention, that is, the furnace shown in FIGS. 1 and 2 and the bright work piece is obtained by carrying out the method of the present invention. It was known that In one typical example, a universal joint forging was annealed at 900 ° C. in heat treatment zone 8 and then cooled to approximately ambient temperature in cooling zone 10. Supply of nitrogen and methanol to each fluid inlet and injector was performed as follows.

Inlets 14 and 16: 220 standard cubic feet per hour (5.9
4 m ³ ) nitrogen.

Ejectors 18 and 20: 400 standard cubic feet per hour (1
1.88 m ³ ) of nitrogen and 2 liters of methanol per hour.

Ejector 30: 100 standard cubic feet per hour (2.7
m ³ ) nitrogen.

Ejector 32: 100 standard cubic feet per hour (2.7
m ³ ) nitrogen.

The flow was split equally between injectors 18 and 20. One liter of methanol per hour decomposes at processing temperatures to produce 20 standard cubic feet (0.54 m ³ ) of carbon monoxide per hour and 40 standard cubic feet (1.08 m ³ ) of hydrogen per hour. Therefore, the total gas flow into the furnace is 1,000 per hour.
Standard cubic feet (27 m ³ ) which are 2,000 standard cubic feet per hour required in the operation performed as in the prior art described above (i.e., to ensure that the released gas is burned at both ends of the furnace). It can be seen that this is half the flow rate of the heat generation gas.

Nitrogen and methanol were supplied at the above rates, and various parts from large castings to small pressed articles were processed in a furnace where the maximum temperature of the heat treatment area was within the range of 720 to 1060 ° C. I was broken.

FIG. 3 shows the changes in the composition of the furnace atmosphere at various points in the furnace when the treatment zone 8 was operated at 970 ° C. As can be seen in this figure, the concentration of hydrogen in the atmosphere in the treatment zone 8 is about 7%, from which it gradually decreases along the cooling zone 10 in the direction of the outlet 6 and reaches the outlet 6. Before that, it fell below 1%, which is a sufficient level for ensuring safety. Similarly, the carbon monoxide level is between 1% and 3.5% in the heat treatment zone 8 which is sufficient to ensure safety at the end of the cooling zone 10 opposite the heat treatment zone 8. It drops to the following values. Similarly, the carbon dioxide concentration also drops from about 0.4% in the heat treatment zone 8 to less than 0.1% at the end of the cooling zone 10 opposite the heat treatment zone 8 (all percentages are% by volume). is there). That is, the gas leaving the outlet 6 of the furnace is substantially free of flammable reducing gas.

In this example, methanol was chosen as the source of reducing gas because some of the workpieces to be treated are oiled. This results in a relatively high dew point of the atmosphere within the heat treatment zone and prevents entrained oil from collecting on the heating element when using a nitrogen methane or nitrogen hydrogen atmosphere. However, because the cooling zone 10 is supplied with nitrogen, a non-reactive atmosphere is predominantly created therein, and thus a bright finished workpiece can be obtained.

The injectors 18 and 20 were designed such that their pipes 22 and 24 were closed at the bottom but provided with orifices on their sides. There, the methanol exiting pipes 26 and 28 hits the closed ends of pipes 22 and 24 and breaks into drops. These drops are carried to nitrogen and pipe 22
And 24 to the treatment area 8 through the orifice. This prevented the relatively fast moving methanol jet from hitting the heating elements in other parts of the furnace before vaporizing. If such a blow were to occur, it would result in carbon deposits on the work piece.

Also, at the levels of hydrogen and carbon monoxide used in the heat treatment zone 8, the ingress of air into the furnace to such an extent that the dew point of the atmosphere in the cooling zone 10 is reduced to a level that will produce inferior quality workpieces. It has been found that it is generally desirable to direct the nitrogen from the injector 30 toward the curtain 34 so as not to increase the.

A humidification drum 82 was used to prevent soot from adhering to the work piece and furnace structure by adding water vapor to the atmosphere, especially if the work piece is oily or greasey.

When processing large pressed articles, a flame curtain was created under the mesh belt 11 at the entrance end of the furnace. The purpose is to consume oxygen in the air trapped under the press.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a mesh belt furnace for carrying out the method of the present invention, FIG. 2 is a schematic diagram showing a flow circuit for supplying nitrogen and methanol to the furnace of FIG. 1, and FIG. , A graph showing a typical example of the composition of the atmosphere at various points along the length of the furnace, 2 ... Meshbelt heat treatment furnace, 4 ... Workpiece inlet, 6
...... Same exit, 8 ...... Heat treatment area, 10 ...... Cooling area, 1
1 ... Mesh belt, 12 ... Belt feed roller, 1
4, 16 ... Gas supply inlet, 18, 20 ... Nitrogen / methanol injector, 30, 32 ... Nitrogen injector, 34 ... Curtain, 38 ... Flue, 40 ... Sliding plate, 50 ...
… Nitrogen supply pipeline, 52 …… Methanol supply pipeline, 82 …… Humidifier,

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Robert Debitz Chauppman, North Yorkshire, UK, Harrogate, Decle, Mystal House (No address) (56) Reference JP-A-53-125210 (JP, A) Sho 52-38105 (JP, U) Japanese Patent Sho 49-44843 (JP, B2)

Claims (1)

[Claims] 1. A method of heat treating a discontinuous metal work piece in a continuous furnace comprising an inlet, a heat treatment zone, a cooling zone and an outlet which are provided sequentially, wherein air is introduced into the furnace through the inlet and the outlet. To substantially prevent entry,
Introducing a reducing gas and a non-reacting gas into the heat treatment zone, the non-reacting gas at one or more points in the cooling zone to prevent gas from flowing out of the heat treatment zone through the cooling zone. To provide a gas flow from the cooling zone through the heat treatment zone towards the inlet, making the concentration of reducing gas in the heat treatment zone higher than the concentration of reducing gas in the cooling zone, and A method comprising the steps of passing the metal part through the furnace from an inlet to an outlet.