JP3581140B2 - Continuous carburizing furnace - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a continuous carburizing furnace for carburizing an object to be treated in an atmosphere gas for carburizing.
[0002]
[Prior art]
In a conventional continuous carburizing furnace, a heating zone, a carburizing zone, a diffusion zone, a cooling zone, a soaking zone, and the like are provided in the furnace, and these have a structure communicating with each other spatially. Doors are provided at the entrance and the exit of the furnace, respectively, and a frame curtain is provided outside the door. The tray on which the object to be processed is loaded is configured to sequentially pass through these zones while being conveyed by the pusher. A predetermined flow rate of a carrier gas (endothermic modified gas, CO 20 to 23%) is introduced into each of the zones of temperature rise, carburization, and diffusion. In addition, the carbon potential of the carburizing / diffusion zone is set to be higher than that of the temperature raising zone by air and butane gas separately supplied to each zone.
[0003]
[Problems to be solved by the invention]
However, in the conventional continuous carburizing furnace as described above, the atmospheric gas of the carburizing / diffusion zone having a high carbon potential flows into the heating zone, and soot is generated on the surface of the workpiece still having a low temperature. May cause unevenness. As a result, the quality of the carburizing treatment was not stable. On the other hand, when the doors at the entrance and exit of the furnace are opened and closed every cycle, the atmosphere in the furnace is disturbed, and it takes time to recover to the original state. Therefore, a longer treatment time is required as compared with the carburization treatment in a general batch furnace. Further, if the carbon potential of the atmosphere in the carburizing / diffusion zone is reduced, the quality of the treatment is adversely affected.
[0004]
In view of the above-mentioned conventional problems, an object of the present invention is to provide a continuous carburizing furnace capable of rapidly performing carburizing / diffusion treatment and having stable treatment quality.
[0005]
[Means for Solving the Problems]
The present invention relates to a continuous carburizing furnace for carburizing an object to be treated in an atmosphere gas for carburizing, wherein a conveying device for conveying the object to be treated, and a conveyed object to be treated are subjected to a first atmosphere. A temperature raising zone for raising the temperature in the gas, and a temperature increasing zone provided upstream of the temperature raising zone. The first atmosphere gas in the temperature raising zone is guided to the upstream side and exhausted by adjusting a valve opening. A pre-exhaust valve, a carburizing / diffusion zone provided downstream of the heating zone to perform a carburizing treatment and a diffusion treatment on the object to be treated in a second atmospheric gas, An openable and closable intermediate door for partitioning the zone, and provided downstream of the carburizing / diffusion zone to adjust the valve opening to guide the second atmosphere gas in the carburizing / diffusion zone to the downstream side. An exhaust valve is provided after the exhaust (claim 1).
In the continuous carburizing furnace configured as described above, due to the presence of the exhaust valve before and after the valve opening is adjusted and the presence of the intermediate door, the atmosphere gas in the temperature raising zone flows upstream, and the atmosphere gas in the carburizing / diffusion zone flows downstream. Flows to the side. Thus, it is possible to prevent the atmosphere gas in the carburizing / diffusion zone from being mixed with the atmosphere gas in the heating zone, thereby preventing the carbon potential of the carburizing gas in the carburizing / diffusion zone from lowering. Further, by maintaining the gas flow, it is possible to prevent the atmospheric gas in the carburizing / diffusion zone from flowing into the temperature raising zone. Therefore, generation (sooting) of soot in the temperature raising zone can be suppressed.
[0006]
Further, in the continuous carburizing furnace (Claim 1), the transfer device may send a tray on which an object to be processed is placed by a hearth roller (Claim 2).
The tray feeding by the hearth roller can provide an intermediate door and can greatly reduce the time required for the empty furnace due to the step change as compared with the conventional pusher type.
[0007]
In the continuous carburizing furnace (claim 1), an inlet purge chamber and an outlet purge chamber may be provided on the upstream side of the front exhaust valve and on the downstream side of the rear exhaust valve, respectively (claim 3).
In this case, since the presence of each purge chamber prevents the outside air (air) from being sucked into the furnace, it is possible to prevent the carburizing gas concentration from being reduced very little when the furnace door is opened and closed, and to recover the reduction quickly. be able to.
[0008]
Further, in the continuous carburizing furnace (Claim 1), a carrier gas having a high CO concentration of 25% or more of CO is preferably introduced to generate the first and second atmosphere gases (Claim 4).
The carrier gas in this case is a modified gas having a higher concentration than the conventional CO of 20 to 23%, and contributes to the improvement of the carburizing efficiency.
[0009]
Further, in the continuous carburizing furnace (Claim 1), a cooling zone provided with a cooling device is provided downstream of the carburizing / diffusion zone, and an openable and closable second intermediate door that partitions between the two zones is provided. (Claim 5).
In this case, the cooling of the object to be processed can be promoted by setting the temperature decreasing zone separated from the carburizing / diffusion zone.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a view of a continuous carburizing furnace according to an embodiment of the present invention as viewed from a side in a transport direction. In the figure, the continuous carburizing furnace includes, in order from the upstream side (left side), an inlet purge chamber 1, a pre-exhaust valve 2, a heating zone 3, a carburizing zone 4, a diffusion zone 5, a cooling zone 6, It has a soaking zone 7, an oil tank 8 for quenching, a rear exhaust valve 9, and an outlet purge chamber 10. Note that the carburizing zone 4 has a first carburizing zone 41 and a second carburizing zone 42. The front exhaust valve 2 and the rear exhaust valve 9 can adjust the valve opening. Further, an openable and closable first intermediate door 11 that partitions the heating zone 3 and the carburizing zone 4, a closable second intermediate door 12 that partitions the diffusion zone 5 and the cooling zone 6, and a cooling zone 6. An openable and closable third intermediate door 13 for partitioning the heat zone 7 is provided.
[0011]
A hearth roller 15 for transporting a tray 14 on which an object is placed is laid in the furnace. The oil tank 8 includes an elevator 16 that moves the tray 14 up and down. A preparation table 17 is provided in front of the inlet purge chamber 1, and a rear table 18 is provided outside the outlet purge chamber 10. In the heating zone 3, a W-type regenerative burner 21 is provided. This is higher in efficiency and more effective in saving energy than the conventionally used electric heater. Also, the amount of CO ₂ emitted into the furnace is suppressed. In addition, as a specific example of the temperature setting, the target temperature of the heating zone 3 and the temperatures of the carburizing / diffusion zones 4 and 5 are 950 ° C., and the temperature of the soaking zone 7 is 850 ° C. The temperature of a conventional general carburizing zone is 930 ° C., and in the present embodiment, a higher temperature is employed to improve the carburizing efficiency.
[0012]
A carrier gas (methanol decomposition gas: 33% of CO, 67% of H ₂ ) is pumped from the methanol vaporizer 19 to the heating zone 3, the carburizing zone 4 and the diffusion zone 5. 33% of CO has a higher concentration than conventional 20 to 23% of CO, and contributes to improvement of carburizing efficiency. The methanol vaporizer 19 is a device that indirectly heats methanol with a heating medium oil to generate thermally decomposed methanol gas. Conventionally, a shift furnace has been used as such an apparatus, and is a furnace that shifts a mixed gas of air and butane gas at 1150 ° C. with a Ni catalyst. Methanol vaporizers are significantly cheaper and have a smaller installation space than the shift furnace.
[0013]
Although not shown, air or butane gas can be introduced into each zone separately from the carrier gas, and an atmosphere gas is constituted by the whole. By controlling the amount of air or butane gas introduced, the carbon potential of each zone can be set to a desired value. This value is, for example, 0.4% in the temperature raising zone 3, 1.1 to 1.3% in the carburizing and diffusion zones 4 and 5, and 1.0% in the soaking zone 7. In the carburizing zone 4, the carbon potential of the first carburizing zone 41 is set to a value slightly lower than that of the second carburizing zone.
In the cooling zone 6, which is separated from the carburizing / diffusion zones 4 and 5 by the second intermediate door 12, an air cooling device for introducing air (outside air) into a cooling pipe to cool the furnace is used as a cooling device. With the provision, cooling of the object to be processed can be promoted.
[0014]
FIG. 2 is a sectional view showing a schematic configuration of a portion from the inlet purge chamber 1 to the temperature raising zone 3. In the figure, a front door 1a and a rear door 1b are provided in an inlet purge chamber 1, and the front door 1a is opened and closed by a driving unit 1c, and the rear door 1b is opened and closed by a driving unit 1d. Further, a door 3a provided in the temperature raising zone 3 is opened and closed by a driving unit 3b. The door 3a is provided with a ventilation hole 3a1 penetrating therethrough. A front exhaust valve chamber 2R communicating with the front exhaust valve 2 is interposed between the inlet purge chamber 1 and the temperature raising zone 3, and this internal space is always inside the temperature raising zone 3 through the ventilation hole 3a1. Communicates with space. The front exhaust valve 2 is configured to cover the exhaust port 2b of the exhaust pipe 2a with a slight gap, and to cover the lid 2c, and has a function of adjusting the valve opening by adjusting the position of the lid 2c. If necessary, the lid 2c is widely opened (moved upward) to exhaust the atmospheric gas. A ring burner 2d is disposed around the exhaust port 2b, and burns and discharges an atmospheric gas containing CO to be exhausted. When the inside of the furnace becomes a negative pressure at the time of entering and exiting the processing object, the ring burner 2d is provided. Is introduced into the furnace, and oxygen is not introduced into the furnace. In addition, illustration of gas pipe connection to the inlet purge chamber 1 and the temperature raising zone 3 is omitted.
[0015]
FIG. 3 is an enlarged view of the temperature rising zone 3 in FIG. 1 and the first intermediate door 11 provided on the downstream side thereof. The intermediate door 11 is an oblique door whose opening and closing direction is slightly inclined with respect to a vertical line, and has a configuration in which a door portion 11a suspended from a chain or the like moves up and down a slit portion 20a formed in the heat insulating material 20. . The lower end 11a1 when the door is closed is inserted between the roller gaps of the hearth roller 15. In such an oblique door structure, the door portion 11a is pressed against the heat insulating material 20 by its own weight, so that the airtightness is higher than that of the structure of the vertical door (however, it is not enough to completely shut off the ventilation). The third intermediate door 13 (FIG. 1) has a similar structure (however, the inclination is reversed). The second intermediate door 12 is a vertical door and is mainly intended for heat insulation, and has almost no airtightness.
[0016]
FIG. 4 is a cross-sectional view showing a schematic configuration of a portion from the heat equalizing zone 7 to the outlet purge chamber 10. In the figure, a door 7a provided at the end of the heat equalizing zone 7 is opened and closed by a driving unit 7b. The door 7a is provided with a ventilation hole 7a1 penetrating therethrough. The internal space of the oil tank 8 communicates with the rear exhaust valve 9. Like the front exhaust valve 2 (FIG. 2), the rear exhaust valve 9 is configured to cover the exhaust port 9b of the exhaust pipe 9a with a slight gap between the rear exhaust valve 9 and the lid 9c. It has the function of adjusting the valve opening. If necessary, the lid 9c is widely opened (moved upward) to exhaust the atmospheric gas. A ring burner 9d is arranged around the exhaust port 9b. The internal space of the oil tank 8 is always in communication with the internal space of the heat equalizing zone 7 through the ventilation hole 7a1. The outlet purge chamber 10 is provided with a front door 10a and a rear door 10b. The front door 10a is opened and closed by a driving unit 10c, and the rear door 10b is opened and closed by a driving unit 10d.
[0017]
Returning to FIG. 1, the carrier gas is introduced into the temperature raising zone 3 and the carburizing / diffusion zones 4 and 5 with the first, second and third intermediate doors 11, 12 and 13 closed. By closing these intermediate doors 11, 12, and 13, the carburizing / diffusion zones 4 and 5 become independent spaces separated at the front and rear, and the atmosphere gas in the zones can be stably maintained at a high CO concentration. . This has the effect of stabilizing the quality of the carburizing / diffusion treatment. In addition, the presence of these intermediate doors 11, 12, and 13 makes it easy to arbitrarily set the carbon potential in each of the zones from the heating zone 3 to the soaking zone 7.
[0018]
To give an example of the amount of the carrier gas introduced, 200 CFH is introduced into the heating zone 3 and 500 CFH is introduced into the carburizing and diffusion zones 4 and 5. That is, the ratio of the amount introduced into the heating zone 3 and the amount introduced into the carburizing / diffusion zones 4 and 5 is 2: 5. In the front exhaust valve 2 and the rear exhaust valve 9, a gap is normally secured between the exhaust ports 2b, 9b and the lids 2c, 9c, thereby controlling the pressure of the atmospheric gas. At this time, the valve opening of the front exhaust valve 2 and the valve opening of the rear exhaust valve 9 are set in accordance with the above ratio. That is, if the valve opening of the front exhaust valve 2 is 2, the valve opening of the rear exhaust valve 9 is 5. Further, a first intermediate door 11 exists between the temperature raising zone 3 and the carburizing / diffusion zones 4 and 5, and partitions both spaces. As a result, the atmosphere gas (first atmosphere gas) in the heating zone 3 is exhausted from the front exhaust valve 2 and the atmosphere gas (second atmosphere gas) in the carburizing / diffusion zones 4 and 5 is exhausted from the rear exhaust valve 9. The resulting gas flow is created. Although the third intermediate door 13 has a certain degree of airtightness, it does not impede the gas flow at this time. Therefore, as indicated by the white arrow in FIG. 1, the atmospheric gas in the heating zone 3 flows upstream toward the front exhaust valve 2, and the atmospheric gas in the carburizing / diffusion zones 4 and 5 flows toward the rear exhaust valve 9. Flows downstream. Once such a gas flow is established, the amount of atmospheric gas flowing from the carburizing / diffusion zones 4 and 5 into the temperature raising zone 3 is small even when the first intermediate door 11 is opened thereafter.
[0019]
Next, the processing operation of the continuous carburizing furnace configured as described above will be described for each transport step.
《Preparation table → Inlet purge chamber》
When carrying the tray 14 placed on the preparation table 17 into the inlet purge chamber 1, first, the inlet purge chamber 1 is evacuated. After the evacuation is completed, the air is replaced with air, and the front door 1a (FIG. 2) is opened. Here, the tray 14 is carried into the inlet purge chamber 1 by the hearth roller 15. After carrying in, the front door 1a is closed.
[0020]
《Inlet purge chamber → heating zone》
The inlet purge chamber 1 is evacuated, and after the evacuation is completed, it is replaced with an atmospheric gas. After the replacement is completed, the front exhaust valve 2 and the rear exhaust valve 9 are opened (this means that the lids 2c and 9c are completely raised, not the valve opening adjustment). At the same time, the ring burners 2d and 9d are ignited. Next, the rear door 1b of the inlet purge chamber 1 and the door 3a of the heating zone 3 are opened, and the tray 14 is carried into the heating zone 3. After loading, the rear door 1b of the inlet purge chamber 1 and the door 3a of the temperature raising zone 3 are closed. Then, extinguish the fire of the ring burners 2d and 9d. Immediately after the tray 14 is carried into the heating zone 3, the CO% of the carburizing / diffusion zones 4 and 5 drops by about 2%, but this returns immediately.
[0021]
《Heating zone → carburizing zone → diffusion zone → cooling zone → soaking zone》
The tray 14 is conveyed by the hearth roller 15 while opening and closing the first to third intermediate doors 11, 12, and 13. As described above, even when the first intermediate door 11 is opened, the gas flow is maintained. Therefore, even if the atmosphere gas having a high carbon potential in the carburizing / diffusion zones 4 and 5 flows into the heating zone 3, the amount thereof is small.
[0022]
《Soaking zone → oil tank》
After completion of the soaking process, in FIG. 4, when the sensor (not shown) detects that the tray 14 has reached the position just before the door 7a, the front exhaust valve 2 and the rear exhaust valve 9 are opened. At the same time, the ring burners 2d and 9d are ignited. Next, the door 7a is opened, and the tray 14 is placed on the elevator 16 (FIG. 1). At this time, the pressure inside the furnace increases due to the thermal expansion of the atmosphere, and the flames emitted from the front and rear exhaust valves 2 and 9 increase. Subsequently, the door 7a is closed, the elevator 16 is moved down, and the object to be processed on the tray 14 is immersed in oil and quenched. Here, the inside of the furnace has a negative pressure, and the exhaust gas burned by the ring burners 2d and 9d is sucked into the furnace. After a lapse of a predetermined time, the fires of the ring burners 2d and 9d are extinguished, and the front exhaust valve 2 and the rear exhaust valve 9 are closed to their original positions.
[0023]
《Oil tank → exit purge chamber》
After the quenching is completed, the elevator 16 is raised and the tray 14 is raised. Further, the outlet purge chamber 10 is evacuated, and after the evacuation is completed, the outlet purge chamber 10 is replaced with atmospheric gas. After the replacement is completed, the front door 10a of the outlet purge chamber 10 is opened, and the tray 14 is loaded. After carrying in, the front door 10a is closed.
[0024]
《Outlet purge chamber → rear table》
First, the outlet purge chamber 10 is evacuated. After the evacuation is completed, the air is replaced with air, and the rear door 10b is opened. Here, the tray 14 is carried out to the rear table 18 (FIG. 1). Thereafter, the rear door 10b is closed. Thus, all the steps such as carburizing of the tray 14 are completed.
[0025]
In the continuous carburizing furnace as described above, the atmosphere gas in the heating zone 3 flows upstream and the atmosphere gas in the carburizing / diffusion zones 4 and 5 flows downstream from the first intermediate door 11, so that It is possible to prevent the atmosphere gas in the carburizing / diffusion zones 4 and 5 from being mixed with the atmosphere gas in the temperature raising zone 3 to prevent the CO concentration in the carburizing / diffusion zones 4 and 5 from decreasing. Accordingly, it is possible to always maintain the atmosphere having a high carbon potential and shorten the carburizing / diffusion processing time. Further, by providing the inlet purge chamber 1 and the outlet purge chamber 10, the suction of outside air (air) is prevented, the decrease in the CO concentration at the time of opening and closing the door is hardly suppressed, and the decrease is quickly recovered. be able to. Therefore, the atmosphere of a high carbon potential can be more reliably maintained, and the carburizing / diffusion processing time can be reduced.
Further, by maintaining the gas flow, it is possible to prevent the atmospheric gas in the carburizing / diffusion zones 4 and 5 from flowing into the heating zone 3, so that the generation (sooting) of soot can be suppressed and the quality of treatment can be reduced. A stable continuous carburizing furnace can be provided.
[0026]
In the above embodiment, the carrier gas of methanol decomposition is 33% CO. However, it is needless to say that the carrier gas is not limited to 33%. For example, a high CO concentration of 25% or more, which is sufficiently higher than the conventional CO of 20 to 23%, is suitable for improving the carburizing efficiency. However, it is possible to use a conventional carrier gas of 20 to 23% CO for the continuous carburizing furnace of the present invention. Needless to say, a carrier gas diluted with N ₂ or the like or a carrier gas generated by another method may be used.
[0027]
In the conventional continuous carburizing furnace, when the lot of the workpiece is changed and the carburizing conditions are changed, the next workpiece cannot be processed unless all the processing operations of the workpiece are completed. On the other hand, in the above-described embodiment, the intermediate doors 11 to 13 are provided, and the tray 14 on which the object to be processed is transported by the hearth roller 15 is separated by the intermediate door, and each individual zone is separated by the hearth roller. The transport speed can be changed. Therefore, the processing of the next processing object becomes possible before all the processing operations are completed for the previous processing object, and the empty furnace time due to the step change (change of the carburizing condition) can be greatly reduced.
[0028]
【The invention's effect】
The present invention configured as described above has the following effects.
According to the continuous carburizing furnace of claim 1, due to the presence of the exhaust valve and the intermediate door before and after the valve opening is adjusted, the atmospheric gas in the heating zone flows upstream, and the atmospheric gas in the carburizing / diffusion zone flows downstream. Therefore, it is possible to prevent the atmosphere gas in the carburizing / diffusion zone from being mixed with the atmosphere gas in the heating zone, thereby preventing the carbon potential of the carburizing gas in the carburizing / diffusion zone from lowering. Therefore, the carburizing / diffusion zone can always maintain the high carbon potential atmosphere and shorten the carburizing / diffusion processing time. In addition, by maintaining the gas flow, it is possible to prevent the atmospheric gas in the carburizing / diffusion zone from flowing into the temperature increasing zone, so that the generation (sooting) of soot in the temperature increasing zone can be suppressed. It is possible to provide a continuous carburizing furnace having a stable quality.
[0029]
According to the continuous carburizing furnace of the second aspect, the intermediate door can be provided by the tray feed by the hearth roller as compared with the conventional pusher type, and the empty furnace time due to the step change can be greatly reduced.
[0030]
According to the continuous carburizing furnace of the third aspect, the presence of each purge chamber prevents the outside air (air) from being sucked into the furnace, so that a decrease in the concentration of the carburizing gas at the time of opening and closing the door of the furnace can be reduced to a very small amount. In addition, since the decrease can be quickly recovered, the atmosphere with a high carbon potential in the carburizing / diffusion zone can be more reliably maintained, and the carburizing / diffusion processing time can be shortened.
[0031]
According to the continuous carburizing furnace of claim 4, the carrier gas is a modified gas having a higher concentration than the conventional CO of 20 to 23%, and contributes to the improvement of the carburizing efficiency.
[0032]
According to the continuous carburizing furnace of the fifth aspect, the cooling of the object to be treated can be promoted by setting the temperature decreasing zone separated from the carburizing / diffusion zone.
[Brief description of the drawings]
FIG. 1 is a view of a continuous carburizing furnace according to one embodiment of the present invention as viewed from a side in a transport direction.
FIG. 2 is a sectional view showing a schematic configuration of a portion from an inlet purge chamber to a temperature raising zone in the continuous carburizing furnace of FIG.
FIG. 3 is an enlarged view of a portion of a temperature raising zone and a first intermediate door provided downstream thereof in the continuous carburizing furnace of FIG. 1;
FIG. 4 is a cross-sectional view showing a schematic configuration of a portion from a soaking zone to an outlet purge chamber in the continuous carburizing furnace of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Inlet purge chamber 2 Front exhaust valve 3 Heating zone 4 Carburizing zone 5 Diffusion zone 6 Cooling zone 9 Rear exhaust valve 10 Outlet purge chamber 11 First intermediate door 12 Second intermediate door 14 Tray (workpiece)
15 Hearth roller (transportation device)

Claims (5)

A continuous carburizing furnace for carburizing an object to be treated in an atmosphere gas for carburizing,
A transport device for transporting the workpiece;
A temperature-raising zone for raising the temperature of the transported workpiece in the first atmospheric gas;
A pre-exhaust valve that is provided upstream of the heating zone and adjusts a valve opening degree to guide the first atmosphere gas in the heating zone upstream and exhaust the first atmosphere gas;
A carburization / diffusion zone provided downstream from the temperature-raising zone and performing carburization treatment and diffusion treatment on the object in the second atmosphere gas;
An openable and closable intermediate door that partitions the heating zone and the carburizing / diffusion zone,
An exhaust valve that is provided downstream of the carburizing / diffusion zone and adjusts the valve opening to guide the second atmosphere gas in the carburizing / diffusion zone to the downstream and exhaust the same. Features continuous carburizing furnace. 2. The continuous carburizing furnace according to claim 1, wherein the transfer device sends the tray on which the object to be processed is loaded by a hearth roller. 3. 2. The continuous carburizing furnace according to claim 1, wherein an inlet purge chamber and an outlet purge chamber are provided upstream of the front exhaust valve and downstream of the rear exhaust valve, respectively. 2. The continuous carburizing furnace according to claim 1, wherein a carrier gas having a high CO concentration of 25% or more is introduced to generate the first and second atmosphere gases. The continuous carburizing furnace according to claim 1, further comprising a cooling zone provided with a cooling device on a downstream side of the carburizing / diffusion zone, and a second openable and closable intermediate door that partitions between the two zones.

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