JP5828425B2 - Continuous carburizing furnace and continuous carburizing method - Google Patents

Description

  The present invention relates to a continuous carburizing furnace and a continuous carburizing method for continuously carburizing a workpiece in a carburizing atmosphere gas.

  In a continuous carburizing furnace, a temperature raising chamber, a carburizing chamber, a diffusion chamber, a descending greenhouse, a quenching chamber, and the like are sequentially arranged in the horizontal direction. The chambers are partitioned by an openable / closable partition door, and an atmosphere gas for carburizing is supplied to the temperature raising chamber, the carburizing chamber, and the diffusion chamber.

  The temperature raising chamber is provided with a lateral loading port for loading a product to be processed, and the loading port is opened and closed by a loading door. When the product to be processed is carried into the temperature raising chamber, that is, when the loading / unloading port is opened / closed, the atmospheric gas in the temperature raising chamber inevitably flows to the outside, and the outside air flows instead. Due to the inflow of the outside air, the atmospheric gas in the temperature raising chamber is rapidly cooled and contracted, so that an amount of outside air that supplements the contracted volume is further sucked into the temperature rising chamber. As a result, a large change occurs in the composition of the atmospheric gas in the heating chamber. This may adversely affect the quality of the processed product.

  In order to prevent this, it is necessary to return the composition of the changed atmospheric gas to an appropriate range. However, if time is taken for this, the supply of the article to be processed to the subsequent carburizing chamber is delayed. A long time is required for the carburizing process.

  Therefore, as shown in Patent Documents 1 and 2, in order to quickly recover the turbulence in the room atmosphere that occurs when the article to be processed is carried into the heating chamber, a vacuum purge chamber is provided in front of the heating chamber. Yes. According to this, it is said that the time required for carrying in the article to be processed, and consequently the lead time of the carburizing process, is shortened, and an efficient carburizing process is possible.

JP 2004-10945 A JP 2000-180066 A

  However, in the above-described conventional configuration, there is a step of carrying out the article to be processed into the vacuum purge chamber, evacuating the indoor air, and then introducing atmospheric gas, nitrogen gas or the like into the vacuum purge chamber. However, there is a problem that the effect of shortening the lead time is limited and the cost of atmospheric gas or nitrogen gas is increased.

  In addition, since a vacuum purge chamber and a means for evacuation are required, it is difficult to reduce the size of the entire apparatus and reduce equipment costs.

  Furthermore, apart from those of Patent Documents 1 and 2, as a problem with conventional continuous carburizing furnaces that do not have a vacuum purge chamber, if a large amount of outside air is allowed to flow into the temperature raising chamber, oxygen in the flowing outside air is the atmosphere. There was also the possibility of causing abnormal combustion in the temperature rising chamber when mixed with gas.

  The present invention has been made in view of the circumstances as described above, and can greatly reduce the change in composition of the atmospheric gas at the time of carrying the article to be processed into the temperature raising chamber, can shorten the lead time of the carburizing process, and the entire apparatus. Therefore, the present invention intends to provide a continuous carburizing furnace and a continuous carburizing method that can achieve miniaturization and cost reduction, and that do not have the problem of abnormal combustion.

In order to solve the above problems, a continuous carburizing furnace according to the present invention includes a temperature raising chamber, a carburizing chamber adjacent to the temperature raising chamber, an openable / closable partition door that partitions the temperature raising chamber and the carburizing chamber, and the temperature raising chamber. An inlet for the article to be processed formed at the bottom of the sheet, a loading door for opening and closing the inlet, an elevator for carrying the article to be processed from the inlet to the temperature raising chamber, and the object to be treated in the temperature raising chamber A transfer means for transferring a product to the carburizing chamber, and a gas supply pipe for supplying an atmospheric gas for carburizing treatment to the temperature raising chamber , wherein the carry-in door is a support means for the product to be processed, The carry-in door is moved up and down by the operation of the elevator, and is provided with an open / close speed control means for controlling the open / close speed of the carry-in door, and the supply amount of the atmospheric gas into the heating chamber based on a signal from the open / close speed control means Ru and a gas quantity adjusting means for adjusting (claim 1).

  According to the present invention, the atmospheric gas for the carburizing process is supplied to the temperature raising chamber through the gas supply pipe. With the partition door between the temperature raising chamber and the carburizing chamber closed, the loading port at the bottom of the temperature raising chamber is opened, the elevator is operated, and the article to be processed is carried into the temperature raising chamber. Then, the carry-in port is closed, and the temperature rise process of the product to be processed is performed in the temperature raising chamber. Thereafter, the partition door is opened, and an article to be processed is transferred to the carburizing chamber for subsequent carburizing treatment, and the partition door is closed. These series of operations are repeated.

  In the present invention, since the carry-in entrance is formed at the bottom of the temperature raising chamber, when the carry-in door is opened by opening the carry-in door, the atmospheric gas in the temperature rise chamber is difficult to flow out. This is because there is a heated atmospheric gas that is lighter than the atmosphere in the heating chamber, and there is convection, so that the gas flows out from the downward inlet as compared to the conventional example where the inlet is sideways. This is because it is considered difficult.

  If the outflow of the atmospheric gas is suppressed when the carry-in port is opened, the inflow of outside air into the heating chamber can be suppressed, so that a large change does not occur in the composition of the atmospheric gas in the heating chamber. For this reason, the composition of the atmospheric gas in the temperature raising chamber can be returned to the original appropriate range in a short time, and the product to be processed can be smoothly supplied to the subsequent carburizing chamber. Therefore, the lead time of the carburizing process can be shortened. Unlike the conventional technique, since there is no step of introducing the atmospheric gas into the vacuum purge chamber, the cost of the atmospheric gas or the like is saved and the cost is reduced. Further, since a vacuum purge chamber and a vacuum exhaust means are not required, the entire apparatus can be reduced in size and the equipment cost can be reduced.

  Furthermore, since the amount of outside air flowing into the temperature rising chamber is small, there is little risk that oxygen contained in the flowing outside air mixes with the atmospheric gas in the temperature rising chamber to cause abnormal combustion.

By the operation of the prior Symbol elevator, since the closing operation of the loading door and the loading of the workpieces to temperature raising chamber are simultaneously performed, thereby improving the working efficiency. Further, by controlling the opening / closing speed of the carry-in door to an appropriate speed at which the gas inside and outside the heating chamber is not disturbed by the opening / closing speed control means, the inflow of outside air into the heating chamber can be further reduced. Furthermore, the supply amount of the atmospheric gas into the temperature raising chamber is adjusted by the gas amount adjusting means based on a signal from the opening / closing speed control means, so that the atmosphere gas in the temperature raising chamber is opened and closed when the carry-in door is opened and closed. Since composition change can be suppressed as much as possible, the composition of the atmospheric gas can be returned to the original state in a short time. For this reason, the temperature raising step can be completed in a short time, and the next article to be processed W can be carried into the temperature raising chamber in a short time.

As a form of preferred embodiment, the gas amount adjustment means, illustrating the opening operation the state like that Ru increase the amount of gas supplied to the heating chamber during the loading door (claim 2). In this way, it is possible to further reduce the amount of outside air flowing into the temperature raising chamber when the loading door is opened, that is, when the loading port is opened.

As a preferred embodiment, a mode in which the opening / closing speed of the carry-in door is 1 cm / second is exemplified (claim 3 ). In this way, the inflow of outside air into the temperature raising chamber can be further suppressed.

On the other hand, in the continuous carburizing method according to the present invention, the inlet of the bottom of the heating chamber is opened with the partition door between the heating chamber and the carburizing chamber to which the gas for carburizing treatment is supplied, being opened. The product to be processed is carried into the temperature raising chamber, the carry-in port is closed, the temperature rising treatment of the product to be processed is performed in the temperature raising chamber, the partition door is opened, the product to be processed is transferred to the carburizing chamber, and the partition Close the door, a continuous carburizing how to repeatedly perform a series of processes that, loading door for opening and closing the loading opening is a support means of the processed products, the temperature raising chamber in accordance with the opening and closing speed of the loading door The amount of atmospheric gas supplied to the inside is adjusted (claim 4 ).

As a preferred embodiment, a mode in which the opening / closing speed of the carry-in door is 1 cm / second is exemplified (Claim 5 ).

As a form of preferred embodiment, the at the time of opening operation of the loading door, illustrate embodiments supplied to many the temperature raising chamber the gas than when said loading door is closed (Claim 6).

  Since the effect by the method of this invention is self-evident from the said effect about the said continuous carburizing furnace by this invention, the overlapping description is abbreviate | omitted.

1 is an overall view of a continuous carburizing furnace according to an embodiment of the present invention. It is explanatory drawing of the Example of this invention. It is a graph which shows an experimental result. It is a graph which shows an experimental result. It is a graph which shows an experimental result. It is a graph which shows an experimental result. It is a graph which shows an experimental result. It is a graph which shows an experimental result. It is a graph which shows an experimental result.

  Hereinafter, a continuous carburizing furnace and a continuous carburizing method according to an embodiment of the present invention will be described with reference to the accompanying drawings.

  As shown in FIG. 1, a continuous carburizing furnace 1 according to an embodiment of the present invention includes a heating chamber 2, a carburizing chamber 3, a diffusion chamber 4, a descending greenhouse 5, and a quenching chamber 6 in this order. Between the doors 7, 8, 9, 10 that can be freely opened and closed are disposed.

  At the bottom of the temperature raising chamber 2 is a carry-in port 11 for the workpiece W, and the carry-in port 11 is opened and closed by a carry-in door 12. The article W to be processed inserted from the carry-in port 11 is subjected to a predetermined heat treatment while being sequentially moved through the chambers by a transfer means 13 such as a pusher or a roller hearth. Each of the partition doors 7, 8, 9, and 10 is in a partitioned (closed) state during the heat treatment in each chamber, and is opened when the workpiece W is moved from one chamber to the next chamber to be processed. Allow the product W to move between the rooms.

  Gas supply lines 14, 15, 16, 17, and 18 are connected to the chambers, and predetermined gases necessary for heat treatment are supplied to the chambers through these gas supply lines. Further, exhaust gas lines 19, 20, 21, 22, and 23 are disposed in the respective chambers, and gas is discharged from the respective chambers through these exhaust gas lines.

  The quenching chamber 6 includes an upper best 24 and a lower oil tank 25. The oil tank 25 stores quenching oil. The article to be processed W carried into the vestable 24 is lowered by a lifting device (not shown), immersed in the quenching oil in the oil tank 25, and subjected to a quenching process. Thereafter, the article W to be processed is raised by the lifting device and returned to the best 24.

  In the best, a carry-out port 26 for carrying out the hardened workpiece W and a carry-out door 27 for opening and closing the carry-out port 26 are arranged. The unloading door 27 is opened, and the to-be-quenched workpiece W is unloaded from the vestable 24 in the quenching chamber 6 to the outside through the unloading port 26.

  In the continuous carburizing furnace 1, atmospheric gas for carburizing treatment or the like is supplied to the chambers through the gas supply lines 14, 15, 16, 17, and 18. In the state where the partition door 7 between the temperature raising chamber 2 and the carburizing chamber 3 is closed, the entrance 11 at the bottom of the temperature raising chamber 2 is opened, and the article to be processed enters the temperature raising chamber 2 from below the entrance 11. W is carried in. Then, the carry-in port 11 is closed, and the temperature increase process of the article W to be processed is performed in the temperature increase chamber 2. Thereafter, the partition door 7 is opened, the workpiece W is transferred to the carburizing chamber 3 for carburizing treatment, and the partition door 7 is closed. The next article W to be processed is carried into the empty heating chamber 2 in the same manner as described above. When the treatment in the carburizing chamber 3 is finished, the products to be processed W are sequentially sent to the diffusion chamber 4, the descending greenhouse 5, and the quenching chamber 6, and the necessary processing is performed on the products to be processed W in each chamber. The These series of operations are repeatedly executed.

  The greatest feature of the present embodiment is that the carry-in port 11 for carrying the workpiece W into the continuous carburizing furnace 1 is disposed at the bottom of the temperature raising chamber 2 (conventional one). The workpiece inlet of the continuous carburizing furnace was disposed on the side face of the temperature raising chamber). Then, the workpiece W is lifted up from below the temperature raising chamber 2 by the elevator 28 and is carried into the temperature raising chamber 2 through the carry-in port 11.

  According to research by the inventors of the present invention, when the carry-in entrance 11 is formed at the bottom of the temperature raising chamber 2, when the carry-in door 12 is opened by opening the carry-in door 12, Atmospheric gas is difficult to flow out. This is because there is a heated atmospheric gas that is lighter than the atmosphere in the temperature raising chamber 2 and there is convection, so that the carry-in port is directed downward from the carry-in port 11 as compared with the conventional example. This is because gas is considered difficult to flow out.

  If the outflow of the atmospheric gas is suppressed when the carry-in port 11 is opened, the inflow of outside air into the temperature raising chamber 2 is also suppressed, so that there is no significant change in the composition of the atmospheric gas in the temperature raising chamber 2. For this reason, the composition of the atmospheric gas in the temperature raising chamber 2 can be returned to the original appropriate range in a short time, and supply of the article to be processed to the subsequent carburizing chamber 3 can be performed smoothly. Therefore, the lead time of the carburizing process can be shortened. Unlike the conventional technique, since there is no step of introducing the atmospheric gas into the vacuum purge chamber, the cost of the atmospheric gas or the like is saved and the cost is reduced. Further, since a vacuum purge chamber and a vacuum exhaust means are not required, the entire apparatus can be reduced in size and the equipment cost can be reduced.

  Further, since the amount of outside air flowing into the temperature rising chamber 2 is small, there is little risk that oxygen contained in the flowing outside air mixes with the atmospheric gas in the temperature rising chamber 2 to cause abnormal combustion.

  The carry-in door 12 and the elevator 28 may be provided separately. However, in the present embodiment, the carry-in door 12 also serves as a support means for the article W to be processed, and the carry-in door 12 is raised and lowered by the operation of the elevator 28. By doing so, the operation of the elevator 28 causes the closing operation of the carry-in door 12 and the loading of the article W to be processed into the temperature raising chamber 2 at the same time, so that the work efficiency is improved and a separate opening / closing means is provided. There is no need to provide it, and the equipment cost can be reduced.

  The elevator 28 may have any specific configuration as long as it can move the carry-in door 12 as a support of the workpiece W in a horizontal state. For example, as shown in FIG. 1, a workpiece placing table 29 is provided on the carry-in door 12, the carry-in door 12 is supported by a lift 30, and an appropriate number of guide pillars are provided around the lift 30. 31 is disposed. Then, by moving the lifting platform 30 up and down along the guide pillar 31, the workpiece mounting table 29 and the carry-in door 12 are lifted and lowered simultaneously.

  Examples of the drive source 32 of the lifting platform 30 include a hydraulic cylinder and a motor. Examples of means for drivingly connecting the drive source 32 and the lifting platform 30 include a combination of a chain and a gear, a wire and a wire winding drum. Or a combination of a rack and a pinion. In the case of using a rack and a pinion, a motor and a drive pinion connected to the motor are provided on the lifting platform, and the drive pinion can be engaged with a rack disposed in the vertical direction to move up and down.

  The continuous carburizing furnace 1 preferably includes a gas amount adjusting means 33 that increases the amount of gas supplied into the heating chamber 2 when the carry-in door 12 is opened. This is because the amount of outside air flowing into the temperature raising chamber 2 when the carry-in door 12 is opened, that is, when the carry-in port 11 is opened, can be further reduced.

  Furthermore, it is preferable to have an opening / closing speed control means 34 for controlling the opening / closing speed of the carry-in door 12. In addition, the gas amount adjusting means 33 preferably adjusts the amount of gas supplied into the temperature raising chamber 2 in accordance with the opening / closing speed of the carry-in door 12. In this way, the amount of outside air flowing into the temperature rising chamber 2 can be further reduced by adjusting the gas supply amount to the temperature rising chamber 2 according to the opening / closing speed of the carry-in door 12. It is.

  Specifically, a flow rate adjusting valve is provided as the gas amount adjusting means 33 on the gas supply line 14 to the temperature raising chamber 2. On the upstream side of the flow rate adjusting valve 33, there is an open / close valve 35 for controlling the gas supply to the temperature raising chamber 2.

  The elevator 28 is provided with a controller for adjusting the output of the drive source as the opening / closing speed control means 34 of the carry-in door 12. When the drive source 32 is a hydraulic cylinder, a flow rate adjusting valve such as a valve with an electric motor that controls the flow rate of hydraulic oil supplied to the hydraulic cylinder can be used as the controller 34. When the drive source 32 is a motor, an inverter, a servo motor controller, or the like can be used as the controller 34. By controlling the operation of the flow rate adjusting valve 33 based on the signal from the controller 34, the amount of gas supplied into the temperature raising chamber 2 is adjusted in accordance with the opening / closing speed of the carry-in door 12.

  According to studies by the inventors of the present invention, the opening / closing speed of the carry-in door 12 is preferably low. This is because as the opening / closing speed of the carry-in door 12 becomes faster, the gas around the carry-in entrance 11 is more intensely disturbed, and the amount of outside air flowing into the temperature raising chamber 2 and the atmospheric gas inside the temperature raising chamber 2 go outside. This is because the amount of spillage increases. Accordingly, the opening / closing speed of the carry-in door 12 is set to a low speed (for example, 1 cm / second) such that the gas inside and outside the temperature raising chamber 2 is not disturbed by the opening / closing of the carry-in door 12.

  On the other hand, when the opening / closing speed of the carry-in door 12 is lowered, the time during which the carry-in entrance 11 is opened is increased accordingly. For this reason, the atmospheric gas in the temperature raising chamber 2 flows out to the outside, and the opportunity for the outside air to flow into the temperature raising chamber increases. Therefore, in the present embodiment, the amount of gas supplied into the heating chamber 2 is controlled by the gas amount adjusting means 33 so that the chance of outside air inflow does not increase even if the opening / closing speed of the carry-in door 12 is reduced. Increase. For example, while the carry-in port 11 is open, a gas, for example, 1.5 times the gas supply amount when the carry-in port 11 is closed is supplied. Thereby, it becomes difficult for outside air to flow into the heating chamber 2, which is preferable.

  According to the present embodiment, the composition change of the atmospheric gas in the temperature raising chamber 2 is suppressed as much as possible when the carry-in door 12 is opened and closed, so that the atmospheric gas composition can be returned to the original state in a short time. . For this reason, the temperature raising step can be completed in a short time, and the next article W to be processed is brought into the temperature raising chamber 2 in a short time such as 30 minutes or less, or 15 minutes or less which could not be considered in the conventional carburizing furnace. Can be brought in.

<Example 1>
The inventors of the present invention conducted various tests in order to demonstrate the effects of the present invention. That is, as shown in FIG. 2, using the experimental container 36 corresponding to the temperature raising chamber 2, the downward door (corresponding to the carry-in door) 37 of the experimental container 36 is opened and closed while introducing the gas corresponding to the atmospheric gas, The atmosphere in the experimental container 36 was measured.

<Explanation of laboratory equipment>
As shown in FIG. 2, a door 37 of 26 mm × 26 mm is provided at the lower part (bottom) of the experimental container 36 of 100 mm × 100 mm × 150 mm. The downward door 37 opens and closes an opening 38 (corresponding to a carry-in entrance) at the bottom of the experimental container.

A heating device 39 is disposed in the experimental container 36, and the inside of the experimental container 36 can be heated to 100 to 500 ° C. by the heating device 39. N ₂ gas is supplied into the experimental vessel 36 as an atmospheric gas via the mass flow controller 40.

  Thermocouples 41 and 42 for measuring room temperature are disposed at two locations inside the experimental container 36. One (41) is for measuring the room temperature near the door 37, and the other (42) is for measuring the room temperature on the far side away from the door 37.

  In addition, a sampling line 43 is provided for measuring the oxygen concentration in the experimental container 36, and a pump 44, a flow meter 45, and an oxygen concentration meter 46 are disposed on the sampling line 43. The sample gas that has passed through the oximeter 46 is returned to the experimental container 36 through a return pipe 47.

  The values measured by the thermocouples 41 and 42 and the oximeter 46 are recorded by a recording device 48.

  As a comparative example, instead of the downward door 37, an experimental container provided with a lateral door on the lateral side surface (the other configuration is the same as the experimental container of the example) is used, and a comparative experiment is performed under the same conditions as described above.

<Experiment method>
First, the inside of the experimental container 36 is heated to 300 ° C. using the heating device 39. A constant amount of N ₂ gas is supplied into the experimental container 36, and the atmosphere in the experimental container 36 is replaced with N ₂ gas.

Here, since the volume of the experimental container is 1.5 L, for example, when the supply amount of N ₂ gas is 100 mL / min, gas replacement can be performed four times in one hour. Thus, the ratio between the gas supply amount (flow rate) and the volume of the container is referred to as the number of gas replacements (the number of gas replacements per hour).

  In the experiment, the number of gas replacements is set to 6, and it is confirmed that the oxygen concentration in the experimental container 36 has reached a predetermined value (for example, 250 ppm or less), and the downward door 37 of the experimental container 36 is removed. The door opening / closing speed is 1 cm / second.

<Experiment 1>
Ten seconds later, the downward door 37 of the experimental container 36 was closed, and the oxygen concentration and the temperature of the atmosphere were measured. The result is as shown in FIG. Moreover, the time change of the oxygen concentration in the experiment container by an Example and a comparative example is shown in FIG. From FIG. 4, it can be seen that the amount of inflowing oxygen is lower than the sideways door when the carry-in door is turned downward. The reason why the oxygen concentration has increased since the door was closed is due to a time lag between sampling and measurement.

  As shown in FIG. 4, the change in oxygen concentration at the downward door was 189 ppm in terms of volume ratio of the initial value of oxygen concentration (before opening the door), and reached a maximum value of 4862 ppm after about 50 seconds. For the sideways door, the initial value was 166 ppm, and after about 42 seconds, the maximum value was 82500 ppm. That is, by using the downward door, the inflow of outside air can be suppressed to about 1/17 compared to the lateral door.

<Experiment 2>
After 10 seconds, the oxygen concentration in the experimental container was measured in the same manner as in Experiment 1 except that the downward door was left open without closing the downward door of the experimental container, and the change was recorded. Under the same conditions, the oxygen concentration in the experimental container was measured with the side door open, and the change was recorded. The results are as shown in FIG.

  From FIG. 5, it can be seen that in the case of a downward door, the oxygen concentration hardly increases even when the door is left open for a long time. From this, it is considered that the downward door is less likely to cause abnormal combustion than the lateral door.

<Example 2>
From Experiment 1, it was found that the amount of oxygen flowing in when the carry-in door was turned downward decreased.

By the way, oxygen in the outside air that has flowed into the heating chamber reacts with CO in the carburizing gas in the heating chamber to generate CO ₂ , thereby reducing the carbon potential of the indoor atmosphere. For this reason, in order to suppress fluctuations in the atmosphere of the carburizing chamber, the oxygen concentration in the heating chamber is returned to a predetermined value or less until the article to be processed is transferred from the heating chamber to the next carburizing chamber. preferable. Specifically, when the residence time of the article to be processed is 14 minutes in the temperature raising chamber, it is preferable to keep the oxygen concentration in the temperature raising chamber during this time, for example, 750 ppm or less. Therefore, in the same experimental apparatus as in Example 1, the target is to set the oxygen concentration 14 minutes after closing the downward door to 750 ppm or less.

<Experiment 3>
Experiments were conducted in the same manner as in Example 1, and the relationship between elapsed time and oxygen concentration was investigated by changing the gas flow rate (number of substitutions). The result is as shown in FIG.

  As can be seen from FIG. 6, in the four-time replacement, the oxygen concentration is about 1000 ppm in 14 minutes (840 seconds), and the oxygen concentration cannot be reduced to 750 ppm or less within 14 minutes. By replacing the gas flow rate 6 times and 12 times, the oxygen concentration can be reduced to 750 ppm or less within 14 minutes. However, the cost of the gas is increased by 1.5 times and 2 times compared to the replacement by four times as the gas flow rate is increased, which is an increase in cost.

  If the gas flow rate is replaced four times, but only when the downward door is opened, the replacement is performed 12 times, and further after the downward door is closed, the replacement is performed four times. Although the gas cost is increased compared to the 4-time replacement, the cost can be significantly reduced as compared with the 6-time replacement and the 12-time replacement, which is preferable within an allowable range.

<Experiment 4>
An experiment was conducted in the same manner as in Example 1 except that the door was opened, and the relationship between the opening time of the downward door and the oxygen concentration was investigated. The result is as shown in FIG.

  FIG. 7 shows that the shorter the opening time of the downward door, the smaller the increase in oxygen concentration. If the door opening time is shorter than 10 seconds, it is expected that the amount of increase in oxygen concentration can be further reduced.

<Experiment 5>
FIG. 8 shows comparison data between the case where the door opening / closing speed is 1 cm / second and the case where the door opening / closing speed is 5 cm / second under a constant gas flow rate. For example, the number of times of replacement (replacement rate per time of the heating chamber volume) about 4 times is set as the running cost target value. However, from the experimental data of FIG. 8, the oxygen inflow rate changes due to the difference in opening / closing time of the entrance door at a replacement rate of 8 times or less (the faster the door opening / closing speed, the larger the oxygen inflow rate). It is expected that the difference in the oxygen inflow amount at the door opening / closing speed will be further increased in the turn replacement. In the downward door structure, the oxygen inflow amount at the opening time reaches a peak with time (from FIG. 5). Therefore, the slower the door opening / closing speed, the more the oxygen inflow amount can be reduced, leading to the stabilization of the atmosphere. However, since slowing down the door opening / closing speed may cause other functional deterioration (temperature increase delay, furnace temperature reduction) and the like, it is preferable to have a function of varying the door opening / closing speed.

<Example 3>
FIG. 9 shows data obtained by evaluating the safety of the downward door. The experiment was performed in the same manner as in Experiment 1 except that the furnace temperature was 90 ° C, 130 ° C, 280 ° C, 310 ° C, and 380 ° C, and the maximum increase in oxygen concentration was evaluated. The increase amount of the oxygen concentration is proportional to the temperature in the furnace, and is 15000 ppm or less (1.5% or less) even at 1000 ° C., which is the oxygen concentration below the explosion limit of hydrogen. Since carburizing temperature is normally performed at about 850 to 950 ° C., safety is high.

  In a conventional carburizing furnace having a side door, it cannot be said that there is no risk of explosion due to abnormal combustion. This is presumed to be because the oxygen inflow amount at the sideways door (FIGS. 4 and 5) is large, and it is closer to the explosion critical point.

  On the other hand, in the carburizing furnace having the downward door structure according to the present embodiment, the oxygen inflow amount can be significantly suppressed as compared with the conventional furnace. From FIG. 9, at a temperature of 1000 ° C. or lower, the explosion critical point (oxygen concentration 3.6%) is greatly below, so higher safety can be obtained. Moreover, the carburizing furnace having the downward door structure according to the present embodiment can be widely used for an atmospheric furnace of 1000 ° C. or lower.

Claims (6)

A temperature raising chamber, a carburizing chamber adjacent to the temperature raising chamber, an openable / closable partition door that divides the temperature raising chamber and the carburizing chamber, an inlet for an article to be processed formed at the bottom of the temperature raising chamber, and the loading A loading / unloading door that opens and closes a mouth; an elevator that loads an article to be processed from the carry-in entrance into the temperature raising chamber; a transfer unit that transfers the article to be treated in the temperature raising chamber to the carburizing chamber; A gas supply pipe for supplying the atmospheric gas into the temperature raising chamber , the carry-in door is a support means for the article to be processed, and the carry-in door is lifted and lowered by the operation of the elevator, comprising a closing speed control means for controlling the opening and closing speed, Ru and a gas quantity adjusting means for adjusting the supply amount of the atmospheric gas into the heating chamber on the basis of a signal from the opening and closing speed control means, a continuous carburizing furnace. The continuous carburizing furnace according to claim 1, wherein the gas amount adjusting means increases the amount of gas supplied into the temperature raising chamber when the carry-in door is opened . The continuous carburizing furnace according to claim 1 or 2, wherein an opening / closing speed of the carry-in door is 1 cm / second . Opening the inlet of the bottom of the heating chamber in a state where the partition door between the heating chamber and the carburizing chamber to which the gas for carburizing treatment is supplied is closed, and carrying the article to be processed into the heating chamber, Repeating the series of processes of closing the carry-in entrance, performing the temperature increase process of the processed product in the temperature increasing chamber, opening the partition door, transferring the processed product to the carburizing chamber, and closing the partition door a be that continuous carburizing method, loading door for opening and closing the loading opening is a support means of the processed products, adjusting the supply amount of the atmospheric gas into the heating chamber in accordance with the opening and closing speed of the loading door A continuous carburizing method. The continuous carburizing method according to claim 4 , wherein an opening / closing speed of the carry-in door is 1 cm / second . Wherein at the time of opening operation of the loading door, it is supplied more to the temperature raising chamber the gas than when said loading door is closed, the continuous carburizing method of claim 5.

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