JP2023093805A - Vacuum carburization method and vacuum carburization apparatus - Google Patents

Abstract

To provide a technique for suppressing a consumption of a carburization gas by a reaction with an object other than an object to be processed in a carburization furnace and for suppressing a degradation of a carburization quality of the object to be processed in a vacuum carburization method.SOLUTION: A vacuum carburization method includes: a pretreatment step of supplying a carburization gas to a carburization furnace in a depressurized and heated state, measuring a carbon monoxide gas concentration in an exhaust gas from the carburization furnace, and supplying the carburization gas to the carburization furnace until the carbon monoxide concentration becomes below a predetermined threshold level; and a carburization step of arranging an object to be processed inside the carburization furnace in the depressurized and heated state after the pretreatment step.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a vacuum carburizing method and a vacuum carburizing apparatus.

There is known a vacuum carburizing method that compares the time change of the theoretical hydrogen partial pressure ratio in a carburizing furnace with the time change of the actually measured hydrogen partial pressure ratio, and determines the degree of variation in carburizing quality based on the degree of approximation. (For example, Patent Document 1). In this vacuum carburizing method, the carburizing reaction in the furnace is quantified by measuring the hydrogen partial pressure in the carburizing furnace during treatment, and the carburizing quality is controlled by feeding back the value to the carburizing gas input amount and time. are doing.

JP 2012-007240 A

If the carburizing gas is consumed by the reaction with objects other than the object to be processed, such as the inner wall of the carburizing furnace or the structure in the carburizing furnace, the carburizing gas to react with the object to be processed will be insufficient, resulting in insufficient quality. may not be obtained.

The present disclosure can be implemented as the following forms.

(1) According to one aspect of the present disclosure, a vacuum carburizing method is provided. In this vacuum carburizing method, a carburizing gas is supplied to a carburizing furnace in a decompressed and heated state, the concentration of carbon monoxide in the exhaust gas from the carburizing furnace is measured, and the concentration of carbon monoxide reaches a predetermined threshold value. a pretreatment step of supplying the carburizing gas to the carburizing furnace until the temperature of the carburizing gas is reduced to the following; and a carburizing step.
According to this aspect of the vacuum carburizing method, the pretreatment process can remove foreign matter in the carburizing furnace, and can suppress deterioration in the carburizing quality of the object to be processed. By properly setting the threshold value of the carbon monoxide concentration in the pretreatment step, it is possible to supply an appropriate amount of carburizing gas to obtain a sufficient carburizing quality. Therefore, unnecessary consumption of carburizing gas in the pretreatment process can be suppressed.
(2) In the carburizing step of the above aspect, the threshold value may be any concentration of 5% by volume or more and 15% by volume or less.
According to this aspect of the vacuum carburizing method, it is possible to suppress or prevent excessive supply of carburizing gas in the pretreatment process while suppressing deterioration in the carburizing quality of the object to be processed.
(3) In the carburizing step of the above aspect, the threshold value may be 10% by volume.
According to this aspect of the vacuum carburizing method, it is possible to further suppress or prevent excessive supply of the carburizing gas in the pretreatment process while further suppressing deterioration of the carburizing quality of the object to be processed.
(4) The carburizing step of the above aspect may further include a furnace cleaning step of supplying air to the carburizing furnace whose temperature has been raised, prior to the pretreatment step.
According to this form of the vacuum carburizing method, foreign substances in the carburizing furnace can be removed by a simple method of combustion in the furnace, while oxides generated in the furnace cleaning process can be removed in the pretreatment process.
(5) According to a second aspect of the present disclosure, a vacuum carburizing method is provided. This vacuum carburizing method includes a pretreatment step of supplying a predetermined supply amount of carburizing gas used for cleaning the carburizing furnace to a decompressed and heated carburizing furnace; and a carburizing step of placing an object to be processed in the heated carburizing furnace and supplying the carburizing gas.
According to the vacuum carburizing method of this aspect, it is possible to suppress deterioration in the carburizing quality of the object to be processed with a simple configuration.
(6) In the vacuum carburizing method of the above aspect, in the pretreatment step, the supply amount when the carburizing furnace has been used many times is larger than the supply amount when the number of times the carburization furnace has been used is small. , the carburizing gas may be supplied.
According to this aspect of the vacuum carburizing method, it is possible to suppress or prevent deterioration in carburizing quality due to an increase in the cumulative number of times the carburizing furnace is used.
(7) According to another aspect of the present disclosure, a vacuum carburizing apparatus is provided. This vacuum carburizing apparatus is provided in a carburizing furnace, a carburizing gas supply source storing carburizing gas, a carburizing gas supply path connecting the carburizing gas supply source and the carburizing furnace, and the carburizing gas supply path. a supply amount adjusting device for adjusting the supply amount of the carburizing gas to the carburizing furnace; a gas discharge passage connected to the carburizing furnace; and carbon monoxide provided in at least one of the carburizing furnace and the gas discharge passage. A concentration sensor and a control device for controlling the supply amount adjusting device are provided. The control device supplies the carburizing gas to the carburizing furnace in a decompressed and heated state, measures the concentration of carbon monoxide in the exhaust gas from the carburizing furnace, and performing a pretreatment of supplying the carburizing gas to the carburizing furnace until the carburizing gas reaches a threshold value or less; Supply carburizing gas.
According to this vacuum carburizing apparatus, foreign substances in the carburizing furnace can be removed by pretreatment, and deterioration of the carburizing quality of the object to be processed can be suppressed. By properly setting the carbon monoxide concentration threshold in the pretreatment, it is possible to supply an appropriate amount of carburizing gas to obtain a sufficient carburizing quality. Therefore, unnecessary consumption of carburizing gas in the pretreatment can be suppressed.
The present disclosure can also be implemented in various forms other than the vacuum carburizing method and the vacuum carburizing apparatus. For example, it can be realized in the form of a manufacturing method of a vacuum carburizing apparatus, a control method of a vacuum carburizing apparatus, a computer program for realizing the control method, a non-temporary recording medium recording the computer program, or the like.

1 is an explanatory diagram showing a schematic configuration of a vacuum carburizing apparatus as a first embodiment of the present disclosure; FIG. FIG. 4 is a process diagram showing a vacuum carburizing method performed by the vacuum carburizing apparatus of the present embodiment; FIG. 4 is a process drawing showing the details of the pretreatment process performed in the vacuum carburizing method of the present embodiment. Explanatory drawing which shows typically the carburizing reaction of carburizing gas and a process object. FIG. 4 is an explanatory view schematically showing the reaction between foreign matter on the inner wall of the carburizing furnace and the carburizing gas. FIG. 4 is an explanatory diagram showing an example of the relationship between the amount of carburizing gas supplied and the concentration of carbon monoxide in the exhaust gas, which is obtained by experiment. Explanatory drawing which shows the evaluation result of the carburizing quality of the process object with respect to the presence or absence of a pretreatment process.

A. First embodiment:
FIG. 1 is an explanatory diagram showing a schematic configuration of a vacuum carburizing apparatus 100 as a first embodiment of the present disclosure. The vacuum carburizing apparatus 100 places a workpiece WK such as steel in a carburizing furnace in a decompressed and heated state, and brings the surface of the workpiece WK into contact with the carburizing gas, thereby removing carbon from the carburizing gas from the surface of the workpiece. Dissolve and diffuse in the surface layer. The vacuum carburizing apparatus 100 includes a carburizing gas supply source 31, a supply amount adjusting device 32, a vacuum pump 33, a carburizing gas supply passage 38, a gas discharge passage 39, a carburizing furnace 20, and a control device 80. there is

Carburizing gas is stored in the carburizing gas supply source 31 . Hydrocarbon gases such as acetylene gas, butane gas, propane gas, and ethane gas can be used as the carburizing gas. In this embodiment, the carburizing gas supply source 31 stores acetylene gas.

The carburizing gas supply path 38 connects the carburizing gas supply source 31 and the carburizing furnace 20 . The carburizing gas supply path 38 is a flow path for supplying the carburizing gas from the carburizing gas supply source 31 to the processing chamber 26 in the carburizing furnace 20 . The supply amount adjusting device 32 is provided in the middle of the carburizing gas supply path 38 . The supply amount adjusting device 32 adjusts the supply amount of the carburizing gas to the carburizing furnace 20 under the control of the control device 80 . In this embodiment, the supply amount adjusting device 32 supplies a predetermined supply amount of the carburizing gas to the carburizing furnace 20 by opening and closing the internal valve element at a predetermined timing. The control device 80 can adjust the supply amount of the carburizing gas for each predetermined supply amount by increasing or decreasing the number of valve opening times of the valve element of the supply amount adjustment device 32 . However, the supply amount of the carburizing gas is not limited to adjustment by the number of times the valve body is opened by the supply amount adjustment device 32, and may be adjusted using various adjustment methods such as flow rate adjustment by the opening degree of the valve body. .

The gas discharge passage 39 is a passage connected to the carburizing furnace 20 for discharging the gas in the processing chamber 26 to the outside. The vacuum pump 33 is provided in the middle of the gas discharge path 39 . The vacuum pump 33 sucks gas from the processing chamber 26 and discharges it to the outside through the gas discharge path 39 under the control of the control device 80 .

The carburizing furnace 20 includes an insulating wall 22 , an exchange door 24 , a processing chamber 26 , a heater 28 , a temperature sensor 42 and a pressure sensor 44 . The processing chamber 26 is a space provided inside the carburizing furnace 20 and defined by the inner wall 22</b>S of the heat insulating wall 22 . A processing target WK is arranged in the processing chamber 26 . The heater 28 heats the processing target WK by increasing the temperature of the processing chamber 26 under the control of the control device 80 . A temperature sensor 42 detects the temperature of the processing chamber 26 . A pressure sensor 44 detects the pressure in the processing chamber 26 . Obtained results of the temperature sensor 42 and the pressure sensor 44 are output to the control device 80 .

The exchange door 24 functions as part of the heat insulating wall 22 and is mainly used to exchange the WK to be processed. The workpiece WK before machining is put into a workpiece exchange chamber (not shown) in which the internal pressure of the machining chamber 26 after decompression is reduced to the same level, and exchanged with the workpiece WK after machining through the exchange door 24. . As a result, the workpiece WK can be exchanged while the machining chamber 26 is held in a decompressed state. Also, by opening the exchange door 24, the processing chamber 26 can be exposed to the atmosphere.

The vacuum carburizing apparatus 100 further includes a CO concentration sensor 40 for measuring the carbon monoxide concentration of exhaust gas from the carburizing furnace 20 . CO concentration sensor 40 can use a known carbon monoxide concentration sensor. It may be a sensor. In the present embodiment, the CO concentration sensor 40 is provided in the gas exhaust passage 39 on the exhaust side, that is, on the downstream side of the vacuum pump 33 . However, the CO concentration sensor 40 may be provided upstream of the vacuum pump 33 in the gas discharge path 39, may be provided in the processing chamber 26, or may be provided in each of these plural locations. A detection result by the CO concentration sensor 40 is output to the control device 80 .

The control device 80 is a microcomputer having a CPU 82 as a central processing unit and a memory 84 such as RAM and ROM. The memory 84 stores various programs for realizing the functions provided in this embodiment, and the programs read from the ROM are expanded on the RAM and executed by the CPU 82 .

In this embodiment, the control device 80 controls the supply amount adjusting device 32 , the heater 28 and the vacuum pump 33 based on the detection results of the CO concentration sensor 40 , the temperature sensor 42 and the pressure sensor 44 . Specifically, the control device 80 outputs a control signal corresponding to the supply amount of the carburizing gas to the supply amount adjustment device 32 to control the supply amount adjustment device 32 and supply the carburizing gas to the carburizing furnace 20. Control the amount and timing of carburizing gas supply. The control device 80 controls the timing of discharging the carburizing gas by controlling the vacuum pump 33 while referring to the detection result of the pressure in the processing chamber 26 from the pressure sensor 44. Maintain a predetermined decompressed state. The control device 80 controls the heater 28 while referring to the detection result of the temperature of the processing chamber 26 from the temperature sensor 42 to heat the processing chamber 26 and the processing target WK to a predetermined temperature. The control device 80 controls the heater 28 so that the temperature of the processing chamber 26 is kept constant at an arbitrary temperature of 900° C. or higher, for example. In the present embodiment, the control device 80 further refers to the carbon monoxide concentration detection result from the CO concentration sensor 40, and supplies the carburizing gas to the carburizing furnace 20 until the carbon monoxide concentration becomes equal to or lower than a predetermined threshold value. perform a pretreatment step to supply the

FIG. 2 is a process chart showing the vacuum carburizing method performed by the vacuum carburizing apparatus 100 of this embodiment. In this embodiment, the vacuum carburizing method shown in FIG. 2 is started with the temperature of the processing chamber 26 raised to a predetermined temperature by the control of the heater 28 by the controller 80 .

In step S20, an in-furnace cleaning step is performed. In the furnace cleaning process, the exchange door 24 is opened to expose the heated processing chamber 26 to the atmosphere. The furnace cleaning process is also called burnout. By supplying air to the processing chamber 26 whose temperature has been raised, foreign matter such as free carbon accumulated in the processing chamber 26 by, for example, so-called sooting, can be burned and removed. According to the in-furnace cleaning process, the processing chamber 26 can be cleaned by a simple method.

In this embodiment, when the carburizing process is performed a plurality of times over a plurality of WKs to be processed, the furnace cleaning process is performed only before the first carburizing process. However, the cleaning process in the furnace is not limited to this, and the cleaning process may be performed at an appropriate timing, such as once every few hours, once a day, or once a week, depending on the amount of foreign matter accumulated in the processing chamber 26. and may be performed each time before each of the multiple carburizing steps. The in-furnace cleaning step may be omitted when the amount of foreign matter deposited in the processing chamber 26 is small.

In step S30, a pretreatment step is performed. In the pretreatment process, as will be described later, the control device 80 controls the heater 28, the vacuum pump 33, and the supply amount adjusting device 32 to supply carburizing gas to the processing chamber 26, thereby cleaning the processing chamber 26. done. In this embodiment, the processing chamber 26 is in a high temperature and reduced pressure state, which is the same condition as the carburizing process. However, the condition is not limited to this, and any condition suitable for cleaning the processing chamber 26 may be set. The pretreatment process is performed while the workpiece WK is not placed in the machining chamber 26 . In this embodiment, when the carburizing process is performed multiple times, the pretreatment process is performed only after the in-furnace cleaning process and before the first carburizing process. However, it is not limited to this, and the pretreatment process may be performed every time before each carburizing process. The pretreatment process may be performed even when the in-furnace cleaning process is not performed.

In step S40, a carburizing step is performed. The control device 80 controls the supply amount adjusting device 32 and the vacuum pump 33 based on the decompression/heating conditions according to the carburizing quality required for the WK to be processed. A predetermined amount of carburizing gas is supplied to the processing chamber 26 by the supply amount adjusting device 32 , and part of the carburizing gas is discharged by the vacuum pump 33 . When the carburizing gas comes into contact with the workpiece WK heated in the machining chamber 26, carbon in the carburizing gas dissolves from the surface of the workpiece WK.

In step S50, a diffusion step is performed. In the diffusion process, the control device 80 stops the supply amount adjusting device 32 to interrupt the supply of the carburizing gas, and controls the vacuum pump 33 to exhaust the gas from the processing chamber 26 . When the WK to be processed is heated, the carbon dissolved in the surface layer diffuses. From the viewpoint of increasing the carbon diffusion rate, the carburizing process and the diffusion process may be alternately repeated multiple times.

In step S60, a hardening step is performed. In the quenching process, the carburized workpiece WK is cooled at a predetermined cooling rate, for example, by oil cooling, air cooling, or water cooling. As a result, the austenitic structure of the surface layer, which is the carburized layer, can be transformed into the martensitic structure. A tempering process may be further performed after the quenching process. In the tempering process, the quenched workpiece WK is heated to a temperature below the austenite transformation point and then cooled. Thereby, the toughness of the workpiece WK can be increased.

FIG. 3 is a process chart showing the details of the pretreatment process performed in the vacuum carburizing method of this embodiment. After the furnace interior cleaning process is completed, the controller 80 controls the vacuum pump 33 to reduce the pressure in the processing chamber 26 to a predetermined pressure in step S32. In this embodiment, the pressure value after pressure reduction is the same as the pressure value after pressure reduction in the carburizing step, such as several hundred Pa, for example. However, the decompression condition in the pretreatment step is not limited to this, and may be a pressure value different from that in the carburizing step. In order to keep the processing chamber 26 heated, the controller 80 keeps the heater 28 on.

In step S34, a carburizing gas is supplied to the processing chamber 26 in a decompressed and heated state. Specifically, the control device 80 controls the opening and closing of the supply amount adjusting device 32 only once to supply a predetermined amount of carburizing gas to the processing chamber 26 . The control device 80 further controls the vacuum pump 33 to control the timing of discharging the carburizing gas while referring to the detection result of the pressure in the processing chamber 26 from the pressure sensor 44, thereby reducing the pressure in the processing chamber 26. Hold.

In step S<b>36 , the control device 80 refers to the detection result of the CO concentration sensor 40 and obtains the carbon monoxide concentration C<b>1 in the exhaust gas discharged from the gas discharge passage 39 . In the pretreatment process, the detection timing of the carbon monoxide concentration C1 by the CO concentration sensor 40 is not limited to the timing after the step S34, and may be every exhaust timing from the processing chamber 26, or at predetermined time intervals. may be repeated with

In step S38, the control device 80 compares the acquired carbon monoxide concentration C1 with a predetermined threshold value CT. The threshold CT is pre-stored in the memory 84 . If the carbon monoxide concentration C1 is greater than the threshold CT (S38: YES), the controller 80 returns to step S34 and further supplies a predetermined amount of carburizing gas to the processing chamber 26. When the carbon monoxide concentration C1 is equal to or lower than the threshold CT (S38: NO), the control device 80 ends the pretreatment process and shifts to the carburizing process. That is, the control device 80 repeatedly supplies the carburizing gas until the carbon monoxide concentration C1 becomes equal to or lower than the threshold CT.

The effects of the pretreatment process provided in the vacuum carburizing method of this embodiment will be described with reference to FIGS. 4 to 7. FIG. FIG. 4 is an explanatory diagram schematically showing the carburizing reaction between the carburizing gas and the WK to be processed. FIG. 5 is an explanatory view schematically showing the reaction between the foreign matter on the inner wall 22S of the carburizing furnace 20 and the carburizing gas. As shown in FIG. 4, in the carburizing process, when a carburizing gas 90 such as acetylene gas is supplied to the processing chamber 26, the supplied carburizing gas 90 causes a carburizing reaction with the surface of the WK to be processed. In this carburizing reaction, if the carburizing gas is acetylene gas, a reaction of H2C2→2C+H2 takes place. That is, in the carburizing reaction on the surface of the WK to be processed, carbon dissolves in the surface of the WK to be processed and hydrogen is released.

On the other hand, as shown in FIG. 5, the inner wall 22S of the heat insulating wall 22 is oxidized due to, for example, aging deterioration of the carburizing furnace 20, inflow of air into the processing chamber 26, implementation of the furnace cleaning process, and the like. Objects 96 may accumulate. In the pretreatment step, a carburizing gas 90 is supplied to the processing chamber 26 to cause a reduction reaction with oxides 96 . In this reduction reaction, if the carburizing gas is acetylene gas, a reaction of H2C2→H2+2CO takes place. That is, in the pretreatment process executed in the present embodiment, the carburizing gas 90 is subjected to a reduction reaction with the oxide 96 deposited on the inner wall 22S of the heat insulating wall 22, thereby removing the oxide 96 as a foreign matter and removing the oxide 96. Wash 26.

Here, hydrogen 94 is generated by a carburizing reaction with the workpiece WK, as shown in FIG. Further, as shown in FIG. 5, hydrogen 94 is discharged together with carbon monoxide 98 in the reduction reaction between the carburizing gas and the oxide 96 of the inner wall 22S other than the WK to be processed as shown in FIG. Therefore, in the conventional technique of measuring the hydrogen partial pressure in the carburizing furnace 20, in addition to the hydrogen generated by the reaction of the carburizing gas with the WK to be processed, the hydrogen generated by the reaction with the oxide 96 in the processing chamber 26 is measured. It is conceivable that the degree of variation in the carburizing quality cannot be properly determined by detecting also, and sufficient carburizing quality cannot be obtained.

Carbon monoxide 98 is generated only in reduction reactions. In the present embodiment, in the pretreatment process, the carbon monoxide concentration C1 is measured by the CO concentration sensor 40, and the carburizing gas 90 is supplied until the carbon monoxide concentration C1 becomes equal to or lower than the threshold value CT. It can be determined whether the object 96 has been sufficiently removed.

FIG. 6 is an explanatory diagram showing an example of the relationship between the amount of carburizing gas supplied and the concentration of carbon monoxide in the exhaust gas obtained by experiment. The vertical axis in FIG. 6 indicates the carbon monoxide concentration (% by volume), and the horizontal axis indicates the amount of carburizing gas supplied to the processing chamber 26 of the carburizing furnace 20 . In addition, in this embodiment, as described above, the supply amount adjusting device 32 supplies a predetermined flow rate each time the valve is opened. The supply amounts V1 to V4 shown on the horizontal axis correspond to the total supply amount of the carburizing gas supplied when the valve is opened one to four times.

Graphs G1 and G2 shown in FIG. 6 show experimental results using the carburizing furnace 20 of the vacuum carburizing apparatus 100 . Specifically, it is the result of measuring the carbon monoxide concentration C1 each time the carburizing gas is supplied and discharged by the supply amount adjusting device 32 using the carburizing furnace 20 of the vacuum carburizing apparatus 100 . Graph G1 is the result of using a so-called new carburizing furnace 20 that has not been used, that is, has zero accumulated number of times of use. Graphs G11 and G12 are so-called N-increase results under the same conditions, and show the results for each sample under the same conditions. Graph G2 is the result of using the carburizing furnace 20 that has been in use for two years. is. Graphs G21 and G22 are so-called N-increase results under the same conditions, and show the results for each sample under the same conditions. In the experiments using the carburizing furnace 20 of both graphs G1 and G2, the furnace cleaning process was performed, and then the processing chamber 26 was evacuated by the vacuum pump 33 and the carburizing gas was supplied by the supply amount adjusting device 32. was carried out under the same conditions as those of the pretreatment process described with reference to FIG.

As shown in FIG. 6, the experiment yielded the following results.
(Result 1) In any of the graphs G11, G12, G21, and G22, the carbon monoxide concentration in the exhaust gas decreases as the supply amount of the carburizing gas increases. That is, it can be understood that the oxide 96 in the processing chamber 26 is removed by supplying the carburizing gas.
(Result 2) When the amount of carburizing gas supplied is the same, the carbon monoxide concentration in graph G2 is higher than the carbon monoxide concentration in graph G1. That is, the concentration of carbon monoxide in the exhaust gas discharged from the carburizing furnace 20 with a large number of cumulative uses is higher than the concentration of carbon monoxide in the exhaust gas from the carburizing furnace 20 with a small number of cumulative uses. From this, it can be understood that the deposition amount of the oxide 96 in the processing chamber 26 increases as the cumulative number of times of use increases.
(Result 3) In the graphs G11 and G12, with the supply amount V1, the deposit amount of foreign matter in the initial state of the unused carburizing furnace 20 is about 12% by volume. On the other hand, in the carburizing furnace 20 in which the number of times of cumulative use of the carburizing gas indicated by the graphs G21 and G22 is large, the carbon monoxide concentration becomes less than 15% by volume due to the supply of the carburizing gas at the supply amount V2, and the carbon monoxide concentration becomes less than 15% by volume. It is possible to clean the carburizing furnace 20 to the same extent as in the initial state. Therefore, for example, when it is desired to achieve both carburization quality and productivity, it is possible to set the threshold value CT at 15% by volume to control the carburization quality.
(Result 4) As shown in the graphs G11 and G12, in the unused carburizing furnace 20, when the carbon monoxide concentration is less than 5% by volume, the slope of the decrease in carbon monoxide concentration becomes small. Therefore, for example, when it is desired to sufficiently clean the processing chamber 26, it is possible to control the carburizing quality by setting the threshold value CT at 5% by volume.

FIG. 7 is an explanatory diagram showing evaluation results of the carburizing quality of the WK to be processed with respect to the presence or absence of the pretreatment process. The vertical axis in FIG. 7 indicates the effective hardened layer depth (mm). The effective hardened layer depth was evaluated by measuring the distance from the surface of the WK to be processed to a position with a Vickers hardness of HV550 in accordance with Japanese Industrial Standards (JIS G 0557).

A group of plots P1 shows the test results of the samples in which the pretreatment process was omitted after the furnace cleaning process and the carburizing process was performed. Plot group P2 is a sample in which the pretreatment process is performed after the furnace cleaning process is performed, the pretreatment process is terminated when the CO concentration becomes 10% by volume or less, and the carburizing process is performed thereafter. be. The test results are shown for the samples after the carburizing process. The number of samples for each of the plot groups P1 and P2 is both four.

The target value TG shown in FIG. 7 is the effective hardened layer depth required for the workpiece WK as a product. As shown by the plot group P1 in FIG. 7, it can be understood that the sample without pretreatment has a shallower effective case depth and lower carburization quality than the sample with pretreatment. It is believed that this is because the carbon in the carburizing gas that should be used in the carburizing process was consumed by the oxide in the processing chamber 26 .

On the other hand, as shown by the plot group P2, it can be understood that the samples with pretreatment have a deeper effective case depth and a higher carburization quality than the samples without pretreatment. Further, if the CO concentration is 10% by volume, all the samples included in the plot group P2 are equal to or greater than the target value TG, and the effective hardened layer depth required for the WK to be processed as a product can be obtained. . Based on these results, the CO concentration threshold CT is set at 10% by volume in the present embodiment. However, the threshold CT is not limited to 10% by volume, and may be set to any value based on the carburizing quality required for the WK to be processed, the effect on the carburizing gas supply amount, and the like. For example, the threshold CT is preferably set at a concentration of 5% by volume or more and 15% by volume or less based on the experimental results in FIG.

As described above, according to the vacuum carburizing method of the present embodiment, the carburizing gas 90 is supplied to the carburizing furnace 20, and the carbon monoxide concentration C1 of the exhaust gas from the carburizing furnace 20 is measured. A pretreatment step of supplying the carburizing gas 90 to the carburizing furnace 20 until the concentration C1 becomes equal to or less than a predetermined threshold, a carburizing step of placing the WK to be processed inside the carburizing furnace 20 and supplying the carburizing gas 90; It has By supplying the carburizing gas to the processing chamber 26 in the pretreatment process, the foreign matter such as the oxide 96 deposited in the processing chamber 26 of the carburizing furnace 20 can be removed and the processing chamber 26 can be cleaned. Consumption of carburizing gas by foreign matter can be suppressed, and deterioration of carburizing quality in the WK to be processed can be suppressed or prevented. By measuring the carbon monoxide concentration C1, it is possible to estimate the amount of carburizing gas consumed for cleaning the processing chamber 26 in the pretreatment process and the degree of progress of cleaning the processing chamber 26. FIG. For example, by setting the threshold CT at which a sufficient carburizing quality is obtained, it is possible to supply an appropriate amount of carburizing gas for obtaining a sufficient carburizing quality in the pretreatment process. Therefore, unnecessary consumption of carburizing gas in the pretreatment process can be suppressed, and productivity can be increased.

In the vacuum carburizing method of the present embodiment, the threshold CT is set at any concentration of 5% by volume or more and 15% by volume or less. By setting the threshold value CT at a carbon monoxide concentration of 15% by volume or less, it is possible to obtain a carburizing quality that is at least the same level as the carburizing quality when an unused carburizing furnace 20 is used. By setting the carbon monoxide concentration to 5% by volume or more, it is possible to suppress or prevent excessive supply of carburizing gas in the pretreatment step.

According to the vacuum carburizing method of this embodiment, the threshold CT is set at 10% by volume. Carburizing quality required for the workpiece WK can be efficiently obtained without excessively supplying carburizing gas in the pretreatment process.

According to the vacuum carburizing method of the present embodiment, the furnace cleaning step of supplying air to the carburizing furnace 20 whose temperature has been raised is provided prior to the pretreatment step. Foreign matter such as free carbon deposited in the processing chamber 26 can be removed by a simple burnout method. In addition, the oxide 96 generated in the furnace cleaning process can be removed by the pretreatment process, and deterioration of the carburizing quality due to the furnace cleaning process can be suppressed or prevented.

B. Other embodiments:
(B1) In the first embodiment, in the pretreatment step, the carbon monoxide concentration C1 of the exhaust gas from the carburizing furnace 20 is measured, and the carburizing furnace continues until the carbon monoxide concentration C1 becomes equal to or lower than the predetermined threshold value CT. An example of supplying the carburizing gas 90 to 20 is shown. On the other hand, a configuration may be adopted in which the threshold CT is not used in the preprocessing step. For example, in the pretreatment step, a predetermined amount of carburizing gas may be supplied to the carburizing furnace 20 . According to this form of the vacuum carburizing method, the CO concentration sensor 40 can be omitted, and the number of parts of the vacuum carburizing apparatus 100 can be reduced. Also, control by the control device 80 can be simplified.

Predetermined feed rate means the feed rate that can be used to clean the processing chamber 26 and is the amount of carburizing gas that can be consumed to remove contaminants such as oxide 96 deposited in the processing chamber 26. . The supply amount of the carburizing gas is preferably set based on the experimental results shown in FIG. The supply amount of the carburizing gas can be set, for example, by using the supply amount that shows that the carbon monoxide concentration is 10% by volume or less in the experimental results shown in FIG. Specifically, as shown in the graph G1, when using an unused carburizing furnace 20, it is possible to set the supply amount of the carburizing gas to be V2. As shown in graph G2, when using the carburizing furnace 20 with a large cumulative number of times of use, the amount of carburizing gas supplied in the pretreatment process is set to be larger than when using the carburizing furnace 20 with a small cumulative number of times of use. preferably. For example, when using a carburizing furnace 20 that has been used a large number of times, it is possible to set the supply amount of carburizing gas to be V4. According to this aspect of the vacuum carburizing method, even if the amount of oxide 96 deposited in the processing chamber 26 increases due to an increase in the cumulative number of times the carburizing furnace 20 is used, it can be removed by the pretreatment process. can. Therefore, it is possible to suppress or prevent deterioration of carburizing quality due to an increase in the cumulative number of times the carburizing furnace 20 is used.

The controller and techniques described in this disclosure may be implemented by a dedicated computer provided by configuring a processor and memory programmed to perform one or more functions embodied by the computer program. may be Alternatively, the controller and techniques described in this disclosure may be implemented by a dedicated computer provided by configuring the processor with one or more dedicated hardware logic circuits. Alternatively, the control units and techniques described in this disclosure can be implemented by a combination of a processor and memory programmed to perform one or more functions and a processor configured by one or more hardware logic circuits. It may also be implemented by one or more dedicated computers configured. The computer program may also be stored as computer-executable instructions on a computer-readable non-transitional tangible recording medium.

The present disclosure is not limited to the embodiments described above, and can be implemented in various configurations without departing from the scope of the present disclosure. For example, the technical features in the embodiments corresponding to the technical features in the respective modes described in the Summary of the Invention column may be used to solve some or all of the above problems, or Substitutions and combinations may be made as appropriate to achieve part or all. Also, if the technical features are not described as essential in this specification, they can be deleted as appropriate.

DESCRIPTION OF SYMBOLS 20... Carburizing furnace 22... Thermal insulation wall 22S... Inner wall 24... Exchange door 26... Processing chamber 28... Heater 31... Carburizing gas supply source 32... Supply amount adjusting device 33... Vacuum pump 38... Carburizing Gas supply path 39 Gas discharge path 40 CO concentration sensor 42 Temperature sensor 44 Pressure sensor 80 Control device 82 CPU 84 Memory 90 Carburizing gas 94 Hydrogen 96 Oxide 98 Carbon monoxide 100 Vacuum carburizing equipment WK Processing object

Claims (7)

A vacuum carburizing method,
A carburizing gas is supplied to the carburizing furnace in a decompressed and heated state, and the carbon monoxide concentration of the exhaust gas from the carburizing furnace is measured, and the carburizing is performed until the carbon monoxide concentration is equal to or lower than a predetermined threshold. a pretreatment step of supplying the carburizing gas to the furnace;
After the pretreatment step, a carburizing step of placing the object to be processed in the carburizing furnace in a decompressed and heated state and supplying the carburizing gas;
Vacuum carburizing method. 2. The vacuum carburizing method according to claim 1, wherein the threshold value is any concentration of 5% by volume or more and 15% by volume or less. 3. The vacuum carburizing method according to claim 2, wherein the threshold is 10% by volume. The vacuum carburizing method according to any one of claims 1 to 3,
Further, a furnace cleaning step of supplying air to the carburizing furnace whose temperature has been raised is provided before the pretreatment step,
Vacuum carburizing method. A vacuum carburizing method,
a pretreatment step of supplying a predetermined supply amount of carburizing gas used for cleaning the carburizing furnace to the carburizing furnace in a decompressed and heated state;
After the pretreatment step, a carburizing step of placing the object to be processed in the carburizing furnace in a decompressed and heated state and supplying the carburizing gas;
Vacuum carburizing method. The vacuum carburizing method according to claim 5,
In the pretreatment step, the carburizing gas is supplied such that the supply amount when the carburizing furnace has been used a large number of times is larger than the supply amount when the carburization furnace has been used a small number of times.
Vacuum carburizing method. A vacuum carburizing apparatus,
a carburizing furnace;
a carburizing gas supply source that stores carburizing gas;
a carburizing gas supply path connecting the carburizing gas supply source and the carburizing furnace;
a supply amount adjusting device provided in the carburizing gas supply passage for adjusting the supply amount of the carburizing gas to the carburizing furnace;
a gas discharge path connected to the carburizing furnace;
a carbon monoxide concentration sensor provided in at least one of the carburizing furnace and the gas discharge path;
and a control device that controls the supply amount adjustment device,
The control device supplies the carburizing gas to the carburizing furnace in a decompressed and heated state, measures the concentration of carbon monoxide in the exhaust gas from the carburizing furnace, and performing a pretreatment of supplying the carburizing gas to the carburizing furnace until it becomes equal to or less than the threshold;
After the pretreatment is performed, the object to be processed is placed inside the carburizing furnace in a decompressed and heated state, and the carburizing gas is supplied.
Vacuum carburizing equipment.

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