Gas carburizing furnace and method for diagnosing abnormalities in a gas carburizing furnace

Abstract

In the gas carburizing process, this system enables early detection of abnormalities in the gas carburizing furnace. [Solution] In a gas carburizing furnace for gas carburizing workpieces, the furnace is provided with a processing chamber to which enriched gas is supplied, a gas concentration measuring unit for measuring the gas concentration in the processing chamber in order to calculate the carbon potential in the processing chamber, a flow rate measuring unit for measuring the supply flow rate of the enriched gas supplied to the processing chamber, and a control unit that controls the supply flow rate of the enriched gas so that the carbon potential measurement value calculated based on the gas concentration becomes a predetermined carbon potential target value. Furthermore, the control unit is configured to execute control to determine that an abnormality has occurred in the gas carburizing furnace when the supply flow rate of the enriched gas with adjusted flow rate is not the appropriate flow rate set in advance according to the carbon potential target value.

Description

Technical Field

[0001] The present invention relates to a gas carburizing furnace and an abnormality diagnosis method for a gas carburizing furnace. Background Art

[0002] As a heat treatment for improving the durability of automobile parts, mechanical parts and the like made of steel materials, carburizing treatment is known which hardens the workpiece surface by dissolving carbon into the workpiece surface (part surface). As one specific carburizing treatment method, there is gas carburizing treatment in which enriched gas is supplied into a carburizing furnace, and carburizing of a workpiece is performed while the inside of the carburizing furnace is maintained in an atmosphere having a predetermined carbon potential and a predetermined temperature.

[0003] As a conventional technology related to gas carburizing treatment, Patent Document 1 discloses that an index value of carbon potential determined by the ratio of the CO₂ gas concentration in the furnace atmosphere to the square of the CO gas concentration is adjusted to a predetermined value corresponding to the furnace temperature by adjusting the valve opening degree of a flow control valve that supplies endothermic modified gas into the furnace. In this method, in a control region where the control target value of the carbon potential index value is constant, when the actually measured value of the index value falls within a certain range relative to the control target value, the valve opening degree is changed by a predetermined amount according to the valve opening degree at this time point. The atmosphere control method described in Patent Document 1 attempts to prevent excessive overshoot of carbon potential.

[0004] Patent Document 2 proposes a carburizing method that mitigates the deviation between the measured value of carbon potential based on the O₂ concentration in the furnace during carburizing treatment and the actual value, and reduces the cost required for enriched gas. Prior Art Documents Patent Documents

[0005] Patent Document 1 Japanese Unexamined Patent Application Publication No. 2005-076109 Patent Document 2 Japanese Patent Publication No. 2020-196943 [Overview of the project] [Problems that the invention aims to solve]

[0006] When controlling the atmosphere inside a furnace using the method described in Patent Document 1, the carbon potential value calculated from the CO2 gas concentration and CO gas concentration is used as the measured value of the carbon potential of the furnace atmosphere. However, during operation, malfunctions or other abnormalities may occur in the equipment used to measure the CO2 gas concentration or CO gas concentration. When an abnormality occurs in the gas concentration measuring equipment, the carbon potential value calculated from the above gas concentration will not reflect the actual carbon potential of the furnace atmosphere. In this case, the atmosphere control inside the furnace will be carried out based on an incorrect carbon potential value that does not reflect the actual carbon potential of the furnace atmosphere, and proper atmosphere control cannot be achieved.

[0007] Furthermore, when controlling the furnace atmosphere using the method described in Patent Document 2, the carbon potential value calculated from the O2 gas concentration and furnace temperature is used as the measured value of the carbon potential of the furnace atmosphere. However, when a gas containing CH4 (methane), such as natural gas, is used as the enrichment gas, the CH4 decomposes, turns into soot, and accumulates at the electrode of the O2 concentration meter, making it impossible to accurately measure the O2 gas concentration of the furnace atmosphere. For this reason, in the furnace atmosphere control method described in Patent Document 2, if there is a malfunction in the O2 gas concentration measuring instrument, the carbon potential value calculated from the O2 gas concentration and furnace temperature will not reflect the actual carbon potential of the furnace atmosphere, making it impossible to perform appropriate atmosphere control.

[0008] As described above, in conventional atmospheric control methods for gas carburizing processes, atmospheric control may be performed without detecting abnormalities in the gas concentration measuring equipment used to calculate the carbon potential, resulting in an inability to perform proper atmospheric control. Furthermore, the fact that proper atmospheric control is not being performed is only discovered when the desired carburizing quality is not achieved during product inspection of the workpiece after carburizing. Therefore, conventional atmospheric control methods cannot detect early on when a gas carburizing furnace is in a state where it cannot perform carburizing properly.

[0009] This invention has been made in view of the above circumstances, and aims to enable early detection of abnormalities in a gas carburizing furnace during gas carburizing treatment. [Means for solving the problem]

[0010] One aspect of the present invention, which solves the above problems, is a gas carburizing furnace for performing gas carburizing treatment of a workpiece, comprising: a treatment chamber to which enriched gas is supplied; a gas concentration measuring unit for measuring the gas concentration in the treatment chamber for calculating the carbon potential in the treatment chamber; a flow rate measuring unit for measuring the supply flow rate of the enriched gas supplied to the treatment chamber; and a control unit that controls the supply flow rate of the enriched gas so that the carbon potential measurement value calculated based on the gas concentration becomes a predetermined carbon potential target value, wherein the control unit determines that an abnormality has occurred in the gas carburizing furnace when the flow rate of the enriched gas supply, which has been adjusted, is not an appropriate flow rate set in advance according to the carbon potential target value.

[0011] Another aspect of the present invention relates to a method for diagnosing an abnormality in a gas carburizing furnace that performs gas carburizing of a workpiece, wherein the gas carburizing furnace adjusts the supply flow rate of enriched gas supplied to the processing chamber so that a carbon potential measurement value calculated based on the gas concentration in the processing chamber to which the enriched gas is supplied becomes a predetermined carbon potential target value, and it is determined that an abnormality has occurred in the gas carburizing furnace when the flow rate of the enriched gas supplied, which has been adjusted, is not an appropriate flow rate set in advance according to the carbon potential target value. [Effects of the Invention]

[0012] According to the present invention, it is possible to detect an abnormality in the gas carburizing furnace at an early stage during the gas carburizing process. [Brief explanation of the drawing]

[0013] [Figure 1] This figure shows a schematic configuration of a gas carburizing furnace according to an embodiment of the present invention. [Figure 2] This is a schematic top view of a gas carburizing furnace showing the mounting position of the oxygen sensor. [Figure 3] This is a flowchart illustrating an example of a method for diagnosing abnormalities in a gas carburizing furnace according to an embodiment of the present invention. [Figure 4] This figure schematically shows actual data on the enrichment gas supply flow rate when a product with the desired carburization quality is obtained. [Figure 5] This figure shows the range of the appropriate enriched gas supply flow rate, which was set based on the above performance data. [Figure 6] This is a flowchart illustrating another example of a method for diagnosing abnormalities in a gas carburizing furnace according to an embodiment of the present invention. [Modes for carrying out the invention]

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present specification and drawings, elements having substantially the same functional configuration are denoted by the same reference numerals, and duplicate description thereof is omitted.

[0015] FIG. 1 is a diagram showing a schematic configuration of a gas carburizing furnace 1 according to the present embodiment. The gas carburizing furnace 1 in the present embodiment is a continuous gas carburizing furnace capable of sequentially loading workpieces W as objects to be processed into the furnace and sequentially performing carburizing treatment on each workpiece W moving in the furnace.

[0016] As shown in FIG. 1, the gas carburizing furnace 1 includes, from the inlet side to the outlet side of the furnace (from the left side to the right side in FIG. 1), as processing chambers for performing predetermined heat treatment on the workpieces W, a preheating chamber 2, a carburizing chamber 3, a diffusion chamber 4, a temperature lowering chamber 5, and an oil tank 6 in this order. When the workpiece W passes through the preheating chamber 2, the carburizing chamber 3, the diffusion chamber 4, the temperature lowering chamber 5, and the oil tank 6, the workpiece W is subjected to carburizing quenching treatment. The workpiece W is a component such as an automobile part made of steel, other mechanical parts, or the like, for example.

[0017] On the inlet side of the preheating chamber 2, there are provided a carry-in port 10 for carrying in the workpiece W, and a liftable door 11 that opens and closes the carry-in port 10. Between the preheating chamber 2 and the carburizing chamber 3, there are provided a passage port 12 through which the workpiece W passes, and a liftable shutter 13 that closes the passage port 12. Between the carburizing chamber 3 and the diffusion chamber 4, there are provided a passage port 14 through which the workpiece W passes, and a liftable shutter 15 that closes the passage port 14. Between the diffusion chamber 4 and the temperature lowering chamber 5, there are provided a passage port 16 through which the workpiece W passes, and a liftable shutter 17 that closes the passage port 16.

[0018] Even when the passage ports 12, 14, and 16 are closed by the shutters 13, 15, and 17, gaps exist between the passage ports 12, 14, 16 and the shutters 13, 15, 17, respectively. Therefore, even when the passage ports 12, 14, and 16 are closed by the shutters 13, 15, and 17, the atmospheres in the processing chambers of the preheating chamber 2, the carburizing chamber 3, the diffusion chamber 4, and the temperature lowering chamber 5 communicate with each other through the gaps.

[0019] An outlet side of the temperature lowering chamber 5 is provided with a passage port 18 through which a workpiece W passes, and a liftable door 19 that opens and closes the passage port 18. A hole 19a is formed in the door 19, and the atmospheres in the temperature lowering chamber 5 and the oil tank 6 communicate with each other through the hole 19a. Further, the oil tank 6 is provided with a carry-out port 20 for carrying out the workpiece W, and a liftable door 21 that opens and closes the carry-out port 20. Quenching oil is stored in a lower portion inside the oil tank 6, and the workpiece W in the oil tank 6 is configured to be liftable between an oil storage region and a space above the storage region.

[0020] A roller conveyor 30 for conveying the workpiece W is provided at the bottom portions inside the preheating chamber 2, the carburizing chamber 3, the diffusion chamber 4, and the temperature lowering chamber 5. The workpiece W is carried in from a carry-in port 10 by the roller conveyor 30, passes through the passage ports 12, 14, 16, and 18, is subjected to quenching treatment in the oil tank 6, and is then carried out from the carry-out port 20.

[0021] Modified gas (RX gas) supply passages 40, 41, 42, 43, and 44 for supplying modified gas are respectively connected to the preheating chamber 2, the carburizing chamber 3, the diffusion chamber 4, the temperature lowering chamber 5, and the oil tank 6. The modified gas mainly consists of CO (carbon monoxide) gas, H₂ (hydrogen) gas, and N₂ (nitrogen) gas, and contains trace amounts of CO₂ (carbon dioxide) and H₂O (water). This modified gas is supplied from a modified furnace (not shown) for generating modified gas. The supply flow rate of the modified gas is preset in accordance with the target value of carbon potential in each treatment chamber, and the modified gas is supplied to each treatment chamber at a constant flow rate during the operation of the gas carburizing furnace 1.

[0022] The modified gas supply lines 40, 41, 42, 43, and 44 are each equipped with modified gas flow rate control valves 45, 46, 47, 48, and 49, respectively. The opening degree of each modified gas flow rate control valve 45 to 49 is adjusted based on a control signal output from the control unit 100, which will be described later. Upstream of the modified gas flow rate control valves 46, 47, and 48, modified gas flow meters 50, 51, and 52 are provided as flow rate measuring units to measure the supply flow rate of modified gas flowing through the modified gas supply lines 41, 42, and 43. The measured value information of the modified gas supply flow rate measured by each modified gas flow meter 50 to 52 is output to the control unit 100, which will be described later.

[0023] The carburizing chamber 3, diffusion chamber 4, and cooling chamber 5 are supplied with enriched gas (C m H n Enriched gas supply lines 60, 61, and 62, which supply, for example, city gas, are connected to each other. Enriched gas flow control valves 63, 64, and 65 are provided in enriched gas supply lines 60, 61, and 62, respectively, and the opening degree of each enriched gas flow control valve 63 to 65 is adjusted based on a control signal output from a control unit 100, which will be described later. Upstream of the enriched gas flow control valves 63, 64, and 65, enriched gas flow meters 66, 67, and 68 are provided as flow rate measuring units to measure the supply flow rate of enriched gas flowing through the enriched gas supply lines 60, 61, and 62. The measured value information of the enriched gas supply flow rate measured by each enriched gas flow meter 66 to 68 is output to the control unit 100, which will be described later.

[0024] An air supply passage 70 is connected to the cooling chamber 5. An air flow control valve 71 is provided in the air supply passage 70.

[0025] An exhaust passage 80 is connected to the upper part of the preheating chamber 2, and an exhaust passage 81 is connected to the upper part of the oil tank 6. The atmosphere inside the preheating chamber 2 and the atmosphere inside the oil tank 6, as well as the atmosphere inside the carburizing chamber 3, diffusion chamber 4, and cooling chamber 5 that flow into the preheating chamber 2 or oil tank 6, are discharged through the exhaust passage 80 or exhaust passage 81.

[0026] Each of the preheating chamber 2, carburizing chamber 3, diffusion chamber 4, and cooling chamber 5 is equipped with a fan 90 on its ceiling to agitate the atmosphere within each chamber. Additionally, each of the preheating chamber 2, carburizing chamber 3, diffusion chamber 4, and cooling chamber 5 is equipped with a heater (not shown) to heat the atmosphere within each chamber.

[0027] Figure 2 is a schematic diagram of the gas carburizing furnace 1 viewed from above. As shown in Figure 2, oxygen sensors 95, 96, 97, and 98 are provided on the side walls of the preheating chamber 2, carburizing chamber 3, diffusion chamber 4, and cooling chamber 5, respectively, to measure the oxygen gas concentration in the atmosphere inside each processing chamber. The measured oxygen gas concentration information from each of the oxygen sensors 95 to 98 is output to the control unit 100, which will be described later, and is used to calculate the carbon potential inside each processing chamber.

[0028] As shown in Figures 1 and 2, the gas carburizing furnace 1 is controlled by a control unit 100. The control unit 100 is a computer equipped with, for example, a CPU and memory, and has a program storage unit (not shown).

[0029] The program storage unit stores programs for achieving predetermined heat treatments in each processing chamber of the gas carburizing furnace 1. For example, the program storage unit stores a program for calculating the carbon potential in each processing chamber—preheating chamber 2, carburizing chamber 3, diffusion chamber 4, and cooling chamber 5—using a well-known calculation method based on the measured oxygen gas concentration values ​​measured by oxygen sensors 95, 96, 97, and 98. The program storage unit also stores a program for determining whether the enriched gas supply flow rate measured by enriched gas flow meters 66, 67, and 68 is an appropriate flow rate preset according to the target carbon potential values ​​in each processing chamber—carburizing chamber 3, diffusion chamber 4, and cooling chamber 5. Furthermore, the program storage unit also stores programs for controlling the enriched gas supply flow rate and for performing various determinations, as described in the flowchart below.

[0030] The above program may be recorded on a computer-readable storage medium and installed from that storage medium to the control unit 100. Furthermore, the control unit 100 may be configured to perform all functions as a control device on the equipment side of the gas carburizing furnace 1, or it may consist of an equipment-side control device and an external control device. For example, the control unit 100 may be configured to transmit measured value information of the enriched gas supply flow rate, etc., from the programmable logic controller (PLC) of the gas carburizing furnace 1 to an external server, and for the external server to determine whether the enriched gas supply flow rate is appropriate.

[0031] The general configuration of the gas carburizing furnace 1 according to this embodiment has been described above. Next, a method for diagnosing abnormalities in this gas carburizing furnace 1 will be described.

[0032] Figure 3 shows an example of a flowchart illustrating an abnormality diagnosis method. While the flowchart in Figure 3 illustrates a method for diagnosing abnormalities in the gas carburizing furnace 1 based on atmospheric information within the carburizing chamber 3, one of the processing chambers of the gas carburizing furnace 1, a similar abnormality diagnosis method can be applied to other processing chambers to which enrichment gas and modified gas are supplied (e.g., diffusion chamber 4, cooling chamber 5, etc.). Furthermore, the steps described below are not limited to being performed by automatic control by the control unit 100. For example, the step involving judgment may be performed by an operator.

[0033] (Step S1) First, the carbon potential in the carburizing chamber 3 into which the workpiece W is loaded is measured. Specifically, the carbon potential in the carburizing chamber 3 is calculated using a well-known calculation method, using the ambient temperature in the carburizing chamber 3 and the measured oxygen gas concentration in the carburizing chamber 3 measured by the oxygen sensor 96. In this embodiment, the carbon potential calculated here is referred to as the carbon potential measurement value (CP measurement value).

[0034] (Step S2) Next, the supply flow rate of enriched gas into the carburizing chamber 3 is adjusted so that the above CP measurement value matches the preset carbon potential target value (CP target value). Specifically, the opening degree of the enriched gas flow control valve 63 is adjusted to increase or decrease the supply flow rate of enriched gas into the carburizing chamber 3.

[0035] (Step S3) Next, it is determined whether the adjusted enriched gas supply flow rate is the appropriate flow rate pre-set according to the CP target value. The appropriate flow rate according to the CP target value is the enriched gas supply flow rate set assuming that the loading quantity and packaging are the same for each type of workpiece being processed, when processing the workpiece under the atmosphere of the CP target value. Such an appropriate flow rate according to the CP target value is set in advance before the carburizing treatment of the workpiece to be carburized is carried out. As mentioned above, the appropriate enriched gas flow rate according to the CP target value is set for each type of workpiece being processed, and an example of the detailed setting method will be explained with reference to Figures 4 and 5.

[0036] Figure 4 schematically shows the actual data of the enrichment gas supply flow rate in the carburizing chamber when a product with the desired carburizing quality is obtained at a certain CP target value. In this figure, the actual data of the enrichment gas supply flow rate for multiple processing lots of the same product that have been carburized in the past is plotted together, and such actual data is stored in the control unit 100, for example. As shown in Figure 4, the enrichment gas supply flow rate fluctuates over time, and the reason for this fluctuation is that step S2 is executed in accordance with the fluctuation of the CP measurement value in the carburizing chamber 3.

[0037] Based on the actual enrichment gas supply flow rate data shown above, the appropriate enrichment gas supply flow rate is set when the desired carburizing quality is obtained at a certain CP target value, as shown in Figure 5. For example, by setting the upper limit of the enrichment gas supply flow rate for each elapsed time from the data plotted in Figure 4 as the upper limit of the appropriate flow rate, and the lower limit of the enrichment gas supply flow rate for each elapsed time as the lower limit of the appropriate flow rate, the appropriate flow rate used in step S3 is set.

[0038] In step S3, if the enriched gas supply flow rate is at the appropriate flow rate set according to the CP target value, the gas carburizing furnace 1 is operating normally. In this case, steps S1 and S2 are executed to continue adjusting the enriched gas supply flow rate based on the CP measurement value.

[0039] On the other hand, if the enriched gas supply flow rate in step S3 is not the appropriate flow rate set according to the CP target value, an abnormality in the gas carburizing furnace 1 is suspected. For example, if the gas carburizing furnace 1 is in a normal state, the enriched gas supply flow rate into the carburizing chamber 3 should be within the range of the appropriate flow rate set according to the CP target value, due to the execution of step S2 described above. Nevertheless, if the enriched gas supply flow rate falls outside the range of the appropriate flow rate according to the CP target value, it means that even though the enriched gas supply flow rate is adjusted in step S2, the adjusted enriched gas supply flow rate is an unnatural flow rate when compared to past carburizing treatment performance data in which the desired quality was obtained.

[0040] Therefore, in step S3, a determination is made as needed to determine whether the enriched gas supply flow rate is the appropriate flow rate set according to the CP target value. If the enriched gas supply flow rate is not the appropriate flow rate, it is determined that the gas carburizing furnace 1 is in an abnormal state where it cannot perform proper carburizing treatment. In this embodiment, in order to identify the cause of the abnormality in such a case, the following steps S4 to S6 are performed.

[0041] (Step S4) In step S4, it is determined whether the enriched gas supply flow rate is greater than the appropriate flow rate. If the enriched gas supply flow rate is greater than the appropriate flow rate in step S4, step S5 is executed. On the other hand, if the enriched gas supply flow rate is less than the appropriate flow rate in step S4, step S6 is executed.

[0042] (Step S5) In step S5, it is determined whether the supply flow rate of the modified gas from the modified furnace (not shown) is appropriate. The appropriate flow rate of the modified gas is predetermined according to the CP target value in each processing room, and a method commonly used by those skilled in the art can be applied to determine the appropriate flow rate.

[0043] In step S5, if the modified gas supply flow rate is at the appropriate rate, it is determined that the abnormality in the gas carburizing furnace 1 is caused by an abnormality in the oxygen sensor 96. When an abnormality occurs in the oxygen sensor 96, the oxygen gas concentration in the carburizing chamber 3 cannot be accurately measured, and the adjustment of the enriched gas supply flow rate in step S2 described above cannot be properly performed. In such cases, maintenance work such as replacing the oxygen sensor 96 is performed.

[0044] On the other hand, in step S5, if the modified gas supply flow rate is not appropriate, it is determined that there is an abnormality in the piping connecting the modified furnace (not shown) to the carburizing chamber 3. When a malfunction such as a leak of modified gas occurs in the piping, the predetermined amount of modified gas is not supplied to the modified gas supply passage 41, and the CP measurement value in the carburizing chamber 3 deviates from the CP target value. However, in step S2 described above, the supply flow rate of the enrichment gas is adjusted, not the modified gas whose supply flow rate is abnormal, making it difficult to maintain an appropriate carburizing atmosphere in the carburizing chamber 3. In the event of such a piping abnormality, the location of the abnormality in the piping is identified and maintenance work such as replacement is performed.

[0045] (Step S6) In step S6, it is determined whether the hydrocarbon component (CH component) of the modified gas supplied from the modified furnace (not shown) is at an appropriate level. The appropriate level of the hydrocarbon component of the modified gas is predetermined according to the target modified gas composition and modification temperature, and a method commonly used by those skilled in the art can be applied to determine the appropriate level.

[0046] In step S6, if the hydrocarbon component of the modified gas is at an appropriate level, it is determined that the abnormality in the gas carburizing furnace 1 is caused by a malfunction in the oxygen sensor 96. It is found that, due to such a malfunction in the oxygen sensor 96, the oxygen gas concentration in the carburizing chamber 3 is not accurately measured, and the adjustment of the enrichment gas supply flow rate in step S2 described above is not being performed properly. If there is a malfunction in the oxygen sensor 96, the abnormality is addressed by performing maintenance work, such as replacing the oxygen sensor 96.

[0047] On the other hand, in step S6, if the hydrocarbon components of the modified gas are not at the appropriate level, it is determined that there is a malfunction in the modified furnace (not shown) equipment. If a modified gas with a predetermined composition corresponding to the CP target value is not produced due to such a malfunction in the modified furnace equipment, the CP measurement value in the carburizing chamber 3 will deviate from the CP target value. However, in step S2 described above, the supply flow rate of the enriched gas is adjusted rather than the modified gas with an inappropriate hydrocarbon component, making it difficult to maintain an appropriate carburizing atmosphere in the carburizing chamber 3. Malfunctions in the modified furnace can occur, for example, due to soot accumulation on the walls inside the modified furnace or deterioration of the catalyst used in the modified furnace. In such cases, maintenance work such as burnout or catalyst replacement inside the modified furnace is performed.

[0048] As explained above, in the method for determining abnormalities in the gas carburizing furnace 1 according to this embodiment, the existence of step S3 illustrated in Figure 3 makes it possible to detect an abnormality in the gas carburizing furnace 1 before product inspection of the workpiece W removed from the gas carburizing furnace 1. In other words, an abnormality in the gas carburizing furnace 1 can be detected early, even during the carburizing process of the workpiece W.

[0049] Furthermore, in order to identify the cause of the abnormality in the gas carburizing furnace 1, it is preferable to perform at least one of steps S5 and S6 shown in Figure 3. When steps to identify the cause of the abnormality, such as step S5 and step S6, are performed, a control signal is output from the control unit 100 to notify that an abnormality has occurred, and this is communicated to the operator via a display unit such as a display or an audio generating unit such as a speaker.

[0050] The flow for identifying the cause of the abnormality in the gas carburizing furnace 1 is not limited to that exemplified in Figure 3, and for example, step S7 as shown in Figure 6 may be performed. Step S7 is performed when the modified gas supply flow rate was appropriate in step S6, and in step S7, it is determined whether the seasoning performed when the gas carburizing furnace 1 starts up has been properly carried out. Seasoning is a process performed as one of the furnace start-up operations, and before the workpiece W is brought into the gas carburizing furnace 1, the process involves heating each processing chamber and supplying a predetermined gas to each processing chamber to create an atmosphere with a target carbon potential and maintaining it for a certain period of time.

[0051] In step S7, if the seasoning was performed correctly, it is determined that an abnormality has occurred in the oxygen sensor 96. In this case, the abnormality in the gas carburizing furnace 1 is addressed by, for example, replacing the oxygen sensor 96. On the other hand, in step S7, if the seasoning was not performed correctly, it is determined that an abnormality has occurred due to a defect in the startup procedure of the gas carburizing furnace 1. In this case, the abnormality in the gas carburizing furnace 1 is addressed by performing the seasoning again.

[0052] In the above example, when measuring the carbon potential, the carbon potential was calculated based on the oxygen gas concentration in the processing chamber measured by an oxygen sensor. However, the method for calculating the carbon potential is not limited to a method that uses the measured oxygen gas concentration. For example, the carbon potential may be calculated using a well-known method that utilizes the measured carbon dioxide concentration in the processing chamber using a carbon dioxide (CO2) infrared analyzer. In other words, the configuration of the gas concentration measuring unit for measuring the gas concentration in the processing chamber to calculate the carbon potential in the processing chamber is not limited to an oxygen sensor or a carbon dioxide infrared analyzer.

[0053] Furthermore, although the gas carburizing furnace 1 in the above example was a continuous gas carburizing furnace capable of continuously performing preheating, carburizing, diffusion, cooling, and quenching treatments of the workpiece W, it may also be a batch-type gas carburizing furnace. Even with a batch-type gas carburizing furnace, the processes of steps S2 and S3 described above can be applied to the treatment chamber that supplies the enrichment gas and the modified gas, allowing for early detection of abnormalities in the gas carburizing furnace.

[0054] Here, we will explain the effects and results of introducing the gas carburizing furnace according to this embodiment. In the atmospheric carburizing process for automotive parts, when using a conventional gas carburizing furnace, the number of consecutive defective lots caused by oxygen sensor malfunctions was 4 per year. On the other hand, when using the gas carburizing furnace according to this embodiment, the malfunction was detected early by performing the malfunction diagnosis shown in Figure 3, resulting in 0 consecutive defective lots caused by oxygen sensors (no occurrences).

[0055] Although embodiments of the present invention have been illustrated above, the present invention is not limited to these examples. It will be obvious to those skilled in the art that various modifications or alterations can be conceived within the scope of the technical idea described in the claims, and these will naturally also fall within the technical scope of the present invention.

[0056] For example, the constituent elements of the above embodiments can be combined in any way. From such any combination, the functions and effects of each constituent element in the combination will naturally be obtained, as well as other functions and effects that will be obvious to those skilled in the art from the description herein.

[0057] Furthermore, the effects described herein are merely descriptive or illustrative and not limiting. In other words, the technology relating to this disclosure may produce other effects that are obvious to those skilled in the art from the description herein, in addition to or instead of the effects described herein. [Industrial applicability]

[0058] This invention can be applied to gas carburizing treatment of workpieces such as automobile parts and machine parts. [Explanation of symbols]

[0059] 1. Gas Carburizing Furnace 2 Preheating chamber 3 Carburizing chamber 4 Diffusion chamber 5 Cooling chamber 6 Oil tank 10 Loading entrance 11 Doors 12, 14, 16, 18 Passage gate 13, 15, 17 Shutter 19 Doors 20 Exit 21 Doors 30 Roller conveyor 40-44 Transformed gas supply lines 45-49 Modified gas flow control valve 50-52 Modified Gas Flow Meter 60-62 Enriched gas supply route 63-65 Enrichment gas flow control valve 66-68 Enriched gas flow meter 70 Air supply path 71 Air flow control valve 80, 81 Exhaust passage 90 Fans 95-98 Oxygen Sensor 100 Control Unit Double job

Claims

1. A gas carburizing furnace for performing gas carburizing treatment on a workpiece, The processing room to which enriched gas is supplied, A gas concentration measuring unit for measuring the gas concentration in the processing chamber in order to calculate the carbon potential in the processing chamber, A flow rate measuring unit for measuring the supply flow rate of enriched gas supplied into the processing chamber, The system includes a control unit that controls the supply flow rate of the enriched gas so that the carbon potential measurement value calculated based on the gas concentration becomes a predetermined carbon potential target value, A gas carburizing furnace, characterized in that the control unit performs control to determine that an abnormality has occurred in the gas carburizing furnace when the supply flow rate of the enriched gas, whose flow rate has been adjusted, is not an appropriate flow rate set in advance according to the carbon potential target value.

2. The gas carburizing furnace according to claim 1, characterized in that the control unit determines whether the flow rate of the modified gas in the processing chamber is a preset appropriate flow rate when the supply flow rate of the enriched gas, whose flow rate has been adjusted, is greater than the appropriate flow rate.

3. The gas carburizing furnace according to claim 2, characterized in that the control unit determines that an abnormality has occurred in the gas concentration measuring unit when the supply flow rate of the modified gas is at the appropriate flow rate.

4. The gas carburizing furnace according to claim 1, characterized in that the control unit determines whether the hydrocarbon components of the modified gas in the processing chamber are at a preset appropriate value when the supply flow rate of the enriched gas, whose flow rate has been adjusted, is less than the appropriate flow rate.

5. The gas carburizing furnace according to claim 4, characterized in that the control unit determines that an abnormality has occurred in the gas concentration measuring unit when the hydrocarbon component is at the appropriate value.

6. A method for diagnosing abnormalities in a gas carburizing furnace that performs gas carburizing treatment on a workpiece, The gas carburizing furnace adjusts the supply flow rate of enriched gas supplied to the processing chamber so that the carbon potential measurement value, calculated based on the gas concentration in the processing chamber to which the enriched gas is supplied, reaches a predetermined carbon potential target value. An abnormality diagnosis method characterized by determining that an abnormality has occurred in the gas carburizing furnace when the supply flow rate of the enriched gas, whose flow rate has been adjusted, is not the appropriate flow rate set in advance according to the carbon potential target value.

7. The abnormality diagnosis method according to claim 6, characterized in that when the supply flow rate of the enriched gas, which has been adjusted for flow rate, is greater than the appropriate flow rate, the cause of the abnormality of the gas carburizing furnace is identified based on whether or not the supply flow rate of the modified gas in the processing chamber is at a preset appropriate flow rate.

8. The abnormality diagnosis method according to claim 7, characterized in that when the supply flow rate of the modified gas is the appropriate flow rate, it is determined that an abnormality has occurred in the gas concentration measuring unit that measures the gas concentration.

9. The abnormality diagnosis method according to claim 6, characterized in that when the supply flow rate of the enriched gas with controlled flow rate is less than the appropriate flow rate, the cause of the abnormality of the gas carburizing furnace is identified based on whether or not the hydrocarbon components of the modified gas in the processing chamber are at a preset appropriate value.

10. The abnormality diagnosis method according to claim 9, characterized in that when the hydrocarbon component is at the appropriate value, it is determined that an abnormality has occurred in the gas concentration measuring unit that measures the gas concentration.

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