Gas carburizing furnace and method for diagnosing abnormality in gas carburizing furnace

Abstract

A gas carburizing furnace comprising: a treatment chamber to which an enriched gas is supplied; a gas concentration measurement unit that measures the gas concentration in the treatment chamber in order to calculate the carbon potential in the treatment chamber; a flow rate measurement unit that measures a supply flow rate of the enriched gas supplied into the treatment chamber; and a control unit that performs control for adjusting the supply flow rate of the enriched gas so that a carbon potential measurement value calculated on the basis of the gas concentration becomes a prescribed carbon potential target value, wherein the control unit performs control for determining that an abnormality has occurred in the gas carburizing furnace when the supply flow rate of the flow-rate-adjusted enriched gas is not a proper enriched gas flow rate that has been set in advance according to the carbon potential target value.

Description

Gas Carburizing Furnace and Abnormality Diagnosis Method for Gas Carburizing Furnace

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

[0002] As a heat treatment for improving the durability of automobile parts, mechanical parts and the like made of steel materials, carburizing treatment in which carbon is solid-dissolved in a workpiece surface (part surface) to harden the workpiece surface is known. 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 technique related to gas carburizing treatment, Patent Document 1 discloses an atmosphere control method for a heat treatment furnace. In this method, 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 controlled to a predetermined value corresponding to the furnace temperature by adjusting the valve opening degree of a flow rate 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 with respect 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.

[0005] Japanese Patent Application Publication No. 2005-076109, Japanese Patent Application Publication No. 2020-196943

[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 an abnormality occurs 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.

[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 the appropriate enriched gas 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 adjusted supply flow rate of the enriched gas is not the appropriate enriched gas flow rate preset according to the carbon potential target value.

[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.

[0013] This figure shows a schematic configuration of a gas carburizing furnace according to an embodiment of the present invention. This is a top view of the gas carburizing furnace schematically showing the mounting position of the oxygen sensor. This is a flowchart illustrating an example of an abnormality diagnosis method for a gas carburizing furnace according to an embodiment of the present invention. This figure schematically shows actual data of the enrichment gas supply flow rate when a product with the desired carburization quality is obtained. This figure shows the range of the appropriate enrichment gas supply flow rate set based on the above actual data. This is a flowchart illustrating another example of an abnormality diagnosis method for a gas carburizing furnace according to an embodiment of the present invention.

[0014] Embodiments of the present invention will be described below with reference to the drawings. In this specification and the drawings, elements having substantially the same functional configuration are denoted by the same reference numerals, and redundant explanations will be omitted.

[0015] Figure 1 is a diagram showing the schematic configuration of the gas carburizing furnace 1 according to this embodiment. The gas carburizing furnace 1 in this embodiment is a continuous gas carburizing furnace that can sequentially load workpieces W, which are objects to be processed, into the furnace and sequentially perform carburizing treatment on each workpiece W as it moves inside the furnace.

[0016] As shown in Figure 1, the gas carburizing furnace 1 is equipped with a preheating chamber 2, a carburizing chamber 3, a diffusion chamber 4, a cooling chamber 5, and an oil tank 6 in order from the furnace inlet to the outlet (from left to right in Figure 1) as processing chambers for performing a predetermined heat treatment on the workpiece W. The workpiece W undergoes carburizing and quenching treatment by passing through these preheating chamber 2, carburizing chamber 3, diffusion chamber 4, cooling chamber 5, and oil tank 6. The workpiece W is, for example, a part made of steel, such as an automobile part or other machine part.

[0017] The entrance to the preheating chamber 2 is provided with an entrance 10 for bringing in the workpiece W, and a movable door 11 for opening and closing the entrance 10. Between the preheating chamber 2 and the carburizing chamber 3, there is a passage 12 through which the workpiece W passes, and a movable shutter 13 for closing the passage 12. Between the carburizing chamber 3 and the diffusion chamber 4, there is a passage 14 through which the workpiece W passes, and a movable shutter 15 for closing the passage 14. Between the diffusion chamber 4 and the cooling chamber 5, there is a passage 16 through which the workpiece W passes, and a movable shutter 17 for closing the passage 16.

[0018] Even when the passage openings 12, 14, and 16 are blocked by the shutters 13, 15, and 17, gaps still exist between the passage openings 12, 14, and 16 and the shutters 13, 15, and 17. Therefore, even when the passage openings 12, 14, and 16 are blocked by the shutters 13, 15, and 17, the atmospheres inside each of the processing chambers—the preheating chamber 2, the carburizing chamber 3, the diffusion chamber 4, and the cooling chamber 5—are in communication with each other through these gaps.

[0019] The exit side of the cooling chamber 5 is provided with a passage 18 through which the workpiece W passes, and a movable door 19 that opens and closes the passage 18. The door 19 has a hole 19a formed in it, and the atmosphere inside the cooling chamber 5 and the oil tank 6 are in communication with each other through this hole 19a. The oil tank 6 is also provided with an outlet 20 for transporting the workpiece W, and a movable door 21 that opens and closes the outlet 20. The lower part of the oil tank 6 stores quenching oil, and the oil tank 6 is configured so that the workpiece W can move up and down between the oil storage area and the space above it.

[0020] A roller conveyor 30 for transporting workpieces W is provided at the bottom of the preheating chamber 2, carburizing chamber 3, diffusion chamber 4, and cooling chamber 5. The workpieces W are brought in from the entrance 10 by the roller conveyor 30, pass through the passages 12, 14, 16, and 18, undergo quenching treatment in the oil tank 6, and then discharged from the exit 20.

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

[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, the diffusion chamber 4, and the 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 at the ceiling to agitate the atmosphere inside 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 inside 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 within each processing chamber 2 to 5. 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 within each processing chamber 2 to 5.

[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 for explaining an abnormality diagnosis method. The flowchart in Figure 3 illustrates a method for diagnosing an abnormality in the gas carburizing furnace 1 based on atmospheric information in the carburizing chamber 3, which is one of the processing chambers of the gas carburizing furnace 1. This abnormality diagnosis method can be similarly applied to other processing chambers to which enrichment gas and modified gas are supplied (e.g., diffusion chamber 4, cooling chamber 5, etc.). Furthermore, each step described below is not limited to being performed by automatic control by the control unit 100. For example, the step of making a determination may be performed by an operator.

[0033] (Step S1) First, the carbon potential in the carburizing chamber 3 into which the workpiece W is placed 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 CP measurement value above becomes the preset target value of carbon potential (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 (appropriate enriched gas flow rate) that has been set in advance according to the CP target value. The appropriate flow rate (appropriate enriched gas flow rate) according to the CP target value is the enriched gas supply flow rate that is set on the premise that the loading number and packaging are the same for each type of workpiece to be processed when processing the workpiece to be processed under an 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 to be 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 with 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 enriched gas supply flow rate data shown above, the appropriate enriched gas supply flow rate is set, as shown in Figure 5, so that the desired carburizing quality can be obtained at a certain CP target value. For example, by setting the upper limit of the enriched 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 enriched 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, then 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 understood that the gas carburizing furnace 1 is in an abnormal state in which 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 (appropriate enriched gas 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 transformed gas supplied from the transforming furnace (not shown) is the appropriate flow rate (appropriate flow rate of transformed gas). The appropriate flow rate of the transformed gas supply (appropriate flow rate of transformed gas) is set in advance according to the CP target value in each processing room, and a method that is normally practiced 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 an appropriate flow rate, it is determined that the abnormality of the gas carburizing furnace 1 is caused by the abnormality of 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 the aforementioned step S2 is not appropriately performed. In such a case, maintenance work such as replacement of the oxygen sensor 96 is performed, for example.

[0044] On the other hand, in step S5, if the modified gas supply flow rate is not an appropriate flow rate, it is determined that there is an abnormality in the pipe connecting from the modified furnace (not shown) to the inside of the carburizing chamber 3. When a problem such as leakage of modified gas from the pipe occurs, a predetermined amount of modified gas is not supplied to the modified gas supply passage 41, and the measured CP value in the carburizing chamber 3 deviates from the CP target value. However, in the aforementioned step S2, the supply flow rate of the enriched gas is adjusted instead of the modified gas having an abnormal supply flow rate, so it becomes difficult to maintain the inside of the carburizing chamber 3 in an appropriate carburizing atmosphere. When such a pipe abnormality exists, the location where the pipe abnormality occurs is specified, 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 an appropriate value. The appropriate value for the hydrocarbon component of the modified gas is preset according to the target component of the modified gas and the modified temperature, and a method commonly practiced by those skilled in the art can be applied for the method of determining the appropriate value.

[0046] In step S6, if the hydrocarbon component of the modified gas is an appropriate value, it is determined that the abnormality of the gas carburizing furnace 1 is caused by the abnormality of the oxygen sensor 96. It is found that due to such an abnormality of 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 the aforementioned step S2 is not normally performed. When there is an abnormality in the oxygen sensor 96, the abnormality is handled by performing maintenance work such as replacing the oxygen sensor 96, for example.

[0047] On the other hand, in step S6, if the hydrocarbon component of the reformed gas is not within the appropriate range, it is determined that there is an abnormality on the equipment side of the reforming furnace (not shown). If a reformed gas with a predetermined composition corresponding to the CP target value cannot be generated due to such an abnormality on the equipment side of the reforming furnace, the measured CP 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 instead of adjusting the reformed gas whose hydrocarbon component is inappropriate, which makes it difficult to maintain an appropriate carburizing atmosphere in the carburizing chamber 3. Abnormalities of the reforming furnace are caused by, for example, the adhesion of soot to the inner wall of the reforming furnace or the deterioration of the catalyst used in the reforming furnace, so in such cases, maintenance work such as burnout in the reforming furnace or catalyst replacement is performed.

[0048] As described above, in the abnormality determination method for the gas carburizing furnace 1 according to the present embodiment, the provision of step S3 illustrated in FIG. 3 enables detection of an abnormality occurring in the gas carburizing furnace 1 before product inspection of the work W unloaded from the gas carburizing furnace 1. In other words, an abnormality of the gas carburizing furnace 1 can be detected at an early stage even during the carburizing treatment of the work W.

[0049] In addition, in order to identify the cause of the abnormality occurring in the gas carburizing furnace 1, it is preferable to perform at least one of step S5 and step S6 shown in FIG. 3, for example. When a step for identifying the cause of an abnormality, such as step S5 and step S6, is executed, a control signal for notifying that an abnormality has occurred is output from, for example, the control unit 100, and the notification is sent to the operator via a display unit such as a display or a sound 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 at the appropriate flow rate in step S6. 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 part of the furnace startup work, in which, before the workpiece W is brought into the gas carburizing furnace 1, the inside of each processing chamber is heated and a predetermined gas is supplied to each processing chamber to create an atmosphere with a target carbon potential, which is then maintained for a certain period of time.

[0051] In step S7, if the seasoning was performed properly, 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 properly, 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 that measures the gas concentration in the processing chamber for calculating 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 embodiment 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.

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

[0059] 1 Gas carburizing furnace 2 Preheating chamber 3 Carburizing chamber 4 Diffusion chamber 5 Cooling chamber 6 Oil tank 10 Inlet 11 Doors 12, 14, 16, 18 Through-holes 13, 15, 17 Shutter 19 Door 20 Outlet 21 Door 30 Roller conveyor 40-44 Modified gas supply line 45-49 Modified gas flow control valve 50-52 Modified gas flow meter 60-62 Enriched gas supply line 63-65 Enriched gas flow control valve 66-68 Enriched gas flow meter 70 Air supply line 71 Air flow control valve 80, 81 Exhaust line 90 Fan 95-98 Oxygen sensor 100 Control unit W Work

Claims

1. A gas carburizing furnace for performing gas carburizing treatment on a workpiece, comprising: a treatment chamber to which enrichment 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 enrichment gas supplied to the treatment chamber; and a control unit that controls the supply flow rate of the enrichment 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 controls the determination that an abnormality has occurred in the gas carburizing furnace when the flow rate of the enrichment gas supply, after flow rate adjustment, is not the appropriate enrichment gas flow rate set in advance according to the carbon potential target value.

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

3. The gas carburizing furnace according to claim 2, wherein 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 of the modified gas.

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

5. The gas carburizing furnace according to claim 4, wherein 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 an abnormality in a gas carburizing furnace that performs gas carburizing treatment on a workpiece, wherein the gas carburizing furnace adjusts the supply flow rate of enriched gas supplied to the treatment chamber so that the carbon potential measurement value calculated based on the gas concentration in the treatment chamber to which the enriched gas is supplied becomes a predetermined carbon potential target value, and when the flow rate adjusted supply flow rate of the enriched gas is not the appropriate enriched gas flow rate preset according to the carbon potential target value, it is determined that an abnormality has occurred in the gas carburizing furnace.

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

8. The abnormality diagnosis method according to claim 7, wherein when the supply flow rate of the modified gas is at the appropriate flow rate of the modified gas, 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, wherein when the supply flow rate of the enriched gas with controlled flow rate is less than the appropriate flow rate of the enriched gas, 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, wherein 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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