Patent Application
20150079527
The present invention relates to a method for heat treatment, a heat treatment apparatus, and a heat treatment system, and more particularly relates to a method for heat treatment, a heat treatment apparatus, and a heat treatment system using Ellingham diagram information and having excellent mass productivity.
For heat treatment of metal, various heat treatments have conventionally been used depending on application purposes, the heat treatments including a standardization treatment such as annealing/normalizing, a hardening/toughening treatment, such as quenching/tempering and thermal refining, and a surface hardening treatment, such as nitriding and surface improvement. While these atmosphere heat treatments are performed in atmosphere gases, such as atmospheric air, inert gases, oxidizing gases, and reducing gases, which are supplied to a heat treatment furnace, the properties of metals that are subjected to the heat treatments are drastically changed by components of these atmosphere gases. Accordingly, it is necessary to control the components of the atmosphere gases supplied into the heat treatment furnace with sufficient precision and to visualize the status of the atmosphere in the furnace with high precision.
As a first conventional technology that performs feedback control on the flow rate of the gas supplied to a heat treatment furnace in response to a signal coming from an oxygen potentiometer placed inside the heat treatment furnace, a method of adjusting the atmosphere gas in a bright annealing furnace disclosed in Patent Literature 1 (Japanese Patent Laid-Open No. 3-2317) will be described with reference to
The mixed gas is heated and combusted at high temperature (1100° C.) in a gas converter with heating function 15, and then the gas is quenched and dehumidified in a gas quenching/dehumidifier system 16, before being supplied to a bright annealing furnace 17. Oxygen partial pressure is measured by the oxygen potentiometer 18 provided inside the bright annealing furnace 17, and based on this measurement value, carbon potential (CP) is calculated by a carbon potential computation controller 19. Then, the calculated value is compared with a preset carbon content in an object to be treated, and the flow rate of hydrocarbon gas supplied to the gas mixer 13 is feedback-controlled via the flow control valve V1 so that the calculated value is matched with the preset carbon content. This prevents oxidation and decarbonization of the material to be treated in the bright annealing furnace 17.
Next, as a second conventional technology, a method of controlling furnace gas in bright heat treatment disclosed in Patent Literature 2 (Japanese Patent Laid-Open No. 60-215717) will be described with reference to
In
A carbon monoxide analyzer 23 also detects the partial pressure of residual carbon monoxide in the heat chamber 21, and when the detection value is higher than a set value set in a carbon monoxide partial pressure setting unit 25, inert gas, such as nitrogen, is discharged to the outside of the furnace while being supplied to the heat chamber 21, so that the amount of residual carbon monoxide is controlled to be constant. As a consequence, even when moisture, oxides, and oil and fat adhere to the surface of metals to be treated, the bright treatment is implemented without causing oxidation, decarbonization, carbon deposition, and carburization.
Now, as a third conventional technology, a method and an apparatus for heat treatment disclosed in Patent Literature 3 (Patent No. 4521257) will be described with reference to
In
Moreover, there is provided a sequencer 39 that controls the process in a carburizing treatment device, the sequencer 39 being configured to execute a command to cause the regulator 38 to stop and/or resume PID adjustment in accordance with the status of the carburizing device. Accordingly, during a heat treatment period including the time of opening an opening of the furnace, the CP is controlled to be constant.
Next, as a fourth conventional technology, a method and an apparatus for preventing coloration of a plate passing through reducing atmosphere furnace disclosed in Patent Literature 4 (Japanese Patent Laid-Open No. 11-80831) will be described with reference to
In
As a fifth conventional technology, a method of calculating heat treatment conditions by using an Ellingham diagram to reduce metal oxide to metal is disclosed in Patent Literature 5 (WO 2007/061012).
In a first conventional technology disclosed in Patent Literature 1, in order to provide deoxidizing and decarbonizing atmosphere for heat treatment materials in the bright annealing furnace, the hydrocarbon amount is set to be within 1 to 20% of exothermic converted gas, and the amount of hydrocarbon to be mixed is corrected to an appropriate amount in proportion to a carbon content of the materials to be treated and in accordance with an oxygen partial pressure value inside the furnace measured by the oxygen potentiometer. However, no theoretical and specific description is provided regarding how to correct the appropriate amount. Moreover, it is stated that scale and decarbonization are not caused under the conditions of CO=21% vol, CO2=0.5% vol, and CO/CO2=42 in Table 1. However, no description is provided regarding where these conditions are positioned in a preferred range and what are prerequisites of the preferred range.
Therefore, the method of adjusting atmosphere gas in the bright annealing furnace in this gazette cannot flexibly cope with the case of the preferred conditions being changed, and the like.
In the method of controlling furnace gas in the bright heat treatment disclosed in Patent Literature 2, controlling the residual oxygen amount and the residual carbon monoxide amount to be constant are described, though no description is provided regarding how to determine a preferred condition range, i.e., the range of the bright treatment which does not cause decarbonization.
Furthermore, in the method and apparatus for heat treatment disclosed in Patent Literature 3, a description is given of calculating carbon potential based on the oxygen concentration output from an oxygen sensor and performing feedback control on the flow rate of enrich gas so that the carbon potential converges to a set value in a carburization heat treatment. However, the feedback control is only performed so that the carbon potential converges to the preset value, and it is impossible to identify where, in the preferred condition range and in the condition range out of the preferred conditions, the furnace is currently operated. Moreover, when the preferred conditions are changed or the like, it is impossible to dynamically cope with the change. Furthermore, it is not at all discussed that when defective articles are generated in mass production, operation conditions of the furnace are analyzed based on preset optimum conditions and signals from sensors from an operation history, and failure analysis of a lot that includes the defective articles is performed.
The method and apparatus for preventing coloration of a plate passing through reducing atmosphere furnace disclosed in Patent Literature 4 have the same problem as the conventional technology disclosed in Patent Literature 3.
In the heat treatment methods disclosed in Patent Literatures 1 to 4, there is no description or suggestion about displaying the status of the heat treatment furnace in operation on a display device in the form of a point on an Ellingham diagram in real time.
As for a metal manufacturing method disclosed in Patent Literature 5, calculation of ΔG0 is disclosed in paragraph [0011] in this gazette. However, using this ΔG0 as means for displaying the status of the heat treatment furnace in operation, and how to control the status of the heat treatment furnace expressed by ΔG0 are not disclosed.
In all the documents stated above, no disclosure is made about visualizing the current status of atmosphere in the furnace with high precision and controlling the status of the furnace by using the visualized information.
The present invention provides a method for heat treatment, a heat treatment apparatus, and a heat treatment system which suitably solved the aforementioned problems.
The heat treatment apparatus of the present invention includes: a heat treatment furnace that heat-treats materials to be treated; a gas supply device that supplies atmosphere gas to the heat treatment furnace; a control system that controls the gas supply device by referring to sensor information from a sensor; a standard formation Gibbs energy computation unit that calculates a standard formation Gibbs energy of the atmosphere gas in the heat treatment furnace by referring to the information from the sensor; and a display data generation unit that generates an Ellingham diagram of the heat treatment furnace and the standard formation Gibbs energy as display data to be displayed on the Ellingham diagram corresponding to temperature of the heat treatment furnace.
The display data generation unit generates the display data including a control range of the heat treatment furnace in the Ellingham diagram.
Moreover, the control range includes: a first control range indicative of a normal operation range of the heat treatment furnace; a second control range outside the first control range, wherein when a status on the Ellingham diagram is out of the first control range and goes into the second control range, an alarm is output but operation is continued; and a third control range outside the second control range, wherein when the status goes into the third control range, operation of the heat treatment apparatus is stopped.
The standard formation Gibbs energy computation unit may perform computation by using any information or a plurality of information pieces from oxygen partial pressure, carbon monoxide partial pressure and carbon dioxide partial pressure, and hydrogen partial pressure and dew point information to calculate the standard formation Gibbs energy.
Further, the standard formation Gibbs energy computation unit may compute the standard formation Gibbs energy by using any one of the following methods including: a method for computation with use of a carbon monoxide sensor and a carbon dioxide sensor or a method for computation with use of only the carbon dioxide sensor if the partial pressure of carbon monoxide is obtained in advance; a method for computation with use of a hydrogen sensor and a dew-point sensor or a method for computation with use of only the dew-point sensor if the partial pressure of hydrogen is obtained in advance; a method for computation with use of an oxygen sensor; and a method for computation with use of a combination of the above-described methods.
The heat treatment apparatus may include a status monitoring & abnormality processing unit that directly monitors a status on the Ellingham diagram, outputs an alarm when the status deviates from the first control range, and outputs control information so as to stop the operation of the heat treatment apparatus when the status shifts to the third control range.
The heat treatment apparatus may include a heat treatment database that stores at least one of process information on the materials to be treated, log information about operation of the heat treatment apparatus, and accident information.
Moreover, a plurality of process conditions for evaluation are set for the materials to be treated, the materials to be treated that are heat-treated in each of these conditions are evaluated, and the control range is defined based on the evaluation results.
When a lot number of the materials to be treated is specified in case where the status of the materials to be treated shifts in sequence, the Ellingham diagram of the materials to be treated may sequentially be displayed on an identical screen or a plurality of screens.
The heat treatment database may include: a file of materials to be treated that stores a list or a library of the materials to be treated including at least one of carbon steel and steel containing an alloy element; and a process control file that stores a list or a library of the heat treatment including at least one of a bright treatment, a refining treatment, and a hardening/tempering treatment.
Further, the heat treatment apparatus may include a display device that simultaneously or switchingly displays at least two or more out of the Ellingham diagram, a chart indicative of time transition in control parameter of the heat treatment apparatus, and the information from the sensor.
The sensor and the control system may be connected via a communication line, so that the control system may monitor in real time whether the sensor and the communication line normally operate, while performing offset correction and noise correction of a signal from the sensor.
A heat treatment system of the present invention is a heat treatment apparatus including: a heat treatment furnace that heat-treats materials to be treated; a gas supply device that supplies reducing gas to the heat treatment furnace; a control system that controls the gas supply device by referring to sensor information from a sensor; a standard formation Gibbs energy computation unit that calculates standard formation Gibbs energy of the atmosphere gas in the heat treatment furnace by referring to the information from the sensor; a display data generation unit that generates an Ellingham diagram of the heat treatment furnace and the standard formation Gibbs energy as display data to be displayed on the Ellingham diagram corresponding to temperature of the heat treatment furnace; and a terminal device that displays the display data via a communication line, while transmitting the control information for controlling the control system.
A method for heat treatment of the present invention is a method for heat treatment that heat-treats materials to be treated in atmosphere gas supplied to a heat treatment furnace, the method including: calculating standard formation Gibbs energy of the atmosphere gas in the heat treatment furnace by referring to information from respective sensors that detect a status during heat treatment; and generating an Ellingham diagram of the heat treatment furnace and the standard formation Gibbs energy as display data to be displayed on the Ellingham diagram corresponding to temperature of the heat treatment furnace.
The method for heat treatment, the heat treatment apparatus, and the heat treatment system according to the present invention can display an Ellingham diagram, a control range, and an operational status of the heat treatment furnace on a display device, so that the operational status of the heat treatment furnace can be monitored in real time from a perspective of the Ellingham diagram.
The method for heat treatment, the heat treatment apparatus, and the heat treatment system according to the present invention can grasp whether or not the status of the heat treatment furnace is within the control range set on the Ellingham diagram and two-dimensionally grasp a margin to a boundary of the control range when the status is in the control range. Furthermore, the control range is divided into a normal operation range, an alarm output/continuous operation range set outside the normal operation range, and an operation stop range set further outside the alarm output/continuous operation range to normalize a control method in each range, so as to achieve decrease in occurrence rate of a defective lot and reduction in operation stop period. As a consequence, the heat treatment apparatus excellent in mass productivity can be provided.
Further in the method for heat treatment, the heat treatment apparatus, and the heat treatment system according to the present invention, sensor signals regarding the operational status, shift in system status on the Ellingham diagram and the like are stored as log data, which makes it easy to perform failure analysis and the like. Moreover, alarm information can be sent to persons concerned before fatal shutdown occurs, and quick recovery to the normal operation condition can be implemented.
Further in the method for heat treatment, the heat treatment apparatus, and the heat treatment system according to the present invention, data about materials to be treated and treatment processes is stored in a database as libraries. When the materials to be treated and the treatment processes are changed, it becomes possible to swiftly switch the operation of the heat treatment furnace by selecting these libraries. Therefore, the present invention is also applicable to limited manufacture with a wide variety.
Furthermore, when the method for heat treatment, the heat treatment apparatus, and the heat treatment system according to the present invention are applied to the bright annealing heat treatment, it becomes unnecessary to execute after-treatments, such as acid pickling performed after the heat treatment since the product surface is bright-finished, or it becomes possible to omit a process (such as cutting, etching and polishing) for removing a decarburized layer after the heat treatment since decarbonization does not occur on the surface in the process of the heat treatment.
Hereinafter, the embodiments of a method for heat treatment, a heat treatment apparatus, and a heat treatment system of the present invention will be described with reference to the drawings.
Moreover, there are provided a gas supply device 52 that generates the atmosphere gas that is supplied to the heat treatment furnace 51, a control system 53 that controls temperature of the heat treatment furnace 51 and controls the gas supply device 52 and the like in response to signals from various sensors, and a terminal device 54 that reciprocally outputs and inputs information via the control system 53 and a communication line 55.
The heat treatment furnace 51 includes various sensors, and more specifically includes a temperature sensor 511 that measures temperature, an oxygen sensor 517 that measures residual oxygen (O2) partial pressure, a hydrogen sensor 515 that measures hydrogen (H2) partial pressure, and a dew-point sensor 516 that measures a dew point inside the heat treatment furnace 51.
There are also provided a gas sampling device 512 that samples a part of the atmosphere gas in the heat treatment furnace 51, and a CO sensor 513 and a CO2 sensor 514 that respectively measure carbon monoxide (CO) partial pressure and carbon dioxide (CO2) partial pressure of the sampled atmosphere gas by using infrared ray spectroscopy. The atmosphere gas analyzed with the CO sensor 513, the CO2 sensor 514, and the dew-point sensor 516 is discharged as analysis exhaust gas.
Although the temperature sensor is an indispensable sensor, it is not necessary to provide all the other sensors. More specifically, there are following methods of measuring standard formation Gibbs energy ΔG0 of the heat treatment furnace 51: (1) a method of using the CO sensor 513 and the CO2 sensor 514 or a method of using only the CO2 sensor 514 when the partial pressure of carbon monoxide is provided in advance; (2) a method of using the hydrogen sensor 515 and the dew-point sensor 516 or a method of using only the dew-point sensor 516 when the partial pressure of hydrogen is provided in advance; (3) a method of using the oxygen sensor 517; and (4) a method of using a combination of the methods (1) to (3). In accordance with these methods (1) to (4), necessary sensors may be provided.
The gas supply device 52 includes: a flow control valve 521A that controls a flow rate of hydrocarbon gas such as town gas, methane (CH4), propane (C3H8), and butane (C4H10); a flow control valve 521B that controls an air flow rate; a flowmeter 522A and a flowmeter 522B that respectively measure flow rates of flow rate-controlled hydrocarbon gas and air; and a mixer 523 that mixes the flow rate-controlled hydrocarbon gas and air, in response to control signals of a control unit 534.
The mixed gas mixed in the mixer 523 produces an exothermic chemical reaction and combusts in the gas converter 524, and the further-combusted high-temperature converted gas is water-cooled to about 40° C. with a water cooler 525. The water-cooled gas is dehumidified in a dehumidifier 526 and is supplied as DX gas to the dew-point sensor 527 and to a drain hole. More specifically, when the conditions such as the temperature of the heat treatment furnace 51 do not satisfy specific heat treatment conditions, the gas is discharged to the drain hole from the dehumidifier 526 without being supplied to the heat treatment furnace 51.
Although the dew-point sensor 527 is provided in order to detect deviation of the dew point from a normal standard range due to occurrence of abnormalities in the gas supply device 52 and the like, the precision of the dew-point sensors which are currently available on the market leaves much to be desired. Accordingly, any one of the following methods may be used or a plurality thereof may be used in union: (1) a method of detecting whether or not a dew point is normal by using dew point information from the dew-point sensor and information from an unillustrated hydrogen sensor provided on an output portion of the gas supply device 52; (2) a method of detecting whether or not the dew point is normal by using information from an unillustrated oxygen sensor provided on the output portion of the gas supply device 52; (3) a method of detecting whether or not the dew point is normal by using information from an unillustrated carbon dioxide sensor provided on the output portion of the gas supply device 52; and (4) a method of detecting whether or not the dew point is normal by using information from unillustrated carbon monoxide sensor and carbon dioxide sensor provided on the output portion of the gas supply device 52. This method also applies to the following embodiments.
Meanwhile, when the heat treatment furnace 51 meets given heat treatment conditions, gas is started to be supplied from the dehumidifier 526 to the heat treatment furnace 51. This prevents the atmosphere gas from being supplied to the heat treatment furnace 51 when the heat treatment conditions of the heat treatment furnace 51 are not yet satisfied.
After steam (H2O) partial pressure is finally measured with the dew-point sensor 527, the gas from the dehumidifier 526 is supplied to the heat treatment furnace 51 as atmosphere gas. The dew-point sensor 527 may be configured integrally with the dehumidifier 526.
The control system 53 has a display device 531 that displays an operational status of the heat treatment furnace, more specifically, a point that represents the status on an Ellingham diagram, and information such as a control range set on the Ellingham diagram. The control system 53 also has an input device 532 that outputs input information to an arithmetic processor 533. Further, there is provided an arithmetic processor 533 that uses signals from various sensors placed inside the heat treatment furnace 51 and from the CO sensor 513, the CO2 sensor 514, and the dew-point sensor 527 provided outside the heat treatment furnace 51 and uses the information stored in a heat treatment database 535 to perform arithmetic processing. The arithmetic processor 533 also outputs control signals for controlling the flow control valves 521A, 521B and the like to the control unit 534. There are also provided the control unit 534 that controls the heater 518, the flow control valve 521A and the like in response to the control signals from the arithmetic processor 533, and the heat treatment database 535 that stores and manages material information on the materials to be treated 519, process information about the heat treatment, information about the control range, log information about operation of the heat treatment apparatus, accident data, and the like.
Moreover, the various sensors, such as the temperature sensor 511, the oxygen sensor 517, the CO sensor 513, and the CO2 sensor 514, are connected to the control unit 534 or the arithmetic processor 533 via the communication line 56, such as a dedicated sensor bus, a general-purpose bus, or a wireless LAN. The control unit 534 or the arithmetic processor 533 monitors in real time whether or not the various sensors and the communication line 56 normally operate, while performing processing such as detection of signals from various sensors, sampling, A/D conversion, waveform equivalence, offset correction, and noise correction.
Next, the configuration and operation of the arithmetic processor 533 will be described with reference to
The arithmetic processor 533 includes: a sensor I/F 67 that receives signals from various sensors; an oxygen partial pressure computation unit 61 that calculates the oxygen partial pressure in the heat treatment furnace 51 with reference to the signals from the oxygen sensor 517 input via the sensor I/F 67; a CO/CO2 partial pressure ratio computation unit 62 that calculates a CO/CO2 partial pressure ratio with reference to signals input from the CO sensor 513 and the CO2 sensor 514; and an H2/H2O partial pressure ratio computation unit 63 that calculates H2 partial pressure with reference to a signal from the hydrogen sensor 515 while calculating an H2/H2O partial pressure ratio with reference to a signal from the dew-point sensor 516.
A ΔG0 (standard formation Gibbs energy) computation unit 64 refers to the calculation results calculated respectively in the oxygen partial pressure computation unit 61, the CO/CO2 partial pressure ratio computation unit 62, and the H2/H2O partial pressure ratio computation unit 63 to calculate ΔG0 (standard formation Gibbs energy) of the heat treatment furnace 51 in operation, and outputs the calculation result to a display data generation unit 65, the control unit 534, and a status monitoring & abnormality processing unit 66.
There are several methods of calculating ΔG0, and some typical calculation methods will be described below.
ΔG0=RT.lnP(O2) (1)
[Reaction among CO—CO2—O2]
2CO+O2=CO2 (2)
ΔG0(2)=−564980+173.3T (J−.mol−1) (3)
RTlnP(O2)=ΔG0(2)−2RTln(P(CO)/P(CO2)) (4)
[Reaction among H2—H2O—O2]
2H2+O2=2H2O (5)
ΔG0(5)=−496070+111.5T (J.mol−1) (6)
RT.lnP(O2)=ΔG0(5)−2RTln(P(H2)/P(H2O)) (7)
Here, R represents a gas constant, T represents absolute temperature, P(O2) represents oxygen partial pressure (O2 partial pressure), P(CO) represents carbon monoxide partial pressure (CO partial pressure), P(CO2) represents carbon dioxide partial pressure (CO2 partial pressure), P(H2) represents hydrogen partial pressure (H2 partial pressure), and P(H2O) represents partial pressure of water (steam) (H2O partial pressure).
In the above-stated formulas, ΔG0 can be calculated from the oxygen partial pressure P(O2) by using the formula (1). The formula (2) represents a reaction among carbon monoxide (CO), oxygen (O2) and carbon dioxide (CO2), while the formula (3) indicates that ΔG0 (standard formation Gibbs energy) in this system of reaction is calculated with a linear function of absolute temperature (T).
Based on the formula (4), RTlnP(O2) can be calculated by using a partial pressure ratio between carbon monoxide (CO) partial pressure and carbon dioxide (CO2) partial pressure, by which ΔG0 can be obtained.
The formula (5) represents a reaction among hydrogen (H2), oxygen (O2) and a steam (H2O), while the formula (6) indicates that ΔG0 (standard formation Gibbs energy) in this system of reaction is calculated with a linear function of absolute temperature (T).
Based on the formula (7), RTlnP(O2) can be calculated by using a partial pressure ratio between hydrogen (H2) partial pressure and steam (H2O) partial pressure, by which ΔG0 can be obtained.
Next, the sensors necessary for calculation of ΔG0 will be described.
When attention is focused on the formula (1), ΔG0 can be calculated when the absolute temperature T and the oxygen partial pressure P(O2) are detected. Therefore, the temperature sensor 511 and the oxygen sensor 517 may be provided.
When attention is focused on the reaction among CO—CO2—O2 to calculate ΔG0 (standard formation Gibbs energy) by using the formula (4), the CO partial pressure and the CO2 partial pressure need to be detected. Accordingly, the sensors to be provided may be the CO sensor 513 and the CO2 sensor 514. When the CO partial pressure is obtained in advance, only the CO2 sensor 514 may be provided.
When attention is focused on the reaction among H2—H2O—O2 to calculate ΔG0 (standard formation Gibbs energy) by using the formula (7), the H2 partial pressure and the H2O partial pressure need to be detected. Accordingly, the sensors to be provided may be the hydrogen sensor 515 and the dew-point sensor 516. When H2 partial pressure is obtained in advance, only the dew-point sensor 516 may be provided.
Moreover, precision may be enhanced by such a method of calculating ΔG0=RTlnP(O2) according to the formula (1), ΔG0=RTlnP(O2)=ΔG0 (2)−2RTln (P(CO)/P(CO2)) according to the formula (4), and ΔG0=ΔG0 (5)−2RTln (P(H2)/P(H2O)) according to the formula (7) and selecting a method estimated to have the highest precision, or averaging, weighted-averaging or statistically processing respective calculation results.
Returning to the description with reference to
The display device 531 displays the display data output from the display data generation unit 65 with temperature as an abscissa and ΔG0 as an ordinate, in which standard formation Gibbs energy of the materials to be treated 519 at respective temperatures is displayed as an approximate straight line L1 while standard formation Gibbs energy in the reaction of 2C+O2=2CO is displayed as an approximate straight line L2. A control range R1 and a status P1 of the heat treatment furnace 51 calculated by the ΔG0 (standard formation Gibbs energy) computation unit 64 are simultaneously displayed on an Ellingham diagram. The status P1 is updated at every sampling time by various sensors, e.g., at every second on a display screen. While the control range R1 and the status P1 are essential as the information displayed on the display device 531, the approximate straight line L1 and the approximate straight line L2 are not necessarily essential in mass-production heat treatment apparatuses. Moreover, the update period may arbitrarily be set.
With reference to the Ellingham diagram displayed on the display device 531, an operator of the heat treatment apparatus illustrated in
The status monitoring & abnormality processing unit 66 monitors in real time the parameters including temperature, O2 partial pressure, CO partial pressure, CO2 partial pressure, H2 partial pressure, H2O partial pressure in the heat treatment furnace 51, a CO/CO2 partial pressure ratio, an H2/H2O partial pressure ratio, and ΔG0, while reading the control range R1 corresponding to the materials to be treated 519 and the like from the heat treatment database 535 and outputting an abnormal signal to the control unit 534 when the above-described parameters deviate from the specified control range.
A description is now given of a second embodiment of the heat treatment apparatus of the present invention with reference to
The heat treatment apparatus described in
A description is now given of a third embodiment of the heat treatment apparatus of the present invention with reference to
A gas supply device 82 illustrated in
In the heat treatment apparatus of the present embodiment, the chemical reaction in the gas converter 824 causes the flow rate of air to be lowered, so that it is defined as an endothermic reaction. Although use of a catalyst is devised to cause a stable chemical reaction, reaction temperature inside the gas converter 824 may sometimes varies and CO partial pressure and CO2 partial pressure may become different from their set values. Moreover, in order to generate RX gas from the gas converter 824, the flow control valve 521B is tightened to lower the air flow rate. However, if the air flow rate is excessively lowered, soot is generated, which drastically change CO partial pressure and CO2 partial pressure from their set values. Accordingly, an appropriate air flow rate is maintained, and hydrocarbon gas (raw gas) such as propane and butane is supplied as it is, or the hydrocarbon gas is mixed with RX gas generated in the gas converter 824 and is supplied to the heat treatment furnace 51 together with the RX gas, so that CO partial pressure and CO2 partial pressure inside the heat treatment furnace 51 can be kept stable.
In the heat treatment apparatus in the third embodiment, which is unlike the heat treatment apparatus in the second embodiment, the heat treatment furnace 51 has atmosphere gas with a high CO partial pressure and a low CO2 partial pressure. Specifically, while the CO partial pressure is about 10% in the heat treatment apparatuses according to the first and second embodiments, the CO partial pressure is about 20% in the heat treatment apparatus of this embodiment, which is generally twice as large as the CO partial pressure in the heat treatment apparatuses according to the first and second embodiments. Accordingly, in the heat treatment apparatus of this embodiment, the materials to be treated 519 can be heat-treated in the atmosphere having strong reducing property, so that decarbonization can be prevented and efficient bright treatment can be performed. In the present embodiment, steel materials which are decarbonized as raw materials can be recarburized. At the same time, in the heat treatment apparatus of this embodiment, there is a problem that the high CO partial pressure and the low CO2 partial pressure cause a problem that soot generation (sooting) tends to occur. In this embodiment, the CH4 sensor 520A that measures CH4 partial pressure, which is a particularly important factor of occurrence of sooting, is used to measure CH4 partial pressure of the converted gas supplied to the heat treatment furnace 51. At the same time, CH4 partial pressure of the atmosphere gas taken in via the gas sampling device 512 is measured by a CH4 sensor 520B. More specifically, in order to prevent occurrence of sooting due to the CH4 partial pressure of the converted gas output from the gas converter 824 becoming higher than a specified value, the control unit 534 performs continuous monitoring of CH4 partial pressure with the CH4 sensor 520A, while controlling the flow control valve 521C to adjust the flow rate of hydrocarbon gas with reference to a computing signal resulting from computing a sensor signal from the CH4 sensor 520A with the arithmetic processor 533. Moreover, the CH4 partial pressure information measured by the CH4 sensor 520B is sent to the control unit 534 or the arithmetic processor 533, and in a similar way as described in the foregoing, the control unit 534 controls the flow control valve 521C to adjust the flow rate of hydrocarbon gas. More specifically, in the heat treatment apparatus of this embodiment, CH4 partial pressure is doubly measured and feedback control is performed based on the measured values to prevent occurrence of sooting. In other words, CH4 partial pressure of the atmosphere gas supplied to the heat treatment furnace 51 and CH4 partial pressure of the atmosphere gas in the heat treatment furnace 51 are simultaneously measured so as to perform control that prevents occurrence of sooting, so that the heat treatment furnace 51 may stably be operated. The configuration of the arithmetic processor 533 and the calculating method of ΔG0 in the present embodiment are basically similar to those in the first and second embodiments.
A description is now given of a fourth embodiment of the heat treatment apparatus of the present invention with reference to
A gas supply device 92 illustrated in
CH3OH->CO+2H2 (8)
In the heat treatment apparatus in the fourth embodiment, as in the heat treatment apparatus in the third embodiment, the heat treatment furnace 51 has atmosphere gas having a high CO partial pressure and a low CO2 partial pressure. Accordingly, heat treatment is performed in the atmosphere having a strong carburization property, so that the high-carbon material to be treated 519 can be prevented from being decarbonized, and efficient bright treatment can be performed. Like the heat treatment apparatus in the third embodiment, the heat treatment apparatus of this embodiment has a problem that sooting tends to occur. Accordingly, as in the third embodiment, CH4 sensors 520A and 520B and a CO2 sensor 514′ are provided, so that the flow rate of methanol is controlled with a flow control valve 521D.
In the present embodiment, steel materials which are decarbonized as raw materials can be recarburized. Although not illustrated, the atmosphere in the furnace may be diluted by using inert gas, such as nitrogen gas.
The configuration of the arithmetic processor 533 and the calculating method of ΔG0 in the present embodiment are basically similar to those in the first to third embodiments.
A description is now given of a fifth embodiment of the heat treatment apparatus of the present invention with reference to
A gas supply device 102 illustrated in
While the configuration of an arithmetic processor 10533 and the calculating method of ΔG0 in this embodiment are basically similar to those in the first to fourth embodiments, the CO/CO2 partial pressure ratio computation unit 62 illustrated in
A description is now given of a sixth embodiment of the heat treatment apparatus of the present invention with reference to
The gas supply device 112 illustrated in
Although the dew-point sensor 527 detects a dew point of the nitrogen gas serving as carrier gas, it is hard to control the dew point of nitrogen gas itself in this embodiment. Accordingly, the arithmetic processor 10533 compares the information input from the dew-point sensor 527 with a set value stored in the heat treatment database 535 and controls to output an alarm when the dew point is larger than the set value. In this case, the dew-point sensor 527 may be replaced with an oxygen sensor or the like, so as to indirectly detect whether or not the dew point of carrier gas is normal.
The configuration of the arithmetic processor 10533 and the calculating method of ΔG0 in this embodiment are basically similar to those of the above-described fifth embodiment. In this embodiment, as in the fifth embodiment, CO partial pressure and CO2 partial pressure are not detected, so that it is not necessary to provide the CO sensor and the CO2 sensor.
In the above embodiments, the dew-point sensor 527 is provided on an output portion of the gas supply devices 52, 72, 82, 92, 102 and 112, and the dew point of the atmosphere gas supplied from these gas supply devices 52, 72, 82, 92, and 102 is controlled to be a set value or below. However, a CO sensor, a CO2 sensor, a hydrogen sensor, and an oxygen sensor may be provided on the output portion of the gas supply devices 52, 72, 82, 92, 102 and 112, so that CO partial pressure, CO2 partial pressure, H2 partial pressure, H2O partial pressure, and O2 partial pressure may be controlled to be equal to their respective set values.
Next, the heat treatment database 535 illustrated in
The heat treatment database 535 includes, as illustrated in
The process control file 122 stores specific process names, such as bright treatment, refining treatment, and hardening/tempering treatment, and process conditions corresponding to the process names in a table format or as a library for each material to be treated 519. The process conditions include, as respective default values, temperature of the heat treatment furnaces 51 and 101, CO partial pressure, CO2 partial pressure, H2 partial pressure, H2O partial pressure, and O2 partial pressure, a CO/CO2 partial pressure ratio as a result of computation in the CO/CO2 partial pressure ratio computation unit 62, an H2/H2O partial pressure ratio as a result of computation in the H2/H2O partial pressure ratio computation unit 63, ΔG0 (standard formation Gibbs energy) as a result of computation in the ΔG0 computation unit 64, gas flow rates, such as a hydrocarbon flow rate, an air flow rate, a hydrogen flow, and a nitrogen flow rate from the flowmeters 522A to 522F, and a liquid flow rate such as a methanol flow rate, conveyance rates of the materials to be treated 519, and time control and process sequences of these parameters.
Based on an instruction from the input device 532, the arithmetic processors 533 and 10533 read from the heat treatment database 535, a table or library specified from the file of materials to be treated 121 and the process control file 122 which are stored in the form of a table or a library, and displays the table or library on the display device 531. An operator confirms the displayed content, and if the displayed heat treatment conditions are acceptable, the operator starts the heat treatment under the conditions. Therefore, in the case of changing the heat treatment, the heat treatment can easily be changed based on the above-described procedures, so that the heat treatment such as the bright treatment, the refining treatment, and the hardening/tempering treatment can promptly and flexibly be implemented.
As illustrated in
In
The log file 124 has a log data file 1241 that stores parameters from respective sensors in real time, the parameters including temperature of the heat treatment furnaces 51 and 101, CO partial pressure, CO2 partial pressure, H2 partial pressure, H2O partial pressure, and O2 partial pressure, a CO/CO2 partial pressure ratio, an H2/H2O partial pressure ratio, flow rates of gas or liquid that passes through the flowmeters 522A to 522F, conveyance rates of the materials to be treated 519, and ΔG0. The log file 124 also has an accident data file 1242 including the above log data file for the second control range and third control range illustrated in
Now, the control unit 534 will be described with reference again to
By using ΔG0 from the ΔG0 (standard formation Gibbs energy) computation unit 64 and the information on the control range R1, the control unit 534 controls the flow control valves 521A, 521C, 521D, and 521E to control various gas flow rates and a flow rate of liquid such as methanol so that the status expressed by ΔG0 is aligned with the center of the control range. The control range R1 is in a region set below the approximate straight line L1, where the materials to be treated 519 are reduced. At the same time, the control range R1 is also set below the approximate straight line L2, so that carbon (C) is also in a reduction region. This prevents a problem of decarbonization due to oxidation of carbon present on the surface of the materials to be treated 519.
The atmosphere gas inside the heat treatment furnace 51 and 101 is more oxidizing as ΔG0 is higher in the Ellingham diagram, whereas the atmosphere gas is more reducing as ΔG0 is lower in the Ellingham diagram. If the flow control valve 521A illustrated in
When the flow control valve 521D of
Further, when the flow control valve 521E of
When abnormalities occur in operation of the furnace, the control unit 534 stops operation of the heat treatment apparatus by such an action as stopping a conveyance mechanism that conveys the materials to be treated 519 to the heat treatment furnaces 51 and 101, based on the information from the status monitoring & abnormality processing unit 66.
When abnormalities occur, the control unit 534 outputs an abnormal signal to the display data generation unit 65. Upon reception of the signal, the display data generation unit 65 executes alarm processing such as blinking the status P1 displayed on the display device 531 or issuing an alarm sound.
A description is now given of the method for heat treatment and the heat treatment apparatus of the present invention with reference to a flow chart illustrated in
In step S1, by using the input device 532, the materials to be treated 519 that are heat treatment target this time and a heat treatment process therefor are selected from a menu displayed on the display device 531. For example, carbon steel is selected as the materials to be treated 519, and P1 process is selected from the bright treatment as a heat treatment process.
Next, in step S2, the arithmetic processors 533 and 10533 read process conditions, Ellingham diagram information, and a control range from the heat treatment database 535, and output these pieces of information to the control unit 534 and the display device 531. In step S31, based on the received process conditions, the control unit 534 starts to control various gas flow rates and the flow rate of liquid such as methanol by controlling the heater 518, the flow control valves 521A, 521C, 521D, 521E, and the like so that temperature and ΔG0 are positioned at the center of the control range depicted in the Ellingham diagram. At the same time, the display device 531 displays the Ellingham diagram information and the control range in step S32.
Next, in step S4, various sensors output the detected sensor information to the arithmetic processors 533 and 10533 directly or via the control unit 534. The arithmetic processors 533 and 10533 generate ΔG0 calculated by the formulas (1), (4) and (7) with reference to the O2 partial pressure, the CO/CO2 partial pressure ratio, and the H2/H2O partial pressure ratio calculated in the respective computation units 61 to 64, or ΔG0 calculated based on computation results of the plurality of formulas, as display data to be displayed on the Ellingham diagram of the display device 531, together with the control range and the approximate straight lines L1 and L2 illustrated in
Next, in step S6, the status monitoring & abnormality processing unit 66 determines whether or not the operational status of the heat treatment furnace 51 and 101 is within the control range of the Ellingham diagram. When the operational status is within the control range of the Ellingham diagram, the status monitoring & abnormality processing unit 66 instructs the control unit 534 to continue operation. In step S7, the control unit 534 outputs control information for continuous operation to an unillustrated conveyance mechanism for the materials to be treated 519, the heater 518, and the flow control valves 521A, 521C, 521D, and 521E.
Contrary to this, when the operational status is out of the control range of the Ellingham diagram, the status monitoring & abnormality processing unit 66 instructs the display data generation unit 65 to execute alarm processing such as blinking the status P1 on the display device 531 or issuing an alarm sound. At the same time, as illustrated in
As a consequence, when the status P1 is out of the first control range, an urgent mail or the like is sent to the PC of a production management engineer and the like, so that the production management engineer can quickly access the accident data file 1242 in the heat treatment database 535. The production management engineer analyzes the data in the accident data file 1242 by using an accident analysis tool to find out the cause of the accident, and gives instructions to a production site to cope with the situation.
Next, the processing in the case where the operational status of the heat treatment furnaces 51 and 101 is out of the first control range of the Ellingham diagram in step S6 will be described in detail with reference to
When the status shifts from the first control range indicative of the normal operation to the second control range, the status monitoring & abnormality processing unit 66 instructs the display data generation unit 65 to execute alarm processing in step S8. At the same time, the status monitoring & abnormality processing unit 66 transmits alarm information to the terminal device 54 in real time via the communication line 55.
When the status shifts from the first control range to the second control range, the control unit 534 performs feedback control in real time so that the status returns to the first control range. As illustrated in
When the status goes into the third control range (No in step S11), operation of the heat treatment furnaces 51 and 101 are stopped as illustrated in step S13 in both of the automatic operation mode and the manual operation mode so as to prevent production of defective articles. Specifically, a conveying operation of a conveyor or a roller that conveys the materials to be treated 519 is stopped to prevent new materials to be treated 519 from being input into the heat treatment furnaces 51 and 101. Once the status goes into the third control range as illustrated in
When it is determined in step S11 that the operational status of the heat treatment furnaces 51 and 101 is within the second control range of the Ellingham diagram, operation is continued in step S12, and in step S6 or step S11, continuous monitoring of the operational status is performed to check which control range the status is positioned at.
In order to provide more detailed description with respect to the above-described operation, consider the case where the status P1 in the first control range shifts to a status P2 in the second control range in
As described in the foregoing, the control range is divided into the first control range to the third control range, and the control method is adjusted for each range, so that decrease in occurrence rate of defective lots and reduction in operation stop period are achieved. As a consequence, the heat treatment apparatus excellent in mass productivity can be provided.
While
Meanwhile, the information (C) displays detailed control parameters in the status indicated in the information (A) or (B).
The method for heat treatment and the heat treatment apparatus according to the present invention are controlled by using the control range in the control range file 123 illustrated in
In step S21, materials to be treated which are subjected to evaluation for determination of the control range are selected from various materials to be treated, such as carbon steel and steel containing an alloy element. In step S22, a process suitable for the materials to be treated that are selected in step S22, e.g., a process P1 of the bright treatment or the like, is selected. Next, in step S23, a plurality of process conditions for evaluation are prepared based on default process conditions of the selected process. Then, one process condition is selected from these process conditions for evaluation, and in step S24, the materials to be treated are heat-treated by using the heat treatment apparatuses illustrated in
Next, in step S25, parameters including temperature of the heat treatment furnace 61, O2 partial pressure, CO partial pressure, CO2 partial pressure, H2 partial pressure, H2O partial pressure, a CO/CO2 partial pressure ratio, an H2/H2O partial pressure ratio, gas flow rates such as a hydrocarbon flow rate, an air flow rate, a hydrogen flow and a nitrogen flow rate from the flowmeters 522A to 522F, and a flow rate of liquid such as a methanol flow rate, and ΔG0 are each stored as evaluation log data in the log data file 1241.
In step S26, it is determined whether or not all the process conditions for evaluation are tried. If all the process conditions for evaluation are not tried, a process condition for evaluation which is not yet tried is selected in S23, and processing in steps S24 and S25 is repeated so as to repeat the heat treatment in all the process conditions for evaluation.
In step S27, each material to be treated which is heat-treated in each process for evaluation is estimated. More specifically, color, surface hardness, present/absence and degree of decarbonization and carburization, and the like are estimated for each material to be treated. Based on the evaluation result, a control range which satisfies target specifications is determined in step S28.
A description is now given of other embodiments of the heat treatment apparatus of the present invention with reference to
When a lot number of the materials to be treated 519 is specified through the input device 532, it is possible to instantly display on the display device 531 which zone and which status on the Ellingham diagram the materials to be treated 519 of that lot number are present, together with the position of the zone and the process conditions. As for the lot in the cooling zone, an Ellingham diagram in the heating zone where the lot was previously heat-treated can be traced back and displayed.
An area above a straight line expressed by 2Fe+O2=2FeO represents an iron oxidation region, while an area below the straight line represents iron reduction region. An area above a straight line expressed by 2C+O2=2CO represents a carbon oxidation region, while an area below the straight line represents a carbon reduction region, i.e., a region free from decarbonization.
As specifically described in the foregoing, preferred control ranges are determined for various materials to be treated and their processes based on the flow of
In the above description, various gases, such as hydrocarbon gas, hydrogen gas, and nitrogen gas, are supplied to the gas supply device from gas supply sources, such as unillustrated tanks provided outside the gas supply device.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-071226 | Mar 2012 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2013/058038 | 3/21/2013 | WO | 00 |
