JP5390139B2 - Carbon potential calculation device - Google Patents

Description

The present invention relates to a carbon potential calculation device that calculates a carbon potential (Carbon Potential: CP) of an atmosphere in a furnace based on a CO ₂ concentration or an O ₂ concentration in a heat treatment furnace such as a carburizing furnace or a carbonitriding furnace.

  Conventionally, tempered steel is remarkably superior in terms of the combination of strength and toughness, but its wear resistance is inferior to that of carburized and quenched, and fatigue failure due to repeated stress is a problem. In such a component, the strength at the surface is important because fatigue cracks are generated near the surface. Therefore, from this point of view, a gas carburizing method is generally known as a surface hardening treatment for an article that requires strength against wear resistance and fatigue fracture.

This gas carburizing method is suitable for large-scale production. LPG and other hydrocarbon gases are converted into endothermic gas (gas transformed by an endothermic reaction using a catalyst) via a shift furnace and introduced into the carburizing furnace. It is a method to do. This endothermic modified gas is called a “carrier gas” and is composed of a mixed gas containing, for example, H ₂ , CO, CH ₄ , CO ₂ , O ₂ , H ₂ O and the like. Since the carburization reaction is governed by an equilibrium constant based on the partial pressure of each gas and is in a balanced state while maintaining mutual relation, any one of specific gases (for example, H ₂ O, CO ₂ , O ₂ ). If the flow rate of the carburizing gas is controlled so as to always maintain a specific value, the reaction can proceed in one direction. The carbon potential (hereinafter abbreviated as “CP”) indicates the carburizing ability in such a controlled state.

  In addition, even if an equilibrium relationship is established for the entire furnace air, the steel surface tends to be misaligned due to insufficient flow, etc., and not all of the decomposed C is adsorbed. May cause sooting to become soot. In order to improve such a state and increase the carburizing capacity, a raw gas such as propane called “enrich gas” is directly added to the furnace by about 0.5 to 1%. In addition to the gas carburizing method described above, there are a carburizing method, a liquid carburizing method, a solid carburizing method, a vacuum carburizing method, a plasma carburizing method, and the like.

FIG. 7 is a schematic configuration diagram of a carburizing furnace disclosed in Patent Document 1 below as an example of the gas carburizing method. As shown in the figure, the gas carburizing method of Patent Document 1 below includes a CO ₂ sensor 102 that samples the atmospheric gas in the carburizing furnace 101 and detects the CO ₂ concentration in the atmospheric gas inside the furnace, and the furnace in the furnace. An oxygen sensor 103 for detecting the oxygen concentration in the inner atmosphere gas is provided. The introduction of the enriched gas 104 is started while the furnace temperature T is raised, and the apparent carbon potential CP ₁ calculated based on the CO ₂ concentration and the apparent carbon potential CP ₂ calculated based on the oxygen concentration The difference (CP ₂ −CP ₁ ) is obtained, and the flow rate of the enriched gas 104 is adjusted so that the difference (CP ₂ −CP ₁ ) approaches a predetermined value.

Further, in Patent Document 1, the system configuration performs PID control of the enriched gas using a carburizing furnace and various sensors. However, in order to perform drive control of such a carburizing furnace, a CO ₂ sensor or O ₂ disposed in the carburizing furnace. There is also known a carbon potential calculation device that calculates the CP value of the furnace atmosphere based on the CO ₂ concentration and O ₂ concentration measured by a sensor.
Japanese Patent No. 3973795 Japan Heat Treatment Technology Association, Japan Metal Heat Treatment Industry Association, edited by Saburo Misawa, “Introduction to Heat Treatment Technology: Metal Heat Treatment Technician / Examination Text”, Okawa Publishing (published July 2004), pages 28-30

Incidentally, in the conventional carbon potential computing device, such as temperature: 1000 ° C., CO concentration of 20%, as a condition (both fixed values), Fig. 8 when calculating the CP value based on the O ₂ concentration from the O ₂ sensor It becomes a graph as shown in. As shown in the figure, the CP value gradually increases as the EMF (electrmotive force) indicating the O ₂ concentration, which is the input from the O ₂ sensor, increases. If the upper limit value (CP value = 1.68% in the figure) is exceeded, the CP value decreases even if the EMF input value increases.

Therefore, in the conventional carbon potential calculation device, when the CP value based on the O ₂ concentration exceeds the output upper limit value, as shown in FIG. 9, the CP value is increased to 2.0%, which is the upper limit of the CP value. Thereafter, even when the input value of the EMF rises, the process of uniformly defining the CP value = 2.0% is performed.

  However, when the CP value is uniformly treated as 2.0% when the output of the CP value exceeds the upper limit value, the CP value exceeds the output upper limit value (for example, CP value = 1.68%). As described above, when the apparatus is used, there is a problem that measurement control is disturbed due to a sudden change in input value, and accurate CP value control cannot be stably performed.

Therefore, the present invention has been made in view of the above problems, and even if the output upper limit value of the CP value calculated based on the O ₂ concentration is exceeded, the carbon potential calculation capable of performing stable CP value control. The object is to provide an apparatus.

In order to achieve the above object, the carbon potential calculation device according to claim 1 is based on the O ₂ concentration, CO concentration, and temperature in the furnace atmosphere detected by a sensor unit installed in the heat treatment furnace. A carbon potential calculation device for calculating the carbon potential of an atmosphere,
A setting unit for setting an input upper limit value of the O ₂ concentration detected by the sensor unit;
When the calculated carbon potential exceeds the output upper limit value, a calculation unit that performs a proportional calculation of the calculated carbon potential based on the input upper limit value of the O ₂ concentration set by the setting unit;
It is provided with.

（式中、ｔは前記センサ部によって検出された炉内雰囲気中の温度（℃）であり、ＣＯは前記センサ部によって検出された炉内雰囲気中のＣＯ濃度（％）であり、ＰＯ ₂ は炉内雰囲気中のＯ ₂ 濃度から算出される酸素分圧である。） The carbon potential calculation device according to claim 2 calculates the carbon potential of the furnace atmosphere based on the O ₂ concentration, the CO concentration, and the temperature in the furnace atmosphere detected by a sensor unit installed in the heat treatment furnace. An arithmetic unit,
A value obtained by integrating the saturated carbon content of austenite calculated by using the following equation 3 to the value obtained by dividing the CO concentration by the square root of the oxygen partial pressure calculated from the O ₂ concentration in the furnace atmosphere is 2. An arithmetic unit for calculating the carbon potential using the following Equation 4 when the number is 7622 or more is provided.

(Where t is the temperature (° C.) in the furnace atmosphere detected by the sensor unit, CO is the CO concentration (%) in the furnace atmosphere detected by the sensor unit, and PO ₂ is (This is the oxygen partial pressure calculated from the O ₂ concentration in the furnace atmosphere .)

The carbon potential calculation device according to claim 3 is the carbon potential calculation device according to claim 1 or 2, wherein the O ₂ concentration, the CO concentration, and the temperature calculated by the calculation unit are set according to the setting from the setting unit. And a display unit for simultaneously displaying the carbon potential based on the CO ₂ concentration, the CO concentration calculated based on the calculation unit, and the carbon potential based on the temperature.

According to the carbon potential calculation device of the present invention, even when the CP value calculated based on the O ₂ concentration exceeds the output upper limit value, the proportional calculation is performed up to the upper limit value of the CP value. Stable CP value control can be performed without disturbance.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram showing a configuration of a carbon potential calculation device according to the present invention, FIG. 2 is a schematic diagram of a front panel of the same device, and FIG. 3 shows a CP value calculation based on O ₂ concentration in the same device. FIG. 4 is an explanatory diagram for explaining CP value calculation based on the CO ₂ concentration in the apparatus, and FIG. 5 is a correction of the CP value calculated based on the O ₂ concentration in the apparatus. FIG. 6 is a graph showing the relationship between the EMF and the CP value when the CP value calculated based on the CO ₂ concentration is corrected in the same apparatus. .

  First, the configuration of the carbon potential calculation device according to the present invention will be described with reference to FIGS.

  As shown in FIG. 1, the carbon potential calculation device 1 (hereinafter abbreviated as CP calculation device) of this example includes a setting unit 11, a calculation unit 12, a display unit 13, and an alarm unit 14. The CP computing device 1 is electrically connected to a sensor unit 20 that is installed in a heat treatment furnace 30 such as a carburizing furnace or a carbonitriding furnace that is a measurement target and detects various states of the atmosphere in the furnace.

The sensor unit 20, CO ₂ sensor 21 for detecting a CO ₂ concentration (%) of CO ₂ concentration in the furnace atmosphere to be measured by an infrared absorption method, also the CO concentration in the furnace atmosphere by an infrared absorption method CO sensor 22, O ₂ sensor 23 for detecting the the O ₂ concentration using the oxygen ion conductivity of the zirconia solid electrolyte O ₂ concentration in the furnace atmosphere in EMF (mV) for detecting the CO concentration (%), the furnace It consists of various sensors such as temperature sensor 24 (in this example, K thermocouple, R thermocouple, S thermocouple) that detects the temperature (° C) in the internal atmosphere, and the detection data detected by each sensor It is output to the calculation unit 12.

As shown in FIG. 2, the setting unit 11 includes a plurality of various keys provided at predetermined positions on the front panel of the apparatus, and various settings can be performed by user key operations. As the setting contents, input switching of the CO ₂ sensor 21 / O ₂ sensor 23, switching of display contents displayed on the display unit 13 (for example, simultaneous display of CO ₂ concentration only, O ₂ concentration only, CO ₂ / O ₂ concentration) , O ₂ concentration / CO ₂ concentration, CO concentration, setting of one of temperature as a fixed value, setting of scale upper limit value of CO ₂ sensor 21 which varies depending on the manufacturer, selection setting of thermocouple to be used, CP value Setting of correction values (inclination correction value, shift correction value, external contact correction value) for making the CP value calculated at the time of correction close to the true value, EMF input upper limit value setting for proportional calculation of CP value, etc. Various settings related to CP value calculation can be performed.

Computing unit 12, As1 calculating means 12a, PO ₂ calculating unit 12b, As2 calculating unit 12c, CP value calculating means 12d, CO ₂ calculation means 12e, constant computing means 12f, CP value correcting means 12 g, CP value proportional operation means 12h The calculation of the CP value based on various detection data (CO ₂ concentration in the furnace atmosphere, O ₂ concentration, CO concentration, temperature), correction of the calculated CP value, and When the CP value exceeds the output upper limit value, proportional calculation based on the EMF input upper limit value is performed.

Here, a calculation method of the CP value will be described. In the calculation of the CP value, the CP value is calculated based on the O ₂ concentration or the CO ₂ concentration. In order to improve the calculation accuracy of the CP value, one input value of O ₂ concentration / CO ₂ concentration, CO concentration, and temperature is set as a fixed value.

First, when the CP value is calculated from the O ₂ concentration, the CO concentration (fixed value), and the temperature, As1 (saturated carbon amount of austenite) is calculated by the As1 calculating means 12a using the following formula 5, and the following formula 6 is used. The PO ₂ (oxygen partial pressure) measured in this way is calculated by the PO ₂ computing means 12b, and As2 (austenite saturation is obtained using the following equation 7 obtained by regression analysis from the relationship between the saturated carbon content of austenite and the temperature. Carbon amount) is calculated by the As2 calculation means 12c.

Then, the CP value is calculated by the CP value calculating means 12d from the following formula 8 or 9 using PO ₂ and As2 calculated by the above formulas 6 and 7. In addition, when Equation 9 is used, the saturation carbon amount (As2) of austenite is added to the value obtained by dividing the CO concentration (CO) by the square root (PO ₂ ^1/2 ) of the oxygen partial pressure calculated in Equation 6 above. Used when the obtained value (L) is L ≧ 2.7622.

Further, based on the detected temperature, the CO concentration (fixed value), the As1 calculated by the above Equation 5 and the CP value calculated by the Equation 8 or 9, the CO ₂ concentration is calculated by the CO ₂ calculating means 12e using the following Equation 10. You can also

Next, when calculating the CP value from the CO ₂ concentration, CO concentration (fixed value), and temperature, As1 is calculated by the As1 calculating means 12a using the above equation 5, and K (calculation constant) using the following equation 11. ) Is calculated by the constant calculation means 12f.

  Then, the CP value is calculated by the CP calculating means 12d from the following equation 12 using As1 and K calculated by the above equations 5 and 11.

Note that the CP value based on the O ₂ concentration, the Co concentration, and the temperature and the CP value based on the CO ₂ concentration, the CO concentration, and the temperature can be calculated individually or simultaneously according to the input settings.

  Next, a CP value correction method will be described. When the CP value calculated using any one of the above formulas 5 to 12 is corrected, the CP value correcting unit 12g performs the correction using the following formula 13. A to C in the equation are correction values set by the setting unit 11 and indicate A: inclination correction value, B: shift correction value, C: external contact correction value, and the external contact correction value is external. It is added only when the contact signal is ON.

  Next, the proportional calculation of the CP value will be described. When the proportional calculation of the CP value calculated using any one of the above formulas 5 to 12 is performed, the CP value after the output upper limit value of the CP value is based on the EMF input upper limit value set by the setting unit 11. Is automatically calculated by the CP value proportional calculation means 12h. Note that the EMF input upper limit value used at this time indicates the EMF value when CP = 2.0, which is the upper limit of the CP value.

The display unit 13 includes a numerical value display area 13a that emits and displays numerical values or characters by a plurality of 7-segment displays, and a status display area 13b that lights / flashes in response to various settings or an alarm output from the alarm unit 14. As shown in FIG. 2, it is provided on the front panel of the device. The display unit 13 displays the CP value based on the O ₂ concentration calculated by the calculation unit 12 and the CP value based on the CO ₂ concentration individually or simultaneously, the CO ₂ concentration detected by the sensor unit 20, the O ₂ concentration, the CO 2 The concentration, temperature, and the like are displayed according to the setting contents by the setting unit 11.

The alarm unit 14 is configured by a ringing device such as a buzzer or a display device such as an LED lamp. For example, when the connection with the sensor unit 20 is broken, when the detection data input from the sensor unit 20 is abnormal, the CP value is calculated. According to the result, when | CP value (O ₂ ) −CP value (CO ₂ ) |> deviation set value (predetermined arbitrary value), an alarm output (sounding, lighting / flashing) for notifying the outside Etc.).

Next, a specific embodiment of the above-described CP arithmetic device 1 will be described with reference to FIGS. Here, as an implementation condition, the temperature is 1000 ° C., the CO concentration is 25% of the fixed value, the O ₂ concentration is 1000 mV, the Co ₂ concentration is 1.0%, and the input upper limit value of the EMF set by the setting unit 11 is 1300 mV, The proportional calculation after calculating the CP value from the O ₂ concentration will be described as the first embodiment, and the proportional calculation after calculating the CP value from the CO ₂ concentration will be described as the _second embodiment.

<Example 1>
As shown in FIG. 3, first, PO ₂ is calculated using the above equation 6 (PO ₂ = 2.994E-17), and As2 is calculated using the above equation 7 (As2 = 1.181E-11). Then, based on PO ₂ and As2 calculated by the above formulas 6 and 7, the CP value is calculated by using the above formula 8. (CP = 0.081).

  Then, the CP value calculated based on the input upper limit value of the EMF set by the setting unit 11 is automatically calculated so as to be proportional to the upper limit value of the CP value, so that the CP value proportional to the EMF as shown in FIG. It becomes the graph of.

<Example 2>
As shown in FIG. 4, first, As1 is calculated using Equation 5 (As1 = 1.579), and K, which is a calculation constant, is calculated using Equation 11 (K = 2.093). Then, based on As1 and K calculated by the above formulas 5 and 11, a CP value is calculated by using the above formula 12 (CP = 0.080).

  Then, by automatically calculating the CP value calculated based on the input upper limit value of the EMF set by the setting unit 11 so as to be proportional to the upper limit value of the CP value, the CP value proportional to the EMF as shown in FIG. It becomes the graph of.

Thus, CP computing device 1 described above, O ₂ concentration from the CO ₂ concentration or O ₂ sensor 23 from the CO ₂ sensor 21, the temperature, calculates the CP value based furnace atmosphere CO concentration. Then, based on the input upper limit value of the EMF set by the setting unit 11, the calculated value after the output upper limit value of the CP value is automatically calculated so as to be proportional to the upper limit value of the CP value.

  As a result, even when the CP value exceeds the output upper limit value of the CP value, since the proportional calculation is performed up to the upper limit value of the CP value, stable CP value control is performed without disturbing the measurement control. be able to.

  As mentioned above, although the best form in this invention was demonstrated, this invention is not limited with the description and drawing by this form. That is, it is a matter of course that all other forms, examples, operation techniques, and the like made by those skilled in the art based on this form are included in the scope of the present invention.

It is a schematic block diagram which shows the structure of the carbon potential calculating apparatus which concerns on this invention. It is the schematic of the front panel of the apparatus. It is an explanatory view for explaining a CP value calculation based on the O ₂ concentration in the apparatus. It is an explanatory view for explaining a CP value calculation based on the CO ₂ concentration in the apparatus. Is a graph showing the relationship between the EMF and the CP value when correcting the calculated CP value based on the O ₂ concentration in the apparatus. It is a graph showing the relationship between the EMF and the CP value when correcting the calculated CP value based on the CO ₂ concentration in the apparatus. It is a block diagram of the carburizing furnace which performs a general gas carburizing method. It is a graph showing the relationship between the calculated CP value and EMF based on the O ₂ concentration in the carbon potential conventional equipment. FIG. 9 is a partially enlarged explanatory diagram when the graph of FIG. 8 is corrected by a conventional method.

Explanation of symbols

1 ... Carbon potential computing device (CP computing device)
11 ... setting unit 12 ... computing unit (12a ... As1 calculating means, 12b ... PO ₂ calculating means, 12c ... As2 calculating means, 12d ... CP value calculating means, 12e ... Co ₂ calculating means, 12f ... constant computing means, 12 g ... CP value correcting means, 12h... CP value proportional calculating means)
13: Display section (13a: Numerical display area, 13b: Status display area)
14 ... alarm unit 20 ... sensor unit (21 ... CO ₂ sensor, 22 ... CO sensor, 23 ... O ₂ sensor, 24 ... temperature sensor)
30 ... Heat treatment furnace

Claims (3)

A carbon potential computing device that calculates the carbon potential of the furnace atmosphere based on the O ₂ concentration, CO concentration, and temperature in the furnace atmosphere detected by a sensor unit installed in the heat treatment furnace,
A setting unit for setting an input upper limit value of the O ₂ concentration detected by the sensor unit;
When the calculated carbon potential exceeds the output upper limit value, a calculation unit that performs a proportional calculation of the calculated carbon potential based on the input upper limit value of the O ₂ concentration set by the setting unit;
A carbon potential calculation device characterized by comprising: A carbon potential computing device that calculates the carbon potential of the furnace atmosphere based on the O ₂ concentration, CO concentration, and temperature in the furnace atmosphere detected by a sensor unit installed in the heat treatment furnace,
A value obtained by integrating the saturated carbon content of austenite calculated by using the following Equation 1 to the value obtained by dividing the CO concentration by the square root of the oxygen partial pressure calculated from the O ₂ concentration in the furnace atmosphere is 2. A carbon potential calculation device comprising a calculation unit for calculating the carbon potential using the following formula 2 when the value is 7622 or more.

(Where t is the temperature (° C.) in the furnace atmosphere detected by the sensor unit, CO is the CO concentration (%) in the furnace atmosphere detected by the sensor unit, and PO ₂ is (This is the oxygen partial pressure calculated from the O ₂ concentration in the furnace atmosphere .) The carbon potential based on the O ₂ concentration, the CO concentration, and the temperature calculated by the calculation unit according to the setting from the setting unit, and the carbon based on the CO ₂ concentration, the CO concentration, and the temperature calculated by the calculation unit. The carbon potential calculation device according to claim 1, further comprising a display unit that simultaneously displays the potential.

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