JPH09138216A - O2 sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely measure the concentration of carbon inside a furnace and to make the life of a sensor long by a method wherein the burnout air in a proper amount is blown on an external electrode and on a solid electrolyte by a burnout-air introduction pipe installed by particularly partitioning the inside of a sheath pipe and soot which is stuck is removed. SOLUTION: When the amount of carbon is measured by an O2 sensor 1, the reference air is introduced up to an internal electrode 6b from a reference- air introduction pipe 8, an in-furnace atmosphere gas which is introduced from a measuring-gas introduction port 12 is supplied directly to an external electrode 6a, and an electromotive force which is generated by the oxygen concentration difference of a solid electrolyte 2 generated across the electrodes 6a, 6b is taken out as a carbon amount signal. Then, after a lot treatment has been finished or at every definite time, the solenoid valve of an air supply unit is changed over, the burnout air in a definite amount is blown on the electrolyte 2 and on the electrode 6a via a burnout-air introduction pipe 11, soot (precipitated carbon) which is stuck to the electrolyte 2 and to the electrode 6a is burned, and an oxidized burning gas is discharged to the outside of the sensor 1 from the measuring-gas introduction port 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention particularly relates to an O ₂ sensor used for measuring carbon concentration in a carburizing atmosphere gas.

[0002]

_2. Description of the Related Art In an O ₂ sensor used in a carburizing furnace, soot (precipitated carbon) is apt to adhere to the solid electrolyte when the atmosphere in the furnace is over-carburizing and sooting, which causes false electromotive force. It occurs and the reaction speed decreases and normal measurement cannot be performed. Furthermore, if soot adheres to the external electrodes, the external electrodes are consumed and the life of the O ₂ sensor is significantly reduced.

Therefore, conventionally, as shown in FIG.
Burnout of a fixed amount (about 1 to 2 L / min) at regular intervals so as to diffuse into the entire inside of the sheath tube 9 from a burnout air inlet 10 provided in the sheath tube 9 formed of a _two- sensor tubular body. Supplying air. As a result, the soot attached to the solid electrolyte 2 and the external electrode 6a is burned by the burnout air, and the oxidized combustion gas is discharged from the measurement gas inlet 12.

[0004]

SUMMARY OF THE INVENTION However,
In the conventional O ₂ sensor, the supplied burnout air diffuses into the entire inside of the sheath tube or is discharged before the air is supplied to the electrode section, so that the burnout air is introduced from the inlet to the sooting. In some cases, the required amount of air did not reach the periphery of the solid electrolyte outer electrode. In addition, there is a problem that it is difficult to grasp an accurate inflow amount of the burnout air for removing the soot adhering to the solid electrolyte and the alumina tube portion.

Further, particularly in a furnace in which high carbon carburizing or carburizing raw gas and air / carbon dioxide are added to carry out metamorphic carburizing in the furnace, the amount of soot attached to the electrode portion increases, and an accurate burn is performed. When the amount of out-air cannot be supplied to the electrode part, there is also a problem that the sensor life is significantly shortened. Therefore, the present invention has been made by paying attention to the above-mentioned unsolved problems of the related art, and by connecting the burnout air introduction port to the electrode section for burning and removing soot by an air introduction pipe, It is an object of the present invention to provide an O ₂ sensor capable of accurately measuring the carbon concentration in a furnace by projecting a large amount of burn air onto an external electrode and a solid electrolyte, and further prolonging the service life.

[0006]

In order to solve the above problems, an O ₂ sensor according to the present invention comprises a solid electrolyte, external electrodes and internal electrodes attached to both ends of the solid electrolyte, and An oxygen sensor comprising a solid electrolyte, the outer electrode, and a sheath tube containing the inner electrode, and a burnout air inlet provided by opening a part of the sheath tube, at least the burnout air inlet It is characterized in that a burnout air introduction pipe is provided between the external electrode and the vicinity of the solid electrolyte so as to communicate with each other.

As a result, the required amount of burnout air supplied to the burnout air introduction port passes through the inside of the burnout air introduction pipe and is directed from the discharge port near the external electrode and the solid electrolyte toward the external electrode and the solid electrolyte. Is discharged. Then, the soot adhering to the external electrode and the solid electrolyte is oxidized by the burnout air to become a combustion gas and then discharged to the outside.

Further, the inside of the sheath tube is specially defined, and a burnout air introducing pipe is provided between the burnout air introducing port and the vicinity of the external electrode so as to communicate with each other. As a result, when the solid electrolyte is not in contact with the measurement atmosphere in the carburizing furnace, soot does not adhere to the solid electrolyte. Therefore, only the soot adhering to the external electrode is burned and removed to prevent the external electrode from being consumed.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an O ₂ sensor of the present invention will be described below with reference to the drawings. As shown in FIG. 1, 1 is an O ₂ sensor, and in this embodiment, it is used especially for measuring the carbon concentration contained in the furnace atmosphere gas of the carburizing furnace 10.

First, the principle of the O ₂ sensor 1 will be briefly described. As shown in FIG. 2, electrodes 6 made of platinum are attached to both sides of the solid electrolyte 2 and the electrodes 6 are heated at a high temperature of about 650 ° C. When a difference in oxygen concentration is applied to both electrodes, oxygen ions move from the high concentration side to the low concentration side (in the direction of the arrow in the figure), and an electromotive force E is generated between the two electrodes due to this ion conductivity.

If the electromotive force E is R, the gas coefficient, T is the absolute temperature, F is the Faraday constant, P ₁ is the oxygen partial pressure in the reference electrode gas, and P ₂ is the oxygen partial pressure in the gas to be measured. Is expressed by the following equation (1). E = (RT / nF) TLog (P ₁ / P ₂ ) [mV] (1) Therefore, if P ₁ is the oxygen partial pressure in the air of 0.21 atm, the electromotive force E changes to the oxygen in the measurement gas. The partial pressure P ₂ can be obtained.

Further, the atmosphere gas in the carburizing furnace has an equilibrium state represented by the following equations (2) to (4) at each temperature. 2CO = C + CO ₂ (2) CO + H ₂ O = CO ₂ + H ₂ (3) CO + 0.5O ₂ = CO ₂ (4) Based on the relationships of the above formulas (1) to (4) Under the condition that the partial pressure of CO gas in the furnace atmosphere is constant, the electromotive force E and the temperature T (t
When +273) ° C. is obtained, the amount of carbon can be calculated.

Next, as shown in FIG. 1, the O ₂ sensor 1 used here is perpendicular to the furnace wall 5 with its tip inserted to a position representative of the temperature of the furnace atmosphere 4 of the carburizing furnace 10. It is attached by screwing it into the socket 5a. As shown in FIG. 3, inside the O ₂ sensor 1, a solid electrolyte 2 and external electrodes 6a and internal electrodes 6b made of platinum attached to both ends of the solid electrolyte 2 are formed.
An internal electrode protection tube 7 fitted to the outer periphery of the solid electrolyte 2 on the internal electrode 6b side, and a reference provided inside the internal electrode protection tube 7 for introducing reference air to the end surface of the internal electrode 6b. An air introduction pipe 8, a sheath pipe 9 including the external electrode 6a, the solid electrolyte 2, the internal electrode 6b, and the internal electrode protection pipe 7, and a burn provided by opening a part of the sheath pipe 9 outside the furnace. A burn-out air introduction pipe in which the out-air introduction port 10 is communicated with the burn-out air introduction port 10 of the sheath pipe 9 to the vicinity of the external electrode 6a, and the tip opening is cut toward the external electrode 6a and the solid electrolyte 2. 11
And a measurement gas introduction port 12 for introducing the atmosphere gas in the furnace, which is provided by opening a part of the sheath tube 9.

The solid electrolyte 2 is made of zirconia (ZrO ₂ ) in which Calcia (CaO) or yttria (Y ₂ O ₃ ) is stabilized, and is a pellet of a necessary amount for suppressing change due to thermal expansion. The internal electrode 6a and the external electrode 6b attached to both ends of the electrode are configured to generate a contact potential difference at high temperature.

The internal electrode protection tube 7 is made of alumina, which has excellent heat resistance and mechanical shock resistance, and is fitted and connected to the end of the solid electrolyte 2 in order to cope with changes in thermal expansion. ing. Further, the reference air introduction pipe 8 inside the internal electrode protection pipe 7 has a composition close to the thermal expansion coefficient of alumina to improve heat resistance.

Furthermore, since the sheath tube 9 is made of stainless steel having thermal inertia, the temperature changes of the internal electrode protection tube 7 and the reference air introduction tube 8 with respect to the temperature inside the furnace can be slowed down. O ₂ sensor 1 configured in this way
As shown in FIG. 1, during normal carbon amount measurement, after passing through the filter 14 and the pump 15 inside the air supply unit 13 to form clean air of a constant pressure, the flow meter 16 measures the O ₂ sensor. 1, the reference air of a constant pressure is sent out to the reference air introduction port 20 through the pipe, and from there, passes through the reference air introduction pipe 8 inside the O ₂ sensor 1 and the internal electrode. 6b
The reference air is introduced up to.

On the other hand, the external electrode 6a is directly supplied with the atmospheric gas in the furnace introduced from the measurement gas introduction port at the tip of the sheath tube 9. Thereby, the inner and outer electrodes 6 of the solid electrolyte 2 are
Oxygen ions move from the inner electrode 6a to the outer electrode 6a due to the difference in oxygen concentration generated between a and 6b, and the electromotive force generated thereby passes through the sheath tube 9 which is an electric conductor of the outer electrode 6a to It is output to a metal connector 17 (not shown) attached to the furnace, and further output from a thermocouple 18 attached to the furnace wall 5 to measure the temperature inside the furnace near the O ₂ sensor 1 to control the temperature inside the furnace. 1-5 for the calculation result input to the converter 18 together with the temperature signal
It outputs to a controller and a recorder as a carbon amount signal of [V].

Next, O_TwoSolid electrolyte 2 at the tip of sensor 1
And the soot adhering to the external electrode 6a is finished,
Alternatively, when removing at regular intervals, the air supply unit
Burn by switching the solenoid valve inside
Out air passes through piping and burn out air inlet
A certain amount (here 1-2 L / min) of burnout
Air is supplied, and this is the reference air guide inside the sheath tube 9.
Pass through the inlet pipe 8 _TwoSolid electrolyte 2 at the tip of sensor 1
And the vicinity of the external electrode 6a and reach the burnout energy.
The soot attached by the ar is CO due to the oxidation reaction._Twoetc
From the measurement gas inlet 12 after becoming the oxide of
The soot that adheres to the outside is burned and removed.
It is.

Thus, the burnout air inlet 1
By connecting the solid electrolyte 2 and the external electrode 6a from 0 to the outer electrode 6a by the burnout introduction pipe, the supplied burnout air diffuses into the entire inside of the protective pipe, and the solid electrolyte 2 and the external electrode 6a are diffused. Without being discharged to the outside of the O ₂ sensor 1 before being supplied, a necessary amount of air is made to reach directly from the burnout air introduction port 10 to the periphery of the solid electrolyte 2 and the external electrode 6a which are causing soot, It is possible to reliably remove the soot by burning.

In this embodiment, a burnout introduction pipe 11 that communicates from the burnout air introduction port 10 to the solid electrolyte 2 and the external electrode 6a is provided,
Although the soot that adheres to the solid electrolyte 2 and the external electrode 6a is burned and removed, as shown in FIG.
For example, in the case of an O ₂ sensor having a structure in which the solid electrolyte 2 is covered with a protective body and does not come into contact with the measurement atmosphere gas, a burnout introduction pipe communicating only from the burnout air introduction port 10 to the vicinity of the external electrode 6a. It is also possible to provide 10.

Further, in this embodiment, the burnout air introducing port 10 is directly connected to the surface of the solid electrolyte 2 and a part of the external electrode 6a by one burnout introducing pipe 11. It is not necessarily limited to this, but a plurality of burnout air introduction pipes 1
By radially providing 1 around the solid electrolyte 2 and the external electrode 6a, burnout air can be supplied to the entire surfaces of the solid electrolyte 2 and the external electrode 6a.

[0022]

As described above, according to the O ₂ sensor of the present invention, since the air introduction pipe for communicating the burnout air introduction port inside the protection pipe and the vicinity of the external electrode is provided, it is appropriate. A sufficient burnout air amount can be supplied to the external electrode and the solid electrolyte to reliably remove the soot that has adhered by combustion, thereby maintaining accurate measurement of the carbon concentration in the furnace. Further, it is possible to prevent the deterioration of the electrodes of the O ₂ sensor and prolong the service life.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an O ₂ sensor according to an embodiment of the present invention.

FIG. 2 is a principle diagram showing the principle of an O ₂ sensor.

FIG. 3 is a sectional view of an essential part showing an O ₂ sensor according to an embodiment of the present invention.

FIG. 4 is a sectional view of an essential part showing an O ₂ sensor according to another embodiment of the present invention.

FIG. 5 is a cross-sectional view of essential parts showing a conventional O ₂ sensor.

[Explanation of symbols]

1 is an O ₂ sensor 2 is a solid electrolyte 4 is a furnace atmosphere 5 is a furnace wall 6 is an electrode 6a is an external electrode 6b is an internal electrode 7 is an internal electrode protection pipe 8 is a reference air introduction pipe 9 is a sheath pipe 10 is a burnout air Inlet 11 is a burnout air inlet 12 is a measurement gas inlet 13 is an air supply unit 14 is a filter 15 is a pump 16 is a flow meter 17 is a metal connector 18 is a thermocouple 19 is a protector 20 is a reference air inlet

Claims (2)

[Claims] 1. A solid electrolyte, an external electrode and an internal electrode attached to both ends of the solid electrolyte, a sheath tube including the solid electrolyte, the external electrode, and the internal electrode, and a part of the sheath tube. An oxygen sensor formed by opening a burnout air introduction port, the inside of the sheath tube is particularly defined, and the burnout air introduction port is provided between the burnout air introduction port and the vicinity of the external electrode and the solid electrolyte. An oxygen sensor, which is provided with a burnout air introducing pipe that communicates between them. 2. A solid electrolyte, an external electrode and an internal electrode attached to both ends of the solid electrolyte, a sheath tube including the solid electrolyte, the external electrode, and the internal electrode, and a part of the sheath tube. An oxygen sensor comprising a burnout air introduction port opened by opening the inside of the sheath tube and defining the inside of the sheath pipe, the oxygen sensor being provided between the burnout air introduction port and the vicinity of the external electrode. An oxygen sensor characterized in that a burnout air introduction pipe is provided to communicate between them.