JP3949059B2 - Heat treatment furnace atmosphere control device - Google Patents

Description

[0001]
The present invention relates to an atmosphere control device for a heat treatment furnace, and more particularly to an atmosphere control device for a heat treatment furnace that performs gas carburization, gas carbonitriding, bright atmosphere heat treatment, and the like.
[0002]
[Prior art]
Conventionally, as a heat treatment method such as gas carburizing, a gas (hereinafter referred to as an endothermic gas), which is a mixture of a hydrocarbon-based gas and air and is transformed using an endothermic modified gas generator, is supplied into the furnace, In order to obtain a carbon potential, a method of adding a hydrocarbon-based gas (hereinafter referred to as an enriched gas) has been widely employed. However, in recent years, from the viewpoint of energy saving, as shown in JP-A-54-54931, JP-A-61-159567, JP-A-4-63260, etc. There is a tendency that a direct carburizing method in which carburizing is performed without introducing a shift gas generating furnace by directly introducing gas.
[0003]
[Problems to be solved by the invention]
However, the carburizing rate in the direct carburizing method is strongly influenced by the carburizing period and the diffusion period. In the former, direct decomposition of hydrocarbon gas or the like (raw gas) is the main effect on carburization, and in the latter, the Boudouard reaction is the main. Therefore, in the case of direct introduction of the hydrocarbon gas or the like into the furnace, the degree of decomposition differs depending on the amount of addition and the temperature of the atmosphere (of course, depending on the loaded state of the charged product). As a result, there has been a problem that hydrocarbon-based gas or the like is added more than necessary for carburizing and becomes soot and accumulates in the furnace, or the processed material is sooted.
[0004]
In addition, when operating without knowing that it is within the sooting range described above, there has been a problem of shortening the life of the oxygen sensor.
[0005]
The object of the present invention is to eliminate the above-mentioned conventional drawbacks.
[0006]
[Means for Solving the Problems]
The atmosphere control device for a heat treatment furnace of the present invention includes a furnace shell, a heater for heating in the furnace, an oxygen partial pressure in the furnace, and CH _4. The partial pressure measuring means, means for introducing methane, propane or butane gas and oxidizing gas as hydrocarbon-based gas into the furnace, means for controlling the introduction amount of these gases into the furnace, and means for controlling the above Residual CH _{4 in} furnace Characterized in that to stop the supply of the hydrocarbon gas when the value is turned upward from the lowered.
[0009]
The oxidizing gas is air or CO ₂ gas.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0011]
FIG. 1 is an explanatory view of an atmosphere control apparatus for a heat treatment furnace according to the present invention.
[0012]
In FIG. 1, 1 is a furnace shell, 2 is a heat-resistant brick forming the furnace shell 1, 3 is a fan for stirring the atmosphere, 4 is a heater for heating, 5 is a thermocouple for controlling the temperature in the furnace, and 6 is a furnace, for example. Direct insertion type zirconia type solid electrolyte oxygen partial pressure measuring sensor, 8 is a CH ₄ partial pressure measuring tube, 10 is a CH ₄ partial pressure analyzer, 11 is a hydrocarbon-based gas supply pipe introduced into the furnace, Reference numeral 12 denotes a control valve, 13 is a supply pipe for an oxidizing gas introduced into the furnace, 14 is a control valve, 15 is an arithmetic unit, and 16 is a controller that sends a control signal to the control valves 12 and 14.
[0013]
FIG. 2 shows the relationship between the carburizing time and the carburizing depth due to the difference in carbon potential. When the carbon potential during carburizing is high, it is already possible to finish carburizing in a shorter time than when it is low. It is known that in the Fe-C system equilibrium diagram, it is not suitable for actual operation when entering the sooting zone as shown by the oblique lines in FIG.
[0014]
In order to increase the carbon potential, a large amount of enriched gas (hydrocarbon-based gas) is preferably added. Looking at the passage of time after the addition of the enriched gas, as shown in FIG. 3, when the charging weight is constant at 150 kg and C ₄ H ₁₀ gas is used, A (flow rate 2.5 liter / min), B (1.4 In both cases (liter / min) and C (1.0 liter / min), as the carburizing time t elapses, the amount of residual CH ₄ starts to decrease and then increases, and the treated product generates sooting. On the other hand, in the case of D (0.5 liter / min), the amount of residual CH ₄ becomes almost constant and sooting does not occur. The difference is that in the case of A (2.5 liters / min), B (1.4 liters / min), and C (1.0 liters / min), the steel has absorbed carbon due to the large amount of addition. The reason is that undecomposed CH ₄ increases, whereas D (0.5 liter / min) is because the steel can absorb carbon. Therefore, analyzing the amount of residual CH ₄ and controlling its value will prevent sooting.
[0015]
In the Fe-C equilibrium diagram, the maximum carbon solid solution amount is constant when the temperature is determined, and sooting can be prevented by measuring the oxygen partial pressure corresponding to that value.
[0016]
Accordingly, in the present invention, in order to prevent sooting, the oxygen partial pressure is measured by measuring the electromotive force of the oxygen partial pressure measuring sensor 6, and the control valve 12 is closed when the oxygen partial pressure reaches a set value. To.
[0017]
In the present invention, the oxygen partial pressure measurement and the CH ₄ partial pressure measurement are performed in parallel, either when the oxygen partial pressure reaches the set value or when the CH ₄ partial pressure reaches the set value. The adjustment valve 12 may be closed at an early point.
[0018]
Example 1
[0019]
Using a batch furnace, 150 kg of treated material was charged, and carburizing operation was performed at 930 ° C. for 4 hours using C ₄ H ₁₀ gas as a hydrocarbon gas and CO ₂ gas as an oxidizing gas.
[0020]
In this case, as shown in FIG. 3, in the case of adding a hydrocarbon gas of 1.0 liter / min or more, the amount of CH ₄ increases with the passage of time. This is because the residual CH ₄ is undecomposed. Accumulating in the furnace, sooting increases.
[0021]
FIG. 4 shows the relationship between carburizing elapsed time when no sooting occurs, the amount of residual CH ₄ gas in the furnace and the amount of CH ₄ gas added, and the amount of hydrocarbon-based gas added is 2.5 liters / min. In this case, sooting occurs, but according to the method of the present invention, sooting is prevented because the introduction of the hydrocarbon gas is stopped.
[0023]
As the oxidizing gas, air or CO ₂ gas is used.
[0024]
【The invention's effect】
As described above, according to the present invention, in the atmospheric heat treatment such as gas carburizing, gas carbonitriding, and bright heat treatment, the addition amount of hydrocarbon gas or the like is controlled corresponding to the CH ₄ partial pressure and oxygen partial pressure of the atmosphere. Thus, sooting can be prevented in advance.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of an atmosphere control apparatus for a heat treatment furnace according to the present invention.
FIG. 2 is a diagram showing the influence of carburizing time on the carburizing depth due to the difference in carbon potential.
FIG. 3 is a diagram showing the relationship between the amount of residual CH ₄ and the carburizing time due to the difference in the enriched gas addition amount.
FIG. 4 is a diagram showing changes in residual CH ₄ amount and added C ₄ H ₁₀ flow rate as a result of carburizing at 930 ° C. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Furnace shell 2 Heat-resistant brick 3 Atmosphere stirring fan 4 Heating heater 5 Thermocouple 6 Oxygen partial pressure measuring sensor 8 CH ₄ partial pressure measuring pipe 10 CH ₄ partial pressure analyzer 11 Hydrocarbon gas supply pipe 12 Control valve 13 Supply pipe for oxidizing gas 14 Control valve 15 Arithmetic unit 16 Controller

Claims (1)

A furnace shell, a furnace heater, the oxygen partial pressure in the furnace, and the CH ₄ partial pressure measuring means, means for introducing methane, propane or butane gas and oxidizing gas as the hydrocarbon gas into the furnace If, Ri more formed and means for controlling the introduction amount for the furnace of gases, means for the control, the residual CH ₄ in the furnace Value heat treatment furnace atmosphere control apparatus characterized that you stop the supply of the hydrocarbon gas when turned upward from the lowered.

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