JPS585258B2 - Carbon concentration control method in gas carburizing furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of controlling carbon concentration in a gas carburizing furnace in which an organic liquid that produces a protective gas and an organic liquid that produces a carburizing gas are directly supplied into the furnace.

In this type of gas carburizing furnace (for example, a shift furnace, a drip field furnace, etc.), when performing a diffusion treatment, it is necessary to reduce the carbon concentration (carbon potential) to a predetermined value.

Conventional control methods simply stop the supply of organic liquid for carburizing gas generation and wait for the carbon concentration to fall naturally, but at that time the workpiece has already reached an equilibrium state, so the carbon It takes one hour or more for the concentration to drop to a predetermined value.

Therefore, not only is the diffusion process time-consuming and inefficient, but the diffusion process cannot be controlled with high precision.

The present invention has been made in view of the above-mentioned circumstances, and by supplying air during the diffusion process, the carbon concentration can be reduced to a predetermined value in an extremely short period of time, thereby increasing efficiency and improving the accuracy of the diffusion process itself. An object of the present invention is to provide a method for controlling carbon concentration in a gas carburizing furnace.

Hereinafter, a preferred embodiment of the apparatus used in the control method according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic sectional view showing one embodiment.

The inside of the carburizing furnace body 1 is kept airtight by an insulating lid 2.

A heating element 3 is provided on the inner wall of the carburizing furnace body 1 to heat the inside of the furnace to a predetermined temperature.

A workpiece (not shown) is placed in a retort 4 provided in the furnace.

The ventilator 5 circulates the gas within the furnace in the direction of the arrow in the figure.

Part of the exhaust gas from the exhaust pipe 6 for gas sampling and gas pressure adjustment in the furnace is led to the analyzer 7 and the other part to the exhaust port 8, where a flare-up can be seen after the adjustment. .

As long as the fuel is burning after this adjustment, the pressure will remain higher than the gas pressure inside the furnace.

An analysis data signal from the furnace gas analyzer 7 is transmitted to the controller 9 .

A first organic liquid (for example, ethyl acetate) that generates carburizing gas is stored in the container 11.
The organic liquid is guided to the supply pipe 10 with its flow rate controlled by the control valve 13.

Further, a second organic liquid (for example, methyl alcohol) that generates a protective gas (also referred to as a carrier gas) is stored in the container 12, and this second organic liquid is passed through the control valve 14 to the supply pipe. Guided by 10.

This supply pipe 10 communicates with the inside of the carburizing furnace main body 1 .

The control valves 13 and 14 open and close according to control signals from the control device 9 to control the flow rate of the organic liquid.

A bypass passage 21 is provided in parallel to the control valve 13 that controls the flow rate of the first organic liquid that generates the carburizing gas.

Further, a bypass path 22 is provided in parallel with the control valve 14 that controls the flow rate of the second organic liquid that generates the protective gas.

These bypass channels 21.22 are equipped with valves 23.24.

Another pipe 31 leading to the inside of the carburizing furnace body 1 is connected to a valve 32.
The air supply device 33 is connected to an air supply device 33 that supplies clean air through the air supply device 33.

An example of the operation or control method of the apparatus having the above configuration will be described with reference to FIG. 2.

In Figure 2, a is the temperature, b is the carbon concentration (carbon potential), c is the CO2 (carbon dioxide) concentration, d is the supply current to the heating element 3, and e is the supply amount of the second organic liquid for generating protective gas. , f is the supply amount of the first organic liquid for carburizing gas generation, g
is a time chart showing temporal changes in the supply amount of clean air.

First, heating is started at time t0, and the temperature inside the furnace is increased.

At time t1 after the start of heating, the control valve 14 and the valve 24 of the bypass path 22 are opened, and a large amount of protective gas generation second valve 24 is opened.
of organic liquid is supplied into the furnace.

At time t2 when the temperature inside the furnace reaches a predetermined temperature (for example, 930° C.), the valve 24 of the bypass passage 22 is closed and a fixed amount of the second organic liquid is supplied.

At the same time 12, the control valve 13 and the valve 23 of the bypass path 21 are opened, and a large amount of the first organic liquid for carburizing gas generation is supplied into the furnace.

Therefore, the carbon concentration increases from time t2 and reaches a predetermined concentration (for example, 0.95%) at time t3.

At time t3, the valve 23 of the bypass path 21 is closed, and the control valve 13 controls the supply of the first organic liquid in an amount necessary to maintain a predetermined carbon concentration (0.95%).

At time t4, when this state (strong carburization) is maintained until time t4, the valve 32 is opened and a large amount of clean air is supplied to perform a diffusion process to lower the carbon concentration (for example, to 0.75%).

A small amount of clean air is supplied during the diffusion process.

Next, at time t5, heating is stopped and the temperature inside the furnace is lowered to the quenching temperature (for example, 850° C.).

At this time, a large amount of clean air is supplied.

Next, quenching is performed four times, for example, at times t6, t7, t8, and t9.

During this hardening process, the insulating lid 2 of the carburizing furnace is opened once, so the valves 23 and 24 of the bypass paths 21 and 22 are opened at each point after the insulating lid 2 is closed.
A large amount of the second organic liquid is supplied.

In addition, in order to compensate for the temperature drop when the insulating lid 2 is opened, the heating element 3 is also supplied at each time t6. A large amount of current is supplied at t7, t8, and t9.

In addition, in the CO2 concentration curve of FIG. 2c, if clean air is supplied (that is, the valve 32 opens) at a value slightly lower than the predetermined CO2 concentration, as shown by the broken line and the numbers in parentheses, better results will be obtained. Get results.

In the above explanation, when switching from strong carburizing to diffusion (
At time t4) or when the temperature is lowered to the quenching temperature during diffusion, the workpiece has already reached an equilibrium state.

Therefore, conventionally, the carbon concentration usually does not decrease to a predetermined value even after one hour or more has passed.

This is particularly noticeable in the case of pit furnaces.

In this embodiment, clean air is supplied at a fixed amount (for example, 11/min).
~51/m1n) or a certain amount plus a temporarily large amount (for example, a certain amount plus 11/min to 101/rnin)
is supplied into the carburizing furnace and mixed with the carburizing gas, so that the carbon concentration decreases to a predetermined value within, for example, 5 to 20 minutes.

Furthermore, in the case of a conventional pit furnace, when the insulating lid is opened, the carburizing gas is burned and replaced with air outside the furnace.

Therefore, even if the insulating lid was closed next, the furnace was left open for a long time until the carbon concentration of the gas in the furnace rose to a predetermined value.

In this embodiment, the first and second organic liquids are passed through the bypass path 21.
．． 22, the carbon concentration in the furnace rises to a predetermined value in a very short time.

Note that these effects can also be obtained when applied to a box-shaped furnace having a closed quenching tank other than a bit furnace.

Therefore, since the carbon concentration can be controlled to a predetermined value in a short time, the carburizing time can be accurately regulated and the accuracy of the carburizing depth can be improved.

In addition, when charging multiple workpieces at once and quenching them one by one in a pit-type gas carburizing furnace, the control time required to recover the carbon concentration in the carburizing gas and stabilize it at a predetermined value is short. , it is possible to reduce variations in heat treatment characteristics of multiple workpieces.

As explained in the embodiments above, according to the carbon concentration control method of the present invention, the carbon concentration is lowered by supplying air during the diffusion process, so it is possible to reduce the carbon concentration to a predetermined value in an extremely short time. This not only improves efficiency, but also allows the carbon concentration to be lowered quickly in a short period of time, contributing to improving the accuracy of the diffusion process itself.

Note that the present invention is not limited to the above-mentioned embodiments, and various modifications can be made without departing from the gist of the present invention.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional front view showing one embodiment of the present invention;
FIG. 2 is a time chart for explaining FIG. 1. DESCRIPTION OF SYMBOLS 1... Carburizing furnace body, 2... Insulating lid, 3... Heating element, 4... Retort, 5... Ventilator, 6...
Exhaust pipe, 7... Analyzer, 8... Exhaust port, 9...
Control device, 10... Supply pipe, 11.12... Container,
13.14... Control valve, 21.22... Bypass path, 23, 24, 32... Valve, 31... Pipe, 33...
・Air supply device.

Claims (1)

[Claims] 1 In a gas carburizing furnace to which a first organic liquid that generates a carburizing gas and a second organic liquid that generates a protective gas are directly supplied, the carbon concentration is reduced by supplying air during the diffusion treatment. A carbon concentration control method characterized by controlling.