JPS59118880A - Method for dropping and raising temperature of gas carburizing furnace and for regulating internal atmosphere of said furnace - Google Patents

Abstract

PURPOSE:To reduce the time required to operate a furnace again by keeping the inside of the furnace in an inert gaseous atmosphere until a carburizing gas is introduced after the beginning of a temp. drop when the operation of the furnace is suspended and started again. CONSTITUTION:When the temp. of a gas carburizing furnace is dropped to suspend the operation of the furnace, an inert gas is introduced into the furnace after the beginning of the temp. drop to remove the carburizing gas and to fill the inside of the furnace with an inert gaseous atmosphere. During the suspension of the furnace, the inside of the furnace is kept in the inert gaseous atmosphere. When the temp. of the furnace is raised to start the operation again, the temp. is raised in the inert gaseous atmosphere after ignition until a carburizing gas is introduced. The carburizing gas is then introduced by a larger volume than the volume during operation to regulate the internal atmosphere of the furnace. Thus, the time required to operate the furnace again is reduced.

Description

Detailed Description of the Invention This invention lowers the temperature of a gas carburizing furnace when the operation is suspended, increases the temperature after the operation suspension period ends to adjust the atmosphere in the furnace, and then restarts the furnace after the operation suspension period ends. The present invention relates to a method for lowering and increasing the temperature of a gas carburizing furnace and adjusting the atmosphere inside the furnace, which can shorten the time required for carburizing.

When restarting a gas carburizing furnace after a long-term suspension of operation, sufficient care must be taken to ensure that the quality of the processed product does not deteriorate after restarting.

Conventionally, when lowering or increasing the temperature of the gas carburizing furnace described above and adjusting the atmosphere inside the furnace, the steps as shown in FIG. 1, for example, have been taken. In other words, when lowering the temperature of the gas carburizing furnace, after carburizing the last part, the carburizing gas (RX gas) is degassed at 850°C, and the furnace is cooled to an atmospheric atmosphere. After the furnace is out of operation, leave it as it is, and after the outage period, to raise the temperature, ignite the furnace with the atmosphere inside the furnace, raise the temperature to 850'A, and then carburize. After that, the furnace atmosphere is adjusted by introducing carburizing gas (raw carburizing gas such as butane gas) after passing the gas. At the same time, the same amount was introduced, and this state was continued until the dew point of the atmosphere in the furnace approached -lO'Ciζj, and when the dew point reached a predetermined value, charging of parts was started. .

However, in such a conventional method of lowering the temperature, shoulder temperature, and adjusting the atmosphere in the furnace of a gas carburizing furnace,
! At temperatures i and A, the inside of the furnace is in an atmospheric atmosphere and the supply of carburizing accelerating gas N6j- introduced is the same as during operation. It takes a considerable amount of time (in the tfS1 diagram, it takes 25 to There was a problem in that the carburized parts could not be charged during this time (about 36 hours). Therefore, there is a shortage of parts in the next process, and in order to avoid a shortage of parts, it is necessary to make and store carburized products before the temperature of the furnace cools down, which increases intermediate inventory and makes it difficult to manage parts. This caused the problem that it became complicated.

Therefore, in order to shorten the time from the end of the suspension period to the start of operation of the gas carburizing furnace, it is possible to shorten the heating time of the furnace. This was not easy to achieve due to problems such as deformation of the burner and burner capacity.

This invention has been made to address the above-mentioned conventional problems, and when raising the temperature and adjusting the atmosphere in the furnace after the end of the suspension period of the gas carburizing furnace, the atmosphere in the furnace is adjusted after raising the temperature. In addition, we have developed a method for lowering and increasing the temperature of a gas carburizing furnace, and adjusting the atmosphere inside the furnace, so that the furnace can be restarted immediately after its suspension period. is intended to provide.

Completion of furnace atmosphere adjustment in a gas carburizing furnace is defined as the point when the furnace atmosphere becomes stable. In this state, the temperature gradient within the furnace wall becomes constant, and Co2,
This is also the point at which N20 (moisture) etc. are no longer released, and the biggest causes of delay in completing the furnace atmosphere adjustment are the temperature gradient of the furnace wall and the release of CO2 and moisture.This invention addresses these points. This was done with a focus on
I was able to shrink it.

That is, the temperature decrease in the gas carburizing furnace according to the present invention.

y1 Temperature and furnace atmosphere adjustment method: When lowering the temperature of the gas carburizing furnace, it is more desirable to introduce an inert gas such as Nx gas into the furnace after the temperature has started lowering, and to use a carburizing gas such as Rx gas. At one temperature above the explosion danger temperature, the furnace is removed and the temperature is lowered by creating an inert gas atmosphere inside the furnace.While the furnace is out of service, the inside of the furnace is maintained mainly in an inert atmosphere of scum, and when the temperature reaches A. From the time of ignition until the introduction of carburizing gas, inert gas is reintroduced into the furnace as necessary to create an inert gas atmosphere inside the furnace and the temperature is set to A, and after temperature A, the carburizing gas is more preferably at a temperature above its explosive dangerous temperature, and when adjusting the atmosphere in the furnace after raising the temperature, more preferably the temperature in the furnace is higher than the operating temperature to promote carburization of butane gas, etc. The amount of raw gas used during operation is increased, for example 2 to 3 times the amount of acid used during operation, and after adjusting the atmosphere in the furnace, the temperature inside the furnace is lowered to the temperature during operation, and the amount of carburizing accelerating residue is reduced. It is characterized by the fact that it does not reach the amount during operation).

When lowering the temperature of the carburizing furnace, Nx is added to the furnace from the time the temperature begins to decrease.
Inert gas such as gas is introduced, but this Nx gas contains a few percent of Co and N2, and most of the rest is N2.
It is a gas that contains almost no CO2 or N20 compared to the atmosphere. By introducing an inert gas such as Nx gas to such an extent that the pressure inside the furnace is higher than the atmospheric pressure when the temperature of the furnace is lowered, when the temperature of the body 11 is 11, and when the temperature is A, air can enter the furnace. CO2 and N20 are added to the furnace wall bricks.
Effectively reduces defense to 1 from being absorbed.

By introducing an inert gas such as Nx gas into the furnace during the above-mentioned temperature drop, the carburizing scum such as Rx gas in the furnace is stirred. It is best to capture it at a temperature of 2. This Rx residue as carburizing gas is N2: 40%, N2: 40%
, Co:20%, but in this invention,
It is also applicable to a gas carbonitriding furnace using carbonitriding waste obtained by adding 5 to 10% NH3 to the Rx gas, and is included within the scope of the present invention.

In this way, the inside of the furnace is mainly maintained in an inert gas atmosphere while the furnace is not in operation. After that, the temperature is lowered to a certain level, for example, 200 °C or lower, the furnace is closed, and a non-719 gas is released into the furnace.
It is also possible to leave it in a bottle and let it cool naturally,
It is also possible to maintain an inert gas atmosphere inside the furnace by continuously introducing an inert gas into the furnace from when the furnace temperature is lowered to when it is at rest and at R temperature. .

Next, when raising the temperature of the furnace, an inactive gas is introduced into the furnace as necessary to introduce carburizing scum from the time of ignition into the furnace, and an inert scum atmosphere δ is heated. Then, a carburizing gas is introduced, and the inert gas is removed by tJl for gas replacement. In this case, it is more desirable that the carburizing scum be introduced at a temperature higher than its explosive temperature.

When adjusting the atmosphere in the furnace after the furnace has reached its temperature, a larger amount of carburizing accelerating residue such as butane gas or propane gas is introduced than during operation, for example, 2 to 3 times the amount during operation. This carburizing accelerating gas has the function of accelerating the decomposition of CO2 and N20 when they exist in the furnace.
g) By introducing it to an extent that is less than L, it is possible to shorten the time for adjusting the atmosphere in the furnace.

Further, when adjusting the atmosphere inside the furnace, it is more desirable to set the humidity inside the furnace higher than the temperature during operation, for example, to the maximum allowable temperature of the furnace. By increasing the temperature inside the furnace in this way,
This not only allows the temperature gradient of the furnace wall to reach −··>jl more quickly, but also has the effect of making it difficult to sweeten the carburization promoting gas introduced during furnace atmosphere adjustment.

Next, embodiments of the present invention will be described based on the drawings.

FIG. 2 shows an embodiment of the present invention, with temperature plotted on the vertical axis and time plotted on the horizontal axis.

In this embodiment, the atmosphere inside the gas carburizing furnace is Rx
Dregs (N2: 40%, N2: 40%.

CO: 20%) and enriched gas (carburization accelerating gas, C4H, o), and the treatment temperature was 900°C.

First, after completing the carburizing and quenching of the last part, the temperature started to decrease, and at 850'C, Nx gas (C02:0
．． 05%, Co: 1.8% lN2: 1.0%, N2
: Residue) is started to be introduced, the introduction of Rx gas is stopped, and degassing is performed. After this degassing, N
While introducing gas, temperature reduction is resumed and the temperature is lowered to below 200°C.

Note that it took 24 hours after the completion of quenching to reach this temperature drop. At this point, all of the furnace equipment was stopped, the furnace door and exhaust pipe were closed, Nx gas was sealed in the furnace, and the furnace was then cooled by natural cooling.

In this state, when the temperature of the furnace is to be increased after a long period of inactivity (summer vacation, winter vacation, etc.) of the furnace ends, Nx gas is first introduced into the furnace and ignited. In this embodiment, the temperature A is approximately the same as before, 300°C x 2.5) 1r, 40
0℃X1. 'OHr.

500°OXI, OHr, 600℃X2.5Hr.

700℃ into an Rx gas atmosphere.Then, the furnace temperature was increased to 9.
Set the temperature to 00°C and start adjusting the atmosphere inside the furnace.

In this furnace atmosphere adjustment, enrich gas (carburization promoting gas, C4H, etc.) is introduced 2 to 3 times as much as during operation, and the furnace atmosphere is made to be Rx gas and enrich gas, with a dew point of 11.
Wait until the temperature reaches 0'C, and after the specified atmosphere is reached, run the furnace dry to check for abnormalities in the furnace, and after confirming the atmosphere and dew point, start charging the γa+ product.

Then, adjust the flow rate of carburizing gas while watching the change in dew point), and then infrared! Control I/Roll automatically using the ICO2 analyzer and do the same as during operation.

FIG. 3 shows the operation of the embodiment shown in FIG.
ff13 is a diagram showing the results of investigating the dew point change in the furnace during the adjustment of the furnace atmosphere in the conventional operation shown in the figure.
As shown in the figure, the dew point of the furnace atmosphere is clearly lowered and stabilized more clearly in the case of the present invention than in the conventional case, and it can be seen that the time for adjusting the furnace atmosphere can be considerably shortened.

The following table shows the results of measuring the hardness after heat treatment of the parts first charged into the furnace after adjusting the furnace atmosphere in the conventional example shown in Fig. 1 and the embodiment of the present invention shown in Fig. 2. In this example, a transmission gear (SCr420H) was selected as the component, and a continuous gas carburizing furnace was used, and the carburizing temperature was 900°C1 quenching temperature.

The temperature was 870°C.

As shown in the table above, according to the present invention, the furnace atmosphere Rμ
Even when the adjustment time is significantly reduced compared to the conventional case,
We were able to obtain very excellent results that were comparable to those of conventional methods.

In addition, the above embodiment shows a case where after the temperature inside the furnace is lowered to 200°C or less, all equipment of the furnace is stopped, the m of the furnace and the exhaust pipe are closed, and Nx gas is sealed. However, in addition to this, Nx gas is not sealed, and N
The temperature may be lowered while introducing x gas.

In addition, the temperature during the furnace atmosphere adjustment was set to 900, which is the same as during operation.
'C, but as shown in Fig. 2 with provisional temperature J, the temperature inside the furnace is raised to a temperature close to the maximum allowable temperature of the furnace, for example, 920°C, and maintained. Wait until the dew point of the atmosphere reaches around 110 degrees Celsius, then lower the furnace temperature to the operating temperature (900 degrees Celsius), run it dry, check the furnace for abnormalities, and confirm the atmosphere and dew point. The charging of parts may be started after this is completed. In this case, not only can the temperature gradient of the furnace wall be made more constant, but also the sweetening temperature of the carburizing accelerating scum introduced during the adjustment of the furnace atmosphere can be shifted by ℃. It has become clear that the furnace atmosphere adjustment time can be reduced by 71 hours.

Furthermore, 1. In the described embodiment, a case is shown in which Rx gas is used as the carburizing gas, but good cooling can also be achieved when carbonitriding gas containing 5 to 10% NH added to this Rx gas is used. I was able to get results.

In addition, it is also possible to further shorten the furnace atmosphere adjustment time by introducing a catalyst into the furnace during the furnace atmosphere adjustment to help decompose the enriched gas.

As explained above, according to the present invention, when lowering the temperature of a gas carburizing furnace and raising the temperature after the end of the suspension period 11JJ to adjust the atmosphere in the furnace, when lowering the temperature, the temperature inside the furnace is lowered after the temperature has started lowering. Introducing an inert gas to eliminate the carburizing gas and creating an inert gas atmosphere inside the furnace to lower the temperature, and maintaining the inside of the furnace mainly in an inert gas atmosphere while the furnace is not in operation.
When the temperature is high, the temperature is raised by keeping the inside of the furnace in an inert gas atmosphere from the time of ignition until the introduction of the carburizing gas, and after the temperature has reached y, the carburizing gas is introduced and the atmosphere inside the furnace is adjusted after the temperature has risen. In this case, since the amount of carburizing accelerating gas was introduced in a larger amount than during operation, when the atmosphere in the furnace was adjusted by raising the temperature after the operating unit 11- period of the gas carburizing furnace, The time it takes to adjust the furnace atmosphere and start operation can be significantly shortened compared to conventional methods, and the gas carburizing furnace can be restarted immediately after its suspension period. There is no need to stock up on a large number of parts before suspending operations, and as a result, there is little intermediate inventory during the suspension period, which can significantly reduce parts management costs and prevent parts deterioration due to poor management. It has excellent effects such as being able to prevent as much as possible! I get caught.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are explanatory diagrams illustrating methods for temperature lowering, temperature increasing, and furnace atmosphere adjustment in a gas carburizing furnace according to a conventional example and an embodiment of the present invention in relation to furnace temperature and time, respectively; FIG. 3 is an explanatory diagram showing the results of examining changes in the dew point inside the furnace during furnace atmosphere adjustment in the furnace atmosphere adjustment method according to the conventional example and an embodiment of the present invention.

Claims (2)

[Claims] (1) Dreg immersion) When lowering the temperature of the companion furnace and raising the temperature after the end of the operation unit IE period to adjust the atmosphere in the furnace, when lowering the temperature,
After the phloem starts, an inert gas is introduced into the furnace to eliminate the IQ stage gas, and the temperature is lowered by creating an inert gas atmosphere inside the furnace. An active gas atmosphere is maintained, and when raising the temperature, the inside of the furnace is kept in an inert gas atmosphere from the time of ignition until the introduction of the carburizing gas, and after the temperature is raised, the carburizing scum is introduced. When adjusting the atmosphere in the furnace after raising the temperature, increase the amount of carburizing accelerating gas than during operation.
A method for lowering and increasing temperature in a gas carburizing furnace and adjusting the atmosphere inside the furnace, which is characterized by introducing the method. (2) F? Temperature lowering, temperature increasing, and furnace atmosphere of the gas carburizing furnace according to claim (1), wherein the furnace temperature is made higher than the temperature during operation when adjusting the furnace atmosphere after humid temperature. Adjustment method.