JPH0248618B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a continuous vacuum carburizing furnace, in particular, to a continuous vacuum carburizing furnace, which has three chambers consisting of a first heating chamber, a second heating chamber, and a cooling chamber, and two chambers that partition these three chambers. This invention relates to a three-chamber, two-door type continuous vacuum carburizing furnace consisting of an intermediate vacuum door and its operating method.

<Prior art> The vacuum carburizing method involves heating an object to be heated in a vacuum furnace, introducing hydrocarbon gas into the furnace, carburizing the object, then diffusing it, and then rapidly cooling (quenching) to harden the carburized part.
Compared to conventional gas carburizing methods, carburizing can be performed at higher temperatures, so carburizing time is shortened, and the surface carbon concentration and carburizing depth of the heated object can be controlled by adjusting the carburizing and diffusion times. Unlike the conventional gas carburizing method, this method has rapidly become popular because there is no oxygen in the carburizing gas atmosphere and no abnormal surface layer is generated (see Japanese Patent Publication No. 31976/1983).

Therefore, in such a vacuum carburizing process, the applicant proposed a two-chamber, one-door type semi-continuous vacuum carburizing furnace as shown in Fig. 1 (Japanese Patent Application No. 56-21826 (Tokyo Patent Application No. 57-137417)). (See.) This furnace has a heating element of 1A.
A heating chamber 1 consisting of a heating chamber 1 and a heat insulating material 1B, a vacuum furnace body 4 in which the heating chamber 1 is installed, and a cooling chamber 6 that stores a coolant 7 inside and can be made airtight by attaching a lid 9 are connected. A heating power source E connected to the heating element 1A of the heating chamber 1, a vacuum exhaust source V and a carburizing gas source C connected to the vacuum furnace body 4, a charging door 2, an intermediate vacuum door 5, and an unloading door. 10, a transfer means 3 for the object to be heated M, a vacuum exhaust source V connected to the lid 9, and a pressurized gas source G.

The operating method of this semi-continuous vacuum carburizing furnace is as shown in Table 1.
After introducing air into the tank to bring it to atmospheric pressure, open the charging door 2.
is opened, the cold first heat target M1 is charged by the transfer means 3, and the charging door 2 is immediately closed (first step). Next, the first object to be heated M1 is vacuum heated to a predetermined carburizing temperature, and then carburized in an atmosphere of carburizing gas supplied from the carburizing gas source C for a predetermined period of time.
Next, the supply of the carburizing gas is stopped, the vacuum is created again, and the carbon is vacuum heated to the predetermined temperature or slightly higher than that, and the carbon that has entered the first heat target M1 is vacuum diffused, and then the predetermined quenching is performed. lower the temperature to
This quenching temperature is maintained for a predetermined period of time. During this time, the cooling chamber 6 is evacuated (second step). Next, the intermediate vacuum door 5 is opened, the high-temperature heat object M1 is transferred to the lifting platform 8 in the cooling chamber 6 by the transfer means 3, and the intermediate vacuum door 5 is immediately closed (third step). Next, while pressurizing the cooling chamber 6 by injecting non-oxidizing gas from the heated gas source G, the lifting platform 8 is lowered to move the first heated object M1 to a coolant (oil oil) at a predetermined temperature. ) 7 for rapid cooling (quenching) treatment, and after introducing air into the heating chamber 1 of the invention to bring it to atmospheric pressure, the charging door 2 is opened to cool the second chamber in a cold state.
The object to be heated M2 is charged, and the charging door 2 is immediately closed (fourth step). Next, the second heat target M2 is heated under vacuum in the same manner as the first heat target M1, and subjected to carburizing treatment, diffusion treatment, cooling to the quenching temperature, and the like. In the meantime, the cold object M1 placed on the lifting platform 8 is raised to a predetermined position, and at the same time, the cooling chamber 6 is returned to the atmospheric pressure state, and the unloading door 10 is opened to remove the object M1. It is carried out of the furnace, the carrying-out door 10 is closed, and the cooling chamber 6 is immediately evacuated (fifth step). Thereafter, in the steady state, the third, fourth, and fifth steps were repeated at predetermined intervals. Note that the normal coolant 7 is Fan F.
The mixture is stirred by

In this proposed furnace, air is introduced into the heating chamber 1 at a high temperature (approximately 820°C) when the material to be heated M is charged into the heating chamber 1, and air is generated by carburizing gas during the carburizing process. Since the soot adhering to the heating element 1A and the heat insulating material 1B can be burned out, the temperature of the heating element 1A cannot be controlled due to soot adhesion, which was easily caused in the past (shooting, etc.)
It was possible to prevent the deterioration of the heat insulating properties of the heat insulating material 1B.

<Problems to be Solved by the Invention> However, although the proposed furnace has an improved operating rate and processing capacity compared to the conventional furnace, the processing capacity is still unsatisfactory.

For example, so that the carburization depth reaches about 1.2mm
In the case of vacuum carburizing at 1040° C., each object to be heated M stays in the heating chamber 1 for about 155 minutes and in the cooling chamber 6 for about 5 minutes, as shown in FIG. As a result, one batch of heated material M (approximately 400 kg) is carried out (vacuum carburizing) approximately every 160 minutes.
Therefore, the processing capacity per unit time was low (150 kg/h).

This invention can eliminate these drawbacks, and can burn out the soot that adheres to the heating element and insulation material, which is generated by carburizing gas during carburizing treatment, resulting in the inability to control the temperature of the heating element and the insulation material. In addition to preventing a decrease in the heat insulation properties of The purpose is to provide a continuous vacuum carburizing furnace that can be improved and its operating method.

<Means for Solving the Problems> The gist of the present invention is as follows: (1) A charging door and an unloading door are provided at the charging inlet and unloading port formed at the front and rear of the furnace, respectively, and The first heating chamber for carburizing treatment, the second heating chamber for diffusion treatment, and the cooling chamber are arranged in the first heating chamber and the second heating chamber for diffusion treatment, respectively, and a means for transferring the object to be heated is disposed in each of these chambers. Second
The heating chamber is divided by a first intermediate vacuum door, the second heating chamber and the cooling chamber are divided by a second intermediate vacuum door, and the first heating chamber is connected to a heating power source, a vacuum exhaust source, and a carburizing gas source. The second heating chamber is connected to a heating power source and a vacuum evacuation source, and is constructed of a heating element and a heat insulating material that are chemically and mechanically stable under atmospheric pressure conditions and vacuum pressure conditions in a high-temperature environment. A continuous system consisting of a heating element and heat insulating material that are chemically and mechanically stable under vacuum pressure, a means for cooling the heated object installed in the cooling chamber, and connected to a condensing gas source and a vacuum exhaust source. After charging the vacuum carburizing furnace and (2) the cold object to be heated into the first heating chamber at high temperature and atmospheric pressure,
After vacuum heating to a predetermined carburizing temperature, and then carburizing the object in a carburizing gas atmosphere, the vacuum is applied again, and then the vacuum carburized and high-temperature object is transferred to a second chamber under high temperature and vacuum pressure. After the object to be heated is transferred to a heating chamber and subjected to a diffusion treatment, a predetermined quenching temperature is maintained, and then the high temperature object to be heated, which is maintained at the quenching temperature, is transferred to a cooling chamber under vacuum pressure and cooled by means of cooling means. After quenching, the vacuum carburized and quenched material is transported out of the furnace from the cooling chamber, which has been brought to atmospheric pressure.
After the object to be heated is sequentially transferred from each of the first heating chamber, the second heating chamber, and the cooling chamber, the subsequent object to be heated is sequentially and continuously carried into each of the chambers for processing. This is a method of operating a continuous vacuum carburizing furnace.

<Example> Hereinafter, an example of the continuous vacuum carburizing furnace of the present invention will be described with reference to FIG. The first heating chamber 11 and the second
The heating chambers 16 each include a resistance heating element that has high high-temperature strength, does not cause thermal cracks or evaporates even in a high-temperature vacuum state, and does not oxidize and burn even when directly exposed to air in a high-temperature state.
For example, a silicon carbide heating element that has undergone recrystallization treatment, a silicon carbide heating element that has an alumina spray coating layer formed on its surface, a Ni-Cr alloy that generates heat if the maximum heating temperature is 1000℃ or less and the vacuum pressure is about 0.2 Torr. Heating elements 11A and 16A, which are chemically and mechanically stable, such as metal or Fe-Cr alloy heating elements, have low thermal conductivity and are chemically and mechanically stable even when repeatedly exposed to vacuum or air at high temperatures. Insulating materials 11B and 16B made of a refractory material such as high-purity ceramic fiber
Consists of.

Next, the first heating chamber 11 is placed in a vacuum furnace body 14 connected to a vacuum exhaust source V and a carburizing gas source C.
At the same time, the heating element 11A and its heating power source E are connected, and a charging door 12 is connected to the charging port 14A formed on the front end side of the vacuum furnace body 14.
A first intermediate vacuum door 15 is disposed at each transfer port 14B formed on the rear end side.

connected to the vacuum furnace body 14 in an airtight manner,
and placing the second heating chamber 16 in the vacuum furnace body 17 connected to the vacuum exhaust source V, and connecting the heating element 16A and its heating power source E;
Further, a second intermediate vacuum door 18 is provided at the transfer port 17A of the vacuum furnace body 17.

A cooling chamber 20 containing a coolant 21 is connected to the vacuum furnace body 17, and a lid 23 connected to a repressurizing gas source G and an evacuation source V is airtightly attached to the top of the cooling chamber 20. Export port 2 formed in this cooling chamber 20
A carry-out door 22 is provided at 0A. Further, a fan F immersed in the coolant 21 is attached to a side wall of the cooling chamber 20.

Next, as means for transferring the object to be heated M, conveyors 13A and 13C are disposed within the vacuum furnace body 14, and a conveyor 13B is disposed within the first heating chamber 11. Inside the vacuum furnace body 17, a conveyor 13D,
13F, a conveyor 1 is installed in the second heating chamber 16.
3E is installed. Conveyors 13G and 13H are disposed in the cooling chamber 20, and a lifting platform 19 that can be raised or lowered is disposed between these conveyors 13G and 13H, and the heated object M is a coolant serving as a cooling means. It is possible to go up and down to 21.

Although not shown in this continuous vacuum carburizing furnace,
A temperature and pressure control device for each heating chamber, a transfer control device for the heated object M, an opening/closing control device for the loading door 12, the first and second intermediate vacuum doors 15 and 18, and the unloading door 22 are attached.

Next, a method of operating the continuous vacuum carburizing furnace of this embodiment will be explained.

In this continuous vacuum carburizing furnace, as shown in Table 2,
After introducing air into the high-temperature first heating chamber 11 that has been heated to a predetermined temperature (approximately 820°C) and brought to atmospheric pressure,
The charging door 12 is opened, the cold first object to be heated M1 is charged by the transfer means 13, and the charging door 1 is immediately opened.
2 (first step). Next, the first heated object M
After vacuum heating 1 to the specified carburizing temperature (approximately 1040℃),
Carburizing is performed in an atmosphere of carburizing gas supplied from carburizing gas source C for a predetermined period of time. After that, the supply of carburizing gas is stopped and vacuum is created again. During this time, the second heating chamber 16, which has been heated to a predetermined temperature (approximately 820° C.), is evacuated (second step). Next, the first intermediate vacuum door 15 is opened and the vacuum carburized high-temperature first heat object M1 is transferred to the second heating chamber 16 by the transfer means 13.
and immediately close the first intermediate vacuum door 15 (third step). Next, the first heat target M1 is vacuum heated to a temperature equal to or slightly higher than the carburizing temperature, and the carbon that has entered the first heat target M1 through the carburizing process is diffused, and then a predetermined temperature is applied. The temperature is lowered to the quenching temperature (approximately 820℃) and held for a specified period of time.
During that time, air is introduced into the first heating chamber 11 at a high temperature (approximately 820° C.), and the carburizing gas is generated by the carburizing gas supplied during the carburizing process.
The soot (carbon particles) adhering to 1B is burned off to return it to atmospheric pressure, the charging door 12 is opened, the cold second heated material M2 is charged, and the charging door 12 is immediately closed. . Meanwhile, the cooling chamber 20 is evacuated (fourth step). Next, in the first heating chamber 11, the second heated object M2
is subjected to the same vacuum heating and carburizing treatment as the first heat target M1. On the other hand, the second intermediate vacuum door 18 is opened and the high-temperature first heated object M1 is transferred from the second heating chamber 16 to the lifting platform 19 of the cooling chamber 20 by the transfer means 13;
Immediately close the second intermediate vacuum door 18 (fifth step). Next, in order to restore the pressure in the cooling chamber 20, non-oxidizing gas is injected from the restoration gas source G to achieve a predetermined low pressure state, and the lifting table 19 is lowered into the coolant (oil) 21. The first heated object M1 is heated to a high temperature.
After the quenching (quenching) treatment, the lifting platform 19 is raised to a predetermined position. On the other hand, the first intermediate vacuum door 15 is opened, the second heated object M2 is transferred from the first heating chamber 11 to the second heating chamber 16 in a vacuum state, and the first intermediate vacuum door 15 is immediately closed (sixth step ). Next, in the second heating chamber 16, the second heat target M2 is subjected to a diffusion treatment, lowered to the quenching temperature, maintained, etc. in the same manner as the first heat target M1, and further, when the cooling chamber 20 returns to the atmospheric pressure state, the above-mentioned recovery is performed. At the same time as the supply of pressurized gas is stopped, the carry-out door 22 is opened to carry out the first heated object M1 out of the furnace, and the carry-out door 2
At the same time as closing the cooling chamber 20, the cooling chamber 20 is brought into a vacuum state. On the other hand, air is introduced into the high-temperature first heating chamber 11 to perform the same soot burning process as described above, and when the pressure returns to atmospheric pressure, the charging door 12 is opened and the cold third heat object M3 is charged. , immediately close the charging door 12 (seventh step). Thereafter, in the steady state, the fifth, sixth, and seventh steps are repeated at predetermined intervals. Note that the coolant is usually stirred by a fan F.

For example, so that the carburization depth reaches about 1.2mm
In the case of vacuum carburizing at 1040°C, as shown in FIG. Remain for 5 minutes. As a result, the vacuum carburizing time for each object to be heated is approximately 155 minutes, but as shown in Table 2, in the steady state, there are no objects to be heated in the first heating chamber 11, second heating chamber 16, and cooling chamber 20. M stays (7th
(See process). This allows one batch of heated material M (approximately 400
Kg) is vacuum carburized and transported approximately every 75 minutes, which increases processing capacity to approximately 320 kg per unit time.

Therefore, the operating steps of the continuous vacuum carburizing furnace of this embodiment include the three steps of carburizing treatment, diffusion treatment, and rapid cooling, similar to those of the conventional semi-continuous vacuum carburizing furnace.
Since carburizing and diffusion are performed in separate heating chambers, the cycle time for 1.2 mm carburization has been reduced to approximately 75 minutes (compared to 160 minutes for conventional furnaces).
It is possible to reduce processing costs and processing man-hours by about half.

In addition, in the case of vacuum carburizing at 1040°C, when the carburizing depth is further increased, as shown in Table 3, it is necessary to lengthen the residence time of the heated material in the first heating chamber 11 and the second heating chamber 16. However, the diffusion time in the second heating chamber 16 needs to be extended at a greater rate than the carburizing time in the first heating chamber 11.

However, since the continuous vacuum carburizing furnace of the embodiment has two chambers, the first heating chamber 11 for carburizing treatment and the second heating chamber 16 for diffusion treatment, as shown in FIG. The second heating chamber 16 is larger than the first heating chamber 11.
is increased to increase the number of heated objects staying in the second heating chamber 16, and after staying in the second heating chamber 16 for a predetermined time, the heated objects are transferred one by one to the cooling chamber 20. In both cases, the cycle time can be significantly shortened compared to the previously proposed semi-continuous vacuum carburizing furnace.

In addition, in this embodiment, the temperature of the heating element 11A is controlled by reducing the resistance value of the heating element 11A, which has adhered to the heating element 11A and the heat insulating material 11B in the first heating chamber 11 through the vacuum carburizing treatment of the preceding heated object. The soot that causes failure or insulation failure or impairs the insulation properties of the heat insulating material 11B is burned out by introducing air and released to the outside of the furnace without causing any hindrance to the heating element 11A or the heat insulating material 11B. Because the object to be heated can be charged, the first
The temperature of the heating chamber 11 can be easily controlled, and the heat insulating material 11
The insulation effect of B is not impaired.

<Operations and Effects of the Invention> As described above, the continuous vacuum carburizing furnace and the operating method thereof according to the present invention can introduce air into the high-temperature heating chamber for carburizing treatment, and can also reduce the heating element and heat insulating material of the heating chamber. Since it is made of a material that does not oxidize and burn even when exposed to air at high temperatures, soot adhering to the heating element or insulation material can be burned off without causing any problems, preventing the inability to control the temperature of the heating element due to soot adhesion. It is possible to prevent the insulation properties of the insulation material from deteriorating.

Further, the continuous vacuum carburizing furnace and the operating method thereof according to the present invention have two heating chambers, one for carburizing treatment and one for diffusion treatment.
It is composed of several chambers, and the subsequent heated object can be carburized during the diffusion treatment, and all the chambers can be operated efficiently, so that the processing capacity per unit time can be improved. In particular, in the continuous vacuum carburizing furnace according to the present invention, it is possible to retain a plurality of objects to be heated in the heating chamber for diffusion treatment for a predetermined time without hindering the carburizing treatment or quenching treatment. In processes that require a deep carburization process, the time required for diffusion process is significantly longer than the time required for carburizing process, so in such processes, the processing capacity can be significantly improved compared to conventionally proposed furnaces. Can be done.

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams showing a conventionally proposed semi-continuous vacuum carburizing furnace and an example of its operation. Figures 3 and 4 are diagrams showing the continuous vacuum carburizing furnace of the present invention and an example of its operation. Figure 3 is a schematic diagram showing the structure of the continuous vacuum carburizing furnace, and Figure 4 is a diagram showing the structure of the continuous vacuum carburizing furnace. It is a temperature curve diagram of a hot object over time. 11...First heating chamber, 11A...Heating element, 11
B...Insulating material, 12...Charging door, 13...Transfer means, 14A...Charging port, 15...First intermediate vacuum door, 16...Second heating chamber, 16A...Heating element, 1
6B...Insulating material, 18...Second intermediate vacuum door, 20
...Cooling room, 20A...Export port, 21...Coolant, 22...Export door, C...Carburizing gas source, E...
...Heating power source, G...Repressurized gas source, M...Heat target, V...Vacuum exhaust source.

【table】

Claims (1)

[Scope of Claims] 1. A charging inlet and an unloading door formed at the front and rear of the furnace are respectively provided with a charging door and an unloading door, and the front, center and rear of the furnace are respectively provided with a first heating chamber for carburizing treatment. , a second heating chamber and a cooling chamber for diffusion treatment, and each of these chambers is provided with means for transferring the heated object,
The first heating chamber and the second heating chamber are separated by a first intermediate vacuum door, the second heating chamber and the cooling chamber are partitioned by a second intermediate vacuum door, and the first heating chamber is separated by a heating power source and a vacuum. The second heating chamber is connected to an exhaust source and a carburizing gas source, and is composed of a heating element and a heat insulating material that are chemically and mechanically stable in high-temperature environments at atmospheric pressure and vacuum conditions. It is connected to a gas source and is composed of a heating element and heat insulating material that are chemically and mechanically stable in a high-temperature environment and vacuum state, and a means for cooling the heated object is installed in the cooling room, and a repressurizing gas source and vacuum exhaust are installed. A continuous vacuum carburizing furnace characterized in that it is connected to a power source. 2. After charging the cold object to be heated into the first heating chamber at high temperature and atmospheric pressure, vacuum heating it to a predetermined carburizing temperature, and then carburizing the object in a carburizing gas atmosphere.
After creating a vacuum again, the high-temperature heat object subjected to vacuum carburization is transferred to the second heating chamber under high temperature and vacuum pressure, and after the heat object is diffused, a predetermined quenching temperature is maintained, and then The high-temperature heat object held at the quenching temperature is transferred to a cooling chamber under vacuum pressure and rapidly cooled by a cooling means, and then the vacuum carburized and quenched object is discharged from the cooling chamber at atmospheric pressure to the outside of the furnace. After carrying out the process and sequentially transferring the object to be heated from each of the first heating chamber, second heating chamber, and cooling chamber, subsequent objects to be heated are successively carried into each of the chambers for processing. A method of operating a continuous vacuum carburizing furnace characterized by: