JP2001240954A - Vacuum carburizing method, and carburizing furnace therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carburizing furnace to implement a carburizing method in which the number of ethylene molecules in a carburizing chamber is substantially nonincreased from the beginning to the terminating period of carburization when ethylene and hydrogen are used as the vacuum carburizing gas. SOLUTION: The vacuum carburizing furnace comprises a carburizing chamber 2 to carburize a work inside, a vacuum carburizing gas feed means 4 to feed the vacuum carburizing gas containing ethylene gas and hydrogen gas to the work in the carburizing chamber 2 from the top, and an evacuating means 6 to suck the gas in the carburizing chamber 2 from the bottom of the work. It further comprises an increase/decrease detecting means 33 to detect the increase/decrease of the number of molecules of ethylene gas, and an exhaust quantity adjusting means 7 to adjust the exhaust quantity of the vacuum carburizing gas to be exhausted from the carburizing chamber 2 based on the increase/decrease of the number of molecules of ethylene gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a vacuum carburizing method and a carburizing furnace for performing the vacuum carburizing method.

[0002] In the present specification, "gas carburization" means gas carburization performed under atmospheric pressure, and "vacuum carburization" means gas carburization performed under reduced pressure.

[0003]

2. Description of the Related Art FIG. 6 shows a conventional carburizing furnace.

This carburizing furnace is for performing vacuum carburizing. The carburizing furnace is a carburizing chamber surrounded by a vacuum vessel (51) and a wall formed of high-purity ceramic fiber in the vacuum vessel (51). (52), an oil tank chamber (53) provided adjacent to the carburizing chamber (52), and a vacuum gauge (54) for mechanically detecting the amount of displacement of the diaphragm. Was omitted, but the gas for vacuum carburizing was introduced into the carburizing chamber (52) by a gas introduction pipe which penetrated the wall of the vacuum vessel (51) and the carburizing chamber (52) and whose tip was located in the carburizing chamber (52). It is being introduced.

The pressure in the carburizing chamber (52) is detected by a vacuum gauge (54), and the pressure in the carburizing chamber (52) is adjusted to a predetermined value based on the detected value. In this example, acetylene gas is used as the carburizing gas. A vacuum carburizing method using ethylene gas is also known. The present invention relates to a method and an apparatus using ethylene gas as a carburizing gas.

[0006]

In the above-mentioned conventional carburizing furnace and vacuum carburizing method, the total pressure of the mixed gas of the gas decomposed and generated in the furnace and the gas for vacuum carburizing is absolutely reduced by carburizing. This means that pressure is being measured.

In the carburizing process, it is desirable to supply ethylene to the carburizing chamber with a higher degree of accuracy as the process proceeds with the aim of suppressing the generation of soot and the like. From such a viewpoint, the present inventors have monitored the behavior of gas molecules in the system during the carburization process using ethylene with a quadrupole mass spectrometer, and found the following. In other words, in the carburizing process, more ethylene molecules are required at the beginning than at the end,
Since the conventional apparatus measures the absolute pressure of the total pressure in the carburizing chamber, the amount of ethylene in the carburizing chamber cannot be controlled. Actually, when the experiment was conducted at a pressure of 60 to 70 Torr, the detected value of ethylene increased to about twice at the end of the conventional carburization compared to the initial stage of carburization, and it followed the course opposite to that required by the process. I knew it was there.

[0008] An object of the present invention is to solve the above-mentioned problems. When ethylene and hydrogen are used as a vacuum carburizing gas, the number of ethylene molecules in the carburizing chamber does not substantially increase from the beginning to the end of carburization. It is an object of the present invention to provide an excellent vacuum carburizing method capable of minimizing carburization variation in a large-capacity patch and minimizing the occurrence of carburizing, and a carburizing furnace for performing the method.

[0009]

Means for Solving the Problems and Effects of the Invention In order to solve the above problems, a vacuum carburizing method according to the present invention supplies a vacuum carburizing gas containing ethylene gas and hydrogen gas to a carburizing chamber and supplies air. In the vacuum carburizing method for exhausting the vacuum carburizing gas, the number of ethylene molecules in the carburizing chamber does not substantially increase from the beginning to the end of carburizing.

According to this method, there is sufficient ethylene present at the beginning of carburizing which requires a large amount of carbon source to reduce carburizing variability, and at the end of the period when less carbon source is required, ethylene is used. Since the number of molecules does not increase, generation of soot can be suppressed.

Further, the carburizing furnace of the present invention has a carburizing chamber for carburizing a work therein, and a vacuum carburizing gas for supplying a vacuum carburizing gas containing ethylene gas and hydrogen gas to the work in the carburizing chamber from above. In a carburizing furnace equipped with an air supply unit and a vacuum exhaust unit that sucks gas in the carburizing chamber from below the work, an increase / decrease detection unit that detects an increase / decrease in the number of molecules of ethylene gas and an amount of the ethylene gas detected by the increase / decrease detection unit. An exhaust amount adjusting means for adjusting an exhaust amount of the vacuum carburizing gas exhausted from the carburizing chamber based on an increase or a decrease in the number of molecules, wherein the vacuum carburizing gas supply means uniformly applies the vacuum carburizing gas to the workpiece. A gas dispersing means for dispersing and supplying air is provided, and the vacuum exhaust means is branched and connected to a plurality of vacuum exhaust ports for uniformly exhausting the carburizing gas.

In this carburizing furnace, the above method can be easily implemented. In addition, the carburizing gas is uniformly dispersed and supplied over the entire peripheral surface of the workpiece, and the plurality of exhausted and evacuated pipes are evacuated so that approximately the same amount of gas flows. Even if they are arranged at different positions in, a high-quality treated product uniformly carburized can be obtained.

It is preferable to use a quartz vacuum gauge for the increase / decrease detection means. A quartz vacuum gauge measures pressure by using the phenomenon that the resonance impedance of a quartz oscillator changes according to pressure, but a vacuum carburizing gas containing ethylene gas and hydrogen is introduced into the furnace. Then, when performing vacuum carburizing treatment by controlling the pressure using this vacuum gauge while simultaneously evacuating, the number of ethylene molecules is kept substantially constant during the carburizing process, and the required good results are obtained with good reproducibility, It turned out to be suitable for mass production. The principle is currently being elucidated.

In the above furnace, the gas dispersing means is provided with a horizontal gas introducing pipe extending through the carburizing chamber and extending to above the work, and a gas dispersing means provided in a branched shape from the introducing pipe and at a lower portion of the peripheral wall. It may include one or more closed-end horizontal gas branch pipes having a plurality of gas outlets spaced apart in the axial direction.

According to the above furnace, the structure of the gas supply means for vacuum carburizing is simplified and the apparatus is inexpensive.

Further, a wall of the carburizing chamber is formed of a heat insulating material and an airtight material covering the outside thereof, and a gas carburizing gas supply means for supplying a gas for carburizing into the carburizing chamber; May be provided with gas exhaust means for gas carburizing for exhausting gas, and a stirring fan provided at the upper part of the carburizing chamber.

In this furnace, gas carburizing as well as vacuum carburizing can be performed.

Further, the gas dispersing means includes a rotatable vertical gas introduction pipe penetrating the wall of the carburizing chamber from above, a plurality of gas dispersion means extending radially from the lower end of the gas introduction pipe and being axially spaced below the peripheral wall. And a horizontal gas branch pipe having a plurality of closed-end gas outlets.

In this way, the structure of the gas supply means for vacuum carburizing can be simplified and the apparatus can be made inexpensive.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 show a vacuum carburizing furnace according to a first embodiment of the present invention.

The furnace (1) comprises a carburizing chamber (2) having a wall (w) formed of a heat insulating material and a metal plate covering the outside thereof, and a carburizing chamber (2).
An oil tank chamber (3) provided adjacent to the gas supply path (4) for supplying a gas for vacuum carburizing to the carburizing chamber (2);
A vacuum evacuation path (6) used for evacuating the vacuum carburizing gas in the carburizing chamber (2) during vacuum carburizing and for evacuating the carburizing chamber (2), and a crystal vacuum gauge (33). , A pressure regulator (34) and a motor valve (32). Although not shown in the drawings, the carburizing furnace (1) has a well-known loading / unloading device and an oil tank chamber (3) that carry a work into and out of the oil tank chamber (3) from outside to the oil tank chamber (3). ) And a known carry-in / out device for carrying the work into the carburizing chamber (2) from the carburizing chamber (2) and carrying the work from the carburizing chamber (2) to the oil tank chamber (3).

The carburizing chamber (2) communicates with the oil tank chamber (3) through a work loading / unloading opening and closing by a door (2a), and the oil tank chamber (3)
Is formed with a work loading / unloading opening and closing that is opened and closed by a door (3a). Further, a plurality of radiant tube heaters (12) are arranged in the carburizing chamber (2) so that the temperature inside the carburizing chamber (2) is raised to a predetermined temperature.

Further, a nitrogen gas supply pipe (24) for pressure recovery is connected to the carburizing chamber (2), while a vacuum pump (1) is connected to the oil tank chamber (3).
5) and a nitrogen gas supply pipe (16) for pressure recovery.
The carburizing chamber (2) and the oil tank chamber (3) are connected by a pipe (25) so that the internal pressure can be made equal.
The heat insulating material of the wall (w) is a ceramic fiber formed by vacuum compression molding, so that gas penetration is prevented.

The vacuum carburizing gas supply path (4) is provided in a carburizing chamber (2).
A gaseous mixture of ethylene and hydrogen is supplied as a carburizing gas to a vertical gas inlet pipe (10) penetrating the upper wall of the carburizing chamber (2), and radially from the lower end of the gas inlet pipe (10). A plurality of extended horizontal gas branch pipes (11). Although not shown, a plurality of gas blowing holes are formed at a lower portion of the peripheral wall of the gas branch pipe (11) at intervals in the axial direction.

The introduction pipe (10) is a connection pipe (1) whose upstream side is branched.
8) is connected via a rotary joint (17).
Then, the introduction pipe (10) is connected to the driving machine (1
3), for example, rotating about a vertical axis by an electric motor. An ethylene cylinder (8) and a hydrogen cylinder (9) are connected to a branch end of the connection pipe (18). Connection pipe
Regulators (20) and (21) are provided on the downstream side of the cylinders (8) and (9) in the branch portion of (18). Although not shown, a flow meter or the like is also provided at the branch portion. A gas introduction valve (23) is provided in a portion that is not branched.

The evacuation path (6) includes a manifold (26) having a plurality of evacuation ports opened at the bottom of the carburizing chamber (2). The vacuum exhaust ports of the manifold (26) are arranged in two rows at predetermined intervals in the front, rear, left and right so that the amount of gas flowing through each vacuum exhaust port is equal when exhausting gas, such as during vacuum carburization. Are arranged.

The manifold (26) is provided with a horizontal gas outlet pipe (2).
7) is connected. The gas outlet pipe (27) is connected to a vacuum pump (28) via a pipe branched into two paths on the way. A large vacuum valve (30) is provided on one of the branches in the piping,
On the other side, a small vacuum valve (31) and a motor valve (32) are arranged.

The crystal vacuum gauge (33) is connected to a pressure controller (34), and the motor valve (32) is connected to the pressure controller (34). The pressure controller (34) and the motor valve (32) are publicly known, and a detailed description thereof will be omitted.

In the furnace (1), the distance between the upper end of the effective space in the carburizing chamber (2) and the branch pipe (11) is 100 to 15
About 0 mm is preferable. The diameter of the gas outlet of the branch pipe (11) is preferably about 3 mm, and the pitch is preferably 32 to 53 mm. Further, it is preferable to form about ten vacuum exhaust ports of the manifold (26) below the effective space.

More preferably, they are arranged in two rows of five pieces each.
The diameter of the manifold (26) is preferably about 20 mm.

In the furnace (1) configured as described above, vacuum carburizing is performed as follows. The following pressure values were used for furnace (1) unless otherwise specified.
Is the actual absolute pressure inside.

The inside of the carburizing chamber (2) is treated at a processing temperature (normally 930 to 1).
050 °). At the same time, the inside of the carburizing chamber (2) is evacuated (usually 1 Torr (133.32 Pa) or less) by a vacuum pump (28). At this time, the large vacuum valve (30) is opened and the small vacuum valve (31) is closed. On the other hand, a nitrogen gas is supplied into the oil tank chamber (3) from a nitrogen gas supply pipe (16) for pressure recovery, and the pressure in the oil tank chamber (3) is set to the atmospheric pressure.

Then, after opening the door (3a) and carrying the work into the oil tank chamber (3), the door (3a) is closed. Next, the oil tank room
The inside of (3) is evacuated by a vacuum pump (15) (normally 1 Torr (13
3.32Pa) or less), and pipe (25) between the oil tank room (3) and the carburizing room (2).
To make the same pressure.

After the oil tank chamber (3) and the carburizing chamber (2) have the same pressure,
Open the door (2a), carry the workpiece into the carburizing chamber (2), and open the door (2a).
And wait until the inside of the carburizing chamber (2) has returned to the processing temperature.
After the temperature is restored, the workpiece is held and preheated in the carburizing chamber (2) for a predetermined time (normally 40 minutes or more). At this time, the pressure in the oil tank chamber (3) is restored to about 600 Torr (79992 Pa).

After the completion of the preheating, the vacuum carburizing gas is supplied into the carburizing chamber (2) by opening the vacuum carburizing gas introduction valve (23). At this time, the pressure of the vacuum carburizing gas supplied by the regulators (20) and (21) is adjusted to be about 750 Torr (0.1 MPa).

When supplying gas for vacuum carburization, a gas introduction pipe (10)
Is rotated about a vertical axis by a driving machine (13), and while the branch pipe (11) rotates above the work, the vacuum carburizing gas is supplied and the supplied vacuum carburizing gas is uniformly applied to the work. The gas for vacuum carburizing is dispersed and supplied.

Further, since the lining of the wall (w) is a gas barrier material, the amount of the carburizing gas permeating the wall is very small, so that the carburizing gas supplied into the permeation chamber (2) can be effectively used. It is not sooted by carburizing.

On the other hand, when the vacuum carburizing gas is supplied, the large vacuum valve (30) is closed, the small vacuum valve (31) is opened, and the carburizing chamber is opened.
Exhaust the gas in (2). At this time, the pressure in the carburizing chamber (2) is measured by the vacuum gauge (33), the opening of the motor valve (32) is adjusted by the pressure controller (34), and the gas exhausted from the carburizing chamber (2) is The amount is adjusted.

For example, when the pressure measured by the vacuum gauge (33) is 50 Torr, the same amount of gas as the vacuum carburizing gas supplied to the carburizing chamber (2) is exhausted from the carburizing chamber (2). To determine the displacement. The displacement of the gas changes according to the change in the measurement value measured by the vacuum gauge (33),
The number of ethylene molecules in (2) is kept substantially constant.
At this time, the actual pressure in the carburizing chamber (2) changes with the change in the displacement, but usually 25 to 65 Torr (3333 to 8665.8 Pa)
Is kept. Note that the number of ethylene molecules may be slightly reduced.

After carburizing for a predetermined time, the small vacuum valve
(31) is closed, the large vacuum valve (30) is opened, and the inside of the carburizing chamber (2) is evacuated by the vacuum pump (28) to perform diffusion treatment. After the completion of the diffusion processing, the temperature of the work is lowered to the quenching temperature and the work is uniformly heated. Thereafter, the large vacuum valve (30) is closed, nitrogen is supplied to the carburizing chamber (2) from the nitrogen gas supply pipe (24) for decompression and the pressure is restored to 600 Torr (79992 Pa), and then the carburizing chamber (2) and the oil tank chamber ( 3) and the same pressure, carburizing chamber (2)
The work is carried out to the oil tank chamber (3) and quenched in the oil tank chamber (3).

In the following, five samples (manufactured by SCM420H2) arranged at different positions in the height direction and the length direction of the furnace (1) in the furnace (1) in the basket on which the object to be processed having a gross of 240 kg is mounted. Is preheated at 1 Torr (133.32 Pa) and 950 ° C. for 100 minutes, carburized at 50 Torr (6666 Pa) and 950 ° C. 7
0 min, 1 Torr (133.32 Pa), diffusion at 950 ° C. 50 min, 1
Torr (133.32 Pa), soaking at 850 ° C. for 30 minutes, and quenching at 600 Torr (79992 Pa).
Surface hardness of each sample as a result of tempering at 0 ° C. for 90 minutes,
FIG. 3 is a table showing the depth of the hardened layer and the surface carbon concentration.
The flow rate of ethylene gas at the time of air supply is 10 L / min.
And the flow rate of hydrogen is 5 L / min.

From this figure, it can be seen that the surface hardness, hardened layer depth and surface carbon concentration of each sample are almost uniform, and that this furnace (1) can perform vacuum carburization with high quality. In addition, since the heat insulating material that forms the inside of the wall (w) is formed by vacuum-compressing ceramic fibers, the carburizing gas is hardly stained, and the carburizing gas supplied to the carburizing chamber is effective. It is used for carburizing and the control of the carburizing gas pressure becomes easy.

Next, a furnace (40) according to a second embodiment of the present invention will be described with reference to FIGS. First
The same parts as those of the furnace (1) of the embodiment and the corresponding parts are denoted by the same reference numerals and description thereof will be omitted.

The furnace (40) is different from the furnace (1) of the first embodiment in that the gas supply means (41) for vacuum carburizing is also capable of performing gas carburizing.

The vacuum carburizing gas supply means (41) is provided with first and second horizontal gas inlets provided so as to extend from the side of the vertical wall of the carburizing chamber to the upper side of the work and to face each other. A plurality of gas outlets (not shown) extending from the first inlet pipe (43) toward the second inlet pipe (44) and extending in the lower part of the peripheral wall at an axial distance are provided at the pipes (43) and (44). A plurality of gas-closed pipes (4
5), extending from the second inlet pipe (44) toward the first inlet pipe (43) side and alternately with the first inlet pipe side gas branch pipe (45), and extending axially below the peripheral wall. A plurality of gas outlet pipes (46) having a plurality of gas outlet holes (not shown) spaced apart from each other and having a closed end at the end thereof are provided on the second inlet pipe side.
The furnace (40) is a stirring fan provided at the upper part of the carburizing chamber.
(42), gas carburizing gas supply path (5) for supplying gas carburizing gas to carburizing chamber (2), and gas carburizing gas exhaust pipe (35) for exhausting gas carburizing gas during gas carburizing It is provided with.

Also in this vacuum carburizing gas supply means (41), the vacuum carburizing gas is supplied uniformly over the entire peripheral surface of the work. Further, the procedure for performing vacuum carburization is not different from the furnace (1) of the first embodiment. In the carburizing furnace (40) of this embodiment, a gas supply path for gas carburizing (5) and a gas exhaust pipe for gas carburizing (35) to enable gas carburizing.
In addition, a fan (42) for stirring the atmosphere in the furnace is provided, and gas carburization can be performed.

When gas carburizing is performed, nitrogen gas is supplied into the carburizing chamber (2) by a nitrogen gas supply pipe (24).
Repressurize inside. Thereafter, nitrogen gas is supplied from the gas supply path (5) for gas carburizing. When the pressure in the carburizing chamber (2) rises above the atmospheric pressure, nitrogen gas is discharged from the gas carburizing gas exhaust pipe (35). When the purge in the carburizing chamber (2) is performed for a predetermined time, the gas introduced from the gas carburizing gas supply path (5) is switched to the endothermic furnace gas and introduced.

After flowing a carburizing gas of at least 3 to 7 times the volume of the carburizing chamber (2), the treated product is carried into the carburizing chamber (2) to be carburized. The processing procedure during gas carburizing is the same as the procedure in a conventional carburizing furnace dedicated to gas carburizing, and detailed description is omitted.

In the furnace (40), similarly to the furnace (1) of the first embodiment, the upper end of the effective space and the branch pipes (45) (4)
The distance from 6) is preferably about 100 to 150 mm. The diameter of the gas outlets of the branch pipes (45) and (46) is preferably about 3 mm, and the pitch is preferably 32 to 53 mm.

In the furnaces (1) and (40) of the above embodiment, a radiant tube heater is used as a heating device. However, the heating device is not limited to this, and appropriate heating may be performed according to processing conditions and the like. An apparatus may be used.

[Brief description of the drawings]

FIG. 1 is a schematic view of a carburizing furnace according to a first embodiment of the present invention.

FIG. 2 is a plan view of a main part of the carburizing furnace.

FIGS. 3 (a), (b), and (c) are diagrams showing the results of comparing the surface hardness, hardened layer depth, and surface carbon concentration of a plurality of samples vacuum carburized in the same carburizing furnace.

FIG. 4 is a schematic view of a main part of a carburizing furnace according to a second embodiment of the present invention.

FIG. 5 is a diagram corresponding to FIG. 2 in the carburizing furnace.

FIG. 6 is a schematic view of a conventional carburizing furnace.

[Explanation of symbols]

(1) (40) Carburizing furnace (2) Carburizing chamber (4) (41) Vacuum carburizing gas supply means (5) Gas carburizing gas supply means (6) Vacuum exhaust means (7) Displacement adjusting means ( 10) Vertical gas inlet pipe (11) Horizontal gas branch pipe (26) Manifold with multiple vacuum exhaust ports (32) Exhaust volume adjustment means (motor valve) (33) Increase / decrease detection means (crystal vacuum gauge) (34) Displacement adjustment means (pressure controller) (35) Gas exhaust pipe for gas carburizing (42) Stirring fan (43) (44) First and second gas introduction pipes (45) (46) First gas introduction Pipe side, second gas introduction pipe side gas branch pipe (w) Carburizing chamber wall

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Shu Matsubara 229 Kahata-cho, Tenri-shi, Nara Koyo Thermo System Co., Ltd. F-term (reference) 4K028 AA01 AC03 AC08 4K063 AA05 AA15 AA16 BA02 CA03 DA01 DA15 DA19 DA28 DA33 DA34

Claims (5)

[Claims] In a vacuum carburizing method, a vacuum carburizing gas containing ethylene gas and hydrogen gas is supplied to a carburizing chamber and the supplied vacuum carburizing gas is exhausted. A vacuum carburizing method characterized in that the number of ethylene molecules does not substantially increase. 2. A carburizing chamber for carburizing a work therein, a vacuum carburizing gas supply means for supplying a vacuum carburizing gas containing ethylene gas and hydrogen gas to a work in the carburizing chamber from above, and a carburizing chamber. In a carburizing furnace equipped with vacuum evacuation means for sucking out the gas from below the work, based on the increase / decrease detection means for detecting the increase / decrease in the number of ethylene gas molecules and the increase / decrease in the number of ethylene gas molecules detected by the increase / decrease detection means An exhaust amount adjusting means for adjusting an exhaust amount of the vacuum carburizing gas exhausted from the carburizing chamber, wherein the vacuum carburizing gas supply means uniformly supplies the vacuum carburizing gas to the work and supplies the gas. A carburizing furnace, characterized in that the evacuation means is branched and connected to a plurality of evacuation ports for uniformly exhausting the carburizing gas. 3. A gas dispersing means comprising: a horizontal gas introducing pipe extending through a carburizing chamber and extending above a work; a plurality of gas dispersing means being provided in a branched shape from the introducing pipe and being provided at a lower portion of a peripheral wall at an axial interval. 1 or 2 with gas outlets
The carburizing furnace according to claim 2, further comprising the above-mentioned horizontal gas branch pipe with a closed end. 4. A gas carburizing gas supply means for supplying a gas carburizing gas into a carburizing chamber, wherein a wall of the carburizing chamber is formed of a heat insulating material and an airtight material covering the outside thereof. The carburizing furnace according to claim 2 or 3, further comprising a gas carburizing gas exhaust means for exhausting gas, and a stirring fan provided at an upper portion of the carburizing chamber. 5. A gas dispersing means, comprising: a rotatable vertical gas introduction pipe penetrating from the top of a wall of a carburizing chamber; and a plurality of gas dispersion means extending radially from a lower end of the gas introduction pipe and being axially spaced below a peripheral wall. 3. A carburizing furnace according to claim 2, comprising a plurality of horizontal gas branch pipes each having a closed end and having a plurality of gas discharge holes.