JPH11257869A - Heat treatment furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an unacceptable article from being produced by eliminating the scattering of temperature in a heat treatment furnace, especially around a powder molded body and making uniform the degreasing and sintering at each part of the power molded body. SOLUTION: A retort box 26 that is surrounded by a heater 22 and heat- insulating materials 10, 15, and 23 and further accommodates a power molded body where a sweep gas supply part 24 is connected is provided in a vacuum chamber 1 with double wall structure and a cooling water channel 5. Preferably, shutters 13 and 18 are provided at the end part heat-insulating materials 10 and 15 for surrounding the retort box 26, respectively, on the other hand shutters 13 and 18 are provided at the rear of the shutter 18, a high melting-point conductor is included between a heater electrode that is supported through the heat- insulating materials 10, 15, and 23 and a watercool power supply electrode that is supported through the vacuum chamber 1, and also a sheet whose main constituent is graphite is applied to the inner-periphery surface of the heat- insulating materials 10, 15, and 23.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing a binder such as a thermoplastic resin and a molding aid (hereinafter simply referred to as "green body") from a powder compact (hereinafter simply referred to as "green body") of metal, ceramics or the like. The present invention relates to a heat treatment furnace used for producing a sintered part.

[0002]

2. Description of the Related Art Conventionally, as one method of manufacturing a mechanical part having a complicated shape, a binder made of a thermoplastic resin, a molding aid and the like is added to a powder of metal, ceramics, etc. and mixed to form a predetermined shape. That is, there is provided a method of manufacturing a sintered component by heating a so-called green body in a vacuum and further in an atmosphere to remove the binder contained in the green body.

[0003]

In the manufacture of the above sintered parts, if the temperature inside the vacuum furnace, especially around the green body, varies, the degreasing and sintering at each part of the green body are not performed uniformly, resulting in an unsatisfactory result. A good product was generated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and aims at equalizing the temperature around the green body during degreasing and sintering of the green body, preventing the occurrence of defective products, and preventing the occurrence of a switch. The purpose of the present invention is to provide a heat treatment furnace capable of improving the gas supply efficiency, rapidly cooling after sintering, prolonging the life of the furnace, and providing high-quality and inexpensive sintered products. I do.

[0005]

According to the present invention, in order to achieve the above object, the present invention is directed to a vacuum chamber having a double-walled structure having a cooling water passage surrounded by a heater and a heat insulating material. And a retort box for accommodating a green body connected to a sweep gas supply unit.

[0006] According to this configuration, the periphery of the retort box is heated by the heater, the temperature inside the retort box is made uniform, and the heating and degreasing of the green body contained in the inside are performed uniformly. The supply of the sweep gas is also performed efficiently.

According to a second aspect of the present invention, both ends of the heat insulating material surrounding the retort box are provided with shutters, respectively.
On the other hand, a cooling fan directed to the retort box is provided behind the shutter.

According to this configuration, the two shutters are opened and the cooling fan is driven to drive the cooling gas between the vacuum chamber having the cooling water passage and the heat insulating material and into the retort box portion inside the heat insulating material. It is possible to quickly circulate and cool after completion of sintering.

A third aspect of the present invention is that a high melting point conductive material is interposed between a heater electrode provided through the heat insulating material and a water-cooled power supply electrode provided through the vacuum chamber. It is. According to this configuration, the temperature of the heater electrode and its peripheral portion is not lowered by the water-cooled power supply electrode as in the related art, and the uniformity of the temperature in each part in the furnace is improved, resulting in excellent quality. A sintered product can be provided, and generation of defective products can be prevented.

According to a fourth aspect of the present invention, a sheet containing graphite as a main component is adhered to an inner peripheral surface of the heat insulating material. According to this configuration, it is possible to prevent the deterioration of the heat insulating material due to the adhesion of the binder removed at the time of degreasing as well as to improve the heat insulating effect, and to prolong the furnace life.

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an embodiment of the present invention. FIG. 1 is an overall plan view, FIG. 2 is a front view of FIG.
3 is a left side view of FIG. 2, FIG. 4 is an enlarged vertical sectional view of the vacuum chamber, FIG. 5 is a sectional view taken along line VV of FIG. 4, and FIG.
FIG. 7 is an enlarged cross-sectional view of the retort box and the water electrode.

The vacuum chamber-1 has a central main body 2 and
It is composed of a front door 3 and a rear door 4 provided at both ends thereof,
Further, the main body 2, the front door 3, and the rear door 4 each have a double wall structure, and each have a cooling water passage 5 therebetween. In the figure, 6 is a water injection and circulation port, respectively.

The front door 3 and the rear door 4 are respectively supported by the main body 2 so as to be openable and closable by hinges 7. Further, at both ends of the main body 2, locking devices 8 for the front door 3 and the rear door 4 are provided. A binder collection pot 9 is provided at the bottom.

Further, to the front door 3, an end heat insulating material 10 for closing the front door 3 side of a heat insulating material 23 provided on the main body 1 side, which will be described later, is attached by a support portion 11. A shutter 13 for opening and closing an opening 12 formed in the material 10 and a drive cylinder 14 for the shutter 13 are provided.

The rear door 4 is provided with an end heat insulating material 15 for closing a rear door 4 side of a heat insulating material 23 provided on the main body 1 side, which will be described later, by a support portion 16. Shutter 18 for opening and closing the opening 17 formed in the member 15, a drive cylinder 19 for the shutter 18, and a cooling fan 20 toward the retort box 26, which will be described later, behind the shutter 18, and a cooling fan 20 for the cooling fan 20. A drive motor 21 is provided.

According to the present invention, a heater 22, a heat insulating material 23, an end heat insulating material 10 provided on the front door 3 and a rear door are provided in the vacuum chamber 1, specifically, in the main body 2. 4
A retort box 26 is provided which accommodates a green body 25 which is surrounded by the end heat insulating material 15 provided with the swivel gas supply unit 24.

The retort box 26 is mounted and supported on a hearth rail 28 supported by a hollow member 27 erected in the vacuum chamber 1, and inside thereof, as shown in FIG. A multi-stage shelf 29 for accommodating a green body 25 is provided, and the shelf 29 is opened at both ends alternately as shown in FIG. 1 so that the sweep gas supplied from the sweep gas supply section 24 is supplied to each shelf. 29, that is, the portion of the green body 25 accommodated in the upper surface of the shelf 29 is meandered to the outside of the heat insulating material 23 from the lower exhaust port 42.
That is, it is provided so as to be discharged into the vacuum chamber-1.

The heater 22 is of a radiant tube type and is provided from the front door 3 to the rear door 4 so as to surround the retort box 26. The heat insulating material 23 is provided on the outside at a required interval.

The heat insulating material 10 and the end heat insulating materials 15, 23
Is made of a heat-resistant brick or the like, and a sheet 30 mainly composed of graphite is adhered to the inner peripheral surface thereof.

Next, the heater electrode 31 will be described. The heater electrode 31 is made of carbon or the like.
As shown in FIG.
It is supported through three parts.

On the other hand, a water-cooled power supply electrode 32 connected to a power supply (not shown) is made of copper, is formed as a double pipe having a cooling water passage 33 therein, and has a cooling water supply port 34 and a circulation port 35. The heater electrode 31 is supported through the vacuum chamber 1 at an appropriate distance from the heater electrode 31.

Conventionally, the heater electrode 31 and the water-cooled power supply electrode 32 are directly connected. However, in the present invention, a high melting point is provided between the heater electrode 31 and the water-cooled power supply electrode 32. Conductor, preferably molybdenum (melting point: 2625
C.) or a high melting point conductor 36 made of tungsten (melting point: 3410 ° C.) or the like.

Table 1 below shows comparative examples of furnace temperature distributions with and without the high melting point conductor.

[0024]

[Table 1] That is, this is a comparative example in which the high-melting-point conductor 36 is interposed between the heater electrode 31 and the water-cooled power supply electrode 32 and not interposed.

The temperature measurement points shown in Table 1 are J
Nine points defined by IS, namely, four points at the upper four corners, four points at the lower four corners, and nine points at the center of the furnace in the furnace. All the experiments were the same except for the presence or absence of the high-melting-point conductor 36.

As is clear from the table, the maximum temperature difference at the nine points when the high-melting-point conductor was not interposed was 27 ° C., but the high-melting-point conductor was interposed. In this case, the maximum temperature difference was 4.5 ° C., and a very remarkable difference was confirmed.

Next, the vacuum apparatus will be described. A pipe 37 provided from an appropriate position of the main body 2 of the vacuum chamber-1 is connected to a diffusion pump 39 via a water-cooled baffle 38, and further connected to the diffusion pump 3
8, a mechanical booster 40 and a rotary pump 41 are sequentially connected.

Further, a branch pipe 40 is provided from the water-cooled baffle 38 of the pipe 37 at a point closer to the vacuum chamber 1 and is connected to the mechanical booster 40 so that the suction by the rotary pump 41 is taken. It is configured to be switchable.

That is, the vacuum chamber-1 is rotated by the rotary pump 41 via the water-cooled baffle 38, the diffusion pump 39 and the mechanical booster 40.
In addition to the above, it is possible to perform the suction in the vacuum chamber 1 by the rotary pump 41 only through the mechanical booster 40 without passing through the diffusion pump 39. Is configured.

An example of removing the binder and manufacturing a sintered part in the heat treatment furnace having the above-described configuration will be described below.

First, the powder compact, that is, the green body 25, is prepared by a known method. Next, the green bodies 25 are arranged on a shelf 29 in the retort box 26, the front door 3 is opened, and the retort box 26 is supplied onto a hearth rail 28.

Thereafter, the door is closed, the rotary pump 41 and the mechanical booster 40 are driven to evacuate, and then the heater 22 heats the retort box 26. At the same time, cooling water is circulated in the water channel 5 of the vacuum chamber-1.

As a result, a molding aid having a low melting point, for example, a low molecule such as paraffin is evaporated from the green body 26 and partially degreased, and the paraffin and the like are exhausted from the lower exhaust port 42 of the retort box 26. From the vacuum chamber-1.

The paraffin and the like discharged into the vacuum chamber-1 condense and adhere to the inner peripheral surface of the vacuum chamber-1 because the inner peripheral surface of the vacuum chamber-1 is cooled.

At the same time, the paraffin and the like contained in the exhaust gas to the vacuum device were collected by a water-cooled baffle 38 provided in the pipe 37 and a diffusion pump 39 to remove the paraffin and the like. The exhaust gas is discharged to the outside via a mechanical booster 40 and a rotary pump 41.

The removal of paraffin and the like condensed on the inner peripheral surface of the vacuum chamber-1 can be achieved by supplying hot water instead of cooling water to the water channel 5 and dissolving it. Paraffin etc. are in a vacuum chamber
The sample is collected in a binder-collecting pot 9 provided at the bottom of the main body 2 constituting 1.

Thereafter, the temperature of the retort box 26 is raised by the heater 22, and the remaining polymer binder is degreased. In this degreasing, the switch
The sweep gas is supplied from the gas supply unit 24, and the supplied sweep gas is meandered in the retort box 26, and promotes the degreasing of the green body 25 on the shelf 29.

At the time of the degreasing using the sweep gas, the exhaust to the vacuum device is performed via the mechanical booster 40 and the rotary pump 41 from the pipe 37 without passing through the diffusion pump 31.

Thereafter, when the completion of the degreasing is confirmed, the supply of the sweep gas is stopped, the sintering is performed while maintaining the high temperature and the high vacuum, and when the sintering is completed, the shutters 13 and 18 are opened and the cooling fan is opened. 20 is driven to quench the sintered product.

That is, the shutter 13 is pulled rearward by the driving cylinder 14 and the opening 12 provided in the end heat insulating material 10 is opened, and at the same time, the shutter 18 is moved rearward and laterally by the driving cylinder 19. The opening 17 provided in the end heat insulating material 15 is opened.

Thereafter, when the cooling fan 20 is rotated by suction, the cooling gas inside the heat insulating material 23 and the end heat insulating materials 10 and 15 is sucked from the opening 17 to form the vacuum chamber 1 having the cooling water passage 5 therein. The retort box 26 and the sintered components therein can be rapidly cooled by being cooled and circulated between the heat insulating material 23 and the end heat insulating materials 10 and 15.

[0042]

According to the present invention, there is no variation in the temperature inside the heat treatment furnace, especially around the green body.
Therefore, the degreasing and sintering in each part of the green body are made uniform, and the occurrence of defective products is prevented.

[Brief description of the drawings]

FIG. 1 is an overall plan view of a heat treatment furnace of the present invention.

FIG. 2 is a front view of FIG.

FIG. 3 is a left side view of FIG. 2;

FIG. 4 is an enlarged vertical sectional view of a vacuum chamber.

FIG. 5 is a sectional view taken along line VV of FIG. 4;

FIG. 6 is an enlarged sectional view of a heater electrode and a water-cooled electrode part.

FIG. 7 is a schematic sectional view of a retort box section.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vacuum chamber 10, 15, 23 Insulation material 13, 18 Shutter 20 Cooling fan 22 Heater 24 Sweep gas supply part 25 Powder compact 26 Retort box 30 Sheet 31 Heater electrode 32 Water cooling electrode 36 High melting point conductor

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Hideki Yamaguchi 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd.

Claims (4)

[Claims] 1. A retort for accommodating a powder compact which is surrounded by a heater and a heat insulating material in a vacuum chamber (1) having a double wall structure and having a cooling water passage, and further connected to a sweep gas supply unit. A heat treatment furnace comprising a box (26). 2. Insulating materials at both ends surrounding the retort box are provided with shutters (13) and (18), respectively, while a cooling fan (20) directed toward the retort box is provided behind the shutter. Claim 1
2. The heat treatment furnace according to 1. 3. A high melting point conductor (36) is interposed between a heater electrode (31) supported through the heat insulating material and a water-cooled power supply electrode supported through the vacuum chamber. The heat treatment furnace according to claim 1 or 2, wherein: 4. The heat treatment furnace according to claim 1, wherein a sheet containing graphite as a main component is adhered to an inner peripheral surface of the heat insulating material.