JPH01174893A - Vacuum furnace - Google Patents

Abstract

PURPOSE:To prevent soot adhesion from being made and easily remove scales of soot and eliminate maintenance service without needing frequent exchanges of electric insulators by making the surface of an electric insulator smooth below a specified surface roughness. CONSTITUTION:A heater 5 made of graphite and placed in a housing chamber 4 generates heat by resistant heat, heats heating articles W mainly by radiant heat, for example, up to a temperature not so much exceeding 1000 deg.C and is held by conductive members 7, 7 made of graphite and connected to an alternating power source 6. The base part of the conductive member 7 is supported on a furnace shell 2 by the use of insulators 8 made of ceramic, cylindrical electric insulators 9 are fixed on a heat insulating material 3 in the part in which the conductive member 7 of the heat insulating material 3 is penetrated, and a clearance is provided between the conductive member 7 and the electric insulator 9. Since the electric insulator 9 is exposed in high temperature and scales of soot are easy to adhere to it, porcelain glaze is applied on the surface of alumina porcelain into which alumina powder is formed and based, and surface roughness is made 0.7 or less.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a vacuum furnace for heat treating, sintering, melting, etc. a workpiece in a vacuum.

[Conventional technology]

In a vacuum heat treatment furnace, for example, an electric insulator made of a fired body of an inorganic material such as alumina porcelain is used as an electric insulator that supports or surrounds a conductive member that supplies electricity to an electric heater installed in the furnace. ing. This electric insulator had a rough surface, which is the result of firing a molded body of a ceramic base material.

[Problem that the invention seeks to solve]

However, in vacuum heat treatment furnaces, carbon is often used as the heat insulating material forming the storage chamber for the processed material provided in the furnace and as the electric heater, so the carbon becomes hot in vacuum and vaporizes. Because soot adheres to the rough surface of electrical insulators and causes a decrease in insulation, electrical insulators must be replaced in a short period of time, making maintenance time-consuming. In addition, in furnaces such as ion carburizing furnaces that feed CH-based gas into a vacuum furnace, soot resulting from the carbon content in this CH-based gas is added, so the contamination of electrical insulators is even more severe. Ta.

The present invention solves the above-mentioned conventional problems, and aims to provide a vacuum furnace in which soot does not easily adhere to the electrical insulator, the adhered soot can be easily removed, and maintenance is not required.

[Means for solving problems]

However, the vacuum furnace of the first invention of this application is a vacuum furnace equipped with an electrical insulator made of a fired body of an inorganic material, in which the surface of the electrical insulator is smooth with a surface roughness of 017S or less. This is a vacuum furnace characterized by the following.

Further, the vacuum furnace of the first invention of this application is a vacuum furnace equipped with an electric insulator made of a fired body of an inorganic material, and the surface of the electric insulator is smooth with a surface roughness of 0.73 or less. A vacuum furnace characterized in that a gas flow passage is provided along the surface, and a gas blowing device is provided for blowing a non-oxidizing atmospheric gas into the gas flow passage.

[Function] In the vacuum furnace of the present invention, the surface of the electrical insulator is a smooth surface with a surface roughness of 0.7S or less, so soot is difficult to enter into the minute recesses on the surface, and the soot that has entered is also prevented from entering the recesses. Hard to stick. Therefore, the amount of soot adhering to the surface of the electrical insulator is small, and the adhering soot can be easily removed by applying vibration or rubbing.

Furthermore, in the vacuum furnace of the second invention, the non-oxidizing atmospheric gas flowing in the gas flow path blows off the soot that has begun to adhere to the recesses on the surface of the electrical insulator, further reducing the amount of soot adhering to the surface. be converted into

〔Example〕

An embodiment of the first invention will be described below with reference to FIGS. 1 and 2. FIG.

In the figure, 1 is a vacuum heat treatment furnace, 2 is a steel furnace shell, and 3 is an insulating material made of graphite I1m that forms a storage chamber 4 into which the workpiece W is charged, and is supported by the furnace shell 2 and grounded. has been done. Reference numeral 5 denotes a graphite heater provided in the storage chamber 4, which generates heat by resistance heat and heats the heated object W mainly by radiant heat, for example, 100
It is heated to a temperature of about 0° C. and is held by a graphite conductive member 7.7 connected to an AC power source 6.

The base of the conductive member 7 is supported on the furnace shell 2 by a ceramic insulator 8, and a cylindrical electrical insulator 9 is fixed to the heat insulator 3 at the portion of the heat insulator 3 through which the conductor 7 penetrates. A gap 10 is provided between the conductive member 7 and the electrical insulator 9. Since the electrical insulator 9 is exposed to high temperatures, soot tends to adhere to it, so the surface of the alumina porcelain made by molding and firing alumina powder is coated with porcelain glaze, and the surface roughness is set to 0.7S.

Further, 11 is a vacuum pump connected to an exhaust port 2a provided in the furnace shell 2, and 12 is a hearth on which the workpiece W is placed, which is fixed to the furnace shell 2 via supporting legs (not shown).

In the vacuum heat treatment furnace 1 having the above configuration, the degree of vacuum is 10'T.
orr, after 20 operations of heating and vacuum hardening at the internal temperature of the storage chamber 4 at 1050°C for 30 minutes, the electrical insulator 9
When we inspected the parts, we found that there was only a small amount of soot attached.
Also, the attached soot could be easily removed by brushing or the like. On the other hand, as a comparative example, the furnace was operated under the same conditions as above using an electrical insulator 9 with a polished surface with a surface roughness of 3S without glazing. It was not possible to remove enough soot by just scrubbing it with a brush.

Next, FIGS. 3 and 4 show an embodiment of the second invention, and the same parts as in FIGS. 1 and 2 are designated by the same reference numerals. Reference numeral 21 denotes a gas blowing pipe, the tip of which opens from the outside of the storage chamber 4 toward the gap 10 forming a gas flow path.

Reference numeral 22 denotes a gas supply source for supplying non-oxidizing atmospheric gas such as nitrogen gas or hydrogen gas to the gas blowing pipe 21 under pressure, and together with the gas blowing pipe 21 forms the gas blowing device 20. 23 is an insulator that holds the gas blowing pipe 21 on the furnace shell 2.

In the vacuum heat treatment furnace 24 having the above configuration, the degree of vacuum is set to
orr, and acetylene gas was supplied at 10ρ/min as a carbon removal gas into the storage chamber 4 by a gas supply device (not shown).
Nitrogen gas was supplied from the gas supply source 22 to the gas blowing pipe 21 at a rate of 4j/n+in, and otherwise the operation was carried out under the same conditions as in the previous example. As a result, almost no soot was found on the surface of the electrical insulator 9 on the gap 10 side. On the other hand, as a comparative example, an electrical insulator 9 with a polished surface with a surface roughness of 3S without glazing was used and the furnace was operated under the same conditions as above. A large amount of soot also adhered to the surface of the tank, and it was difficult to remove it.

This invention is not limited to each of the above embodiments, but
For example, the constituent material of the electrical insulator 9 may be other than those mentioned above. Furthermore, in the above embodiment, since the surface of the electrical insulator 9 is glazed, the surface roughness can be easily reduced to 0.7 S or less. Surface roughness of 0.7 S or less can also be obtained by using raw materials and polishing and finishing after shaping and firing. Further, gas flow passages through which non-oxidizing atmospheric gas flows may be provided on the outer periphery of the electrical insulator 9 or on both the inner and outer peripheries.

Further, the present invention can be applied to various vacuum furnaces equipped with electrical insulators of various shapes, such as the electrical insulator surrounding the cathode in an ion carburizing furnace.

〔Effect of the invention〕

As explained above, according to the present invention, the surface of the electrical insulator is made smooth with a surface roughness of 0.7 or less, so that it is difficult for soot to adhere to it, and the attached soot can be easily removed. This eliminates the need for frequent replacements and provides a vacuum furnace that requires less maintenance.

[Brief explanation of the drawing]

FIG. 1 is a vertical sectional view of a vacuum heat treatment furnace showing an embodiment of the first invention, FIG. 2 is a detailed view of part A in FIG. 1, and FIG. 3 is a longitudinal sectional view showing an embodiment of the second invention. 1 is a diagram corresponding to FIG. 1, and FIG. 4 is a diagram corresponding to FIG. 2. DESCRIPTION OF SYMBOLS 1... Vacuum heat treatment furnace, 5... Heater, 9... Electric insulator, 10... Gap, 20... Gas blowing device,
21... Gas blowing pipe, 22... Gas supply source, 24...
...Vacuum heat treatment furnace.

Claims (1)

[Scope of Claims] 1. A vacuum furnace equipped with an electrical insulator made of a fired body of an inorganic material, characterized in that the surface of the electrical insulator is smooth with a surface roughness of 0.7S or less. vacuum furnace. 2. In a vacuum furnace equipped with an electrical insulator made of a fired body of an inorganic material, the surface of the electrical insulator is smooth with a surface roughness of 0.7S or less, and a gas flow path is provided along the surface. 1. A vacuum furnace comprising a gas blowing device for blowing non-oxidizing atmospheric gas into the gas flow path.