JPH07110990B2 - Ion carburizing furnace - Google Patents

Description

TECHNICAL FIELD The present invention relates to an ion carburizing furnace for ion carburizing an object to be treated.

(Prior art) Recently, as a method of hardening the surface of an object to be processed such as a steel material, a carrier gas such as argon is introduced into a vacuum container in which the object to be processed is introduced, and sputtering is performed, followed by a treatment comprising a CH-based gas. Ion carburization (also called plasma carburization) in which a gas is introduced to generate a glow discharge between an object to be processed and an anode and ionized carbon is driven to the surface of the object to be processed has been put into practical use. FIG. 7 shows an example of an apparatus for this treatment method, 1 is a furnace shell made of steel, 2 is an anode also serving as a heat insulating material made of graphite, 3 is a cathode made of stainless steel, and its base is an insulator 4 It is fixed to the furnace shell 1 via. Reference numeral 5 denotes an object to be processed attached to a mounting jig, and 6 denotes a graphite hearth on which the object to be processed 5 is placed, which is fitted to the upper end of the cathode 3.
7 is a graphite rod-shaped heater that generates heat by resistance heating,
The object to be processed 5 is heated and heated mainly by radiant heat, and 8 is a tubular gas manifold made of graphite for supplying a processing gas. Further, 9 is a vacuum pump connected to the furnace shell 1.

(Problems to be Solved by the Invention) By the way, in the ion carburizing furnace 10 having the above configuration, the cathode 3
When the temperature rises, the vacuum sealing material in the insulator 4 deteriorates and the electrical insulation deteriorates. Therefore, in order to prevent this, use a cylindrical water-cooled cathode for circulating cooling water inside the cathode 3. There is. However, since this water-cooled cathode 3 is exposed in the furnace, when CH ₃ gas such as C ₃ H ₈ or CH ₄ is charged into the furnace as a processing gas, soot is generated on the surface of the low-temperature cathode 3. There is a problem in that arcing (abnormal discharge) occurs in which the arc adheres and instantly flies due to the generation of soot, fluctuates the glow discharge voltage, destabilizes the operation of the ion carburizing furnace, and promotes wear of the cathode 3. .

This invention solves the above-mentioned conventional problems, and aims to provide an ion carburizing furnace capable of stabilizing the operation of the ion carburizing furnace and reducing cathode wear by preventing arcing occurring in the cathode. Is.

(Means for Solving Problems) An ion carburizing furnace according to the first invention of the present application has an anode, a water-cooled tubular cathode, and a heater for heating an object to be processed in a furnace shell connected to a vacuum pump. In an ion carburizing furnace equipped with
The outer peripheral portion of the cathode protruding into the furnace shell is surrounded by a tubular body made of an electrically insulating material, and between the tubular body and the cathode, a gas flow space having a gas outlet at the upper portion is formed. It is an ion carburizing furnace configured to connect a gas flow space to a purge gas supply source, flow the purge gas through the gas flow space, and let the purge gas flow into the furnace through the gas outlet.

The ion carburizing furnace of the second invention of this application is an ion carburizing furnace having an anode, a water-cooled tubular cathode and a heater for heating an object to be treated in a furnace shell connected to a vacuum pump. The outer peripheral portion of the cathode protruding into the furnace shell is surrounded by a tubular body made of an electrically insulating material, and between the tubular body and the cathode, a gas flow space having a gas outlet at the upper portion is formed, At least a portion of the outer peripheral portion of the cylindrical body near the furnace shell is surrounded by an outer cylinder made of an electrically insulating material, and a gas flow passage having a gas outlet at an upper portion is formed between the outer cylinder and the cylindrical body. ,
A structure in which the gas flow space and the gas flow passage are connected to a purge gas supply source, a purge gas is caused to flow in the gas flow space and the gas flow passage, and the purge gas is caused to flow into the furnace through the gas outlets. Ion carburizing furnace.

(Operation) In the ion carburizing furnace of the present invention, the purge gas circulates in the gas flow space formed between the cathode and the cylinder as an upward flow, and the CH-based gas enters the gas flow space to reach the surface of the cathode. Therefore, even if the cathode is water-cooled and the temperature is low, the soot does not adhere to the surface due to the CH-based gas. Further, since the tubular body is made of an electrically insulating material, it prevents the glow discharge from directly flying from the anode to the cathode, and does not cause arcing even if soot is attached to a part of the tubular body.

Further, in the ion carburizing furnace of the second invention, since the purge gas also flows as an upward flow in the gas flow passage formed between the cylindrical body and the outer cylinder, the surface of the cylindrical body adjacent to the low temperature cathode and having a slightly low temperature The side is also exposed to the upward flow of purge gas to prevent soot from adhering to the cylinder due to CH-based gas, and the outer cylinder is made of electrically insulating material, so even if soot adheres to the cylinder, the Prevents glow discharge from flying to the cylinder.

(Embodiment) An embodiment of the first invention will be described below with reference to FIGS.

7, those parts which are the same as those corresponding parts in FIG. 7 are designated by the same reference numerals, and a description thereof will be omitted. The tubular cathode 3 is fixedly attached to the furnace shell 1 via an insulator 11, and the inside of this cathode 3 is a water conduit.
It has a double-tube water-cooled structure with 12 as the center,
Reference numeral 13 is a water supply port that is connected to the water conduit 12 and is connected to a cooling water supply source, and 14 is a drainage port. As shown in FIG. 3, the insulator 11 has an annular ventilation passage 15 on its inner circumference, and is provided on the flange portion of the insulator 11 and has an air supply port 16 communicating with this ventilation passage 15.
A purge gas supply source 17 for supplying a purge gas composed of a non-oxidizing gas such as hydrogen, argon or nitrogen is connected to the. On the other hand, a cathode component 18 having a collar 18a is fitted on the cathode 3, and the cathode component 18 is fitted into and disengaged from a seat 6a protruding from the bottom surface of the hearth 6. Reference numeral 20 denotes a cylindrical body made of a heat-resistant electric insulating material such as alumina, the lower end of which is fixedly held by an insulator 19 fitted in the insulator 11. Flange portion 20a formed on the upper end of the cylindrical body 20
The annular gas outlet 2 is provided between the flange 18a on the cathode 3 side and
1 is formed, and a gas distribution space 22 is provided between the cylindrical body 20 and the cathode 3.
Are formed. The gas circulation space 22 communicates with the ventilation passage 15 described above. Reference numeral 23 denotes an annular insulator fixed to the furnace shell 1, which is provided as necessary to protect and support the inner circumference of the cathode charging hole 2a formed in the anode 2. As shown in FIG. 1, a DC power supply 24 is connected between the cathode 3 and the anode 2, and the heater 7 has an AC power supply 25 for heating.
Are connected. 26 is a processing gas supply source connected to the gas manifold 8, 27 is a gate valve type inlet door, and 28 is an air cylinder for raising and lowering the door.

In the ion carburizing furnace 29 having the above structure, when a purge gas such as hydrogen is supplied from the purge gas supply source 17 into the gas supply port 16, the purge gas flows into the gas distribution space 22 through the ventilation passage 15 and the inside of the space. It flows as an ascending liquid and flows into the furnace through the gas outlet 21. In this state, exhaust of the furnace shell 1, cooling of the cathode 3 with cooling water, heating of the object 5 to be processed by the heater 7, supply of a processing gas composed of CH 2 -based gas from the gas manifold 8, and the anode 2 and the object to be processed. Ion carburization is performed by a conventional method for generating glow discharge between the objects 5. During this ion carburizing process, the invasion of the processing gas into the surface portion of the cathode 3 is blocked by the purge gas flowing out to the upper portion through the gas flow space 22, and soot is prevented from adhering to the cathode 3. Further, the tubular body 20 made of an electrically insulating material prevents the glow discharge from directly flying from the anode 2 to the cathode 3, and arcing does not occur if soot is attached to a part of the outer surface of the tubular body 20.

Ion carburizing furnace 29 with the above configuration (however, inner diameter of furnace shell 1 = 1600
mm) mounts SCM420 automotive parts to a mounting jig 500
Propane gas 7.5 / min is used as the processing gas for the object 5 to be mounted, and hydrogen gas is 1 / min (per cathode) as the purge gas to be charged into the cathode 3 part, at 950 ° C. Ion carburization for 1 minute was performed. As a comparative example, an ion carburizing process was performed under the same conditions using an ion carburizing furnace 10 of the same size in which the cathode 3 shown in FIG. 7 was exposed in the furnace. As a result, arcing during processing did not occur in the examples of the present invention, whereas in the comparative examples
Occurrence of arcing was observed 2 to 3 times per 10 minutes, and replacement by cathode wear was unnecessary for one year in the example of the present invention, whereas replacement was performed once a month in the comparative example. Was necessary.

Next, FIGS. 5 and 6 show an embodiment of the second invention, in which the same parts as those in FIGS. 3 and 4 are designated by the same reference numerals.

Reference numeral 30 denotes an outer cylinder externally fitted to a portion of the cylindrical body 20 close to the furnace shell 1 with a space therebetween, and an outer cylinder body 31 whose lower end is fixedly held by an insulator 33 fixed to the furnace shell 1, The heat insulating material 32 is lined on the inner peripheral surface of the outer cylinder body. The outer cylinder body 31 is made of a heat-resistant electric insulating material such as alumina, and the heat insulating material 32 is made of a ceramic fiber such as alumina. 34 is an outer cylinder
An annular gas flow passage formed between 30 and the cylindrical body 20, the gas flow passage 34 communicating with the gas flow space 22 via a gas inlet 35 formed in the insulator 23. 36 is a gas flow passage 34
Is an annular gas outlet formed at the upper end of the. The other structure is the same as that of the first embodiment of the present invention.

In this embodiment, in addition to the same effects as in the above embodiment, a part of the purge gas supplied into the gas flow space 22 flows into the gas flow passage 34 through the gas inlet 35,
The gas flow passage 34 flows as an upward flow, and the gas outlet 36
Flows into the furnace from. This prevents soot from adhering to the outer peripheral surface of the tubular body 20. In addition, since the outer cylinder 30 surrounds the portion of the cylinder body 20 near the furnace shell, even if soot adheres to the outer periphery of the cylinder body 20, it is possible for the glow discharge to fly directly from the anode 2 to the cylinder body 20. It can be prevented. Further, in this embodiment, the heat insulating material of the outer cylinder 30 is used.
32 protects the tubular body 20 by its heat insulating action and prevents damage due to thermal shock of the tubular body 20 and contributes to improvement of durability, but in some cases, the attachment of the heat insulating material 32 is omitted. May be.

Using a furnace having the same structure as the ion carburizing furnace 29 except that the above-mentioned outer cylinder 30 was additionally provided, and performing ion carburizing treatment under the same conditions as in the above-mentioned embodiment, no arcing occurred during the treatment, and the cathode The replacement due to wear of the cylinder 30 was not necessary for one year, and the replacement due to damage of the cylinder 30 was not necessary for 1.5 years.

The present invention is not limited to the above embodiments, and for example, the supply of the purge gas to the gas flow passage 34 is performed by the ventilation passage 15
Alternatively, the outer cylinder 30 may surround the cylinder over the entire length of the cylinder 20, or the cylinder 20 may have a simple cylindrical shape with a small diameter. The shape and specific structure of each part may be other than the above. Also, the anode 2, the hearth 6, the heater 7, the gas manifold 8, etc.
It may have another structure.

(Effect of the Invention) As described above, according to the present invention, the purge gas charged in the cathode portion prevents the entry of CH-based gas into the cathode surface portion, and the gas insulating space is constituted by the electrically insulating material. As a result, the degree of electrical insulation is improved, arcing due to the attachment of soot to the cathode surface is prevented, and the operation of the ion carburizing furnace can be stabilized and the wear of the cathode can be reduced.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an ion carburizing furnace showing an embodiment of the first invention, FIG. 2 is a sectional view taken along the line AA of FIG. 1, and FIG. 3 is an enlarged vertical section of a cathode portion in FIG. FIG. 4 is a sectional view taken along the line BB in FIG. 3, FIG. 5 is a view corresponding to FIG. 3 showing an embodiment of the second invention, and FIG. 6 is a line CC in FIG. Sectional view, No. 7
The drawing is equivalent to FIG. 2 showing an example of a conventional ion carburizing furnace. 1 ... Furnace shell, 2 ... Anode, 3 ... Cathode, 7 ... Heater,
9 ... Vacuum pump, 11 ... Insulator, 15 ... Ventilation path, 16 ...
… Air supply port, 17 …… Purge gas supply source, 18 …… Cathode component,
20 …… Cylinder, 21 …… Gas outlet, 22 …… Gas distribution space,
29 …… Ion carburizing path, 30 …… Outer cylinder, 31 …… Outer cylinder body, 32
…… Insulation material, 34 …… Gas flow passage, 35 …… Inlet, 36 ……
Gas outlet.

Claims (2)

[Claims] 1. An ion carburizing furnace having an anode, a water-cooled tubular cathode, and a heater for heating an object to be treated in a furnace shell connected to a vacuum pump. The cathode protruding into the furnace shell. The outer peripheral part of is surrounded by a cylinder made of an electrically insulating material, and a gas flow space having a gas outlet in the upper part is formed between the cylinder and the cathode, and the gas flow space is connected to a purge gas supply source. Then, the ion carburizing furnace configured such that the purge gas is circulated in the gas circulation space and the purge gas is caused to flow into the furnace through the gas outlet. 2. An ion carburizing furnace having an anode, a water-cooled tubular cathode, and a heater for heating an object to be treated in a furnace shell connected to a vacuum pump, and the cathode protruding into the furnace shell. The outer peripheral portion of is surrounded by a cylindrical body made of an electrically insulating material, and between the cylindrical body and the cathode, a gas flow space having a gas outlet at the upper part is formed, and at least the furnace of the outer peripheral portion of the cylindrical body is formed. A portion near the shell is surrounded by an outer cylinder made of an electrically insulating material, and a gas flow passage having a gas outlet at an upper part is formed between the outer cylinder and the cylinder, and the gas distribution space and the gas distribution are formed. An ion carburizing furnace configured such that the passage is connected to a purge gas supply source, the purge gas is circulated in the gas circulation space and the gas flow passage, and the purge gas is caused to flow into the furnace through the gas outlets.