JPH0832955B2 - 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. 5 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 black smoke, 3 is a cathode made of stainless steel, and its base is an insulator. It is fixed to the furnace shell 1 via 4. 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. Reference numeral 7 denotes a graphite rod-shaped heater that generates heat by resistance heating and heats the object to be treated 5 mainly by radiant heat, and 8 denotes a tubular gas manifold made of graphite for supplying a treatment 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-described structure, when the temperature of the cathode 3 becomes high, the vacuum sealing material in the insulator 4 is deteriorated and the electric insulation property is deteriorated. For this purpose, a cylindrical water-cooled cathode for circulating cooling water inside the cathode 3 is used. 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. .

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide an ion carburizing furnace capable of preventing arcing occurring in the cathode and stabilizing the operation of the ion carburizing furnace and reducing cathode wear. To do.

(Means for Solving the Problems) In order to achieve the above object, the ion carburizing furnace of the present invention has an anode, a water-cooled tubular cathode and a heating object for heating in a furnace shell connected to a vacuum pump. In an ion carburizing furnace provided with a heater, a metal inner cylinder surrounding the outer circumference of the cathode, and an outer cylinder made of a heat insulating material surrounding the outer circumference of the inner cylinder,
It is attached to the furnace shell in an insulated state from the anode and the furnace shell via an electric insulating material, and is formed between the inner space formed between the cathode and the inner cylinder and between the inner cylinder and the outer cylinder. A gas inflow port is provided in each lower part of the outer space and a gas outflow port is provided in each upper part, and each gas inflow port is connected to a purge gas supply source so that the purge gas is supplied as an upward flow in the inner space and the outer space. The purge gas was made to flow and flowed out into the furnace through the gas outlets.

(Operation) In the ion carburizing furnace of the present invention, the purge gas flows as an upward flow in the inner space formed between the cathode and the inner cylinder, and the CH-based gas enters the inner space and contacts the surface of the cathode. Therefore, even if the cathode is water-cooled at a low temperature, soot does not adhere to the surface due to CH-based gas. Also, the outer cylinder made of heat insulating material prevents the glow discharge from flying directly from the anode to the cathode, and the purge gas also flows as an upward flow in the outer space formed between the outer cylinder and the inner cylinder, so Both sides of the inner cylinders, which are adjacent to each other and have a slightly low temperature, are also exposed to the upward flow of the purge gas, and soot is prevented from adhering to the inner cylinder due to the CH-based gas.

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

5, those parts which are the same as those corresponding parts in FIG. 5 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 connected to a cooling water supply source, and 14 is a drainage port. As shown in Fig. 4, the insulator 11 has four grooves on its inner circumference.
An annular head 17 having a hole 16 communicating with the groove 15 is fixedly attached to the lower surface of the insulator 11.
The air supply port 18 of the header 17 is connected to a purge gas supply source 19 for supplying a purge gas composed of a non-oxidizing gas such as hydrogen, argon and nitrogen. On the other hand, a ring-shaped insulator 20 is fitted on the cathode 3 and the insulator 20 is fitted on the insulator 20.
A gas outlet 21 having the same shape as the groove 15 is provided. Reference numeral 22 denotes an inner cylinder made of metal such as stainless steel, both ends of which are supported by the insulators 11 and 20, and an annular inner space 23 is formed between the inner cylinder 22 and the cathode 3. Reference numeral 24 is a gas outlet provided at four upper portions of the inner cylinder 22, and reference numeral 25 is a gas inlet to an outer space 29 (described later) provided at four lower portions of the inner cylinder 22. Also
An outer cylinder 26 made of a heat insulating material has a lower end fixedly attached to the furnace shell 1 via an insulator 27, and an annular gas outlet 28 is formed between the upper end and the cathode 3. An outer space 29 is formed between the cylinder 22 and the outer cylinder 26. As shown in FIG. 1, a DC power supply 30 is connected between the cathode 3 and the anode 2, and an AC power supply 31 for heating is connected to the heater 7. Reference numeral 32 is a processing gas supply source connected to the gas manifold 8, 33 is a gate valve type inlet door, and 34 is an air cylinder for raising and lowering the door.

In the ion carburizing furnace 35 having the above structure, if a purge gas such as hydrogen is supplied into the header 17 from the purge gas supply source 19, the purge gas flows into the inner space 23 from the gas inlet 15a at the upper end of the groove 15, and the inside It flows as an upward flow in the space 23 and flows out from the gas outlets 21 and 24 into the furnace via the gas outlet 28 of the outer cylinder 26. Further, a part of the purge gas flowing from the gas inlet port 15a flows into the outer space 29 from the gas inlet port 25, flows in the outer space 29 as an ascending flow, and then flows into the gas outlet port 28.
Flows into the furnace from. 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 the 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 inner space 23, so that the soot is prevented from adhering to the cathode 3. Similarly, soot is prevented from being attached to the inner cylinder 22.

Ion carburizing furnace 35 with the above configuration (however, inner diameter of furnace shell = 16
00mm) SCM420 automotive parts as mounting jigs
A mixed gas of propane gas 5 / min and nitrogen gas 5 / min is used as a processing gas for 0 of the processed object 5 mounted,
In addition, hydrogen gas as a purge gas to be charged into the cathode 3 part is reduced to 0.
Ion carburizing treatment was performed at 950 ° C. for 60 minutes using 2 / min (per cathode). 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. 5 was exposed in the furnace. As a result, arcing during processing did not occur in the example of the present invention, whereas in the comparative example arcing was observed 2-3 times per 10 minutes, and replacement due to wear of the cathode was The example of the invention was unnecessary for one year, whereas the comparative example required replacement once a month.

The present invention is not limited to the above embodiment, for example, the gas outlet of the inner space 23 may be opened directly into the furnace without passing through the outer space 29, or the gas inlet 25 to the outer space 29. Also, the shape and specific structure of each part may be other than the above, such as communicating directly with the head 17 part without passing through the inner space 23. Further, the anode 2, the hearth 6, the heater 7, the gas manifold 8 and the like may have other structures.

(Effects of the Invention) As described above, according to the present invention, the purge gas charged into the cathode portion prevents the CH-based gas from entering the cathode surface portion, and prevents the arcing due to the attachment of soot to the cathode surface. Thus, the operation of the ion carburizing furnace can be stabilized and the wear of the cathode can be reduced.

[Brief description of drawings]

1 is a longitudinal sectional view of an ion carburizing furnace showing an embodiment of the present invention, FIG. 2 is a sectional view taken along the line AA of FIG. 1, and FIG.
FIG. 4 is an enlarged vertical sectional view of the cathode portion in the figure, and FIG.
FIG. 5 is a cross-sectional view taken along line -B, and FIG. 5 is a view corresponding 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 ... Groove, 15a ...
Gas inlet, 17 ... Hedda, 18 ... Air inlet, 19 ... Purge gas supply source, 20 ... Insulator, 21 ... Gas outlet, 22 ...
… Inner cylinder, 23 …… Inner space, 24 …… Gas outlet, 25 …… Gas inlet, 26 …… Outer cylinder, 27 …… Insulator, 28 …… Gas outlet, 29 …… Outer space, 35 …… Ion carburizing furnace.

Claims (1)

[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 inner cylinder and an outer cylinder made of a heat insulating material that surrounds the outer circumference of the inner cylinder are attached to the furnace shell in an insulating state with respect to the anode and the furnace shell via an electrical insulating material, and the cathode and the A gas inlet is provided in each lower part of the inner space formed between the inner cylinder and the outer space formed between the inner cylinder and the outer cylinder, and a gas outlet is provided in each upper part, and each gas inlet is provided. An ion carburizing furnace configured to be connected to a purge gas supply source and to cause the purge gas to flow in the inner space and the outer space as an upward flow and to flow the purge gas into the furnace through the gas outlets.