KR20100105128A - Muliti-purpose plasma heat-treatment apparatus - Google Patents

Abstract

Disclosed is a multipurpose vacuum heat treatment apparatus capable of performing heat treatment on a workpiece or surface heat treatment such as carburization and nitriding using a cathode network heated by plasma in a vacuum atmosphere. If a screen is installed between the treatment furnace and the object to be treated without using a heater or burner, which is a heating device of the existing heat treatment device, the main wall of the heat treatment furnace is the anode and the screen surrounding the object is the cathode. Plasma is generated between and the screen. The cathode screen heated by the plasma heats the workpiece, so that the temperature can be adjusted by adjusting the applied voltage. The form of the negative electrode screen has a reticulated expanded metal plate, a punched metal plate, a mesh shape, and the like. The treatment gas uses a H2, Ar, N, CxHy gas, etc. to make the entire interior of the cathode screen and the heat treatment furnace into a plasma atmosphere. Depending on the type of treatment gas, nitriding treatment, carburization treatment and heat treatment are possible.

Description

 Multipurpose Plasma Heat Treatment Equipment {MULITI-PURPOSE PLASMA HEAT-TREATMENT APPARATUS}

The present invention relates to a multi-purpose plasma heat treatment apparatus, and more specifically, the screen is installed so as to surround the object to be treated, the cathode is applied to the screen, and the main wall of the heat treatment furnace is subjected to high voltage to the anode, the cathode screen by ion sputtering Is heated. At this time, since the cathode screen is heated by the action of ion sputtering, the present invention relates to a multi-purpose plasma heat treatment apparatus in which an object to be treated can be heated without using a conventional heating device such as a heater or a burner.

In addition, the present invention relates to a multi-purpose plasma heat treatment apparatus capable of general heat treatment, nitriding treatment, carburizing, or carburizing nitriding treatment using H, Ar, N, and CxHy-based gases introduced without using a separate heating means.

Conventional heat treatment apparatuses use high frequency, electric heaters, gas burners and the like as heat sources to satisfy the mechanical properties required by the object. This method has problems in terms of high energy consumption, burden on the environment due to the treatment gas, and treatment quality.

In the case of heat-treating steel or nonferrous parts, a method of minimizing oxidation due to heating has emerged because the brightness, which is a metal characteristic of the part surface, is lost. Vacuum furnaces have been developed as furnaces suitable for the purpose, and vacuum furnaces are classified into heat resistant (cold wall) and external heat (thermal wall).

The heat-resistant vacuum furnace, which is mainly used in the vacuum furnace, is operated with the internal pressure of 10 ^-2 to 10 ^-5 torr, and the heating element enclosed by the radiant heat blocking wall is made of graphite, tungsten or molybdenum, The fan is operated in an atmosphere of nitrogen or an inert gas upon cooling. In this case, since the wall surface of a furnace is water-cooled, it is also called cold wall surface type.

In addition, the processing temperature is suitable for precision heat treatment of various metal materials such as molds, tool steels, stainless steel, etc., with a processing temperature of 1000 ° C. or higher, and the gas or vacuum degree used can be variously selected according to the material to be heat treated. Cooling is carried out in an atmosphere of high purity inert gas so as not to lose brightness, depending on the size of the material or part. Recently, a vacuum furnace capable of encapsulating high pressure nitrogen gas of 3 to 5 atmospheres in order to shorten the cooling rate in accordance with the enlargement of heat treatment parts has also been developed.

An external heat type (heat wall type) vacuum furnace is a furnace in which vacuum extraction heat resistant steel or tubular retort is incorporated, and is used at a temperature of 1000 ° C. or higher. The walls of the furnace are classified into various types such as belt type, pot type, box type, and tubular type. After the vacuum furnace is maintained in the furnace, hydrogen gas is encapsulated at atmospheric pressure together with inert gas such as nitrogen and argon in the retort. Such external heat type vacuum furnaces are used as bright annealing of special metals such as steel or nonferrous materials.

As described above, a temperature raising device for heating a processed product in the most representative vacuum heat treatment device among the heat treatment devices is variously used, and such a temperature rising device is expensive. Various thermal insulation methods and protective gases such as inert gases are used to obtain the brightness and uniform temperature of the processed products. Although no harmful gas is used in the vacuum heat treatment, in general, heat treatment uses a gas that inhibits the environment in order to maintain a protective atmosphere.

On the other hand, the conventional nitriding treatment device has been developed in various ways, as a representative and the most environmentally friendly ion nitriding device initially applied a cathode voltage directly to the product using a cold wall surface. Target water heating method and heated to effect ion sputtering using H _2, N _2, Ar gas or the like. This method takes considerable processing time to heat the workpiece because it applies the cathode voltage directly to the workpiece without using a separate heating device, and it is difficult to obtain a uniform temperature, so that when processing a large amount The phenomenon of failing to treat the workpiece uniformly often occurs.

Therefore, in order to shorten the uniform temperature and nitriding treatment time inside the furnace, a nitriding device equipped with a separate heating device inside the thermal wall surface heat treatment device was developed, and a large amount of the workpieces could be treated uniformly. .

An example of such a vacuum plasma surface heat treatment apparatus is schematically shown in FIG.

Referring to FIG. 1, a thermal wall type vacuum plasma surface heat treatment apparatus 10 includes a cylindrical nitriding furnace 11, a main body 12 coupled to the nitriding furnace 11 so as to be opened and closed, and the main body 12. ) And a heater 13 for raising the temperature of the interior to about 600 ° C. In the main body 12, a jig 14 for displaying an object P to be displayed is provided at a position spaced apart from the main body 12 and the heater 13 by a predetermined distance.

The vacuum line 15 is connected to one side of the main body 12 to make the internal atmosphere of the nitriding furnace 11 into a vacuum state. When the workpiece is set on the jig 14, the inside of the main body 12 is maintained in a vacuum state. The vacuum line 15a is connected to a vacuum pump 15 that is separately provided outside the main body 12.

In order to convert the inside of the main body of the nitriding treatment furnace 11 into a vacuum nitriding state, a gas supply line 17 for supplying nitrogen gas mixed with hydrogen gas is connected to one side of the main body 12. Further, in order to create a condition in which nitrogen gas in the plasma nitriding state can be adsorbed on the surface of the product P to be treated, a power supply unit 16 capable of applying a high voltage (about 500 V) is provided with a nitriding furnace 11. Is installed on. The power supply unit 16 is provided such that the positive electrode is connected to the main body 12 and the negative electrode is connected to one side of the jig 14 on which the object is set.

The main body 12 of the nitriding furnace 11 is rotatable around the supporter 19 so as to be easily set within the nitriding furnace 11 so that the object to be processed P can be set. And a cooler for lowering the temperature of the heated body 12.

Inside the nitriding furnace 11, the main body 12 of the positive electrode and the jig 14 of the negative electrode are set. When the power supply unit applies current, sputtering occurs on the surface of the workpiece P in the state of being electrically conductive with the cathode, whereby nitrogen is adsorbed. That is, the nitrogen gas ionized with cations reacts with the cathode in the jig 14, and moves to the surface of the object to be nitrided and adsorbed in the air.

More specifically, a processing gas containing hydrogen, nitrogen, or argon gas is supplied to the inside of the chamber at a predetermined pressure, and a glow discharge is generated between the workpiece to be connected to the cathode and the chamber wall set to the anode. When a DC voltage of 100 V to 1000 V is applied to the jig set as the cathode, discharge occurs in the chamber. This discharge is called glow discharge, and the current density in this case is several mA / cm ² . The glow discharge is sustained by the secondary electrons emitted by the collision of ions (or photons) with the cathode and ionizing the gas. Plasma nitridation is a cation stuffing that activates the surface of the material to speed up the nitriding rate and easily nitride the refractory material. In addition, plasma nitridation does not use toxic gases such as ammonia, and only uses gases such as nitrogen gas and hydrogen, so that the emitted gases have the advantage of clean heat treatment without harmful gases.

In the conventional plasma-nitriding surface heat treatment apparatus having the advantages as described above, the jig and the workpiece itself serve as a negative electrode. Therefore, when such a configuration is applied to a large heat treatment apparatus, the to-be-processed object set inside the main body is not uniformly heat treated. In addition, in the case where the workpiece has a sharp edge part, the edge part has a problem that the edge part is heat treated thicker than the flat part due to the electrical characteristics.

On the other hand, when glow discharge occurs, nitrogen gas collides with the electrons emitted from the cathode and is ionized, and nitrogen ions are accelerated at high speed by a sudden cathode drop phenomenon immediately before the surface of the workpiece, and collide with the surface of the workpiece. The kinetic energy is converted into thermal energy by the collision, and the temperature of the workpiece is increased. With this action, Fe, C, O elements evaporate on the surface of the workpiece. In this case, nitrogen ions are adsorbed directly on the surface to form nitrides, or the evaporated iron (Fe) particles combine with activated nitrogen ions in the plasma to form iron nitride (FeN), which is the nitride of the workpiece. Adsorbed back to the surface.

Since the adsorbed iron nitride is unstable, it is separated into Fe ₂ N, Fe ₃ N, Fe ₄ N, and the like, and some of the separated nitrogen diffuses into the object to form a hardened layer.

Applicant has developed a new multi-purpose plasma nitriding device based on the background technology of general heat treatment and hot-wall ion nitride device. Inert gas hydrogen, argon, or the like is used to generate a plasma on the cathode screen instead of the workpiece, thereby heating the cathode screen. Thermal energy of the heated cathode screen is transferred to the object to be heated to perform the plasma heat treatment. In addition, when H, Ar, N ₂ , CxHy gas, or the like is used as the processing gas, ions sputtered on the cathode screen may react with the treated product to perform thermal surface treatment such as nitriding, carburizing, carburizing and nitriding.

Accordingly, an object of the present invention is to propose a multipurpose plasma heat treatment apparatus of a new concept, and to provide a multipurpose plasma heat treatment apparatus having a porous cathode screen installed along a wall of a heat treatment furnace. The multipurpose plasma heat treatment apparatus according to the present invention may be provided with a plurality of layered cathode screens to increase the plasma density.

When the cathode screen is perforated, a porous cathode discharge occurs on the surface of the screen. The electrons accelerated by the cathode drop increase in ionization rate in a vacuum at a predetermined distance from the object under the influence of the opposite cathode electric field. Since the generation of secondary electrons is encouraged by the increased ionization rate or the cathode collision of the gas, the current density is increased by the vibration of the electrons, so that the workpiece can be quickly surface treated.

Another object of the present invention is to provide a plasma heat treatment apparatus that can heat-treat an object without using a separate heating device by utilizing the mid-curve cathode discharge effect of the porous cathode screen heated by plasma energy and ion sputtering. will be.

In order to achieve the above and other objects of the present invention, according to an embodiment of the present invention, a heat treatment furnace maintained in a vacuum state, a power supply for applying a high voltage to the heat treatment furnace, and to support the object A plasma heat treatment apparatus having a jig for providing a plasma heat treatment apparatus including at least one or more layers of porous cathode screens disposed between a jig and an inner wall of a heat treatment furnace to surround the jig.

The cathode voltage is applied to the porous cathode screen from the power supply, and the anode voltage is applied from the power supply to the main wall of the heat treatment furnace.

Into the inside of the heat treatment furnace, any one gas selected from the group consisting of N ₂ , H ₂ , Ar, C ₃ H ₈ , and CH ₄ gas is supplied to perform light heat treatment, nitriding, carburizing, or carburizing and nitriding heat treatment.

The porous cathode screen is made of any one of reticulated metal plate (Expanded Metal), perforated metal (Punched Metal), and mesh-shaped plate, the spacing between the porous cathode screen is 10 to 100 mm.

According to the above-described configuration, since the porous cathode screen is installed around the jig and the object is heated using the plasma thermal energy generated from the cathode screen, a separate heating device is not required. Therefore, the structure of the plasma heat treatment apparatus of the present invention can be simplified than the conventional general heat treatment apparatus, it can bring the effect of reducing the energy consumption cost. In addition, the plasma heat treatment apparatus of the present invention has an effect of obtaining a very excellent temperature uniformity in the object to be treated because the plasma generated on the cathode screen surrounding the object to move the heat energy to the object. Therefore, the plasma heat treatment apparatus of the present invention can heat-treat a complicated shape or a large product.

In particular, since the high cathode potential is not directly applied to the workpiece in the surface treatment process, problems such as arcing, partial overheating, porous cathode, and uneven temperature, which are problems of conventional ionization, can be solved. .

In addition, the present invention does not cause damage such as general ion nitriding to the workpiece by ions generated in the cathode screen instead of the workpiece by using the porous cathode effect in the porous cathode screen without using a separate heating device. In addition, the treatment temperature can be controlled and the surface treatment can be performed for each type of steel.

Hereinafter, with reference to the accompanying drawings will be described in detail the configuration of the plasma nitride surface heat treatment apparatus according to an embodiment of the present invention.

2 is a view schematically showing a plasma nitride surface heat treatment apparatus according to an embodiment of the present invention.

Plasma nitride surface heat treatment apparatus 100 according to the present invention is a cylindrical heat treatment furnace 111, the main body 112 coupled to open and close to the heat treatment furnace 111, and the jig in which the workpiece (P) is disposed ( 114).

The vacuum line 115 is connected to one side of the main body 112 to make the internal atmosphere of the heat treatment furnace 111 in a vacuum state. When the workpiece is set on the jig 114, the inside of the main body 112 is maintained in a vacuum state. The vacuum line 115a is connected to a vacuum pump 115 that is separately provided outside the main body 112.

In order to convert the inside of the main body of the heat treatment furnace 11 into a vacuum nitridation state, a gas supply line 117 is connected to one side of the main body 12 to supply nitrogen gas mixed with hydrogen gas. In addition, a power supply unit 116 capable of applying a high voltage (about 500 V) is installed in the heat treatment furnace 111 in order to create a condition in which the nitrogen gas in the plasma state can be adsorbed onto the surface of the product P to be treated. do. The power supply unit 116 is installed such that the positive electrode is connected to the main body 112 and the negative electrode is connected to one side of the jig 114 on which the object is to be set.

The main body 112 of the heat treatment furnace 111 is supported by the pivotable arm 119a around the supporter 119 so that the object to be processed P can be easily set in the heat treatment furnace 111. And a cooler for lowering the temperature of the heated body 112.

In the plasma heat treatment apparatus 100 according to the present invention, the nitrogen gas in the cation state is formed on the surface of the workpiece P while the DC current supplied from the power supply unit 116 does not flow directly into the workpiece P. A porous cathode screen 170 is provided between the wall of the heat treatment furnace and the workpiece to be effectively adsorbed. The upper end of the porous cathode screen 170 is fixed to the cover of the heat treatment furnace 111, and the lower end is positioned adjacent to the jig 114 located at the lowermost end.

Porous cathode screen 170 is made of stainless steel or non-ferrous metal, it is preferable that a plurality of openings are formed in a mesh form on the surface by processing such as punching, piercing.

An example of porous cathode screen 170 is shown in FIG. 3. FIG. 3A is a plan view showing a metallased screen of an expanded metal plate, and FIG. 3B is a plan view showing a perforated screen having a circular shape of a hole, and FIG. 3C is a perforated shape having a rectangular shape of a hole. It is a top view which shows a screen, and FIG. 3D is a top view which shows the screen of a mesh shape.

An anode voltage is applied to the circumferential wall of the heat treatment furnace 111 and a cathode voltage is applied to the porous cathode screen 17 so that a high voltage cathode potential is projected between the circumferential wall of the heat treatment furnace 111 and the porous cathode screen 170. Accordingly, the workpiece P and the jig 114 are surrounded in the floating potential, and the position where the plasma is generated is generated in the porous cathode screen 170 and not in the surface of the workpiece.

Plasma is generated in a porous cathode screen, such as unplated steel (mesh), and plasma energy generated in the porous cathode screen is transferred to the workpiece to heat the workpiece to the treatment temperature. In this case, the plasma contains ions, electrons and other active particles that will come into contact with the workpiece.

In the illustrated embodiment, porous cathode screens 170 spaced at predetermined intervals are installed. Openings perforated in the porous cathode screen 170 may have a shape of a circle, triangle, square, oval, etc., the diameter is not particularly limited.

As in this embodiment, by installing the porous cathode screen 170, the electrons accelerated by the cathode drop can increase the ionization rate in the vacuum at a certain distance under the influence of the opposite cathode electric field. In addition, since secondary electrons are generated due to ionization degree or cathode collision of gas, there is also an effect that a high current density appears due to the vibration of electrons.

The processing gas is supplied to the entire inner circumference of the heat treatment furnace through a supply pipe (not shown) provided between the circumferential wall of the heat treatment furnace 111 and the porous cathode screen 170. As a result, the active particles can be heated with plasma energy for a predetermined time by heating all the workpieces disposed above the jig 114 through the mesh of the porous cathode screen, thereby thermally treating the workpieces.

By using the above-described porous cathode screen 170, even if a large number of workpieces of a complicated shape are arranged on the jig 114, since the high cathode potential is not directly applied to the workpiece, the surface roughness of the product is improved. . In addition, since plasma thermal energy generated in the porous cathode screen 170 is directly transmitted to the workpiece, no additional heat source is required. In more detail, a general heat treatment method for performing heat treatment using a non-reactive gas requires a separate heating device, but since the device of the present invention uses plasma thermal energy, it can be simplified than a general heat treatment device. Thereby, the manufacturing cost is effective. In addition, since the temperature raising device is not operated, energy costs can be reduced.

In order to increase the thermal surface treatment rate, a low voltage (100 V to 200 V) is applied to the jig so that the active species nitrogen gas generated in the porous cathode screen actively moves to the cation of the workpiece.

Therefore, the cations of the activated nitrogen are uniformly attached to the surface of the workpiece P in a state where a high voltage current does not flow directly. Therefore, when there is a sharp edge part in the product P, it is nitrided to a uniform thickness like the flat part.

In particular, according to the present invention, a voltage of 500 to 700V is applied to the porous cathode screen 170, and since one or more layers of the porous cathode screen are maintained at regular intervals, high thermal energy is generated by the vacuum cathode discharge effect, and the target object is treated. The water P and the jig 114 are surrounded in the floating potential. The high temperature plasma thermal energy generated by the porous cathode screen 170 may be transferred to the object to be heat treated.

The processing gas is supplied to the entire inner circumferential surface of the heat treatment furnace through a supply pipe provided between the main wall of the heat treatment furnace 111 and the porous cathode screen 170. As a result, the workpiece on which the active particles are placed on the jig 117 through the porous cathode screen is in constant contact with the plasma particles for a predetermined time.

More specifically, the processing gas is uniformly distributed in the heat treatment furnace through a plurality of supply pipes (not shown) between the main wall of the heat treatment furnace 111 and the porous cathode screen 170. Active particles face the same cathodes by one or more porous cathode screens 170, maximizing the vacuum cathode discharge effect, resulting in high plasma thermal energy and ionization rate. For this reason, even if only the porous cathode screen is installed, surface treatment and heat treatment can be performed without using a separate temperature raising device.

According to the above-described configuration, not only the surface-treatment such as nitriding, carburizing, or nitriding can be treated with a complicated shaped workpiece, but also a plurality of workpieces can be processed simultaneously.

The apparatus according to the invention also solves the disadvantages of conventional surface treatment processes. Specifically, the apparatus of the present invention has problems such as limitations in shape, arc generation, temperature unevenness, long processing time, etc., which are disadvantages of the ion nitriding process, and production cost increase by using a heater, which is an expensive auxiliary heat source. Can be solved.

The apparatus of the present invention can not only simply surface-treat the workpiece, but also thermal surface treatment using high temperature heat. Thus, in the case of some steels, the nitriding treatment rate increases at a suitable temperature and deeply nitrides from the surface.

The apparatus of the present invention can be applied as a multipurpose plasma heat treatment apparatus that can not only heat-treat an object to be treated but also utilize plasma thermal energy generated from a cathode screen. For most metals, the thermal surface treatment rate increases at a moderate temperature and hardens deeply from the surface. For example, an alloy steel such as SKD11 is subjected to thermal surface treatment in a short time at 500 ° C, mechanical structural carbon steel such as S45C at 580 ° C, and stainless steel at about 350 ° C. Conventional cold-wall ion nitridation treatment is applied to a high voltage plasma directly to the product without using a heater to perform the nitriding treatment for a long time of at least 20 hours. In addition, in recent years, the most frequently used thermal wall type nitriding apparatus has applied a high voltage (500V to 800V) directly to an object to be processed by using a heater as an auxiliary heat source inside the furnace, thereby greatly reducing the processing time. According to the present invention, a high voltage is applied to a cathode screen instead of an object by using a cathode discharge on at least one porous cathode screen without using a separate temperature raising device, and thus does not affect the object to be treated at all. By controlling the furnace treatment temperature there is an effect that can quickly perform the surface treatment.

In addition, the apparatus according to the present invention can be used for plasma heat treatment of the workpiece, since the plasma can be heat-treated by using a gas or the like which is not reactive with the workpiece.

Although the present invention has been described with reference to the above embodiments, the protection scope to be protected is not limited by the above embodiments. The protection scope of the present invention is determined by the following claims.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view showing a thermal wall type plasma nitride surface heat treatment apparatus according to the prior art.

2 is a cross-sectional view showing a plasma heat treatment apparatus according to a preferred embodiment of the present invention.

3 is a plan view showing an example of a porous cathode screen, FIG. 3A shows a metallased screen of expanded metal plate, FIG. 3B shows a perforated screen with a circular shape of a hole, and FIG. 3C shows a perforated screen in which the shape of the hole is rectangular, and FIG. 3D shows a mesh-shaped screen.

<Explanation of symbols for the main parts of the drawings>

111: heat treatment furnace

116: power supply

117: gas supply line

114: jig

170: porous cathode screen

Claims (4)

A plasma heat treatment apparatus comprising a heat treatment furnace maintained in a vacuum state, a power supply unit for applying a high voltage to the inside of the heat treatment furnace, and a jig for supporting an object to be processed, And at least one or more layers of porous cathode screens disposed between the jig and the inner wall of the heat treatment furnace to surround the jig. The method of claim 1, A cathode voltage is applied to the porous cathode screen from a power supply and a cathode voltage is applied from a power supply to a main wall of the heat treatment furnace. The method of claim 1, In the heat treatment furnace, any one gas selected from the group consisting of N ₂ , H ₂ , Ar, C ₃ H ₈ , and CH ₄ gas is supplied to perform light heat treatment, nitriding, carburizing, or carburizing and nitrification heat treatment. Plasma heat treatment apparatus, characterized in that. The method of claim 2, The porous cathode screen is made of any one of a reticulated whole metal plate (Expanded Metal), a perforated plate (Punched Metal), and a mesh-shaped plate, the plasma heat treatment apparatus, characterized in that the spacing between the porous cathode screen is 10 to 100 mm.

Images