KR101519189B1 - Method and system for nitriding bore of pipe with hollow cathode discharge - Google Patents

Abstract

TECHNICAL FIELD The present invention relates to a technique for nitriding an inner wall surface of an object having a depth such as a pipe, and is intended to provide an inner nitriding technique using a Hollow Cathode Discharge (HCD).
Accordingly, it is an object of the present invention to design a conductive jig system in which a hollow body or intaglio member itself to be nitrided is used as a cathode, and a plurality of such objects can be fixed, and a power supply is applied to the jig system, The body or the intaglio member itself acts as a hollow cathode, causing a hollow cathode discharge in the inner space, and nitriding the inner wall surface of the cathode member with the generated plasma.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method and apparatus for nitriding internal electrodes using a hollow cathode discharge,

TECHNICAL FIELD The present invention relates to a technique for nitriding an inner wall surface of a pipe-like object, and more particularly, to a method and apparatus for inner wall nitriding using Hollow Cathode Discharge (HCD).

Some automotive, aircraft, and other mechanical accessories are in the form of pipes, tubes, or engraved shapes, and the durability of these accessories is often required for the interior walls. Nitriding is a typical surface treatment that imparts hardness and corrosion resistance to metallic parts. Nitriding is also a technique that requires high-level process control in actual implementation. Plasma nitridation is desirable from the viewpoint of quality such as process efficiency and nitriding depth, but nitriding of the recessed portion is not easy.

Generally, nitriding treatment to form a nitride with nitrogen diffused to the metal surface hardness and corrosion resistance, as processing methods for improving the wear resistance, fatigue strength and the like, carburization, high-frequency heat treatment, etc. Unlike other surface hardening method and the lecture transformation point (A ₁ transformation point: 723 ° C) or less (less than 600 ° C), it is used in precision mechanical parts, automobile parts, and molds because of less heat treatment deformation. The nitriding process belongs to the diffusion penetration method which is distinct from the surface coating method of modifying the surface by depositing a hard or functional substance on the surface of the material.

The nitrification treatment can be roughly divided into gas nitriding, liquid nitriding (salt bath nitriding), plasma nitriding (ion nitriding), and the like. In the case of gas nitriding, a nitriding layer is formed on a metal product by exposure to gaseous ammonia (NH ₃ ) atmosphere heated to about 560 to 580 ° C. for about several hours, However, it has a disadvantage that it takes a long time to realize commercialization characteristics and it can be applied only to dedicated materials, and that a post-treatment device is required due to the use of ammonia gas, which is a harmful substance.

Liquid nitration (salt bath nitriding) is a method of adding a metal product to cyanide (CN ^- ) or cyanic acid (CN ^- ) salt and nitriding it in liquid phase. But their use is gradually diminishing in that they require post-treatment due to the formation of a porous nitrogen compound layer and that toxic substances are used.

Plasma nitrification (ion nitridation) is a method of forming a nitride layer on a metal product by using nitrogen ions formed by glow discharge, and it is disadvantageous in that it is difficult to operate and high equipment cost is required. However, Ions, it is possible to shorten the treatment time and to easily control the structure and depth of the nitride layer. In particular, the ratio of the nitriding technology to the rutting technology is gradually increasing due to the absence of harmful substances and pollution.

On the other hand, among the plasma surface treatment techniques, it has been recognized that the surface treatment using the hollow cathode discharge phenomenon is undesirable because of the inherent strong discharge, resulting in local overheating or damage to the product, resulting in a high defect rate.

In addition, when attempting to treat the hollow cathode discharge phenomenon on the surface of the engraved portion, as disclosed in Korean Patent Laid-Open No. 10-2008-0098826, a discharge cathode is disposed in the pipe to cause a hollow cathode discharge, , Installation cost and effort due to installation is not suitable for mass production, and there is no industrial benefit.

Therefore, an object of the present invention is to provide a high-quality nitriding treatment technology in a short time, intensively, in a short period of time, in a hollow body without any additional heating process due to high density ion concentration and heat generation by using a hollow cathode discharge, .

It is still another object of the present invention to provide a mass-production nitriding technique for the inner diameter portion of metal parts including a hollow body and other intaglio machined metal products, and to provide a hollow cathode discharge of the same shape So that the nitriding treatment of thousands of articles can be performed in a single step.

According to the above object, according to the present invention, a negative electrode to be nitrided is used as a negative electrode, a power is applied to the negative electrode to cause a hollow cathode discharge in a hollow space or a hollow space inside the negative electrode, Respectively.

That is,

A vacuum chamber;

A conductive jig installed in the vacuum chamber;

A plurality of conductive hollow bodies or engraved members fixed in contact with the conductive jig and fixed to one conductive jig;

A gas supply connected to the vacuum chamber;

A power supply device,

One of the positive electrode and the negative electrode of the power source device is connected to the vacuum chamber and the other is connected to the conductive jig to supply power,

And a process gas including nitrogen is supplied through the gas supply unit to cause a hollow cathode discharge in the hollow or depressed portions of the plurality of conductive hollow bodies or intaglio members to nitridize the inner wall surface of the hollow portion or the wall surface of the engraved portion The inner diameter nitriding treatment system can be provided.

The present invention also provides an internal nitriding processing system, wherein the conductive jig is supported by an insulator in the vacuum chamber.

Further, in the present invention, it is possible to provide the internal nitriding processing system, wherein the nitriding treatment is performed at room temperature, and no separate heat treatment apparatus is provided in the vacuum chamber.

Further, the present invention is characterized in that the conductive jig includes a plate-shaped jig frame, the plate-shaped jig frame has a plurality of holes, and a plurality of conductive hollow bodies or engraved members are fixed to the holes The inner diameter of the inner diameter of the inner diameter of the inner diameter of the inner diameter of the inner diameter of the inner diameter of the inner diameter-

Further, in the present invention, in the power supply for the nitriding process, the nitriding degree of the hollow body or the intaglio members, which are the object to be processed, is controlled by controlling the applied voltage, And the nitriding treatment is performed by increasing the current.

Further, the present invention is characterized in that nitrogen and hydrogen are injected into the vacuum chamber, the fraction of nitrogen in the injected gas is 10 to 100%, the process pressure is maintained in the range of 0.05 to 10 Torr, And a nitriding treatment is performed by applying electric power to the inner diameter nitriding treatment system.

Further, the present invention can provide an internal nitriding processing system, characterized in that after the nitriding treatment, the object to be processed is cooled in a vacuum chamber and then unloaded from the vacuum chamber.

According to the present invention, a hollow cathode discharge can be generated by using a to-be-processed material such as a pipe having a hollow body shape as a cathode, thereby nitriding the inner wall surface of the hollow body with high quality. , It is advantageous in that the mass productivity is very high since a plurality of objects to be processed in one chamber are fixed to the conductive jig and simultaneously processed at the same time.

Further, the present invention controls the applied voltage to control the hollow cathode discharge, thereby inducing the nitriding characteristic of the inner wall surface of the hollow body to a desired level, so that a separate heat treatment step, which is often performed in the nitriding treatment, Simplification of the process is also an advantage.

1 is a cross-sectional view for explaining a nitriding treatment apparatus of the present invention.
FIG. 2 is a photograph of the shape of a hollow cathode discharge generated in a plurality of hollow bodies according to the present invention.
FIG. 3 is a contour appearance photograph of a result of corrosion after 5% of the processing and detachment to observe the cross-sectional structure after applying the inner nitriding treatment according to the present invention.
Fig. 4 is a photograph of the inner diameter portion cross-sectional nitrification structure according to the present invention.
5A and 5B are photographs showing the hardness of the inner diameter portion of the product after the nitriding treatment according to the present invention (FIG. 5A: the hardness of the surface portion of SCM415 hollow metal product before nitriding: 250.4 HV 0.3 kgf, Surface hardness in SCM415 hollow body metal product: 663.7 HV 0.3 kgf).
FIG. 6 is a photograph showing the depth hardness in the depth direction from the surface of the inner diameter portion after the nitriding treatment according to the present invention. FIG.
FIG. 7 is a graph of hardness distribution in the depth direction of the inner diameter portion after the nitriding treatment according to the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Fig. 1 is a sectional view showing a configuration of an apparatus for nitriding a hollow cathode discharge according to the present invention.

A vacuum chamber 100 made of a conductive metal such as SUS is provided with a gas supply unit 200, a vacuum exhaust pipe 300 and a power supply 400, and a conductive jig system is installed in the vacuum chamber 100. The conductive jig system may be configured such that the jig frames 600 and 610 are connected to form an electrical closed loop as a whole and have a plurality of closed loops in one closed loop. The conductive jig system is constructed on the basis of a plate type jig base 620 to which one polar terminal of the power source 400 is connected and the jig base 620 is insulated from the body 100 of the chamber 100 by an insulator 700. [ do. The object to be processed 900 having a hollow body or an engraved portion is fixed to the jig frame 600 and nitrided, and a large number of objects 900 can be charged, which is suitable for mass production. It is preferable that the cooling fan 800 is also provided because it is of special advantage to perform the cooling of the object 900 in the chamber 100 after the process.

The vacuum exhaust pipe 300 connects the vacuum chamber 100 to the vacuum pump 310. A rotary pump for realizing an initial vacuum (10 Torr or less) from the atmospheric pressure state and a booster pump for realizing process vacuum are connected to a vacuum pump 310 ).

Hereinafter, the nitriding process will be described in detail with reference to the principle thereof.

First, a plurality of metal objects 900 to be machined with a hollow body or engraved are fixed to the jig frame 600 on a plate at predetermined intervals and charged into the chamber 100. The jig frame 600 has a circular or square plate as a basic structure and a plurality of holes suitable for the jig frame 600 are inserted therein to fix and fix the hollow object 900. The plate jig frame 600 Are stacked at intervals and fixed to the columnar jig frame 610 by stacking layers.

When the jig system is disposed inside the vacuum chamber 100, the electrode opposite to the jig system must be kept in contact with the vacuum chamber 100 which is in a ground state. For this purpose, the vacuum chamber 100 and the jig system The jig insulator 700 is placed between the jig base 620 of the vacuum chamber 100 so that the jig system maintains the insulation state with respect to the vacuum chamber 100 and maintains the electric connection with the power source 500. The structure of the jig insulator 700 may be made of other insulators including ceramics and should have sufficient durability to bear the load of the jig system and the hollow object 900 to be nitrided.

Next, the interior of the chamber 100 is evacuated to a vacuum degree of about 0.05 Torr to 10 ^-4 Torr by a vacuum pump 310.

The gas supply regulates the flow rate through the valve 210 and supplies the gas to the gas injection port 230 via the supply pipe 220. That is, the mixed gas of N ₂ and H _{2 is} injected at a predetermined ratio through the gas supply unit 200 to a pressure atmosphere of 0.05 to 10 Torr, and the gas is supplied to the jig base 620 through the feed- The electrode of one polarity, preferably the cathode, is connected and the other electrode is connected to the chamber 100. The specific gravity of the N ₂ gas in the injected N ₂ and H ₂ mixed gas is 10 to 100% by volume, and the diameter of the hollow object 900 to be nitrided to a process pressure in the range of 0.05 to 10 Torr Or by changing the process pressure according to the characteristics of the nitride layer required by the product.

When a power source 400 is operated to apply a constant electric power, a plurality of workpieces 900 connected in series serve as one hollow cathode due to the shape thereof, causing a hollow cathode discharge to induce a plasma to the inner wall surface of the hollow body A plasma is formed in the hollow or engraved part without any extra effort. Therefore, the nitrogen injected into the chamber can be made into an atomic state through the effect of the hollow cathode discharge (HCD) formed directly on the inner wall surface of the object 900 to form a uniform nitride layer on the inner surface of the hollow body or the intaglio member have.

At this time, the value of the applied power may be 5 to 100 kW. The value of the applied electric power is increased in proportion to the quantity and total surface area of the object 900 to be charged. The electric power value to be applied may vary depending on the material type of the material to be processed and the heat treatment conditions. However, in the case of the hollow body 900 to be processed of the same material, the proper voltage value is kept constant , And the total power value is increased by a method of increasing the current value.

The negative electrode applied to the jig system is a direct current (DC) or pulse voltage and reaches the hollow object 900 to be fixed to the jig frame 620 to form a glow discharge and a hollow cathode discharge on the inner diameter surface, Due to the exothermic phenomena and the high ion density, nitrogen penetrates and diffuses into the inside surface of the hollow body, and a nitrogen compound layer and a nitrogen diffusion layer are formed.

Since the present invention provides a hollow cathode discharge in the wall surface of the object 900 to supply the energy required for nitriding the wall surface in the object to be treated by the discharge, it is unnecessary to separately perform the heat treatment process, A sufficient nitriding quality can be obtained, and the process is carried out at room temperature without the need to provide a separate heater in the process chamber 100.

Immediately after the nitriding process, nitrogen gas is injected into the process chamber 100 up to 100 to 400 Torr. After the nitriding process, the nitrogen gas is circulated through the cooling fan 800 mounted in the chamber, The object to be processed 900 is cooled. And the introduction of an inert N ₂ gas through the gas injection unit 200 utilized under convection atmosphere in the heat transfer medium the hollow body to be processed 900, the jig system and rapidly cooling the remaining atmospheric gas in the vacuum chamber 100 .

Cooling in the chamber 100 as described above makes it possible to maintain the quality of the nitrided film of the nitrided object 900 to be excellent. When exposed to the atmosphere at a high temperature, the film is oxidized or reacted with other components, And the like can be prevented. And a cooling step in which the internal temperature of the chamber is naturally cooled so as to reach at least about 150 캜 or less immediately after the nitriding process.

After the nitriding process and the cooling process are completed, the vent and the hollow body 900 to be vacuumed are introduced into the vacuum chamber 100 by injecting atmospheric gas and low-purity N ₂ gas into the vacuum chamber 100 at room temperature and atmospheric pressure, Proceed with unloading.

Hereinafter, the operation and effect of the present invention will be described in more detail with reference to examples of specimen production.

The object 900 on which the inner diameter portion nitriding process of the hollow body using the hollow cathode discharge effect of the present invention proceeds includes SCM415 and an iron (Fe) based metal including SUS and STD steel, aluminum (Ai), titanium (Ti) , Chrome (Cr), and the like.

The shape of the object 900 to be subjected to the inner diameter portion nitriding process of the hollow body using the hollow cathode discharge effect may be a cylindrical shape with a diameter of several to several hundreds of mm and a length of 50 to 1,000 mm, The present embodiment is a process for nitriding the forged SCM415 steel having a diameter of 20 mm and a length of 170 mm as a material to be processed.

1,000 SCM415 steel specimens were prepared and charged into the vacuum chamber 100. The specimens were fixed to the jig system at regular intervals. The hollow specimens were moved to the inside of the neck to facilitate the movement of the process gas Both holes are open and are fixed to the jig frame 600 at the side or both of the holes of the specimen 900 for the hollow body to be nitrided to be applied, .

Each of the jig frames 600 of the jig system is plate-shaped and supports five jig frames 600 by fixing 200 specimens of the hollow body 900 to one jig frame 600 to form one 1,000 specimens were processed in the chamber.

The process pressure is set to 500 to 700 mTorr with uniform pressure throughout the entire range, and such an appropriate pressure is a very important parameter for uniform quality nitriding in many specimens.

The power was applied to the jig to supply 5 to 100 kW power, and it was confirmed whether or not the process was favorably proceeded in the nitriding process. The nitriding process was carried out by discriminating whether the uniformity of the discharge was uniform and the color and brightness represented by the hollow cathode discharge and plasma. And in the case of the SCM 415 hollow metal product nitriding process for a more precise implementation of the present embodiment, a hollow cathode discharge and a plasma shape as shown in Fig. 2 appeared. At this time, it is found that the shape of the hollow body 900 to be processed has a greater dominance than the type of the material in the hollow cathode discharge shape.

When it is confirmed that a proper hollow cathode discharge is formed as shown in FIG. 2, the nitriding process is performed according to the depth of nitridation and the type of nitridation to be realized. The nitriding depth is proportional to the nitriding time, and the nitriding process is carried out for a suitable time in accordance with the intended use and required characteristics of the hollow body 900 to be processed. The nitriding process of the SCM 415 hollow metal product of the present example was conducted for 2 hours and the process was performed while keeping the output voltage constant in the range of 300 to 650 V while maintaining the process pressure and the gas composition ratio constant.

After completion of the nitriding process, N ₂ gas of low purity is injected into the vacuum chamber 100, inert N ₂ gas is injected at an internal pressure of about 200 to 400 Torr, the cooling fan 800 is operated, . The N ₂ gas filled in the vacuum chamber 100 acts as a heat transfer medium and flows in the convection atmosphere by the cooling fan 800 to the inside of the hollow body 900, And is transferred to and exchanged with the outer wall of the vacuum chamber 100 provided with the cooling line to enable rapid cooling.

In SCM 415 hollow metal products, cooling by the use of cooling fan (800) was applied for 1 hour. After confirming the internal temperature of the chamber which was lowered to 100 ° C or less, ventilation was performed and taken out of the vacuum chamber (100) .

The results of the internal nitriding treatment of the above-mentioned SCM 415 hollow metal product are shown in FIGS. 3 to 6, and FIGS. 4, 5 and 6 show the result of the internal nitriding treatment after 5% (Fig. 3) and photographs of the inner diameter portion of the nitrided tissue (Fig. 4, photographs of the inner diameter portion of the nitrided tissue, the total depth of penetration of the nitrified nitrifying agent can be divided to about 360 탆) The hardness of the inner diameter portion of the product before and after the product (FIG. 5a: the hardness of the surface portion of the SCM415 hollow metal product before the nitriding treatment: 250.4 HV 0.3 kgf, FIG. 5b: the surface hardness of the SCM415 hollow metal product after the nitriding process: 663.7 HV 0.3 kgf), a photograph of the depth-direction deepness hardness measurement from the inner diameter surface (FIG. 6: photograph of SCM415 hollow core section hardness distribution measurement after nitriding, hardness measurement load 0.05 kgf) and graph of FIG. 7 (SCM 415 hollow body nitriding treatment After In diameter depth direction deeper hardness distribution graph) it is the analysis result according to the embodiment.

The analysis results after the nitriding treatment show that the nitriding treatment of SCM 415 steel (hardness before nitriding: about 250 HV 0.05 kgf) for forging is about 3 hours including cooling time (2 hours of nitriding, 1 hour of cooling) It was confirmed that the nitriding layer having a total penetration depth of 300 μm or more and a hardness value of 550 HV or more and an effective penetration depth of 60 μm or more was formed only by the process application. This can be a great advantage in terms of nitriding efficiency, mass productivity, energy consumption, and eco-friendly process compared with the inner diameter nitriding processes which have been required for several tens of hours. It can be applied to various materials such as nonferrous metals.

It is to be understood that the invention is not limited to the disclosed embodiment, but is capable of many modifications and variations within the scope of the appended claims. It is self-evident.

100: chamber
200: gas supply part
210: Valve
220: supply pipe
230: Gas nozzle
300: Vacuum exhaust pipe
310: Vacuum pump
400: Power supply
500: Feedthrough
600, 610: jig frame
620: jig base
700: jig insulator
800: Cooling fan
900: the material to be treated

Claims (6)

A vacuum chamber;
A conductive jig installed in the vacuum chamber;
A plurality of conductive objects to be contacted with and fixed to the conductive jig, the conductive objects having a hollow portion or an engraved portion;
A gas supply connected to the vacuum chamber;
A power supply device,
One of the positive electrode and the negative electrode of the power source device is connected to the vacuum chamber and the other is connected to the conductive jig to supply power,
A process gas containing nitrogen is supplied through the gas supply unit to cause a hollow cathode discharge in each hollow or intaglio part of the plurality of to-be-processed objects, thereby nitriding the inner wall surface of the hollow part or the wall surface of the intaglio part,
Wherein the heat treatment is not performed by a separate heating device for the nitriding treatment. The inner diameter nitriding system according to claim 1, wherein the conductive jig is supported by an insulator in the vacuum chamber. delete [2] The apparatus of claim 1, wherein the conductive jig includes a plate-shaped jig frame, the plate-shaped jig frame has a plurality of holes, and a plurality of conductive hollow bodies or engraved members are fixed to the holes And the inner diameter of the inner diameter of the inner diameter of the inner diameter of the inner diameter portion. The method of claim 1, wherein, in the power supply for the nitriding process, the nitriding degree of the hollow body or the intaglio members, which are the object to be processed, is controlled by controlling the applied voltage, Wherein the nitriding treatment is performed by increasing the current. 2. The method of claim 1, wherein nitrogen and hydrogen are introduced into the vacuum chamber, the nitrogen fraction in the injected gas is 10 to 100% by volume, the process pressure is maintained in the range of 0.05 to 10 Torr, Of the inner diameter of the inner diameter portion of the inner diameter of the inner diameter portion of the inner diameter portion of the inner diameter portion.

Images