KR20140045072A - Method and system for nitriding bore of pipe with hollow cathode discharge - Google Patents

Abstract

The present invention relates to a technique of nitriding the inner surface of an object having a depth of a pipe and, more specifically to a technique of nitriding a bore with hollow cathode discharge (HCD). A hollow body or an engraved member which is subjected to nitridization is itself, used as a cathode, and a conductive jig system is designed to fix thousands of workpieces. Power is applied to the jig system, and the hollow or the engraved member itself functions as the hollow cathode, so that the inner surface of the cathode member is nitrided by the plasma generated by the hollow cathode discharge formed in the inner space.

Description

METHOD AND SYSTEM FOR NITRIDING BORE OF PIPE WITH HOLLOW CATHODE DISCHARGE}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for nitriding an inner wall surface of an object having a depth such as a pipe, and more particularly, to a method and an apparatus for internal nitridation using Hollow Cathode Discharge (HCD).

Automotive, aircraft, and other mechanical parts are in the form of pipes, tubes, or engraved shapes, and the durability of these parts is often required on their inner walls. Nitriding is a typical surface treatment that gives hardness and corrosion resistance to metal parts, and nitriding is a technology that requires high process control in actual implementation. Plasma nitridation may be preferable in terms of process efficiency and quality of nitriding depth, but internal diameter nitriding of the intaglio portion is not easy.

In general, nitriding is a processing method of forming nitrides by diffusion of nitrogen on metal surfaces to improve surface hardness, corrosion resistance, abrasion resistance, fatigue strength, and the like. Unlike other surface hardening methods such as carburization and high frequency heat treatment, the transformation point of steel (A ₁ transformation point: Because it is processed at a temperature of 723 ° C. or less (less than 600 ° C.), heat deformation is small, so it is widely used in precision machine parts, automobile parts, and molds. Nitriding is a diffusion penetration method that is clearly distinct from the surface coating method of modifying the surface by depositing a hard or functional material on the surface of the material.

Nitriding can be classified into gas nitriding, liquid nitriding (salt nitriding), and plasma nitriding (ion nitriding). Among these, in the case of gas nitriding, a nitride layer is formed on a metal product by exposing it for several tens of hours in a gaseous ammonia (NH ₃ ) atmosphere heated to about 560 to 580 ° C. It has the advantages, but it takes a long time to realize the commercialization characteristics, and can be applied only to a dedicated material, there is a disadvantage that a post-treatment device is required due to the use of ammonia gas, a harmful substance.

The advantage that into the metal product to a salt can be a way to have the nitriding process in the liquid phase, to form a fairly deep nitride layer in a short time the liquid nitride (salt yokjil screen) is cyanide (CN ^{- -)} or cyanate (CN) However, due to the formation of a porous nitrogenous compound layer, its use is gradually decreasing in that post-treatment is necessary and that toxic substances are used.

Plasma nitriding (ion nitriding) is a method of forming a nitride layer in a metal product using nitrogen ions formed by glow discharge, which is difficult to operate and requires high installation cost, but has high energy nitrogen Treatment with ions can shorten the treatment time, control the structure and depth of the nitride layer, and in particular, there is no harmful substances and pollution, and the proportion thereof is gradually increasing compared to other nitriding technologies.

On the other hand, the surface treatment using the hollow cathode discharge phenomenon of the plasma surface treatment technology has been recognized to be unfavorable because of the high failure rate due to local overheating or damage to the product due to the unique strong discharge.

In addition, when attempting the surface treatment of the intaglio portion of the hollow cathode discharge phenomenon, as shown in the Republic of Korea Patent Application Publication No. 10-2008-0098826, since the cathode for the discharge is provided in the pipe to produce a hollow cathode discharge, the processing of the cathode itself However, it is unsuitable for mass production processing due to equipment cost and effort due to installation.

Therefore, an object of the present invention is to simplify the inner wall surface of the intaglio member by using hollow cathode discharge and high-density nitriding treatment technology in a fast time intensively without the additional heating process by high density ion concentration and heat generation Is to provide.

It is still another object of the present invention to provide a mass-produced nitriding technique for the inner diameter of metal parts including hollow bodies and other engraved metal products. It is formed uniformly throughout the chamber, so that it is possible to carry out nitriding treatment of thousands of units in a single process.

In accordance with the above object, the present invention uses the intaglio member itself to be nitrided as a cathode, and applies a power thereto to nitride the inner wall surface of the cathode member with a plasma generated by generating a hollow cathode discharge in the hollow body or the space inside the intaglio member. To be treated.

That is, the present invention,

A vacuum chamber;

A conductive jig installed in the vacuum chamber;

A plurality of conductive hollow bodies or intaglio members fixed in contact with the conductive jig and fixedly disposed in one conductive jig;

A gas supply unit connected to the vacuum chamber; and

A power supply;

One of the anode and the cathode of the power supply device is connected to the vacuum chamber, the other is connected to the conductive jig to supply power,

By supplying a process gas including nitrogen through the gas supply unit, the hollow cathode discharge to the hollow or intaglio of the plurality of conductive hollow body or intaglio member to nitriding the hollow inner wall surface or the intaglio inner wall surface An internal hardening treatment system can be provided.

In another aspect, the present invention, it is possible to provide an internal nitriding treatment system, characterized in that the conductive jig is supported by an insulator in the vacuum chamber.

In addition, the present invention, the nitriding treatment is carried out at room temperature, it is possible to provide an internal nitriding treatment system, characterized in that no separate heat treatment apparatus is provided in the vacuum chamber.

In addition, the present invention, the conductive jig, the plate-shaped jig frame, the plate-shaped jig frame, has a plurality of holes (hole), a plurality of conductive hollow body or intaglio members are fixed to the hole An internal diameter nitriding treatment system can be provided.

In addition, the present invention, in the power supply for the nitriding treatment process, the degree of nitriding for the hollow body or the intaglio member to be treated is controlled by adjusting the applied voltage, and applied according to the increase in the number of the workpieces in the vacuum chamber It is possible to provide an internal diameter nitriding treatment system characterized in that the nitriding treatment is performed by increasing the current.

In addition, the present invention, in the vacuum chamber, nitrogen and hydrogen are injected, 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 5 to 100 kW An internal diameter nitriding treatment system may be provided by applying electric power to nitriding treatment.

In addition, the present invention can provide an inner diameter nitriding treatment system characterized in that after the nitriding treatment is finished, the workpiece is cooled in the vacuum chamber and then unloaded from the vacuum chamber.

According to the present invention, by using a workpiece such as a pipe forming a hollow body as a cathode to produce a hollow cathode discharge to nitriding the inner wall of the hollow body with high quality, and does not require a separate cathode electrode configuration, the installation is simple For example, since a plurality of objects to be treated in one chamber are fixed to the conductive jig and processed simultaneously at once, the mass productivity is very high.

In addition, since the present invention induces the nitriding characteristics of the inner wall of the hollow body to a desired level by controlling the hollow cathode discharge by controlling the applied voltage, it is possible to perform nitriding treatment at room temperature without requiring a separate heat treatment process that is commonly performed in nitriding treatment. Process simplification is also an advantage.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing for demonstrating the nitriding treatment apparatus of this invention.
2 is a photograph of a hollow cathode discharge shape generated in a plurality of hollow bodies according to the present invention.
Figure 3 is a photograph of the appearance of the contrast of the results corroded by 5% nital after processing to observe the cross-sectional structure after the internal nitridation treatment according to the present invention.
Figure 4 is an internal diameter cross-sectional nitriding tissue photograph according to the present invention.
5a and 5b is a comparison of the internal diameter surface hardness of the product before and after the nitriding treatment according to the present invention (Fig. 5a; surface hardness of the internal diameter of the SCM415 hollow metal product before nitriding treatment; 250.4 HV 0.3 kgf, Figure 5b; nitriding treatment SCM415 hollow metal product inner diameter surface hardness; 663.7 HV 0.3 kgf).
6 is a photograph of depth-depth core hardness measured from the inner diameter surface after nitriding treatment according to the present invention.
7 is a graph of inner diameter depth direction core hardness distribution after nitriding treatment according to the present invention.

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

1, the structure of the apparatus for nitriding by the hollow cathode discharge of this invention is shown by sectional drawing.

The 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 source 400, and a conductive jig system is installed inside the vacuum chamber 100. The conductive jig system is a jig frame (600, 610) is connected to form an electrical closed loop as a whole, it can be configured to have a plurality of closed loops in one closed loop. The conductive jig system is constructed based on a plate-shaped jig base 620 to which one polar terminal of the power supply 400 is connected, and the jig base 620 is isolated from the chamber 100 body by the insulator 700. do. The to-be-processed object 900 having the hollow body or the intaglio portion is fixed to the jig frame 600 to be nitrided, and can be charged with a large number of to-be-processed objects 900, which is very suitable for mass production. Since the cooling of the workpiece 900 after the process is carried out in the chamber 100 is particularly advantageous, the cooling fan 800 may also be provided.

The vacuum exhaust pipe 300 is connected to the vacuum pump 310 from the vacuum chamber 100, the rotary pump to implement the initial vacuum (10 Torr or less) from the atmospheric pressure, the vacuum pump 310 as a booster pump to implement the process vacuum degree ) Can be configured.

Hereinafter, the nitriding treatment step will be described in detail with the principle thereof.

First, a plurality of metal workpieces 900 which are hollow or engraved are fixed to the jig frame 600 on a plate at regular intervals and loaded into the chamber 100. The jig frame 600 has a circular or rectangular plate as a basic structure, and a number of suitable holes are drilled therein, and the hollow jig frame 600 is inserted into and fixed to the plate-shaped jig frame 600. Layers are stacked at intervals and fixed to the pillar-shaped jig frame 610.

When the jig system is disposed inside the vacuum chamber 100, the vacuum chamber 100 and the jig system must be insulated from the vacuum chamber 100 which is in contact with the electrode opposite to the jig system and becomes grounded. The jig insulator 700 is positioned between the jig bases 620 so that the jig system maintains an insulated state from the vacuum chamber 100 and an energized state with the power source 500. The configuration of the jig insulator 700 may be made of other insulators including ceramics, and should have sufficient durability to withstand the load of the hollow workpiece 900 to which the jig system and the nitriding treatment are to be applied.

Next, the inside of the chamber 100 is vacuumed with a vacuum pump 310 at a vacuum of about 0.05 Torr to 10 ⁻⁴ Torr.

The gas supply is supplied by adjusting the flow rate through the valve 210 to the gas injection port 230 through the supply pipe 220. That is, the N ₂ and H ₂ mixed gas is injected at a predetermined ratio through the gas supply unit 200 to make a pressure atmosphere of 0.05 to 10 Torr, and the feed through 500 is applied to the jig base 620 to supply the power 400. An electrode of one polarity, preferably a 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 body 900 to which the nitriding treatment is to be applied is applied to a process pressure of 0.05 to 10 Torr. Can be controlled by varying the process pressure depending on the nitriding layer properties required by the product.

When a predetermined power is applied by operating the power source 400, the plurality of workpieces 900 connected in series each act as one hollow cathode due to its shape to generate a hollow cathode discharge, thereby inducing plasma to the inner wall of the hollow body. Plasma is formed in the hollow or intaglio without any extra effort. Therefore, through the effect of hollow cathode discharge (HCD) formed directly on the inner wall surface of the workpiece 900, the nitrogen injected into the chamber can be made atomic so that a uniform nitride layer can be formed on the inner wall 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 power is increased in proportion to the quantity and the total surface area of the workpiece 900 to be charged. The power value applied may vary depending on the type of material and heat treatment conditions of the object, but in the hollow body object 900 of the same material, the appropriate voltage value for each material is kept constant as the number of charges increases. And increase the total power value by increasing the current value.

The cathode applied to the jig system is a direct current (DC) or a pulse voltage, and reaches the hollow workpiece 900 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 phenomenon and the high ion density, nitrogen penetrates and diffuses into the inner surface of the inner diameter of the hollow body, forming a nitrogen compound layer and a nitrogen diffusion layer.

The present invention generates a hollow cathode discharge on the inner wall of the workpiece 900 to supply all the energy required for nitriding the inner wall of the workpiece by discharge, so that the heat treatment process that is commonly provided in the nitriding process does not need to be performed separately. A sufficient nitriding quality can be obtained, and the process is performed at room temperature without the need to install a separate heater in the process chamber 100.

Immediately after the nitriding process, nitrogen gas is injected into the process chamber 100 up to 100-400 Torr, and after the nitriding treatment, the nitrogen gas is operated to cause convection by operating a cooling fan 800 mounted inside the chamber. The workpiece 900 is cooled for a time. While inert N ₂ gas is injected through the gas injection unit 200, the atmospheric gas remaining in the hollow body to be processed 900, the jig system, and the vacuum chamber 100 is rapidly cooled under a convection atmosphere. .

Cooling in the chamber 100 as described above enables the quality of the nitride film of the nitrided workpiece 900 to be excellently maintained, which, when exposed to the atmosphere at a high temperature, causes the film to oxidize or react with other components to discolor. This is because degeneration of the back can be prevented. Thus, a cooling step is provided to naturally cool the chamber to reach at least less than about 150 ° C. immediately after the nitriding process.

After the nitriding and cooling process is completed, the vent and the hollow workpiece 900 to release the vacuum degree by injecting atmospheric gas and low purity N ₂ gas into the vacuum chamber 100 at room temperature and atmospheric pressure are taken out. Unloading proceeds.

Hereinafter, the operation and effects of the present invention will be described in more detail with reference to the embodiment for preparing the specimen as follows.

The workpiece 900 to which the internal diameter nitriding of the hollow body is processed using the hollow cathode discharge effect of the present invention is made of SCM415, iron (Fe) -based metals including SUS and STD steels, aluminum (Ai) and titanium (Ti). It may be a metal material capable of forming non-ferrous metal nitrides, such as chromium (Cr).

The shape of the workpiece 900 subjected to the internal diameter nitriding of the hollow body using the hollow cathode discharge effect is a hollow body having a cylindrical shape or similar shape having a diameter of several to several hundred mm and a length of 50 to 1,000 mm. It is a processed metal product. In this embodiment, nitriding treatment was performed using a forged SCM415 steel in the form of a pipe having a diameter of 20 mm and a length of 170 mm.

1,000 specimens of SCM415 steel were prepared and loaded into the vacuum chamber 100, and the specimens were fixed to the jig system at regular intervals. In this case, the hollow body specimens were used to smoothly move the process gas to the inner diameter. Both holes were open and fixed to the jig frame 600 in a position to allow the sides or both holes of the hollow workpiece 900 to be nitrided to be opened. You have to.

Each jig frame 600 of the jig system has a plate shape, and 200 pieces of the hollow workpiece 900 are fixed to one jig frame 600 to support five jig frames 600 to support one overall. 1,000 specimens were processed in the chamber.

The process pressure was 500 ~ 700mTorr with uniform pressure in the whole range. This proper pressure is a very important variable for uniform quality nitriding on many specimens.

The power was applied to the jig to supply 5 ~ 100kW power, and it was confirmed whether or not the desired process progressed during the nitriding treatment process, and the nitriding process was performed by determining whether the hollow cathode discharge was uniformly distributed, and the color and brightness indicated by the hollow cathode discharge and the plasma. In the case of SCM 415 hollow metal product nitriding treatment for a more clear implementation of the present embodiment, the hollow cathode discharge and the plasma shape as shown in FIG. 2 appeared. In the hollow cathode discharge shape at this time, it was found that the shape of the hollow workpiece 900 had a greater control than the type of material.

When it is confirmed that an appropriate hollow cathode discharge is formed as shown in FIG. 2, the nitriding treatment process is performed according to the nitriding depth and the nitriding form to be maintained by maintaining it. The nitriding penetration depth is proportional to the nitriding treatment time, and nitriding treatment is performed for an appropriate time in accordance with the intended use and required characteristics of the hollow object to be processed 900. Nitriding treatment of the SCM 415 hollow metal product of the present embodiment was carried out for 2 hours, the idle power value was applied to maintain the output voltage in the range of 300 to 650V, and the process pressure and injection gas composition ratio were kept constant.

After completion of the nitriding process, low-purity N ₂ gas is injected into the vacuum chamber 100 and filled with an inert N ₂ gas from about 200 to 400 Torr of internal pressure, and the cooling fan 800 is operated to cool the convection atmosphere. Proceeded. The N ₂ gas filled in the vacuum chamber 100 serves as a heat transfer medium, and heats the hollow workpiece 900 and the jig system and other heated zones in the convection atmosphere by the cooling fan 800. Transfer to and replace the outer wall of the vacuum chamber 100 having a cooling line to enable fast cooling.

In the SCM 415 hollow metal products, cooling by using the cooling fan 800 was applied for 1 hour, and after confirming the temperature inside the chamber lowered to 100 ° C. or lower, proceed with aeration and take out the vacuum chamber 100 to a representative specimen. The analysis was conducted.

3 to 6 show the internal diameter nitriding treatment of the SCM 415 hollow metal product, and FIGS. 4, 5, and 6 are 5% nital after processing to observe the cross-sectional structure after internal nitriding treatment, respectively. The external photograph of the hollow body corroded by (Fig. 3) and the internal diameter cross section nitrided tissue picture (Fig. 4; internal diameter cross section nitrided tissue picture, can be distinguished up to about 360μm in the total nitride penetration depth visually distinguished), nitriding treatment Comparison of the surface hardness of internal diameter of the product before and after (Fig. 5a; Internal hardness of SCM415 hollow metal product before nitriding; 250.4 HV 0.3 kgf, Fig. 5b; Internal hardness of SCM415 hollow metal product after nitriding; 663.7 HV 0.3 kgf), depth depth measurement from the inner diameter surface (Fig. 6; SCM415 hollow body cross-sectional hardness distribution measurement after nitriding treatment, hardness measurement load 0.05kgf) and the graph of Fig. 7 (SCM 415 hollow body nitriding application After In diameter depth direction deeper hardness distribution graph) it is the analysis result according to the embodiment.

In the analysis result after the nitriding treatment, the nitriding treatment of SCM 415 steel (material hardness before nitriding: about 250 HV 0.05 kgf) by forging about 3 hours (2 hours nitriding, 1 hour cooling) including cooling time Through the application alone, it was confirmed that a nitride layer having an overall penetration depth of 300 μm or more and an effective penetration depth of 60 μm or more having a hardness value of 550 HV or more was formed. This can be a great advantage in terms of nitriding efficiency, mass productivity, energy consumption reduction, and eco-friendly processes compared with internal nitriding processes that required up to several tens of hours. It can be applied to various materials such as non-ferrous metals, and its range of use is expected to be considerable in the future.

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 unit
210: valve
220: supply pipe
230: gas nozzle
300: vacuum exhaust pipe
310: vacuum pump
400: power
500: feed through
600, 610: jig frame
620: jig base
700: jig insulator
800: cooling fan
900: object to be processed

Claims (6)

A vacuum chamber;
A conductive jig installed in the vacuum chamber;
A plurality of conductive hollow bodies or intaglio members fixed in contact with the conductive jig and fixedly disposed in one conductive jig;
A gas supply unit connected to the vacuum chamber; and
A power supply;
One of the anode and the cathode of the power supply device is connected to the vacuum chamber, the other is connected to the conductive jig to supply power,
By supplying a process gas including nitrogen through the gas supply unit, the hollow cathode discharge to the hollow or intaglio of the plurality of conductive hollow body or intaglio member to nitriding the hollow inner wall surface or the intaglio inner wall surface Internal nitriding treatment system. The internal nitriding treatment system of claim 1, wherein the conductive jig is supported by an insulator in the vacuum chamber. The internal nitriding treatment system according to claim 1 or 2, wherein the nitriding treatment is performed at room temperature, and a separate heat treatment apparatus is not provided in the vacuum chamber. The jig frame of claim 3, wherein the conductive jig includes a plate-shaped jig frame, and the plate-shaped jig frame includes a plurality of holes, such that the plurality of conductive hollow bodies or the intaglio members are fixed to the holes. Internal nitriding treatment system, characterized in that. The method of claim 3, wherein in the application of power for the nitriding treatment process, the degree of nitriding of the hollow body or the intaglio members to be processed is controlled by adjusting an applied voltage, and applied according to an increase in the number of objects in the vacuum chamber. Internal nitriding treatment system characterized in that the nitriding treatment by increasing the current. According to claim 3, Into the vacuum chamber, nitrogen and hydrogen are injected, 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, 5 to 100 kW of Internal nitriding treatment system, characterized in that the nitriding treatment by applying electric power.

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