KR101467060B1 - Plasma heating type haeting furnace with hollow heater - Google Patents

Abstract

The present invention relates to an energy-saving plasma tempering furnace system in which a metal part such as a metal mold of the present invention is heat-treated using plasma.
According to the present invention, a plasma screen is provided with a hollow screen for generating plasma and auxiliary heaters arranged on the outside thereof. The temperature is raised by an auxiliary heater at the beginning of tempering, and when a temperature is reached, plasma is generated to keep the temperature in the vacuum chamber constant, Tempering was carried out. In order to keep the temperature constant, the PID control method was adopted to measure the cooling water temperature and feed back the temperature.
The vacuum tempering of the present invention is advantageous in that it can save a great deal of energy because there is little energy loss, and the lifetime of equipment is also prolonged.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a plasma heating method using a hollow heater,

More particularly, the present invention relates to a heating furnace for performing vacuum cold tempering and high temperature tempering of steel parts after metal mold, vacuum carburization and vacuum heat treatment of the present invention, more specifically, The present invention relates to a plasma heating type heating furnace system that reduces both the performance and the dispersion of the product in the next process such as the reduction of the post-processing, thereby simultaneously saving resources and saving energy.

The mold and machine parts are made of steel material, which must undergo quenching and tempering (Q / T) heat treatment. As the heat treatment method of high-grade mold material has already been generalized to vacuum heat treatment, and automobile parts such as vacuum carburizing are becoming more and more advanced, development of technology for upgrading the quality of vacuum by increasing the quality of vacuum is rising. On the other hand, in the case of tempering, a heating heater such as a low-cost nichrome or a cantal is attached to heat the substrate using radiant heat as a heat source. However, since the amount of radiation of the heater is low at low temperatures, it is difficult to maintain the temperature. There is a problem that an oxide layer is formed at a low temperature due to moisture or oxygen contained in the nitrogen. If a vacuum tempering device is incorporated by inserting a fan, there is a problem that the cost of the equipment is increased.

In the case of metal molds, several methods of vacuum tempering have been introduced to reduce or eliminate surface oxide films. However, heating methods including a heater, a reflector, and a heat insulating material after vacuum are generally used (for example, Korean Patent Laid- 0104876). In this case, it is difficult to maintain a constant temperature suitable for tempering at a low temperature region, that is, about 200 to 600 ° C. This is because the radiation pattern of the heater is not constant at low temperatures. Rather, at low temperatures, a hot air blow or an oven type is suitable. This is because it is difficult for the heater to emit heat at low temperatures.

Theoretically, there is a case of application to a high temperature heating using a glow discharge or a plasma nitriding process, but there is no case used in vacuum tempering. In the case of low temperature tempering in the conventional radiant heating method, since the technique of maintaining the tempering temperature in a reflection form is used, there is a problem that a lot of heat is emitted to the furnace wall, or in the case of the direct heating method, .

Accordingly, an object of the present invention is to provide a heating furnace system of a plasma heating method capable of performing tempering while maintaining a constant temperature within a temperature range of about 200 to 600 ° C. Another object of the present invention is to provide a heating furnace system of a plasma heating type which can minimize heat treatment efficiency and energy loss by a combination design of a structure of a heating furnace, an arrangement of auxiliary electrodes, and a power application method.

Accordingly, in the present invention, an auxiliary heater is further provided in addition to the plasma generating hollow screen. In the initial tempering step, the temperature is raised and tempered by the auxiliary heater. When the temperature is stabilized by the rise to some extent, plasma is generated to perform plasma tempering In order to prevent the problematic arc discharge when the plasma tempering is performed from the beginning and to maintain a certain level of the tempering temperature, the temperature was controlled by the PID control method.

That is,

A vacuum chamber;

A hollow screen installed in the vacuum chamber;

A plurality of auxiliary heaters arranged outside the hollow screen; And

And a power supply for applying electric power to the hollow screen and the auxiliary heater,

An object gas to be tempered is placed in the hollow screen, an auxiliary gas containing hydrogen is introduced to start tempering at the initial stage of the tempering operation, the tempering is started by raising the temperature of the auxiliary heater,

Thereafter, power is applied to the hollow screen to generate plasma to perform plasma tempering, thereby providing an energy-saving plasma heating type heating furnace system.

In order to maintain the tempering temperature constant in the vacuum chamber, the temperature is checked using a temperature sensor, and the temperature change is fed back to the auxiliary heater and the electric power applied to the hollow screen Can be controlled by a PID control method.

In addition, the present invention can provide an energy saving plasma heating type heating furnace system, wherein the hollow screen includes at least one of a porous screen and a mesh screen.

Further, the present invention is characterized in that the wall surface of the vacuum chamber includes a passage through which cooling water can flow, a cooling water inlet and an outlet, and checks a difference between the cooling water temperature before the introduction and the outflow cooling water temperature, As a feedback, the energy to be applied to the auxiliary heater and the hollow screen is controlled by a PID control method, thereby providing an energy saving plasma heater type heating furnace system.

In addition, the present invention can provide an energy saving plasma heating type heating furnace system, wherein the reflector is provided outside the auxiliary heater, and the reflector is a quadruple reflector made of stainless steel.

In addition, the present invention can provide an energy saving type plasma heating type heating furnace system, wherein the tempering temperature is maintained at a constant temperature of about 150 to 600 ° C.

Further, the present invention can provide an energy saving type plasma heating type heating furnace system, wherein the temperature reached by operating the auxiliary heater at an initial stage of tempering is set to about 150 to 180 캜.

Further, according to the present invention,

A hollow screen is provided in the vacuum chamber and a plurality of auxiliary heaters are provided outside the hollow screen,

Placing an object to be tempered in the hollow screen,

In the initial stage of the tempering by adding the additive gas containing hydrogen, the auxiliary heater is operated to start the tempering by raising the temperature,

Thereafter, electric power is applied to the hollow screen to generate plasma to perform plasma tempering, thereby providing an energy-saving plasma tempering method.

Further, the present invention is characterized in that the wall surface of the vacuum chamber includes a passage through which cooling water can flow, a cooling water inlet and an outlet, and checks a difference between the cooling water temperature before the introduction and the outflow cooling water temperature, As a feedback, the power to be applied to the auxiliary heater and the hollow screen is controlled by the PID control method.

According to the present invention, it is possible to maintain the temperature of tempering at a relatively low temperature at a constant level. At the initial stage of tempering, heating is performed using an auxiliary heater to protect the initial plasma electrode, Current and low power, so that it is possible to save the energy, and at the same time, the plasma is heated by the plasma heat source caused by the collision of the atmospheric gas and the electron in the screen.

Fig. 1 is a cross-sectional view and a partial enlarged cross-sectional view schematically showing the construction of a heating furnace of the present invention.
2 is a schematic view showing the construction of a double screen in the heating furnace of the present invention.
3 is a plan sectional view schematically showing the construction of the heating furnace of the present invention.
4 is a cross-sectional view for explaining the cooling system of the heating furnace of the present invention.
5 is a flowchart illustrating a PID control system for maintaining the tempering temperature of the present invention at a constant level.

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

The plasma heating heating furnace system of the present invention has a hollow screen, preferably a double screen, installed in a vacuum chamber, and a plasma is generated by applying electric power thereto to heat the plasma using the energy of plasma generated in the screen. To maintain a uniform temperature, and to temper the object to be processed such as a mold or a machine part located on the inner jig at a predetermined temperature.

The double screen is powered by a hollow electrode having substantially the same potential to generate a plasma at a gap between the screens. The temperature of the plasma is substantially constant as long as the plasma state is maintained stably. Therefore, It is very suitable. In the screen itself, thermal electrons are generated, but the temperature is lower than the plasma temperature, so the tempering is mainly performed by plasma.

However, in spite of the advantage of vacuum tempering using the plasma as described above, arc discharge tends to occur in an initial stage of tempering, i.e., a plasma generating step in which the temperature in the chamber is room temperature. When the arc discharge occurs, the screen temperature in the chamber rises locally so that equipment such as a screen or a power supply device may be damaged. Unlike the intention to temper at a certain temperature, rapid temperature change may be a problem. It happens.

Therefore, the present invention is configured to perform plasma tempering using plasma generation, and further include an auxiliary heater. In the initial process, an auxiliary heater is operated to reach a predetermined temperature, and then plasma is generated to perform stable plasma tempering. That is, the auxiliary heater disposed around the outside of the hollow screen is operated to start the tempering with the temperature in the chamber reaching about 150 to 180 DEG C, and then electric power is applied to the hollow screen to generate plasma to generate a stable plasma, It is possible to prevent arc discharge caused by heating and to perform vacuum plasma tempering at a constant temperature of about 150 to 600 ° C.

Also, in order to maintain the temperature of the vacuum plasma tempering constant, the present invention applies a PID control method that real-time controls the power applied to the auxiliary electrode and the hollow screen by checking the chamber temperature in real time. That is, the outer wall of the chamber is designed as a cooling water passage, and the temperature difference between the cooling water and the cooling water is detected. Simultaneously controlling the auxiliary heater and the plasma generating power based on the preset maximum temperature of the chamber, Is maintained at a constant level.

In the following, matters necessary for the preferable implementation of the present invention such as the equipment configuration of the heating furnace will be described in more detail.

Fig. 1 is a schematic cross-sectional view of a heating furnace of the present invention, and Fig. 2 shows the construction of a double screen employed in the heating furnace of the present invention in more detail.

The double screen is composed of a porous screen 100 having holes 150 and a mesh screen 200 arranged in parallel on the inside or outside thereof. The mesh screen has a plurality of holes 250 do. It is preferable that the diameter of the hole 150 of the porous screen 100 is 15 to 30 mm and the diameter of the hole 250 formed by the mesh is 5 mm. The thickness of the mesh skeleton is about 1 mm, and the holes 150 of the porous screen 100 are covered with a mesh. The interval between the screens may be about 10 to 50 mm, and 30 mm in this embodiment. The above-mentioned double-screen configuration does not cause a shading problem as compared with a single screen or a double-screened screen 100, but it is not essential and it is not essential that the multi- It is possible to use any one of the screens 200 or construct a dual screen with a single kind.

FIG. 3 is a plan view showing a schematic configuration of the heating furnace according to the present invention, showing an auxiliary heater 300 installed outside the dual screen and a reflection plate 350 installed outside the heater. The auxiliary heater 300 is heated by using a joule heat of a hot wire by applying power to the hot wire, which is generally used, by winding it on a rod. A reflector 350 for reflecting the radiation radiated from the auxiliary heater to the outside so as to prevent the radiant heat from being radiated to the outside is provided and a stainless steel plate having a thickness of 1.5 mm is used in consideration of the efficiency of the reflector 350 and the boundary between heating and cooling 4-fold at intervals of 3 mm to obtain a quadruple reflector (350). The distance between the reflection plate 350 and the chamber outer wall 400 is about 30 mm. The auxiliary heater 300 is installed at a distance of 20 to 100 mm, preferably 60 mm, from the double screen, and the distance between the auxiliary heater 300 and the reflection plate 350 is 20 to 70 mm, preferably 50 mm.

In addition, in the case of the present embodiment, power supply to the auxiliary heater 300 is performed on the side of the chamber ceiling.

When the plasma is generated and heated by applying electric power to the hollow double screen during the heat treatment of the object to be processed, the initial resistance is high and the current consumption is large and the power consumption is increased. As described above, there is a fear of arc generation. Accordingly, in the present invention, the auxiliary heater 300 disposed outside the screen is initially operated at the initial stage of the heat treatment, and the temperature is rapidly raised to a low current and a low power to be heat treated, and a predetermined temperature (for example, 150 to 180 ° C) Thereafter, a plasma discharge is generated to perform a plasma heat treatment, so that energy can be saved through the entire process. The applied electric power to the auxiliary heater 300 may be about 120 kW / t, and the applied electric power to the hollow screen for plasma generation may be DC or DC pulse power within 10 to 20 kW irrespective of the weight of the object to be processed, , And the DC or DC pulse applied power may vary depending on the gas pressure.

Materials to be treated mainly include mold steels, such as STD61, STD11, STH51, which are also illustrative and not limiting.

An atmospheric gas containing hydrogen is added to the vacuum chamber provided with the auxiliary heater 300 and the hollow screen for generating plasma, and the substrate is heated (tempering) while maintaining a constant temperature in a low temperature zone, particularly a tempering temperature zone of about 200 to 600 ° C. Thereby realizing energy high efficiency which is characteristic of the plasma heating furnace and having the advantage that all the applied power is transmitted as tempering energy. In particular, the auxiliary heater 300 maintains a uniform amount of heat required for tempering in conjunction with the auxiliary heater 300 on the wall surface of the chamber. The auxiliary heater 300 is not formed of a conventional ceramic block, and is used for an aging process of materials such as aluminum and stainless steel , And high-speed cooling is possible. Unlike the conventional heating method using only a plasma in which the auxiliary heater and the auxiliary electrode are installed, the vacuum heating and plasma generating apparatus is rapidly heated up to a temperature of about 200 to 550 DEG C, which is a temperature at which the hydrogen gas actively acts as a reducing gas, A plasma heater is used to raise the temperature up to the hydrogen reduction temperature and then an auxiliary heater is used to maintain the uniform temperature.

In the present invention, a product is heated using a power source including a reflection plate 350 and an internal double screen, and simultaneously a large amount of active species of hydrogen is used by using the same, and the number of times of collision of electrons in the plasma is increased, It was designed. In this case, if the amount of generated species is changed on the double screen, the amount of active species is reduced. To prevent this, the deficient portion of the certain amount of heat is supplemented in the auxiliary heater operation by energy monitoring, .

 The vacuum tempering of the present invention as described above can maintain a high degree of vacuum and does not require a high current of the conventional SCR type and can raise the temperature to a corresponding temperature by only about 1/3 of the consumed power of the conventional system, The energy loss can be minimized.

Meanwhile, in the present invention, the following temperature control is configured to maintain a constant temperature.

That is, the chamber outer wall 400 has a cooling water passage 500 at an interval to allow cooling water to flow therein, and the inlet ports 550, 551 and 555 and the outflow ports 570, 571 and 575 are formed therein, (For example, 300 DEG C) is set in advance, and the cooling water temperature before the inflow and the cooling water temperature flowing out are measured, and the electric power applied to the auxiliary heater 300 and the hollow screen . Figure 4 illustrates the cooling water flow of the present invention well. The inlet ports 550, 551 and 555 and the outlet ports 570 and 571 and 575 are formed at the lower end of the chamber, the middle portion and the upper end, respectively, , 571 and 575, respectively.

The temperature control was controlled by a PID control method in which the applied electric power and the amount of electric power to be applied to the hollow screen were obtained by differentiating and integrating the temperature variable when the auxiliary heater was turned on and off. Further, the amount of heat loss is calculated by checking the water temperature rise amount, and the power is controlled to be supplied only to the minimum change width of the energy. Here, a control system using the calorimetric equation was constructed (see FIG. 5).

Thus, high-efficiency energy-saving tempering can be performed.

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

100: Porous screen
150, 250: hole,
200: Mesh screen
300: auxiliary heater
350: reflector
400: chamber outer wall
500: Cooling water passage
550, 551, 555: (cooling water) inlet
570, 571, 575: (cooling water) outlet

Claims (9)

A vacuum chamber;
A hollow screen having a double structure spaced apart from the screen, the hollow screen including a porous screen or a mesh screen;
A plurality of auxiliary heaters arranged outside the hollow screen; And
And a power supply for applying electric power to the hollow screen and the auxiliary heater,
An object gas to be tempered is placed in the hollow screen, an auxiliary gas containing hydrogen is introduced to start tempering at the initial stage of the tempering operation, the tempering is started by raising the temperature of the auxiliary heater,
Thereafter, electric power is applied to the hollow screen to generate a plasma by using a double hollow screen as a plasma generating electrode to perform plasma tempering,
Wherein the dual structure hollow screen is constituted by a porous screen, a mesh screen, a porous screen, a porous screen or a mesh screen and a mesh screen. The method as claimed in claim 1, wherein, in order to maintain a constant tempering temperature in the vacuum chamber, the temperature is checked using a temperature sensor, and the power applied to the auxiliary heater and the hollow screen is controlled by a PID control method And a control unit for controlling the heating unit. delete The vacuum chamber of claim 1, wherein the wall surface of the vacuum chamber includes a passage through which cooling water can flow, a cooling water inlet and an outlet, and checks the difference between the cooling water temperature before the introduction and the outflow cooling water, Wherein the power applied to the auxiliary heater and the hollow screen is controlled by a PID control method. The apparatus of claim 1, wherein the auxiliary heater has a reflector outside the auxiliary heater, and the reflector is a quadruple reflector made of stainless steel. The apparatus according to claim 1, wherein the tempering temperature is maintained at a constant temperature of about 150 to 600 ° C. The apparatus according to claim 1, wherein a temperature at which the auxiliary heater is activated and reached at an initial stage of the tempering operation is set at about 150 to 180 ° C. A hollow screen is provided in the vacuum chamber and a plurality of auxiliary heaters are provided outside the hollow screen,
Placing an object to be tempered in the hollow screen,
The auxiliary heater including the hydrogen gas is charged and the auxiliary heater is operated at the initial stage of the tempering so that the temperature is increased to 150 to 180 ° C to start the tempering,
The method of claim 1, wherein the hollow screen is used as an electrode for plasma generation, and a plasma is generated by applying electric power to perform plasma tempering, thereby maintaining a constant temperature of 150 to 600 캜 during the tempering process. The vacuum chamber as claimed in claim 8, wherein the wall surface of the vacuum chamber includes a passage through which cooling water can flow, a cooling water inlet and an outlet, and checks the difference between the cooling water temperature before the introduction and the outflow cooling water, Wherein the energy applied to the auxiliary heater and the hollow screen is controlled by a PID control method.

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