KR101119497B1 - Heat Treatment Furnace Having a Furnace Gas Circulating Equipment - Google Patents

Abstract

The present invention provides a method for heating the heated gas in the furnace to the outside of the furnace in order to rapidly raise and cool the workpiece to a desired temperature or to improve the characteristics of the surface hardening heat treatment such as gas nitriding, nitriding, carburizing or carburizing. The present invention relates to a heat treatment furnace having a gas circulation device for circulating by induction and injecting into a furnace again.

Gas circulation, heat treatment, surface reaction, rapid heating, rapid cooling

Description

Heat Treatment Furnace Having a Furnace Gas Circulating Equipment

The present invention relates to a heat treatment furnace equipped with a gas circulation device, and more particularly, to improve the surface reaction characteristics during surface hardening heat treatment or to rapidly heat and cool a target object to a desired temperature. It relates to a heat treatment furnace characterized by having a gas circulation device for guiding to the outside of the furnace to circulate and inject into the furnace again.

The heat treatment method of metal material is surface hardening method that hardens only the surface of the material to obtain excellent wear resistance, fatigue resistance, corrosion resistance, etc. Can be divided by law.

In addition, all the heat treatment process is made of three steps of the temperature increase, the main heat treatment, and cooling after charging the material in the furnace for heat treatment.

The temperature rise is a process of heating the material at a predetermined main heat treatment temperature, and this heat treatment is a process of imparting desired characteristics to the material by maintaining a predetermined time at the process temperature, and cooling the material of the high temperature state subjected to this heat treatment to room temperature It's a process.

In the heat treatment process using gas such as gas nitriding, gas nitrocarburizing, gas carburizing, and gas carbonitriding, which are typical surface hardening heat treatment methods, ammonia, Gas molecules such as endothermic gas, nitrogen, and carbon dioxide are adsorbed on the surface of the material and then diffused into the material. The heat treatment is performed. In order to obtain high surface hardness, corrosion resistance and fatigue strength after heat treatment, high nitrogen and Carbon concentration is required.

For example, when the concentration of nitrogen and carbon on the surface is increased, the gas nitride carburization rate also increases, and a thick ε-single phase (Fe ₃ (CN)) having excellent corrosion resistance and abrasion resistance can be obtained.

However, the concentration of nitrogen and carbon atoms on these surfaces is determined by the feed rate from the furnace gas. That is, the gas inside the furnace accidentally collides with the surface of the material and the collision gas is adsorbed on the surface of the material and diffuses into the material.The higher the concentration of gas in the furnace, the more the number of times the gas in the furnace collides with the surface of the material. The concentration of species that invades and diffuses on the surface of the is high and its penetration depth is also large.

However, increasing the amount of gas such as ammonia, endothermic gas, nitrogen, and carbon dioxide injected into the furnace can increase the gas concentration in the furnace, thereby increasing the number of collisions between the surface of the object and the gas, resulting in increased gas costs or air pollution. As a problem occurs and the endothermic cold gas is injected into the furnace, the temperature in the furnace where the gas is injected decreases relatively, resulting in unevenness in the temperature distribution of the furnace, resulting in quality deviation or low temperature. There is a problem such as additional energy costs for the temperature increase in the furnace area.

In order to solve these problems and obtain excellent properties after surface hardening, many studies have been conducted on surface hardening heat treatment processes such as gas flow rate, gas composition, heat treatment temperature or heat treatment time, but the heat treatment time is excessively long There is still a problem to be solved in the technical aspects of the surface hardening heat treatment which is practically difficult to increase the concentration arbitrarily.

On the other hand, quenching heat treatment, which is one of the typical general heat treatment methods, generally heats steel in a temperature range of 800 ° C. to 950 ° C. for a predetermined time, and then quenches it with oil or a water-soluble refrigerant. In quenching heat treatment, the larger the thickness of the object to be treated, the longer the temperature rising time of heating to the present heat treatment temperature.

In other words, the present heat treatment time at this time means the time after charging the processing object in the furnace and both the inside and the outside of the processing object have reached a predetermined temperature. In order for the inside / outside to reach a predetermined temperature uniformly, a constant temperature raising time is required, which includes the amount of the loaded workpiece, the thickness of the workpiece, the surface state of the workpiece, the shape of the workpiece, the heating source, It depends on the heating method.

In the tempering heat treatment carried out at 150 ℃ ~ 650 ℃ similarly, the temperature increase is required, but the heating rate is different for each material part during the temperature increase, the hardness deviation occurs, this heating time is more than 1/2 of the total time of quenching and tempering heat treatment Since it occupies, there is a problem in terms of heat treatment time and economics.

In addition, normalizing heat treatment or softening steels for the purpose of uniformity of uneven and coarse structure after casting, forging or rolling, improve machinability, plastic workability, removal of residual stress, adjustment of crystal grain or structure, etc. The target annealing heat treatment is heated to a temperature of 750 ° C. to 950 ° C. depending on the material, followed by furnace cooling or air cooling after holding for a predetermined time. At this time, as in the quenching and tempering heat treatment, a considerable temperature raising time is required for uniformly heating the inside and outside of the object to a predetermined temperature.

In addition, there is a case in which the high temperature during the heat treatment should be cooled to a predetermined temperature quickly. At this time, since both the heat treatment furnace and the object to be treated must be cooled to a predetermined temperature, cooling takes a certain time.

Accordingly, the present invention has been made in view of the problems of the prior art, and an object of the present invention is to circulate the heated gas in the furnace to obtain excellent characteristics at the shortest possible processing time during surface hardening heat treatment, and to increase the temperature rapidly. And to provide an in-gas gas circulation device that can shorten the heat treatment time through rapid cooling.

Other objects and advantages of the invention will be described below and will be appreciated by the embodiments of the invention.

In order to achieve this object, according to the present invention, in the heat treatment furnace for the heat treatment by charging the metal material to be processed in the interior of the furnace, the heat treatment furnace to quickly increase the temperature and cool the target object to a desired temperature Or a gas for guiding and circulating the gas in the furnace heated in the furnace to the outside of the furnace for the purpose of improving the characteristics of the surface hardening heat treatment including gas nitrification, gas nitriding, gas carburization or gas carburization nitriding. Provided is a heat treatment furnace comprising a circulation device.

In the present invention, the gas circulation device, at least one gas circulation pipe that is a circulation passage of the furnace gas, at least one circulation fan or blower installed in the path of the gas circulation pipe for forced circulation of the gas in the furnace, At least one gas flow direction control device installed in the path of the gas circulation pipe to control the flow direction of the circulating gas, and at least one gas installed in the path of the gas circulation pipe to control the flow rate of the circulating gas And a flow control device.

In addition, at least a part of the gas circulation pipe is embedded between the inner wall and the outer wall of the heat treatment furnace.

At least one cooling trap for cooling the circulating gas may be installed in at least one path of the gas circulation pipe.

Hereinafter, the present invention will be described in detail with reference to FIGS. 1 and 2.

FIG. 1 is a schematic cross-sectional view of a heat treatment furnace with an in-gas gas circulation system according to an embodiment of the present invention, and FIG. 2 is a schematic stage of a structure in which a cooling trap is added to the heat treatment furnace of FIG. 1.

1 and 2, the heat treatment furnace 10 of the present invention is a furnace (11: also referred to as retort) for charging and heat-treating the object to be processed, and the heating element 12 for heating the inside of the furnace 11 A heating unit 13 surrounded by the furnace, a stirring fan 14 for stirring the circulating gas and the atmosphere gas in the furnace 11, and a circulation pipe 15 connected to one side of the furnace 11 to transfer the circulating gas 15. ), A gas flow rate control valve 16 for adjusting the flow rate of the circulating gas, a circulation fan 17 for forcibly circulating the gas in the furnace 11 through the circulation pipe 15, and a flow direction of the circulating gas It includes a gas flow control valve 18 for controlling.

The furnace 11 is provided at one side of the atmosphere gas inlet 11a for injecting the atmosphere gas, the circulating gas inlet 11c for injecting the circulating gas and the other side of the furnace 11 to discharge the waste gas The waste gas discharge port 11b and the circulation gas discharge port 11d for discharging the circulating gas to the circulation pipe 15 are provided.

The circulation pipe 15 is formed extending from the circulating gas discharge port 11d and then separated into an external circulation pipe 15a and an internal circulation pipe 15b for selecting the flow of the circulating gas by the gas flow control valve 18. Finally, the outer circulation pipe 15a and the inner circulation pipe 15b are integrated before the circulating gas inlet 11c so that the circulating gas is injected into the circulating gas inlet 11c.

The outer circulation pipe 15a is used as a path for cooling the furnace 11 by cooling the circulating gas. The inner circulation pipe 15b is a furnace 11 as the circulating gas is warmed and circulated through the heat generating unit 13. It is used as a path for heating the processing object in the head).

The circulation fan 17 is composed of a sealed impeller and an electric motor driving the same, and a blower may be used instead of the circulation fan.

The circulating gas may be discharged from one portion of the upper / lower portion or the side portion of the furnace 11 and injected into another portion of the furnace 11. For example, the circulating gas flows out from the upper circulating gas discharge port 11d and is injected into the lower circulating gas inlet 11c and circulated.

In this case, in order to prevent the cooling of the circulating gas and to heat the inside of the furnace 11, the circulating gas is transferred through the inner circulation pipe 15b provided between the inner wall 11e and the outer wall 11f of the furnace 11. When the plurality of internal circulation pipes 15b are connected in parallel, the effect is higher.

1 and 2, the stirring fan 14 inside the furnace 11 stirs the atmospheric gas from the atmospheric gas inlet 11a and the circulating gas from the circulating gas inlet 11c. The stirred gas is heated by the heat generating unit 12 so that the waste gas is discharged to the waste gas outlet 11b, and the circulating gas is transferred to the circulation pipe 15 by the circulation fan 17 through the circulating gas outlet 11d. .

The circulating gas is forcibly conveyed by the circulation fan 17 by adjusting the flow rate of the gas by the gas flow rate control valve 16. The gas flow control valve 18 controls the circulated gas to be selectively transported to the external circulation pipe 15a or the internal circulation pipe 15b. The selectively transported circulating gas is flowed back into the circulating gas inlet 11c and continuously circulated, so that the gas in the furnace 11 may be cooled or heated.

On the other hand, in order to rapidly cool the furnace 11 to a predetermined temperature, the circulating gas is circulated through the external circulation pipe 15a. At this time, as shown in Figure 2, by attaching the cooling trap 20 to the external circulation pipe 15a in the same configuration as shown in Figure 1 can further increase the cooling efficiency.

In the case of gas nitriding or gas nitrocarburizing heat treatment, the growth rate and phase of the compound layer at a given temperature are determined by the supply rate of nitrogen and carbon components to the surface. It is proportional to the number of collisions between the injected gas molecules and the material surface. As the number of collisions between these gas molecules and the surface of the material increases, the concentration of nitrogen and carbon on the surface increases, so that the nitriding rate increases, and a thick ε-single phase (Fe ₃ (CN)) having excellent corrosion resistance and abrasion resistance can be obtained quickly. .

However, in the conventional gas nitriding process, since the injected gas molecules accidentally collide with the surface of the material in the gas flow direction, nitriding is performed. Therefore, in order to efficiently obtain a thick ε − single phase, the concentration of gas such as ammonia and carbon dioxide in the injected gas may be reduced. There is a need to increase or increase the total flow rate, which causes problems with air pollution or economics caused by these gases.

If the gas in the furnace is forcedly circulated, the number of collisions between these gas molecules and the surface of the material increases per unit time, so that the surface chemical reaction on the surface of the material becomes active and a thick ε-single phase can be easily obtained. Reducing or reducing the use of harmful gases such as ammonia, carbon dioxide, and in particular, reducing the use of carbon dioxide, a gas that causes global warming, there is also an economic effect of securing the carbon emission rights.

For example, in a gas nitriding furnace with a volume of 4.5 m ³ , the amount of injected gas is approximately 40 m ³ per hour, and when the gas in the furnace is circulated using a circulation device with a circulation capacity of 3,600 m ³ per hour, the volumetric exchange rate (volume of gas supply volume ) Is 800 times per hour, which increases the amount of injected gas to 32,000 m3 per hour, thus increasing the number of collisions between the gas molecules and the surface of the workpiece, resulting in high nitrogen and carbon concentrations on the surface of the material. The desired epsilon-single phase (Fe ₃ (CN)) can be efficiently obtained.

Gas nitriding is usually carried out below 700 ° C. Since most of the heat transfer by convection is carried out below this temperature, this gas circulation is particularly effective during gas nitriding.

Gas carburizing and gas carbonitriding are mainly carbon and nitrogen on the surface of materials in a mixture of endothermic gas, enrich gas and small amount of ammonia gas at temperatures between 850 ° C and 1050 ° C. Is a step of adsorbing and diffusing to perform surface heat treatment. At this time, by increasing the concentration of carbon and nitrogen on the surface of the material, the concentration gradient can be increased to increase the diffusion rate, thereby increasing the depth of the hardened carburized and carburized nitride layers.

At this time, a large amount of input gas is introduced to deepen the depth of the hardened layer. As in the gas nitriding, circulating the gas in the furnace, it is possible to realize the effect of increasing the carbon and nitrogen concentration on the material surface with a relatively small amount of gas. It can deepen the depth and thus reduce the amount of gas injected.

The gas nitriding, gas nitriding, gas carburizing, gas carburizing, and gas carburizing nitriding require a temperature raising process for heating to a predetermined main heat treatment temperature. When gas is circulated in the furnace, high temperature in-gas gas molecules collide with the material surface to increase convection. It is possible to shorten the temperature rise time by facilitating heat transfer by the rapid heat treatment.

In addition, the temperature of the furnace where the gas is injected decreases due to cold gases such as ammonia, carbon dioxide, and nitrogen that are injected from the outside. By circulating the furnace gas and injecting the cold gas into the furnace again, the temperature deviation in the furnace is reduced. Can be.

In general heat treatment methods such as quenching and tempering heat treatment, annealing heat treatment, normalizing, and the like, a temperature raising process is required to uniformly heat the inside and outside of the material at a predetermined main heat treatment temperature. As the degree of heat treatment is different, the hardness is different for each part, and if the heating is performed quickly with such a gas circulation device, the hardness difference is reduced by reducing the difference in heating rate for each part by direct heat transfer caused by the collision between the gas molecules and the surface of the workpiece. Can be.

That is, by circulating the gas in the furnace, the number of collisions between the gas molecules in the furnace and the surface of the material is increased to increase the temperature increase rate due to convection, so that the entire material surface can be heated quickly and uniformly or the overall heat treatment time can be reduced.

In addition, there is a case in which the rapid cooling to a predetermined temperature at a high temperature during the heat treatment, but the heat treatment furnace and the heated object have to be cooled to a predetermined temperature, it takes time to cool. At this time, if the gas inside the furnace is taken out of the furnace and re-injected into the furnace, rapid cooling is possible.In this case, a cooling trap is installed around the circulation pipe and the cooling water or cold air passes through the inside to increase the cooling effect. Can be.

The circulating gas outlet and the inlet may be installed in any of the upper and lower parts and the side of the furnace, but in order to increase the gas circulation efficiency, the gas outlet and the inlet may be installed at the parts facing each other.

The amount of gas circulation in the furnace is not particularly limited, and the control of the amount of circulation gas may be performed by adjusting the size of the circulation fan or blower, or by attaching a variable circulation fan capable of adjusting the rotation speed or installing a control valve.

The material of the gas circulation device may be heat resistant steel, stainless steel, Ti and Ti alloys, inconel alloys, monel alloys, etc. in consideration of heat resistance and corrosion resistance.

On the other hand, the gas circulation device in the furnace can be applied to a fit furnace, a sealed quench furnace, a fluidized bed furnace, a continuous furnace, there is no particular limitation on the type of furnace if the furnace can be attached to the gas circulation device. .

In-house gas circulation system can increase the concentration of elements on the surface of the material during surface hardening heat treatment using gas to improve the treatment characteristics or shorten the total heat treatment time. It is economically advantageous, as it can shorten time and further increase production.

In addition, the amount of gas injected during the surface heat treatment can be reduced, or the amount of toxic gas such as ammonia in the gas, or the amount of gas used for global warming, such as carbon dioxide, can be reduced, and thus the economic effect of securing carbon emission rights can be obtained.

(Example 1)

1,000 pieces of S45C material, 5 cm wide, 5 cm high and 10 cm high were charged to a furnace with an internal volume of 3.95 m ³ and maintained at 860 ° C, and the time at which the center of the material in the center of the furnace reached 860 ° C was measured. As a result, it took 150 minutes in the conventional case without using the gas circulation system.

Under the same conditions, heating was performed while circulating gas in the furnace at 50 m ³ per minute using the gas circulation system of the present invention, which took 110 minutes.

From these results, according to the present embodiment, the heating time was found to be reduced by 27%.

At this time, the furnace gas circulation system was composed of a variable circulation fan and two gas circulation pipes installed between the outer wall and the retort. The material of the gas circulation pipe was Inconel 600.

(Example 2)

After loading 500 mild steel pipes with a diameter of 28 mm, a thickness of 0.8 mm and a length of 3,000 mmL, into a furnace with a retort diameter of 1200 mmΦ and a height of 3,500 mmL (the total surface area of the pipes is 264 m2 and the total weight is 823 kg), Treatment temperature 565 ℃, total flow rate 40m ³ / hr, thickness 18 consisting of ε-phase and γ'-phase mixed phase when treated for 4 hours in a mixed gas atmosphere of 60% ammonia, 10% carbon dioxide and 30% nitrogen gas. A µm compound layer was obtained.

On the other hand, except that the total flow rate is 28 m ³ / hr, under the same conditions as described above, the gas circulation apparatus of the present invention was processed while circulating the gas in the furnace at 55 m ³ per minute, whereby a single ε-phase was obtained. The 21-micrometer-thick compound layer comprised was obtained.

From these results, according to this embodiment, a single ε-phase was obtained while reducing the amount of gas by 30%.

At this time, the gas circulation system in the furnace was composed of a variable circulation fan and two gas circulation pipes installed between the outer wall and the retort, and the material of the gas circulation pipe was Inconel 600.

(Example 3)

After this a SCM415 material diameter of 10mm × 20mm × 20mm-like charged into the 50mmΦ, a height of 1,000mmL experiment, total injected gas flow rate was 1.2m ³ / hr, value Enriched gas, 0.8% propane, and others are endothermic type gas Under the condition of, it was subjected to carburization heat treatment at 925 ° C. for 4 hours, and then tempered at 205 ° C. for 2 hours to obtain an effective hardening depth (550 Hv) of 0.55 mm.

On the other hand, except that the total flow rate was 0.9 m ³ / hr, under the same conditions as above, the treatment was performed while circulating the gas in the furnace at ³ m ³ per minute using the gas circulation system of the present invention, and the effective hardening depth (550 Hv) Was 0.56 mm, similar to when the furnace gas was not circulated.

From these results, according to this embodiment, the injection gas was able to save about 25%.

At this time, the gas circulation system in the furnace was composed of a blower and one gas circulation pipe installed between the outer wall and the retort, and the gas amount was controlled by a valve installed between the blower and the furnace, and the material of the gas circulation pipe was Inconel 600.

As described above, although the present invention has been described by way of limited embodiments and drawings, the present invention is not limited thereto and is intended by those skilled in the art to which the present invention pertains. Of course, various modifications and variations are possible within the scope of equivalents of the claims to be described.

1 is a schematic cross-sectional view of a heat treatment furnace with an in-gas gas circulation system according to an embodiment of the present invention.

2 is a schematic cross-sectional view of a heat treatment furnace with an in-gas gas circulation system according to another embodiment of the present invention.

DESCRIPTION OF THE REFERENCE NUMERALS

10: heat treatment furnace 11: furnace

12: heating element 13: heating portion

14: stirring pan 15: circulation piping

16 gas flow control valve 17 circulation fan

18: gas flow control valve 20: cooling trap

11a: atmosphere gas inlet 11b: waste gas outlet

11c: circulating gas inlet 11d: circulating gas outlet

11e: inner wall 11f: outer wall

15a: External circulation piping 15b: Internal circulation piping

Claims (4)

In the heat treatment furnace for the heat treatment by charging the metal material to be processed in the furnace, Furnace having an outer wall and an inner wall, the charge of the workpiece and heat treatment, A heating unit installed between the outer wall and the inner wall of the furnace and surrounded by a heating element for heating the inside of the furnace, and The heated object in the furnace for the purpose of rapidly raising and cooling the workpiece in the furnace to a desired temperature or for improving the characteristics of the surface hardening heat treatment including gas nitriding, gas nitriding, gas carburizing or gas carburizing. It is provided with a gas circulation device for injecting the gas in the furnace into the outside of the furnace and circulated again, and injected into the furnace, The gas circulator A circulation pipe providing a circulation passage of the gas in the furnace, the internal circulation pipe for circulating gas to be heated inside the heat generating unit and then circulated into the furnace, and the circulating gas to be transferred out of the heat generating unit to cool the furnace. Said circulation pipe having an external circulation pipe for circulating therein, Is installed in the path of the gas circulation pipe, the gas flow rate control valve is installed in the gas circulation pipe portion of the circulating gas is discharged from the furnace to control the flow rate of the circulating gas, A circulation fan or blower installed in a path of the gas circulation pipe to circulate the gas in the furnace through the circulation pipe; And a gas flow control valve installed in a path of the gas circulation pipe and controlling a flow direction of the circulating gas to selectively transfer the circulating gas to the internal circulation pipe or the external circulation pipe. The furnace of claim 1 wherein the furnace is Atmospheric gas inlet for injecting the atmosphere gas provided on one side, Is installed adjacent to the atmosphere gas inlet circulating gas inlet for injecting circulating gas, A waste gas outlet provided on the other side for discharging waste gas, and It includes a circulating gas discharge port for discharging the circulating gas to the circulation pipe, The circulation pipe is formed extending from the circulating gas outlet, and is separated into the internal circulation pipe and the external circulation pipe by the gas flow control valve, and finally, the internal circulation pipe and the external circulation pipe are before the circulating gas inlet. Heat treatment furnace, characterized in that integrated to inject the circulating gas into the circulating gas inlet. 3. The method of claim 2, The gas flow rate control valve, the circulation fan or blower, and the gas flow control valve are sequentially installed in the circulation pipe extending from the circulation gas discharge port. The inner circulation pipe is a plurality of heat treatment furnace, characterized in that connected in parallel between the inner wall and the outer wall of the furnace. The gas circulation system of claim 2, And a cooling trap installed in the external circulation pipe to cool the circulating gas passing through the external circulation pipe.

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