JP6136681B2 - Heat treatment equipment - Google Patents

Description

  The present invention relates to a heat treatment facility for performing a carbonitriding and quenching process on an article to be processed.

Conventional heat treatment equipment for carburizing and quenching products to be treated is known as a continuous furnace type heat treatment equipment and a batch furnace type heat treatment equipment, but in the case of the former continuous furnace type heat treatment equipment, productivity is improved. However, it is difficult to increase the number of processing chambers as necessary, and there is a problem that the expansion of the equipment is limited.
On the other hand, the latter batch furnace type heat treatment equipment has problems such as low processing efficiency and poor productivity.

Under such circumstances, a plurality of carburizing chambers and quenching chambers are provided as batch furnace type processing chambers, and a transfer unit for delivering the products to be processed between these chambers, and the products to be processed are carburized in the carburizing chambers. At the same time, the entire transport unit is run to receive the carburized product from the carburizing chamber, keep it at the quenching temperature in the heat retaining chamber provided in the transport unit, and transport it to the quenching chamber for quenching. A heat treatment facility has been proposed.
For example, Patent Document 1 and Patent Document 2 listed below disclose this type of heat treatment equipment.

FIG. 9 specifically shows an example of the heat treatment facility disclosed in Patent Document 1.
As shown in the figure, this heat treatment equipment has a plurality of carburizing chambers 200 and quenching chambers 202 as batch processing chambers, and a transfer unit 206 that runs on rails 204.
The carburizing chamber 200 performs a carburizing process on the article to be processed W, and the quenching chamber 202 includes an oil cooling bath inside to quench the article to be processed W after the carburizing process.
Here, the carburizing chamber 200 is provided with a heat insulating material 226, a heater 224, a fan for convection heating that generates gas convection inside and promotes heating in the temperature rising period of the workpiece W, and a motor 222 that rotates the fan. ing.

The transfer unit 206 has a delivery chamber 208 at the front and a heat retaining chamber 210 at the rear. The heat insulation chamber 210 is provided with a heat insulating material 226 and a heater 212, and the workpiece W carburized by the heater 212 is kept at a quenching temperature.
On the other hand, the front delivery chamber 208 delivers the workpiece W between the plurality of carburizing chambers 200 and the quenching chambers 202 and between the heat retaining chambers 210.

In the heat treatment facility shown in FIG. 9, the transfer unit 206 receives the workpiece W from the upstream process in the delivery chamber 208, and then travels on the rail 204 and passes it to any of the carburizing chambers 200. Carburize.
After carburizing, the transfer unit 206 receives this from the carburizing chamber 200 to the delivery chamber 208 and then transfers it to the heat retaining chamber 210, where the workpiece W is gradually cooled from the carburizing temperature to the quenching temperature and then brought to the quenching temperature. Keep warm.
For example, after gradually cooling from a carburizing temperature of about 950 ° C. to a quenching temperature of about 850 ° C., the temperature is kept at a quenching temperature of 850 ° C.

The transport unit 206 travels to the position of the quenching chamber 202 while performing the heat retaining step at such slow cooling and quenching temperature, and then the workpiece W in the heat retaining chamber 210 is passed through the delivery chamber 208 to the quenching chamber 202. Pass to.
The quenching chamber 202 performs quenching by immersing the received workpiece W in an oil cooling bath and quenching it. Then, the workpiece W after quenching is discharged from the opening on the side opposite to the rail 204.

In the heat treatment facility shown in FIG. 9, a processing chamber such as the carburizing chamber 200 can be added as necessary, and can easily cope with an increase or decrease in production amount.
In addition, since the transfer unit 206 has a two-chamber structure including a delivery chamber 208 and a heat retaining chamber 210, after receiving the carburized product W from the carburizing chamber 200 and transferring it to the heat retaining chamber 210, a new process from the upstream process is performed. A new workpiece W is received by the delivery chamber 208, and immediately thereafter, can be inserted and set into the carburizing chamber 200 that has been emptied by the removal of the workpiece W, so that the carburizing chamber 200 is empty. The processing capacity can be maximized by minimizing time, and a part of the heat treatment from carburization to quenching in the heat retaining chamber 210, that is, the step of slow cooling and holding at the quenching temperature is interrupted. You can continue without it. Moreover, this can be performed by using a process of transferring the workpiece W from the carburizing chamber 200 to the quenching chamber 202, and the carburizing and quenching process can be performed with high efficiency as a whole.

  By the way, as a method of carburizing treatment for refining crystal grains, the carburized product is subjected to primary carburizing treatment at a high temperature of about 950 ° C., for example, and then the product to be treated is temporarily cooled and then lower than the primary carburizing. A secondary carburizing process is performed at a temperature, for example, about 850 ° C. (In the above-described intermediate cooling, the article to be processed is forcibly cooled to a temperature lower than the temperature of the secondary carburizing. Preferably, the A1 transformation point. Forcibly cool to a lower temperature).

In the heat treatment facility shown in FIG. 9, if the above-described intermediate cooling can be performed in the heat retaining chamber 210 of the transfer unit 206, it is advantageous that the heat retaining chamber 210 can be effectively used for the intermediate cooling.
However, in the heat treatment facility shown in FIG. 9, the heat retaining chamber 210 only includes a heater 212 for heat retaining, and has a function of forcibly cooling the workpiece W to a temperature lower than the temperature of the secondary carburizing. Therefore, the two-stage carburizing process at the different carburizing temperatures cannot be performed.

The heat treatment facility disclosed in Patent Document 2 aims to solve such problems, and an example thereof is specifically shown in FIGS. 10 and 11.
In this heat treatment facility, as shown in the figure, in addition to a heater 212 for heating and keeping the workpiece W in the heat retaining chamber 210, a cooling gas (N ₂ gas) is supplied to the heat retaining chamber 210. An outlet 214, a cooling fan 216 and a motor 218 for agitating and circulating the supplied cooling gas in the heat retaining chamber 210, a heat exchanger 220 for reducing the temperature by passing the cooling gas through heat exchange, and the like are provided. It has been.

That is, in the heat treatment equipment shown in FIG. 10, the heat retaining chamber 210 has both a function of heating the product to be processed W and keeping the temperature, and a function of cooling the product to be processed W by applying a gas flow of the cooling gas. .
FIG. 11 shows a heat pattern at the time of heat treatment in the heat treatment facility shown in FIG. 10, and the heat insulation process H and the cooling (intermediate cooling) process M in FIG. Executed by.

By the way, when the nitriding process is performed in addition to the carburizing process in the heat treatment facility shown in FIG. 9, a nitriding gas inlet for introducing a nitriding gas is provided in the carburizing chamber 200 so that the carburizing chamber 200 has a nitriding function. Can be considered.
In this nitriding, ammonia gas is generally used as the nitriding gas. In the nitriding treatment, the ammonia gas is decomposed to generate active nitrogen, and the active nitrogen diffuses into the steel and hardens the steel surface layer.
At that time, undecomposed ammonia gas remains, but this undecomposed ammonia gas is a corrosive gas, and the in-furnace parts in the carburizing chamber 200 are corroded by the ammonia gas and consumed in a short period of time. .
Therefore, although it is necessary to update the part, there is a problem that it is actually difficult to update the part.
This point will be specifically described below.

Ammonia gas reacts with copper and corrodes it. On the other hand, there are many parts containing copper in the carburizing chamber 200. For example, the carburizing chamber 200 is provided with a convection heating fan that generates gas convection and promotes heating of the workpiece W during the temperature rising period as described above, and a motor 222 that rotates the fan. A copper coil is used for the motor 222.
Copper is also used for the conductor of the heater 224 disposed in the carburizing chamber 200.

  The carburizing chamber 200 is also provided with a water cooling panel for protecting the motor 222 for convection heating from heat, or a water cooling panel for protecting the rubber packing of the door that opens and closes the opening. However, since it is necessary to increase the cooling efficiency inside the high-temperature carburizing chamber 200, copper panels are also used for these water-cooled panels.

Carbon is used for the heater 224 and the heat insulating material 226 disposed in the carburizing chamber 200, but this carbon also reacts with ammonia gas to cause wear.
In addition to corrosion of parts using copper and wear of heaters and heat insulating materials, in the inside of the carburizing chamber 200, soot accumulates on and adheres to the carbon heater 224, or the carbon heat insulating material 226 has a soot. There is a problem that the whole is hardened by the impregnation, which makes it difficult to partially replace the internal parts such as the motor and the heater. For the replacement, it is necessary to update the whole including the heater and the heat insulating material. It becomes necessary and it costs a lot of money.
This also applies to the heat treatment facility of Patent Document 2 shown in FIG.

In view of the above, it is difficult to provide a nitriding function in the carburizing chamber 200 and perform carburizing and nitriding in the carburizing chamber 200. Therefore, it may be possible to provide a nitriding chamber dedicated to nitriding separately from the carburizing chamber. In this case, since a new nitriding chamber is added, a large cost is required.
In addition, when providing a dedicated nitriding chamber, it is substantially necessary to provide the nitriding chamber in a number corresponding to the number of carburizing chambers in terms of processing efficiency, and it is difficult to actually employ it.

JP 2006-63363 A JP 2008-170116 A

  The present invention is based on the circumstances as described above, and does not cause a problem when the carburizing chamber is provided with a nitriding function, and does not increase the cost by providing a dedicated nitriding chamber. The object of the present invention is to provide heat treatment equipment for carbonitriding and quenching that can be performed at low cost.

  Thus, according to the first aspect of the present invention, (A) a plurality of batch-type carburizing chambers and at least one quenching chamber arranged along the transfer track, and (B) a workpiece to be processed and kept warm by a heater. A heat insulation chamber, and a delivery chamber for delivering the article to be processed between the carburization chamber and the quenching chamber, and between the heat insulation chamber, and are configured separately from the carburization chamber and the quenching chamber. A carburizing unit, carburizing the article to be treated in the carburizing chamber, and running the entire conveying unit to receive the carburized article received from the carburizing chamber in the heat retaining chamber. In a heat treatment facility that keeps the quenching temperature and transports it to the quenching chamber for quenching, a nitriding gas guide for introducing a nitriding gas into the heat retaining chamber of the transport unit An inlet is provided, and the heat retaining chamber is configured also as a nitriding chamber, and nitriding treatment is performed on the article to be treated in the heat retaining chamber using a process of transporting the article to be treated after carburizing to the quenching chamber. It is characterized as follows.

  According to a second aspect of the present invention, in the first aspect, the carburizing chamber includes a primary carburizing chamber that performs primary carburizing at a high temperature and a secondary carburizing chamber that performs secondary carburizing at a temperature lower than the primary carburizing. And the transport unit receives the second carburized product to be processed from the secondary carburization chamber and transports it to the quenching chamber, and performs nitriding treatment on the product to be processed using the transport process. While being provided as two transport units, separately from the second transport unit, a space between the cooling chamber that accommodates the article to be processed and cools by a gas cooling device, and the primary carburizing chamber and the secondary carburizing chamber. And a delivery chamber for delivering the article to be processed to and from the cooling chamber, the carburizing chamber and the quenching chamber are separated from each other and run independently to perform the primary carburizing treatment. A first transfer unit is provided that receives a processed product from the primary carburizing chamber, performs intermediate cooling to a temperature lower than the temperature of the secondary carburizing in the cooling chamber, and then passes the processed product to the secondary carburizing chamber. Features.

  According to a third aspect of the present invention, in any one of the first and second aspects, the transfer unit having the heat retaining chamber configured also as the nitriding chamber quenches the article to be processed using the transfer step. The article to be treated is subjected to nitriding while being kept at a temperature.

  According to a fourth aspect of the present invention, in the second aspect of the present invention, the first transport unit receives and transports an article to be processed from an upstream process and passes it to the first carburizing chamber.

Effects and effects of the invention

As described above, the present invention travels the entire transport unit, keeps the processed product received from the carburizing chamber at the quenching temperature in the heat retaining chamber, transports it to the quenching chamber and delivers it to the quenching chamber. In heat treatment equipment that performs carburizing and quenching, a process is adopted in which a nitriding gas inlet is provided in the heat retaining chamber of the transfer unit, the heat retaining chamber is also configured as the nitriding chamber, and the article to be processed after carburizing is transported to the quenching chamber. In accordance with the present invention, there is no problem when the carburizing chamber has a nitriding function, and a dedicated chamber for nitriding is newly added. Carburizing treatment for the products to be processed using the heat insulation chamber originally provided in the transfer unit without installation, and therefore without the cost for installation. It becomes possible to inexpensively perform nitriding and quenching with.
In addition, the nitriding treatment can be performed using a process of conveying the article to be processed after the carburizing process to the quenching chamber by the transfer unit, and the efficiency of the carbonitriding and quenching process can be effectively increased.

  That is, according to the present invention, in addition to the advantage that it is possible to easily cope with the increase in production volume by adding a carburizing chamber or a quenching chamber, the carburizing-nitriding-quenching heat treatment for the workpiece is interrupted in the middle. The conveyance and nitriding treatment by the conveyance unit can be executed without any problem.

  Note that the above-described heat retaining chamber in the transfer unit does not need a gas cooling device for forcibly cooling the article to be processed. Therefore, when the heat retaining chamber is also used as a nitriding chamber, it is used for the gas cooling device. There is virtually no problem of corrosion of the copper-based parts being reacted with ammonia gas.

  In addition, a water cooling panel may be provided in the heat insulation chamber to prevent overheating of the rubber packing of the door, but since the temperature in the heat insulation chamber is low, a steel panel is used even if a copper one is not used as the water cooling panel. be able to. This also avoids the problem of copper corrosion in the water-cooled panel.

However, the heat retaining chamber is provided with a heat retaining heater and a heat insulating material, and these are usually made of carbon, so there is a possibility that the ammonia gas and the heater or the heat insulating material react and wear out, but the heat retaining chamber is a carburizing chamber. Unlike carburizing gas, there is no problem that the carburizing gas generates soot and the soot adheres to or is impregnated with the heater or the heat insulating material.
Therefore, when necessary, it is possible to replace the required part and update it.
Similarly, if copper is used as the conductor of the heater, the copper reacts with the ammonia gas and causes a problem of corrosion. However, since the carburizing gas is not introduced into the heat insulation chamber, it is necessary to replace the copper conductor. When this happens, it can be easily replaced partially.

According to the first aspect of the present invention, vacuum exhaust means for evacuating the carburizing chamber, the delivery chamber of the transfer unit, and the heat retaining chamber can be provided.
By doing in this way, a to-be-processed product can be vacuum-carburized and nitrided under vacuum.

Next, as a carburizing chamber, a primary carburizing chamber that performs primary carburizing at a high temperature and a secondary carburizing chamber that performs secondary carburizing at a lower temperature are provided as carburizing chambers. While receiving the second carburized article to be processed from the secondary carburizing chamber and transferring it to the quenching chamber, the article to be processed is provided as a second transfer unit that performs nitriding treatment at a quenching temperature while using the transfer process. In addition to the second transfer unit, a cooling chamber and a delivery chamber are provided for storing the product to be processed and cooled by the gas cooling device, and the first carburized product is received from the primary carburizing chamber and cooled. A first transport unit is provided that is intermediate cooled to a temperature lower than the temperature of the secondary carburization in the chamber, preferably to a temperature lower than the A1 transformation point, and then delivered to the secondary carburizing chamber. .
In other words, the present invention is applied to a carbonitriding process in which the present invention is carburized in two stages at different temperatures, and intermediate cooling is performed between them.

  In this way, when carburizing is performed on an article to be processed in two stages, and then nitriding and quenching are performed, the heat retaining chamber of the transfer unit 206 in the heat treatment facility of Patent Document 2 shown in FIG. It is also conceivable that 210 has a nitriding function for the article to be processed, that is, the heat retaining chamber 210 in FIG. 10 is also used as a nitriding chamber.

However, in the heat retaining chamber 210 in FIG. 10, the cooling gas is cooled by passing the cooling gas between the cooling fan 216 driving motor 218 that cools the workpiece W with the cooling gas (N ₂ gas) and the water cooling pipe. A heat exchanger 220 or the like is provided, and a copper coil is used for the motor 218, or a copper pipe with high cooling efficiency is used as a pipe of the heat exchanger 220. Accordingly, when a nitriding gas is introduced into the heat retaining chamber 210 and nitriding is performed there, there arises a problem that parts using copper are consumed in a short period due to corrosion. Therefore, it is difficult to configure such a heat retaining chamber 210 also as a nitriding chamber.

  In addition, the heat retaining chamber 210 in FIG. 10 includes a work for intermediate cooling of the article to be treated between the primary carburization at a high temperature and the secondary carburization at a temperature lower than this, and the treatment to be further subjected to the secondary carburization. Two jobs of maintaining the product at the quenching temperature must be performed by one transfer unit, and if the number of carburizing chambers is more than a certain level, the operating rate on the carburizing chamber side is lowered.

  It takes a long time for the intermediate cooling of the article to be processed in the heat insulation chamber 210. Therefore, while the article to be processed is put in the heat insulation chamber 210 and the intermediate cooling process is performed, the heat treatment chamber 210 is in the middle of the intermediate treatment. The product W is blocked and the work to be transported to the quenching chamber cannot be performed while maintaining the quenching temperature of the article to be treated after the secondary carburization.

Therefore, in this case, another transfer unit is provided, and the article to be treated after the secondary carburization is held at the quenching temperature in the heat retaining chamber of the transfer unit, and is transported to the quenching chamber where it is transferred to the quenching chamber. It is convenient to deliver the product to be processed.
By doing so, the efficiency of the heat treatment for carburizing and quenching can be effectively increased.

In this case, it is necessary to provide a heat retaining chamber that holds the article to be treated after the secondary carburization at the quenching temperature with a function of intercooling the article to be treated after the primary carburization toward the subsequent secondary carburization. Therefore, it is not necessary to provide such a heat retaining chamber with a gas cooling device for forcibly cooling the article to be processed.
By utilizing this point, if the nitriding function is given to the heat retaining chamber of the transport unit on the side that maintains the quenching temperature of the article to be treated after the secondary carburizing, the heat retaining chamber that was originally necessary as the transport unit is obtained. The nitriding chamber can be configured as it is.

  Claim 2 of the present invention is constructed under such a point of view, and according to the heat treatment equipment of claim 2, carburization in two stages of primary carburizing and secondary carburizing for the article to be processed is performed. It is possible to perform nitriding treatment in addition to performing treatment and quenching treatment, and it is also possible to use the two transport units while sharing their roles, so that two stages for the article to be treated are obtained. Carburizing, quenching, and nitriding heat treatment can be performed efficiently and without waste.

  According to the second aspect of the present invention, vacuum evacuation means for evacuating the primary and secondary carburizing chambers, the delivery chamber and the heat retaining chamber of the second transport unit, and the delivery chamber and the cooling chamber of the first transport unit may be provided. it can.

  In the present invention, the conveyance unit having the above-described heat retaining chamber configured also as a nitriding chamber is subjected to nitriding treatment on the article to be treated while keeping the article to be treated at the quenching temperature by using the conveyance process. (Claim 3).

  Moreover, in Claim 2, a 1st conveyance unit can receive and convey the to-be-processed goods from an upstream process, and can make it pass to a 1st carburizing chamber (Claim 4).

  In the present invention, the heat retaining chamber is provided with a heat insulating material and a heater for heating and heat-treating the product to be processed in a space surrounded by the heat insulating material, and the delivery chamber has a product to be processed. A delivery mechanism for delivering can be provided.

  In addition, when transferring the product to be processed, the transfer unit is placed at a position where the delivery chamber faces the processing chamber such as the carburizing chamber or quenching chamber, and the delivery chamber is moved to the processing chamber together with the heat retaining chamber and the cooling chamber. Advancing and retreating means may be provided for advancing and airtightly docking in the processing chamber, and for retracting and separating the delivery chamber from the processing chamber after delivery.

  Further, the plurality of processing chambers are arranged in a straight line in the direction perpendicular to the delivery direction with openings for delivering the workpieces to and from the transport unit in the same direction. In addition, the opening for delivery of the object to be processed can be provided in a direction facing the opening of the processing chamber, and can be made to travel linearly along the arrangement direction of the processing chamber.

  In the present invention, a rail is provided as the transfer track, and the transfer unit is provided with a traveling carriage that travels on the rail, and the delivery chamber, the heat retaining chamber, or the cooling chamber is provided on the traveling carriage. I can keep it.

It is a figure showing the whole heat treatment equipment composition of one embodiment of the present invention. FIG. 3 is a cross-sectional view showing an internal structure of a carburizing chamber and a first transfer unit in the same embodiment. FIG. 3 is a sectional view taken along line III-III in FIG. 2. FIG. 4 is a plan view of the carburizing chamber and the first transfer unit. It is operation | movement explanatory drawing of the delivery mechanism in the same embodiment. It is sectional drawing which showed the internal structure of the 2nd conveyance unit in the same embodiment. It is a top view of the 2nd conveyance unit. It is the figure which showed each process of the heat processing in the embodiment with the heat pattern. It is the figure which showed an example of the conventional heat processing equipment. It is the figure which showed an example of the heat processing equipment different from the conventional FIG. It is the figure which showed the heat pattern in the heat processing equipment of FIG.

Next, embodiments of the present invention will be described in detail below.
FIG. 8 shows various steps of the heat treatment in the present embodiment together with the heat pattern for the article W to be processed.
As shown in the figure, here, the workpiece W is carburized in two stages at different temperatures, and further subjected to nitriding and quenching.
Specifically, the workpiece W is heated to the primary carburizing temperature of 950 ° C. in step K1 and soaked, and then in step K2, the primary carburizing for the workpiece W at a temperature of 950 ° C. Processing, specifically carburizing and subsequent diffusion.
Thereafter, the workpiece W is subjected to intermediate cooling in step K3. Here, a gas flow of a cooling gas is applied to the workpiece W in a high temperature state of 950 ° C., and the workpiece W is forcibly cooled to a low temperature of 100 to 650 ° C. by gas cooling.

After intermediately cooling the article to be processed W in this way, a secondary carburizing process is performed on the article to be processed W this time.
Specifically, the intermediate-cooled article W to be treated is reheated to 850 ° C., which is the secondary carburizing temperature, and then the article W to be treated is subjected to secondary carburizing treatment at 850 ° C. in step K5.
When the secondary carburizing process is completed, the article W to be processed is nitrided at the same temperature of 850 ° C.
The temperature of 850 ° C. is also the quenching temperature in this embodiment. Therefore, the nitriding process in the process K6 performs nitriding while maintaining the workpiece W at the quenching temperature. After the nitriding treatment, the workpiece W is quenched and quenched from the quenching temperature.
Incidentally, in this embodiment, the processes K1 and K2 are performed over 190 minutes, and the intermediate cooling of the subsequent process K3 is performed over 20 minutes.
Further, the subsequent reheating of the process K4 and the carburizing process of the process K5 are performed over 100 minutes, and then the nitriding process of the process K6 is performed over 20 minutes, and further the subsequent quenching process of the process K7 is performed over 10 minutes. Do.

FIG. 1 shows a schematic overall configuration of the heat treatment equipment of this embodiment.
In the figure, reference numeral 10 denotes a rail that is a conveyance track extending linearly in the left-right direction in the figure, and a plurality of batch-type processing chambers, here carburizing chambers 12-1, 12-2, 12, along the rail 10. -3, 12-4, 12-5 and one quenching chamber 14 are arranged in a line in a straight line with an opening 44 (see FIG. 2), which will be described later, facing upward in the figure in the same direction. Yes.
In this embodiment, the carburizing chambers 12-1, 12-2, 12-3 perform a primary carburizing process on the workpiece W at a temperature of 950 ° C., and the carburizing chambers 12-4, 12-5 Thereafter, a secondary carburizing process is performed on the workpiece W at a temperature of 850 ° C.

A charging table 16 is provided on the right end side in FIG. 1, and the workpiece W from the upstream process is first placed on the charging table 16.
The article W to be processed placed on the charging table 16 is subjected to primary carburizing and secondary carburizing treatment by the carburizing chambers 12-1, 12-2, 12-3 and 12-4, 12-5. After being nitrided, it is quenched in the quenching chamber 14 and then discharged to the extraction table 18 at the left end side in the figure and the lower side of the quenching chamber 14 in the figure, and subsequently extracted to the downstream process. The

The heat treatment equipment of this embodiment includes a first transport unit 20-1 and a second transport unit 20-2 that run on the rail 10 in addition to the carburizing chambers 12-1 to 12-5 and the quenching chamber 14. doing.
The first transfer unit 20-1 receives the workpiece W on the charging table 16 and travels on the rail 10, and enters the carburizing chamber 12-1, 12-2, 12-3 in the carburizing chamber 12-1, 12-2. Insert.
Alternatively, the articles W to be processed after the primary carburizing treatment in these carburizing chambers 12-1 to 12-3 are received from the carburizing chambers 12-1 to 12-3 and run on the rail 10, and other carburizing chambers are received. Charge to 12-4 and 12-5, where the secondary carburization is performed.
On the other hand, the second transport unit 20-2 receives the workpiece W after the secondary carburizing process from the carburizing chambers 12-4 and 12-5, travels on the rail 10, passes it to the quenching chamber 14, and passes there. Quenching treatment.
The second transfer unit 20-2 also performs a nitriding process on the workpiece W after the secondary carburizing process in the transfer process. This point will be described in detail later.

FIG. 2 shows the internal structure of the carburizing chamber 12-1 and the first transfer unit 20-1.
As shown in the figure, the carburizing chamber 12-1 has a bottomed cylindrical furnace shell 22 and a heat insulating material (here, made of carbon) 24 disposed therein.
The heat insulating material 24 constitutes a bottomed cylindrical heat insulating wall 25. And the heat insulation wall 25 forms the processing chamber 26 inside.
A suction port 32 is provided in the carburizing chamber 12-1. The suction port 32 is connected to a vacuum pump (both not shown) through a suction tube, and the inside of the carburizing chamber 12-1 is vacuum-sucked by the vacuum pump.

In addition to the suction port 32, the carburizing chamber 12-1 is provided with a supply port 34 for supplying a carburizing gas such as acetylene gas.
The carburizing gas supplied from the supply port 34 is once guided to the header 36, and further from the branch pipe 37 following the header 36 and the nozzle 38 provided in the branch pipe to the inside of the carburizing chamber 12-1, specifically the heat insulating wall 25. It is introduced into the inner processing chamber 26. Although one nozzle 38 is provided in the branch pipe 37 here, a plurality of nozzles 38 may be provided.
The supply port 34 is supplied with nitrogen gas in addition to the carburizing gas. These carburizing gas and nitrogen gas are alternatively introduced into the carburizing chamber 12-1 by a switching valve.

Nitrogen gas supplied in the processing chamber 26 is agitated and convected on the heat insulation wall 25, and a convection heating fan 39 that promotes the temperature rise in the temperature rise period of the article W to be processed is rotated. A motor 40 is provided.
The heat insulation wall 25 is provided with a water cooling panel 41 in the vicinity of the motor 40 for protecting the motor 40 from heat.
Here, a copper panel is used as the water cooling panel 41.

The carburizing chamber 12-1 is provided with a sliding door type door 42 that opens and closes the opening 44. The door 42 is slid on the inner surface of the flange 48 by the cylinder 46, and in the closed state, the opening 44 is hermetically sealed through the rubber packing.
The door 42 is provided with a plate-like heat insulating material 55 so as to move integrally. The heat insulating material 55 closes the opening 52 of the cylindrical heat insulating wall 25.
In the carburizing chamber 12-1, a water cooling panel 51 for protecting the rubber packing for hermetically sealing the opening 44 from heat is also provided on the inner surface side of the door 42. The water cooling panel 51 is also a copper panel.

  Although the structure of the carburizing chamber 12-1 has been described above, the other carburizing chambers 12-2, 12-3, 12-4, and 12-5 have basically the same structure.

On the other hand, the quenching chamber 14 has an oil cooling bath inside, and the workpiece W after the secondary carburizing treatment charged in the second transport unit 20-2 is immersed in the oil cooling bath to quench and quench. I do.
The quenching chamber 14 has an opening 44 on the same side as the carburizing chambers 12-1 to 12-5, that is, an upper side in FIG. 1, and an opening 44 on the opposite side (lower side in the figure), The openings 44 are opened and closed by a sliding door type door 42. In FIG. 1, 46 is a cylinder that opens and closes the door 42.

In FIG. 2, the first transport unit 20-1 has a traveling carriage 90 that travels on the rail 10, and further, on the traveling carriage 90, a cooling chamber 56 (to be described later) together with the delivery chamber 54 and a direction orthogonal to the rail 10. 2 has a connecting carriage 92 that moves forward and backward in the left-right direction in FIG. 2 to connect and disconnect the delivery chamber 54 and the cooling chamber 56 to and from the carburizing chambers 12-1 to 12-5.
94 is a cylinder for moving the connecting carriage 92 in the left-right direction in FIG. 2 by a minute stroke. The cooling chamber 56 and the delivery chamber 54 are moved back and forth in the left-right direction in FIG. It can be moved.
In this embodiment, the connecting carriage 92, the roller 96, the cylinder 94, and the like constitute advance / retreat means.

  The first transport unit 20-1 is for intermediate cooling of the delivery chamber 54 at the front part on the carburizing chambers 12-1 to 12-5 side and the workpiece W at the rear part on the opposite side in the process K3 of FIG. A cooling chamber 56 is provided.

The delivery chamber 54 has a pressure-resistant cylindrical cylindrical wall 58, and a storage chamber 60 for storing the workpiece W is formed therein.
The accommodation chamber 60 is provided with a delivery mechanism 62.
The delivery mechanism 62 delivers the workpiece W between the carburizing chambers 12-1 to 12-5 and the rear cooling chamber 56, and as shown in FIG. 5, the fork portion 62A and the horizontal slide member 62B. 62C, and the product to be processed W is delivered by the fork 62A by sliding them horizontally.

The delivery chamber 54 is provided with a suction port 63, which is connected to a vacuum pump 64 shown in FIG. 4 through a suction pipe 66 A, and the interior of the delivery chamber 54 is vacuum-sucked by the vacuum pump 64. It has come to be.
On the suction pipe 66, an on-off valve 68A made of an electromagnetic valve is provided, and the suction port 63 and the vacuum pump 64 are connected and disconnected by opening / closing the on-off valve 68A.

The delivery chamber 54 is also provided with a supply port 70 as shown in FIG. 4, and nitrogen gas is supplied into the delivery chamber 54 through the supply port 70.
The front end of the delivery chamber 54, that is, the left end in FIG. 2, is an opening 72 having no door. The delivery chamber 54 is provided with a flat frame-shaped packing 74 around the opening 72.
The delivery chamber 54 is moved forward to the carburizing chambers 12-1 to 12-5 in a state where the frame packing 74 is brought into airtight contact with the outer surfaces of the carburizing chambers 12-1 to 12-5. Docked at -1 to 12-5.

On the other hand, the latter cooling chamber 56 has a heat insulating material (made of carbon) 78 inside a furnace shell 76 having a bottomed cylindrical shape, and the heat insulating material 78 constitutes a heat insulating wall 80.
The heat insulating wall 80 forms a storage chamber 82 on the inner side, and the product W to be processed is stored therein.
A frame 84 is provided in the storage chamber 82. The article W to be processed in the storage chamber 82 is placed on and supported by the gantry 84.

As shown in FIG. 3, the cooling chamber 56 is provided with a suction port 86 for vacuum suction of the inside thereof. This suction port 86 is connected to the vacuum pump 64 as shown in FIG. On the other hand, it is connected through the suction pipe 66B.
An opening / closing valve 68B made of an electromagnetic valve is provided on the suction pipe 66B, and the suction port 86 and the vacuum pump 64 are connected and disconnected by the opening / closing operation of the opening / closing valve 68B.

The cooling chamber 56 is also provided with a supply port 88 for supplying nitrogen gas therein as a cooling gas to the furnace shell 76.
In addition, a heat exchanger 98 that lowers the temperature by heat exchange by passing the supplied nitrogen gas between water-cooled pipes, and the nitrogen gas cooled thereby are stirred and circulated in the cooling chamber 56. A cooling fan 100 and a motor 102 for rotating the cooling fan 100 are provided, and these constitute a gas cooling device for the workpiece W.
Here, a copper pipe is used for the water cooling pipe of the heat exchanger 98, and a copper coil is used for the motor 102.

In this gas cooling device, as the cooling fan 100 rotates, the temperature-reduced nitrogen gas flows downward through the opening 104 in the upper part of the heat insulating wall 80 and hits the workpiece W. It flows out of the opening 106, passes through the heat exchanger 98 again, and is cooled there. And the to-be-processed goods W are cooled, producing such a circulation flow.
The cooling chamber 56 is provided with doors 110 and 112 made of heat insulating material for opening and closing the upper opening 104 and the lower opening 106 of the heat insulating wall 80, and these are opened and closed by the cylinders 114 and 116. .

In addition, a cooling water pipe 118 for preventing overheating of the cooling fan 100 is provided in the cooling chamber 56 above the upper opening 104 in the heat insulating wall 80, and a heater is provided in the heat insulating wall 80. 120 (made of carbon) is provided.
That is, in this embodiment, the cooling chamber 56 is also provided with a heat retaining function for retaining the workpiece W together with the cooling function.

  As shown in FIG. 2, an opening 122 is provided between the cooling chamber 56 and the delivery chamber 54, more specifically, at the end of the cooling chamber 56 on the delivery chamber 54 side. The cylinder 124 is opened and closed by a door 128 that slides on the inner surface of the flange 126.

As in the carburizing chamber 12-1, the door 128 of the cooling chamber 56 is also provided with a plate-shaped heat insulating material 130 that opens and closes the opening 129 of the heat insulating wall 80 so as to move integrally therewith. The door 128 is provided with a water cooling panel 132 for protecting the rubber packing that hermetically seals the opening 122 from heat.
The water cooling panel 132 is also a copper panel.

Next, FIG. 6 shows the internal structure of the second transport unit 20-2 in FIG.
The second transport unit 20-2 has a delivery chamber 54 at the front and a heat insulation chamber 134 at the rear.
The internal structure of the second transport unit 20-2 is mostly the same as the internal structure of the first transport unit 20-1, and here, only the reference numerals are given to the same structural parts, and detailed description thereof is omitted.
A storage chamber 82 surrounded by a heat insulating wall 80 is formed inside the heat retention chamber 134 at the rear of the second transport unit 20-2, and the workpiece W is heated and kept warm in the storage chamber 82. A heater (made of carbon) 136 is provided.
The furnace shell 76 is provided with a supply port 138 for supplying a nitriding gas, here an ammonia gas, into the heat retaining chamber 134.

Ammonia gas supplied from the supply port 138 passes through the header 140 and is introduced into the storage chamber 82 from the branch pipe 141 and the introduction port (nitrogen gas introduction port) at the tip of the nozzle 142 protruding into the storage chamber 82. A single branch pipe 141 may be provided with a plurality of nozzles 142.
That is, the heat retaining chamber 134 of the second transport unit 20-2 has a function of nitriding the article to be processed W in addition to a function of heating and keeping the article to be processed W. That is, the heat retaining chamber 134 is also configured as a nitriding chamber.

  Also in the heat retaining chamber 134, the door 128 is provided with a water cooling panel 144 for protecting the rubber packing for hermetically sealing the opening 122 from heat, but here, a steel panel is used as the water cooling panel 144. It is used.

In this embodiment, the first transfer unit 20-1 receives and transfers the workpiece W on the charging table 16 of FIG. 1 and transfers it to one of the carburizing chambers 12-1, 12-2, 12-3. To charge.
Any of the carburizing chambers 12-1, 12-2, and 12-3 that has received the workpiece W performs a primary carburizing process on the workpiece.
The first transport unit 20-1 takes out the workpiece W that has been subjected to the primary carburizing process from any one of the carburizing chambers 12-1 to 12-3, performs intermediate cooling in the cooling chamber 56, and then performs the processing. The product W is charged into one of the carburizing chambers 12-4 and 12-5.
Any of the carburizing chambers 12-4 and 12-5 receiving this performs a secondary carburizing process on the workpiece W.

When the secondary carburizing process is completed, the second transfer unit 20-2 takes out the workpiece W after the secondary carburizing from any one of the carburizing chambers 12-4 and 12-5, and this is used for the nitriding chamber. Nitriding is performed in the heat retaining chamber 134 that also serves as a heat treatment chamber, which is then transferred to the quenching chamber 14.
The quenching chamber 14 that has received the article to be processed W after nitriding is immersed in an internal oil cooling bath to quench and quench.
Then, the workpiece W after quenching is discharged from the quenching chamber 14 onto the extraction table 18.

In this embodiment, the first transfer unit 20-1 receives the workpiece W from the charging table 16 and loads it into the carburizing chambers 12-1 to 12-3, and receives the carburizing chambers 12-1 to 12-1. 12-3 performs a primary carburizing process on the workpiece W inside, and the first transfer unit 20-1 takes out the workpiece W after the primary carburizing process from the carburizing chambers 12-1 to 12-3. While the intermediate cooling is performed in the cooling chamber 56, the second transfer unit 20-2 performs the second carburizing process while moving the charging to the carburizing chambers 12-4 to 12-5. W is taken out from the carburizing chambers 12-4 to 12-5, conveyed, and transferred to the quenching chamber 14 simultaneously.
For this reason, the heat treatment including the primary carburizing process and the secondary carburizing process for the workpiece W and the intermediate cooling between them can be performed with high efficiency and high efficiency.

In addition, in this embodiment, the second transport unit 20-2 moves the workpiece W after the secondary carburization from the carburizing chambers 12-4 to 12-5, transports them to the quenching chamber 14, and loads them. During the process, the nitriding process for the article to be processed after the secondary carburization is performed simultaneously with the other heat treatment steps.
Thereby, the two-stage carburizing process, the nitriding process, and the quenching process for the workpiece W can be performed with high efficiency.
Details of the main part of the series of heat treatment will be specifically described below.

First, the first transport unit 20-1 receives the workpiece W on the charging table 16 by the delivery mechanism 62 in the delivery chamber 54 and accommodates it in the delivery chamber 54.
Thereafter, the first transport unit 20-1 moves to any carburizing chamber, here, for example, the position of the carburizing chamber 12-2, and transports the workpiece W.

  Thereafter, the first transport unit 20-1 moves the delivery chamber 54 forward by a small distance to the carburizing chamber 12-2 side together with the rear cooling chamber 56 by the cylinder 94, and moves the frame packing 74 at the tip of the delivery chamber 54 to the carburizing chamber. It is docked with respect to the carburizing chamber 12-1 so as to be in close contact with the outer surface of the 12-2.

  Then, with the door 128 to the cooling chamber 56 closed, the inside of the delivery chamber 54 is vacuumed by the vacuum pump 64 through the suction port 63, and the inside of the delivery chamber 54 reaches a vacuum pressure similar to that of the carburizing chamber 12-1. Depressurized.

  When the pressure in the delivery chamber 54 becomes a vacuum pressure comparable to the pressure in the carburizing chamber 12-2, the door 42 of the carburizing chamber 12-2 is opened, and the workpiece W in the delivery chamber 54 is delivered to the delivery mechanism. The processing chamber 26 in the carburizing chamber 12-2 is charged by 62 and set on the gantry 30.

  The inside of the carburizing chamber 12-2 is maintained in advance at a primary carburizing temperature of 950 ° C., and the workpiece W charged in the primary carburizing chamber 12-2 is heated immediately after charging. The temperature is raised to 950 ° C., which is the primary carburizing temperature.

  At this time, in order to promote the temperature rise, nitrogen gas is supplied into the carburizing chamber 12-2 from the supply port 34, and the convection heating fan 39 is rotated so that the convection heating by the convection heating fan 39 and the heater 28 are performed. Due to the radiant heat generated by, the article to be processed W is quickly heated to the primary carburizing temperature of 950 ° C.

When the workpiece W is heated to the primary carburizing temperature of 950 ° C., the nitrogen gas inside the carburizing chamber 12-2 is evacuated through the suction port 32, and the inside of the carburizing chamber 12-2 is set again to the set vacuum pressure. Depressurized.
Thereafter, the gas introduced into the carburizing chamber 12-2 is switched from the nitrogen gas to the carburizing gas through the supply port 34, and the workpiece W is carburized.
Thereafter, the article to be processed W is continuously maintained at a temperature of 950 ° C. in a state where the supply of the carburizing gas is stopped, and the diffusion treatment of the carbon that has entered the article to be processed W is performed.

When the primary carburizing process for the article to be processed W is completed in this way, the first transfer unit 20-1 once separated from the carburizing chamber 12-2 is moved forward again toward the carburizing chamber 12-2 and delivered. The chamber 54 is docked to the carburizing chamber 12-2.
Then, with the door 128 between the delivery chamber 54 and the cooling chamber 56 opened, the inside of the delivery chamber 54 and the inside of the cooling chamber 56 are vacuumed by the vacuum pump 64 to make them vacuum pressure.

  Thereafter, the door 42 of the carburizing chamber 12-2 is opened, and the article W to be processed after the primary carburizing process in the carburizing chamber 12-2 is moved into the delivery chamber 54 and subsequently cooled from the delivery chamber 54. The workpiece W is moved to the chamber 56 and accommodated in the cooling chamber 56.

When the workpiece W is accommodated in the cooling chamber 56, the door 128 is closed, and then the vacuum suction in the cooling chamber 56 is stopped, and then nitrogen gas as the cooling gas is supplied into the cooling chamber 56 from the supply port 88. At the same time, the gas cooling device is operated to apply the cooling gas to the workpiece W, and the workpiece W is forcibly intercooled by the gas flow.
When the intermediate cooling is performed in the cooling chamber 56, the heater 120 can keep the temperature constant when the temperature is lowered to the target temperature.

  The first transport unit 20-1 performs the intermediate cooling on the workpiece W as described above while moving away from the carburizing chamber 12-2, and the workpiece W cooled to the target temperature This time, it is charged through either the carburizing chamber 12-4 or 12-5 for secondary carburizing through the delivery chamber 54.

  The workpiece W charged in the carburizing chambers 12-4 to 12-5 is then reheated to a secondary carburizing temperature of 850 ° C. in the carburizing chamber and then to a secondary carburizing temperature of 850 ° C. When it reaches, the secondary carburizing process is performed inside the carburizing chambers 12-4 to 12-5 while being kept at a constant temperature.

The workpiece W subjected to the secondary carburizing process in the carburizing chambers 12-4 to 12-5 is taken out from the carburizing chambers 12-4 to 12-5 by the second transfer unit 20-2 in FIG. 2 Transferred to the heat retaining chamber 134 of the transport unit 20-2.
The heat retaining chamber 134 also functions as a nitriding chamber, and the article W to be processed that has been transferred into the heat retaining chamber 134 is subjected to nitriding treatment in a vacuum in the heat retaining chamber 134.

  Specifically, in the heat insulation chamber 134 that is vacuum-sucked with the door 128 of FIG. 6 closed, the article W to be processed is kept at the quenching temperature and the nitriding temperature 850 ° C. by heating with the heater 136, and the heat insulation state. Thus, the nitriding gas is introduced into the storage chamber 82 from the nozzle 142, and the nitriding process is performed on the workpiece W.

  The second transport unit 20-2 performs such nitriding processing at the nitriding position P1 at the left end shown in FIG. 1, and moves to the right in the drawing when the nitriding processing is completed. W is brought to the front of the quenching chamber 14 and subsequently charged into the quenching chamber 14.

  At this time, in the second transfer unit 20-2, after the delivery chamber 54 is docked with respect to the quenching chamber 48, the inside of the delivery chamber 54 is first vacuumed with the door 128 closed, and then the delivery chamber 54 Nitrogen gas is supplied to the inside 54 through the supply port 70 to bring the inside into an atmospheric pressure state.

Subsequently, after the vacuum suction inside the heat retaining chamber 134 is stopped, nitrogen gas is supplied into the interior through the supply port 88, and the interior is brought into an atmospheric pressure state.
In this state, the door 128 and the door 42 on the quenching chamber 14 side are opened, and the workpiece W after carburizing and nitriding in the heat retaining chamber 134 is charged into the quenching chamber 14 via the delivery chamber 54.

The quenching chamber 14 that has received the workpiece W is immersed in an oil-cooled tank provided therein to quench and quench.
The workpiece W that has been quenched is then discharged to the extraction table 18 on the lower side in FIG. 1 through the opening 44 on the opposite side of the rail 10 from the quenching chamber 14.
Then, the article W to be processed discharged onto the extraction table 18 is subsequently taken to a downstream process.

As described above, in the present embodiment, the heat retaining chamber 134 of the second transfer unit 20-2 is provided with the nitriding gas supply port 138 and the nozzle 142 having the nitriding gas introducing port at the tip, and the heat retaining chamber 134 also serves as the nitriding chamber. The nitriding treatment is performed on the workpiece W using the process of conveying the workpiece W after the carburizing treatment to the quenching chamber 14, and according to this embodiment, the carburizing chamber The second transport unit 20-2 originally has no problem when the nitriding function is provided, and a new chamber dedicated for nitriding is not provided. It becomes possible to perform carburizing processing, nitriding processing, and quenching processing on the article to be processed W at low cost by using the heat retaining chamber 138 provided.
In addition, the nitriding treatment can be performed by using a process of transporting the workpiece W after the carburizing process to the quenching chamber 14 by the second transport unit 20-2, thereby effectively increasing the efficiency of the carbonitriding quenching process. be able to.

  That is, according to the present embodiment, in addition to the advantage that the production volume can be easily increased by adding the carburizing chamber 12-1 and the like and the quenching chamber 14, the carburizing-nitriding-quenching for the workpiece W is performed. The nitriding treatment by the second transport unit 20-2 can be performed without interrupting the heat treatment.

  Note that the above-described heat retaining chamber 134 in the second transfer unit 20-2 does not require a gas cooling device for forcibly cooling the article W to be processed, and therefore the heat retaining chamber 134 is also used as a nitriding chamber. In such a case, there is substantially no problem that the copper-based parts used in the gas cooling device react with ammonia gas and corrode.

  The heat insulation chamber 134 is provided with a water cooling panel 144 that prevents overheating of the rubber packing of the door. However, since the temperature in the heat insulation chamber 134 that keeps the workpiece W at the quenching temperature is low, the water cooling panel 144 is intentionally made of copper. A steel panel can be used without using one. This also avoids the problem of copper corrosion in the water-cooled panel.

However, since the heat retaining chamber 136 is provided with a heater 136 and a heat insulating material 78, and these are made of carbon, there is a possibility that the ammonia gas reacts with the heater 136 and the heat insulating material 78 and wears out. Unlike the carburizing chamber, the chamber 134 does not have a problem that the carburizing gas generates soot and the soot adheres to or is impregnated with the heater 136 or the heat insulating material 78.
Therefore, when necessary, it is possible to replace the required part and update it.
Similarly, copper reacts with ammonia gas as a conductor of the heater 136 and corrodes. However, since the carburizing gas is not introduced into the heat insulation chamber 134, it is easy to replace the copper conductor when it is necessary. Can be partially replaced.

  Further, according to the heat treatment facility of the present embodiment, the two-stage carburizing treatment and the quenching treatment of the article W to be processed, that is, the primary carburizing and the secondary carburizing, and the nitriding treatment can be performed at the same time. In addition, it is possible to use the two transport units while sharing their roles, thereby making it possible to perform two-stage carburizing, quenching and nitriding heat treatments on the workpieces with high efficiency and without waste. .

  Although the embodiment of the present invention has been described in detail above, this is merely an example, and the present invention can be configured in various forms without departing from the spirit of the present invention.

12-1, 12-2, 12-3, 12-4, 12-5 Carburizing chamber 14 Quenching chamber 20-1 First transport unit 20-2 Second transport unit 54 Delivery chamber 56 Cooling chamber 134 Heat insulation chamber 120, 136 Heater 138 Supply port W Product to be processed

Claims (4)

(A) a plurality of batch-type carburizing chambers and at least one quenching chamber disposed along a transfer track;
(B) a carburizing chamber that accommodates the article to be treated and is kept warm by a heater; and a delivery chamber that delivers the article to be treated between the carburizing chamber and the quenching chamber and between the heat retaining chambers, A transport unit configured separately from the chamber and the quenching chamber;
And carburizing the article to be treated in the carburizing chamber, running the entire transport unit, and keeping the article to be treated after carburizing treatment received from the carburizing chamber at a quenching temperature in the heat retaining chamber. In the heat treatment equipment for carrying and quenching to the quenching chamber,
A step of providing a nitriding gas introduction port for introducing a nitriding gas into the heat retaining chamber of the transport unit, forming the heat retaining chamber also as a nitriding chamber, and transporting the article to be treated after carburizing to the quenching chamber; A heat treatment facility characterized in that the product to be treated is nitrided by using the heat retaining chamber. The carburizing chamber according to claim 1, wherein a primary carburizing chamber that performs primary carburizing at a high temperature and a secondary carburizing chamber that performs secondary carburizing at a temperature lower than the primary carburizing are provided as the carburizing chamber,
The transport unit receives the second carburized product to be processed from the secondary carburization chamber and transports it to the quenching chamber, and uses the transport process to perform nitriding on the product to be processed. While provided as a unit,
Separately from the second transfer unit, the cooling chamber for accommodating the article to be processed and cooled by a gas cooling device, and between the primary carburizing chamber and the secondary carburizing chamber and between the cooling chambers. A delivery chamber for delivering an article to be treated; and a separate and independent running from the carburizing chamber and quenching chamber; receiving the article to be treated that has undergone primary carburizing treatment from the primary carburizing chamber; A heat treatment facility, wherein a first transfer unit is provided which is intermediate-cooled to a temperature lower than the temperature of the secondary carburizing in the cooling chamber and then delivered to the secondary carburizing chamber.   3. The transfer unit according to claim 1, wherein the transfer unit having the heat retaining chamber configured to serve also as the nitridation chamber is configured to keep the article to be processed at a quenching temperature using the transfer step. A heat treatment facility characterized by subjecting an article to be treated to nitriding treatment.   3. The heat treatment equipment according to claim 2, wherein the first transport unit receives and transports an article to be processed from an upstream process, and passes it to the first carburizing chamber.

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