JP2002235102A - Multi-functional sintering furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multi-functional sintering furnace performing three treatments of preliminary sintering, permanent sintering and degassing by one furnace by preventing degradation of the furnace performance caused by adhesion of decomposition products generated from a material to be sintered during the preliminary sintering (degreasing) to a heater, or the like. SOLUTION: A straightening plate 11 is disposed between a heater 2 disposed along an inner wall of a furnace body inside the furnace body 1 of the sintering furnace and the material 5 to be sintered placed inside the heater, so as to surround the periphery of the material to be sintered with a space from the heater and the material to be sintered. Carrier gas and cover gas fed inside the furnace body can be straightened so as to flow downwardly inside and upwardly outside the straightening plate to prevent adhesion of the decomposition product generated from the material to be sintered to the heater.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sintering furnace, and more particularly, to a multifunctional sintering furnace capable of performing pre-sintering, main sintering, and degassing of an object to be sintered in a single furnace. It is related to kilns.

[0002]

2. Description of the Related Art For example, in producing MOX (uranium-plutonium mixed oxide) fuel used in a nuclear reactor, various additives such as a lubricant and a binder are added and mixed to a mixed oxide raw material powder. After the mixture is formed into pellets, a step of sintering is required. The sintering step includes three steps of preliminary sintering (degreasing), main sintering, and degassing. The sintering furnace for performing the main sintering and degassing is, for example, a sintering furnace as shown in FIG. Furnaces are conventionally used.

In this sintering furnace, a heater 2 is provided inside a furnace body 1 along the inner wall of the furnace, and a mounting table 3 is provided inside the heater. Further, a reflector 4 for insulating the radiant heat so that the heat from the heater 2 does not radiate to the outside of the furnace body 1 is provided between the heater 2 and the inner wall of the furnace body 1. An upper reflector 4a and a lower reflector 4b are provided for the same purpose. A heater electrode 6 for supplying power to the heater 2 extends outside the furnace body through the reflector 4 and the furnace body 1 and is electrically connected to a power source (not shown). The pre-sintered pre-degreased sintering object 5 is placed on the mounting table 3, and power is supplied to the heater electrode 6 so that the sintering object can be sintered at about 1700 ° C.

[0004] From a carrier gas supply port 7 opened at the bottom of the furnace 1, a mixed gas of nitrogen gas + hydrogen gas or argon + hydrogen gas is supplied to make the inside of the furnace a reducing atmosphere during the main sintering process. The supplied carrier gas is exhausted from an exhaust port 8 opened at the top of the furnace body. In addition, a gas similar to the carrier gas is supplied from a cover gas supply port 9 opened to the reflector 4 near the heater electrode 6. Most of the additives added and mixed in the sintering material are decomposed and removed by the pre-sintering process.
Since the remaining trace amount of the additive is decomposed during the main sintering process and a decomposition product gas is generated, the heater electrode 6 can be protected from the decomposition product gas by covering the heater electrode 6 with a cover gas. . The cover gas is exhausted from the exhaust port 8 together with the carrier gas.

[0005] The sintering furnace shown in FIG. 2 is further provided with a suction port 10 for bringing the inside of the furnace body into a vacuum atmosphere during the degassing process. That is, when the sintering object after the main sintering process is degassed, the valve 7v of the pipe connected to the carrier gas supply port 7, the valve 8v of the pipe connected to the exhaust port 8, and the cover gas supply port The pipe 9 connected to the pipe 9 is closed, the valve 10 v connected to the suction port 10 is opened, and a vacuum pump (not shown) is used to suction the furnace. Gas treatment can be performed.

[0006]

The sintering furnace shown in FIG. 2 performs the main sintering process in a reducing atmosphere in the furnace and then changes to a vacuum atmosphere to perform not only the main sintering process but also the degassing process. However, when it is used in a preliminary sintering process performed before the main sintering process, there are the following problems.

That is, the purpose of the preliminary sintering process is to decompose the additives in the object to be sintered and remove it as a decomposition product gas from the object to be sintered (degreasing) prior to the main sintering process. Therefore, a large amount of decomposition product gas is generated during processing. Such decomposition product gas adheres to the heater and other furnace components, and lowers the insulation resistance of the heater and does not reach the degree of vacuum at the time of degassing, thereby affecting the performance of the sintering furnace. Therefore, it was difficult to perform the preliminary sintering, the main sintering, and the degassing in the same furnace.

[0008] However, if the three processes of pre-sintering, main sintering, and degassing can be performed in the same furnace, there is a great merit in reducing the number of furnaces to be installed and shortening the processing time. In the prior art, measures to prevent adhesion of decomposition products to heaters and furnace components during pre-sintering have been a major issue.

Accordingly, the present invention is intended to prevent a decomposition product generated from a material to be sintered at the time of pre-sintering from adhering to a heater or the like and affecting the sintering performance.
An object of the present invention is to provide a multifunctional sintering furnace capable of performing three processes of a main sintering process and a degassing process in the same furnace.

[0010]

That is, a multifunctional sintering furnace according to the present invention comprises a heater disposed inside a furnace body of a sintering furnace along an inner wall of the furnace, and a heater provided between the heater and the inner wall of the furnace. A reflector disposed therebetween, a sintering object mounting table disposed inside the heater, a heater electrode extending through the furnace body and the reflector to the outside of the furnace body, and opening at the bottom of the furnace body. A carrier gas supply port, an exhaust port opening at the top of the furnace body, a cover gas supply port opening at the reflector near the heater electrode, and a suction port for suctioning the inside of the furnace body to create a vacuum. In a sintering furnace, the periphery of the sintering object is spaced from the heater and the sintering object between the heater and the sintering object mounted on the sintering object mounting table. The current plate is arranged so as to surround it,
Outside the current plate, the cover gas supplied to the inside of the furnace body flows downward, and inside the current plate, the carrier gas and the cover gas supplied to the inside of the furnace flow are rectified so as to flow upward, and It is characterized in that the decomposition products generated from the residue can be prevented from adhering to the heater.

According to a preferred embodiment of the present invention, the reflector is also provided at the upper part and the lower part of the furnace body, the upper end of the current plate is in close contact with the upper reflector of the furnace body, and the lower end is connected to the lower reflector of the furnace body. Are arranged so that a gap is formed between them.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments shown in the drawings. FIG. 1 shows an embodiment of a multifunctional sintering furnace according to the present invention, and the same members as those in the conventional sintering furnace shown in FIG.

Referring to the detailed structure of FIG. 1, this sintering furnace is composed entirely of a bottomed stainless steel cylindrical furnace body 1 and has a detachable lid 1a provided at the top of the furnace body.
The object to be sintered can be taken in and out from the top of the furnace body. The O-ring 1b keeps the hermetic seal between the lid 1a and the upper end surface of the furnace body. The heat-insulating hollow structure 1c fixed to the lower surface of the lid 1a and the disk-like structure suspended from the lower surface of the structure 1c. The upper reflector 4a is integrated with the lid 1a, and by removing the lid 1a by lifting it up, the heat insulating structure 1b and the upper reflector 4a are also removed, so that the object to be sintered can be taken in and out of the furnace. . An annular upper reflector 4c is provided on the outer periphery of the disc-shaped upper reflector 4a, and is fixed to the upper peripheral edge of the side reflector 4.

A sintering work table 3 provided at the center of the furnace inside the heater 2 is supported by a support 3a placed at the bottom of the furnace via a support 3b.

As the heater 2 in this embodiment, a cylindrical mesh heater divided into three is used, and the side reflector 4 has a cylindrical shape like the furnace body, and the material of the heater and the reflector is both resistant. High-temperature deformable molybdenum is used.

At the time of processing, an atmosphere gas suitable for the processing is supplied from a cover gas supply port 9 opened to the side reflector 4 near the heater electrode 6 and a carrier gas supply port 7 opened to the bottom of the furnace body. , Rises inside the furnace and is discharged from an exhaust port 8 at the top of the furnace body. For example, M
In sintering the OX fuel pellets, a mixed gas of nitrogen gas + hydrogen gas or argon + hydrogen gas is supplied as a carrier gas and a cover gas in order to make the inside of the furnace a reducing atmosphere.

The structure described above is the same as that of the conventional sintering furnace shown in FIG. 2, but in the sintering furnace of the present invention shown in FIG. The point that the current plate 11 is disposed between the heater 5 and the heater 2 so as to surround the periphery of the heater 5 at a distance from the heater 2 and the heater 5 differs from the conventional structure. Is different. The current plate 11 has a cylindrical shape and surrounds the sintering object without any gap. The upper end thereof is in close contact with the annular upper reflector 4c, and the lower end thereof is arranged so as to form a gap with the lower reflector 4b. I have. As a material of the current plate 11, for example, high-temperature deformation-resistant molybdenum can be preferably used. Since the heater 2 is heated to the same high temperature as the heater by the radiant heat of the heater 2, the heat of the heater is not shut off.

When pre-sintering is performed using the sintering furnace of the present invention provided with the current plate 11, the cover gas and the carrier gas supplied from the cover gas supply port 9 and the carrier gas supply port 7 It flows in the furnace as indicated by the white arrow,
The decomposition product gas generated from the gas flows as shown by the black arrow in the figure, and a streamline in a certain direction is formed. That is, the cover gas supplied from the cover gas supply port 9 is:
It hits the upper part of the current plate 11, flows downward along the current plate 11 and the heater 2 outside the current plate, goes around the inside of the current plate from the gap below the current plate, and flows upward with the carrier gas supplied from the carrier gas supply port 7. It flows upward along the inside of the current plate and wraps around the sintering object 5, and is discharged from the exhaust port 8.

In this manner, the contact between the heater 2 and the decomposition product gas such as additives generated from the sintering object 5 is cut off by the gas flow flowing downward along the heater 2 and the rectifying plate 11. In addition, the adhesion of the decomposition product gas to the heater electrode 6 and the heater 2 can be effectively and reliably prevented. In addition, since the ascending flow of the cover gas and the carrier gas constantly flows along the inside of the current plate 11, it is possible to prevent the decomposition product gas from adhering also inside the current plate 11.

As a result, the sintering performance of the furnace due to the adhesion of the decomposition product gas is not hindered. The main sintering process can be performed. Further, after completion of the main sintering, the valve 7v of the carrier gas supply port 7, the valve 9v of the cover gas supply port 9, and the exhaust port 8
By closing all the valves 8v and opening the valve 10v connected to the suction port 10 to make the inside of the furnace a vacuum atmosphere, the degassing process can be performed as it is. Further, as described above, a series of pre-sintering, main sintering, and degassing may not be continuously performed on one object to be sintered, and after performing the pre-sintering process several times, ,
The main sintering process and the degassing process may be repeated several times using the same sintering furnace.

[0021]

[Experimental example] A simulated MOX fuel pellet containing zinc stearate as an additive was used as a material to be sintered, and the following sintering, main sintering and degassing treatments were performed using the sintering furnace of the present invention shown in FIG. Performed under the conditions.

Pre-sintering process: A mixed gas of nitrogen and hydrogen gas is supplied into a furnace as a carrier gas and a cover gas, and heated to about 800 ° C. Main sintering process: A mixed gas of nitrogen and hydrogen gas is supplied into the furnace as a carrier gas and a cover gas, and is heated to about 1700 °
Heating. Degassing process: The inside of the furnace is sucked to reduce the degree of vacuum to about 7.1 × 10
^-2 Pa (initial), heated to about 900 ° C.

The treatment was performed twice in total in the order of pre-sintering twice, main sintering once, pre-sintering five times, main sintering once and degassing once, for a total of ten times. In any of the processes, the insulation resistance of the heater was good, and a desired degree of vacuum was obtained in the degassing process. From this, it is understood that the adhesion of the decomposition product gas generated from the object to be sintered to the heater or the like during the preliminary sintering process is effectively prevented.

[0024]

As can be seen from the above description, according to the multifunctional sintering furnace of the present invention, the heater provided inside the furnace body of the sintering furnace, and the sintering object placed inside the heater, During the pre-sintering, a flow rectifying plate is provided to rectify the cover gas and carrier gas supplied to the inside of the furnace in a certain direction. It is possible to effectively and reliably prevent the decomposition product gas from adhering to the heater and other furnace components.

[0025] Thus, the pre-sintering, main sintering and degassing processes can be arbitrarily combined and continuously performed in one sintering furnace without deteriorating the furnace performance due to the adhesion of decomposition product gas. A possible multifunctional sintering furnace can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an embodiment of a multifunctional sintering furnace of the present invention.

FIG. 2 is an explanatory view showing an example of a conventional sintering furnace.

[Explanation of symbols]

 1: furnace body 2: heater 3: sintering object mounting table 4: side reflectors 4a, 4c: upper reflector 4b: lower reflector 5: sintering object 6: heater electrode 7: carrier gas supply port 8: exhaust port 9: Cover gas supply port 10: Suction port 11: Rectifier plate

Claims (2)

[Claims] 1. A heater disposed inside a furnace body of a sintering furnace along an inner wall of a furnace, a reflector disposed between the heater and the inner wall of the furnace, and a heater disposed inside the heater. An installed sintering object mounting table, a heater electrode extending through the furnace body and the reflector and extending to the outside of the furnace body, a carrier gas supply opening opening at the furnace body bottom, and an exhaust opening opening at the furnace body top. A sintering furnace provided with a cover gas supply port opening to the reflector near the heater electrode, and a suction port for sucking the inside of the furnace body to create a vacuum, wherein the heater and the sintering object mounting table are provided. A rectifying plate is provided between the heater and the sintering object so as to surround the sintering object at an interval from the heater and the sintering object. Outside the current plate, the cover gas supplied to the inside of the furnace body flows downward. Inside the current plate, the carrier gas and the cover gas supplied to the inside of the furnace body are rectified so as to flow upward so that decomposition products generated from the sintering material can be prevented from adhering to the heater. Multifunctional sintering furnace characterized by the following. 2. The reflector is also provided on the furnace body upper part and the furnace body lower part, and the upper end of the straightening plate is in close contact with the furnace body upper reflector, and the lower end forms a gap between the furnace body lower reflector. The multifunctional sintering furnace according to claim 1, wherein the furnace is arranged as follows.