JPH10170161A - Degrease sintering method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance degrease sintering performance effectively with no possibility of internal contamination of furnace or explosion. SOLUTION: A degrease atmosphere is limited to a processing space S1 in an inner box 2 disposed in a furnace 1 and the air Y is introduced directly into the processing space S1. A material to be processed is then degreased under a low pressure oxygen atmosphere while discharging the air Y directly to the outside of the furnace 1 and a transition is made to a sintering process by raising the temperature in the furnace 1 continuously. Consequently, degrease and sintering processed can be carried out continuously without causing any internal contamination of the furnace due to a binder and degrease process can be progressed efficiently when it is combined with oxidizing decomposition due to the air Y and low pressure atmosphere setting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a degreasing sintering method suitably applied to a metal injection molding process.

[0002]

2. Description of the Related Art Conventionally, as a method for degreasing and sintering a metal injection molded product, an atmosphere is introduced into a special degreasing furnace, and the object to be treated arranged in the furnace is degreased with stirring. That is being done. When the air is introduced into the atmosphere, the oxygen component contained in the air oxidizes and decomposes the binder, so that the removal of the binder can proceed efficiently. Then, after the completion of degreasing, the object to be processed is taken out of the furnace, transferred to a sintering furnace, and shifted to a sintering step.

[0003]

However, in such a method, the object to be treated comes into contact with the outside air between the degreasing step and the sintering step, so that water and other impurities are easily mixed into the object to be treated, and the purity is low. In addition, it is difficult to obtain a high-quality product, and there is a problem that the overall processing efficiency is reduced. On the other hand, it has been considered as an effective means to solve the problems associated with the transfer of the furnace by performing the entire process from degreasing to sintering in a single furnace. However, if such a continuous process is employed in a conventional sintering furnace, the introduced atmosphere not only burns the heater and heat insulating material in the furnace by oxidation, but also causes the binder vapor existing near the heater to be exposed to the oxygen atmosphere. If the heater is ignited by the electric discharge of the heater, the entire furnace may be exploded. Further, if the gas is stirred in the furnace, the above problem is promoted, but it becomes difficult to perform uniform degreasing on the object without providing a stirrer.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to effectively improve the performance of a degreasing sintering process without the danger of burning or explosion in a furnace. It is an object of the present invention to provide a degreasing sintering method capable of performing the following.

[0005]

In order to achieve the above object, the present invention takes the following measures.
That is, the degreasing and sintering method of the present invention is to provide an inner box having an exhaust port and an inlet at a position where the inner box can be heated by a heater in a furnace, and to accommodate an object to be processed in the inner box. Introduce oxygen or oxygen mixed gas directly into the furnace from outside the furnace, and perform degreasing on the workpiece under a reduced-pressure oxygen atmosphere while directly exhausting the gas outside the furnace. It is characterized by performing sintering on the object to be processed.

As a specific embodiment, the inside of the inner box is slightly depressurized than the inside of the furnace, an inert gas is introduced into the inside of the furnace, and the gas is constantly introduced into the processing space in the inner box. A method of preventing the backflow of the binder by performing the pressure flow, a method of improving the airtightness of the inner box, and the like are given. By such a method, the degreasing atmosphere is limited to the processing space in the inner box, and if the degreasing process is performed so that the gas does not leak into the furnace space, burnout due to oxidation of the components in the furnace is performed. Is effectively avoided, and at the same time, since the binder vapor does not leak around the heater during degreasing, the binder vapor does not ignite and explode due to the discharge of the heater. It is possible to proceed safely. In addition, by performing degreasing under a reduced pressure atmosphere, the binder or decomposed components evaporate at a lower vapor pressure than in the case of performing degreasing under atmospheric pressure, so that degreasing can be efficiently advanced, and a stirrer can be used. Even without using, it is possible to perform uniform degreasing.

On the other hand, when a large number of workpieces are to be degreased simultaneously, in addition to the above-described method, gas is supplied to the shelf on which the workpieces are arranged so that the flow direction matches the direction of heat transfer by the heater. It is also effective to perform degreasing on the object to be processed while exhausting air from the central portion of the substrate. If you do this,
Degreasing proceeds sequentially from the processing object located closest to the heater, and the binder evaporated from the processing object is discharged through the exhaust port located on the downstream side. Without being exposed again to the binder vapor coming out of the object to be treated, and the performance and efficiency of the degreasing treatment and the quality of the final product can be more effectively improved.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows a heat treatment furnace used when carrying out the degreasing sintering method of this embodiment. This heat treatment furnace is disposed at a position where it can be heated by the heater 14 in the furnace 1 and has an inner box 2 for closing the processing space S1 inside.
And an inner exhaust system 3 for directly exhausting the processing space S1 to the outside of the furnace 1, and a furnace 1 in a furnace space S2 located outside the inner box 2.
An external introduction system 4 for introducing external gas X from outside and an internal introduction system 5 for introducing air Y as an oxygen mixed gas directly from outside the furnace 1 to the processing space S1.

Specifically, the furnace 1 has a heating chamber 13 surrounded by a heat insulating material 12 made of graphite felt inside a furnace body 11, and the heating chamber 13 is provided with a heater 14 made of graphite and an inner box 2. The processing object W can be put in and taken out by opening and closing the lid 11a forming a part of the furnace body 11 together with the lid 12a forming a part of the heat insulating material 12. One end of the furnace 1 is connected to the furnace space S2 through the furnace body 11, and the other end is connected to the furnace space 11 in order to close the lids 11a and 12a and to evacuate the furnace space S2 after storing the workpiece W therein. An external exhaust system 6 connected to the vacuum pump P via a valve 61 is provided.

The inner box 2 is located at the center of the heater 14 in the heating chamber 13 and is made of graphite which is heated by the heater 14.
1 and a lid 22 disposed at a position to close the opening at both ends. The inner box 2 cannot exhibit complete airtightness due to the property of the material called graphite and the structure in which the box body 21 can be opened and closed by the lid 22. A certain amount of gas flow can be allowed through the contact gap or the like.
The processing space S1 inside the inner box 2 has a multi-stage shelf structure as shown in FIGS. 1 to 3, and an opening 2e is provided at the center of the shelf floor 2a of each stage. It communicates with the internal exhaust system 3 via an exhaust port 2c provided in the bottom wall, and a gap 2f is provided between the end portion and the lid 22, and these gaps 2f are provided in the inlet provided in the top wall. It communicates with the internal introduction system 5 via 2b. The gas introduced from the internal introduction system 5 into the inner box 2 through the introduction port 2b
It is introduced into the shelf floor 2a of each stage via f, flows therethrough, and then flows out from the exhaust port 2c to the internal exhaust system 3 through the opening 2e. The inner box 2 is provided with a preheating space 53 at the entrance of the inlet 2b. In the preheating space 53, the gas is preheated to the temperature of the processing space S1, and then is circulated around the processing object W.

The inner exhaust system 3 has one end connected to the inner box 2 through the furnace body 11 and the heat insulating material 12, and the other end connected to the trap 31 and the suction side of the vacuum pump P constituting the outer exhaust system 6. It is connected via a valve 32. The external introduction system 4 has one end connected to the inner furnace space S2 through the furnace body 11 and the other end connected to a gas supply source 41 via a valve 42. Is filled with an inert gas X such as N ₂ or Ar.

The internal introduction system 5 has one end connected to the inner box 2 through the furnace body 11 and the heat insulating material 12 and the other end connected to the gas supply source 5.
1 is connected via a valve 52, and the gas supply source 51 is constituted by a cylinder, a compressed air pump or the like capable of supplying air Y. Next, the degreasing sintering method of this embodiment using this heat treatment furnace will be described. First, the processing object W is set in the inner box 2. Next, the outer exhaust system 6 and the inner exhaust system 3 are operated, and when the furnace space S2 and the processing space S1 have a certain degree of vacuum, the valve 61 of the outer exhaust system 6 is closed and at least the inner exhaust system 3 is operated. In this state, the valve X of the external introduction system 4 is opened to introduce the gas X into the furnace space S2. At the same time, the heater 14 is energized to start the degreasing process on the workpiece W. As a result, in the furnace 1, the gas X introduced into the furnace space S2 reaches the processing space S1 through the contact gap between the inner box main body 21 and the lid 22, as shown by the arrow in the figure, and further. A gas flow is formed that is exhausted out of the furnace 1 through the internal exhaust system 3. Further, the valve 52 of the internal introduction system 5 is also opened, and the air Y is directly introduced into the inner box 2 from outside the furnace 1. As a result, the introduced air Y comes into contact with the processing object W when flowing around the processing object W, and performs a catalytic action to promote oxidative decomposition of the binder. That is, when oxygen comes into contact with the binder, it is oxidized and decomposed to CO2.
_{Since it is 2} or H ₂ O, it has an effect of accelerating degreasing.
The decomposed gas does not leak into the furnace space S2 together with the binder vapor and the air Y, and the gas X
At the same time, after being discharged to the internal exhaust system 3 through the exhaust port 2c of the inner box 2, harmful components are captured in the trap 31 and exhausted through the vacuum pump P. FIG. 4 is a process explanatory diagram showing the above in more detail, and the first half of the degreasing process is performed in the inner box 2.
The interior is adjusted to a low pressure of, for example, about 700 to 600 Torr, and the degreasing is advanced.
Degreasing proceeds while intermittently switching between a reduced pressure state of about rr and the above-described weakly reduced pressure state. By performing such control, a low-molecular-weight binder is mainly removed in the first half of degreasing, and a high-molecular-weight binder, which is difficult to degreasing, is mainly removed in the second half of degreasing on the workpiece W by cracking or sagging (deformation). Without removing. During the degreasing step, the temperature of the inner box 2 is about 360 ° C., and the temperature at which the oxidation of graphite starts (380 ° C.)
C) It is as follows. At this time, the temperature of the heater 14 is about 500
° C, but protected by inert gas.

When the above degreasing step is completed,
The introduction of the air Y through the internal introduction system 5 is stopped, the temperature inside the inner box 2 is finally raised to about 1400 ° C., and the degassing step and the sintering step are performed as shown in FIG. And
Lastly, a cooling mechanism (not shown) provided in the furnace 1 is operated to take out a finished product which has been subjected to all the steps through the cooling step. As described above, in the degreasing sintering method of the present embodiment, the inner box 2 having the exhaust port 2c and the inlet 2b is provided inside the furnace 1 at a position that can be heated by the heater 14, and the inner box 2 The workpiece W is accommodated, air Y is directly poured into the inner box 2 from the outside of the furnace 1, and the gas is directly exhausted to the outside of the furnace 1 while degreasing the workpiece W under a reduced-pressure oxygen atmosphere. Then, the inside of the inner box 2 is replaced with a vacuum atmosphere,
For sintering.

As described above, the degreasing atmosphere is limited to the processing space S1 in the inner box 2, and the processing space S1 is separated from the furnace space S2.
Since the degreasing process is performed so that the gas does not leak to the inside, various problems in the furnace components such as the heater 14 and the heat insulating material 12 and the burnout due to oxidation can be effectively avoided. At the same time, since the binder vapor does not leak around the heater 14 during degreasing, the binder vapor does not ignite and explode due to discharge of the heater 14 or the like, Oxidative decomposition can proceed safely. In addition, by performing degreasing in a reduced pressure atmosphere, it is possible to evaporate the binder or decomposed components with a lower vapor pressure than in the case of performing degreasing under atmospheric pressure, so that degreasing can proceed efficiently. It becomes possible. Furthermore, since degreasing and sintering are performed continuously, there is no deterioration of the workpiece W after degreasing, and stable processing can be efficiently performed.

In addition to the above, in this embodiment, the direction of heat transfer by the heater 14 is directed from the periphery of the inner
Flow direction is also directed from the periphery of the inner box 2 to the center, and the two directions are substantially the same. Therefore, the degreasing proceeds sequentially from the processing object W closest to the heater 14, and the processing object W
The binder evaporated from the air is discharged through the exhaust port 2c located on the downstream side as shown by the arrow in the figure, so that the workpiece W on the upstream side once degreasing has proceeded to the downstream side where degreasing is in progress. This does not cause a problem of being exposed again to the binder vapor coming out of the material W, and also has a soaking effect that a central portion of the inner box 2 that is hardly heated by the flow of gas from the surroundings is heated. Performance and efficiency can be more effectively increased.

The specific configuration of each part is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, as shown in FIGS. 5 and 6, a guide tube 26 having an exhaust hole 26a at the center is provided in the inner box so as to communicate with the inner exhaust system 3;
As shown in FIG. 8, a gap 27 may be provided between the two shelves, or a partition having a hollow partition plate 28 provided at the center thereof so as to communicate with the internal exhaust system 3 may be used. The material of the inner box may be a metal such as Mo. Although air is used as the oxygen mixed gas in the above embodiment, other oxygen mixed gas or pure oxygen can be used. Furthermore, in the above embodiment, the inner introduction system 5 is flowing only air, it may be switched in the middle of the process in inert gas such as N _2. Also, T
In the case of a material that is easily affected by oxidation such as i, hydrogen is introduced into the processing space S1 in the inner box 2 through the inner introduction system 5 after the degreasing is completed, and the workpiece W is continuously reduced and reduced. You may make it.

[0017]

The present invention is embodied in the form described above and has the following effects. That is, in the degreasing sintering method of the present invention, an inner box for accommodating an object to be treated is provided in a furnace, and oxygen or an oxygen mixed gas is directly flown into a processing space in the inner box from outside the furnace, and the gas is supplied to the furnace. The object to be processed is degreased under a reduced-pressure oxygen atmosphere while directly evacuating to the outside, and the furnace is continuously heated to perform sintering.

For this reason, the degreasing treatment can be carried out by oxidative decomposition without causing the burnout due to the contamination or oxidation of the components inside the furnace or the explosion accident of the furnace due to the ignition of the binder vapor near the heater. It is possible to improve the quality of the product, the processing efficiency of the entire degreasing sintering process, the safety, and the like more effectively than in the past, in combination with the continuous execution of the sintering process. In addition, in the present invention, by setting the degreasing atmosphere to a reduced pressure oxygen atmosphere, the evaporation of the binder can be efficiently advanced, and the homogenization can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view showing one embodiment of the present invention.

FIG. 2 is an enlarged sectional view of a main part of FIG.

FIG. 3 is a plan sectional view of FIG. 2;

FIG. 4 is a process explanatory view of the embodiment.

FIG. 5 is a sectional view corresponding to FIG. 2, showing another embodiment of the present invention.

FIG. 6 is a plan sectional view of FIG. 5;

FIG. 7 is a view corresponding to FIG. 3, showing still another embodiment of the present invention.

FIG. 8 is a view corresponding to FIG. 3, showing still another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Furnace 2c ... Exhaust port 2b ... Inlet 14 ... Heater W ... Workpiece Y ... Air

Claims (1)

[Claims] An inner box having an exhaust port and an inlet is provided at a position where it can be heated by a heater in a furnace. An object to be processed is stored in the inner box, and oxygen or oxygen is contained in the inner box. Degas the workpiece under a reduced-pressure oxygen atmosphere while introducing the mixed gas directly from outside the furnace, and exhausting the gas directly from the furnace,
A degreasing sintering method comprising continuously heating the furnace and sintering the workpiece.