JPS5810963B2 - Continuous sintering furnace for powder metallurgy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to the removal of lubricants, etc. from molded parts (hereinafter simply referred to as burn-off).

) Concerning a continuous sintering furnace for powder metallurgy that reduces time and consumption of protective atmosphere gas.

Sintered parts are economical and have excellent dimensional accuracy, so
The production volume of automotive parts, mainly, has increased dramatically in recent years, and the emergence of a sintering furnace capable of mass production is currently awaited.

By the way, the sintering process of powder metallurgy generally consists of (1) a burn-off process in which the lubricant (zinc stearate, etc.) used when pressing the powder metallurgy is vaporized and removed by heating, and (2) the lubricant is removed. (3) a cooling step in which the sintered part is cooled in the protective atmosphere to a temperature at which it will not oxidize in the atmosphere;

During each of the above steps, if insufficient removal of the lubricant in the burn-off step, disturbance of the protective atmosphere during the sintering step, etc. occur, roughness such as "blister" will occur in the treated material, such as a molded part.

Therefore, in conventional sintering furnaces, direct combustion heating methods cannot be used at all because strict restrictions are required on the protective atmosphere surrounding the treated material in order to prevent the surface of the treated material from becoming rough. Therefore, the burn-off process in (1) above is
It was necessary to conduct the process for a long time by indirect heating in a protective atmosphere, the length of the furnace was long, and a large amount of protective atmosphere gas was required.

In addition, since the exit of the sintering furnace is sealed using a sealing mechanism such as a frame curtain method or an asbestos sheet hanging method, there is no sufficient sealing effect and the consumption of protective atmosphere gas increases. There was a drawback.

Furthermore, in the case of a flame curtain type seal, the treated material is heated at the furnace outlet, so there is a risk that the surface of the treated material will be oxidized and colored.

This invention was made in view of the above drawbacks, and
The purpose of this is to place a direct-fired burner in the burn-off zone of a continuous sintering furnace, and to install a gas static pressure sealing mechanism that uses a protective atmosphere gas as a sealing gas at the extraction end of the cooling zone. To create a mixed atmosphere of the combustion generated gas of the direct-fired burner and the protective atmosphere gas inside the furnace, and heat the treated material with the direct-fired burner, thereby shortening the burn-off time and significantly reducing the consumption of adjusted atmosphere gas. The purpose is to provide a powder metallurgy continuous sintering furnace that can perform the following steps.

Hereinafter, this invention will be explained in detail with reference to an embodiment shown in the drawings.

FIG. 1 is a longitudinal cross-sectional view showing the overall configuration of a continuous sintering furnace for iron-based powder metallurgy, for example. A mesh belt 4 wound around the rollers 2 and 3 extends, and the mesh belt 4 is rotated by a drive roller 5 from the loading port 1a side to the extraction port 1b side.

A plurality of direct-fired burners 6.6 are provided at predetermined intervals on the side of the charging port 1a in the furnace body 1, and the treated material (not shown) is conveyed by the mesh belt 4.

) constitutes a burn-off zone A that removes lubricant.

A plurality of electric heaters 8 are provided as heating means over a certain distance on the side of the extraction port 1b, which is connected to the burn-off zone A via the first intermediate door 7, so that the treated material that has completed the burn-off process is provided with a plurality of electric heaters 8 as heating means. Sintering zone B for heating and sintering
It consists of

In this case, the first intermediate door 7 in the sintered zone B
If a second intermediate door 9 is provided at a predetermined distance from the preheating zone B', the temperature therebetween is slightly lower than the temperature in the sintering zone B. Burn-off zone A
A rapid temperature change from the sintered zone B to the sintered zone B can be prevented.

The sintering zone B and the preheating zone B/ have a supply port 1.
A reducing gas is supplied as a protective atmosphere gas via a 0.10 mL gas.

Further, the sintering zone B in the furnace main body 1 is connected to the extraction port 1b side connected through the third intermediate door 12, and the sintering zone B is placed over a predetermined distance on the side of the extraction port 1b after the completion of the sintering process, which is conveyed by the mesh belt 4. It constitutes an annealing zone C that slowly cools the treated material in a reducing atmosphere.

In addition, between this slow cooling zone C and the extraction port 1b, as shown in FIG. 2, a water cooling jacket 13 is provided to surround the mesh belt 4 for radiant cooling of the treated material after the slow cooling process. , and a side circulation type jet pump 14 is provided within this water cooling jacket 13 to constitute a cooling zone.

On the other hand, immediately after the cooling zone, that is, the processing material extraction port 1
A sealing mechanism 15 using the same atmospheric gas as the reducing gas supplied into the furnace body 1 is provided above the mesh belt 4 in b.

As shown in FIG. 3, this sealing mechanism 15 includes a pair of sulins N6a and 17a arranged at a predetermined distance from each other on each lower surface.
In addition, it is composed of nozzle boxes 16 and 17 provided in a roughly inverted V shape, and each nozzle box 1
6.17, reducing gas is supplied from the pressure pump 11 via the control valves 18a, 18a.

Then, the reducing gases from the pair of sulins h16a and 17a are blown toward the bottom plate 19 provided at the bottom of the mesh belt 4 so as to diagonally cross each other in front of each other, and between the pair of gas flows R and R, A static pressure region P higher than the internal pressure of the main body 1 is formed.

In the above configuration, the driving roller 5 is now driven to move the mesh belt 4 from the charging port 1a side of the furnace body 1 to the extraction port 1b.
At the same time, a protective atmosphere gas, that is, a reducing gas is supplied to the preheating zone B', the sintering zone B1, and the slow cooling zone C to fill the furnace body 1, and the pressure pump 11 is driven. Then, reducing gas is supplied to each nozzle box 16,17.

As a result, the reducing gases are blown from the pair of sulins N6a and 17a of each nozzle box 16.17 toward the bottom plate 19 in the inner angle direction to each other, and between the pair of gas flows R and R, the internal pressure of the furnace main body 1 is A static pressure region P higher than that is formed.

Therefore, the extraction port 1b for the reducing atmosphere gas in the furnace body 1
Outflow to the outside of the furnace body 1 from the side and intrusion of outside air are prevented, and the high static pressure area P and the gas flow on the furnace body 1 side reduce the reducing atmosphere inside the furnace body 1 from the charging port 1a side. A stable atmosphere flow is ensured.

Next, after operating the burner 6 and electric heater 8, and operating the water cooling jacket 13 and jet pump 14,
A treated material (not shown) that has been pressed in advance in a pressing process.

) is placed on the mesh belt 4 and carried into the furnace main body 1 through the charging port 1a.

When the treated material first enters the burn-off zone A, the treated material is transported to the fourth
It is heated to about 600-800°C, as shown in the graph of the figure.

At the same time, the gas generated at this time is mixed with the reducing atmosphere flowing toward the charging port 1a, and the protective atmosphere in the burn-off zone A becomes oxidizing to zinc stearate, which is a lubricant during pressing of the treated material. The atmosphere is adjusted to have a composition that is reducing to the treated material, that is, iron-based materials.

Therefore, zinc stearate, which is a lubricant, is removed from the treated material in a short period of time by oxidation and vaporization by the heated atmosphere with a minimum amount of protective atmosphere gas, and roughening of the surface of the treated material is prevented.

Moreover, the reducing atmosphere inside the furnace is created by the high static pressure area P formed at the extraction end and the flow of sealing gas on the side of the furnace body 1.
Since it always flows to the charging port 1a side, the contaminated atmosphere in the burn-off zone is quickly discharged from the charging port 1a without being retained in the burn-off zone, and it is reliably prevented from flowing into the sintering zone B.

Next, the treated material that has undergone the burn-off process as described above is transported to the preheating zone B' by the mesh belt 4, and as shown in the graph of FIG.
and sintering zone B to a predetermined temperature.

Here, the treated material is kept at a temperature below which the pores are rapidly filled in the preheating zone B', and the remaining lubricant is completely removed, and the treated material is transported to the next step, the sintering zone B. As shown in the graph in Figure 4, approximately 1100℃ to 1150℃
is heated and sintered.

The heating temperature in the case where the preheating zone B' is not provided is as shown by the dotted line in FIG.

Subsequently, the treated material that has undergone the sintering process is transported to an annealing zone C by a mesh belt 4, where it is cooled to about 800°C, and then transported to a cooling zone where it is radiantly cooled by a water cooling jacket 13. Due to the synergistic effect of the jet pump 14 and convection cooling caused by the flow of the atmosphere in the furnace, cooling is achieved while suppressing soot generation.

Then, as shown in the graph of FIG. 4, when the temperature of the treated material reaches about 150° C., the treated material is taken out from the extraction port 1b by the mesh belt 4 to the outside of the furnace main body 1 as a finished product.

In addition, in the above embodiment, a case was explained in which a mesh belt 4 was used as a means for conveying the processing material.
It goes without saying that similar effects can be obtained with tray pusher type, walking beam type and roller hearth type.

Furthermore, although the case has been described in which an electric heater is used as a means for heating the sintered zone, it goes without saying that similar effects can be obtained by using indirect heating methods such as a radiant tube burner or a Matsufuru method.

As described above, according to the present invention, the treated material charged from the charging end is maintained in a reducing state by the protective atmosphere gas in the burn-off zone, and is heated by a direct burner to perform burn-off. This allows the furnace to be filled with a conventional endothermic gas atmosphere, reducing the burn-off time to approximately 60% compared to the burn-off zone using the indirect heating method. To,
A sealing mechanism is provided that seals the inside and outside of the furnace body by ejecting the protective atmosphere gas supplied to the nozzle box from a pair of nozzles arranged in a roughly inverted V shape, and creating a static pressure area in the gas flow. Therefore, an atmosphere flow can be formed in the furnace atmosphere that flows toward the charging side.
The burn-off zone is purged with a large amount of generated gas from the burner and a protective atmosphere gas, resulting in smooth burn-off, preventing roughening of the treated material, and producing high-quality products.

Additionally, the amount of protective atmosphere gas can be reduced by about 50% compared to conventional furnaces.

[Brief explanation of the drawing]

Fig. 1 is a vertical sectional view showing the overall configuration of an embodiment of the present invention, Fig. 2 is a cutaway view taken along the line 1-1 in Fig. 1, Fig. 3 is an enlarged view of the sealing mechanism, and Fig. 4 shows each band. It is a graph showing the temperature state of. 1...furnace body, 1a...charging port, 1b...extraction port, 4...
...Mesh belt, 6... Direct fire burner, 8... Electric heat heat, 10... Atmosphere gas supply port, 15... Seal mechanism, A... Burn-off zone, B'... Preheating zone, B... Burning Tie, C... slow cooling zone, D... cooling zone.

Claims (1)

[Claims] 1. A burn-off zone equipped with a direct burner that heats the treated material charged from the charging end while maintaining it in a reducing state, a sintering zone equipped with an electric heater or indirect heating means, and a cooling zone. A protective atmosphere gas supply port is provided in the sintering zone, and a pair of nozzles are arranged in a roughly inverted V-shape at the processing material extraction end of the cooling zone. A continuous sintering furnace for powder metallurgy, characterized by being equipped with a sealing mechanism consisting of a box.