JPH09291302A - Continuous sintering furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To dissolve such problems that the surface of sintered material (product) after sintering becomes whity and loses glossness and at the same time, extreme decarburization on the surface layer part thereof is easily developed, in a continuous sintering furnace having nitrogen base gas atmosphere in the furnace. SOLUTION: This sintering furnace is produced with a sintering part for sintering a green compact 2 under nitrogen base gas atmosphere and a dewaxing part 5, in which previous to sintering of the green compact 2 in the sintering part, the green compact 2 laid on a carrying means 3 continuously shifted at the fixed speed in the furnace is quickly heated with a gas combustion type heating means 4 arranged at the front part of the sintering part and at the upper part of the green compact and lubricating agent included in the green compact 2 is oxidized, decomposed, gasified and removed. Then, in the dewaxing part 5, a flame shut-off member 11 for preventing direct contact of the flame of the heating means 4 with the green compact 2 over the position having 40-60% of the distance L from a green compact discharging position 9 in the dewaxing part 5 to a green compact advancing hole position 10 is arranged between the heating means 4 and the green compact 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous sintering furnace for sintering a green compact in a nitrogen-based gas atmosphere, and specifically, a nitrogen-based gas containing hydrogen or the like. Prior to sintering the green compact in the atmosphere, in the dewaxing part located on the front side of the sintered part, the rapid heating to remove the lubricant contained in the green compact should be optimized. Due to
In particular, the present invention relates to a continuous sintering furnace which can prevent decarburization in the sintering step and rough skin on the surface of a sintered body and can easily mass-produce a high quality sintered body.

[0002]

2. Description of the Related Art In the compaction molding of metal powder, friction between the die and the metal powder in the powder compacting press for filling and pressurizing the metal powder and between the metal powder particles is reduced to improve the compactability For improvement, it is common to add a lubricant mainly composed of zinc stearate to the metal powder.

Since this lubricant decomposes and gasifies at a temperature considerably lower than the sintering temperature (about 700 ° C. or less), the green compact containing the lubricant is suddenly sintered in the high temperature region (about 1100 ° C.). In this case, the lubricant contained in the green compact rapidly decomposes and gasifies, which often causes destruction or swelling of the green compact. Therefore, before sintering, the lubricant is usually removed by a dewaxing step in which heat treatment is performed at a temperature lower than the sintering temperature in advance.

By the way, in a continuous sintering furnace in which the green compact is continuously conveyed from the dewaxing section to the sintering section, the atmosphere in the furnace is conventionally a metamorphic gas atmosphere using a hydrocarbon gas as a raw material. However, recently, from the viewpoint of economical efficiency and safety, it is becoming mainstream to make the atmosphere in the furnace a high-purity nitrogen-based gas atmosphere containing hydrogen gas (about 5 to 10%).

[0005]

However, when the atmosphere in the furnace is set to the nitrogen-based gas atmosphere, there arises a new problem which has not occurred so much in the case of the conventional metamorphic gas.

That is, when the atmosphere in the furnace is set to the nitrogen-based gas atmosphere, the surface of the sintered body (product) after sintering becomes cloudy and has no gloss, and at the same time, the surface layer of the sintered body is extremely exposed. A new problem has arisen that decarburization is likely to occur. This causes deterioration of product quality, which is a big problem in mass production.

Therefore, an object of the present invention is to perform a dewaxing part for decomposing / gasifying and removing the lubricant contained in the green compact before sintering the green compact in the sintering part of the furnace. Prevents decarburization in the sintering process and rough skin on the surface of the sintered body, which were problems when the atmosphere in the furnace was set to the nitrogen-based gas atmosphere by optimizing rapid heating in Then, it is intended to provide a continuous sintering furnace capable of easily mass-producing high-quality sintered bodies.

[0008]

In order to achieve the above object, the continuous sintering furnace of the present invention has a sintering section for sintering a green compact under a nitrogen-based gas atmosphere, and Prior to sintering the green compact, place the green compact placed on the conveying means that moves continuously in the furnace at a constant speed on the front side of the sintering part and above the green compact. It has a dewaxing part which is rapidly heated by the arranged heating means of the gas combustion system, and oxidizes and decomposes / gasifies and removes the lubricant contained in the green compact. The flame of the heating means is applied to the green compact from the position of the powder compact discharge port of the dewaxing part to the position of 40 to 60% of the distance between it and the powder compact inlet port. A flame blocking member is provided to prevent direct contact.

Further, the conveying means is a mesh belt type, the heating means is a plurality of gas burners, the flame blocking member is a wire mesh or a heat-resistant plate having a hole, and the thermocouple for measuring the furnace temperature is a flame. More preferably, it is arranged below the blocking member.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a part of a main part including a dewaxing part of a continuous sintering furnace according to the present invention, which is taken out and cut in a longitudinal direction, and FIG. 1 is a cross-sectional view taken along the line AA of FIG.
Reference numeral 2 is a green compact, 3 is a conveying means, 4 is a heating means, 5 is a dewaxing portion, 11 is a flame blocking member, and 13 is a thermocouple.

The continuous sintering furnace 1 shown in the figure has a sintering part (not shown) for sintering the green compact 2 in a nitrogen-containing gas atmosphere containing hydrogen, and the green compact in this sintering part. Prior to sintering the body 2, the green compact 2 placed on the conveying means 3 which continuously moves in the furnace at a constant speed is placed on the front side of the sintering part and at the front side of the green compact 2. It has a dewaxing section 5 which is rapidly heated by a gas combustion type heating means 4 arranged above and oxidizes and decomposes / gasifies and removes the lubricant contained in the green compact 2.

The transport means 3 is preferably a mesh belt type, but may be a trolley type, a base plate type, or a roller hearth type, and is not particularly limited.

The heating means 4 preferably uses a plurality of gas burners. Specifically, these gas burners are preferably arranged in the upper portion 6 of the dewaxing portion 5 in alignment with the longitudinal direction 7 and the width direction 8.

The dewaxing section 5 is provided between the heating means 4 and the green compact 2 and between the green compact discharge port 9 and the green powder inlet 10 of the dewaxing zone 5. Distance L of 40-60
A flame blocking member 11 for preventing the flame of the heating means 4 from coming into direct contact with the green compact 2 is provided at the position of%.

The arrangement of the flame blocking member 11 is changed to the dewaxing portion 5
From the green compact outlet position 9 to the green compact inlet / outlet position 10
40 to 60% of the distance L between the powder compact 2 and the powder inlet 2 side of the dewaxing portion 5 is set so that the temperature of the powder compact 2 increases rapidly from the temperature outside the furnace. Nevertheless, it exhibits oxidative properties
Since the temperature does not rise up to 400 ° C, even if the flame of the heating means 4 directly contacts the green compact, the green compact is not oxidized.
Rather, it is desirable to raise the green compact temperature rapidly up to the temperature range of 400 ° C, so it is preferable that the flame directly contacts the green compact, and therefore the green compact temperature should be 400
The flame blocking member 11 is provided only at the above-mentioned position where the temperature is not lower than 0 ° C.

For the flame blocking member 11, it is preferable to use a wire mesh or a perforated heat-resistant plate.

As the material of the flame blocking member 11, it is preferable to use a refractory or the like in addition to a heat resistant metal material such as stainless steel.

Further, the width W of the flame blocking member 11 must be at least a width at which the flame does not directly contact the upper surface of the green compact 2. That is, when the width W of the flame blocking member 11 is arranged on the conveying means 3 with the green compacts 2 aligned in one line along the longitudinal direction 7 of the dewaxing portion 5, the width of the green compacts 2 is reduced. Width W ₁
As described above (FIG. 2), when the green compacts 2 are arranged on the conveying means 3 in two or more rows along the longitudinal direction 7 of the dewaxing portion 5, as shown in FIG. Lined green compact 2
Among them, the distance a between the outer ends of the two outermost green compacts 2a and 2b is set to be equal to or greater than a.

As another mode of arranging and placing the green compacts 2 on the conveying means 3, as shown in FIG. 4, the green compacts 2 are stacked on the conveying means 3 in a plurality of stages. It may be placed on, and is not particularly limited.

Furthermore, in order to control the furnace temperature, a thermocouple 13 for measuring the temperature is arranged in the dewaxing section 5. The thermocouple 13
When the heating means 4 directly heats the furnace, the furnace temperature cannot be properly controlled. In this case, therefore, the thermocouple 13 is preferably arranged below the flame blocking member 11. In such a case, by disposing the thermocouple 13 below the flame blocking member 11, the thermocouple 13 is shielded from the direct radiation of the heating means 4 by the flame blocking member 11 as compared with the conventional continuous sintering furnace. The combustion amount increased by 20% when the control temperature was set to the same value.

In the sintered body manufactured by using the continuous sintering furnace of the present invention having the above-mentioned structure, the lubricant in the green compact 2 can be completely removed by the dewaxing section 5, No soot or rough skin was observed.

The above description merely shows part of the embodiments of the present invention, and various modifications can be made within the scope of the claims.

[0023]

EFFECTS OF THE INVENTION The continuous sintering furnace of the present invention has the problems of decarburization in the sintering step and roughening of the surface of the sintered body, which have been a problem when the atmosphere in the furnace is set to the nitrogen gas atmosphere. Therefore, it is possible to provide a continuous sintering furnace that can easily mass-produce high-quality sintered bodies.

[Brief description of drawings]

FIG. 1 is a cross-sectional view in which a part of a main part including a dewaxing part of a continuous sintering furnace according to the present invention is extracted and cut in a longitudinal direction.

2 is a cross-sectional view taken along the line AA of FIG.

FIG. 3 shows the green compact 2 along the longitudinal direction 7 of the dewaxing portion 5
It is a figure which shows the distance a between the outer ends of the two outermost powder compacts 2a and 2b when they are placed side by side in rows or more and placed on the conveying means 3.

FIG. 4 is a diagram showing another embodiment in which the green compacts 2 are stacked on a plurality of stages and placed on the conveying means 3.

[Explanation of symbols]

 1 Continuous sintering furnace 2 Green compact 3 Conveying means 4 Heating means 5 Dewaxing part 6 Upper part of dewaxing part 7 Longitudinal direction of dewaxing part 8 Width direction of dewaxing part 9 Dieselizing powder discharge port of dewaxing part 10 Powder inlet of dewaxing part 11 Flame blocking member 12 Moving direction of carrier 13 Thermocouple

Claims (3)

[Claims] 1. A sintering section for sintering a green compact under a nitrogen-based gas atmosphere, and a furnace inside the furnace continuously at a constant speed prior to sintering the green compact. Lubricant contained in the green compact is rapidly heated by the gas combustion type heating means arranged on the front side of the sintering part and above the green compact, which is placed on the moving conveying means. In a continuous sintering furnace having a dewaxing part that oxidizes, decomposes, gasifies, and removes, the dewaxing part is provided between the heating means and the green compact and at the dewaxing part. A flame blocking member that prevents the flame of the heating means from coming into direct contact with the green compact is provided from the outlet position to a position 40 to 60% of the distance between the outlet and the powder inlet position. Characteristic continuous sintering furnace. 2. The dewaxing of the continuous sintering furnace according to claim 1, wherein the conveying means is a mesh belt type, the heating means is a plurality of gas burners, and the flame blocking member is a wire mesh or a heat-resistant plate having a hole. apparatus. 3. A dewaxing apparatus for a continuous sintering furnace according to claim 1, wherein a thermocouple for measuring the furnace temperature is arranged below the flame blocking member.