JPH0893448A - Gas filter and manufacture thereof - Google Patents

Abstract

PURPOSE: To have an opening hole part hardly closed, and collect fine particles on a sufficient surface area by forming a gas filter with a sheet shaped sintered body on which a plurality of penetrating holes are formed from an outside supplementally. CONSTITUTION: A filter which is formed of a sheet shaped sintered body 1 on which several penetrating holes 4 are formed from an outside supplementally is used as the filter which is formed in such constitution that sufficient surface area is obtained and also closing of the filter is hardly generated, in order to collect soot included in exhaust gas of an internal combustion engine and fine particle (particulate) of several μm and less of hydrocarbon system. More preferably, the sheet shaped sintered bodies 1 are used by being laminated in a layer shape. Such a gas filter is manufactured in such a way that composition 2 including sintered powder and binder is formed in a sheet shape, a plurality of penetrating holes 4 are formed on the composition 2 by penetrating means 3 for forming the penetrating holes 4 on a surface, and then the composition 2 is sintered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter for trapping fine particles contained in gas.

[0002]

2. Description of the Related Art For example, exhaust gas from an internal combustion engine contains soot and hydrocarbon-based particles of several μm or less. These fine particles are usually called particulates. This particulate matter is especially abundant in the exhaust gas of diesel engines, and has hindered the use of NOx decomposition catalysts used in ordinary gasoline engines. Therefore, in order to apply a catalyst for NOx decomposition to the gas of a diesel engine, a filter that traps particulates before the gas contacts the catalyst is required. As such a filter, a filter based on a metal mesh as described in Japanese Patent Application Laid-Open No. 5-141218 has heretofore been used.

Recently, since a filter with higher performance is required, a filter made of a porous sintered body as described in JP-A-61-53716 has been developed. Further, there is known a filter layer formed by sintering ceramics or metal in a metal net as described in JP-A-5-245317.

[0004]

The above-mentioned porous ceramics filter and a filter having a layer of a sintered body are excellent in the purpose of trapping particulates, but the viscosity of hydrocarbons is high. When the high particulate matter is captured, there is a problem that the opening portion of the filter is likely to be closed and the filter life is significantly reduced depending on the conditions.

Further, in the case of a filter using a metal mesh, in order to capture particulates such as particulates, it is necessary to process the wire into an extremely fine wire to make the mesh fine, which increases the cost. 61-531
As described in Japanese Patent Publication No. 76-76, it is effective to increase the surface area in order to capture particulates, but a simple metal net has a problem that the surface area cannot be increased as compared with a porous sintered body. .

In view of the above-mentioned problems, an object of the present invention is to provide a gas filter which is difficult to close the openings and has a surface area sufficient for capturing fine particles.

[0007]

The present inventor has studied a filter having a structure in which a sufficient surface area for trapping fine particles is obtained and clogging is unlikely to occur, and a through hole is formed instead of a simple sintered body layer. It was found that the formed sintered body makes it possible to obtain a filter having less clogging problems in addition to a surface having a large adsorption surface area due to the sintered body.

That is, the present invention is a gas filter characterized by comprising a sheet-shaped sintered body in which several through holes are additionally formed from the outside. Further, preferably, the gas filter is characterized in that the sheet-shaped sintered body is laminated in layers.

The production method of the present invention is a production method for obtaining the above-described gas filter of the present invention, in which a composition containing a powder to be sintered and a binder is formed into a sheet shape, and then the surface is formed. After the plurality of through holes are formed in the composition by a penetrating means for forming a through hole in the composition, the composition is sintered.

[0010]

One of the greatest features of the present invention is that the sintered body has through holes instead of a simple sintered body layer. That is, the filter of the present invention has at least two sizes, that is, extremely small pores formed by sintering and relatively large pores additionally penetrated from the outside by a mechanical means. Has holes. As a result, the minute particulates in the gas are generated in the above-mentioned relatively large pores (through holes).
Will pass through, but will be captured by the porous sintered body itself around it. Large particulates in the gas are also captured in the above through holes. Since the through holes are larger than the size of the porous holes of the sintered body, there is an effect that clogging (blockage) can be prevented. In the above-mentioned conventional metal net, in order to capture fine particles such as particulates, it is necessary to make the fine wire diameter of the metal extremely thin, which causes a problem of high cost and use in a high temperature oxidizing atmosphere such as exhaust gas. It is difficult to work with an alloy that forms an oxide film, such as Fe-Cr-Al steel, which is suitable for the above, and it is difficult to obtain a wire mesh with a small mesh.

On the other hand, according to the present invention, since the filter is formed by forming the through hole in the sintered body itself, there is no difficulty in processing into a fine wire. Further, since the through hole of the present invention can be mechanically formed even in the state of a composition before sintering, that is, a so-called green body, it is not necessary to control the porous body to have a low strength by sintering, and the strength can be improved. It is possible to construct a high and flexible filter. It can be wound into a cylinder like a metal mesh filter,
It is convenient to fold or construct a multilayer filter layer. If the thickness of the filter is too thick, bending processing becomes difficult, so the thickness of the filter is 300 μm.
The following is desirable. Further, since the filter of the present invention is made of a sintered body, the surface can be made porous and has an extremely high surface area. Therefore, it is possible not only to trap the particulates and the like merely by the difference in the opening diameter, but also to trap them by adsorption on the surface.

As the penetrating means defined in the manufacturing method of the present invention, an aggregate of needles such as Kenzan, a roller having a plurality of protrusions on the surface, and the like can be used.
Ordinary drilling method, by pressing these penetrating means to a sheet-shaped composition containing a powder and a binder,
Through holes can be easily formed in the composition. Conversely, even if the sheet-shaped composition is pressed against an aggregate of needles or a roller having thin protrusions, a through hole can be formed in the composition, and the movement of the sheet-shaped composition and the penetrating means is relative. You should adopt the good movement of. After becoming a sintered body,
It will be handled in the same way as a thin metal plate, and it will be difficult to form minute through holes. Therefore, it is effective to form the through holes in the state of the composition before sintering described above.

As the powder to be sintered according to the present invention, stainless steel is preferable in consideration of corrosive environment such as exhaust gas. Particularly preferably, in order to reduce thermal fatigue damage due to exhaust gas,
A low coefficient of thermal expansion is preferable, and a ferritic stainless steel having a lower coefficient of thermal expansion than an austenitic stainless steel is preferable. Typical steel powders used in the present invention include ferritic stainless steels such as SUS430, SUS429, and SUS434, and SUS304, SUS316, SUS347, SU when corrosion resistance is required.
Austenitic stainless steel such as SXM7, SUS410, SUS416, S when strength is also required
US420J1, J2, SUS440C, etc. can be used. Most preferable are Fe-Cr-Al steels such as JIS FCH1 and FCH2 which have excellent heat resistance.

In the present invention, Fe-C is used as the powder raw material.
The reason why r-Al steel is preferable is as follows. Cr is C
An oxide film mainly composed of r ₂ O ₃ is formed, but in order to further secure heat resistance, Al ₂ which has excellent film protection and adhesion
It is effective to add Al to form an oxide film of O ₃ . The preferable amount of Cr is 15-30%, and more preferably 1
It is 8-28%. In addition, Al is an element that increases the thermal expansion coefficient, and it is preferable that the amount is small in order to prevent thermal fatigue damage, and the higher is preferable from the viewpoint of oxidation resistance. The preferred amount of Al is 2-12%. In the present invention, since it is used as an alloy powder, deterioration of cold workability due to an increase in the amount of Al does not pose a problem, so 5% or more of Al can be added. A more preferable range is 5-9%.

In the present invention, the above-mentioned Fe-Cr-Al is used.
It goes without saying that not only steel but also rare earth elements including Y and Sc, typically La and Ce, can be added to this alloy system as a conventional means for enhancing the adhesion of the coating and further improving the heat resistance. Excessive addition of a rare earth element forms an oxide at the grain boundary to form a path for oxygen and promotes oxidation, so 0.1% or less is desirable. Further, as the alloy system, it is possible to use Ni-based heat-resistant alloys such as Inconel 600, Inconel 601, Inconel 690, and Hastelloy X, which have excellent heat resistance.

[0016]

EXAMPLES First, the composition is shown in Table 1, and the average particle size is 5 μm.
A raw material powder adjusted to m was prepared. To this raw material powder, 0.84 vol% stearic acid, 10 vol% water, and 0.84 vol% glycerin were added and mixed with a Henschel mixer. The sheet-like composition was obtained by passing the obtained mixture through a roll gap. A penetrating means 3 having a plurality of needle-like protrusions like a sword mountain shown in FIG. 2 was pressed against the sheet-shaped composition 2 to form a penetrating hole 4. afterwards,
The obtained composition was treated at 1350 ° C. for 2 hours, 10 minus 3
Sintering was performed in a vacuum under a square Torr to obtain a sheet-shaped sintered body 1.

[0017]

[Table 1]

Table 2 shows the average thickness of the obtained filters,
Measurement result of average aperture diameter of through-hole, and JIS Z
90 ° bending test result specified by 2248, 600 ° C ×
The results obtained by heating in the atmosphere for 10 hours and at 1000 ° C. for 10 hours and evaluating the oxidation resistance as the oxidation weight increase are shown. The increase in oxidation was evaluated by the increase in weight with respect to the surface area when the outer dimension of the sheet-shaped sintered body was assumed to be a flat plate having no thickness.

[0019]

[Table 2]

A photograph of the surface micro-sintered structure of a typical gas filter of the present invention is shown in FIG. As is clear from FIG. 1, it is understood that the surface of the gas filter of the present invention is porous and a large surface area can be secured. Further, it can be seen that the through hole formed by the through means has a porous surface on the inner wall of the through hole due to sintering, and a surface effective for capturing fine particles is formed.

Further, as shown in Table 2, among the samples of the present invention, sample No. using Fe-Cr-Al alloy powder was used.
Sample Nos. 1 to 7 in the oxidation resistance test at 1000 ° C. used commercially available stainless steel powder. It can be seen that compared with Nos. 8 and 9, the increase in the amount of oxidation is small and the oxidation resistance is excellent. In addition, all the samples of the present invention were good in the 90-degree bending test without being damaged, and thus it can be seen that they can be wound in multiple layers in a tubular shape and used for a multilayer filter.

[0022]

According to the present invention, since it has a sintered surface with a large surface area, it effectively acts as a filter for trapping particulates such as particulates. In addition, the present invention has an advantage that the problem of filter blockage is small because it has a through hole. Furthermore, the gas filter of the present invention can be bent, and it is also useful because it can be wound in multiple layers in a tubular shape to form a filter layer.

[Brief description of drawings]

FIG. 1 is a photograph showing a 300-fold surface sintered metal microstructure of the gas filter of the present invention.

FIG. 2 is an explanatory view showing an example of a manufacturing process of the present invention.

[Explanation of symbols]

1 sheet-like sintered body, 2 sheet-like composition, 3 penetrating means, 4 through-holes

Claims (3)

[Claims] 1. A gas filter, comprising a sheet-shaped sintered body having a plurality of through holes additionally formed from the outside. 2. A gas filter, comprising a plurality of sheet-shaped sintered bodies, each having a plurality of through holes additionally formed from the outside, laminated in layers. 3. A composition containing a powder to be sintered and a binder is formed into a sheet shape, and then a plurality of through holes are formed in the composition by a through means for forming the through holes. A method for producing a gas filter, which comprises sintering the composition.