JPH0584409A - Ceramic filter - Google Patents

Abstract

(57) [Summary] [Structure] At least the portion of the ceramic thin tube composed of porous partition walls that is easily destroyed by thermal shock is a porous material made of a material having a linear expansion coefficient of 20 to 1000 ° C which is equal to or higher than the linear expansion coefficient of the ceramic thin tube. A filter characterized by being wrapped in the body. [Effect] In the ceramic filter of the present invention, by covering the ceramic thin tube with a porous body made of a material having a linear expansion coefficient of 20 to 1000 ° C. or higher than that of the ceramic thin tube, the ceramic thin tube is constantly subjected to compressive stress. In addition, it prevents damage and cracks due to shocks and thermal shocks, which are weak points of ceramics, and enables safe handling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter which is resistant to thermal shock and is used for microfiltration of foods and chemicals, purification of exhaust gas from internal combustion engines and the like.

[0002]

2. Description of the Related Art In the production of beverages such as beer, sake and wine, foods and pharmaceuticals, there is a filtration step for removing unnecessary substances such as yeast, fine proteins and colloidal substances. Filter materials used for filtration in the chemical field of foods, pharmaceuticals, etc. are required to be chemically stable and have excellent heat resistance. Ceramic filters are used for microfiltration of foods, chemicals, etc. due to the properties of their materials that are chemically stable and have excellent heat resistance. Ceramic filters are also used as filters for removing particles contained in the exhaust gas of diesel engines due to their excellent heat resistance.

[0003]

In the conventional ceramic filter, cracks may occur inside when a thermal shock is applied. In order to reduce this problem, cordierite or the like having a low coefficient of thermal expansion is applied. For example, in a ceramic filter for removing particles contained in exhaust gas of a diesel engine, accumulation of particles and combustion removal of particles are alternately repeated, but local heat generation due to combustion or subsequent cooling process. Therefore, cracks may occur inside the ceramic filter. Cracks are more likely to occur as the ceramic filter becomes larger. Such a problem also occurs when burning off the clogging of the filter for microfiltration of food.

On the other hand, as a method for improving the thermal shock resistance, an example in which a pore-forming material such as granular resin is mixed with a ceramic raw material and compression-molded, and then the pore-forming material is incinerated and removed to obtain a porous body having a high porosity Is disclosed in Japanese Patent Laid-Open No. 1-239071. However, even this method is not a basic solution for improving the thermal shock resistance of the ceramic filter, and there has been a demand for the development of means for further improving the thermal shock resistance.

The present invention has been made to solve the above problems, and an object thereof is to obtain a ceramic filter which is resistant to thermal shock.

[0006]

Means for Solving the Problems The above-mentioned problem is that the linear expansion coefficient of 20 to 1000 ° C. has a linear expansion coefficient of 20 to 1000 ° C. at least in a portion of the ceramic thin tube made of porous partition walls which is easily broken by thermal shock. The problem can be solved by arranging it so that it is wrapped in a porous body made of the above substances.

The ceramic filter of the present invention comprises a ceramic thin tube and a porous body that encloses the thin tube, and usually has an outer cylinder for housing this. The outer diameter of the ceramic thin tube is 0.8 mm or more and 10 mm or less. If it is less than 0.8 mm, the fluid resistance of the filtrate increases, and if it exceeds 10 mm, the filtration area per unit volume decreases. A preferable outer diameter is 1 mm or more and 5 mm or less. The thickness of the partition wall of the ceramic thin tube is preferably 50 μm or more and 500 μm or less. If it is less than 50 μm, the mechanical strength of the capillaries will be problematic, and if it exceeds 500 μm, the pressure loss due to filtration will be large and an economic problem will occur. There is no particular limitation on the length of the thin tube, which is determined according to the application. In addition, since ceramic thin tubes are used as filter media, it is desirable that almost all of the pores of the partition walls are communicating pores, and the porosity is 20%.
% To 80%. If it is less than 20%, the filtration efficiency is poor,
This is because if it exceeds 80%, the mechanical strength of the thin tube will be problematic. It is suitable that the average pore diameter is usually 0.1 μm or more and 10 μm or less. There is no particular limitation on the ceramic material forming the thin tube. For example, oxides such as alumina, zirconia, mullite and cordierite. Nitride such as silicon nitride, titanium nitride, aluminum nitride. Carbides such as silicon carbide and titanium carbide. Oxynitrides like Sialon. Carbonitrides such as titanium carbonitride can be applied. The raw material may be synthetic powder or crushed powder. Also, whiskers, short fibers, or long fibers may be used.

The porous body may be wrapped around at least a portion of the ceramic thin tube which is easily broken by thermal shock. Normally, the ceramic thin tube except for the openings at both ends of the thin tube is used.
It is preferable to cover the entire circumference with a porous body made of a substance having a linear expansion coefficient of up to 1000 ° C. that is equal to or higher than the linear expansion coefficient of the ceramic thin tube. With such a structure, a compressive stress is always applied to the ceramic thin tube, and the ceramic thin tube becomes a filter resistant to thermal shock. As the substance forming the porous body, a material having heat resistance and corrosion resistance necessary according to the use environment of the filter such as the type of fluid to be filtered is appropriately selected. A wide variety of such materials can be selected, but metals or ceramics are usually preferred. For example, it may be a pure metal such as aluminum or titanium, an alloy such as stainless steel or an aluminum alloy, a particle such as Al-SiC, a composite material containing short fibers or long fibers, or an intermetallic compound such as NiTi. The pore diameter of the porous body needs to be larger than the pore diameter of the partition wall of the ceramic thin tube, and the average pore diameter is usually about 10 to 1000 times, preferably about 50 to 200 times the partition wall of the ceramic thin tube. The porous body wraps and supports the ceramic thin tube, and it is necessary that the porous body and the ceramic thin tube are merely in close contact with each other, or even if they are bonded, the bonding strength is weak. This is because, if the adhesive strength is increased, the ceramic capillary tube is rather damaged during heating. The porous body only needs to be in a state of supporting the ceramic thin tube, for example, a double tube may be formed, and the outer side of the ceramic thin tube, that is, the space between the thin tubes is filled with the porous body. Good.

The number of the thin tubes covered with the porous body is not particularly limited and may be one or plural. The number of thin tubes is appropriately determined according to the required filtration flow rate and filtration area. When covering a plurality of thin tubes, the arrangement of the thin tubes is not particularly limited, and for example, a quadrangle formed by a line connecting the centers of adjacent thin tubes may be a tetragonal tetragonal array. It may be a diagonal arrangement in which the inside angles of the quadrangle are parallelograms with equal sides of 60 degrees and 120 degrees. The orthorhombic arrangement is desirable from the viewpoint of increasing the filtration area per unit volume. It is desirable that the distance (pitch) between the ceramic thin tube and the adjacent ceramic thin tube is 100 μm to 20 mm. If it is less than 100 μm, it becomes difficult to evenly attach the porous body when the outside of the ceramic capillary is filled with the porous body. On the other hand, if it exceeds 20 mm, the filtration area per unit volume becomes small and the filtration efficiency deteriorates. By setting the pitch of the capillaries to 100 μm to 20 mm, it is possible to manufacture the ceramic filter of the present invention having a filtration area per unit volume of ² to 2600 m ² / m ³ .

The outer cylinder is for accommodating the ceramic thin tube wrapped by the porous body so that the fluid to be filtered does not escape to the outside. The inner volume of the capillaries should be at the minimum capacity capable of accommodating the thin tube assembly, and it is therefore desirable to have a shape corresponding to the outer shape of the porous body enclosing the thin tubes. The material of the outer cylinder does not leak the fluid to the outside, and may have heat resistance, corrosion resistance, etc. required depending on the required physical strength and the type of fluid, and is appropriately selected from metals, ceramics, plastics, etc. It

As a method of wrapping the ceramic thin tube with a porous body, a method of filling the raw material powder of the porous body around the ceramic thin tube standing upright in the outer mold, a method of filling the ceramic thin tube with the raw material powder of the porous body There are methods such as a method of generating electrostatic force and a method of applying an organic adhesive to the outer periphery of the thin tube to attach the raw material powder of the porous body. For example, as a method of filling, the raw material powder of the porous body may be simply filled around the thin tube that has been erected in advance in the outer die, or the lower lid of the forming die may be filled to obtain uniform filling. However, it may be lowered so that the filling position is always at the same height. Also,
Vibration may be applied to make the filling more uniform. By sintering the filler thus obtained and binding the powder particles to each other, a filter having a porous body wrapped around a ceramic capillary can be obtained. Also, when using electrostatic force,
A voltage difference of 15 kV or more is applied between the ceramic thin tube to which the organic adhesive is applied in advance and the raw material powder of the porous body to generate an electrostatic force, and the powder is blown toward the ceramic thin tube. The powder that has flown into the capillary adheres to the adhesive on the surface of the capillary and covers the entire circumference of the capillary. A filter having a porous body wrapped around a ceramic thin tube can be obtained by bundling a necessary number of thin tubes having the powder adhered all around and sintering. Alternatively, an organic adhesive may be applied to the surface of the ceramic thin tube, and the raw material powder for the porous body may be sanded thereon, and the required number may be bundled and sintered as described above. Whichever method is used, a filter having a porous body covered with a ceramic thin tube can be obtained.

In the ceramic filter of the present invention, of the end faces of the porous body that wraps the ceramic thin tube, both end faces except the opening of the ceramic thin tube and the gap between the outer cylinder and the both end faces of the porous body are all sealed to obtain the ceramic thin tube. The gap between the opening and the side surface of the porous body and the outer cylinder is left open. By adopting such a structure, the fluid to be filtered always passes through the ceramic thin tube, and the filtered fluid passing through the wall surface of the ceramic thin tube passes through the porous body and exits from the side surface of the porous body. The material for sealing the end face of the porous body and the sealing between the end face of the porous body and the outer cylinder may be rubber, plastic, metal, or ceramics, but metal or ceramics is desirable from the viewpoint of corrosion resistance and heat resistance, and the sealing material is dense. Must be quality. In addition, the sealing material does not peel off the sealing thickness,
It suffices that the fluid to be filtered and the filtered fluid can be separated from each other, and for example, about 1 mm to 20 mm is desirable.

Needless to say, when the ceramic filter of the present invention is used, a lid body to which fluid supply and discharge pipes are connected is usually attached to both ends of the outer cylinder.

[0014]

In the ceramic filter of the present invention, the circumference of the ceramic thin tube is covered with a porous body made of a substance having a linear expansion coefficient of 20 to 1000 ° C. which is equal to or higher than the linear expansion coefficient of the ceramic thin tube, so that ?) A compressive stress is applied, and the occurrence of cracks due to external shock and thermal shock due to handling etc. is reduced.

[0015]

【Example】

Example 1 First, average pore diameter 1 μm, porosity 35%, outer diameter 2 mm, inner diameter
316 ceramic thin tubes of 1.5 mm, length 220 mm, composition 99.7% Al ₂ O ₃ and alumina tubes 95 mm in outer diameter, 85 mm in inner diameter, 220 mm in length and 80 mm in diameter, 2 circular disks made of stainless steel and 5 mm in diameter One 100 mm alumina plate was prepared. Two stainless steel discs were formed with 316 holes with a diameter of 2.1 mm at a pitch of 4 mm in an oblique arrangement, and one of them was provided with a ceramic thin tube. Next, fix the lower end of the alumina tube to the alumina plate with an adhesive, and put the thin tube that was previously erected on the stainless steel disk with the stainless steel disk facing down into the bonded alumina tube. With a mean particle size of 200 μm in the gap
₃ C ₂ powder was filled while vibrating. After the filling, another stainless plate was passed through the ceramic thin tube from above so that the distance between the thin tubes did not change. The filling was sintered at 1390 ° C. for 6 hours under an argon atmosphere. The sintered body was taken out from the alumina mold, and the stainless disk portions on both end surfaces were cut and removed to obtain a ceramic filter in which an alumina thin tube having a diameter of 85 mm and a length of 200 mm was covered with a chromium carbide porous body. Put this ceramic filter in the atmospheric furnace, 400
After holding at ℃ for 1 hour, it was taken out, immersed in water at 18 ℃ and rapidly cooled, but no abnormality was found in the filter.

Comparative Example 1 In the same manner as in Example 1 above, an alumina thin tube was erected on a stainless disk and placed in the alumina tube. Chromium carbide powder was filled from a stainless disc up to a height of 15 mm, and
Sintered as in. The obtained sintered body was cut and the stainless disk was removed to obtain a ceramic filter in which one end 10 mm of the alumina thin tube was covered with the chromium carbide porous body.
This filter was placed in an atmospheric furnace in the same manner as in Example 1 above, and
After holding at 0 ° C. for 1 hour, it was taken out, immersed in water at 18 ° C. and rapidly cooled, and the alumina thin tube was broken.

Example 2 In the same manner as in Example 1 above, an alumina thin tube was erected on a stainless disk and the stainless disk was placed in the alumina tube. Particle size 50 ~ in the gap between the ceramic thin tube and the alumina tube
300 μm of crushed titanium sponge powder was filled while vibrating. After the filling, another stainless plate was passed through the ceramic thin tube from above so that the distance between the thin tubes did not change. This packing is heated to 1050 ° C in a vacuum atmosphere of 10 ^-4 Torr.
Sintered for 2 hours. Take out the sintered body from the alumina mold, cut and remove the stainless disk parts on both ends,
A ceramic filter in which an alumina thin tube having a diameter of 85 mm and a length of 200 mm was covered with a titanium porous body was obtained. One end surface of this ceramic filter was fixed and the other end was made a free end, and the fixed one was given a vibration strength of 5 G in the direction perpendicular to the axial direction of the alumina thin tube for 30 seconds. No abnormality was found in the filter after vibration.

The filter was dropped from a height of 1 m onto a concrete floor, but no abnormality was found in the filter.

Comparative Example 2 In the same manner as in Example 2 above, an alumina thin tube was erected on a stainless disk and put in the alumina tube. The crushed powder of titanium sponge was filled from a stainless disc up to a height of 15 mm, and then sintered as in Example 2. Cut the obtained sintered body and remove the stainless steel disc, and
A ceramic filter in which only mm was covered with a titanium porous body was obtained. The porous body side of this filter was fixed in the same manner as in Example 2, and a vibration strength of 5 G was applied for 30 seconds. After the vibration starts,
Soon some filters broke. Also, one 200 mm alumina thin tube not covered with the porous body was dropped onto the concrete floor from a height of 1 m. The dropped filter was damaged from the end face.

Example 3 First, 210 ceramic thin tubes having an average pore diameter of 0.4 μm, a porosity of 35%, an outer diameter of 2 mm, an inner diameter of 1.5 mm, a length of 300 mm and a composition of 99.7% Al ₂ O ₃ and a length of 270 mm, a width of 220 mm, An alumina mold with a height of 10 mm was prepared. The alumina mold 2 has a shape in which four rectangular frames are stacked as shown in FIG. The two inner sheets are each divided at the center (not shown), and two U-shaped pieces face each other to form a rectangular frame. Ceramic thin tube 1 is 3 mm on the surface of each frame that touches each other.
Semicircular grooves 3 are formed at equal intervals so that they can be arranged at intervals. The thickness of each frame is 2 mm for the outer two and 3 mm for the inner two. FIG. 1 shows a state in which ceramic tubules are arranged in this alumina type and assembled, and the ceramic tubules are obliquely arranged in three stages with 70 stages in each stage.
A mold in which thin tubes were arranged was filled with irregular-shaped titanium powder having a particle size of 100 μm while vibrating, and the thin tubes were covered with titanium. This packing is heated to 950 ° C in a vacuum atmosphere of 10 ^-4 Torr.
Sintered for 3 hours. After the sintering, the alumina mold was taken out by removing the two outer frames in the vertical direction and the two inner frames in the front-rear direction, and the sintered body was taken out. Both ends were cut to obtain a ceramic filter in which a plate-shaped ceramic thin tube having a length of 250 mm, a width of 220 mm, and a height of 10 mm was covered with a titanium porous body.
This ceramic filter was applied with a vibration strength of 5 G for 30 seconds in the direction perpendicular to the axial direction of the alumina thin tube in the same manner as in Example 2. No abnormality was found in the filter after vibration.

When this filter was dropped from a height of 1 m onto a concrete floor, no abnormality was found in the filter.

[0022]

EFFECT OF THE INVENTION The ceramic filter of the present invention is made by compressing a ceramic thin tube with a porous body made of a material having a linear expansion coefficient of 20 to 1000 ° C. which is equal to or higher than the linear expansion coefficient of the ceramic thin tube. Stress is applied to prevent damage and cracks due to shock and thermal shock, which are weak points of ceramics, and can be handled with peace of mind.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view showing a state in which ceramic capillaries are arranged in a mold in order to manufacture a ceramic filter according to an embodiment of the present invention.

[Explanation of symbols]

 1 ... Ceramic thin tube 2 ... Alumina type 3 ... Arrangement groove

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location C04B 38/00 303 Z 7202-4G F01N 3/02 301 B 7910-3G

Claims (3)

[Claims] 1. A ceramic thin tube composed of porous partition walls is at least 20 to 10 parts that are easily broken by thermal shock.
A filter characterized in that it is wrapped in a porous body made of a substance having a linear expansion coefficient of 00 ° C. or more that of the ceramic thin tube. 2. The filter according to claim 1, wherein the porous body is a metal. 3. A ceramic thin tube composed of a porous partition wall is arranged in a container, and 20 to 1000 is provided in a space outside the thin tube inside the container.
A method for producing a filter, which comprises filling a powder of a substance having a linear expansion coefficient at 0 C or higher than that of the ceramic thin tube and then heating the powder to bond the powder to each other to form a porous body.