KR101380965B1 - Process for Preparation of Silicon Carbide Segment for Honeycomb Ceramic Filter - Google Patents

Abstract

The present invention relates to a method for producing a silicon carbide segment for honeycomb ceramic filters, which is a soot filtration device (DPF), comprising a process of drying, molding, cutting, plugging, and sintering a segment molding cut to a predetermined size after extrusion. In order to prevent local hot spots from occurring during the drying process, the transfer path of the segment molding provides a method of manufacturing the silicon carbide segment, which includes changing the predetermined pattern with respect to the microwave application position of the microwave dryer.

The honeycomb ceramic filter manufactured by this method prevents the occurrence of hot spots in the microwave drying process, thereby preventing deformation such as bending and warping, and ultimately having excellent filtering performance since the physical properties of the segments become uniform. .

Description

Process for Preparation of Silicon Carbide Segment for Honeycomb Ceramic Filter

1 is a perspective view of a silicon carbide segment for a general honeycomb ceramic filter;

2 is a schematic diagram of a filtering process of a general honeycomb ceramic filter;

3A is a schematic diagram of a microwave drying process of a silicon carbide segment molding for a honeycomb ceramic filter according to one embodiment of the present invention, and FIG. 3B is a partial vertical cross-sectional view thereof;

4A is a perspective view of a dry setter for silicon carbide segments in accordance with one embodiment of the present invention, and FIG. 4B is a front view of a silicon carbide mounted state in the dry setter of FIG. 4A.

The present invention provides a method for producing a silicon carbide segment for a honeycomb ceramic filter, which is a soot filtration device (DPF), by a process including a step of microwave drying and sintering after cutting a segment molding cut into a predetermined size after extrusion. In the drying process, the transfer path of the segmented molding is directed to a method for producing a honeycomb ceramic filter, which is configured to be changed in a predetermined pattern with respect to the application position of microwaves in the microwave dryer so that no local hot spots occur during drying.

Recently, there has been a serious environmental problem such as an abnormal weather phenomenon caused by air pollution, and there is a tendency to increase interest in diesel vehicles in which harmful gases such as carbon monoxide (CO) and hydrocarbon (HC) are less discharged than gasoline vehicles to be. However, diesel vehicles have a problem in that a large amount of particulate matter such as nitrogen oxides (NOx), soot, and the like is emitted. Accordingly, research on a diesel particulate filter (hereinafter referred to as DPF) for removing particulate matter from exhaust gas generated from diesel engines of diesel vehicles has been actively conducted.

The DPF collects particulate matter and the like in diesel exhaust gas, injects diesel fuel as fuel at predetermined intervals, and collects by reaction with a catalyst coated on a ceramic filter using exhaust heat generated during operation of the vehicle. It is a device that regenerates a filter by oxidizing the substance into harmless carbon dioxide, water, and the like.

A honeycomb ceramic filter made of a honeycomb structure is mainly used for such a smoke filtering apparatus.

FIG. 1 is a schematic perspective view of a segment 10 for a general honeycomb ceramic filter, and FIG. 2 is a schematic view of a filtering process of the honeycomb ceramic filter of FIG.

Referring to these figures, the ceramic segment 10 has the form of a hexagonal column which is generally rectangular in cross section, and a plurality of cells 12, 13 communicating with each other in both cross sections 20, 30 thereof are to be formed. The partitions 11 are formed in a lattice-like structure that intersects them. The cells 12 and 13 are plugged in an alternating arrangement manner to form a closed cell 12 sealed by a plug and an open cell 13 in which a plug is not formed, Or a checkerboard pattern.

In the ceramic segment 10 for the honeycomb ceramic filter having such a structure, the particulate matter 40 of the exhaust gas flows into the open cell 13 opened in the front surface 20 of the honeycomb ceramic filter 10 to have an adjacent porosity. After passing through the partition 11, it is discharged to the open cell 13 opened in the rear surface 30. At this time, the particulate matter of the exhaust gas is collected in the micro-pores (not shown) formed in the partition 11 or the inner end 15a of the plug 15 located in the closed cell 12 on the rear surface. That is, the particulate matter contained in the exhaust gas is filtered by being caught by the porous partition 11 while passing through the closed cell 12 in the open cell 13 at the front surface 20 but closed in the rear surface 30. .

When the collected fine particles accumulate excessively in the honeycomb ceramic filter, the pressure loss of the filter is increased and the output of the engine is reduced. Therefore, the collected fine particles are periodically used by external ignition means such as an electric heater or a burner. The combustion is performed to regenerate the honeycomb ceramic filter. Therefore, the honeycomb ceramic filter adopts an alternate regeneration method in which two ones are installed so that one side can be used when the other is being regenerated.

The silicon carbide segment for honeycomb ceramic filters, which is such a soot filtration device (DPF), is generally produced by sintering a segment molding cut into a predetermined size after extrusion through microwave drying and hot air drying.

The microwave drying step is a step of drying a predetermined object by radiating microwaves generated from a microwave oscillator such as a magnetron into a drying apparatus, wherein the drying apparatus is generally formed in a plane with both an inner wall surface, an upper surface, and a lower surface. . Therefore, when the microwaves output from the microwave oscillator are transmitted to the drying apparatus, the microwaves are reflected after hitting the inner wall surface of the drying chamber and the planes such as the upper and lower surfaces of the drying chamber, so that they tend to be deflected without being uniformly distributed.

This non-uniform dispersion of microwaves results in the maximum and minimum drying points in the dry matter, and in particular, hot spots occur locally, since the paste components do not exhibit a complete uniform distribution in the extruded segments. Causes many problems.

First, deformation, such as bending or twisting, may occur in the segment molding, and the physical properties of the segment may be deteriorated, which may be reflected in the final manufactured segment, resulting in defects, or cracks in use.

Second, as the organic materials contained in the hot spots are melted or decomposed, the micropores to be formed in the segment may be destroyed or deformed in the subsequent firing process, thereby lowering the filtering efficiency.

However, to date, there is no technique for preventing such hot spots from occurring.

In this regard, as a technique for preventing deformation of a segment generated during a heating process of a hot air drying method, for example, Korean Patent Application Publication No. 2005-0002887 discloses that at least one surface of an outer circumferential wall of a carrier on which a segment is mounted is provided. The technique which comprises so that the inclination angle with respect to a horizontal plane may be 15-35 degree | times is disclosed. According to the above technique, the problem of deformation occurring while the segment is mounted on the carrier can be solved somewhat, but it has been found that it does not solve the problem of forming hot spots in the segment.

In addition, Japanese Patent Application Laid-Open No. 2001-130970 and Japanese Patent Application Laid-Open No. 2001-130973 disclose a technique of using a top carrier and a bottom carrier to enclose a ceramic segment in a state of being in close contact with each other to apply pressure to a molded body. However, the above technologies have a problem in that the cost of manufacturing is increased due to the complicated structure of the carrier itself, such as using a combination of two carriers (hot air drying jig) and a configuration for pressurizing the molded body when it is mounted. Furthermore, there is a disadvantage in that the probability of cell breakage of the segment increases during the pressing process.

In addition, Japanese Patent Application Laid-Open No. 2003-145521 discloses a technique for rotating the surface facing the carrier of the segment molding upwards in the middle of the microwave drying process to prevent deformation of the segment molding occurring during the drying process. . However, experiments conducted by the present inventors confirmed that hot spots still occur in the segment molded article even when the above technique is used. In addition, by lifting and rotating the segment molding which is not completed in the drying process, it is highly likely to cause deformation of the segment molding by an external force, and the rotation process of the segment molding is not easy from the technical point of view. There are many problems such as being there.

US Pat. No. 5,322,363 discloses a technique in which a turn table is installed in a dryer for uniform drying of a segment molding, thereby placing a segment on the turn table and rotating about an axis. However, the above technique does not move the position of the center portion of the segment, and in particular, it is not possible to prevent hot spots that occur intensively in the center portion, and because the segment is mounted on a turn table, a series of processes are performed, so that it is difficult to carry out a continuous process or However, it is not preferable in terms of the cost of the process.

Therefore, by preventing the occurrence of local hot spots on the segment molding during microwave drying, there is no need for a technique for producing a segment having a uniform physical properties and high filtering efficiency without causing deformation, distortion, etc. in the segment molding. It is true.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

After in-depth study and various experiments, the present inventors changed the transfer path of the segment molding in a predetermined pattern with respect to the application position of the microwave in the microwave dryer during the microwave drying process, thereby causing local hot spots in the segment molding. It prevents the deformation, such as bending, torsion, etc. in the segment molding, and since the physical properties are uniform, ultimately confirming that the filtering efficiency can be increased and the present invention has been completed.

Accordingly, the present invention is a method for producing a silicon carbide segment for honeycomb ceramic filter as a soot filtration device (DPF) by a process including a step of microwave drying and sintering after cutting a segment molding cut to a predetermined size after extrusion, In order to prevent local hot spots from occurring in the segment molding during the microwave drying process, the conveying path of the segment molding is configured to be changed in a predetermined pattern with respect to the microwave application position of the microwave dryer.

In a specific example, the manufacturing process of the silicon carbide segment for the honeycomb ceramic filter may include, for example, extruding the segment composition paste (1), cutting the extrudate to a predetermined size (2), and cutting the molded product. It may be composed of a first drying step (3), a second drying step using a hot air (4), and a sintering step (5) to a microwave.

According to the present invention, in the microwave drying process, as the pattern is changed to the microwave application position of the microwave dryer, a uniform hot spot is possible, so that local hot spots (hot spots) may be generated due to uneven distribution of paste components. spots can be prevented.

Therefore, it is possible to solve the problem of deformation, such as bending and torsion, in the segment molding caused by hot spots, and to uniformize the physical properties of the segment molding, thereby preventing defects or cracks from occurring in the final manufactured segment. Ultimately, segments with good filtering performance can be produced.

The hot spot is found to occur mainly in the center of the segment molding. This is because, during the melt extrusion of the segment composition paste, moisture outside the extrudate of the semi-melt (reaction solid state) discharged from the extruder is partially dried, so that the amount of moisture contained in the center of the extrudate is contained outside. Since it is relatively larger than the amount of, it is presumed that a large amount of water present in the center of the extrudate upon application of microwaves causes high heat.

Therefore, the pattern of change of the transfer path is such that the transfer path of the center point of the segment molded product is a straight line between the start point and the end point with respect to the straight path of the start point and the end point when the segment molded product passes through the microwave dryer. It is preferably configured to deviate from the path.

In one preferred example, the changing pattern of the conveying path may result in a single wave type or reciprocating waveform with respect to the straight path.

That is, since the conveying path of the segment molding is formed in a wave shape, the position of the center portion of the segment molding is moved up and down, so that the possibility of microwave concentration in a specific portion of the segment molding is reduced, whereby hot spots are generated at the center point of the segment molding. It can be minimized.

In order that the drying process can be carried out in a continuous process, it can be preferably configured to pass through the microwave dryer with the segment molding positioned on the conveyor belt.

On the other hand, the segment molding is preferably carried in a carrier that can be moved by an external force on the conveyor belt. Therefore, it is possible to minimize the occurrence of deformation, such as bending or twisting, of the segment molding from being affected by external materials or during drying.

In one preferred embodiment, the segment moldings consist of an overall elongated hexahedral structure and correspondingly the carrier has a structure (V-dry setter) comprising a receiving portion formed with one side edge of the segment facing downward. Can be done. Therefore, since the vertical cross-sectional shape of the carrier is V-shaped, the contact surface pressure can be reduced while widening the contact area with the segment molding.

The position of the carrier can be changed in various ways. In one preferred embodiment, the carrier is moved along the transfer guide by installing a transfer guide at a position spaced apart from the upper surface of the conveyor belt by a predetermined height inside the microwave dryer. The location can be changed. Therefore, the segment molding can prevent the microwaves from being concentrated on a specific part of the segment molding by changing the path by a conveyance guide provided in a predetermined pattern while the carrier on which it is mounted is transferred by the conveyor belt.

The extrusion process may be achieved by extrusion molding a paste comprising, for example, SiC powder and fibers, organics as binders, oxides, moisture, and the like as the segment composition. The segment molding extruded by the extrusion process is subjected to a cutting process of cutting to a predetermined size, and then the segment molding is mounted on a carrier and moved to a dryer. The carrier used in the molding step and the carrier used in the drying step may be the same or different. If they are identical to each other, for example, during the extrusion process, one support surface of the carrier is almost horizontal to receive the molded product at such a support surface, and then the carrier is changed to a predetermined angle to perform a drying process to uniformly dry the molded product. Can be configured to be possible.

The extrudates contain moisture, solvents, and the like, and when such components are present, they prevent the bonding of the sintering components in the sintering process and thus weaken the overall strength of the segment, thereby preventing handling and facilitating handling in subsequent processes. To this end, a drying step of removing these liquid components is performed.

As a drying process, hot air drying is generally performed, but hot air drying is preferable in view of economical efficiency of the process and complete removal of moisture, but since drying proceeds from the outside of the segment molding, it takes a lot of time to remove moisture from the inner (core) part. It takes a disadvantage that the deformation process such as bending of the segment is likely to occur in the drying process. Therefore, before performing hot air drying, the drying process may be performed by microwaves to remove moisture from the core portion.

In the microwave drying step, the output of the microwave is not particularly limited. When the output is low, the drying time is long, which is not preferable in terms of efficiency of the manufacturing process, and when the output of the microwave is high, the binder is ignited. For example, when the size of the ceramic molded body is 33 mm × 33 mm × 300 mm, the number of cells is 31 / cm ² , and the thickness of the partition wall is 0.35 mm, for example, 0.5 to 4 kW or so. .

The hot air drying is not particularly limited, and for example, hot air drying means such as ventilation or hot air circulation may be used.

In some cases, in the case of a honeycomb structure having a ceramic component as a main component, a sintering process may be further performed after the drying process for the mutual coupling reaction of the ceramics. Sintering conditions, such as the said sintering temperature and a sintering atmosphere, can be suitably determined according to a ceramic raw material. For example, a standard cordierite plug may be sintered at a temperature of about 1400 ° C., and may be lowered to a temperature range of about 900 to 1300 ° C., depending on the type of plug.

In addition, when the honeycomb structure is used as a filter such as a DPF, a process of selectively plugging pores of the segment is performed. The plugging process may be performed at any stage after the extrusion molding process, If it is necessary to perform the sintering process, it may be preferable to be carried out before the sintering process in consideration of the efficiency of the process.

The segment molded product having a ceramic as a main component can be used in various filters or carriers, and especially when the main component contains silicon carbide having excellent heat resistance and hardly deforming at high temperatures, the segment molded article can be preferably used.

The present invention also provides a silicon carbide segment for a honeycomb ceramic filter manufactured by the above method, and a honeycomb ceramic filter manufactured by joining a plurality of the silicon carbide segments.

The shape of the silicon carbide segments may vary and, in one preferred embodiment, the silicon carbide segments may have a rectangular parallelepiped structure in cross section.

The ceramic filter may be manufactured by bonding, drying, and sintering a plurality of segments into an adhesive layer made of an adhesive paste. On the other hand, the number of silicon carbide segments bonded to each other is appropriately determined according to a desired standard of the honeycomb ceramic filter on which the catalyst component is supported.

Structure and manufacturing method of the honeycomb ceramic filter is known, the detailed description thereof will be omitted herein.

The present invention also provides a drying set for mounting a segment.

In the present invention, the dry setter for mounting the segment refers to a kind of carrier on which a segment molding is mounted when moving to a drying apparatus for a microwave drying process in manufacturing a silicon carbide segment for a honeycomb ceramic filter, and one side edge of the segment molding is lower The housing is formed to face the at least one opening formed on the housing so as to minimize the contact area of the molded article with respect to the housing.

Through the openings formed on the housing, the reflected microwaves are also applied to the surface of the segment facing the housing, whereby heating efficiency can be increased, and vapor, solvent component, etc. generated in drying can evaporate. Therefore, the drying efficiency can also be increased.

The material of the dry setter is not particularly limited as long as the temperature rise due to microwave heating is lower than the temperature rise of the ceramic molded body itself, and it is appropriate that the loss factor for the microwave is smaller than the loss factor of the ceramic material. This is because the smaller the loss coefficient is, the more the temperature rise during microwave heating is suppressed, so that the temperature of the dry setter can be kept lower than the temperature of the ceramic formed body. As a specific example, melamine resin, glass fiber, epoxy resin, calcined ceramic material, Teflon® resin, mica resin, alumina resin, polyethylene resin, silicone resin and the like can be used.

In one preferred example, the drying set may have a structure including a V-shaped accommodating portion and a plurality of indentations formed on both sides of the accommodating portion to communicate with the accommodating portion in a vertical cross section. Here, preferably, the indentation may be formed at a position corresponding to the minimum drying point of the microwave so that the segment molding may be uniformly dried.

Hereinafter, the present invention will be further described with reference to the drawings according to embodiments of the present invention, but the scope of the present invention is not limited thereto.

3A schematically illustrates a microwave drying process of a silicon carbide segment molding for a honeycomb ceramic filter according to one embodiment of the present invention, and FIG. 3B schematically illustrates a vertical cross section thereof.

First, referring to FIG. 3A, a microwave oscillator 310 such as a magnetron is mounted on the top and bottom of the microwave dryer 300, respectively, to radiate microwaves generated from the oscillator into the dryer 300. The desired dry matter is dried. Since the inner wall surface, the upper surface and the lower surface of the dryer 300 are all formed in a plane, when the microwave output from the microwave oscillator 310 is radiated to the dryer 300, the microwaves and the inner wall surface of the dryer 300; After hitting the planes of the upper, lower, and the like, they are reflected and deflected without being uniformly distributed.

Both sides 330a and 330b of the dryer 300 may be open or open to allow the segment molding 200 to pass through continuously and automatically. At this time, both sides (330a, 330b) is provided with a radio wave absorber (not shown) can prevent the leakage of radio waves.

The segment molding 200 is conveyed along the conveyor belt 320 in a state of being perpendicular to the traveling direction of the conveyor belt 320 moving in the longitudinal direction. In this case, the segment molding 200 may be transported in a mounted state by a carrier (not shown). The segment molding 200 may include a time point at which the center point of the segment molding 200 enters the dryer by a plurality of transfer guides 340 installed in the dryer 300 at a position spaced apart from the conveyor belt 320. It is conveyed while drawing a large semicircle so as to deviate from the straight path S between the discharged end points. Such a transfer path may vary as described above, such as a single waveform or a reciprocating waveform.

The shape of changing the conveying path of the segment molding 200 at the position where the conveying guides 340 are spaced apart from the conveyor belt 320 can be more clearly seen in FIG. 3B.

That is, microwaves may be uniformly applied by the positional variation of the segment molding 200, and in particular, as the center point of the segment molding 200 moves, a hot spot phenomenon intensively occurring at the center point may be prevented. Accordingly, the deformation of the segment molding 200 does not occur, such as bending or warping, and since the physical properties of the final manufactured segment are uniform, it may ultimately have a very good filtering performance.

4A shows a perspective view of a dry setter of silicon carbide segments according to one embodiment of the invention, and FIG. 4B shows a front view of a silicon carbide segment mounted on the dry setter according to FIG. 4A.

Referring to these drawings, the dry setter 400 is composed of a receiving portion 410 and a plurality of indentation 420. The accommodating part 410 is formed in a V shape in a vertical cross section, and is accommodated so that one side edge of the segment molding 200 faces the lower end. The indentation part 420 is formed at both sides of the accommodating part 410 to communicate with the accommodating part 410. That is, the segment molding 200 is transferred along the conveyor belt in the dryer while being mounted on the drying setter 400. Therefore, the reflected microwave can also be applied to the surface facing the receiving portion 410 of the segment molding 200, so that uniform drying is possible, and gaseous components such as water vapor generated by drying through the indentation 420 Since it can be discharged, it is excellent in terms of drying efficiency.

While the above has been described above with reference to embodiments according to the present invention, those of ordinary skill in the art to which the present invention pertains can make various applications and modifications within the scope of the present invention. will be.

As described above, in the method of manufacturing the silicon carbide segment for honeycomb ceramic filter according to the present invention, in the microwave drying process, the transfer path of the segment molded product may be applied to the microwave application position of the microwave dryer so that no local hot spot occurs during drying. By changing to a predetermined pattern, it is possible to prevent hot spots from occurring in the segment in the microwave drying process, thereby to prevent deformation, such as bending and warping, and to uniformize the physical properties of the segment, thereby ultimately having excellent filtering performance.

Claims (11)

A method of manufacturing a silicon carbide segment for a honeycomb ceramic filter, which is a soot filtration device (DPF), by a process including a step of microwave drying, a hot air drying, and then sintering a segment molded product cut into a predetermined size after extrusion, In order to prevent local hot spots from occurring during the microwave drying process, the conveying path of the segment molding is changed in a predetermined pattern with respect to the application position of microwaves in the microwave dryer, The change pattern of the transfer path is characterized in that the transfer path of the center point of the segment molding is separated from the straight path of the starting point and the end point with respect to the straight path of the starting point and the end point when the segment molding passes through the microwave dryer. Way. delete The method of claim 1, wherein the change pattern of the transfer path forms a single waveform or a reciprocating waveform with respect to the linear path between the start point and the end point. The method of claim 1 wherein the segment molding passes through a microwave dryer in a state of being placed on a conveyor belt. 5. A method according to claim 4, wherein the segment moldings are mounted and transported in a carrier which can be moved by an external force on a conveyor belt. 6. The structure according to claim 5, wherein the segment molding has an overall elongated hexahedral structure, and correspondingly, the carrier includes a receiving portion formed in a V shape so that one side edge of the segment faces the bottom (V-drying). Setter) characterized in that consisting of. The manufacturing method according to claim 4, wherein a inside of the microwave dryer is provided with a transfer guide capable of changing the position of the carrier being transferred at a position spaced apart from the upper surface of the conveyor belt by a predetermined height. A dry setter in which the segment molding is mounted when manufacturing a silicon carbide segment for a honeycomb ceramic filter by a process including microwave drying, hot air drying, and sintering a segment molding cut to a predetermined size after extrusion. And a receiving part formed with one side edge of the molding facing the lower end, and at least one opening formed on the receiving part so as to minimize the contact area of the segment molding with respect to the receiving part. 9. The segment mounting apparatus of claim 8, wherein the drying setter includes a receiving portion formed in a V-shape in a vertical cross section and a plurality of indentations formed on both sides of the receiving portion to communicate with the storing portion. Dry setter. A silicon carbide segment for a honeycomb ceramic filter made by the method according to claim 1. A honeycomb ceramic filter manufactured by joining a plurality of silicon carbide segments according to claim 10.

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