JPH07185264A - Honeycomb heater - Google Patents

Abstract

PURPOSE:To improve the efficiency of deodorizating effect, extend the life of a catalyst, and prevent the deterioration of an electrode part by uniformizing the temperature distribution by heating of a catalyst-carrying honeycomb heater by electricity application. CONSTITUTION:The temperature distribution is uniformized by installing electrode parts 1a, 1b in a honeycomb heater, cutting the corners as to prevent overheating of the outer circumference part where the rib 3 is thick and electric current converges, and forming a slit or a U-shape groove so as to heighten the electric resistance in the outer circumference part. Overheating is prevented and the deterioration of the electrode parts due to oxidation is prevented by making the surface area of an open part large by altering the shape of the cell near the electrode parts 1a, 1b.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a hot air heater for heating,
The present invention relates to a high-temperature heater for industrial use, a heater for carrying a catalyst or a heater for deodorizing a toilet, a heater for purifying exhaust gas of an internal combustion engine of an automobile, and the like, and a honeycomb heater used for these.

[0002]

2. Description of the Related Art Heretofore, there have been hot air heaters and hair dryers using lead titanate having a positive resistance temperature characteristic as a material using a honeycomb heater. The structure of this honeycomb heater is one in which electrodes are provided perpendicularly to the ventilation passages of the cell, and the resistance temperature characteristic is a positive characteristic, so even if the wall thickness of the outer peripheral part is increased in order to strengthen the structure, the temperature The distribution was uniform and there was no problem of heat concentration.

Further, as disclosed in Japanese Utility Model Laid-Open No. 4-46389, the electrodes of the honeycomb ceramic heater body are formed in an arc shape, and the distance between the opposing electrodes is minimum at the end and maximum at the center. Therefore, there is one in which the electric resistance of the central portion is increased to prevent the central portion from being overheated, so that the temperature distribution of blown air due to ventilation is made uniform. In Japanese Unexamined Patent Publication No. 5-115793, when electrodes are provided at the center and the outer periphery of an electric heating type cylindrical honeycomb body for heating a catalyst at engine start (at cold start) in an exhaust gas purifying apparatus, In order to prevent overheating of the central part due to current concentration and to uniformly heat the honeycomb body, the width of the honeycomb body in the exhaust gas flow direction increases from the outer circumference to the center, and the energization area is almost constant from the center to the outer circumference. In some cases, the blowing temperature distribution of the honeycomb body is made uniform.

[0004]

The honeycomb heater used in the present invention is a resistor having a slightly negative resistance-temperature characteristic, and the electrode is also located on the outer peripheral portion parallel to the ventilation passage of the cell. is there. It is necessary to increase the number of cells in order to support the catalyst and enhance the catalytic effect, but in order to avoid an increase in pressure loss during ventilation due to this, if the wall thickness of the cell, that is, the thickness of the rib is reduced, it is especially the outer circumference. If the electrode layer is formed by spraying a metal such as Al or Ni on the opposing outer peripheral portions, the electrode layer may peel due to the difference in the coefficient of thermal expansion during energization. . Even if electrodes are formed by brazing a lead wire or a lead plate on the outer peripheral portion, the strength of the electrode portion cannot be increased.

If there are electrodes facing each other on the outer peripheral portion, a current flows in parallel to the ribs of the cell. Therefore, if the resistance of the ribs is uneven, the current concentrates on the portion having a small resistance and the temperature distribution of the heater becomes ununiform. It becomes uniform, the efficiency of the catalyst effect does not increase, and it is difficult to improve the catalyst life. When the resistance temperature characteristic is a negative characteristic, these things are remarkable.

[0006] Therefore, an object of the present invention is to provide a honeycomb heater in which the strength of the outer peripheral portion is improved and the temperature distribution is uniform.

[0007]

According to the present invention, conductive material such as SiC and metallic auxiliary material Si are extrusion-molded and fired in a nitrogen atmosphere to react N ₂ with metallic Si to produce Si ₃ N _Four
Electrodes that are parallel to the ventilation direction of the cell are provided on the outer peripheral portion of the honeycomb heater, and the shape of the outer peripheral portion on the side where the current flows or the shape of the cell is made uniform while maintaining mechanical strength. The shape is such that the temperature distribution is uniform during ventilation, and the shape of the cell is changed to prevent the electrode portion from overheating.

[0008]

[Function] Since only a part of the outer peripheral portion of the honeycomb heater is thicker than the thickness of the rib of the internal cell, the strength of the entire heater is maintained by that portion, and at the same time, the resistance value of each portion viewed from the electrode is It is almost the same as the resistance value of the cell. Further, by changing the shape of the cell in the vicinity of the electrode portion or the outer peripheral portion on the conduction side to increase the opening area, the ventilation resistance is reduced, overheating of the electrode portion is prevented, and the temperature distribution is made uniform.

[0009]

EXAMPLE The material of the honeycomb heater of the present invention may be a metal or a ceramic, and the manufacturing method will be described especially for a material comprising a ceramic containing SiC as a main component.

As shown in FIG. 1, firstly, in order to obtain a predetermined resistance value as a main material, the average grain size is 2 when the grain size is 40 μm or less and the cell wall, that is, the rib 3 of the cell is small in thickness.
30 parts by weight of SiC having a particle size of 6 μm or less and metallic Si having a particle size of 6 μm
40 parts by weight and 30 parts by weight of Si ₃ N ₄ having a particle size of 1 μm were mixed, and a water-soluble methyl cellulose or polyvinyl alcohol as a binder, glycerin as a plasticizer, and an acrylic dispersant were added thereto. Add water, and mix and knead water while adjusting the hardness to an appropriate level. Cell number 70 / cm ² , cell rib thickness 0.27
mm square cell with outer rib thickness of 0.4 mm
Using the mold of No. 3, the outer peripheral rib having a thickness larger than the inner rib is extruded by a high-pressure vacuum forming machine. The formed product is cut into a predetermined length with a wire saw or the like, heated by microwave and dried. When the molded body is degreased and fired in a nitrogen atmosphere at 1100 ° C. to 1400 ° C., the metal Si in the raw material reacts with nitrogen to form silicon nitride, which can be bonded to silicon carbide to obtain a good sintered body. . At this time, the pressure of the nitrogen atmosphere may be normal pressure or a pressurized state, or may be a mixed gas with an inert gas such as argon or helium.

In order to stabilize the electric resistance value of the obtained sintered body and reduce the increase rate of the electric resistance value during use, 70
Heat treatment is performed in the atmosphere at 0 ° C. to 1200 ° C., preferably 800 ° C. for 4 hours. The porosity of the obtained sintered body is 35%.
The average pore size is 0.02 μm, and the final size is 40 × 40 ×.
It becomes 15 mm ^t .

Next, Al, which is a conductive material, was thermally sprayed to a thickness of 0.2 mm on the opposing outer peripheral portions of the honeycomb ceramic heater to form an electrode layer, and the sprayed surface had an A of 0.5 mm ^t .
The electrode plate clad with the 1-Si alloy and the brazing material is preheated and ultrasonically bonded. The peel strength of the electrode plate at this time is 8 kg
Although f can withstand practical use, if the thickness of the ribs of the electrode portions 1a and 1b is the same as that of the cell, it becomes 2 kgf, and it is necessary to increase the thickness of the ribs of the electrode portion. Further, since the electrode portion also generates a large thermal stress due to overheating by energization, it is necessary to increase the thickness of the rib.

Next, by supporting a catalyst on this honeycomb ceramic heater, it is possible to remove and deodorize toxic gases such as carbon monoxide and ammonia. As a method of supporting the catalyst, for example, it is immersed in an aqueous solution containing Mn ions such as manganese hydroxide to deposit Mn oxide or hydroxide on the surface, which is then heat-treated at high temperature to be converted into manganese dioxide. An appropriate amount to be loaded is about 20 to 100 g per 1000 cm ^{3 of the} honeycomb ceramic heater. Similarly, a noble metal acid aqueous solution may be used.

Thus, the original shape of the honeycomb-shaped ceramic heater according to the present invention is obtained. However, the electrode portion is not shown in FIG.

AC1 is added to the ceramic heater shown in FIG.
When 00 V was applied to generate heat, the temperature of the conductive portion at the outer peripheral portion where the rib thickness was large exceeded 400 ° C. and was 200 ° C. or less inside.

Therefore, according to the present invention, in order to make the temperature of each part of the ceramic heater uniform, as shown in FIG. 2 or 3, all the thick parts of the ribs 2a, 2b of the conductive part in the outer peripheral part are removed or the electrode part thereof is removed. When a part close to was left, the temperature difference of each part was within 30 ° C.

The present invention is a method for making the temperature of each part uniform while maintaining the strength of the outer peripheral part, as shown in FIG.
A plurality of slits 5 are provided in the molding direction at the time of extrusion molding to 2b to electrically shut off and prevent overheating. Also,
As shown in FIG. 5, by removing the corner 6 without electrically interrupting the conducting portions 2a and 2b, the width of the conducting portion 2a and 2b can be narrowed as compared with the inside, and as shown in FIG. By providing a plurality of V-shaped slits 7 in parallel or by providing a large U-groove 8 in the current direction of the conducting portions 2a, 2b as shown in FIG. 7, the electric resistance value is increased or the ventilation resistance is lowered to obtain a temperature distribution. To make it uniform.

Next, according to the present invention, as shown in FIG. 8, the shape of a plurality of cells 9 in the vicinity of the conducting portions 2a, 2b on the outer peripheral portion is changed to make the opening area larger than that of the inner cells, thereby increasing the ventilation volume. By increasing the amount, heat exchange is facilitated, overheating is prevented, and the temperature distribution is made uniform.

Further, in the present invention, the heat resistant temperature of the electrode layer 1a, 1b on which the Al--Si alloy (not shown) is sprayed is about 400.degree. Since it is difficult to secure reliability, as shown in FIG. 9, the shape of a plurality of cells 10 in the vicinity of the electrode portions 1a and 1b is changed to increase the opening area to reduce the air blowing resistance and increase the air blowing amount. By lowering the temperature of the part, the oxidative corrosion of the electrode layer and the electrode plate is prevented.

It should be noted that the present invention is not limited to the shape shown in FIG. 1, and the cell shape and the outer shape of the ceramic heater can take various shapes such as a circle or a polygon. The cell density is preferably 16 / cm ^{2 to} 100 / cm ² , and the rib thickness is preferably 0.1 to 0.3 mm.

[0021]

According to the present invention, by making the thickness of the electrode portion of the honeycomb heater larger than that of the rib of the cell, it is possible to prevent the electrode portion from being damaged by an external force applied to the electrode portion or a thermal stress during heating. You can

Further, by removing a part or all of the conducting portion on the outer peripheral portion of the honeycomb heater, the temperature distribution can be made uniform while maintaining the mechanical strength of the electrode portion.

By providing a plurality of slits in the conductive portion on the outer peripheral portion during extrusion molding of the honeycomb heater, it is possible to reduce current concentration and make the temperature distribution uniform while maintaining the mechanical strength of the conductive portion.

By making the width of the conducting portion on the outer peripheral portion of the honeycomb heater narrower than that of the inside, the temperature distribution can be made uniform while maintaining the mechanical strength of the conducting portion.

By increasing the opening area of the cells adjacent to the conducting portion on the outer peripheral portion of the honeycomb heater, the amount of ventilation increases, heat exchange becomes easy, and the temperature distribution becomes uniform.

By increasing the opening area of the cells adjacent to the electrode portion of the honeycomb heater, the electrode portion is not overheated and deterioration due to oxidation of the electrode plate or the electrode layer is prevented in the same manner, and long-term reliability is ensured. Can be secured.

[Brief description of drawings]

FIG. 1 is a perspective view of a honeycomb heater showing an embodiment of the present invention.

[Fig. 2] Fig. 2 is a perspective view of a honeycomb heater in which an outer peripheral portion is deleted, which is another embodiment of the present invention.

[Fig. 3] Fig. 3 is a perspective view of a honeycomb heater according to another embodiment of the present invention in which a part of an outer peripheral portion is deleted.

[Fig. 4] Fig. 4 is a perspective view of another embodiment of the present invention, a honeycomb heater provided with slits in the extrusion molding direction.

FIG. 5 is a perspective view of a honeycomb heater according to another embodiment of the present invention, in which a corner of an outer peripheral portion is deleted.

FIG. 6 is a perspective view of a honeycomb heater in which a V-shaped slit is provided in a current conducting portion which is another embodiment of the present invention.

[Fig. 7] Fig. 7 is a perspective view of a honeycomb heater in which a U groove is provided in a current conducting portion according to another embodiment of the present invention.

FIG. 8 is a perspective view of a honeycomb heater having a large opening area in the vicinity of a current conducting portion according to another embodiment of the present invention.

FIG. 9 is a perspective view of a honeycomb heater having a large opening area in the vicinity of an electrode part according to another embodiment of the present invention.

[Explanation of symbols]

 1a, 1b Electrode part 2a, 2b Current conduction part 3 Cell rib 5 Slit 6 Corner 7 V-shaped slit 8 U groove

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location F01N 3/24 ZAB K F24H 3/00 B H05B 3/02 A 7512-3K 3/14 C 7512-3K

Claims (6)

[Claims] 1. In a ceramic heater which contains a conductive material, silicon carbide, and is formed into a honeycomb shape and sintered to carry a catalyst, the wall thickness of the cell at the outer peripheral portion is made larger than the wall thickness of the inner cell, A honeycomb heater characterized in that an electrode portion for electric heating is provided on a part of the outer peripheral portion. 2. The honeycomb heater according to claim 1, wherein a part or all of the current conducting portion on the outer peripheral portion is deleted to make the temperature distribution uniform. 3. The honeycomb heater according to claim 1, wherein a plurality of slits are provided in a molding direction in a current conducting portion at an outer peripheral portion at the time of extrusion molding so as to electrically cut off or increase an electric resistance value to obtain a temperature distribution. A honeycomb heater characterized by being made uniform. 4. The honeycomb heater according to claim 1, wherein a corner is deleted in a current conducting portion on an outer peripheral portion in parallel with a current direction, or a U groove or a plurality of slits are provided to narrow a current conducting region. The honeycomb heater is characterized by increasing the electric resistance value and making the temperature distribution uniform. 5. The honeycomb heater according to claim 1, wherein an opening area of a plurality of cells adjacent to a current conducting portion on an outer peripheral portion is increased to reduce a ventilation resistance and to make a temperature distribution uniform. A honeycomb heater. 6. The honeycomb heater according to claim 1, wherein an opening area of a plurality of cells adjacent to the electrode portion is increased to reduce air flow resistance and prevent overheating of the electrode portion. Honeycomb heater.