JPH04246226A - Resistance regulating type heater - Google Patents

Abstract

PURPOSE:To obtain a resistance regulating heater which is excellent in durability and temperature rise characteristics and provided with even heating characteristics and increased heating area. CONSTITUTION:Electrodes 14 are provided in a honey-comb construction body 13, and slits 11 are provided between the electrodes 14. The slits 11 are formed at a specified angle relative to partitions 10 of the honey-comb construction body 13 to regulate resistance across the terminals 14.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heater made of a honeycomb structure and having a resistance adjustment function. These can be suitably used as consumer heaters such as hot air heaters, and industrial heaters such as preheaters for purifying automobile exhaust gas.

0002

[Prior Art] Recently, catalysts and catalyst carriers have been developed for purifying nitrogen oxides (NOX), carbon monoxide (CO), and hydrocarbons (HC) in exhaust gas emitted from internal combustion engines such as automobiles. In addition to the conventionally known porous ceramic honeycomb structures, metal honeycomb structures have started to attract attention.

On the other hand, as exhaust gas regulations become stricter, there is a strong desire to develop heaters and the like that reduce emissions during cold starts. As such a honeycomb structure, for example, Japanese Patent Publication No. 58-23138 and Utility Model Application No. 6
The method described in Japanese Patent No. 3-67609 has been proposed.

[0004] Japanese Patent Publication No. 58-23138 discloses a foil type metal honeycomb structure. This honeycomb structure is made by mechanically deforming a flat plate into a corrugated shape and rolling it up together with the flat plate to form a metal base. Then, the surface of the metal substrate is oxidized to form an aluminum oxide film, and this film supports a high surface area oxide such as alumina, and is further impregnated with precious metals, etc., and is used as a catalyst for purifying automobile exhaust gas. be.

Further, Japanese Utility Model Application Publication No. 63-67609 discloses the use of a metal monolithic catalyst, which can conduct electricity, in which a metal carrier is coated with alumina, as a preheater.

[0006]

[Problems to be Solved by the Invention]] However, in the foil type metal honeycomb structure described in Japanese Patent Publication No. 58-23138, the adhesion with the catalyst layer is poor due to the poor porosity of the metal substrate on which the coating is formed. The disadvantage is that the catalyst is weak, and the catalyst is easily peeled off due to the difference in thermal expansion between the ceramic catalyst and the metal base. Additionally, during the operation cycle, the telescope phenomenon in which metal-to-metal joints separate and deform into convex parts in the direction of gas flow is likely to occur, which can cause serious operational problems. However, there are problems in that the rolling yield of the foil is low and the manufacturing cost is high. Also, Utsukai Showa 63-
The preheater of Publication No. 67609 was also published in 1986-231.
Similar to Publication No. 38, there is a drawback that the catalyst tends to peel off due to the difference in thermal expansion between the alumina and the metal carrier, and at the same time, the metal-to-metal joint of the metal base peels off during operation.
There is a problem in that an insulating part is formed, causing uneven current, and uneven heat generation.

Furthermore, the preheater disclosed in Japanese Utility Model Application Publication No. 63-67609 generates heat by simply passing electricity from the inner circumference to the outer circumference of a foil-type metal honeycomb structure, and its resistance is not adjusted ( In other words, the desired resistance is not adjusted only by the material, dimensions, and rib thickness), and the temperature rise characteristics are not only insufficient, but because the electrodes are provided on the inner periphery, the center does not act as a catalyst,
Moreover, there is a problem in that it causes pressure loss. Furthermore,
The disadvantage is that the electrodes are easily detached by the gas flow.

[0008] Therefore, the present applicant has previously proposed a heater in which a honeycomb structure is provided with at least two electrodes for energizing, and a resistance adjustment mechanism is provided between the electrodes.
(Patent Application No. 96866/1999). The present invention provides further improvements to this heater.

[0009]

[Means for Solving the Problems] That is, according to the present invention, at least two electrodes for supplying electricity are provided in a honeycomb structure having a large number of through holes, and a partition wall of the honeycomb structure is provided between the electrodes. A resistance-adjustable heater is provided, characterized in that the resistance between the electrodes is adjusted by forming slits at a predetermined angle to heat the gas fluid in the through holes in the honeycomb structure.

Further, according to the present invention, there is provided a resistance-adjustable heater having a heater function and an exhaust gas purifying function, which is formed by supporting a catalyst on the honeycomb structure. Moreover, in the above, it is preferable to use, as the honeycomb structure, one obtained by forming a powder raw material into a honeycomb shape and sintering it.

[0011]

[Operation] In the present invention, electrodes are provided in a honeycomb structure having a large number of through holes, and slits are formed between the electrodes at a predetermined angle to the partition walls of the honeycomb structure to adjust the resistance between the electrodes. This is a resistance-adjustable heater. That is, by adjusting the resistance, the heat generation property can be controlled, and it becomes possible to raise the temperature locally or globally in accordance with various uses.

[0012] Furthermore, it is preferable that the above-mentioned honeycomb structure is produced by forming a powder raw material into a honeycomb shape and sintering it. In this case, it is preferable to use so-called powder metallurgy and extrusion molding, which have the advantage of simplifying the process and reducing costs. Further, it is preferable that the heater is formed into a honeycomb structure (integrated body) using powder raw materials, since the telescope phenomenon does not occur and uniform heat generation can be achieved.

[0013]Patent application No. 2-9686, which is the applicant's earlier application.
In No. 6, the example suggests that each cell of the honeycomb structure is approximately square, and the slit, which is a resistance adjustment mechanism, is provided in the same direction as the cell partition wall.
In that case, when a current is passed between the electrodes, no current flows through all the ribs (partition walls) between the electrodes (that part does not generate heat),
It has been found that the overall heat generation may be insufficient.

Accordingly, the present invention solves the above problem by forming the slits not in the same direction but at a predetermined angle with respect to the partition walls of the honeycomb structure. When the slits are formed in this way, current flows through all the ribs (partition walls) between the electrodes, so the heat generating area increases compared to the above case, and as a result, the heat exchange surface area increases.

To explain this based on the drawings, when the slits 11 are formed at a predetermined angle with respect to the direction of the partition walls 10 of the honeycomb structure, the square cell structure 12 between the slits 11 is formed as shown in FIG. It is in a state where it has a predetermined angle with respect to the current flow direction. On the other hand, the patent application Hei 2-
In the case of the heater No. 96866, as shown in FIG. 2, in the square cell structure 12 between the slits 11, half of the partition walls 10a are formed in the same direction as the current flow direction. Therefore, in the case of the cell structure shown in FIG. 1, compared to the cell structure shown in FIG. 2, current flows through many ribs (partition walls) 10, resulting in an increased resistance and an increased heat generating area.

[0016] In the resistance-adjustable heater of the present invention, the surfaces of the partition walls and pores of the metallic honeycomb structure are coated with Al2O.
It is preferable to coat with a heat-resistant metal oxide such as 3 or Cr2O3 because heat resistance, oxidation resistance, and corrosion resistance are improved.

The constituent material of the honeycomb structure, which is the base of the present invention, is not limited as long as it is made of a material that generates heat when energized, and may be either metal or ceramic, but metal has high mechanical strength. Therefore, it is preferable. In the case of metals, for example, stainless steel, Fe-Cr-Al, Fe-C
Examples include those made of materials having compositions such as r, Fe-Al, Fe-Ni, W-Co, and Ni-Cr. Among the above, Fe-Cr-Al, Fe-Cr, and Fe-Al are preferable because they have excellent heat resistance, oxidation resistance, and corrosion resistance, and are inexpensive. Furthermore, if it is made of metal, it may be formed into a foil type.

The honeycomb structure of the present invention may be porous or non-porous, but when supporting a catalyst, the porous honeycomb structure has strong adhesion to the catalyst layer. This is preferable because peeling of the catalyst due to differences in thermal expansion hardly occurs. Further, even in the case of a non-porous honeycomb structure, since the present invention includes a resistance adjustment mechanism such as a slit, thermal stress is relaxed and cracks are less likely to occur.

Next, an example of a method for manufacturing a metallic honeycomb structure among the honeycomb structures of the present invention will be explained. First, to obtain the desired composition, for example, Fe powder, Al powder, C
A metal powder raw material is prepared using R powder or an alloy powder thereof. Next, the metal powder raw material prepared in this way is mixed with an organic binder such as methyl cellulose or polyvinyl alcohol, and water, and then this mixture is extruded into a desired honeycomb shape.

[0020] When mixing the metal powder raw material, organic binder, and water, it is recommended to mix an antioxidant such as oleic acid with the metal powder before adding water, or use a metal powder that has been previously treated to prevent oxidation. It is preferable to do so. Next, the extruded honeycomb molded body is fired at 1000 to 1400°C in a non-oxidizing atmosphere. Here, it is preferable to perform the firing in a non-oxidizing atmosphere containing hydrogen because the organic binder is decomposed and removed using Fe or the like as a catalyst, and a good sintered body can be obtained.

[0021] If the firing temperature is less than 1000°C, the molded body will not be sintered, and if the firing temperature exceeds 1400°C, the obtained sintered body will be deformed, which is not preferable. Note that, desirably, the surfaces of the partition walls and pores of the obtained sintered body are then coated with a heat-resistant metal oxide. Preferred methods for coating with this heat-resistant metal oxide include the following methods.

■Metal honeycomb structure in an oxidizing atmosphere for 70 minutes
Heat treatment at 0-1100°C. (2) The surfaces of the partition walls and pores of the sintered body are plated with Al (for example, vapor phase plating), and heat treated at 700 to 1100°C in an oxidizing atmosphere. ■ Immersed in molten metal such as Al and heated to 700-1100℃ in an oxidizing atmosphere.
Heat treated with ■ Use alumina sol etc. to coat the partition walls and pore surfaces of the sintered body, and apply a 700 to 1100
Heat treat at ℃.

[0023] The heat treatment temperature is preferably 900 to 1100°C in terms of heat resistance and oxidation resistance. Next, in the obtained honeycomb structure, slits are provided between the electrodes, which will be described later, in various ways. In addition, in the above case,
Although the slits were formed in the honeycomb structure after firing,
It can also be carried out after drying or after molding.

[0024] The metallic honeycomb structure obtained as described above is usually provided with electrodes on the partition wall or inside the outer circumference by means of brazing, welding, etc.
A resistance-adjustable heater of the present invention is manufactured. This metallic honeycomb structure has a resistance value of 0.001 as a whole.
It is preferable to form it so that it may be in the range of Ω to 0.5Ω.

Further, it is preferable to further support a catalyst on the surface of the above-mentioned metallic honeycomb structure because it is expected that the temperature will increase due to the exhaust gas purification reaction (heat of oxidation reaction, etc.).

The catalyst supported on the surface of the metallic honeycomb structure is one in which a catalytically active substance is supported on a carrier having a large surface area. Here, as the carrier having a large surface area, for example, Al2 O3 type, TiO2 type, S
Typical examples include iO2-Al2O3 type and perovskite type. Examples of catalytically active substances include noble metals such as Pt, Pd, and Rh, Cu, and N.
Examples include base metals such as i, Cr, and Co. Among the above, Pt, Pd, and Rh are added to the γ-Al2 O3 system.
It is preferable to carry 10 to 100 g/ft3 of .

The honeycomb shape of the honeycomb structure in the present invention is not particularly limited, but specifically, for example, 6 to 1500 cells/In2 (0.9 to 233 cells/In2).
It is preferable to form the cell density so as to have a cell density in the range of .cm2). Further, the thickness of the partition wall is preferably in the range of 50 to 2000 μm.

Furthermore, as mentioned above, the honeycomb structure may be porous or non-porous, and its porosity is not limited, but it should be in the range of 0 to 50%, preferably less than 25%, in order to improve its strength properties. , desirable in terms of oxidation resistance and corrosion resistance. Further, when supporting a catalyst, it is preferable to have a porosity of 5% or more from the viewpoint of adhesion with the catalyst layer.

[0029] In the present invention, the honeycomb structure is
It refers to an integrated structure having a large number of through holes partitioned by partition walls, and its outer shape can be cylindrical, rectangular, oval, etc., and the cross-sectional shape (cell shape) of the through holes can be circular, polygonal, etc. Various arbitrary shapes such as a square shape and a corrugated shape can be used.

[0030]

EXAMPLES The present invention will be explained in more detail below based on Examples, but the present invention is not limited to these Examples.

(Example 1) Production of sample A: Fe-20C
Fe powder, F
Blend e-Cr powder and Fe-Al powder, and add organic binder (methyl cellulose) and antioxidant (oleic acid) to this.
, water was added to prepare clay, which was extruded and dried, as shown in Figure 3, with a rib thickness of 8 mil and a cell density of 300.
Outer diameter 110mmφ with square cells/square inch
, a dried honeycomb body with a thickness of 30 mm was created, and then slits 11 were formed so that the number of cells between the slits 11 was 6, and the slits 11 were provided in the same direction as half of the partition walls 10a of the ribs (partition walls) 10. A molded body having a honeycomb structure was obtained.

Next, by firing this honeycomb molded body in an H2 atmosphere, an outer diameter of 92 mmφ and a thickness of 25 mm was obtained.
A honeycomb structure 13 was obtained. Next, this honeycomb structure 13 was coated with γ-Al2O3, and then precious metals Pt and Pd were coated at 30 g/ft3 and 6 g/ft, respectively.
3 was supported and fired at 600° C. to obtain a honeycomb structure 13 supporting a catalyst. After that, electrodes 14 were set at two locations on the outer wall to obtain a heater catalyst A.

Manufacture of sample B: A molded body having a honeycomb structure of the same shape obtained by using the same material and the same extrusion molding and drying method as in the manufacture of sample A above, and having the same slit spacing as sample A, By slit length and number of slits,
As shown in FIG. 4, a honeycomb structure 13 was obtained in which slits 11 were provided so that the slit direction was at 45° with respect to the cell partition walls 10.

Further, this honeycomb structure 13 was subjected to the same process as sample A to obtain heater catalyst B, which had the same shape and the same exothermic cross-sectional area as heater catalyst A, but differed only in the angle of the slits with respect to the cell partition walls. .

Prior to evaluation, the electrical resistances of heater catalysts A and B were measured and found to be the same, 0.04 Ω, respectively, and the effective catalyst volumes were also the same, 133 cm 3 .

[Evaluation] Performance evaluation of the heater catalyst is shown in Figure 5.
The experiment was carried out using the apparatus shown in . That is, the exhaust gas from the gasoline engine 20 is cooled to 120° C. in the cooler 21 and then introduced into the heater catalyst 22, and at the same time as the evaluation start time, the temperature of the thermocouple 24 in the heater catalyst 22 is changed by the 24V battery 23 to the heater catalyst 22. Electricity was applied to the heater catalyst 22 for 60 seconds while performing on-off control by the controller 25 so that the temperature was 350°C. At this time, the average purification rate of HC, CO, and NOX for 60 seconds was measured using the exhaust gas measuring device 26. Table 1 shows heater catalyst A.
, B shows the average purification rate.

[0037]

[Table 1]

[0038]

[Effects of the Invention] As explained above, according to the present invention,
It is possible to provide a resistance-adjustable heater that is highly durable, has excellent temperature rise characteristics, uniform heat generation characteristics, and can control heat generation properties.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a square cell structure between slits in the present invention.

FIG. 2 is an explanatory diagram showing a cell structure in which partition walls 10a are formed in the same direction as the current flow direction.

FIG. 3 is a perspective view showing a heater catalyst A.

FIG. 4 is a perspective view showing a heater catalyst B. FIG.

FIG. 5 is an explanatory diagram showing an apparatus for evaluating the performance of a heater catalyst.

[Explanation of symbols] 10 Partition wall 11 Slit 12 Cell structure 13 Honeycomb structure 14 Electrode

Claims (3)

[Claims] Claim 1: A honeycomb structure having a large number of through holes is provided with at least two electrodes for supplying electricity, and a slit is formed between the electrodes at a predetermined angle with respect to the partition wall of the honeycomb structure. A resistance-adjustable heater, characterized in that the resistance of the honeycomb structure is adjusted to heat the gas fluid in the through holes in the honeycomb structure. 2. A resistance-adjustable heater comprising a catalyst supported on the honeycomb structure according to claim 1 and having a heater function and an exhaust gas purification function. 3. The resistance-adjustable heater according to claim 1, wherein the honeycomb structure is formed by molding powder raw material into a honeycomb shape and sintering it.