JP2523701B2 - Manufacturing method of honeycomb substrate for automobile exhaust gas purifying apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a metal substrate used in an automobile exhaust gas purification apparatus.

(Prior Art) In recent years, exhaust gas regulations for automobiles have been legalized, and catalytic converters have been installed in almost all passenger cars. In the conventional catalytic converter, γ-alumina powder carrying a noble metal catalyst was baked on a honeycomb formed by firing cordierite, but the honeycomb is made of ceramic and is weak against impact, and the back pressure is rather large. There was a drawback. Very recently, attention has been paid to a metal honeycomb made of stainless steel which does not have these drawbacks. The structure of the metal honeycomb is, as disclosed in JP-A-59-162317 and JP-A-56-96726, laminated by laminating flat plates and corrugated plates of heat-resistant stainless steel foil having a thickness of several tens of μm alternately. These are those that are formed or rolled up, and then fixed to each other by brazing or caulking. However, in these metal honeycombs, the brazing work is complicated, and the contact holes between the corrugated plate and the flat plate have an acute-angled portion, which causes a thick γ-alumina powder to adhere to the catalyst reaction. However, there is a drawback that the efficiency is poor because a noble metal catalyst that cannot participate in is generated.

(Problems to be Solved by the Invention) In view of the drawbacks in the conventional metal carrier manufacturing method and structure, the present invention does not use brazing or caulking, and the shape of the holes is almost the same except for the outer peripheral portion of the honeycomb. It is intended to provide a method for producing a metal carrier having a hexagonal shape and having no sharp edges.

(Means for Solving the Problems) The present invention obtains a honeycomb-shaped mother substrate by alternately laminating or winding corrugated plates and flat plates of stainless steel ultrathin plates, and charging the mother substrate into a heat-resistant steel pipe or A mother outer cylinder of the honeycomb is formed by welding the heat-resistant steel plate after winding the periphery with the heat-resistant steel plate, and further, each easily edible wire rod is inserted into each hole of the mother base body, and then both ends of the mother base body are made of steel material. The cross-sectional area of the mother substrate is reduced to 1/4 or less by hot working, and then the mother substrate is cut into a predetermined length, and the easily-cuttable material portion is removed by chemical or electrochemical treatment. A method for manufacturing a honeycomb substrate for an automobile exhaust gas purification device, which comprises:
The second one is the above-mentioned method characterized in that the surface of the easily-cuttable wire rod is coated with Al and is inserted into each hole of the mother substrate, and the third one is the easily-cuttable wire rod and the mother substrate. Al powder or
In the above method, characterized by charging Al powder and Cr powder,
The fourth one is that the cross-sectional area is reduced to 1/4 or less by hot-pressing or hot-rolling the mother substrate, or after cutting this into a predetermined length, the mother substrate is hot-worked to form the mother substrate. The above method is characterized by bending.

 Hereinafter, the present invention will be described in detail.

(Operation) The stainless steel referred to in the present invention is a part that finally constitutes a honeycomb, and if it has oxidation resistance to high temperature engine exhaust gas, it may be a ferrite type, martensite type, austenitic type, Alternatively, any stainless steel of these mixed systems may be used, but it is desirable that it has a high degree of oxidation resistance particularly to engine exhaust gas and that can withstand the hot working according to the present invention. As a component system, C 0.05% or less, Si 4% or less,
Mn 10% or less, Ni 0-60%, Cr 11-30%, Al 0-6%, Mo, C
o, W is 0-10% in total, Ti, Nb, Zr, Hf is 0-3% in total,
Y and REM are in the range of 0 to 0.2% in total, and Mg and Ca are in the range of 0 to 0.01% in total.
It is possible to contain u and B, and the balance is Fe and inevitable impurities.

Next, the ultrathin plate referred to in the present invention may be determined by considering the fact that the thickness will be reduced in the subsequent hot working so as to have a predetermined thickness when finally forming the honeycomb. . Further, in the present invention, corrugated sheets and flat sheets are alternately laminated or rolled up in the same manner as in the case of obtaining a normal honeycomb, and are placed in a mother outer cylinder made of heat-resistant steel. The thickness of the mother outer cylinder is also determined in consideration of the fact that the thickness of the mother outer cylinder is reduced by hot working and finally becomes the outer cylinder. The heat-resistant steel referred to here is steel containing 9% or more of Cr. Next, the easily meltable wire rod to be loaded into each hole of the mother substrate is to secure a space corresponding to a portion to be a hole of the honeycomb, and finally removed by a chemical or electrochemical treatment. It is desirable that it be more easily melted by chemical or electrochemical treatment than the above-mentioned stainless steel or heat-resistant steel that becomes the outer cylinder, and that it has good hot workability, and that satisfies these conditions. Any of low carbon to high carbon steel, low alloy steel, high Mn steel, high Ni steel and the like may be used. In addition, the shape can be selected from linear, rod-shaped, and powder as required. Further, as long as the above conditions are satisfied, not only metals but also oxide powders of Al ₂ O ₃ , MgO, SiO ₂ , CaO, CaCO _{3 and the} like can be used together with the above-mentioned easily-cuttable wire.

Next, in the present invention, a method of coating an easily fusible wire rod with Al for the purpose of increasing the oxidation resistance of the honeycomb body and charging it into the holes of the mother substrate, or Al powder or Al in the gap between the easily fusible wire rod and the mother substrate. With powder
It is possible to enrich A or Al and Cr into the honeycomb through heating and processing in the subsequent hot working by charging Cr powder or the like.

The both ends of the mother substrate thus obtained are covered with steel materials, and the mother substrate is then hot pressed or hot rolled to reduce the cross-sectional area to 1/4 by a hot working method usually used for steel pipes, shaped steel and wire rods.
Reduce to below. Where the cross-sectional area reduction rate is 1 /
The reason for limiting to 4 or less is that the cross-sectional area is reduced to 1/4 or less by hot working, and the result is that the stainless steel thin plate that constitutes the honeycomb is stretched in the longitudinal direction at high temperature under the compressive stress from the outer peripheral portion. , Metal bonding is caused between them, and the cross-section of the easily-cuttable wire rod as the core material also has a shape close to a regular hexagon. The shape of the finished cross section of the outer cylinder may be a circle, an ellipse, or any other desired shape. Further, after or simultaneously with hot working for reducing the cross section, one or both of bending and twisting are carried out by hot working to obtain a finally bent or twisted honeycomb substrate. Thus, the present invention has an advantage that honeycomb substrates of various shapes can be obtained by including hot working.

Next, this is used as a base for a purifying device, for example, for a required length,
When it is cut into 50 to 200 mm and the portion of the easily-cuttable material is dissolved and removed by further chemical or electrochemical treatment, a honeycomb-shaped stainless steel and an outer cylinder of heat-resistant steel enclosing it are left. It should be noted that the chemical or electrochemical treatment here means that there is a large difference in the dissolution rate between the above-mentioned stainless steel forming the honeycomb and the easy-cutting material as the core material. Alternatively, it means a treatment in which an additive is added thereto, and further, a treatment for applying a voltage, an ultrasonic wave or a vibration between the substrate and the solution to promote selective or preferential dissolution during treatment in these solutions.

Further, in the present invention, after the cross-sectional area is reduced by hot working, it is also bent or twisted with respect to the longitudinal direction by hot working, and then cutting and fusing of the core material are performed. A modified honeycomb can be obtained.

 Next, specific examples of the present invention will be described with reference to examples.

(Example-1) A 20Cr-5Al flat plate having a thickness of 0.15 mm and a width of 450 mm was subjected to corrugating with a pitch of 7.5 mm and a height of 3.75 mm, and was rolled up so as to have a diameter of 204 mm while being stacked on the flat plate. A 3.2 mm thick 15Cr-4Al hot-rolled steel plate was wound as the outer cylinder base material while the honeycomb base substrate was being clamped, and the joining portion was TIG welded to form a mother outer cylinder.

Next, after inserting a steel wire having a diameter of 3.2 mm and a length of 450 mm into each hole of the honeycomb (Fig. 1 (a)), both ends were cut out from a carbon steel intermediate plate (thickness 20 mm). Welded the lid and closed it. At this time, the diameter of the lid is 2 mm at the center of the lid.
Was drilled (Fig. 1 (b)). Next, the mother substrate is heated to 1200 ° C.
After heating to 0, it was extruded by hot pressing to reduce the diameter to 73 mm. Next, this was cut into a length of 100 mm, immersed in nitric acid with a concentration of 15%, and the steel wire portion was ablated. At this time, the ablation tank was vibrated by a vibrator to increase the ablation rate, and the extruded material was repeatedly pulled up from the liquid surface, and the acid was appropriately replenished to prevent the acid from deteriorating.

Separately from this, as a comparative material, 5Cr of 15Cr-4Al was used according to the conventional method.
Corrugate a foil with a thickness of 0 μ x 100 mm width at a pitch of 2.5 mm and a height of 1.25 mm, stack it with a flat plate and roll it up to 70φ, and form an outer cylinder with a 1.5 t corrugated plate of 15Cr-4Al, composing honeycomb, An ordinary metal carrier was obtained by brazing the honeycomb and the outer cylinder with Ni brazing. The metal carrier thus obtained is the one obtained by the above-mentioned hot pressing (the method of the present invention) and the total cross-sectional area of the honeycomb.
38 cm ² , the total number of open holes was about 2,300, and the shape of the holes was regular hexagon to modified pentagon (peripheral part) according to the method of the present invention, whereas the comparative material was sinusoidal.

After heat-treating these metal carriers in the atmosphere at 900 ° C for 2 hours, a washcoat layer of γ-Al ₂ O ₃ with an average thickness of 40μ is formed, and a precious metal catalyst of Pt and Rh is supported on the washcoat layer. Therefore, from the weight difference of the metal carrier before and after the treatment, γ-Al ₂ O ₃
Calculate the amount of washcoat carried (including a very small amount of Pt / Rh) and connect it to an engine with a displacement of 1800cc to 2500rp
The exhaust gas purification rate at m and the pressure loss at 5500 rpm were measured.
The results of these measurements and the amount of γ-Al ₂ O ₃ powder carried were divided into the carrier according to the method of the present invention and the one according to the conventional method and compared in Table 1. As can be seen from the table, no significant difference was found in the exhaust gas purification rate by the carrier according to the present invention and the conventional method.
The amount of —Al ₂ O ₃ supported is small according to the method of the present invention, and the pressure loss is also small. This indicates that the carrier according to the method of the present invention can purify the exhaust gas with a smaller amount of platinum catalyst and the load on the engine is also small.

(Example-2) In the same manner as in Example-1, a honeycomb mother substrate was prepared from a thin plate of 15Cr-4Al having a thickness of 0.15 mm, and a steel wire having a thickness of 3 mm was subjected to hot-dip Al plating and inserted into a honeycomb. Then, a metal carrier was obtained by the same method as in Example 1 except for the above. After observing the metallographic structure of the cross section after hot pressing, there was a compound layer of Fe and Al near the surface layer of the steel wire of the core material, and it seems that Al did not diffuse inside it. There was no compound layer on the stainless steel side forming Al, and Al had a structure showing that it was well diffused and solid-solved on the stainless steel side. When the composition on the stainless steel side was measured by EPMA, it was found that the Al concentration near the surface was slightly high, but the average composition was 14Cr-8Al. (Invention No. 2) Separately from this, a honeycomb base body was formed from a 0.15 ton thin plate of SUS 430 (16Cr steel), and an outer cylinder base material was attached in the same manner as in Example-1. A 2.8φ steel wire was inserted into each hole of this honeycomb, and a mixed powder having a weight ratio of Al powder and Cr powder of 1: 1 was packed in the gap between the honeycomb and the steel wire. The front and rear of the mother substrate thus obtained were covered with plain steel thick plates, and a metal carrier was obtained in the same manner as in Example-1. (3 of the present invention) In addition, a metal carrier manufactured by using a 50 μm thick foil of 15Cr-4Al steel used as a comparative material of Example-1 was also included.
The seed metal carrier was directly connected to an engine with a displacement of 2000 cc, the ignition position was shifted so that the exhaust gas temperature was 950 to 1000 ° C., and subjected to a durability test at 5500 rpm for 300 hours. As a result, the comparative material partially extinguished the honeycomb due to abnormal oxidation, whereas the former two materials by the method of the present invention endured the durability test without any particular abnormality.

(Example-3) A part of the round bar-shaped composite material before hot-melting which was hot-pressed in Example-1 was cut out, and the radius was about the radius at the center axis of the round bar by hot forging.
Bending was performed so that the length became 150 mm, the length was cut to 160 mm (center axis length), and the core material was removed by melting in the same manner as in Example-1 to obtain a bent metal carrier (Fig. 2). This shows that the method of the present invention can produce a catalyst carrier of any shape that fits in the space of a small engine room of an automobile.

(Example-4) The round bar-shaped composite material before fusing which was hot pressed in Example-1 was cut into a length of 600 mm, heated to 1200 ° C and twisted 360 ° at both ends. After cooling, it was cut to a length of 140 mm and Example-1
The core material was removed by melting in the same manner as in 1. to obtain a twisted metal carrier as shown in FIG.

(Effects of the Invention) As described above, the present invention makes it possible to obtain a metal carrier having a hole shape close to that of a regular hexagon, which is ideal as a honeycomb carrier for a catalyst, and also to provide a method for producing a bent or twisted metal carrier. It contributes to effective utilization of expensive precious metal catalysts, effective utilization of engine room space, improvement of reaction efficiency of catalysts, etc., and its industrial advantage is extremely large.

[Brief description of drawings]

FIG. 1 is a view showing a metal carrier matrix according to the present invention, and FIG. 2 is a schematic view of a bent metal carrier obtained according to the present invention. FIG. 3 is a schematic view of a twisted metal carrier obtained according to the present invention. 1 ... Honeycomb mother substrate made of stainless steel thin plate, 2 ... Easy-to-melt wire rod for core material, 3 ... Mother outer cylinder, 4 ... Composite of honeycomb mother substrate and core material, 5, 5 '... End plate.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takahashi Yamaguchi 3434 Shimada, Hikari City, Yamaguchi Pref., Nippon Steel Co., Ltd.Hikari Steel Works (72) Inventor Toshiki Tsuruta 3434 Shimada, Hikari City, Yamaguchi Prefecture New Japan Kotsu Works, Ltd. (56) References JP-A-57-9535 (JP, A) JP-A-62-9724 (JP, A)

Claims (4)

(57) [Claims] 1. A honeycomb-shaped mother substrate is obtained by alternately laminating or winding a corrugated plate and a flat plate of a stainless steel ultra-thin plate, and after charging the mother substrate into a heat-resistant steel pipe or winding the periphery with a heat-resistant steel plate. A mother outer cylinder of the honeycomb is formed by welding a heat-resistant steel plate, and each of the holes of the mother base is charged with an easily-meltable wire rod, and then both ends of the mother base are covered with steel, and then the mother base is heated. For automobile exhaust gas purification equipment characterized by reducing the cross-sectional area to 1/4 or less by hot working, then cutting it to a prescribed length, and further removing the easily meltable material part by chemical or electrochemical treatment Manufacturing method of honeycomb substrate. 2. The method according to claim 1, characterized in that the surface of the easily meltable wire rod is coated with Al and is inserted into each hole of the mother substrate. 3. Al powder or Al in the gap between the easily meltable wire and the mother substrate.
Powder and Cr powder are charged, The method of Claim 1 characterized by the above-mentioned. 4. A mother substrate is bent by hot working after the mother substrate is hot pressed or hot rolled to reduce its cross-sectional area to 1/4 or less, or after being cut to a predetermined length. Alternatively, one or both of twisting is performed, and the method according to any one of claims 1 to 3.