WO2022014615A1

WO2022014615A1 - Exhaust pipe

Info

Publication number: WO2022014615A1
Application number: PCT/JP2021/026362
Authority: WO
Inventors: 裕亮尾下; 崇弘冨田
Original assignee: 日本碍子株式会社
Priority date: 2020-07-13
Filing date: 2021-07-13
Publication date: 2022-01-20
Also published as: JPWO2022014615A1

Abstract

This exhaust pipe comprises a metal pipe and an inorganic porous layer provided on a part of the inner surface of the metal pipe through which exhaust gas passes. In this exhaust pipe, an inner diameter D1 of the metal pipe, a thickness d1 of the metal pipe, and a thickness d2 of the inorganic porous layer satisfy both expressions (1) and (2) below.　(1): d2/D1 < 0.12 (2): 0.2 < d2/d1 < 3

Description

Exhaust pipe

This application claims priority based on Japanese Patent Application No. 2020-120263 filed on July 13, 2020. The entire contents of that application are incorporated herein by reference. The present specification discloses techniques relating to exhaust pipes.

Japanese Patent Application Laid-Open No. 2018-031346 (hereinafter referred to as Patent Document 1) describes an exhaust pipe of an internal combustion engine in which an inorganic porous layer (heat insulating material) is arranged between a metal inner pipe and a metal outer pipe. It has been disclosed. In Patent Document 1, an inorganic porous layer is provided between the inner pipe and the outer pipe to insulate the space between the inner pipe and the outer pipe, and the temperature of the exhaust gas flowing into the catalyst provided downstream of the exhaust pipe. The decline is suppressed. By suppressing the temperature drop of the exhaust gas flowing into the catalyst, the warm-up of the catalyst is completed at an early stage.

When the inorganic porous layer is arranged between the double tubes as in Patent Document 1, the adhesion between the tubular body (metal tube) and the inorganic porous layer is not particularly required. However, in the case of providing an inorganic porous layer inside the inner pipe of the double pipe or inside the single pipe in order to prevent the metal pipe and the exhaust gas from coming into direct contact with each other and further suppress the temperature drop of the exhaust gas. The adhesion between the metal tube and the inorganic porous layer is important. It is an object of the present specification to provide an exhaust pipe having improved adhesion between a metal pipe and an inorganic porous layer.

The exhaust pipe disclosed in the present specification may include a metal pipe and an inorganic porous layer provided at a portion of the inner surface of the metal pipe through which the exhaust gas passes. In this exhaust pipe, the inner diameter D1 of the metal pipe, the thickness d1 of the metal plate, and the thickness d2 of the inorganic porous layer may satisfy both of the following formulas (1) and (2).
Equation 1: d2 / D1 <0.12
Equation 2: 0.2 <d2 / d1 <3

The perspective view of the exhaust pipe is shown. A partially enlarged view of the exhaust pipe is shown. The sectional view of the exhaust pipe is shown. The results of the experimental example are shown. The results of the experimental example are shown.

The exhaust pipe disclosed in the present specification includes a metal pipe and an inorganic porous layer provided at a portion of the inner surface of the metal pipe through which the exhaust gas passes. Therefore, the heat transfer of the exhaust gas to the metal pipe is suppressed (the metal pipe is insulated), and the temperature drop of the exhaust gas is suppressed. The term "porous" as used herein means that the porosity (porosity) of the inorganic porous layer is 45% by volume or more. When the inorganic porous layer is provided on the inner surface of the metal pipe, the inner diameter of the exhaust pipe becomes smaller than the inner diameter of the metal pipe by the thickness of the inorganic porous layer (to be exact, twice the thickness). Therefore, the flow velocity of the exhaust gas discharged from the internal combustion engine increases as it passes through the exhaust pipe. When the flow velocity of the exhaust gas increases, the force applied from the exhaust gas to the inorganic porous layer increases, and the inorganic porous layer may be separated from the metal pipe. The exhaust pipe disclosed in the present specification adjusts the thickness of the inorganic porous layer and the metal pipe, and reduces the force received by the inorganic porous layer from the exhaust gas to improve the adhesion between the metal pipe and the inorganic porous layer. Improve. Specifically, in the exhaust pipe, the inner diameter D1 of the metal pipe, the thickness d1 of the metal plate, and the thickness d2 of the inorganic porous layer may satisfy both of the following formulas (1) and (2).
Equation 1: d2 / D1 <0.12
Equation 2: 0.2 <d2 / d1 <3

The above formula (1) means that the thickness (twice the thickness d2) of the inorganic porous layer occupying the inner diameter D1 of the metal pipe is less than 24% in the exhaust pipe. When the thickness of the inorganic porous layer in the inner diameter D1 of the metal tube is less than 24%, the flow velocity of the exhaust gas can be suppressed from being excessively increased, and the force received by the inorganic porous layer from the exhaust gas can be suppressed. .. Further, the above formula (2) means that the thickness (thickness d2) / (thickness d1) of the inorganic porous layer with respect to the metal tube is larger than 20% and smaller than 300%. By making (thickness d2) / (thickness d1) larger than 20%, the inside and outside of the exhaust pipe can be sufficiently insulated by the inorganic porous layer, and the temperature drop of the exhaust gas can be sufficiently suppressed. Further, by making (thickness d2) / (thickness d1) smaller than 300%, deterioration (peeling, cracking, etc.) of the inorganic porous layer due to the difference in thermal expansion coefficient between the inorganic porous layer and the metal tube is suppressed. be able to. (Thickness d2) / (thickness d1) may be 50% or more, 100% or more, 150% or more, or 200% or more. Further, (thickness d2) / (thickness d1) may be 200% or less, 150% or less, 100% or less, or 50% or less.

A coating layer may be provided on the surface of the inorganic porous layer. The coating layer may be provided on the entire surface of the surface of the inorganic porous layer (the surface opposite to the metal tube side), or may be provided on a part of the surface of the inorganic porous layer. By providing the coating layer, the inorganic porous layer can be protected (reinforced). In this case, when the thickness of the coating layer is d3, the following formula (3) may be satisfied in addition to the above formulas (1) and (2).
Equation 3: (d2 + d3) / D1 <0.15

The above formula (3) means that the total thickness "(d2 + d3) x 2" of the inorganic porous layer and the coating layer occupying the inner diameter D1 of the metal pipe is less than 30% in the exhaust pipe. In this case as well, the excessive increase in the flow velocity of the exhaust gas can be suppressed, and the force received by the inorganic porous layer from the exhaust gas can be suppressed. Comparing the above formulas (1) and (3), it is possible that the flow path of the exhaust gas is narrowed (the flow velocity of the exhaust gas is high) by providing the coating layer on the surface (inner surface) of the inorganic porous layer. Permissible. That is, by providing the coating layer on the surface of the inorganic porous layer, the inorganic porous layer is reinforced by the coating layer, and the exhaust gas (force exerted on the inorganic porous layer) having a higher flow velocity than the form in which the coating layer is not provided. Can withstand (strong exhaust gas).

When the coating layer is provided on the surface of the inorganic porous layer, the thickness d2 of the inorganic porous layer and the thickness d3 of the coating layer may satisfy the following formula (4).
Equation 4: d2 / 20≤d3≤d2 / 2

The above formula (4) means that the thickness d3 of the coating layer is 0.05 times or more and 0.5 times or less the thickness d2 of the inorganic porous layer. When the thickness d3 of the coating layer is 0.05 times or more the thickness d2 of the inorganic porous layer, the effect of reinforcing the inorganic porous layer is sufficiently exhibited. Further, when the thickness d3 of the coating layer is 0.5 times or less the thickness d2 of the inorganic porous layer, the thickness d2 of the inorganic porous layer is sufficiently secured, and the metal tube can be more reliably insulated.

The inorganic porous layer may contain ceramic fibers. Further, the inorganic porous layer may be composed of 15% by mass or more of an alumina component and 45% by mass or more of a titania component. Since the inorganic porous layer contains ceramic fibers, the inorganic porous layer itself can absorb the influence of the difference in the coefficient of thermal expansion between the metal tube and the inorganic porous layer. Further, when the inorganic porous layer contains ceramic fibers, it is possible to prevent the strength (mechanical strength) of the inorganic porous layer itself from being lowered. Further, when the inorganic porous layer is composed of 15% by mass or more of an alumina component and 45% by mass or more of a titania component, the shape of the inorganic porous layer can be maintained even when exposed to high-temperature exhaust gas. .. The alumina component contained in the inorganic porous layer may be 25% by mass or more, 30% by mass or more, or 40% by mass or more.

When the coefficient of thermal expansion of the inorganic porous layer is α1 and the coefficient of thermal expansion of the metal tube is α2, the following equation (5) may be satisfied. The phenomenon that the inorganic porous layer is peeled off from the metal tube can be prevented more reliably.
Equation 5: 0.5 <α1 / α2 <1.2

The inorganic porous layer may contain flat plate-shaped plate-shaped ceramic particles. The plate-shaped ceramic particles may have an aspect ratio of 10 or more and 60 or less when the cross section is observed by SEM. The aspect ratio of the cross section of the plate-shaped ceramic particles contained in the inorganic porous layer can be confirmed by observing the cross section of the inorganic porous layer by SEM. The plate-shaped ceramic particles appear in a rod shape in the SEM. The plate-shaped ceramic particles can suppress a decrease in the strength (mechanical strength) of the inorganic porous layer itself. The plate-shaped ceramic particles having a cross-sectional aspect ratio of 10 or more and 60 or less can have an aspect ratio in the manufacturing process of the inorganic porous layer by using, for example, plate-shaped ceramic particles having a cross-sectional aspect ratio of 60 or more and 100 or less as a raw material. Becomes smaller and remains in the inorganic porous as a result. By using the plate-shaped ceramic particles, a part of the ceramic fiber can be replaced with the plate-shaped ceramic particles. Typically, the length of the plate-like ceramic particles (longitudinal size) is shorter than the length of the ceramic fibers. Therefore, by using the plate-shaped ceramic particles, the heat transfer path in the inorganic porous layer is divided, and heat transfer in the inorganic porous layer is less likely to occur. As a result, the heat insulating performance of the inorganic porous layer is further improved.

The inorganic porous layer may contain granular particles of 0.1 μm or more and 10 μm or less. When the inorganic porous layer is formed (baked), the ceramic fibers are bonded to each other via granular particles to obtain a high-strength inorganic porous layer. The thickness of the inorganic porous layer may be 1 mm or more, although it depends on the required performance. The above-mentioned function (heat insulating property) can be fully exhibited. If the thickness of the inorganic porous layer is too thick, it becomes difficult to obtain an improvement in characteristics commensurate with the cost (manufacturing cost, material cost). Therefore, although not particularly limited, the thickness of the inorganic porous layer may be 30 mm or less, 20 mm or less, 15 mm or less, 10 mm or less, and 5 mm or less.

It is preferable that the difference in thermal conductivity between the metal tube and the inorganic porous layer is large. Specifically, the thermal conductivity of the metal tube may be 100 times or more the thermal conductivity of the inorganic porous layer. The thermal conductivity of the metal tube may be 150 times or more the thermal conductivity of the inorganic porous layer, 200 times or more the thermal conductivity of the inorganic porous layer, and the heat of the inorganic porous layer. The conductivity may be 250 times or more, and the thermal conductivity of the inorganic porous layer may be 300 times or more.

The thermal conductivity of the metal tube may be 10 W / mK or more and 400 W / mK or less. The thermal conductivity of the metal tube may be 25 W / mK or more, 50 W / mK or more, 100 W / mK or more, 150 W / mK or more, and 200 W / mK or more. It may be 250 W / mK or more, 300 W / mK or more, or 380 W / mK or more. Further, the thermal conductivity of the metal tube may be 350 W / mK or less, 300 W / mK or less, 250 W / mK or less, 200 W / mK or less, 150 W / mK or less. May be.

The thermal conductivity of the inorganic porous layer may be 0.05 W / mK or more and 3 W / mK or less. The thermal conductivity of the inorganic porous layer may be 0.1 W / mK or more, 0.2 W / mK or more, 0.3 W / mK or more, and 0.5 W / mK or more. It may be 0.7 W / mK or more, 1 W / mK or more, 1.5 W / mK or more, or 2 W / mK or more. The thermal conductivity of the inorganic porous layer may be 2.5 W / mK or less, 2.0 W / mK or less, 1.5 W / mK or less, and 1 W / mK or less. It may be 0.5 W / mK or less, 0.3 W / mK or less, and 0.25 W / mK or less.

The metal tube may be linear, the whole (or a part) may be curved, the intermediate portion may be tapered, or the metal tube may be a branch tube. The inorganic porous layer may cover the entire surface (inner surface) of the metal tube, or may cover a part of the surface of the metal tube. For example, the inorganic porous layer may cover a portion other than the end portion (one end or both ends) of the metal tube.

Further, the inorganic porous layer may be made of a uniform material in the thickness direction (range from the surface in contact with the metal pipe to the surface constituting the flow path of the exhaust gas). That is, the inorganic porous layer may be a single layer. Further, the inorganic porous layer may be composed of a plurality of layers having different compositions in the thickness direction. That is, the inorganic porous layer may have a multi-layer structure in which a plurality of layers are laminated. Alternatively, the inorganic porous layer may have an inclined structure in which the composition gradually changes in the thickness direction. When the inorganic porous layer is a single layer, the exhaust pipe can be easily manufactured (the step of forming the inorganic porous layer on the inner surface of the metal pipe). When the inorganic porous layer has a multi-layered or inclined structure, the characteristics of the inorganic porous layer can be changed in the thickness direction. The structure of the inorganic porous layer (single layer, multi-layer, inclined structure) can be appropriately selected depending on the exhaust pipe.

The porosity of the inorganic porous layer may be 45% by volume or more and 90% by volume or less. When the porosity is 45% by volume or more, the heat insulating property can be sufficiently exhibited. Further, if the porosity is 45% by volume or more, sufficient strength can be secured if the porosity is 90% by volume or less. The porosity of the inorganic porous layer may be 55% by volume or more, 60% by volume or more, or 65% by volume or more. Further, the porosity of the inorganic porous layer may be 85% by volume or less, 80% by volume or less, 70% by volume or less, 65% by volume or less, and 60% by volume. It may be as follows. When the inorganic porous layer has a multi-layer structure or an inclined structure, the porosity of the inorganic porous layer may be 45% by volume or more and 90% by volume or less as a whole, and the porosity may differ in the thickness direction. .. In this case, there may be a portion having a porosity of less than 45% by volume or a portion having a porosity of more than 90% by volume.

The inorganic porous layer is composed of one or more materials of ceramic particles (granular particles), plate-shaped ceramic particles, and ceramic fibers. The ceramic particles, the plate-shaped ceramic particles, and the ceramic fibers may contain alumina and / or titania as constituent components. In other words, the ceramic particles, the plate-shaped ceramic particles, and the ceramic fibers may be formed by alumina and / or titania. That is, the inorganic porous layer may contain 15% by mass or more of an alumina component and 45% by mass or more of a titania component in the entire constituent material (constituting substance). However, the inorganic porous layer contains at least ceramic fibers, although the constituent components are arbitrary (alumina component and titania component may or may not be contained).

The ceramic particles may be used as a bonding material for joining aggregates forming the skeleton of an inorganic porous layer such as plate-shaped ceramic particles and ceramic fibers. The ceramic particles may be granular particles of 0.1 μm or more and 10 μm or less. The ceramic particles may have a larger particle size due to sintering or the like in the manufacturing process (for example, firing process). That is, as a raw material for producing the inorganic porous layer, the ceramic particles may be granular particles having a size of 0.1 μm or more and 10 μm or less (average particle size before firing). The ceramic particles may be 0.5 μm or more, and may be 5 μm or less. As the material of the ceramic particles, for example, a metal oxide may be used. An example of a metal oxide, alumina _(Al _{2 O} 3), spinel (MgAl ₂ O _4), titania _(TiO 2), zirconia _(ZrO 2), magnesia (MgO), mullite _{_{_{(Al 6 O 13 Si 2)}}} , cordierite _{_{(MgO · Al 2 O 3 ·}} SiO 2), yttria _(Y _{2 O} 3), steatite (MgO · _SiO 2), forsterite (2MgO · _SiO 2), lanthanum aluminate (LaAlO _3), strontium titanate (SrTiO ₃ ) and the like can be mentioned. These metal oxides have high corrosion resistance. Therefore, by using the above metal oxide as a material for ceramic particles, it can be suitably applied as a protective layer for an exhaust pipe.

The plate-shaped ceramic can function as an aggregate or a reinforcing material in the inorganic porous layer. That is, the plate-shaped ceramic, like the ceramic fiber, improves the strength of the inorganic porous layer and further suppresses the shrinkage of the inorganic porous layer in the manufacturing process. By using the plate-shaped ceramic particles, the heat transfer path in the inorganic porous layer can be divided. Therefore, by using the plate-shaped ceramic, the heat insulating property can be improved as compared with the form in which only the ceramic fiber is used as the aggregate.

The surface shape (shape observed from the thickness direction) of the flat plate-shaped ceramic particles is not particularly limited, and is, for example, a polygon such as a rectangle, a substantially circular shape, a curved line, and / or an indefinite shape surrounded by a straight line. The longitudinal size when observing the cross section may be 5 μm or more and 100 μm or less. When the size in the longitudinal direction is 5 μm or more, excessive sintering of the ceramic particles can be suppressed. When the size in the longitudinal direction is 100 μm or less, the effect of dividing the heat transfer path in the inorganic porous layer can be obtained as described above, and it can be suitably applied to an exhaust pipe through which high-temperature exhaust gas flows. Further, the plate-shaped ceramic particles may have an aspect ratio of 10 or more and 60 or less in cross section. When the aspect ratio of the cross section is 10 or more, the sintering of the ceramic particles can be satisfactorily suppressed, and when it is 60 or less, the decrease in the strength of the plate-shaped ceramic particles itself is suppressed. As the material of the plate-shaped ceramic particles, in addition to the metal oxide used as the material of the ceramic particles described above, talc (Mg ₃ Si ₄ O ₁₀ (OH) ₂ ), minerals such as mica and kaolin, clay, glass and the like. Can also be used.

The ceramic fiber can function as an aggregate or a reinforcing material in the inorganic porous layer. That is, the ceramic fiber improves the strength of the inorganic porous layer and further suppresses the shrinkage of the inorganic porous layer in the manufacturing process. The length of the ceramic fiber may be 50 μm or more and 200 μm or less. The diameter (average diameter) of the ceramic fiber may be 1 to 20 μm. The ceramic fiber can also be confirmed by observing the cross section of the inorganic porous layer by SEM. The ceramic fibers are substantially circular in the SEM image. That is, the radial cross section of the ceramic fiber appears in the SEM image. Further, when the material of the ceramic fiber is different from other materials constituting the inorganic porous layer, the ceramic fiber can be discriminated (confirmed) by performing EDS analysis. The volume fraction of the ceramic fiber in the raw material for forming the inorganic porous layer may be 5% by volume or more and 25% by volume or less. When the raw material of the inorganic porous layer contains 5% by volume or more of ceramic fibers, the shrinkage of the ceramic particles in the inorganic porous layer can be sufficiently suppressed in the manufacturing process (firing step) of the inorganic porous layer. Further, by setting the volume ratio of the ceramic fiber in the raw material to 25% by volume or less (that is, the volume ratio of the ceramic fiber in the inorganic porous layer is 25% by volume or less), the heat transfer path in the inorganic porous layer is divided. It can be suitably applied to the exhaust pipe. When the material of the ceramic fiber is different from other materials constituting the inorganic porous layer, the ratio (volume ratio) of the ceramic fiber in the inorganic porous layer should be measured by image processing the result of EDS analysis. Can be done.

Incidentally, as a material of ceramic fibers, alumina _(Al _{2 O} 3), spinel (MgAl ₂ O _4), titania _(TiO 2), zirconia _(ZrO 2), magnesia (MgO), mullite _(Al ₆ O 13 _Si 2) , cordierite _{_{(MgO · Al 2 O 3 ·}} SiO 2), yttria _(Y _{2 O} 3), steatite (MgO · _SiO 2), forsterite (2MgO · _SiO 2), lanthanum aluminate (LaAlO _3), strontium The same material as the above-mentioned ceramic particles such as titanate (SrTiO _{3) can be used.} Further, the inorganic porous layer may contain one or more kinds of ceramic fibers formed of the above materials.

In addition, the content of aggregates and reinforcing materials (ceramic fibers, plate-shaped ceramic particles, etc., hereinafter simply referred to as aggregates) in the raw materials for forming the inorganic porous layer is 15% by mass or more and 55% by mass or less. May be. When the content of the aggregate in the raw material is 15% by mass or more, the shrinkage of the inorganic porous layer in the firing step can be sufficiently suppressed. Further, when the content of the aggregate in the raw material is 55% by mass or less, the aggregates are satisfactorily bonded to each other by the ceramic particles. The content of the aggregate in the raw material may be 20% by mass or more, 30% by mass or more, 50% by mass or more, or 53% by mass or more. The content in the raw material may be 53% by mass or less, 50% by mass or less, 30% by mass or less, or 20% by mass or less.

As described above, both the ceramic fiber and the plate-shaped ceramic particle can function as an aggregate and a reinforcing material in the inorganic porous layer. However, in order to surely suppress the shrinkage of the inorganic porous layer after the exhaust pipe is manufactured (after firing), even when both the ceramic fiber and the plate-shaped ceramic particles are used as the aggregate, the inorganic porous layer is used. The content of the ceramic fiber in the raw material when forming the layer may be at least 5% by mass or more. The content of the ceramic fiber in the raw material may be 10% by mass or more, 20% by mass or more, 30% by mass or more, or 40% by mass or more. The content of the ceramic fiber in the raw material may be 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, and 10% by mass. It may be less than or equal to%.

When both ceramic fibers and plate-shaped ceramic particles are used as the aggregate, the ratio (weight ratio) of the plate-shaped ceramic particles to the entire aggregate may be 70% or less. That is, in terms of mass ratio, at least 30% or more of the aggregate may be ceramic fibers. The ratio (weight ratio) of the plate-shaped ceramic particles to the total aggregate may be 67% or less, 64% or less, 63% or less, 60% or less, and 50. It may be less than or equal to%. The plate-shaped ceramic particles are not always essential as an aggregate. The ratio of the plate-shaped ceramic particles to the entire aggregate may be 40% or more, 50% or more, 60% or more, 62% or more, 63% or more. It may be 65% or more. Specifically, the content of the plate-shaped ceramic particles in the raw material for forming the inorganic porous layer may be 5% by mass or more, 10% by mass or more, and 20% by mass or more. It may be 30% by mass or more, and may be 33% by mass or more. The content of the plate-shaped ceramic particles in the raw material may be 35% by mass or less, 33% by mass or less, 30% by mass or less, or 20% by mass or less. It may be 10% by mass or less.

_{SiO 2} contained in the inorganic porous layer may be 25% by mass or less. The formation of an amorphous layer in the inorganic porous layer is suppressed, and the heat resistance (durability) of the inorganic porous layer is improved.

When forming the inorganic porous layer, a raw material in which a binder, a pore-forming material, and a solvent are mixed may be used in addition to ceramic particles, plate-shaped ceramic particles, and ceramic fibers. As the binder, an inorganic binder may be used. Examples of the inorganic binder include alumina sol, silica sol, titania sol, zirconia sol and the like. These inorganic binders can improve the strength of the inorganic porous layer after firing. As the pore-forming material, a polymer-based pore-forming material, carbon-based powder, or the like may be used. Specific examples thereof include acrylic resin, melamine resin, polyethylene particles, polystyrene particles, carbon black powder, graphite powder and the like. The pore-forming material may have various shapes depending on the purpose, and may be, for example, spherical, plate-shaped, fibrous, or the like. By selecting the addition amount, size, shape, etc. of the pore-forming material, the porosity and pore size of the inorganic porous layer can be adjusted. The solvent may be any solvent as long as the viscosity of the raw material can be adjusted without affecting other raw materials, and for example, water, ethanol, isopropyl alcohol (IPA) or the like can be used.

The above-mentioned inorganic binder is also a constituent material of the inorganic porous layer. Therefore, when alumina sol, titania sol, etc. are used to form the inorganic porous layer, the inorganic porous layer contains 15% by mass or more of the alumina component and 45% by mass or more of the titania component in the entire constituent material including the inorganic binder. It may be included.

The composition and raw material of the inorganic porous layer are adjusted according to the metal tube to be protected. In the exhaust pipe disclosed in the present specification, stainless steel such as SUS430, SUS429, SUS444, iron, cast iron, copper, Hastelloy, Inconel, Kovar, nickel alloy and the like can be used. The composition and raw material of the inorganic porous layer may be adjusted according to the coefficient of thermal expansion of the metal tube used. Specifically, when the coefficient of thermal expansion of the inorganic porous layer is α1 and the coefficient of thermal expansion of the metal is α2, the adjustment may be made so as to satisfy the following equation 5. For example, when the metal tube is SUS430, the coefficient of thermal expansion α1 is 6 × 10 ^-6 / K <α1 <14 × 10 ^-6 / K, and more preferably the coefficient of thermal expansion α1 is 6 × 10 ^-6. The composition and raw materials of the inorganic porous layer may be adjusted so that / K <α1 <11 × ^{10-6 / K.} Further, when the metal tube is copper, the coefficient of thermal expansion α1 is 8.5 × 10 ^-6 / K <α1 <20 × 10 ^-6 / K, and more preferably, the coefficient of thermal expansion α1 is 8.5. The composition and raw materials of the inorganic porous layer may be adjusted so that × ^10-6 / K <α1 <18 × ^{10-6 / K.} The value of "α1 / α2" may be 0.55 or more, 0.6 or more, 0.65 or more, 0.75 or more, and 0.8. It may be the above. Further, the value of "α1 / α2" may be 1.15 or less, 1.1 or less, 1.05 or less, or 1.0 or less.
Equation 5: 0.5 <α1 / α2 <1.2

In the exhaust pipe disclosed in the present specification, the above raw material may be applied to the inner surface of the metal pipe, dried and fired to form an inorganic porous layer on the inner surface of the metal pipe. As a method for applying the raw material, dip coating, spin coating, aerosol deposition (AD) method, brush coating, trowel coating, mold cast molding and the like can be used. If the target inorganic porous layer is thick, or if the inorganic porous layer has a multi-layer structure, the application of the raw material and the drying of the raw material are repeated multiple times to adjust the thickness to the target or the multi-layer structure. You may. The above coating method can also be applied as a coating method for forming a coating layer, which will be described later.

As described above, in the exhaust pipe disclosed in the present specification, a coating layer may be provided on the surface of the inorganic porous layer. The material of the coating layer may be a porous or dense ceramic. Examples of the porous ceramic used in the coating layer include zirconia (ZrO ₂ ), partially stabilized zirconia, stabilized zirconia and the like. In addition, yttria-stabilized zirconia (ZrO _2- Y ₂ O ₃ : YSZ), a metal oxide obtained by adding _{Gd 2} O ₃ , Yb ₂ O ₃ , Er ₂ O _3, _{etc. to YSZ, ZrO 2-} HfO _2- Y ₂ O ₃ , ZrO _2- Y ₂ O _3- La ₂ O ₃ , ZrO _2- HfO _2- Y ₂ O _3- La ₂ O ₃ , HfO _2- Y ₂ O ₃ , CeO _2- Y ₂ O ₃ , Gd ₂ Zr ₂ O ₇ , Sm ₂ Zr ₂ O ₇ , LaMnAl ₁₁ O ₁₉ , YTa ₃ O ₉ , Y _0.7 La _0.3 Ta ₃ O ₉ , Y _1.08 Ta _2.76 Zr _0.24 O ₉ , Examples thereof include Y ₂ Ti ₂ O ₇ _{, LaTa 3} O ₉ , Yb ₂ Si ₂ O ₇ , Y ₂ Si ₂ O ₇ , and Ti ₃ O ₅ . Examples of the dense ceramic used in the coating layer include alumina, silica, zirconia and the like. Further, since the ceramic fiber is removed from the constituent material of the inorganic porous layer described above to obtain a low porosity (dense), it may be used as a coating layer. By using the porous or dense ceramic as the coating layer, the inorganic porous layer can be reinforced and the inorganic porous layer can be prevented from peeling off from the surface of the metal tube. When a dense ceramic is used as the coating layer, for example, it is possible to suppress the permeation of high-temperature gas through the inorganic porous layer and the retention of exhaust gas in the inorganic porous layer. As a result, the effect of suppressing the heat transfer of the exhaust gas to the metal pipe can be expected.

The exhaust pipe 10 will be described with reference to FIGS. 1 to 3. The exhaust pipe 10 is provided with an inorganic porous layer 4 on the inner surface of a metal pipe 2 made of SUS430. Further, a coating layer 6 is provided on the surface of the inorganic porous layer 4. The inorganic porous layer 4 is bonded to the inner surface of the metal tube 2, and the coating layer 6 is bonded to the inner surface of the inorganic porous layer 4.

The exhaust pipe 10 was manufactured by immersing the metal pipe 2 in the raw material slurry, drying and firing the metal pipe 2 with the outer surface of the metal pipe 2 masked. Specifically, the outer surface of a pipe (made by SUS430) having an inner diameter of 2R: 18 mm, an outer diameter of 20.4 mm (thickness 2t: 1.2 mm), and a length of 300 mm is immersed in a raw material slurry while being masked, and is made of inorganic porous material. The layer was applied to the inner wall of the pipe. Then, each sample was prepared by drying at 200 ° C. and calcining at 800 ° C. The raw material slurry of the inorganic porous layer 4 includes alumina fibers (average fiber length 140 μm), plate-shaped alumina particles (average particle diameter 6 μm), titania particles (average particle diameter 0.25 μm), and alumina sol (alumina amount 1. 1% by mass), acrylic resin (average particle size 8 μm), and ethanol were mixed to prepare the mixture. The raw material slurry was adjusted so that the viscosity was 2000 mPa · s. The raw material slurry of the coating layer 6 is plate-shaped alumina particles (average particle diameter 6 μm), titania particles (average particle diameter 0.25 μm), alumina sol (alumina amount 1.1% by mass), and acrylic resin (average). Particle size 8 μm) and ethanol were mixed to prepare. That is, the raw material slurry used for molding the coating layer 6 is obtained by removing the alumina fibers from the raw material slurry used for forming the inorganic porous layer 4. The raw material slurry for molding the coating layer 6 was also adjusted so that the viscosity was 2000 mPa · s.

After immersing the metal tube 2 in the raw material slurry for the inorganic porous layer and applying the raw material to the inner surface of the metal tube 2, the metal tube 2 was put into a dryer and dried at 200 ° C. (atmospheric atmosphere) for 1 hour. As a result, an inorganic porous layer 4 having a thickness of 300 μm was formed on the inner surface of the metal tube 2. Then, the step of immersing the metal tube 2 in the raw material slurry for the inorganic porous layer and drying it was repeated three times to form the inorganic porous layer 4 having a thickness of 4t: 1.2 mm on the inner surface of the metal tube 2. Next, the steps of immersing and drying the metal tube 2 on which the inorganic porous layer 4 is formed in the coating layer raw material slurry are performed twice, and the coating layer 6 having a thickness of 6t: 0.6 mm is provided on the inner surface of the inorganic porous layer 4. Formed.

After that, the metal pipe 2 was placed in an electric furnace and fired at 800 ° C. in an atmospheric atmosphere to prepare an exhaust pipe 10. The inorganic porous layer 4 was formed on the entire inner surface of the metal tube 2, and the coating layer 6 was formed on the entire inner surface of the inorganic porous layer 4 (see FIG. 3). The exhaust pipe 10 satisfies the above equations (1) to (3).

(Experimental Example 1)
As described above, the exhaust pipe 10 is provided with the inorganic porous layer 4 and the coating layer 6 on the inner surface of the metal pipe 2. In this experimental example, the total thickness (thickness 4t + thickness 6t) of the inorganic porous layer 4 and the coating layer 6 with respect to the inner diameter 2R of the metal tube 2 and the thickness 4t of the inorganic porous layer 4 with respect to the thickness 2t of the metal tube 2 are obtained. After changing, the adhesion and heat insulating properties of the inorganic porous layer 4 were evaluated. Specifically, a 1.2 mm inorganic porous layer is formed on the inner surface of pipes (made by SUS430) having different sizes (inner diameter and outer diameter), and the surface (inner surface) of the inorganic porous layer is coated with 0.6 mm. This was done with the sample on which the layer was formed. FIG. 4 shows the sizes of the pipe, the inorganic porous layer and the coating layer in each sample. In addition, FIG. 4 also shows the sufficiency of the above formulas (1) to (3) in each sample. In the sample 4, only the inorganic porous layer was formed, and the coating layer was not formed.

Adhesion was evaluated by performing a heating vibration test. In the heating vibration test, each sample was attached to a heating vibration test device, and propane combustion gas was circulated in the pipe for 5 minutes from the heating vibration test device, and then normal temperature air gas was circulated for 5 minutes. The combustion gas was adjusted so that the gas temperature at the end face on the inflow side of the pipe was 900 ° C. at the maximum and the gas flow rate was 2.0 Nm ^{3 / min.} Next, while the combustion gas was continuously supplied into the pipe, vibration in the longitudinal direction (longitudinal direction) was applied to the pipe. The vibration conditions were 100 Hz and 30 G, and vibration was applied for 50 hours. The test was conducted under these conditions, and the appearance of the inorganic porous layer after the test was evaluated. In FIG. 4, the sample with no change in appearance (no cracks and peeling) has "◎", the sample with less than 3 cm has 3 or less cracks, and the sample without peeling has "○" with cracks of 3 cm or more, or cracks with less than 3 cm. Four or more samples without peeling are marked with "Δ", and samples with cracks and peeling are marked with "x".

The heat insulating property was evaluated by conducting a high temperature gas inflow test. In the high temperature gas inflow test, 600 degree high temperature gas is ^{supplied into the pipe at 2 Nm 3} / min, and when the gas temperature flowing through the inner wall of the pipe inlet side end reaches 400 degrees, the inner wall of the pipe outlet side end. The difference from the gas temperature flowing through the pipe was measured and evaluated. In FIG. 4, a sample having a temperature difference of less than 10 degrees is marked with "○", a sample having a temperature difference of 10 degrees or more and less than 15 degrees is marked with "△", and a sample having a temperature difference of 15 degrees or more is marked with "x". ..

As shown in FIG. 4, in Samples 3 to 7, no cracks or peeling were confirmed in the inorganic porous layer after the heating vibration test. A slightly short crack was confirmed in Sample 2. Further, in Sample 8, although peeling was not confirmed, relatively long cracks were confirmed. Further, in

Samples

1 and 9, peeling and cracking were confirmed after the heating vibration test. Sample 1 does not satisfy the above formula (1). Further, the samples 8 and 9 satisfy the above formula (1) but do not satisfy the above formula (2) (exceeding the upper limit value). Of the samples 3 to 7,

samples

5 and 6 did not satisfy the above formula (2) (exceeded the lower limit), but the results after the heating vibration test were good. From this result, the sizes of the metal tube (pipe), the inorganic porous layer and the coating layer satisfy the upper limit values of the above formulas (1) and (2), so that the inorganic material having excellent thermal shock resistance and vibration resistance is excellent. It was confirmed that an exhaust pipe having a porous layer can be obtained.

Samples 3 and 7 satisfy the above formula (3) in addition to the above formulas (1) and (2). On the other hand, the sample 2 satisfies the above formulas (1) and (2), but does not satisfy the above formula (3). From this result, it was confirmed that the thermal shock resistance and the vibration resistance were further improved by satisfying the above formula (3). The sample 1 does not satisfy the above formula (3) either.

Further, as shown in FIG. 4, it was confirmed that the samples 1 to 4, 7 to 9 had good heat insulating properties. On the other hand, it was confirmed that the

samples

5 and 6 had lower heat insulating properties than the other samples.

Samples

5 and 6 satisfy the above formulas (1) and (3), but do not satisfy the lower limit of the above formula (2). That is, the thickness of the inorganic heat insulating layer is thinner than the thickness of the pipe. From this result, if the sizes of the metal pipe, the inorganic porous layer and the coating layer satisfy the lower limit of the above formula (2), an exhaust pipe having an inorganic porous layer having excellent heat insulating properties can be obtained. confirmed. From the above, when the sizes of the metal pipe, the inorganic porous layer and the coating layer satisfy the above formulas (1) and (2), an exhaust pipe having excellent heat insulating properties and excellent adhesion can be obtained. Was confirmed. Further, it was confirmed that the thermal shock resistance and the vibration resistance are further improved by satisfying the above formula (3).

(Experimental Example 2)
As described above, for the inorganic porous layer, a raw material slurry in which alumina fibers, plate-like alumina particles, titania particles, alumina sol, acrylic resin and ethanol are mixed is prepared, a metal tube is immersed in the raw material slurry, and then dried and It was created by firing. In this experimental example, in order to confirm the influence of the amounts of the alumina component and the titania component on the characteristics of the inorganic porous layer, an inorganic porous layer was formed on the surface of the metal plate instead of the metal tube and evaluated. Specifically, the proportions of the alumina fibers, the plate-shaped alumina particles and the titania particles were changed, and the alumina fibers were replaced with mullite fibers and the plate-shaped alumina particles were replaced with the plate-shaped mica to form an inorganic porous layer. The state of the inorganic porous layer after firing was confirmed.

Specifically, the blending amounts of ceramic fibers (alumina fibers, murite fibers), plate-shaped ceramic particles (plate-shaped alumina particles, plate-shaped mica), titania particles, and zirconia particles are changed as shown in FIG. , Plate-shaped ceramic particles, titania particles and zirconia particles are blended so that the total is 100% by mass, and further, 10% by mass of alumina sol (1.1% by mass of alumina contained in the alumina sol), acrylic resin 40 A raw material slurry was prepared by adding mass% and adjusting the slurry viscosity with ethanol. The sample 15 does not use plate-shaped ceramic particles, and the samples 11 to 17, 20, 22 and 23 do not use zirconia particles. Then, for the samples 11 to 18, 21 to 23, the raw material slurry was applied to the SUS430 plate, and for the

samples

19 and 20, the raw material slurry was applied to the copper plate, dried at an air atmosphere of 200 ° C. for 1 hour, and then the air atmosphere 800. It was baked at ° C for 3 hours. The number of times the raw material slurry was applied (the number of times the metal plate was immersed) in each sample was adjusted so that an inorganic porous layer of about 1.2 mm was formed on the metal plate (SUS430 plate and copper plate).

The purpose of this experimental example is to confirm the effect of the amounts of the alumina component (ceramic fiber, plate-shaped ceramic particles) and the titania component on the appearance of the inorganic porous layer (presence or absence of cracks, peeling, etc.). The heat insulating property of the porous layer has not been evaluated.

The appearance of the sample after firing was evaluated. In the appearance evaluation, the presence or absence of cracks and peeling was visually observed. In FIG. 5, "○" is attached to the sample in which crack and peeling did not occur, "△" is attached to the sample in which one of crack and peeling occurred, and "△" was attached to the sample in which both crack and peeling occurred. "X" is attached.

Further, for the prepared samples 11 to 23, measurement of the ratio (mass%) of the alumina component and the titania component in the inorganic porous layer, measurement of the porosity (volume%) of the inorganic porous layer, the inorganic porous layer and the metal. The thermal expansion coefficient of the plate was also measured. Alumina and titania component, ICP emission spectrometer (Hitachi High-Tech Science Ltd., PS3520UV-DD) was used to measure the aluminum and titanium amounts, indicates terms of oxides _{_{_{(Al 2 O 3, TiO 2}}} ) as a result ing.

^{The porosity is the total pore volume (unit: cm 3} / g) measured in accordance with JIS R1655 (a molded body pore size distribution test method by a fine ceramic mercury intrusion method) using a mercury porosity, and a gas substitution formula. It was calculated from the following formula (6) using ^{the apparent density (unit: g / cm 3} ) measured by a density measuring meter (Accupic 1330 manufactured by Micromeritix).
Equation 6: Porosity [%] = total pore volume / {(1 / apparent density) + total pore volume} x 100

The coefficient of thermal expansion was obtained by molding the above-mentioned raw material slurry into a bulk body of 3 mm × 4 mm × 20 mm and then calcining the bulk body at 800 ° C. to prepare a sample for measurement. Then, the measurement sample was measured using a thermal expansion meter in accordance with JIS R1618 (a method for measuring thermal expansion by thermomechanical analysis of fine ceramics). The coefficient of thermal expansion was measured separately for the inorganic porous layer and the metal plate.

In addition, the thermal conductivity of the inorganic porous layers of Samples 11 to 14 and 23 and the metal plates of Samples 11 to 23 was measured. Thermal conductivity was also measured separately for the inorganic porous layer and the metal plate. The thermal conductivity was calculated by multiplying the thermal diffusivity, the specific heat capacity and the bulk density. For the heat diffusion rate, a laser flash method heat constant measuring device is used, and for the specific heat capacity, a DSC (differential scanning calorimetry) is used. Method) was measured at room temperature. For the bulk density of the metal plate, the weight of a bulk body having a diameter of 10 mm and a thickness of 1 mm was measured, and the value obtained by dividing the weight by the volume was taken as the bulk density (unit: g / cm ³ ). The bulk density (unit: g / cm ³ ) of the inorganic porous layer was calculated from the following formula (7). The thermal diffusivity is obtained by molding the above-mentioned raw material slurry into a bulk body having a diameter of 10 mm × 1 mm, and the specific heat capacity is obtained by molding the above-mentioned raw material slurry into a bulk body having a diameter of 5 mm × a thickness of 1 mm, and then each bulk body is 800. A sample for measuring thermal diffusivity and specific heat capacity was prepared and measured by firing at ° C. The measurement results are shown in FIG.
Formula 7: Bulk density of the inorganic porous layer = apparent density × (1-porosity [%] / 100)

As shown in FIG. 5, in Samples 11 to 20, 23, no cracks or peeling were confirmed in the inorganic porous layer after firing. On the other hand, in the sample 21, although peeling was not confirmed, the occurrence of cracks was confirmed. In addition, both cracks and peeling were confirmed in the sample 22. This result shows that when the alumina component (alumina fiber and plate-like alumina particles) in the inorganic porous layer is small (less than 15% by mass) or the titania component is small (less than 45% by mass), the metal during firing is negative. It is shown that the force acts between the inorganic porous layers and the characteristics of the inorganic porous layer are deteriorated. Specifically, since the proportion of the alumina component in the sample 21 is less than 15% by mass, it is presumed that the bonding force between the ceramics (particles, fibers) is reduced and cracks are generated in the inorganic porous layer. Further, since the proportion of the titania component in the sample 22 is less than 45% by mass, it is presumed that the bonding force between the ceramics is lowered and cracks are generated in the inorganic porous layer. Further, in the sample 22, the content of the titania component (titania particles) having a high coefficient of thermal expansion is low, and the ratio of the coefficient of thermal expansion to the metal (α1 / α2) is small (less than 0.5). It is presumed that the inorganic porous layer was separated from the metal based on the difference in thermal expansion. From the above, regardless of the type of ceramic fiber (alumina fiber, mullite fiber) and the type of plate-shaped ceramic particles (plate-shaped alumina particle, plate-shaped mica), 15% by mass or more of alumina component and 45% by mass or more of titania component. It was confirmed that the inorganic porous layer containing the above was less likely to cause deterioration such as cracks and peeling after firing.

Although the embodiments of the present invention have been described in detail above, these are merely examples and do not limit the scope of claims. The techniques described in the claims include various modifications and modifications of the specific examples exemplified above. Further, the technical elements described in the present specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the techniques exemplified in the present specification or the drawings achieve a plurality of purposes at the same time, and achieving one of the purposes itself has technical usefulness.

2: Metal pipe 4: Inorganic porous layer 6: Coating layer 10: Exhaust pipe

Claims

An exhaust pipe provided with a metal pipe and an inorganic porous layer provided at a portion of the inner surface of the metal pipe through which exhaust gas passes.
An exhaust pipe in which the inner diameter D1 of the metal pipe, the thickness d1 of the metal pipe, and the thickness d2 of the inorganic porous layer satisfy both the following formulas (1) and (2).
d2 / D1 <0.12 ... (1)
0.2 <d2 / d1 <3 ... (2)
The exhaust pipe according to claim 1, wherein a coating layer having a thickness of d3 is provided on the surface of the inorganic porous layer, which satisfies the following formula (3).
(D2 + d3) / D1 <0.15 ... (3)
The exhaust pipe according to claim 2, wherein the thickness d2 and the thickness d3 satisfy the following formula (4).
d2 / 20≤d3≤d2 / 2 ... (4)
The exhaust pipe according to any one of claims 1 to 3, wherein the inorganic porous layer contains ceramic fibers and is composed of 15% by mass or more of an alumina component and 45% by mass or more of a titania component.
The exhaust pipe according to any one of claims 1 to 4, wherein the thermal conductivity of the metal pipe is 100 times or more the thermal conductivity of the inorganic porous layer.
The exhaust pipe according to claim 5, wherein the inorganic porous layer has a thermal conductivity of 0.05 W / mK or more and 3 W / mK or less.
The exhaust pipe according to claim 5 or 6, wherein the thermal conductivity of the metal pipe is 10 W / mK or more and 400 W / mK or less.
The exhaust pipe according to any one of claims 1 to 7, which satisfies the following formula (5) when the coefficient of thermal expansion of the inorganic porous layer is α1 and the coefficient of thermal expansion of the metal pipe is α2.
0.5 <α1 / α2 <1.2 ... (5)
The exhaust pipe according to any one of claims 1 to 8, wherein the inorganic porous layer contains plate-shaped ceramic particles.
The exhaust pipe according to any one of claims 1 to 9, wherein the inorganic porous layer contains granular particles of 0.1 μm or more and 10 μm or less.
The exhaust pipe according to any one of claims 1 to 10, wherein the thickness of the inorganic porous layer is 1 mm or more.