JP2588427B2 - Insulated ceramic cast-in-place body and method of manufacturing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an insulated ceramic cast insert having a structure in which an inner layer made of ceramic is formed by metal, and is particularly suitable for use in an exhaust manifold or the like. The present invention relates to a heat-insulated ceramic cast body.

[Conventional technology]

Conventionally, it has been attempted to provide a ceramic inner layer in an exhaust system device such as an exhaust manifold and an exhaust pipe for the purpose of heat insulation. The ceramic inner layer can be formed by applying a ceramic layer to the inner surface of a metal component and firing it.On the other hand, a ceramic component for the ceramic inner layer is formed in advance, and the ceramic component is formed of a metal such as aluminum or cast iron. There is also a casting method, and various methods for producing a heat-insulated ceramic casting product by such a casting method have been proposed (Japanese Patent Publication No. 50-3737, Japanese Patent Publication No. 51-16168, Japanese Patent Application Laid-Open No. No. 126010).
However, since the coefficient of thermal expansion of ceramics is smaller than that of metal, compressive stress is applied to the ceramic sintered body when the cast metal melt is cooled and solidified and contracts. For this reason, there is a problem that microcracks are generated or broken in the ceramic sintered body.

Various proposals have been made to solve such a problem.

JP-A-51-16168 discloses a refractory aggregate having a modulus of elasticity of 200 to 5000 kg / mm ² , a bending strength of 8 to 200 kg / cm ² , a thickness of 1/4 or less of the inner diameter, and a smooth surface. A method for producing a heat-insulated casting, comprising placing a flexible ceramic semi-finished product made of alumina cement in a mold and casting the ceramic semi-finished product with a molten metal is disclosed. Japanese Patent Publication No. 58-37277 discloses a method in which a coating material for preventing cracks due to thermal shock is applied to this flexible ceramic semi-finished product, and then the resulting product is cast. In either method, cracking of the ceramic is prevented by absorbing the compressive stress caused by cooling and solidification of the molten metal by shrinkage within the elastic limit of the ceramic semi-finished product. A similar method is also disclosed in JP-B-52-48602.

Japanese Patent Publication No. 56-37021 discloses a ceramic casting in which a microcrack is generated in advance in the entire structure of a ceramic part, and the microcrack absorbs the compressive stress at the time of casting to prevent the compressive fracture of the ceramic part. We have proposed a manufacturing method for hollow castings.

Furthermore, Japanese Patent Publication No. 60-240365 discloses a method of forming a fibrous body with inorganic fibers, and filling a slurry containing fine pieces of ceramic between individual inorganic fibers on the surface layer of the fibrous body,
This is dried and heated to sinter the fine pieces of the ceramic, dispose the fiber molded body thus treated at a predetermined position in a mold, and place a molten metal in a space containing the inorganic fibers in the mold. And a method of casting a ceramic body to solidify the same.

According to this method, a slurry containing fine ceramic pieces is filled between the individual inorganic fibers of the surface layer of the fiber molded body, and the slurry is dried and heated to sinter the fine ceramic pieces. Includes a ceramic body formed by sintering fine pieces, and a large number of inorganic fibers that are partially embedded in the ceramic body in close contact and extend outside the ceramic body in other parts A structure is formed. This structure is placed at a predetermined position in the mold, and the molten metal is introduced into the space containing the inorganic fibers in the mold. As the molten metal solidifies,
Since the portion of the inorganic fiber extending outside the ceramic body is buried in a state of being closely attached to the main part made of metal, it extends over both the ceramic body and the main part made of metal. The ceramic body and the main part made of metal are firmly bonded by a large number of strongly adhered inorganic fibers.
As a result, a member is obtained in which the ceramic body does not peel from the main part and rattling of the ceramic body does not occur.

[Problems to be solved by the invention]

However, the method of Japanese Patent Publication No. 51-16168 has a problem that it is practically difficult to completely absorb the compressive stress caused by the solidification of the molten metal due to the elastic deformation of the ceramic semi-finished product, thereby preventing cracks and the like. Therefore, this method is not suitable for reliably producing a heat-insulated ceramic cast-in-place casting without cracks or breakage.

In the method of Japanese Patent Publication No. 56-37021, micro-cracks are generated in the ceramic body to relieve the compressive stress at the time of casting. May grow and expand, and the cast body may be broken.

Furthermore, the method disclosed in Japanese Patent Application Laid-Open No. 60-240365 does not solve the problem of cracking and breaking due to compressive stress of cast-in metal.

The object of the present invention is to eliminate such cracking and breaking problems,
An object of the present invention is to provide a heat-insulated cast-in-mold ceramic body which absorbs compressive stress at the time of cast-in and prevents cracks and breakage of the ceramic body, and a method of manufacturing the same.

[Means for solving the problem]

As a result of various studies to achieve the above object, the present invention provides a shrinkable ceramic felt layer on the outer periphery of a ceramic sintered body to absorb the compressive stress generated at the time of casting. The present inventors have found good things and completed the present invention.

That is, the insulated ceramic cast insert and the method of manufacturing the same according to the present invention are characterized in that a ceramic felt layer is formed on a cast-in surface of a ceramic sintered body, and the cast body is cast with a cast-in metal.

 The present invention will be described in detail below.

FIG. 1 is a partially cutaway perspective view showing an example of a heat-insulated ceramic cast insert of the present invention, where 1 is a ceramic layer,
2 is a ceramic felt layer formed on the cast-in surface,
3 is a cast-in metal layer.

The ceramic layer 1 has a high-temperature strength and a heat insulating property, and is made of a material that can sufficiently withstand a thermal shock.
As such a ceramic material, alumina-based ceramics, alumina cement or a mixture thereof is preferable, but ceramics such as aluminocalcinate and silicon nitride can also be used.

Alumina ceramics is prepared by mixing about 0.1 to 5 parts by weight of a sintering aid such as MgO or SiO _{2 with} 100 parts by weight of alumina powder having an average particle size of about 0.3 to 50 μm, if necessary, and then molding by slip casting or the like. And sintering at 1400-1800 ° C. for 0.5-4 hours.

Alumina cement is a cement containing CaO.Al ₂ O ₃ as a main component, and various kinds of particles can be blended for improving fire resistance, heat resistance, strength and the like.

Further, a mixture of alumina ceramics and alumina cement at an appropriate ratio can also be used as the ceramic material. In this case, a fibrous alumina ceramic component may be contained, and the weight ratio of particulate ceramic / fibrous ceramic is preferably in the range of 45/55 to 95/5.

It is desirable that the ceramic layer 1 has a strength of 0.5 kg / mm ² or more, preferably 2.5 kg / mm ² or more.

The ceramic felt layer 2 is formed on the outer periphery of the ceramic layer 1 and is a felt-like layer made of long fibers or short fibers such as alumina, alumina-silica, silicon carbide, zirconia, and glass. When knitting and weaving such as glass fiber are possible, knitted and woven fabrics may be used if workability is good.

The ceramic felt layer 2 acts to reduce the shrinkage stress of the as-cast metal during as-cast. For example, when an aluminum alloy is used as the cast-in metal, shrinkage of not less than the shrinkage amount D (%) represented by the following equation is required.

Here, D: shrinkage amount (%), R _0: the metal layer inside diameter, R _2: ceramic felt layers inside diameter, TE: Aluminum linear thermal expansion coefficient of, MP: aluminum melting temperature, RT: room temperature where, for example, Thickness of ceramic felt layer 2 = 1m
If m, R ₀ = 41 mm, and R ₂ = 40 mm, the linear thermal expansion coefficient TE of aluminum is 23 × 10 ⁻⁶ / deg and (melting point of aluminum alloy−room temperature) = 700 ° C. Becomes The ceramic felt layer 2 must be capable of shrinking so as to absorb 66% of shrinkage at a thickness of 1 mm. For such shrinkage, it is very advantageous to have a felt shape.

The ceramic felt layer 2 having the above shrinkability has a felt density of 0.1 to 3.0 g / cc and a felt thickness of 0.5 mm or more, preferably about 1 to 3 mm.

Such a ceramic felt layer 2 has a diameter of 3 to 10 μm.
It can be prepared by making a ceramic fiber having a length of m and several mm in length by a papermaking method.

As the cast-in metal, a metal such as iron, an aluminum alloy, and a magnesium alloy which can be used for a normal cast-in can be used, but an aluminum alloy is preferable for the purpose of weight reduction.

FIG. 2 is a partially cutaway perspective view showing another embodiment of the insulated ceramic cast insert of the present invention, in which a ceramic felt layer 2 is formed on a cast surface of a ceramic layer 1 and a ceramic layer 1 is formed. A glass layer 4 is formed on the inner surface, and the outer surface of the ceramic felt layer 2 is covered with a metal foil 5 having a higher melting point than the cast metal 3. Reference numeral 6 denotes a machinable ceramic layer provided for improving workability when performing surface processing of the flange portion.

As described above, since the ceramic layer 1 is a fire-resistant and heat-resistant ceramic sintered body, a certain amount of micropores are present. It penetrates and deteriorates the heat insulation performance and reaches the cast-in metal layer 3.
Are too high or melt. In particular, when used for an exhaust manifold, the pressure of the waste gas reaches ² kg / cm ² , and such a problem is likely to occur. Therefore, on the inner surface of the ceramic layer 1,
It is desirable to coat the glass layer 4 to prevent gas flow from permeating, to prevent the heat insulation performance from deteriorating, and to prevent the cast-in metal layer 3 from being heated and melted. In the case of an exhaust manifold, since the waste gas temperature reaches 800 to 900 ° C., it is preferable to use glass whose melting temperature is 1000 ° C. or higher. The glass composition is mainly composed of alumina and silica.
₂ O ₃ , BaO, Na ₂ O, CaO, Li ₂ O, NaCl, SrO, PbO, K ₂ O, Fe
One or more components such as ₂ O ₃ may be added. The difference in the linear thermal expansion coefficient between the ceramic material forming the ceramic layer 1 and the glass forming the glass layer 4 is from −2 × 10 ⁻⁶ to 10 × 10 ^−6.
It is optimally within the range of / ° C.

Further, at the time of casting, a metal having a melting point somewhat higher than that of the cast-in metal 3 is used in order to prevent the molten cast-in metal from penetrating into the ceramic felt layer 2 and improve the flow of the molten metal so as to perform uniform casting. Preferably, the outer surface of the ceramic felt layer 2 is covered with a foil 5. For example, when casting with an aluminum alloy, a commercially available aluminum foil is preferable because it is difficult to dissolve during pouring.

The machinable ceramic layer 6 covers the end face of the ceramic layer 1 and facilitates processing of the end face of the casting. As such machinable ceramics, aluminum titanate or the like can be used.

The heat-insulated ceramic cast body of the present invention can be manufactured by the following method.

FIG. 3 shows an example of producing an exhaust manifold by the method of the present invention.

First, a mold 10 for producing a ceramic molded body and a core 11 to be inserted therein are prepared (A). The ceramic mold 10 may be a resin mold or the like, and the core 11 is preferably made of a material such as wax that can be removed by melting.

The ceramic slurry 12 is cast between the resin mold 10 and the core 11 (B), and then cured (C). Curing is performed in a steam atmosphere for about 6 to 20 hours. Next, release (D),
The core wax is melted and degreased to obtain a ceramic molded body 13 (E). Thereafter, sintering is performed to obtain a ceramic sintered body 14 (F). Thereafter, if necessary, a glass frit is applied to the inner surface of the ceramic
The glass layer is formed by heating at 1400 ° C. for 0.5 to 4 hours and vitrifying (G). A flange 15 made of machinable ceramic is attached to the end face of the ceramic sintered body 14 (H).

On the other hand, a small amount of a binder (for example, highly basic chloride alumina) is added to the ceramic felt 16 and wound around a wooden mold 17 having the same shape as the ceramic sintered body (I), and a ceramic felt layer is formed by a vacuum forming method. Half of that
Make 18, 18. (J)

The two halves are covered with the ceramic sintered body layer 14 and joined, and the joining surface is covered and fixed with a glass fiber woven fabric (K). If necessary, this is covered with a metal foil and then cast-molded with a cast-in metal (L).

INDUSTRIAL APPLICABILITY The insulated ceramic cast insert of the present invention can be used in a wide range of fields such as ports and pipes, including exhaust manifolds.

(Operation)

In the heat-insulated ceramic cast insert of the present invention,
Since the ceramic felt layer 2 which can be shrunk in accordance with the compressive stress caused by the solidification of the stuffed metal is interposed between the ceramic layer 1 and the stuffed metal layer 3, the compressive stress generated at the time of stuffing is reduced by the ceramic felt. Absorption by the layer 2 prevents the ceramic layer 1 from cracking and breaking. And, unlike the conventional example, microcracks are not generated in advance in the ceramics layer,
There is no risk of breakage due to the growth of microcracks.

Example 1 Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1 A resin mold having a cylindrical cavity was prepared, a cylindrical Styrofoam core having the same shape as the inner surface of the exhaust manifold was set therein, and the following composition between the resin mold and the core was prepared. Was injected.

Alumina powder (particle size: 40 μm): 55 parts by weight Alumina cement: 30 parts by weight Alumina fiber (average fiber length mm): 20 parts by weight Water: 37 parts by weight After elution and degreasing, bake at 1400 ° C for 2 hours,
A ceramic sintered body for a ceramic inner layer was formed.

On the other hand, a high-base chlorinated alumina was added as a binder to a felt (thickness: 3 mm, density: 0.19 g / cc) made of short alumina fibers having an average diameter of 5 μm and an average fiber length of 2.5 mm, and the felt molded body was halved by vacuum molding. Was prepared, and two of the felt felt compacts were put together on a ceramic compact, and the joint surface was covered with a glass fiber woven cloth and fixed.

Next, a molten aluminum alloy was poured and cast-molded to obtain a heat-insulated ceramic cast-in-place casting.

In this case, no crack or destruction was observed in the ceramic layer.

When the engine exhaust gas of about 800 ° C. was passed through this casting, the surface temperature increased as shown in graph a of FIG. 4, but even after 30 minutes from the start of use, the surface temperature was about It was about 400 ° C. On the other hand, in the cast body which was cast without the ceramic felt layer, cracks were observed in the ceramic layer, and the surface temperature increased to about 500 ° C. after 30 minutes by the same heating test.
(Graph c) From this, it can be seen that the ceramic felt layer in the casting of the present invention has an effect of preventing cracks and breakage, and also has an excellent heat insulating effect.

Example 2 In Example 1, after firing the ceramic, a glass frit having the following composition was applied to the inner surface of the ceramic sintered body, heated at 1200 ° C. for 30 minutes to vitrify, and the thickness was 0.25 mm.
Glass layer. Next, in the same manner as in Example 1, alumina fiber felt was covered, and the felt joint surface was fixed with a glass fiber woven fabric, and then further covered with a commercially available aluminum foil. Molding was performed.

In this case, the cast-in molding was performed extremely smoothly, and no crack or breakage of the ceramic sintered body was recognized. Further, when an engine exhaust gas of about 800 ° C. was passed through the casting, as shown in graph b of FIG. 4, the rise in surface temperature was slight, and after 30 minutes, the surface temperature was slightly reduced.
It was found that the temperature was 250 ° C., indicating an extremely excellent heat insulating effect.

Glass frit composition SiO ₂ : 65 parts by weight Al ₂ O ₃ : 20 parts by weight CaO: 8 parts by weight K ₂ O: 4 parts by weight BaO: 2 parts by weight Na, Cl: <1 part by weight Example 3 Average particle size 0.5 μm 100 parts by weight of alumina powder was mixed with 1 part by weight of MgO as a sintering aid, molded by a slip casting method, and then sintered at 1550 ° C. for 2 hours to obtain a length of 20 μm.
A test piece A having a diameter of 40 mm, an outer diameter of 40 mm and a thickness of 4 mm was prepared. Further, a ceramic felt having a thickness of 3 mm and a density of 0.2 g / cc made of alumina fiber was attached to a sintered body having the same size as the test piece A to obtain a test piece B. For comparison, a test piece C of the same size made of aluminocalcite, which is a conventional casting ceramic, was prepared.

A load was applied to each test piece to determine the relationship between the strain and the load. The results are shown in FIG. As is clear from FIG. 5, in the test piece B having the ceramic felt layer, the load hardly increased in the initial strain stage (strain was absorbed by the ceramic felt layer), and the load increased after the contraction of the ceramic felt layer was completed. It can be seen that destruction occurs. In addition, the initial strain amount is a size that can sufficiently absorb the compressive strain when it is cast with an aluminum alloy, and it can be seen that there is no risk of cracking or breakage due to the compressive stress when the cast product is cast as cast . On the other hand, it can be seen that the test piece c made of aluminocalcite suffered from microcracks and insufficient mechanical strength.

〔The invention's effect〕

According to the present invention, the compressive stress at the time of casting can be absorbed, and the compressive fracture of the ceramic layer can be prevented,
In addition, there is no possibility of ceramic layer destruction due to the growth of microcracks.

Moreover, the heat-insulated ceramic cast-in-place casting of the present invention has excellent heat-insulating properties. In particular, when a glass layer is formed on the inner surface of the ceramic layer, the heat-insulating effect is further improved.

When such a heat-insulated ceramic cast body of the present invention is used for an exhaust manifold, the outlet temperature thereof becomes high (approximately 50 ° C. rise), so that the NOx removing catalyst can act efficiently and emission characteristics can be improved. There is also the advantage that it can be improved.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing an example of the heat-insulated ceramic cast body of the present invention, and FIG. 2 is a partially cutaway perspective view showing another example of the heat-insulated ceramic cast body of the present invention. FIG. 3 is a flowchart showing an example of manufacturing a heat-insulated ceramic cast insert (exhaust manifold) according to an embodiment of the present invention. FIG. FIG. 5 is a graph showing the relationship between the surface temperature and the gas flow time in the case of performing the test. FIG. 5 is a graph showing the relationship between the amount of strain and the load in the load test of each test piece of Example 3. DESCRIPTION OF SYMBOLS 1 ... Ceramic layer 2 ... Ceramic felt layer 3 ... Cast-in metal layer 4 ... Glass layer 5 ... Metal foil

Continued on the front page (72) Inventor Harumi Taketomi 1-4-1 Chuo, Wako-shi, Saitama Pref. Wako Research Laboratory, Honda R & D Co., Ltd. (72) Hiromi Matsuura 1-4-1 Chuo, Wako-shi, Saitama Inside the Wako Laboratory, Honda R & D Co., Ltd. (72) Inventor Eiji Takahashi Inside the Wako Lab.

Claims (8)

(57) [Claims] 1. A heat-insulated ceramic cast insert, comprising a ceramic layer, a ceramic felt layer and a cast-in metal layer in this order from the inside. 2. The heat-insulated ceramic insert body according to claim 1, wherein said ceramic felt layer is made of Al ₂ O _3.
A heat-insulated ceramic stuffed cast made of felt made of fiber, wherein the stuffed metal layer is made of an aluminum alloy. 3. The heat-insulated ceramic cast insert according to claim 1, further comprising a glass layer on an inner surface of said ceramic layer. 4. The insulated ceramic cast insert according to claim 1, further comprising a machinable ceramic layer at an end. 5. A method for producing a heat-insulated ceramic cast insert having a ceramic layer, a ceramic felt layer and a cast-in metal layer in this order from the inside, wherein: (a) forming a ceramic sintered body as the ceramic layer; b) depositing a ceramic felt layer around the ceramic sintered body; and (c) forming the cast-in metal layer by pouring a cast-in metal melt into a mold. 6. The method according to claim 5, wherein, after the outer periphery of the ceramic felt layer is covered with a metal foil, a molten metal of the stuffed metal is injected to form the stuffed metal layer. And how. 7. The method according to claim 5, wherein the ceramic felt layer is formed after applying and firing a glass frit on an inner surface of the ceramic sintered body. 8. The method according to claim 5, further comprising the step of performing a cast-in casting after attaching a machinable ceramic sintered body to an end face of the ceramic sintered body. .