JPH0357551A - Internal chill method for ceramics body - Google Patents

Abstract

PURPOSE:To prevent the cracking and breakdown of a ceramics body by providing a cushion layer on the outer periphery of the ceramics body, further coating the outside periphery thereof with a metallic shell, and then executing internal chill. CONSTITUTION:Alumina/silica fibers are wound on the outer periphery of the cylindrical ceramics body 1 to provide the cushion layers 2 and this layer is covered with the metallic shell 3 made of a stainless steel. The metallic shell 3 is formed by fixing the bisected shells 3a, 3b by spot welding 5.... The shells are internally chilled with a molten metal 4 after the fixing thereof. The thermal impact and clamping force on the ceramics body at the time of the internal chill are additionally relieved in this way and the generation of the crack and breakdown in the ceramics body are prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for casting a ceramic body for producing a ceramic-metal composite product.

<Prior Art> Recently, in order to improve the thermal efficiency between internal combustion engines, attempts have been made to form high-temperature areas of internal combustion engines using ceramics that have excellent heat resistance, thermal shock resistance, and heat insulation properties. It is a so-called ceramic engine, and is applied to hollow cylindrical parts such as exhaust boats and exhaust manifolds.

? In order to compensate for the lack of strength of brittle ceramics, parts are used in which the outer periphery of a hollow ceramic body is tightly wrapped with metal. Such parts can be manufactured by casting using molten metal. The material for the hollow ceramic body is aluminum titanate (A
I2TiO5), zirconia (zr02), alumina (A]■03'). Silica (Sin2) etc., and aluminum alloy as molten metal (casting metal),
It is common to use iron-based alloys, etc.

However, if a hollow ceramic body is simply cast using molten metal, cracks or destruction often occur in the hollow ceramic body. The causes of this are: a) the clamping force of solidification contraction of the molten metal is applied to the hollow ceramic body; b) the coefficient of thermal expansion of ceramics is 3 x 10''~8
The force due to the difference in the coefficient of thermal expansion between the two is F, is loaded onto the hollow ceramic body. c) The temperature of the surface of the hollow ceramic body rises rapidly when it comes into contact with molten metal, but this is not the case inside the body, and this significant temperature gradient causes thermal stress in the hollow ceramic body due to the difference in expansion (so-called thermal shock). ). There are three possible reasons.

In particular, if a hollow ceramic body has an irregularly shaped portion, stress concentration occurs there and cracks are likely to occur.

Conventionally, as a method to prevent such cracking and destruction of hollow ceramic bodies during casting, the outer surface of hollow ceramic bodies has been coated with ceramic vapor, various refractory mortars, asbestos fibers, glass fibers, metal ta fibers, etc. A method of casting with an intermediate layer for buffering and heat insulation.
-12057, JP 6021173, JP 60-166
156, 60-169656, 60-180558
, No. 60-227963, etc. In addition, in order to prevent cracks and destruction of the cast metal, there is a method of using a specific iron-based alloy, as proposed in JP-A-60-216966, or a method of providing the above-mentioned intermediate layer.

<Problem to be Solved by the Invention> The above-mentioned intermediate layer made of a hard refractory material needs to be porous in order to play the role of buffering and heat insulation. For example, in JP-A No. 60-21173, a mixture of refractory powder and thermoplastic resin is applied to a hollow ceramic body, and the resin is thermally decomposed and volatilized by heating to make the intermediate layer as porous as possible. That's what I do.

However, the porous intermediate layer is easily penetrated by molten metal, and the more holes and gaps in the intermediate layer, the faster and more molten metal penetrates into the intermediate layer. If the molten metal penetrates into the intermediate layer, it will not be sufficiently insulated to prevent thermal shock, and it will not be able to efficiently absorb the tightening force caused by the solidification and contraction of the molten metal.

Therefore, the present applicant previously filed a patent application for a method of wrapping a penetration prevention member such as a metal tape around the outer periphery of the intermediate layer (Japanese Patent Application No. 66536), but even then, cracks and breakage of the hollow ceramic body still occur. has not yet been completely prevented. In particular, it is not possible to sufficiently alleviate the clamping force caused by solidification shrinkage of molten metal on ceramics, and restrictions have been forced on the design of the materials and shapes of ceramic cast products.

The present invention has been made in view of the following two problems, and its purpose is to prevent thermal shock and tightening of the ceramic body.
It is an object of the present invention to provide a method for casting a ceramic body that does not cause cracking or destruction by applying even less force.

<Means for Solving the Problems> A method for casting a ceramic body according to the present invention that can achieve the above object is to provide a cushion layer made of a refractory material on the outer periphery of the ceramic body, and further cover the outer periphery with a metal shell (metal shell). It is characterized by being covered with a shell) and then cast.

It is sufficient that the cushion layer has fire resistance that can withstand the high heat of molten metal and elasticity that can be deformed to the extent that it can cope with dimensional variations in the ceramic body and metal shell. The cushioning material may be any material that has been used for the conventional intermediate layer, such as amorphous materials such as ceramic fibers and ceramic hollow granulated powder.

The cushion layer can be provided by an appropriately selected method depending on the properties of the material, such as by directly attaching the material to the outer periphery of the ceramic body, or by fixing it by using a binder or by wrapping support wire around it. good. Alternatively, the ceramic body may be inserted into a metal shell, and the gap therebetween may be filled with the material of the cushion layer.

The metal shell may be attached so as to completely cover the outer periphery of the metal shell so that molten metal does not penetrate into the cushion layer, and, if necessary, the divided partial shells may be combined together.

While the metal shell must have a certain strength, it must not melt easily or shrink more than the solidification shrinkage of the molten metal, so its thickness and material selection are important. As the material for the metal shell, a metal should be used that has a melting point comparable to or higher than that of the metal for the casting, and a coefficient of thermal expansion smaller than that of the metal for the casting.

The method of the present invention is applicable to
・It can be applied to obtain ceramic castings for boats, exhaust manifolds, etc. It goes without saying that it can be applied not only to the automobile field.

<Function> When the Ayugurumi method is implemented as described above, the metal shell takes over the clamping force caused by the solidification and contraction of the molten metal during casting, thereby preventing excessive load on the cushion layer and the ceramic body. The metal shell also retains cushion debris and prevents molten metal from penetrating the layer. The cushion layer supplements the buffering and heat insulating effects of the metal shell, and also makes it possible to attach the metal shell even if the ceramic body or metal shell has different shapes and dimensions.

<Example> Hereinafter, examples of the method for casting a ceramic body of the present invention will be described with reference to the drawings, but these examples are not intended to limit the gist of the present invention in any way.

Example 1 FIG. 1 is a sectional view showing a ceramic cylindrical casting product produced by the method of this example, and FIG. 1a is an enlarged view of section A in the figure. The material of the ceramic cylindrical body 1 used here is aluminum titanate, and a cushion layer 2 of alumina/silica long fibers is provided on the outer periphery of the ceramic cylindrical body 1. This cushion layer 2 is made of an amorphous ``cotton'' material, exhibits a low elastic modulus, and deforms under a small load.Also, there are many voids between the fibers, and it has excellent heat insulation properties. (Heat transfer rate 0.2 kcal/nrhr・°C)
.

A metal shell 3 is attached to surround this cushion layer 2. The shell 3 is made of an iron-based alloy (stainless steel plate) having a higher melting point than the cast metal (aluminum alloy). Since this is a material having a smaller coefficient of thermal expansion than the casting metal 4, excessive load on the cushion layer 2 and the ceramic cylindrical body 1 due to the clamping force of solidification shrinkage of the aluminum alloy 4 during casting is prevented.

The method for manufacturing this cast product will be explained using FIG. 2.

Ceramic cylindrical body 1 with outer diameter 40[I+11, thickness 4cm]
-L alumina/silica H & fiber to a thickness of 3 mI on the outer periphery of the
A cushion 2 is provided by winding it around I1, and it is covered with a stainless steel metal shell 3 having a thickness of 2 mm. The metal shell 3 has two parts 3a and 3b that are spot welded 5 and 5.
It is fixed by... After fixing metal shell 3, thickness 4
■Cast the molten metal to about 4 degrees.

Cast products obtained in this manner are obtained by a method in which a cushion layer is provided and the cast product is cast (Comparative Example 1), and a method in which the cast product is directly cast without providing a cushion layer or a metal shell (Comparative Example In comparison with the cast product obtained in 2), the amount of outer diameter shrinkage and cracking incidence of the ceramic cylindrical body were investigated. The results are shown in FIG.

From the figure, it can be seen that according to the method of this example, cracking of the ceramic cylindrical body due to the clamping force caused by solidification contraction of the molten metal can be prevented.

Example 2 This example is an example of application to a large, irregularly shaped pipe. Fourth
As shown in the figure, when a curved pipe-shaped ceramic cylinder 1 is cast, a metal shell 3c is divided into a plurality of parts.
, 3d and 3e are used. Each metal shell is provided with a gap 6 having at least a width δ as shown in FIG. 4b. This gap 6 can absorb the amount of deformation δ caused by solidification shrinkage of the molten metal 4.

This principle will be explained with reference to FIG. The shape D of the metal shell after casting is smaller than the shape C before casting. This is due to the shrinkage amount 61 due to the solidification shrinkage of the molten metal.
The shell 3o moves relatively toward the shell 3Il1 by the same amount. This movement causes the metal shell 3n to have a width δ2 (≧61
) If there is a gap 6, the process will be carried out smoothly, or if it is not there, the metal shell will be deformed to the ceramic side, leading to destruction of the ceramic body. This embodiment is an effective technique when applied to exhaust boats, exhaust manifolds, etc.

<Effects of the Invention> According to the casting method of the present invention, a cushion layer is provided on the outer periphery of the ceramic body, and the outer periphery is further covered with a metal shell before being cast. Thermal shock and clamping force are further alleviated, and the ceramic body will no longer be cracked or destroyed.

Therefore, it is possible to manufacture ceramic cast products with a high yield and reduce costs.

In addition, the degree of freedom in designing materials, shapes, etc. is increased, and it becomes possible to manufacture ceramic cast products with higher performance.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing a ceramic casting product obtained by the method of an embodiment of the present invention, Fig. 1a is an enlarged view of part A in Fig. 1, Fig. 2 is a process diagram of an embodiment, Fig. 3 is a diagram showing the effect of one embodiment in comparison with a comparative example, Fig. 4 is a sectional view showing one state of the casting process of another embodiment, and Fig. 4b is section B in Fig. 4. The enlarged view, FIG. 5, is an explanatory diagram of the metal shell changing during casting. In the figure: 1... Ceramic cylindrical body 2... Cushion layer 3 (3a, 3b, 3c to 3n) - Metal shell 4
... Casting metal (molten metal)

Claims (1)

[Claims] A method for casting a ceramic body, which is characterized in that a cushioning layer made of a refractory material is provided on the outer periphery of the ceramic body, and the outer periphery is further covered with a metal shell before being cast.