JPH02263557A - Method for including ceramic as internal chill - Google Patents

Abstract

PURPOSE:To prevent breakage of a ceramic part and to improve durability of an internally chilled product by uniformly form porous carbide layer on surface of the ceramic part. CONSTITUTION:At the time of drawing up the ceramic pipe 1 after dipping into PVC(polyvinyl chloride) solution 4, cooling and solidifying, PVC layer is formed on outer peripheral surface of the ceramic pipe 1. Successively, the ceramic pipe 1 is charged into an electric furnace 6 and the temp. is raised and held for prescribed time. During this period, the PVC layer becomes free from hydrogen chloride to form the porous carbide layer 2. Successively, the ceramic pipe 1 is used as a core of a mold 7 for casting and by pouring the molten metal 9 of aluminum or cast iron, etc., from a pouring tool 8 to include this as internal chill, the metal layer is formed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a ceramic casting method, more specifically,
This relates to a method of encasing ceramics with excellent heat insulating properties in metal.

[Conventional technology]

BACKGROUND ART In order to improve the performance of engines installed in vehicles, such as increasing output and improving fuel efficiency, research and development is actively being conducted on the adoption of lean combustion systems and efficient use of exhaust energy.

As a result, the exhaust temperature tends to rise further, so by using ceramics with high heat insulation and heat resistance, it is possible to improve the reliability of each component and reduce the heat load. The downsizing of cooling systems has been considered and some have been put into practical use.0 For example, the practical application of ceramics such as aluminum titanate and cordierite to exhaust system parts such as exhaust boats and exhaust manifolds for reciprocating engines. (■
Ceramic material &
Components for Eng.
ineJ19B13, pp. 1135-1143, ■5A
IE Dingechnica IPaper 88087
(See B).

When applying ceramics in this way, since the strength and toughness of the ceramics themselves are low, it is practically essential to form the outer wall part with metal, and the manufacturing method is generally to form the outer wall into a desired shape. A method has been adopted in which a single ceramic part formed in the form of metal is cast in metal.

[Problem to be solved by the invention]

However, when ceramic parts are cast with metal, there are various problems as illustrated below.

(i) Ceramics with excellent heat resistance, such as aluminum titanate and cordierite, have lower strength and toughness than metals. Therefore, parts such as pipe shapes made of such materials are cast in metals such as aluminum and cast iron.

Since the thermal expansion coefficient of the metal is larger than that of the ceramic during the cooling process after the metal solidifies, the ceramic component may be destroyed due to contraction of the metal.

(11) During casting, if high-temperature molten metal comes into direct contact with room-temperature ceramic parts, the ceramic parts will be subject to thermal shock, which may cause large thermal stress to occur inside the ceramic parts and cause them to break. is high.

(iii) When a cast product is assembled into an actual machine with the ceramic parts and metal in contact and is repeatedly started and stopped, the difference in thermal expansion between the ceramic parts and the cast metal causes a gap between the metal and the ceramic parts. compression·
Ceramic parts have a usability that causes fatigue failure due to repeated tensile loads.

In order to solve the above-mentioned problem, the present applicant f''-Yos proposed a method in Japanese Patent Application No. 63-211988 in which ceramic parts are wrapped with metal tape and then cast in metal. , Japanese Patent Application No. 1-18652 discloses a method of forming a film layer made of aluminum having a higher melting point than the molten metal for casting on the surface of a ceramic part, and then casting the ceramic part. A method of sequentially covering with a material (for example, a porous metal body) and a penetration prevention member (for example, a thin metal sheet) that prevents the penetration of molten metal and then casting the material was proposed in tL in Li2 (March 1989). However, the method proposed by the present applicant may also cause problems. For example, in Japanese Patent Application No. 63-211988 and dated March 18, 1989, If a ceramic component has a recess, a metal tape or the like may float at that location, and molten metal may come into direct contact with the ceramic component during pouring. In addition, if the ceramic part has branched parts or has a complicated shape, it is difficult to wrap metal tape etc. around the branched parts. However, there are problems such as the limited range of application is limited to aluminum alloys.

The present invention is intended to solve the problems in the prior art described above.An object of the present invention is to prevent ceramic parts from being easily destroyed when they are cast into metal;
To provide a method that is applicable even if the ceramic parts have a complicated shape and can easily obtain a ceramic cast product in which the ceramic parts are not easily destroyed by heat load during use.

[Means to solve the problem]

That is, the method for casting ceramics of the present invention involves applying an organic polymer material to the surface of a ceramic part to be cast, and then carbonizing the organic polymer material by heating the ceramic part to form a porous carbide layer. Then, the ceramic component is then cast with metal through the porous carbide layer.

The material of the ceramic component may be a conventional material such as aluminum titanate.

Further, properties such as size and shape of the ceramic parts are selected as appropriate. The shape may be, for example, block-like or pipe-like.

Examples of metals in which ceramic parts are cast include aluminum, iron, and alloys thereof.

Organic polymer materials include natural or synthetic polymeric resins, melamine resins, urea resins, polycarbonates, alkyd resins, and epoxy resins that can be applied in a thin film and form a porous carbide layer by heating. , polyester, polyamide, polystyrene, polyolefin, etc. Examples of rubber include natural rubber, butyl rubber, styrene-butadiene rubber, chloroprene rubber,
Neoprene rubber, etc.

These resins or rubbers can be used alone or in combination, and are dissolved in a suitable solvent or melted without a solvent and applied to a predetermined thickness.

The application method may be a conventional method such as a spraying method or a dipping method.

Furthermore, when heating a ceramic component whose surface is coated with an organic polymer material, the material of the organic polymer material and the heating conditions are selected so that the organic polymer material does not flow and be removed from the ceramic component.

The coating thickness of the organic polymer material is determined so that the thickness of the porous carbide layer formed by carbonizing the organic polymer material is sufficient to relieve stress due to contraction of the metal.

The amount of shrinkage after the molten metal solidifies will be specifically considered below.

When considering using aluminum titanate pipes with a circular outer diameter cross section as ceramic parts and casting aluminum as the metal, the outer diameter of the pipe is 40 m.
m, and assuming that the aluminum is in contact with the outside surface of the pipe, the amount of shrinkage from the time the molten aluminum solidifies until it reaches room temperature is calculated by the following formula (1): % Formula % () [In the formula, δ is the amount of shrinkage (m m), D represents the pipe outer diameter (mm), α represents the coefficient of thermal expansion (“0”), and T represents the solidification temperature (melting point °C)).

In the case of aluminum, α=23.5×10゛6℃,
T=850°C, and when calculated by substituting this into formula (I), δ is 0.13 mm. That is, the radius is 0.3 mm, and it is preferable that the thickness of the carbide layer is at least about this range.

In other cases, the optimal carbide layer thickness is determined in the same manner as above, and the coating thickness of the organic polymer material that can obtain the optimal carbide layer thickness is determined.

Ceramic parts with a porous carbide layer formed on the surface are
It is placed as a core in a casting mold, and molten metal is poured into it to cast it.

[For production]

By uniformly forming a porous carbide layer on the surface of ceramic parts, the porous carbide layer acts as a heat insulating layer and a stress relaxation layer, which prevents the ceramic parts from breaking during casting. The durability of the material is improved.

〔Example〕

The invention will be explained in further detail in the following examples. Note that the present invention is not limited to the following examples.

Fig. 1 (&) to C) shows an embodiment of the method of the present invention. After immersing it in a solvent-free solution, it is pulled out and allowed to cool and solidify. At this time, the end face of the ceramic pipe 1 is closed as necessary to prevent PVC from entering inside. Figure 2 (
As shown in a), 270 layers 5 with a thickness of 1 to 2 mm are formed on the outer peripheral surface of the ceramic pipe 1.Next, as shown in FIG. 1(b), the ceramic pipe 1 is placed in an electric furnace 6. , the temperature was increased to 700°C at a rate of 20°C per minute and held for 10 minutes. Meanwhile, the PVC layer 5 is dehydrochlorinated at about 350°C.

A porous carbide layer 2 shown in FIG. 2(b) is formed at 600 to 700°C. The formation of porosity at this time occurs because pores are generated inside the PVC layer 5 due to the generation of combustion gas and are carbonized as they are. Note that the thickness of the carbide layer 2 is 0.7 to L, S
mm (70 to 80% of the thickness of the PVC layer) Then, as shown in FIG. 1(C), the ceramic pipe 1 is used as the core of the casting mold 7, When pouring molten metal 9 such as aluminum or cast iron from the top and casting it, the second
A metal layer 3 is formed as shown in Figure (C).

Fig. 3 shows a cross-sectional view of an example of a product obtained by the method of the present invention, Fig. 3(a) is a longitudinal cross-sectional view, and Fig. 3(b) is a half-sectional view in the smoke direction. . From this, it can be seen that the porous carbide layer 2 exists on the outer periphery of the cylindrical ceramic component l with a thickness sufficient to withstand contraction after the molten metal solidifies, and the metal layer 3 surrounds the porous carbide layer 2. I understand.

〔Effect of the invention〕

As described above, the ceramic casting method of the present invention involves applying an organic polymer material to the surface of a ceramic part to be cast, and then heating the ceramic part to carbonize the organic zarimer material to form a porous carbide layer. is formed, and then the ceramic component is cast with metal through the porous carbide layer, so various effects can be achieved as exemplified below.

l) Since the porous carbide layer relieves the stress caused by the contraction of molten metal after solidification during casting, excessive force is not applied to the ceramic parts, and breakage of the ceramic parts during casting is prevented.

2) By interposing the porous carbide layer, the molten metal and the ceramic part do not come into direct contact during casting, and therefore the thermal shock that the ceramic part receives is alleviated, thereby preventing the ceramic part from breaking due to thermal shock. .

3) Since the porous carbide layer relieves the stress caused by expansion and contraction of the metal layer during use during casting, the ceramic parts are less likely to be damaged and the durability of the cast product is improved.

4) Since the ceramic parts are coated with molten resin, it is possible to form a porous carbide layer uniformly on the surface even if the shape of the ceramic parts is complex, and it is possible to form a porous carbide layer uniformly on the surface of the ceramic parts of any shape. It can also be applied to

5) Properties such as porosity and thickness of the porous carbide layer can be changed by appropriately selecting the type of organic polymer material, coating thickness, heating conditions, etc. Various modifications are possible depending on casting conditions, etc., and the range of application is wide.

[Brief explanation of drawings]

Figures 1 (a) to C) are explanatory diagrams of an embodiment of the ceramic casting method of the present invention, and Figures 2 (a) to C) are illustrations of the cross-sectional shape of the ceramic pipe in the method of Figure 1. Figures 3(a) and 3(b) for explaining the changes are cross-sectional views of an example of a product obtained by the method of the present invention. In the figure, 1... Ceramic vibe 2... Carbide layer 3...
・Metal layer 4...PVC solution 5...p
VC layer 6...Electric furnace 7...Casting chamber
8...Pouring tool 9...Molten metal Fig. 2 (θ) (b) (C) (a) J $3 Fig. (b)

Claims (1)

[Claims] An organic polymer material is applied to the surface of a ceramic part to be cast, and then the ceramic part is heated to carbonize the organic polymer material to form a porous carbide layer. A method for casting ceramics, comprising: casting the ceramic parts with metal.