JPS6199537A - Durable casting mold - Google Patents

Abstract

PURPOSE:To provide a durable non-metallic casting mold which is highly strong, is repeatedly usable and yields a good casting by impregnating silicon carbide to the surface layer of a mold formed of carbon. CONSTITUTION:This durable casting mold 1 is formed of carbon and the impregnated layer 2 of silicon carbide is formed to the surface part of the mold which contacts with a molten metal. The mold 1 is formed by molding, for example, pulverous carbon powder (may be graphite powder) under pressure to a prescribed shape, subjecting the molding to packed calcination at about 2,500 deg.C and impregnating SiC to such molding. The impregnation of SiC which acts as an antioxidant is executed by enveloping the carbon mold subjected to the above-mentioned molding and calcination with about 3-4mu pulverous SiC powder and heating the same to a high temp. The thickness of the layer 2 is preferably >=3mm and the content. of SiC in the layer 2 is about 5-20% but is not limited thereto.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) This invention relates to a casting mold that can be used repeatedly.

(Technical background) The material for durable molds that can be used repeatedly after being molded once must have the following properties: 1) be resistant to thermal shock; 1) have excellent air permeability;
It must have small thermal expansion, be stable with respect to temperature, not cause abnormal expansion or embrittlement due to crystal transformation, etc., be unlikely to react with molten metal, and have excellent mechanical strength and heat resistance.

In the past, research has been done on molds based on various refractories other than metal molds as durable molds, but all of these have major drawbacks such as firing temperatures of around 1500°C, low thermal conductivity, and easy chipping. However, it has not yet been fully put into practical use.

On the other hand, in the case of molds, the cooling effect is large, so there is a problem that cast iron products in particular tend to become white pig iron and are energy consuming. In addition, since the mold has poor gas escape, it is necessary to provide a vent hole, and the amount of deformation is large, resulting in precision problems, and there are also disadvantages in that a coated mold is essential.

(Objective of the Invention) The present invention was made in view of the above circumstances, and an object thereof is to provide a non-metallic durable mold that has excellent strength, can be used repeatedly, and can yield good quality castings. .

(Disclosure of the Invention) The present invention is characterized in that the surface layer of a mold made of carbon is impregnated with silicon carbide.

(Example) Fig. 1 shows an example of a durable mold according to the present invention.This durable mold 1 is made of carbon, and the surface part of the mold that comes into contact with the molten metal is coated with a silicon carbide impregnated layer. 2 is formed. This durable mold 1 is made by press-molding, for example, fine carbon powder (graphite powder is also acceptable) into a predetermined shape.
Silicon carbide (Si) is filled and fired at a high temperature of around 0°C.
It can be shaped by impregnating it with C).

The impregnation of silicon carbide, which acts as an antioxidant,
This can be done by wrapping a fired carbon mold in fine silicon carbide powder of about 3 to 4 microns and heating it to a high temperature. This forms a silicon carbide-rich layer 2 on the surface of the carbon mold 3. This impregnation! The thickness of the impregnated layer 2 is preferably 3 layers or more, more preferably 5 layers or more. In normal production, it is sufficient if the thickness of the impregnated layer 2 is about 5 layers. The content of silicon carbide in this impregnated layer 2 is about 5 to 20%, but is not limited to this.

Furthermore, in order to obtain a good casting surface and a highly accurate product during casting, the air permeability of the mold needs to be 0.01 or more. Furthermore, it is preferable to make the thermal conductivity of the mold as high as possible for molds such as those for aluminum alloys, but in the case of cast iron, if the thermal conductivity is high, it tends to become white, so it is not preferable to make it too high. In order to obtain a D-shaped structure in the cast state, the thermal conductivity of the mold must be 30 KCa/m.
It is preferable that Hr”c or less, 2 to 10KC:al
It is preferable to set it to 1/■Hr''O.

FIG. 2 is a graph showing the relationship between the temperature and coefficient of thermal expansion of the durable mold 1 obtained as described above, where A represents the impregnated layer 2 of the durable mold 1 according to the present invention, and B represents the durable mold 1. Each of them is made of silica. As you can see from the same figure,
It can be seen that the mold of the present invention has extremely small thermal expansion (almost O in this temperature range) and is suitable as a mold material.

In addition, Figure 3 is a graph showing the oxidation resistance, where a is the oxidation rate of plain graphite at 800°C, and b is the oxidation rate of graphite impregnated with 1% silicon carbide at 800°C.
C and d indicate the oxidation rate at 1000°C of 9i containing 10% and 20% silicon carbide, respectively. From the same figure, it can be seen that 9I containing 10 to 20% silicon carbide exhibits remarkable oxidation resistance. Recognize.

The if table shows the physical properties and usage results of examples of durable molds manufactured by the above method.The durable molds according to the present invention have excellent durability, and if used, D It can be seen that a casting with a mold-like structure and no gas defects can be obtained.

Table 1 Note that since this durable mold 1 does not react with molten metal, there is no need for a coating mold, and it is lighter than a metal mold, making it possible to significantly reduce manufacturing costs.

(Effects of the Invention) As is clear from the above description, the durable mold according to the present invention has excellent durability and is capable of producing good quality castings.

[Brief explanation of the drawing]

Figures 1 (a) and (b) are a cross-sectional view and an enlarged cross-sectional view of the surface of an example of a durable mold according to the present invention, and Figure 2 is a graph showing the relationship between temperature and coefficient of thermal expansion. Figure 3 is a graph showing oxidation resistance. ■...Durable mold, 2...Impregnated layer. Patent Applicant Shigeru Oka Agent Patent Attorney Hiroshi Sugawara No. 2, No. 3, Figure 1 (H) d

Claims (1)

[Claims] (1) A durable mold made by impregnating the surface layer of a mold made of carbon with silicon carbide.