KR20010073437A - Ceramic shell mold using graphite manufacturing technology & method for investment casting process - Google Patents

Abstract

PURPOSE: A mold manufacturing method for precision casting is provided to obtain a product excellent in surface quality by using graphite as slurry and sand material for reducing gas holes on the product surface. CONSTITUTION: A graphite is used as slurry and sand material in casting stainless steel or precipitation hardening stainless steel doped with a large amount of chromium. Oxygen is contained in steel during solidification after casting, and coupled with graphite through reaction before reacting with chromium. This creates a graphite coating layer on the surface of a precision casting product to prevent oxygen from reacting with chromium thereby reducing the number of gas holes created through reaction of chromium and oxygen in a great number. The surface defect of the precision casting product can be improved without changing chemical or mechanical features of the product.

Description

Mold casting technology and method using graphite {CERAMIC SHELL MOLD USING GRAPHITE MANUFACTURING TECHNOLOGY & METHOD FOR INVESTMENT CASTING PROCESS}

The present invention aims to obtain a high quality casting surface by blocking oxygen (O ₂ ) that penetrates into the surface during solidification of the molten metal after casting in order to eliminate gas hole defects due to chromium oxidation at the same manufacturing process and low cost as in the present.

In the mold manufacturing of conventional stainless steel-based precision casting, zircon and chamotte are used as a slurry and sand material, and molten metal is poured into a mold manufactured by repeating coating and drying. In this case, there is a disadvantage in that defects are generated on the surface of the casting as chromium is oxidized by reacting with chromium on the surface layer by oxygen penetrating through the mold to the molten surface.

In order to solve the above problems, in general, when molten metal solidifies after casting of chromium-added stainless steel or precipitated hardened steel, oxygen penetrates into the molten surface through the mold. In the part where the solidification rate of the surface of the product is slow, a relatively large gas hole called BLACK SPOT is generated, and in the part where the solidification speed is high, a relatively small pin hole occurs. The test was carried out with varying conditions, and many materials were applied to mold making, but good results could not be obtained. However, when graphite (GRAPHITE) was used as slurry and sand material, a good product surface was obtained. Casting oxygen product reacts with graphite before reacting with chromium The result is a significant reduction in gas holes produced by reaction with oxygen on the surface.

As a result of casting the product by manufacturing the mold by the improvement method among the various test methods, the results as shown in Fig. 5 and Fig. 7 were obtained.

Fig. 4 and Fig. 6 show the defective products due to gas hole defects.

Before working with the above method, the surface defect products as shown in Fig. 4 and Fig. 6 accounted for 70-80%, so that the products could not be produced, but the surface defects caused by gas holes when cast into the mold made of graphite were used. Almost eliminated the results.

1: Wax Model (WAX PATTERN)

2: Existing mold made of ZIRCON and CHAMOTTE materials

3: Mold made by adding GRAPHITE to ZIRCON and CHAMOTTE materials

4: Defective product cast by the existing mold (aircraft parts)

5: Passed product cast by the invention mold (aircraft parts)

Figure 6: Defective product cast by the existing mold (aircraft parts)

Fig. 7: Passed product cast by invention mold (aircraft parts)

<Description of Symbols for Main Parts of Drawings>

1: 1st and 2nd ZIRCON COATING layer

2: 3-7th CHAMOTTE COATING Floor

3: 5th GRAPHITE COATING Floor

4: BLACK SPOT phenomenon

The present invention is to make a graphite coating layer in a certain layer of the mold used in the manufacture of precision castings of stainless steel series or precipitated hardened steel containing a large amount of chromium to block oxygen penetration to obtain a good surface by removing the surface defects of the precision castings .

In the current manufacturing process, it is possible to improve the surface defects without making any change in the characteristics (chemical composition, mechanical properties) of the precision casting by making the graphite coating layer on a certain layer of the mold without the need for additional process and additional equipment.

Test Example 1

Figure 4 shows the defects when using the mold manufactured by the conventional method. When the casting was cast with the mold 3 coated with graphite slurry and sand in the 5th coating layer, the surface defects were removed as shown in Fig. 5.

Test Example 2

Figure 6 shows the defects when using the mold manufactured by the conventional method. When the mold is cast with the graphite slurry and sand coated mold 3 in the 6th coating layer, the surface defect is removed as shown in Fig. 7.

Claims (2)

All precision casting products manufactured using graphite as a casting material All methods of using graphite as a casting material when manufacturing casting molds for precision casting