JPH042335B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is directed to high-pressure castings used in silica sand molds for vacuum casting.
This invention relates to a coating method for a composite coating material for Mn alloy cast steel. [Prior Art] In high Mn alloy cast steel castings, products with beautiful casting surfaces could not be obtained unless basic olivine sand containing MgO as the main component was used. For this reason, it is necessary to use different molding sands for high Mn alloy cast steel castings and other castings, and sand that is a mixture of basic olivine sand and acidic silica sand cannot be used as molding sand, so it is very difficult to manage sand. It was inconvenient. Therefore, there was a desire to manufacture high Mn alloy cast steel castings using silica sand. However, when high-Mn cast steel uses silica sand in the mold, MnO generated on the surface of the molten metal by oxidation during casting reacts with SiO ₂ , the main component of the foundry sand used in the mold, and the mold surface becomes As a result, there is a problem that seizure defects occur on the casting surface of high Mn alloy cast steel. Particularly in the case of thick-walled castings, a reaction occurred due to the thermal influence at the interface between the molten metal and the mold, causing defects. MgO-based or
The casting method of JP-A-60-61139, in which one or two types of Cr ₂ O ₃ type coating agents are applied to the film, is sufficiently effective for thin-walled castings, but as mentioned above, it is not suitable for thick-walled castings. There was a problem, as it reacted with silica sand and caused seizure defects. [Problems to be Solved by the Invention] (1) The mold referred to in JP-A-60-61139 is a thin-walled casting, and reactions and seizures cannot be prevented with thick-walled castings of this type of quality. (2) No effect can be obtained by coating methods using known coating materials. In order to promote the effect, we will develop refractories and construction methods that are different from conventional technology, and will be able to obtain a beautiful casting surface that is superior to thin-walled castings even with thick-walled castings. (3) Conventional mold coating adhesive strength cannot maintain the adhesive strength of coating materials for thick-walled castings. That is, it is necessary to make the coating layer somewhat thick and to prevent peeling and penetration resistance due to the composition of the composite coating and appropriate binder. In order to solve the above problems, it is an object of the present invention to improve the coating method for preventing the reaction between casting and silica sand, and to provide a method for constructing a refractory material in which no reaction occurs. [Means for solving the problem] The present invention uses silica sand to perform vacuum casting to produce high-Mn
As a result of various research into methods for manufacturing alloy steel castings, we have developed a new molding method that can produce beautiful casting surfaces by devising a coating method for mold coating materials. That is, the technical means of the present invention uses a mold using silica sand, undercoats a film for vacuum casting with an MgO-based coating material, and then coats it with either an Al ₂ O ₃ -based coating material or a ZrO ₂ -based coating material. This is a coating method for a coating mold for vacuum casting of high Mn alloy cast steel, which is characterized by applying a topcoat on the mold material. The structure of the present invention consists of an MgO-based refractory and an Al ₂ O ₃ or ZrO _2- based refractory, and is a coated mold in which the MgO-based refractory is coated in one layer and the top coat is coated with an Al ₂ O ₃ or ZrO ₂ refractory. In order to paint these, we took into account the particle size structure of aggregates such as MgO, Al ₂ O ₃ or ZrO ₂ , and the composition of solvents and binders, and created composite coating materials with sufficient strength and fire resistance as shown below. Use the same materials. (1) Grade up of refractories (MgO, Al ₂ O ₃ ). In the case of JP-A-60-61139, MgO of 80% by weight or more was sufficient, but in the present invention, both MgO and Al ₂ O ₃ type are 90% by weight or more, and the particle size is smaller than that of the MgO type of the lower layer _. The O ₃ or ZrO ₂ type was made into coarse particles to prevent cracking resistance and shorten drying time. (2) As shown in Table 1, improvements in adhesive strength were investigated and resolved from both aspects of peelability and abrasion.

[Effect]

The high Mn alloy cast steel to which the method of the present invention is applied includes, for example, C: 0.2-1.5% by weight Mn: 5-29% by weight Ni: 1.0-5.0% by weight Cr: 15.0-18.0% by weight Other chemical components include Cu, It is a special alloy steel containing Mo etc. The reason why high Mn alloy cast steel seizes is that when Mn oxidizes and produces a basic substance MnO, this reacts with SiO ₂ in the silica sand to form silicate (MnO/SiO ₂ ).
Since this has a low melting point (below 1170℃), a chemical reaction between the molten metal and the mold causes seizure. MgO-based coating material has a basic component, and by applying this as an undercoat and then painting a neutral component Al ₂ O ₃ -based or ZrO _2- based coating material, it is possible to produce thicker castings than thin-walled castings. When molten high Mn alloy cast steel is poured, the reaction on the mold surface due to the reaction between SiO ₂ and MnO in the silica sand is inhibited and blocked, resulting in the occurrence of seizure defects on the beautiful casting surface. You can get something with less. This method is a coating method for thick-walled high-Mn alloy cast steel, and a highly refractory neutral material is applied between the MnO generated on the surface of the molten metal, the basic MgO base material that comes in contact with this, and the silica sand (acidic). However, this is a method to prevent direct reaction with SiO ₂ by using the Sanderch method. It is desirable that the MgO-based coating material or the Al ₂ O ₃ -based coating material be of high quality with a content of 90% or more. If the content of MgO or Al ₂ O ₃ is less than 90% by weight in the wall thickness range of 40 to 60 mm, a reaction occurs and seizure defects occur in the above-mentioned thick-walled high-Mn alloy casting. It is desirable that the coating concentration be 60 to 65 Baumé (Be') and the film thickness be approximately 200 to 300 μm for MgO, Al ₂ O ₃ , and ZrO ₂ . In addition, MgO-Al ₂ O ₃ or ZrO ₂ -based double-layer coating materials are slightly thicker than conventional coating materials, so in order to improve adhesive strength with the film and dry quickly, MgO, Al ₂ O ₃ , the composition of aggregates such as ZrO ₂ is adjusted to 75-78% by weight (solution 18.7-21% by weight)
Weight%, organic binder 3.1-3.5% by weight, inorganic dispersion material
0.2 to 0.5% by weight) is preferably blended in an amount of about 22 to 25% by weight. When using a two-layer coating type, that is, a composite coating type, unlike conventional coating types, the adhesive strength with the film must be increased, and the coating film must be thicker.
Since the particle size of conventional coating molds is fine, cracks occur when applied, which causes penetration and seizure. To this end, as a method to prevent the aggregate itself from cracking and to apply two layers, the conditions for applying coarse particles and the particle size composition, and the drying (quick drying in this case) of the solvent after application. The particle size structure of such aggregates is preferably within the range shown in Table 2.

〔Example〕

Next, the method of the present invention will be explained with reference to examples. The vacuum casting mold was made using the silica sand shown in Tables 3 and 4 to form a 650mm x 600mm x 60mm mold as shown in Figure 1.
A mm-thick high Mn alloy cast steel plate was manufactured. This was coated with the MgO-based coating material shown in Table 5, and then the Al ₂ O ₃ -based coating material shown in Table 6 was applied on top of it, and the composition is shown in Table 7 instead of Al ₂ O ₃ . _ZrO2
A composite mold coated with a ZrO ₂ -based coating material consisting of a silicate material of zirconium oxide was fabricated. The particle size structure and solvent (including binder) composition of the aggregate of the coating material in this case are shown in Tables 8, 9 and 9.
Table 10 shows the mixing ratio of aggregate and solvent (including binder). For comparison, a vacuum casting mold of the same shape was coated with MgO coating material and molded. Next, high Mn containing chemical components as shown in Table 12
Alloy cast steel is melted in a 1 ton high frequency furnace and then
It was poured into the above mold at a temperature range of 1540 to 1560°C, and a high Mn alloy cast steel plate shown in FIG. 1 was vacuum cast. Comparisons were made of the casts: those coated with MgO-based coating material alone, those coated with a composite coating of the MgO-Al ₂ O ₃ -based coating material of the present invention, and those coated with a composite coating of MgO-ZrO ₂ -based coating material. The baking condition of the casting surface was observed. The results are shown in Table 13. The upper mold surface 4 and lower mold surface 5 in Table 13 are as shown in FIG. The coating material
Seizure occurs when MgO alone is used, and the lower the MgO content, the greater the seize. On the other hand, the MgO-Al ₂ O ₃ -based coating material or
The mold with a composite coating of MgO-ZrO ₂ type coating material had a very beautiful casting surface, and although there was a slight defect area due to seizure on the upper surface, there was no difference between the two and compared to conventional castings. It has improved dramatically.

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〔Effect of the invention〕

As described above, the present invention is applicable to molds using silica sand when producing thick-walled high-Mn alloy castings by vacuum casting.
By applying a two-layer coating of MgO type and Al ₂ O ₃ or ZrO ₂ type coating material, a high Mn alloy cast steel product with a good casting surface can be vacuum cast. Moreover, a beautiful cast steel product with excellent quality and almost no surface defects can be obtained. In addition, there is no need to use different molding sand depending on the type of steel, which can be expected to reduce costs and make extremely advantageous casting possible.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a casting method for a high Mn alloy cast steel casting. Figure 2 shows the upper mold surface of the same casting.
It is a perspective view of a lower die surface. 1...High Mn alloy cast steel product, 2...Weir, 3...Riser, 4...Upper die surface, 5...Lower die surface.

Claims (1)

[Claims] 1. The film surface of the silica sand mold vacuum casting mold is coated with a magnesia-based undercoat mold material, and then the top surface of the undercoat mold material is overcoated with one of alumina refractories or zirconia refractories, resulting in a two-layer coating. A mold coating method for vacuum casting.