JP2001129640A - Method of casting thin, flat article and cast article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide thin and flat, especially circular or ring-shaped cast articles excellent in wear resistance and heat resistance, with small primary dendrite arm spacing and free from any casting defects by stack molding process. SOLUTION: A chiller is placed on most part of the surface of at least one side of the cavity in the casting mold in which the thin, flat articles are manufactured, and casting is performed after stacking the casting mold. Because of the effect of the chiller, the cooling speed of the molten metal inside the cavity becomes faster, the grain size of the crystals becomes fine, and the dendrite arm spacing(DASII) becomes 3-20 μm. As a result, the hardness and tensile strength of the articles are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stack mold which is particularly suitable for casting a product such as a high chromium heat-resistant cast iron material requiring a relatively thin and flat shape having a relatively high wear resistance and tensile strength. Related to the law.

[0002]

2. Description of the Related Art Thin-walled flat products such as discs and rings have a large outer shape but are thin. Therefore, the method of using one mold at a time requires a small volume of the product in the mold, resulting in low efficiency. Due to the poor quality, the product may be cast by a stack mold method or the like, which can cast a large number of products at once to increase mass productivity. For example, JP-A-62-2
Japanese Patent No. 40140 discloses that a relatively flat disk is cast by a stack mold method. Usually, products cast using the stack mold method are thin-walled products, so that the cooling rate is faster than that of thick-walled products, crystal grains are relatively small, and casting defects such as shrinkage are unlikely to occur.

[0003]

[0003] Industrial products usually have higher performance and higher function with the progress of technology, and therefore, the characteristics required for each component are also higher. When the sophistication of parts is required, thickening of the product and reinforcement by ribs and the like can be considered, but there is a problem such as an increase in the weight of the product. Therefore, as a method for easily increasing the strength of a product, there is an increase in hardness and an increase in tensile strength of a material. When high hardness and high tensile strength are required, it is conceivable to change the material used. However, changing the material itself leads to high alloying, so that an expensive alloy element or the like may be used, which leads to an increase in material cost. An object of the present invention is to obtain a product with improved characteristics without changing the shape or the material.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the hardness and tensile strength of a thin flat product without losing mass productivity, eliminating casting defects, refining crystal grains. The present inventors have conducted intensive studies and found that, in order to improve the characteristics without changing the material, the smaller the crystal grain size and the smaller the primary crystal dendrite arm spacing (hereinafter referred to as DASII), the higher the hardness and tensile strength. Therefore, in order to achieve the above object, it was necessary to increase the cooling rate of the molten metal in the cavity and to make DASII and the crystal grain size fine.

Specifically, the first invention is characterized in that when casting a thin-walled flat product by the stack mold method, a chill is placed on at least a part of a mold surface of a product cavity and the product is cast. This is a method for casting flat products.

[0006] The mold used in the stack mold method is
Green mold, shell mold, self-hardening mold (phenol urethane mold, furan bake mold, etc.), gas curing mold (CO
₂ molds, cold box molds, etc.).

Here, the chill is preferably a copper alloy or the like having good heat conductivity. However, if the chill is made of an alloy of the same material, it is not necessary to sort the chill when the chill is mixed when the return scrap is melted.

According to a second aspect of the present invention, the size of the chill is approximately the same as or larger than the product area, and the thickness of the chill is 1/2 or more of the product thickness. This is a method for casting a thin, flat product, characterized by casting using a certain chill. The reason why the thickness of the chill is set to be not less than 1/2 of the product thickness is that when the thickness is smaller than that, the heat capacity of the product becomes larger than the heat capacity of the chill, and the role of the chill cannot be fulfilled. Is not possible.

A third aspect of the present invention is a thin-walled flat product characterized in that the cast thin-walled flat product has a DASII average of 3 μm to 20 μm in the product.

[0010] In a fourth aspect, the thin-walled flat product comprises:
The thin flat product is characterized by being a high chromium heat resistant cast iron material and a ring-shaped nozzle ring for turbocharger. Here, the reason why the material is high-chromium heat-resistant cast iron is that it has excellent wear resistance and heat resistance, and is relatively easy to cast.

Here, the reason that DASII is limited to 3 μm to 20 μm is that DASII is required to improve hardness and tensile strength.
II needs to be 20 μm or less. However, DASII
If it is too small, it will be too hard and brittle, so it needs to be 3 μm or more. Therefore, DASII was set to 3 μm to 20 μm.

[0012]

1 and 2 show an example of a stack molding method for carrying out the present invention. A thin flat product 17 shown in FIG. 3 was cast. The dimensions of the product 17 are 116 mm in outer diameter, 66 mm in inner diameter, and 14 mm in thickness.

Using a phenol urethane mold as a mold 2, a stack mold machine was used to mold each mold provided with runners 5, 6, a cavity 3, and a chill storage section 4. Six cavities 3 were arranged on each stage. In the present invention, 1
A cooling metal storage unit 4 was formed on the upper surface of the two molds 2, and a cavity 3 was formed on the lower surface. However, in some cases, the chill storage section 4 and the cavity 3 may be provided in the same place on the upper surface,
It is also possible to provide a cavity 3 on the upper surface and a chill storage unit 4 on the lower surface. Also, the number can be freely changed depending on the size of the mold and the size of the product.

Next, a chill 17 'is attached to the entire chill storage 4 of one mold. The chill 17 ′ used this time has the same shape as the product 17 and is made of the same material as the high-chromium heat-resistant cast iron (C: 1.23%, Si: 1.77%, Mn: 0.
54%, Ni: 0.76%, Cr: 33.0%, Mo:
Fe) containing 2.3% and the balance containing unavoidable components was used. The molds 20 to 25 to which the chillers 17 'had been attached were sequentially stacked, and six-tiered. Since there is no casting frame, the stack mold clamping frame 10 is placed below the lowermost mold 25 and on the uppermost mold 20, and the clamping bolt 11 and the nut 1
In step 2, tightening was performed so that the molten metal did not leak from the mating surface of the stack mold 1. In this embodiment, the case where the mold is not provided is shown. However, when the mold is provided with the cast frame, the mold may be stacked as it is to form a stack mold. The mold 2 was provided with a convex dowel 9 on the upper surface and a concave dowel receiver 9 'on the lower surface, so that the molds 2 were aligned vertically so as not to shift each stage when the molds 2 were stacked. On the uppermost mold 20, a spout 7 having a pouring spout 8 prepared separately was placed in alignment with the runner 5. The runners 5, 6 and the cavity 3 of the lowermost mold 25 were filled with the same material as the mold 2 (backfilled runner 13) to prevent the molten metal from leaking out.

A high-chromium heat-resistant cast iron is poured from the pouring port 8 of the finished stack mold 1. The pouring temperature was 1540 ° C. The molten metal reaches the cavity 3 of each stage via the runners 5 and 6. After the molten metal reaches the cavity 3, the molten metal is cooled substantially uniformly by the effect of the cooling metal 17 'and solidified to form a product 17.

When the solidification is completed, the stack mold 1 is broken, and the product 30 with the runners 5, 6 is taken out.
The chill 30 'can be collected together with the mold material. Runs 5, 6
And the product 17 is completed.

If no chill is used for comparison,
For the product, the mold 2 was made in exactly the same manner as described above, the chiller storage section 4 was filled with the same material as the mold, a stack mold was made, and the product was made by casting at the same pouring temperature.

A product is arbitrarily selected from each of 1, 3, and 5 steps from the top of the stack mold, and the cross section of the product is mirror-polished, and DASII is obtained from the microstructure.
Zero visual fields were measured and the average was calculated. The hardness of the cooled metal surface was measured, and a tensile test piece was prepared, and then the tensile strength was measured.
Table 1 shows the results and the presence / absence of casting defects. DA
Regarding SII, it can be seen that the SII is 8 to 15 μm in the case with the chill, and is finer than in the case without the chill. The hardness is higher than that of HB341 to 352 with chill and that of HB302 without chill.
It can be seen that the value is 739 to 773 MPa in the case of having the chill, and is higher than that of 599 to 702 in the case of having no chill.
Further, with respect to casting defects, there are almost no casting defects when there is a chill, and there are casting defects when there is no chill.

[0019]

[Table 1]Stack Tier DASII hardness Tensile strength Casting defect Remarks  (μm) (HB) (Mpa) Example 1 15 341 773 Fine cooling 3 10 352 755 None Cooling 5 8 341 739 None Cooling comparative example 1 28 302 702 Yes No cooling 3 26 302 671 Yes No chill 5 2 302 599 Yes No chill

[0020]

According to the present invention, in the stack mold, a cooling metal is applied to at least one surface of at least one side of the product part.
SII was also refined, and a product having hardness and tensile strength was obtained.

[0021]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a stack mold in which molds are overlapped.

FIG. 2 (a) is a plan view showing the upper surface of one mold. (B) The figure which shows the AA cross section. (C) A plan view showing the lower surface of one mold.

FIG. 3 (a) Plan view of product and chill (b) Elevation view of product and chill

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Stack mold 2 Mold 3 Cavity 4 Cooler storage part 5, 6 Runner 7 Gate section 8 Filler port 9 Dowel 9 'Dowel receiver 10 Stack mold tightening frame 11 Bolt 12 Nut 13 Filled runner 17 Product 17' Cold Stacking mold 20-25 Stack mold with cooling

Claims (4)

[Claims] 1. A method of casting a thin-walled flat product, wherein a cold mold is placed on at least a part of a mold surface of a product cavity when casting a thin-walled flat product by a stack mold method. . 2. The chill according to claim 1, wherein the size of the chill is substantially the same as or larger than the product area.
A method of casting a thin flat product, wherein the chill is cast using a chill having a thickness equal to or more than の of the product thickness. 3. The thin, flat product according to claim 1, wherein the primary dendrite arm spacing is 3 μm to 20 μm on average in the product. 4. The thin flat product according to claim 3, wherein the thin flat product is a high-chromium heat-resistant cast iron material and is a ring-shaped nozzle ring for a turbocharger.