JPH06269924A - Reducing pressure casting method with gas permeable mold - Google Patents

Abstract

PURPOSE:To provide the optimum casting method for producing a steel casting product having no casting defect, such as misrun, blow hole, with good productivity, at the time of casting a thin casting of particularly, a thin cast stainless steel, cast heat resistant steel, etc. CONSTITUTION:In the reducing pressure casting method with a gas permeable mold, casting is performed in the reduced pressure by arranging a reducing pressure sucking hole 11 near a cavity 2 of the last filling part of molten metal 3 in the gas permeable mold 1, connecting the cavity to the reducing pressure sucking hole through a sucking member 10 and connecting a pressure reducing device 12 to the reducing pressure sucking hole. The casting is executed so as to satisfy the following inequalities, 0.1-10-4Xc<=b/a<=0.2-10-3Xc, and in the case of applying releasing agent on the gas permeable mold, 0.1-10-4Xc<=b/a<=0.4-10-3Xc (wherein, a: gas permeability of the sucking member, b: gas permeability of the gas permeable mold, c: reduced pressure value in the reducing pressure sucking hole (mmHg)).

Description

[Detailed description of the invention]

[0001]

INDUSTRIAL APPLICABILITY The present invention is most suitable for the production of thin-walled castings, especially thin-walled stainless steel and heat-resistant cast steel castings free from casting defects such as clumsiness and blowholes with good productivity. related to a manufacturing method.

[0002]

2. Description of the Related Art Thin-walled castings partially having a wall thickness of 5 mm or less solidify rapidly after molten metal is poured and brought into contact with a mold. For this reason, the fluidity of the molten metal deteriorates, and imperfect rotation defects and the like are likely to occur.

[0003] In addition, thin-walled castings having a complicated shape are likely to involve air and gas generated from the mold during casting, and gas defects such as blowholes are likely to occur in the casting after solidification. It is extremely difficult to

A common method for solving this problem is the lost wax casting method. This lost wax casting method uses a ceramic mold, and the mold is heated to 700°C during casting.
By heating to ~900°C, the cooling rate of the molten metal during filling is slowed down, and the fluidity of the molten metal is improved. However, due to the use of expensive ceramic molds, the production cost of castings is also considerably high.

Japanese Patent Publication No. 60-35227 discloses that the cavity in the mold is decompressed to cast the molten metal under suction to improve the fluidity of the molten metal. again,
Japanese Patent Application Laid-Open No. 180642/1986 discloses a vacuum casting method in which molten metal is poured into a chamber containing an air-permeable mold after vacuum suction is performed.

[0006] In Japanese Patent Laid-Open No. 57-31463, molten metal is injected into the product cavity while sucking the inside of the product cavity of the mold through a ventilation hole provided at the farthest position from the sprue position in the product cavity. However, there is a disclosure of casting with improved fluidity of the molten metal. This Japanese Patent Laid-Open No. 57-
In Japanese Patent No. 31463, since the entire inner surface of the product cavity is sucked, the suction effect is small in the necessary parts, and the molten metal is disturbed in the product cavity, and casting defects are likely to occur due to entrainment of air, slag, and slag.

[0007] As a countermeasure against this, Japanese Patent Application Laid-Open No. 60-
In Japanese Patent No. 56439, a refractory material filter having better air permeability than gypsum is provided from the vicinity of the final filling part of the molten metal in the product cavity to the outer surface of the gypsum mold, and suction casting is performed by enhancing the decompression effect of the product cavity. by
There is a disclosure of a gypsum mold for vacuum casting that yields thin-walled castings free from dead-turn defects and free from gas defects caused by entrainment of air.

Japanese Patent Laid-Open No. 4-147760 discloses that by providing a suction guide that forms a suction passage between the required portion of the mold space and the outside of the mold, the portion requiring reduced pressure is locally decompressed and sucked. There is a disclosure of a sand mold for suction casting for casting thin-walled castings that have increased effects and eliminate gas defects by allowing the gas generated during pouring to be naturally exhausted to the outside of the mold without being affected by the suction. .

[0009]

However, the method disclosed in Japanese Patent Publication No. 60-35227 is complicated in terms of holding the mold for immersing the mold in the molten metal and the structure for immersing the mold.

[0010] Further, in Japanese Patent Laid-Open No. 180642/1986, since the entire mold is sucked, the flow of the molten metal is likely to be disturbed, and defects such as blowholes are likely to occur, and there is a risk of explosion of generated gas from the mold.

[0011] Further, Japanese Patent Application Laid-Open No. 60-56439 states that
Since gypsum is used as the mold, many steps are required to manufacture the gypsum mold, resulting in poor productivity. In addition, since the gypsum mold itself has poor air permeability, the pressure in the cavity (back pressure) increases during casting, resulting in poor fluidity as a whole.

[0012] Further, Japanese Patent Application Laid-Open No. 4-147760 states that
A process for providing a suction guide that forms a suction passage is required in the sand mold, and the productivity is still insufficient, suction is localized, and the suction passage has less air permeability than the sand mold, so suction is not possible. small effect.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide an optimal manufacturing method for manufacturing thin-walled castings free from casting defects such as clumsiness and blowholes with high productivity and safety at a low cost. .

[0014]

DISCLOSURE OF THE INVENTION In order to achieve the above objects, the vacuum casting method using an air-permeable mold according to the first aspect of the present invention is provided with a vacuum suction port near the cavity of the final filling portion of the air-permeable mold, A vacuum casting method using an air-permeable mold in which the cavity and the vacuum suction port are connected by a suction member, and a vacuum device is connected to the vacuum suction port for vacuum casting, wherein casting is performed according to the following equation. .

[0015] 0.1-10-4 xc≤b/a≤0.2-10-3 xc however, a: air permeability of the suction member b: air permeability of air-permeable mold c: value of reduced pressure in vacuum suction port (mmHg)

As the suction member, a ceramic filter, a sand mold using sand coarser in grain size than the main mold, or an air-permeable member such as a vent hole through which molten metal does not penetrate is used.

Next, in the vacuum casting method using the air-permeable mold according to the second aspect of the present invention, a vacuum suction port is provided in the vicinity of the cavity of the final filling portion of the molten metal, and the cavity and the vacuum suction port are connected by a suction member. Then, in a vacuum casting method using an air-permeable mold, the joint surface of the air-permeable mold and/or the air-permeable mold are coated, and a decompression device is connected to the vacuum suction port for vacuum casting. It is characterized by

[0018] 0.1-10-4 xc≤b/a≤0.4-10-3 xc however, a: air permeability of the suction member b: air permeability of air-permeable mold c: value of reduced pressure in vacuum suction port (mmHg)

Further, in the vacuum casting method using the air-permeable mold according to the present invention, a riser and/or a discharge is provided in the vicinity of the final filling portion of the molten metal, and the vacuum suction port is provided for the riser and/or the discharge. It is provided in the vicinity, and the pressure reduction value on the side of the pressure reduction suction port is made larger than the pressure reduction value on the side into which the molten metal is injected.

[0020]

[Function] In the first invention, the air permeability b of the air permeable mold
and the ratio b/a of the air permeability a of the suction member is 0.2-10-3 x
The reason why the pressure is set to c or less is to generate a pressure gradient in the cavity for casting sound castings without causing defects such as non-rotating thin-walled castings partially having a thickness of 5 mm or less.

The air permeability ratio b/a is set to 0.1-1.
The reason why the ratio is 0 -4 ×c or more is that the ratio b/a is 0.1-10 -4
If it is less than xc, the pressure gradient in the cavity becomes too large, and casting defects such as blowholes tend to occur.

In the second aspect of the present invention, the ratio b/
The reason why a is 0.4 - 10 -3 ×c or less is partly because
This is because a pressure gradient is generated in the cavity for casting sound castings without defects such as unrotating thin-walled castings having a thickness of mm or less.

The air permeability ratio b/a is set to 0.1-1.
The reason why the ratio is 0 -4 ×c or more is that the ratio b/a is 0.1-10 -4
If it is less than xc, the pressure gradient in the cavity becomes too large, and casting defects such as blowholes tend to occur.

[0024] By providing a riser and/or a discharge near the final filling portion of the molten metal, the molten metal is replenished against the solidification shrinkage of the poured molten metal, and the slag and gas caught in the molten metal are accumulated. , to prevent slag and gas from entering the casting cavity.

[0025] If the pressure reduction value on the pressure reduction suction port side is made larger than the pressure reduction value on the side into which the molten metal is injected, the fluidity of the molten metal is secured and improved without disturbing the flow of the molten metal.

[0026] If a vacuum suction port is provided in the air-permeable mold, air permeability around the vacuum suction port is ensured, and gas generated during pouring is also effectively removed.

[0027] When the air-permeable mold is transported and positioned by a transport device (not shown), the air-permeable mold is decompressed and sucked by the decompression device from the decompression suction port opened toward the outer surface of the permeable mold.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION A method for manufacturing thin-walled castings according to the present invention will now be described with reference to the drawings. FIG. 1 is a longitudinal sectional view of a permeable mold used in the present invention. In FIG. 1, the permeable mold 1 has a hollow cylindrical cavity 2 with an outer diameter of 45 mm, a thickness of 2.5 mm, and a length of 200 mm with a core 8, and flange portions with an outer diameter of 80 mm and a thickness of 10 mm at both ends. Two bosses with a diameter of 10 mm and a height of 15 mm are formed on the outer peripheral surface of the cavity 2 . Breathable mold 1 has air permeability of 120-2
00 (No. 6 to No. 8 silica sand in this embodiment) cold box type is used. A sprue 5 is provided near one end of the permeable mold 1, and continuously with this sprue 5, a filter 6 and a weir 7 are provided at the bottom of the sprue. A riser 9 that also serves as a discharge is installed on the flange portion on the opposite side of the sprue 5. - 特許庁A vacuum suction port 11 opened toward the bottom surface of the permeable mold 1 is provided in the vicinity of the discharge and combined use riser 9, and ventilation is provided between the discharge and combined use riser 9 and core 8 and the reduced pressure suction port 11. degrees 180-22
00 (No. 4 to No. 6 sand layers in this embodiment) suction member 10 is provided. In addition, the air-permeable mold 1 coated on the inner surface of the product cavity is also partially used. The tip of a flexible tube from a decompression device 12 is brought into close contact with the opening of the decompression suction port 11 to perform decompression suction. Decompression was performed so that the decompression value in the decompression suction port 11 was in the range of -200 to -40 mmHg before pouring molten metal. Table 1 shows the chemical composition of the cast steel.

[0029]

[Table 1] Chemical composition of cast steel (% by weight) C. Si Mn P. S. Cr Fe _{0.11 1.1 0.6 0.01 0.01 17.3} remaining

After casting, the permeable mold 1 is carried out on a roller conveyor by an extruder to the next demolding station. Then, the permeable mold 1 before casting is carried into the pouring station. The above steps were repeated to cast the required number of thin-walled castings.

[0031] By the above method, a flanged cylindrical thin-walled cast steel casting was prepared with air permeability without coating shown in Table 2.
Air permeability a of the suction member, pressure reduction value c (mmH
10 pieces were cast under each of 24 kinds of conditions with g) changed. Table 2 also shows the number of casting defects after casting (casting defects such as non-rotating defects, leak defects, entrainment of air, blowholes, etc. were examined). Based on the results in Table 2, FIG. ], indicating that no defect occurred (○) and that a defect occurred (x).

In addition, the air permeability b of the coated air-permeable mold shown in Table 3, the air permeability a of the suction member, the pressure reduction value c inside the pressure reduction suction port
Even under 24 conditions with different values (mmHg), each
Cast individually. Table 3 also shows the number of casting defects after casting (casting defects such as non-rotating defects, leak defects, entrainment of air, blowholes, etc. were examined). Based on the results in Table 3, FIG.
/a [permeability of air-permeable mold (b)/permeability of suction member (a)] indicates no defects (o) and defects (x).

[0033]

[Table 2] Casting conditions and number of casting defects in permeable mold without coating Breathable mold of the suction member Decompression suction port Permeability of casting defects Permeability Internal decompression value The number of occurrences (b) (a) b/a (mmHg) Example 1 190 543 0.35 −171 0 〃 2 165 1269 0.13 -126 0 〃 3 135 964 0.14 -145 0 〃 4 127 907 0.14 - 74 0 〃 5 174 967 0.18 - 57 0 〃 6 142 747 0.19 -111 0 〃 7 126 663 0.19 -137 0 〃 8 122 610 0.20 -197 0 〃 9 146 695 0.21 - 48 0 〃 10 130 565 0.23 - 66 0 '' 11 186 689 0.27 - 84 0 '' 12 127 577 0.22 - 97 0 '' 13 196 726 0.27 - 150 0 '' 14 154 570 0.27 -171 0 15 164 547 0.30 -166 0 16 165 516 0.32 -184 0

(Continued from Table 2) Casting conditions and number of casting defects in permeable mold without coating Breathable mold of the suction member Decompression suction port Permeability of casting defects Permeability Internal decompression value The number of occurrences (b) (a) b/a (mmHg) Comparative Example 17 142 1775 0.08 -178 2 〃 18 176 2200 0.08 -110 3 〃 19 134 406 0.33 - 52 3 20 166 488 0.34 - 57 2 21 145 392 0.37 - 93 4 22 143 298 0.48 -166 1 23 166 307 0.54 -141 2 24 149 266 0.56 -195 3

[0035]

[Table 3] Casting Conditions and Number of Casting Defects in Breathable Mold with Coating Breathable Mold of the suction member Decompression suction port Permeability of casting defects Permeability Internal decompression value The number of occurrences (b) (a) b/a (mmHg) Example 51 124 954 0.13 - 56 0 〃 52 163 1019 0.16 −105 0 〃 53 133 831 0.16 −153 0 〃 54 175 625 0.28 −174 0 〃 55 177 632 0.28 − 83 0 〃 56 146 503 0.29 −144 0 〃 57 154 497 0.31 − 61 0 〃 58 159 468 0.34 −117 0 〃 59 143 421 0.34 −181 0 〃 60 188 508 0.37 − 72 0 〃 61 158 395 0.40 -139 0 〃 62 162 405 0.40 − 45 0 〃 63 128 312 0.41 − 92 0 〃 64 137 304 0.45 −192 0 〃 65 185 356 0.52 −164 0 〃 66 189 350 0.54 -185 0

(Continued from Table 3) Casting Conditions and Number of Casting Defects in Breathable Mold with Coating Breathable Mold of the suction member Decompression suction port Permeability of casting defects Permeability Internal decompression value The number of occurrences (b) (a) b/a (mmHg) Comparative Example 67 175 1944 0.09 −176 2 ″ 68 181 2263 0.08 −116 4 ″ 69 158 304 0.52 − 55 3 ″ 70 139 188 0.74 − 70 4 ″ 71 194 318 0.61 − 98 2 〃 72 145 230 0.63 −161 3 〃 73 146 216 0.68 −197 2 〃 74 169 235 0.72 −147 1

As shown in Tables 2 and 3 and FIGS. 2 and 3, within the scope of the present invention, the pressure reduction value in the vacuum suction port side cavity is greater than that in the sprue side cavity, and the injection speed of the molten metal is The casting was fast, the molten metal was less likely to be disturbed, and there was little entrainment of air. On the other hand, in comparative examples outside the scope of the present invention, some casting defects such as non-rotation and blowholes occurred.

[0038]

Effect of the Invention As described above, according to the vacuum casting method using the air-permeable mold of the present invention, the fluidity of the molten metal is improved without disturbing the flow of the molten metal, and the gas generated during pouring is effectively removed. It is possible to manufacture thin-walled castings without casting defects such as crookedness and blowholes. In addition, mass production is possible by providing a vacuum suction port in a normal permeable mold and using a conveying device or the like, thereby improving productivity. Moreover, since no box, chamber, or the like containing a mold is used, there is little risk of explosion.

[Brief description of the drawing]

FIG. 1 is a vertical cross-sectional view showing an embodiment of a vacuum casting method using an air-permeable mold according to the present invention;

[Fig. 2] Casting results in a vacuum casting method using an air-permeable mold without coating the air-permeable mold. air permeability (b)/
Air permeability (a) of the suction member], no defects (○)
FIG. 10 is a diagram showing occurrence of defects (×);

[Fig. 3] In a vacuum casting method using an air-permeable mold, the results of casting in which the air-permeable mold is coated are shown. air permeability (b)/
Air permeability (a) of the suction member], no defects (○)
FIG. 10 is a diagram showing occurrence of defects (×);

[Description of symbols]

1: Breathable mold, 2: Cavity, 3: Molten metal,
4: ladle, 5: sprue, 6: filter,
7: weir, 8: core, 9: riser, 1
0: suction member, 11: decompression suction port, 12: decompression device.

Claims (5)

[Claims] 1. A vacuum suction port is provided in the vicinity of a cavity of a final filling portion of a molten metal of an air-permeable mold, a suction member is connected between the cavity and the vacuum suction port, and a decompression device is connected to the vacuum suction port. A vacuum casting method using an air-permeable mold, characterized in that casting is performed according to the following formula. 0.1-10 -4 ×c ≤ b ^/ a ≤ 0.2-10 ^-3 ×c where a: air permeability of suction member b: air permeability of mold c: pressure reduction value in vacuum suction port (mmHg ) 2. A vacuum suction port is provided in the vicinity of the cavity of the final filling portion of the molten metal of the gas-permeable mold, the cavity and the vacuum suction port are connected by a suction member, and the joint surface and/or A vacuum casting method using an air-permeable mold, in which the air-permeable mold is coated, and a decompression device is connected to the vacuum suction port for vacuum casting, wherein casting is performed according to the following formula. . 0.1-10-4×c≦b/a≦0.4-10-3×c where a: air permeability of suction member b: air permeability of mold c: pressure reduction value (mmHg ) [Claim 3] A riser and/or
3. A vacuum casting method using an air-permeable mold according to claim 1 or 2, wherein a spit is provided. 4. The vacuum casting method using an air-permeable mold according to any one of claims 1 to 3, wherein said vacuum suction port is provided in the vicinity of said riser and/or spit. 5. The pressure reduction value on the pressure reduction suction port side is made larger than the pressure reduction value on the side into which the molten metal is injected.
5. A vacuum casting method using an air-permeable mold according to claim 4.