JPH11285780A - Method for casting cast product having hollow part and core used for the product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a casting method of a cast product having a hollow part with which the mixing of a gas generated from a core into the cast product is prevented and the generation of a gas defect in the cast product having an oil passage can be restrained and the core used for the product. SOLUTION: This core 1 which has a gas vent hole 2 of 0.5-1.0 mm diameter extended to the longitudinal direction and >=4 mm the outer diameter, is arranged in a master mold 5 through gaggers 7a and 7b. Successively, a molten metal 3 is solidified while sucking a gas vent hole 2 at a higher value than a value subtracting the static water pressure of the molten metal on the surface of the core 1 from a pressure loss in the gas vent hole 2. The gas vent hole 2 arranges a thermally decomposable resin material in the inner part of a sand mold and the thermal decomposable resin material is decomposed by heating the sand mold to form the gas vent hole.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting method suitable for manufacturing a casting having a hollow portion used in an aircraft or the like, and a core used therein, and more particularly, to preventing generation of gas defects in the casting. TECHNICAL FIELD The present invention relates to a casting method for a casting having a hollow portion capable of being used and a core used therein.

[0002]

2. Description of the Related Art When performing casting, there is a method of forming a hollow portion in a casting by disposing a core at a predetermined position in a main mold. However, at the time of casting, including the case where the core is used, the core is heated, so that gas is generated from the binder that solidifies the sand that constitutes the core. This gas penetrates into the casting to generate gas defects.

Therefore, a casting method for suppressing generation of gas defects has been proposed (Japanese Patent Application Laid-Open No. 8-33944).
In the conventional method described in this publication, at the time of molding a main die or a core, a pipe capable of sucking a gas is arranged inside the pipe, and a gas exhaust device is connected to the pipe. Casting is performed while reducing the pressure inside the main mold or the core.

According to this conventional method, since the pressure inside the main mold or the core is forcibly reduced, it is possible to suppress gas from being mixed into the casting.

A core that efficiently sucks gas generated from the core and air in the cavity of the mold has been proposed (Japanese Utility Model Laid-Open No. 7-3844). The core described in this publication has a hollow structure, and the hollow portion is provided with a vent. The gas generated from the core can be discharged from the mold by performing the casting while sucking the hollow portion from the vent. Also, the air in the mold cavity is also sucked through the core,
Gas defects are less likely to occur.

[0006]

However, when forming an oil passage for passing oil as a hollow portion in a casting used for an aircraft or the like by these methods, the generation of gas defects in the casting is sufficiently reduced. There is a problem that cannot be prevented. Further, the oil passage core has an elongated shape, and there is a problem that it is difficult to form a hollow portion and provide a pipe therein.

The present invention has been made in view of such a problem, and it is possible to prevent gas generated from a core from being mixed into a casting and to suppress generation of gas defects in a casting having an oil passage. An object of the present invention is to provide a method for casting a casting having a hollow portion and a core used therein.

[0008]

SUMMARY OF THE INVENTION According to the present invention, there is provided a method for casting a casting having a hollow portion having a diameter of 0.5 to 2.0 mm, a gas vent hole extending in a longitudinal direction, and an outer diameter of 4 mm or more. Arranging a core in the main mold via a baseboard;
Solidifying the molten metal while sucking the gas vent hole at a value higher than the value obtained by subtracting the hydrostatic pressure of the molten metal cast on the surface of the core from the pressure loss in the gas vent hole. Features.

In the present invention, since the suction pressure of the gas inside the gas vent hole at the time of casting is appropriately regulated, the gas generated from the core is discharged from the gas vent hole to the outside of the mold. Thereby, generation of gas defects in the casting can be prevented.

[0010] The core according to the present invention is a core having an outer diameter of 4 mm or more and having a gas vent hole extending in the longitudinal direction, wherein the gas vent hole is formed by disposing a thermally decomposable resin material inside a sand mold. Is formed by decomposing the thermally decomposable resin material by heating the resin, and has a diameter of 0.5 to 2.0 mm.

In the present invention, a vent hole having a diameter of 0.5 to 2.0 mm is formed in the core, and the vent hole is formed by using a thermally decomposable resin material. Because it is, the shape is stable. In other words, it is easy to mold, and hardly collapses after molding.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of intensive experiments and research conducted by the present inventors to solve the above-mentioned problems, a vent hole having an appropriate outer diameter is formed inside a core used for forming an oil passage. When formed using a decomposable resin, when the molten metal is poured into the mold and solidified, the gas inside the vent hole is suctioned at an appropriate pressure to prevent the occurrence of gas defects in the casting. I found what I could do.

First, the core used in the present invention will be described. The core used in the present invention has a gas vent hole extending in the tube axis direction. The outer diameter of the core is 4 mm or more, and the diameter of the vent hole is 0.5 to 2.0 mm.

If the outer diameter of the core is less than 4 mm, it is extremely difficult to form a vent hole therein. When the diameter of the gas vent hole is less than 0.5 mm, it becomes difficult to suck the gas inside the gas vent hole. on the other hand,
If the diameter of the gas vent hole exceeds 2.0 mm, the strength of the mold is reduced because the diameter of the core of the oil passage is small. Therefore, as described above, the outer diameter of the core is 4 mm or more, and the diameter of the vent hole is 0.5 to 2.0 mm.
The diameter of the oil passage is usually 30 mm or less, and the outer diameter of the core usually used for forming the oil passage is also 30 mm or less. However, the present invention is not limited to this, and is not limited to this. Depending on the diameter of the oil passage to be made, the outer diameter of the core can be greater than 30 mm.

[0015] A thermally decomposable resin material is used for manufacturing the core. Specifically, when molding a core, a thermally decomposable resin material is arranged at the radial center of the sand mold. And, for example,
Sinter the sand mold at 250 ° C. At this time, the thermally decomposable resin is decomposed and discharged from the sand mold. Thereby, a core having a gas vent hole is manufactured.

Next, the conditions for suctioning the gas inside the gas vent hole when the molten metal is poured into the mold and solidified will be described.
The present inventors, in order to prevent the occurrence of gas defects,
When casting the molten metal, it was found that the value obtained by subtracting the suction pressure from the pressure loss in the gas vent hole needs to be lower than the pressure of the metal head. That is, it is necessary to perform suction at a pressure higher than a value obtained by subtracting the pressure of the metal head from the pressure loss in the gas vent hole. Here, the pressure of the metal head is the hydrostatic pressure of the molten metal at the position of the core. The pressure loss in the gas vent hole is obtained as the sum of the pressure loss in the tube axis direction and the radial pressure loss of the gas vent hole, but the pressure loss in the radial direction is the pressure loss in the tube axis direction. Since it is extremely small compared to, it can be ignored.

Next, a casting method according to an embodiment of the present invention will be described. FIG. 1 is a schematic diagram showing a state in which a molten metal is poured into a mold in a casting method according to an embodiment method of the present invention. Lower mold 5a used in the method of the present embodiment
A suction hole 6 is formed inside the main die 5 including the upper die 5b. The suction hole 6 is branched at one place, and two openings 6a and 6b are provided on the upper surface of the lower mold 5a. Note that, on the openings 6a and 6b, skirting boards 7a and 7b which are sand molds and support and position the core 1 are arranged. Suction holes 8 are also formed in the baseboards 7a and 7b, and the suction holes 8 are provided at positions matching the suction holes 6 at the openings 6a or 6b. A core 1 having a U-shaped tube shape is arranged with both ends thereof supported by baseboards 7a and 7b. The core 1 may be supported by another member (not shown). The core 1 has the gas vent holes 2 formed by using the thermally decomposable resin material as described above. Further, both ends of the gas vent hole 2 are arranged at positions matching the suction holes 8. The outer diameter of the core 1 is 4 mm or more, and the diameter of the vent hole 2 is 0.5 to 2.0 mm.

When the molten metal 3 is poured into the mold in which the core 1 is arranged and solidified as described above, a suction device (not shown) is inserted from the end of the suction hole 6 where the opening 6a or 6b is not provided. ) Is used to suck the gas inside the suction hole 6. The suction pressure at this time is larger than the value obtained by subtracting the pressure of the metal head from the pressure loss in the gas vent hole 2. In FIG. 1, the height of the metal head is indicated by a. Since the gas vent hole 2 is connected to the suction hole 6 via the suction hole 8, the gas inside the gas vent hole 2 is also sucked by the suction device by sucking the gas inside the suction hole 6.

In the method of the present embodiment, since the core 1 is manufactured using a thermally decomposable resin material, the gas vent hole 2 having a desired diameter can be formed. In addition, since the molten metal 3 is solidified while using the core 1 while sucking the gas inside the gas vent hole 2 at an appropriate suction pressure, the gas generated from the core 1 by heating during the solidification is in the molten metal 3. Without being mixed into the mold, the air is exhausted to the outside of the mold by the suction device through the suction hole 8 and the suction holes 6a or 6b. Therefore, generation of gas defects in a casting cast from the molten metal 3 is suppressed.

It is desirable to coat the surface of the core by forming a metal coating mold by welding and depositing a metal coating mold on the surface of the core or by forming it by Zn plating or the like. By forming such a coating mold, generation of gas defects can be more reliably prevented. As a method of forming a mold, there is a method in which fine aluminum powder is applied to the surface of a core and heated to melt.

Examples of the thermally decomposable resin include a wax resin and a polystyrene resin.

[0022]

EXAMPLES Examples of the present invention will be specifically described below in comparison with comparative examples that fall outside the scope of the claims.

First, three types of cores were manufactured. One type relates to Example 1 of the present invention, and a vent hole is formed using a thermally decomposable resin material. The outer diameter of the core of Example 1 is 10 mm, and the length is 170 mm. The diameter of the vent hole is 1 mm.

The other one has no gas vent hole.
Although it is not, a mold is formed on the surface. Soshi
The length and the outer diameter are the same as in the first embodiment. This
This is referred to as Comparative Example 2. In addition, one other type is degassing
No holes and no molds were formed. This length and outer diameter are also
This is the same as in the first embodiment. This is referred to as Comparative Example 3.What
Note that there are six samples in Example 1 and four in Comparative Example 2.
And Comparative Example 3 has six samples.

Next, these cores were placed in a mold, and in Example 1, while the gas in the vent hole was sucked at a pressure of 0.15 (kgf / cm ² ), Comparative Example 2 and 3
In, the melt at 750 ° C. was poured into a mold and solidified without suction. At this time, the depth from the upper surface of the molten metal to the core is 150 mm.

Then, the length of the linear defect as a gas defect in the obtained casting was measured. Then, the length per linear defect was calculated for each sample. These results are shown in FIG. FIG. 2 is a graph showing the linear defect length of each sample. The amount Q of gas generated from each core per unit time and unit weight of the core was 0.05 (ml / g · sec). Here, the gas amount Q is the amount of gas generated when a sample taken from the core was placed in a test tube and the test tube was left in a heating furnace at 700 ° C. for 5 minutes.

As shown in FIG. 2, in the first embodiment,
Although linear defects hardly occurred, Comparative Examples 2 and 3
In, many linear defects such as those exceeding 100 mm per line occurred.

Embodiment 1 will be further described. The pressure loss Δp ₁ in the longitudinal direction in the vent hole is obtained by setting the pipe friction coefficient to λ,
Let the length of the vent hole be l, its diameter d, the gas density ρ,
Assuming that the flow velocity of the gas is v, it can be obtained by the following equation (1).

[0029]

Δp ₁ = λ × (l / d) × (ρ / 2) × v ²

In this test, the gas generation amount Q was 0.05
(Ml / g · sec) and the gas flow rate v is 140 (cm / g
Seconds). Further, the pipe friction coefficient λ is the Reynolds number Re.
Is expressed as (64 / Re), and the Reynolds number R
e is expressed as (v × d / ν) when the kinematic viscosity coefficient ν is used. Then, the gas density ρ is set to 1.5 (kg / m
Assuming ³ ) and substituting into Equation 1 above, Equation 2 below is obtained.

[0031]

Δp ₁ = (128 / π) × (ν × 1 × ρ × Q /
d ⁴ ) ≒ 0.11 (kgf / cm ² )

The value of the kinematic viscosity coefficient ν is 2.1 × 10 ^-4
(Cm ² / sec).

On the other hand, the radial pressure loss Δ in the gas vent hole
p ₂ can be obtained by the following equation 3 where K is the air permeability of the core, r is its radius, and V is the gas flow rate per unit length.

[0034]

Δp ₂ = (1 / K) × (1 / (2 × π × r)) × V

In this test, the air permeability K of the core was 100
(Ml · cmH ₂ O / cm · min) and the gas flow rate V per unit length was 6.3 × 10 ⁻⁴ (cm ³ ). Then, when the radius r and the like are substituted into Equation 3, Δp ₂ = 0.0
0002 (kgf / cm ² ). Although the pressure loss of the gas vent hole is the sum of the pressure loss Δp ₁ and the pressure loss Δp ₂ , the pressure loss Δp ₂ can be ignored because it is extremely small as compared with the pressure loss Δp ₁ .

Further, the pressure of the metal head is obtained as a product of the height of the metal head (the depth from the upper surface of the molten metal to the core) and the density of the molten metal (2.4 (g / cm ² )). It is about 0.04 (kgf / cm ² ).

As described above, in the first embodiment, the pressure loss (0.11 (kgf / cm ² )) and the suction pressure (0.
15 (kgf / cm ² )) (−0.04 (k
gf / cm ² )) is the pressure of the metal head (0.04 (k)
gf / cm ² )). Therefore, the suction pressure of Example 1 is within the range specified by the present invention.

[0038]

As described above in detail, according to the method of the present invention, since the suction pressure of the gas inside the gas vent hole at the time of casting is properly defined, the gas generated from the core is vented. It is discharged from the hole to the outside of the mold. Thereby, generation of gas defects in the casting can be prevented. Further, in the present invention, since the vent hole is formed by using a thermally decomposable resin material for the core, the shape is stable. In other words, it is easy to mold, and hardly collapses after molding.

[Brief description of the drawings]

FIG. 1 shows a casting method according to an embodiment method of the present invention.
It is a schematic diagram which shows the state in which the molten metal was poured into the casting mold.

FIG. 2 is a graph showing the linear defect length of each sample.

[Explanation of symbols]

 1; core 2; gas vent 3; molten metal 5; main die 5a; upper die 5b; lower die 6, 8; suction holes 6a, 6b; openings 7a, 7b;

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Mamoru Nakata 1100 Higashiyama, Umedo, Oyasu-cho, Inaba-gun, Mie Pref. Kobe Steel, Ltd.

Claims (2)

[Claims] 1. A step of disposing a core having a diameter of 0.5 to 2.0 mm, a vent hole extending in a longitudinal direction, and an outer diameter of 4 mm or more in a main mold through a baseboard; Solidifying the molten metal while sucking the gas vent hole at a value higher than the value obtained by subtracting the hydrostatic pressure of the molten metal cast on the surface of the core from the pressure loss in the gas vent hole. A method of casting a casting having a hollow portion. 2. A core having an outer diameter of 4 mm or more and having a gas vent hole extending in a longitudinal direction, wherein the gas vent hole is formed by disposing a thermally decomposable resin material inside a sand mold and heating the sand mold. A core formed by decomposing a thermally decomposable resin material and having a diameter of 0.5 to 2.0 mm.