JP2021016896A - Method for evaluating casting propriety of horizontal hole - Google Patents

Abstract

To provide a method for evaluating the casting propriety of a horizontal hole for casting the horizontal hole excellent in a finished state.SOLUTION: When the following formulas (1) and (2) are satisfied, where a thickness of coating 6 is t (mm), a diameter of a hole 3 containing the coating 6 is D (mm), a density of molten metal 5 is ρm (g/cm3), a density of the coating 6 is ρt (g/cm3), a bulk density of casting sand 4 filled in the hole 3 is ρs (g/cm3), the gravitational acceleration is g, a depth from an upper surface of the sand mold to the center of the hole 3 is h (mm), a coefficient in an expression of allowable pressure for buckling of a cylinder is K, and the Young's modulus of the coating agent 6 is Et, it is determined that a horizontal hole having a stable shape can be cast without filling the molding sand 4 in the hole 3. KEt(t/D)3>(ρm-ρa)gh...Expression (1), ρa=[{D2-(D-2 t)2}ρt+(D-2 t)2ρs]/D2...Expression (2).SELECTED DRAWING: Figure 2

Description

The present invention relates to a method for evaluating the possibility of casting a horizontal hole, which evaluates whether or not a horizontal hole having a stable shape can be cast in a vanishing model casting method for casting a casting having a horizontal hole.

The vanishing model casting method is considered to be the most suitable method for forming holes inside a casting (called "casting") by casting. Here, in the vanishing model casting method, a mold formed by applying a mold coating agent to the surface of a foamed model is buried in casting sand, and then a molten metal is poured into the mold to eliminate the foamed model and form a molten metal. It is a method of casting a casting by substituting.

In Patent Document 1, a mold release agent having a bending strength satisfying a predetermined condition is used, and the hole portion of the foam model, which is a portion where a hole is formed, is set at an angle satisfying a predetermined condition with respect to the horizontal direction. A method of casting a vanishing model is disclosed.

Japanese Patent No. 6470141

By the way, if the hole is not sufficiently filled with casting sand, seizure may occur at the center of the hole when "casting" is performed. In addition, if the holes are not sufficiently filled with casting sand, the mold release agent will be crushed in the radial direction of the holes by the static pressure from the molten metal when "casting" is performed. Poor shape may occur in the center.

An object of the present invention is to provide a method for evaluating the castability of a horizontal hole, which can cast a horizontal hole having a good finished state.

In the present invention, a mold formed by applying a mold coating agent to the surface of a foam model having a hole having a circular cross section extending in the lateral direction is embedded in casting sand forming a sand mold, and then a metal is placed in the mold. It is evaluated whether or not the lateral hole having a stable shape can be cast in the vanishing model casting method in which the molten metal is poured to eliminate the foamed model and replace the molten metal with the molten metal to cast a casting having a lateral hole. , A method for evaluating whether or not a horizontal hole can be cast, the thickness of the coating agent is t (mm), the diameter of the hole containing the coating agent is D (mm), and the density of the molten metal is ρ _m (g). / Cm ³ ), the density of the coating agent is ρ _t (g / cm ³ ), the bulk density of the casting sand filled in the hole is ρ _s (g / cm ³ ), the gravity acceleration is g, and the sand mold h (mm) from the top surface of the depth to the center of the hole of the coefficients in the equation of the allowable pressure of the buckling cylinder K, the Young's modulus of the coating agent when the E _t, the following equation When the conditions (1) and (2) are satisfied, it is determined that the horizontal hole having a stable shape can be cast without filling the hole with the casting sand, and the average density of the hole is set to ρ _d ( When g / cm ³ ), the length l (mm) of the hole portion satisfies the following formula (3), and the bulk density ρ _s (g) of the casting sand filled in the hole portion. When / cm ³ ) satisfies the following formula (4), it is determined that the horizontal hole having a stable shape can be cast.
KE _t (t / D) ³ > (ρ _m −ρ _a ) gh ・ ・ ・ Equation (1)
ρ _a = [{D ^2- (D-2t) ² } ρ _t + (D-2t) ² ρ _s ] / D ² ... Equation (2)
l ² ≤ 0.04 / {(ρ _m −ρ _d ) g} × D ・ ・ ・ Equation (3)
ρ _s ≧ 1.43 ・ ・ ・ Equation (4)

According to the present invention, when the above formulas (1) and (2) are satisfied, it is determined that a horizontal hole having a stable shape can be cast without filling the hole with casting sand. If the above equations (1) and (2) are satisfied, the allowable buckling pressure in the hole becomes higher than the static pressure from the molten metal. By making the allowable buckling pressure in the hole higher than the static pressure from the molten metal, it is possible to prevent the mold release agent from buckling in the radial direction of the hole. Therefore, by satisfying the above equations (1) and (2), it is possible to cast a horizontal hole having a good finished state without filling the hole with casting sand. On the other hand, when the length l of the hole portion satisfies the above formula (3) and the bulk density ρ _s of the casting sand filled in the hole portion satisfies the above formula (4), the shape is stable. Judge that the horizontal hole can be cast. If the bulk density ρ _s of the casting sand filled in the hole satisfies the above equation (4), it means that the casting sand is sufficiently filled in the hole. By sufficiently filling the holes with casting sand, it is possible to prevent the mold release agent from buckling in the radial direction of the holes. Therefore, by satisfying the above formula (3) and making the bulk density ρ _s of the casting sand in the hole satisfy the above formula (4), it is possible to cast a horizontal hole having a good finished state. ..

It is a cross-sectional view of a sand mold. It is an enlarged view of a hole part. It is an enlarged view of the hole part, and is the figure which shows the state which the mold release agent was crushed. It is sectional drawing of a hole part. It is a known graph which shows the coefficient K in the formula of the permissible pressure of buckling of a cylinder. It is a figure which shows the evaluation result.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

(Disappearing model casting method)
The method for evaluating the castability of a horizontal hole according to the embodiment of the present invention evaluates whether or not a horizontal hole having a stable shape can be cast in a vanishing model casting method for casting a casting in which a horizontal hole is formed.

As shown in FIG. 1, which is a cross-sectional view of the sand mold, in the disappearance model casting method, a mold 1 formed by applying a mold coating agent to the surface of a foam model is embedded in casting sand (dry sand) forming the sand mold 2. After that, a molten metal is poured into the mold 1 to eliminate the foam model and replace it with the molten metal, thereby casting a casting. This vanishing model casting method is considered to be the most suitable method for casting, for example, a casting having a small hole having a diameter of 18 mm or less and a length of 50 mm or more by "casting". In the present embodiment, a casting having a horizontal hole is cast by using a foam model having a hole 3 having a circular cross section extending in the lateral direction. Here, the horizontal direction includes the horizontal direction.

The vanishing model casting method includes a melting step of melting metal (cast iron) to form a molten metal, a molding step of molding a foam model, and a coating step of applying a mold coating agent to the surface of the foam model to form a mold. Have. Furthermore, the disappearance model casting method is a molding process in which the mold is buried in casting sand and the casting sand is filled in every corner of the mold, and molten metal (molten metal) is poured into the mold to melt the foam model. It has a casting step of replacing the molten metal, a cooling step of cooling the molten metal poured into the mold into a casting, and a separation step of separating the casting and the casting sand.

As the metal to be melted, gray cast iron (JIS-FC250), flake graphite cast iron (JIS-FC300), or the like can be used. Further, as the foam model, a foam resin such as Styrofoam can be used. Further, as the mold release agent, a mold release agent for silica-based aggregate can be used. Further, as the cast sand, "silica sand" containing SiO ₂ as a main component, zircon sand, chromate sand, synthetic ceramic sand and the like can be used. A binder or a curing agent may be added to the cast sand.

Here, the thickness t (mm) of the mold release agent applied to the foam model is preferably 1 mm or more and 3 mm or less. This is because when the thickness of the mold release agent is 3 mm or more, it is necessary to repeat the application and drying of the mold release agent three times or more, which is troublesome and the thickness tends to be uneven.

(Evaluation method for casting of horizontal holes)
An enlarged view of the hole 3 is shown in FIG. In Patent Document 1, regardless of the filling state of the casting sand 4 in the hole portion 3, if the mold release agent 6 is not damaged by the static pressure of the molten metal 5, a horizontal hole having a good finished state can be cast. It was a viewpoint that it could be done.

However, if the hole 3 is not sufficiently filled with the casting sand 4, seizure may occur at the center of the horizontal hole when "casting" is performed. Further, if the hole 3 is not sufficiently filled with the casting sand 4, as shown in FIG. 3, which is an enlarged view of the hole 3, when "casting" is performed, the static pressure from the molten metal 5 is applied. As a result, the mold release agent 6 is crushed in the radial direction of the hole portion 3, which may cause a shape defect in the central portion of the lateral hole.

Therefore, in the present embodiment, when the following equations (1) and (2) are satisfied, it is determined that a horizontal hole having a stable shape can be cast without filling the hole 3 with the casting sand 4.
KE _t (t / D) ³ > (ρ _m −ρ _a ) gh ・ ・ ・ Equation (1)
ρ _a = [{D ^2- (D-2t) ² } ρ _t + (D-2t) ² ρ _s ] / D ² ... Equation (2)

Here, as shown in FIG. 4, which is a cross-sectional view of the hole portion 3, D (mm) is the diameter of the hole portion 3 containing the mold release agent 6. Further, ρ _m (g / cm ³ ) is the density of the molten metal 5, ρ _t (g / cm ³ ) is the density of the mold coating agent 6, and ρ _s (g / cm ³ ) is in the hole 3. It is the bulk density of the filled casting sand 4. Further, g is the gravitational acceleration, and h (mm) is the depth from the upper surface of the sand mold 2 to the center of the hole 3. Further, K is a coefficient in an expression of allowable pressure of buckling of cylindrical, E _t is the Young's modulus of the coating agent 6.

ρ _t and _Et are measured in advance by weight measurement, bending test, etc. of the mold release agent 6 to be used. K can be read from the known graph shown in FIG. In FIG. 5, R is the radius of the hole 3 containing the mold release agent 6.

If the mold release agent 6 around the hole 3 is regarded as a cylinder, the allowable buckling pressure Pe of the cylinder can be expressed by the left side of the equation (1). If the above equations (1) and (2) are satisfied, the allowable buckling pressure Pe in the hole 3 becomes higher than the static pressure from the molten metal 5. By setting the allowable buckling pressure Pe in the hole 3 to be higher than the static pressure from the molten metal 5, the mold release agent 6 can be prevented from buckling in the radial direction of the hole 3. Therefore, by satisfying the above equations (1) and (2), it is possible to cast a horizontal hole having a good finished state without filling the hole 3 with the casting sand 4.

Further, in the present embodiment, when the length l (mm) of the hole 3 satisfies the following formula (3), the bulk density ρ _s (g / cm) of the casting sand 4 filled in the hole 3 is satisfied. ^{When 3} ) satisfies the following formula (4), it is judged that a horizontal hole having a stable shape can be cast.
l ² ≤ 0.04 / {(ρ _m −ρ _d ) g} × D ・ ・ ・ Equation (3)
ρ _s ≧ 1.43 ・ ・ ・ Equation (4)

Patent Document 1 discloses the following equation (5).
cos ² θ ≤ 0.04 / {(ρ _m −ρ _d ) g} × D / l ²・ ・ ・ Equation (5)

Here, θ is an angle with respect to the horizontal direction, and ρ _d (g / cm ³ ) is the average density of the holes 3. The average density ρ _d of the hole 3 is the density ρ of the casting sand 4 filled inside the hole 3 and the density ρ _{c of the} mold coating agent 6 applied and dried on the surface of the hole 3, respectively. It is averaged (weighted average) according to the thickness of. In the equation (5), when θ = 0, the above equation (3) is obtained.

If the bulk density ρ _s of the casting sand 4 filled in the hole 3 satisfies the above equation (4), the casting sand 4 is sufficiently filled in the hole 3. By sufficiently filling the hole 3 with the casting sand 4, the mold release agent 6 can be prevented from buckling in the radial direction of the hole 3. Therefore, by satisfying the above formula (3) and making the bulk density ρ _s of the casting sand 4 in the hole 3 satisfy the above formula (4), a horizontal hole having a good finished state is cast. be able to.

(Casting evaluation)
Next, the length l of the hole 3 is made different in the range of 10 to 100 mm, and the bulk density ρ _s of the casting sand 4 filled in the hole 3 is made different in the range of 0 to 1.7 g / cm ^3. The castability was evaluated. Here, the thickness t of the mold release agent 6 applied to the foam model was set to 1 mm, and the diameter D of the hole 3 containing the mold release agent 6 was set to 10 mm. The evaluation was carried out by the same casting method using gray cast iron (JIS-FC250) having the same composition.

As the mold release agent 6, one having a bulk density ρ _c of 1.3 to 1.5 g / cm ³ , a room temperature bending strength of more than 1.5 MPa, and an aggregate diameter of 100 μm was used. Further, as the casting sand 4, "silica sand" containing SiO ₂ as a main component was used. The evaluation result is shown in FIG.

In the formula (3), assuming that the density ρ _m of the molten metal 5 is 7.2 g / cm ³ and the average density ρ _d of the hole ³ is 1.4 g / cm ³ , the length l of the hole 3 is about 83 mm. .. Therefore, from the viewpoint of Patent Document 1, it can be determined that if the length l of the hole 3 is 83 mm or less, a horizontal hole having a good finished state can be cast. Further, from the evaluation results, it can be seen that if the bulk density ρ _s of the casting sand 4 filled in the hole 3 is 1.43 g / cm ³ or more, a horizontal hole having a stable shape can be cast. From the above, it can be seen that by satisfying the above equations (3) and (4), it is possible to cast a horizontal hole having a good finished state.

Further, the 0.023MPa the right side (head pressure) of the formula (1), when the Young's modulus E _t of the coating agent 6 and 3 MPa, from equation (1), the coefficient K becomes 7.5.

Here, the Young's modulus E _t of the coating agent 6, the deflection amount 0.8~1.9mm of actually measured lateral hole was determined by substituting the equation (6) below. In formula (6), δ (mm) is the amount of deflection of the lateral hole, l _t (mm ⁴ ) is the moment of inertia of area of the mold coating agent 6, and w (N / mm) is the hole due to the static pressure of the molten metal. it is a force to (buoyancy) ([rho _m gh) part 3. Here, the moment of inertia of area l _t is 290 mm ⁴ , the length l of the hole 3 is 100 mm, the density ρ _{m of the} molten metal 5 is 7.2 g / cm ³ , and the depth h is 400 mm. As a result, the Young's modulus E _t was 3 to 7 MPa, so the Young's modulus E _t was set to 3 MPa for safety.
_{E t = δ × 384l t /} wl 4 ··· (6)

When the coefficient K is 7.5, the length l of the hole 3 is 13.5 mm from the graph shown in FIG. From the evaluation results, if the length l of the hole 3 is 13.5 mm or less, a horizontal hole having a stable shape can be cast without filling the hole 3 with casting sand 4 (bulk density ρ _s = 0). You can see that it can be pulled out. From the above, by satisfying the above equations (1) and (2), it is possible to cast a horizontal hole having a good finished state without filling the hole 3 with the casting sand 4. Understand.

(effect)
As described above, according to the method for evaluating the castability of horizontal holes according to the present embodiment, when the above equations (1) and (2) are satisfied, the hole 3 is not filled with the casting sand 4. However, it is judged that a horizontal hole with a stable shape can be cast. If the above equations (1) and (2) are satisfied, the allowable buckling pressure in the hole 3 becomes higher than the static pressure from the molten metal 5. By making the allowable buckling pressure in the hole 3 higher than the static pressure from the molten metal 5, the mold release agent 6 can be prevented from buckling in the radial direction of the hole 3. Therefore, by satisfying the above equations (1) and (2), it is possible to cast a horizontal hole having a good finished state without filling the hole 3 with the casting sand 4.

On the other hand, when the length l of the hole 3 satisfies the above formula (3) and the bulk density ρ _s of the casting sand 4 filled in the hole 3 satisfies the above formula (4). It is judged that a horizontal hole with a stable shape can be cast. If the bulk density ρ _s of the casting sand 4 filled in the hole 3 satisfies the above equation (4), the casting sand 4 is sufficiently filled in the hole 3. By sufficiently filling the hole 3 with the casting sand 4, the mold release agent 6 can be prevented from buckling in the radial direction of the hole 3. Therefore, by satisfying the above formula (3) and making the bulk density ρ _s of the casting sand 4 in the hole 3 satisfy the above formula (4), a horizontal hole having a good finished state is cast. be able to.

Although the embodiments of the present invention have been described above, only specific examples are illustrated, and the present invention is not particularly limited, and specific configurations and the like can be appropriately redesigned. In addition, the actions and effects described in the embodiments of the present invention merely list the most preferable actions and effects resulting from the present invention, and the actions and effects according to the present invention are described in the embodiments of the present invention. It is not limited to what has been done.

1 Mold 2 Sand mold 3 Hole 4 Casting sand 5 Molten melt 6 Mold release agent

Claims (1)

A mold formed by applying a mold coating agent to the surface of a foam model having a hole having a circular cross section extending in the lateral direction is embedded in casting sand forming a sand mold, and then molten metal is poured into the mold. Casting of horizontal holes, which evaluates whether or not the horizontal holes having a stable shape can be cast in the vanishing model casting method of casting a casting having horizontal holes formed by eliminating the foam model and replacing it with the molten metal. It is a method of evaluating whether or not it can be removed.
The thickness of the coating agent is t (mm), the diameter of the hole containing the coating agent is D (mm), the density of the molten metal is ρ _m (g / cm ³ ), and the density of the coating agent is ρ _t (g / cm ³ ), the bulk density of the foundry sand filled in the hole is ρ _s (g / cm ³ ), the gravity acceleration is g, and the depth from the upper surface of the sand mold to the center of the hole. the h (mm), the coefficients in the equation of allowable pressure buckling cylinder K, the Young's modulus of the coating agent when the E _t, if it meets the following formula (1) and (2) , It is judged that the horizontal hole having a stable shape can be cast without filling the hole with the casting sand.
When the average density of the holes is ρ _d (g / cm ³ ), the length l (mm) of the holes satisfies the following formula (3), and the holes are filled. When the bulk density ρ _s (g / cm ³ ) of the cast sand satisfies the following equation (4), it is determined that the horizontal hole having a stable shape can be cast. Method.
KE _t (t / D) ³ > (ρ _m −ρ _a ) gh ・ ・ ・ Equation (1)
ρ _a = [{D ^2- (D-2t) ² } ρ _t + (D-2t) ² ρ _s ] / D ² ... Equation (2)
l ² ≤ 0.04 / {(ρ _m −ρ _d ) g} × D ・ ・ ・ Equation (3)
ρ _s ≧ 1.43 ・ ・ ・ Equation (4)