JP2011110577A - Lost foam pattern casting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To set a casting time in a lost foam pattern casting method exactly and with high accuracy. <P>SOLUTION: In the lost foam pattern casting method, a melt is poured into a mold formed by embedding a pattern comprising a resin foaming body in casting sand and a product is cast while losing the pattern by the melt. The casting time during casting is set corresponding to the modulus of the pattern (the volume of the pattern divided by the surface area of the pattern). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a disappearance model casting method, and more particularly, to an optimum casting time setting method.

  A model with a desired shape obtained by molding a resinous foam is embedded in the molding sand to form a mold, and molten metal is poured into the mold to burn and disappear the model and replace it with a casting. The law is known. In this method, a proposal has been made to determine the optimum casting time based on the ratio between the casting time when casting the molten metal into the gap and the casting time when performing the disappearance model casting (Patent Document). 1).

JP 2003-340547 A

  However, in the disappearance model casting method, the higher the modulus (model volume / model surface area), the lower the discharge of combustion gas generated when the model burns out of the mold, which is different from the casting time of void casting. Show the behavior. For this reason, it has been found that the casting time of void casting with different moduli is not proportional to the casting time of vanishing model casting. Therefore, there is a demand for providing an accurate and highly accurate casting time setting method in the disappearance model casting method.

  Therefore, an object of the present invention is to provide a vanishing model casting method in which the casting time can be set accurately and with high accuracy.

  The vanishing model casting method of the present invention is a vanishing model casting method in which a molten metal is poured into a mold in which a model made of a resinous foam is embedded in foundry sand, and the product is cast while the model is eliminated by the molten metal. The casting time during casting is set according to the modulus of the model (volume of the model ÷ surface area of the model).

  According to the present invention, by setting the casting time during casting according to the modulus of the model, the casting time in the disappearance model casting method can be set accurately and with high precision.

ｔ：鋳込み時間（ｓ）
Ｗ：鋳込み重量（ｋｇ）
Ａ’：湯口面積（ｃｍ^２）
ρ：溶湯密度（ｇ／ｃｍ^−３）
ａ，ｂ：定数
ｍ：モジュラス（模型の体積÷模型の表面積）
ｇ：重力加速度
Ｈ’：湯口から模型上端までの高さ（ｃｍ） In the present invention, the casting time is calculated by the following formula (1).

t: Casting time (s)
W: Casting weight (kg)
A ': Gate area (cm ² )
ρ: Molten metal density (g / cm ⁻³ )
a, b: constant m: modulus (model volume / model surface area)
g: Gravitational acceleration H ': Height from the gate to the top of the model (cm)

  Further, the present invention is characterized in that the casting time calculated from the formula (1) is compared with the casting time at the time of actual casting, and the presence or absence of a casting defect is determined based on the difference between the two.

  Furthermore, the present invention is characterized in that a casting simulation is performed based on the casting time calculated from the formula (1).

  According to the present invention, by setting the casting time at the time of casting according to the modulus of the model, the casting time in the disappearance model casting method can be set accurately and with high accuracy, and a cast product with excellent quality can be obtained. There is an effect that it can be obtained.

It is sectional drawing of the casting_mold | template which showed the vanishing model casting method of this invention notionally. It is a conceptual diagram explaining the mechanism by which casting time changes with the size of the modulus of a model, Comprising: The casting model with a comparatively small modulus is shown. It is a conceptual diagram explaining the mechanism by which casting time changes with the size of the modulus of a model, Comprising: The casting model with a comparatively large modulus is shown. The graph which shows the relationship between C '(constant) required when calculating casting time in an Example, and the modulus of a model. It is a graph which shows the casting time calculated according to the modulus of the model in an Example.

Embodiments according to the present invention will be described below with reference to the drawings.
FIG. 1 shows a cross section of a mold 1 conceptually showing a vanishing model casting method according to an embodiment. The mold 1 is configured by burying a model 3 in foundry sand 2 filled in a casting frame (not shown).

  A gate 4 connected to the model and a runner 5 connected to the gate 4 are formed around the model 3 in the foundry sand 2. The runner 5 is provided with a plurality of openings (two in FIG. 1) to the upper surface of the mold 1, and a gate 6 is provided in one (right side in FIG. 1). Further, the runner 5 on the other opening side is particularly a gas vent passage 7, and a filter 8 for releasing only the combustion gas to the atmosphere outside the mold 1 is provided in the gas vent passage 7.

  The mold 1 is manufactured according to the following procedure. First, a mold-forming agent having graphite as a main component and having excellent fire resistance is applied to the surface of the model 3 and sufficiently dried. On the other hand, the runner 5 (including the gas vent passage 7) 5 and the gate 4 are formed in the cast frame by a method such as assembling a paper tube, and the model 3 is arranged and supported at a substantially central portion in the cast frame. At this stage, a filter 8 is also disposed in the gas vent passage 7. Thereafter, the casting sand 2 is filled in the casting frame, the model 3 is buried, and the gate 6 is installed.

  As the foundry sand 2, new sand or old sand such as zircon sand, chromite sand, and synthetic ceramic sand is used in addition to quartz sand mainly composed of quartz. A binder and a curing agent are added to the foundry sand 2 as necessary.

  The runner 5 and the gate 4 are formed with commercially available products having a diameter of 30 to 70 mm (for example, Kao's quaker casting runner pipes: EG runners CF-30S, CF-50S, CF-70S, etc., the main component is recycled pulp. ) Etc. are used. The filter 8 is made of a porous material or the like formed by mixing an appropriate binder with sand equivalent to No. 2 silica sand and having a thickness of about 40 mm. The height H from the gate surface to the gate 6 as the upper surface of the model 3 is preferably 700 mm, and the head pressure in this case is about 0.044 MPa.

The model 3 is obtained by hand-molding a synthetic resin foam such as expanded polystyrene into a desired shape. As the coating agent, for example, Kao Quaker PC260 manufactured by Kao Corporation is used, and is applied to the surface of the model with a thickness of 1.5 to 3.5 mm and an air permeability of about 10 mm ² .

  Thus, the mold 1 is manufactured. According to this mold 1, when molten metal (molten metal material) is poured from the gate 6, the molten metal reaches the model 3 through the runner 5 and the gate 4, and the model 3 disappears by being melted with the molten metal. The molten space is filled in the disappearing space. That is, the model 3 is replaced with molten metal. A large amount of combustion gas is generated at the initial stage of pouring in which the model 3 burns, and the combustion gas is discharged to the atmosphere through the filter 8 in the gas vent passage 7 at the most downstream side of the runner 5. A part of the combustion gas passes through a coating film formed by applying a coating agent to the surface of the model 3, and further passes through the foundry sand 2 and is discharged to the atmosphere.

  In the present invention, based on the fact that the casting time becomes longer as the modulus of the model (model volume / model surface area) increases, the following old casting time formula (2) and past castings From the data, a formula (1) of the casting time considering the modulus was created. (Formula (2) is published by Maruzen Co., Ltd. edited by Japan Foundry Association, revised 4 edition casting manual: described on page 85)

ｔ：鋳込み時間（ｓ）
Ｗ：鋳込み重量（ｋｇ）
Ａ’：湯口面積（ｃｍ^２）
ρ：溶湯密度（ｇ／ｃｍ^−３）
ａ，ｂ：定数
ｍ：モジュラス（模型の体積÷模型の表面積）
ｇ：重力加速度
Ｈ’：湯口から模型上端までの高さ（ｃｍ）

t: Casting time (s)
W: Casting weight (kg)
A ': Gate area (cm ² )
ρ: Molten metal density (g / cm ⁻³ )
a, b: constant m: modulus (model volume / model surface area)
g: Gravitational acceleration H ': Height from the gate to the top of the model (cm)

ｃ：流量係数
Ａ：鋳物に対するゲート開口（せき）の断面積（ｃｍ^２）
Ｈ：有効水頭

c: Flow coefficient A: Cross-sectional area (cm ² ) of gate opening (cough) with respect to casting
H: Effective head

  Here, the conventional equation (2) is effective when the gate area is smaller than the gate area, but in the disappearance model casting method, a large amount of gas is generated when the model burns in the mold. It is necessary to vent the gas from the gate by making the gate area larger than the gate area. Therefore, in the conventional formula (2), the casting time uses the cross-sectional area of the gate opening as a parameter. In the present invention, the casting time is replaced with the gate area.

  Here, the mechanism that the casting time becomes longer as the modulus increases will be described with reference to FIGS. These drawings schematically show the casting model. When the model of the casting model 1 in FIG. 2 has a surface area S, a volume V, and a wall thickness w, the model of the casting model 2 in FIG. 3 becomes the model in FIG. In contrast, the volume is the same and the wall thickness is doubled, thus the surface area is halved.

The amount of combustion gas passing through the coating agent applied to the model surface per unit time and the modulus per unit time will be compared. Since the amount of coating agent passing gas per unit time is proportional to the surface area of the coating mold, the ratio of coating agent passing gas amount per unit time is
Model 1: Model 2 = a · S: aS / 2 (a is a constant)
= 2: 1 (3)
It becomes.

On the other hand, because the modulus is the ratio of volume / surface area,
Modulus ratio Model 1: Model 2 = V / S: 2V / S
= 1: 2 (4)
It becomes.

  From the above formulas (3) and (4), it can be seen that when the modulus is doubled, the amount of the coating agent passing gas per unit time is halved. That is, as the modulus increases, the amount of combustion gas per unit volume increases and the internal pressure of the mold increases. It is considered that the casting time becomes longer as the internal pressure of the mold becomes higher. Therefore, when calculating the casting time in the disappearance model casting method, it is necessary to consider the modulus of the model.

  By calculating the casting time in the disappearance model casting method as described above, the following additional casting matters can be implemented.

-Early casting defect determination By comparing the actual casting time t1 (seconds) with the casting time t2 (seconds) calculated by the calculation method according to the present invention, the casting defect determination can be made earlier. . The relationship between t1 and t2 and the type of casting defect are determined as follows, for example. The constant σ is defined by 3σ≈6 in the present invention.

t1> t2 + 3σ: Poor water runoff, residue defect (undissolved model)
t1 <t2-3σ: Insufficient casting amount, coating bite That is, if there is a significant difference between the actual casting time and the calculated casting time, it is determined that some casting defect has occurred in the product. be able to. Thus, if it is determined that a casting defect has occurred, there is a production advantage in that the time loss of the cooling time can be shortened by blowing again immediately before crushing the mold.

-Casting time parameter for melt flow analysis By using the casting time calculated by the calculation method according to the present invention for calculation for melt flow analysis, the melt filling temperature, final filling site, etc. can be simulated with high accuracy. Therefore, the reliability of the simulation result can be increased.

  A coating agent (60-65 Baume) was applied to the surface of a model molded from expanded polystyrene having an outer dimension of 750 × 800 × 430 (mm) and a modulus of 2.15, and then dried, as shown in FIG. A mold was formed with the same structure as that of the mold, and casting was performed. The casting material was FC300 (flaky graphite cast iron), the temperature of the molten metal during pouring (casting temperature) was 1380 ° C., and the cast weight was 1.2 tons (cast sample 1 in Table 1). In the same manner, casting samples 1 to 6 shown in Table 1 were obtained by performing casting in which the casting weight was 1 to 13 tons and the modulus of the model was changed in the range of 1.9 to 2.5. Table 1 shows the casting conditions and the calculated casting time.

Here, the calculation formula leading to the above formula (1) will be described.
From the above equation (2), the following equation (5) is obtained. Formula (5) is the casting time when the modulus is not considered.

  Substituting the casting conditions in Table 1 into equation (5), the respective constants C ′ are obtained. Table 2 shows the calculation results.

Next, C ′ and the modulus of the model are graphed (FIG. 4), and the following approximate expression (6) is obtained.
(Here, the constants a and b are a = 0.0012 and b = 1.9995)
C = 0.0012m ^-1.0955 (6)
Substituting approximate expression (6) into expression (5) yields expression (1).
Then, when the modulus value m = 1.8, 2.0, 2.2, 2.4 is substituted into the equation (1), the graph shown in FIG. 5 is obtained.

  In FIG. 5, the actual measured value of the casting time in the casting samples 1-6 shown in Table 1 is shown. In addition, the case where W / A ′ is common to casting samples Nos. 5 and 6 and the casting time is set only by the above formula (2) without considering the modulus is shown (indicated by ×). When this modulus is not considered and the present invention is compared, when the modulus is not considered, the casting time is 18 seconds later than the present invention, and the final filling temperature is about 20 ° C. lower. Therefore, according to the present invention, it has been found that the casting time can be set to an appropriate time, and at the same time, a casting of good quality can be reliably obtained.

DESCRIPTION OF SYMBOLS 1 ... Mold 2 ... Foundry sand 3 ... Model 4 ... Gate 5 ... Runway 6 ... Spout 7 ... Degassing passage 8 ... Filter

Claims (4)

In the disappearance model casting method in which a molten metal is poured into a mold in which a model made of a resinous foam is embedded in foundry sand, and the product is cast while the model is lost by the molten metal,
A vanishing model casting method characterized in that a casting time during casting is set according to the modulus of the model (volume of the model ÷ surface area of the model). The disappearance model casting method according to claim 1, wherein the casting time is calculated by the following formula (1).

t: Casting time (s)
W: Casting weight (kg)
A ': Gate area (cm ² )
ρ: Molten metal density (g / cm ⁻³ )
a, b: constant m: modulus (model volume / model surface area)
g: Gravitational acceleration H ': Height from the gate to the top of the model (cm)   3. The disappearance model according to claim 2, wherein the casting time calculated from the formula (1) is compared with the casting time during actual casting, and the presence or absence of casting defects is determined based on the difference between the casting times. Casting method.   The vanishing model casting method according to claim 2, wherein a casting simulation is performed based on a casting time calculated from the equation (1).

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