JP3325266B2 - Vanishing model casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting method for a vanishing model, and more particularly to a vanishing model casting method in which a gas generated from the vanishing model is gradually released from a mold through a discharge passage.

[0002]

2. Description of the Related Art The vanishing model casting method is also referred to as a full mold method. Generally, a vanishing model made of polystyrene foam or the like is buried in a sand mold, and molten metal is poured to remove the vanishing model by the heat of the hot water. This is a casting method in which a casting is formed by filling a gap with a molten metal while vaporizing and disappearing, and is widely used particularly for manufacturing a press die.

[0003] The vanishing model casting method has many advantages, such as casting into an accurate shape. However, on the other hand, casting defects occur due to poor gas vent adjustment, the model strength is low, and deformation tends to occur. However, there is a drawback that strong sand filling cannot be performed, the packing density is insufficient, the mold strength is insufficient, and seizure is caused.

As a technique relating to gas venting, Japanese Patent Application Laid-Open No. 5-261470 discloses a method in which a ventilation path communicating with an exhaust port is provided inside a vanishing model.
Japanese Patent Application Laid-Open No. 11-90583 discloses a method for forcibly discharging generated gas to the outside through molding sand while suctioning an external gas. A possible full mold casting method is disclosed.

[0005]

However, Japanese Patent Laid-Open Publication No.
No. 61470, JP-A-8-206777, and JP-A-11-90583, a method for more efficiently discharging a gas generated from a disappearing model to the outside of a mold to obtain a cast product with few defects. In this case, since the discharge speed of the combustion gas is too high, the pressure distribution of the gas layer generated in the mold becomes large, and the molten metal blows up along the ventilation path. As a result, the turbulence of the molten metal in the mold becomes large, and the residue and generated gas may be involved in the molten metal, which may promote the generation of defects.

[0006] It is an object of the present invention to provide an improved vanishing model casting method in which a high quality casting with few residual defects can be obtained by adjusting the pressure distribution of a gas layer in a mold.

[0007]

SUMMARY OF THE INVENTION The present invention is directed to a method of pouring a mold in which a model having a through-hole formed in a casting sand is buried, and removing the model by pouring the model with the hot water. The present invention relates to a vanishing model casting method for casting, in which a gas generated by the disappearance of the model is gradually released to the outside of the mold through a discharge passage provided with an exhaust gas suppressing means, and casting is performed. Further, the present invention is directed to pouring a mold in which a model having a through hole formed in casting sand is buried and casting a product while erasing the model with the poured hot water. The present invention relates to a method for preventing hot water turbulence in a vanishing model casting method, wherein casting is performed while slowly releasing gas generated by the disappearance of gas through a discharge passage provided with a discharged gas suppressing means to the outside of the mold.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A vanishing model casting method of the present invention will be described with reference to FIG. The casting mold includes a casting flask 4, casting sand 7 inside the casting flask 4, a model 1 buried in the casting sand 7, and the like, and a gate 5 communicating with the model 1 is provided at the upper left side. Model 1
Is formed in the same shape as the product by using expanded polystyrene, and a through hole 2 is provided. Foundry sand 7
No. 5.5 silica sand, containing an appropriate amount of binder. To form the mold, first, a coating agent 3 having excellent fire resistance is applied to the surface of the model 1 and then sufficiently dried. After the runner 6 is formed in the flask 4, the model 1 is fixed, buried with the casting sand 7, and the gate 5 is installed. At that time, the inside of the through-hole 2 is made to be a space, and a discharge pipe communicating with the through-hole 2 is provided to form a discharge passage 8. The discharge pipe serving as the discharge passage 8 is made of ceramic.
As an exhaust gas suppressing means, refractory particles 9 such as alumina molded with a binder are filled and buried in molding sand 7 so as to make the through hole 2 communicate with the atmosphere.

When the molten metal is poured from the gate 5, the molten metal melts the model 1 and accumulates in the mold. On the other hand, from the discharge passage 8,
It is confirmed that the gas of the model 1 melted and burned by the hot water is discharged, but since the refractory particles are filled,
The gas is released slowly.

As described above, in the present invention, the gas generated by burning and disappearing of the model (hereinafter referred to as generated gas) is gradually released to the outside of the mold. Here, the term "controlled release" means that the generated gas is not forcibly discharged almost simultaneously with its generation, but is discharged while suppressing the discharge amount. By releasing the generated gas to the outside of the mold in this manner, the turbulence of the molten metal in the mold can be controlled. Further, the exhaust gas suppressing means is a means having air permeability that can achieve the sustained release by providing the means, refractory particles and a layer thereof, a back pressure valve,
For example, a refractory particle and its layer and a back pressure valve are more preferable from the viewpoint of prevention of molten metal blowing and casting quality.

In the present invention, the first pressure loss (calculated value) of the gas passing through the discharge passage is 0.05 to 5000 g.
/ Cm ² , more preferably 0.1
To 1000 g / cm ² , more preferably 0.5 to
100 g / cm ² , particularly preferably 1 to 50 g / cm ²
cm ² . Here, the pressure loss is a pressure difference before and after the exhaust gas suppressing means (upstream and downstream of the gas flow path), and the pressure on the exhaust side of the exhaust passage may be any, but is preferably atmospheric pressure. The first pressure loss (calculated value) is obtained by calculation in accordance with the following procedure. First, as shown in FIG.
(Range / min) is varied to obtain respective pressures when the pressurized air is circulated, and a calibration curve is created based on the pressures.
The first pressure loss (calculated value) is obtained by calculating the gas generation amount per unit time (L / min) from the casting time and the gas generation amount V which is expected, and linearly approximating the calibration curve to the gas flow rate.
Is found. Here, "casting and forging and heat treatment" (August 1995
According to FIG. 3 on page 27 of the Monthly Publication, the amount of pyrolysis gas generated at 1000 ° C. was 650 cm ³ /
g, polymethyl methacrylate: 980 cm ³ / g. When a material other than these is used, V is obtained by measurement. This first pressure loss (calculated value) has an advantage that an experiment is easy and can be easily obtained.

In the present invention, the second pressure loss (actually measured value) of the gas passing through the discharge passage is 0.5 to 500.
0 g / cm ² , more preferably 5 g / cm ^2.
To 1000 g / cm ² , particularly preferably 10 to 5 g / cm ^2.
00 g / cm ² . This second pressure loss (actual value)
Is the maximum value when the pressure change on the inlet side of the exhaust gas suppressing means is measured by a pressure gauge (gauge pressure). The second pressure loss (actually measured value) is more difficult to experiment than the first pressure loss, but has the advantage of higher correlation with casting quality.

Further, when the exhaust gas suppressing means is constituted by refractory filling, that is, when the exhaust gas suppressing means comprises a refractory layer, the exhaust gas suppressing means has a first air permeability (outside the calibration curve). 0.5 to 2)
000, more preferably 5 to 1000, particularly preferably 50 to 800. The air permeability is measured according to JACT test method M-1 "air permeability test method". In this test method, the air permeability is calculated by (V × h) / (P × A × t). In the present invention, V is the amount of generated pyrolysis gas (cm ³ ) calculated from the above-mentioned extrapolation of the calibration curve, h is the filling thickness of the refractory or the like (cm), and P is the first of the discharged gas in the discharge passage. Pressure loss (calculated value) (g / cm ² ), A is the cross-sectional area of the discharge passage (cm ² ), and t is the casting time (second).

Further, in the present invention, the second air permeability (calculated value at an air flow rate of 2 L / min) is 100 to 10,000,000,0.
00, even 200-1,000,000, especially 250-
It is preferable to use emission gas suppression means of 500,000, especially 300 to 100,000. The second air permeability is the air permeability when the air flow rate is 2 L (2000 ml) / min, and is determined by 2000 × h / (P × A).

As the breathable refractory layer, a refractory particle formed by adding a binder or the like to a refractory particle, or a so-called ceramic foam filter obtained by immersing a ceramic slurry in urethane foam and then firing the same is used. And the former is preferred. The average particle size of the refractory particles is preferably 0.1 to 10 mm, more preferably 0.5 to 5 mm, and examples thereof include metal or oxide particles thereof, such as alumina, silica sand, zircon sand, chromite sand, and synthetic ceramic sand. The refractory has a thickness of 0.5 to 20 cm, further 1 to 10 cm, depending on the area and shape of the discharge passage.
It is preferable that the filler be filled in such an amount that:

The back pressure valve is a valve that can set the pressure in the gas flow direction lower on the rear side (downstream of the gas flow path) than on the front side (upstream of the gas flow path) of the valve. Any of a spring type low pressure valve, a needle type and the like may be used, and the exhaust gas suppressing means is formed by installing them in the exhaust passage.

The diameter, installation position, number, etc. of the discharge pipes serving as the discharge passages are determined by the shape and size of the model. The discharge passage is preferably formed by a cylindrical, preferably ceramic, exhaust pipe having a diameter of 30 cm or less, preferably 1 to 10 cm. The number may be appropriately determined so as to ensure a desired air permeability.
It is preferable to provide one wire per 10,000 cm ³ , preferably 1,000 to 10,000 cm ³ .

When the hollow thin tube is used as the exhaust gas suppressing means, the thin tube may be installed so as to be in contact with the model. The hollow capillary can also serve as a discharge passage. The hollow capillary is
It is preferable that the inner diameter is 0.1 to 5 cm and the length is 30 cm to 5 m, more preferably the inner diameter is 0.5 to 2 cm and the length is 40 cm to 2 m.

A model made of a synthetic resin foam is used. As the synthetic resin foam, a foam such as polystyrene, polymethyl methacrylate, or a copolymer thereof is used.

A through hole is formed in the model. In particular, as shown in FIG. 1, it is preferable to form a discharge passage 8 provided with a discharge gas suppressing means and a through hole communicating with the runner 6. In order to accurately control the sustained release of the pyrolysis gas, it is necessary to intensively guide the gas to the exhaust gas suppressing means. Therefore, it is preferable to form a through hole communicating with the discharge passage and the runner in the model. The through-hole may be formed at the time of model production, or after the model production, may be formed by a heated metal rod or the like, or a drill or a laser, or may be cut with a cutter knife or the like, and then an adhesive tape or the like may be formed. It may be formed by sticking to the model surface.
The diameter, formation position, number, and the like of the through holes are determined according to the shape and size of the model.

A coating layer is formed on the model by a coating agent. In the present invention, since there is little need to discharge gas through the coating film, as the coating agent, besides commercially available ones, the particle size is 10 μm or less, preferably 1 to 1, which cannot be conventionally used in the conventional full mold method. What contains a refractory aggregate having a fine particle size of 10 μm can also be used.
Thereby, the surface smoothness of the coating film is improved, and the surface smoothness of the casting is also improved. Conventionally, when a coating agent containing a refractory aggregate having a small particle size was used in the vanishing model casting method, the air permeability of the coating film was reduced, and residue defects and gas defects were increased. Such a problem is solved by the vanishing model casting method of the present invention. In addition, by forming a coating layer having a thickness of 2 to 10 mm to form a high-strength coating layer, refractory particles having a large particle diameter (1 mm or more) can be used to improve the filling property. Examples of the refractory aggregate in the coating composition include graphite, zircon, magnesia, alumina, silica and the like. In addition, as a binder for the coating composition, in the aqueous system, water-soluble polymers such as sodium polyacrylate, starch, methyl cellulose, polyvinyl alcohol, sodium alginate, gum arabic, and emulsions of various resins such as vinyl acetate,
In the case of alcohols, it is preferable to add various resins that are soluble or dispersed in alcohol from the viewpoint of coating strength.
The addition amount is preferably 0.5 to 10 parts by weight based on 100 parts by weight of the refractory aggregate.

As the foundry sand used for casting, in addition to silica sand containing quartz as a main component, new sand such as zircon sand, chromite sand, and synthetic ceramic sand or recycled sand is used. Foundry sand can be used without adding a binder, in which case the filling property is good, but if strength is required, it is better to add a binder and cure with a curing agent. preferable.

In the method of the present invention, the generated gas is gradually released to the outside, so that casting can be performed while suppressing turbulence during pouring. This is because the back pressure appropriate for pouring, preferably the back pressure enough to achieve the first and second pressure losses, is reduced by using the exhaust gas suppressing means having the first and second air permeability. This is considered to prevent the occurrence of turbulence (such as blow-back of the molten metal during casting) and quick pouring.

[0024]

According to the present invention, since the generated gas is gradually released without being forcibly discharged, the pressure distribution of the gas layer in the mold is reduced, and residue defects are dramatically reduced as compared with the conventional method. Reduced.

As a further effect, the gas discharge property is controlled as compared with the conventional full mold method, so that blow-back during casting and blow-up of molten metal from the gas discharge port are suppressed, and work safety is improved. Is improved.

Further, unlike the conventional full molding method, since there is little need to discharge gas through the coating film, the surface smoothness of the casting is reduced by using a coating agent containing a refractory aggregate having a small particle diameter. The strength of the coating film can be increased by improving the thickness or forming a thick coating layer.

[0027]

EXAMPLE 1 A metal rod having a diameter of 3 mm was heated on a foam model 1 (made of expanded polystyrene) having a size of 120 mm × 80 mm × 250 mmH.
The through holes 2 were formed as shown in FIG. The diameter of the through hole 2 was about 4 mm.

A cylindrical ceramic tube having an inner diameter of 4 cm (length 30 c)
m), a spherical alumina 9 having a diameter of 2 mm containing an ester-curable phenol resin was filled so as to have a thickness (h) of 2.5 cm and cured to form a discharge passage 8.

With respect to the discharge passage 8, the pressure loss P
The measurement was performed as shown in FIG. As a result, the air ventilation speed 1 L /
Min, P = 0.02 g / cm ² , P = 0.08 g / cm ^{2 at} an air flow rate of 3 L / min, and P = 0.15 g / cm ² at an air flow rate of 5 L / min. In this embodiment, since the casting time (t) is set to 10 seconds, the gas discharge per unit time is about 172 L / min. Therefore 172L /
The first pressure loss P in minutes is 6 g / cm ² .

The weight of the foam model 1 of this embodiment is 44
g from the above-mentioned literature values of the amount of pyrolysis gas generated at 1000 ° C. for polystyrene, the pyrolysis gas generation amount V of this foam model was 28,600 cm ³ , and the gas discharge amount was 28.6 L / 10 sec ≒ 172 L. / Min.

From the above, in this embodiment, V = 28600
cm ³ , h = 2.5 cm, P = 6 g / cm ² , A = 12.
6 cm ² (3.14 × 2 × 2), t = 10 seconds, and the first air permeability of the spherical alumina packed layer as the exhaust gas suppressing means is (V × h) / (P × A × t) = (28600x
2.5) / (6 × 12.6 × 10) = 95.

The pressure loss at an air flow rate of 2 L / min is 0.05 g / cm ² , whereby the second air permeability is (2000 × 2.5) / (0.05 × 1
2.6) = 7937.

On the surface of the model 1 in which the through holes are formed,
(80 Baume) was applied and dried, followed by molding according to FIG. Cast iron material is FC-250, casting temperature is 140
It was 0 ° C. The condition at the time of casting and the quality of the obtained casting (the state of the casting surface) were evaluated.

At the time of casting, a pressure change on the inlet side of the discharge passage 8 provided with the spherical alumina packed layer 9 as a discharge gas suppressing means was measured by a pressure gauge (gauge pressure) to obtain a second pressure loss.

The evaluation results and the casting time, the first pressure loss (calculated value), the second pressure loss (actually measured value), and the first air permeability of the exhaust gas suppressing means (calculation from the extrapolated gas flow rate of the calibration curve) Table 1 shows the second air permeability (calculated value at an air flow rate of 2 L / min). The composition of the mold wash was 40% by weight of silica powder (average particle size: 8 μm), 10% by weight of flaky graphite,
The content was 5% by weight of a vinyl acetate binder, 40% by weight of water, 0.5% by weight of a nonionic surfactant, and 4.5% by weight of bentonite.

Examples 2 to 4 Casting was carried out in the same manner as in Example 1 except that the casting time, pressure loss and air permeability of the exhaust gas suppressing means were changed as shown in Table 1, and the same evaluation was performed. Table 1 shows the results.

In Example 2, spherical alumina having a diameter of 0.5 mm was filled to a thickness of 2 cm. Pressure loss P in the discharge passage, air aeration rate 1L / in min P = 0.47 g / cm ^2, the air aeration rate 3L / min P = 1.41 g / cm ^2, P is an air aeration rate of 5L / min
= 2.36 g / cm ² .

In Example 3, spherical alumina having a diameter of 5 mm was filled to a thickness of 2 cm. The pressure loss P in the discharge passage is P at an air ventilation rate of 1 L / min.
= 0.0033g / cm ^2, air aeration rate 3L / in min P = 0.0099g / cm ^2, the air aeration rate 5L / min was P = 0.0165g / cm ^2.

In Example 4, spherical alumina having a diameter of 0.1 mm was filled to a thickness of 2.5 cm. The pressure loss P in the discharge passage is 1 L /
The min P = 1.36g / cm ^2, air aeration rate 3L / in min P = 1.72g / cm ^2, the air aeration rate 5L / min was P = 2.22g / cm ^2.

Embodiment 5 The inner diameter is 8.8 mm and the length is 600 m as exhaust gas suppressing means.
Casting was carried out in the same manner as in Example 1 except that a stainless steel thin tube of m was used and no discharge passage was provided (the thin tube also served as the discharge passage), and the same evaluation was performed. The capillary was placed so as to communicate with the through hole of the model. The pressure loss P in this discharge passage is P = 0.02 g at an air ventilation speed of 1 L / min.
/ Cm ² , P = 0.09 g / at an air flow rate of 3 L / min.
cm ² , P = 0.16 g / c at an air flow rate of 5 L / min.
m ² . Table 1 shows the results.

Comparative Example 1 Casting was performed in the same manner as in Example 1 except that the discharge passage 8 was not provided, and the same evaluation was performed. Table 1 shows the results.

Comparative Example 2 The procedure of Example 1 was repeated except that the discharge passage was not filled with alumina balls, and the same evaluation was performed.
Table 1 shows the results.

Comparative Example 3 Casting was performed in the same manner as in Example 1 except that a model having no through hole was used, and the same evaluation was performed.
Table 1 shows the results.

[0044]

[Table 1]

(Note 1): In Example 5 and Comparative Example 2, since the alumina balls were not filled, the filling thickness could not be specified, and the air permeability could not be obtained.

(Note 2): No numerical value because exhaust gas suppression means is not used. Comparative Example 1 can be regarded as equivalent to a system in which exhaust gas suppressing means having an extremely large pressure loss is installed.

(Note 3): No numerical value because no exhaust gas suppression means was used. Comparative Example 1 can be considered to be equivalent to a system in which exhaust gas suppression means having an extremely low air permeability is installed.

(Note 4): The calculation could not be performed because the amount of pyrolysis gas passing through the exhaust gas suppressing means could not be grasped.

(Note 5): ◎ is the best overall evaluation, and means that the evaluation decreases in the order of ○, Δ, × below. X is a practically problematic level.

In Table 1, the casting quality is slightly deteriorated in Example 5 in which the same pressure loss as in Example 1 occurs. The reason for this is that in Example 5, a thin tube is used. It is considered that there is a difference in the flow rate of the exhaust gas between the center and the wall surface, and this is affecting.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a vanishing model casting method of the present invention.

FIG. 2 is a schematic diagram showing a method of measuring airflow resistance.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Model 2 Through-hole 8 Exhaust passage 9 Refractory particles

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Takeshi Narishima 2606 Kabane-cho, Akaga-cho, Haga-gun, Tochigi Prefecture Inside Kao Co., Ltd. (72) Inventor, etc. 56) References JP-A-8-206777 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22C 1/00-9/30

Claims (10)

(57) [Claims] 1. A vanishing model casting method in which a mold having a through hole formed in casting sand is poured into a mold in which the model is buried, and a product is cast while the model is lost by the poured hot water. A vanishing model casting method in which the gas generated by the disappearance of the model is cast while being gradually released to the outside of the mold through a discharge passage provided with a gas emission suppressing means. 2. The vanishing model casting method according to claim 1, wherein the first pressure loss (calculated value) of the gas passing through the discharge passage is 0.05 to 5000 g / cm ² . 3. The vanishing model casting method according to claim 1, wherein the second pressure loss (actually measured value) of the gas passing through the discharge passage is 0.5 to 5000 g / cm ² . 4. The vanishing model casting according to any one of claims 1 to 3, wherein the first air permeability (calculated from the calibration curve extrapolated gas flow rate) of the exhaust gas suppressing means is 0.5 to 2,000. Law. 5. The second air permeability (calculated value at an air flow rate of 2 L / min) of the exhaust gas suppressing means is 100 to 10,000.
The vanishing model casting method according to any one of claims 1 to 4, wherein the quenching method is 0.000. 6. The vanishing model casting method according to claim 1, wherein the exhaust gas suppressing means comprises refractory particles. 7. The vanishing model casting method according to claim 1, wherein the exhaust gas suppressing means comprises a back pressure valve. 8. The vanishing model casting method according to claim 1, wherein a model coated with a mold wash containing a refractory aggregate having a particle size of 10 μm or less is used. 9. The casting is carried out by releasing the generated gas to the outside so as to suppress turbulence during pouring.
8. The vanishing model casting method according to any one of 8 above. 10. When pouring a mold in which a through-hole is formed in a casting sand into a mold in which the model is buried, and casting the product while erasing the model with the poured hot water, A method for preventing hot water turbulence in a vanishing model casting method, wherein casting is performed while gas generated by disappearance is gradually released to the outside of the mold via a discharge passage provided with a discharge gas suppressing means.