JP2002254135A - Mold manufacturing method for casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mold manufacturing method for casting capable of improving strength at high temperature in which molten metal can be cast while maintaining heating temperature or also improving operability of mold- disassembly by increasing a breaking-down property of the mold after casting, and further facilitating control of a caking agent, and furthermore easily adjusting bonding strength of the impregnated caking agent, when casting a thin-walled exhausting system parts, which are made of heat-resistant cast steel such as austenite heat-resistant cast steel and the like, having 2 to 3 mm of thickness in major portions. SOLUTION: After forming a mold in a desired shape by caking binder containing metal of the I group of the periodic table at 4 to 25 weight % in molding sand, an inorganic caking agent including SiO2 /Na2 O with 3 and over of mole ratio is impregnated and increased in temperature, and then, molten metal is cast. Further, the inorganic caking agent is a silicate solution or colloidal silica.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting mold, and more particularly, to a method of manufacturing a casting mold in which an inorganic binder is impregnated, heated and molten metal is cast.

[0002]

2. Description of the Related Art Casting molds into which a molten metal is cast (hereinafter, "casting molds" are simply referred to as "molds") include shell molds, cold box molds, etc., which are formed using an organic binder. There is. In a cavity formed in these molds, molten metal such as cast steel is heated at a temperature of about 1500 ° C. to 16 ° C.
When casting is performed at a high temperature of 00 ° C., organic substances contained in the organic binder are burned to generate decomposition gas, and gas defects are liable to occur in the cast casting. In addition, since it is difficult to preheat the mold itself to a high temperature in a mold molded using an organic binder, if the molten metal is cast into a mold having a cavity in which narrow portions are continuous, the molten metal is cast during casting. Some of them may harden and cause poor running. For this reason, it was difficult to cast a thin product. This is considered to avoid the above-mentioned problem by using an inorganic binder having high heat resistance, but it is difficult to mold the inorganic binder because the binding strength is weak. However, when the molten metal is cast, there is a problem that the mold in a portion in contact with the molten metal is sintered and the strength is partially increased, and the disintegration of the cast after casting is deteriorated.

In order to solve this problem, Japanese Patent Laid-Open No. Hei 3-2487 discloses a method.
No. 40 discloses that molding sand is made by adding an organic binder to molding sand.
Add impurities to colloidal silica or add water
Add colloidal silica to the glass_Two/ Na_TwoO
Impregnated with an inorganic binder having a molar ratio of 4.5 to 6.0
After drying at low temperature or microwave drying under reduced pressure,
Burn organic matter with and maintain mold shape with inorganic binder
There is a description of a mold making method. The publication also states that inorganic
A surfactant is added to the binder and impregnation is performed under reduced pressure.
No, adjust the thickness of the impregnated layer by pressure and impregnation time
There is. The publication also states that colloidal silica is SiO
_TwoExtremely high bending strength at room temperature due to extremely high content
Low and cannot be used as a mold,
(SiO _Two/ Na_TwoO mole ratio of about 4.3) or sodium silicate
(About 2.4 to 3.3), the transverse rupture strength becomes too high and collapses
There is also a statement that there is a problem with gender. And Japanese Patent Laid-Open No. 3-2
According to Japanese Patent No. 48740, the obtained mold is at room temperature.
With sufficient strength and no seizure, molten metal injection
Good sand removal after use
Generation of gas from the mold,
Mold production with good productivity.
Reduce drying time by performing microwave drying
It can also be done.

Further, Japanese Patent Application Laid-Open No. 7-232967 discloses that (a) a step of forming a molded body using an aggregate and a first binder; and (b) a group 4A or 4B group of the periodic table. Excluding) a metal alkoxide of Group 3A or 3B and one or more metal alkoxides selected from partial hydrolysates thereof, and an alcohol solution containing an alkali compound of an alkali metal or an alkaline earth metal. (C) impregnating and hydrolyzing the molded article body formed by the step (a) with the binder of step (a); (c) drying the molded article body and firing it at a high temperature; There is a description. And Japanese Patent Laid-Open No. 7-2329
According to Japanese Patent Publication No. 67, since the second binder is an alcohol solution, it is easy to penetrate into the molded article body,
It is efficiently impregnated from the surface to the inside, and can increase the mold strength from low to high temperatures. When the core is formed, since gas generation from the core during casting is small, it can be used as it is for green mold casting, die casting or die casting, and the second core described above is used for the core. This makes it possible to impregnate the binder. In addition, since the strength inside the mold has not increased, the disintegration after casting is good and the workability of mold release is good, and pouring into a high-temperature mold immediately after firing the mold improves the run-around, and the product It is said that it becomes possible to cast thin products such as stainless cast steel.

[0005]

In recent years, exhaust system components such as an exhaust manifold, a supercharger housing, and a diffuser have been used in austenitic heat-resistant systems to ensure durability when exposed to exhaust gas exceeding 1000 ° C. Heat-resistant cast steel such as cast steel, and in order to secure the initial function of the exhaust gas purifying catalyst at the time of starting the engine, it is required that the thickness of the main part be reduced to 2-3 mm in order to reduce the heat capacity. . To this end, it is said that the molten metal is preferably cast at a high temperature of about 1500 to 1600 ° C. in a mold maintained at a high temperature.

[0006] However, the above-mentioned Japanese Patent Application Laid-Open No. Hei 3-2487.
In the mold described in Japanese Patent No. 40, if the molten metal is cast at about 1500 to 1600 ° C. while maintaining the high temperature after firing the mold, the cast may not be able to cast due to insufficient high-temperature strength of the mold. If it does, it cannot be collapsed after the molten metal is poured, and the casting after casting may be liable to be sanded. Also,
It is substantially difficult to control the thickness of the impregnated layer of the binder by controlling the impregnation time.

On the other hand, in the mold described in Japanese Patent Application Laid-Open No. 7-232967, since the second binder is an alcohol solution, the second binder excessively permeates into the molded article body, resulting in poor disintegration after pouring. . In addition, since an organic material having some toxicity is used in the raw materials, there is a risk of health problems, and it is necessary to improve these drawbacks and to provide an environmentally friendly mold. Also, the raw material is about ten times higher than the inorganic binder, and it takes time to complete, resulting in an increase in mold cost and casting cost. In addition, Japanese Patent Application Laid-Open
Alkali metals used in Japanese Patent No. 232967 need to be more carefully managed since their properties are basically unstable.

The present invention has been made in view of the above problems, and is directed to a heat-resistant cast steel such as an austenitic heat-resistant cast steel.
When casting a thin exhaust system component with a main part thickness of 2 to 3 mm, the high temperature strength of the mold that can cast the molten metal while maintaining the high temperature after firing, or the collapse of the mold after casting Another object of the present invention is to provide a mold capable of improving the workability of mold release by increasing the moldability, further facilitating the control of the binder, and easily adjusting the bonding strength of the impregnated binder.

[0009]

Means for Solving the Problems The present inventors have used a mold for casting a molten metal while maintaining a high temperature after firing. The mold contains a metal of Group 1 of the periodic table in a binder, and contains SiO ₂ / Na ₂ O. It has been found that the above problem can be solved by using an inorganic binder having a specified molar ratio, and the present invention has been reached.

That is, according to the method for producing a mold of the present invention, a molding sand is formed into a desired shape by bonding a binder containing a metal of Group 1 of the periodic table to a molding sand, and then a SiO ₂ / Na ₂ O molar ratio is obtained. Is 3
It is characterized in that the above-mentioned inorganic binder is impregnated, the temperature is raised, and a molten metal is cast. Here, SiO ₂ / Na ₂ O
The reason why the molar ratio is 50 or more is that if the molar ratio of SiO ₂ / Na ₂ O is less than 3, the high-temperature strength is too large, the disintegration is deteriorated, and the service time is shortened. Preferably it is 5-100.

[0011] In the present invention, the periodic table 1 in the binder
It is preferable to contain 4 to 25% by mass of a group III metal. Here, the reason that the metal of Group 1 of the periodic table is contained in an amount of 4 to 25% by mass is that if it is less than 4%, a cured layer is not formed on the mold and the high-temperature strength is reduced. On the other hand, if it exceeds 25%, the high-temperature strength is too large and the disintegration property deteriorates.

Further, in the present invention, it is preferable that the inorganic binder is an aqueous silicate solution or colloidal silica. When the inorganic binder is an aqueous silicate solution or colloidal silica, the management of the binder is facilitated.
The concentration of SiO ₂ / Na ₂ O can be easily adjusted by, for example, adding water to a commercially available silicate aqueous solution having a predetermined molar ratio within a dilutable range.

[0013]

Embodiments of the present invention will be described below in detail. (Embodiment) FIG. 1 is a sectional view of a main part of a mold according to an embodiment, and FIG. 2 is a schematic sectional view of an apparatus for impregnating an inorganic binder. In FIG. 1, reference numeral 1 denotes a mold.
Is composed of a main mold 2 composed of a lower mold 2a and an upper mold 2b, and a core 3 disposed in the main mold 2. A cavity 4 formed by the main mold 2, the core 3, and the like has a gap of a main part. The main mold 2 is provided with a gate 5 and a runner 6. And
The lower mold 2a, the upper mold 2b, and the core 3 are manufactured by the following steps. The lower mold 2a, the upper mold 2b, and the core 3 are prepared by using a molding method such as a shell mold method, a cold box method, or a furan method, with molding sand and a binder containing 4 to 25% by mass of a metal of Group 1 of the periodic table. Knead and mold. Then, the lower mold 2a and the upper mold 2b are charged into the impregnating device shown in FIG. 2, and the inorganic binder 22 stored in the lower half of the decompression chamber 21 by a vacuum pump is used as colloidal silica. After immersion, the decompression chamber 21 was depressurized, and colloidal silica was
Impregnated into the fine pores of the sand grains. The colloidal silica is impregnated with SiO ₂ / Na ₂ O at a molar ratio of preferably 3 or more.

Next, the lower mold 2a taken out of the impregnating device,
The upper mold 2b and the core 3 are subjected to microwave drying. Further, the lower mold 2a, the upper mold 2b and the core 3 are assembled to form the mold 1
And put in a firing furnace (not shown),
Baking at 1200 ° C. × 1 hour. By firing the mold, the organic binder is burned off and the Si in the inorganic binder is removed.
O ₂ / Na ₂ O is sintered in the fine pores of the sand grains, and the sand grains are connected. Then, a molten metal having a high temperature of about 1500 to 1600 ° C., for example, of a heat-resistant austenitic cast steel composition, is cast from the gate 5 into a mold of about 800 to 1000 ° C. maintained at a high temperature immediately after firing. The main mold 2 is impregnated with colloidal silica SiO ₂ / Na ₂ O in a molar ratio of 3 or more and fired, and therefore has a high temperature strength enough to withstand the molten metal. Also, since the mold 1 is preheated to a high temperature of about 800 to 1000 ° C., which is close to the temperature at which the molten metal is cast, the flow of the molten metal into the cavity 4 becomes good. Next, after the casting, the temperature is returned to the room temperature, and the mold 1 and the casting are separated. The core 3 is impregnated with SiO ₂ / Na ₂ O of colloidal silica as an inorganic binder at a molar ratio of 50 or more,
The core 3 is easily disintegrated and separated from the casting because it has been fired and the bond between the sand grains is relatively weak.

[0015]

Next, an embodiment will be described. Periodic Table 1
After molding a 20 × 10 × 60 (mm) bending test piece and a φ50 × H50 (mm) collapsible test piece with molding sand mixed with a binder containing varying mass ratio of group metal. , And charged to the impregnation apparatus. Then, the test piece was impregnated with the inorganic binder stored in the decompression chamber of the impregnation device as a colloidal silica or silicate aqueous solution while changing the molar ratio and concentration of SiO ₂ / Na ₂ O, and then microwave dried. . Further, the test piece was placed in a firing furnace and fired at 1000 ° C. for 1 hour in the atmosphere. Next, the residual strength (N / cm ² ) and high-temperature strength (N / cm ² ) of the bending test specimen after firing were measured. The residual strength (N / cm ² ) was measured at a span of 50 mm and a radius at both ends of 2 m in a state where the bending test piece returned to normal temperature.
m was set on a metal fulcrum, a load at a constant speed was applied from above by a pressure wedge, and the maximum load when the bending test specimen was broken was determined. The high-temperature strength (N / cm ² )
Immediately after taking out the bending test piece in a state where the high temperature was maintained immediately after firing from the furnace, the span was 50 mm, and both tip radii were 2 mm.
mm was set on a metal fulcrum, a load at a constant speed was applied from above by a pressure wedge, and the maximum load when the bending test specimen was broken was determined. Since the mold requires a residual strength of 200 N / cm ² or more in terms of handling,
When the transverse rupture force is less than 200 N / cm ² (×), 200 to 50
The ^{0N / cm 2 (○),} 500N / cm 2 or more (◎)
Was evaluated. Further, since at least the high-temperature strength is required to be 100 N / cm ² or more in casting the high-temperature molten metal, the transverse rupture strength is less than 100 N / cm ² (×),
The 0~300N / cm ² (○), was evaluated 300N / cm ² or more as (◎). On the other hand, using a collapsible test piece as a core, a molten metal having an austenitic heat-resistant cast steel composition was cast, and after casting, the degree of sand on the casting was evaluated. In addition, the evaluation of disintegration was evaluated as (◎) when sand was dropped by one shot blast, (○) when 2-3 times, and (×) when more than 3 times. Table 1 shows the test results and evaluation results of the residual strength and the high-temperature strength, and the evaluation results of the disintegration property.

(Table 1) Inorganic binder SiO in the painter_Two/ N_TwoOEvaluation results  Group 1 metal (%) Type Molar ratio Residual strength High temperature strength Collapsible  Comparative Example 1-Colloidal Silica 2 × × × Comparative Example 2-Colloidal Silica 40 ○ ○ × Example 1 Na 6 Colloidal Silica 5 ◎ ◎ ○ Example 2 Na 12 Colloidal Silica 30 ◎ ◎ ◎ Example 3 K15 Silicate Aqueous Solution 60 ○ ○ ◎ Example 4 K 24 silicate aqueous solution 115 ○ ○ ◎ Comparative Example 3 Na 7 colloidal silica 2 ○ ○ × Comparative Example 4 Na 7 silicate aqueous solution 2 × ○ × Comparative Example 5 Na 30 silicate aqueous solution 60 × ○ ×

From Table 1, Examples 1 and 2 show that the template binder contains 4 to 25% of Na, which is a Group 1 metal of the periodic table,
Since colloidal silica SiO ₂ / Na ₂ O is impregnated in a molar ratio of 3 or more and calcined, the residual strength,
It can be seen that the mold has high-temperature strength. In Examples 3 and 4, the mold binder contained 4 to 25% of K, which is a Group 1 metal of the periodic table,
The ₂ / Na ₂ O impregnated as 3 or more ranges in a molar ratio, since the firing, it is understood that the disintegrating good mold. On the other hand, since the molds of Comparative Examples 1 and 2 do not contain a Group 1 metal of the periodic table in the mold binder, any of the residual strength, high-temperature strength and disintegration are low. Comparative Examples 3 and 4
Is made of N, which is a Group 1 metal of the periodic table, in a mold binder.
a is 4 to 25%, but the colloidal silica or silicate aqueous solution has a SiO ₂ / Na ₂ O molar ratio of less than 3, low room temperature strength and high temperature strength. The molar ratio of SiO ₂ / Na ₂ O in the aqueous solution is 3 or more, but Na, which is a Group 1 metal of the Periodic Table in the template binder, is 4%.
In any of Comparative Examples 1 to 6, the mold containing a molten metal of high temperature immediately after maintaining the sintering temperature after firing the mold. As yet, the problem remains.

[0018]

As described above in detail, the mold of the present invention has a binder containing a metal of Group 1 of the periodic table in a binder, and an aqueous solution of silicate or S of colloidal silica as an inorganic binder.
By changing the molar ratio of iO ₂ / Na ₂ O and impregnating, the high-temperature strength at the time of casting a high-temperature molten metal immediately after firing and the disintegration when separating from a casting after casting are adjusted. Since a binder is used, management is relatively easy.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a mold according to an embodiment.

FIG. 2 is a schematic sectional view of an apparatus for impregnating an inorganic binder.

[Explanation of symbols]

 1: Mold 2: Main mold 2a: Lower mold 2b: Upper mold 3: Core 4: Cavity 5: Gate 6: Runner 21: Decompression chamber 22: Inorganic binder 23: Vacuum pump

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Eiji Nakano, Inventor 35, Nagahama-cho, Kanda-cho, Kyoto-gun, Fukuoka Prefecture Inside the Kyushu Plant of Hitachi Metals Co., Ltd. F-term in Kyushu Plant (reference) 4E092 AA02 AA09 AA18 AA19 BA02 BA11 CA03

Claims (4)

[Claims] After a molding sand is formed into a desired shape by adhering a binder containing a metal of Group 1 of the periodic table to a molding sand, SiO _{2 is formed.}
A method for producing a casting mold, characterized by impregnating an inorganic binder having a molar ratio of / Na ₂ O of 3 or more, raising the temperature, and casting a molten metal. 2. The method for producing a casting mold according to claim 1, wherein the binder contains 4 to 25% by mass of a metal belonging to Group 1 of the periodic table. 3. The method according to claim 1, wherein the inorganic binder is an aqueous silicate solution. 4. The method according to claim 1, wherein the inorganic binder is colloidal silker.