JPH10328780A - Coated sand for casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coated sand for casting which can produce a casting having an extremely small and extremely thin cast portion at a high temperature while suppressing the occurrence of seizure, cracking, and gaze. SOLUTION: The coated sand has 90 to 96.5% by weight of high-purity silica whose particle size distribution of aggregate is 25% or less for 100 mesh residue, 70% or more for 100 to 200 mesh, and 15% or less for 200 mesh passage. %, And a phenol resin is used for the binder. The purity of the high-purity silica is 98% or more as SiO ₂ . The coated sand is used, for example, as a core sand for manufacturing a core piece 3 attached to a part of a core 1 for a water jacket used in manufacturing a Siamese type cylinder block.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated sand for castings, and more particularly to a coated sand for castings which is suitable as a core sand when molding a casting having an extremely small and extremely thin cast portion at a high temperature. is there.

[0002]

2. Description of the Related Art A cylinder block is a basic component of an engine, and its main role is to guide a reciprocating motion of a piston, support a crankshaft, cool a cylinder, and the like. A water jacket is provided around the cylinder bore for cooling the cylinder.

In order to reduce the weight and size of the engine, the thickness of the partition wall between the cylinder bores is reduced as much as possible (8 to 8).
11mm), no water jacket between the bores,
A so-called Siamese type cylinder block has been widely used in recent years. In this cylinder block, since cooling water does not flow between the bores, the cooling between the bores is insufficient compared to the full jacket type.

[0004] If the cooling between the bores is insufficient, the bores are distorted due to an increase in the wall temperature, and the oil in the oil pan spills into the combustion chamber and is discharged as gas. There is also a problem that if the bore wall temperature rises significantly, nitrogen oxides (NOx) and smoke in the exhaust gas increase.

[0005] The water jacket is formed by a core when the cylinder block is formed by casting. Therefore, it is sufficient that a thin portion for casting between the bores is formed integrally with the core for the water jacket so that a flat hole for passing the cooling water can be formed between the bores when casting the cylinder block. However, when a conventional core is used, a high temperature (about 1330 °
The size of the hole on the small diameter side of the hole capable of casting the cylinder block with a high yield by preventing the insertion (sighting), cracks and the like at the time of casting in C) was limited to approximately 2.2 mm.

Instead of using a sand core to cast a hole for passing cooling water, a flat pipe having a thickness of 1 mm (width 17 mm, thickness 3 mm) is provided at a position corresponding to the space between the bores of the core for the water jacket. Are arranged, and a pipe is arranged in the partition wall between the bores in the state of cast wool to form a hole for passing cooling water.

[0007]

However, in the case of the prior art in which a flat pipe is cast between bores in the state of cast wool instead of using a sand core, the pipe is placed at a predetermined position on a core for a water jacket. It takes time to embed. Also, since the thickness of the flat pipe is as thin as 1 mm, if the pipe is cast in an empty state, the pipe is deformed by the pressure of the molten metal acting on the pipe at the time of casting. It is necessary to cast in a filled state, and to remove the filling after casting. Accordingly, the number of steps is increased and a special flat pipe is required, so that the manufacturing cost is increased.

The width of the cooling water passage to be formed between the cylinder bores is very narrow as compared with the width of the water jacket. Therefore, if a so-called gaze (insertion), which is a defect on the casting surface caused by the intrusion of the molten metal into the gap between the sand grains during casting, occurs even if it is a defect that is allowed in the water jacket, it is not allowed in the cooling water passage. In addition, since the width of the cooling water passage is very narrow, it is very difficult to remove the plug formed on the inner surface of the cooling water passage by post-processing, and the cylinder block in which the plug is generated becomes a defective product. The yield at the time of manufacturing blocks is reduced.

When the core for the water jacket is formed, when the cast portion between the cylinder bores is formed integrally with the water jacket using the same core sand, the thickness limit is almost as described above. 2.2 mm, making it difficult to make the partition wall between the cylinder bores thinner. In addition, a core that can form a hole with a small diameter of approximately 2.2 mm on the small diameter side by casting requires careful handling in order to prevent the thin-walled part from being damaged during handling. There is also the problem of being bad.

Instead of core sand using silica sand which is generally used as an aggregate, core sand made of a typical inorganic substance having excellent heat resistance (eg, magnesium oxide, aluminum oxide, zircon sand) is used. Was prepared, and experiments were carried out. During casting, phenomena such as the aggregate being (melted), being broken off, being deformed, and the like, and being able to withstand handling when forming the core, were produced. No one that can withstand use was obtained.

In addition to the water jacket, there is a similar problem in molding a casting having a very small or extremely thin cast portion at a high temperature. The present invention has been made in view of the above-mentioned conventional problems, and has as its object, when forming a casting having an extremely small and extremely thin cast-out portion at a high temperature, seizure, cracks, and eyes are generated. It is an object of the present invention to provide a coated sand for castings capable of producing a precision casting by suppressing the occurrence of the above problem.

[0012]

In order to achieve the above object, the coated sand for casting according to the first aspect of the present invention has a purity of at least 98% as silicon dioxide (SiO ₂ ).
Aggregate is made of high-purity silica having a particle size of 00 to 200 mesh as a main component. As the binder, a general phenol resin-based binder as a so-called shell sand binder can be used. When a novolak-type phenol resin is used, a curing agent is required, and hexamethylenetetramine is generally used as the curing agent. It is preferable to use calcium stearate as a catalyst. When a resol type phenol resin is used, a curing agent is not required. In addition to the phenolic resin, other casting binders can be used.

The particle size of the high-purity silica is 25% or less with 100 mesh residue, and 70% with 100 to 200 mesh.
As described above, it is preferable that the pass through 200 mesh is 15% or less. That is, 70% or more of the meshes having a mesh size of 100 to 200 are combined so that the remaining mesh mesh is 25% or less and the 200 mesh mesh is 15% or less. More preferably, the remaining 100 mesh is 10% or less,
85% or more of 200 mesh, 5 passing of 200 mesh
% Or less.

The weight percentage of the high-purity silica in the coated sand is 90 to 96.5%, and the balance is a binder and a curing agent. The weight ratio of the binder to the high-purity silica (aggregate) is 3.5 to 10%, preferably 4.
0-7.0%, More preferably, it is 4.5-6.0%.

In order to form a casting having an extremely small and extremely thin cast portion at a high temperature (for example, 1300 ° C. or higher) to enable the production of a precision casting, seizure, cracking, and gaze occur during pouring. Need to be suppressed. In order to prevent seizure, it is necessary to suppress the melting and softening of the aggregate at the temperature of the molten metal. Since high-purity silica is crystallographically hexagonal quartz and has a melting point of 1550 ° C., the aggregate does not melt at the temperature of the molten metal, and seizure is suppressed.

The cause of cracks is rapid expansion during pouring. In addition, when a fine crack occurs, a gaze may be generated at the portion. High-purity silica has a coefficient of linear expansion of 3.0 × 10 ⁻⁶ , and magnesium oxide, which is another typical inorganic substance known as a refractory, has a coefficient of linear expansion of ^{17.10 −6} .
5 × 10 ⁻⁶ ), aluminum oxide (linear expansion coefficient 8.0 ×)
Very small compared to ^10-6 ). Therefore, it is presumed that even if the molten metal is rapidly heated by the molten metal at the time of pouring, the distortion is small, cracks are suppressed, and as a result, the shape is maintained.

The gaze is caused by the infiltration of the molten metal into the gaps between the sand grains of the mold.
The main component (with a weight ratio of 7 to 200 mesh)
0% or more), and in combination with the above-mentioned small thermal expansion, it is difficult to generate eyes. In addition, the fact that the particle size distribution is not wide helps to ensure the strength to withstand the hot metal pressure during pouring.

Since the weight ratio of the high-purity silica to the coated sand is 90 to 96.5% (the remainder is a binder and a curing agent), the molding of the core and the subsequent handling are easy. If the amount of the binder (resin) is less than 3.5%, the coated sand becomes too dry and molding becomes difficult, and even if it can be molded, it tends to be damaged during subsequent handling. If the amount of the binder is more than 10%, it becomes too sticky and difficult to mold, and gas is generated at the time of casting to generate bubbles.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in which the present invention is applied to a coated sand used for a core piece for forming a cooling water passage of a water jacket of a diesel engine.

FIG. 1 is a schematic perspective view of a core for a water jacket used when manufacturing a quadruple Siamese type cylinder block of an engine. As shown in FIG. 1, a core 1 for a water jacket is a core body 2 for a water jacket.
And a core piece 3 for forming a cooling water passage hole in a partition wall between adjacent cylinder bores. The core body 2 for a water jacket has an upper portion corresponding to a space between adjacent cylinder bores and facing each other,
A pair of fitting grooves 4 are formed, each of which is open at the top and side. Both ends of the core piece 3 are fitted in the fitting grooves 4, and are arranged at predetermined positions corresponding to the spaces between adjacent cylinder bores.

As the material of the core body 2 for the water jacket, the same core sand as the conventional one, for example, a resin-coated sand (shell sand) having a resin content of about 2% is used. On the other hand, a material different from the material of the core body 2 for a water jacket, that is, the coated sand according to the present invention, is used as the material of the core piece 3.

As the coated sand (resin coated sand), a coated sand using high-purity silica made of artificial SiO ₂ as an aggregate is used. More specifically, high-purity silica (purity SiO ₂ : 9) is used as an aggregate.
9.8%) 100-200 mesh product 100% (10
0 g), 5% (5 g) of a binder, 2% (2 g) of an aqueous solution of hexamethylenetetramine, and 1% (1 g) of an aqueous solution of calcium stearate.

In the mixing, first, high-purity silica and a phenol resin are mixed by heating to 140 ° C. At this time, it is easier to uniformly mix the phenol resin without using the phenol resin in the form of pellets but using the phenol resin which has been pulverized in advance into powder. This mixing takes about one hour. Next, when a curing agent is added and mixed well, and then a catalyst is added and mixed well, the surface of the high-purity silica is coated with a phenol resin. The mixture prepared in this manner is called a coated sand. The coated sand has an appropriate flowability with a light feeling and is excellent in moldability by a mold. The catalyst is not always necessary, but by adding the calcium stearate aqueous solution, mixing becomes easy, and the work when putting the coated sand into the mold when manufacturing the core piece by leaching the mixture becomes easier. .

The curing agent and the catalyst are expressed in terms of weight in the form of an aqueous solution, and since a part of the water evaporates during mixing in a heated state, the proportion of high-purity silica in the coated sand as the final product Is greater than 93%.

The finished coated sand is formed into a predetermined shape (length 55 mm, width 37 mm, thickness 1.0 to 1.8 mm)
Approximately 10 g is put into the hollowed-out template and pressed with pressure. When pressed into the template, the coated sand is in a state similar to moderately wet sand, so that it can be pressed into a shape corresponding to the shape of the mold portion without collapse. Then 180
Bake for 1 hour at ° C. By this treatment, the resin coated on the surface of the coated sand is hardened and the sand grains are bonded to each other. Thereafter, when the core piece is naturally cooled, the core piece is spontaneously separated from the mold part due to a difference in thermal expansion coefficient between the core piece and the template.

The core piece 3 formed as described above
Are fitted into the fitting grooves 4 of the core body 2 for a water jacket, and the core body 2 for a water jacket and the core piece 3 are fixed with a coating material to form the core 1 for a water jacket. You. Since the strength of the core piece 3 at normal temperature is large, damage during handling is greatly reduced without paying much attention to the handling of the core piece 3. Further, instead of the worker attaching the core piece 3 to the core body 2 for the water jacket manually, it is also possible to automatically attach the core piece 3 by a robot.

The core 1 for a water jacket constructed as described above is assembled in another core and then housed in a mold. In this state, the cast iron heated to about 1400 ° C. is poured into the mold. Then, a cylinder block is formed in which the desired precise cast hole (cooling water passage) communicates with the water jacket.

The high-purity silica mainly composed of particles having a particle size of 100 to 200 mesh, which is used as an aggregate, provides the core made of this coated sand with a low expansion property and a non-seizure property. It plays a role in preventing the occurrence of insertion. High-purity silica is crystallographically hexagonal quartz, has a linear expansion coefficient of 3.0 × 10 ⁻⁶ , a specific gravity of 2.65, and a melting point of 1550 ° C. Magnesium oxide has a linear expansion coefficient of 17.5 × 10 ⁻⁶ , a specific gravity of 3.65, and a melting point of 2800.
° C and aluminum oxide has a coefficient of linear expansion of 8.0 × 1
0 ^-6 , specific gravity 4.0, melting point 2054 ° C. Quartz has a feature that the linear expansion coefficient is very small as compared with magnesium oxide and aluminum oxide. Therefore, even if it is rapidly heated, the distortion is small, and it is considered that no crack is generated as a result.

Conventionally, quartz sand used as an aggregate has quartz as a main component, but contains a large amount of impurities. As a result, the coefficient of linear expansion is larger than that of quartz, resulting in a larger strain, and as a result, it was not possible to satisfy the results. There is. Further, silica sand is a natural product, and therefore has a large variation in quality, and the quality of the obtained coated sand also varies, resulting in low reliability and a low yield of a final product (cast). On the other hand, in the case of using artificial SiO ₂ as a raw material, the variation in quality is small and a product of constant quality can be obtained.
Yield is improved.

Further, even the same high-purity silica is affected by the particles used. If it becomes fine powder, the disintegration after casting is poor. In addition, the formability is reduced even if it is coarse. Moderate particle size is 10
Although it is 0 to 200 mesh, even if the 100 to 200 mesh is not 100%, the particle size distribution is such that the remaining 100 mesh is 25% or less, the 100 to 200 mesh is 70% or more, and the 200 mesh passage is 15% or less. I just need. As a particle size distribution with which more preferable results can be obtained, 100% residue is 10% or less, and 100 to 200 mesh is 85%.
% Or more and 5% or less through 200 mesh.

As the binder, a commonly used phenol resin can be used, and other casting binders can also be used. The amount of the binder (phenol resin) used is 3.5 to 3.5 in terms of weight ratio to the high-purity silica (aggregate).
It is about 10%, preferably 4.0 to 8.0%, and more preferably 4.5 to 6.5%. If the amount of the resin is less than 3.5%, the material becomes dry and molding becomes difficult. If the amount of the resin is more than 10.0%, it becomes too sticky and difficult to mold, and gas is generated at the time of casting to generate bubbles. The amount of the phenol resin is about twice the amount (2 to 3%) used in the conventional core sand. Therefore, the amount of gas generated by the decomposition of the phenol resin during casting increases. However, since the absolute amount of the coated sand of the core piece 3 is very small compared to the absolute amount of the core sand of the core body 2 for the water jacket, the increase in the gas amount as a whole is small and adversely affects the casting. Has no effect. In addition, by increasing the amount of the phenol resin to about twice that of the conventional case, the moldability and the strength at normal temperature that can prevent damage when handling the core piece 3 are ensured.

(Examples and Comparative Examples) Next, Examples and Comparative Examples which embody the present invention will be described. (Example 1) High purity silica (100 to 200 mesh 1)
(00%) 50 g and pre-ground phenol resin 2.5 g
And heated in a stainless steel vat at a temperature of 140 ° C. for 1 hour, taken out, added with 1.0 g of an aqueous solution of hexamethylenetetramine and 0.5 g of an aqueous solution of calcium stearate, and mixed with a spatula (spatula) for about 1 hour (coated) (Rate of aggregate in sand: 93% by weight, ratio of binder in coated sand: 4.6% by weight, amount of binder to aggregate: 5.0% by weight). The finished coated sand is 55mm long, 37mm wide,
Approximately 10 g was put into a template that was hollowed out to a thickness of 1.0 to 1.8 mm, and was molded at 180 ° C under pressure to form a core piece. This core piece was placed at a predetermined position of a core body for a water jacket used for casting a cylinder block of a diesel engine, and the cylinder block was cast. Then, the cylinder block was cut with an engine cutter, and the cast water state of the cooling water passage was observed. Table 1 shows the results. (Example 2) As high-purity silica in Example 1, 1
A coated sand was prepared in the same manner as described above, except that the 00 mesh residue was 20% or less, the 100 to 200 mesh was 75% or more, and the 200 mesh passage was 5%, and the other conditions were the same. A core piece was formed with this coated sand, and a cylinder block was cast. Then, the casting state of the cooling water passage was observed in the same manner as in Example 1. Table 1 shows the results. (Example 3) In Example 1, the amount of the phenol resin was changed to 3.
A coated sand was prepared under the same conditions except that the weight was 5 g (the ratio of the aggregate in the coated sand: 91% by weight, the ratio of the binder in the coated sand:
6.4% by weight, binder amount to aggregate: 7.0% by weight). A core piece was formed with this coated sand, and a cylinder block was cast. Then, the casting state of the cooling water passage was observed in the same manner as in Example 1. Table 1 shows the results. (Comparative Example 1) In Example 1, the amount of the phenol resin was set to 1.
A coated sand was prepared under the same conditions except that the weight was 0 g (the ratio of the aggregate in the coated sand: 95% by weight, the ratio of the binder in the coated sand:
1.9% by weight, binder amount to aggregate: 2.0% by weight). A core piece was formed with this coated sand, and a cylinder block was cast. Then, the casting state of the cooling water passage was observed in the same manner as in Example 1. Table 1 shows the results. (Comparative Example 2) A coated sand was prepared in the same manner as in Example 1 except that the aggregate was 50 g of aluminum oxide and the phenol resin was 0.6 g, and the other conditions were the same (proportion of the aggregate in the coated sand: 96% by weight, Ratio of binder in coated sand: 1.2% by weight, binder amount to aggregate: 1.2% by weight). A core piece was formed with this coated sand, and a cylinder block was cast. Then, the casting state of the cooling water passage was observed in the same manner as in Example 1. Table 1 shows the results. Comparative Example 3 A coated sand was prepared in the same manner as in Example 1 except that the aggregate was 50 g of aluminum oxide and the phenol resin was 2.5 g, and the other conditions were the same (the ratio of the aggregate in the coated sand: 93% by weight, (Ratio of binder in coated sand: 4.6% by weight, amount of binder based on aggregate: 5.0% by weight). A core piece was formed with this coated sand, and a cylinder block was cast. Then, the casting state of the cooling water passage was observed in the same manner as in Example 1. Table 1 shows the results. (Comparative Example 4) A coated sand was prepared in Comparative Example 2 by using 50 g of magnesium oxide as an aggregate and 0.6 g of a binder as K-17C (trade name: Denka Poval, manufactured by Denki Kagaku Kogyo KK). (Ratio of aggregate occupying: 98.8% by weight, ratio of binder in coated sand: 1.2% by weight, amount of binder based on aggregate: 1.2% by weight). A core piece was formed with this coated sand, and a cylinder block was cast.
Then, the casting state of the cooling water passage was observed in the same manner as in Example 1. Table 1 shows the results. (Comparative Example 5) A coated sand was prepared as in Comparative Example 2 except that the aggregate was 50 g of magnesium oxide and the binder was 2.5 g of K-17C (trade name: Denka Povar, manufactured by Denki Kagaku Kogyo KK) (coated sand). Of the aggregate in the coated sand: 95.2% by weight, the ratio of the binder in the coated sand: 4.8% by weight, the binder amount to the aggregate: 5.0% by weight). A core piece was formed with this coated sand, and a cylinder block was cast. Then, the casting state of the cooling water passage was observed in the same manner as in Example 1. Table 1 shows the results. (Comparative Example 6) In Comparative Example 2, the aggregate was changed to zircon sand 5
A coated sand was prepared by setting 5.0 g of Alon D (trade name: Aron Ceramic D, manufactured by Toagosei Co., Ltd.) as a binder (proportion of aggregate in coated sand: 91% by weight, occupied in coated sand). Binder ratio: 9% by weight, binder amount to aggregate: 1
0% by weight). A core piece was formed with this coated sand, and a cylinder block was cast. Then, the casting state of the cooling water passage was observed in the same manner as in Example 1.
Table 1 shows the results. (Comparative Example 7) In Example 1, the aggregate was set to 50 g of white sand.
The other conditions were the same to prepare a coated sand (the ratio of the aggregate in the coated sand: 93% by weight, the ratio of the phenolic resin in the coated sand: 4.6% by weight, the binder amount to the aggregate: 5.0). weight%). A core piece was formed with this coated sand, and a cylinder block was cast. Then, the casting state of the cooling water passage was observed in the same manner as in Example 1. Table 1 shows the results.
Shown in

[0033]

[Table 1]

When high-purity silica is used as an aggregate,
In each of Examples 1 and 2 in which the amount of the binder (phenol resin) used is 5% by weight of the aggregate and Example 3 in which the amount of the binder is 7% by weight, the molding of the core piece is performed favorably. At the same time, the handling of the core piece after molding became easier. Further, the cooling water passage was formed well in the cylinder block obtained by casting without eyes or seizure.

However, in the case of Comparative Example 1 in which the binder was used in an amount of 2% by weight based on the weight of the aggregate, the coated sand was too dry, so that it was difficult to mold it into a predetermined shape, and it was easily broken during handling after molding. . Further, as an aggregate, white sand of SiO ₂ whose component element is the same as high-purity silica (SiO ₂ % is about 7%)
Also, in the case of Modification 7 using (3%), the molded core piece was easily broken, and cracks and eyes were easily generated during casting.

In each of Comparative Examples 2 to 6 in which a typical inorganic substance other than SiO ₂ was used as an aggregate, satisfactory castings could not be obtained. This embodiment has the following effects.

(A) Since high-purity silica having a purity of 98% or more and a particle size of 100 to 200 mesh as a main component as silicon dioxide (SiO ₂ ) is used as an aggregate, it is rapidly heated by a molten metal during pouring. Even when the casting is performed, the distortion is reduced, the strength to withstand the molten metal pressure at the time of pouring is secured, and the gaze is hardly generated, and the casting having the extremely small (extremely thin) cast-out portion is heated to a high temperature (eg, 1300 ° C. or more). It is possible to mold with. The core for cooling water passage casting, which is used as a part of the core for the water jacket, is formed with this coated sand, so that the partition wall between adjacent cylinder bores of the cylinder block of the engine has a thickness of 1. 0 to
A very small (very thin) cooling water passage of 1.8 mm can be formed.

(B) Since synthetic high-purity silica having a controlled particle size is used as an aggregate, it can be mixed with conventional shell sand or cold sand (aggregate is a blend of natural silica sand or artificial sand such as cerabeads). On the other hand, variations in characteristics such as bending strength of the manufactured core pieces are extremely small, and the incidence of defective products can be greatly reduced.

(C) The ratio of the amount of resin used for the coated sand is larger than the ratio of the amount of resin used for the core sand for the conventional water jacket core. Is small with respect to the amount of coated sand of the entire core for a water jacket, so that there is no problem even if the gas amount increases during casting.

(D) Since the aggregate of the coated sand is high-purity silica, it is the same as silicon dioxide, which is the main component of the shell sand that is the material of the core body for the water jacket. Therefore, there is no problem even if the core sand for the water jacket, in which the core sand of the core piece is mixed, is used as the return sand as the core sand for the water jacket at the time of mold release.

The present invention is not limited to the above embodiment, but may be embodied as follows, for example. (1) The purity of high-purity silica used as aggregate is S
i O ₂ : The purity is not limited to 99.8%, but may be 98% or more, and preferably 99% or more.

(2) When a phenol resin requiring a curing agent is used as a binder, a catalyst (aqueous calcium stearate) need not be used. But,
The use makes it easier to adjust the flowability of the coated sand to a state suitable for handling.

(3) A phenol resin that does not require a curing agent (resole type phenol resin) may be used as a binder. Further, a thermosetting resin (for example, urea resin) other than the phenol resin or a curing agent other than hexamethylenetetramine may be used. Other casting binders can also be used.

(4) The present invention is not limited to a core piece for a water jacket, and may be used for a core for a cast-out portion used for manufacturing a casting having another extremely small and extremely thin cast-out portion. The inventions other than those described in the claims that can be grasped from the embodiment and the modified examples will be described below together with their effects.

(1) In the invention according to any one of claims 1 to 3, a phenolic resin binder is used, and its weight ratio to the aggregate is set to 3.5 to 8%. In this case, it is easy to uniformly form a binder film on the surface of the aggregate, and the strength of the molded core is increased and the variation is reduced.

(2) In the invention of (1), a novolak-type phenol resin is used, hexamethylenetetramine is used as a curing agent, and an aqueous solution of calcium stearate is used as a catalyst. In this case, the flowable coated sand that is easy to handle can be easily prepared.

[0047]

As described in detail above, claims 1 to 3 are described.
By using the coated sand of the invention described in (1), a cast product having an extremely small and extremely thin cast-out portion can be manufactured while suppressing the occurrence of seizure, cracking, and gaze at high temperatures. For this reason, for example, a very small (ultra-thin) flat cooling of 1.0 to 1.8 mm that cannot be formed between the bores of a siamese type cylinder block by a molding method using a conventional core for a water jacket. Holes for water passage can be cast out.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of a core for a water jacket.

[Explanation of symbols]

1 core for water jacket, 2 core body for water jacket, 3 core piece.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshio Fujita 2-1-1 Toyota-cho, Kariya-shi, Aichi Prefecture Inside Toyota Industries Corporation (72) Inventor Toshio Sano 2-1-1, Toyota-cho, Kariya-shi, Aichi Stock (72) Inventor Tsujihiko Yasuda 107, Takanedai, Midori-ku, Nagoya City, Aichi Prefecture (72) Inventor Mineaki Kabayama 214 Uehonjo, Myojin Setocho, Naruto City, Tokushima Prefecture

Claims (3)

[Claims] (1) a purity of 98 as silicon dioxide (SiO ₂ );
%. A coated sand for casting containing high-purity silica as an aggregate, the main component of which is 100% or more and a particle size of 100 to 200 mesh. 2. The particle size of the high-purity silica is 25% or less for 100 mesh residue and 70% for 100 to 200 mesh.
As mentioned above, 200 mesh passage is 15% or less.
The coated sand for casting according to 1. 3. The coated sand for casting according to claim 1, wherein a weight ratio of the high-purity silica to the coated sand is 90 to 96.5%.