JP3207660B2 - Foundry sand and casting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molding sand which can be used in the metal casting industry and a method of casting a casting using the same.

[0002]

2. Description of the Related Art The metal casting industry has long been developed for casting castings used for building members, industrial articles and the like. In recent years, it has been widely used in the production of precision parts used for OA equipment and the like, and it is desired to establish an accurate and precise casting production technique.

[0003] The foundry sand used in the above-mentioned foundry industry becomes a prototype of the foundry and is in direct contact with the casting at the time of casting. Therefore, it must have sufficient formability and thermal stability upon contact with the molten metal. In order to prevent defects such as cavities, blows and scoops, it is necessary to have air permeability enough to allow gas to be introduced to the outside when molten metal is cast. Furthermore, when casting precision equipment, it is required that the entire casting has strictly uniform quality, so that the cooling rate of the molten metal must be constant in each part of the casting, and the thermal conductivity When casting a casting such as a copper alloy or a bismuth alloy having a high content, it is necessary to quickly release heat in order not to cause uneven shrinkage, and high heat conductivity is required for casting sand.

Until now, relatively inexpensive silica sand particles have been widely used as a material for molding sand. Further, in order to cast a higher quality casting, sand obtained by grinding olivine (olivine sand) has been used as casting sand. Further, spherical or egg-shaped carbon particles or coke particles, copper,
It has been used as a suitable material for casting metals and alloys such as bronze, brass and iron. These have been put to practical use by imparting appropriate tackiness by using an appropriate binder at the same time, thereby ensuring moldability.

However, the above-mentioned silica sand or the like does not have sufficient thermal stability, and when the temperature of the molten metal becomes high, for example, more than 1000 ° C., a crack is generated in the mold due to friction, shrinkage, etc. of the molten metal, and There was a drawback that stripes and holes were formed in the steel, making it impossible to cast a high quality casting.

[0006] In order to solve the above-mentioned drawbacks, carbon or coke obtained in the petroleum industry is used in 2000 to 2800.
U.S. Pat. Nos. 2,830,342 and 2830 discloses a technique for removing volatile substances by heating to about 1100.degree.
No. 013. In addition, even without performing the high-temperature treatment as described above, first, the carbon or coke is heated and separated into hydrocarbon vapor and spherical or egg-shaped coke particles, and then the separated coke particles are further heated. Then, the heating temperature will be 1000-15000 ° F
(About 550 to 830 ° C.) is disclosed in Japanese Patent Application Laid-Open No. 4-251629, in which a molding sand having thermal stability can be obtained at low cost.

[0007]

However, the above-mentioned technique is intended to ensure thermal stability and to suppress the deterioration of casting quality due to released gas and the like even at high temperatures due to molten metal during casting. As described above, in order to cast a precision instrument whose demand has been increasing in recent years, it is essential to have high thermal conductivity in addition to thermal stability, and these requirements have not been satisfied. In addition, coke obtained by the above technology has many small holes in the particles and is inferior in physical strength, making it difficult to form a precise mold, and is not suitable for casting of precision equipment. Had.

In view of the above, the present invention provides a molding sand having sufficient moldability, thermal stability and air permeability, high thermal conductivity and sufficient strength, and a casting method using the same. The purpose is to do so.

[0009]

SUMMARY OF THE INVENTION The gist of the present invention is to provide graphitized carbon particles obtained by heating coke in forming molding sand and having a particle diameter of 0.1 to 1.0 m.
m is used. Another aspect of the present invention resides in casting a casting using the above-mentioned foundry sand. Hereinafter, the present invention will be described in detail.

[0010] Usually, "coke" refers to a carbonaceous porous solid obtained by carbonizing coal at a high temperature and used as a fuel. In the present specification, coke refers to the above-mentioned "coke". In addition, liquid coke obtained as a by-product in the petroleum refining industry shall be included. The coke used in the present invention is a relatively inexpensive raw material obtained as a fuel or a by-product in the coal refining industry and the petroleum refining industry, and contains impurities containing about 5% by weight of an organic substance containing carbon as a main component. It is a thing.

The above coke is usually obtained by heating coal or petroleum as its raw material, thereby mixing the pitch and the like. As the coke in the present invention, any of coal coke obtained from coal, coal pitch coke obtained by mixing pitch with coal coke, and petroleum coke obtained from petroleum can be used.

The above coke is first pulverized if necessary, and then pitch, tar, etc. are added to impart tackiness, and the resulting coke is kneaded at a high temperature of about 150 to 250 ° C., and then cooled. It is desirable to grind again. The above step is not necessarily essential for obtaining the coke of the present invention, but is a preferable step for making the coke of the present invention uniform.

The coke obtained by the above process can be pressurized in order to densify the crystal structure. The above-mentioned pressurization can be performed by mechanical pressurization using a normal press machine.However, in order to remove crystal anisotropy and obtain denser carbon particles, for example, a tertiary press such as a cold isostatic press is used. It is better to do a former press. The above pressure is usually 700
It can be performed at about 1300 kgf / cm ² .

The pressurized coke volatilizes the mixed pitch and other organic substances by primary firing at about 1000 ° C. In this process, the carbon particles undergo polycondensation in the solid phase, and the remaining organic substance forms a carbon crystal structure due to the growth of the aromatic plane, and can be made carbonaceous as a whole.

The coke after the first firing is 2800 ° C.
It is graphitized by a degree of secondary firing. In this process, the carbon particles acquire three-dimensional regularity, and the crystal structure grows to be graphitic (graphite). In the present invention, 50% or more of the carbon particles are graphite which is completely graphitized carbon.
If the amount of graphite is less than 50%, the thermal conductivity is not sufficient and the object of the present invention cannot be achieved. The greater the amount of graphite, the better, and more preferably, 100% of the carbon particles are graphite.

In the graphite of the present invention, crystallites (crystallites) having a crystal structure are crosslinked to each other to form a polycrystalline structure. In a crystallite, as shown in FIG. 1, theoretically, planar six-membered carbon rings are linked to form a layered structure, and the carbon-to-carbon distance in the planar six-membered carbon is theoretically 1. The lattice constant of a unit cell of 42 angstroms and a hexagonal system as a three-dimensional crystal is a = b = 2.
46 angstroms, c = 6.71 angstroms. In each layered structure, carbon atoms are firmly bonded by covalent bonds, and the respective layered structures are vertically weaker by van der Waals (van de Waals).
r Waals) force.

The carbon before the secondary firing is 3 to 10 k
Although it has only a thermal conductivity of about cal / m · h · ° C., the carbon after the secondary firing is 50 to 140 kca
It has a thermal conductivity of about 1 / m · h · ° C. Also, the porosity in the carbon particles (micropore)
s)) is extremely small due to the crystal structure developed by the primary firing and the secondary firing, and has acquired a dense structure excellent in strength.

In the present invention, the carbon after the above-mentioned secondary firing is pulverized by an ordinary method, and then the carbon is pulverized.
The particles are classified so as to have a constant particle size of about 1 to 1.0 mm. If the particle diameter is less than 0.1 mm, the particles are too fine to obtain sufficient moldability and air permeability as foundry sand, and if it exceeds 1.0 mm, the moldability is poor and the casting is cast. The skin becomes so bad that an accurate and precise casting cannot be obtained. The above-mentioned pulverization can be performed by coarse pulverization using a normal jaw crusher and then finely pulverized by a roller mill or the like, and in some cases, particles having a particle diameter in the above range can be obtained only by the jaw crusher. it can. The carbon particles after the pulverization need not be spherical or egg-shaped, and the effects of the present invention are not reduced even if they are rounded or polygonal. The classification can be performed, for example, by an ordinary method using a vibration sieve or a rotary sieve.

When the carbon particles of the present invention obtained as described above are used as molding sand, it is not necessary to include a large amount of a binder because the carbon has sufficient strength. In order to impart a casting sand, about 10 to 40% by weight of a binder can be added to form molding sand. 10% by weight of binder
If it is less than 40%, the object of the present invention cannot be achieved due to poor moldability, and if it exceeds 40% by weight, the strength and thermal conductivity are reduced, and the object of the present invention cannot be achieved. More preferably, it is 30% by weight.

As the above-mentioned binder, those usually used as a binder in molding sand can be used. For example, bentonite, clay, starch, sugar, bone powder, sodium silicate, thermoplastic resin, thermosetting resin, oil Core,
Cement and the like can be mentioned. These binders can be appropriately determined depending on the type of casting material (cast metal) to be cast. For example, when casting a zinc alloy or the like, sodium silicate is suitable as a binder.

The foundry sand of the present invention can be used for casting by a method usually used in the casting industry. That is, molding the molding sand into a shape having a surface having a desired form to form a mold, casting a molten metal so as to be in contact with the mold surface, cooling and solidifying the metal. To produce a casting, and then removing the mold to obtain a casting.

The casting metal applicable to the casting method of the present invention is not particularly limited, but is a zinc alloy used for precision equipment, a zinc aluminum alloy (ZAS) for a simple mold, a bismuth alloy, a copper alloy. , Brass, iron and the like can be cast very suitably by applying the casting method of the present invention. Copper alloy is more suitable as a casting metal to which the casting method of the present invention can be applied.

In the production of special carbon products such as carbon electrodes for electric discharge machining, jigs for electronic component production, parts for semiconductor production, structural parts for heat resistance, etc., which are attracting attention due to the recent development of advanced industrial technology, High density graphite materials are used. These are prepared by first adding pitch and tar to coke, kneading them at a high temperature, forming them under pressure, and then performing primary firing at about 1000 ° C. to make carbonaceous materials, and then secondary firing at about 3000 ° C. to obtain graphite. A cylindrical material, a rectangular parallelepiped, or the like graphite material is cut and machined as appropriate to produce a product. In this process, a large amount of chip particles are generated. These chip particles are made of high-density graphite, but are made into particles, and should be discarded without being used as the special carbon product.

As the carbon particles used in the foundry sand of the present invention, the above-mentioned swarf particles have characteristics that can be sufficiently applied. By containing a binder,
It can be used as the foundry sand of the present invention. When using the swarf particles of the high-density graphite material used in the production of the specialty carbon product as the foundry sand of the present invention, waste materials are efficiently reused, so that low-cost, high-quality foundry sand is used. And environmental pollution caused by industrial waste can also be suppressed.

[0025]

Since the molding sand of the present invention is mostly made of graphitized carbon particles, it has not only sufficient moldability, thermal stability and air permeability but also molding sand having high thermal conductivity. Therefore, it is possible to cast a high-quality casting without causing uneven shrinkage or a casting cavity when casting precision equipment. In addition, the porosity in the particles is extremely small due to the developed crystal structure, and it has acquired a dense structure with excellent strength. A casting very close to a mold can be obtained, and steps such as cutting for making the casting after casting into a final product such as a structural part or a mold can be reduced.

Further, the high thermal conductivity allows the molten metal to be cooled more quickly in the casting process, which also contributes to an improvement in productivity. Furthermore, because it has a graphite mold surface, the surface of the casting metal becomes smooth during casting,
Good casting surface.

[0027]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to only the following examples. Example 1 50 parts by weight of a coal-based calcined coke having an average particle diameter of 15 μm,
50 parts by weight of coal-based raw coke having an average particle diameter of 15 μm and 30 parts by weight of coal-based pitch were uniformly kneaded at 130 ° C. to obtain a raw material composition. After cooling, the raw material composition is pulverized into coarse particles, and the pulverized particles are filled in a rubber bag, and pressure-molded by a cold isostatic press at a surface pressure of 1300 kgf / cm ^{2 to} obtain an outer diameter of 900 mm and an overall length of 1800 mm. A cylindrical molded body was obtained. Next, after this molded body was primarily fired to 1200 ° C., the obtained primary fired product was directly heated to 2800 ° C. for secondary firing, and then allowed to cool to obtain an isotropic graphite material. After the graphite material obtained above is pulverized by a jaw crusher, it is further pulverized by a roller mill and then pulverized.
The particles were classified by a vibrating sieve having a mesh size of 35 mesh at the upper limit to obtain carbon particles. 30 parts by weight of sodium silicate was added to 70 parts by weight of the carbon particles, and a molding sand was obtained according to a conventional method.

The above-mentioned foundry sand was put into a mold, and a casting sand mold was formed using a wooden mold having a product shape. After removing the wooden mold, add about 4 parts of Mitsui Kinzoku's zinc alloy for injection molding.
Cast at 50 ° C and solidify by cooling to produce a casting,
Thereafter, the mold was removed to obtain a casting. The casting sand mold used in the above casting method was able to form a deep rib shape of 5 mm or less, which had been difficult to form so far, with high strength, so that the cast casting could have a precise shape. The subsequent production process such as reshaping of the precision part could be significantly shortened. In addition, the cooling of the cast metal was completed in a very short time, thereby shortening the time required for the casting process. The obtained casting was of high quality with no shrinkage unevenness or casting cavities in each part, despite having a precise shape.

[0029]

According to the present invention, there is provided a molding sand having sufficient formability, thermal stability and air permeability, high thermal conductivity and sufficient strength, and a casting method using the same. be able to. When using the swarf particles of the high-density graphite material as the foundry sand of the present invention, a high-quality foundry sand can be obtained at a low cost by reusing the material that has been discarded so far, and the environment due to industrial waste can be obtained. Contamination can also be suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a crystal lattice of graphite according to the present invention.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B22C 1/00-1/26

Claims (3)

(57) [Claims] 1. A carbon particles obtained by heating after the coke processed under pressure, the pressure of the pressure treatment, 70
0 to 1300 kgf / cm ² , and the obtained carbon particles have a particle diameter of 0.1 to 1.0.
mm, graphite of which 50% by weight or more is graphitized
Molding sand, which is a preparative. Wherein 10 to 40 wt% of the binder comprising claim 1, wherein the foundry sand. 3. A mold is formed by molding the molding sand according to claim 1 into a shape having a surface having a desired shape, and a molten metal is cast into contact with the mold surface. A method for producing a casting by cooling and solidifying a metal to produce a casting, and then obtaining the casting by removing the mold.