JP2006167741A - Spherical molding sand - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a casting mold which can maintain its strength, and does not cause gas defects, and can produce a casting having a smooth surface even when the quantity of a binder added is small. <P>SOLUTION: The spherical molding sand is manufactured by the flame fusion process (Verneuil's method), and has a mean grain size of 0.03 to 0.1 mm. Preferably, the spherical molding sand contains Al<SB>2</SB>O<SB>3</SB>and/or SiO<SB>2</SB>as main components. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a spherical casting sand and a casting mold used for casting molds such as cast steel, cast iron, aluminum, copper and alloys thereof.

  Conventionally, silica sand has been widely used as foundry sand. Since silica sand is a mineral product, its form is irregular, lacks fluidity, and has poor filling properties. Therefore, the surface of the mold made of silica sand is rough, and therefore the surface of the cast product (casting) is rough, and the load on the polishing process, which is a subsequent process, is increased. In addition, quartz, which is a constituent mineral of silica sand, undergoes crystal transformation to cristobalite or the like due to the thermal load during casting and collapses due to volume change at that time, so that silica sand has low regeneration efficiency as foundry sand. As means for solving these problems, spherical casting sand (for example, see Patent Document 1), high silicic acid spherical casting sand and a method for producing the same (for example, see Patent Document 2) are disclosed. In these, the raw material composition is granulated into a spherical shape and then fired in a rotary kiln or the like. However, the spheroidity of the obtained foundry sand is low, so that the fluidity and filling properties are insufficient, and the effect of improving the roughness of the foundry surface is small. Moreover, since it is a sintering method, only a porous material having many open pores and high water absorption can be obtained. As a result, the strength of the mold is insufficient, and a large amount of binder is required at the time of producing the mold, which increases gas defects and makes it difficult to regenerate as foundry sand. As a method for solving this, spheroidal molding sand (for example, Patent Document 3) is disclosed, but the smoothness of the obtained casting surface is desired to be further improved.

  On the other hand, in the production of castings, when trying to produce a casting with a smoother surface, the average particle diameter of the foundry sand must be made finer. In order to decrease, it was necessary to add a large amount of binder. In particular, in organic binders, there is a growing concern about gas defects due to the pyrolysis gas of the binder. That is, it was very difficult to achieve both a good casting surface and a casting without gas defects.

Therefore, in order to make a casting with a smooth surface, a method has been used in which a mold is made with relatively rough foundry sand and a mold is applied to the surface. Scratches and sagging occur, deteriorating the appearance of the casting.
JP-A-4-367349 (page 2) JP-A-5-169184 (2nd page) JP 2004-202577 A (2nd page)

  An object of the present invention is to provide a mold that can maintain the mold strength even when the amount of the binder added is small, does not cause gas defects, and provides a casting with a smooth surface.

  As a result of intensive studies on the spherical casting sand by the flame melting method, the present inventors have a very limited range of average particle diameter, which is completely different from the prior art. It has been found that a casting with no reduction, conversely excellent mold strength, and using such foundry sand can be produced with a smoother surface and free from gas defects, thereby completing the present invention. It was.

  The present invention relates to a spherical casting sand produced by a flame melting method and having an average particle diameter of 0.03 to 0.1 mm.

  The present invention also relates to a mold obtained by using the spherical casting sand of the present invention, a casting production method using the casting mold without forming a mold, and a casting production method using the casting mold as skin sand. About.

  According to the present invention, there is provided a foundry sand capable of realizing a mold capable of obtaining a cast having a high strength, few gas defects, and a smooth surface.

  The spherical foundry sand of the present invention has an average particle diameter in the range of 0.03 to 0.1 mm. The average particle diameter is preferably 0.03 to 0.07 mm, more preferably 0.04 to 0.07 mm, from the viewpoint of obtaining a smooth casting and the flowability of the kneaded sand.

  The average particle diameter can be determined as follows. That is, the diameter (mm) is measured when the sphericity from the particle projection cross section of the spherical casting sand particles is 1, while the major axis diameter (mm) and the minor axis of the spherical casting sand particles are measured when the sphericity <1. The diameter (mm) is measured to determine (major axis diameter + minor axis diameter) / 2, and the average value of the average particle diameter (mm) is obtained for any 100 spherical cast sand particles. . The major axis diameter and the minor axis diameter are defined as follows. When the particle is stabilized on a plane and the projected image of the particle on the plane is sandwiched between two parallel lines, the width of the particle that minimizes the distance between the parallel lines is called the minor axis diameter. The distance when a particle is sandwiched between two parallel lines in a direction perpendicular to the line is called the major axis diameter.

In addition, the major axis diameter and minor axis diameter of the spherical casting sand particles are obtained by obtaining an image (photograph) of the particles with an optical microscope or a digital scope (for example, VH-8000 type, manufactured by Keyence Corporation). It can be obtained by analysis. The sphericity is obtained by image analysis of the obtained image to determine the area of the particle projection cross section of the particle and the perimeter of the cross section, and then [the area of the same area as the area of the particle projection cross section (mm ² )] The circumference of the perfect circle (mm)] / [perimeter of the particle projection cross section (mm)] is calculated, and the obtained values are averaged for any of 50 spheroidal molding sand particles.

  The spherical shape which is the shape of the spherical casting sand of the present invention refers to a sphericity of 0.88 or more, preferably 0.90 or more. Whether or not it is spherical can be determined by observing the foundry sand with an optical microscope or a digital scope (for example, VH-8000, manufactured by Keyence Corporation), for example, as described in Examples below. it can.

  Further, from the viewpoint of improving strength and fluidity, the spherical casting sand of the present invention preferably has a sphericity of 0.95 or more, more preferably 0.98 or more, and 0.99 or more. Is more preferred.

The composition of the spherical casting sand of the present invention is preferably composed mainly of Al ₂ O ₃ and / or SiO ₂ from the viewpoint of fire resistance and thermal expansion. Here, the “main component” means that 60% by weight or more of Al ₂ O ₃ and / or SiO ₂ is contained in a total amount in all the components of the foundry sand. Furthermore, from the viewpoint of improving fire resistance, the total amount thereof is preferably 65 to 100% by weight, more preferably 80 to 100% by weight, based on all components of the spherical casting sand.

Further, the Al ₂ O ₃ / SiO ₂ weight ratio is preferably 1 to 15. From the viewpoint of improvement in fire resistance and casting sand regeneration efficiency, 1.2 to 12 is more preferable, and 1.5 to 9 is more preferable.

Incidentally, as it may be included as a component other than the main component in the spherical molding sand of the present invention, for _{example, MgO, Fe 2 O 3,} TiO 2, K 2 O, and metal oxides Na ₂ O and the like. When Fe ₂ O ₃ and TiO ₂ are contained, their content is preferably 10% by weight or less. Further, the content of Fe ₂ O ₃ is preferably 10% by weight or less. When K ₂ O and Na ₂ O are contained, the total content is preferably 3% by weight or less, more preferably 2% by weight or less.

  In addition, the water absorption rate (% by weight) of the spherical casting sand of the present invention includes suppression of an increase in the amount of binder used due to absorption of the binder used in the production of the mold into the casting sand, improvement of the mold strength, etc. From the viewpoint, it is preferably 3% by weight or less, more preferably 0.8% by weight or less, and further preferably 0.3% by weight or less. The water absorption can be measured according to the method for measuring the water absorption of JIS A1109 fine aggregate.

  In addition, the water absorption rate of spherical cast sand is usually lower when the sand is prepared by a flame melting method and the same sphericity as compared with sand prepared by a firing method other than the method.

  On the other hand, when the sphericity of the spherical casting sand of the present invention is 0.98 or more, the spherical casting sand is a known casting sand having low fluidity such as silica sand (casting sand having a sphericity of less than 0.98). If it is contained in the mixture, preferably 50% by volume or more, the foundry sand made of the mixture can sufficiently exhibit the desired effect of the present invention. That is, if the spherical foundry sand of the present invention is gradually added to the known foundry sand as described above, the desired effect of the present invention will be exhibited depending on the amount added, but the cast comprising the above mixture. When the spherical cast sand of the present invention having the predetermined sphericity is contained in 50% by volume or more in sand, the effect becomes more remarkable. In addition, as content of the spherical foundry sand of this invention whose sphericity is 0.98 or more in the foundry sand which consists of the said mixture, More preferably, it is 60 volume% or more, More preferably, it is 80 volume% or more. Accordingly, as the spherical casting sand of the present invention, one having a sphericity of 0.98 or more is particularly suitable because of its excellent utility. In addition, since the foundry sand containing 50% by volume or more of such spherical sand can exhibit the same effect as the spherical sand of the present invention, such foundry sand is also included in the present invention. That is, according to the present invention, there is provided a casting sand containing 50% by volume or more of spherical casting sand having an average particle diameter of 0.03 to 0.1 mm and a sphericity of 0.98 or more, which is produced by a flame melting method. The

  As described above, the spheroidal sand of the present invention is produced by a flame melting method as exemplified in JP-A No. 2004-202577. In particular, in the production of the spherical molding sand of the present invention, powder particles having an average particle diameter of 0.02 to 0.12 mm may be used as a starting material, and may be melted and spheroidized in a flame. The particles may be obtained by classification after flame melting.

  In the process of melting and spheroidizing the powder particles as the starting material in the flame, the starting material as described above is dispersed in a carrier gas such as oxygen and melted by being put into the flame to be spheroidized. (Flame melting method). In a preferred embodiment, it is put into the following flame.

The flame to be used can be generated by burning a fuel such as propane, butane, methane, natural liquefied gas, LPG, heavy oil, kerosene, light oil, pulverized coal and the like with oxygen. Further, the powder particles can be suitably melted and spheroidized even in a plasma jet flame generated by ionizing N ₂ inert gas or the like.

  The spherical sand of the present invention and the cast sand composed of a mixture of the foundry sand and known casting sand (hereinafter, these cast sands are abbreviated as the foundry sand of the present invention) are cast steel, cast iron, aluminum, magnesium, copper. And can be suitably used for mold applications such as alloys thereof. In particular, non-ferrous metals such as aluminum, magnesium, and copper alloys, particularly aluminum, are preferable because the pouring temperature is relatively low, and the effect of smoothing the casting surface is particularly large. Moreover, since the casting surface comparable to a main mold | type is obtained as cores, such as die-casting, low pressure casting, and die casting, it is used suitably. It can also be used as a filler for metals, plastics and the like.

  The mold composition of the present invention preferably comprises the above spherical casting sand and a binder that binds them. As binder, inorganic binder such as inorganic salt such as clay, water glass, silica sol, ethyl silicate, sulfate, phosphate, nitrate, or furan resin, phenol resin, furan phenol resin, urethane resin, unsaturated polyester resin, An organic binder such as an alkyd resin is preferably used. As the curing method, a conventionally known curing method such as a self-curing method, a heat curing method, a gas curing method or the like is used, but a self-curing method or a heat curing method is preferably used. These binder and spherical casting sand are mixed, and a mold is formed according to a known method.

  The spherical foundry sand of the present invention has one of the major features in that it has a specific average particle size, and preferably has a specific component composition and high sphericity. With such a configuration, it is possible to produce a casting mold having excellent fluidity, high strength and a smooth surface. In addition, the mold can be manufactured with a smaller amount of binder than in the prior art, and is easy to regenerate.

  Moreover, in the present invention, the casting sand is spherical and the surface of the sand is smooth. Therefore, even if the particle diameter is made finer, the mold strength does not decrease. Rather, it is preferable because the moldability is increased because the filling property is improved, the amount of the binder added can be reduced, and the gas defects can be reduced.

  The spheroidal sand of the present invention is suitably used in alkali phenol molds and shell mold methods.

  From the viewpoint of obtaining a high-strength casting mold, it is preferable that the binder is used in an amount of 0.05 to 5 parts by weight with respect to 100 parts by weight of the foundry sand of the present invention.

  The mold obtained from the foundry sand containing the spherical foundry sand of the present invention exhibits the maximum effect when used as a surface in contact with the foundry, that is, skin sand. In particular, from the viewpoint of the air permeability of the mold for filling the molten metal, conventionally known foundry sand including the foundry sand by the flame melting method is used for the surface not in contact with the casting. In particular, when the average particle size of the foundry sand is 0.05 mm or less, it is preferable to use an aggregate having an average particle size of 0.015 mm or more for the back sand.

  Moreover, you may use conventionally well-known foundry sand whose average particle diameter is 0.150 mm or more about the part in which the smoothness of a casting surface is not requested | required.

  The mold composition thus obtained has a high strength and a smooth surface. Therefore, when casting with this casting mold, it is possible to obtain a casting with a small surface roughness and a small load on the polishing step which is a subsequent step. Since a smooth casting can be obtained without using a coating mold, the dimensional fluttering of the casting due to the reduction in the coating process of the coating mold and the variation in the coating thickness of the coating mold is reduced. Further, depending on the shape, surface smoothness equivalent to that of a mold can be obtained, so that it is not necessary to create an expensive mold.

  In particular, it is useful for casting parts having inner surfaces that are in contact with fluids such as gas, oil, and water that are difficult to machine, such as automobile exhaust manifolds, engine parts, pump parts, machine tool parts having sliding surfaces, and the like.

  Moreover, a structure with a smooth surface can be obtained by further processing the casting appropriately. As the said structure, a metal mold | die, an engine member, a machine tool member, a building member, the frame of an electrical appliance, etc. are mentioned, for example.

  Casting molds, castings and structures having excellent properties as described above, machines, equipment using the same, and the like are included in the present invention.

Example 1
97% by weight of Al ₂ O ₃ and SiO ₂ in total, Al ₂ O ₃ / SiO ₂ weight ratio is 1.7, water content is 0% by weight, average particle size is 0.12 mm, major axis diameter / A mullite powder (synthetic mullite powder manufactured by Shibata Ceramics) having a minor axis diameter ratio of 1.5 is used as a starting material, the powder is used as a carrier gas, and LPG (propane gas) is used in an oxygen ratio (volume ratio) of 1 Was put into a flame (about 2000 ° C.) burned in 1. to obtain monodispersed spherical casting sand. The obtained foundry sand contains 97% by weight of Al ₂ O ₃ and SiO ₂ in a total amount, the Al ₂ O ₃ / SiO ₂ weight ratio is 1.7, the average particle size is 0.095 mm, and the sphericity Was 0.99, the water absorption was 0.3% by weight, and the particle density was 2.9 g / cm ³ . An alkali phenol binder was added to the foundry sand, mixed and cured according to a self-hardening mold making method to obtain a mold composition. Specifically, 0.24 parts by weight of a curing agent QX130 (manufactured by Kao Quaker Co., Ltd., an alkali phenol curing agent) is added to 100 parts by weight of the foundry sand, mixed with a mixer, and then Kaoh Step S660 (Kao Quaker). 1.2 parts by weight of an alkali phenol resin) were added and mixed, filled into a wooden mold having an inner diameter of 50 mm × height of 50 mmH, and then removed from the wooden mold after 24 hours, and the mold strength was measured.

  Also, using this mold composition, the core shown in FIG. 1 is prepared using a mold, and is set in a main mold (created with No. 6 cinnabar) as shown in FIG. Hot water (component AC4C) was poured. The smoothness of the core mold and the core surface of the casting was measured as surface roughness (centerline average roughness: Ra) with a surface roughness measuring instrument (Surfcoder SE-30H, manufactured by Kosaka Laboratory). The smaller the Ra, the better the surface smoothness. The results are shown in Table 1.

Example 2
Foundry sand was obtained in the same manner as in Example 1 except that the foundry sand obtained in Example 1 was adjusted to an average particle size of 0.065 mm by sieving. Evaluation similar to Example 1 was performed using this foundry sand. The results are shown in Table 1.

Example 3
Foundry sand was obtained in the same manner as in Example 1 except that the foundry sand obtained in Example 1 was adjusted to an average particle size of 0.055 mm by sieving. Evaluation similar to Example 1 was performed using this foundry sand. The results are shown in Table 1.

Comparative Example 1
Foundry sand was obtained in the same manner as in Example 1 except that the average particle size of the raw materials was changed to 0.15 mm. The average particle size of the obtained foundry sand was 0.13 mm. Evaluation similar to Example 1 was performed using this foundry sand. The results are shown in Table 1.

Comparative Examples 2 and 3
Using the same raw material powder as in Example 1, spherically granulated particles using a spray dryer were baked in an electric furnace to obtain spherical foundry sand having an average particle diameter shown in Table 1. Evaluation similar to Example 1 was performed using the foundry sand. The results are shown in Table 1.

Comparative Examples 4 and 5
By using a commercially available Albany silica sand and appropriately classifying it, a casting sand having a particle size shown in Table 1 was obtained. Evaluation similar to Example 1 was performed using the foundry sand. The results are shown in Table 1.

  From these results, when a mold is produced using spherical casting sand produced by a flame melting method having an average particle diameter of 0.1 mm or less, a very smooth casting can be obtained. However, it can be seen that, unlike the casting sands of other manufacturing methods, high strength can be maintained, so that it is not necessary to increase the amount of binder added and gas defects can be reduced. In addition, the result of Table 1 was put together in the graph of FIG. In FIG. 3, “actual” means an example, and “ratio” means a comparative example.

Example 4
The casting sand having the average particle size of 0.065 mm in Example 2 was used as skin sand, and No. 5 silica sand was used as backing sand, thereby producing a mold having the shape of FIG. The thickness of the skin sand was about 1 cm to 4 cm. The molten aluminum was poured with this mold. The resulting casting had a very smooth surface and no gas defects.

Comparative Example 6
The same test as in Example 4 was performed using the silica sand having an average particle size of 80 μm used in Comparative Example 5 as skin sand. In order to ensure sufficient mold strength, the amount of resin added was 2.8%. Although the obtained casting had a portion with a clean surface, a gas defect occurred.

Examples 5 and 6 and Comparative Example 7
RCS was manufactured using the foundry sands of Examples 1 and 3 and Comparative Example 1. Specifically, after casting sand was heated at 150 ° C., 1.0 part by weight of phenol resin (AV Light, Asahi Organic Materials Co., Ltd.) was added to 100 parts by weight of foundry sand and kneaded. Next, the temperature was lowered to 105 ° C., and at this temperature, the hexamethylenetetramine aqueous solution (concentration 18% by weight) (curing agent) was 0.83 parts by weight (100% by weight in terms of solid content) with respect to 100 parts by weight of foundry sand. ) Added and kneaded, and further kneaded while blowing cold air. Further, RCS was obtained by adding 0.05 parts by weight of calcium stearate (lubricant) to 100 parts by weight of foundry sand and kneading to improve fluidity.

  The obtained RCS was filled in a core mold having the shape shown in FIG. 1 and fired at 250 ° C. for 90 seconds to obtain a core mold. The bending strength of the mold was measured according to JIS K-6910 method.

  Further, the core mold obtained above was set in a main mold (created with No. 6 cinnabar) as shown in FIG. 2, and molten aluminum (component AC4C) was poured. The smoothness of the core mold and the core surface of the casting was measured as surface roughness (centerline average roughness: Ra) with a surface roughness measuring instrument (Surfcoder SE-30H, manufactured by Kosaka Laboratory). The smaller the Ra, the better the surface smoothness. The results are shown in Table 2.

Schematic of core used in examples and comparative examples Schematic of aluminum casting method using the core shown in FIG. A graph summarizing the relationship between the average particle size of the foundry sand of the examples and comparative examples and the mold strength

Claims (6)

Spherical foundry sand having an average particle size of 0.03 to 0.1 mm manufactured by a flame melting method. The spherical foundry sand according to claim 1, comprising Al ₂ O ₃ and / or SiO ₂ as a main component. A mold obtained by using the spherical foundry sand according to claim 1 or 2. A method for producing a casting, wherein the mold according to claim 3 is used without forming a coating mold. The manufacturing method of the casting which uses the casting_mold | template of Claim 3 as skin sand. The method for producing a casting according to claim 4 or 5, wherein the casting is an aluminum casting.

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