JP5178366B2 - Stucco material for mold manufacturing for precision casting and mold for precision casting using the same - Google Patents

Description

  The present invention relates to a stucco material for producing a precision casting mold and a precision casting mold using the same, and in particular, for a precision casting that can advantageously obtain a beautiful casting and can be easily reused after use. The present invention relates to a precision casting mold manufacturing stucco material suitably used for manufacturing a mold, and a precision casting mold using the same.

  Conventionally, the lost wax method (investment casting method) is known as a precision casting method for obtaining a casting with particularly excellent dimensional accuracy and surface roughness. And the manufacture of the precision casting mold used for this lost wax method has generally been performed as follows. That is, first, a wax model having a desired product shape is manufactured, and then this wax model is immersed (dipped) in a ceramic slurry containing fine ceramic aggregates, and then a stucco material ( A ceramic coating layer (innermost layer) is formed on the surface of the wax model by sprinkling (stuccoing) refractory sand) and drying. Then, the soldering model in which the ceramic coating layer is formed is further subjected to the dipping, stuccoing and drying coating layer forming steps by repeating the process a plurality of times (4 to 10 times) in the same manner as described above. A plurality of ceramic coating layers (thickness: about 3 to 10 mm) are laminated and formed on the surface of the model. Thereafter, the wax model in which the plurality of ceramic coating layers are formed is heated to melt and remove the wax model, and then, the plurality of ceramic coating layers from which the wax model has been removed is fired to thereby form a plurality of ceramics. A precision casting mold comprising a shell layer is completed. And at the time of casting, a casting will be manufactured by casting a molten metal in the cavity of the casting_mold | template produced by removing this wax model.

  By the way, as stucco materials used in the production of a precision casting mold by the lost wax method, sand particles such as chamotte particles, mullite particles, alumina particles, silica particles, zirconia particles, and zircon particles have been conventionally used. . Among them, in particular, zircon grains are produced by using the stucco material as a stucco material because the mold is chemically stable to the molten metal, and defects such as insertion of the molten metal into the mold wall are unlikely to occur. Since castings with beautiful casting surface can be advantageously obtained, they are widely used in general (edited by the Japan Foundry Association Precision Casting Research Group, “Precision Casting”, Nikkan Kogyo Shimbun, January 1984) Issue, p.31-36 (Non-Patent Document 1) and Japanese Patent Application Laid-Open No. 61-289944 (Patent Document 1), Japanese Patent Application Laid-Open No. 7-47444 (Patent Document 2), etc.).

However, such zircon grains are low in natural production, and since the production areas are unevenly distributed, in recent years, the price of raw materials has soared, and it has become difficult to obtain them. Therefore, the use as a stucco material has become difficult. Furthermore, although zircon grains have ZrO ₂ and SiO ₂ as chemical components, it is usually difficult to control the chemical composition with the Al ₂ O ₃ system components used together as stucco materials. In addition, it is difficult to reuse the used mold, and in addition, since the radioactive material is contained in a small amount, there is a problem that the disposal is expensive.

  Under such circumstances, Japanese Patent Application Laid-Open No. 2005-324253 (Patent Document 3) proposes a precision casting mold comprising a ceramic shell layer that does not contain any zircon grains from the viewpoint of reducing the cost of waste disposal. . However, such a precision casting mold is generally simply a stucco material that does not contain zircon grains by increasing the composition ratio of mullite grains, alumina grains, etc. blended with the zircon grains in the stucco material. In such a precision casting mold, a high fire resistance mold can be obtained from the high melting temperature of alumina grains and mullite grains. As compared with grains, problems such as fusion (seizure) of stucco materials and insertion of molten metal are easily caused, and it is difficult to obtain a smooth casting surface.

JP 61-289944 A Japanese Unexamined Patent Publication No. 7-47444 JP 2005-324253 A Edited by the Japan Foundry Association Precision Casting Research Committee, “Precision Casting”, published by Nikkan Kogyo Shimbun, January 1984, p. 31-36

  Here, the present invention has been made in the background as described above, and the problem to be solved is precision casting in which a casting having a beautiful casting surface can be advantageously obtained without using zircon grains. It is an object to provide a stucco material for producing a precision casting mold that can be advantageously used in the production of a casting mold, and a precision casting mold using the same.

  And as a result of intensive investigations to solve such problems, the present inventors have made refractory porous materials composed of mullite crystals or mixed crystals of mullite and corundum, which contain a specific proportion of alumina and silica. The inventors have found that a spherical particle having a specific particle diameter and apparent porosity is effective for solving the above-mentioned problems, and has completed the present invention.

  Accordingly, the present invention has been completed based on such knowledge, and is suitable for various aspects as listed below in order to solve the problems described above or the problems grasped from the description of the entire specification. However, each aspect described below can be adopted in any combination. It should be noted that aspects or technical features of the present invention are not limited to those described below, and can be recognized based on the description of the entire specification or the inventive idea disclosed therein. Should be understood.

(1) Al ₂ O ₃ : 70 to 90% by weight, SiO ₂ : 10 to 30% by weight and other oxides: 0 to 5% by weight, and composed of mullite crystals or mixed crystals of mullite and corundum. A stucco material for producing a casting mold for precision casting, comprising particles of a refractory porous spherical particle having a particle diameter of 0.05 to 0.5 mm and an apparent porosity of 5 to 14%.

(2) The above refractory porous spherical particles are further mixed with at least one other alumina / silica-based particle in a proportion of 30% by weight or less. A stucco material for producing a mold for precision casting according to the aspect (1).

(3) A precision casting mold obtained by using the stucco material according to the aspect (1) or (2).

(4) The mold wall is composed of a plurality of ceramic shell layers, and among these ceramic shell layers, the innermost layer in contact with the molten metal uses the stucco material described in the above aspect (1) or (2). On the other hand, at least one ceramic shell layer outside the innermost layer is formed using the refractory porous spherical particles and / or other alumina / silica-based particles as a stucco material. The casting mold for precision casting according to the above aspect (3), characterized in that:

(5) The above aspect (3) or (3), wherein an inorganic binder composed of colloidal silica or ethyl silicate is blended as a binder in the slurry used to form the ceramic shell layer constituting the mold wall. The precision casting mold as described in 4).

(6) The precision casting mold according to the aspect (5), wherein at least one kind of alumina / silica-based particles is suspended as an aggregate in the slurry.

(7) The recovered particles obtained by crushing and sieving the precision casting mold according to any one of the above aspects (3) to (6) may be used in place of or together with the alumina / silica-based particles. The precision casting mold according to any one of the above aspects (3) to (6), wherein the precision casting mold is used.

  Thus, in the stucco material for precision casting mold production according to the present invention, the mullite crystal or the mixed crystal of mullite and corundum, which is excellent in fire resistance and has a low coefficient of thermal expansion and is composed of a predetermined ratio of alumina and silica. Since the fire-resistant porous spherical particles are composed of the above, the fire resistance of the precision casting mold produced using the same is effectively improved. As a result, the rough surface of the casting caused by the chemical reaction with the molten metal and seizure (fusion) of the stucco material can be advantageously prevented, and the dimensional accuracy of the resulting casting is obtained. This can advantageously prevent the occurrence of variations and mold breaks and cracks during casting.

  Moreover, in the present invention, since the refractory porous spherical particles constituting the stucco material are spherical particles having a specific particle diameter, clogging of the sand is good, and therefore, it is produced using the spherical particles. In a casting obtained using a precision casting mold, it is possible to advantageously prevent the occurrence of defects such as insertion that causes roughness of the casting surface, and a smooth casting surface with a low surface roughness. Is advantageously obtained.

  Furthermore, since the refractory porous spherical particles constituting the stucco material for producing a precision casting mold according to the present invention have a porous structure having a specific apparent porosity, such particles will be coated with a slurry. When it is sprinkled on the model, it can be adhered to the wax model in an advantageous and strong manner. Therefore, during casting of a precision casting mold manufactured using such a stucco material, It can be advantageously prevented that a part of the mold wall in contact with the molten metal collapses before or during pouring, so that a casting having a beautiful casting surface with no rough casting surface is advantageous. Will be obtained.

  In addition, in the stucco material for manufacturing a precision casting mold according to the present invention, the refractory porous spherical particles constituting the stucco material are composed of mullite crystals or mixed crystals of mullite and corundum that do not contain zircon grains. Therefore, after the precision casting mold manufactured using the same is used, it has an advantage that it can be easily reused.

By the way, the stucco material for mold production for precision casting according to the present invention comprises Al ₂ O ₃ : 70 to 90% by weight, SiO ₂ : 10 to 30% by weight and other oxides: 0 to 5% by weight, and mullite. Although the crystal or mixed crystals of mullite and corundum is made of a refractory porous spherical particles composed, in which, mullite _{crystals, 3Al 2 O 3 · 2SiO 2} ~2Al 2 O 3 · SiO 2 chemical The composition is composed of 71.8-77.3 wt% Al ₂ O ₃ and 28.2-22.7 wt% SiO ₂ (“Ceramics Engineering Handbook (Second Edition) [Application]” 2002 In the case of such refractory porous spherical particles, among the crystal components constituting the refractory porous spherical particles, the main component is mullite crystals. Become.

  And in the present invention, the stucco material for mold production for precision casting is composed of refractory particles mainly composed of such mullite crystals or composed of mullite crystals or mixed crystals of mullite and corundum. Such a mullite crystal or a mixed crystal of mullite and corundum generally shows SK37-SK39 (1820 ° C.-1880 ° C.) as a Zegel cone fire resistance as defined in JIS-R-2204 (1999). A mold obtained by using such a stucco material for producing a mold for precision casting because it exhibits equivalent or higher fire resistance than zircon grains having a fire resistance of SK37 (1825 ° C). The fire resistance of this is advantageously excellent. As described above, in the stucco material for manufacturing a precision casting mold according to the present invention, since the fire resistance of the mold formed using the same is excellent, the molten metal and the mold wall are fused at the time of casting. Thus, it is possible to advantageously prevent the occurrence of surface roughness due to seizure on the surface (cast surface) of the obtained casting.

  Moreover, in the stucco material for mold production for precision casting according to the present invention, the stucco material is made of mullite crystal having excellent thermal expansion characteristics (low thermal expansion coefficient) or a refractory composed of mullite and corundum mixed crystal. Since it is composed of particles, the dimensional accuracy of the casting cast by the mold obtained by using it is advantageously excellent, and defects such as cutting and cracking of the mold occur during casting. Such a thing can also be advantageously prevented.

In addition, when the ratio of Al ₂ O ₃ in the refractory particles constituting the stucco material for producing precision casting molds is larger than the above range, in other words, the amount of SiO _{2 in} the refractory particles. However, if it is less than the above range, the proportion of corundum crystals in the refractory particles will increase, thereby improving the fire resistance of such particles, but the coefficient of thermal expansion will be increased. In a mold manufactured using such refractory particles as a stucco material, problems such as deterioration of the dimensional accuracy of the resulting casting and breakage or cracking of the mold are caused. On the other hand, when the proportion of Al ₂ O _{3 in} the refractory particles is smaller than the above range, and the proportion of SiO _{2 in} the refractory particles is larger than the above range, the crystal structure in the refractory particles However, it deviates from the composition consisting of mullite crystals or mixed crystals of mullite and corundum, and SiO ₂ crystals are included. In that case, since the fire resistance of the obtained mold is lowered, problems such as seizure (fusion) are caused in the casting obtained by using such a mold.

Moreover, in the stucco material for mold production for precision casting according to the present invention, the particles constituting the stucco material include Al ₂ O ₃ and SiO _{2 which} are components constituting the mullite crystal or the mixed crystal of mullite and corundum. In addition, 0 to 5% by weight of other oxides may be included. Such other oxide is not particularly limited in the present invention, and is generally Fe as an impurity contained in a raw material for forming a mullite crystal or a mixed crystal of mullite and corundum. Examples thereof include oxides such as ₂ O ₃ , MgO, CaO, Na ₂ O, K ₂ O, and P ₂ O ₅ . If the content of other oxides is too large, the fire resistance of the resulting mold deteriorates and problems such as seizure (fusion) occur. The content is limited to about wt%, preferably about 0 to 3 wt%.

Further, the stucco material for producing a casting mold for precision casting according to the present invention is a refractory material composed of mullite crystal or mixed mullite and corundum crystal composed of Al ₂ O ₃ , SiO ₂ and other oxides in a specific proportion as described above. It consists of spherical particles having a particle diameter of 0.05 to 0.5 mm. Thus, in the stucco material for mold production for precision casting that is the subject of the present invention, since the particles constituting the stucco material are spherical particles having a specific particle diameter, it is used. When the mold is manufactured, the sand of the resulting mold is well clogged. Therefore, in the casting cast by the precision casting mold manufactured using the mold, there is a defect such as an insertion that causes the roughening of the casting surface. Such occurrence can be advantageously prevented, and a smooth casting surface having a low surface roughness can be advantageously obtained. In particular, the stucco material for mold production for precision casting is the first ceramic shell layer, that is, the innermost ceramic shell layer (ceramic) that forms the casting surface of the resulting casting by contacting the molten metal during casting. When used to form a coating layer), the particle size of the refractory spherical particles is preferably about 0.1 to 0.3 mm, more preferably 0.1 to 0.3 mm. It will be about 0.2 mm.

  In the above refractory spherical particles, if the particle diameter becomes too small, the refractory spherical particles adhering to the stucco material made of such particles when sprinkled on the wax model coated with the slurry are small. Since the thickness of the ceramic coating layer (ceramic shell layer) formed thereby becomes too thin, the advantageous characteristics of the above-described stucco material for precision casting mold production cannot be fully exhibited, and the resulting mold Insufficient fire resistance may cause problems such as seizure (fusion). On the other hand, when the particle diameter of the refractory spherical particles is too large, the surface roughness of the mold wall obtained using the sphere becomes high. There is a possibility that the surface of the casting becomes rough due to rough surface roughness or casting defects such as insertion.

  Further, in the refractory spherical particles constituting the precision casting mold manufacturing stucco material according to the present invention, “spherical” means that it has a substantially spherical shape, and has an acute angle portion. Any rounded spherical shape is acceptable, and includes an elliptical sphere shape and a spindle sphere shape. However, in the present invention, a circularity (circular area equivalent circumference / particle projection image contour circumference) is generally 0.6 or more, preferably 0.7 or more, more preferably 0.8 or more. Will be used.

  Moreover, such a stucco material for producing precision casting molds has a porous structure with an apparent porosity of 5 to 14%, preferably 6 to 13%. Thus, in the stucco material for precision casting mold production that is the subject of the present invention, the refractory spherical particles as described above have a porous structure having a specific apparent porosity. Then, when such particles are sprinkled on the slurry coated on the wax model and adhere to the slurry, the slurry in contact with the holes opening on the surface of the particles enters the holes, and thereby the surface tension exerted thereby Such a refractory porous spherical particle is advantageously adhered firmly on the wax model.

  When the refractory particles constituting the stucco material do not have such a porous structure, the contact area between the stucco material and the slurry is small, and the surface tension acting between them is small. Therefore, in a mold manufactured using such a stucco material, the stucco material (refractory particles) may fall off before or during casting. In addition, in the case of complex wax models, stucco material may leak out at the corners, etc., so in castings cast with such molds, There is a problem that defects such as rough skin are caused.

  In addition, in such a refractory porous spherical particle, when the apparent porosity is too larger than the above-mentioned range, the volume occupied by the pores in the particle becomes too large, and it is easy to wear. In the mold obtained by the above, there is a possibility that sufficient strength may not be ensured, on the other hand, if the apparent porosity of the refractory porous spherical particles is too small than the above range, the surface of the particles is opened. There is a possibility that the density of pores to be reduced becomes too low, and the effect of improving the adhesion to the slurry as described above cannot be sufficiently exhibited.

By the way, when manufacturing the stucco material for precision casting mold manufacturing according to the present invention as described above, the manufacturing method is not particularly limited, and any known method for manufacturing refractory particles can be used as appropriate. For example, silica sand, silica stone, refractory clay, clay mineral, clay, kaolin, van earth shale, bauxite, andalusite, kyanite, sillimanite, aluminum hydroxide, alumina, calcined alumina, etc. After preparing the slurry, the refractory raw material forming the mullite crystal or the mixed crystal of mullite and corundum is appropriately combined so that the composition of Al ₂ O ₃ and SiO ₂ becomes the above-mentioned specific ratio, The slurry is granulated into a sphere by a spray dryer method, or the slurry is dehydrated and dried and then granulated into a sphere by a granulator. After granulation, it can be produced by firing in a firing furnace such as a rotary kiln, tunnel kiln or shuttle kiln.

  In addition to the method for obtaining refractory porous spherical particles by granulating particles having a predetermined shape as described above and then firing, for example, a refractory raw material as described above is used in a high-temperature heating furnace. After making it into a molten state, it is possible to obtain refractory porous spherical particles by blowing off with pressurized air, or to obtain refractory porous spherical particles by a known flame melting method or the like. Is possible.

Furthermore, such refractory porous spherical particles are not limited to those produced as a granulated product from the above-mentioned refractory raw materials, but those obtained by processing natural sand grains into a spherical shape. There is no problem even if it is used. For example, a natural material composed of Al ₂ O ₃ : 70 to 90% by weight, SiO ₂ : 10 to 30% by weight and other oxides: 0 to 5% by weight, and composed of mullite crystals or mixed crystals of mullite and corundum. After pulverizing and sizing the above-mentioned refractory material having a predetermined apparent porosity, the surface of the sand is removed using a polishing machine such as a rotary kramer, sand shine, sand fisher, or hybridizer. What was obtained by sieving after removing an acute angle part by grinding | polishing can also be used.

  In addition, in the stucco material for producing a casting mold for precision casting according to the present invention, at least one of other alumina / silica-based particles is further added to the refractory porous spherical particles as described above. Even if they are mixed together, there is no problem. When such a stucco material is used to form the ceramic coating layer (ceramic shell layer) of the innermost layer (first layer), such other alumina / silica particles are 30% by weight or less. It will be mixed in the ratio used as content. If the content of the other alumina-silica-based particles is excessively increased, the content of the refractory porous spherical particles is relatively decreased. In castings that are cast using a mold manufactured using such a stucco material, rough surface due to insertion, seizure (fusion), etc., or the surface roughness of the casting surface is rough. This is because there is a risk of becoming. On the other hand, when a stucco material containing other alumina / silica-based particles is used to form the second and subsequent ceramic coating layers (ceramic shell layers) on the outer layer side than the innermost layer. The content is not particularly limited. The ceramic shell layer after the second layer is not in direct contact with the molten metal at the time of casting, and is not a surface that forms the casting surface of the resulting casting, so the content of such other alumina / silica particles is large. Even if it becomes, it is because the bad influence which it has on the beauty of the casting skin of the casting cast by it is few.

  The other alumina / silica particles described above refer to alumina particles, silica particles, and alumina-silica particles other than the above-mentioned fire-resistant porous spherical particles, and contain fire-resistance that contains alumina and / or silica as a main component. Oxide particles, for example, silica sand, silica particles, cristobalite particles, trizimanite particles, quartz particles, fused silica particles, chamotte particles, calcined kaolin particles, mullite particles, alumina particles, calcined alumina particles, sintered alumina particles, Those obtained by crushing fused alumina particles, corundum particles, etc. to particles having a size of about 0.05 to 0.5 mm are used alone or in combination. Further, the particle shape is not limited to a spherical shape, but may be an angular shape, and is not limited at all.

  By the way, when a precision casting mold is manufactured using the precision casting mold manufacturing stucco material according to the present invention, for example, the following process is performed.

  First, in the same manner as in the prior art, a large number of wax models having the shape of the target casting are produced, and an appropriate number of the produced wax models, together with a wax model that becomes a part of the gate, runner, and weir, Build a tree by assembling together.

  Next, the tree (wax model) surface is coated with the slurry by dipping the tree in a ceramic slurry that has been suspended by stirring with a stirrer.

  The slurry used therein is not particularly limited in the present invention. Conventionally, the slurry used for forming a ceramic shell layer in the lost wax method (investment method) has been known. Any of these various slurries can be selected as appropriate, but preferably, an inorganic binder made of colloidal silica or ethyl silicate is used, and it is blended in a medium such as water or alcohol as necessary. Thus, the prepared one is advantageously used.

  Here, as the colloidal silica as the inorganic binder, those in which ultrafine amorphous silica having a particle diameter of about 3 to 200 nm is stably dispersed in a dispersion medium are generally used. Among these, as such colloidal silica, silica sol having a silica particle diameter of about 3 to 30 nm and dispersed at a concentration of about 20 to 40% by weight is particularly preferably used. Further, as ethyl silicate, tetraethyl orthosilicate, ethyl silicate 40, ethyl silicate 28, or the like is preferably used.

  In addition, it is desirable that at least one kind of alumina / silica-based particles composed of a refractory oxide containing alumina or silica as a main component as described above is suspended as an aggregate in the slurry. In addition, when suspending such alumina / silica-based particles in a slurry, in order to stably float and disperse the particles without allowing them to settle in the slurry, the particle diameter is less than 0.2 mm. It is preferred that it is less than 0.1 mm. Further, it is desirable that the alumina / silica-based particles are suspended in the slurry at a ratio of about 40 to 90% by weight.

  Furthermore, for the slurry, various surfactants, gelation accelerators, and the like are appropriately added as necessary, as in the known slurry conventionally used in the lost wax method (investment method). It will be included.

  In the production of a precision casting mold according to the present invention, a tree (wax model) dipped in such a slurry is lifted from the slurry, and then the tree is coated and adhered. Before the slurry dries, the stucco material for producing a precision casting mold according to the present invention as described above is sprinkled (stuccoed). In addition, when the stucco material is sprinkled, any conventionally known sprinkling method is appropriately employed.For example, a drop-type sprinkling method in which sprinkling is performed by dropping the stucco material in a rainy state or a tree is used. The target stuccoing is performed by adopting a solid fluidized bed type sprinkling method in which the stucco material is suspended by floating in the container and air blown out from the bottom of the container. .

  Thereafter, the tree (wax model) covered with the stucco material according to the present invention is subjected to natural drying or mechanical drying to form the first ceramic coating layer as the innermost layer. According to the ceramic shell mold method, a series of coating layers including dipping, stuccoing, and drying are further formed in the same manner as described above for the wax model on which the first ceramic coating layer is formed. By repeating the process a plurality of times (4 to 10 times), a plurality of ceramic coating layers (thickness: about 3 to 10 mm) are laminated and formed on the wax model.

  Thus, in the manufacture of the precision casting mold that is the subject of the present invention, the ceramic coating layer of the innermost layer (first layer) is formed using the stucco material for precision casting mold manufacturing according to the present invention as described above. Since a single layer of the ceramic coating layer is formed on the tree (wax model), the coating layer forming process is repeated a plurality of times, so that a plurality of ceramic coating layers serving as mold walls are laminated. However, it is preferable that at least one ceramic coating layer outside the innermost layer is formed using the refractory porous spherical particles and / or other alumina / silica-based particles as a stucco material.

  That is, the ceramic coating layer (ceramic shell layer) that contacts the molten metal at the time of casting and forms the casting surface of the resulting casting is the innermost layer (first layer) ceramic coating layer. As the stucco material for forming the ceramic coating layer (ceramic shell layer), the stucco material for precision casting mold production according to the present invention is used, while the ceramic coating layer outside the innermost layer is used as the fireproof porous material according to the present invention. In addition to the spherical particles, the other alumina / silica-based particles described above or a mixture thereof can be used as appropriate. Thus, in the precision casting mold to be obtained, the excellent effects as described above are obtained. This is advantageous economically.

  More preferably, the precision casting mold manufacturing stucco material used in manufacturing the precision casting mold according to the present invention has a particle diameter that increases from the innermost ceramic coating layer to the outermost ceramic coating layer. Will be. As a result, the surface roughness of the inner layer forming the casting surface of the casting is lowered by contacting with the molten metal during casting, and the casting surface of the resulting casting is advantageously smooth and beautiful with no defects such as insertion. In addition, the strength of the obtained mold can be advantageously improved.

  Next, the ceramic coating layer thus laminated on the tree (wax model) is heated to about 120 to 150 ° C. in an autoclave to melt and remove the wax model. By firing the plurality of ceramic coating layers from which the wax model has been removed in a firing furnace at a temperature of 800 to 1100 ° C. for 30 minutes to 1 hour, a precision casting mold comprising a plurality of ceramic shell layers is obtained. It is.

  When a casting is manufactured using the precision casting mold manufactured as described above, the casting is manufactured by pouring a molten metal into the cavity of the mold formed by removing the wax model. However, in the present invention, the casting method of the casting is not limited in any way, for example, the pouring method, the reverse pressure method, the suction casting method, the centrifugal casting method, etc. Any conventionally known method is advantageously used.

In a casting cast using such a precision casting mold according to the present invention, as described above, the casting of the precision casting mold is formed in contact with the molten metal during casting to form the casting surface of the resulting casting. Since the ceramic shell layer of the innermost layer is configured using the stucco material for mold production for precision casting according to the present invention, from the Al ₂ O ₃ and SiO ₂ in the refractory particles constituting such a stucco material. Due to the excellent fire resistance of the mullite crystal or the mixed crystal of mullite and corundum, the cast surface of the resulting casting will be beautiful, free from roughening due to seizure (fusion), etc., and its excellent thermal expansion characteristics As a result, the dimensional accuracy of the casting is advantageously high, and the occurrence of cutting and cracking of the mold is advantageously prevented, and the occurrence of defective products can be advantageously suppressed. .

  Moreover, in the present invention, since the stucco material for producing a mold for precision casting is a spherical refractory particle having a specific particle size, the casting surface of the obtained mold is free from roughening due to insertion or the like. The stucco material is strongly adhered by the slurry because it has a smooth structure with a low surface roughness and a specific apparent porosity. The surface of the casting surface is beautiful with no roughness of the casting surface due to the collapse.

  And, such a precision casting mold according to the present invention, after the casting is cast as described above, is crushed by a crusher such as a jaw crusher or a roll breaker, further sieved, recovered, recovered As a grain, it will be used again for mold making. For example, when producing the target precision casting mold, it can be advantageously used as a stucco material or as an aggregate suspended in a slurry instead of or together with the alumina / silica-based particles. .

  As described above, in the precision casting mold according to the present invention, the stucco material for producing the precision casting mold constituting the casting mold does not contain zircon grains and is made of mullite crystal or a mixed crystal of mullite and corundum. Most of the mold components are composed of alumina and silica, and the chemical composition can be easily controlled. Therefore, it is easy to reuse the recovered grains of the mold after using the mold. Even when it is discarded, since it does not contain zircon grains containing radioactive materials, its cost can be advantageously reduced compared to a mold manufactured using a stucco material containing zircon grains. It is.

  The preferred embodiments of the present invention have been described in detail above, but these are merely examples, and the present invention is interpreted in a limited manner by the specific description according to such embodiments. It should be understood that it is not.

  For example, in the above-described embodiment, the precision casting mold according to the present invention is manufactured by the ceramic shell mold method, but the stucco material for manufacturing the precision casting mold according to the present invention is such a ceramic shell. In addition to the molding method, for example, it can also be advantageously used for the production of a precision casting mold by a solid molding method in which a refractory material filled in a container is backed up and cast. Even in the precision casting mold obtained by such a solid mold method, the excellent effects as described above are similarly realized. Further, when producing a precision casting mold by such a solid mold method, the stucco material for producing a precision casting mold according to the present invention can be advantageously used as backup sand.

  Hereinafter, some examples of the present invention will be shown and the present invention will be more specifically clarified, but the present invention is not limited by the description of such examples. It goes without saying. In addition to the following examples, the present invention includes various changes and modifications based on the knowledge of those skilled in the art without departing from the spirit of the present invention, in addition to the above specific description. It should be understood that improvements can be made.

<Example 1>
After using aluminum hydroxide and clay mineral as the Al ₂ O ₃ source material and the SiO ₂ source material, respectively, pulverizing them and preparing slurry according to a conventional method, the obtained slurry was sprayed by a spray dryer method. By granulating, a spherical granulated product was obtained. Then, the obtained granulated material is fired at various firing temperatures and firing times to produce refractory particles having various apparent porosity, and sieved to obtain the following table. Various refractory particles A to H (particle diameter: 0.1 to 0.2 mm) having an apparent porosity as shown in FIG. Further, the crystal phase of such refractory particles was identified by chemical analysis and X-ray diffraction measurement. As a result, Al ₂ O ₃ : 71.2 wt%, SiO ₂ : 26.3 wt%, and other oxidations Product: 2.5% by weight, and was confirmed to be composed of mullite crystals or mixed crystals of mullite and corundum. And about the produced fireproof particle AH, the following tests were each performed.

-Adhesion test-
A slurry is prepared by mixing and suspending 30% by weight of colloidal silica as a binder and 70% by weight of mullite grains as an aggregate, and in this slurry, a substantially rectangular wax model (35 mm wide) X vertical 150 mm x thickness 10 mm) was dipped. Then, the refractory particles produced above were stuccoed against the wax model coated with the slurry. And after drying such a stuccoed wax model, the presence or absence of adhesion leakage of refractory particles at the corners of the wax model is visually observed. If the adhesion leakage is severe, ×, if there is a slight adhesion leakage Was evaluated as Δ, and the case where there was no adhesion leakage was evaluated as ○. The results are also shown in Table 1 below.

−Abrasion resistance test−
500 g of 10 mmφ porcelain balls are put into a 3 L porcelain mill, and 1 kg of the refractory particles produced above are added to the mill and rotated at a rotation speed of 20 rpm for 30 minutes. It was. Thereafter, the refractory particles in the mill are taken out and sieved to obtain the weight of particles pulverized to 0.1 mm or less, and the weight ratio (weight of particles pulverized to 0.1 mm or less (kg ) / 1 kg × 100), the wear rate (%) was determined. The results are also shown in Table 1 below.

  As apparent from the results in Table 1, in the refractory particles C to G whose apparent porosity is within the scope of the present invention, there is no adhesion leakage to the corner of the wax model, and the wear rate. It was confirmed that it has the adhesion and strength required as a stucco material from the point of less than 10%. On the other hand, in the case of refractory particles A having an apparent porosity of less than 5% and an apparent porosity of 1.3% and refractory particles B having an apparent porosity of 3.9%, It was recognized that adhesion leakage of refractory particles (stucco material) occurred at the corners. Further, in the case of the refractory particles H having an apparent porosity larger than 14%, the wear rate was 10% or more, and it was recognized that it was difficult to practically use as a stucco material.

<Example 2>
First, as a stucco material for mold production for precision casting, a mullite crystal or a refractory material forming a mixed crystal of mullite and corundum is pulverized and mixed to prepare a slurry, and a spherical granulated material is formed by a spray dryer method. After granulation, the obtained granulated material is fired in a rotary kiln, crushed using a jaw crusher and a roll breaker, and sieved to obtain a chemical composition and apparent porosity as shown in Table 2 below. Fire-resistant particles (fire-resistant porous spherical particles) 1a to 1e having a particle shape and a particle diameter were prepared. In addition, by changing the refractory raw material, the blending ratio thereof, and the firing conditions, etc., refractory particles (refractory porous spherical particles) 2a to 2a having various chemical compositions and apparent porosity as shown in Table 2 below. 2c, 3a-3b, 4a-4c, 5a, 6a-6b and 7a-7b were prepared, respectively.

  On the other hand, pulverized mullite grains, alumina grains, chamotte grains, fused silica grains and recovered grains 1 as other alumina / silica-based particles that are further mixed with the above refractory particles as stucco materials for precision casting mold production The mullite particles a to e, the alumina particles a to c, and the chamotte particles a having the particle shapes and particle diameters shown in Table 2 below by sieving into particles having the particle diameters shown in Table 2 below. -B, fused silica particles a, and recovered particles 1a were prepared. In addition, said collection | recovery grain 1 is obtained by crushing the casting_mold | template produced in order to obtain the specimen 4 mentioned later with a jaw crusher and a roll breaker.

  The chemical composition of each prepared particle was determined by identifying the crystal phase by X-ray diffraction measurement. Further, from the results of X-ray diffraction measurement, all of the refractory particles 1a to 1e, 2a to 2c, 3a to 3b, and 4a to 4c are composed of mullite crystals or a mixed crystal of mullite and corundum. confirmed.

  Furthermore, the apparent porosity (%) of each particle was determined according to JIS-R-2205 (1992) “Measurement method of apparent porosity, water absorption rate and specific gravity of refractory brick”.

Next, as aggregates suspended in the slurry for producing precision casting molds, mullite particles, fused silica particles, alumina particles, and recovered particles 2 are crushed and sieved to form particles of 45 μm or less. Were mixed in the compositions shown in Table 3 below to prepare aggregates 1-4. The recovered particles 2 are obtained by crushing a mold prepared to obtain a specimen 7 to be described later with a jaw crusher and a roll breaker. Moreover, when the chemical composition of the recovered grains 2 was determined by identifying the crystal phase by X-ray diffraction measurement, Al ₂ O ₃ : 52.5 wt%, SiO ₂ : 44.7 wt%, and other oxides: 2 0.8% by weight.

  Then, the prepared aggregates 1 to 4 were mixed and suspended in colloidal silica as a binder to prepare slurry for precision casting mold production, respectively. The aggregate content in the slurry was 70% by weight, and the colloidal silica content was 30% by weight.

-Sample 1-
A substantially rectangular wax model (width 35 mm × length 150 mm × thickness 10 mm) was prepared and dipped in the slurry containing the aggregate 1 prepared above. Next, before the slurry covering the wax model is dried, the refractory particles 1a prepared above are stuccoed, and then dried at 40 ° C. for 120 minutes, whereby the first layer (innermost layer) is formed. A ceramic coating layer was formed.

  In addition, for the wax model formed with the first ceramic coating layer, the aggregate 1 is used as the aggregate suspended in the slurry, and the refractory particles 1b are used as the stucco material. Except for the above, dipping, stuccoing and drying were performed in the same manner as the formation of the first ceramic coating layer. And the ceramic coating layer of the 2nd layer-the 4th layer was formed by repeating it 3 times.

  Further, for the wax model formed with the four ceramic coating layers obtained above, the aggregate 2 is used as the aggregate suspended in the slurry, and the refractory particles 1c are used as the stucco material. Except for this, dipping, stuccoing, and drying were performed in the same manner as the formation of the first ceramic coating layer. And the ceramic coating layer of the 5th layer-the 8th layer was formed by repeating it 4 times.

  Thereafter, the wax model formed with the eight ceramic coating layers is heated at 900 ° C. for 5 minutes to melt and remove the wax model, and then the ceramic coating layer from which the wax model has been removed is heated at 1100 ° C. By baking for 90 minutes, the casting_mold | template which consists of eight ceramic shell layers was obtained.

  Then, a 300 series stainless steel melt is cast into the obtained mold at a casting temperature of 1650 ° C., and after the melt is solidified, the mold is separated and sandblasting is performed by corundum particles having a particle size of # 100, thereby removing sand. Thus, a sample 1 was obtained.

  About the obtained specimen 1, the difference in dimension from the mold [(vertical length of the specimen-longitudinal length of the wax model) / (longitudinal length of the wax model) × 100] It was calculated by measuring the dimensions. The results are also shown in Table 4 below.

  Further, the surface roughness (Ra) of the specimen 1 was measured with a surface roughness meter (Surfcom, manufactured by Tokyo Seimitsu Co., Ltd.). The obtained results are also shown in Table 4 below.

  Further, the obtained specimen 1 and the mold (ceramic shell layer) used for casting the specimen 1 are visually observed, and casting defects such as rough skin, insertion, seizure, mold cuts and cracks, etc. The presence or absence was confirmed. The results are also shown in Table 4 below.

  In addition, the overall evaluation was performed by considering the dimensional difference from the mold, the surface roughness, and the presence or absence of casting defects comprehensively as ◯ when there is no practical problem as a cast product, and × when there is a problem. . The results are also shown in Table 4 below.

-Sample 2
As the stucco material for forming the ceramic coating layer of the first layer, in the same manner as in the above-mentioned sample 1 except that a mixture of 75% by weight of the refractory particles 1a and 25% by weight of the mullite particles a is used. Then, a mold was prepared, and using this mold, casting was performed in the same manner as described above to obtain a specimen 2. And about the obtained specimen 2, like the specimen 1, it investigated the dimensional difference with a casting_mold | template, surface roughness, and the presence or absence of a casting defect, and performed comprehensive evaluation based on those results. . The results are also shown in Table 4 below.

-Sample 3-5
As the aggregate to be mixed in the slurry, those shown in the following Table 4 are used, respectively, and those shown in the following Table 4 are used as the stucco materials, respectively. Then, a mold was prepared, and using this mold, casting was performed in the same manner as described above to obtain specimens 3 to 5. Then, for the obtained specimens 3 to 5, in the same manner as the specimen 1, the dimensional difference with the mold, the surface roughness, and the presence or absence of casting defects were examined, and comprehensive evaluation was performed based on the results. I did it. The results are also shown in Table 4 below.

-Samples 6-10-
As aggregates mixed in the slurry, those shown in Table 5 below are used, respectively, and those shown in Table 5 below are used as stucco materials, respectively. Samples 6 to 10 were obtained by preparing molds and casting using the molds at a casting temperature of 1650 ° C. using the melts shown in Table 5 below. Then, for the obtained specimens 6 to 10, in the same manner as the specimen 1, the dimensional difference from the mold, the surface roughness, and the presence or absence of casting defects were examined, and comprehensive evaluation was performed based on the results. I did it. The results are also shown in Table 5 below.

-Samples 11-16-
As the aggregate to be mixed in the slurry, those shown in the following Table 6 are used, respectively, and the stucco materials shown in the following Table 6 are used, respectively. A mold was prepared, and samples 11 to 16 were obtained by casting using the mold shown in Table 6 below and casting at a casting temperature of 1650 ° C., respectively. And about the obtained specimens 11-16, like the specimen 1, it investigates a dimensional difference with a casting_mold | template, surface roughness, and the presence or absence of a casting defect, and also performs comprehensive evaluation based on those results. I did it. The results are also shown in Table 6 below.

  As apparent from the results of Table 2 and Tables 4 to 6, as the stucco material constituting the ceramic shell layer (ceramic coating layer) of the first layer (innermost layer), the refractory particles 1a to 1c and 2a according to the present invention are used. In the specimens 1 to 10 obtained using ˜2c, 3a to 3b, and 4a to 4c, it was found that the dimensional difference from the mold was small and the dimensional accuracy was excellent. Further, it was confirmed that the casting surface had a smooth and beautiful casting surface with low surface roughness and no casting defects such as rough surface, insertion and seizure.

  In addition, the recovered particles 1a obtained by crushing and sieving the mold prepared to obtain the specimen 4 and the mold prepared to obtain the specimen 7 are crushed and sieved. In the recovered grains 2 obtained by dividing, since the mold (ceramic shell layer) does not contain zircon, the ceramic shell layers of the fifth to eighth layers of the specimen 9 are formed. As a part of the stucco material to constitute, and as an aggregate to be mixed with the slurry constituting the ceramic shell layers of the fifth layer to the eighth layer of the specimen 10, any of them can be advantageously used easily. In addition, even in the specimen 9 and specimen 10 obtained using such recovered grains 1a and recovered grains 2, no occurrence of defects was observed.

  On the other hand, as a stucco material constituting the ceramic shell layer of the first layer (innermost layer), there is a specimen 11 obtained by using refractory particles 1d containing particles having a particle diameter larger than 0.5 mm. It was confirmed that the cast skin was rough. This is because the particle diameter of the refractory particles (stucco material) constituting the innermost ceramic shell layer is too large, so that the surface roughness of the mold wall in contact with the molten metal is increased, thereby increasing the surface roughness of the casting skin. This is thought to be because the degree has increased. Moreover, in the specimen 12 obtained by using the refractory particles 1e having a particle diameter smaller than 0.05 mm as the stucco material constituting the first ceramic shell layer, Mold seizure was observed. This is because the particle diameter of the refractory particles (stucco material) is too small, the thickness of the innermost ceramic shell layer formed becomes thin, and the fire resistance of the mold wall in contact with the molten metal becomes insufficient. It is believed that there is.

In addition, as a stucco material constituting the ceramic shell layer of the first layer (innermost layer), the refractory material has an Al ₂ O ₃ content of less than 70% by weight and an SiO ₂ content of more than 30% by weight. In the specimen 13 obtained using the conductive particles 5a, the seizure of the mold on the casting surface was observed. This is because the refractory particles (stucco material) constituting the innermost ceramic shell layer contain SiO ₂ crystals, so that the fire resistance of the mold wall in contact with the molten metal is reduced. Conceivable.

Furthermore, as the stucco material constituting the ceramic shell layer of the first layer (innermost layer), the content of Al ₂ O ₃ is more than 90% by weight and the content of SiO ₂ is less than 10% by weight. In the specimen 14 obtained using the refractory particles 6a, cutting of the mold was observed. This is presumably because the thermal expansion characteristics of the mold deteriorated due to the increased proportion of corundum crystals in the refractory particles (stucco material) forming the ceramic shell layer.

Furthermore, as the stucco material constituting the ceramic shell layer of the first layer (innermost layer), refractory particles 7a having a content of other oxides other than Al ₂ O ₃ or SiO _{2 of} more than 5% by weight are used. In the specimen 15 obtained in this way, the mold was seized onto the casting surface. This is because the content of oxides other than Al ₂ O ₃ or SiO ₂ in the stucco material forming the innermost ceramic shell layer is increased, and the crystal ratio of mullite crystals or corundum crystals excellent in fire resistance is relative. This is considered to be because the fire resistance of the mold wall in contact with the molten metal was lowered.

In addition, as the stucco material constituting the ceramic shell layer of the first layer (innermost layer), the proportion of other alumina / silica-based particles (here, mullite particles a) other than the above refractory particles is more than 30% by weight. In the specimen 16 obtained by using the material mixed in the above, seizure of the mold to the casting surface was observed. This is because the ratio of other alumina / silica-based particles in the stucco material forming the innermost ceramic shell layer is increased, and the content ratio of refractory particles composed of mullite crystals or corundum crystals excellent in fire resistance is relatively high. This is considered to be because the fire resistance of the mold wall in contact with the molten metal was lowered.

Claims (7)

Particles comprising Al ₂ O ₃ : 70 to 90% by weight, SiO ₂ : 10 to 30% by weight and other oxides: 0 to 5% by weight, and composed of mullite crystals or mixed crystals of mullite and corundum. A stucco material for producing a mold for precision casting, characterized by comprising fire-resistant porous spherical particles having a particle diameter of 0.05 to 0.5 mm and an apparent porosity of 5 to 14%.   The refractory porous spherical particles are further mixed with at least one other alumina / silica-based particle in a proportion of 30% by weight or less. Stucco material for manufacturing precision casting molds as described.   A precision casting mold obtained by using the stucco material according to claim 1 or 2.   The mold wall is laminated and configured with a plurality of ceramic shell layers, and among these ceramic shell layers, the innermost layer in contact with the molten metal is formed using the stucco material according to claim 1 or 2. On the other hand, at least one ceramic shell layer outside the innermost layer is formed using the refractory porous spherical particles and / or other alumina / silica-based particles as a stucco material. The precision casting mold according to claim 3.   The slurry used for forming the ceramic shell layer constituting the mold wall is blended with an inorganic binder made of colloidal silica or ethyl silicate as a binder. Precision casting mold.   6. The precision casting mold according to claim 5, wherein at least one kind of alumina / silica-based particles is suspended as aggregate in the slurry. The recovered particles obtained by crushing and sieving the precision casting mold according to any one of claims 3 to 6 are used in place of or in combination with the alumina / silica-based particles. The precision casting mold according to any one of claims 3 to 6, wherein the casting mold is a precision casting mold.