JP2005288447A - Resin composition for shell mold, and resin-coated sand for shell mold coated with the resin composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resin composition for shell mold which can prevent the crack of a coke at the casting time and can reduce the amount of thermally decomposed products such as tar and soot at the casting time, and to provide a resin-coated sand for shell mold using the resin composition. <P>SOLUTION: This resin composition contains 0.5-10 mass pts. boehmite having ≤10 nm average grain diameter (short diameter) per 100 mass pts. thermosetting resin. As this embodiment, the average grain diameter (short diameter) of the boehmite is 5-50 nm, the aspect ratio of the boehmite is 1-100, and the boehmite of 0.5-10 mass pts. is incorporated in the thermosetting resin of 100 mass pts. The resin coated sand for shell mold is composed of refractory partivle coated with the resin composition, wherein the refractory particle is a mullite based porous particle. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a resin composition for shell mold and a resin-coated sand for shell mold coated with the resin composition. More specifically, the present invention relates to a mold (main mold or core) used in a shell mold casting method. The present invention relates to a resin composition for a shell mold that can be used in manufacturing, can reduce the thermal expansion of a core during casting, and can reduce the amount of spear generated from the core after casting, and a resin-coated sand for a shell mold using the same It is.

  Conventionally, in sand mold casting of non-ferrous castings such as aluminum alloys, magnesium alloys and copper alloys, and iron castings such as cast steel and cast iron, a thermosetting mold material formed by coating a resin binder for molds on refractory particles. Are widely used as main molds and cores.

  Among these molds, especially complex shaped cores such as cylinder heads are prone to cracking or cracking (hereinafter referred to as core cracking) in the casting of light alloys. (Vaning) will be formed. As a method for solving such a problem, a shell mold binder having a low thermal expansion property and mainly composed of a bisphenol A-modified novolac phenol resin has been proposed. (Patent Document 1)

  However, in recent years, automobile cast iron castings manufactured by the shell mold casting method tend to be thinner in accordance with higher performance and weight reduction of automobiles. The occurrence of casting defects such as soot defects caused by sag and soot has become a problem. When a shell mold binder mainly composed of the bisphenol A-modified novolac phenol resin is used, the resin is highly thermally decomposable, so that it is easy to generate scum and soot, and the amount generated is inevitably increased. Problems arise and further improvements are sought.

  Further, the present applicant has proposed a phenol resin composition excellent in thermal conductivity and mechanical strength in which boehmite having a specific particle diameter is blended with a phenol resin (Japanese Patent Application No. 2003-195087). There was no mention of using the resin composition in casting applications such as a shell mold casting method.

Japanese Patent Laid-Open No. 2001-321883

  Therefore, the present invention has been made against the background of the above circumstances, and can prevent cracking of the core during casting, and further reduce the amount of pyrolysis products such as spear and soot during casting. An object of the present invention is to provide a resin composition for a shell mold and to provide a resin-coated sand for a shell mold using the same.

  As a result of intensive studies to solve the above problems, the present inventors have used, as a resin composition for a shell mold, a mixture of boehmite having a specific particle diameter with respect to a thermosetting resin. It has been found that it is effective for countermeasures against core cracks during casting and is effective in reducing pyrolysis products, and has completed the present invention.

  That is, the resin composition for a shell mold of the present invention is characterized by containing a thermosetting resin and boehmite having an average particle diameter (short diameter) of 100 nm or less, preferably 5 to 50 nm. Preferably, the boehmite has an aspect ratio of 1 to 100. Moreover, it is preferable to mix | blend said boehmite 0.5-10 mass parts with respect to 100 mass parts of thermosetting resins, and it is more preferable to mix | blend 0.8-5 mass parts.

  The resin-coated sand for shell mold of the present invention is a resin-coated sand for shell mold composed of fire-resistant particles coated with the above resin composition for shell mold, and the fire-resistant particles are mullite porous particles. It is preferable that

  By using the resin composition for a shell mold of the present invention, the thermal expansion of the resin-coated sand is lowered, and core cracks during casting, particularly core cracks in light alloy castings with complex shapes can be prevented. .

  Moreover, the generation | occurrence | production of the creep and soot etc. which arise with the thermal decomposition of the resin composition at the time of casting can be reduced, and casting defect phenomena, such as a soot defect, can be prevented.

  Furthermore, the strength at the time of molding a mold can be improved by producing a resin-coated sand for shell mold using mullite porous particles as refractory particles.

  The thermosetting resin used in the present invention is not particularly limited as long as it is used as a binder for foundry sand. In the presence or absence of a curing agent or a curing catalyst such as hexamethylenetetramine and peroxide. Resins that exhibit thermosetting properties upon heating, such as phenol resins, melamine resins, urea resins, xylene resins, epoxy resins, polyfunctional acrylamide resins (Japanese Patent Publication No. 7-106421), unsaturated polyesters, diallyl phthalate resins And alkyd resins. These may be used alone or in combination of two or more. Among the thermosetting resins, from the viewpoint of the effect of the present invention, a formaldehyde resin typified by a phenol resin or a melamine resin, particularly a phenol resin is preferable.

  The phenol resin is a solid or liquid condensation product obtained by reacting phenols and aldehydes in the presence of an acidic catalyst and / or a basic catalyst (for example, resin liquid, varnish or emulsion). It is a phenol resin that develops thermosetting by heating in the presence or absence of the curing agent or curing catalyst described above, specifically, a novolac type phenol resin, a resol type phenol resin, a nitrogen-containing resol type phenol resin, and Benzyl ether type phenol resin and low expansion-providing components such as bisphenol A and purified residue in the production of bisphenol A as disclosed in JP-A-57-68240, alone or in the presence of phenol Low-expansion phenolic resins obtained by reacting with aldehydes, the production process of these resins Modifications obtained by mixing or reacting with any compound after production, such as epoxy resin, melamine resin, urea resin, xylene resin, vinyl acetate resin, polyamide resin, urea compound, melamine compound, epoxy compound, and cashew oil A phenol resin etc. are illustrated.

  The boehmite used in the present invention is an inorganic compound containing at least 90% or more of aluminum hydroxide oxide represented by the general formula AlO (OH). In the present invention, a fine boehmite having an average particle diameter (short diameter) of 100 nm or less is used, preferably 1 to 100 nm, more preferably 5 to 50 nm, and most preferably 10 to 20 nm. If the average particle (minor axis) is larger than 100 nm, it is not preferable because there is a tendency that the mold strength is lowered and the casting and soot are increased during casting. The shape of the boehmite is not particularly limited, and various shapes such as a spherical shape, a plate shape, a needle shape, a cylindrical shape, and an amorphous shape are used. From the viewpoint of easy availability and improvement of mechanical strength, the shape of the boehmite is not limited. Alternatively, a cylindrical shape is preferable, and the aspect ratio {= average particle diameter (major axis) / average particle diameter (minor axis)} is preferably 1 to 100, more preferably 5 to 50. . In the present invention, boehmite having such a fine size that the average particle diameter (short diameter) is 100 nm or less is hereinafter referred to as “nanoalumina”.

  The compounding amount of nano-alumina in the present invention is appropriately determined according to the required characteristics and application of the resin composition for shell mold, but 0.5 to 10 parts by mass with respect to 100 parts by mass of the thermosetting resin. Is preferred, more preferably 0.5 to 5 parts by mass, and even more preferably 0.7 to 2 parts by mass. If the amount is less than 0.5 parts by mass, the effects of low thermal expansion and reduction of dirt and soot are not sufficiently exhibited, and if the amount exceeds 10 parts by mass, the strength tends to decrease.

  Further, the resin composition for a shell mold of the present invention has various additives as necessary for improving the quality, for example, silane coupling such as γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, etc. Agents, lubricants such as ethylene bisstearoamide, methylene bisstearoamide, carboxylic acid chlorides such as isophthalic acid chloride, phosphonic acid chlorides, phosphonyl chlorides and the like can be used.

  Examples of the method for producing a resin composition for a shell mold in the present invention include a method of adding and mixing a thermosetting resin and nanoalumina while pulverizing, a method of melting and mixing nanoalumina in a molten thermosetting resin, In addition, there is a method of adding a thermosetting resin and nanoalumina simultaneously or separately to refractory particles to be described later, and any method can be used as long as nanoalumina can be uniformly dispersed. It is not limited.

  The resin-coated sand for shell mold of the present invention is obtained by blending refractory particles such as silica sand and the resin composition for shell mold described above.

  The refractory particles used in the present invention form a base material for a mold, and may be any inorganic particles having fire resistance that can withstand casting and a particle size suitable for mold formation, and is not particularly limited. Examples of such refractory particles include silica sand, olivine sand, zircon sand, chromite sand, alumina sand and other special sand, ferrochrome slag, ferronickel slag, converter slag and other slag particles, Examples thereof include mullite-based porous particles such as Naigai Cera Beads (trade name, ITOCHU CERATECH Co., Ltd.), or regenerated particles recovered and regenerated after casting. These may be used alone or in combination of two or more. Among these, mullite porous particles that contain many chemical components close to nanoalumina and easily contribute to the development of strength by interaction are preferable.

  The compounding amount of the resin composition for shell mold in the resin coated sand for shell mold is not limited in general because it differs from the viewpoint of the type of resin used, the required mold strength and core disintegration, Generally, it is in the range of 0.2 to 5 parts by mass, preferably in the range of 0.5 to 3 parts by mass with respect to 100 parts by mass of the refractory particles.

  As a method for producing a resin-coated sand for shell mold using the resin composition for shell mold of the present invention, for example, preheated refractory particles and resin composition for shell mold in a kneader such as a whirl mixer or a speed mixer. And so on, and then adding a hexamethylenetetramine (curing agent) aqueous solution and disintegrating the bulk contents into particles by cooling with air blowing, and adding calcium stearate (lubricant). It can also be produced by a coating method such as a semi-hot marling method or a cold marling method.

  The reason why the resin composition of the present invention and the resin-coated sand for shell mold using the resin composition exhibit an excellent low thermal expansion coefficient and dust reduction effect is not clear, but is presumed as follows.

  By mixing or kneading the phenolic resin and nanoalumina, the nanoalumina is uniformly dispersed in the resin composition, and a part of the nanoalumina chemically bonds with the hydroxyl group of the phenolic resin, thereby having a bulky molecular structure. It seems that an intermolecular space is generated during the thermal decomposition of the mold, and this space alleviates the stress of the expansion of the foundry sand with respect to the heat, so that the effect of low thermal expansion is achieved. Moreover, since nano alumina itself contains oxygen, the oxygen index in the resin composition is increased, and it is presumed that the burning effect of organic substances during casting is promoted and the effect of reducing dust is exerted. Furthermore, when mullite porous sand containing a large amount of alumina is used as the refractory particles, the nano-alumina and mullite porous sand are in a state of having a coupling agent-like interaction. It is thought that it contributes to the improvement of strength.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples. “Parts” and “%” mean “parts by mass” and “% by mass”.

  The evaluation method of the resin-coated sand of Examples and Comparative Examples is as follows.

(1) Bending strength The bending strength (N / cm ² ) was measured according to JIS K 6910 (baked at 250 ° C. for 60 seconds).

(2) Generation amount of pyrolysis product After placing four test pieces (size 10 mm x 10 mm x 60 mm) for measuring bending strength in a glass test tube (inner diameter 27 mm x length 200 mm), the opening of the test tube A glass wool (about 2.5 g) weighed in advance was inserted in the vicinity to make a measuring device for pyrolysis products. Next, the measuring device was placed in a tubular heating furnace maintained at 600 ° C. and heat-treated for 6 minutes, then taken out and allowed to cool to room temperature. Thereafter, the glass wool was taken out from the measuring instrument, and its mass was measured. The generation amount (mg) of the thermal decomposition product was calculated by subtracting the glass wool mass (mg) before the heat treatment from the glass wool mass (mg) after the heat treatment.

(3) Thermal expansion coefficient (%)
After installing a test piece (30mmφ x 50mmH) in a high-temperature foundry sand tester adjusted to a furnace temperature of 1000 ° C, the thermal expansion amount of the test piece measured every predetermined time is calculated by the following formula. Rate.
Coefficient of thermal expansion (%) = {(after heat exposure−before heat exposure) test piece length} / (test piece length before heat exposure) × 100

Example 1
100 parts by weight of novolak-type phenolic resin (trade name SP610, manufactured by Asahi Organic Materials Co., Ltd.), boehmite {CAM9010, manufactured by Saint-Gobain, average particle diameter (short diameter) 10 nm, average particle diameter (long diameter) 90 nm, aspect ratio 9} 0 .5 parts by mass was melt-mixed, and a silane coupling agent and a lubricant were further added to prepare a novolac type phenolic resin composition. Next, 7 kg of Cera beads preheated to about 150 ° C. (Mitrite porous particles made by ITOCHU CERATECH Co., Ltd.) and 140 g of the adjusted novolak type phenol resin composition were put into a whirl mixer manufactured by Enshu Iron Works Co., Ltd. and kneaded for 60 seconds. Then, 126 g of an aqueous solution in which 21 g of hexamethylenetetramine was dissolved in 105 g of water was added. Knead until the lump of sand is broken while blowing with a blower, add 7 g of calcium stearate, knead for 15 seconds, and discharge from the mixer to obtain a resin-coated sand for shell mold. The bending strength and pyrolysis product The amount generated was measured. The results are shown in Table 1.

Examples 2-7
Except having changed boehmite into the compounding quantity shown in Table 1, it carried out similarly to Example 1, and obtained the resin coated sand for shell molds, and measured the bending strength and the generation amount of the thermal decomposition product. The results are shown in Table 1.

Examples 8-10
In Example 1, refractory particles were changed from cera beads to flattery (Australian refractory particles mainly composed of silica sand), and boehmite was changed to the blending amount shown in Table 2 in the same manner as in Example 1. A resin-coated sand for shell mold was obtained, and its bending strength and the amount of pyrolysis products generated were measured. The results are shown in Table 2.

Comparative Examples 1-3
Resin coated sand for shell molds was obtained in the same manner as in Example 1 except that the formulation was changed as shown in Table 1. The bending strength and the amount of pyrolysis products generated were measured. In Comparative Example 3, Cerasur BMB {average particle diameter (minor axis) 1 μm, aspect ratio 2} manufactured by Kawai Lime Industry Co., Ltd. was used as boehmite. The results are shown in Table 1.

Comparative Examples 4-5
Resin coated sand for shell mold was obtained in the same manner as in Example 8 except that boehmite was not added and the formulation was changed as shown in Table 2. The bending strength and the amount of pyrolysis products generated were measured. The results are shown in Table 2.

  FIG. 1 is a graph showing the relationship between the amount of nanoalumina added and the bending strength of a resin-coated sand for shell mold when mullite porous sand (Cerabeads) is used as the foundry sand. From FIG. 1, the strength improved when the amount of nano alumina added was up to 1.0 part by mass, and the strength decreased when the amount was 1.0 part by mass or more.

  FIG. 2 is a graph showing the relationship between the amount of pyrolysis product generated and the amount of nanoalumina added. From FIG. 2, the effect of reducing the amount of pyrolysis products generated is not observed when the amount of nano alumina added is 0.5 parts by mass, but a sharp decrease is seen from 0.5 parts by mass to 1.0 parts by mass. . In 1.0 mass part or more, every time the nano alumina addition amount increases, a slight decrease is observed. Regarding the thermal expansion coefficient, the effect of reducing the thermal expansion coefficient is recognized by the addition of nano-alumina, although it is very small.

  Table 2 shows the bending strength of the shell-molded resin-coated sand in the case of using commonly used imported dredged sand flattery as foundry sand, the bending strength of Examples 8 to 10, the amount of pyrolysis products generated, The measurement result of a thermal expansion coefficient is shown. Moreover, it shows in the comparative example 5 of the shell mold method resin coated sand at the time of using the bisphenol A modified phenol resin used as low temperature expansion as a prior art. In Comparative Example 4 and Examples 8 to 10, low thermal expansion is shown by adding nano alumina. In Comparative Example 5 and Examples 8 to 10, the addition of nano-alumina shows a more effective low thermal expansion than when bisphenol A-modified phenol resin is used. From these results, from the characteristic balance of bending strength, pyrolysis product generation amount, and thermal expansion coefficient, the amount of nano alumina added is about 1 part by mass with respect to 100 parts by mass of the thermosetting resin, It is presumed that the appropriate amount is preferably 0.5 to 10 parts by mass, more preferably 0.8 to 5 parts by mass.

  As is apparent from Tables 1 and 2, a specific boehmite is used in combination with a mold resin in a specific addition amount and kneaded with foundry sand, and used as kneaded sand without reducing the mold strength. In addition, it is possible to reduce the generation amount of pyrolysis products such as organic-derived spear and soot at the time of casting. In particular, when mullite porous sand is used as foundry sand, the strength can be slightly improved by a specific amount of boehmite. Furthermore, the novolac type phenolic resin binder often used in the shell mold method has the effect of making it low thermal expansion without using low expansion bisphenol A-modified novolac phenolic resin. It is possible to prevent the core from cracking during casting without increasing soot and soot.

  The resin composition for a shell mold of the present invention is suitably used for production of a mold such as a main mold and a core used in a shell mold casting method in the field of non-ferrous castings and cast iron.

FIG. 1 is a graph showing the relationship between the amount of nanoalumina added and the bending strength of resin-coated sand for shell molds when mullite porous sand (Cerabeads) is used as foundry sand. FIG. 2 is a graph showing the relationship between the amount of nano alumina added and the amount of pyrolysis products generated for resin-coated sand for shell molds when mullite porous sand (Cerabeads) is used as the foundry sand. is there.

Claims (5)

  A resin composition for a shell mold comprising 0.5 to 10 parts by mass of boehmite having an average particle diameter (short axis) of 100 nm or less with respect to 100 parts by mass of a thermosetting resin.   2. The resin composition for a shell mold according to claim 1, wherein the average particle size (minor axis) of boehmite is 5 to 50 nm.   The resin composition for a shell mold according to claim 1 or 2, wherein the boehmite has an aspect ratio of 1 to 100.   A resin-coated sand for a shell mold comprising fireproof particles coated with the resin composition for a shell mold according to any one of claims 1 to 3. The resin-coated sand for shell mold according to claim 4, wherein the refractory particles are mullite porous particles.

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