JP4701035B2 - Casting method - Google Patents

Description

  The present invention relates to a casting method for forming a heat-resistant modified layer on the surface of a cast product.

  In recent years, aluminum and aluminum alloys are lightweight and excellent in workability, corrosion resistance, and mechanical properties, and thus are widely used in household goods such as aircraft, railway vehicles, automobile parts, and sashes. Aluminum can be formed by a variety of methods, but among them, the die casting method, which has high dimensional accuracy, high strength, and little machining, is most suitable for mass production.

  Here, the die-casting machine used for the die-casting method is a casting apparatus that press-molds molten metal in the melting pot from an injection part into a mold made of hot tool steel. This apparatus is classified into a cold chamber type and a hot chamber type.

  The cold chamber die-casting machine is provided with an injection part and a melting pot separately, and it is necessary to pour hot water every casting cycle, so an oxide film is formed by contact between the molten metal and air, and this generated oxidation There is a high probability that the coating will be involved in the injection and the product will be defective, and there is a high probability that a shape defect will occur due to a decrease in the molten metal temperature. On the other hand, the hot chamber die-casting machine is installed in the melting pot where the gooseneck of the injection part is heated, and continuous pouring is possible and the casting cycle is fast. The probability that a shape defect or the like due to a temperature drop occurs is very low.

  Thus, although the hot chamber type die-casting machine has excellent properties, there is a problem that the heated portion is deteriorated by heat. In particular, since the melting point of aluminum is as high as 660 ° C., parts such as melting pots and gooseneck are always exposed to temperatures of about 600 to 700 ° C. and thus deteriorate early. A type die-casting machine is used.

  Therefore, in order to solve the problems when using a hot chamber die casting machine for forming aluminum, the surface of the structural member of parts that require high heat resistance such as a melting pot is coated with excellent heat resistance. Formation of layers is being considered. As a method of forming such a coating layer, for example, a method of forming a coating layer by spraying a coating material having excellent heat resistance on the surface of a metal as a base material or welding and overlaying, a casting surface on a mold A method of forming a coating layer by applying a casting material made of metal powder having excellent heat resistance to the surface and casting has been proposed. However, since the thermal spraying and welding overlaying used in the former method requires a lot of man-hours and increases costs, casting with a coating material, which is the latter method, has been widely performed.

  In Patent Document 1 (FIG. 4), metal powder A having high-functional properties such as heat resistance, wear resistance, and corrosion resistance, metal powder B having a melting point lower than that of metal powder A, and an organic binder are mixed. An adhesion layer 31 made of a coating material is placed on the casting surface of the mold 32 and a molten metal (base material) is cast from the gate 33, so that the metal powder B is melted by the heat of the molten metal and the metal powder A is embraced. Discloses a technique for depositing a molten metal to form a high-functional coating layer on the surface of a cast product.

  The improvement technique of the coating layer formation method of the cast product by the coating material disclosed in Patent Document 1 is a kind of liquid phase sintering state (powdered refractory metal-molten low melting point) at the interface between the coating material and the molten metal. (Metal-molten base metal alloy) is generated and the coating layer is firmly welded to the base metal alloy. It can be said that the purpose is to have a highly functional physical property, that is, to bond a metal powder having a high melting point more firmly to the base metal alloy in a limited amount of heat.

Patent Document 2 (FIG. 5) is a further improvement of Patent Document 1 and forms irregularities on the surface of the coating material 41 provided on the surface of the coating mold 44 of the mold 42 composed of the sand mold 43 and the coating mold 44. By doing so, the contact area between the molten metal and the coating material is increased, the heat absorption amount of the coating material is increased, and the coating material and the base metal alloy are more firmly welded.
Japanese Patent Publication No. 5-20187 JP 2004-74202 A

  By the way, in these conventional technologies, the aim is to strengthen the welding between the coating material and the base metal alloy by blending the metal powder having a low melting point, but the heat of the molten base material alloy is used. However, a large amount of heat is required for strong welding between the coating material and the base material alloy. Therefore, a sufficient heat source can be secured when the product shape of the cast product is a lump, but there is a high probability of causing poor welding because a sufficient amount of heat cannot be secured when the shape is a thin plate, and there is a problem that the product shape is restricted. is there.

  The present invention solves the above-mentioned problems of the prior art, and a modified layer having heat resistance, oxidation resistance, and corrosion resistance is very easily and at low cost on the surface of a cast product. An object of the present invention is to provide a casting method capable of forming even a shaped product.

In order to solve the above-mentioned problems, the casting method of the present invention forms at least the surface of a mold with compounded sand obtained by mixing recovered sand containing SiO ₂ and iron oxide particles having an average particle size larger than that of recovered sand. The first step,
A second step of casting a molten metal into the mold to produce a cast product.

  According to the casting method of the present invention, the molten metal is simply cast into the mold formed in the first step by a normal method, and in the second step, the recovered sand is recovered at the interface between the mold and the molten metal. Since a modified layer composed of iron oxides in which iron oxide particles enter and adhere between the sand is formed, the modified layer can be easily formed on the surface of the resulting cast product. Here, in the modified layer, the recovered sand improves the heat resistance, while the iron oxide serves as a binder to strengthen the bond between the recovered sand and the base alloy and to use the recovered sand. To compensate for the lack of toughness and improve mechanical strength.

  In addition, since the mold produced in the first step, that is, the sand mold formed with the blended sand itself plays the role of the covering material in the above-mentioned conventional technology, the first step is similar to the normal molding step. What is necessary is just to mold a mold, and as a whole, the number of man-hours does not increase as much as a normal casting method.

  Moreover, since iron oxides, such as an oxide scale generate | occur | produced as a waste material in a general casting process, can be utilized as an additive to compounding sand, raw material cost does not increase. Furthermore, waste that conventionally required processing costs can be recycled in the present invention, which leads to a reduction in total production costs.

In the casting method, the molten metal may be a heat resistant ferrite alloy.
When a heat resistant ferrite alloy is used as the molten metal, the heat resistance of the entire cast product can be further improved in combination with the high heat resistance of the base alloy.

In the casting method, the recovered sand may be an artificial ceramic whose surface has a porous shape.
When an artificial ceramic whose surface has a porous shape is used as the collected sand, the binding state between the modified layer and the base material alloy can be further strengthened.

Further, in the casting method, in the first step, the blended sand may be disposed only in the places where the surface modification is necessary, and the casting mold may be formed with ordinary casting sand in the other places.
By forming such a mold, it is possible to form a modified layer only on the surface of the mold corresponding to a portion that requires modification on the surface of the product. In general, mixing iron oxide particles with casting sand may lead to deterioration of the casting sand. By mixing iron oxide particles only in the necessary part of the mold, the possibility of deterioration of the casting sand can be reduced. It can be kept to a minimum, and the burden of reclaiming the casting sand can be reduced.

  In the casting method of the present invention, a modified layer having heat resistance, oxidation resistance, and corrosion resistance is formed on the surface of the cast product very easily and at low cost, and even for products of any shape. It becomes possible to provide a casting method that can be used.

Hereinafter, embodiments of the present invention will be described in detail.
The casting method according to the present embodiment includes a first step of forming at least a surface of a mold with mixed sand obtained by mixing recovered sand and iron oxide particles having an average particle diameter larger than that of recovered sand, and a molten metal in the mold. And a second step of producing a cast product by casting.

  According to the casting method of the present invention, the molten metal is simply cast into the mold formed in the first step by a normal method, and in the second step, the recovered sand is recovered at the interface between the mold and the molten metal. Since a modified layer composed of iron oxides in which iron oxide particles enter and adhere between the sand is formed, the modified layer can be easily formed on the surface of the resulting cast product. Here, in the modified layer, the recovered sand improves the heat resistance, while the iron oxide serves as a binder to strengthen the bond between the recovered sand and the base alloy and to use the recovered sand. To compensate for the lack of toughness and improve mechanical strength.

  When this modified layer is formed, it is presumed that the following reaction is performed between the recovered sand in the blended sand and the iron oxide.

2FeO + SiO ₂ → 2FeO · SiO ₂ (1)
Or
2Fe ₂ O ₃ + 2SiO ₂ → 2Fe ₂ SiO ₄ + O ₂ (2)

The aforementioned iron oxide is considered to be represented by 2FeO.SiO ₂ (or Fe ₂ SiO ₄ ). This iron oxide is called fayalite and has a very large strength, and it is considered that the formation of this fayalite provides a very strong bond between the recovered sand and the base metal alloy. It is done. Further, the oxidation resistance of the cast product is improved and the corrosion resistance is improved as compared with the case where the iron oxide film is formed on the surface of the cast product.

Furthermore, in this embodiment, by using recovered sand having a deteriorated fire resistance, it is possible to supply SiO ₂ used for this chemical reaction, as will be described later. Further, by making the average particle size of the iron oxide particles larger than the average particle size of the recovered sand, a gap between the recovered sands is ensured, and from the mold surface to the inside of the cast product (for example, in the left direction in FIG. 1), firelite It facilitates the chemical reaction related to formation to proceed.

  In the present embodiment, when the modified layer is formed, if a part of the iron oxide particles is melted, the chemical reaction (1) or (2) occurs, so that a large amount of heat is not required. For this reason, there is no need to consider the properties depending on the product shape, which has been a problem in the past, such that a sufficient amount of heat cannot be secured for forming the modified layer depending on the product shape of the cast product. It becomes possible to correspond to the shape.

  FIG. 1 shows a mechanism for forming a modified layer in the casting method of the present embodiment, that is, a process in which molten metal 11 melted immediately after casting cools and solidifies to form a cast product. FIG. 1A is a schematic diagram illustrating a mechanism by which a modified layer 14 is formed. FIG. 1A illustrates a state immediately after pouring, FIG. 1B illustrates a modified layer forming process, and FIG. FIG. 1 (d) shows the state after mold release. In the figure, the blended sand 5 is constituted by the recovered sand 5a and the iron oxide particles 5b.

In FIG. 1 (a) ~ (d) , as the recovered sand 5a, can be preferably used those containing silicon dioxide (SiO _2). Among these, it is preferable to use recovered sand further containing alumina from the viewpoint that using a mold having a small linear expansion coefficient can reduce the thermal expansion of the mold during casting.

As such recovered sand containing silicon dioxide and alumina, for example, Cerabead (registered trademark) of foundry sand can be used. Cerabeads (registered trademark) is an artificial ceramic made of 62% alumina (Al ₂ O ₃ ) and 38% silicon dioxide (SiO ₂ ). The particle shape is round and the particle size is uniform, and the coefficient of thermal expansion is Foundry sand characterized by very low. Here, this Cerabead (registered trademark) is used in a state in which the average particle diameter is adjusted to 100 to 150 μm through a regeneration cycle of molding, pouring, mold breaking, grinding, cooling, and polishing.

  The particle shape of Cerabeads (registered trademark) is originally a round shape, but as shown in FIG. 1 (a), a part of the surface of the recovered sand 5a is broken and has a porous shape. The alkali metal contained in the resin, the curing agent, and the like that have entered the porous portion of the recovered sand increases the thermal expansion coefficient of the recovered sand, that is, decreases the fire resistance. Further, as shown in FIG. 1 (a), the recovered sand 5a contains a large number of fine particles with further reduced fire resistance.

On the other hand, as the iron oxide particles 5b, for example, particles obtained by pulverizing and sieving oxide scale attached to the surface of a cast product after mold release or after high-temperature atmospheric heat treatment can be used. Although this oxide scale is originally generated in large quantities in foundries and forging factories, it is usually treated as waste. In this oxide scale, ferric oxide (Fe ₂ O ₃ ) is mainly present, and ferrous oxide (FeO) may be partially included. In addition, in this embodiment, the thing adjusted to the average particle diameter larger than collection | recovery sand, for example, 200-300 micrometers, is used.

  In this way, the average particle size of the recovered sand 5a contained in the blended sand 5 is set to 100 to 150 μm, and the average particle size of the iron oxide particles 5b is set to 200 to 300 μm. The formation of iron oxide such as can be performed preferentially.

  Such recovered sand 5a and iron oxide particles 5b are mixed with this recovered sand 5a at a ratio of 5 to 90% by weight as blended sand 5, and further, self-hardening sand containing a resin and a curing agent is added. Make a mold (sand mold). At this time, care must be taken not to ramify the blended sand so as to leave an appropriate gap between the particles.

  Here, in the conventional technique, a casting surface of a mold that becomes the surface of a cast product is formed at the time of molding, a coating material (general) is applied thereon, and a predetermined thickness is further formed thereon. Since the covering material has to be formed, the number of steps is large, and the metal powder constituting the covering material is an expensive material containing a rare earth element, so that there is a problem that the cost increases. In particular, in the case of Patent Document 2, since the unevenness is formed on the surface of the covering material, the cost becomes excessive.

  In the present embodiment, the mold produced in the first process, that is, the sand mold formed with the blended sand itself plays the role of the covering material in the above-described prior art, and therefore the normal molding process in the first process. The mold may be formed in the same manner as in the above, and the number of man-hours does not increase particularly in the same manner as a normal casting method as a whole in combination with the second step described later. For this reason, work can be facilitated and cost can be reduced. Furthermore, since the mold produced in the first step plays the role of a coating material in the prior art, a modified layer can be formed on the surface even for cast products of any shape.

  In FIG. 1 (a), the blended sand 5 is a mixture of the recovered sand 5a and the iron oxide particles 5b, and is cured with an appropriate space between the particles, and melted at about 1600 ° C. The metal 11 is cast.

  In FIG. 1 (b), when the molten metal 11 is cast, the iron oxide particles 5b in contact with the molten metal 11 are melted and the recovered sand 5a having a reduced fire resistance is also melted to form a molten zone 12. . The molten zone 12 enters the inside of the mold (mixed sand side) by the pressure of the molten metal 11.

  In FIG. 1 (c), in the melting zone 12, firelite 13 is generated by the reaction of the formula (1) or the formula (2) described above between the recovered sand 5 a and the iron oxide particles 5 b. The firelite 13 takes particles with high fire resistance in the recovered sand 5a during the solidification process, and firmly bonds the base metal alloy formed from the molten metal 11 and the recovered sand 5a to the surface of the cast product. Then, a modified layer 14 composed of the recovered sand 5a and the firelite 13 is formed.

  In FIG. 1 (d), when the cast product is obtained by releasing the mold and the surface of the cast product is cleaned, the recovered sand 5a fixed so as to be held in the firelite 13 is formed on the surface of the base metal alloy. The modified layer 14 is exposed.

  FIG. 2 is a diagram for explaining the setup when casting a gooseneck used as a melt pump body of a hot chamber type aluminum die-casting machine as an application example of the present embodiment, and FIG. 2 (a) is a perspective view. FIG. 2B is a cross-sectional view taken along line XX ′ in FIG.

  In the setup of FIG. 2, self-hardening sand 10 is filled in a metal frame 0, and a mold, that is, a sand mold is formed by the wooden body 2. On the mold, based on the plan, that is, the mold design, the gate 1, the core 3, the hot water 4, the cold gold 6, and the hanging weir 9 are arranged, the upper and lower metal frames 0 are fastened with the fastening bracket 7, and the hanging tool 8 And set to the pouring (casting) posture. The gooseneck formed in this way is immersed in a molten aluminum pot of a hot chamber casting apparatus and used as a pump for molten aluminum, for example, so that the contact point with the molten aluminum may be eroded by the aluminum. There is. Therefore, in the present embodiment, the blended sand 5 in which the recovered sand 5a and the iron oxide 5b are mixed is disposed at a contact point (outer surface and inner surface) with aluminum. In particular, as shown in FIG. 2 (b), since the space between the wooden main body 2 and the feeder 4 is in contact with aluminum inside the gooseneck, the blended sand 5 is placed on the inner wall surface and the surface of the core 3. Arranged.

  The mold thickness of the blended sand portion is appropriately set depending on the thickness of the product (gooseneck), the heat resistant temperature, the service life, and the like. In order to arrange this blended sand, a dedicated wooden mold may be used, but this is not necessary when a modified layer is provided on the entire surface of the product.

  Alternatively, the blended sand may be disposed only in the places where surface modification is required, and the mold may be formed with ordinary casting sand in other places. By forming such a mold, it is possible to form a modified layer only on the surface of the mold corresponding to a portion that requires modification on the surface of the product. For example, in FIG. 1, since the modified layer is provided on the product surface of the core 3, the blended sand 5 is arranged. However, when the modified layer is unnecessary, this portion of the blended sand 5 is provided. Is unnecessary, and normal casting sand can be used.

  In general, mixing iron oxide particles with casting sand may lead to deterioration of the casting sand. By mixing iron oxide particles only in the necessary part of the mold, the possibility of deterioration of the casting sand can be reduced. It can be kept to a minimum, and the burden of reclaiming the casting sand can be reduced.

  As the molten metal (base material alloy) 11 cast into the mold, it is possible to use heat-resistant ferrite alloys such as JIS standard SCS-1, SCS-2, AHS-1, AHS-2, and AHS-3. These are alloys with high heat resistance to aluminum. In addition, these alloys have a low nickel (Ni) content, so that they have poor wettability to aluminum and are not easily eroded.

  In general, the casting temperature is about 1600 ° C., but since the melting point of iron oxide 5b is 1600 ° C. or less, the iron oxide 5b near the casting surface is also melted by the heat of the molten metal 11, so For this purpose, a large amount of heat is not required. For this reason, as described above, it is possible to deal with a wide variety of product shapes.

(Example 1)
A test piece having a diameter of 21 mm, a length of 270 mm, and a weight of 1200 g was prepared using the surface modified casting method of the present invention.

(First step)
The blended sand is made by adjusting recycled and recycled Cerabeads (registered trademark) within an average particle size of 100 to 150 μm, and adjusting the oxide scale generated at a foundry to an average particle size of 200 to 300 μm. Obtained by mixing. The obtained blended sand was placed at a proper position of the self-hardening sand constituting the sand mold and molded.

(Second step)
As the base metal alloy, a heat-resistant ferrite alloy corresponding to JIS standard AHS-1 was used, and the mixture was heated to 1600 ° C. and cast into a sand mold formed of self-hardening sand and blended sand.
When the mold was released after cooling and the surface of the cast product was cleaned, a modified layer made of Cerabead (registered trademark) and Fayalite was formed on the surface of the cast product as shown in FIG.

  Here, FIG. 3A is a schematic diagram of a micrograph (magnification 50 times) of the modified layer, and FIG. 3B is a schematic diagram of a micrograph (magnification 400 times) of the modified layer.

(Comparative Example 1)
In the molding process (first process), a test piece having a diameter of 21.5 mm, a length of 270 mm, and a weight of 1210 g was prepared in the same process as in Example 1 except that blended sand was not used.
When the mold was released after cooling and the surface of the cast product was cleaned, the surface of the cast product was a normal casting surface.

(Comparative Example 2)
In the second step, a test piece having a diameter of 20 mm, a length of 250 mm, and a weight of 1010 g was prepared in the same process as Comparative Example 1 except that the base alloy was a JIS standard SKD61 equivalent.
When the mold was released after cooling and the surface of the cast product was cleaned, the surface of the cast product was a normal casting surface.

(Erosion test)
Each test piece was immersed in a molten metal pot of an aluminum die cast machine to perform an erosion test. The temperature of the molten aluminum was 650 to 700 ° C., and the liquid level changed by about 20 cm with the operation. The test piece was pulled up about every 1 hour and 30 minutes, and the state of surface melting was observed visually, and the work of immersing in the molten metal pot was repeated. When 12 hours had elapsed from the start of the test, the test was terminated. After cooling the test piece, aluminum stuck to the surface was dropped with dilute hydrochloric acid, and the weight was measured.

  As described above, it was found that the test piece in which the modified layer was formed by the surface modification casting method of the present invention had almost no melting loss and extremely high heat resistance.

It is the model explaining the mechanism of the modified layer formation of the surface modification casting method which is embodiment of this invention, (a) Immediately after pouring, (b) Process of forming a modified layer, (c) After solidification, d) It represents after mold release. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of a surface modification casting method according to an embodiment of the present invention, in which (a) is a perspective view and (b) is a cross-sectional view taken along line X-X ′ of (a). (A) It is a schematic diagram of the microscope picture (50 times magnification) of a modified layer, (b) It is a schematic diagram of the microscope picture (400 times magnification) of a modified layer. It is a figure for demonstrating the setup of the surface coating layer formation method in the conventional casting method. It is a figure for demonstrating the setup of the surface coating layer formation method in the conventional casting method.

Explanation of symbols

0 metal frame 1 sprue 2 wooden body 3 core 4 feeder 5 blended sand 5a recovered sand 5b iron oxide 6 cold gold 7 fastening bracket 8 hanging bracket 9 hanging weir 10 self-hardening sand 11 molten metal (base metal alloy)
12 Melting zone (iron oxide, recovered sand)
13 Fayalite 14 Modified layer

Claims (5)

A first step of forming at least the surface of the mold with compounded sand obtained by mixing recovered sand containing SiO ₂ and iron oxide particles having an average particle size larger than that of recovered sand;
And a second step of casting a molten metal that is a heat-resistant ferrite alloy into the mold to produce a cast product.   SiO ₂ A first step of forming at least the surface of the mold with compounded sand obtained by mixing recovered sand containing a mixture of iron oxide particles having an average particle size larger than that of recovered sand;
  A second step of casting a molten metal into the mold to produce a cast product,
  The blended sand is obtained by mixing iron oxide particles in a proportion of 5 to 90% by weight with respect to recovered sand.   SiO ₂ A first step of forming at least the surface of the mold with compounded sand obtained by mixing recovered sand containing a mixture of iron oxide particles having an average particle size larger than that of recovered sand;
  A second step of casting a molten metal into the mold to produce a cast product,
  The casting method, wherein the recovered sand contained in the blended sand has an average particle size of 100 to 150 μm, and the iron oxide particles have an average particle size of 200 to 300 μm.   In the casting method as described in any one of Claims 1-3,
  A casting method, wherein the recovered sand is an artificial ceramic whose surface has a porous shape.   In the casting method as described in any one of Claims 1-4,
  In the first step, the blended sand is disposed only in the places where the surface modification is necessary, and the casting mold is formed with normal casting sand in the other places.