JP2007030027A - Method for forming water soluble core, and method for casting aluminum alloy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a water soluble core practical by providing a method for manufacturing a hollow core using a water soluble core having excellent flow-ability, fill-ability, and improved strength even with wet sand charged with slurry, and further by providing a method for making the core with a short time cycle. <P>SOLUTION: The method for manufacturing a sand core by mixing casting sand with a water soluble binder so as to become slurry, and next by supplying the slurry into a die, and then by drying and forming the supplied slurry into the sand core comprises a step (a first step) for supplying the slurry state casting sand into the die under pressure, a step (a second step) for drying and solidifying the slurry state casting sand existing in the neighborhood of the wall of the die by heating the die, and also for making wet sand by discharging moisture from the slurry state casting sand by carrying out pressurized blowing for the inside of the die, and further for discharging the un-solidified sand existing in the central portion of the die by carrying out pressurized blowing, and a step (a third step) for drying and forming the casting sand by carrying out hot air blowing. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for molding a water-soluble core using a water-soluble core binder with improved strength without reducing fluidity and filling properties. The present invention also relates to an aluminum alloy casting method using a water-soluble core.

  A casting is manufactured by press-fitting molten metal into a mold and rapidly solidifying it. In such precision casting technology, a core is widely used to provide a space inside a precision casting such as a machine part. For example, the core is indispensable for the production of the internal space of the cylinder using aluminum alloy and the cooling medium passage inside the exhaust.

  In order to increase the strength of the core, binders such as resins and inorganic salts are used. In particular, by using an inorganic salt as a core binder, a water-soluble core that can reduce the amount of gas generated at the time of casting and can perform core sand removal with water after casting is considered. However, none has been put into practical use or mass production. The reason is that it is difficult to obtain the necessary core strength because there is no binding force of the binder.

That is, when adding a binder such as an inorganic salt to the core foundry sand,
1) Increasing the binder amount improves the core strength.
2) The binder is dissolved in water (saturated concentration) and added to the foundry sand. Therefore, an increase in the amount of binder results in an increase in the amount of water.
3) The increase in water results in a decrease in the fluidity of the foundry sand and hinders the filling property of the foundry sand into the core mold.

  Thus, if only the binder is added to the foundry sand, both the core strength and the fluidity of the foundry sand cannot be achieved. Therefore, a technique for improving the core strength without increasing the binder amount is required.

  The following Patent Document 1 discloses inorganic composite particles obtained by coating inorganic particles with graphite with a binder for the purpose of improving fluidity, filling properties, and moldability, and the coating amount of graphite is 100 parts by weight of inorganic particles. On the other hand, the invention of sand for casting made of inorganic composite particles having a weight ratio of 0.1 to 50 parts by weight and a binder to graphite of 0.002 to 2 is disclosed. However, the binder used is a phenol resin, a furan resin, or pitch, and does not obtain a water-soluble core as in the present invention.

  By the way, there has been no report of molding with water-soluble inorganic core sand. This is because, when the foundry sand kneaded with the water-soluble binder is blown into the mold, the fluidity is very poor, so that a core sufficiently filled with foundry sand cannot be formed.

  In the course of developing a method for making a water-soluble binder and foundry sand into a slurry state and filling the mold, the present inventors converted the water present in the binder crystals that bind the core into water vapor during casting. Therefore, it was recognized as a technical problem to cause gas defects in castings.

  In order to prevent the moisture present in the water-soluble binder crystals from becoming water vapor during casting and causing gas defects in the cast product, the core can be dried, or gas can be vented by drilling the core. It is usually considered to make a hole. However, these methods are not sufficient for preventing the above-described defects, and also cause an increase in energy and cost. For this reason, there has been a technical problem of wanting to make a hole during molding.

  As a method of solving the technical problem, according to the conventional shell method, dry shell sand is blown from the upper part of the mold into the mold and then blown downward, and vibrations such as a vibrator are applied to form an unfired shell. It was thought that the sand would fall out of the lower inlet by gravity to create a cavity in the core. In this case, since the mold is heated to about 300 ° C., the shell sand in the vicinity of the mold surface starts thermosetting. For this reason, the shell sand in the vicinity of the mold surface does not fall, and can be hollowed out while leaving a necessary meat pressure.

The present inventors tried the same method in the slurry molding method, but it was found that only the vicinity of the blowing port could be removed in the slurry molding method. The reason is that when sand and a sufficient amount of liquid (slurry) are present, the fluidity is very good. It is body sand and its fluidity is very poor. For this reason, even if a vibrator is added, it is hard to drop by gravity. If a large amount of binder is left between the sand grains, gravity drop is possible, but there is a problem that the core surface after molding and drying is rough and impractical.
Japanese Patent Laid-Open No. 2002-263882

  In view of the above problems, the present invention provides a method for producing a hollow core even in wet sand after slurry filling, using a water-soluble core having excellent fluidity and filling properties and improved strength. An object of the present invention is to provide a molding method with a shortened cycle and to make a water-soluble core practical.

  The inventors of the present invention have found that the core can be hollowed by a specific method when the foundry sand is replaced with conventional dry sand to form a water-soluble inorganic binder slurry, and the present invention has been achieved.

  That is, first, the present invention is an invention of a molding sand core molding method, in which a water-soluble binder is mixed with casting sand to form a slurry, and the slurry is filled into a mold, and then the filler is filled. In a molding sand core molding method for drying and molding, a step (first step) of pressurizing and filling the slurry-like molding sand into the mold, and heating the mold to form the slurry near the mold wall Is dried and solidified, and is blown under pressure into the mold to discharge moisture from the slurry-like foundry sand to form wet sand, and further blown under pressure to form unsolidified sand at the center of the mold And a step (third step) of blowing hot air to dry the molding sand and molding.

  In the molding sand core molding method of the present invention, the pressure filling into the mold in the first step is performed from below and sucked from above, and the pressure blow into the mold in the second step is performed. It is preferable to perform pressure blow from above, exhaust from below, and dry / molding in the third step by blowing hot air from below and opening the top.

  In particular, it is preferable to reverse the foundry sand core molding device between the first step and the second step and to reverse the foundry sand core molding device again between the second step and the third step.

  In the present invention, when the heating of the mold in the second step is performed at about 100 ° C., specifically at 80 ° C. to 120 ° C., the slurry casting sand is preferably partially solidified near the mold wall.

  In the present invention, the viscosity of the slurry obtained by mixing a water-soluble binder with the foundry sand is preferably 4 to 12 cp.

  As the water-soluble binder, a water-soluble inorganic salt binder or an organic binder can be used, but a water-soluble inorganic salt binder is preferable because it does not burn when heated.

  As a measure of the amount of foundry sand and water-soluble binder to be kneaded, the weight ratio of foundry sand and water-soluble binder is preferably 1: 0.1 to 1: 5, and 1: 0.5 to 1: 1. It is more preferable that

The water-soluble binder used in the casting sand core molding method of the present invention is inorganic or organic, and is not particularly limited. From the magnesium ion (Mg ²⁺ ), sodium ion (Na ⁺ ), and calcium ion (Ca ²⁺ ). A water-soluble core comprising at least one water-soluble inorganic salt comprising a combination of a selected cation and an anion selected from SO ₄ ²⁻ , CO ₃ ²⁻ , HCO ₃ ²⁻ , and B ₄ O ₇ ⁻ A binder is preferably exemplified. The inorganic salt composed of a combination of these specific cations and anions satisfies the strength, solubility, and filling properties as a binder. More specifically, at least one selected from magnesium sulfate (MgSO ₄ ), sodium carbonate (Na ₂ CO ₃ ), sodium borate (Na ₂ B ₄ O ₇ ), and sodium sulfate (Na ₂ SO ₄ ). Is mentioned.

  In the present invention, the water-soluble inorganic salt binder is selected from silica sand (silica powder), alumina, potassium titanate, silicon carbide, zircon silicate, fibrous potassium titanate, titanium oxide, zinc oxide, iron oxide and magnesium oxide. One or more inorganic fillers can be added. By adding an inorganic filler, the high-temperature strength of the water-soluble core is further improved, resulting in the practicality of being excellent in handling of the molded core.

  The specific inorganic filler used in the present invention is present near the contact point of the foundry sand particles whose surface is coated with the inorganic salt binder, and enhances the binding force of the foundry sand particles. The average particle size is preferably about several μm to several tens of μm in the vicinity of the contact point of the foundry sand.

  Furthermore, in this invention, it is preferable that the inorganic fine powder is filled with the clearance gap between the sands for casting by which the surface was coat | covered with the water-soluble inorganic salt binder. Here, the inorganic fine powder is filled in the gaps between the foundry sand particles whose surfaces are coated with the inorganic salt binder to enhance the binding force of the foundry sand particles. Specifically, one or more selected from kaolin and talc such as kaolinite, decaite, and halosite are preferably exemplified. The average particle size is preferably about several μm to several tens of μm for filling the gaps in the foundry sand.

  As the foundry sand particles used in the present invention, those conventionally known can be used. Specifically, it is preferable to use SiC, alumina, mullite, silica, or zircon. These have excellent strength and low thermal expansion coefficient and are relatively easily available, and can produce water-soluble cores excellent in strength, dimensional accuracy, and the like.

  The water-soluble core formed by the present invention is a water-soluble core in which the surface of casting sand particles is coated with a water-soluble inorganic salt binder, and has sufficient core strength and fluidity (fillability). .

  Secondly, the present invention is an aluminum alloy casting method using a water-soluble core formed by the casting sand core molding method described above. Since a water-soluble core is used, sand removal after casting is easy. According to the present invention, for example, a precision casting such as an aluminum alloy cylinder can be manufactured.

  In the present invention, it is possible to cope with environmental problems by collecting and reusing the water-soluble core binder after sand removal. Using a slurry-like mixture of foundry sand and water-soluble binder, the slurry was filled into a mold, the slurry was dried and molded to form a foundry sand core, and then passed through a casting process and a sand removal process. Thereafter, the water-soluble binder is recovered as an aqueous solution, and water is separated from the obtained aqueous solution by evaporation or the like to recover the water-soluble binder. The recovered water-soluble binder is reused in the above molding sand core molding method. By repeatedly reusing the water-soluble inorganic salt binder, it becomes a molding method of a foundry sand core with less environmental load. After recovering the water-soluble inorganic salt binder as an aqueous solution, it is possible and preferable to concentrate the water-soluble inorganic salt by dialysis using an ion exchange membrane.

  Recovery and reuse (reuse) of water-soluble core binder makes it possible to recover almost all of the waste that has been difficult to treat with waste water containing water-soluble core binder as a large amount of industrial waste. It can be used again as a water-soluble core binder. This not only solves environmental problems, but can also significantly reduce the manufacturing cost of aluminum alloy cylinders and the like.

  According to the present invention, the mold is heated to dry and solidify the slurry-like foundry sand in the vicinity of the mold wall, and pressure is blown into the mold to discharge moisture from the slurry-like foundry sand. By providing a step (second step) in which the wet sand is further blown out and the unsolidified sand at the center of the die is discharged (second step), a mold having a complicated shape can be produced hollow even if an inorganic binder is used. The casting defect due to the generated gas can be eliminated if the inlet side is opened for standby during casting. Moreover, since it becomes hollow when drying and hardening in a 3rd process, the passage of hot air becomes very good and drying time can be shortened.

  Furthermore, as an effect of using a slurry-like mixture of foundry sand and a water-soluble binder, the slurry is filled in a mold, and the slurry is dried and molded to form a foundry sand core. The permeability of the slurry of foundry sand and water-soluble binder is improved, and the warm strength of the foundry sand core can be increased. In particular, by using a water-soluble core binder made of a water-soluble inorganic salt, a water-soluble core having both sufficient core strength and water solubility can be obtained. Further, by using this water-soluble core, it is possible to perform casting that does not lose its shape during casting and can be easily removed after casting.

That is, the effects of the present invention are enumerated as follows.
1. Even if an inorganic binder is used according to the present invention, a mold having a complicated shape can be produced in a hollow shape, and casting defects due to the generated gas can be eliminated if the blow-off port side is opened by standby during casting.
2. In the third step, when it is dried and cured, it is hollow, so that the hot air is very good and the drying time can be shortened.
3. Since the foundry sand discharged in the second step returns into the blow head, it can be used effectively in the next cycle molding and no loss sand is generated. In addition, there is no reduction in strength during reuse.
4). As other effects of the hollow core, the weight of the core is reduced, the total amount of gas generated during casting is reduced, and the handleability can be expected to be improved by being light.

In addition to the above direct effects, the following effects are also exhibited.
5. Since excessive moisture is removed by pressure-blowing from above into a mold filled with slurry-like foundry sand, the molding time can be shortened in the case of a slurry with much moisture. Even when a slurry-like inorganic binder is used, a large amount of water can be quickly removed, and slurry falling and scattering when the blow head is removed can be prevented, so that molding can be performed without reducing productivity.
6). When the mold is rotated during slurry filling, even a complicatedly shaped mold can be filled to every corner. Gravity can be effectively used for a portion that is difficult to be filled by rotation of 90 to 360 degrees depending on the shape.
7). When filling with pressure in the mold of the first step from below and when blowing into the mold of the second step from above, reducing the suction from the opposite side of the mold to improve filling properties and shortening the water removal time Can be planned.
8). Even if an inorganic binder is used, a mold having a complicated shape can be filled with sand, and a hollow core can be formed.
9. The slurry-like sand is prepared simply by adding a binder having a predetermined concentration to the sand so as to form a slurry. (Excess binder is discharged together with air, so no control is required)
10. The boiling point of water is lowered by the reduced pressure, and the mold temperature can be lowered because water evaporates and hardens at a lower temperature.
11. Due to the temperature difference in the core, the distribution of salt concentration becomes dense on the mold surface (outside of the core). When the gap between the casting sand particles is filled with the salt, the core surface becomes smooth and the casting surface roughness is improved.
12 Since the cured binder dissolves and the core collapses by immersing the casting in water, sand separation (sand removal) is possible. At this time, if the binder solution itself is used, the taken-out foundry sand becomes a slurry having a composition close to that before molding. According to the present invention, since a small amount of water is added to adjust the binder concentration and the slurry can be handled as it is as a slurry-like casting sand, a so-called sand recycling step is not necessary. That is, it is not necessary to make it equivalent to fresh sand, and all regeneration processes such as roasting and polishing can be omitted.
13. Since the slurry of foundry sand and water-soluble binder mixed at a predetermined ratio is blown, the handling and weighing of the slurry is easy, and there is little fear of drying, and the handling is easy.
14 When the foundry sand is reused in the process, the binder adheres to the sand, but according to the present invention, it can be treated as pre-kneaded sand, so the so-called sand recycling process becomes unnecessary. There is no need for roasting or polishing to make it equivalent to fresh sand.

  Although the principle of action that the warm strength of the core can be increased by using the water-soluble inorganic salt is not necessarily elucidated, the water-soluble inorganic salt crystals on the surface of the casting sand are smoothly and uniformly coated. Thus, it is presumed that the crystal strength is exhibited and the warm strength of the molded core is increased.

In FIG. 1, each molding process of the foundry sand core of this invention is shown.
FIG. 1A shows a slurry sand filling step, in which pressurized filling air 3 is blown in a state where casting sand 1 slurried with an inorganic water-soluble binder solution is placed in a blow head 2. Since the blow head 2 and the mold 4 are in communication and in close contact with each other through the introduction pipe 5 and the blowing nozzle 6, the foundry sand 1 is filled in the cavity 7 in the mold. At this time, since the foundry sand is made into a slurry with a large amount of binder solution, it can be filled to every corner in a state close to a liquid. It is effective to use the vacuum suction 14 in the first step. (End of step 1)

  FIG. 1 (b) is a quick exhaust / hollowing process. When the pressurized air 8 is blown, the slurry liquid excessive for filling the sand is discharged out of the mold together with the air, and the state of the slurry is changed to the wet sand state. Become. At this time, since the mold is heated to about 100 ° C., the foundry sand in the vicinity of the mold surface starts to dry and harden. Next, the pressurized air is quickly exhausted 10 and at the same time, the pressurized blow 8 is introduced from above, and the central uncured wet casting sand 9 is discharged. Pressurized air from the top varies greatly depending on the height and shape of the core, but 0.01 to 0.1 Mpa is appropriate, and if it is too high, only a thin-walled core can be formed. (End of step 2)

FIG. 1C shows a drying / molding process. When the blow head is replaced with the hot air head 11, the hot air 12 for drying is inserted, and the exhaust 13 is discharged from the upper part, the inside of the cavity where the moisture becomes low in the second process. The foundry sand is dried and molded. (End of step 3)
Finally, after the molding is completed, the mold is opened, and the molded mold 15 is taken out.

An embodiment of the present invention will be described below with reference to FIG.
Using dry mullite artificial sand as foundry sand, 10 g (10%) of magnesium sulfate (MgSO ₄ ) and 10 g (10%) of sodium carbonate (Na ₂ CO ₃ ) were dissolved per 100 cc of water as a water-soluble inorganic salt binder. An aqueous solution was used. These foundry sands and a water-soluble inorganic salt binder aqueous solution were mixed at a ratio of 1: 0.5. From the state in which the foundry sand 1 made into a slurry with the obtained inorganic water-soluble binder solution is put in the blow head 2, the pressurized air 3 is blown and simultaneously the vacuum suction 14 is performed from above. Since the blow head 2 and the mold 4 are in communication with and in close contact with each other via an introduction pipe 5 in which an opening reaches the blown slurry, the foundry sand 1 is filled in the cavity 7 in the mold. At this time, since the foundry sand is made into a slurry with a large amount of binder solution, it is filled to every corner in a state close to a liquid. (The above, 1st process: Slurry sand filling process)

  Next, when the pressurized air 8 is blown, the slurry liquid excessive for hardening the filled sand is discharged out of the mold together with the air, so that the slurry is changed to the wet sand state. At this time, since the mold is heated to about 100 ° C., the foundry sand in the vicinity of the mold surface starts to dry and harden. Next, pressurized air is quickly exhausted 10 and at the same time, a pressure blow 8 is introduced from above, and the central uncured wet casting sand 9 is discharged. Thereby, quick exhaust and hollowing are performed. (The above, 2nd process: rapid exhaustion and hollowing process)

  Next, instead of the blow head, the hot air head 11 is set, and after waiting for a predetermined hot air waiting time, hot air 12 for drying is put in from the lower part, and the foundry sand in the slurry state is dried and molded in a mold. In addition to drying with hot air, heating of the mold is also effective, and there is a method of heating the foundry sand by microwave instead of heating the mold. Finally, after completion of molding, the mold is opened and the hollow core 15 is taken out. (End of third step: drying / molding step)

  The mold is heated to dry and solidify the slurry-like foundry sand in the vicinity of the mold wall, and pressure is blown into the mold to discharge moisture from the slurry-like foundry sand to form wet sand. By providing a step (second step) for discharging the unsolidified sand at the center of the mold by pressure blowing, a mold having a complicated shape can be produced hollow even if an inorganic binder is used. In addition, casting defects due to the generated gas can be eliminated if the inlet side is opened for standby during casting. Furthermore, since it becomes hollow when drying and curing in the third step, the flow of hot air becomes very good and the drying time can be shortened. Thus, the present invention contributes to the spread of casting using a water-soluble core.

Each shaping | molding process of the foundry sand core of this invention is shown.

Explanation of symbols

1: Slurry foundry sand, 2: Blow head, 3: Pressurized air, 4: Mold, 5: Introduction pipe, 6: Nozzle, 7: Cavity, 8: Pressurized blow, 9: Wet sand like foundry sand, 10: rapid exhaust, 11: hot air head, 12: hot air, 13: exhaust, 14: vacuum suction.

Claims (11)

  In a molding sand core molding method in which a water-soluble binder is mixed with foundry sand to form a slurry, the slurry is filled into a mold, and then the filled is dried to be molded. A step of first filling the mold with pressure (first step), heating the mold to dry and solidify the slurry-like foundry sand in the vicinity of the mold wall, and pressurizing and blowing the slurry into the mold Moisture is discharged from the shaped casting sand into wet sand, further blown under pressure to discharge unsolidified sand at the center of the mold (second step), and hot air is blown to dry the foundry sand. A molding sand core molding method comprising a molding step (third step).   Pressurization and filling into the mold in the first step is performed from below and sucked from above, and pressure blow into the mold in the second step is performed from above and exhausted from below. The method for molding a casting sand core according to claim 1, wherein drying and molding in the third step are performed by blowing hot air from below and opening the top.   3. The molding sand core molding method according to claim 1, wherein the molding sand core molding apparatus is inverted between the first process and the second process and between the second process and the third process. .   The casting sand core molding method according to any one of claims 1 to 3, wherein the heating of the mold in the second step is performed at 80 ° C to 120 ° C.   The molding method for a foundry sand core according to any one of claims 1 to 4, wherein a viscosity of the slurry obtained by mixing the foundry sand with a water-soluble binder is 4 to 12 cp.   The molding method for a foundry sand core according to any one of claims 1 to 5, wherein the water-soluble binder is a water-soluble inorganic salt binder.   The method for molding a molding sand core according to any one of claims 1 to 6, wherein a weight ratio of the molding sand to the water-soluble binder is 1: 0.1 to 1: 5. The water-soluble binder is a cation selected from magnesium ion (Mg ²⁺ ), sodium ion (Na ⁺ ), and calcium ion (Ca ²⁺ ), SO ₄ ²⁻ , CO ₃ ²⁻ , HCO ₃ ²⁻ , B _4. O ₇ ^- foundry sand core according to any one of claims 1 to 7, wherein the water-soluble core binder consisting of one or more water-soluble inorganic salt comprising a combination of an anion selected from Molding method.   One kind of inorganic filler selected from silica sand (silica powder), alumina, potassium titanate, silicon carbide, zircon silicate, fibrous potassium titanate, titanium oxide, zinc oxide, iron oxide and magnesium oxide as the water-soluble binder. The method for forming a foundry sand core according to any one of claims 1 to 8, wherein the above is added.   10. The foundry sand according to claim 1, wherein, when the foundry sand and the water-soluble binder are mixed, an inorganic fine powder is blended and kneaded in addition to the foundry sand particles and the water-soluble binder. The core molding method.   An aluminum alloy casting method using a water-soluble core formed by the casting sand core molding method according to any one of claims 1 to 10.

Images