JP2006289396A - Method for manufacturing mold - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing the mold, with which even in the case that the addition quantity of a binder is reduced, the higher mold strength can be obtained and regenerating characteristic of sand can be improved. <P>SOLUTION: The method for manufacturing the mold, is performed, by which the binder is added into a spherical molding sand manufactured with a flame fusion method, and the mold is manufactured by injecting carbon dioxide gas. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a mold in which the amount of binder added is reduced by combining spherical casting sand produced by a flame melting method in a method for forming a mold using carbon dioxide gas as a curing agent.

  As a binder used for molding a mold, an organic binder that can be cured with carbon dioxide gas, which is excellent in safety, has attracted attention.

An organic binder composition that can be cured with carbon dioxide gas is disclosed in Patent Document 1, for example. On the other hand, Patent Document 2 discloses improving the working environment, mold sand filling property and casting quality by molding using a specific organic carbon dioxide curing binder in the reduced pressure molding method. Yes.
Japanese Unexamined Patent Publication No. 2000-15389 JP-A-9-52144

  However, even with these methods, the mold strength cannot be said to be sufficient, and therefore it is necessary to add a large amount of binder, which causes poor sand regeneration.

  An object of the present invention is to provide a method for producing a mold that can obtain higher mold strength and improve sand reproducibility even if the amount of binder is reduced.

  The present invention relates to a method for producing a mold in which molding is performed by adding a binder and blowing carbon dioxide gas into a spherical casting sand produced by a flame melting method.

  ADVANTAGE OF THE INVENTION According to this invention, even if it reduces binder addition amount, the mold manufacturing method which can obtain higher mold intensity | strength and can also improve sand reproducibility is provided.

  In this invention, a casting_mold | template can be shape | molded by adding a binder to the spherical casting sand manufactured by the flame melting method, and blowing in carbon dioxide gas. Specifically, casting sand obtained by kneading foundry sand and a binder with a kneading machine is filled into a mold by blowing or manual filling, and then carbon dioxide gas is blown to cure the foundry sand filled in the mold to form a mold. Can be molded. The binder used in the present invention is a carbon dioxide curable binder, and examples thereof include an organic binder and an inorganic binder.

  In the present invention, it is preferable to mold the mold by a reduced pressure molding method from the viewpoint of improving the mold strength. Below, the case where it shape | molds by the pressure reduction molding method is demonstrated in detail. Examples of the pressure molding method include a pressure molding method and a VRH molding method.

  First, the pressure molding method is a method in which casting sand is instantaneously filled into a casting frame or a core box at a high vacuum pressure, and then a curing gas is passed through the main mold or core under reduced pressure to produce a mold. It is. More specifically, as a main mold forming method, a casting frame is set on a hollow pattern plate having a vent plug, and a binder is provided in a hopper having a plurality of foundry sand outlets. When casting air is kneaded and placed on the casting frame, and air is instantaneously sucked by operating a valve on the decompression side, the casting sand in the hopper is instantaneously sucked and filled into the casting frame. In addition, if you want to increase the degree of filling, put a film or flat plate on the top of the casting sand and suck it again. In this case, the carbon dioxide gas in the air is shut off, so the merit of extending the working time of the casting sand is extended. Also have. When molding the core, install a vertical split core box with a vent plug on the inner surface of the mold cavity, place a hopper containing cast sand mixed with a binder on it, and operate the decompression valve. When the inside of the cavity is sucked instantaneously, the foundry sand in the hopper is filled into the core cavity vigorously. Next, in order to ventilate the carbon dioxide gas, a gashing lid or a film is placed on the core box, sucked from the core box, and then the foundry sand is hardened by supplying carbon dioxide gas.

  Although the aeration conditions are not particularly limited, the standard is 20 to 500 liters / minute, and the aeration pressure of carbon dioxide gas is preferably in the range of 0.1 to 5 atm, more preferably 0.5 to 3 atm. The amount of carbon dioxide used is preferably 5 to 300 parts by weight with respect to 100 parts by weight of the binder. The degree of decompression of the cavity is not particularly limited, but is preferably 0 to 0.1 MPa, and more preferably 0.0001 to 0.04 MPa. Here, such a molding method is referred to as a pressure molding method. By molding using a binder, the filling property of the foundry sand is further improved, and a high-strength mold can be molded. In addition, a high-quality casting can be produced by casting using a binder that is cured using non-toxic carbon dioxide gas.

  In the VRH molding method, a model is filled with foundry sand kneaded with a binder, placed in a sealed container, the inside of the container is depressurized and air in the mold is removed, and then the hardening gas in the container is introduced. In this method, the mold is uniformly cured by filling the mold uniformly with the gas and promoting the reaction with the binder in the mold. In the present invention, by using the spherical casting sand produced by the flame melting method, a high-quality casting can be produced even if the amount of the binder is reduced.

  In the present invention, when molding by the VRH molding method, the degree of vacuum after filling the molding model with the molding sand kneaded with the binder and placing it in the sealed container is usually 0 to 0.05 MPa, which is practically preferable. Is preferably 0.001 to 0.01 MPa. The holding time is also related to the capacity of the sealed container and the vacuum pump, but is usually within 30 minutes, and reaches 0.001 MPa within about 10 minutes after opening the pressure reducing valve connected to the vacuum pump of the sealed container, Replace the sealed container with carbon dioxide. The time required for this is several seconds to several minutes, and the mold is taken out with the pressure in the sealed container equivalent to about atmospheric pressure. The amount of carbon dioxide used as a standard in the VRH molding method is preferably 5 to 300 parts by weight, more preferably 20 to 200 parts by weight, based on 100 parts by weight of the binder.

  The spherical casting sand used in the method of the present invention is produced by a flame melting method as disclosed in JP-A No. 2004-202577.

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

The main component of the spherical casting sand is not particularly limited, and conventionally known refractories and refractory raw materials obtained by spheronization by a flame melting method are used. The powder particles are dispersed in a carrier gas such as oxygen, and are melted and spheroidized in the following flame. Occurs flame propane, butane, methane, natural liquefied gas, LPG, heavy oil, kerosene, gas oil, and that is generated by burning the fuel oxygen pulverized coal etc., ionizes the N ₂ inert gas or the like used Plasma jet flames can be used.

Among these refractories and refractory raw materials, those containing SiO ₂ as the main component, those containing Al ₂ O ₃ and SiO ₂ as the main components, MgO and SiO from the viewpoint of fire resistance and availability. Those having ₂ as a main component are preferred. Among them, those mainly containing Al ₂ O ₃ and SiO ₂ are preferable.

  Here, the “main component” means that the above components are contained in a total amount of 60% by weight or more in the total components of the foundry sand. As the content of the main component, from the viewpoint of improving fire resistance, the total amount of these components is preferably 85 to 100% by weight, more preferably 90 to 100% by weight, based on all the components of the spherical casting sand.

Incidentally, as it may be included as a component other than the main component in the spherical molding sand of the present invention, for _{example, Fe 2 O 3, TiO 2} , K 2 O, and metal oxides Na ₂ O and the like. These are derived from starting materials.

When Fe ₂ O ₃ and TiO ₂ are contained, their content is preferably 5% by weight or less. Further, the content of Fe ₂ O ₃ is more preferably 2.5% by weight or less, and further preferably 2% by weight or less. When K ₂ O and Na ₂ O are contained, the total content is preferably 3% by weight or less, more preferably 1% by weight or less.

In the case of mainly composed of Al ₂ O ₃ and _{SiO 2, Al 2 O 3 /} SiO 2 weight ratio is preferably 1 to 15. From the viewpoint of improvement in fire resistance and casting sand regeneration efficiency, 1.2 to 12 is preferable, and 1.5 to 9 is more preferable. Further, when only Al ₂ O ₃ and SiO ₂ or SiO ₂ are the main components, CaO and MgO may be included as components other than the main components. In that case, from the viewpoint of improving the fire resistance of the spherical casting sand, the total content thereof is preferably 5% by weight or less.

In the case of the main component MgO and SiO _2, the weight ratio of MgO / SiO ₂ is preferably 0.1 to 10 is. From the viewpoints of easiness of spheroidization, corrosion resistance, fire resistance, and improvement in recycle efficiency of foundry sand, 0.2 to 9 is preferable, and 0.3 to 5 is more preferable.

When MgO and SiO ₂ are the main components, Al ₂ O ₃ can be included as a component other than the main components. Although this originates in a raw material, 10 weight% or less is preferable as content from a viewpoint of the corrosion-resistant improvement of a spherical casting sand.

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

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

  Examples of the organic binder used in the present invention include those containing a water-soluble alkaline phenol resin and a compound selected from boric acid compounds, aluminate compounds, and stannic acid compounds. Examples of water-soluble alkaline phenol resins include phenolic and formaldehyde resins, especially phenols and formaldehyde resins, bisphenols and formaldehyde resins, or phenols, bisphenols, and formaldehyde co-condensation resins. Or a catalyst may be included. These will be described below.

  Prepare phenolic raw materials for phenolic and formaldehyde resins by preparing formaldehyde resins that use phenols and bisphenols alone or formaldehyde cocondensation resins that use phenols and bisphenols at the same time. obtain.

  Examples of phenols include phenol, cresol (ortho, meta, para), and resorcin. Examples of bisphenols include bisphenol A, bisphenol F, bisphenol S, and bisphenol Z.

  The content of the water-soluble alkali phenol resin in the organic binder is preferably 50 to 99% by weight, and more preferably 70 to 90% by weight.

  The organic binder used in the present invention contains a compound selected from boric acid compounds, aluminate compounds and stannic acid compounds. Examples of the boric acid compounds include boric acid compounds such as boric acid and borax, and boric acid esters. Examples of the aluminate compounds include sodium aluminate, potassium aluminate, lithium aluminate and the like. Examples of stannic acid compounds include sodium stannate, potassium stannate, lithium stannate and the like. The content of these compounds is preferably 0.1 to 30% by weight, more preferably 3 to 15% by weight, in the organic binder. These compounds are used for crosslinking in a resin in an organic binder, for example, an alkaline water-soluble phenol resin.

  Examples of the inorganic binder used in the present invention include water glass such as sodium silicate.

  As the binder, an organic binder is preferable from the viewpoint of improving the mold strength.

  The binder is preferably added in an amount of 0.5 to 2.0 parts by weight, and more preferably 0.5 to 1.5 parts by weight, with respect to 100 parts by weight of the spherical casting sand.

  In order to further increase the mold strength, glycol ethers such as cellosolve, carbitol, triethylene glycol ethers may be added as an additive at the time of the reaction of the resin or at the end of the reaction. It is 0.1-30 weight part with respect to a weight part, Preferably it is 5-20 weight part. The addition time may be added at the time of kneading adjustment of the foundry sand, and a silane coupling agent may be further added.

  Conventionally, foundry sand used in vacuum molding, for example, imported quartz sand, domestic quartz sand, alumina sand, zircon sand, chromite sand, synthetic mullite sand as described in JP-A-9-52144 (Patent Document 2) (Cerabeads), olivine sand, metal powder, metal oxide powder, etc.), a sufficient strength could not be obtained with a binder addition amount of 1.0 part by weight or less with respect to 100 parts by weight of foundry sand. On the other hand, in the present invention, the mold strength is drastically increased by using spherical foundry sand produced by the flame melting method as the foundry sand and curing the carbon dioxide gas together with the binder. Therefore, the amount of binder added can be greatly reduced, and sand reproducibility can be improved. That is, if the mold is produced by the production method, it can be used as reclaimed sand, so that excellent mold strength can be exhibited without much load.

<Types of foundry sand>
Below, the foundry sand used by the Example and the comparative example is demonstrated.

Examples 1-3, 6, 9-11
97% by weight of Al ₂ O ₃ and SiO ₂ in total, Al ₂ O ₃ / SiO ₂ weight ratio is 1.7, moisture content is 0% by weight, average particle size is 0.31 mm, major axis diameter / A mullite powder (synthetic mullite powder manufactured by Shibata Ceramics) having a minor axis diameter ratio of 1.5 is used as a starting material, oxygen is used as a carrier gas, and LPG (propane gas) is used as an oxygen ratio (volume ratio). It was put into a flame (about 2000 ° C.) burned in No. 1 to obtain monodispersed spherical casting sand. The resulting foundry sand contains 97% by weight of Al ₂ O ₃ and SiO ₂ in total amount, the Al ₂ O ₃ / SiO ₂ weight ratio is 1.7, the average particle size is 0.26 mm, and the sphericity Was 0.99, the water absorption was 0% by weight, and the particle density was 2.9 g / cm ³ .

Example 4
The spheroidal foundry sand used in Example 1 was regenerated based on the following reclaimed sand preparation method to obtain reclaimed sand.

Examples 5 and 8
Monodispersed spherical casting sand was obtained in the same manner as in Example 1 except that the starting material had an average particle size of 0.9 mm and a major axis / minor axis ratio of 1.7. The obtained foundry sand contains 97% by weight of Al ₂ O ₃ and SiO ₂ in total amount, the Al ₂ O ₃ / SiO ₂ weight ratio is 1.7, the average particle size is 0.69 mm, and the sphericity Was 0.97, the water absorption was 0% by weight, and the particle density was 2.8 g / cm ³ .

Example 7
The spheroidal foundry sand used in Example 5 was regenerated based on the following reclaimed sand preparation method to obtain reclaimed sand.

Comparative Examples 1-4, 8-10
Flattery silica sand (Australia) was used as natural silica sand.

Comparative Example 5
The flattery silica sand used in Comparative Example 1 was reclaimed based on the following reclaimed sand preparation method to obtain reclaimed sand.

Comparative Example 6
Sintered spherical artificial ceramic foundry sand (trade name: Cerabeads # 750 (manufactured by ITOCHU CERATECH)) was used.

Comparative Example 7
Artificial ceramic casting sand by melt granulation obtained by atomization method (trade name: ESPARL # 75 (manufactured by Yamakawa Sangyo Co., Ltd.))

<Preparation method of reclaimed sand>
Add and mix the binder shown in Table 1 into fresh sand, harden with carbon dioxide gas using the reduced pressure molding method (VRH molding method), and cast (material: FCD-450 (pour temperature is 1410) C.), uncoated type), and the recovered sand was applied to a crusher and regenerated using an M-type rotary reclaimer manufactured by Nippon Casting Co., Ltd. (first regeneration). The resulting reclaimed sand is added and mixed with the binder shown in Table 1 and cured using carbon dioxide gas, and then cast (material: FCD-450 (the pouring temperature is 1410 ° C), uncoated Type). The casting sand was collected and regenerated from this mold in the same manner as described above, and the regenerated sand was regenerated 10 times.

  In addition, in the case of the spherical casting sand manufactured by the flame melting method, in the molding for the above-mentioned regeneration, the amount of binder added is 0.7 parts by weight with respect to 100 parts by weight of the molding sand. went. On the other hand, in the case of flattery silica sand, in the molding for the above regeneration, the mold strength was low when the resin addition amount was 0.7 parts by weight. Therefore, 3.5 parts by weight was added to 100 parts by weight of foundry sand and recycled. Made a mold for.

<Measurement method of acid consumption>
The acid consumption represents the amount of alkali components such as alkali metals remaining in the foundry sand, and is defined by the “Foundry Sand Acid Consumption Test Method” defined in the Japan Casting Technology Association Standard: “JACT Test Method S-4”. ”And measured. In reclaimed sand, the closer to the value in fresh sand, the better the sand reproducibility.

<Measurement method for loss on ignition>
Loss on ignition (LOI) is the mass change rate of the substance that thermally decomposes and burns in addition to the adsorbed moisture, interlayer moisture, and crystal moisture remaining in the foundry sand. It was measured in accordance with “Method for loss on ignition of foundry sand” defined in “Method S-2”. In reclaimed sand, the closer to the value in fresh sand, the better the sand reproducibility.

<Evaluation>
Using the above foundry sand, the test piece (having a diameter of 50 mm and a height) was added by the following molding method with the addition amount of the binder shown in Table 1 (parts by weight of binder with respect to 100 parts by weight of foundry sand). Is 50 mm). Table 1 shows the compressive strength of the obtained test piece mold after 1 hour.

(1) Atmospheric pressure molding method Mixing molding sand and binder in Table 1 with a batch mixer for 1 minute, filling into a gas curing wood mold with 8 test pieces, gas temperature 30 ° C, air flow rate 20 liters / minute Carbon dioxide was aerated for 30 seconds at a gas pressure of 0.2 MPa to obtain a mold (a test piece having a diameter of 50 mm and a height of 50 mm).

(2) Pressure molding method The binder shown in Table 1 is a polyfilm shown in Table 1 in order to increase the pot life and filling degree on a cast frame placed on a hollow pattern plate having a vent plug. Put the hopper with multiple casting sand outlets on the casting frame and actuate the valve on the decompression side to instantly suck the air, Suction filled. The degree of vacuum at this time was 0.008 MPa. After the suction filling, the degree of decompression was lowered, so that the degree of decompression was maintained as it was, and then the carbon dioxide gas valve was opened and the curing gas was fed to obtain a mold (a test piece having a diameter of 50 mm and a height of 50 mm).

(3) VRH molding method Casting sand kneaded with the binder shown in Table 1 is placed in a 100-liter sealed container, depressurized to 0.003 MPa, and after depressurization, carbon dioxide is sent to atmospheric pressure. The mold (test piece having a diameter of 50 mm and a height of 50 mm) was taken out from the sealed container. At this time, the time required to reach 0.003 MPa was 3 minutes, and the time required to reach atmospheric pressure by feeding carbon dioxide gas was 1 minute.

In addition, the binder in Table 1 is as follows.
Organic binder: (water-soluble alkali phenol resin: 79.5% by weight, borax: 5% by weight, γ-aminopropyltriethoxysilane: 0.5% by weight, phenyl monoethylene glycol ether: 15% by weight)
・ Inorganic binder: Water glass

Claims (5)

A method for producing a mold, wherein molding is performed by adding a binder and blowing carbon dioxide gas into a spherical casting sand produced by a flame melting method. The method for producing a mold according to claim 1, wherein 0.5 to 2.0 parts by weight of the binder is added to 100 parts by weight of the spherical casting sand. The method for producing a mold according to claim 1 or 2, wherein the binder is an organic binder. The method for producing a mold according to any one of claims 1 to 3, wherein molding is performed by a reduced pressure molding method. 5. The method for producing a mold according to claim 4, wherein the reduced pressure molding method is an absorption molding method or a VRH molding method.