JP6738956B1 - Mold recycled sand, resin coated sand and mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mold reclaimed sand having excellent low thermal expansion property and also excellent in mold strength, a resin coated sand containing the reclaimed sand, and a mold obtained by curing and molding the resin coated sand. SOLUTION: A mold reclaimed sand containing at least 45 to 75% by mass of SiO2, 10 to 30% by mass of Al2O3, 2 to 12% by mass of Fe2O3 and 3 to 20% by mass of MgO, and having a size of 150 μm to 300 μm. Mold reclaimed sand, in which the particles sieved in between contain particles having a BET specific surface area of 1.5 m2/g or less. [Selection diagram] Fig. 4

Description

The present invention relates to a mold reclaimed sand, a resin coated sand and a mold.

Examples of castings formed by using a resin coated sand (hereinafter referred to as RCS) as a mold (generally also referred to as a core) include, for example, automobile engine parts, brake parts, and power transmission devices. Parts, intake and exhaust system parts, etc. In recent years, such castings have been made thinner and lighter, and all of them tend to have higher definition. Therefore, the requirements for dimensional stability (low thermal expansion and high mold strength, etc.), low outgassing, low odor, etc. are becoming more stringent for RCS.
RCS is an aggregate of natural silica sand, artificial silica sand, reclaimed sand, special sand (ceramic sand, zircon sand, chromite sand, olivine sand, etc.) coated with a resin composition. When the content of the resin composition is increased, there is a problem that the resin composition generates a thermal decomposition gas (including water) during casting, which easily causes gas defects in the casting. The content of the resin composition is preferably as low as possible with respect to the aggregate which occupies at least mass %. On the other hand, the mold strength tends to decrease due to the small content of the resin composition in the RCS. Due to such a situation, there is a limit in improving various characteristics of RCS depending on the type and characteristics of the resin in the resin composition.
Therefore, in order to improve various properties of RCS, it is more effective to improve the properties of the aggregate together with the resin composition. Among the aggregates, natural silica sand and special sand, which tend to be excellent in mold strength and low thermal expansion, have a problem that they are expensive. Therefore, artificial silica sand and reclaimed sand, which are relatively inexpensive, are attracting attention. Among them, from the viewpoint of manufacturing cost and recycling, there is a method of effectively utilizing reclaimed sand obtained by collecting and reclaiming waste sand obtained by separating the mold (hereinafter, also referred to as mold reclaimed sand). Coveted.

The mold reclaimed sand needs to be obtained by collecting and reclaiming waste sand (also referred to as mold waste sand). The mold waste sand is generally a mixture of various aggregates and impurities such as metals and metal compounds. including. In this regard, a method is known in which the waste sand is subjected to a magnetic separation treatment to remove metal powder, metal pieces, and the like, and also to remove magnetic deposits, and also to remove waste substances containing carbides to regenerate the waste sand. (For example, see Patent Document 1).

JP, 2017-074604, A

However, studies by the present inventors have revealed that it is difficult for the conventional mold reclaimed sand to have both low thermal expansion and strength of the formed mold, and there is room for further improvement.
Therefore, the present invention provides a mold reclaimed sand having an excellent low thermal expansion property and an excellent mold strength, a resin coated sand containing the mold reclaimed sand, and a mold formed by curing and molding the resin coated sand. The purpose is to do.

The present inventor, as a result of repeated diligent research, found that the above-mentioned problems can be solved if "particles subjected to predetermined sieving contain magnetic particles containing particles having a predetermined specific surface area or less". The invention was completed.

That is, the present invention relates to [1] to [7].
[1] Mold reclaimed sand containing at least 45 to 75 mass% of SiO ₂ , 10 to 30 mass% of Al ₂ O ₃ , ₂ to 12 mass% of Fe ₂ O ₃ and ₃ to 20 mass% of MgO. The mold regenerated sand, wherein the particles sieved between 150 μm and 300 μm contain particles having a BET specific surface area of 1.5 m ² /g or less.
[2] The template reclaimed sand according to the above [1], wherein the particles sieved between 150 μm and 300 μm contain particles having a BET specific surface area of 0.7 to 1.5 m ² /g.
[3] The mold reclaimed sand according to the above [1] or [2], which is magnetic sand obtained by subjecting the waste mold sand to magnetic separation and polishing.
[4] The mold reclaimed sand according to the above [3], wherein the magnetic separation treatment includes magnetic separation treatment with a magnetic flux density of more than 5,000 G.
[5] A resin coated sand containing the mold reclaimed sand according to any one of the above [1] to [4] and a resin composition.
[6] The resin composition is a phenol resin, polyethylene, polypropylene, polyolefin, polystyrene, polyethylene terephthalate, polyvinyl alcohol, polyphenylene ether, polybutylene terephthalate, polyether ether ketone, polyacetal, polymethyl methacrylate, polylactic acid, furan resin, The resin coated sand according to the above [5], containing at least one resin selected from the group consisting of urethane resins, urea resins, melamine resins and biomass-derived resins.
[7] A mold obtained by curing and molding the resin coated sand according to the above [6].

According to the present invention, it is possible to provide mold reclaimed sand having excellent low thermal expansion properties and excellent mold strength. The mold reclaimed sand of the present invention has excellent low thermal expansion properties and can improve the mold strength more than conventional mold reclaimed sand. In addition, since the mold reclaimed sand uses (recycles) waste mold sand, the manufacturing cost is low.
Further, according to the present invention, a resin coated sand (RCS) containing the reclaimed sand of the present invention can be provided. Further, it is possible to provide a mold obtained by curing and molding the RCS.

It is an example of a schematic diagram of an apparatus that can be used for the magnetic separation treatment when producing the reclaimed sand of the present invention. It is another example of the schematic diagram of the apparatus which can be used for the magnetic separation process when manufacturing the mold reclaimed sand of this invention. It is another example of the schematic diagram of the apparatus which can be used for the magnetic separation process when manufacturing the mold reclaimed sand of this invention. It is a flowchart which shows one preferable aspect of the method of manufacturing the mold reclaimed sand of this invention.

Hereinafter, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

[Mold Reclaimed Sand]
The present invention is a mold reclaimed sand containing at least 45 to 75 mass% of SiO ₂ , 10 to 30 mass% of Al ₂ O ₃ , ₂ to 12 mass% of Fe ₂ O ₃ and ₃ to 20 mass% of MgO. That is, the mold reclaimed sand is such that the particles sieved between 150 μm and 300 μm contain particles having a BET specific surface area of 1.5 m ² /g or less.
The reason for paying attention to “particles sieved between 150 μm and 300 μm” is that particles having a predetermined range of particle diameters have a large influence on the BET specific surface area if the variation in particle diameter is large. This is because the influence of the size of the particles can be eliminated as much as possible by specifying the BET specific surface area by specifying As a result, the BET specific surface area becomes a value that sufficiently reflects the degree of unevenness of the surface shape of the particles. That is, it means that the smaller the BET specific surface area is, the less irregular the surface shape of the particles is, and the more the surface tends to become flat.
The “particles sieved between 150 μm and 300 μm” refers to particles that pass through a sieve with an opening of 300 μm but do not pass through a sieve with an opening of 150 μm.

The inventors of the present invention have found that by setting the BET specific surface area of the particles contained in the reclaimed sand mold to the above value, the resin in the RCS adheres to the reclaimed sand with high strength and the mold strength is improved. Therefore, the mold reclaimed sand of the present invention has a low content of SiO _{2 and} a relatively large content of Al ₂ O ₃ , Fe ₂ O ₃ and MgO, and thus is excellent in low thermal expansion. The adhesive strength per unit adhesive area was higher than that in the case of the reclaimed mold sand having no predetermined BET specific surface area, and the mold strength could be improved.

In the mold reclaimed sand of the present invention, the content of the particles having a BET specific surface area of 1.5 m ² /g or less in the particles sieved between 150 μm and 300 μm is preferably 30 mass from the viewpoint of improving the mold strength. % Or more, more preferably 50% by mass or more, further preferably 80% by mass or more, particularly preferably 90% by mass or more, and may be substantially 100% by mass.

For the BET specific surface area 1.5 m ² / g or less of particles mold reclaimed sand contains the present invention, the BET specific surface area, from the viewpoint of mold strength, preferably 0.7~1.5m ² / g, more It is preferably 0.7 to 1.3 m ² /g, and may be 0.8 to 1.2 m ² /g.
According to the study by the present inventors, the small BET specific surface area of the particles contained in the reclaimed mold sand has an effect of reducing the adsorption rate of water in RCS and the mold, and as a result, during casting. It was found that the effect of suppressing the gas defect of was obtained. Generally, magnetically-bonded sand tends to have a large BET specific surface area, but the magnetically-bonded sand (B) of the present invention can have the BET specific surface area made small, and thus the above-mentioned characteristics can be obtained.

The mold reclaimed sand of the present invention is "magnetic sand" obtained by subjecting the mold waste sand to magnetic separation and polishing, and more specifically, "magnetic sand (B)" produced by the production method described below. In particular, the magnetic separation process can be easily manufactured by including the magnetic separation process having a magnetic flux density of more than 5,000 G. Here, in the present invention, the one obtained as a magnetic substance in the magnetic separation process with such a magnetic flux density is referred to as magnetic sand, and the one from which the magnetic substance is removed in the magnetic separation process with such a magnetic flux density is non-magnetic. This is called sand landing.
As described above, since the mold reclaimed sand (magnetic sand (B)) of the present invention is obtained by collecting the mold waste sand and performing each of the above treatments, as described above, at least SiO ₂ is 45 to 75. %, Al ₂ O ₃ is contained in 10 to 30 mass %, Fe ₂ O ₃ is contained in 2 to 12 mass %, and MgO is contained in 3 to 20 mass %. The mold reclaimed sand (magnetic sand (B)) of the present invention contains 45 to 65% by mass of SiO ₂ , 12 to 25% by mass of Al ₂ O ₃ , ₃ to 10% by mass of Fe ₂ O ₃ , and 4 of MgO. It is preferable that the content of SiO ₂ is 50 to 65% by mass, SiO ₂ is 50 to 65% by mass, Al ₂ O ₃ is 15 to 22% by mass, Fe ₂ O ₃ is ₃ to 8% by mass, and MgO is 5 to 15% by mass. It is more preferable that the content is %. In addition, the mold reclaimed sand (magnetic sand (B)) of the present invention may contain CaO, TiO ₂ , K ₂ O, Na ₂ O and the like, and the content of each of them is preferably 0. 10 to 3.5% by mass, more preferably 0.30 to 3.0% by mass, 0.30 to 1.5% by mass, or 0.30 to 1.3% by mass. May be. The content of each component is a value obtained according to the fluorescent X-ray analysis test method described in Examples, that is, a value for a large number of particles, not a value for a single particle.
The mold reclaimed sand (magnetic sand (B)) of the present invention is extremely excellent in low coefficient of thermal expansion, and has a mold strength higher than that of magnetic sand obtained by magnetically treating reclaimed sand by a conventional method. Improvements have been achieved.

Hereinafter, one aspect of the method for producing the reclaimed sand of the present invention will be described in detail, but the method for producing reclaimed sand of the present invention is not limited to this aspect.
(Method for producing mold reclaimed sand)
The mold reclaimed sand of the present invention is a non-container containing particles having a BET specific surface area of 0.35 m ² /g or less when the particles are sieved between 150 μm and 300 μm by subjecting the mold waste sand to a polishing treatment and a magnetic separation treatment. Magnetic sand (A) [Hereinafter, it may be simply referred to as "non-magnetic sand (A)". ] And particles having a BET specific surface area of 1.5 m ² /g or less, the particles sieved between 150 μm and 300 μm [B] [hereinafter, simply referred to as “magnetic sand (B)”] Sometimes. ] It is possible to utilize a method for producing reclaimed sand, which is to obtain at least one reclaimed sand selected from the group consisting of: The magnetic sand (B) obtained by the manufacturing method corresponds to the mold reclaimed sand of the present invention.

The mold waste sand that can be used in the manufacturing method is not particularly limited, and the mold waste sand actually formed can be used. The mold waste sand may be waste sand of a mold formed using any raw material, for example, silica sand (natural silica sand, artificial silica sand), artificial sand (sintered sand, molten sand, etc.), ceramic sand, Alumina sand, chromite sand, zircon sand, olivine sand, mullite sand, magnesia, fly ash and the like can be mentioned. The waste mold sand is preferably at least one selected from the group consisting of these. Further, these mold waste sands may be mixed with new sand, may be recovered sand, may be reclaimed sand, and may be selected from the group consisting of new sand, recovered sand and reclaimed sand. It may be a mixed sand of at least two kinds.
The natural silica sand, which is in the state of quartz sand, is distributed as a stratum on the land and developed as a sandy beach at the estuary and the coast, and its production site is not particularly limited. The artificial silica sand is obtained by crushing and sieving a silica stone ore to form a sand. The artificial sand is sand obtained by a sintering method or a melting method. The sintering method is a manufacturing method in which a spherical granulated product obtained by spray granulating a raw material slurry is sintered in a high-temperature firing furnace to grow crystals as much as possible to obtain a dense sintered body. Further, the melting method is a method in which a raw material ore is melted in a melting furnace or the like, blown off by air or the like, and made into a spherical shape by utilizing surface tension at the time of rapid solidification.
New sand is sand that has never been used as a material for molds, etc., and reclaimed sand is obtained by collecting and regenerating waste sand obtained by separating the mold, and collecting it without regenerating it. The collected sand is the recovered sand.

The magnetic separation equipment (the first magnetic flux density is 500 to 1,000 G of magnetic separation) described in Patent Document 1 (JP-A-2017-074604) is used for the mold waste sand distributed in the market. Magnetic flux density of 1,500 to 5,000 G), the magnetic sand having the BET specific surface area can be obtained even if the obtained magnetic sand is appropriately polished with an abrasive. No landing (B) can be obtained and the BET specific surface area is usually larger.

In this manufacturing method, the mold waste sand is subjected to polishing treatment and magnetic separation treatment so as to obtain the magnetic sand (B) (and the non-magnetic sand (A)) having the predetermined BET specific surface area.
In order to manufacture the magnetic sand (B) (and the non-magnetic sand (A)) having the predetermined BET specific surface area, the polishing treatment and the magnetic separation treatment may each be performed once. , Each may be twice or more.
Hereinafter, the polishing process and the magnetic separation process will be described in detail in order.

(Polishing process)
By subjecting the mold waste sand to a polishing treatment, deposits on the surface of the particles of the mold waste sand are scraped off to reduce surface irregularities, and as a result, the resulting magnetic sand (B) (and non-magnetic sand ( Since the BET specific surface area of the particles included in A)) becomes the above value, the mold strength is improved.
The polishing treatment can be carried out in accordance with a known polishing treatment in the method for reclaiming waste sand from a mold, preferably a dry method. For example, the sand particles are blown off by high-speed air to apply impact and friction to remove the deposits, a jet stream type device (a); the sand particles are splashed off by a rotor or a blade, or stirred, and further pressurized by a rotor. The vertical axis rotary type device or the horizontal axis rotary type device (b), in which the sand particles are impacted and rubbed against each other to separate and remove the deposits; A polishing process using various devices such as a vibrating device (c); a grindstone polishing device (d) having a low-speed rotating drum with blades and a high-speed rotating grindstone. Although not particularly limited, at least a polishing treatment using a vibration type device (c) or a grindstone polishing device (d) is performed from the viewpoint of obtaining mold reclaimed sand having the BET specific surface area specified in the present invention. From the same point of view, it is more preferable to perform both the vibration type device (c) and the grindstone polishing device (d). These devices may be used alone or in combination of two or more.

More specific polishing devices include, for example, a rotary reclaimer, a hybrid sand master, a sand fresher, a sand shiner, and the like. In particular, a polishing device provided with a dust collecting means, for example, a hybrid sand master (vibration type device (c), manufactured by Nihon Foundry Co., Ltd.), a sand flasher (grinding wheel polishing device (d), manufactured by Kiyota Casting Machine Co., Ltd.), etc. It is also preferable to use.
The hybrid sand master (manufactured by Nippon Foundry Co., Ltd.) is a device in which a rotary reclaimer and a fluid classifier are integrated. Since the hybrid sand master is a polishing device using a ceramic rotor, it has a long life and further has good polishing efficiency. According to the hybrid sand master, polishing and classification can be performed at the same time.
Sand Fresher (manufactured by Kiyota Casting Co., Ltd.) is a polishing device in which a low-speed rotary drum with blades (rotation speed 10 to 15 rpm) is installed outside a high-speed rotary grindstone. The amount of sand flowing through the gap between the grindstone and the tip of the blade can be adjusted by the movable blade of the low-speed rotating drum arranged outside. While the mold waste sand contacts the surface of the grindstone while passing through this gap, the mold waste sand is polished so as to rotate the balls. By removing the corners on the surface of the waste sand of the mold in this manner, it is possible to approximate the ideal spherical shape. By using both the hybrid sand master and the sand fresher, it becomes easy to produce the mold reclaimed sand having the BET specific surface area specified in the present invention.

Further, various polishing conditions such as the polishing time in the polishing process may be appropriately determined according to the attachment state of the deposit on the particle surface. For example, a processing amount of 1 to 5 t/h (preferably 1.5 to 2.5 t/h) using a sand flasher, a rotational speed of a grindstone of 2,000 to 3,000 rpm, and a rotational speed of a bladed drum around the grindstone. After the first polishing treatment is performed at 10 to 15 rpm and the number of passes is 1 to 3 times (preferably 1 to 2 times), the treatment amount is 1 to 5 t/h (preferably 2 to 4 t/h) using a hybrid sand master. ), the rotation speed of the drum is 1,000 to 3,000 rpm (preferably 1,500 to 2,500 rpm), and the second polishing treatment is preferably performed. The first polishing treatment and the second polishing treatment may be continuously performed, or a step of removing fine powder may be appropriately performed between the first polishing treatment and the second polishing treatment.
The polishing treatment is preferably performed in a state where there is no organic compound, dust, impurities, etc. adhering to the waste mold sand, and therefore, it is preferable to perform the polishing treatment at least after the incineration and firing treatment step described below.

(Magnetization process)
Common mold waste sand usually contains a magnetic material. Examples of the magnetic material include Fe ₂ O ₃ , MgO, and Al ₂ O ₃ . By subjecting the waste sand in the mold to magnetic separation treatment, the non-magnetic sand (A) having the reduced magnetic substance and the magnetic sand (B) having the increased magnetic substance are obtained.
The magnetic separation treatment is preferably more than 5,000 G (Gauss), more preferably 5,500 G or more, further preferably 6,000 G or more, particularly preferably 6,500 G or more, and most preferably 7,000 G or more. An embodiment including treatment is preferred. The upper limit of the magnetic flux density is not particularly limited, but since the effect reaches the ceiling, it is usually 20,000 G or less, 10,000 G or less, or 8,500 G or less. By performing the magnetic separation treatment with the above-mentioned preferable magnetic flux density, weakly magnetized MgO or the like is efficiently removed from the non-magnetic sand (A), and conversely, MgO or the like easily increases in the magnetic sand (B). When the magnetic flux density is 7,000 G or more, the tendency becomes remarkable.

The magnetic separation treatment at the preferable magnetic flux density is not particularly limited, but the magnetic substance (particularly weak magnetic substance) is removed from the non-magnetically adhering sand (A) without lowering the yield, and the magnetically adhering sand (B From the viewpoint of increasing the magnetic substance (particularly weak magnetic substance) in (), it is preferable to carry out after the incineration and firing treatment step.
As described above, since the magnetic separation treatment may be performed twice or more, the magnetic separation treatment with the magnetic flux density of 5,000 G or less is performed before the incineration and firing treatment step, and the magnetic separation treatment with the preferable magnetic flux density is performed. You may implement after the incineration baking process mentioned later. In the magnetic separation process with a magnetic flux density of 5,000 G or less, for example, a magnetic separation process with a magnetic flux density of about 3,000 G, it is possible to remove iron lumps, iron powder, iron sand, etc. Since it cannot be sufficiently removed, by performing magnetic separation treatment with a magnetic flux density of 5,000 G or less before the magnetic separation treatment with the preferable magnetic flux density, iron ingots, iron powder, iron sand, etc. It is possible to prevent the magnetic separation in the magnetic separation process with the above-mentioned preferable magnetic flux density from becoming rough and lowering the yield.

There is no particular limitation on the device for performing the magnetic separation process. For example, (1) a half magnetic outer ring system as shown in FIG. 1, (2) a suspension system as shown in FIG. 2, and (3) as shown in FIG. Examples include a magnet pulley system and (4) a counter-pole type magnetic separation system in which two sets of semi-magnetic outer rings are opposed to each other. In particular, the magnetic separation process with a magnetic flux density of more than 5,000 G is preferably performed by a magnet pulley system.

The magnetic separation processing apparatus of the semi-magnetic outer ring system shown in FIG. The rotary drum 2 having a mechanism that is rotated by a power source (not shown), the inlet side damper 3 having a mechanism that is arranged immediately above the rotary drum 2 and whose opening can be freely adjusted, and the above-mentioned An outlet side separation plate 4 having a mechanism capable of freely adjusting the opening degree so as to have an air gap between the rotating drum 2 and the inlet side damper 3 is disposed directly above the rotating drum 2 and adjacent to the inlet side damper 3. The sand charging port 5, the sand discharging port 6 formed by opening the side of the permanent magnet 1 between the outlet side separating plate 4 and the housing 8 directly below the rotating drum 2 downward, and the rotating drum 2 Immediately below it, a magnetic material discharge port 7 is formed by opening the side opposite to the sand discharge port 6 between the outlet side separation plate 4 and the case 8 downward, and the case 8. The amount of sand in the mold waste sand S discharged from the sand discharge port 6 is reduced by the amount of the magnetic material discharged from the magnetic material discharge port 7.
After adjusting the inlet side damper 3 so that a fixed amount can be cut out, when the mold waste sand S is charged from the sand charging port 5 while the rotary drum 2 is rotated counterclockwise, the upper end of the rotary drum 2 From the position 2a, the mold waste sand S is conveyed in a layered state on the rotary drum 2. When the rotation of the rotary drum 2 progresses and passes through the intermediate point 2b of the rotary drum 2, the mold waste sand S falls from the rotary drum 2 and is discharged from the sand discharge port 6. The magnetic body 9 is conveyed to the lower end 2c of the rotary drum 2 and drops from the rotary drum 2 there. At this time, if the outlet-side separation plate 4 is tilted toward the sand discharge port 6 side, the ratio of the magnetic substance 9 falling at the lower end 2c of the rotary drum 2 to be discharged from the magnetic substance discharge port 7 increases, and conversely, on the outlet side. When the separating plate 4 is tilted toward the magnetic material discharge port 7 side, the ratio of the magnetic material 9 falling at the lower end 2c of the rotary drum 2 to be discharged from the sand discharge port 6 increases. Therefore, the position of the outlet-side separation plate 4 is preferably adjusted to an appropriate position in consideration of the yield of the magnetic body 9.

The suspension type magnetic separation processing apparatus shown in FIG. 2 is one in which a second belt conveyor 11 and a magnet 12 are suspended on a first belt conveyor 10. The magnetic body 9 is attracted to the magnet 12 from the first belt conveyor 10 and drops to a position away from the first belt conveyor 10.
In the magnetic pulley type magnetic separation processing apparatus shown in FIG. 3, a magnet is built in the head pulley 14 of the belt conveyor 13. The magnetic body 9 falls while being drawn to the belt conveyor 13, while the non-magnetic sand 15 falls without being drawn to the belt conveyor 13.
The magnetic body 9 may correspond to the magnetic sand (B) of the present invention.

(Incineration firing treatment process)
It is preferable that the manufacturing method has a step of incinerating and burning the waste sand of the mold.
The incineration firing treatment step is a step of burning organic compounds, dust, impurities, etc. adhering to the mold waste sand. The incineration and firing treatment can be carried out using a roasting furnace such as a rotary kiln, a tunnel kiln, a shaft furnace, or a fluidized bed furnace. In the incineration and firing treatment step, the mold waste sand is incinerated and fired in the furnace while continuously or intermittently charging the mold waste sand into the roasting furnace.
The incineration firing temperature in the roasting furnace is preferably 200 to 900°C, preferably 400 to 850°C, more preferably 500 to 800°C, and further preferably 600 to 800°C. When the incineration firing temperature is 200° C. or higher, dust and the like adhering to the mold waste sand tends to be sufficiently burned. On the other hand, when the incineration firing temperature is 900° C. or lower, the organic compound attached to the mold waste sand tends to be sufficiently burned and removed.
The incineration and firing treatment step may be performed before the polishing treatment and the magnetic separation treatment, or may be performed after the polishing treatment and the magnetic separation treatment, but it may be performed before the polishing treatment and the magnetic separation treatment. preferable.
The incineration and firing treatment process may be performed twice or more while changing the temperature condition.

(Classification process)
The manufacturing method may include a classifying process of the mold waste sand.
When the manufacturing method has a classification treatment step, the classification treatment is preferably performed after the incineration and firing treatment.
The classification treatment step is performed by flowing the mold waste sand treatment product taken out from the polishing treatment or firing treatment process by, for example, an air flow to remove fine powder contained in the mold waste sand treatment product by a dust collector. A preferred embodiment is one that includes a "dust step (i)" and a "sieving step (ii)" for removing foreign matters contained in the template waste sand treated product by sieving.
More specifically, in the dust collecting step (i), the mold waste sand treatment product is caused to flow by an air flow, and is contained in the mold waste sand treatment product, and the shavings that cannot be removed in the previous steps, Fine inclusions such as dust and fine powder are removed by a dust collector in a driven state, whereby fine residues are effectively removed from the waste sand processing product of the mold. In the sieving step (ii), the particle size of the treated waste sand mold product is classified by using a sieve, so that the foreign matter contained in the treated waste sand mold product, which cannot be removed in the previous steps, is removed. As a result, sand having an appropriate particle size can be selectively taken out.

The classification process is not limited to the mode including the dust collecting step (i) and the sieving step (ii). For example, the classification treatment step may include only one of the dust collection step (i) and the sieving step (ii), or the dust collection step (after the sieving step (ii) is performed. It may be a mode for carrying out i). Furthermore, in the classification treatment step, any other known method can be adopted as long as it is a method capable of classifying the mold waste sand into a predetermined size.

FIG. 4 shows a preferred embodiment of the manufacturing method, but the present invention is not limited thereto. As shown in FIG. 4, the collected mold waste sand is subjected to a magnetic separation treatment with a magnetic flux density of about 1,500 G (preferably 1,000 to 2,000 G), preferably by the suspension method, so as to first obtain an iron ingot or the like. Remove the relatively large magnetic material. Then, after crushing, a magnetic separation treatment with a magnetic flux density of about 3,000 G (preferably 2,000 to 3,500 G) is performed, preferably by the half magnetic outer ring method, to remove a slightly small magnetized body such as sand iron. To do. After classifying as necessary, magnetic separation with a magnetic flux density of about 3,000 G (preferably 2,000 to 3,500 G) is performed again, preferably by the half magnetic outer ring method, so that a slightly small amount of sand iron or the like is deposited. The magnetic body is sufficiently removed, and if necessary, classification treatment is performed to remove coarse particles. Next, an incineration and baking treatment is performed at 600 to 800° C., and after appropriately cooling, a first polishing treatment is performed with a grindstone polishing device (d) such as a sand flasher, and then a vibration type device (c) such as a hybrid sand master. ) And perform the second polishing process. Then, if necessary, a classification process is performed, and a magnetic separation process is performed at a magnetic flux density of 6,000 to 8,500 G (preferably about 7,000 G) to obtain the non-magnetic sand (A) and the magnetic sand (B). ), and the magnetic sand (B) can be obtained as the mold manufacturing sand of the present invention.

(About non-magnetic sand (A))
Since the non-magnetized sand (A) obtained with the mold reclaimed sand (magnetic sand (B)) of the present invention is also obtained by collecting the mold waste sand and performing each of the above treatments, at least SiO ₂ It tends to contain 75 to 95% by mass, Al ₂ O ₃ to ₃ to 20% by mass, Fe ₂ O ₃ to 0.05 to 1.5% by mass, and MgO to 0.05 to 1.5% by mass. Non magnetically attracted sand (A) is a SiO ₂ 80 to 95 wt%, the _Al 2 _{O 3} 5 to 12 wt%, the _Fe 2 _{O 3} 0.10 to 1.0 wt% and MgO 0.10 to is preferably one containing 1.0 mass%, a SiO ₂ 85 to 95 wt%, the _Al 2 _{O 3} 5 to 10 wt%, the _Fe 2 _{O 3} from 0.10 to 0.7 wt% and MgO Is more preferably 0.10 to 0.5% by mass. Other, non-magnetically attracted sand (A) _{is, CaO, TiO 2, K 2} O, may contain Na ₂ O or the like, the content thereof, respectively, preferably 0.05 to 1.0 mass %, more preferably 0.10 to 0.7% by mass, still more preferably 0.13 to 0.5% by mass. The content of each component is a value obtained according to the fluorescent X-ray analysis test method described in Examples, that is, a value for a large number of particles, not a value for a single particle.
The non-magnetic sand (A) can further improve the mold strength as compared with the non-magnetic sand obtained by magnetically separating reclaimed sand by a conventional method.

In the non-magnetic sand (A), the content of particles sieved between 150 μm and 300 μm and having a BET specific surface area of 0.35 m ² /g or less is preferably 30 from the viewpoint of improving mold strength. Mass% or more, more preferably 50 mass% or more, further preferably 80 mass% or more, particularly preferably 90 mass% or more, and may be substantially 100 mass%.

For non-magnetically attracted sand (A) the BET specific surface area of 0.35 m ² / g or smaller particles containing the, the BET specific surface area, from the viewpoint of mold strength, preferably 0.10~0.35m ² / g, more preferably 0.10~0.30m ² / g, may be 0.13~0.25m ² / g, it may be 0.15~0.25m ² / g, 0. It may be 18 to 0.25 m ² /g.

Not only the non-magnetic sand (A) obtained by the manufacturing method but also the magnetic sand (B) can be reused as an aggregate of RCS.
The mold reclaimed sand obtained by the production method can be used alone as the RCS aggregate, can be used as a mixture with a new aggregate, or can be used as a mixture with another reclaimed sand. ..

[Resin Coated Sand (RCS) and Manufacturing Method Thereof]
The present invention also provides an RCS containing the reclaimed sand of the present invention (more specifically, an RCS containing the reclaimed sand of the present invention and a resin composition). The RCS is obtained by heat-mixing and kneading the reclaimed sand of the present invention and the resin composition.
The method for producing RCS using the mold reclaimed sand of the present invention is not particularly limited, and a known method can be adopted. Specifically, the mold reclaimed sand of the present invention and, if necessary, other aggregates are heated to preferably 100 to 200°C (more preferably 100 to 170°C, further preferably 110 to 170°C). After mixing and kneading the aggregate and the resin, a curing agent and, if necessary, an additive (for example, a curing accelerator, a filler, a coloring agent, a plasticizer, a stabilizer, a release agent, etc.) Are mixed and kneaded and stirred while cooling until the aggregated aggregates are disintegrated into particles. Then, if necessary, other additives (for example, a lubricant) are added, and the mixture is further kneaded and stirred. The resin, the curing agent, and the additives to be added as necessary are all referred to as a “resin composition”, but it is not necessary that all components are mixed at the time of use, and as described above, You may mix.

The other aggregate, that is, the aggregate other than the reclaimed sand of the present invention, is not particularly limited, for example, silica sand (natural silica sand, artificial silica sand), artificial sand (sintered sand, molten sand) Etc.), ceramic sand, alumina sand, chromite sand, zircon sand, olivine sand, mullite sand, magnesia, fly ash and the like. The other aggregate is preferably at least one selected from the group consisting of these.
These aggregates may be fresh sand, recovered sand, reclaimed sand, or at least two kinds of selected from the group consisting of fresh sand, recovered sand and reclaimed sand. It may be mixed sand.

Each component in the resin composition that can be used in the production of RCS is not particularly limited, and known components can be used. Among them, the resin is not particularly limited, but examples thereof include phenol resins such as novolac type phenol resin; polyethylene; polypropylene; polyolefin; polystyrene; polyethylene terephthalate; polyvinyl alcohol; polyphenylene ether; polybutylene terephthalate; poly. Ether ether ketone; polyacetal; polymethylmethacrylate; polylactic acid; furan resin; urethane resin; urea resin; melamine resin; biomass-derived resins such as lignin. Among these, phenol resin is preferable. The resin may be used alone or in combination of two or more, and is preferably at least one resin selected from the exemplified group.
The case where a phenol resin is used as the resin will be described below.

Examples of the curing agent for the phenolic resin include unsaturated polyester, epoxy resin, polyamide resin, polyisocyanate, aldehyde, formaldehyde-forming compound, polyvalent carboxylic acid, polyvalent carboxylic acid anhydride, unsaturated polyvalent carboxylic acid, Examples thereof include unsaturated polycarboxylic acid anhydrides. The curing agents may be used alone or in combination of two or more.

Examples of the epoxy resin include bisphenol A glycidyl ether type epoxy resin, bisphenol F glycidyl ether type epoxy resin, bisphenol S glycidyl ether type epoxy resin, bisphenol AD glycidyl ether type epoxy resin, phenol novolac type epoxy resin, biphenyl type epoxy resin. , Cresol novolac type epoxy resin and the like. The epoxy resins may be used alone or in combination of two or more.

Examples of the polyisocyanate include aromatic isocyanates such as tolylene diisocyanate and diphenylmethane diisocyanate; araliphatic isocyanates such as xylylene diisocyanate; aliphatic isocyanates such as hexamethylene diisocyanate; alicyclic isocyanates such as isophorone diisocyanate. To be Further, examples of the polyisocyanate include modified polyisocyanate compounds. Specific examples thereof include multimers of polyisocyanate compounds, polyol-modified polyisocyanate compounds, and biuret-modified polyisocyanate compounds. The polyisocyanates may be used alone or in combination of two or more.

Examples of the aldehyde include formaldehyde, paraformaldehyde, trioxane, acetaldehyde, propionaldehyde, chloral, furfural, glyoxal, n-butyraldehyde, caproaldehyde, allylaldehyde, benzaldehyde, crotonaldehyde, acrolein, phenylacetaldehyde, o-toluene. Aldehydes, salicylaldehydes and the like can be mentioned. The aldehydes may be used alone or in combination of two or more.

Examples of the compound that forms formaldehyde include hexamethylenetetramine.
Examples of the polyvalent carboxylic acid, for example, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid and other aliphatic polycarboxylic acids; trimellitic acid, pyromellitic acid, Examples thereof include aromatic polycarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, and 2,6-naphthalenedicarboxylic acid. The polycarboxylic acids may be used alone or in combination of two or more.

Examples of the unsaturated polycarboxylic acid include acrylic acid, crotonic acid, α-ethylacrylic acid, α-n-propylacrylic acid, α-n-butylacrylic acid, maleic acid, fumaric acid, citraconic acid, mesacon. Acid, itaconic acid, etc. are mentioned. The unsaturated polyvalent carboxylic acids may be used alone or in combination of two or more.
Examples of the unsaturated polycarboxylic acid anhydrides include maleic anhydride, itaconic anhydride, citraconic anhydride, cis-1,2,3,4-tetrahydrophthalic anhydride, and the like. The unsaturated polycarboxylic acid anhydrides may be used alone or in combination of two or more.

Among the above, the curing accelerator and the lubricant are preferable as the additives used as necessary.
The curing accelerator is not particularly limited, and examples thereof include cycloamidine compound; quinone compound; tertiary amine; organic phosphine; 1-cyanoethyl-2-phenylimidazole, 2-methylimidazole, 2-phenylimidazole. , 2-phenyl-4-methylimidazole, 2-heptadecylimidazole and other imidazole compounds; slaked lime and the like. The curing accelerator may be used alone or in combination of two or more.
The lubricant is not particularly limited, and examples thereof include calcium stearate, ethylenebisstearic acid amide, oxystearic acid amide, stearic acid amide, methylol stearic acid amide, carnauba wax, montan wax, paraffin wax, and polyethylene wax. Etc. The lubricants may be used alone or in combination of two or more.

The content of the resin composition in the RCS, while maintaining the mold strength, from the viewpoint of avoiding gas defects in the casting due to the thermal decomposition gas (including water) generated by the resin composition during casting, It is preferably as small as possible, for example, preferably 0.5 to 5% by mass, more preferably 0.8 to 4% by mass, still more preferably 1.2 to 3% by mass, and particularly preferably 1.8 to 2.5. It is% by mass.

[Mold and its manufacturing method]
The present invention also provides a mold obtained by curing and molding the RCS of the present invention. As long as the RCS of the present invention is used, the method for producing a mold is not particularly limited, and a known method for producing a mold can be used and applied.
For example, the molding die is filled with RCS (and other RCS if necessary) obtained by the above-described manufacturing method by a known method such as a gravity drop method or a blowing method, and the RCS is cured by heating. After molding, the mold (also referred to as the core) of the present invention can be manufactured by taking it out of the molding die.
Various castings can be manufactured using the mold thus obtained.

Next, the present invention will be described in more detail with reference to the following examples, but these examples do not limit the present invention.
The BET specific surface area, the content of each component, the transverse rupture strength, the thermal expansion coefficient, and the water adsorption rate were measured according to the following methods.

(1. Method for measuring BET specific surface area)
The mold reclaimed sand obtained in each example was obtained by sieving between 150 μm and 300 μm, and the BET specific surface area was measured by the nitrogen adsorption method using this. The measurement conditions are shown below.
・Measuring device: Quadruple specific surface area/pore distribution measuring device, NOVA-TOUCH type (manufactured by Quantachrome Instruments)
-Gas used: Nitrogen gas-Refrigerant (temperature): Liquid nitrogen (-195.8°C)
・Pretreatment condition: 110° C., vacuum degassing for 6 hours ・Measured relative pressure (P/P ₀ ): 0.05<P/P ₀ <0.3 [P ₀ : saturated vapor pressure]
・Sample amount: Approx. 4 g

(2. Method for measuring the content of each component)
The content of each component was analyzed by the fluorescent X-ray analysis test (qualitative) for the template reclaimed sand obtained in each example. As the test method, after pretreatment was carried out according to the following procedure, measurement was carried out under the following conditions.
2.1. Pretreatment [It was carried out in the order of (i)→(ii)→(iii) below. ]
(i) 2 g of the reclaimed sand obtained in each example was dried at 105°C, crushed in a crushing container made of tungsten carbide, and then dried at 105°C.
(ii) Calcination was performed in a muffle furnace at 1,025°C for 1 hour.
(iii) The sample obtained by the above method and lithium tetraborate were mixed at 1:10 to obtain a mixture. The above mixture and a small amount of lithium bromide were put into a platinum crucible and molded into glass beads at about 1,150° C., which was used as a measurement sample.
2.2. Measurement conditions/device type: wavelength dispersive X-ray fluorescence analyzer, LAB CENTER XRF-1700 (manufactured by Shimadzu Corporation)
・Set tube voltage: 40 kV
・Set tube current: 95mA
・Analysis method: Fundamental parameter method (FP method)

(3. Method of measuring transverse rupture strength)
3-1. Test pieces
(1) Material of test piece A mixer (manufactured by Enshu Iron Works Co., Ltd.) was heated to about 130° C. to obtain 100 parts by mass of the reclaimed sand of the mold and a phenol resin for shell mold “HP-230N” (trade name, general-purpose). 2 parts by mass of fast-curing novolac type, manufactured by Hitachi Chemical Co., Ltd.) were added and kneaded for 60 seconds. After that, 0.3 parts by mass of hexamethylenetetramine (curing agent) was added to the mixer and kneaded for about 50 seconds, and then 0.1 parts by mass of calcium stearate (lubricant) was added and stirred for 20 seconds. A resin coated sand (RCS) for a test piece was obtained. Using the RCS, a rectangular columnar test piece having the following size was prepared under the following conditions.
(2) Molding conditions for test pieces and mold temperature: 250°C
-Baking time: 60 seconds-Blow pressure: 0.2 MPa
(3) Test piece size・10mm×10mm×100mmL
3-2. Measurement of flexural strength After cooling the molded test piece to room temperature, the flexural strength was measured using a bending strength tester.
・Span interval: 5 cm (test piece receiving side)

(4. Measuring method of thermal expansion coefficient)
4-1.Test piece
(1) Material of test piece An RCS for a test piece was obtained in the same manner as in "3. Method for measuring transverse rupture strength". Using the RCS, a cylindrical test piece having the following size was prepared under the following conditions.
(2) Molding conditions for test pieces and mold temperature: 250°C
・Blow pressure: 0.1 MPa
・Blow time: 2 seconds ・Firing time: 180 seconds
(3) Test piece size: 30 mm (diameter) x 50 mm
4-2. Measurement of thermal expansion coefficient The length of the test piece after being held for 180 seconds in an electric furnace kept at 1,000°C (after heat exposure) was measured, and the thermal expansion coefficient of the test piece was calculated from the following formula. (Elongation rate) was calculated.
Thermal expansion rate (%)=[(TP length after heat exposure-TP length before heat exposure)/TP length before heat exposure]×100

(5. Method for measuring water adsorption rate)
The water content was measured by the following method and used as an index of the water adsorption rate.
5-1.Test piece
(1) Material of test piece An RCS for a test piece was obtained in the same manner as in "3. Method for measuring transverse rupture strength". Using the RCS, a rectangular columnar test piece having the following size was prepared under the following conditions.
(2) Molding conditions for test pieces and mold temperature: 250°C
-Baking time: 60 seconds-Blow pressure: 0.2 MPa
(3) Test piece size・10mm×10mm×100mmL
5-2. Measurement of Moisture Adsorption Rate Using a test piece (1 piece, about 10 g) manufactured under the above-mentioned conditions, test with a water content measuring instrument “MX-50” (manufactured by A&D Co.) under 120° C. heating condition. The piece was heated and the water content before and after heating the test piece was measured to determine the water adsorption rate from the following formula.
Moisture adsorption rate (%)=[(TP weight before heating−TP weight after heating)/TP weight before heating]×100

[Example 1]
First, a relatively large magnetic substance such as an iron ingot was removed by subjecting the collected waste sand to a magnetic separation treatment with a magnetic flux density of about 1,500 G by the suspension method shown in FIG. Then, after crushing, a slightly small magnetic material such as sand iron was removed by a magnetic separation treatment with a magnetic flux density of about 3,000 G by the half magnetic outer ring method shown in FIG. Next, incineration and firing treatment was performed at 760°C.
Then, it is cooled appropriately, and subjected to a first polishing treatment with a sand flasher (manufactured by Kiyota Casting Machine Co., Ltd.) under the conditions of a wheel rotation speed of 2,500 rpm and a bladed drum rotation speed of 13 rpm around the wheel, and then the hybrid sand. The second polishing process was performed with a master (manufactured by Nippon Foundry Co., Ltd.) under the condition that the drum rotation speed was 2,100 rpm. Then, non-magnetic sand (A) and magnetic sand (B) were obtained by performing magnetic separation treatment with a magnetic pulley system shown in FIG. 3 at a magnetic flux density of about 7,000 G.
Each of the obtained mold reclaimed sand (magnetic sand (B)) was measured according to the method described above. The results are shown in Table 1.

[Comparative Example 1]
The recovered mold waste sand was treated in the same manner as in Example 1 up to the incineration and firing treatment. Then, a rotary reclaimer (manufactured by Nihon Foundry Co., Ltd.) was used to perform a first polishing treatment under a drum rotation speed of 2,200 rpm, and then a hybrid sand master (manufactured by Nihon Foundry Co., Ltd.) was used for drum rotation speed 2. The second polishing process is performed under the condition of 100 rpm. Then, a small magnetic material was removed by a magnetic separation treatment with a magnetic flux density of about 3,000 G to obtain mold reclaimed sand.
Each of the obtained mold reclaimed sands was measured according to the method described above. The results are shown in Table 1.

[Comparative example 2]
The same processes as in Example 1 were carried out except that the magnetic separation was not carried out at the magnetic flux density of about 7,000 G in the magnet pulley system, and mold reclaimed sand was obtained.
Each of the obtained mold reclaimed sands was measured according to the method described above. The results are shown in Table 1.

[Comparative Example 3]
Non-magnetic sand and magnetic sand were obtained in the same manner as in Example 1, except that neither the first polishing treatment nor the second polishing treatment was performed.
Each of the obtained magnetic sands was measured according to the method described above. The results are shown in Table 1.

It can be seen from Table 1 that the coefficient of thermal expansion of the reclaimed sand obtained in Example 1 (magnetic sand (B)) is much smaller than that of the reclaimed sand obtained in Comparative Examples 1 and 2. .. Further, the mold reclaimed sand (Magnetic sand (B)) obtained in Example 1 has a BET specific surface area of 1.5 m ² /g or less, and the magnetic sand (BET specific surface area 1. The bending strength was higher than that in the case of more than 5 m ² /g), and the mold strength could be improved.
From the comparison between Example 1 and Comparative Example 1, it was found that the polishing method after the incineration and firing treatment and the conditions of the magnetic separation treatment are important in order to obtain the target mold reclaimed sand.

S Mold waste sand 1 Permanent magnet 2 Rotating drum 3 Entrance side damper 4 Exit side separation plate 5 Sand input port 6 Sand discharge port 7 Magnetic substance discharge port 8 Housing 9 Magnetic substance 10 First belt conveyor 11 Second belt conveyor 12 magnet 13 belt conveyor 14 head pulley 15 non-magnetic sand

Claims (5)

The S iO ₂ 45 to 75 wt%, the _Al 2 _{O 3} 10 to 30% by weight, a mold reclaimed sand containing _Fe 2 _{O 3} 3 to 20 wt% to 12 wt% and MgO, from 150μm Mold reclaimed sand, wherein the particles sieved to a size of 300 μm are magnetic sand containing particles having a BET specific surface area of 0.7 to 1.3 m ² / g . The mold reclaimed sand according to claim 1, wherein the particles sieved between 150 μm and 300 μm contain particles having a BET specific surface area of 0.8 to 1.2 m ² /g. A resin coated sand comprising the mold reclaimed sand according to claim 1 or 2 and a resin composition. The resin composition is a phenol resin, polyethylene, polypropylene, polyolefin, polystyrene, polyethylene terephthalate, polyvinyl alcohol, polyphenylene ether, polybutylene terephthalate, polyether ether ketone, polyacetal, polymethyl methacrylate, polylactic acid, furan resin, urethane resin, The resin coated sand according to claim 3 , which contains at least one resin selected from the group consisting of a urea resin, a melamine resin, and a biomass-derived resin. A mold obtained by curing and molding the resin coated sand according to claim 4 .