JP5819551B1 - Artificial sand and sand containing binder for mold - Google Patents

Abstract

An object of the present invention is to provide artificial sand in which reduction of mold strength is suppressed even when it is repeatedly used for casting. An artificial sand used as a raw material for a binder-containing sand for a mold, wherein the artificial sand comprises 40 to 90% by weight of alumina and 60 to 10% by weight of synthetic mullite and / or synthetic corundum. Mainly, it has a particle size distribution of 30 to 1180 μm, and has a surface area (cm 2 / cm 3) per unit volume in the range of 60,000 / d to 1,800,000 / d (d is the average particle diameter (μm) of a sphere). And the said subject is solved by the artificial sand characterized by showing the calcium ion elution density | concentration with respect to 0.05 M-HCl aqueous solution of 60 mg / L or less. [Selection] Figure 3

Description

  The present invention relates to artificial sand and binder-containing sand for casting molds. More specifically, the present invention relates to artificial sand and a binder-containing sand for molds in which reduction of mold strength is suppressed even when used repeatedly for casting.

As one of molding methods for producing a mold in the casting industry, for example, there is a shell mold method. In this method, resin-coated sand (resin coated sand: RCS, mold binder-containing sand) is filled in a preheated mold and fired to make a mold.
The binder-containing sand for mold contains an aggregate, a binder, and a lubricant. Here, for example, a resin obtained by curing a thermosetting resin (for example, phenol resin) with a curing agent (for example, hexamethylenetetramine) is used as the binder. In addition, a lubricant is used for easily forming a binder-containing sand for a mold into a desired mold shape (improving fluidity) or preventing product blocking (aggregation). Calcium phosphate is commonly used.
Furthermore, for the purpose of reducing the amount of binder and improving the ease of collapse of the mold after casting, it is possible to use artificial sand that is nearly spherical and has a smooth surface as an aggregate, for example, Japanese Patent Application Laid-Open No. 2003-251434. (Patent Document 1). In Patent Document 1, calcium stearate is exemplified as a lubricant.

JP 2003-251434 A

Also in the field of foundry industry, due to the problem of resource depletion and industrial waste regulations, the waste mold sand that has been once used for casting is regenerated and reused for casting, thereby reducing the amount of waste mold sand that is discarded. It is being considered.
Mold waste sand contains carbides derived from lubricants and binder components used to mold the binder-containing sand for casting into a predetermined shape during casting. In order to recycle the waste mold sand, it is necessary to remove the carbide. However, sufficient mold strength can be obtained even if the mold is produced again using the binder binder-containing sand from which the carbide has been removed. There wasn't. Therefore, it has been desired to provide a binder-containing sand for molds that can exhibit sufficient mold strength even when regenerated.

  The inventors of the present invention examined the cause of the decrease in mold strength due to the regenerated binder-containing sand for molds, and as a result, calcium ions were removed from the artificial sand before mixing with the binder and the carbide was removed. It was found that a certain relationship exists between the elution concentration and the template strength. Specifically, based on the knowledge that the greater the calcium ion elution concentration, the lower the mold strength, the inclusion of artificial sand with a calcium ion elution concentration of a certain value or less as an aggregate can suppress the decrease in mold strength. As a result, the inventors have arrived at the present invention.

Thus, according to the present invention, artificial sand used as a raw material for the binder-containing sand for molds,
The artificial sand is mainly composed of synthetic mullite and / or synthetic corundum of 40 to 90% by weight of alumina and 60 to 10% by weight of silica, has a particle size distribution of 30 to 1180 μm, and is 60,000 / d to 1.8 million / d ( d has a surface area (cm ² / cm ³ ) per unit volume in the range of the average particle diameter (μm) of the spherical material, is derived from mold waste sand generated after casting, and in 0.05 M HCl aqueous solution artificial sand characterized by comprising been adjusted as shown mosquitoes Rushiumuion elution concentration below 60 mg / L in the solution was allowed to stir 1 hour is provided.
Further, according to the present invention, there is provided a mold aggregate comprising an aggregate mainly composed of artificial sand, a binder, and a lubricant, wherein the artificial sand is the artificial sand. A binder-containing sand is provided.

  According to the regeneration method of the present invention, it is possible to provide a binder-containing sand for a mold that can exhibit sufficient mold strength even when regenerated, and an artificial sand that can be used therefor. The inventors have recognized that in the field of the mold industry, it is surprising that calcium ions are associated with a reduction in mold strength.

Further, in any of the following cases, artificial sand used for the binder-containing sand for molds that can exhibit sufficient mold strength even after being regenerated can be provided.
(A) Artificial sand is artificial sand derived from waste mold sand generated after casting.
(B) Artificial sand has a particle shape factor of 1.2 or less.
Furthermore, in any of the following cases, it is possible to provide a binder-containing sand for a mold that can exhibit sufficient mold strength even when regenerated.
(1) The binder is selected from furan resin, phenol resin, oil urethane resin, phenol urethane resin, alkali phenol resin, sodium silicate and bentonite, and the lubricant is calcium stearate.
(2) The binder is contained in an amount of 0.4 to 3 parts by weight with respect to 100 parts by weight of the aggregate, and the lubricant is added in an amount of 0.1 to 100 parts by weight of the aggregate and the binder. 01 to 0.2 parts by weight are included.

It is a schematic explanatory drawing of the roasting furnace used for the Example. It is a schematic explanatory drawing of the trough mill used for the Example. It is a graph which shows the relationship between the bending strength of the caking additive containing sand for Example 1, and calcium ion elution density | concentration. It is a graph which shows the relationship between the number of reproduction repetitions of the binder binder containing sand of Example 2, bending strength, and calcium ion elution density | concentration.

(Artificial sand)
Artificial sand is used as a raw material for binder-containing sand for molds containing aggregates, a binder, and a lubricant.
Artificial sand has the following composition, structure and physical properties.
-Mainly synthetic mullite and / or synthetic corundum of 40 to 90% by weight of alumina and 60 to 10% by weight of silica.
-It has a particle size distribution of 30-1180 μm.
-It has a surface area (cm < ² > / cm < ³ >) per unit volume in the range of 60,000 / d to 1.8 million / d (d is the average particle diameter ([mu] m) of spheres).
-The calcium ion elution density | concentration with respect to the 0.05M-HCl aqueous solution of 60 mg / L or less is shown.

(1) Composition artificial sand, alumina _{(Al 2} O 3) 40 to 90 wt%, of silica sand containing _(SiO 2) 60 to 10 wt% synthetic mullite and / or synthetic corundum. The proportions of alumina and silica can be 60 to 90% by weight and 40 to 10% by weight, respectively. The artificial sand may contain other components such as Fe ₂ O ₃ , Cr ₂ O ₃ , CrO ₂ , MgO, CaO, K ₂ O, and TiO _{2 in} addition to alumina and silica. The proportion of synthetic mullite and / or synthetic corundum in the artificial sand can be 50% by weight or more.

(2) Structure Artificial sand has a particle size distribution of 30 to 1180 μm. If it is smaller than 30 μm, the air permeability of the mold may be lowered. When it is larger than 1180 μm, the surface of the casting may be roughened. Preferred particle size distributions are 212 to 1180 μm (equivalent to JIS 10 and 14), 150 to 820 μm (equivalent to JIS 20 and 28), 106 to 600 μm (equivalent to JIS 35 and 48), 75 to 425 μm (equivalent to JIS 65 and 100), 53 ˜300 μm (equivalent to JIS150 and 200). These particle size distributions include, for example, the types of cast iron or cast steel products (cast iron products, ordinary cast steel products, stainless cast steel products, high Mn steel products, aluminum alloy products, copper alloy products, etc.), cast size, cast wall thickness, etc. It can select suitably according to casting conditions. The artificial sand may contain sand having a size of less than 30 μm within a range where the effects of the invention are not inhibited (for example, 25% by weight or less).
The particle size distribution is a value measured according to the JIS casting sand particle size test method (Z2601). The outline of this method is as follows. For example, a sieve having a nominal size of 30 μm is overlaid with a 1180 μm sieve, a raw material is placed on the 1180 μm sieve, and a screening machine such as a low-tap type sieve is used. What remains between the two sieves is referred to as sand having a particle size distribution of 30-1180 μm.

Furthermore, the artificial sand has a surface area (cm ² / cm ³ ) per unit volume in the range of 60,000 / d to 1,800,000 / d (d is the average particle diameter (μm) of the spheres). For example, artificial sand in the range of 300 to 425 μm will be described as an example. Assuming that the average particle size of the artificial sand is 362.5 μm, which is between 300 μm and 425 μm, the surface area is in the range of 165.5 to 4955.5 cm ² / cm ³ . Here, when the surface area is 1.8 million / d (cm ² / cm ³ ) or more, the unevenness of the artificial sand surface becomes large, and the amount of waste generated by the artificial sand being crushed by the contact between the artificial sands increases. There is. This surface area is a value obtained by measuring the specific surface area per unit g using a specific surface area measuring instrument (BELSORP 28SA AUTOMATIC GAS ADSORPTION APPARATUS: manufactured by Bell Japan Co., Ltd.), and adding the true density to the specific surface area. is there. The surface area per unit volume is preferably 1.6 million / d or less, more preferably 14.45 million / d or less, still more preferably 1.3 million / d or less, and particularly preferably 1.1 million / d or less.

The artificial sand preferably has a round particle shape. Specifically, the particle shape factor, which is an index of roundness, is preferably 1.2 or less, and more preferably 1.1 or less. When the ratio is 1.2 or less, the filling rate of the mold-containing binder-containing sand into the mold is improved, and the air permeability of the mold is improved. Furthermore, since the shape is close to a sphere, the amount of waste generated due to contact between artificial sands can be reduced.
The grain shape factor means a value calculated using a sand surface area measuring device (manufactured by George Fisher). That is, the grain shape factor means a value obtained by dividing the surface area of actual sand grains per gram by the theoretical surface area. The theoretical surface area refers to the surface area when it is assumed that the sand is all spheres. Therefore, the closer the particle shape factor is to 1, the closer to a sphere.
In addition, the surface area per unit volume, the particle shape coefficient, and the particle size distribution of the artificial sand and the binder-containing sand for casting mold are almost the same.

(3) Physical property Artificial sand shows the calcium ion elution density | concentration with respect to the 0.05M-HCl aqueous solution of 60 mg / L or less. With this calcium ion elution concentration, a decrease in template strength can be suppressed. The inventors infer that reason as follows. That is, the binder is obtained by curing the resin with a curing agent. However, the eluted calcium ions prevent the resin from being cured by binding with the resin or consuming the curing agent. Therefore, if the calcium ion elution concentration is lowered, the curing of the resin is not hindered, so that a predetermined mold strength can be realized. The calcium ion elution concentration is desirably as low as possible, preferably 40 mg / L or less, more preferably 30 mg / L or less, still more preferably 20 mg / L or less, and 10 mg / L or less. It is particularly preferred.

(4) Artificial sand production method Artificial sand having the above composition, composition and physical properties can be obtained by melting a raw material of synthetic mullite and / or synthetic corundum containing alumina and silica and blowing air to the melt. . In other words, the melt is blown into a particle having a predetermined particle size distribution in a molten state by being blown with air, and after air crushing, it becomes artificial sand having a predetermined composition, configuration and physical properties by the surface tension of the molten particle itself. . The melting method is not particularly limited, and examples include an arc furnace, a crucible furnace, an induction electric furnace (a high frequency furnace, a low frequency furnace, etc.), a resistance electric furnace, a reflection furnace, a rotary furnace, a vacuum melting furnace, a cupola furnace, and the like. Of these, an arc furnace that is relatively easy to operate is preferred. The predetermined composition, composition and physical properties can be adjusted by adjusting the composition of the raw material of synthetic mullite, the melting temperature, the air speed at the time of air blowing, and the contact angle between the melt and air. Here, the melting temperature is preferably in the range of 1600 to 2200 ° C., the air velocity is preferably 80 to 120 m / sec, and the contact angle is preferably 60 to 90 °. In addition, it is preferable to water-cool after air blowing.

The artificial sand may be artificial sand derived from mold waste sand generated after casting.
Artificial sand derived from mold waste sand generated after casting can be obtained, for example, through the following roasting process and grinding process.
(I) Roasting process A roasting process can be performed under the temperature of the range of 400-1000 degreeC. By subjecting the mold waste sand to the roasting step, the components derived from the lubricant and the binder contained in the mold waste sand are carbonized and partly burned off. By carbonizing the organic substance, the artificial sand can be obtained by easily removing the carbide in the next grinding step.
When the temperature of the roasting process is lower than 400 ° C., the carbonization may not be performed sufficiently, and as a result, the mold strength due to the regenerated mold binder-containing sand (regenerated sand) may be reduced. Moreover, although carbonization can fully be performed when it is higher than 1000 degreeC, depending on the kind of inorganic component which comprises regenerated sand, sand may aggregate by the surface of regenerated sand melting. A more preferable temperature range is 400 to 800 ° C, and a more preferable temperature range is 500 to 800 ° C.

The roasting time can be 0.5 to 2.5 hours, for example. When the roasting time is less than 0.5 hours, the carbonization may not be sufficiently performed. As a result, the mold strength due to the regenerated sand may be reduced. Here, the reason for setting the upper limit of the roasting time to 2.5 hours is that even if the mold waste sand is roasted for a longer period of time, the effect of roasting cannot be expected, and the cost of regeneration is increased due to the consumption of fuel. Because there are things. A more preferable roasting time is 1.5 to 2.5 hours, and a further preferable roasting time is 1.75 to 2.25 hours.
The atmosphere of the roasting step is not particularly limited as long as the binder contained in the mold waste sand can be carbonized, and is usually performed in an atmosphere containing oxygen (for example, in the air).

The configuration of the roasting device is not particularly limited as long as the mold waste sand can be roasted. The mold waste sand in the roasting apparatus may or may not be fluidized, but is preferably fluidized in order to obtain uniformly baked roasted sand. The roasting apparatus may be a batch type or a continuous type. In consideration of the processing efficiency, it is preferable to use a continuous fluid roasting apparatus.
Various types of devices are known as continuous fluid roasting devices. For example, a device having a configuration in which a direction in which sand flows and a direction in which air for flowing sand flows intersects, and a device in which both directions are opposite and parallel to each other can be given. Among these, the latter apparatus is preferable in consideration of thermal efficiency. In particular, an apparatus having a configuration in which the direction in which sand flows is the same as the direction of gravity and the direction in which air flows is opposite to the direction of gravity is preferable because it has high thermal efficiency and can reduce fuel for roasting.

  In the above apparatus in which the direction of sand flow is the same as the direction of gravity, the mold waste sand is introduced from the upper part of the apparatus and falls inside the apparatus. The fallen sand is held as a fluidized bed at a certain position by air blown from the lower part of the apparatus for a certain time. The sand held at a fixed position is roasted for a fixed time by a heating means such as a burner. The sand located in the lower part of the fluidized bed is gradually lowered by the sand supplied to the upper part of the fluidized bed and falls as roasted sand to the bottom of the apparatus. In this apparatus, the heat of already roasted sand in the fluidized bed can be used to heat the waste mold sand that is newly input, and thus has a high thermal efficiency.

(Ii) Grinding process The roasted sand obtained in the roasting process is subjected to the grinding process. By removing the carbides present on the surface of the roasted sand by the grinding process, the mold waste sand can be regenerated into artificial sand as a mold raw material.
The grinding ore may be dry grinding, wet grinding or a combination of both grindings.
In the dry method, the sand is lifted in the apparatus by a high-speed air current and collided with the collision plate. A method using a rotary reclaimer that rotates at high speed by grinding and collision by collision and friction between projecting sand generated by centrifugal force and falling sand, an agitator mill that performs grinding using friction between sand grains, etc. Is mentioned.
On the other hand, the wet method includes, for example, a method using a trough grinding machine that performs grinding treatment by friction between sand grains in a trough in which wings are rotated.

It is preferred that the ore is wet. By being wet, the calcium ion elution concentration from the regenerated artificial sand can be easily suppressed to 40 mg / L or less.
By the way, in the conventional mold binder-containing sand using calcium stearate as a lubricant, when dry grinding, the mold strength decreases when the mold waste sand is repeatedly regenerated from the mold waste sand to the mold binder-containing sand. There was a problem. The inventors measured the calcium ion elution concentration of the artificial sand that had been regenerated repeatedly. As the regeneration was repeated, the calcium ion elution concentration increased, and there was a constant between the calcium ion elution concentration and the template strength. I found that a relationship exists. Thus, the inventors have found that calcium ions can be suppressed from being accumulated in the artificial sand that has been removed and regenerated by wet grinding, so that a reduction in mold strength can be prevented.

(Iii) Others (1) The mold waste sand may be crushed before being subjected to the roasting step. By applying the pulverizer, the aggregate of the waste sand can be crushed, so that the yield of taking out the reclaimed sand from the mold waste sand can be increased.
(2) The mold waste sand may be subjected to a magnetic separator (magnet separator) before being subjected to the roasting step. Since the casting residue contained in the waste sand can be removed by applying the magnetic sorter, the yield of taking out the reclaimed sand from the mold waste sand can be increased.

(3) The roasted sand obtained from the roasting step is preferably subjected to a cooling step before being subjected to the polishing step. By subjecting it to the cooling step, cracking of the roasted sand can be prevented by a rapid temperature change, so the yield of taking out the reclaimed sand from the mold waste sand can be increased. By performing the cooling step while flowing the roasted sand, the roasted sand can be uniformly cooled.
(4) The sand subjected to the grinding process may be classified into reclaimed sand having a desired particle size distribution by being subjected to a classification process.

(Aggregate for mold)
The mold aggregate includes an aggregate, a binder, and a lubricant.
(1) Aggregate Aggregate mainly contains the artificial sand. The content of artificial sand is preferably 50% by weight or more, more preferably 70% by weight or more, and still more preferably 90% by weight or more.
Examples of sand that can be contained in addition to the artificial sand include silica sand, zircon sand, chromite sand, MgO · SiO ₂ sand, and mixed sand of these sands.

(2) Binder The binder is not particularly limited, and examples thereof include furan resin, phenol resin, oil urethane resin, phenol urethane resin, alkali phenol resin, sodium silicate, bentonite and the like. The binder can be cured with a curing agent according to the type. Examples of the curing agent for furan resin include inorganic acids such as sulfuric acid, phosphoric acid, phosphoric ester, and pyrophosphoric acid, and organic acids such as xylene sulfonic acid, toluene sulfonic acid, and benzene sulfonic acid. Examples of the curing agent for the alkali phenol resin include lactones (for example, propionlactone), organic esters such as ethyl formate, methyl formate, and triacetin. Examples of the curing agent for the phenol resin include hexamethylenetetramine. Examples of the curing agent for the phenol urethane resin include triethylamine and pyridine compounds. Examples of the curing agent for sodium silicate include carbon dioxide, dicalcium silicate, and organic ester.

The binder is preferably contained in an amount of 0.4 to 3 parts by weight per 100 parts by weight of the aggregate. When the content is less than 0.4 part by weight, the strength between the molds may be lowered because the bonding between the aggregates is not sufficient. When the content is more than 3 parts by weight, a binder-derived component may adhere to the surface of the casting, or it may take time to regenerate the binder-containing sand for the mold from the mold waste sand. A more preferable content is 0.4 to 2 parts by weight, and a still more preferable content is 0.4 to 1.5 parts by weight.
Artificial sand having the above surface area can reduce the amount of binder than natural sand. When the amount of the binder is small, the influence of the calcium ions to lower the template strength becomes larger, so that the application of the present invention is particularly effective.

(3) Lubricant The lubricant is not particularly limited, and any of those commonly used in the field can be used. Examples thereof include metal salts of higher fatty acids having 10 to 24 carbon atoms. Generally, calcium stearate can be used from the viewpoints of availability, price, and the like.
The lubricant is preferably contained in an amount of 0.01 to 0.2 parts by weight per 100 parts by weight in total of the aggregate and the binder. If the content is less than 0.01 parts by weight, the mold binder-containing sand at the time of mold production is not sufficiently fluid, so that it takes time to produce the mold or the casting surface becomes rough. Sometimes. In addition, there is a high possibility that the binder-containing sand for casting will be blocked inside a flexible container bag for storing the product. When the content is more than 0.2 parts by weight, the strength of the mold may be reduced, or it may take time to regenerate the binder-containing sand for mold from the waste mold sand. A more preferable content is 0.02 to 0.16 parts by weight, a still more preferable content is 0.03 to 0.12 parts by weight, and a particularly preferable content is 0.06 to 0.10 parts by weight.
Note that the amount of lubricant constituting the binder-containing sand for casting is determined by isolating the lubricant using an appropriate solvent, and analyzing the isolated product by infrared spectroscopy, gas chromatography, liquid chromatography, NMR, etc. It can measure by analyzing by a well-known method.

(4) Method for Producing Binder-containing Sand for Mold The binder-containing sand for mold can be produced by a known method. For example, a mixture of the binder and the aggregate is obtained by adding the binder to the mixer while heating and mixing the artificial sand as the aggregate in the mixer. Here, when the binder is obtained by curing a curable resin with a curing agent, the curable resin is first put into the mixer, and then the curing agent is added to cure the curable resin. A binder can be obtained. Next, by introducing the lubricant into the mixer, the mixture of the binder and the aggregate can be mixed with the lubricant. The binder is considered to cover the entire surface or a part of the aggregate. Moreover, it is thought that the lubricant has coat | covered the whole surface or one part surface of the aggregate coat | covered with the binder.

Example 1
(1) Manufacture of aggregate for mold As artificial sand to be an aggregate, ESPAR # 60 (manufactured by Yamakawa Sangyo Co., Ltd .: surface area per unit volume 3300 cm ² / cm ³ , particle size distribution 53-600 μm, particle size factor 1.03, A total of 94% by weight of alumina and silica (77% by weight of alumina and 23% by weight of silica, 40% by weight of synthetic mullite and 10% by weight of synthetic corundum) was used. This artificial sand that has not been subjected to regeneration is referred to as new sand. After the artificial sand was heated to 160 ° C., it was put into a mixer (NSC-1 type manufactured by Enshu Steel Co., Ltd.), and the temperature of the artificial sand was kept at 150 ° C. The mixture of resin and aggregate was obtained by stirring the artificial sand while adding 0.8 parts by weight of resin (Hitachi Chemical Co., Ltd. novolac phenol resin) to 100 parts by weight of the artificial sand. Next, while stirring the mixture, 20 parts by weight of hexamethylenetetramine (curing agent) with respect to 100 parts by weight of the resin and 1.3 parts by weight of water (dispersion medium of the curing agent) with respect to 100 parts by weight of the aggregate. ) Was added to cure the resin and obtain a mixture of binder and aggregate. About 20 seconds after the addition of the curing agent, cooling was started and cooling was performed for about 20 seconds. Next, while stirring the mixture of the binder and the aggregate, 0.06 part by weight of a lubricant (containing 95% by weight or more of calcium stearate component, 95% with respect to 100 parts by weight of the mixture of the binder and the aggregate) The above has a particle diameter of 75 μm or less (manufactured by Kawamura Kasei Kogyo Co., Ltd.) and stirred for about 15 seconds to obtain a binder-containing sand (RCS) for casting mold. In addition, the obtained binder-containing sand for molds was used to remove lumps using a sieve having an opening of 1180 μm.
Bending strength was measured by the following procedure using the obtained binder-containing sand for molds. The bending strength was used as an index indicating the mold strength.

(2) Measurement of bending strength (a) Preparation of test piece for measurement The bending strength of the test piece was measured according to the JACT test method SM-1 bending strength test method (corresponding to JIS K 6910). Specific measurement conditions are described below.
A lower mold having five recesses having a depth of 10 mm, a width of 10 mm, and a length of 60 mm, and an upper mold as a lid were prepared. After the lower mold and the upper mold were heated to 250 ° C. ± 3 ° C., the concave portions were filled with about 50 g of binder-containing sand for molds. The upper surface of the binder-containing sand for mold filling the concave portion was leveled with a sample scraping plate so as to be flat. Thereafter, the lower mold and the upper mold were combined and baked for 60 seconds. After firing, the upper mold was taken, and the fired product was shaved with a flat file so that the upper surface of the lower mold matched the upper surface of the fired product. Then, the test piece was obtained by taking out the fired product from the lower mold. The time from opening the upper die to taking out the test piece from the lower die was 30 seconds.
The obtained test piece was cooled to room temperature (about 25 ° C.) in a desiccator and left as it was until the bending strength was measured.
The test pieces were produced three times, and a total of 15 test pieces were obtained for each type of binder-containing sand for molds.

(B) Measurement of bending strength A pair of convex portions having a tip angle of 60 °, a state-of-the-art curvature of 1.5R, and a length of 10 mm or more are arranged so that the length direction is parallel and the interval is 50 mm. The test piece was placed on the test piece placement table. In addition, the test piece was mounted so that the surface cut by the flat file was not located on the mounting table side and the facing surface (upper surface) side.
A load was applied to the center of the upper surface of the test piece using a pressure wedge having a tip angle of 60 ° and a cutting edge curvature of 1.5R. By applying a load, the load value when the test piece broke was recorded. This load test was performed for every 15 test pieces.

The bending load was calculated from the obtained load value by the following formula.
σfb = 3 × l × P / 2 × W × h ²
(In the formula, σfb is a bending load (kgf / cm ² ), l is a distance between a pair of convex portions of the test piece mounting table (5 cm), P is a load value (kgf), W is a width of the test piece (1 cm) H is the height of the test piece (1 cm)
The bending strength (kgf / cm ² ) was an average value of 15 bending loads.

(3) Regeneration of binder-containing sand for casting mold After crushing the test piece whose bending strength was measured, the pulverized product was divided into 10 pieces of n1 to n10. Ten pulverized products were each regenerated into sand containing a binder for molds. Regeneration was performed only for the roasting process for n1 to n5 and n9 to n10, and the roasting process and the wet grinding process were used for n6 to n8, and the bending strength was measured after the regeneration. However, 10% by weight of fresh sand was added before each roasting step.
The roasting step uses a JFE joint roasting furnace (JTR-G-1 type manufactured by JFE Joint Company) shown in FIG. 1, the roasting temperature is 600 ° C., and the flow differential pressure in the roasting furnace is 4.5 MPa. The amount of sand input was 2.5 t / hour. Under this condition, the actual processing time of the mold waste sand was about 1 hour. In FIG. 1, 1 is a roasting furnace, 2 is a pulverized material inlet, 3 is a burner, 4 is a fluidized bed, 5 is a heat exchanger, 6 is an air inlet for sand flow, 7 is an air inlet for cooling, and 8 is a flow. Cooler, 9 is a sand discharge valve, 10 is an air nozzle, 11 is a flow differential pressure gauge, and 12 is an exhaust gas outlet.
The wet grinding process uses the trough grinding machine shown in Fig. 2 (diameter 609.4 mm x length 1517 mm, 8 stirring blades (impeller), manufactured by Yamakawa Sangyo Co., Ltd.), load current 130 A, sand input For 5 tons / hour, 5 to 10% by weight of water with respect to the input sand, 86 rpm / min of the stirring blade, 45 ° of the stirring blade, and 49100 mm ^{2 in} the area of one stirring blade. It was. Under this condition, the actual processing time of the roasted sand is 10 to 20 minutes. In FIG. 2, 21 is a trough grinder, 22 is a trough, 23 is a stirring blade, 24 is a roasted sand inlet, 25 is a recycled sand outlet, 26 is a spring, 27 is a lid, 26 is a motor, and 28 is a joint. , 29 is a rotating shaft, and 30 is a speed reducer.

(4) Measurement of bending strength from the regenerated binder-containing sand for molds Producing binder-containing sand for molds in the same manner as in step (1) and measuring the bending strength in the same manner as in step (2). did. The obtained bending strength is shown in Table 1.
Table 1 also shows the calcium ion elution concentration of fresh sand and regenerated artificial sand. The calcium ion elution concentration was measured according to the following procedure.
In addition, the surface area per unit volume, the particle size distribution, the particle shape coefficient, and the content ratio of alumina and silica were almost the same in the regenerated aggregate and fresh sand.

(Ion elution concentration)
(1) Preparation of internal standard solution and standard solution-Internal standard solution (Y: 50 mg / L)
25 mL of yttrium standard stock solution (Y: 1000 mg / L, for atomic absorption analysis) manufactured by Kanto Chemical Co., Ltd. was placed in a 500 mL volumetric flask, and purified water was added up to the marked line.
Standard solution (Ca: 100 mg / L)
10 mL of a standard solution IV (Ca: 1000 mg / L) for ICP emission spectroscopic analysis manufactured by Kanto Chemical Co., Ltd. was placed in a 100 mL flask, and purified water was added up to the marked line.
Standard solution (Ca: 10 mg / L)
10 mL of a standard solution (Ca: 100 mg / L) was taken in a 100-mL volumetric flask, and purified water was added up to the marked line.
Standard solution (Ca: 1 mg / L)
10 mL of a standard solution (Ca: 10 mg / L) was placed in a 100-mL volumetric flask, and purified water was added up to the marked line.
Standard solution (Ca: 0.1 mg / L)
10 mL of a standard solution (Ca: 1 mg / L) was placed in a 100-mL volumetric flask, and purified water was added up to the marked line.
Standard solution (Ca: 0.01 mg / L)
10 mL of a standard solution (Ca: 0.1 mg / L) was placed in a 100-mL volumetric flask, and purified water was added up to the marked line.

(2) Preparation of calibration curve (measurement range Ca: 0 to 10 mg / L)
Take 20 mL of the internal standard solution (Y: 50 mg / L) in a 100-mL volumetric flask, standard solution (Ca: 10 mg / L), standard solution (Ca: 1 mg / L), standard solution (Ca: 0.1 mg / L), standard Each solution (Ca: 0.01 mg / L) was added up to the marked line. In addition, as a blank test, 20 mL of an internal standard solution (Y: 50 mg / L) was taken in a 100-mL volumetric flask, and a standard solution in which purified water was added up to the marked line was prepared. These were measured with an ICP emission analyzer (ICPS-8100) manufactured by Shimadzu Corporation, and a relationship line (calibration curve) between the calcium ion concentration and the indicated value was created.

(3) Preparation of sample solution Take 50 g of test sand in a 300 mL polyethylene beaker, add 50 mL of purified water and 50 mL of 0.1 mol / L hydrochloric acid solution, and stir for 1 hour with a magnetic stirrer. After stirring, the mixture was filtered with a glass fiber filter specified in JIS P 3801 filter paper (for chemical analysis). After filtration, the solution was suction filtered again with a membrane filter (pore size 0.45 μm) manufactured by ADVANTEC to obtain a sample solution (stock solution). In addition, as a blank test, 50 mL of purified water and 50 mL of 0.1 mol / L hydrochloric acid solution were taken in a 300 mL polyethylene beaker, and the same operation was performed.

(4) Measurement of sample solution Take 10 mL of the internal standard solution (Y: 50 mg / L) in a 50-mL volumetric flask, add the sample solution (stock solution) to the marked line, and use an ICP emission spectrometer (ICPS-8100) manufactured by Shimadzu Corporation. It was measured. The difference between the obtained calcium ion concentration and the blank test concentration was defined as the calcium ion elution concentration. If the calcium ion concentration exceeds the measurement range of the calibration curve, dilute and adjust the sample solution (stock solution) with purified water so that it is within the measurement range to obtain the sample solution (diluted solution). Take 10 mL of the solution (Y: 50 mg / L) in a 50 mL volumetric flask, add the sample solution (diluent) to the marked line, and measure again with an ICP emission analyzer (ICPS-8100) manufactured by Shimadzu Corporation. Got. When the sample solution (diluted solution) was measured, the calcium ion elution concentration was obtained by subtracting the blank test concentration from the product of the obtained calcium ion concentration and the dilution rate.

The relationship between the bending strength based on Table 1 and the calcium ion elution concentration (vs. 0.05M HCl aqueous solution) is shown in FIG.
From Table 1 and FIG. 3, although bending strength is falling with the increase in calcium ion elution density | concentration, the tendency for the elution amount to become constant at 60 mg / L or less is seen. For this reason, calcium ions have some adverse effect on the curing of the resin during the production of the binder (for example, consumption of the curing agent with these ions, high molecular weight of the resin by chelating reaction of these ions to the cured site of the resin). It is inferred that

Example 2
The relationship between the calcium ion elution concentration and the bending strength of the artificial sand that was repeatedly regenerated was investigated. Specifically, the calcium ion elution concentration of the artificial sand was measured in the same manner as in Example 1 for the case where the regeneration was only roasting and the case where the wet grinding was performed after the roasting. The bending strength of the contained sand was measured in the same manner as in Example 1. The results are shown in Table 2. Table 2 shows the calcium ion elution concentration of fresh sand and the bending strength of the binder-containing sand for casting. The conditions for roasting and wet grinding, and the conditions for producing the binder-containing sand for molds were the same as in Example 1.

Based on Table 2, the relationship between the bending strength and calcium ion elution concentration (vs. 0.05M HCl aqueous solution) (vertical axis) and the number of regeneration repetitions (horizontal axis) is shown in FIG. The vertical axis of the bar graph in FIG. 4 represents the bending strength. The left bar graph at each regeneration count is the mold binder-containing sand regenerated only by roasting, and the right bar graph is the mold regenerated by roasting and wet grinding. It means the bending strength of sand for binder use. Further, the line graph represents the calcium ion elution concentration, and the triangle plot represents the calcium ion elution concentration of the artificial sand regenerated only by roasting, and the circle plot represents the artificial sand regenerated by roasting and wet grinding.
FIG. 4 shows that the bending strength decreases with increasing calcium ion elution concentration, but tends to be constant when the elution amount is 60 mg / L or less. It can be seen that in order to maintain the elution amount at 60 mg / L or less, it is preferable that wet grinding be included in the regeneration process of the binder-containing sand for molds.

DESCRIPTION OF SYMBOLS 1 Roasting furnace, 2 Ground material inlet, 3 Burner, 4 Fluidized bed, 5 Heat exchanger, 6 Sand flow air inlet, 7 Cooling air inlet, 8 Fluid cooler, 9 Sand discharge valve, 10 Air nozzle, 11 Flow differential pressure gauge, 12 exhaust gas outlet, 21 trough grinder, 22 trough, 23 stirring blade, 24 roasted sand inlet, 25 reclaimed sand outlet, 26 spring, 27 lid, 28 joint, 29 rotating shaft, 30 speed reducer , 31 motor

Claims (6)

Artificial sand used as a raw material for binder-containing sand for molds,
The artificial sand is mainly composed of synthetic mullite and / or synthetic corundum of 40 to 90% by weight of alumina and 60 to 10% by weight of silica, has a particle size distribution of 30 to 1180 μm, and is 60,000 / d to 1.8 million / d ( d has a surface area (cm ² / cm ³ ) per unit volume in the range of the average particle diameter (μm) of the spherical material, is derived from mold waste sand generated after casting, and in 0.05 M HCl aqueous solution artificial sand characterized by comprising been adjusted as shown mosquitoes Rushiumuion elution concentration below 60 mg / L in the solution was allowed to stir for 1 hour. The artificial sand, artificial sand of claim 1 that is used in the shell mold process.   The artificial sand according to claim 1 or 2, wherein the artificial sand has a particle shape factor of 1.2 or less.   The artificial sand according to any one of claims 1 to 3, wherein the artificial sand is a binder-containing sand for a mold including an aggregate mainly composed of artificial sand, a binder, and a lubricant. A sand containing a binder for a mold, characterized by being.   The mold binder according to claim 4, wherein the binder is selected from furan resin, phenol resin, oil urethane resin, phenol urethane resin, alkali phenol resin, sodium silicate and bentonite, and the lubricant is calcium stearate. Agent-containing sand.   The binder is contained in an amount of 0.4 to 3 parts by weight with respect to 100 parts by weight of the aggregate, and the lubricant is 0.01 to 100 parts by weight with respect to a total of 100 parts by weight of the aggregate and the binder. The mold-containing binder-containing sand according to claim 5, which is contained in an amount of 0.2 parts by weight.