JP2022126140A - Foundry sand for molding excellent in collapsibility and method of producing the same - Google Patents

Abstract

To provide a foundry sand allowing for practically advantageously forming a mold whose mold collapsibility after casting could have been improved furthermore while achieving the improvement of mold properties, an advantageous method of producing the same, and furthermore a useful coated sand obtainable using such a foundry sand.SOLUTION: A foundry sand, consisting of a refractory aggregate, comprises a shape factor of equal to or smaller than 1.40, a filling rate of equal to or higher than 53%, a content of a clay component adhering to an aggregate surface of equal to or lower than 0.20 mass%, a content of a part soluble in salt acid of equal to or lower than 3 mass% and a thermal conductivity of equal to or greater than 0.25 W/m K.SELECTED DRAWING: None

Description

The present invention relates to a foundry sand for mold making which has excellent collapsibility and a method for producing the same, and particularly to a foundry sand capable of improving mold characteristics and advantageously forming a mold having excellent collapsibility after casting. It also relates to a method that can be advantageously produced, as well as useful coated sands obtained using such foundry sands.

In the production of castings by conventional sand casting, the molten metal is cooled, solidified, and solidified in a mold obtained by molding using casting sand made of various refractory aggregates. It is necessary to remove the main mold and the sand core that make up the mold. Generally, as a method for removing such a mold, particularly the sand core, the temperature of the casting after casting is near normal temperature. After the casting is cooled down to a temperature of 100°C, the sand cores are removed by vibrating the casting using a vibrator such as a knockout machine to break the sand cores. However, since the sand core uses a resin such as phenolic resin as a binder (binder) that binds the foundry sand together, the foundry sand adheres to the resin. There are problems such as that simply applying vibration does not easily disintegrate the casting, and that it takes time to remove the casting sand from the casting.

By the way, in order to collapse the sand core fixed with such resin, it is conceivable to adopt a method of thermally decomposing the resin by heating. In order to decompose the resin, it is necessary to apply a sufficient amount of heat to the sand core. It is possible to decompose and separate the solidified foundry sand that forms the sand core. After such heating, the sand core is allowed to cool for 5 to 6 hours, and then vibration is applied to break the sand core and remove the foundry sand. However, this method has the problem of requiring a long processing time as well as a large amount of heat energy due to the decomposition of the resin. Since it does not work effectively for sand collapse, it was necessary to apply sufficient heat treatment to remove the sand core.

Further, Japanese Patent Application Laid-Open No. 9-182952 proposes a method of removing the core from the inside of the casting by spraying high-pressure water onto the inside of the casting to pulverize the sand core. However, when this high-pressure water is used, the work site will be flooded due to the splashing of the water. In addition to equipment problems such as the need to prepare a device for injecting high-pressure water, the removed sand gets wet with water, so in order to reuse the sand, it is necessary to dry the sand. However, it was inherent in the problem of requiring time-consuming work.

Further, Japanese Patent Application Laid-Open No. 9-1285 discloses a mold for a shell mold containing, as an essential component, a collapsibility improving agent comprising a zinc oxide compound such as ZnO or ZnO.B ₂ O ₃ together with foundry sand and a phenolic resin. A material has been proposed in which a Br-containing organic compound and a halogen-containing compound such as _ZnBr2 are combined with such a zinc oxide compound to further facilitate sand removal after casting. It has been clarified that when such halogen-based additives are used in combination, although the disintegration of the mold is good, there is a problem that corrosion is induced in the casting and the casting mold, and it is not practical. It was difficult to adopt above.

In addition, in JP-A-62-124046 and JP-B-5-79423, mold materials for shell molds contain an alkali metal salt of an aromatic carboxylic acid as a disintegration improving agent, or permanganate. It has been clarified that thermal decomposition products of alkali metal salts or alkaline earth metal salts of acids can be included to improve the collapsibility and sand removal properties of the mold after casting. There is a limit to the improvement of the collapsibility of the mold by adding a property-improving agent, and if the amount of such a disintegration-improving agent used is increased in order to further improve the collapsibility of the mold, the physical properties of the mold deteriorate. There were inherent problems such as causing adverse effects.

Thus, in any of the known methods for improving the collapsibility of a mold, there are problems inherent in each method, and as a method that can advantageously improve the collapsibility of the mold after casting, in practice , could not be adopted as is.

JP-A-9-182952 JP-A-9-1285 JP-A-62-124046 Japanese Patent Publication No. 5-79423

Here, the present invention has been made against the background of such circumstances, and the problem to be solved is to provide a foundry sand for mold making excellent in collapsibility and a method for producing the same. Another problem is foundry sand that can be used to practically and advantageously form a mold with improved mold characteristics and further improved collapsibility of the mold after casting. Another object of the present invention is to provide an advantageous production method thereof and a useful coated sand obtained by using such foundry sand.

In order to solve the above problems, the present invention can be suitably implemented in various aspects as listed below, and each aspect described below can be employed in any combination. is. It should be noted that the aspects and technical features of the present invention are not limited to those described below, and can be understood based on the inventive concept grasped from the description of the entire specification. should be considered.

First, the first aspect of the present invention is a foundry sand comprising refractory aggregates, having a shape factor of 1.40 or less, a filling rate of 53% or more, and clay adhering to the surface of the aggregates. content is 0.20% by mass or less, and the content of hydrochloric acid-soluble components is 3% by mass or less, and has a thermal conductivity of 0.25 W/m·K or more. The foundry sand for mold making with excellent collapsibility is characterized by:

A second aspect of the present invention is characterized in that the refractory aggregate is natural aggregate.

Furthermore, a third aspect of the present invention is characterized in that the refractory aggregate is mainly composed of silica sand.

In addition, a fourth aspect of the present invention is characterized in that the refractory aggregate is regenerated from recovered sand recovered in the casting process.

In order to advantageously obtain the above-described foundry sand for mold making which is excellent in collapsibility, as a fifth aspect of the present invention, (a) the recovered sand recovered in the casting process is: (b) performing a magnetic separation process to separate and remove magnetic metal components mixed in the collected sand; (c) an eddy current sorting step of separating and removing the non-magnetic metal components mixed in the sand to adjust the content of the hydrochloric acid-soluble components containing the non-magnetic metal components in the recovered sand to 3% by mass or less; By subjecting the recovered sand that has undergone the eddy current sorting step to a roasting treatment, the third component other than the sand, including the binder for molds, adhering to or mixed with the recovered sand is denatured or thermally decomposed. and (d) grinding the roasted recovered sand to adjust the particle shape of the recovered sand, adjust the shape factor to 1.40 or less, and adjust the shape factor to 1.40 or less. and a polishing step of removing clay adhering to the surface of particles to obtain molding sand having a clay content of 0.20% by mass or less. To adopt a method for producing foundry sand for molding.

A sixth aspect of the present invention is characterized in that the recovered sand is recovered from a mold obtained by molding using a refractory aggregate made of natural aggregate.

Furthermore, the seventh aspect according to the present invention is characterized in that the recovered sand is recovered from a mold obtained by molding using a refractory aggregate mainly composed of silica sand.

In addition, in the eighth aspect of the present invention, the eddy current sorting process generates eddy currents in non-magnetic metal components in the recovered sand by passing the recovered sand through a rotating magnetic field. It is characterized in that the non-magnetic metal components are separated and removed from the recovered sand by the interaction of the electric current and the rotating magnetic field.

In a ninth aspect according to the present invention, the magnetic separation treatment is repeated a plurality of times at a magnetic flux density of 10000 G or less, and the magnetic flux density adopted in the final magnetic separation treatment is treatment, and in the intermediate magnetic separation treatment, a magnetic flux density that is equal to or higher than the magnetic flux density in the initial magnetic separation treatment and lower than the magnetic flux density in the final magnetic separation treatment is adopted. When a plurality of intermediate magnetic separation processes are performed, the latter magnetic separation process is performed using a magnetic flux density equal to or greater than that in the previous magnetic separation process.

Furthermore, the tenth aspect of the present invention is characterized in that the roasting treatment is carried out at a temperature of 600-800°C.

In the eleventh aspect according to the present invention, the foundry sand having the characteristics described above is used, and by kneading the foundry sand and the foundry binder, the surface of the foundry sand is formed by the foundry binder. The object is a coated sand characterized by being coated.

In a twelfth aspect according to the present invention, the foundry sand obtained by the above-described production method is used, and the foundry sand and the foundry binder are kneaded to form the foundry caking agent on the surface of the foundry sand. The object is a coated sand characterized by being coated with an agent.

Furthermore, a thirteenth aspect of the present invention is characterized in that, in the coated sand as described above, the mold binder is a resin binder.

Furthermore, the fourteenth aspect of the present invention is characterized in that the coated sand further contains a metal oxide.

In addition, in the fifteenth aspect of the present invention, in the coated sand as described above, at least one of an oxate, a phosphate, and an aliphatic condensed phosphate is used as a disintegration improver, Further, it is characterized by being contained.

A sixteenth aspect of the present invention is characterized in that the thermal conductivity of the above-described coated sand is 0.30 W/m·K or more.

The foundry sand for mold making excellent in collapsibility according to the present invention has excellent shape characteristics with a predetermined shape factor and filling rate, and has a clay content of 0.20 mass. % or less, and the content of hydrochloric acid solubles, including non-magnetic metal components, is 3% by mass or less, and has an excellent thermal conductivity of 0.25 W/m K or more. Since it is composed of refractory aggregates, the thermal conductivity of the mold made using such foundry sand can be effectively increased, and as a result, heat during molding can be reduced. As a result, even the inside of the mold obtained by molding can be effectively hardened, and the presence of unhardened portions can be advantageously suppressed or eliminated. In short, such improved thermal conductivity makes it easier for the heat of the molten metal to conduct more evenly throughout the mold during casting, so that the heat of the molten metal binds the refractory aggregates together. By advantageously reducing the binding force of the foundry binder, the disintegrability of the mold can be effectively improved.

Moreover, in the mold obtained by molding using the foundry sand according to the present invention, the internal hardening property can be advantageously enhanced due to the excellent thermal conductivity, and the heating at the time of molding as in the conventional method is possible. Depending on the situation, the presence of uncured portions that cannot be sufficiently cured can be effectively reduced or eliminated, so that homogenization of the mold is realized and the mold characteristics are advantageously improved. In addition, the molding cycle time can be effectively shortened, and the amount of gas generated from the mold during casting can be effectively reduced. blocking can also be advantageously realized.

In addition, the foundry sand having such characteristics can be industrially produced advantageously by subjecting the recovered sand recovered in the casting process to a predetermined reclaiming treatment according to the present invention. . That is, the collected sand collected in the casting process is subjected to a predetermined magnetic separation process, an eddy current separation process, a roasting process, and a polishing treatment process, respectively, so that the desired shape factor, filling rate, clay It is possible to easily and industrially advantageously obtain foundry sand composed of refractory aggregates having excellent thermal conductivity and having a content of 100% and a content of solubles in hydrochloric acid. It becomes.

FIG. 2 is a vertical cross-sectional explanatory view of a sand mold for casting test used for measuring the collapsibility of cores in Examples. FIG. 2 is a vertical cross-sectional explanatory view of an aluminum alloy casting containing a waste core in an example.

By the way, the foundry sand according to the present invention has a predetermined shape factor and filling rate, and has a high thermal conductivity because the content of clay and hydrochloric acid solubles is set to a predetermined amount or less. In this case, as the refractory aggregate that constitutes such foundry sand, any of the refractory non-magnetic inorganic particles that have been conventionally used as foundry sand are similarly employed. Although it is possible, in the present invention, refractory particles mainly composed of silica sand, particularly natural particles (aggregate) are advantageously used in order to improve the thermal conductivity of foundry sand. In addition to using only silica sand (including crushed and sieved silica ore; the same shall apply hereinafter), mixed sand obtained by mixing silica sand with various known foundry sands may be used. In addition, refractory particles reclaimed from reclaimed sand and reclaimed sand thereof, inter alia, reclaimed sand recovered in the casting process, can likewise be used to advantage. However, the refractory aggregate composed of such refractory particles preferably contains 50% by weight or more of SiO ₂ , particularly 60% by weight or more, especially 70% by weight or more of SiO ₂ . It is desirable that there is, by which it can contribute more advantageously to the improvement of the thermal conductivity of the foundry sand.

In the present invention, such refractory particles having a shape factor of 1.40 or less and a filling rate of 53% or more are used. Here, the shape factor of the refractory particles (aggregate) used in the present invention is also called a particle shape factor or a particle shape index, and is generally used as a measure of the outer shape of the particles. , means that the closer the value is to 1, the closer to a sphere (perfect sphere). Such a shape factor is measured by various known methods. There is a method in which the actual surface area of each grain of sand is measured and divided by the theoretical surface area, which is the surface area when all grains of sand are spherical, to obtain the shape factor.

In addition, the filling rate refers to the ratio of the volume of the filled portion of the sand particles to the apparent volume of the foundry sand. is defined as That is, first, 100 ml of a mixed solution of water:methanol=7:3 (weight ratio) was placed in a 200 ml graduated cylinder, and foundry sand (refractory particles) was weighed by pouring into another graduated cylinder. After gradually adding 100 ml of this, seal it up, read the liquid level of the graduated cylinder after confirming that no more bubbles are generated, this value: the difference between Mml and the scale of 200 ml: 200-M, the gap A value obtained by subtracting this porosity: V from 100: 100-V is obtained as a filling rate: X. As the liquid contained in the graduated cylinder, instead of the mixed liquid of water and methanol, it is possible to use water added with a surface active agent or other liquid.

In addition, refractory particles (foundry sand) having a shape factor of 1.40 or less and a filling rate of 53% or more can be removed, for example, by removing small particles, rounding the corners of the particles by polishing, etc. can be obtained by spheroidizing or adjusting the particle size. Among them, if the shape factor is greater than 1.40, there are problems such as difficulty in increasing the filling rate. However, it is difficult to increase the thermal conductivity of the foundry sand, and as a result, it becomes impossible to obtain coated sand (CS) with good thermal conductivity. It also becomes difficult to improve the collapsibility of the mold.

Furthermore, in the foundry sand according to the present invention, the content of clay adhering to the surface of the refractory aggregate constituting the sand is 0.20% by mass or less, and the content of the hydrochloric acid-soluble component in the foundry sand is adjusted to be 3% by mass or less. Clay adhering to the surface of such refractory aggregates can be removed by ordinary polishing. They are separated and removed from the refractory aggregates, which are non-magnetic inorganic particles, by sieving or sorting using a conventionally known eddy current sorter. If the contents of the clay and hydrochloric acid-soluble components exceed the values specified in the present invention, the filling rate of the foundry sand is lowered and the thermal conductivity is deteriorated. difficult to achieve.

As described above, molding sand adjusted to have a thermal conductivity of 0.25 W/m·K or more by specifying the contents of clay and hydrochloric acid-soluble components as well as the shape factor and filling rate is , provides CS with excellent thermal conductivity, which advantageously improves the collapsibility of molds made with such CS.

The refractory particles (refractory aggregate) as described above generally desirably have an AFS index of 30 to 90, preferably 35 to 80, more preferably 40 to 70 AFS It is desirable to have an exponent. If the AFS index is less than 30, the particle size of the refractory particles becomes too large, which may adversely affect the thermal conductivity, may reduce the properties of the mold, and may cause problems such as deterioration of the casting surface. will also be induced. On the other hand, when the AFS index exceeds 90, the particle size of the refractory particles becomes too small, and when kneaded with the foundry binder, the amount of lumps, which are aggregates of the refractory particles, increases. In addition to this, problems such as difficulty in achieving sufficient improvement in thermal conductivity tend to occur.

Here, the foundry sand according to the present invention as described above uses various new sands and used sands as refractory aggregate raw materials, and is subjected to a predetermined treatment to adjust the shape factor and filling rate. Also, by adjusting the content of the clay content and the content of the hydrochloric acid soluble content, it can be easily manufactured as having the desired thermal conductivity. Using the recovered sand recovered in the casting process and then producing the foundry sand according to the present invention is of great practical significance. However, it is important to recycle the waste sand (old sand) generated by demolding molds after casting, and to recycle the recovered sand and reuse it as foundry sand. It is also desirable from the viewpoint of resource saving.

The recovered sand recovered in such a casting process is generated by demolding the mold used in sand casting of non-ferrous castings such as aluminum alloys, magnesium alloys, and copper alloys, and iron castings such as cast iron and cast steel. Collected waste mold sand, which is generally collected from each casting site and accumulated for disposal or treatment, is advantageously utilized.

According to the method for producing foundry sand preferably employed in the present invention, such recovered sand is first subjected to a magnetic separation treatment for removing magnetic metal (magnetic material) components such as iron, An eddy current sorting process for removing non-magnetic metal components such as these is sequentially performed. It should be noted that the two processes can be employed in any order, but advantageously the magnetic separation process will precede the eddy current sorting process.

By the way, in the magnetic separation step of subjecting the collected sand to such a magnetic separation treatment, magnetic force is generally applied at a magnetic flux density of 10000 G or less, preferably from 1000 to 8000 G, into the collected sand. Magnetic metal components such as iron mixed in are efficiently separated and removed as magnetically attracted components. It is recommended for effective removal of magnetic metal components (particles). Specifically, in a plurality of magnetic separation processes, the magnetic flux density employed in the final magnetic separation process is made larger than that in the initial magnetic separation process, and in the intermediate magnetic separation process, the initial A magnetic flux density higher than the magnetic flux density in the magnetic separation treatment of No. 1 and lower than the magnetic flux density in the final magnetic separation treatment is adopted. The subsequent magnetic separation process will be performed using a magnetic flux density equal to or greater than the magnetic flux density in the process. More specifically, for example, first, using a magnetic force sorting device with a magnetic flux density of about 1500 G, large magnetic bodies such as iron ingots are removed, and then using a magnetic force sorting device with a magnetic flux density of about 3000 G, further If necessary, a magnetic force sorting device with a magnetic flux density of about 7000 G is used to remove small magnetic substances such as iron sand. By such a magnetic separation process, the content of magnetic metal components such as iron and magnetic sand grains in the collected sand is generally reduced to 5% by mass or less. For such magnetic separation treatment, various known magnetic separators are used, and for example, a separator called a suspension type magnetic separator, a drum type magnetic separator, or the like is appropriately employed.

In addition, the collected sand is subjected to an eddy current sorting treatment to separate and remove non-magnetic metal components mixed in the collected sand, such as non-ferrous metals such as aluminum alloys, copper alloys, brass, gunmetal, and magnesium alloys. In the case where the eddy current sorting process consisting of the above-described magnetic separation process is performed following the magnetic separation process, the collected sand subjected to the magnetic separation process is classified as necessary, and then, if necessary, the shape After the non-magnetic metal components with large σ are screened out, the eddy current sorting process is performed. The eddy current sorting process employed here utilizes eddy currents generated in non-magnetic metal components by a rotating magnetic field. An eddy current is generated in the non-magnetic metal component that is soluble in hydrochloric acid in the sand, and the non-magnetic metal component is separated and removed from the collected sand by the interaction between the eddy current and the magnetic field. . It should be noted that the collected sand subjected to the eddy current sorting process contains magnetic substances such as iron, which are soluble in hydrochloric acid and which could not be completely removed by the magnetic separation process described above. At least a portion of such remaining magnetic material is removed separately from the sand itself (aggregate) and non-magnetic metal components by the eddy current sorting process. By implementing such an eddy current sorting process, the content of hydrochloric acid-soluble components such as non-magnetic metal components in the collected sand is 3% by mass or less, preferably 1% by mass or less, and more preferably 0.8% by mass. % or less, which makes it possible to further improve the filling property of the reclaimed molding sand and improve the thermal conductivity of the molding sand. On the other hand, if the removal of such hydrochloric acid-soluble matter is insufficient, when a fluidized bed roasting furnace is used as the roasting treatment equipment in the subsequent roasting process, it is installed at the bottom of the roasting furnace. The air outlet is clogged with metal components soluble in hydrochloric acid such as molten non-ferrous metal components, causing problems such as difficulty in sufficiently roasting the recovered sand.

As a sorting device for carrying out such an eddy current sorting process, as a sorter for non-magnetic metals such as aluminum, various types of known structures can be appropriately adopted. Collected sand is placed on the belt, and the belt is driven by rotating at 1800 to 2500 rpm a roll type magnetic pole rotor in which permanent magnets having a magnetic flux density of about 3000 to 10000 G are incorporated, and the magnetic pole rotor is installed. By dropping the collected sand from the belt at the position, the collected sand on the belt is sorted into sand (aggregate) components, which are non-magnetic inorganic particles, and non-magnetic metal components mixed therein. can be used. That is, eddy currents are generated in the non-magnetic metal components mixed in the collected sand on the belt, and the metal components that generate the eddy currents are generated by utilizing the electromagnetic force generated between the eddy currents and the magnetic field of the magnetic pole rotor. uses the repulsive force of the electromagnetic force to draw an arc to repel the magnetic pole rotor and drop it to a position away from the magnetic pole rotor, while non-magnetic inorganic particles such as silica sand that do not generate eddy currents ( Sand particles) are dropped directly below the magnetic pole rotor in the vertical direction to separate non-magnetic metal components from inorganic particles (sand particles) that are non-magnetic non-metal components. . The magnetic metal components remaining in the collected sand are magnetically attached to the belt by the magnetic force of the permanent magnets at the positions where the magnetic pole rotors are arranged, and are dropped from the belt when the belt separates from the magnetic pole rotors. Become.

Next, by such an eddy current sorting treatment, the mixed non-magnetic metal components and other hydrochloric acid-soluble components are separated and removed, and as a result, the content of the hydrochloric acid-soluble components is reduced to 3% by mass or less in the recovered sand. is subjected to a roasting treatment (heating treatment), which denatures (changes) the third component (including various foundry binders) other than the sand (aggregate) that adheres to or is mixed with the recovered sand. Alternatively, a roasting step for thermal decomposition is carried out. By adopting such a roasting process, the organic components such as the organic binding agent, which is the binding agent for the mold, attached to or mixed with the recovered sand are thermally decomposed and removed. An inorganic component such as an inorganic binder used as a binder is denatured or denatured so that it can be easily removed by the polishing treatment in the subsequent polishing treatment step.

The roasting treatment of the collected sand can be appropriately carried out using a conventionally known roasting furnace, but it is advantageous to roast (burn, By using a fluidized bed roasting furnace for the incineration treatment, the roasting treatment of the collected sand can be carried out more advantageously. The roasting treatment temperature is appropriately selected depending on the type of recovered sand to be treated and the type of third component other than sand that adheres to or is mixed with sand. A temperature of about 900° C., preferably about 600 to 800° C. is employed, and the treatment time is generally about 10 minutes to 3 hours, preferably about 30 minutes to 2 hours. Become.

After that, the recovered sand subjected to such roasting treatment is appropriately cooled, classified if necessary, and further subjected to magnetic separation (for example, using a magnetic flux density of about 7000 G). ), a polishing process is carried out to adjust the particle shape of the recovered sand, adjust the shape factor to 1.40 or less, and remove the clay content adhering to the surface of the sand particles of the recovered sand. The desired foundry sand is formed by removing it so that the clay content is 0.20% by mass or less, preferably 0.15% by mass or less.

Such polishing treatment can be carried out by using one or a combination of various known polishing devices conventionally used for polishing recovered sand. Kiyota casting machine), mechanical sand reclaimer: USR (Sintokogyo Co., Ltd.), dry casting sand reclaimer: rotary reclaimer (NRR; Nippon Chuzo Co., Ltd.), hybrid sand master (HSM; Nippon Chuzo Co., Ltd.), etc. can be mentioned. In addition, these polishing apparatuses dry-polish the recovered sand, and are structured so that the fine powder generated during the grinding is sucked and removed at the same time. In addition, it exhibits characteristics such as good yield after polishing.

The foundry sand thus obtained is effectively free of magnetized metal components such as iron, and is effectively free of non-magnetic metal components such as aluminum, gunmetal, brass and other non-ferrous metals derived from castings. In addition, the sand exhibits a good sand shape, and the clay content (fine powder) such as auritic on the sand surface can be removed, so that the filling property is enhanced and the thermal conductivity can be advantageously improved. Therefore, a coated sand ( CS) is advantageously obtained.

In addition, as a binder for a mold used for producing such CS, either an inorganic binder typified by water glass or a resin binder typified by phenolic resin can be used. However, in the present invention, a resin binder is preferably used. As the resin binder, various known ones can be mentioned, for example, phenol resin, furan resin, urethane resin, amine polyol resin, unsaturated polyester resin, diallyl phthalate resin, polyether polyol. It is used by appropriately selecting from among resins and the like, and among them, phenolic resin is advantageously used.

By the way, in the present invention, the phenolic resin suitably used as the resin binder is obtained by reacting phenols and aldehydes in the presence of an acidic catalyst or a basic catalyst, as is well known. A solid or liquid (including varnish and emulsion) condensation product, which is referred to as a novolak type or resol type depending on the type of catalyst used therein, It is a phenolic resin that develops thermosetting properties by heating in the presence or absence of a predetermined curing agent or curing catalyst.

As is well known, novolac-type phenolic resins are formed by condensation reaction using phenols and aldehydes using an acidic catalyst, and resol-type phenolic resins are , using phenols and aldehydes, in the same manner as in the prior art, by causing a condensation reaction with a basic catalyst. These novolac-type phenolic resins and resol-type phenolic resins may be used alone, or may be used by mixing them in appropriate proportions. Modified phenol resins obtained by changing components such as A and naphthol can also be used, and furthermore, phenol resins of the benzylic ether type can also be used.

When a resin binder such as the phenolic resin described above is kneaded with the foundry sand, the amount of the resin binder to be blended is determined in consideration of the type of resin to be used and the required strength of the mold. Although it can be determined as appropriate and cannot be univocally defined, it is generally in the range of about 0.2 to 10 parts by mass with respect to 100 parts by mass of the foundry sand, and is preferable. is in the range of 0.5 to 8 parts by mass, more preferably 1 to 5 parts by mass.

By the way, according to a desirable aspect of the present invention, the CS according to the present invention further contains a metal oxide, thereby further improving the collapsibility of the mold. Such metal oxides generally take the form of particles or powder having an average particle size of 10 μm or less, and are incorporated into the CS when the foundry sand and the foundry binder are kneaded. will be Such metal oxides are specifically oxides of metals such as iron, copper, nickel, cobalt, and zinc, for example, ferrous oxide, ferric oxide, triiron tetraoxide , iron oxide hydroxide, cobaltous oxide, cobaltic oxide, nickelous oxide, nickelic oxide, cuprous oxide, cupric oxide, zinc oxide and the like. The content of such metal oxides is generally about 0.1 to 3 parts by mass, preferably about 0.1 to 1 part by mass, more preferably about 0.1 to 1 part by mass, with respect to 100 parts by mass of foundry sand. .1 to 0.5 parts by mass.

According to another preferred embodiment of the present invention, the CS according to the present invention may also include, together with or instead of the above-mentioned metal oxides, oxysates, phosphate esters and aliphatic condensations as disintegration improvers. At least one of the phosphate esters is further included, thereby effectively improving the collapsibility of molds made using such CS. The oxyacid used here is generally desirably an alkali metal oxyacid, and specifically, alkali metal nitrate, alkali metal permanganate, alkali metal molybdate, tungsten An acid alkali metal salt etc. can be mentioned. Among them, alkali metal nitrates, alkali metal molybdates and alkali metal tungstates are preferred from the standpoint of mold strength, and alkali metal salts of nitric acid such as potassium nitrate and sodium nitrate are particularly preferred. becomes. The content of such an oxyacid salt is generally about 0.1 to 50 parts by mass, preferably about 1 to 20 parts by mass, per 100 parts by mass of the foundry binder. It will happen.

Further, the phosphoric acid ester and/or aliphatic condensed phosphoric acid ester to be contained together with or instead of such oxysalts include, for example, trimethyl phosphate, triethyl phosphate, tributyl phosphate, tri-2-ethylhexyl phosphate, tri Butoxyethyl phosphate, triphenyl phosphate, diethyl-N,N-bis(2-hydroxyethyl)aminomethylphosphonate, various aliphatic and aromatic phosphates such as dibutyl butyl phosphonate, Fyrol PNX (ICL JAPAN Co., Ltd.) (manufactured by the company) and other aliphatic condensed phosphoric acid esters can be mentioned, and from among them, it will be appropriately selected and used. The content of the phosphate ester and/or the aliphatic condensed phosphate ester is generally 0.5 to 30 parts by mass, more preferably 1 part per 100 parts by mass of the binder for molds. A proportion of about 10 parts by mass will be adopted.

In addition, it is also possible to use halogen-based disintegrants in addition to the disintegration improvers described above. Examples of halogen-based disintegrants include tetrabromobisphenol A and trischloroethyl phosphate, but are not limited to these, and various known halogen-based disintegrants can be used.

In the present invention, in addition to the compounding components as described above, if necessary, various additives that have been generally used in the past for the purpose of improving the physical properties of CS and molds, It can be blended appropriately and contained in CS. For example, lubricants that contribute to improving the fluidity of CS include waxes such as paraffin wax, synthetic polyethylene wax, and montanic acid wax; fatty acid amides such as stearamide, oleamide, and erucamide; methylene bis stearin; Alkylene fatty acid amides such as acid amides and ethylenebisstearic acid amides are available, and these can be incorporated during the production of both the resin (binder) and the CS. Stearic acid, stearyl alcohol, metal stearate, lead stearate, zinc stearate, calcium stearate, magnesium stearate, stearic acid monoglyceride, stearyl stearate, hydrogenated oil, etc. can be added during CS production. In addition, benzenecarboxylic acids; benzoic acid, salicylic acid, para-aminobenzoic acid, anthranilic acid, phthalic acid, terephthalic acid, etc., may be included as additives that contribute to improving the curing speed of the mold during the production of both the resin and the CS. is also possible. Furthermore, it is also effective to incorporate a coupling agent that strengthens the bond between the foundry sand and the foundry binder. can be contained during any production of In addition, mold release agents such as paraffin, wax, light oil, machine oil, spindle oil, insulating oil, waste oil, vegetable oil, fatty acid ester, organic acid, graphite fine particles, mica, vermiculite, fluorine-based release agent, silicone-based release agent Mold agents and the like can also be used in the same manner as before.

By the way, when producing the CS according to the present invention using the compounding ingredients as described above, a foundry binder and other compounding ingredients are added to predetermined foundry sand (refractory aggregate) according to a conventional method. Although it will be kneaded, the manufacturing method employed there is not particularly limited, and conventionally known methods such as dry hot coating method, semi-hot coating method, cold coating method, powder solvent method, etc. Any method can be employed. However, in the present invention, after kneading preheated foundry sand and foundry binder in a kneader such as a whirl mixer or a speed mixer, a predetermined curing agent such as hexamethylenetetramine and a curing agent are added. It is recommended to adopt a so-called dry hot coating method in which an aqueous solution of an accelerator, other ingredients, etc. are added, the mass content is separated into granules by air cooling, and then a lubricant such as calcium stearate is added. It will happen. The timing of kneading the foundry binder, curing agent/hardening accelerator, etc. with the foundry sand is appropriately selected based on the knowledge of those skilled in the art. , can be appropriately combined and kneaded.

The thus obtained CS according to the present invention has a thermal conductivity of 0.30 W/m·K or more, preferably 0.33 W/m·K, when measured in its granular form, unlike conventional CS. It has a thermal conductivity of K or higher, which can advantageously contribute to the improvement of mold collapsibility, which is the object of the present invention. Here, the thermal conductivity of CS can be measured in the same manner as the thermal conductivity of molding sand, and they are measured by the unsteady hot wire heating method (probe It will be measured according to the law). Specifically, using a rapid thermal conductivity meter (QTM-710) manufactured by Kyoto Electronics Industry Co., Ltd., the CS to be measured is contained in a predetermined powder container, and a probe (heating wire + thermoelectric The temperature of the heating wire is measured with a thermocouple, and the slope of the obtained temperature rise graph (graph with a logarithmic scale on the time axis) is obtained. , the thermal conductivity of the CS to be measured is determined.

In addition, it is desirable that the CS according to the present invention has a low content of so-called lumps, which are composite particles in which a plurality of foundry sands are combined (aggregated), generated in the manufacturing process. When the CS taken out from the process is sieved, it cannot pass through a 20-mesh sieve, in other words, the amount of lumps on the 20-mesh sieve is 3% by mass or less with respect to the total amount of CS, more preferably It is recommended that the content be 1% by mass or less. On the other hand, if the amount of lumps in the CS increases, the filling ability of the mold for molding the mold into the molding cavity deteriorates, adversely affecting the hardening characteristics of the mold, and mold characteristics such as mold strength. In addition to the fact that it is difficult to sufficiently improve the strength, problems such as insufficient collapsibility of the mold after casting are caused. The content of such lumps is determined by using foundry sand with a particle size index (AFS) within the preferred range related to the present invention, and by limiting the amount of metal oxides having an average particle size of 10 μm or less to be added to the preferred range. This enables control.

Furthermore, when the CS obtained as described above is used to mold a predetermined mold such as a shell mold, the desired mold is molded under heat in order to heat harden the CS. However, such a thermoforming method is not particularly limited, and any conventionally known method can be advantageously used. For example, the CS as described above is filled into a mold preheated to about 150 to 300° C., which has a desired shape space that provides the desired mold, by a gravity drop method, a blow method, or the like, and then cured. After that, the desired casting mold can be obtained by removing the hardened mold from the mold.

Also, using the mold obtained by such molding, a predetermined molten metal such as molten aluminum is cast, and after solidification, vibration is applied to the casting using a vibrator such as a knockout machine, By collapsing the mold, the mold is removed. In the mold using CS according to the present invention, since CS itself has a high thermal conductivity, it is not poured. Deterioration of the foundry binder that binds the foundry sand can be effectively progressed by the heat of the molten metal, and the binding force is advantageously reduced. As a result, the mold (molding sand) can be simply and easily removed.

Some examples of the present invention will be shown below to clarify the present invention more specifically, but the present invention is not subject to any restrictions by the description of such examples. needless to say. In addition to the following examples, and in addition to the specific description above, the present invention includes various changes and modifications based on the knowledge of those skilled in the art, as long as they do not depart from the spirit of the present invention. , improvements, etc. may be added.

In the following description, parts and % mean parts by mass and % by mass, respectively, unless otherwise specified, except that the filling rate is % by volume. Further, the properties of the foundry sand and CS produced below, and the strength and collapsibility of the mold obtained from each CS were evaluated according to the following methods.

-Measurement of AFS rate of change-
According to JACT test method S-6 "Fracturability test method for foundry sand", the friability test of the foundry sand to be measured was carried out, and the foundry sand (original sand) before the test and the foundry sand after the test. , After measuring the particle size distribution of each and calculating the AFS particle size index, the value obtained by dividing the particle size index after the friability test by the particle size index of the raw sand is obtained as a percentage. and let this be the AFS change rate (%).

-Measurement of shape factor-
For each molding sand, a sand surface area measuring instrument (manufactured by George Fisher) was used to measure the actual surface area of sand grains per gram, and the obtained values were assumed to be all spherical. The value obtained by dividing by the theoretical surface area, which is the surface area when

-Measurement of filling rate-
For each foundry sand, the fill factor is determined according to the measurement method described earlier in the present specification.

-Measurement of clay content-
Accurately weigh 50 g of sample sand (foundry sand) to determine the mass of sand before treatment, put it in a 500 ml glass beaker, add 300 ml of water, and add one grain of sodium hydroxide (about 200 mg). Then, after boiling with an electric heater for 30 minutes, the boiling water was discarded, washed with water several times, and then dried with a dryer. Accurately weigh the sand and use it as the sand mass after treatment. Then, the clay content (%) is calculated according to the following formula based on the obtained sand mass.
Clay content (%) = [(mass of sand before treatment) - (mass of sand after treatment)]
/ (mass of sand before treatment) x 100

- Measurement of hydrochloric acid soluble content -
About 10 g of sample sand is precisely weighed and placed in a Kjeldahl tube, and then 50 ml of 20% hydrochloric acid is added to the Kjeldahl tube and heated at 180° C. for about 20 minutes. Next, after this heating, the Kjeldahl tube is cooled, its contents are collected by filtration, thoroughly washed with tap water, dried by heating, and the weight of the hydrochloric acid-treated sample sand is precisely weighed. . Then, the amount of reduction in the sample sand due to the hydrochloric acid treatment is expressed as a percentage, and this is defined as the content of the hydrochloric acid-soluble matter.

－Measurement of thermal conductivity－
Using a rapid thermal conductivity meter: QTM-710 manufactured by Kyoto Electronics Industry Co., Ltd., the thermal conductivity of each sample (CS) is calculated from the temperature rise graph obtained according to the method described in the text of this specification. .

-Measurement of mold strength-
A test piece (width: 10 mm × thickness: 10 mm × length: 60 mm) obtained using each CS (molding temperature: 250 ° C.) was measured with a measuring instrument (manufactured by Takachiho Seiki Co., Ltd.: Measure using a digital molding sand strength tester). Then, using this measured breaking load, the transverse rupture strength is calculated according to the following formula and defined as the mold strength.
Bending strength (N/cm ² )=1.5×LW/ab ²
[However, L: distance between fulcrums (cm), W: breaking load (N), a: width of test piece (cm), b: thickness of test piece (cm)]

-Evaluation of collapsibility-
First, as shown in FIG. 1, a dog-bone type tensile strength test piece 2 having a width of 40 mm, a length of 75 mm, and a thickness of 25 mm is produced from each CS to form a core for the disintegration test. .

Next, an outer mold 4 having a size of 125 mm × 80 mm × 75 mm and having a space slightly larger than the core test piece 2 was separately prepared. A molten aluminum alloy at a temperature of 0.383 is cast to cast a desired casting 6 (see FIG. 2).

After the casting 6 is cooled, vibration is applied to one part of the casting 6 (the part indicated by the white arrow in FIG. 2) with an air hammer at a chipping pressure of 0.3 MPa to remove the casting from the discharge port ( Diameter: 16 mm) The weight of sand discharged from each time is measured, and the measured weight is divided by the total weight when all is discharged, and the amount is expressed in %. There, the larger the numerical value, the better the disintegration property.

-Example 1-
First, using silica sand collected and accumulated from the casting process (recovered silica sand), magnetic separation treatment, eddy current separation treatment, roasting treatment and polishing treatment were performed under the conditions shown in Table 1 below. were carried out sequentially. Specifically, the magnetic separation treatment was repeated using a commercially available magnetic separator by combining three magnetic separation treatments at a magnetic flux density of 1500 G and one magnetic separation treatment at a magnetic flux density of 3000 G. In addition, the eddy current sorting treatment is performed on the recovered silica sand subjected to such magnetic separation treatment using a non-ferrous magnetic separator: ALS type manufactured by Nippon Magnetics Co., Ltd. under the conditions of magnetic flux density: 3000 G and rotation speed: 2200 rpm. It was carried out below. Furthermore, the roasting treatment was performed on the recovered silica sand subjected to the eddy current sorting treatment using a normal fluidized bed roasting furnace under the conditions of temperature: 800° C. and time: 60 minutes. Then, the final polishing treatment is performed by using a commercially available dry casting sand reclaimer: a rotary reclaimer (NRR; manufactured by Nippon Chuzo Co., Ltd.) on the recovered silica sand that has been subjected to the roasting treatment as described above. , under the conditions shown in Table 1 below. Then, for the recovered silica sand subjected to such polishing treatment, the crushing rate, in other words, the AFS change rate, and the yield were determined, and these results are also shown in Table 1 below.

The shape factor, filling ratio, clay content, hydrochloric acid soluble content, AFS index and thermal conductivity of the foundry sand thus obtained, which is composed of recovered silica sand after polishing, were measured according to the methods described above. , and their results are shown in Table 1 below.

- Examples 2 to 6 -
Magnetic separation treatment, eddy current sorting treatment, roasting treatment and polishing were performed in the same manner as in Example 1 under the conditions shown in Table 1 below using recovered silica sand, which is recovered sand recovered from the casting process. The treatments were carried out in sequence to obtain the desired foundry sand. In the polishing process, "USR" used as a polishing apparatus is a mechanical sand reclaimer: USR-II manufactured by Sintokogyo Co., Ltd., and "HSM" is a dry casting manufactured by Nippon Chuzo Co., Ltd. Sand reclaimer: hybrid sandmaster. Further, in Examples 4 and 6, the magnetic separation treatment was performed using three levels of magnetic flux densities of 1500G, 1800G and 3000G.

Then, for the molding sand obtained in each example, the shape factor, filling rate, clay content, hydrochloric acid soluble content, AFS index, and thermal conductivity were measured according to the above-described measurement methods. The results are also shown in Table 1 below.

- Examples 7 to 11 -
In the same manner as in Example 1, the recovered silica sand, which is the recovered sand recovered from the casting process, was subjected to magnetic separation treatment, eddy current separation treatment, roasting treatment and polishing under the conditions shown in Table 2 below. Treatments were performed sequentially. In Example 10, mixed sand (90:10) of recovered sand and Mikawa silica sand (artificial silica sand) was used as the raw material for the refractory aggregate, and Mikawa silica sand was replenished before the polishing step. Further, in Examples 7 to 9, the second-stage magnetic separation treatment was repeated three times at a magnetic flux density of 3000 G, and in Example 11, the magnetic separation treatment was performed in three stages of 1500 G, 3000 G and 7000 G. and the polishing process was carried out in two stages using two types of polishing apparatuses.

Then, the molding sand obtained in each example was measured for shape factor, filling rate, clay content, hydrochloric acid soluble content, AFS index and thermal conductivity in the same manner as in Example 1. , and the results obtained are shown in Table 2 below.

-Comparative Examples 1 to 7-
Recovered silica sand or mixed sand of recovered sand and Mikawa silica sand ( 90:10) or recovered artificial sand (commercially available mullite artificial sand) was subjected to the regeneration treatment shown in Table 3 below to obtain the desired foundry sand. One of the polishing apparatuses used in the polishing process in Comparative Example 7, "SF", is a sand fresher manufactured by Kiyota Casting Co., Ltd., which polishes the surface of sand with a whetstone rotating at high speed. is.

Then, the molding sand obtained in each of the comparative examples was evaluated for shape factor, filling factor, clay content, hydrochloric acid soluble content, AFS index and thermal conductivity in the same manner as in the previous examples. Measurements were taken, and the results are shown in Table 3 below.

-Evaluation of resin-coated sand and mold-
Using the various foundry sands obtained in Examples 1 to 11 and Comparative Examples 1 to 7 above, each resin coated sand (RCS) was prepared, and then each RCS was used to prepare a mold for collapsibility test. (core) was molded.

Specifically, to 100 parts of each molding sand heated to 150°C, a commercially available novolac-type phenolic resin (SP610 manufactured by Asahi Organic Chemicals Co., Ltd., softening point: about 90°C) is added in an amount shown in Tables 4 to 6 below. and the proportions shown in Tables 4 to 6 below of metal oxides, oxysalts or phosphate esters/condensed phosphate esters, kneaded for 50 seconds in a speed mixer, and then 0.23 parts of hexamethylenetetramine. is dissolved in 1.5 parts of water and kneaded until the sand separates into individual particles, then 0.1 part of calcium stearate is added and mixed for 15 seconds. After that, the sand was taken out from the mixer to obtain the desired RCS in which the surface of the foundry sand was coated with the phenolic resin.

Then, the thermal conductivity of the obtained RCS was measured, and a test piece for mold strength evaluation was prepared from each RCS. A test core) was molded, and the mold strength was measured and the mold disintegration test was performed according to the above description, and the results obtained are shown in Tables 4 to 6 below.

As is clear from the comparison of the results in Tables 4 to 6 in which the various molding sands shown in Tables 1 to 3 were evaluated, the molding sands obtained in Examples 1 to 11 all had a shape factor of 1.40. Below, the filling rate is 53% or more, the content of clay adhering to the sand surface is 0.20% by mass or less, the content of hydrochloric acid solubles is 3% by mass or less, and heat Since it has the property of having a conductivity of 0.25 W/m·K or more, it was confirmed that the collapse of the mold after casting progresses immediately when vibration is applied, and the collapse property is extremely good. be done. In particular, in the molds molded from RCS using the foundry sand obtained in Examples 4 to 9, at least one or more of metal oxides, oxyacid salts and phosphoric acid esters/condensed phosphoric acid esters is blended. From what has been shown, all of them show excellent results in terms of mold collapsibility, and the foundry sand obtained in Example 11 has an extremely high filling rate and a high content of hydrochloric acid solubles. Since the amount of phenolic resin used is much lower, it can be recognized that even RCS with a small amount of phenolic resin exhibits high mold strength and is excellent in mold disintegration property.

On the other hand, the foundry sands obtained in Comparative Examples 1 to 7 had at least Since any one of them is outside the scope of the present invention, in the mold disintegration test, if the knockout time of applying vibration is within 10 seconds, the mold will not collapse or will collapse. It was found that the mold could not be sufficiently disintegrated even if it was crushed, and therefore the disintegrability of the mold was inferior.

2 Core test piece 4 Outer mold 6 Casting

Claims (16)

Foundry sand composed of refractory aggregates, having a shape factor of 1.40 or less, a filling rate of 53% or more, and a content of clay adhering to the aggregate surface of 0.20% by mass or less. A mold excellent in collapsibility, further comprising a content of hydrochloric acid solubles of 3% by mass or less and having a thermal conductivity of 0.25 W / m K or more Foundry sand for molding. 2. The foundry sand for mold making with excellent collapsibility according to claim 1, wherein the refractory aggregate is a natural aggregate. 3. The foundry sand for mold making excellent in collapsibility according to claim 1 or 2, characterized in that said refractory aggregate mainly consists of silica sand. 4. A highly collapsible mold for making a mold according to any one of claims 1 to 3, characterized in that the refractory aggregate is recycled from recovered sand recovered in the casting process. foundry sand. a magnetic separation step of performing a magnetic separation treatment on the recovered sand recovered in the casting step to separate and remove magnetic metal components mixed in the recovered sand;
The recovered sand is subjected to an eddy current sorting treatment to separate and remove the non-magnetic metal components mixed in the recovered sand, thereby obtaining the hydrochloric acid-soluble content containing the non-magnetic metal components in the recovered sand. An eddy current sorting step for adjusting the content of the
By subjecting the recovered sand that has undergone the eddy current sorting step to a roasting treatment, the third component other than the sand, including the binder for molds, adhering to or mixed with the recovered sand is denatured or thermally decomposed. baking process,
The roasted recovered sand is polished to adjust the particle shape of the recovered sand and adjust the shape factor to 1.40 or less, and the clay content adhering to the surface of the sand particles of the recovered sand. is removed to obtain casting sand having a clay content of 0.20% by mass or less;
A method for producing foundry sand for mold making having excellent collapsibility, characterized by containing at least: 6. The casting according to claim 5, wherein the recovered sand is recovered from a mold obtained by molding using a refractory aggregate made of natural aggregate. How to make sand. 7. The highly collapsible sand according to claim 5 or 6, wherein the recovered sand is recovered from a mold obtained by molding using a refractory aggregate mainly composed of silica sand. A method for producing foundry sand for mold making. The eddy current sorting process generates eddy currents in the non-magnetic metal components in the recovered sand by passing the recovered sand through a rotating magnetic field, and the interaction between the eddy currents and the rotating magnetic field generates such non-magnetic metal components. Manufacture of the foundry sand for mold making with excellent collapsibility according to any one of claims 5 to 7, characterized in that the magnetic metal component is separated and removed from the recovered sand. Method. The magnetic separation treatment is repeated multiple times at a magnetic flux density of 10000 G or less, and the magnetic flux density adopted in the final magnetic separation treatment is made higher than that in the first magnetic separation treatment, and the intermediate magnetic separation treatment In the magnetic separation treatment, a magnetic flux density that is higher than the magnetic flux density in the initial magnetic separation treatment and lower than the magnetic flux density in the final magnetic separation treatment is adopted, and furthermore, in the case where there are a plurality of such intermediate magnetic separation treatments 9. The magnetic separation process in the subsequent stage is performed using a magnetic flux density equal to or higher than that in the magnetic separation process in the previous stage. A method for producing foundry sand for mold making which is excellent in collapsibility. The method for producing foundry sand for mold making with excellent collapsibility according to any one of claims 5 to 9, characterized in that the roasting treatment is carried out at a temperature of 600 to 800°C. By using the foundry sand according to any one of claims 1 to 4 and kneading the foundry sand with the foundry binder, the surface of the foundry sand is coated with the foundry binder. A coated sand characterized by: The foundry sand obtained by the production method according to any one of claims 5 to 10 is used, and the foundry sand and the foundry binder are kneaded so that the surface of the foundry sand becomes the foundry viscosity. A coated sand characterized by being coated with a binder. 13. The coated sand according to claim 11 or 12, wherein the foundry binder is a resin binder. 14. The coated sand according to any one of claims 11 to 13, further comprising a metal oxide. 15. The composition according to any one of claims 11 to 14, further comprising at least one of an oxate, a phosphate, and an aliphatic condensed phosphate as a disintegration improver. 1. Coated sand according to item 1. 16. The coated sand according to any one of claims 11 to 15, having a thermal conductivity of 0.30 W/m·K or more.

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