JP6406207B2 - How to recycle foundry sand - Google Patents

Description

  The present invention relates to a method for reclaiming foundry sand.

  2. Description of the Related Art Conventionally, a method is known in which foundry sand is recovered from a cast mold, and the foundry sand is regenerated by performing a regeneration process for removing the binder adhering to the foundry sand. Patent Document 1 discloses a regeneration method having a polishing step of polishing the recovered foundry sand with a dry polishing regenerator.

JP 2012-125785 A

  By the way, as a binder used for foundry sand, an organic binder mainly composed of a phenol resin and a polyisocyanate compound or an inorganic binder mainly composed of water glass is used. For example, among molds, high strength is required. For example, it is considered to mold a foundry sand using an inorganic binder, to mold a foundry sand using an organic binder, and to form a sand mold by combining them.

  Such a sand mold (hereinafter sometimes simply referred to as “combined sand mold”) is formed by combining a mold made of foundry sand using an organic binder and a mold made of foundry sand using an inorganic binder. In some cases, reclaimed sand obtained by reclaiming the foundry sand that has been recovered by separating the previous mold may be used. At this time, in the regenerated sand obtained by reclaiming the casting sand recovered by separating the casting mold formed from the foundry sand using the inorganic binder, if the inorganic binder remains on the surface of the reclaimed sand, the regenerated sand is When kneaded with the binder, the organic binder may be accelerated by the inorganic binder.

  For example, it is assumed that an inorganic binder mainly composed of water glass (sodium silicate) is used as the inorganic binder, and an organic binder mainly composed of a phenol resin and a polyisocyanate compound is used as the organic binder.

  In general, in molding with a foundry sand using an organic binder, the urethane reaction between a phenol resin and a polyisocyanate compound is accelerated by aeration of an amine gas such as triethylamine after filling the molding sand with a molding die. The organic binder is cured.

  Here, the urethanization reaction between the phenol resin and the polyisocyanate compound is promoted as long as it activates the carbon of the isocyanate in the polyisocyanate compound without using the amine gas. Examples of the substance that activates the carbon of the isocyanate include a hydroxyl group. In the water glass, a hydroxyl group generated by the reaction of sodium ions with moisture in the air exists. That is, since the hydroxyl group remains in the recycled sand to which the inorganic binder is adhered, the curing of the organic binder is promoted when the recycled sand is kneaded with the organic binder.

  If hardening of the organic binder is promoted before filling the molding sand with reclaimed sand into the mold, the fluidity of the molding sand will be reduced, and the filling rate of the molding sand into the mold will deteriorate. Or, after the mold is filled, the curing accelerating gas supplied to the mold does not sufficiently act, and the strength of the mold formed using the recycled sand does not satisfy the desired strength. Therefore, when making a combination sand mold, it becomes impossible to use reclaimed sand regenerated from foundry sand using an inorganic binder.

  In order to avoid such a problem, in the method for reclaiming foundry sand described in Patent Document 1, the foundry sand collected from a mold or core molded using an inorganic binder is polished to form the foundry sand. Although the process of removing the inorganic binder as an adhering binder is performed, there is a possibility that the inorganic binder on the surface of the foundry sand cannot be removed only by polishing.

  The present invention has been made in view of such points, and the object is to cure the organic binder when the regenerated sand regenerated from the foundry sand using the inorganic binder and the organic binder are kneaded. When molding a sand mold that combines a mold molded with foundry sand using an organic binder and a mold molded with foundry sand using an inorganic binder, it is regenerated from the foundry sand using an inorganic binder. It is to make available recycled sand available.

In order to solve the above-mentioned problems, the present invention is obtained by crushing a sand mold formed by combining a mold made of foundry sand using an organic binder and a mold made of foundry sand using an inorganic binder. A polishing process for polishing the foundry sand, and a roasting process for roasting the foundry sand, wherein the organic binder is mainly composed of a phenol resin and a polyisocyanate compound. The inorganic binder is an inorganic binder mainly composed of water glass. In the roasting step, the foundry sand using the inorganic binder is roasted at a first roasting temperature, and the first binder is used. roasting temperature is an sodium temperature above the boiling point of the inorganic binder, when obtained by kneading the casting sand and the organic binder with the inorganic binder after the roasting step, the Machine binder is at a temperature above the temperature which is not cured, and the things.

  According to this, when the foundry sand after the roasting step and the organic binder are kneaded, the foundry sand is roasted at the first roasting temperature which is a temperature higher than the temperature at which the organic binder is not cured. Thus, it is possible to avoid curing of the organic binder when the organic binder and the regenerated sand (cast sand after roasting) are kneaded.

It is assumed that an inorganic binder mainly composed of water glass (sodium silicate) is used as the inorganic binder, and an organic binder mainly composed of a phenol resin and a polyisocyanate compound is used as the organic binder. In this case, if the first roasting temperature to the temperature on sodium boiling Ten以, since the sodium in the inorganic binder is evaporated, the concentration of sodium ions decreases. As a result, it is possible to prevent sodium ions from reacting with moisture in the air to generate hydroxyl groups, and the reaction between the hydroxyl groups and the organic binder is avoided, so that when the recycled sand and the organic binder are mixed, Curing of the organic binder can be avoided. As a result, foundry sand using an inorganic binder can be used as recycled sand. Further, if the first roasting temperature is set to a temperature equal to or higher than the temperature at which sodium and silicic acid are dissolved, a solid solution of sodium and silicic acid is generated, so that sodium becomes inactive and the concentration of sodium ions decreases. . Even in this case, generation of hydroxyl groups can be prevented and curing of the organic binder can be avoided, so that when the combination sand mold is formed, the regenerated sand regenerated from the foundry sand using the inorganic binder can be used. .

  In one embodiment of the method for reclaiming foundry sand, the first roasting temperature is desirably a temperature of 900 ° C. or higher.

  That is, when the first roasting temperature is set to 900 ° C. or more, at least when an inorganic binder mainly composed of water glass is used as the inorganic binder, the organic binder and the regenerated sand (cast sand after roasting) ) Can be avoided from being cured.

  In the method for reclaiming foundry sand, the roasting step includes the first roasting step of roasting the foundry sand using the organic binder at a second roasting temperature lower than the first roasting temperature; It is desirable to include a second roasting step of roasting foundry sand using an inorganic binder at the first roasting temperature.

  That is, the casting sand using the inorganic binder needs to be treated so that the organic binder does not harden, but the casting sand using the organic binder does not need to be specially treated. Therefore, the foundry sand using the organic binder is roasted at the second roasting temperature lower than the first roasting temperature in the first roasting step, and the foundry sand using the inorganic binder is second roasted. By performing the baking at the first roasting temperature in the baking step, the cost for roasting the foundry sand at the first roasting temperature can be reduced.

  In the method for reclaiming foundry sand, the mold preferably includes one or more cores, and the foundry sand using the inorganic binder is preferably used for the core.

  That is, in general, an inorganic binder is more expensive than an organic binder, but by using casting sand using an inorganic binder as a core, a core for forming a water jacket for a cylinder block, etc. Only molds that require high strength can be made with foundry sand using an inorganic binder. Thereby, the manufacturing cost of a casting_mold | template can be reduced.

  As described above, the method for reclaiming foundry sand according to the present invention includes a polishing step for polishing the foundry sand and a roasting step for roasting the foundry sand, and an inorganic binder is used in the roasting step. Since the foundry sand is roasted at the first roasting temperature, the first roasting temperature is equal to or higher than the temperature at which the organic binder is not hardened when the foundry sand after the roasting step and the organic binder are kneaded. Further, the curing of the organic binder when the regenerated sand regenerated from the casting mold made of the foundry sand using the inorganic binder and the organic binder is kneaded is avoided. As a result, when a sand mold was formed by combining a mold molded with foundry sand using an organic binder and a mold molded with foundry sand using an inorganic binder, it was regenerated from the foundry sand using an inorganic binder. Recycled sand can be used.

It is a flowchart which shows each process of casting including the reproduction | regeneration method of the foundry sand which concerns on embodiment of this invention. It is a flowchart which shows each process of the reproduction | regeneration method of foundry sand. It is a figure for demonstrating the hardening mechanism of the organic binder by amine gas. It is a figure for demonstrating the hardening mechanism of the organic binder by an inorganic binder. The relationship between the roasting temperature in the second roasting step and the sodium ion concentration of the second foundry sand after roasting, and the second foundry sand roasted at the roasting temperature and the roasting temperature in the second roasting step It is a graph which shows the relationship with the intensity | strength of the core shape | molded with the foundry sand using.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a flowchart showing each process of casting including a method for reclaiming foundry sand according to an embodiment of the present invention. In this embodiment, the flowchart when manufacturing a cylinder block is shown as an example.

  In order to manufacture the cylinder block, first, a sand mold used for casting is formed in steps S101 to S104 and steps S105 to S108. In the present embodiment, the sand mold is formed with a casting mold using an organic binder (hereinafter referred to as a first casting sand) and a casting sand (hereinafter referred to as a second casting sand) using an inorganic binder. A sand mold (hereinafter referred to as a combined sand mold) formed by combining with a mold. In the present embodiment, the second foundry sand is used only for a core (hereinafter referred to as a WJ core) for forming a water jacket among a plurality of cores included in the mold, and the first foundry sand is , Used for molds other than WJ core.

  In this embodiment, an inorganic binder mainly composed of water glass (sodium silicate) is used as the inorganic binder, and an organic binder mainly composed of a phenol resin and a polyisocyanate compound is used as the organic binder. The phenol resin is phenol, novolak or a resin derived from these which requires a benzyl ether group in its molecule. Examples of the polyisocyanate compound include diphenylmethane diisocyanate, hexamethylene diisocyanate, and 4,4′-dicyclohexylmethane diisocyanate. In the following description, the term “inorganic binder” simply means an inorganic binder mainly composed of water glass, and the term “organic binder” simply refers to an organic compound mainly composed of a phenol resin and a polyisocyanate compound. It means a binder.

  The molding of the WJ core will be specifically described. First, in step S101, sand and an inorganic binder are kneaded. Thereby, the surface of sand is covered with an inorganic binder, and the 2nd foundry sand is generated. At this time, the sand is silica sand, chromite sand, zircon sand, olivine sand, synthetic mullite sand, alumina aggregate particles, and the like, and may be natural sand or artificial sand. In the next step S102, the second foundry sand is filled into a cavity of a molding die formed from a water jacket of a cylinder block. After filling, in step S103, air having a temperature that does not vitrify the water glass is passed through the mold to dry the inorganic binder. By drying, excess water in the inorganic binder is removed, and the sands are bonded together by the inorganic binder. Thereby, the WJ core is formed. In step S104, the mold is removed and the WJ core is taken out.

  On the other hand, molds other than the WJ core are formed by the cold box method, particularly the amine cold box method. Specifically, first, in step S105, sand and an organic binder are kneaded. Thereby, the surface of the sand is covered with the organic binder, and the first foundry sand is generated. In the next step S106, the first foundry sand is filled into the mold cavity. After filling, in step S107, the amine gas as the catalyst gas is passed between the foundry sands filled. As will be described in detail later, by passing an amine gas, the urethanization reaction between the phenol resin and the polyisocyanate compound proceeds to produce a urethane resin. Thereby, the organic binder is cured and a mold other than the WJ core is formed. In step S108, the mold is removed and a mold other than the WJ core is taken out. As the amine gas, triethylamine, dimethylethylamine, diisopropylamine or the like is used.

  Next, in step S109, a pouring of aluminum alloy or the like is poured into a combination sand mold in which the molds formed in steps S101 to S104 and steps S105 to S108 are combined, and a cylinder block is cast.

  After casting the cylinder block, in step S110, the cast cylinder block is cooled together with the mold.

  After cooling, first sand removal is performed in step S111. The first sanding is performed by applying vibration to the mold from the outside and crushing the mold. In the first sand removal, the foundry sand used for the mold other than the WJ core, that is, the first foundry sand is removed. In general, a mold (in this embodiment, WJ core) molded with foundry sand using an inorganic binder is cast in a mold sand (in this embodiment, other than WJ core) using an organic binder. The strength is higher than that of the mold. Therefore, sanding can be selectively performed on the mold other than the WJ core by applying a vibration having such a strength that the mold other than the WJ core is crushed and the WJ core is not crushed.

  After the first sanding is completed, the foundry sand crushed by the first sanding is recovered in step S112. The foundry sand recovered in step S112 is subjected to a regeneration process in a regeneration step (S115) described later.

  Next, in step S113, second sanding is performed. The second sanding is performed by applying vibration to the WJ core from the outside and crushing the WJ core. Thereby, the sanding out of the second foundry sand is completed. After this step S113, the cylinder blocks that have completed the first and second sanding are collected.

  After the second sanding is completed, the foundry sand crushed by the second sanding is recovered in step S114. The foundry sand collected in step S114 is subjected to a regeneration process in a regeneration step (S115) described later.

  After the collection of each foundry sand is completed, a regeneration process is executed in step S115 to regenerate each foundry sand. Details of the regeneration process in step S115 will be described later.

  The foundry sand regenerated by the regeneration process is stored as reclaimed sand and reused to form the next combination sand mold.

  Next, the reproduction process in step S115 will be described in detail with reference to the flowchart of FIG.

  In the regeneration process, first, in step S201, the first roasting process is executed. In the first roasting step, the foundry sand recovered in step S112 is roasted at the second roasting temperature by a known roasting furnace. Most of the foundry sand roasted in the first roasting step is the first foundry sand. The second roasting temperature is lower than a first roasting temperature described later, and is, for example, about 700 ° C. By roasting the first foundry sand at the second roasting temperature, the organic binder attached to the first foundry sand is burned and burned out. Thereby, the sand of the state which the organic binder has not adhered remains after baking.

  Next, in Step S202, the second foundry sand that has been mixed in the first foundry sand during the first sand removal (Step S111) and the foundry sand recovery (Step S112) is collected. In the first sanding, sanding is performed by vibrations that are strong enough to prevent the WJ core from being crushed, but during the first sanding, a strong load is applied to a part of the WJ core. , A part of the WJ core may be crushed. Therefore, the second foundry sand may be mixed in the foundry sand collected in step S112, and it is necessary to collect the second foundry sand. Here, since the water glass which is the main component of the inorganic binder does not burn out at about 700 ° C., the second foundry sand remains in a state where the foundry sand is bonded to each other even after the first roasting step. That is, the diameter of the second foundry sand after the first roasting step is larger than the diameter of the first foundry sand. Therefore, by using a sieve formed with holes smaller than the diameter of the second foundry sand and larger than the diameter of the first foundry sand, the foundry sand after the first roasting step is sieved, so that the second Foundry sand can be recovered.

  After collecting the second foundry sand, in step S203, the first foundry sand after the first roasting step from which the second foundry sand has been removed is collected.

  Next, a polishing process is performed in step S204. In the polishing process, the second foundry sand collected in steps S114 and S202 is polished by a known polishing machine. By this polishing process, a part of the inorganic binder adhering to the surface of the second foundry sand is scraped off.

  After the polishing is completed, a second roasting process is executed in step S205. In the second roasting step, the polished second foundry sand is roasted at a first roasting temperature by a known roasting furnace.

  After the second roasting process, in step S206, the second foundry sand after the second roasting process is collected.

  In step S203 and step S206, the recovered first and second foundry sands are stored as recycled sand as described above, and are reused to form the next mold.

  Here, when the second foundry sand is regenerated and used as reclaimed sand, if the inorganic binder remains on the surface of the reclaimed sand, when the reclaimed sand is mixed with the organic binder, May cure.

  A mechanism for curing the organic binder will be described with reference to FIGS.

  FIG. 3 shows a mechanism in which the organic binder is cured by the amine gas shown in step S107 of FIG. As described above, in the present embodiment, the organic binder is an organic binder mainly composed of a phenol resin and a polyisocyanate compound. At this time, the carbon of the isocyanate in the polyisocyanate compound has a relatively positive polarity because oxygen and nitrogen, which have higher electronegativity than carbon, are bonded at an angle. When the amine gas is introduced here, the nitrogen in the amine gas has a relatively negative polarity, so the nitrogen in the polyisocyanate compound is activated by the nitrogen in the amine gas, and the carbon and nitrogen of the isocyanate are activated. One of the double bonds is released. Thereafter, the carbon and nitrogen are bonded to a methylol group in the phenol resin, and a urethane resin is generated by this bond. As a result, the organic binder is cured.

  As described above, the organic binder mainly composed of a phenol resin and a polyisocyanate compound is cured by activating the urethanization reaction by activating the isocyanate carbon in the polyisocyanate compound by the amine gas. That is, even if it is something other than amine gas, if it activates the carbon of isocyanate and accelerates the reaction to release one of the double bonds of carbon and nitrogen, it is a phenol resin. The organic binder can be cured by promoting the urethanization reaction between the polyisocyanate compound and the polyisocyanate compound.

  FIG. 4 shows the mechanism by which the organic binder is cured by the inorganic binder. As described above, in this embodiment, the inorganic binder is an inorganic binder mainly composed of water glass. Water glass has deliquescence, and sodium in the water glass reacts with moisture in the air to generate hydroxyl groups as shown in the following chemical formula.

2Na + + 2H2O → 2Na + + 2OH- + H2
That is, hydroxyl groups are generated on the surface of the regenerated sand where the inorganic binder remains, by the reaction of the above chemical formula. Since the hydroxyl group has a negative polarity, when the regenerated sand having the hydroxyl group generated on the surface is kneaded with the organic binder, as shown in FIG. 4, the hydroxyl group plays the role of a catalyst instead of amine gas. Carbon is activated, and one of the double bonds of carbon and nitrogen is released. Thereby, the urethanation reaction of a phenol resin and a polyisocyanate compound is accelerated | stimulated, and hardening of an organic binder is accelerated | stimulated.

  As described above, when the inorganic binder remains on the surface of the regenerated sand and thereby a hydroxyl group is generated, curing of the organic binder is promoted when the regenerated sand and the organic binder are kneaded. If the hardening of the organic binder is promoted before filling the molding sand with reclaimed sand into the mold, the fluidity of the molding sand will decrease and the sand filling rate into the mold will deteriorate. After filling the mold, the amine gas supplied to the mold does not sufficiently act, and the strength of the molded mold does not satisfy the desired strength. Therefore, unless the hydroxyl group is generated on the surface of the reclaimed sand, the reclaimed sand regenerated from the foundry sand using the inorganic binder (that is, the second foundry sand) cannot be used when forming the combination sand mold.

  Therefore, in the present embodiment, the first roasting temperature in the second roasting step for roasting the second foundry sand is set to be the regeneration from the second foundry sand after the second roasting step, that is, the second foundry sand. When the sand and the organic binder are kneaded, the temperature is higher than the temperature at which the organic binder is not hardened, specifically 900 ° C. or higher so as not to generate hydroxyl groups on the surface of the regenerated sand.

  When the first roasting temperature is set to 900 ° C. or higher, the roasting temperature exceeds the boiling point of sodium, so that sodium sublimates and the concentration of sodium ions in the inorganic binder decreases. When the concentration of sodium ions decreases, the reaction shown by the above chemical formula becomes difficult to occur, and the concentration of hydroxyl groups decreases. Therefore, the urethanization reaction between the phenol resin and the polyisocyanate compound is hardly promoted. Thereby, hardening of the organic binder at the time of knead | mixing the reproduction | regeneration sand and organic binder reproduced | regenerated from the 2nd foundry sand is suppressed.

  Further, by setting the first roasting temperature to 900 ° C. or higher, a part of sodium is dissolved in silicic acid in the inorganic binder, and a solid solution of sodium and silicic acid is formed. When a solid solution is formed, sodium becomes inactive and does not ionize, so the concentration of sodium ions in the inorganic binder decreases. As a result, the reaction represented by the above chemical formula is less likely to occur, and the concentration of the hydroxyl group is lowered. Therefore, the urethanization reaction between the phenol resin and the polyisocyanate compound is suppressed, and the regenerated sand regenerated from the second foundry sand and Curing of the organic binder when kneaded with the organic binder is suppressed.

  As described above, by setting the first roasting temperature to a temperature of 900 ° C. or higher, the curing of the organic binder when the recycled sand and the organic binder are kneaded is suppressed. The recycled sand regenerated from the second foundry sand can be used.

  Note that if the roasting temperature is higher than 1200 ° C, the sand constituting the foundry sand may be burned out. Therefore, the first roasting temperature is desirably 900 ° C or higher and 1200 ° C or lower.

  Next, the effect when the first roasting temperature is actually set to 900 ° C. or higher will be described with reference to FIG.

  FIG. 5 shows the relationship between the roasting temperature in the second roasting step and the concentration of sodium ions in the second foundry sand after roasting, and the roasting temperature and the roasting temperature in the second roasting step. The relationship with the intensity | strength of the core shape | molded with the foundry sand using the made 2nd foundry sand is shown. At this time, the core is molded from foundry sand obtained by kneading regenerated sand regenerated from the second foundry sand and an organic binder. In FIG. 5, the broken line graph is a graph representing the sodium ion concentration of the second foundry sand after roasting, and the bar graph represents the strength of the core formed from the regenerated sand regenerated from the second foundry sand. It is a graph to represent, and the line shown with a broken line in a graph is a line showing the standard intensity | strength of core intensity | strength. In the bar graph, the white graph represents the strength of the core immediately after molding, and the hatched graph represents the strength of the core after one hour has passed since molding (hereinafter referred to as strength after 1 hr). Further, in FIG. 5, the bar graph shown on the rightmost side represents the strength of a core formed with fresh sand (cast sand before recycling) as a comparative example. In addition, about the reproduction | regeneration sand roasted at the roasting temperature between 700 degreeC and 800 degreeC, since the intensity | strength of a core was not measured, it is not illustrated. In addition, the core made of reclaimed sand roasted at 700 ° C. is not shown because the strength has decreased to such an extent that it cannot be measured.

  According to the sodium ion concentration graph of FIG. 5, as the roasting temperature is increased from 700 ° C. to 900 ° C., the concentration of sodium ions in the reclaimed sand decreases, and at 900 ° C., the concentration is almost zero. I understand. As described above, this is because sodium sublimates or sodium is dissolved in silicic acid. In addition, even if the baking temperature is slightly increased from 700 ° C., the concentration of sodium ions is reduced because of the temperature distribution in the baking furnace, for example, near the heat source in the baking furnace, This is because the roasting temperature may exceed the boiling point of sodium.

  Further, according to the core strength graph of FIG. 5, when the sintering temperature is increased from 800 ° C. to 900 ° C., the strength immediately after molding and the strength after 1 hr increase, and when the roasting temperature is 900 ° C., fresh sand It can be seen that the strength of the core molded with This is because as a result of the decrease in the sodium ion concentration, the generation of hydroxyl groups is suppressed, and the curing of the organic binder when the regenerated sand regenerated from the second foundry sand and the organic binder are kneaded is suppressed. Further, according to the core strength graph of FIG. 5, when the roasting temperature is 900 ° C., the strength immediately after molding and the strength after 1 hr satisfy the core strength standard, while the roasting temperature is 800 In the case of ° C., it can be seen that the strength immediately after molding meets the strength standard, but the strength after 1 hr does not meet the strength standard. That is, when water glass is used as the inorganic binder, if the first roasting temperature is set to 900 ° C. or higher, the core strength standard is satisfied. It shows that the recycled sand can be used.

  Therefore, in this embodiment, it includes a polishing step for polishing the second foundry sand and a roasting step for roasting the first and second foundry sands, and the second foundry sand is roasted at the first roasting temperature. The first roasting temperature is not less than the temperature at which the organic binder is not hardened when the second foundry sand after the roasting step and the organic binder are kneaded, and thus is regenerated from the second foundry sand. Curing of the organic binder when the recycled sand and the organic binder are kneaded can be avoided. As a result, when the combination sand mold is formed, the regenerated sand regenerated from the second foundry sand can be used.

  The present invention is not limited to the embodiment described above, and can be substituted without departing from the spirit of the claims.

  For example, in the present embodiment, only the second foundry sand is polished in the polishing step. However, the present invention is not limited to this, and all of the first foundry sand and the second foundry sand may be polished.

  Further, in the present embodiment, the roasting process is performed in two steps, the first roasting process and the second roasting process. However, the present invention is not limited to this, and the roasting process is performed only once. It may be. At this time, all of the first foundry sand and the second foundry sand are roasted at the first roasting temperature.

  Furthermore, in the present embodiment, only the WJ core is molded with casting sand using an inorganic binder. However, the present invention is not limited to this, and all the cores are molded with casting sand using an inorganic binder. May be.

  The above-described embodiments are merely examples, and the scope of the present invention should not be interpreted in a limited manner. The scope of the present invention is defined by the scope of the claims, and all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

  The present invention is useful as a method for reclaiming foundry sand using an inorganic binder.

Claims (4)

A method for reclaiming foundry sand obtained by crushing a sand mold formed by combining a mold molded with foundry sand using an organic binder and a mold molded with foundry sand using an inorganic binder,
A polishing step for polishing the foundry sand;
A roasting step of roasting the foundry sand,
The organic binder is an organic binder mainly composed of a phenol resin and a polyisocyanate compound,
The inorganic binder is an inorganic binder mainly composed of water glass,
In the roasting step, the foundry sand using the inorganic binder is roasted at a first roasting temperature,
The first roasting temperature is a temperature equal to or higher than the boiling point of sodium in the inorganic binder, and when the foundry sand using the inorganic binder after the roasting step and the organic binder are kneaded, A method for reclaiming foundry sand, wherein the temperature is equal to or higher than a temperature at which the organic binder is not cured. The method for reclaiming foundry sand according to claim 1,
The first roasting temperature is a temperature of 900 ° C. or higher.
A method for reclaiming foundry sand. The method for reclaiming foundry sand according to claim 1 or 2,
The roasting step is a first roasting step of roasting the foundry sand using the organic binder at a second roasting temperature lower than the first roasting temperature;
A second roasting step of roasting the foundry sand using the inorganic binder at the first roasting temperature.
A method for reclaiming foundry sand. In the reproduction method of foundry sand as described in any one of Claims 1-3,
The mold includes one or more cores,
Foundry sand using the inorganic binder is used in the core.
A method for reclaiming foundry sand.

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