The present disclosure relates to a method of reusing core sand, for example, a method of reusing core sand in which water glass is used as a binder.
Japanese Patent Application Publication No. 2013-111602 (JP 2013-111602 A) discloses a method for forming a sand mold (core) in which water glass is used as a binder to prevent the production of gas from a core during casting.
In general, sand (core sand) for forming a core is reused. During the formation of a core for casting, core sand is mixed with a binder in order to make core sand grains adhere to each other. The core sand can be reused by collecting the core sand, which is not needed after casting, and removing impurities and the binder adhering to the core sand from the core sand.
However, regarding a core in which water glass is used as a binder, it is difficult to separate the core into core sand and water glass. In a case where a sand mold (core) is formed using core sand in which water glass remains, it is difficult to harden the core sand so as to have a sufficient strength. Therefore, a method of reusing core sand in which water glass is used as a binder has yet to be established.
The disclosure provides a method of reusing core sand capable of improving the strength of a core which is formed by reusing core sand in which water glass is used as a binder.
According to an aspect of the disclosure, there is provided a method of reusing core sand including: crushing a core used for casting into granules; heating the granules at a temperature of 300° C. to 550° C.; causing the heated granules to collide against each other such that water glass used as a binder detaches from the core sand; and blowing air into a mixture of the water glass and the core sand, which are detached from each other, such that the core sand is separated and collected from the mixture due to a difference in specific gravity between the water glass and the core sand.
According to the aspect, the granules obtained by crushing the core after casting are heated at a temperature of 300° C. to 550° C. Therefore, the water glass included in the granules is inactivated (modified so as not to inhibit the hardening of water glass during reuse), and the strength of a core formed reusing the core sand can be improved.
According to the aspect of the disclosure, the strength of a core, which is formed by reusing core sand in which water glass is used as a binder, can be improved.
Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:
Hereinafter, an embodiment of the disclosure will be described in detail with reference to the accompanying drawings. However, the disclosure is not limited to the following embodiment. In order to clarify the description, the following description and the drawings are appropriately simplified.
A method of reusing core sand according to the embodiment will be described. In the method of reusing core sand according to the embodiment, water glass is used as a binder. That is, in this method, core sand in which water glass is used as a binder is reused after forming a core using the core sand and using the core for aluminum casting at a casting temperature of 650° C. to 750° C.
Here, first, a mechanism in which the water glass used as the binder during the formation of the core is hardened will be described. Next, a mechanism in which water glass which has been used as a binder inhibits the hardening of water glass newly added as a binder will be described. Next, the method of reusing core sand in which water glass is used as a binder will be described.
Next, the kneaded mixture of the core sand 9, water, and the water glass 15 is put into a mold and fixed. As shown in
As shown in
Next, a mechanism in which the water glass 15 which has been used as a binder (hereinafter, referred to as “used water glass 15”) inhibits the hardening of the water glass 15 newly added as a binder (hereinafter, referred to as “new water glass 15”) will be described. Even when the core sand 9 is reused, water and the new water glass 15 are mixed with the core sand 9, and the mixture is kneaded. The core sand 9 includes the used water glass 15. The used water glass 15 loses its original adhesive force. Due to this reason, as described below, it is presumed that the used water glass 15 has sodium ions. When the core sand 9 including the used water glass 15, water, and the new water glass 15 are mixed with each other, the sodium ions are eluted from the used water glass 15 into water. The sodium ions eluted into water are substituted with hydrogen ions in the new water glass 15. The new water glass 15 has a structure represented by the following formula (3).
In the crushing step, for example, a crushing device 10 is used.
A lump of core is put into the chamber 11, and the rotor 13 swings due to the motor 12. Due to the swinging of the rotor 13, granules of the core collide against each other, or the rotor 13 collides against the core. As a result, the core is crushed. The granules 14 is sieved through the mesh 17 to have a grain size less than a pore size of the mesh 17. As a result, the core is crushed into the granules 14 having a grain size of 3 mm or less.
Next, in the heating step shown in Step S2 of
On the other hand, the active amount of the water glass 15 is obtained based on the amount of the water glass 15 eluted into water by dipping the core sand 9 in water. The active amount of the water glass 15 refers to the amount of active water glass 15. The active water glass 15 refers to water-soluble water glass 15. When dissolved in water, the water-soluble water glass 15 releases sodium ions. As described above, the sodium ions inhibit the hardening of the water glass 15 as a binder. Since the active water glass 15 is water-soluble, the active amount of the water glass 15 included in the core sand 9 can be measured.
As shown in
The remaining amount of the water glass 15 included in the core sand 9 after the crushing step is about 0.53%. The remaining amount includes the amount of the active water glass 15 (water-soluble water glass 15) and the amount of inactive water glass 15 (water-insoluble water glass 15). The active amount of the water glass 15 is about 0.51%. In this way, in a case where the core sand 9 includes the used water glass 15, most of the remaining water glass 15 is the active water glass 15.
In a case where the heating temperature is lower than 300° C., the active amount of the water glass 15 is larger than 0.20%. That is, in a case where the heating temperature is lower than 300° C., most of the water glass 15 remaining in the core sand 9 is the active water glass 15. In a case where the heating temperature is 300° C., the remaining amount of the water glass 15 is 0.43%, and the active amount thereof is 0.20%. Accordingly, the amount of the water-insoluble water glass 15 is 0.23%. In a case where the heating temperature is 350° C., the remaining amount of the water glass 15 is 0.52%, and the active amount thereof is 0.17% which is lower than 0.20%. Accordingly, the amount of the water-insoluble water glass 15 is 0.35%.
In a case where the heating temperatures are 400° C., 450° C., 500° C., and 550° C., the remaining amounts of the water glass 15 are 0.46%, 0.52%, 0.44%, and 0.67%, respectively. At all the heating temperatures, the active amounts are 0.12%, which is lower than 0.20%. Accordingly, the amounts of the water-insoluble water glass 15 are 0.34%, 0.40%, 0.32%, and 0.55%, respectively. In a case where the heating temperatures are 600° C. and 650° C., the remaining amounts of the water glass 15 are 0.44% and 0.45%. At all the heating temperatures, the active amounts are 0.06%, which are lower than 0.20%. Accordingly, the amounts of the water-insoluble water glass 15 are 0.38% and 0.39%, respectively.
By heating the granules 14 at a temperature of 300° C. or higher in the heating step, the amount of the water-soluble water glass 15 is adjusted to be smaller than the amount of the water-insoluble water glass 15 in the water glass 15 included in the granules 14. As a result, the inhibition of the hardening of the core sand 9 during reuse can be prevented.
As the amount of the water glass 15 eluted into water which is added during the formation of a core decreases, the strength of the formed core is improved. In a case where the core sand 9 is reused to form a core, the core has a predetermined strength only when the active amount of the water glass 15 included in the core sand 9 is 0.20% or lower. Accordingly, it is preferable that the heating temperature is 300° C. or higher in consideration of the active amount of the water glass 15 included in the core sand 9. In this way, in the heating step, the water glass 15 remaining in the core sand 9 is inactivated to obtain the water-insoluble water glass 15. Due to the heating, the amount of the water-soluble water glass 15 in the water glass 15 included in the granules is adjusted to be 0.2% or lower with respect to the amount of the granules. As a result, the strength of the core can be improved.
On the other hand, in a case where the heating temperature is higher than 550° C., the core sand 9 is solidified. The core sand 9 and the binder are solidified in the heating device, and thus the core sand 9 cannot be separated from the binder. Accordingly, it is preferable that the heating temperature in the heating step is 300° C. to 550° C.
In the heating step, for example, a heating device 20 is used.
The upper region of the fluid tank 21 is covered with, for example, an upper cover. The inside of the fluid tank 21 is divided by a partition so as to have a labyrinthine structure. For example, air flows through the inside of the fluid tank 21. As a result, a heating target in the fluid tank 21 flows from the inlet 22 to the outlet 23. The plural tube heaters 24 are inserted into the inside of the fluid tank 21 from above.
Each of the tube heaters 24 has a rod shape and has one end connected to a region of the fluid tank 21 near the bottom and the other end protruding from the upper cover of the fluid tank 21. The tube heaters 24 are disposed in the fluid tank 21 at regular intervals. The panel heaters 25 are provided on wall surfaces and the bottom surface of the fluid tank 21.
The core sand 9 as the granules 14 is put into the inlet 22 of the heating device 20. The granules 14 flow through the inside of the fluid tank 21, which is divided by the partition, along with flowing air. For example, air is caused to flow at a flow rate of 1100 L/min in the fluid tank 21. The granules 14 are uniformly heated by the tube heaters 24, which are disposed at regular intervals, and the panel heaters 25. Since the inside of the fluid tank 21 has a labyrinthine structure, the time during which the granules 14 remains in the fluid tank 21 is secured. Since the granules 14 flows along with air, the number of contacts between the granules 14 and impurities is reduced. After heating, the granules 14 is cooled to a polishing temperature of 100° C. or lower using an air-cooling heat exchange method.
Next, in the detaching step shown in Step S3, the heated granules 14 are caused to collide against each other such that the water glass 15 detaches from the core sand 9.
The granules 14 incorporated from the inlet 32 rotates in a vertical direction when the rotor 34 rotates. The rotating speed is 2200 rpm (frequency: 72.0 Hz). As shown in
Next, in the separation and collection step shown in Step S4, air is blown into a mixture of the water glass 15 and the core sand 9, which are detached from each other, such that the core sand 9 is separated and collected from the mixture due to a difference in specific gravity between the water glass 15 and the core sand 9.
The mixture of the water glass 15 and the core sand 9 is put into the chamber 41 through the inlet 42. The core sand 9 put into the chamber 41 is separated due to a difference in specific gravity by air blown from the air blowing port 44. The water glass 15 having a low specific gravity is blown to the air outlet port 45 along with the air, and the core sand 9 having a high specific gravity is blown to the outlet 43. As a result, the core sand 9 is separated and collected from the outlet 43.
In this way, by treating the used core sand 9 in the crushing step (Step S1), the heating step (Step S2), the detaching step (Step S3), and the separation and collection step (Step S4) in this order, the core sand 9 can be reused to form a core (Step S5). During the formation of a core, the core sand 9 is put into a mold and is solidified by heating to form a core. The heating temperature is, for example, a temperature lower than a casting temperature. As a result, the used core sand can be reused such that the formed core has the same strength as that of a core formed using new core sand.
Next, as shown in Step S6, the formed core is used for casting. For example, the core is used for aluminum casting at a casting temperature of 650° C. to 750° C. Next, as shown in Step S7, a post-treatment is performed. In the post-treatment, the used core is shaken off from a casting formed by casting. Next, in order to reuse the core sand 9, the crushing step of Step S1 is performed.
In the method of reusing core sand according to the embodiment, the granules obtained by crushing the core after casting are heated at a temperature of 300° C. to 550° C. Therefore, the water glass 15 included in the granules 14 is inactivated, and the strength of a core formed reusing the core sand can be improved.
Since even a core in which the water glass 15 is used as a binder can be reused, the manufacturing costs can be reduced.
In the crushing step, the core is crushed into the granules 14. As a result, in the heating step, the granules 14 can be uniformly heated. Further, in the detaching step, the water glass 15 can be uniformly detached from the core sand 9.
In the heating step, it is preferable that, due to the heating, the amount of the water-soluble water glass 15 is adjusted to be smaller than the amount of the water-insoluble water glass 15 in the water glass 15 included in the granules 14. In particular, it is preferable that the amount of the water-soluble water glass 15 is adjusted to be 0.2% or lower with respect to the amount of the granules 14. With the above-described configuration, the inhibition of the hardening of the water glass 15 by sodium ions can be reduced, and the strength of a core formed by reusing the core sand can be further improved.
In the heating step, the water glass 15 can be appropriately dried. As a result, the water glass 15 can be easily detached from the core sand 9. In the detaching step, not only the water-soluble water glass 15 but also the water-insoluble water glass 15 can be detached from the core sand 9. Therefore, in the separation and collection step, the amount of the used water glass 15 included in the core sand 9 can be reduced.
Hereinabove, the embodiment of the method of reusing the core sand 9 according to the disclosure has been described. However, the disclosure is not limited to the above-described configuration, and various modifications can be made.
For example, in the embodiment, the method of reusing core sand in which the water glass 15 is used as a binder has been described. However, this reuse method is applicable to not only sand used for forming a core but also sand used for casting.
Number | Date | Country | Kind |
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2015-205849 | Oct 2015 | JP | national |
This application is a Division of application Ser. No. 15/949,394 filed Apr. 10, 2018, which is allowed and claims the benefit of U.S. patent application Ser. No. 15/287,479, filed on Oct. 6, 2016, which is patented and claims priority to Japanese Patent Application No. 2015-205849, filed on Oct. 19, 2015. The disclosure of each of the prior applications is hereby incorporated by reference herein in its entirety.
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Number | Date | Country | |
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20200238367 A1 | Jul 2020 | US |
Number | Date | Country | |
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Parent | 15949394 | Apr 2018 | US |
Child | 16851274 | US |
Number | Date | Country | |
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Parent | 15287479 | Oct 2016 | US |
Child | 15949394 | US |