Sand shape separation method, sand shape separation apparatus, and recycled sand production method

Abstract

To properly separate mixed sand.SOLUTION: The spherical sand and the deformed sand are separated by using a shape separation device equipped with an inclined belt conveyor part, a sand supply part, a side recovery part for recovering the sand on the belt side, and a downstream recovery part for recovering the sand at the downstream end in the belt moving direction. A step of circulating the belt at a predetermined inclination angle and a predetermined movement speed, supplying sand from the sand supply part, and acquiring an area of the sand occupying a region on the belt as a sand area occupancy ratio in a state where the region is viewed from the opposite direction, a step of changing a supply amount of the sand so that the sand area occupancy ratio falls within a predetermined range, collecting the sand in the side collecting part and the downstream collecting part, and obtaining an average circularity and a collection rate of the sand collected in the side collecting part, when the reference average circularity or the reference recovery rate is not satisfied, the spherical sand and the deformed sand are separated from each other by a step of repeating the treatment at a different inclination angle and / or a different supply amount, and a step of performing shape separation by operating the shape separation device under a condition that both are satisfied.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a sand shape separation method, a sand shape separation device, and a method for producing recycled sand, which are used to obtain sand containing spherical sand at a rate equal to or greater than a standard from a sand mixture containing spherical sand and irregularly shaped sand other than spherical sand. [Background technology]

[0002] In the foundry industry, one of the molding methods for making casting molds is the shell molding method, in which resin-coated sand (also known as RCS) is filled into a preheated metal mold and allowed to harden to create a mold.

[0003] RCS contains sand as aggregate and a binder. The inventors have developed a spherical aggregate primarily composed of synthetic mullite to achieve quality superior to that of natural silica sand as an aggregate suitable for RCS (see, for example, Patent Document 1). This aggregate is known as artificial sand. The artificial sand described in Patent Document 1 is spherical and has a small surface area per unit volume, making it less susceptible to breakage or thermal cracks due to contact between foundry sand particles, and is therefore able to maintain its original properties. Therefore, it has the characteristic of being easy to recycle. Furthermore, although not foundry sand, a method for separating hydraulic composition particles such as cement or cement clinker and aggregate particles such as sand or gravel mixed therewith by shape is known, which uses an inclined belt conveyor to perform shape separation, i.e., a shape separation method using an inclined belt conveyor (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-251434 [Patent Document 2] Japanese Patent Application Publication No. 07-000920 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, various types of artificial sand have been developed in the foundry industry in addition to the artificial sand described in Patent Document 1. Businesses that use foundry molds mix various types of sand, including artificial sand, depending on the purpose. As a result, the waste foundry sand after use contains multiple types of sand with different shapes. If specific types of sand could be separated from these, it could be possible to reuse the artificial sand. One known method for shape separation is to use an inclined belt conveyor. However, as mentioned above, the types and proportions of sand contained in waste foundry sand vary, making it difficult to predict their characteristics. On the other hand, shape separation devices using inclined belt conveyors have many parameters related to separation performance, such as the inclination angle of the belt conveyor, the belt movement speed, and the supply amount of objects to be shape-separated. It is not easy to appropriately set these parameters for objects whose characteristics cannot be predicted. The present invention has been made under these circumstances, and provides a method for determining the operating parameters of an inclined belt conveyor type shape separation device so that mixed sand containing sand of various shapes, such as foundry waste sand, can be properly separated and shape separation can be performed. [Means for solving the problem]

[0006] The inventors analyzed the desirable behavior of sand on the belt when using an inclined belt conveyor-type shape separator to separate sand with a standard average circularity or greater. They found that the recovery rate of sand with a standard average circularity or greater that falls to the side of the belt and the sand area occupancy rate on the belt are indicators related to achieving this. They discovered that by obtaining this recovery rate and sand area occupancy rate, it is possible to appropriately set the operating parameters of the shape separator, leading to the present invention. By determining the operating parameters using the recovery rate and sand area occupancy rate of sand with a standard average circularity or greater, spherical sand with a standard average circularity or greater can be efficiently separated from irregularly shaped sand other than spherical sand.

[0007] The present invention provides A method for separating spherical sand and irregularly shaped sand using a shape separation device comprising an inclined belt conveyor section inclined in the width direction of the belt, a sand supply section that supplies sand to the inclined belt conveyor section, a side recovery section that recovers sand that falls to the side in the width direction of the belt, and a downstream recovery section that recovers sand that falls at the downstream end of the belt's moving direction, the method comprising the steps of: rotating the belt at a predetermined inclination angle and a predetermined moving speed; supplying sand from the sand supply section; and, while viewing an area on the belt opposite to the belt, obtaining the area of ​​sand that occupies the area as a sand area occupancy rate; changing the amount of sand supplied per hour so that the sand area occupancy rate falls within a predetermined range; and, while the sand area occupancy rate falls within the predetermined range, recovering sand in the side recovery section and the downstream recovery section; and, and a recovery rate representing the proportion of sand recovered in the side recovery section, and confirming whether the criteria that the average circularity is equal to or greater than a reference average circularity and the recovery rate is equal to or greater than a reference recovery rate are satisfied; a reacquisition step, if the criteria are not satisfied, of rotating the belt with settings relating to the inclination angle, the moving speed, and the supply amount, in which at least one of the inclination angle and the supply amount is changed, and reacquiring the sand area occupancy rate to confirm that it is within the predetermined range; a step, if the sand area occupancy rate acquired in the reacquisition step is within the predetermined range, of executing the confirmation step with the settings at the time when the reacquisition step was executed, and if the criteria are not satisfied, repeating the process from the reacquisition step; and a step, operating the shape separator with the settings in which the criteria are satisfied, to perform shape separation.

[0008] The present invention also provides A method for producing recycled spherical sand and recycled irregularly shaped sand by separating spherical sand and irregularly shaped sand using a shape separator including an inclined belt conveyor section inclined in the width direction of the belt, a sand supply section that supplies sand to the inclined belt conveyor section, a side collection section that collects sand that falls to the side in the width direction of the belt, and a downstream collection section that collects sand that falls at the downstream end of the belt in the moving direction, the method comprising the steps of: rotating the belt at a predetermined inclination angle and a predetermined moving speed; supplying sand from the sand supply section; and, while viewing an area on the belt opposite to the belt, obtaining the area of ​​sand that occupies the area as a sand area occupancy rate; changing the amount of sand supplied per hour so that the sand area occupancy rate falls within a predetermined range; and, while the sand area occupancy rate falls within the predetermined range, collecting sand at the side collection section and the downstream collection section; and, and a step of determining a recovery rate, which indicates the proportion of sand recovered in the side recovery section, to determine whether the average circularity is equal to or greater than a reference average circularity and the recovery rate is equal to or greater than a reference recovery rate, and if the criteria are not satisfied, a step of reacquiring the sand area occupancy rate again to verify that it is within the predetermined range, by rotating the belt with settings related to the inclination angle, the moving speed, and the supply amount, but changing at least one of the inclination angle and the supply amount, if any; a step of executing the confirmation step with the settings used when the reacquisition step was executed if the sand area occupancy rate obtained in the reacquisition step is within the predetermined range, and repeating the process from the reacquisition step if the criteria are not satisfied; and a step of operating the shape separator with settings that satisfy the criteria to perform shape separation.

[0009] The present invention also provides A sand shape separation device is provided, which includes an inclined belt conveyor section inclined in the width direction of the belt, an inclination angle adjustment mechanism for adjusting the angle of the inclination, a belt drive section for moving the belt, a speed adjustment section for adjusting the moving speed of the belt, a sand supply section for supplying sand containing a mixture of spherical sand and irregularly shaped sand to the inclined belt conveyor section, a supply amount adjustment section for adjusting the amount of sand supplied per hour by the sand supply section, a side recovery section for recovering sand that falls to the side in the width direction of the belt, a downstream recovery section for recovering sand that falls at the downstream end in the moving direction of the belt, and a device for calculating the area occupied by sand in a region on the belt based on an image taken by a device facing the region and imaging the sand in the region. [Effects of the Invention]

[0010] According to the present invention, the operating parameters of the inclined belt conveyor type shape separator can be determined, and mixed sand containing sand of various shapes can be appropriately separated by shape. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a perspective view showing an example of the configuration of a shape separation device used in a shape separation method according to the present invention. [Figure 2] FIG. 2 is a perspective view showing the behavior of sand when shape separation of mixed sand is performed using the shape separation device shown in FIG. [Figure 3] FIG. 3 is a perspective view showing a shape separation device having the same configuration as in FIGS. 1 and 2 except that the number of sections in the spherical sand collection tank is one. [Figure 4] 10 is a graph showing the relationship between the sand area occupancy rate and the spherical sand recovery rate in Example 2. [Figure 5] 1 is a graph showing the fraction recovery rate for each fraction in Examples 3 to 3-2. [Figure 6] 1 is a graph showing the average particle size for each section of Examples 3 to 3-2. [Figure 7] 1 is a graph showing the average circularity for each section of Examples 3 to 3-2. [Figure 8] 1 is a graph showing the fraction recovery rate for each fraction in Examples 4 to 4-5. [Figure 9] 1 is a graph showing the fraction recovery rate for each fraction in Examples 4-2, 4-4, and 4-5. DETAILED DESCRIPTION OF THE INVENTION

[0012] An embodiment of the present invention will be described with reference to the drawings. (shape separation device) An example of a shape separator used in the sand shape separation method of the present invention will be described. Figure 1 is a perspective view showing an example of the configuration of a shape separator used in the sand shape separation method of the present invention. As shown in Figure 1, the shape separator 10 includes an inclined belt conveyor unit 11, an inclination angle adjustment mechanism 12, a belt drive unit 13, a speed adjustment unit 14, a sand supply unit 15, a supply amount adjustment unit 16, a recovery unit 17, and an imaging device 18.

[0013] The inclined belt conveyor section 11 includes an upstream roller 11U, a downstream roller 11L, and a belt 11B stretched between them and movable in the direction M indicated by the unidirectional arrow in FIG. 1 . In the examples of the present application described below, the belt conveyor uses an Escon Mini SZV30 manufactured by Sanki Engineering Co., Ltd. The belt 11B is an endless belt inclined in the width direction W of the belt 11B relative to the horizontal plane by an inclination angle adjustment mechanism 12. Mixed sand is dropped onto the surface of the belt 11B from the sand supply section 15, and the mixed sand is allowed to roll on the surface of the belt 11B, thereby enabling shape separation of the mixed sand. Here, mixed sand refers to sand containing a mixture of spherical sand and irregularly shaped sand other than spherical sand. In this specification, spherical sand refers to sand with an average circularity of 0.9 to 1.0, and irregularly shaped sand refers to sand with an average circularity of less than 0.9. The average circularity is the average circularity of the sand, as described in detail below. Examples of spherical sand include spherical artificial sand, irregularly shaped sand whose edges have been rounded off by a mechanical reclaimer such as a reclaimer, and original irregularly shaped sand whose edges have been rounded off through repeated use. In this specification, the sand supplied to belt 11B by sand supply unit 15 is also referred to as original sand. The material of belt 11B is not particularly limited, but may be, for example, rubber, plastic, cloth, metal, alloy, etc., and in this embodiment, polyurethane. The surface material of belt 11B may be the same as or different from that of belt 11B. The surface material of belt 11B may be, for example, rubber, plastic, cloth, metal, alloy, etc., and in this embodiment, polyurethane, the same as the belt. If the surface of belt 11B is made of a material with a low coefficient of friction, sand will roll easily on the surface of belt 11B. If the surface coefficient of friction of belt 11B is high, sand will roll more slowly on the surface of belt 11B. Therefore, the belt surface material must also be taken into consideration when determining the travel speed, inclination angle, and sand supply rate, as described below. The belt 11B is driven by a belt driving unit 13, which will be described later.

[0014] The tilt angle adjustment mechanism 12 tilts the belt 11B in the width direction W by lifting one side of the belt 11B in the direction indicated by the double-headed arrow in FIG. 1 (hereinafter referred to as the width direction W of the belt 11B), which is perpendicular to the substantially horizontal movement direction M of the belt 11B. The tilt angle adjustment mechanism 12 includes a support that can be extended and retracted vertically and fixed at any position, and is installed so that the belt 11B can be tilted without interfering with the movement in the movement direction M. The tilt angle (hereinafter referred to as the tilt angle) is expressed as the angle (°) of the upper surface of the belt 11B of the inclined belt conveyor unit 11 in the width direction W of the belt 11B relative to the horizontal plane. The tilt angle can be appropriately selected so that the average circularity of the sand collected in the spherical sand collection tank is 0.9 or more. For example, the tilt angle is 1° or more and less than 20°, preferably 1 to 18°, more preferably 1 to 16°, and particularly preferably 10 to 16°. If the inclination angle is less than 1°, the spherical sand will roll slowly along the belt surface, and may not fall off the lower side of the belt 11B inclined in the width direction W (hereinafter simply referred to as the side of the belt 11B or the belt side) before reaching the downstream end of the moving direction. On the other hand, if the inclination angle is 20° or more, in addition to the spherical sand, much of the irregularly shaped sand may roll along the belt surface and fall off the side of the belt. In either case, it may not be possible to properly separate the spherical sand from the irregularly shaped sand.

[0015] The belt drive unit 13 includes a motor as a drive source and a mechanism for transmitting the motor's driving force to the downstream roller 11L. In the example shown in FIG. 1, the belt drive unit 13 transmits the motor's driving force to the downstream roller 11L via a belt, but the driving force may also be transmitted to the upstream roller 11U. Alternatively, the belt drive unit 13 may drive a drive pulley provided separately from the downstream roller 11L and the upstream roller 11U. By supplying driving force to the roller or drive pulley, the circumferential surface of the belt 11B stretched between the rollers can be moved in the movement direction M. The belt drive unit 13 may be located anywhere as long as it can supply driving force to the roller or drive pulley. For example, as shown in FIG. 1, the belt drive unit 13 is located adjacent to the downstream roller 11L.

[0016] The speed adjustment unit 14 is a circuit that adjusts the rotational speed of the motor of the belt drive unit 13. In the example shown in FIG. 1, the speed adjustment unit 14 is a control circuit that controls the motor of the belt drive unit 13, and by controlling the rotational speed of the motor, the movement speed of the belt 11B can be set and adjusted. The movement speed of the belt 11B can be selected as appropriate, as long as it is within a range that prevents irregularly shaped sand contained in the sand supplied to the inclined belt conveyor from falling to the side of the belt. In this case, by applying a movement speed within a range that prevents irregularly shaped sand contained in the sand supplied to the inclined belt conveyor from falling to the side of the belt, it is possible to achieve a desirable sand behavior on the belt, where spherical sand is collected in the side collection section and irregularly shaped sand is collected in the downstream collection section. Here, "irregularly shaped sand not falling to the side of the belt" means that irregularly shaped sand does not fall in an amount that would cause the average circularity of the mixed sand collected in the side collection section to be less than 0.9. The specific moving speed of the belt 11B is, for example, 50 m / min or less, preferably 10 to 50 m / min, more preferably 15 to 40 m / min, even more preferably 20 to 40 m / min, and particularly preferably 25 to 40 m / min. By using a moving speed of 50 m / min or less, which prevents irregularly shaped sand contained in the sand supplied to the inclined belt conveyor from falling to the side of the belt, the sand is recovered in the side collection section and the irregularly shaped sand is recovered in the downstream collection section, achieving a favorable sand behavior on the belt. Furthermore, at moving speeds exceeding 50 m / min, depending on the inclination angle and supply rate, much of the irregularly shaped sand may roll and fall to the side of the belt in addition to the spherical sand, potentially resulting in an average circularity of the sand in the side collection section falling below 0.9. On the other hand, at moving speeds below 10 m / min, depending on the inclination angle and supply rate, sand may accumulate on the belt surface, preventing the spherical sand from rolling to the side of the belt, resulting in a low spherical sand recovery rate.

[0017] The sand supply unit 15 is located above the belt 11B near the upstream roller 11U in the direction of movement M. The sand supply unit 15 shown in FIG. 1 is a vibrating feeder equipped with a trough 15T. The trough 15T is composed of a base end member 15B and a terminal end member 15S. The base end member 15B has a rectangular bottom surface (base end bottom surface) and side walls surrounding the base end bottom surface on three sides, with the long sides of the base end bottom surface aligned with the width direction of the belt 11B. The side walls of the base end member 15B rise from the two long sides of the base end bottom surface and the short side of the belt 11B on the higher side (the side opposite the belt side) that is inclined in the width direction W. The terminal end member 15S has a right-angled triangular bottom surface (terminal end bottom surface) with a side wall on one side of the upstream end of the belt 11B. One of the two sides of the bottom of the terminal end portion, which sandwiches the right angle, is connected to the short side of the bottom of the base end portion that has no sidewall, connecting the bottom of the base end portion to the bottom of the terminal end portion. The other side of the bottom of the terminal end portion runs along the width direction of the belt 11B and is connected to the long side of the upstream end of the bottom of the base end portion, and the side wall of the terminal end member 15S is connected to the upstream side wall of the side wall of the base end member 15B. The remaining side of the bottom of the terminal end portion is located above the belt 11B and forms the tip end portion 11F of the trough 15T. The tip end portion 11F corresponds to the portion of the belt 11B that slopes in the width direction W, extending from near the high end to near the low end (to the side of the belt) and has no sidewall. A supply port (not shown in FIG. 1) is provided above the base end member 15B. Mixed sand falls from the supply port onto the base end member 15B, supplying the mixed sand to the base end member 15B of the trough 15T.

[0018] The mixed sand supplied to the base end member 15B of the trough 15T is transported from the base end member 15B to the terminal end member 15S by vibrations applied to the trough 15T by the supply rate adjuster 16, and then falls from the tip end 15F onto the belt 11B. The sand supply unit 15 can supply a predetermined amount of mixed sand per unit time to the surface of the belt 11B. While the sand supply unit 15 is a vibrating feeder in Figure 1, any device capable of supplying a constant amount of sand to the surface of the belt 11B is not limited to a vibrating feeder. For example, a slide gate or screw feeder may be used. When the sand supply unit 15 is a vibrating feeder as shown in Figure 1, the mixed sand can be dispersed over a wide area and dropped onto the belt 11B from the tip end 11F, which has a predetermined length in the width direction of the belt 11B. Dispersing the mixed sand allows the spherical and irregularly shaped sand that fall onto the belt 11B to behave according to their respective shapes.

[0019] The supply rate adjustment unit 16 applies vibration to the trough 15T. By changing the frequency of the vibration applied at a constant amplitude, it is possible to adjust the amount of mixed sand that falls per unit time (supply rate) as it is transported from the base end member 15B to the tip end 15F and falls onto the belt 11B. The most upstream position of the tip end 15F in the movement direction M corresponds approximately to the position (upstream end) where the upstream roller 11U of the inclined belt conveyor unit 11 is located.

[0020] The collection section 17 includes a spherical sand collection tank 17R provided on the side of the belt 11B along the moving direction M of the belt 11B, and an irregular-shaped sand collection tank 17V provided at the downstream end of the moving direction M. The spherical sand collection tank 17R corresponds to the side collection section, and the irregular-shaped sand collection tank 17V corresponds to the downstream collection section.

[0021] The spherical sand collection tank 17R may be a collection tank without any compartments, as shown in Figure 3, or a collection tank divided into two or more compartments along the moving direction M of the belt 11B, as shown in Figures 1 and 2. Note that Figure 3 shows the shape separation device 10 with the same configuration as Figures 1 and 2, except that the spherical sand collection tank 17R has only one compartment. The spherical sand collection tank 17R collects the spherical sand that rolls easily among the mixed sand that falls from the tip end 15F of the sand supply unit 15 onto the belt 11B due to the inclination of the belt 11B and falls from the side of the belt, i.e., collects sand with high roundness. If the spherical sand collection tank 17R has multiple compartments, the number can be set appropriately based on the size of the inclined belt conveyor unit 11, taking into account accuracy and efficiency. The number of compartments can be, for example, 2 or more, 4 or more, 6 or more, 8 or more, 10 or more, or 15 or more. Furthermore, the area of ​​belt 11B corresponding to one section (hereinafter also referred to as the belt portion area) is, for example, 50% or less, 25% or less, 20% or less, 15% or less, or 10% or less of the outer peripheral area of ​​belt 11B.

[0022] The irregular-shaped sand collection tank 17V has one collection tank. This irregular-shaped sand collection tank 17V is a collection tank that collects sand that has remained on the surface of the belt 11B, which is inclined in the width direction, without rolling to the side of the belt and has been transported to the downstream end of the belt 11B in the moving direction M, i.e., a collection tank that collects sand with low circularity. The spherical sand collection tank 17R of the shape separation device 10 is provided to collect spherical sand, and the irregular-shaped sand collection tank 17V is provided to collect irregular-shaped sand. The shape of the irregular-shaped sand collection tank 17V is not limited as long as it can collect sand that has fallen from the downstream end of the moving direction of the belt 11B.

[0023] The imaging device fixing portion 18F provides a means for fixing the imaging device 18 at a position facing the belt 11B, allowing the imaging device 18 to capture an image of an imaging area 18A on the belt 11B. The imaging device fixing portion 18F may be movable so that the imaging position of the imaging device 18 can be changed, or may be fixed. The imaging device 18 may be any device capable of capturing images, and in this embodiment, is a camera. The imaging area 18A is an area in which the imaging device 18 captures an image of the belt 11B facing it. The imaging area 18A may be an area that includes at least one of the locus LU and the locus LL shown in FIG. 2 in the width direction W of the belt 11B, or may be an area closer to the center in the width direction than the locus LU and the locus LL. The imaging area 18A may be an area of ​​any size with the midpoint between the upstream and downstream ends of the belt 11B in the moving direction M as the center of the imaging area, or may be a series of areas including the area of ​​the belt 11B corresponding to the section where the highest recovery rate was obtained in the moving direction M, with that section or one or more sections on the downstream end side of the moving direction M, with that section being the upstream end (starting end) of the imaging area 18A. In a still image obtained by imaging the imaging area 18A with the imaging device 18, the ratio (occupancy rate) of the area occupied by mixed sand to the area of ​​the imaging area 18A is called the sand area occupancy rate.

[0024] The method for measuring the sand area occupancy is not limited as long as it can calculate the area occupied by mixed sand relative to the area of ​​the imaged region 18A for which the sand area occupancy is to be calculated. For example, the sand area occupancy can be calculated using a still image captured by a camera, or by applying Lidar (Light Detection and Ranging) technology. The area occupied by mixed sand can also be calculated automatically by applying image processing to the still image captured by image capture. The imaging device for measuring the sand area occupancy rate may have a resolution sufficient to recognize the outline of each individual mixed sand in the imaging area 18A. In the examples described below, the method used to obtain the sand area occupancy ratio is as follows: A camera is used to capture an image of a certain area on the belt. The captured image is then binarized using software attached to a digital microscope (Digital Microscope, VHX-600, Keyence Corporation). The area of ​​each particle in the binarized image is then calculated, and the ratio to the area of ​​the entire image is then calculated to obtain the sand area occupancy ratio.

[0025] The behavior of the mixed sand that has fallen onto the belt 11B will be described with reference to Figure 2. Figure 2 is a perspective view showing the behavior of the sand when shape separation of mixed sand is performed using the shape separator 10 shown in Figure 1. First, the belt 11B is made to travel in one direction at a travel speed within the above-mentioned range, and mixed sand containing a mixture of spherical sand and irregularly shaped sand is fed into the sand supply section 15. The sand supply section 15 drops a substantially constant amount of mixed sand onto the belt 11B per unit time. The drop position is near the upstream end of the inclined belt conveyor section 11 in the travel direction M, and the mixed sand is dropped in a dispersed manner over a range from the high side of the width direction W of the inclined belt 11B to the sides of the belt.

[0026] In this way, the spherical sand particles that fall onto the surface of the belt 11B tend to roll to the side of the belt due to the inclination of the belt 11B, and are collected in the spherical sand collection tank 17R. The spherical sand particles that fall from the tip 15F of the trough 15T near the side of the belt follow the trajectory T1 shown in Figure 2 and are collected in the spherical sand collection tank 17R near the upstream end. The spherical sand particles that fall near the high side of the width direction W follow the trajectory T2 shown in Figure 2 and are collected in the spherical sand collection tank 17R near the downstream end. The spherical sand particles that fall midway between the high side of the width direction W and the side of the belt, i.e., near the center, follow the trajectory T3 and are collected in the spherical sand collection tank 17R between the upstream and downstream ends.

[0027] With reference to Examples 3 to 3-2 described below, small-sized spherical sand has a harder time rolling than large-sized spherical sand, so it tends to be blocked by irregularly shaped sand on the belt 11B and take longer to be collected in the spherical sand collection tank 17R. This is thought to be because large-sized spherical sand has a larger mass than small-sized spherical sand, so it has a stronger tendency to roll toward the side of the belt, making it easier to avoid or pass over irregularly shaped sand on the belt 11B that does not try to roll toward the side of the belt. Therefore, large-sized spherical sand moves toward the side of the belt more quickly than small-sized spherical sand, and as a result, tends to be collected in the spherical sand collection tank 17R closer to the upstream end. Conversely, small-sized spherical sand has a smaller mass than large-sized spherical sand, so it is more difficult to avoid or pass over irregularly shaped sand on the belt 11B, so it takes longer to move toward the side of the belt and, as a result, tends to be collected in the spherical sand collection tank 17R closer to the downstream end.

[0028] On the other hand, of the mixed sand that falls onto the surface of belt 11B, irregularly shaped sand that is difficult to roll remains and is transported in the moving direction M, even if belt 11B is inclined. Of the irregularly shaped sand, sand that falls near the higher side of belt 11B, which is inclined in the width direction W, follows the trajectory LU shown in Figure 2, falls from the downstream end in the moving direction M, and is collected in irregularly shaped sand collection tank 17V. Sand that falls near the side of the belt follows the trajectory LL and is collected in irregularly shaped sand collection tank 17V. Irregularly shaped sand that falls near the center in the width direction W follows the trajectory LC and is collected in irregularly shaped sand collection tank 17V.

[0029] If the spherical sand collection tank 17R consists of one section, the range of a fixed imaging area 18A may be determined, and images may be taken to calculate the sand area occupancy rate. Here, the fixed imaging area 18A is, for example, an area in the width direction W that includes at least one of the trajectories LU and LL shown in FIG. 2, and is an area between 30% and 60% from the upstream end of the belt 11B in the movement direction M, where 100% is the total length from the upstream end to the downstream end. To calculate the sand area occupancy rate more accurately, the spherical sand collection tank 17R may be divided into multiple sections, and the range of the imaging area 18A may be determined accordingly.

[0030] If the spherical sand collection tank 17R consists of multiple sections, the collection rate (section collection rate) of each section can be calculated based on the total collection volume (mass of collected sand) of each section, and the section with the highest collection rate can be determined. The collection rate of each section can also be calculated from the collection volume of each section based on the mass of sand supplied to the sand supply unit. In this case, attaching a weight sensor to each spherical sand collection tank 17R allows automatic calculation of the collection rate of each section. The area of ​​the belt 11B corresponding to the section with the highest collection rate in the direction of movement M can be set to the upstream end (starting end) of the imaging area 18A, and images can be taken of a series of areas including that section, or one or more sections downstream of that section in the direction of movement M, to calculate the sand area occupancy rate. By capturing images of the section with the highest collection rate, or a series of target areas including that section, and one or more sections downstream of that section in the direction of movement M, it is possible to appropriately capture and evaluate the behavior of the mixed sand on the belt. The collection volume, rather than the collection rate, can also be used to determine the appropriate imaging area 18A.

[0031] The sand area occupancy is a parameter that indicates the degree of dispersion of the mixed sand on the belt 11B, excluding large-sized spherical sand. This is because the large-sized spherical sand is collected in the spherical sand collection tank 17R, which is located upstream of the maximum collection rate range, without being significantly affected by the irregularly shaped sand. After the large-sized spherical sand is collected, the sand area occupancy is determined as small to medium-sized spherical sand and irregularly shaped sand remaining on the belt surface. Small to medium-sized spherical sand is easily affected by the irregularly shaped sand, so it takes time for it to move to the side of the belt. Therefore, the sand area occupancy is related to the behavior of the spherical sand on the belt 11B downstream of the imaging area 18A. A suitable sand area occupancy is, for example, 0.9 to 30%, preferably 0.9 to 21%, and more preferably 0.9 to 12%. If the sand area occupancy rate is between 0.9% and 30%, the mixed sand can be properly separated into spherical sand and irregularly shaped sand. If the sand area occupancy rate is less than 0.9%, the amount of sand that can be collected per hour is small, and efficient shape separation may not be possible. On the other hand, if the sand area occupancy rate is more than 30%, the spherical sand will not roll along the belt surface due to the irregularly shaped sand blocking it, and most of the spherical sand will be collected in the irregularly shaped sand collection tank 17V, which may prevent separation of the spherical sand from the irregularly shaped sand.

[0032] An example of a mixed sand to be shape-separated using the shape separator 10 is recycled mixed sand. Recycled mixed sand is sand processed by roasting waste foundry sand and then processing it through a reclaimer process. To make a casting, a mold is made using sand, molten cast iron is poured into the mold, and after cooling, the mold is broken to remove the casting. Waste foundry sand is the sand from the broken mold. Waste foundry sand includes natural silica sand and artificial sand, and these sands are recycled as mold sand or for other uses. For example, by shape-separating the recycled mixed sand obtained from waste foundry sand, recycled spherical sand and recycled irregular-shaped sand can be recovered as recycled foundry sand. Using the recovered recycled foundry sand reduces the amount of new foundry sand required and ultimately reduces environmental impact. Therefore, it is significant to produce recycled spherical sand and recycled irregular-shaped sand from recycled mixed sand obtained by processing waste foundry sand. Spherical artificial sand is often used in applications requiring particularly high-quality foundry sand. If the artificial sand is magnetic, i.e., if it has the property of being attracted to a magnet, it may be subjected to magnetic separation as a pretreatment to separate it from non-magnetic natural silica sand. In this case, the recycled mixed sand to be subjected to shape separation is the recycled mixed sand after magnetic separation. However, the mixed sand to which the sand separation method of this invention is applied is not limited to recycled mixed sand. This sand shape separation method can also be applied to applications in which new foundry sand, whether artificial or natural, is separated into spherical sand and irregularly shaped sand.

[0033] The method for measuring circularity will be described. The method for measuring circularity in the examples is as follows. Sand collected in a spherical sand collection tank or an irregular-shaped sand collection tank is imaged using a digital microscope (digital microscope, VHX-600, Keyence Corporation), and the image is processed (binarized) using software attached to the digital microscope. The area and perimeter of the particles in the binarized image are measured to calculate circularity, and the circularity of each sand particle is averaged. The average circularity is determined through these procedures. Note that the series of processes may be automated to calculate the average circularity. The circularity is expressed by the following formula, and the closer the circularity is to 1, the closer it is to a perfect circle. Circularity = 4π x area of ​​sand in binarized image / (perimeter of sand in binarized image) 2 If multiple particles overlap, they must be excluded from the binarization. Since the shaded areas of particles with different shading cannot be recognized, only particles with clear outlines are measured as representative particles.

[0034] The supply rate of the sand supply unit 15 is, for example, 0.83 to 8.58 g / s, preferably 1.27 to 5.58 g / s, and more preferably 2.83 to 5.58 g / s. However, these values ​​are reference values ​​for the device used in the examples, in which the length of the belt surface in the moving direction is 1.5 m and the length in the width direction is 0.3 m. The present invention is not limited to these values. There is no limit to the supply rate as long as a certain mass of mixed sand can be supplied per unit time. Furthermore, the supply rate may be measured by a sensor, calculated by conversion from the vibration frequency, or automatically determined based on the measured sand area occupancy rate. In this embodiment, the vibration frequency for the above supply rate is 10 to 27 Hz, preferably 15 to 25 Hz, and more preferably 20 to 25 Hz.

[0035] The average circularity of the raw sand supplied by the sand supply unit 15 is, for example, 0.60 to 0.89, preferably 0.70 to 0.89, more preferably 0.75 to 0.89, and particularly preferably 0.80 to 0.89. If the average circularity of the raw sand is less than 0.60, the proportion of irregularly shaped sand may be too high, which may result in poor separation. In this specification, spherical sand is sand with an average circularity of 0.9 to 1.0, and therefore, if the average circularity of the raw sand is 0.9 or more, the object of the present invention has already been achieved. The proportion of spherical sand in the sand supplied by the sand supply unit 15 is, for example, 5 to 94%. Here, the standard recovery rate can be determined from the proportion of spherical sand contained in the sand supplied from the sand supply unit. For example, if a recovery rate of 80% or more is targeted, when the proportion of spherical sand in the sand supplied by the sand supply unit 15 is 5%, the standard recovery rate is 4%, which is the proportion of spherical sand 5% multiplied by the target lower limit of 80%, and when the proportion of spherical sand is 94%, the standard recovery rate is approximately 75%, which is the proportion of spherical sand 94% multiplied by the target lower limit of 80%.

[0036] The mixed sand collected in the spherical sand collection tank 17R rolls on the surface of the belt 11B inclined in the width direction W and falls from the side of the belt. It has a relatively high degree of circularity. The average circularity of the sand collected in the spherical sand collection tank 17R is, for example, 0.90 or more, 0.91 or more, 0.92 or more, 0.93 or more, 0.94 or more, or 0.95 or more. The reference average circularity is determined according to the purpose of shape separation. That is, it is determined based on the desired average circularity of the spherical sand. In this embodiment, it is 0.9 or more. Depending on the desired average circularity, other values, such as 0.85, may be used. The average particle size of the mixed sand collected in the spherical sand collection tank 17R is, for example, 0.1 to 0.5 mm, preferably 0.15 to 0.45 mm, and more preferably 0.18 to 0.40 mm. The method for calculating the average particle size in this embodiment is as follows. Images of mixed sand particles were captured using a digital microscope (Digital Microscope, VHX-600, Keyence Corporation), and the average particle size was calculated using the software provided with the digital microscope. Specifically, the average particle size was calculated by averaging the particle sizes of each sand particle obtained after binarization and excluding particle groups where multiple sand particles overlap. If the sand collected in the spherical sand collection tank 17R is shape-separated sand from recycled mixed sand processed from waste foundry sand, the collected sand from the spherical sand collection tank 17R contains a large amount of highly circular artificial sand. This sand is also called recycled spherical sand. This allows the waste foundry sand to be reused. This reduces the amount of new sand required and ultimately reduces environmental impact. If the raw sand supplied contains a large amount of highly circular sand, the amount of mixed sand collected in the spherical sand collection tank 17R will be larger.

[0037] A method for separating spherical sand and irregularly shaped sand using the shape separator 10 will be described. The inclination angle adjustment mechanism 12 is adjusted to a desired inclination angle, e.g., 16°, and the belt 11B is rotated at a desired moving speed, e.g., 38 m / min, to supply sand from the sand supply unit 15. The initial sand supply rate is set to, e.g., 5.0 g / s. If there is only one spherical sand collection tank 17R, the imaging area 18A may be determined as an area of ​​any size, with the midpoint between the upstream and downstream ends of the belt 11B in the moving direction M as the center of the imaging area. If there are multiple spherical sand collection tanks 17R, the imaging area may be determined as a series of areas including the belt 11B corresponding to the section with the highest recovery rate, either at the upstream end (starting end) of the imaging area 18A or between that section and one or more sections downstream in the moving direction M. The imaging area 18A is imaged while facing the belt 11B, and the area of ​​sand in the imaging area 18A is obtained as the sand area occupancy rate.

[0038] If the acquired sand area occupancy ratio is not within a preferred range, for example, 0.9 to 21.0%, the amount of sand supplied per hour is changed so that it falls within that range. If the acquired sand area occupancy ratio is within the range of, for example, 0.9 to 21.0%, but is not within a more preferred range, for example, 0.9 to 12%, the amount of sand supplied may be changed to bring it within the more preferred range.

[0039] The belt 11B is rotated to supply sand from the sand supply unit 15 with the inclination angle, movement speed, and supply rate set so that the sand area occupancy rate falls within a desired range, and the sand is collected into the spherical sand collection tank 17R and the irregular-shaped sand collection tank 17V. Images of the collected sand are then acquired using, for example, a digital microscope, and the images are processed (binarized) using software attached to the digital microscope. The area and perimeter of each particle in the binarized image are measured to calculate the circularity of the sand. The average circularity of each particle is then calculated by averaging the circularities of the collected sand. The percentage of sand collected in the spherical sand collection tank 17R is then calculated as the collection rate based on the amount of sand supplied from the sand supply unit 15. It is then confirmed whether the calculated average circularity is equal to or greater than a standard average circularity (e.g., 0.9) and whether the calculated collection rate is equal to or greater than a standard collection rate (e.g., 80%), satisfying these criteria. The process of calculating the average circularity of the recovered sand and checking whether it satisfies the standard for the average circularity, and calculating the recovery rate of the recovered sand and checking whether it satisfies the standard for the recovery rate, corresponds to the confirmation step. If the calculated average circularity meets the standard and the calculated recovery rate meets the standard, the shape separator 10 can be operated with the inclination angle, movement speed, and supply amount settings that meet the standard to perform shape separation.

[0040] On the other hand, if the calculated average circularity is less than the reference average circularity or the calculated recovery rate is less than the reference recovery rate, in other words, if at least one of the calculated average circularity or the calculated recovery rate does not meet the standard, at least one of the inclination angle or the supply rate is changed, and belt 11B is rotated at the same moving speed as when the sand area occupancy rate was previously obtained to supply sand from sand supply unit 15, the sand area occupancy rate is reacquired, and it is confirmed that the reacquired sand area occupancy rate is within the specified range. If at least one of the average circularity or the recovery rate does not meet the standard, the process of changing at least one of the inclination angle or the supply rate, reacquiring the sand area occupancy rate, and confirming that the reacquired sand area occupancy rate is within the specified range corresponds to the reacquisition step.

[0041] If the reacquired sand area occupation ratio falls within a desirable range, e.g., 0.9 to 21.0%, the belt 11B is rotated using the inclination angle, movement speed, and supply rate settings used when the sand area occupation ratio was reacquired, sand is supplied from the sand supply unit 15, and the average circularity and recovery rate of the recovered sand are calculated. It is then confirmed whether the calculated average circularity is equal to or greater than the reference average circularity, and whether the calculated recovery rate is equal to or greater than the reference recovery rate, satisfying both criteria. In other words, a confirmation step is performed using the inclination angle, movement speed, and supply rate settings used when the sand area occupation ratio was reacquired. If at least one of the calculated average circularity or recovery rate does not satisfy the criteria, at least one of the inclination angle or supply rate is changed, and the belt 11B is rotated at the same movement speed as when the sand area occupation ratio was previously acquired, sand is supplied from the sand supply unit 15, the sand area occupation ratio is reacquired, and the reacquired sand area occupation ratio is confirmed to be within the predetermined range. In other words, the above-mentioned reacquisition step is repeated. If both criteria are met, the shape separator 10 may be operated with the tilt angle, moving speed and supply amount set to meet the criteria to perform shape separation.

[0042] On the other hand, if the reacquired sand area occupancy ratio is not within a desirable range, for example, a range of 0.9 to 21.0%, the setting is changed to at least a different supply amount, belt 11B is rotated, sand is supplied from sand supply unit 15, and the sand area occupancy ratio is reacquired. The acquisition of the sand area occupancy ratio can be repeated with at least a different supply amount setting until the sand area occupancy ratio falls within the desirable range.

[0043] If the reacquired sand area occupation ratio is not within the desired range, and at least a different supply rate is set, the reacquired sand area occupation ratio falls within the desired range. Then, belt 11B is rotated at the tilt angle, movement speed, and supply rate settings, sand is supplied from sand supply unit 15, and the average circularity and recovery rate of the recovered sand are calculated. It is possible that at least one of the calculated average circularity or recovery rate does not meet the criteria. In this case, at least one of the tilt angle or supply rate is changed, and belt 11B is rotated at the same movement speed as when the sand area occupation ratio was previously acquired, sand is supplied from sand supply unit 15, and the sand area occupation ratio is again acquired, and it is confirmed that the reacquired sand area occupation ratio is within the specified range. In other words, the above-mentioned reacquisition step is repeated. Then, depending on the reacquired sand area occupancy ratio, either processing is performed when the reacquired sand area occupancy ratio is within the desirable range, or processing is performed when the reacquired sand area occupancy ratio is not within the desirable range.

[0044] If at least one of the average circularity and the recovery rate does not meet the standard, the setting of only one of the inclination angle and the supply rate may be changed, and then the standard for the average circularity and the recovery rate may be reconfirmed without re-obtaining the sand area occupancy rate. That is, if at least one of the average circularity and the recovery rate does not meet the standard, the belt 11B may be rotated with only one of the inclination angle and the supply rate changed, sand may be supplied from the sand supply unit 15, and the sand may be recovered. The average circularity and the recovery rate of the recovered sand may then be calculated to confirm whether they meet the standard without re-obtaining the sand area occupancy rate. If the standard is met, the shape separator 10 may be operated with the inclination angle, movement speed, and supply rate settings that meet the standard, and shape separation may be performed. If at least one of the average circularity and the recovery rate does not meet the standard even after changing only one of the inclination angle and the supply rate, the setting of only one of the inclination angle and the supply rate may be further changed. Then, the belt 11B may be rotated, sand may be supplied from the sand supply unit 15, and the sand may be recovered. Then, without re-obtaining the sand area occupancy ratio, the average circularity and recovery rate of the recovered sand are calculated to confirm whether they satisfy the criteria. In this way, if at least one of the average circularity or recovery rate does not satisfy the criteria, the shape separator 10 may be operated with a setting that changes only one of the inclination angle or the supply amount, and the average circularity and recovery rate of the recovered sand may be calculated without re-obtaining the sand area occupancy ratio to confirm whether they satisfy the criteria, and these processes may be repeated until the criteria are satisfied.

[0045] The process of not re-acquiring the sand area occupancy rate even when only the inclination angle or the supply rate is changed is preferably applied when the difference from the standard is small and it is expected that changing at least one of the inclination angle or the supply rate will result in the average circularity and recovery rate of the recovered sand meeting the standard. A case where it is expected that the standard will be met is when it is possible to predict, to some extent, from past data or experience, how the average circularity and recovery rate of the recovered sand will change when at least one of the inclination angle or the supply rate is changed. For example, this is the case when it is possible to predict how much the inclination angle should be reduced to increase the circularity to the standard circularity. Alternatively, it is possible to predict how much the inclination angle should be increased to increase the recovery rate to the standard recovery rate. Furthermore, this is the case when it is possible to predict how much the supply rate should be increased to increase the recovery rate to the standard recovery rate. However, for example, increasing the supply rate may result in poor dispersion of sand on the belt surface, depending on the belt speed, resulting in a decrease in the recovery rate contrary to prediction.

[0046] The mixed sand collected in the irregular-shaped sand collection tank 17V is sand with a relatively low circularity that falls from the downstream end of the inclined belt 11B in the direction of movement M without rolling on the surface of the belt 11B. The average circularity of the mixed sand collected in the irregular-shaped sand collection tank 17V is not subject to any specific standard, but is typically 0.80 to 0.85. If the mixed sand collected in the irregular-shaped sand collection tank 17V is recycled irregular-shaped sand that has been separated by shape from recycled mixed sand produced by treating waste foundry sand, specific sand with a low circularity will be collected. If the raw sand supplied contains a large amount of sand with a low circularity, the amount of mixed sand collected in the irregular-shaped sand collection tank 17V will also be large. [Example]

[0047] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0048] <Magnetic separation process> In this example, the spherical artificial sand contained in the waste foundry sand is magnetic. Therefore, as a pretreatment, the waste foundry sand was roasted and reclaimed to obtain 1,000 kg of recycled mixed sand. This was then magnetically separated using a magnetic separation treatment device (a counter-pole magnetic separator, model G-30+30, manufactured by Japan Magnetic Separation Co., Ltd.) to remove non-magnetic sand. Finally, 150 kg of magnetic sand was obtained as raw sand.

[0049] <Circularity analysis> The circularity of the resulting raw sand was measured using a digital microscope (VHX-600, Keyence Corporation) to capture images and calculate the circularity using the software provided with the digital microscope. The average circularity of the raw sand was 0.85. The maximum circularity of the raw sand was 0.96, and the minimum was 0.44.

[0050] <Elemental analysis> The obtained raw sand was subjected to elemental analysis using an analytical device (X-ray fluorescence analyzer, ZSX PRIMUS II, Rigaku Corporation), and the results are summarized in Table 1. [Table 1]

[0051] Example 1: Belt inclination angle and sand behavior As shown in Figure 3, a shape separator 10 equipped with a spherical sand collection tank 17R with one division was used. The inclination angle of the belt 11B relative to the horizontal plane in the width direction W was varied to five different values: 16°, 10°, 9°, 5°, and 1°. In each case, the belt 11B was moved in the direction M shown in Figure 1 at a speed of 38.3 m / min. 200 g of raw sand was fed into a vibrating feeder (compact electromagnetic feeder, CF-1, Sinfonia Technology Co., Ltd.) installed in the sand supply section 15, and the raw sand was dropped onto the surface of the belt 11B from the drop opening of the vibrating feeder at a rate of 2.83 g / s. The sand that fell from the side of the belt was collected in the spherical sand collection tank 17R, and the recovery rate and average circularity of the resulting sand were calculated. The results of Example 1 are summarized in Table 2. [Table 2]

[0052] The results in Table 2 indicate that the larger the inclination angle, the higher the spherical sand recovery rate. The recovery rates shown in Table 2 are the ratios of sand recovered in the spherical sand recovery tank 17R to the original sand. The original sand in Example 1 contained approximately 30% spherical artificial sand. The recovery rate exceeded 30% because the original sand contained rounded artificial sand that could not be detected by analytical equipment, in addition to the 30% artificial sand that could be detected by analytical equipment. On the other hand, the smaller the inclination angle, the higher the average circularity tended to be. This is thought to be because sand with higher circularity rolls on the belt surface even at small inclination angles. Furthermore, it was found that spherical sand with an average circularity of 0.9 or higher could be obtained when the inclination angle was between 1 and 16°. However, when the inclination angle was between 1 and 10°, the spherical sand did not move much on the belt 11B, resulting in a low spherical sand recovery rate of less than 10%, and productivity related to spherical sand recovery was not high. However, the average circularity of the sand recovered in the spherical sand recovery tank 17R was high. On the other hand, although not shown in Example 1, when the inclination angle was set to 20°, almost all of the sand fell from the side of the belt and into the spherical sand recovery tank 17R. A practical inclination angle is in the range of 1 to 16°, and when a higher recovery rate is desired, it is 10 to 16°. Based on the relationship between the spherical sand recovery rate and average circularity in Table 2, the experiment in Example 2 was conducted at an inclination angle of 16°, which provides a high spherical sand recovery rate and an average circularity greater than the boundary of 0.9.

[0053] Example 2 Relationship between sand area occupancy rate and recovery rate Using the shape separator 10 shown in Figure 3, the inclination angle of belt 11B relative to the horizontal in the width direction W was set to 16°, and the speed of belt 11B in the movement direction M was set to 27.0, 38.3, and 54.0 m / min. The sand supply rate of the sand supply section 15 was set to 0.83, 0.86, 1.27, 2.83, 5.59, 8.58, 9.46, and 14.46 g / s, respectively, and shape separation was performed. The starting point was 30 cm from the upstream end of belt 11B, and the ending point was 70 cm. The sand area occupancy, recovery rate, and average circularity of the sand collected in the spherical sand collection tank 17R were measured in a region excluding the top and bottom 10% of the belt in the width direction W. The results are shown in Table 3, and a graph plotted in Figure 4. In Figure 4, the X axis represents the sand area occupancy, and the Y axis represents the recovery rate.

[0054] [Table 3]

[0055] The recovery rate shown in Table 3 is the ratio of sand recovered to the original sand in the spherical sand recovery tank 17R. As shown in Figure 4, when the inclination angle is set to a constant value (16°) and the moving speed of belt 11B and the sand supply rate are varied, the sand area occupancy rate and the sand recovery rate in the spherical sand recovery tank 17R show a high correlation. Furthermore, a high recovery rate can be achieved when the sand area occupancy rate is low and the mixed sand on belt 11B is somewhat sparse. When the average circularity was calculated, it was confirmed that almost all spherical sand was 0.9 or higher. The only time the average circularity was less than 0.89 was when belt 11B was moved at the fastest speed of 54.0 m / min. In this case, it is believed that the irregularly shaped sand that fell onto the belt was easily pushed by the moving belt and rolled, tending to fall to the side of the belt. Therefore, the upper limit of the moving speed of belt 11B for obtaining spherical sand with an average circularity of 0.9 or more is 50 m / min, and the moving speed of belt 11B for obtaining spherical sand stably with a high recovery rate should be a little slower; in the examples in Table 3, 38.3 m / min or 27.0 m / min are preferable values. Table 3 shows that when the belt 11B moving speed is 27.0 to 38.3 m / min, the sand area occupation ratio for spherical sand with an average circularity of 0.9 or more is 0.9 to 31.2%, of which the sand area occupation ratio for a recovery rate of 5% or more is 0.9 to 21.0%, and the sand area occupation ratio for a recovery rate of 25% or more is 0.9 to 11.6%. Also, in Table 3, when the belt moving speed is 27.0 m / min and the sand supply rate is 14.46 g / s, the sand area occupation ratio is 31.2%, and the spherical sand recovery rate is 0.91%. It can be seen that when the sand area occupation ratio exceeds 30%, the spherical sand recovery rate drops to a low value of 0.91%, suggesting that most of the spherical sand was recovered in the irregular sand recovery tank 17V. Therefore, the sand area occupation ratio is considered to be the upper limit of 30%.

[0056] Example 3: Sand behavior as revealed by experiments using a divided spherical sand collection tank As shown in Figure 2, a shape separator 10 with a divided spherical sand collection tank 17R was used. The inclination angle of the belt 11B and its horizontal plane was set at 16°. The belt 11B was run at 27 m / min in the direction of movement M. 200 g of new raw sand was fed into a vibrating feeder (compact electromagnetic feeder, CF-1, Sinfonia Technology Co., Ltd.) installed in the sand supply section 15. The raw sand was then dropped onto the surface of the belt 11B from the tip 15F of the vibrating feeder at a feed rate of 2.83 g / s. The sand that fell from the sides of the belt was collected in the spherical sand collection tank 17R, which was divided into 15 equal sections. The recovery rate (section recovery rate) of each section of the resulting sand was calculated. In this example, the section recovery rate was the ratio of the yield of each section to the total amount of sections 1 to 15. The average circularity of each section of the resulting sand was also calculated. Furthermore, the average particle size of each sand section was calculated using software attached to the digital microscope (VHX-600, Keyence Corporation) and images of the sand particles were taken. Regarding the 15 sections, the spherical sand collection tank 17R closest to the upstream roller was assigned number 1, and the numbers were assigned consecutively in the belt movement direction M (hereinafter, the same applies when the spherical sand collection tank 17R is divided into 15 sections).

[0057] Example 3-1 The same procedure as in Example 3 was carried out except that the belt 11B was moved at 38.3 m / min in the moving direction M and the source sand was dropped onto the surface of the belt 11B at a supply rate of 5.59 g / s.

[0058] Example 3-2 The same procedure as in Example 3 was carried out except that the inclination angle between belt 11B and its horizontal plane was set to 10°, belt 11B was run at 38.3 m / min in the moving direction M, and the source sand was dropped onto the surface of belt 11B at a supply rate of 5.59 g / s. The only difference from Example 3-1 was the inclination angle.

[0059] The results of the division recovery rate, average circularity, and average particle size for Examples 3 to 3-2 are summarized in Tables 3-1 to 3-6 (the numbers in parentheses in the Examples represent (inclination angle (°) - belt speed (m / min) - sand supply amount (g / s)). The same applies below). In addition, a graph of each division and division recovery rate for Examples 3 to 3-2 is shown in Figure 5, a graph of the division and average particle size is shown in Figure 6, and a graph of the division and average circularity is shown in Figure 7.

[0060] [Table 3-1]

[0061] [Table 3-2]

[0062] [Table 3-3]

[0063] [Table 3-4]

[0064] [Table 3-5]

[0065] [Table 3-6]

[0066] Tables 3-1 and 3-2 and Figure 5 show that the location of the maximum sectional recovery rate in the 15-section spherical sand collection tank 17R varies depending on the sand supply rate, belt speed, and inclination angle. Specifically, the maximum sectional recovery rate is the third section in Example 3, the fourth section in Example 3-1, and the seventh and eighth sections in Example 3-2. When the inclination angle is small (10°), the sectional recovery rate tends to move from the upstream end to the side of the belt over time. Looking at the overall trend from the upstream end to the downstream end, the sectional recovery rate of the section closer to the downstream end of the belt 11B than the section with the maximum sectional recovery rate tends to decrease as the section approaches the downstream end. This is thought to be because there is less sand available to roll to the side of the belt at the downstream end of the belt 11B. When using multiple sections, the number of sections is not limited to 15. However, because too few sections results in a rough positioning of the imaging area 18A, a number of sections, for example, 10 or more, is preferable.

[0067] Next, referring to Tables 3-3, 3-4, and Figure 6, we found that the sand collected in the downstream section of belt 11B tended to have smaller average particle sizes than the sand collected in the upstream section. As described above, spherical sand with larger average particle sizes, i.e., heavier sand with larger mass, is collected in spherical sand collection tank 17R in the upstream section. Therefore, when heavy sand falls onto belt 11B, it tends to roll to the side of the belt before moving toward the downstream end. In other words, heavy sand is thought to be able to roll to the side of the belt quickly. On the other hand, spherical sand with smaller average particle sizes, i.e., lighter sand with smaller mass, is collected in spherical sand collection tank 17R at the downstream end. Therefore, lighter sand tends to take longer to roll to the side of the belt. Thus, by measuring the average particle size of the section from which spherical sand was collected, we can see that the trajectory of sand on the belt surface differs depending on the average particle size.

[0068] Furthermore, referring to Tables 3-5, 3-6, and Figure 7, it can be seen that the average circularity is almost constant regardless of the position of the division in the spherical sand collection tank. This is thought to indicate that as long as the inclination angle, belt speed, and sand supply rate are within certain ranges, the mixed sand can be separated into spherical sand and irregularly shaped sand regardless of the position of the division. Next, the inclination angle and moving speed of the belt 11B and the supply amount of the sand supply section 15 were changed to investigate the influence of these conditions on the sand area occupancy, recovery rate and division recovery rate.

[0069] Example 4: Effects of inclination angle, moving speed and supply amount on sand area occupancy rate, recovery rate and fractional recovery rate As in Example 3, using a shape separation device 10 having a partitioned spherical sand recovery tank 17R as shown in Figure 2, 200g of new original sand was added to a vibrating feeder (small electromagnetic feeder, CF-1, Symphonia Technology Co., Ltd.) installed in the sand supply section 15, and the original sand was dropped onto the surface of the belt 11B from the drop outlet of the vibrating feeder. The inclination angle of the belt 11B was set to 16°, the moving speed to 27 m / min, and the supply rate to 2.83 g / s. Sand that fell from the side of the belt was collected in the spherical sand collection tank 17R, which was divided into 15 equal sections. The recovery rate of each sand section (section recovery rate) and the amount of original sand supplied were used to calculate the yield of all sections of the spherical sand collection tank 17R as the spherical sand recovery rate. The average circularity of all sections of the spherical sand collection tank 17R was also calculated. Furthermore, an image of the imaging area 18A listed in Table 4 below was taken using a digital camera (EOS KISS X7, Canon Inc.), and the sand area occupancy rate of the captured image was calculated using the image processing software included with the Keyence Corporation VHX-600 digital microscope.

[0070] Example 4-1 The tilt angle was set to 16°, the moving speed to 38.3 m / min, and the feed rate to 2.83 g / s.

[0071] Example 4-2 The tilt angle was set to 16°, the moving speed to 38.3 m / min, and the feed rate to 5.59 g / s.

[0072] Example 4-3 The tilt angle was set to 10°, the moving speed to 38.3 m / min, and the feed rate to 2.83 g / s.

[0073] Example 4-4 The tilt angle was set to 10°, the moving speed to 27 m / min, and the feed rate to 5.59 g / s.

[0074] Examples 4-5 The tilt angle was set to 10°, the moving speed to 38.3 m / min, and the feed rate to 5.59 g / s.

[0075] The results of the imaging area 18A, inclination angle, moving speed, supply amount, recovery rate, sand area occupancy rate and average circularity for Examples 4 to 4-5 are summarized in Table 4, and the results of the classification recovery rates for Examples 4 to 4-5 are summarized in Table 5-1, Table 5-2, Figures 8 and 9.

[0076] [Table 4]

[0077] [Table 5-1]

[0078] [Table 5-2]

[0079] Table 4 shows that the average circularity remained unchanged regardless of the sand supply rate, belt speed, and inclination angle. This is thought to be because, within a certain range of inclination angle, spherical sand rolls on the belt surface, while irregularly shaped sand has difficulty rolling on the belt surface. The recovery rate of spherical sand was higher at an inclination angle of 16° than at an inclination angle of 10°. This is thought to be because, at an inclination angle of 10°, smaller spherical sand is blocked by the irregularly shaped sand and does not roll all the way to the side of the belt before reaching the downstream end. Furthermore, Tables 4, 5-1, 5-2, and Figure 8 show that for Examples 4 to 4-2, which had an inclination angle of 16°, the maximum sectional recovery rate was near section 3, while for Examples 4-3 to 4-5, which had an inclination angle of 10°, the maximum sectional recovery rate was in section 6. This suggests that when the recovery rate is high, the section where the maximum sectional recovery rate is obtained tends to be closer to the upstream end of the belt 11B. When the sand supply rate of the original sand was high, as in Examples 4-2, 4-4, and 4-5, the sand area occupancy rate was higher than in Examples 4, 4-1, and 4-3, at 4.00%, 6.01%, and 4.06%, respectively. This is thought to be because a large amount of sand is scattered on the belt surface when the sand supply rate is high, resulting in a large amount of mixed sand remaining on the belt surface. Furthermore, Tables 4, 5-1, 5-2, and Figure 9 show that the high sand area occupancy rate occurs regardless of the inclination angle at angles between 10 and 16°, i.e., regardless of the maximum spherical sand recovery position. Comparing Examples 4, 4-1, 4-4, and 4-5, the spherical sand recovery rate did not change significantly within the range of travel speeds of 27 to 38.3 m / min, even when the belt speed was changed. Furthermore, comparing Examples 4-1 and 4-2, the sand supply rate in Example 4-2 was approximately twice that of Example 4-1, and the spherical sand recovery rate in Example 4-2 was approximately 1.4 times higher than that in Example 4-1. However, when Examples 4-1 and 4-3 were compared, it was found that the recovery rate in Example 4-1 was more than twice that of Example 4-3, with only the angle being different.

[0080] From the above examples, the following can be said. To achieve proper shape separation using the inclined belt conveyor-type shape separator shown in Figures 1 to 3, spherical sand should be collected in the spherical sand collection tank 17R, and irregular-shaped sand other than spherical sand should be collected in the irregular-shaped sand collection tank 17V. To achieve this, the moving speed of the belt 11B should be set so that the irregular-shaped sand from the mixed sand that falls onto the belt 11B can move to the downstream end along the moving direction M as shown by the trajectories LU, LC, and LL in Figure 2 without rolling off the side of the belt. According to Example 2, this is 50 m / min or less. However, since a slower belt moving speed reduces the amount of sand that can be collected per unit time, the appropriate moving speed must be determined by balancing these two factors. One example of a preferred moving speed range is 25 to 40 m / min.

[0081] The preferred range of the supply amount varies depending on the size of the equipment (shape separator 10). The sand area occupancy rate can be used as an index for determining the supply amount. The preferred supply amount can be determined by setting this sand area occupancy rate to between 0.9% and 30%.

[0082] Furthermore, the results of Example 1 indicate that the greater the inclination angle of the belt 11B, the higher the spherical sand recovery rate. On the other hand, the smaller the inclination angle of the belt 11B, the higher the average circularity of the sand, i.e., the sand with a shape closer to a perfect sphere, tends to be recovered in the spherical sand recovery tank 17R. However, a small inclination angle of the belt results in a small amount of spherical sand being recovered per hour, i.e., low productivity of spherical sand. Therefore, the optimal inclination angle should be determined based on the balance between the average circularity of the recovered sand and the amount recovered per hour. However, since an inclination angle of 20° causes irregularly shaped sand to fall to the side of the belt in addition to the spherical sand, the inclination angle should be set to less than 20°. The optimal inclination angle is an angle at which sand with an average circularity of 0.9 or higher can be obtained in the spherical sand recovery tank. In this case, based on the results of Example 1, the practical inclination angle for separating spherical sand from irregularly shaped sand is in the range of 1 to 16°. An example of a preferred range, taking into account the balance with the amount recovered per hour, is 10 to 16°.

[0083] (1) When performing shape separation of sand using a shape separator with a fixed circumferential length and width of the belt 11B and a variable inclination angle, as shown in Figures 1 to 3, the inclination angle should be set to a value not exceeding the upper limit of the preferred conditions (e.g., 16° based on Example 1). The moving speed should also be set to a value not exceeding the upper limit of the preferred conditions (e.g., 50 m / min based on Example 2) that makes it difficult for irregularly shaped sand to roll. The supply amount from the sand supply unit 15 should be set so that, with an inclination angle of 16° or less and a moving speed of 50 m / min or less, the average circularity of the spherical sand collected in the spherical sand collection tank 17R is equal to or greater than the reference average circularity, and the collection rate is equal to or greater than the reference collection rate.

[0084] (2) When separating the original sand into shapes at a preferred range of inclination angle and travel speed, the amount of sand supplied by the sand supply unit 15 is set so that a predetermined range of sand area occupancy ratio (for example, 0.9 to 11.6% based on Example 2) is obtained. The imaging area 18A for obtaining the sand area occupancy ratio is preferably set to include the section with the largest recovery amount as the upstream end, or that section and one or more series of sections downstream of that section in the direction of travel. It is confirmed that shape separation that satisfies the standard average circularity and standard recovery rate is achieved at that inclination angle, travel speed, and supply amount.

[0085] (3) If shape separation that satisfies the standard average circularity and standard recovery rate is not achieved, the parameters to be adjusted can be determined based on findings from the examples. For example, if the sand collected in the spherical sand collection tank 17R satisfies the standard recovery rate but not the standard average circularity, the inclination angle can be set smaller. On the other hand, if the sand satisfies the standard average circularity but not the standard recovery rate, the inclination angle can be set larger. To improve the accuracy of parameter determination, a curve showing the recovery rate for each section under the specified conditions, as shown in the graph in Figure 5, can be plotted, and the main difference from the ideal curve that satisfies the standard average circularity and standard recovery rate can be determined to determine the parameters to be adjusted. For example, if it is determined that the section where the recovery rate peaks is too close to the downstream end of the belt 11B, the inclination angle can be set larger. This is because a small inclination angle tends to move the section where the recovery rate peaks closer to the downstream end.

[0086] (4) If the amount of sand collected in the first section near the downstream end is small, the percentage of sand collected in the spherical sand collection tank 17R (recovery rate) relative to the sand supplied from the sand supply unit 15 may also be low. This can be explained as follows: When the sand area occupancy rate is low, the spherical sand that rolls easily on the belt 11B falls almost entirely to the side of the belt upstream. Near the downstream end, less sand rolls to the side of the belt, and the spherical sand that is difficult to roll moves straight to the downstream end. This results in a low recovery rate. One method for increasing the recovery rate is to increase the inclination angle, but this is difficult to fine-tune. Increasing the sand supply rate within a desirable range can increase the number of rolling sand particles and increase the recovery rate. This is because a large supply rate tends to produce a gentler peak and a gentler base near the downstream end. In this way, fine-tuning the conditions can be performed to satisfy the standard average circularity and standard recovery rate. [Explanation of symbols]

[0087] 10: Shape separation device, 11: Inclined belt conveyor section, 11B: Belt, 11L: Downstream roller, 11U: Upstream roller, 12: Incline angle adjustment mechanism, 13: Belt drive section, 14: Speed ​​adjustment section, 15: Sand supply section, 15B: Base end member, 15F: Tip section, 15S: End member 15T: Trough, 16: Supply amount adjustment section, 17: Recovery section, 17R: Spherical sand recovery tank, 17V: Irregular shape sand recovery tank, 18: Imaging device, 18A: Imaging area, 18F: Imaging device fixing section

Claims

1. A method for separating spherical sand and irregularly shaped sand using a shape separator including an inclined belt conveyor section inclined in the width direction of the belt, a sand supply section that supplies sand to the inclined belt conveyor section, a side recovery section that recovers sand that falls to the side in the width direction of the belt, and a downstream recovery section that recovers sand that falls at the downstream end of the moving direction of the belt, A step of rotating the belt at a predetermined inclination angle and a predetermined moving speed, supplying sand from the sand supply unit, and obtaining the area of ​​sand occupying the area on the belt while viewing the area on the belt from opposite sides as a sand area occupancy rate; changing the amount of sand supplied per hour so that the sand area occupancy rate falls within a predetermined range; a confirmation step of recovering sand in the side recovery section and the downstream recovery section while the sand area occupancy rate is within a predetermined range, calculating the average circularity of the sand recovered in the side recovery section and the recovery rate representing the proportion of sand recovered in the side recovery section out of the sand supplied from the sand supply section, and confirming whether the criteria that the average circularity is equal to or greater than a standard average circularity and the recovery rate is equal to or greater than a standard recovery rate are satisfied; If the criteria are not satisfied, the belt is rotated with a different setting for at least one of the inclination angle, the moving speed, and the supply amount, and the sand area occupancy is reacquired to confirm that it is within the predetermined range. If the sand area occupancy rate acquired in the reacquisition step is within a predetermined range, the confirmation step is executed with the settings when the reacquisition step was executed, and if the criteria are not satisfied, the process is repeated from the reacquisition step; and operating the shape separator at a setting where the criteria are satisfied to perform shape separation.

2. 2. The shape separation method according to claim 1, wherein, if the criteria are not satisfied in the confirmation step, the re-acquisition step and the repeating step are not executed, and the confirmation step is executed with a setting that changes only one of the inclination angle or the supply amount among the settings related to the inclination angle, the movement speed, and the supply amount, and if the criteria are not satisfied, this step is repeated so that the criteria are satisfied without re-acquiring the sand area occupancy ratio.

3. 2. The shape separation method according to claim 1, further comprising the steps of: if the sand area occupancy ratio acquired in the reacquisition step is not within a predetermined range, changing at least the supply amount setting to bring the sand area occupancy ratio into the predetermined range; executing the confirmation step with the setting when the sand area occupancy ratio is within the predetermined range; and repeating the process from the reacquisition step if the criterion is not satisfied.

4. 2. The shape separation method according to claim 1, wherein the predetermined moving speed is a moving speed within a range in which irregularly shaped sand contained in the sand supplied to the inclined belt conveyor section does not fall to the side of the belt.

5. 2. The shape separation method according to claim 1, wherein the reference average circularity is determined according to the purpose of shape separation, and the reference recovery rate is determined according to the proportion of spherical sand contained in the sand.

6. 2. The shape separation method of claim 1, wherein the step of acquiring the sand area occupancy rate is a step of determining the section in which the maximum recovery rate is obtained in the lateral recovery section divided in the direction of movement of the belt, setting the section in which the maximum recovery rate is obtained or a series of areas including that section and one or more sections downstream of that section in the direction of movement as the target area, and acquiring the sand area occupancy rate using an image obtained by photographing the target area.

7. 2. The shape separation method according to claim 1, wherein the sand supplied from the sand supply unit is recycled mixed sand in which the spherical sand and the irregularly shaped sand are mixed.

8. 5. The shape separation method according to claim 4, wherein the moving speed within a range in which irregularly shaped sand contained in the sand supplied to the inclined belt conveyor does not fall to the side of the belt is 50 m / min or less.

9. 2. The shape separation method according to claim 1, wherein the predetermined range of the sand area occupancy is 0.9% or more and 30% or less.

10. 2. The shape separation method according to claim 1, wherein the tilt angle is 1 to 16 degrees with respect to the horizontal.

11. 2. The shape separation method according to claim 1, wherein the sand supply unit is a vibrating feeder having a trough, the trough having a base end to which sand is replenished and a tip end that supplies the replenished sand to the belt, and the tip end drops sand onto the belt from an end having a predetermined length in the width direction of the belt.

12. A method for producing recycled spherical sand and recycled irregular-shaped sand by separating spherical sand and irregular-shaped sand using a shape separator including an inclined belt conveyor section inclined in the width direction of the belt, a sand supply section that supplies sand to the inclined belt conveyor section, a side recovery section that recovers sand that falls to the side in the width direction of the belt, and a downstream recovery section that recovers sand that falls at the downstream end of the moving direction of the belt, A step of rotating the belt at a predetermined inclination angle and a predetermined moving speed, supplying sand from the sand supply unit, and obtaining the area of ​​sand occupying the area on the belt while viewing the area on the belt from opposite sides as a sand area occupancy rate; changing the amount of sand supplied per hour so that the sand area occupancy rate falls within a predetermined range; a confirmation step of recovering sand in the side recovery section and the downstream recovery section while the sand area occupancy rate is within a predetermined range, calculating the average circularity of the sand recovered in the side recovery section and the recovery rate representing the proportion of sand recovered in the side recovery section out of the sand supplied from the sand supply section, and confirming whether the criteria that the average circularity is equal to or greater than a standard average circularity and the recovery rate is equal to or greater than a standard recovery rate are satisfied; If the criteria are not satisfied, the belt is rotated with a different setting for at least one of the inclination angle, the moving speed, and the supply amount, and the sand area occupancy is reacquired to confirm that it is within the predetermined range. If the sand area occupancy rate acquired in the reacquisition step is within a predetermined range, the confirmation step is executed with the settings when the reacquisition step was executed, and if the criteria are not satisfied, the process is repeated from the reacquisition step; and operating said shape separator at a setting where said criteria are satisfied to perform shape separation.

13. A method for producing recycled spherical sand and recycled irregularly shaped sand as described in claim 12, wherein, if the criterion is not met in the confirmation step, the confirmation step is performed without performing the re-acquisition step and the repeating step, with only one of the settings related to the inclination angle, movement speed, and supply amount changed, namely, the inclination angle or the supply amount, and if the criterion is not met, this step is repeated so that the criterion is met without re-acquiring the sand area occupancy rate.

14. A method for producing recycled spherical sand and recycled irregularly shaped sand as described in claim 12, further comprising the steps of: if the sand area occupancy ratio acquired in the re-acquisition step is not within a predetermined range, changing at least the supply amount setting to bring the sand area occupancy ratio into the predetermined range; executing the confirmation step with the setting when the sand area occupancy ratio is within the predetermined range; and repeating the process from the re-acquisition step if the criterion is not satisfied.

15. an inclined belt conveyor portion inclined in the width direction of the belt; a tilt angle adjustment mechanism for adjusting the tilt angle; a belt drive unit that moves the belt; a speed adjusting unit that adjusts the moving speed of the belt; A sand supply unit that supplies sand containing a mixture of spherical sand and irregularly shaped sand to the inclined belt conveyor unit; a supply amount adjusting unit that adjusts the amount of sand supplied per hour by the sand supply unit; a side recovery section that recovers sand that falls to the side in the width direction of the belt; a downstream collecting section that collects sand falling at the downstream end of the belt in the moving direction; A sand shape separation device comprising: a device for determining the area occupied by sand in the area on the belt based on an image taken by a device facing the area and imaging the sand in the area.

Images