Sand washer with adjustable powder content and control method thereof

Abstract

The application discloses a sand washer with adjustable powder content, which comprises a barrel and a feeding mechanism; a conical sieve disc is detachably arranged in the inner cavity of the barrel below the feeding mechanism; a plurality of sieve holes are formed in the sieve disc, and the sieve holes are divided into at least three annular regions along the radial direction; the sieve hole diameters between adjacent annular regions increase in a stepped manner from the center to the edge; the barrel further comprises a rotating shaft at the center of the sieve disc; a support is arranged on the rotating shaft; a plurality of scrapers are uniformly distributed above the sieve disc in the circumferential direction; the lower edge of the scraper is in contact with or has a gap with the upper surface of the sieve disc; one end of the scraper is connected with the support; a driving motor is arranged below the sieve disc; the lower end of the rotating shaft extends downward, penetrates through the center of the sieve disc and is connected with the output shaft of the driving motor. The application has the advantages that the rising water flow speed can be controlled independently in different regions, the accurate closed-loop adjustment of the powder content of finished sand can be realized, the coarse sand cleaning time is prolonged, and the cleanliness of the finished sand is improved.

Description

Technical Field

[0001] This invention relates to the technical field of sand washing equipment for building material production, and particularly to a sand washing machine with adjustable powder content and its control method. Background Technology

[0002] Counter-current sand washing machines utilize rising water flow to clean and classify sand and gravel, offering advantages such as compact structure, low energy consumption, and high classification accuracy. However, existing counter-current sand washing machines have the following shortcomings: ① The particle size of the classified sand is fixed by the equipment structure (inclined tube height and angle), resulting in a fixed powder content in the finished sand. This makes it impossible to flexibly adjust the washing process according to the different requirements of downstream concrete production (e.g., C30 concrete requires 5%~7% powder content, while C50 and above require 3%~5% powder content). ② Insufficient cleaning of coarse sand: In traditional counter-current sand washing machines, coarse sand settles quickly, resulting in a short residence time in the washing chamber. The rising water flow has limited effect on scouring the clay on the surface of the coarse sand. For materials with high mud content and high viscosity, a mud film may remain on the surface of the coarse sand, leading to substandard cleanliness of the finished sand. Therefore, there is an urgent need for a counter-current sand washing machine that can adjust the powder content of the finished product online while simultaneously enhancing the cleaning effect of coarse sand. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a sand washing machine that can adjust the powder content of the finished product online and at the same time enhance the cleaning effect of coarse sand.

[0004] To solve the above-mentioned technical problems, the present invention provides a sand washing machine with adjustable powder content, including a cylinder, a feeding mechanism installed at the top of the cylinder; an overflow groove installed on the upper part of the outer wall of the cylinder; a discharge pipe connected to the bottom of the cylinder, and a discharge valve installed on the discharge pipe; a conical screen plate with a smaller top and a larger bottom is detachably installed in the inner cavity of the cylinder below the feeding mechanism; the screen plate has a plurality of screen holes, and the screen holes are divided into at least three annular regions in the radial direction; the screen hole diameters in each annular region are the same, and the screen hole diameters between adjacent annular regions increase in a stepped manner from the center to the edge; It also includes a vertically arranged rotating shaft at the center of the rotating screen; a bracket is installed on the rotating shaft; several scrapers are evenly distributed around the screen above it; the lower edge of the scraper contacts or maintains a gap with the upper surface of the screen; one end of the scraper is connected to the bracket; a drive motor is installed below the screen; the lower end of the rotating shaft extends downward and passes through the center of the screen, and the output shaft of the drive motor is connected to the lower end of the rotating shaft. A gap is left between the edge of the screen and the inner wall of the cylinder; several connecting plates are connected at intervals along the edge of the screen, and the connecting plates are detachably installed on the support plates on the inner wall of the cylinder by bolts. The drive motor is a submersible motor, which is connected to the rotating shaft via a coupling; a sealing component is provided at the center of the screen plate, and the rotating shaft passes through the sealing component and slides and seals with it.

[0005] Furthermore, the bottom of the cylinder is conical, and several water distribution holes are provided on its bottom wall; a water replenishment chamber is fixedly connected to the bottom of the cylinder, and the water replenishment chamber is connected to the inner cavity of the cylinder through the water distribution holes; (number of partitions - 1) concentrically arranged annular partitioning rings are fixedly connected inside the water replenishment chamber, dividing the water replenishment chamber into several independent water replenishment chambers; each water replenishment chamber is connected to an external water source through an independent water inlet pipe; each water inlet pipe is equipped with an electric regulating valve and an electromagnetic flow meter.

[0006] Furthermore, the feeding mechanism includes a feeding hopper, the bottom of which is connected to a feeding pipe via a conveying pipe; the central axis of the discharge port of the feeding pipe is parallel to but does not coincide with the central axis of rotation of the screen disc, and there is an eccentricity between them.

[0007] Furthermore, a fluid return mechanism is installed above the screen plate within the inner cavity of the cylinder; the feed pipe passes through the fluid return mechanism; the fluid return mechanism is composed of several inclined tube assemblies and is fixed or resting on a bracket; the bracket is connected between the feed pipe and the cylinder to support the fluid return mechanism; each inclined tube assembly has a guide hole inside, and all guide holes are arranged obliquely along the same preset direction. The cross-section of the guide hole is hexagonal; the angle between the hole wall and the horizontal plane is 55°~60°, and the height h is 800mm~900mm; the inclined tube assembly is made of polyvinyl chloride (PVC) material.

[0008] Furthermore, the inner cavity of the cylinder is equipped with concentrically arranged guide cylinders, the same number as the separating baffle rings, located below the screen plate. The inner diameter of each guide cylinder is the same as the inner diameter of the separating baffle ring, and each guide cylinder is positioned directly above the separating baffle ring. A gap is left between the bottom of each guide cylinder and the bottom of the cylinder.

[0009] Furthermore, several rollers are rotatably mounted above the sieve disc, and the rollers and scrapers are arranged alternately along the circumference; the rollers are rotatably mounted on the mandrel; and the mandrel is mounted on the bracket.

[0010] Furthermore, the arm end of the bracket is provided with a vertically oriented elongated hole, and a mandrel seat is slidably disposed in the elongated hole; the mandrel is fixed on the mandrel seat, and an upper spring and a lower spring are respectively provided above and below the mandrel seat, so that the mandrel seat can float up and down along the elongated hole; the floating stroke of the mandrel seat is 5~15mm, and the combined force of the upper spring and the lower spring keeps a gap of 2~5mm between the roller and the upper surface of the screen.

[0011] Furthermore, an elastic floating device is provided between the scraper and the support, allowing the scraper to move elastically in the vertical direction.

[0012] Furthermore, the scraper is made of polyurethane or wear-resistant rubber; the elastic floating device is a leaf spring; the scraper is mounted on the bracket via the leaf spring, one end of the leaf spring is fixedly connected to the bracket, and the other end is a free end, with the scraper fixed to the lower surface of the free end of the leaf spring; the elasticity of the leaf spring ensures that the scraper is always pressed against the upper surface of the screen plate, and allows the scraper to lift upwards when it encounters a hard object.

[0013] Furthermore, the outermost guide tube can be suspended from the inner wall of the cylinder by a cantilever, and the inner guide tube can be suspended from the inner wall of the outer guide tube by a cantilever.

[0014] Furthermore, the electric regulating valve, electromagnetic flow meter, and drive motor are all electrically connected to the controller; after the finished sand is discharged, it is conveyed by a conveyor, which is equipped with an online powder content detection device; the online powder content detection device is electrically connected to the controller; the controller is equipped with a target powder content setting module, and automatically adjusts the opening of the electric regulating valve according to the deviation between the powder content detected in real time by the online powder content detection device and the target powder content, based on the relationship between the deviation and the preset threshold.

[0015] The present invention also provides a method for controlling the powder content of the above-mentioned sand washing machine, comprising the following steps: S1. The measured value of powder content Pv of the discharged finished sand is obtained in real time through an online powder content detection device; S2. The controller calculates the difference between the measured powder content Pv and the target powder content Sp: e = Sp - Pv; S3. When |e|≦ε, the system is in a stable state, and the controller controls the electric regulating valve to maintain the current opening; ε is a preset threshold. When e>ε, the controller controls the opening of the electric regulating valve corresponding to the inner ring water supply chamber and / or the middle ring water supply chamber to decrease, thereby reducing the upward water flow velocity in the inner ring and / or middle ring areas and allowing more fine sand to settle into the bottom flow. When e When ε is reached, the controller increases the opening of the electric regulating valve corresponding to the inner ring water supply chamber and / or the middle ring water supply chamber, thereby increasing the upward water flow velocity in the inner ring and / or middle ring areas and reducing the amount of fine sand settling into the bottom flow. S4. Repeat steps S1-S3 until |e| ≦ε, so that the powder content of the finished product is stabilized near the target value Sp.

[0016] Beneficial effects of this invention: This invention divides the water replenishment chamber into several independent water replenishment chambers using several partition rings. The opening of the corresponding electric regulating valve in each chamber can be individually adjusted, thereby regulating the water flow velocity in different radial regions within the cylinder. The outer ring zone uses a high upward flow velocity to slow down coarse sand settling and extend the washing time; the inner ring zone uses a lower upward flow velocity. By adjusting the water flow in the inner ring zone, the content of fine sand in the finished sand can be controlled, i.e., the powder content. Compared to existing technologies that only produce "de-sludge sand," this invention is the first to achieve active control of the finished sand gradation by a single sand washing unit, meeting the differentiated needs of various downstream applications for sand powder and fine sand content. By independently controlling the upward water flow velocity in each zone, combined with the pre-dispersion and forced distribution mechanism, precise closed-loop adjustment of the powder content in the finished sand is achieved, while extending the coarse sand washing time and improving the cleanliness of the finished sand.

[0017] The screen, combined with the rollers and scraper, ensures that even if the feed pipe is off-center, the scraper can force the material to cover the entire screen, and the rollers can break up the clumps, resulting in even and dispersed feed and preventing local accumulation. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the internal structure of Example 1; Figure 2 This is a top view of the installation of the roller and scraper in Example 1; Figure 3 This is a top view of the sieve disc in Example 1; Figure 4 for Figure 1 Enlarged view of a local structure.

[0019] In the diagram, 1-cylinder, 2-water replenishment chamber, 3-second dividing baffle ring, 4-first dividing baffle ring, 5-first water replenishment chamber, 6-second water replenishment chamber, 7-third water replenishment chamber, 8-water distribution hole, 9-water inlet pipe, 10-support, 11-screen plate, 12-first screen hole, 13-second screen hole, 14-third screen hole, 15-rotating shaft, 16-roller, 17-scraper, 18-fluid return mechanism, 19-feed pipe, 20-feed hopper, 21-overflow trough, 22-first guide cylinder, 23-second guide cylinder, 24-discharge pipe, 25-discharge valve, 26-drive motor. Detailed Implementation

[0020] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0021] Example 1 A sand washing machine with adjustable powder content, such as Figure 1-4 As shown, the device includes a cylinder 1, with a feeding mechanism installed at the top; an overflow groove 21 is installed on the upper part of the outer wall of the cylinder 1; a discharge pipe 24 is connected to the bottom of the cylinder 1, and a discharge valve 25 is installed on the discharge pipe 24; a conical screen 11, which is smaller at the top and larger at the bottom, is detachably installed in the inner cavity of the cylinder 1 below the feeding mechanism; the screen 11 has a number of screen holes, and the screen holes are divided into at least three regions in the radial direction; in this embodiment, the number of regions is three; the screen holes opened from the center to the edge of each region are the first screen hole 12, the second screen hole 13, and the third screen hole 14, respectively; the screen hole diameters in each region are the same, and the screen hole diameters between adjacent regions increase in a stepwise manner from the center to the edge; that is, the diameter of the first screen hole 12 is smaller than that of the second screen hole 13, and the diameter of the second screen hole 13 is smaller than that of the third screen hole 14.

[0022] A gap is left between the edge of the sieve disc 11 and the inner wall of the cylinder 1; in this embodiment, a number of connecting plates are connected at intervals along the edge of the sieve disc 11, and the connecting plates are detachably installed on the support plate of the inner wall of the cylinder 1 by bolts; in another embodiment, other detachable connection structures can also be used between the inner wall of the cylinder 1 and the sieve disc 11.

[0023] In this embodiment, the cone surface of the sieve disc 11 forms an angle of 40° with the horizontal plane. The diameter of the sieve holes in the central area is 1~3mm, and the opening rate is 5%~15%; the diameter of the sieve holes in the middle area is 4~6mm, and the opening rate is 15%~25%; the diameter of the sieve holes in the outer area is 8~12mm, and the opening rate is 30%~40%.

[0024] It also includes a vertically arranged rotating shaft 15 at the center of the rotating screen 11; a bracket 10 is mounted on the rotating shaft 15; several scrapers 17 are evenly distributed circumferentially above the screen 11; the lower edge of the scraper 17 contacts or maintains a gap with the upper surface of the screen 11; one end of the scraper 17 is connected to the bracket 10; a drive motor 26 is installed below the screen 11; the lower end of the rotating shaft 15 extends downward and passes through the center of the screen 11, and the output shaft of the drive motor 26 is connected to the lower end of the rotating shaft 15; in this embodiment, the drive motor 26 is a submersible motor, which is connected to the rotating shaft 15 through a coupling; a sealing assembly is provided at the center of the screen 11, and the rotating shaft 15 passes through the sealing assembly and slides and seals with it.

[0025] Specifically, the bottom of the cylinder 1 is conical, and several water distribution holes 8 are opened on its bottom wall. A water replenishment chamber 2 is fixedly connected to the bottom of the cylinder 1, and the water replenishment chamber 2 is connected to the inner cavity of the cylinder 1 through the water distribution holes 8. Two concentric annular dividing rings are fixedly connected inside the water replenishment chamber 2, namely the first dividing ring 4 and the second dividing ring 3, dividing the water replenishment chamber 2 into three independent water replenishment chambers, namely the first water replenishment chamber 5, the second water replenishment chamber 6, and the third water replenishment chamber 7. Each water replenishment chamber is connected to an external water source through an independent water inlet pipe 9. Each water inlet pipe 9 is equipped with an electric regulating valve and an electromagnetic flow meter. The three water replenishment chambers are not interconnected and can independently control the water inlet flow rate.

[0026] Specifically, the feeding mechanism includes a feeding hopper 20, the bottom of which is connected to a feeding pipe 19 via a conveying pipe. The central axis of the discharge port of the feeding pipe 19 is parallel to but not coincident with the rotational central axis of the screen disc 11, with an eccentricity between them. The specific value of the eccentricity needs to ensure that the material does not fall onto the rotating shaft 15 and the support 10 after exiting the feeding pipe 19. The purpose of the offset of the feeding pipe 19 is to avoid the rotating shaft 15 and the support 10 located above the center of the screen disc 11, preventing the material from falling directly onto the rotating shaft 15 or the support 10 and causing accumulation and interference; at the same time, the offset material discharge, combined with the sweeping action of the scraper 17, can make the material evenly distributed on the entire conical surface of the screen disc 11.

[0027] In this embodiment, the conveying pipeline can be designed in a spiral shape, which can slow down the material feeding speed.

[0028] Specifically, a fluid return mechanism 18 is installed above the screen plate 11 in the inner cavity of the cylinder 1; the feed pipe 19 passes through the fluid return mechanism 18; the fluid return mechanism 18 is composed of several inclined tube assemblies and is fixed or placed on a bracket; the bracket is connected between the feed pipe 19 and the cylinder 1 to support the fluid return mechanism 18; each inclined tube assembly has a guide hole inside, and all guide holes are arranged obliquely along the same preset direction. In this embodiment, the cross-section of the guide hole is hexagonal; the angle between the hole wall and the horizontal plane is 55°~60°, and the height h is 800mm~900mm; the inclined tube assembly is made of polyvinyl chloride (PVC) material. In another embodiment, the cross-section of the guide hole can also be circular, and the angle and height can be flexibly adjusted.

[0029] Specifically, within the inner cavity of the cylinder 1, below the screen plate 11, are two concentrically arranged guide cylinders, namely the first guide cylinder 22 and the second guide cylinder 23. The inner diameter of each guide cylinder is the same as the inner diameter of the partition ring, and each guide cylinder is positioned directly above the partition ring. A gap is left between the bottom of each guide cylinder and the bottom of the cylinder 1. The guide cylinders can isolate the rising water flow generated by different water supply chambers, prevent large-scale lateral flow during the rising process, and ensure that the water flow velocity in each area within the cylinder 1 can be easily controlled independently.

[0030] In this embodiment, the top of the guide tube is kept 5-10mm away from the lower surface of the screen plate 11 to prevent vibration interference during operation; the bottom of the guide tube is left with a gap of 20-50mm between it and the bottom wall of the cylinder 1, allowing the settled sand and gravel to fall freely from the bottom of the guide tube into the discharge port.

[0031] Specifically, several grinding rollers 16 are rotatably mounted above the screen 11, with the grinding rollers 16 and scrapers 17 arranged alternately in the circumferential direction; the grinding rollers 16 are rotatably mounted on a mandrel; the mandrel is mounted on a support 10. The rotation of the rotating shaft 15 can drive the support 10, the mandrel, and the grinding rollers 16 to revolve around the rotating shaft 15, and the grinding rollers 16 can grind and disperse the clumps of material that fall onto the screen 11.

[0032] Specifically, an elastic floating device is provided between the scraper 17 and the bracket 10, so that the scraper 17 can move elastically in the vertical direction.

[0033] Specifically, the elastic floating device is a leaf spring; the scraper 17 is mounted on the bracket 10 via the leaf spring, one end of the leaf spring is fixedly connected to the bracket 10, and the other end is a free end, and the scraper 17 is fixed to the lower surface of the free end of the leaf spring; the elasticity of the leaf spring makes the scraper 17 always press against the upper surface of the screen plate 11, and allows the scraper 17 to lift up when it encounters a hard object.

[0034] Specifically, the scraper 17 is made of polyurethane or wear-resistant rubber.

[0035] Specifically, in this embodiment, the outermost guide tube is suspended from the inner wall of the cylinder 1 by a cantilever, and the inner guide tube is suspended from the inner wall of the outer guide tube by a cantilever. In another embodiment, the top of the guide tube can be directly installed at the lower end of the sieve plate 11.

[0036] Specifically, the electric regulating valve, electromagnetic flow meter, and drive motor are all electrically connected to the controller; after the finished sand is discharged, it is conveyed by a conveyor equipped with an online dust content detection device; the online dust content detection device is electrically connected to the controller; the controller has a target dust content setting module, and automatically adjusts the opening of the electric regulating valve according to the deviation between the dust content detected in real time by the online dust content detection device and the target dust content, based on the relationship between the deviation and a preset threshold. The online dust content detection device is existing technology.

[0037] Example 2 Compared to Embodiment 1, the mounting structure of the grinding roller 16 is upgraded to a floating structure. Specifically, the arm end of the bracket 10 has a vertically oriented elongated hole, within which a mandrel seat is slidably mounted. The mandrel is fixed to the mandrel seat, and an upper spring and a lower spring are respectively provided above and below the mandrel seat, allowing the mandrel seat to float up and down along the elongated hole. The floating stroke of the mandrel seat is 5~15mm, and the combined force of the upper and lower springs maintains a 2~5mm gap between the grinding roller 16 and the upper surface of the screen plate 11. Compared to Embodiment 1, the advantage of the floating grinding roller 16 is that it can automatically avoid large foreign objects, reducing the risk of jamming and damage, and improving operational reliability; it can also avoid hard contact between the grinding roller 16 and the screen plate 11, extending their lifespan.

[0038] Example 3 A method for controlling the powder content of the above-mentioned sand washing machine includes the following steps: S1. The measured value of powder content Pv of the discharged finished sand is obtained in real time through the online powder content detection device 14. S2. The controller calculates the difference between the measured powder content Pv and the target powder content Sp: e = Sp - Pv; S3. When |e|≤ε, the system is in a stable state, and the controller controls the electric regulating valve to maintain the current opening; ε is a preset threshold. When e>ε, the controller controls the opening of the electric regulating valve corresponding to the inner ring water supply chamber and / or the middle ring water supply chamber to decrease, thereby reducing the upward water flow velocity in the inner ring and / or middle ring areas and allowing more fine sand to settle into the bottom flow. When e When ε is reached, the controller increases the opening of the electric regulating valve corresponding to the inner ring water supply chamber and / or the middle ring water supply chamber, thereby increasing the upward water flow velocity in the inner ring and / or middle ring areas and reducing the amount of fine sand settling into the bottom flow. S4. Repeat steps S1-S3 until |e| ≤ ε, so that the powder content of the finished product is stabilized near the target value Sp.

[0039] Working principle of the invention: External water sources enter the first water supply chamber 5, the second water supply chamber 6, and the third water supply chamber 7 respectively through three independent water inlet pipes 9, and enter the inner cavity of the cylinder 1 through the water distribution hole 8, forming an upward water flow at different speeds in the inner cavity of the cylinder 1.

[0040] The sand-water mixture to be washed enters from the feed hopper 20 and falls onto the biased area of ​​the screen plate 11 through the feed pipe 19. The drive motor 26 drives the rotating shaft 15 to rotate, and the scraper 17 sweeps the falling material along the circumferential direction, making it evenly distributed on the conical surface of the screen plate 11; the roller 16 crushes the material, breaking up the clay clumps. Under the action of gravity and centrifugal force on the screen plate 11, some small particles fall into the inner cavity of the first guide cylinder 22 through the first screen hole 12; medium particles fall into the inner cavity of the second guide cylinder 23 through the second screen hole 13; large particles roll outward along the conical surface and fall into the area between the second guide cylinder 23 and the inner wall of the cylinder 1 through the third screen hole 14 and the gap between the screen plate 11 and the inner wall of the cylinder 1. The water flow velocity is different in the three areas, with the water flow velocity being the slowest in the inner area and the water flow velocity being the fastest in the outer area. The water flow velocity in each area can be individually adjusted.

[0041] Coarse particles, under the relatively large upward water flow in the outer ring, can slow down their settling and prolong their residence time, allowing them to be thoroughly cleaned before settling to the bottom. Medium particles, under the upward water flow in the middle ring, sink slowly, undergoing effective cleaning during this process. Some fine particles, under the upward water flow in the inner ring, sink slowly, undergoing effective cleaning during this process. Meanwhile, some smaller particles and mud powder are carried upward by the upward water flow and enter the fluid return mechanism 18. Some fine sand settles back within the inclined tube of the fluid return mechanism 18. The finest mud overflows through the fluid return mechanism 18 into the overflow trough 21 and is finally discharged from the overflow trough 21. When a certain amount of material accumulates at the bottom of the inner cavity of the cylinder 1, the discharge valve 25 is automatically opened to discharge the cleaned finished sand. The finished sand contains coarse sand, medium sand, and fine sand, with the fine sand being the "powder" in the "adjustable powder content" setting. The accumulation of material at the bottom of the inner cavity of the cylinder 1 can be monitored by installing a density detection device.

[0042] When the powder content of the finished sand is detected to be lower than the preset value, the controller controls the opening of the electric regulating valve corresponding to the first water supply chamber 5 to decrease, reducing the upward water flow velocity in the corresponding area. Simultaneously, it can control the opening of the electric regulating valve corresponding to the second water supply chamber 5 to decrease. When the powder content of the finished sand is detected to be higher than the preset value, the controller controls the opening of the electric regulating valve corresponding to the first water supply chamber 5 to increase, increasing the upward water flow velocity in the corresponding area. Simultaneously, it can control the opening of the electric regulating valve corresponding to the second water supply chamber 5 to increase, thereby adjusting the content of fine sand in the finished sand, i.e., the powder content. By adjusting the opening of the electric regulating valves corresponding to the second water supply chamber 6 and the third water supply chamber 7, the upward water flow velocity in the inner cavity area (middle area) of the second guide cylinder 23 and the area between the inner wall of the second guide cylinder 23 and the cylinder body 1 (outer layer area) can be controlled, thereby adjusting the settling time of large and medium-sized sand particles and the degree of cleaning of large and medium-sized sand particles.

[0043] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A sand washing machine with adjustable powder content, characterized in that: The device includes a cylinder (1), with a feeding mechanism installed at the top of the cylinder (1); an overflow groove (21) is installed on the upper part of the outer wall of the cylinder (1); a discharge pipe (24) is connected to the bottom of the cylinder (1), and a discharge valve (25) is installed on the discharge pipe (24); a cone-shaped screen plate (11) with a smaller top and a larger bottom is installed in the inner cavity of the cylinder (1) below the feeding mechanism; the screen plate (11) has several screen holes, and the screen holes are divided into at least three annular regions along the radial direction; the screen hole diameters in each annular region are the same, and the screen hole diameters between adjacent annular regions increase in a stepwise manner from the center to the edge; It also includes a vertically arranged rotating shaft (15) at the center of the rotating screen (11); a bracket (10) is installed on the rotating shaft (15); several scrapers (17) are evenly distributed around the screen (11) in the circumferential direction above the screen (11); the lower edge of the scraper (17) contacts or maintains a gap with the upper surface of the screen (11); one end of the scraper (17) is connected to the bracket (10); a drive motor (26) is installed below the screen (11); the lower end of the rotating shaft (15) extends downward and passes through the center of the screen (11), and the output shaft of the drive motor (26) is connected to the lower end of the rotating shaft (15); The bottom of the cylinder (1) is conical, and several water distribution holes (8) are provided on its bottom wall; a water replenishment chamber (2) is fixedly connected to the bottom of the cylinder (1), and the water replenishment chamber (2) is connected to the inner cavity of the cylinder (1) through the water distribution holes (8); (number of partitions - 1) concentric ring-shaped partitions are fixedly connected inside the water replenishment chamber (2) to divide the water replenishment chamber (2) into several independent water replenishment chambers; each water replenishment chamber is connected to an external water source through an independent water inlet pipe (9); each water inlet pipe (9) is equipped with an electric regulating valve and an electromagnetic flow meter.

2. The sand washing machine with adjustable powder content according to claim 1, characterized in that: The feeding mechanism includes a feeding hopper (20), and the bottom of the feeding hopper (20) is connected to a feeding pipe (19) through a conveying pipe; the central axis of the discharge port of the feeding pipe (19) is parallel to and does not coincide with the rotation central axis of the screen plate (11), and there is an eccentricity between the two.

3. The sand washing machine with adjustable powder content according to claim 2, characterized in that: A fluid return mechanism (18) is installed above the screen plate (11) in the inner cavity of the cylinder (1); the feed pipe (19) passes through the fluid return mechanism (18); the fluid return mechanism (18) is composed of several inclined tube assemblies and is fixed or placed on a bracket; the bracket is connected between the feed pipe (19) and the cylinder (1) and is used to support the fluid return mechanism (18); each inclined tube assembly is provided with a guide hole, and each guide hole is arranged obliquely along the same preset direction.

4. The sand washing machine with adjustable powder content according to claim 3, characterized in that: The inner cavity of the cylinder (1) is located below the sieve plate (11) and is equipped with concentrically arranged guide cylinders of the same number as the separating baffle rings. The inner diameter of each guide cylinder is the same as the inner diameter of the separating baffle ring, and each guide cylinder is located directly above the separating baffle ring. A gap is left between the bottom of each guide cylinder and the bottom of the cylinder (1).

5. The sand washing machine with adjustable powder content according to claim 4, characterized in that: Several rollers (16) are rotatably mounted above the sieve disc (11), and the rollers (16) and scrapers (17) are arranged alternately in the circumferential direction; the rollers (16) are rotatably mounted on the spindle; the spindle is mounted on the bracket (10).

6. The sand washing machine with adjustable powder content according to claim 1, characterized in that: An elastic floating device is provided between the scraper (17) and the bracket (10) so that the scraper (17) can move elastically in the vertical direction.

7. The sand washing machine with adjustable powder content according to claim 6, characterized in that: The elastic floating device is a leaf spring; the scraper (17) is mounted on the bracket (10) by the leaf spring, one end of the leaf spring is fixedly connected to the bracket (10), and the other end is a free end. The scraper (17) is fixed to the lower surface of the free end of the leaf spring; the elasticity of the leaf spring makes the scraper (17) always press against the upper surface of the screen plate (11) and allows the scraper (17) to lift up when it encounters a hard object.

8. The sand washing machine with adjustable powder content according to claim 4, characterized in that: The outermost guide tube can be suspended on the inner wall of the cylinder (1) by a cantilever, and the inner guide tube can be suspended on the inner wall of the outer guide tube by a cantilever.

9. The sand washing machine with adjustable powder content according to any one of claims 1-8, characterized in that: The electric regulating valve, electromagnetic flow meter, and drive motor (26) are all electrically connected to the controller. After the finished sand is discharged, it is conveyed by a conveyor. The conveyor is equipped with an online powder content detection device. The online powder content detection device is electrically connected to the controller. The controller is equipped with a target powder content setting module. Based on the deviation between the powder content detected in real time by the online powder content detection device and the target powder content, the controller automatically adjusts the opening of the electric regulating valve according to the relationship between the deviation and the preset threshold.

10. The method for controlling the powder content of a sand washing machine with adjustable powder content according to claims 1-9, characterized in that: Includes the following steps: S1. The measured value of powder content Pv of the discharged finished sand is obtained in real time by the online powder content detection device (14); S2. The controller calculates the difference between the target powder content value Sp and the measured powder content value Pv: e = Sp - Pv; S3. When |e|≤ε, the system is in a stable state, and the controller controls the electric regulating valve to maintain the current opening; ε is a preset threshold. When e>ε, the controller controls the opening of the electric regulating valve corresponding to the inner ring water supply chamber and / or the middle ring water supply chamber to decrease, thereby reducing the upward water flow velocity in the inner ring and / or middle ring areas and allowing more fine sand to settle into the bottom flow. When e When ε is reached, the controller increases the opening of the electric regulating valve corresponding to the inner ring water supply chamber and / or the middle ring water supply chamber, thereby increasing the upward water flow velocity in the inner ring and / or middle ring areas and reducing the amount of fine sand settling into the bottom flow. S4. Repeat steps S1-S3 until |e| ≤ ε.

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