Pneumatic-assisted high-precision negative-pressure screening system and method for detecting content of fine powder in machine-made sand

Abstract

The invention discloses a pneumatically-assisted high-precision negative-pressure screening system and method for detecting the content of fine powder in machine-made sand, the pneumatically-assisted high-precision negative-pressure screening system comprises a screening device, an air source system and an intelligent control unit, and a pneumatic anti-sticking feeding unit, a negative-pressure rotational flow screening unit and a fine powder collecting unit are arranged in a screening device body; the air source system comprises a positive pressure air supply loop driven by a micro air compressor and a negative pressure suction loop driven by a vacuum pump; the pneumatic anti-sticking feeding unit comprises a feeding hopper of a double-wall jacket structure, an annular high-pressure air knife is arranged at the neck of the feeding hopper, the pressure rotational flow screening unit comprises a sealing cavity, and a sealing turbulent flow cover, a standard screen with a miniature vibration motor and a negative pressure dust collection conical hopper are sequentially arranged in the cavity from top to bottom. The intelligent control unit automatically adjusts the rotating speed of the vacuum pump and the pulse injection frequency of the rotational flow air nozzle based on feedback signals of the negative pressure sensor, three-dimensional force field dynamic coupling of suction, blowing and vibration is achieved, the problems of fine powder agglomeration and screen mesh blockage are effectively solved, and automatic and efficient screening is achieved.

Description

Technical Field

[0001] This invention belongs to the technical field of building material testing equipment, specifically relating to a pneumatically assisted high-precision negative pressure sieving system and method for detecting the fine powder content of manufactured sand. Background Technology

[0002] In the application of manufactured sand as concrete aggregate, the stone powder content (i.e., particles with a diameter less than 0.075 mm) is one of the key technical indicators for measuring its quality. According to the current national standard GB / T 14684-2022 "Construction Sand", laboratories typically use a process of "drying—weighing—sieving—re-weighing" to determine the stone powder content, with the sieving stage mainly relying on a shaking sieve machine. However, existing sieving equipment has the following drawbacks in actual operation: (1) Feeding residual error: After the manufactured sand is dried, its fine stone powder is very easy to generate static electricity due to the drying environment. During the transfer to the screening equipment, a large amount of it is adsorbed on the feeding funnel, the inner wall of the container, etc., resulting in a reduction in the actual sample mass participating in the screening.

[0003] (2) Screen clogging: The standard screen used to intercept particles larger than 0.075 mm has a very small aperture. Fine particles are easily embedded in or clog the screen holes, resulting in a significant reduction in the effective screening area and a decrease in screening efficiency, which further affects the stone powder throughput.

[0004] (3) Particle agglomeration effect: Due to van der Waals forces and electrostatic forces, micro powder particles are prone to agglomeration, forming "pseudo-coarse particles" with a size larger than the actual particle size. Under traditional sieving conditions that rely solely on mechanical vibration, such agglomerates are difficult to disagglomerate and pass through the sieve, resulting in the measured stone powder content being lower than the actual value.

[0005] Currently, most industry improvements to address these issues focus on automated weighing, but generally neglect the core requirement of whether the screening process itself can achieve "cleanliness and thoroughness." Summary of the Invention

[0006] The purpose of this invention is to provide a pneumatically assisted high-precision negative pressure sieving system and method for detecting the content of fine powder in manufactured sand. This system can effectively solve the problems of easy agglomeration of fine powder and easy clogging of the screen, improve the accuracy and precision of the detection results, and reduce manual cleaning errors to achieve automatic and efficient sieving.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A pneumatically assisted high-precision negative pressure sieving system for detecting the fine powder content of manufactured sand includes a sieving device, an air source system, and an intelligent control unit. The intelligent control unit includes a microcontroller (MCU) and a power module. The sieving device includes a device body, within which, from bottom to top, are sequentially arranged a pneumatic anti-sticking feeding unit, a negative pressure cyclone sieving unit, and a fine powder collection unit. The air source system is integrated at the rear of the sieving device and includes a miniature air compressor, a vacuum pump, and a solenoid valve group communicating with the intelligent control unit, forming a positive pressure air supply circuit and a negative pressure suction circuit, respectively. The solenoid valve assembly is connected to a positive pressure air supply circuit driven by a miniature air compressor, which is electrically connected to the intelligent control unit. The positive pressure air supply circuit is connected to the pneumatic anti-sticking feeding unit to achieve the anti-sticking feeding function. The negative pressure suction circuit is directly driven by a vacuum pump, the suction end of which is connected to the negative pressure cyclone screening unit to form a stable negative pressure environment during the screening process. The vacuum pump is controlled by the intelligent control unit through a power module. The negative pressure suction circuit is equipped with a negative pressure sensor electrically connected to the intelligent control unit to detect the pressure difference change in the airflow channel during the screening process. The negative pressure suction circuit is also equipped with an independent vacuum solenoid valve for air path isolation. The pneumatic anti-sticking feeding unit includes a feeding funnel located on the top of the device body. The feeding funnel adopts a double-walled jacket structure, including an outer wall made of a high-strength sealing plate and an inner wall integrally formed of porous sintered metal. The inner wall has a connected microporous structure, forming a closed pressure equalizing air chamber between the inner and outer walls. The pressure equalizing air chamber is connected to a positive pressure air supply circuit and is used to form a micron-level air film on the surface of the porous inner wall to isolate the material. An annular high-pressure air knife with a downward-angled nozzle is provided at the neck of the feeding funnel. The annular high-pressure air knife is connected to the output end of a solenoid valve group through its air inlet. The input end of the solenoid valve group is connected to the positive pressure air supply circuit and is controlled by an intelligent control unit to open and close. It is used to spray a high-speed airflow to perform a circumferential purging and zeroing of the inner wall of the channel when the feeding ends. The discharge port at the neck of the feeding funnel is connected to the inlet of the negative pressure cyclone screening unit located in the middle of the device body. The negative pressure cyclone screening unit includes a highly airtight sealed cavity. From top to bottom, the sealed cavity is provided with a sealing baffle, a standard sieve with a micro vibration motor, and a negative pressure dust suction cone. The inner side of the top wall of the sealing baffle is provided with several cyclone jet nozzles arranged tangentially. The airflow ejected by the cyclone jet nozzles forms a spiral tangential flow field on the screen surface of the standard sieve. The drive solenoid valve of the cyclone jet nozzle is electrically connected to the control output terminal of the intelligent control unit. The high-frequency pulse electrical signal output by the intelligent control unit controls its opening and closing. The power input terminal of the micro vibration motor of the standard sieve is electrically connected to the vibration drive output terminal of the intelligent control unit through a wire. The intelligent control unit provides a high-frequency drive electrical signal to make the motor vibrate continuously, causing the material on the screen surface to jump. The bottom outlet of the negative pressure dust collection cone is connected to the micro powder collection unit and vacuum pump through a pipe. When the vacuum pump is started, the negative pressure dust collection cone forms a continuous vertical negative pressure difference below the standard sieve, generating a strong vertical suction force that forces micro powder smaller than the mesh size to pass through the sieve quickly. The vacuum pump starts, establishing an initial negative pressure environment. During the screening process, the negative pressure sensor monitors the pressure difference changes in the airflow channel in real time. The intelligent control unit dynamically adjusts the vacuum pump speed based on the difference between the real-time pressure difference in the screening chamber of the negative pressure cyclone screening unit and the target negative pressure to maintain the negative pressure stable within the range of 200~500Pa. When the actual pressure difference is detected to be close to the critical threshold or when the rate of change of the pressure difference per unit time shows a positive sudden change, the intelligent control unit outputs a high-frequency control signal to the solenoid valve of the cyclone jet nozzle to increase its pulse jet frequency, thereby increasing the horizontal spiral tangential shear force to break up the particle agglomerates and prevent the screen from clogging.

[0008] Furthermore, the micro powder collection unit includes a slide rail drawer assembly located at the bottom of the device body and a collection cup placed therein. The upper port of the collection cup is airtightly connected to the lower outlet of the negative pressure suction cone through a sealing ring. An exhaust channel is provided at the rear of the slide rail drawer assembly, which is connected to the air inlet of the vacuum pump. A HEPA secondary filter assembly is provided at the connection of the exhaust channel.

[0009] Furthermore, the screening device also includes a transparent observation window disposed on the device body and a touch operation panel electrically connected to the intelligent control unit. The position of the transparent observation window corresponds to the negative pressure cyclone screening unit, and the communication interface of the touch operation panel is electrically connected to the intelligent control unit.

[0010] This invention also provides a pneumatically assisted high-precision negative pressure sieving method for detecting the fine powder content of manufactured sand, comprising the following steps: Step 1: System initialization and parameter settings: The target negative pressure value is preset in the touch operation panel of the intelligent control unit. The pressure threshold for activating the pulse cleanup algorithm The sieving stability determination time t and the pressure sampling frequency The target negative pressure value The value range is 200-500 Pa; when the screening device is started, the intelligent control unit opens the solenoid valve of the positive pressure air supply circuit, and compressed air is filled into the pressure equalization chamber of the pneumatic anti-sticking feeding unit to establish a stable air film layer on the inner wall surface of the feeding funnel. Step 2, Non-destructive feeding and purging: The pre-weighed dried sand sample is poured into the pneumatic anti-sticking feeding unit. The sample falls to the standard sieve under the action of air film isolation and gravity. After all the sample has fallen in, the intelligent control unit triggers the solenoid valve of the annular high-pressure air knife. The high-pressure gas forms a surrounding airflow barrier to purge the channel for 3 to 5 seconds to ensure that no micro powder is retained in the neck of the feeding funnel. Step 3: Constant pressure closed-loop screening based on incremental PID: When the feed port is closed, the micro vibration motor of the standard screen is started, and at the same time the vacuum pump is started to establish an initial pressure difference in the negative pressure air path. Under the synergistic effect of the three-dimensional force field of "suction (vertical negative pressure) + blowing (spiral wind shearing) + vibration (mechanical bouncing)," the material is in a fluidized boiling state. During the screening process, the negative pressure sensor uses Real-time monitoring of pressure difference changes in the airflow channel. The intelligent control unit filters the received differential pressure signal and then calculates the actual negative pressure at the current moment. With target value deviation Subsequently, an incremental PID algorithm is used to calculate the control increment. The formula is as follows: In the formula, This is the proportionality coefficient. The integral coefficient is... These are the differential coefficients; The intelligent control unit will The power module receives real-time feedback to continuously adjust the vacuum pump's speed, offsetting wind resistance fluctuations caused by changes in mesh aperture, and achieving the target negative pressure value. Based on this, maintain the dynamic balance of negative pressure within the screening chamber; Step 4: Pulse vortex anti-blockage adaptive adjustment based on differential pressure change rate: The intelligent control unit has a unit of time After data collection, calculate the rate of change of pressure difference: The intelligent control unit continuously monitors the actual pressure difference. and pressure difference change rate When the actual pressure difference Approaching the set critical threshold or rate of change of pressure difference When a drastic positive change occurs, it indicates that the effective air permeable area of ​​the screen is decreasing rapidly. At this time, the intelligent control unit outputs a high-frequency pulse signal to increase the opening frequency and spray intensity of the solenoid valve of the swirling jet nozzle. The high-speed spiral tangential airflow generates a strong horizontal shear force on the screen surface, which quickly breaks up the "pseudo-coarse particle" agglomerates and realizes the adaptive adjustment of "detecting the clogging trend - automatically strengthening the screen cleaning". Step 5, Safety Protection Control: When the intelligent control unit detects the actual pressure difference A sharp increase and exceeding the critical threshold If a serious blockage or air circuit abnormality is detected in the screening chamber of the negative pressure cyclone screening unit, the system alarm will be automatically triggered and the air supply system will be shut down immediately until the fault is cleared. Step 6: Determination of sieving endpoint and collection of fine powder: As the micro-powder gradually passes through the standard sieve and falls into the negative pressure dust collection cone, the amount of fine powder on the sieve surface decreases, and the pressure difference fluctuation gradually smooths out. When the pressure difference change rate... Approaching 0 and actual pressure difference Maintain stability at the target negative pressure value When the preset sieving stability judgment time t is reached, the intelligent control unit determines that the sieving is completely completed and shuts down the sieving device; most of the particles fall into the collection cup, and a very small amount of extremely fine floating dust is intercepted by the HEPA secondary filter component at the exhaust channel; pull out the sliding drawer assembly, take out the collection cup for weighing.

[0011] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention completely solves the problem of electrostatic adsorption and residue of dried stone powder during the feeding process by using the gas film layer technology formed by porous sintered metal inner wall. Combined with the three-dimensional synergistic screening of negative pressure cyclone, it eliminates the need to rely on tedious manual brushing of the screen, freeing up manpower. Compared with the traditional shaking screen machine, this device is faster and more accurate in detecting results, realizing automatic and efficient screening. (2) The present invention uses an intelligent control unit to analyze the real-time signal received by the negative pressure sensor and the preset value to calculate the flow field state in the screening chamber. The PID algorithm is used to automatically adjust the speed of the negative pressure fan and the pulse frequency of the swirl jet nozzle. During the screening process, the intelligent control unit continuously detects the feedback signal and dynamically balances the intensity of the three "suction-blowing-vibration" until the screening is completed. This can effectively prevent the clogging and agglomeration of the 0.075mm microporous screen. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the overall three-dimensional structure of the screening device of the present invention; Figure 2 This is a partially enlarged cross-sectional view of the neck of the feeding funnel of the present invention; Figure 3 This is a partial cross-sectional view of the screening device of the present invention; Figure 4 This is a schematic diagram of the spiral tangential airflow distribution generated by the swirling jet nozzle; Figure 5 This is a block diagram of the electrical control system of the present invention; Figure 6 This is a schematic diagram of the gas path connection principle of the present invention.

[0013] In the diagram: 1-Pneumatic anti-stick feeding unit; 11-Feeding funnel; 12-Annular high-pressure air knife; 2-Negative pressure cyclone screening unit; 21-Sealed baffle; 22-Standard sieve; 23-Negative pressure dust suction cone; 24-Cyclone jet nozzle; 3-Micro powder collection unit; 31-Slide rail drawer assembly; 32-Collection cup. Detailed Implementation

[0014] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0015] The pneumatically assisted high-precision negative pressure sieving system for detecting the fine powder content of manufactured sand described in this embodiment includes a sieving device, an air source system, and an intelligent control unit.

[0016] like Figure 1 , Figure 2 As shown, the screening device includes a device body, and from bottom to top, a pneumatic anti-sticking feeding unit 1, a negative pressure cyclone screening unit 2, and a micro powder collection unit 3 are arranged in sequence.

[0017] The air supply system is integrated at the rear of the screening device, including a micro air compressor, a vacuum pump, and a solenoid valve group that communicates with the intelligent control unit, which respectively constitute a positive pressure air supply circuit and a negative pressure suction circuit.

[0018] like Figure 6 As shown, the solenoid valve group is connected to a positive pressure air supply circuit driven by a miniature air compressor. The miniature air compressor is electrically connected to the intelligent control unit. The positive pressure air supply circuit is connected to the pneumatic anti-sticking feeding unit 1 to achieve the anti-sticking feeding function. The negative pressure suction circuit is directly driven by a vacuum pump, and its suction end is connected to the negative pressure cyclone screening unit 2. During the screening process, a stable negative pressure environment is formed, allowing fine particles to be efficiently suctioned and screened against agglomeration through cyclone action. The vacuum pump is controlled by the intelligent control unit through the power module. The negative pressure suction circuit is equipped with a negative pressure sensor electrically connected to the intelligent control unit to detect the pressure difference change in the airflow channel during the screening process, thereby identifying the screen blockage status. The negative pressure suction circuit is also equipped with an independent vacuum solenoid valve for air path isolation.

[0019] The pneumatic anti-sticking feeding unit 1 includes a feeding funnel 11 located at the top of the device body. The feeding funnel 11 adopts a double-walled jacket structure, including an inner wall and an outer wall. The inner wall is a porous body with a connected microporous structure, integrally formed by molding and sintering stainless steel powder. It forms an interconnected microporous network inside, with an average pore size of 5~10μm. Gas can pass through the entire wall surface uniformly, while solid particles are blocked because their particle size is larger than the pore size, thus achieving the function of "gas permeable but powder impermeable". The outer wall is a high-strength sealing plate, forming a closed pressure equalization air chamber between the inner and outer walls. The pressure equalization air chamber is connected to the positive pressure air supply circuit of the air source system. When positive pressure gas is introduced, a micron-level air film is formed on the surface of the inner wall of the feeding funnel 11 to isolate the material from contact with the inner wall and effectively prevent powder adhesion.

[0020] A ring-shaped high-pressure air knife 12 with a downward-angled nozzle is provided at the neck of the feeding hopper 11. The ring-shaped high-pressure air knife 12 is connected to the output end of the solenoid valve group through its air inlet 13, and the input end of the solenoid valve group is connected to the positive pressure air supply circuit. When the feeding process is completed, the intelligent control unit triggers the solenoid valve to open, and high-pressure gas enters the pressure equalization chamber of the ring-shaped high-pressure air knife 12 and is ejected at high speed from the annular gap, forming a surrounding airflow barrier at the neck of the feeding hopper 11, which quickly cleans the inner wall of the channel.

[0021] The discharge port at the neck of the feeding hopper 11 is connected to the inlet of the negative pressure cyclone screening unit 2 located in the middle of the device body. For example... Figure 1 , Figure 3 As shown, the negative pressure cyclone screening unit 2 includes a highly airtight sealed cavity. From top to bottom, the sealed cavity is equipped with a sealing turbulence hood 21, a standard sieve 22 with a micro-vibration motor, and a negative pressure dust collection cone 23. The inner side of the top wall of the sealing turbulence hood 21 is provided with several cyclone jet nozzles 24 arranged tangentially to generate a downward spiraling turbulent airflow. The airflow ejected from the cyclone jet nozzles 24 forms a spiral tangential flow field on the sieve surface, generating horizontal shearing force to break up agglomerated "pseudo-coarse particles," such as... Figure 4 As shown.

[0022] Meanwhile, the bottom outlet of the negative pressure suction cone 23 is connected to the micro powder collection unit 3 and the vacuum pump through a pipe. When the vacuum pump is started, the negative pressure suction cone 23 forms a continuous vertical negative pressure difference below the standard sieve 22, generating a strong suction force in the vertical direction, which forces micro powder smaller than the mesh to pass through the sieve quickly.

[0023] The solenoid valve driving the cyclone jet nozzle 24 is electrically connected to the control output of the intelligent control unit. Its opening and closing are controlled by a high-frequency pulse electrical signal output from the intelligent control unit, achieving pulsed airflow cleaning of the screen. The power input of the micro-vibration motor of the standard screen 22 is electrically connected to the vibration drive output of the intelligent control unit via a wire. The intelligent control unit provides a high-frequency drive electrical signal, causing the motor to vibrate continuously, driving the material on the screen surface to bounce. Through the three-dimensional force field coupling of "suction (vertical negative pressure) + blowing (spiral wind shearing) + vibration (mechanical bouncing)," the material exhibits a violent "fluidized boiling" state on the screen surface, greatly improving screening efficiency and preventing mesh clogging.

[0024] The micro powder collection unit 3 includes a slide rail drawer assembly 31 located at the bottom of the device body and an independent collection cup 32 placed inside it. The slide rail drawer assembly 31 can be pulled out as a whole for easy cleaning or replacement of the collection cup 32. When the micro powder collection unit 3 is pushed into the closed position, the upper port of the collection cup 32 and the lower outlet of the negative pressure dust suction cone 23 are airtightly connected through a sealing ring to ensure that the negative pressure airflow during the sieving process is directly introduced into the collection cup 32 through the cone 23, preventing dust from escaping.

[0025] An exhaust channel is provided at the rear of the slide-type drawer assembly 31, which connects to the air inlet of the vacuum pump. In order to protect the core components of the pneumatic system, a HEPA secondary filter assembly is provided at the connection of the exhaust channel. This assembly is connected in series in the air path to intercept extremely fine floating dust (PM2.5 level) that fails to settle into the collection cup 32, preventing dust from entering the vacuum pump cavity and causing wear, while also ensuring that the exhaust gas is clean and environmentally friendly.

[0026] The screening device also includes a transparent observation window mounted on the device body and a touch control panel electrically connected to the intelligent control unit. The transparent observation window is positioned corresponding to the negative pressure cyclone screening unit 2 and is used to observe the working status inside the screening chamber in real time. The touch control panel's communication interface is electrically connected to the intelligent control unit for human-machine interaction, including parameter setting, start / stop control, and operating status display.

[0027] The intelligent control unit, comprising a microcontroller (MCU) and a power module, is integrated into an independent electrically isolated chamber within the device body. This electrically isolated chamber is located on the inner back of the touch control panel or in the upper rear area of ​​the device body. This electrically isolated chamber is physically isolated from the negative pressure cyclone screening unit 2 and the air supply system, effectively preventing high-frequency mechanical vibrations and accidental leaks of fine dust generated during the screening process from interfering with or damaging precision electronic components, thus ensuring the long-term stability of the equipment.

[0028] The principle block diagram of the electrical control system is as follows Figure 5As shown, the vacuum pump starts, establishing an initial negative pressure environment. During the screening process, the negative pressure sensor monitors the pressure difference changes in the airflow channel in real time. The intelligent control unit dynamically adjusts the vacuum pump speed based on the difference between the real-time pressure difference in the screening chamber of the negative pressure cyclone screening unit 2 and the target negative pressure, maintaining the negative pressure stable within the range of 200~500Pa. When the actual pressure difference is detected to be close to the critical threshold or when the rate of change of the pressure difference per unit time shows a positive abrupt change, the intelligent control unit outputs a high-frequency control signal to the solenoid valve of the cyclone jet nozzle 24, increasing its pulse jet frequency to increase the horizontal spiral tangential shear force, thereby breaking up the particle agglomerates and preventing screen clogging.

[0029] A pneumatically assisted high-precision negative pressure sieving method for detecting the fine powder content of manufactured sand: Step 1: System initialization and parameter settings: The target negative pressure value is preset in the touch operation panel of the intelligent control unit. The pressure threshold for activating the pulse cleanup algorithm The sieving stability determination time t and the pressure sampling frequency The target negative pressure value The value range is 200-500 Pa; when the screening device is started, the intelligent control unit opens the solenoid valve of the positive pressure air supply circuit, and compressed air is filled into the pressure equalization chamber of the pneumatic anti-sticking feeding unit 1, establishing a stable air film layer on the inner wall surface of the feeding funnel 11.

[0030] Because the feeding funnel 11 has a porous structure, the gas passes through the wall evenly to form a stable micron-level gas film layer, which effectively prevents electrostatic adsorption during subsequent feeding.

[0031] The screening stability determination time t is the shortest duration required for the differential pressure to remain stable at the target value. The system uses this time to determine whether the screening has ended.

[0032] Step 2, Non-destructive feeding and purging: The pre-weighed dried sand sample is poured into the pneumatic anti-sticking feeding unit 1. The sample falls to the standard sieve 22 below the sealed baffle 21 under the action of air film isolation and gravity. After the sample has completely fallen in, the intelligent control unit triggers the solenoid valve of the annular high-pressure air knife 12. The high-pressure gas forms a surrounding airflow barrier to purge the channel for 3 to 5 seconds to ensure that no micro powder is retained in the neck of the feeding funnel 11.

[0033] Step 3: Constant pressure closed-loop screening based on incremental PID: When the feed port is closed, the micro vibration motor of the standard sieve 22 is started, and at the same time the vacuum pump is started to establish the initial pressure difference in the negative pressure air path. Under the synergistic effect of the three-dimensional force field of "suction (vertical negative pressure) + blowing (spiral wind shearing) + vibration (mechanical bouncing)," the material is in a fluidized boiling state. During the screening process, the negative pressure sensor uses Real-time monitoring of pressure difference changes in the airflow channel. The intelligent control unit filters the received differential pressure signal and then calculates the actual negative pressure at the current moment. With target value deviation Subsequently, an incremental PID algorithm was used to calculate the control increment. The formula is as follows: In the formula, This is the proportionality coefficient. The integral coefficient is... is the differential coefficient.

[0034] The intelligent control unit will The power module receives real-time feedback to continuously adjust the vacuum pump's speed, offsetting wind resistance fluctuations caused by changes in mesh aperture, and achieving the target negative pressure value. Based on this, maintain the dynamic balance of negative pressure within the screening chamber.

[0035] Step 4: Pulse vortex anti-blockage adaptive adjustment based on differential pressure change rate: To prevent the 0.075mm microporous screen from clogging due to fine powder agglomeration, the system incorporates a differential prediction mechanism. The intelligent control unit measures the time taken within a unit of time... After data collection, calculate the rate of change of pressure difference: The intelligent control unit continuously monitors the actual pressure difference. and pressure difference change rate When the actual pressure difference Approaching the set critical threshold or rate of change of pressure difference When a drastic positive change occurs, it indicates that the effective air-permeable area of ​​the screen is decreasing rapidly (i.e., signs of blockage are appearing). At this time, the intelligent control unit outputs a high-frequency pulse signal to increase the opening frequency and injection intensity of the solenoid valve of the swirling jet nozzle 24. The high-speed spiral tangential airflow generates a strong horizontal shear force on the screen surface, quickly breaking up the "pseudo-coarse particle" agglomerates, and realizing the adaptive adjustment of "detecting blockage trend - automatically strengthening screen cleaning".

[0036] Step 5, Safety Protection Control: When the intelligent control unit detects the actual pressure difference A sharp increase and exceeding the critical threshold If a serious blockage or air circuit abnormality is detected in the screening chamber of the negative pressure cyclone screening unit 2, the system alarm will be automatically triggered and the air supply system will be shut down immediately (the vacuum pump and positive pressure air supply will be shut down) until the fault is cleared, so as to protect the core components of the pneumatic system.

[0037] Step 6: Determination of sieving endpoint and collection of fine powder: As the fine powder gradually passes through the standard sieve 22 and falls into the negative pressure dust collection cone 23, the amount of fine powder on the sieve surface decreases, and the pressure difference fluctuation gradually smooths out. When the pressure difference change rate... Approaching 0 and actual pressure difference Maintain stability at the target negative pressure value When the preset sieving stability judgment time t is reached, the intelligent control unit determines that sieving is completely completed and shuts down the sieving device. The vast majority of particles fall into the collection cup 32, while a very small amount of extremely fine floating dust is intercepted by the HEPA secondary filter component at the exhaust channel. Pulling out the sliding drawer assembly 31 and removing the collection cup 32 for weighing allows for high-precision calculation of the fine powder content in the manufactured sand.

Claims

1. A pneumatically assisted high-precision negative pressure sieving system for detecting the fine powder content of manufactured sand, characterized in that, It includes a screening device, an air supply system, and an intelligent control unit; the intelligent control unit includes a microcontroller (MCU) and a power module; the screening device includes a device body, and from bottom to top, a pneumatic anti-sticking feeding unit (1), a negative pressure cyclone screening unit (2), and a micro powder collection unit (3) are arranged in sequence; the air supply system is integrated at the rear of the screening device and includes a micro air compressor, a vacuum pump, and a solenoid valve group that communicates with the intelligent control unit, which respectively constitute a positive pressure air supply circuit and a negative pressure suction circuit; The solenoid valve group is connected to the positive pressure air supply circuit driven by the micro air compressor, which is electrically connected to the intelligent control unit; the positive pressure air supply circuit is connected to the pneumatic anti-sticking feeding unit (1) to realize the anti-sticking feeding function; the negative pressure suction circuit is directly driven by the vacuum pump, and the suction end of the vacuum pump is connected to the negative pressure cyclone screening unit (2) to form a stable negative pressure environment during the screening process; the vacuum pump is controlled by the intelligent control unit through the power module to start and stop; the negative pressure suction circuit is equipped with a negative pressure sensor electrically connected to the intelligent control unit to detect the pressure difference change in the airflow channel during the screening process; the negative pressure suction circuit is also equipped with an independent vacuum solenoid valve for air path isolation; The pneumatic anti-sticking feeding unit (1) includes a feeding funnel (11) set on the top of the device body. The feeding funnel (11) adopts a double-wall jacket structure, including an outer wall made of a high-strength sealing plate and an inner wall integrally formed by porous sintered metal. The inner wall has a connected microporous structure, and a closed pressure equalization air chamber is formed between the inner and outer walls. The pressure equalization air chamber is connected to the positive pressure air supply circuit and is used to form a micron-level air film on the surface of the porous inner wall to isolate the material. A ring high-pressure air knife (12) with a downward-sloping nozzle angle is provided at the neck of the feeding funnel (11). The ring high-pressure air knife (12) is connected to the output end of the solenoid valve group through its air inlet (13). The input end of the solenoid valve group is connected to the positive pressure air supply circuit and is controlled by the intelligent control unit to open and close. It is used to spray high-speed airflow to perform a surrounding purging and zeroing of the inner wall of the channel at the end of feeding. The neck outlet of the feeding funnel (11) is connected to the inlet of the negative pressure cyclone screening unit (2) located in the middle of the device body; the negative pressure cyclone screening unit (2) includes a highly airtight sealed cavity, and from top to bottom, a sealing turbulence hood (21), a standard sieve (22) with a micro vibration motor and a negative pressure dust suction cone (23) are arranged in sequence. The inner side of the top wall of the sealing turbulence hood (21) is provided with several cyclone jet nozzles (24) arranged in the tangential direction. The airflow ejected by the cyclone jet nozzles (24) forms a spiral tangential flow field on the screen surface of the standard sieve (22); the drive solenoid valve of the cyclone jet nozzle (24) is electrically connected to the control output terminal of the intelligent control unit, and its opening and closing are controlled by the high-frequency pulse electrical signal output by the intelligent control unit; the power input terminal of the micro vibration motor of the standard sieve (22) is electrically connected to the vibration drive output terminal of the intelligent control unit through a wire, and the intelligent control unit provides a high-frequency drive electrical signal to make the motor vibrate continuously, driving the material on the screen surface to jump; The bottom outlet of the negative pressure dust collection cone (23) is connected to the micro powder collection unit (3) and the vacuum pump through a pipe. When the vacuum pump is started, the negative pressure dust collection cone (23) forms a continuous vertical negative pressure difference below the standard sieve (22), generating a strong suction force in the vertical direction, which forces micro powder smaller than the mesh to pass through the sieve quickly. The vacuum pump starts to establish an initial negative pressure environment; During the screening process, the negative pressure sensor monitors the pressure difference change in the airflow channel in real time. The intelligent control unit dynamically adjusts the speed of the vacuum pump according to the difference between the real-time pressure difference in the screening chamber of the negative pressure cyclone screening unit (2) and the target negative pressure, so as to maintain the negative pressure stable within the range of 200~500Pa. When the actual pressure difference is detected to be close to the critical threshold or the unit time change rate of the pressure difference shows a positive sudden change, the intelligent control unit outputs a high-frequency control signal to the solenoid valve of the cyclone jet nozzle (24) to increase its pulse jet frequency, so as to increase the horizontal spiral tangential shear force, thereby breaking the particle agglomerates and preventing the screen from clogging.

2. The pneumatically assisted high-precision negative pressure sieving system for detecting the fine powder content of manufactured sand according to claim 1, characterized in that, The micro powder collection unit (3) includes a slide rail drawer assembly (31) located at the bottom of the device body and a collection cup (32) placed therein. The upper port of the collection cup (32) is airtightly connected to the lower outlet of the negative pressure dust collection cone (23) through a sealing ring. An exhaust channel is provided at the rear of the slide rail drawer assembly (31) and connected to the air inlet of the vacuum pump. A HEPA secondary filter assembly is provided at the connection of the exhaust channel.

3. The pneumatically assisted high-precision negative pressure sieving system for detecting the fine powder content of manufactured sand according to claim 2, characterized in that, The screening device also includes a transparent observation window set on the device body and a touch operation panel electrically connected to the intelligent control unit. The position of the transparent observation window corresponds to the negative pressure cyclone screening unit (2), and the communication interface of the touch operation panel is electrically connected to the intelligent control unit.

4. A pneumatically assisted high-precision negative pressure sieving method for detecting the fine powder content of manufactured sand based on the system described in claim 3, characterized in that, Includes the following steps: Step 1: System initialization and parameter settings: The target negative pressure value is preset in the touch operation panel of the intelligent control unit. The pressure threshold for activating the pulse cleanup algorithm The sieving stability determination time t and the pressure sampling frequency The target negative pressure value The value range is 200-500 Pa; start the screening device, the intelligent control unit opens the solenoid valve of the positive pressure air supply circuit, and compressed air is filled into the pressure equalization chamber of the pneumatic anti-sticking feeding unit (1), and a stable air film layer is established on the inner wall surface of the feeding funnel (11). Step 2, Non-destructive feeding and purging: The pre-weighed dried sand sample is poured into the pneumatic anti-sticking feeding unit (1). The sample falls to the standard sieve (22) under the action of air film isolation and gravity. After all the sample has fallen in, the intelligent control unit triggers the solenoid valve of the annular high-pressure air knife (12). The high-pressure gas forms a surrounding airflow barrier to purge the channel for 3 to 5 seconds to ensure that no micro powder is retained in the neck of the feeding funnel (11). Step 3: Constant pressure closed-loop screening based on incremental PID: When the feed port is closed, the micro vibration motor of the standard sieve (22) is started, and at the same time the vacuum pump is started to establish the initial pressure difference in the negative pressure air path. Under the three-dimensional force field coordination of "suction (vertical negative pressure) + blowing (spiral wind cutting) + vibration (mechanical bouncing)," the material is in a fluidized boiling state. During the screening process, the negative pressure sensor uses Real-time monitoring of pressure difference changes in the airflow channel. The intelligent control unit filters the received differential pressure signal and then calculates the actual negative pressure at the current moment. With target value deviation ; Subsequently, an incremental PID algorithm is used to calculate the control increment. The formula is as follows: In the formula, This is the proportionality coefficient. The integral coefficient is... These are the differential coefficients; The intelligent control unit will The power module receives real-time feedback to continuously adjust the vacuum pump's speed, offsetting wind resistance fluctuations caused by changes in mesh aperture, and achieving the target negative pressure value. Based on this, maintain the dynamic balance of negative pressure within the screening chamber; Step 4: Pulse vortex anti-blockage adaptive adjustment based on differential pressure change rate: The intelligent control unit has a unit of time After data collection, calculate the rate of change of pressure difference: The intelligent control unit continuously monitors the actual pressure difference. and pressure difference change rate When the actual pressure difference Approaching the set critical threshold or rate of change of pressure difference When a violent positive change occurs, it indicates that the effective air permeable area of ​​the screen is decreasing rapidly. At this time, the intelligent control unit outputs a high-frequency pulse signal to increase the opening frequency and spray intensity of the solenoid valve of the swirling jet nozzle (24). The high-speed spiral tangential airflow generates a strong horizontal shear force on the screen surface, which quickly disperses the "pseudo-coarse particle" agglomerates and realizes the adaptive adjustment of "detecting the clogging trend - automatically strengthening the screen cleaning". Step 5, Safety Protection Control: When the intelligent control unit detects the actual pressure difference A sharp increase and exceeding the critical threshold If a serious blockage or air circuit abnormality is detected in the screening chamber of the negative pressure cyclone screening unit (2), the system alarm will be automatically triggered and the air supply system will be shut down immediately until the fault is cleared. Step 6: Determination of sieving endpoint and collection of fine powder: As the fine powder gradually passes through the standard sieve (22) and falls into the negative pressure dust collection cone (23), the amount of fine powder on the sieve surface decreases, and the pressure difference fluctuation gradually becomes smoother. When the pressure difference change rate... Approaching 0 and actual pressure difference Maintain stability at the target negative pressure value When the preset sieving stability judgment time t is reached, the intelligent control unit determines that the sieving is completely completed and shuts down the sieving device; most of the particles fall into the collection cup (32), and a very small amount of extremely fine floating dust is intercepted by the HEPA secondary filter component at the exhaust channel; pull out the slide rail drawer assembly (31) and take out the collection cup (32) for weighing.

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