Acoustic signal analysis method and apparatus for ball mill grinding efficiency evaluation

Abstract

The present invention relates to an acoustic signal analysis method and system for ball mill grinding efficiency evaluation. More specifically, the present invention provides an acoustic signal analysis method for ball mill grinding efficiency evaluation, the method being performed by an acoustic signal analysis system and comprising the steps of: collecting an acoustic signal, which is collected during a ball mill process and emitted outside a container; performing a fast Fourier transform on the basis of the acoustic signal so as to obtain frequency-specific acoustic signal intensities; and extracting acoustic signals that require analysis.

Description

Acoustic signal analysis method and device for evaluating ball mill grinding efficiency

[0001] The present invention relates to a method and device for analyzing acoustic signals for evaluating ball mill grinding efficiency, and more specifically, to a method and device for analyzing acoustic signals performed by an acoustic signal analysis system, the method comprising: a step of collecting acoustic signals collected during a ball mill process and emitted outside a container; a step of performing a fast Fourier transform based on the acoustic signals to obtain acoustic signal intensities by frequency; and a step of extracting acoustic signals requiring analysis.

[0002] The ball mill process is a process that grinds powder by using the kinetic energy generated when the balls rise and fall while rotating a cylindrical container containing powder (dry) or slurry (wet) and balls. It is a relatively inexpensive piece of equipment among various types of fine grinding process equipment and is used in many industrial sites that use fine powder to control powder properties. In this ball mill process, powder grinding characteristics are affected by various factors such as slurry composition, ball size, volume occupied by the input materials inside the container, container shape, rotation speed, milling time, and temperature. Therefore, in order to observe the change in powder condition that occurs during the ball mill process, it is necessary to stop the equipment, collect samples, and analyze them using analysis equipment. This process is time-consuming, and there is a problem that it is difficult to check the powder condition by stopping the equipment every time and collecting samples in an actual production process.

[0003] However, in processes using powder, the particle size of the powder is a factor that greatly affects the molding, sintering, and slurry properties, and if the particle size of the powder is not controlled consistently, there is a problem that the product quality cannot be maintained consistently. Therefore, to solve this problem, various methods are being used to analyze the grinding state of the powder without stopping the equipment, such as installing analysis equipment in the powder transport pipe to analyze the particle size and shape of the powder, or installing a pipe that circulates around the outside of the container. However, these methods can only be used for inspection during the process of moving on to the next process after the end of the milling process, or there are problems such as the flow of materials inside the container becoming unstable due to the pipe connected to the outside.

[0004] The present invention has been made to solve the problems of the prior art described above, and the present invention provides a device configuration and a signal analysis method necessary for evaluating the degree of powder grinding using an acoustic signal generated during a ball mill grinding process without modifying the form that affects the flow of material inside a ball mill container or stopping the equipment, thereby maintaining the degree of powder grinding constant or shortening the analysis time for developing a new ball mill recipe, thereby improving powder quality and recipe development efficiency after the ball mill process.

[0005] In order to achieve the above-mentioned object, the present invention provides an acoustic signal analysis method for evaluating ball mill grinding efficiency, characterized by comprising the steps of: collecting acoustic signals collected during a ball mill process and emitted outside a container; performing a fast Fourier transform based on the acoustic signals to obtain acoustic signal intensities by frequency; and extracting acoustic signals requiring analysis.

[0006] It is preferable that the source of the acoustic signal collected during the above ball mill process is any one selected from the operating noise of the motor and the rotating shaft, the friction and impact noise between the internal materials and the container due to the rotation of the container, and external noise.

[0007] It is preferable that the acoustic signal requiring the above analysis is an acoustic signal that changes according to the grinding of the powder.

[0008] It is preferable that a step of filtering out acoustic signals not related to powder grinding be included.

[0009] It is preferable that the acoustic signal not related to the powder grinding that is the filtering target is an acoustic signal generated from a ball mill or a combination of a ball mill and a container.

[0010] It is preferable that the acoustic signal related to powder grinding is a first acoustic signal generated from the ball mill, the container, and the ball, or a second acoustic signal generated from a combination of the first acoustic signal and the dispersion medium, or a third acoustic signal generated from a combination of the first acoustic signal and the slurry.

[0011] It is desirable to determine that the point at which the slope of the increase in the integrated intensity of the acoustic signal converges to 0 is the point at which the powder crushing limit is reached.

[0012] It is desirable to record an acoustic signal by determining the point in time when the powder grinding limit is approached, and then grind the powder until the same state as the acoustic signal is reached.

[0013] It is desirable to judge the accuracy of the sound intensity obtained and analyzed during the milling process by comparing it with the grinding efficiency expressed by the equation below.

[0014] Grinding efficiency = (Initial average particle size - Average particle size at time t) / Initial average particle size × 100

[0015] The step of collecting acoustic signals collected during the ball mill process and emitted outside the container; the step of collecting acoustic signals during the milling of powder and storing them as a file in the form of acoustic data; the step of performing a fast Fourier transform based on the acoustic signal to obtain acoustic signal intensity by frequency; the step of converting acoustic data into frequency data through a fast Fourier transform; the step of deriving acoustic signal intensity from the frequency data; and the step of deriving acoustic signal integrated intensity from the derived acoustic signal intensity are preferably further included.

[0016] It is preferable that the method further includes a step of collecting acoustic signals during milling of powder and storing them as a file in the form of acoustic data; and a step of classifying the type of sound from the acoustic data according to milling conditions.

[0017] It is preferable that the method further includes a step of deriving an integrated intensity of an acoustic signal from the derived acoustic signal intensity; and then, a step of analyzing a change in the integrated intensity of an acoustic signal in a frequency domain from a change in the size of the powder due to milling.

[0018] It is preferable that the method further include a step of confirming whether similarity between particle size change and integrated intensity of acoustic signal is secured; and a step of repeating fast Fourier transform until similarity is secured.

[0019] It is desirable that the integrated intensity of the acoustic signal be calculated by squaring the intensity of the acoustic signal after the fast Fourier transform.

[0020] It is desirable to measure the acoustic signal after the ball mill is in operation and set the data after the acoustic signal has stabilized as the initial value.

[0021] The present invention provides an acoustic signal analysis device for evaluating ball mill grinding efficiency, which performs the aforementioned method for analyzing acoustic signals, and includes: a microphone for acquiring acoustic signals from a ball mill and converting them into electrical acoustic signals; an audio interface for amplifying or mixing acoustic signals transmitted from the microphone; and a computer connected to the microphone and the audio interface and equipped with a program including an algorithm for fast Fourier transform.

[0022] It is desirable to install sound-absorbing material in the ball mill to block the inflow of sound signals generated from external noise and internal reflections.

[0023] According to the present invention as described above, the configuration of a device and a signal analysis method necessary for evaluating the degree of powder grinding using an acoustic signal generated during a ball mill grinding process are provided without modifying the form that affects the flow of material inside a ball mill container or stopping the equipment, thereby maintaining the degree of powder grinding constant or shortening the analysis time for developing a new ball mill recipe, thereby improving the powder quality and recipe development efficiency after the ball mill process.

[0024] Figure 1 is a schematic diagram showing an acoustic analysis system according to one embodiment of the present invention;

[0025] Figure 2 is a before and after graph of removal of reflected sound and external noise using sound absorbing material during the operation of an acoustic analysis system according to one embodiment of the present invention.

[0026] FIG. 3 is a schematic diagram showing the type of energy generated during the ball mill grinding process when the acoustic analysis system according to one embodiment of the present invention is applied to a ball mill.

[0027] Figure 4 is a schematic diagram showing the impact form of the ball and powder.

[0028] Figure 5 is a schematic diagram showing the change in acoustic signal according to milling time when an indirect impact occurs between a ball and powder.

[0029] Figure 6 is an electron microscope photograph showing the shape of raw material powder according to one embodiment of the present invention.

[0030] Figure 7 is a graph showing the particle size distribution of raw material powder according to one embodiment of the present invention.

[0031] Figure 8 is an electron microscope photograph showing changes in powder shape according to milling time of raw powder according to one embodiment of the present invention.

[0032] Figure 9 is a graph showing changes in particle size according to milling time of raw powder according to one embodiment of the present invention.

[0033] Figure 10 is a graph showing the change in grinding efficiency and sound intensity according to the milling time of raw material powder according to one embodiment of the present invention.

[0034] Figure 11 is a graph showing the change in the integrated intensity of the sound signal before / after applying the sound absorbing material in the frequency range for obtaining the integrated intensity of the sound signal according to an embodiment of the present invention, and

[0035] Figure 12 is a photograph before and after installing a sound-absorbing material according to an embodiment of the present invention into a ball mill.

[0036] Hereinafter, embodiments of the present invention will be described in more detail with reference to the attached drawings. However, the present invention is not limited to the embodiments disclosed below and may be implemented in various forms. These embodiments are provided solely to ensure complete disclosure of the present invention and to fully inform those skilled in the art of the scope of the invention. The drawings may be partially exaggerated in size to accurately illustrate the embodiments of the present invention.

[0037]

[0038] 1. Analysis Principle

[0039] After collecting the acoustic signals emitted outside the container and performing a fast Fourier transform, the acoustic signal intensity for each frequency can be obtained, and using this, only the necessary portion of the acoustic signals emitted during the ball mill process can be separated and analyzed.

[0040] For example, the Fourier transform can be used to analyze the frequency spectrum of a music file to extract the frequency components of each sound or to calculate signal intensity across frequency bands. Furthermore, the Fourier transform can be used to analyze image characteristics across frequency bands in video data.

[0041] The process of performing a fast Fourier transform is as follows.

[0042] a. The sound signal collected through the microphone is saved as a sound file through an audio interface (in Example 1, a 120-second recorded file is used).

[0043] b. A sound file consisting of time-domain data is converted into frequency-domain data on a computer having a program for fast Fourier transform processing installed, and additional calculations may be performed on the sound signal intensity after fast Fourier transform to ensure similarity between the particle size change and the integrated intensity of the sound signal. For example, in Example 1, the sound signal intensity value after FFT transformation was squared to ensure similarity with the particle size analysis before calculating the integrated intensity of the sound signal. As with the square processing of the sound signal intensity in Example 1, an additional calculation formula for the sound signal intensity after FFT transformation may be modified to reduce the difference from the particle size analysis in the future.

[0044] In the process of carrying out the present invention, the commercial program SIGVIEW was used, and in Example 1, the result of squaring the sound signal intensity after fast Fourier transform (sound signal intensity 2 ) was used to calculate the integrated intensity of the acoustic signal.

[0045] In order to obtain data with a similar trend to particle size analysis, the frequency range used for calculating the acoustic recording time and the acoustic signal integrated intensity is adjusted, and if necessary, additional calculations are performed on the acoustic signal intensity after FFT conversion as in Example 1, and this process is repeated until the similarity to particle size analysis is confirmed.

[0046] c. Using acoustic data according to milling conditions, the types of sounds generated during the grinding process are classified, and the changes in the integrated intensity of the acoustic signal in the frequency range affected by the powder are analyzed. Immediately after the ball milling process starts, the material inside the container is not uniformly distributed, so the acoustic signal is not stable. Therefore, the data after the acoustic signal stabilizes as the material inside the container is uniformly distributed is set as the initial value, and in Example 1, the first acoustic data was measured at the 5-minute mark of the ball milling. However, the measurement time of the first acoustic data is not fixed at 5 minutes, and can change depending on the type and amount of powder, milling speed, etc.

[0047] d. Using the particle size analysis results of the sample recovered at the same time as the acoustic signal measurement time, the correlation between the grinding efficiency according to the milling composition and the change in the integrated intensity of the acoustic signal is confirmed as shown in Fig. 10.

[0048] e. Using the correlation obtained from d, the degree of grinding according to the change in acoustic signal in the corresponding milling composition is evaluated.

[0049]

[0050] The sources of acoustic signals collected during the ball mill process include the operating noise of the motor and rotating shaft due to the operation of the ball mill, the friction and impact noise between internal materials and the container due to the rotation of the container, and external noise. As illustrated in Fig. 3, when the ball mill is operated, the powder to be ground is positioned between the balls in a cylindrical container containing a large number of balls and the balls, and the powder is ground during this process, and the balls apply compression force, friction force, and impact to the powder, and heat energy, vibration energy, and acoustic energy are generated accordingly.

[0051] Figure 12 shows photographs before and after installing sound-absorbing material on a ball mill. (A) Photo is a photograph before installing sound-absorbing material on a ball mill, (B) Photo shows sound-absorbing material installed on the outside of the ball mill, and (C) Photo shows sound-absorbing material installed on the inside of the ball mill. Sound-absorbing material is installed to block noise that may come in from outside around the ball mill. As shown, black sound-absorbing material was attached and installed on the outside and inside of the device. By installing sound-absorbing material on the inside and outside of the equipment box to block outside noise and allow only the sound signal generated during the milling process to be fully heard by the microphone, outside noise and internal reflections could be reduced.

[0052] In addition, as illustrated in Fig. 4, the impact sound when there is no powder is louder than the impact sound when there is powder between the balls. Even when there is powder between the balls, the impact sound between the balls is perceived to be louder when there is an indirect impact compared to when the powder is directly impacted, that is, when the powder between the balls is positioned but is located near the contact point between the balls, so that the impact of the powder by the ball is mitigated compared to when there is direct impact between the balls.

[0053] As illustrated in Fig. 5, powder pulverization during the ball milling process is mainly caused by impact applied to the powder by balls that rise and then fall, resulting in destruction and particle size reduction. In this process, the change in the ratio of ball-powder collision patterns due to the reduction in powder particle size causes a change in the acoustic signal emitted outside the container. That is, as the powder is pulverized, the ball-to-ball impact sound becomes clearer, and therefore, the degree of powder pulverization can be determined by analyzing the change in the ball-to-ball impact sound. In other words, by utilizing these characteristics, only the portion of the frequency-specific acoustic signal that changes due to powder pulverization can be separated, and then the degree of powder pulverization can be analyzed through the difference from the initial acoustic signal.

[0054] Meanwhile, the specifications of the slurry and container used in the present invention are as follows, and these are only specific materials and weights for explaining the examples, and should not be construed as being limited thereto.

[0055] Powder CA-5M Alumina 199.87g Dispersing medium Distilled water 199.87g Ball 99.5% 10mm Alumina ball 1998.70g Container MC nylon (1L) Rotation speed 60% r c

[0056] 2. Analysis device

[0057] Meanwhile, the analysis device of the present invention comprises a microphone for acquiring sound from a ball mill and converting it into an electrical sound signal; an audio interface for amplifying or mixing the sound signal transmitted from the microphone; and a computer connected to the microphone and the audio interface and equipped with a program including an algorithm for fast Fourier transform.

[0058] The configuration of the device for acoustic analysis during the ball mill process illustrated in Fig. 1 is as follows.

[0059]

[0060] A. Ball milling

[0061] A ball mill uses a conventional ball mill device. A ball mill is a type of crusher, usually equipped with a cylindrical container (described below) that rotates and is connected to a motor so that two rods rotate in the same direction.

[0062]

[0063] B. Cylindrical container loaded with powder or slurry, balls

[0064] A ball mill container with approximately the same length and diameter is mounted on the ball mill and rotates according to the operation of the ball mill. It is used to crush powders through the impact or friction caused by the falling balls, or to mix different types of powders. If only powders are contained in the container, it is classified as a dry type, and if a dispersion medium such as a slurry is included, it is classified as a wet type.

[0065]

[0066] A. Microphone for collecting sound signals

[0067] The sound of collision between balls falling from a ball mill container and the container wall, the sound of collision between balls when there is no powder, and the sound of collision between balls disturbed by powder during powder grinding are measured and the collected sound signals are transmitted to a computer as described below for analysis.

[0068]

[0069] A. Sound-absorbing material to remove external noise and internal reflections.

[0070] As illustrated in Fig. 2, when comparing the 1500 Hz noise generated when sound-absorbing material was applied and when it was not, the sound-absorbing effect on noise was greater when sound-absorbing material was applied than when it was not applied, and the sound-absorbing effect was particularly prominent for the ball mill and the container containing the ball. In addition, the sound-absorbing effect was observed for all frequencies, even when it was not 1500 Hz.

[0071]

[0072] Audio interface for storing audio signals

[0073] A sound card is an audio input / output device used for professional audio work on a personal computer. Back in the Windows 98 era, some models didn't even support the Windows native audio API, and instead only supported specialized APIs like ASIO, distinguishing them from general sound cards. However, current models are also suitable for general use.

[0074]

[0075] B. Computer for acoustic signal analysis

[0076] The computer for acoustic signal analysis is equipped with a computational program that constructs a fast Fourier transform algorithm used to analyze the collected acoustic signals as described above. The time spectrum is first derived, and then the frequency spectrum is derived through a fast Fourier transform, and this spectrum is then analyzed.

[0077]

[0078] 3. Analysis method

[0079] A. To filter out acoustic signals unrelated to powder grinding, the acoustic signals generated when operating a soundproofed ball mill in the following combinations are recorded.

[0080] ①. Ball mill (when the ball mill and container are separated)

[0081] ②. Ball mill + container

[0082] ③. Ball press + container + ball

[0083] ④. Ball press + container + ball + dispersion medium

[0084] ⑤. Ball mill + container + ball + slurry (dispersant + powder + additive)

[0085]

[0086] The above example applies to wet ball mills, but can also be used for dry ball mills.

[0087]

[0088] B. Among the acoustic signals recorded in “A”, the frequency range of the acoustic signal that is common to ①~② is excluded from subsequent analysis as background noise.

[0089]

[0090] ③~⑤ (1st acoustic signal ~ 3rd acoustic signal) are used to check the frequency at which the acoustic signal is generated in the ball mill process under the corresponding conditions.

[0091]

[0092] A. The analysis is performed using the change in the integrated intensity of the acoustic signal in the frequency range confirmed in “Da”, and an appropriate analysis method is applied depending on the purpose of use.

[0093] In ③, the sound signal generated by the ball is the strongest, and in ④, the sound signal generated by water is added, but as the water acts as a sound absorber, the type of sound generated in ③ is attenuated. Afterwards, the powder added in ⑤ also acts as a sound absorber, so the sound is attenuated once more.

[0094] In Fig. 11, such changes in the integrated intensity of the acoustic signal can be confirmed. Therefore, although it is possible to measure the acoustic signal by measuring ⑤ from the beginning, there is a problem in that it is difficult to refer to it when determining the boundary with the background noise occurring in ① and ②. In ① and ②, the acoustic signal in the frequency domain for calculating the integrated intensity of the acoustic signal exists, however weakly, and this can be confirmed in Fig. 11. Therefore, ③ and ④, which have relatively large acoustic signal sizes, are measured and used to set the boundary with the background noise area. For example, as shown in the figure, when shielded with a sound-absorbing material, the acoustic intensity of ② was 14 a.u, but the acoustic intensity of ③ increased to 78582 a.u. Therefore, it can be seen that the difference is large and the boundary can be set clearly.

[0095]

[0096] 4. Determining the powder grinding limit

[0097] The point at which the slope of the increase in the integrated intensity of the acoustic signal converges to 0 is when the powder grinding limit is reached. In the ball milling process, the change in the size of the acoustic signal is a result of the change in the powder size, and the powder grinding occurs when the magnitude of the pressure applied to the powder exceeds the strength of the powder. Figure 5 is a schematic diagram of the change in the size of the acoustic signal due to the change in the powder size. At this time, the pressure during powder grinding is mainly due to the pressure applied to the powder by the ball during the ball-powder collision, and the magnitude of the pressure is determined by the kinetic energy that the ball has during the collision. Since the maximum kinetic energy of the ball during the ball mill has a fixed value depending on various factors determined by the milling conditions (such as the rotation speed of the ball mill, the shape and material of the container, the characteristics and composition ratio of the materials charged into the container, etc.), all milling processes have a constant grinding limit unless there is a change in the milling conditions (or a change in composition due to a chemical reaction during the ball mill). Therefore, if milling is performed for a certain period of time under conditions where the powder does not agglomerate, the grinding limit is reached, where no further change in powder size is observed even if the milling time increases. Through this, we know that the grinding limit exists under any milling conditions, but the grinding limit and the milling time required for it are determined by various factors, and the search for it relies on data collection through experiments rather than theoretical calculations using formulas. This is shown in Fig. 9. It can be seen that as the milling time increases, the particle size of the powder shifts to the left overall and gradually decreases. However, it can be seen that the grinding limit gradually approaches as time passes, and therefore, the point at which there is almost no change in particle size can be defined as the grinding limit.

[0098] In the ball mill conditions of Example 1, the grinding limit was not reached through the change in slope until 144 hours of milling, but it can be confirmed that the state is close to the grinding limit through the change in slope approaching 0.

[0099]

[0100] 5. Powder particle size analysis

[0101] After collecting 5 or more samples at regular time intervals or in a section you want to focus on between the start of the ball mill and the powder grinding limit time, analyze the particle size and substitute the resulting values ​​into the integrated intensity value of the acoustic signal to calculate the particle size of the powder using the acoustic signal intensity.

[0102] As shown in Fig. 10, it can be confirmed that the slope of the change in the integrated intensity of the acoustic signal and the milling efficiency according to the milling time have similarities. Therefore, by calculating the milling efficiency corresponding to the acoustic intensity measured at a specific point in time, the particle size (d) of the current powder can be calculated. 50 ) can be estimated.

[0103] Milling efficiency (%) matching sound intensity = (A(t)-A min )×G max / (A max -A min )

[0104] d according to milling efficiency 50 (t) = -(G(t)×d 50 (0) / 100 - d 50 (0))

[0105] A(t): Acoustic integrated intensity measured at milling time t

[0106] A max : Acoustic integral intensity of the maximum milling time measured

[0107] A min : Acoustic integral intensity of the lowest measured milling time

[0108] G max : Grinding efficiency at the maximum milling time measured

[0109] G(t): Grinding efficiency at milling time t

[0110] d 50 (0): d of raw powder 50 (㎛)

[0111] d 50(t): d of powder after milling time t 50 (㎛)

[0112]

[0113] Calculation Example 1) d when the sound intensity of 16,700 is measured under the milling conditions of Example 1 50 Estimated value

[0114] Milling efficiency (%) matching sound intensity = (16700-5314)×74.0 / (18961-5314) = 61.8%

[0115] d corresponding to 61.8% milling efficiency 50 (t) = -(61.8×6.08 / 100 - 6.08) = 2.33㎛

[0116]

[0117] 6. Powder grinding quality control

[0118] By recording the acoustic signal when the powder control is completed and then pulverizing the powder using a ball mill until the same state as the acoustic signal is reached, a powder that is pulverized evenly can be obtained.

[0119]

[0120] <Evaluation of analysis results>

[0121] As can be seen in Figure 10, the increase in the integrated intensity of the acoustic signal and the change in grinding efficiency calculated using the particle size analysis results are consistent. The accuracy of the acoustic intensity obtained and analyzed during the milling process in the graph can be assessed by comparing it with the grinding efficiency expressed in the equation below.

[0122] Grinding efficiency = (Initial average particle size - Average particle size at time t) / Initial average particle size × 100

[0123] Because tolerances vary depending on user requirements, a uniform range cannot be provided. However, the tolerance of products currently used in industrial production lines is approximately ±2%. These products, like separately installed analytical equipment, require sample extraction and pretreatment processes to create conditions suitable for measurement to enhance accuracy. This creates an environment different from the one in which powder is actually placed during milling, and thus carries the risk of not accurately reflecting the characteristics of the powder during milling. Therefore, the ±5% tolerance of the present invention, which does not require separate sample pretreatment and can estimate changes in powder particle size during milling, can be considered a sufficiently meaningful result.

[0124] Error Cause 1: The present invention is an analysis method based on acoustic signal conversion using a fast Fourier transform. It can be confirmed that the error between the acoustic signal integrated intensity and milling efficiency gradually decreases after a certain milling time (see Figure 10). In order to obtain data with high frequency resolution in acoustic signal conversion using a fast Fourier transform, it is necessary to secure the acoustic signal for a sufficiently long period of time. This is because the frequency resolution is inversely proportional to the measurement time. The acoustic signals generated during the series of processes in which the balls rise and fall during ball mill operation must also be recorded in the sound file. However, due to the nature of the ball milling process during which grinding occurs, long-term recording inevitably involves changes in the powder size, which is affected by changes in the acoustic signal due to rapid particle size changes in the early stage of milling, as shown in Figure 9. Therefore, the analysis method of the present invention performs acoustic analysis using a sound file that contains all the acoustic signals related to the changing powder particle size during the recording time. Therefore, there is a discrepancy between the analysis results measured by the particle size analysis equipment and the acoustic signal integrated intensity. In particular, in the initial milling section where the powder grinding speed is fast, the change in the integrated intensity of the acoustic signal tends to be less than the change in particle size.

[0125] Source of error 2: Particle size analysis using a particle size analyzer installed separately for particle size analysis of powder after milling generally goes through a preprocessing process for accurate measurement, and this process includes an ultrasonic treatment process to create a sample condition optimized for the analysis conditions of the analysis equipment. Therefore, in the early stage of milling, cracks may exist in the particles, but some of the uncrushed particles may be separated during the ultrasonic treatment process, reducing the particle size. As a result, the error between the integrated intensity of the acoustic signal and the particle size analysis results may increase in the early stage of milling, and as the milling progresses, the difference between the analysis equipment decreases due to a decrease in the number of particles that exist in a cracked but uncrushed state.

[0126] It is believed that the error due to the aforementioned causes can be narrowed to ±1% by setting optimized acoustic analysis conditions suitable for future milling conditions.

[0127]

[0128] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the specific embodiments described above, and various modifications can be made by a person having ordinary skill in the art to which the invention pertains without departing from the gist of the present invention as claimed in the claims. Furthermore, such modifications should not be understood individually from the technical idea or prospect of the present invention.

Claims

1. It is performed by an acoustic signal analysis system, A step of collecting acoustic signals collected during a ball mill process and emitted outside the container; A step of performing a fast Fourier transform based on the above acoustic signal to obtain the acoustic signal intensity for each frequency; and A step of extracting an acoustic signal requiring analysis; An acoustic signal analysis method for evaluating ball mill grinding efficiency, characterized in that it includes.

2. In paragraph 1, A method for analyzing acoustic signals for evaluating ball mill grinding efficiency, characterized in that the source of the acoustic signal collected during the ball mill process is any one selected from the operating noise of the motor and the rotating shaft, the friction and impact noise between internal materials and the container due to the rotation of the container, and external noise.

3. In paragraph 1, An acoustic signal analysis method for evaluating ball mill grinding efficiency, characterized in that the acoustic signal requiring the above analysis is an acoustic signal that changes according to the grinding of powder.

4. In paragraph 3, A step of filtering out acoustic signals not related to powder grinding; An acoustic signal analysis method for evaluating ball mill grinding efficiency, characterized in that it includes.

5. In paragraph 4, An acoustic signal analysis method for evaluating ball mill grinding efficiency, characterized in that the acoustic signal unrelated to the powder grinding that is the filtering target is an acoustic signal generated from a ball mill or a combination of a ball mill and a container.

6. In paragraph 4, An acoustic signal analysis method for evaluating ball mill grinding efficiency, characterized in that the acoustic signal related to powder grinding is a first acoustic signal generated from a ball mill, a container, and a ball, or a second acoustic signal generated from a combination of the first acoustic signal and a dispersion medium, or a third acoustic signal generated from a combination of the first acoustic signal and a slurry.

7. In paragraph 1, An acoustic signal analysis method for evaluating ball mill grinding efficiency, characterized in that the point at which the slope of the increase in the integrated intensity of the acoustic signal converges to 0 is determined to be the point at which powder grinding is limited.

8. In paragraph 7, An acoustic signal analysis method for evaluating ball mill grinding efficiency, characterized in that an acoustic signal is recorded by determining a point in time approaching the powder grinding limit, and then grinding the powder until a state identical to the acoustic signal is reached.

9. In paragraph 1, An acoustic signal analysis method for evaluating ball mill grinding efficiency, characterized in that the accuracy of the acoustic intensity obtained and analyzed during the milling process is judged by comparing it with the grinding efficiency expressed by the equation below. Grinding efficiency = (Initial average particle size - Average particle size at time t) / Initial average particle size × 100 10. In paragraph 1, A step of collecting acoustic signals that are collected during the ball mill process and emitted outside the container; A step of collecting acoustic signals during milling of powder and storing them as a file in the form of acoustic data is further included; A step of obtaining the frequency-specific acoustic signal intensity by performing a fast Fourier transform based on the above acoustic signal; A step of converting acoustic data into frequency data through fast Fourier transform; A step of deriving sound signal intensity from frequency data; and A step of deriving an integrated intensity of an acoustic signal from the derived acoustic signal intensity; An acoustic signal analysis method for evaluating ball mill grinding efficiency, characterized in that it further includes.

11. In paragraph 10, A step of collecting acoustic signals during milling of powder and saving them as a file in the form of acoustic data; thereafter, A method for analyzing acoustic signals for evaluating ball mill grinding efficiency, characterized in that it further includes a step of classifying the type of sound from acoustic data according to milling conditions.

12. In paragraph 10, A step of deriving the integrated intensity of the acoustic signal from the derived acoustic signal intensity; thereafter, A step of analyzing the change in the integrated intensity of an acoustic signal in the frequency domain from the change in the size of the powder due to milling; An acoustic signal analysis method for evaluating ball mill grinding efficiency, characterized in that it further includes.

13. In paragraph 10, A step for confirming whether similarity between particle size change and integrated intensity of acoustic signal is secured; and A step of repeating the fast Fourier transform until similarity is secured; An acoustic signal analysis method for evaluating ball mill grinding efficiency, characterized in that it further includes.

14. In paragraph 10, An acoustic signal analysis method for evaluating ball mill grinding efficiency, characterized in that the acoustic signal integrated intensity is calculated by squaring the acoustic signal intensity after fast Fourier transform.

15. In paragraph 10, An acoustic signal analysis method for evaluating ball mill grinding efficiency, characterized in that the acoustic signal is measured after the ball mill is operated and the data after the acoustic signal has stabilized is set as the initial value.

16. Execute the method for analyzing the sound signal of paragraph 1, A microphone for acquiring sound from a ball mill and converting it into an electrical sound signal; An audio interface for amplifying or mixing the sound signal transmitted from the microphone; and A computer connected to the above microphone and audio interface and equipped with a program including an algorithm for fast Fourier transform; An acoustic signal analysis device for evaluating ball mill grinding efficiency, characterized in that it includes.

17. In paragraph 16, An acoustic signal analysis device for evaluating ball mill grinding efficiency, characterized in that a sound-absorbing material is installed in the ball mill to block the inflow of sound signals generated from external noise and internal reflections.

Images