Method for testing friction coefficient of powder

Abstract

The invention discloses a method for testing the friction coefficient of powder. A used testing device comprises a Haake rotational rheometer, a flexible rotor, a metal rod, a bottom bracket and a data acquisition system, a flexible rotor is installed on a rotating shaft of the rheometer, a steel ball is installed at the bottom of the flexible rotor, and the steel ball is in direct contact with the powder in the testing process; the metal rods are arranged on the bottom bracket, and a space formed by the metal rods is used for placing powder to be detected; the bottom bracket is mounted on a platform of the Haake rotational rheometer; according to the method, stress overload protection is set based on a Haake rotational rheometer and the flexible rotor, a reasonable measurement gap is adopted according to the particle size distribution characteristics of actual powder or positive pressure, a steel ball at the bottom of the flexible rotor is made of hardened steel, and a metal rod on a bottom bracket is made of quenched steel. According to the method, reliable and accurate test results can be obtained under safe and convenient conditions, and friction coefficient comparison between different powder materials is facilitated.

Description

Technical Field

[0001] The present invention belongs to the technical field of powder engineering testing, relates to the field of powder particle friction coefficient testing, and particularly relates to a method for testing the powder friction coefficient. Background Art

[0002] The particle size distribution, morphology (e.g., spherical, rod-shaped, needle-shaped), wettability, and surface roughness of powder particles significantly affect their friction coefficient. Mechanical friction is widely present in today's industrial production and scientific experiments. The friction coefficient is a key powder property in production and experiments, and is also an essential physical parameter for numerical simulation of related mechanical motion. Although traditional methods such as translation and rotation can measure static or quasi-static friction coefficients, they are insufficient for characterizing dynamic friction and the friction behavior of particles under certain temperature and shear rate coupling conditions.

[0003] In the powder industry and in the production of composite materials, dynamic contact and friction between particles significantly impact process efficiency and safety. Furthermore, with the continued development and widespread adoption of discrete element method (DEM) numerical simulation technology, high-precision powder friction coefficients have become a crucial physical property parameter for constructing such numerical models. Determining the powder friction coefficient during dynamic processes provides crucial data support for optimizing production processes and improving process safety and efficiency. Summary of the Invention

[0004] In response to the deficiencies in the prior art, the purpose of the present invention is to provide a testing method for the friction coefficient of powders, to obtain the force law corresponding to the powder particles during movement, and to obtain the friction coefficient of the powder particles under certain temperature and shear rate under the premise of safety and accuracy, so as to guide the design and optimization of related process such as powder movement and mixing.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A method for testing the friction coefficient of powder, wherein the testing device used in the method includes a Haake rotational rheometer, a flexible rotor, a steel ball, a metal rod, a bottom bracket and a data acquisition system;

[0007] The Hake rotational rheometer has a flexible rotor installed on its rotating axis, with a steel ball mounted at its bottom. During testing, the steel ball comes into direct contact with the powder. Multiple metal rods are arranged obliquely in the conical space of the bottom bracket, and the space enclosed by the metal rods is used to hold the powder to be tested. A temperature sensor and temperature controller are installed in the bottom bracket to monitor the temperature in real time during the test. The entire bottom bracket is fixed to the platform of the Hake rotational rheometer via threads. A data acquisition system is connected to the temperature sensor, temperature controller, and the rotating axis of the Hake rotational rheometer via cables to read and control the test data from the temperature sensor, temperature controller, and the rotating axis of the Hake rotational rheometer.

[0008] The following steps are involved:

[0009] Step 1: Before starting the test, the powder to be tested for friction coefficient is measured using a laser particle size distribution analyzer to obtain the particle size distribution of the powder, and the corresponding medium particle size D is recorded. 50 ;

[0010] Step 2: Install a flexible rotor with a steel ball on the rotating axis of the Haake rotational rheometer, install a metal rod on the bottom bracket, add pure water to the temperature controller, and adjust the gap between the flexible rotor and the metal rod to zero using the data acquisition system;

[0011] Step 3: Raise the flexible rotor to a position 10 to 20 cm from the bottom bracket, and load the powder into the space enclosed by the metal rods on the bottom bracket, ensuring that the powder covers the bottom groove of the conical space of the bottom bracket and does not exceed the top of the conical space of the bottom bracket;

[0012] Step 4: Determine the gap between the flexible rotor and the metal rod. Method 1 is based on the median particle size D of the powder. 50 Set the measuring gap so that the measuring gap is equal to the median particle size D of the powder to be measured. 50 , keep the gap unchanged during the measurement process; the second method is to set the gap according to the positive pressure between the flexible rotor and the powder, and keep the positive pressure unchanged during the measurement process;

[0013] Step 5: Use a constant temperature, constant speed, or constant stress measurement method. Select the constant speed or constant stress mode, set the test temperature and speed or stress, data acquisition time, and the total number of data points. Set the stress overload upper limit to 2 to 2.5 bar.

[0014] Step 6: Start the test, record the friction coefficient, test temperature, speed or stress test parameters, and wait for the rotation to stop to complete one round of testing; change the test temperature, speed or stress, and continue to complete the next round of testing according to steps 3 to 5; obtain the speed or stress-friction coefficient data corresponding to different temperatures and draw a relationship diagram.

[0015] The present invention also includes the following technical features:

[0016] Specifically, there are three metal rods, which are arranged in a centrally symmetrical manner, with an angle of 120° between any two of them.

[0017] Specifically, the steel ball has a Rockwell hardness of 50-60.

[0018] Specifically, the metal rod is made of quenched steel bar with a Rockwell hardness of 25-30.

[0019] Specifically, the surfaces of the steel ball and the metal rod are coated with lubricant.

[0020] Specifically, in step 4, when the gap between the flexible rotor and the metal rod is determined according to the positive pressure between the flexible rotor and the powder, the positive pressure is 1 to 3N.

[0021] Compared with the prior art, the present invention has the following technical effects:

[0022] The method of the present invention is based on a Haake rotational rheometer and a flexible rotor, and is provided with stress overload protection. A reasonable measurement gap is adopted according to the particle size distribution characteristics or positive pressure of the actual powder. The steel ball at the bottom of the flexible rotor is made of hardened steel, and the metal rod on the bottom bracket is made of quenched steel. They need to be inspected and replaced according to the number of experiments and powder characteristics to avoid large test system errors caused by equipment accessories.

[0023] The method of the present invention can obtain reliable and accurate test results under safe and convenient conditions, and is conducive to the comparison of friction coefficients between different powder materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the installation of the steel ball, metal rod and bottom bracket of the present invention.

[0025] Figure 2 for Figure 1 Top view of .

[0026] Figure 3 A rotation speed-friction coefficient curve was prepared for an embodiment of the present invention.

[0027] The meaning of each number in the figure is:

[0028] 1. Steel ball, 2. Metal rod, 3. Bottom bracket, 4. Powder. DETAILED DESCRIPTION

[0029] The present invention provides a method for testing the friction coefficient of powder. The testing device used in the method includes a Haake rotational rheometer, a flexible rotor, a steel ball, a metal rod, a bottom bracket and a data acquisition system. Figure 1 and 2 shown.

[0030] The Hake rotational rheometer features a flexible rotor with steel balls mounted on its rotating axis. A steel ball is mounted at the bottom of the flexible rotor, providing direct contact with the powder during testing. Metal rods are arranged at an angle within the conical space of the bottom bracket. The three rods are arranged symmetrically, with a 120° angle between each other. The space enclosed by the rods is used to hold the powder to be tested. The flexible rotor base utilizes hardened steel balls with a Rockwell hardness of 50-60. The metal rods mounted on the bottom bracket utilize hardened steel bars with a Rockwell hardness of 25-30. The steel balls and rods are lubricated. A temperature sensor and temperature controller are installed within the bottom bracket for real-time temperature monitoring during testing. The entire bottom bracket is screwed onto the Hake rotational rheometer platform. A data acquisition system is connected to the temperature sensor, temperature controller, and the rotating axis of the Hake rotational rheometer via cables, enabling the system to read and control test data from these sensors, temperature controller, and the rotating axis.

[0031] The testing method of the present invention comprises the following steps:

[0032] (1) Before starting the test, the powder to be tested for friction coefficient is measured using a laser particle size distribution analyzer to obtain the particle size distribution of the powder, and the corresponding medium particle size D is recorded. 50 ;

[0033] (2) A flexible rotor with a steel ball is installed on the rotating axis of the Haake rotational rheometer, three metal rods are installed on the bottom bracket, an appropriate amount of pure water is added to the temperature controller, and the gap between the flexible rotor and the metal rods is zeroed through the data acquisition system;

[0034] (3) Raise the flexible rotor to a position 10 to 20 cm away from the bottom bracket, and load an appropriate amount of powder into the space formed by the three metal rods on the bottom bracket so that the powder covers the bottom groove of the conical space of the bottom bracket and does not exceed the top of the conical space of the bottom bracket;

[0035] (4) First, there are two ways to determine the gap between the flexible rotor and the three metal rods. The first way is to determine the gap between the flexible rotor and the three metal rods based on the median particle size D of the powder. 50 Set the measuring gap so that the measuring gap is equal to the median particle size D of the powder to be measured. 50 , keep the gap unchanged during the measurement process; the second method is to set the gap according to the positive pressure between the flexible rotor and the powder, and keep the positive pressure unchanged during the measurement process; when choosing to determine the gap between the flexible rotor and the three metal rods according to the positive pressure between the flexible rotor and the powder, the positive pressure is 1~3N.

[0036] (5) Use the constant temperature and constant speed (or constant stress) measurement method, select CR (constant speed) or CS (constant stress) mode, set the test temperature and speed (or stress), data acquisition time and the total number of data points, and set the stress overload upper limit to 2-2.5 bar;

[0037] (6) Start the test, record the test parameters such as friction coefficient, test temperature, speed (or stress), etc., and wait for the rotation to stop, completing one round of testing; change the test temperature, speed or stress, and continue to complete the next round of testing according to steps (3) to (5); obtain the speed (or stress)-friction coefficient data corresponding to different temperatures, and draw a relationship diagram;

[0038] The test method employed above utilizes a flexible rotor at a constant temperature and speed (or constant stress), with stress overload protection implemented during the rotation test. If visible scratches appear on the surface of the steel ball or metal rod, they must be replaced before retesting.

[0039] Specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent modifications made on the basis of the technical solution of this application fall within the protection scope of the present invention.

[0040] Example 1:

[0041] This embodiment provides a method for testing the friction coefficient of powders. The testing apparatus used in this method includes a Haake rotational rheometer, a flexible rotor, a steel ball, a metal rod, a bottom bracket, and a data acquisition system. A flexible rotor with a steel ball is mounted on the rheometer's rotating axis. A steel ball is mounted on the bottom of the flexible rotor, directly contacting the powder during testing. The metal rod is mounted on the bottom bracket, creating a space for the powder to be tested. The entire bottom bracket is mounted on the platform of the Haake rotational rheometer.

[0042] The device is equipped with stress overload protection and adopts a reasonable measurement gap according to the actual particle size distribution characteristics of the powder or the positive pressure. The steel ball at the bottom of the flexible rotor is made of hardened steel, and the metal rod on the bottom bracket is made of quenched steel. They need to be inspected and replaced according to the number of experiments and powder characteristics to avoid large test system errors caused by equipment accessories.

[0043] Based on the Haake rotational rheometer and the flexible rotor, the powder friction coefficient test steps of the present invention are as follows:

[0044] (1) Before starting the test, two commonly used powders were selected as test samples, denoted as powder 1 and powder 2. The particle size distribution of the powders to be tested for friction coefficient was measured using a laser particle size distribution analyzer, and the corresponding median particle size D was recorded. 50 , the test results were 279μm and 155μm respectively, which served as the basis for gap setting in subsequent tests;

[0045] (2) A flexible rotor with a steel ball is installed on the rotating axis of the rheometer. The bottom of the flexible rotor is made of hardened steel balls with a Rockwell hardness of 50 to 60. Three metal rods are installed on the bottom bracket of the rheometer. The metal rods are made of quenched steel bars with a Rockwell hardness of 25 to 30. The surfaces of the steel balls and metal rods are coated with lubricant.

[0046] Add an appropriate amount of pure water to the temperature controller and adjust the gap between the rotor and the metal rod to zero through the data acquisition system;

[0047] (3) Raise the flexible rotor to a position approximately 20 cm from the bottom bracket, and load an appropriate amount of powder into the space formed by the three metal rods on the bottom bracket so that the powder covers the bottom groove of the conical space of the bottom bracket but does not exceed the top of the conical space of the bottom bracket;

[0048] (4) According to the median particle size D of the powder 50 Set the measuring gap so that the measuring gap is equal to the median particle size D of the powder to be measured. 50 , keep the gap unchanged during the measurement process; first test powder 1, and set the gap to 0.28mm;

[0049] (5) Use the constant temperature and constant speed measurement method, select the CR (constant speed) mode, set the test temperature to 25°C, set the speed range to 0-30 r / min, set the data acquisition time to 90 s, set the total number of data points to 180, and set the stress overload upper limit to 2.0 bar;

[0050] (6) Start the test, record the friction coefficient, test temperature, speed and other test parameters, and wait for the rotation to stop, and complete a round of testing. Keep the set temperature and speed conditions unchanged, replace the test sample with powder 2, set the measurement gap to 0.16mm, and continue to complete the next round of testing according to steps (4) to (5). Obtain the speed-friction coefficient data corresponding to different temperatures, and draw the speed-friction coefficient curve, such as Figure 3 .

[0051] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0052] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. To avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0053] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for testing the friction coefficient of powder, characterized in that: The testing device used in this method includes a Haake rotational rheometer, a flexible rotor, a steel ball, a metal rod, a bottom bracket, and a data acquisition system; The Hake rotational rheometer has a flexible rotor installed on its rotating axis, with a steel ball mounted at its bottom. During testing, the steel ball comes into direct contact with the powder. Multiple metal rods are arranged obliquely in the conical space of the bottom bracket, and the space enclosed by the metal rods is used to hold the powder to be tested. A temperature sensor and temperature controller are installed in the bottom bracket to monitor the temperature in real time during the test. The entire bottom bracket is fixed to the platform of the Hake rotational rheometer via threads. A data acquisition system is connected to the temperature sensor, temperature controller, and the rotating axis of the Hake rotational rheometer via cables to read and control the test data from the temperature sensor, temperature controller, and the rotating axis of the Hake rotational rheometer. The following steps are involved: Step 1: Before starting the test, the powder to be tested for friction coefficient is measured using a laser particle size distribution analyzer to obtain the particle size distribution of the powder, and the corresponding medium particle size D is recorded. 50 ; Step 2: Install a flexible rotor with a steel ball on the rotating axis of the Haake rotational rheometer, install a metal rod on the bottom bracket, add pure water to the temperature controller, and adjust the gap between the flexible rotor and the metal rod to zero using the data acquisition system; Step 3: Raise the flexible rotor to a position 10 to 20 cm from the bottom bracket, and load the powder into the space enclosed by the metal rods on the bottom bracket, ensuring that the powder covers the bottom groove of the conical space of the bottom bracket and does not exceed the top of the conical space of the bottom bracket; Step 4: Determine the gap between the flexible rotor and the metal rod. Method 1 is based on the median particle size D of the powder. 50 Set the measuring gap so that the measuring gap is equal to the median particle size D of the powder to be measured. 50 , keep the gap unchanged during the measurement process; the second method is to set the gap according to the positive pressure between the flexible rotor and the powder, and keep the positive pressure unchanged during the measurement process; Step 5: Use a constant temperature, constant speed, or constant stress measurement method. Select the constant speed or constant stress mode, set the test temperature and speed or stress, data acquisition time, and the total number of data points. Set the stress overload upper limit to 2 to 2.5 bar. Step 6: Start the test, record the friction coefficient, test temperature, speed or stress test parameters, and wait for the rotation to stop to complete one round of testing; change the test temperature, speed or stress, and continue to complete the next round of testing according to steps 3 to 5; obtain the speed or stress-friction coefficient data corresponding to different temperatures and draw a relationship diagram.

2. The method for testing the friction coefficient of powder according to claim 1, wherein: There are three metal rods, which are arranged in a centrally symmetrical manner, with an angle of 120° between any two of them.

3. The method for testing the friction coefficient of powder according to claim 1, wherein: The steel ball has a Rockwell hardness of 50-60.

4. The method for testing the friction coefficient of powder according to claim 1, wherein: The metal rod is made of quenched steel bar with a Rockwell hardness of 25-30.

5. The method for testing the friction coefficient of powder according to claim 1, wherein: The surfaces of the steel ball and the metal rod are coated with lubricant.

6. The method for testing the friction coefficient of powder according to claim 1, wherein: In step 4, when the gap between the flexible rotor and the metal rod is determined according to the positive pressure between the flexible rotor and the powder, the positive pressure is 1 to 3N.

Images