The particle wear index testing device is used to evaluate the wear resistance of materials under the action of particle media. One of its core functions is to accurately measure the frictional force through a wear testing machine to quantify the degree of material wear. The following are the detailed methods and technical points for measuring friction in the device:
1、 Principle of Friction Measurement
In the particle wear test, the frictional force mainly comes from the following two aspects:
Sliding friction between particles and material surfaces: During the movement of particles, they slide relative to the surface of the sample, generating tangential friction.
The impact and cutting effect of particles on materials: When high-speed particles impact the surface of materials, in addition to the normal impact force, tangential force components (i.e. frictional force components) are also generated.
Friction measurement requires the use of sensors to convert mechanical signals into electrical signals, which are then processed by a data acquisition system to output the results.
2、 Key measurement methods and technologies
1. Direct measurement method: high-precision force sensor
Sensor type:
Strain gauge force sensor: detects friction force through changes in strain gauge resistance, suitable for low-speed, steady-state wear tests.
Piezoelectric force sensor: using the piezoelectric effect to measure dynamic friction, with a high response frequency (up to kHz level), suitable for high-speed particle impact testing.
Capacitive force sensor: non-contact measurement, suitable for high temperature or corrosive environments, but the accuracy is greatly affected by the medium.
Installation location:
Sample fixture end: The sensor is directly connected to the sample to measure the total frictional force of particles on the sample (considering the influence of fixture stiffness).
Inside the particle flow channel: Install sensors on the particle conveying pipeline or rotating disc to measure the tangential force of the particle fluid (requiring calibration of particle distribution uniformity).
Calibration requirements:
Use standard weights or force calibration devices (such as tensile machines) to perform static calibration on the sensor, with a deviation of ≤± 0.5% FS (full range).
Dynamic calibration requires simulating actual wear conditions (such as particle impact frequency and velocity) to ensure frequency response characteristics match.
3. Multi parameter coupling measurement method
Combining normal force and friction coefficient:
Simultaneously measure the normal force.
Suitable for studying the influence of particle shape and size on friction behavior (such as comparing spherical particles with angular particles).
Acoustic emission signal assisted analysis:
Monitoring the elastic waves generated by particle impact through acoustic emission sensors, combined with friction data to determine the wear mechanism (such as fatigue wear or cutting wear).
High speed camera and image processing:
Capture particle motion trajectories, establish a particle velocity friction relationship model based on friction data, and optimize experimental parameters such as particle flow velocity and concentration.
3、 Composition of Friction Measurement System
Sensor module:
Selecting the maximum friction force for the range coverage test (usually 20% -50% of the normal force) is essential for overload protection function.
Protection level ≥ IP65, preventing particle dust from entering and causing signal drift.
Signal conditioning module:
The amplifier gain is adjustable and compatible with sensors of different ranges.
The cut-off frequency of the low-pass filter is ≥ 10 times the highest test frequency (if the particle impact frequency is 100Hz, the cut-off frequency of the filter is ≥ 1kHz).
Data collection module:
Sampling rate ≥ 1kHz to ensure capturing of dynamic friction peak values.
Support multi-channel synchronous acquisition (such as simultaneous measurement of parameters such as normal force, tangential force, temperature, etc.).
Software analysis module:
Real time display of friction curve, supporting data export (such as CSV, Excel format).
Automatically calculate wear indices (such as unit frictional energy, wear rate, etc.) and generate test reports.
4、 Error control and optimization measures
Sensor installation error:
Ensure that the sensor axis is aligned with the direction of friction, with a deviation of ≤± 1 ° (which can be calibrated using a laser alignment instrument).
The stiffness of the fixture should be ≥ 10 times the stiffness of the specimen to avoid force transmission loss caused by elastic deformation.
Environmental interference:
The temperature fluctuation in the laboratory is ≤± 2 ℃, and the humidity is ≤ 60% RH (to prevent sensor drift).
Electromagnetic shielding: The sensor cable is made of twisted pair and covered with a metal braided layer, with a grounding resistance of ≤ 1 Ω.
Particle media influence:
Uniformity of particle size distribution: D50 deviation ≤± 10% (detected by laser particle size analyzer).
Particle shape control: Avoid fluctuations in friction measurement values caused by elongated or sheet-like particles.
Dynamic response optimization:
The natural frequency of the sensor is ≥ 5 times the highest test frequency (if the particle impact frequency is 100Hz, then the natural frequency of the sensor is ≥ 500Hz).
The cutoff frequency of the anti aliasing filter in the data acquisition system matches the sampling rate (following the Nyquist theorem).
5、 Typical application cases
1. Testing of wear-resistant materials for mining machinery
Experimental conditions:
Particle: Quartz sand (particle size 0.5-1.0mm, Mohs hardness 7).
Sample: High chromium cast iron liner plate (hardness HRC ≥ 58).
Friction measurement: Strain gauge force sensor (range 0-1000N), installed at the end of the specimen fixture.
Result analysis:
Friction fluctuates periodically with time (related to the frequency of particle impact), and the peak friction force is proportional to the kinetic energy of the particles.
2. Wear test of air particle two-phase flow on aircraft engine blades
Experimental conditions:
Particle: Alumina ceramic particles (particle size 10-20 μ m, density 3.9g/cm ³).
Sample: Nickel based high-temperature alloy turbine blade (surface coating is YSZ thermal barrier coating).
Friction measurement: Piezoelectric force sensor (range 0-50N, frequency response 0-10kHz), installed at the edge of the rotating disk.
Result analysis:
When high-speed airflow carries particles to impact blades, the friction signal exhibits high-frequency noise characteristics (which need to be denoised through wavelet transform).
Coating peeling threshold: When the peak friction force exceeds 20N, microcracks begin to appear in the coating.
6、 Technological development trends
Miniaturization and Integration:
Develop MEMS (Micro Electro Mechanical Systems) force sensors to achieve in-situ measurement of frictional forces (such as embedding them inside the sample).
Intelligent and adaptive control:
Combining machine learning algorithms to automatically adjust particle flow velocity or load based on changes in friction, optimizing experimental efficiency.
Multi physics field coupling test:
Synchronously measure parameters such as friction, temperature, and strain to study the thermal mechanical coupling effect during the wear process.
summary
In the particle wear index test device, friction force measurement needs to be combined with direct method (force sensor) and indirect method (torque/power method), and data reliability should be improved through multi parameter coupling analysis. Key technologies include high-precision sensor selection, dynamic error control, and environmental interference suppression. In practical applications, it is necessary to choose a suitable measurement scheme based on experimental conditions such as particle type, velocity, and load, and strictly follow calibration and maintenance specifications to ensure the accuracy of wear index evaluation.