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Wen | Yu Yingsha
Editor|Yuyingsha
Rolling bearings are indispensable support components in rotating machinery, due to the harsh operating environment, failures occur from time to time, and the failure rate of the outer ring is the largest during the operation of axlebox bearings. Therefore, the following experiment mainly studies the vibration characteristics of the outer ring when it fails.
In addition, many scholars only study the characteristics of bearing faults under single working conditions, and the vibration characteristics caused by faults under different working conditions are also very important.
Therefore, the vibration characteristics of bearings under different fault sizes, fault locations and different loads are experimentally studied, which provides a basis for the movement of other components and lays a foundation for bearing fault diagnosis.
Analysis of factors influencing bearing failure response
CRH3 train bearing appearance state inspection found that there is a 3mm 50mm peeling area in the outer ring raceway of the bearing, and the outer ring raceway is seriously rusted, if not found in time, with the increase of operating mileage, the damage size will gradually increase.
Studying the change law of bearing fault response with damage size can effectively prevent bearing failure in advance, minimize the number of wheelset replacements, and ensure the normal operation of EMUs.
According to the parameters of a certain column of CRH3, a vehicle model is established based on Simpack, including the car body, frame, first series suspension, second series suspension, rotary arm axlebox, bearing, wheelset, and all structures are rigid bodies.
Figure 2 shows the topology of the vehicle, with No. 5 force element used as the first series suspension between the axlebox and the frame, and No. 5 force element used as the second series suspension between the frame and the car body.
Without wheel-rail disturbances, the vehicle runs on an ideal straight road, the axlebox does not vibrate, and the bearing is subjected to a load of 59.5 kN of gravity of the car body.
In order to simulate the actual operating environment, the five-stage spectrum is applied, the vehicle speed is set to 250km/h, and the simulation results of the axlebox bearing load are shown in the figure below, the axial load received by the bearing is repeated around 0kN, about 0-2kN, and the radial load received by the bearing is repeated up and down the vehicle weight force, about 55-65kN, which provides a basis for subsequent analysis.
Creation of geometric models
In this experiment, a double-row tapered roller bearing of a train was used as the research object, and the bearing geometry model with outer ring spalling fault was established by using SolidWorks 3D modeling software, and the main parameters were shown in Table 1.
For the spalling fault of the outer ring raceway, on the basis of the normal bearing, a rectangular groove is cut off, the assembly drawing of the bearing is shown in Figure 4, and the simulated vibration acceleration signal extracts the vertical signal of the maximum force on the outer ring of the bearing.
The bearing geometry was imported into the dynamics software and assembled, and the bearing material was GCr15 steel, with a density of 7850kg/m3, an elastic modulus of 210GPa, and a Poisson's ratio of 0.3.
Setting of bearing contact relationship: The contact between the roller and other components is calculated using the Hertzian contact, penalty function method.
There are many contact relationships in bearings, including rollers and inner ring raceways, rollers and outer ring raceways, rollers and cages, a total of 114 pairs of contact relationships.
Set each pair of contacts as a contact pair, with the source boundary being the roller cylinder and the target boundary being the inner and outer ring raceways and cage contact surfaces.
Rigid-flex coupling setting: the bearing inner and outer rings and cages are set as flexible bodies, bearing rollers are set as rigid bodies, fig. 6 is the comparison of the vibration acceleration of rigid-flex coupling bearings and rigid bearings, and the vibration response generated when the rigid body and rigid body are in contact is too large.
In order to speed up the calculation speed, the rollers are considered as rigid bodies, and other components are considered as flexible bodies, and rigid rollers are in contact with other flexible components to overcome the above two shortcomings.
When the bearing is running stably, there is a proportional relationship between the rotational speed between the bearing elements, which can be used as a tool to verify the correctness of the model, when the outer ring of the bearing is fixed, and the inner ring rotates the fixed shaft at ωo as the speed.
The roller and cage speeds in the bearing bearing zone are ωr and ωc as shown in equations (1) and (2):
Formula: dm is the bearing section diameter; Db is the roller diameter; αi is the bearing contact angle.
Table 2 and Table 3 show the comparison results between the theoretical value and the simulated value of bearing speed, and the theoretical value and simulation value error of cage and roller speed are within a reasonable range, which verifies the rationality of the model built in this paper.
Fig. 7 shows the vibration time domain diagram of the bearing outer ring failure, and the time interval between adjacent shocks is 0.0048s.
The time domain map envelope is demodulated to obtain the vibration frequency domain diagram of the bearing in Figure 8, and the corresponding fault frequency of the simulation is 208Hz, and the error between the theoretical value of 209Hz is 0.05%, which further verifies the effectiveness of the model.
Effect of damage scale on bearing vibration characteristics
With the change of bearing damage scale, the dynamic response will show a certain transformation law.
In the following experiment, the radial load of the bearing is 75kN and the axial load is 2.5kN, and the influence of different damage widths and different damage depths on the dynamic response of the bearing when the damage is in the center of the bearing zone is studied.
The type of impact produced by different damage scales is also different, as shown in Figure (a), when the scale of damage is small, the roller moves from position 1 to position 2 to position 3 from entering the fault area to the fault area, and only receives one impact at position 2, so an impact will be generated.
Figure (b) shows that when the scale of the damage is large, the roller receives one impact at position 1 and position 3 from entering the fault zone to exiting the fault area, resulting in a total of two impacts.
Fig. 10 shows the maximum bearing time domain response for different fault widths, and the amplitude of bearing vibration acceleration increases as the damage width increases.
In Figure 11, fs represents the frequency conversion, fo represents the characteristic frequency of bearing outer ring fault, under different damage widths, the characteristic frequency of bearing faults is the same, and with the increase of damage width, the amplitude of bearing fault characteristic frequency becomes larger and larger.
Figure 12 shows that when the damage depth is 2mm, the damage width is 2mm, 4mm, 6mm, the bearing vibration acceleration time history, when the damage width is 2mm, 4mm, the shock signal is single shock, when the damage width is 6mm, the shock signal becomes double shock.
Effect of different damage depths on bearing dynamic response
Fig. 13 shows the maximum time domain response of bearings at different fault depths, with the amplitude of bearing vibration acceleration increasing as the depth of damage increases.
It can be seen from Figure 14 that the characteristic frequency of bearing faults is the same under different damage depths, and with the increase of damage depth, the amplitude of bearing fault characteristic frequency becomes larger and larger, but the amplitude of change is less than the damage width.
Figure 15 shows that when the damage width is 4mm and the damage depth is 1mm, 2mm and 3mm, the bearing vibration acceleration time history, with the increase of the damage depth, the shock signal becomes more and more obvious.
Overall, the larger the bearing damage size, the more obvious the fault characteristics, in which the influence of the damage width on the fault signal is greater than the damage depth, in addition, when the bearing damage width is large, the bearing fault impact will change from single impact to double impact.
When the bearing is damaged, the damage position is different, and the bearing dynamic response will also change, as shown in Figure 16, F is represented as the bearing is subjected to radial load, the 12-point directional damage is in the bearing zone, the 3-point directional damage is at the junction of the bearing area and the non-bearing zone, and the 6-point directional damage is in the non-bearing zone.
The simulation results are shown in Figure 17. When the damage location is in the non-bearing zone (6 points) and the junction of the bearing area and the non-bearing area (3 points), the maximum vibration acceleration of the bearing is around 15m/s2.
When the damage location is in the bearing zone (12 points), the maximum vibration acceleration of the bearing is around 50m/s2, which is much higher than the other two cases.
It can be seen from Figure 18 that when the bearing damage position is in the bearing area, the fault frequency and frequency multiplication of the outer ring are more obvious, and the fault characteristics of the other two situations are not obvious.
This is due to the large contact force between the roller and the inner and outer ring in the bearing bearing area, and the greater the impact generated by the roller when passing through the fault, the larger the amplitude of the characteristic frequency of the fault. It also shows that the closer the bearing damage is to the bearing area, the easier the fault diagnosis is.
The effect of load on bearing vibration characteristics
During train operation, the load is not constant, and the dynamic response of the bearing is also different under the action of different loads.
The following experiments study the effects of different axial loads and radial loads on the dynamic response of bearings when the damage width is 4mm, the damage depth is 2mm, and the damage location is in the center of the bearing area.
Figure 19 shows the maximum vibration acceleration values for different radial loads, and it can be seen that with the increase of radial loads, the amplitude of the bearing vibration acceleration time domain response increases significantly.
It can be seen from Figure 20 that the characteristic frequency of faults of bearings with different radial loads remains unchanged, and the response amplitude increases significantly.
Figure 21 shows that when the axial load is 2.5kN and the radial load is 45kN, 60kN, 75kN, 90kN, the bearing vibration acceleration time history, with the increase of radial load, the impact of bearing failure gradually increases.
Figure 22 shows the maximum vibration acceleration for different axial loads, and the amplitude of the bearing vibration acceleration time domain response increases slightly as the axial load increases.
It can be seen in Figure 23 that the fault characteristic frequency of different axial load bearings is the same, and the amplitude of the fault characteristic frequency increases slightly.
Figure 24 shows that when the radial load is 60kN and the axial load is 2.5kN, 5kN, 7.5kN, the bearing vibration acceleration time history, it can be seen that the radial load change has little effect on the bearing vibration response.
In summary, when the bearing is under a large force, with the increase of the force, the impact of the fault becomes larger, and the amplitude of the characteristic frequency of the bearing failure increases, among which the influence of radial load on bearing vibration is much greater than that of axial load, indicating that the larger the bearing load, the greater the impact on other components when the fault occurs.
conclusion
In the above experiment, according to the operating state of the axlebox bearing and the vibration response of the bearing failure under different working conditions, the bearing roller is set as a rigid body and other components are set as a flexible body, and a finite element model with faulty rigid-flex coupling of train axlebox bearings is established.
The effectiveness of bearing speed and fault frequency is verified by experiments, and the dynamic characteristics of bearing faults under different fault sizes, different fault locations and different loads are simulated and analyzed, and the following conclusions are obtained:
First: According to the operating characteristics of axlebox bearings, the experiment establishes a rigid-flex coupling model that considers the bearing rollers as rigid bodies and other components as flexible bodies.
The shortcomings of excessive vibration response of full rigid body and long finite element simulation time of fully flexible body are improved, and the dynamic response under bearing failure can be reflected more realistically and quickly.
Second: the size of the bearing failure is different, and the type of impact produced is also different.
When the bearing fault reaches a certain width, the displacement shock generated by the fault changes from single impact to double shock.
The experiment modifies the assumption that the vibration shock caused by raceway spalling is simply considered as a single shock without considering the fault size, and the degree of bearing failure can be inferred by the vibration response at the time of bearing failure, which provides a reference for establishing the dynamic equation in the bearing fault state.
Third: the bearing vibration response is related to the bearing fault size, fault location, and load size.
The larger the bearing damage size, the closer to the bearing area, the greater the force (when the load is large), the more obvious the characteristic frequency of the fault, among which, the influence of the damage width on the fault signal is greater than the damage depth, and the influence of radial load on the fault signal is greater than that of axial load.
In this experiment, the vibration characteristics of bearings under different working conditions were simulated under various working conditions, and it can be seen that the vibration response under bearing faults is related to various factors.
When diagnosing bearing faults through bearing vibration signals, it is necessary to consider many factors such as fault size, fault location, and load situation. The simulation results in this paper can provide a reference for bearing fault diagnosis.