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One-time lubrication life test of motor rotor bearing

by:JNSN     2021-10-29
The oil-lubricated ball bearings used in the motor rotor are characterized by small load, high precision, long life, small friction torque and high stability. Under normal working conditions, an important factor affecting bearing service life, friction torque and reliability is bearing lubrication. When the bearing is under specific working conditions (such as a vacuum-tight environment, etc.), it can only rely on the lubricating oil contained in the cage to maintain the lubrication of the bearing and maintain the normal operation of the motor rotor, which is a one-time lubrication. The special working environment (vacuum airtightness) and long-life requirements of the motor rotor are difficult to meet the requirements even if oil-containing cage bearings are used. A suitable oil supply system must be provided and supplementary oil supply can be provided to ensure the full lubrication of the bearings. When supplying oil to the bearing, it is necessary to analyze the lubrication state of the bearing to determine the approximate time to replenish the oil.

Although there are many theoretical calculation formulas and application experience for bearing lubrication, they have considerable limitations. The mathematical models and empirical coefficients of the calculation formulas are generally established under ideal process quality conditions, and the obtained values u200bu200boften deviate from the actual values. The complexity and systematic nature of bearing lubrication determines that test and test analysis are an important basis for testing bearing lubrication design.

The one-time lubrication life of a bearing refers to the time during which the bearing can maintain normal operation without external supplementary lubrication. The way of bearing failure is not fatigue failure, but accuracy failure due to insufficient lubrication, which in turn causes bearing wear failure. In order to study the impact of one-time lubrication on the life of motor bearings, a 1:1 simulation test was carried out under the same working conditions.

1 Test method

16 sets of 7004 ball bearings are divided into 8 groups for (motor rotor) bearings are generally used in pairs. During the test, the running current, voltage and speed of the motor rotor are monitored and recorded. When the operating current of the motor exceeds the current performance index and an abnormality occurs, the bearing is considered to be invalid.

Before the test, the bearings are screened and evaluated, and qualified bearings are selected for testing. The test method and process are as follows:

(1) Wash and dry the bearing according to the cleaning specification.

(2) The cage is treated according to the oil immersion process.

(3) According to the running-in specification, the initial running-in is carried out after the bearing is assembled.

(4) After initial running-in, install the bearing into the motor rotor according to the assembly process.

(5) According to the actual working conditions, a one-time lubrication life test is carried out on the bearing. During the test, the running current, voltage and speed of the motor rotor are monitored and recorded.

(6) After the end of the life test, make a curve diagram of the motor running current with time according to the test data, and make a bearing lubrication life curve according to the curve diagram; and analyze the life curve.

2 Test equipment and conditions

The test equipment is a bearing running-in tester. The equipment can drive the bearing to run through the drive motor, and at the same time has the function of collecting and recording bearing running-in data; the bearing running motor adopts an ironless brushless DC motor. Real-time monitoring and recording of the current, voltage and speed of the test bearing motor are realized by the test equipment, and the current change curve with time can be accurately drawn, and the current fluctuation change and the fluctuation of the bearing friction torque can be judged in time.

Test conditions:

(1) Ambient temperature (20±5)℃, vacuum degree ≤10Pa.

(2) The axial load of the bearing is 30~40N (meet the working requirements of the motor rotor).

(3) The bearing speed is operated according to the actual working speed of the motor rotor of 5600r/min.

3 Test results and analysis

The test focused on real-time monitoring and recording of the current, voltage and speed of the motor rotor, and based on the test data, the curve of time and operating current was made. Due to the relatively long duration of the test It is long and the amount of test data is large. Therefore, this article only draws the curve of the bearing operating current with time based on the test data, as shown in Figure 1.

According to the 8 sets of curves in Figure 1, after sorting, the corresponding lubrication life curve of the bearing in the one-time lubrication process can be obtained, as shown in Figure 2.

It can be seen from the curve in Fig. 2 that the bearing has been running for about 25 months under a one-time lubrication state, and the whole test process is divided into 4 stages: sufficient lubrication stage, lubrication balance stage, and insufficient lubrication Phase and lubrication failure phase.

When the lubrication state of the bearing is completely destroyed, the temperature rise and operating current of the bearing increase sharply, accompanied by a noticeable harsh dry friction sound. The operation time of the lubrication failure area is less than 1 month.

4 Conclusion

(1) Without supplementary oil supply to the motor rotor bearings, the service life of the bearings can only meet 22 months of normal continuous operation.

(2) The lubrication time for the supplementary lubrication of the motor rotor bearing should be selected before the bearing is insufficiently lubricated, considering that the bearing may have microscopic dry friction and insufficient lubrication in the latter half of the lubrication balance zone. Performance is not shown), in order to ensure the reliability of bearing lubrication, the oil supply time can be appropriately advanced to 15 to 18 months.

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