Abstract: Sliding bearings are key components of speed increasing hydraulic couplings. This article analyzes and summarizes the failure mode of sliding bearings that has occurred in the past, identifies 16 common causes, and then conducts technical research on the causes of failures. 15 effective measures have been developed and applied to the design and production of speed increasing hydraulic couplings, achieving significant results. Fault tree analysis has also been conducted on the failure of sliding bearings.

Keywords: sliding bearings; Failure handling measures; Fault Tree Analysis

Bearings are an important link that affects the lifespan of the entire machine. In a speed increasing hydraulic coupling, sliding bearings are used to reduce radial dimensions due to the high power and speed transmitted. Once the bearing fails and needs to be replaced, the entire machine must be disassembled before proceeding, so the bearing has a significant impact on the working ability of the host. In the speed increasing hydraulic coupling, sliding bearings are key components. Due to design, manufacturing, installation, and usage reasons, the failure of sliding bearings can occur, which is a malignant accident with serious consequences.

The failure of sliding bearings can be classified into several types based on their mechanisms, including wear, fatigue corrosion, and cavitation corrosion wear. The main failure modes of sliding bearings in speed increasing hydraulic couplings belong to the first two types. Fatigue failure can also be classified as fatigue wear. The common types of wear failure Z are adhesive wear and abrasive wear. The reason for adhesive wear is that under boundary lubrication conditions, the oil film is damaged or foreign objects are embedded in the metal surface of the bearing, causing direct contact between the metal surfaces of the shaft and the bearing locally, frictional heating, resulting in an increase in oil temperature and a decrease in viscosity. Sometimes, the heating causes the surface metal to flow, ultimately resulting in biting and sticking, making the machine unable to operate in an instant.

The general appearance of bearing damage is unstable operation and abnormal noise; Another appearance manifestation is the increase in bearing temperature. This situation may occur for damage caused by tight bearing installation or poor lubrication. A sudden increase in operating temperature under constant working conditions is generally a sign of bearing damage.

Based on the above symptoms, we can monitor the working condition of the bearing by measuring temperature or vibration.

There are many reasons for bearing damage, some of which are normal damage, while others are caused by working conditions, assembly, maintenance, and other factors, and are considered abnormal damage. For example, tight fitting, poor lubrication, oil contamination without cleaning, iron filings, metal powder from gear wear entering the bearing through the lubrication system to accelerate bearing wear, water in the oil, and condensed water formed by rapid cooling of bearings that generate heat during operation can also cause bearing corrosion.

In order to avoid the recurrence of similar accidents, reduce losses, and ensure that the sliding bearings in the coupling are truly controlled in the design, development, production, experimentation, installation, maintenance, operation, and management stages, and to comprehensively improve the quality of the sliding bearings, we have conducted reliability research on the sliding bearings based on the successful experience of previous development and production, as well as the lessons learned from various failures that have caused losses and impacts. We have also referred to reference [2]. The fundamental task of reliability research is to take all measures to minimize and avoid various failures, extend the service life of products as much as possible, and improve the quality indicators measured by product time. That is to say, the fault analysis and handling measures for the failure of sliding bearings in speed increasing hydraulic couplings are the core content of reliability research on sliding bearings. We conducted a root cause analysis of the faults in the sliding bearings and developed corresponding measures for handling them. We also conducted a fault tree analysis.

1. Reason for failure

Based on the analysis and summary of the previous failure mode of sliding bearings, and on this basis, we conducted reliability research and found that the causes of sliding bearing failure are as follows:

(1) Improper installation;

(2) The oil wedge is installed in the opposite direction, resulting in the inability to form a lubricating oil film;

(3) The material of Babbitt alloy does not meet the requirements;

(4) Impurities or foreign objects entering the bearing in the oil;

(5) The thrust bearing has serious defects such as Babbitt alloy peeling and looseness;

(6) The casting temperature of the thrust tile is too high, causing the grain size of the Babbitt alloy to become coarse and the performance to decrease;

(7) No ultrasonic testing was conducted;

(8) Unreasonable design;

(9) The thrust tile does not have a good "hanging lining";

(10) Scratches on the working surface of the bearing shell;

(11) Excessive bearing clearance;

(12) Excessive water content in lubricating oil;

(13) Cut off oil or insufficient lubricating oil;

(14) Lubricating oil temperature is too high;

(15) The positioning pin hole of the thrust disc thrust tile is too shallow, causing uneven force on the thrust tile and resulting in temperature rise and tile burning;

(16) Poor contact of thrust tile.

2. Handling measures

To address the causes of failures in sliding bearings and ensure further improvement in their quality, we have conducted technical research and strengthened the study of fault handling measures. The main measures formulated are as follows:

(1) Correct installation;

(2) Check if the direction of the oil wedge is correct to ensure the formation of a lubricating oil film;

(3) Strictly ensure that the composition of Babbitt alloy meets the standards;

(4) Remove impurities and foreign objects from the oil to ensure the cleanliness of the lubricating oil;

(5) Ultrasonic inspection must be conducted on the thrust bearing shell to strictly control its quality;

(6) Improve the casting quality of bearing shells;

(7) Reasonable design;

(8) The thrust tile must be 'lined' according to regulations;

(9) Repair or replace the scratched bearings on the working surface;

(10) Scratch bearings with excessive clearance;

(11) Check if the cooler (heat exchanger) is leaking, or replace it with new oil to solve the problem of high water content in the oil;

(12) Increase the supply of lubricating oil to ensure good lubrication of the bearings;

(13) Strengthen cooling measures, improve cooling efficiency, and reduce oil temperature;

(14) Check whether the positioning pin of the thrust tile is correctly positioned to prevent uneven force on the thrust tile caused by improper positioning;

(15) Check if the thrust tile contacts correctly.

3. Fault Tree Analysis

The fault tree analysis of sliding bearing failure is shown in Figure 1.

Figure 1 Fault Tree of Sliding Bearing Failure in Speed Increasing Hydraulic Coupling

4. Conclusion

(1) 16 common causes of sliding bearing failure have been identified;

(2) Developed 15 measures for handling the failure of sliding bearings;

(3) Fault tree analysis was conducted on the failure of sliding bearings.

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