several reasons why bearings can be damaged or fail
Generally speaking:
• 1/3 fail due to fatigue
• 1/3 fail due to lubrication problems (wrong lubricant, wrong quantity, wrong lubrication interval)
• 1/6 fail due to contamination (ineffective seals)
• 1/6 fail for other reasons
(improper handling and mounting, heavier or different loading than anticipated, wrong or inadequate fits) The figures vary depending on the industry or application. In the pulp and paper industry, for example, a major cause of bearing failure is contamination and inadequate lubrication, not fatigue.
Each of these events produces a unique damage imprint, called a pattern. Consequently, by examining a damaged bearing carefully, it is possible, in the majority of cases, to find the root cause of the damage. Based on the findings, corrective actions can be taken to prevent a recurrence of the problem.
When to replace a bearing?
The amount of time from the first (initial) damage until the bearing becomes unserviceable can vary considerably. At higher speeds, it can take a few seconds. In large, slow rotating machines, it can take months. The question, “When should I replace the bearing?”, is best answered by monitoring
the condition of the bearing ( Inspection and troubleshooting),
If a damaged bearing goes undiagnosed and is not replaced before it fails catastrophically, secondary damage to the machine and its components can result. Also, when a bearing fails catastrophically, it can be difficult, even impossible, to determine the root cause of the failure.
How to Inspection during operation
Early indications of bearing damage enable a user to replace bearings during regularly scheduled maintenance, avoiding otherwise costly unscheduled machine downtime due to bearing failure. Important parameters for monitoring machine conditions include noise, temperature, and vibration.
Bearings that are worn or damaged usually exhibit identifiable symptoms. Many possible causes could be responsible and need to be investigated. For practical reasons, not all machines or machine functions can be monitored using advanced systems. In these cases, trouble can be detected by looking at or listening to.
Oilless Bushing Inspection Guidelines
When inspecting a mounted bearing, Viiplus recommends following these general guidelines:
• Clean the external surface of the machine.
• Remove the housing cover, or the housing cap, to expose the bearing.
• Take lubricant samples for analysis. For oil lubrication, take samples from the sump/reservoir. For grease-lubricated open bearings, take samples from various positions within the bearing. Visually inspect the condition of the lubricant. Often impurities can be detected by spreading a thin layer on a sheet of paper and examining it under light.
• Clean the exposed external surfaces of the bearing with a lint-free cloth. Inspection
• Inspect the exposed external surfaces of the bearing for fretting corrosion. Inspect the bearing rings for cracks.
• For sealed bearings, inspect the seals for wear or damage.
• Where possible, rotate the shaft very slowly and feel for uneven resistance in the bearing. An undamaged bearing turns smoothly.
Grease lubricated open bearings in dedicated bearing housings, e.g. split Plummer blocks, can be subject to a more detailed in-situ inspection as follows:
• Remove all grease around the bearing.
• Remove as much grease from the bearing as possible using a non-metallic scraper.
Lubrication way
Bearing failure and fatigue life of wind turbine
The failure rate of gearbox, motor and other key components in wind turbine transmission system is high, and the failure of gearbox and motor is caused by bearing failure.
With the rapid development of wind power technology, the requirements for the overhaul and maintenance of the wind turbine is becoming more and more strict, due to the change of the unit type, size, service environment as well as the installation error and so on reasons, lead to bearing failure mechanisms are also different, so the bearing failure analysis is varied, the wind generator and chooses the bearing mostly belong to large bearing, However, due to the particularity of size and working environment, large bearings are often damaged by local deformation, local vibration, and temperature rise, which is not the same as ordinary bearings. Therefore, the bearing status of wind turbines should be monitored in real-time effectively and maintained reasonably at the best time.
There are a variety of characteristic signals (vibration, acoustic emission, stress, temperature, lubricating oil, etc.) in wind turbine bearings. All kinds of characteristic signals can reflect the health state of bearings to a certain extent, so the characteristic signals can be used for fault analysis and diagnosis of bearings.
The overall strength and life of bearings can be improved by the control of load, clearance, rotational speed, and the modification of the rolling body.
Research on bearing Fault Diagnosis of Wind Turbine: Early parts change characteristic of fault symptoms will cause a series of various physical quantities, at the same time, the fluctuations of a single physical characteristic may be caused by several parts, such as, when the yaw system of gear and bearing fatigue failure, will cause the vibration of the generator rotor, which destroy the generator’s internal balance, Then the fault signal will be attached to the electrical characteristic quantity or vibration characteristic quantity of the stator and rotor of the generator. Therefore, it is necessary to combine the actual situation of bearings in different parts and the differences of different units and transform from the previous single and multi-feature longitudinal data fusion analysis method to the multi-angle analysis method, so as to seek the fault data characteristics and evolution rules of bearings in various parts.
