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Bearing failure analysis method?

release time:2018-05-26
In the process of analyzing bearing failures, there are often many intricate and complicated phenomena. The results of various experiments may be inconsistent or unclear. This requires repeated experiments and demonstrations in order to obtain sufficient evidence or counter-evidence. Only by using the correct analytical methods, procedures, and procedures can the true cause of failure be found.
Under normal circumstances, bearing failure analysis can be roughly divided into the following three steps: failure to collect physical and background data, macro-inspection and micro-analysis of the physical failure.

1. Failure to collect physical and background material
As much as possible, collect the parts and fragments of the failed item. Fully understand the working conditions, use process, and manufacturing quality of failed bearings. Specific content includes:
(1) Design conditions of the bearing such as the load, rotation speed, and working conditions of the main engine.
(2) The failure of the bearing and other parts of the relevant part, the type of bearing failure.
(3) Bearing installation and operation records. Whether there is abnormal operation during operation.
(4) Whether the actual load in bearing operation is in line with the original design.
(5) The actual rotation speed of the bearing and the frequency of occurrence of different rotation speeds.
(6) Whether there is a sharp increase in temperature or smoke during failure, and whether there is noise or vibration.
(7) Is there any corrosive medium in the working environment? Is there any special surface oxidation or other staining color between the bearing and the journal?
(8) Bearing installation records (including re-inspection of bearing size tolerances before installation), original bearing clearances, assembly and alignment, how bearing housing and frame rigidity are, and whether there is any abnormality in installation.
(9) Whether the bearing operation has thermal expansion and power transmission changes.
(10) Lubrication of the bearing, including the brand, composition, color, viscosity, impurity content, filtration, replacement, and supply of the lubricant, and collection of the precipitate.
(11) Whether the material of the bearing is correct and whether the quality of the material meets the relevant standards or pattern requirements.
(12) Whether the bearing manufacturing process is normal, whether the surface has plastic deformation, and whether there is surface grinding burn.
(13) Repair and maintenance records of failed bearings.
(14) Failure of the same batch or similar bearing.
It is very difficult to meet all of the above requirements in the collection of actual background materials. However, the more data collected, the more confident it will be to obtain the correct conclusions.
2. Macro inspection
The macro inspection of the failed bearing (including dimensional tolerance measurement and surface condition inspection analysis) is the most important part of failure analysis. The overall visual inspection provides an overview of the failure of the bearing and the characteristics of the damaged part, estimates the cause of the failure, reviews the size, shape, location, quantity, and characteristics of the defect, and intercepts the appropriate site for further microscopic inspection and analysis. The macro inspection includes:
(1) Changes in shape and size (including vibration analysis, dynamic function analysis, and roundness of raceway).
(2) Changes in clearance.
(3) Whether there is corrosion or not, what type of corrosion is, and whether it is directly related to failure.
(4) Whether there are cracks, crack morphology and fracture properties.
(5) What type of wear is and how effective it is for failure.
(6) Observe the condition and location of discoloration on the working surface of each component of the bearing to determine its lubrication condition and surface temperature effect.
(7) Mainly observe the failure characteristic area for abnormal wear, foreign particles embedded, cracks, scratches, and other defects.
(8) Cold-acid pickling or hot-acid pickling test to inspect the original surface of bearing parts for soft spots, decarburized layers, and burns, especially for surface grinding burns.
(9) Use an X-ray stress measuring instrument to measure the change in stress before and after bearing operation.
As a result of macro inspections, the form and cause of failure can sometimes be basically judged. However, to further determine the nature of the failure, more evidence must be obtained for micro analysis.
3. Microscopic analysis
Microscopic analysis of failed bearings includes optical metallography, electron microscopy, probes, and electron spectroscopy. Mainly based on the change of the microstructure of the failure characteristic area and the analysis of the fatigue source and the crack source, it provides more sufficient criteria or anti-evidence for the failure analysis. The most common and common method in microscopic analysis is optical metallographic analysis and surface hardness testing. The analysis should include:
(1) Whether the material quality meets the relevant standards and design requirements.
(2) Whether the basic organization of the bearing parts and the quality of heat treatment meet the relevant requirements.
(3) Whether or not there is a decarburized layer, a bentonite, and other surface modification layers in the surface layer.
(4) Measure the depth of the surface strengthening layer and multi-layer metal layers of the carburized layer, the shape and depth of the corrosion pit or crack, and determine the cause and nature of the crack based on the shape of the crack and the characteristics of both sides of the structure.
(5) Determine the degree of deformation, temperature rise, type of material, and process according to grain size, microstructure deformation, local phase transition, recrystallization, and phase aggregation.
(6) Measure basic hardness, hardness uniformity, and hardness change in failure area.
(7) fracture observation and analysis. The fractures were observed qualitatively by a scanning electron microscope and measured.
(8) Electron microscopy, probes, and electron energy spectroscopy can measure the composition of fractures in the fatigue source and crack source analysis, and find the nature of the fracture and the cause of the fracture.
The three steps of the general method of bearing failure analysis described above are a step-by-step analysis process from the table to the inside. The contents of each specific step should be based on the type and characteristics of bearing failure, depending on the specific circumstances, but the analysis step is indispensable. And throughout the analysis process, the results of the analysis should always be related to many factors that affect the bearing failure.