04-07-2014, 04:47 PM
Monitoring the Ball bearing lubrication condition by Shock pulse and Acoustic Emission measurement
“Monitoring the Ball bearing lubrication condition.docx (Size: 1.12 MB / Downloads: 23)
ABSTRACT
Lubricant(grease) is a vital requirement of ball bearing system. Grease not only protects ball bearing from wear and tear but performs various other functions that are essential for proper functioning of ball bearings. The lubricant(grease) under different conditions attains different properties which in turn affect the performance of the ball bearings. The effect of the condition of the lubricants on the performance of the ball bearings is well documented.
My work involves an experimental study of the lubricant (grease)condition, in the ball bearing, under different operating conditions, using the shock pulse method and acoustic emission measurement method. The result will help in choosing the optimum conditions
INTRODUCTION
Ball bearings are considered to be most critical components of household applications to heavy machineries like locomotives and turbines. Grease is the most widely used lubricant for ball bearings mainly because they are relatively easy to handle and require only the simplest sealing devices. Greases are typically used in areas where a continuous supply of oil can not be retained, such as open bearing or gears. Factors to be considered when selecting greases are the type of grease, which in turn depends on operating temperatures, water resistance, oxidation stability etc. The other factor includes characteristics like viscosity and consistency. There are several ways to moniter and measure the severity of ball bearing lubrication problems. Vibration analysis, acoustic emission, and shock pulse are just a few of the methods used today ,To detect the ball bearing lubrication condition measurement. Most lubrication practices are often performed on a time basis, which can result in over lubrication causing premature bearing failure. For the monitor of the ball bearing lubrication condition we will use the two most affective measurement method like shock pulse and acoustic emission.
SHOCK PULSE MEASUREMENT
In the shock pulse method the development of ultrasonic mechanical shock waves, which are caused by the impact of rolling elements, is developed . The defect is in the bearing races are rolling element itself caused by lubrication failure. The method uses a piezo- electric accelerometer tuned mechanically and electrically to a resonant frequency around 32 kHz. The shock pulse caused by impacts set up damped oscillations in the transducer at its resonant frequency. The measurement of maximum value of damped transient gives an indication of the condition of anti friction bearings. The shock pulse value of generated by good bearing has been found empirically to be dependent upon the bearing bore diameter and speed.
This value is called initial shock pulse value is substracted from the shock pulse value of the bearing to be tested to obtain a nornalized shock pulse value that is indicative of bearing
ACOUSTIC EMISSION MEASUREMENT
Acoustic emission can be described as ashock wave inside a material, which is under stress. The shock wave causes the surface of the material to move, and this movement is measured with a very sensitive sensor. The shock, or transient elastic wave, is generated by a rapid release of energy from a local source with in the material. The sources of acoustic emission (AE) comprise different mechanisms of deformation and fracture including the fracture of crystallites, crack nucleation and growth, several mechanisms involving dislocations, phase transformations in materials, boiling and electrical discharges. Each of these mechanisms is characterized by a rapid collective motion of a group of atoms.
In order to evaluate the significance of an AE source and to interpret the AE signal, different parameters can be extracted from the signal. The signal waveform depends on the characteristics of the source, on the path of the signal from the source to the sensor, on the
WORK DONE SO FAR
LITERATURE REVIEW
Miettinen and andersson [1]:- Investigated to clarify how the contaminants in the grease influence The AE of the rolling bearing. In this paper, the result of tests with clean greases and with deliberately contaminated greases, and the influence of the cleaning and re-greasing of the bearing of discussed. The result showed that the AE measurement indicated very clearly the lowest contaminants concentration included in the study that was as low as 0.02% weight. Small size contaminants particles generated a higher AE pulse count level than large size particles. The AE times signal analysis method proved to be a suitable method to indicate the hardness of the contaminants particles. Cleaning the bearing of contaminants and re- greasing with a clean grease reduce the AE level of the bearing. They have shown that
1. Clean greases give rise to more noise, i.e vibrations, especially at higher frequencies, than a clean mineral oil used for reference.
2. The highest level of the AE, for grease contaminated with the same proportion of ferrous contaminants, was obtained with the contaminant having the smallest average particals size.
3. The hardness with the contaminants was more clearly reflected by the AE time signal than the AE pulse count measurements.
4. The cleaning and re- greasing of a bearing that had been running with contaminated grease gave a reduction in the AE level of the bearing, to a level which was about one half of the AE level with the contaminated grease, but after the cleaning and re-greasing the AE level was still much higher than it had been when the bearing was new and lubricated with clean grease.
RESEARCH GAPS
Various studies have been published regarding ball bearing condition related to failure in inner race and outer race ,and many method has been used for the condition of roller bearing like vibration analysis ,wavelet technique, HFRT, acoustic emission and also many paper related to film thickness ,contaminated grease used in ball bearing, deterioration of lubricants under the influence of electric field ,modelling of grease lubrication, but my study is more focus on the condition of lubricant(grease) in the ball bearing under the different load and speed with the help of SPM and AE, and also discuss the condition of lubricant(grease) in the various parameter
EXPERIMENTAL SET –UP
in this chapter , description of the experimental setup, procedure for data collection from the set-up and the complete acoustic emission (AE) ,shock pulse apparatus details explain .
the signal has been taken from the test rig from AE,and shock pulse measurement.
3.3.1 acoustic temission set-up
It is widely recognized that ae is gaining ground as a non- destructive technique(NDT) for helth diagnosis on rotating bearing.the source of AE is attributed to the release of stored elastic energy that manifests it self in the from of elastic waves that release of stored elastic energy that manifests itself in the from of elastic waves that propagate in all directions on the surface of a material.thease detectable AE waves can provide useful information about helth condition of bearing and lubricant.,
AE sensor-name WD sensor S/N,Peak frq. 519.53kHz, max value -63.53(dB)
Preamplifier-brand physical acoustics carporator 2/4/6 gain,60 dB,40dB,20Db
Data proceser.data physical acoustics corporation,
Laptop with software.