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Cement machinery bearing fault analysis and treatment

Cement machinery bearing fault analysis and treatment

2020-09-07

The bearing of cement machinery equipment is a vulnerable part, its running state directly affects the performance of the whole equipment.In cement machinery equipment, there are many cases of equipment failure caused by the early failure of rolling bearings.Therefore, to find out the source of the fault, take remedial measures to eliminate the fault, is one of the keys to improve the system operation rate.

A rolling bearing fault analysis

Vibration analysis of rolling bearing

The typical failure mode of rolling bearings is simply fatigue spalling in rolling contact.The spalling surface area is about 2mm2 and the depth is up to 0.2mm ~ 0.3mm, which can be determined by the vibration detection by the monitor.Spalling may occur on the inner seat surface, outer seat, or on the rolling body.Among them, the inner seat ring due to high contact stress, the occurrence of rupture is more.

Among all kinds of diagnostic techniques for rolling bearings, the vibration monitoring method is still the most important one.In general, the time domain analysis method is simple, suitable for small noise interference, is a simple diagnosis of a good method;Among the frequency-domain diagnosis methods, the resonance demodulation method is the most mature and reliable, which is suitable for precise diagnosis of bearing faults.The time-frequency analysis method is similar to the resonance demodulation method in that it can correctly describe the time and frequency characteristics of fault signals and has more advantages.

Analysis of the damage form of rolling bearing and remedial measures

(1) Overload.Severe surface spalling and wear indicate the failure of the rolling bearing due to early fatigue due to overload (in addition to a certain degree of fatigue due to too tight fit).The overload will also cause serious wear of bearing ball raceways, large area of spalling and sometimes accompanied by overheating.The remedy is to reduce the bearing load or increase the bearing capacity.

(2) Overheating.A change in color of the roller raceway, ball or retainer indicates overheating of the bearing.The rise of the temperature will reduce the role of lubricants, so that oil desert is not easy to form or completely disappear.If the temperature is too high, the material of raceway and steel ball will anneal and its hardness will decrease.This is mainly the heat disadvantageous or the heavy load, the high speed condition cooling insufficient cause.The solution is sufficient heat dissipation and additional cooling.

(3) Vibration erosion under low load.Elliptical wear marks in the axial position of each ball indicate failure due to excessive external vibration or low load corrosion when the bearing is not working and no lubricating film is produced.The remedy is to isolate the bearing or add anti-wear additives to the bearing grease.

(4) Installation problem.Mainly pay attention to the following aspects:

First, pay attention to the application of force.If there are intervals of pit on the raceway, the load has exceeded the elastic limit of the material.This is due to static overload or severe impact (e.g., hammer hitting the bearing during installation).The correct installation method is to apply force only to the ring to be pressed (do not push the outer ring when the inner ring is installed on the shaft).

Second, pay attention to the mounting direction of angular contact bearings.Angular contact bearings have an elliptical contact zone and bear axial thrust only in one direction.When the bearing is assembled in the opposite direction, the bearing surface will produce groove wear belt because the ball is at the edge of the raceway.Therefore, attention should be paid to the correct direction of installation.

Third, pay attention to alignment.The wear marks of the steel ball are skewed and not parallel to the raceway direction, indicating that the bearing is not in alignment during installation.If the deflection > 16000, easy to cause the bearing temperature rise and serious wear.The reason may be that the shaft has bending, the shaft or the box body has burr, the clamping surface of the locking mother is not perpendicular to the thread axis and so on.Therefore, the installation should pay attention to check the diameter jump condition.

Fourth, should pay attention to the correct cooperation.The circumferential wear or discoloration on the contact surface of the inner and outer rings of the bearing is caused by the loose match between the bearing and its matching parts.The oxide produced by abrasion is a kind of pure brown abrasive. As a result, the bearing will suffer from further wear, heat and noise, as well as a series of problems such as diameter jump. Therefore, proper coordination should be paid attention to when assembling.

For example, there is a serious spherical wear track at the bottom of the racetrack, which indicates that the bearing clearance becomes smaller due to too tight fit, and the bearing will soon fail due to wear and fatigue due to the increase of torsional distance and the increase of bearing temperature.At this point, as long as the radial clearance is properly restored and the interference quantity is reduced, this problem can be solved.

Fifth, normal fatigue failure.Normal fatigue failure is characterized by irregular material spalling on any running surface (such as raceway or ball) and gradual expansion resulting in increased amplitude.If the life of ordinary bearings can not meet the requirements of use, only to choose a new more advanced bearing, or improve the specification of the first class bearing, to improve the bearing capacity.

Sixth, improper lubrication.All rolling bearings require continuous lubrication with a high quality lubricant to maintain their design performance.The bearing is protected from direct contact between metals by an oil film formed on the rolling body and the seat ring.If it is well lubricated, friction can be reduced so that it does not wear out.

The viscosity of grease or lubricating oil is the key to ensure the normal lubrication of the bearing under running condition.It is also important that the lubricating grease be kept clean and free of solid or liquid impurities.The viscosity of the oil is too low to provide sufficient lubrication, causing the seat ring to wear out quickly.At the start of the race of the surface of the metal and metal roller friction direct contact with each other, make its surface polishing the dry friction  very smooth  which in turn causes the seat surface by grinding roller surface grain of dust fracturing.Surface darkening and loss of luster can be observed at first, and eventually form dents and flaky fatigue flaking.The remedy is to replace the lubricating oil or grease according to the needs of the bearings.

Particles in lubricating oil or grease contamination, even though these contaminant particles smaller than average oil film thickness, but because of hard particles  still produce abrasion, even through the oil film and bearing surfaces to produce local stress, which dramatically shorten the bearing life.The concentration of water in the lubricating oil or grease, even as low as 0.01%, is enough to shorten the original life of the bearing by half.If water dissolves in oil or grease, the service life of the bearing decreases with increasing water concentration.The remedy is to replace the unclean oil or grease;Better filters should be installed at ordinary times, sealing should be increased, and clean operation should be paid attention to during storage and installation.

Seventh, corrosion.Red or brown stains on raceways, steel balls, retainers, and inner and outer ring surfaces indicate corrosion failure of bearings due to exposure to corrosive liquids or gases.It will lead to increased vibration, increased wear, increased radial clearance, decreased preload, and fatigue failure in the limit.The remedy is to allow fluid to drain from the bearing or to increase the overall and external seal of the bearing.

Fault causes and treatment of fan bearings

According to incomplete statistics, the failure rate of the fan vibration in the cement plant is 58.6% at the highest, because the vibration will cause the fan operation unbalance.Among them, improper adjustment of bearing firming sleeve will lead to abnormal temperature rise and vibration of the bearing.

Such as a cement plant in the equipment maintenance during the replacement of fan blade.Both sides of the wheel blade are fixed with fixed sleeve and bearing housing bearing.The fault of high temperature and high vibration value of free bearing will occur in the re-test.

It is found that the bearing roller in a specific position of the rotating shaft also rolls in the non-load area when the upper cover of the bearing housing is removed and the mounting clearance may be insufficient.The measurement shows that the internal clearance of the bearing is only 0.04mm and the eccentricity of the rotating shaft is up to 0.18mm.

Due to the large span of the left and right bearing, it is difficult to avoid the deflection of the rotating shaft or the error of the bearing installation Angle. Therefore, the large fan adopts the spherical roller bearing which can be automatically adjusted to the center.But when the internal clearance of the bearing is insufficient, the internal rolling parts of the bearing due to the limitation of movement space, its automatic function of the heart is affected, vibration value will increase instead.The internal clearance of the bearing decreases with the increase of the fit tightness, and the lubricating oil film cannot be formed. When the clearance of the bearing operation drops to zero due to the temperature rise, if the heat generated by the bearing operation is still greater than the heat escaped, the bearing temperature will climb rapidly.At this time, if not immediately stop, the bearing will eventually burn.The excessive tightness of the bearing inner ring and shaft is the cause of the abnormal high temperature of the bearing in this case.

During treatment, remove the setting sleeve, readjust the fitting tightness of the shaft and the inner ring, and take 0.10mm clearance after replacing the bearing.After reinstallation, restart the fan, and the vibration value and operating temperature of the bearing return to normal.

Bearing internal clearance is too small or the design and manufacturing precision is not good are the main reasons for the high running temperature of the bearing, in order to facilitate the installation, repair and maintenance of the fan equipment, generally in the design of the bearing housing bearing with taper hole bearing inner ring.However, it is also easy to cause problems due to the negligence of the installation procedure, especially the proper clearance adjustment.The internal clearance of the bearing is too small and the operating temperature rises rapidly;Bearing inner ring taper hole and tight sleeve fit too loose, bearing is easy to loose because of the fit surface and burn in a short time.

To sum up, bearing failure, should be in the design, maintenance lubrication management, operation and other aspects of the use of attention.This can reduce the maintenance cost of machinery and equipment, and extend the operation rate and service life of machinery and equipment.


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