Case Study of a heavily damaged 22226 Spherical Roller Bearing
A two row convex symmetrical spherical roller bearing 22226 with W33 lubrication holes was received and found to be in a completely disintegrated condition. The bearing components were seen to be coated in thick dirty grease that contained numerous slivers of sharp metal.
The parts of the outer ring were loosely re assembled to form as much of the complete outside diameter ring as possible. On inspection of the bearing outer surface outer was found to show evidence of having been fitted normally, no fretting marks or evidence of outer ring rotation within the housing were recognised .
The two sides of the load carrying raceway were turned to. The running path to one side or the raceway was only very lightly marked It was considered that this light marking was possible due to the bearing having served only a short time in service or alternatively that very little radial load had been carried by the raceway and rollers at this side of the bearing. The opposing raceway running path was severely scuffed and had extensive evidence of metallic pick up and wear upon it. The outer edges of the raceway were deformed and small cracks were seen to have begun to form. These cracks had resulted in material starting to chip away from the ring side face.
Such differences in raceway condition are classical where a bearing is subjected to abnormally high levels of uneven and abnormal loading. The cracking at the edge of the heavily worn raceway indicated that there had been a higher than acceptable thrust loading acting on the bearing from a single fixed direction..
The inner ring had marks within its bore that suggested rotation upon the shaft had taken place. Fretting marks and areas where heavy metallic pick up and smearing had taken place were identified
The raceways of this ring had heating discoloration to a shade of deep blue. There were bearing rotation and running marks clearly seen on both sides of the load carrying raceways. The one raceway side was lightly marked and tarnished but had no areas of real distress caused by un natural running. The opposite side of the raceway had extensive markings due to pitting wear and areas of metallic build up. Within this build up were points of indentation suggesting that the rollers had locked and not rotated freely at some time during service. .
The rollers all had clear evidence of an applied thrust loading upon them with running marks clearly visible to one side only. Approximately half the rollers had been crushed and severely damaged this damage most likely occurred as the bearing failed catastrophically at the end of the failure cycle .
Wear was evident on the cage fingers and deformation of the cage pockets was also evident. This damage was as a result of the lubricating grease becoming contaminated as well as the lubricating grease having the oils in the soap being dissipated allowing metal to metal contact to occur.
From the evidence gathered, it was concluded that that the bearing was fitted in a condition where it experienced an unacceptably high percentage of thrust loading.
Such thrust loading can occur for a number of reasons. The most common of which are:
• Damage to the shaft, journal or housing that prevents the bearing seating correctly.
• Incorrect adjustment of other bearings in the assembly or incorrect alignment of the housing.
• The locking arrangement of the assembly being incorrectly tightened or coming loose.
• An abnormally high service load is imposed on the machine into which the bearing is fitted causing internal breakages and movement of the bearing assembly.
• An incorrectly adjusted drive coupling or belt drive.