EQUIPMENT: BF3202 Gluten Fan Bearing inspection
TECHNOLOGIES USED: Oil Analysis
Photo 1: Opened bearing showing the poor condition of the lubricant, sludge build up on non-contact surfaces, thrust bearing groves nearly filled in with sludge. Journals and thrust plate surfaces in good condition.
In September 05, Dodge SleeveOil bearings were installed on a 600hp center hung process fan. Almost immediately oil analysis began showing ferrous wear in the form of very small black oxides and small flakes of steel in the inboard (motor side) bearing. Vibration levels were normal and the bearing operated within normal temperature range. A method of filtering the housing was developed and the oil was cleaned up.
INVESTIGATION:
Route oil samples consistently came in with very dark oil due to suspended black oxides and small steel flakes. During the September 06 the bearing was opened up for inspection and the top of the bearing was removed. There was buildup of sludge in the housing. All journal surfaces looked good with minimal wear marks, clearance was checked and within normal range. During this inspection the thrust collar was found to be loose and rotating on the shaft, and was tightened up. Some wear was noticed around the shaft in the location of the oil rings, these wear paths were well burnished and are not considered abnormal. The housing was cleaned out as best it could be. The lower half bearing insert was not removed at that time. Oil samples continued to show ferrous wear particles.
A fretting corrosion problem between the bearing insert and housing was suspected and on, June 19, 2008 the bearing was again opened for inspection and the lower bearing half was rolled out.
The fan side bearing saddle and corresponding surface of the bearing insert were badly eroded from loose fit between the bearing insert and housing (see photos). The motor side bearing saddle and insert surfaces were normal and did not show any movement. A buildup of black sludge was on all surfaces and especially thick build-up in the thrust bearing oil groves. Bearing surfaces looked good and were smooth with few particle tracks in the shaft and thrust surfaces. The bearing and housing were thoroughly cleaned and reassembled.
Photo 2: Badly eroded bearing saddle on left, caused by loose fit and fretting corrosion.
Photo 3: Badly eroded bearing insert, caused by loose fit and fretting corrosion.
Photo 4: Detail of fretting damage on bearing insert
CONCLUSION:
It is suspected that the housing is not correctly aligned with the shaft, and the bearing insert is supported more by the motor side bearing saddle and floating some in the fan side bearing saddle causing the fretting of the fan side surfaces. These surfaces will continue to wear during use and require a complete new bearing assembly for correction.
The bearing is performing satisfactorily for now and a new bearing and housing will be ordered for installation during the next extended availability.
