The following terms are used are used in the operation of DREAM and in the technical papers and
application notes published on this web site:
- Angle - The contact angle in degrees between the rolling elements and the race.
- Data Variations (DV) - Variations or errors in process parameters such as rotation
frequency (fr), numbers of rolling elements (Nrol) or bearing element dimensions.
- Defect Level - the stage of development of a particular defect type, expressed is
ascending order of seriousness as no defect, incipient (detectable, but not leading to failure
in a predictable period of time), medium, or severe (no possibility of ensuring long term
operation, may be operated temporarily with more frequent retesting until automatic
indication of failure).
- Defect Type - The following types of defects are identified:
- Revolution around the outer race - a defect of installation and not of the bearing that can
be caused by high thrust loads, imbalance, coupling misalignment, and self-excited rotor
oscillations. With this installation defect, high dynamic loads from the shaft revolving
synchronously with the shaft are applied to the bearing outer race. One of the most common
causes of this defect are installation errors that do not allow proper axial clearance for the
bearing that should float axially.
- Nonuniform radial tension of bearing - usually caused by bearing housing clearance
errors or high axial loads. This defect can lead to seizure of the bearing, slip of race, and
breakage of cages or races. This defect occurs when the radial load of the friction surface is
significantly dependent on the angle of the inner (rotating) race position.
- Misalignment of the outer race - a maintenance defect of the bearing that can lead rapid
race wear at the points of maximum load. In this situation, the maximum load applied to the
races is concentrated at two opposing points on the outer race.
- Wear of the outer race - pitting of a part of the outer race, usually appears early and
develops slowly. This defect is distinguished from cavities of the outer race by the lack of
shock pulses produced by contact between the rolling elements and the outer race.
- Cavities on the outer race - a defect that can develop quickly at any stage of a bearing's
life. This defect is typically caused by race wear, the appearance of race cracks, and impact
loads during maintenance or transportation of the machinery.
- Wear of the inner race - a relatively slowly developing defect. This defect is distinguished
from cavities on the inner race by the lack of shock pulses in the vibration data.
- Cavities on the inner race - a defect that can develop quickly at any stage of a bearing's
- Wear of balls, rollers or cage - results from pitting of a part of one or a group of rolling
elements. This is a defect that develops slowly and is distinguished from cavities on the balls
and rollers by the lack of associated shock pulses in the vibration data. This defect is
characterized by a periodic increase in the friction coefficient between the bearing elements
and reaches a maximum when the maximum loads are applied to the defective bearing
- Cavities, spallings of balls and rollers - a defect generated by impacts between rolling
element impacts on races which leads to rapid wear of the rolling elements and the cage.
- Complex defect - defects of two or more surfaces. A high risk combination of defects on
multiple bearing surfaces because of the possible appearance of dynamic loads applied to
the cage which can lead to cage breaks.
- Slip of race - a very high risk defect usually caused by changes in bearing fit or by bearing
- Defects of lubrication - typically caused by a lack or excess or lubricant, destruction of the
lubricant structure, or impurities - a defect that should be corrected as soon as possible.
- Designation - the manufacturer's name for the bearing.
- Din - diameter of the bearings inner race or inner raceway.
- dNrol - the acceptable variations in the number of rolling elements allowing successful
diagnostics with errors in the specification of the number of rolling elements.
- Dout - the diameter of the outer raceway.
- Drol - the diameter of the bearings rolling elements.
- Failure Danger - this bearing failure danger indication is generated when a slip of the race
in the housing occurs, a severe defect of lubrication, severe wear of balls, rollers or cage, or
two and more severe defects of different roll surfaces appear.
- Fin - the ball-pass frequency on the inner race.
- F_high - the high cut off frequency of the band pass filter of the envelope detector.
- F_low - the lower cut off frequency of the band pass filter of the envelope detector.
- Fr - the differential rotation speed of the bearing inner and outer races -the shaft rotation
- Fout - the outer race ball-pass frequency.
- Frol - the rotation frequency of the rolling elements.
- Frol - the rotation frequency of the rolling elements.
- Fs - Full scale envelope spectrum frequency.
- History - a report file where all diagnostics results are presented.
- Max - the maximum value of variation in the input data for Frot (%) with which the program
will still identify the defect type.
- MTBF - Mean time before failure.
- Not identified defect (unidentified defect) A defect that differs from the 12 types that the
program can identify, usually caused by interfering signals from other machine elements or by
operator error. The operator can:
- check whether the processed spectrum belongs to the chosen Measurement Point.
- check the data in the Measurement Point.
- check the data in the Bearings Designation
- check the data in the Bearings Designation.
- Nrol - the number of rolling elements in the bearing.
- Service life - The time period in months during which the bearing is intended to work
without replacement (Mean time before failure - MTBF).