SKF Bearing Fault Characteristic Frequency

Writer: Eric Bearing Limited

What is the characteristic frequency of SKF bearing failure

The characteristic frequency of SKF rolling bearing failure is the vibration frequency generated by the bearing failure. There are four typical bearing fault characteristic frequencies: BPFO-outer ring fault characteristic frequency; BPFI-inner ring fault characteristic frequency; BSF-rolling element fault characteristic frequency and FTF-cage fault characteristic frequency.

The characteristics of SKF rolling bearing fault characteristic frequency

1. The failure frequency of SKF bearings is different from other failure frequencies;
2. SKF bearing failure frequency is a non-integer multiple of the speed frequency;
3. The sum frequency of the fault frequencies of the inner and outer rings = "bearing rolling element passing frequency" (number of rolling elements X RPM);
4. SKF bearing inner ring failure frequency is often accompanied by a sideband of 1 X speed frequency;
5. The magnitude of the fault frequency of the SKF bearing outer ring is higher than the magnitude of the fault frequency of the bearing inner ring;
6. SKF bearing failure generally occurs first before the rolling element and cage failure is the frequency of the inner ring or outer ring failure;
7. SKF bearing cage failure frequency (FTF) usually does not appear at its fundamental frequency;
8. When the rolling element itself fails, not only the rolling element failure frequency (BSF), but also the cage failure frequency (FTF) will often occur;
9. When the SKF bearing frame breaks, the rolling element rotation failure frequency may occur;

10. When more than one rolling element is faulty, the number of faulty rolling elements x the frequency of the characteristic frequency of the rolling element failure will occur. If there is a failure on the 5 balls or rollers, there will often be a frequency of 5X BSF;  SKF 61808-2RS1 bearings online , pls click here : 

11. The allowable vibration amplitude of SKF bearing failure frequency cannot be absolutely limited. It is not only related to the specific machine and speed, but also has a lot to do with the path of bearing failure frequency transmission. The most obvious sign indicating bearing damage is the existence of harmonic frequencies of bearing failure frequencies, especially if these frequencies are accompanied by 1X speed frequency or other bearing failure frequency sidebands, the SKF bearing should be replaced as soon as possible.

12. SKF bearing condition of low-speed machine evaluatedIt is recommended to collect both time-domain waveform and (FFT) spectrum when evaluating machine bearing condition, especially when the speed is less than 100 rpm. When the speed is very low, the pulse generated when the rolling element rolls through the defects on the inner and outer rings of the bearing does not have enough energy to produce a clear frequency in the FFT spectrum that can be detected, but it may still be clearly seen in the time domain waveform.

13. Place the vibration sensor as close as possible to the bearing area of ​​the bearing, especially when the SKF bearing only supports radial loads.

14. Improper SKF bearing load and installation problems
If the SKF bearing load is improper or the installation is improper, for example, when installing a new bearing, if the interference fit between the bearing and the bearing seat is too tight, the SKF bearing "clicks" into the bearing seat, causing the internal clearance of the bearing to change and the rolling elements Forced to be pressed against the inner and outer rings of SKF bearings. When this happens, the bearing will immediately produce the fault frequency of SKF bearing outer ring and inner ring when starting.

Excessive load was applied to SKF bearings due to improper installation. Although the actual damage may not have occurred yet, if this failure problem is not detected and measures are taken to correct it, the SKF bearing will be damaged long before its expected life.

15. Frequency of poor lubrication of SKF bearings
The characteristic is that there are 3 or 4 spikes in the range of 900 to 1600 Hz, and the difference frequency between the spikes is 80 to 130 Hz. A well-lubricated SKF bearing may also include these frequency components, however, their amplitude is very small, about 1.27mmn/s or less. When the lubrication is poor, the amplitude increases to 2.54 to 5.08mm/s.