In this example

A traditional FFT (in blue) misses the spacing of the impacts seen in the waveform. With enveloped data, shown in yellow a clear train of harmonics at the frequency of the impacts can be seen. Note, these impacts are at only 0.6 Hz or 35RPM. Traditional sampling cannot reveal these impacts or resolve peaks at a such low frequencies, while enveloping can.

Raw Data

Enveloped Data

In another example

The image shows a concerning trend on a high-criticality bearing. There are obvious peaks in the raw FFT spaced at the BPFO (80 Hz). In addition, there appear to be peaks higher in the spectrum spaced at an unknown higher frequency.

When enveloped

The FFT displays harmonics of the BPFI (123 Hz) with side bands of the run speed (15 Hz). Using enveloping, both BPFO and BPFI faults can be detected and tracked over time.

BPFO peaks spaced at 80 Hz

Dryer Cans Case Studies

Dryer cans are pressurized steam vessels that make direct contact with fiber for drying purposes. When steam exchanges heat, it becomes condensate which then must be evacuated with a syphon.

Some common failure modes seen on dryer cans are:

  • Bearing lubrication
  • Bearing failures
  • Steam Leaks (washing out bearings)
  • Condensate Locking/Evacuation Issues
  • Looseness
Fault Type

Condensate Evacuation Fault

Time Wave Form
  • Typically appears like a misalignment
  • Will often see ‘M’ and ‘W’ shapes

Frequency Spectrum

  • 2x will likely be the dominant frequency with 1x sometimes being elevated

Recommended Action

  • Use an Infrared gun to check temperature (30-50F lower than nearby cans) -does this lower temperature indicate a problem? What is the significance of this lower temperature
  • Check if discharge valves are open or locked

Root Cause

  • A plugged syphon/discharge valve
  • Discharge valve being in the closed position
Condensate evacuation fault machine health data chart.
Fault Type

Bearing Wear

Frequency Spectrum
  • Harmonics of the bearing frequency and even low amplitudes can still indicated bearing wear is present
  • With bearing wear, sides at the spacing of the run speed can be seen

Recommended Action

  • Plan for replacement on next scheduled outage

Root Cause

  • A combination of: Steam flushing out lubrication; Pulp/water infiltration into bearing; General wear over time
Fault Type

Bearing Damage

Run speed
78RPM

Issue
Condensate can fail to evacuate from dryer cans resulting in less drying capacity and higher wear on the bearings

Monitoring Technique
Low pass filter with alarms for temperature and vibration.

Result
Early detection of a developing fault, which ensured work order could be executed quickly with minimal system instability and full drying capacity.

Example: Flooded Dryer Can

Example: Flooded Dryer Can Vibration (Blue) Temperature (Red)
Vibration (Blue) Temperature (Red)