🎧 Field Diaries : Episode 4

“When Trending Isn’t Enough”

🗓️ The Situation

A recent visit to a large industrial processing site started with a straightforward request from the Plant Manager:

“Our online system shows overall vibration values increasing on our mill gearbox. Can you tell us why?”

Their permanently installed monitoring system is excellent for trending. It shows when vibration amplitudes are rising.

But it doesn’t show why.

And as it turns out:

The online system wasn’t wrong. It just doesn’t speak fluent “root cause.”

📈 The Symptom

The system indicated:

• Rising overall vibration values

• No frequency breakdown available

• No visibility of harmonic structure

• No mechanical source identification

Overall values are like a dashboard warning light. Important — but not diagnostic.

🔍 The Investigation

Using portable vibration analysis equipment, full spectra and time waveforms were captured at key locations across the drive system.

Findings included:

• Elevated 1× running speed at the gearbox input

• Increased 1× Harmonic presence

• Increased overall velocity levels

• No dominant bearing defect frequencies

• Gear mesh activity consistent with recent machining and bedding-in

The gearbox had recently been removed and reinstalled during routine maintenance.

That detail mattered.

🌀 The Root Cause

The shaft-mounted gearbox cooling fan had been damaged during reinstallation.

Three vanes were broken off.

Because the fan is mounted directly to the gearbox shaft, any mass loss immediately becomes rotational imbalance.

That imbalance manifested clearly in the vibration signature:

• Increased 1× amplitude

• Harmonic growth

• Elevated overall values

• A structural response pattern resembling rotational looseness

Not random noise. Not internal failure.

Just physics doing what physics does.

🎯 Field Reflection

Elevated overall vibration values are a starting point — not a conclusion.

Credit must be given to the site team for taking their condition monitoring seriously. The rising trend was identified early through their online system, and action was taken before assumptions were made. That proactive approach is fundamental to effective asset management.

It is particularly important to monitor equipment closely during commissioning and after major maintenance interventions. When machinery is returned to service, it enters a critical stabilisation period. This phase often determines whether the asset will return to stable service — or whether underlying conditions will surface.

Increased monitoring during this period is not excessive caution; it is sound engineering practice.

Detailed frequency analysis in this case confirmed the condition was externally induced imbalance rather than internal mechanical deterioration.

Clear diagnosis enables proportionate action — and proportionate action protects both the asset and the maintenance budget.