Bearing noise on 16 blowers — found on the first visit

The Setup

Our customer is an industrial oven and thermal-systems OEM in western India. They had built a large industrial curing oven for their own end-customer — a high-security research facility in southern India — using a bank of 16 belt-driven centrifugal air-circulation blowers we supplied, plus two exhaust fans, each moving 8,500 CMH at 150 mmWC in 200 °C service. Two things made this a hard call to answer: the end-user needed to start the oven urgently, and the site is a restricted facility where no cameras or mobile phones are allowed — so there was no way to diagnose the fault remotely from photos or video. Someone had to go, with the right method and the right spares in hand.

The Complication

Four of the blowers were reported with abnormal "bearing noise." Because the site was camera-restricted, the customer could not send us the video or photographs we would normally use to triage — they told us plainly: depute an engineer to physically check and resolve it, and it is urgent. On a belt-driven fan, "bearing noise" is a reasonable first guess, but it is not always the bearing — and swapping four sets of bearings on a hunch, at a site you can only reach with pre-cleared entry passes, is exactly the wrong way to work. We needed the actual cause, found once, on one trip.

The Diagnosis & Fix

First, we closed out the most serious question with data: each fan had passed its pre-dispatch works test to the IS 4894 method before it ever left our works — noise and vibration were good at dispatch — so a manufacturing fault at source was ruled out on evidence, not assertion. Then we deputed a service technician to the facility with entry passes, carried spare bearings in case any were genuinely bad, and — because remote tools were impossible — did it the disciplined way on site: a full vibration survey of all sixteen blowers and both exhaust fans (motor and blower, drive-end and non-drive-end, in mm/s), not just the four that were flagged.

The fix followed the finding, not the guess: re-tension and tighten the belt-tension bolts on the affected fans, replace the single worn bearing (with its adapter sleeve), then prove it — a repeat vibration survey and a 2-hour endurance run at operating condition, oven door open and closed. We also fed the lesson back into our own engineering: a design change to the plug-fan motor mounting plate to keep post-installation vibration low on future units, and installation recommendations to the customer (flexible bellows on the exhaust-fan inlet and outlet; close the open gap around the circulation-fan outlet) to raise performance, lower motor current and extend fan life.

The Result

• Answered fast, found fast: acknowledged the same day, and the root cause was found on the first day on site — despite a restricted facility that ruled out any remote diagnosis and needed pre-cleared entry passes.
• No manufacturing defect: the fans had passed their pre-dispatch works test to the IS 4894 method; the cause was installation-origin loose belt-tension hardware, honestly reported as such.
• Measured and verified: worst-case vibration across the fan bank was brought down to within accepted running limits (from around 7 to under 3.5 mm/s on the worst units) and held stable through a 2-hour hot endurance run, with motor current comfortably inside the motor rating.
• Signed off closed: the customer's site authority signed the resolution report and the complaint was closed.

The Takeaway + Call to Action

A fan that "sounds like the bearing" is not always a bearing — and the fastest resolution comes from a method that finds the real cause on the first visit, even when the site won't let you diagnose from your desk.

— Jitamitra Electro Engineering · Technical Services

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