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Alex

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A very rare oportunity, a story I would like to share with you. I was called to balance an overhung 37 kW suction fan in a printing factory. It is used for the paper leftovers. The balancing should have been done after bearing + housing change. Their idea was to change the bearings and the housing type with some other type (from classic SKF two-part housing to a Timken Part Number TAPG11K115S, Tapered Adapter Four-Bolt Pillow Block). I was not involved in the overhaul so I can't tell what was wrong, only guessing. But it was terribly WRONG!

We started the fan, the bearing nuts get loose and the 200 kg rotor at 2770 RPM suddenly moved axialy to the cover (great luck because we were thinking about to leave the cover behind). The sparks initiated a fire and we should all thank to automatic fire extinguishing system. The worst of all, when the personel were each one Usain Bolt, I couldn't escape because I was standing on top of the working lift. So I have had a luck someone turned the fan off. No one was hurt.

What I found the most memorable is that I recorded a moment when it happened [smile]  

P.S.: After they went back to standard machine parts, the balancing was successful.


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fburgos

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Reply with quote  #2 
wow 175mm/s... that is something scarry, im glad no one got hurt.
Danny Harvey

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Reply with quote  #3 
It was pretty bad BEFORE it came loose.  Then it became time to run.

That is an external adapter with a lockwasher. If it came loose there, it likely either wasn't fully tightened or the lockwasher wasn't engaged with the nut after tightening.

After it expands beyond the 1 15/16" +- shaft diameter, the single inlet suction shoves it as far as it can and it keeps turning until it's turned off or something breaks.

And you thought it was going to be another boring balance job[smile]
Alex

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Danny, they said the instructions were 33 Nm torque, I don't know where that came from but it doesn't seem logic.
Danny Harvey

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Reply with quote  #5 
That's not much torque....
Dan Timberlake

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Reply with quote  #6 
TAPG11K115S

https://www.timken.com/wp-content/uploads/2016/10/10785_SRB-Solid-Block-Housed-Unit-Catalog-1.pdf

TA series page 53-54 shows either measured axial drive up of several  0.001s of and inch,  or even simpler  "tang counting" when tightening the big lock nut.
None of that tricky clearance reduction measurement required.

There is also frightening and confusing mention of  locking collars having a setscrews.
"How to Convert a SOLID-BLOCK housed unit from Expansion (floating) to Fixed Flange Cartridge and Flange Block • Loosen the Teflon-tipped set screw that locks the retaining nut in place. • Tighten the retaining nut by tapping it with a hammer and punch, rotating the retaining nut clockwise until tight. It is not possible to overtighten the retaining nut. • Tighten the Teflon-tipped set screw. Pillow Block • Follow the directions above for flange bearings on both nuts on either side of the housing. NOTE When converting a solid-block housed unit from expansion to fixed on a mounted bearing, the locking-collar set screws must be released to allow the insert to move both in the housing and on the shaft."

On page 49 there is a table showing 35 Nm torque for some 3/8" setscrews, but that is for the wimpier EC series bearings.

Then on page 40-41 the "V-lock" style also has locking set screws in collars. Those setscrews have similar 35 Nm torques.
At first glance the V-lock is only used with 2 bolt pillow blox.
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