In a message dated 25/04/2005 20:50:57 GMT Standard Time, k7fm@teleport.com
writes:
But they regularly lubricate them. I no longer make slanderous comments
about sleeve bearings.
Ball bearings have lower friction for a given load bearing capability, but
are noisier. For heavy loads (like steam locomotive axle boxes), roller
bearings (in the small size, needle bearings) are better. But for things like
small
fans, an 'oilite' (sintered phosphor bronze) sleeve bearing, well impregnated
with oil, is in my opinion, going to take a hell of a lot of beating,
because of its lower noise, lower cost and longer life.
Back in 1996, a Boeing 747 - 400 on a BA flight from Johannesburg to London
was over Abbeville in northern France at about 0630 when a passenger called
the flight attendant and complained about sparks, smoke and flames coming out
of a ventilation grill by his feet. The cabin crew moved him to another seat
(!), and called the guys up front. The co pilot shot a fire extinguisher
through the grill, the Captain declared a Mayday, made an emergency landing at
Heathrow, and the passengers evacuated. The problem turned out to be a ball
race in the three phase fan of a humidifier, which had seized after only 3000
or
so hours. The situation was was exacerbated because Boeing had managed
(quite accidentally) to fit a 25 amp breaker to protect wiring rated at 4
amps,
instead of a 2.5 amp breaker. Now if aircraft quality bearings can fail that
soon, what does it say for cheap fan bearings? (Can't remember if it was
lubrication failure - anyone wanting full details can find them in the AAIB
accident reports for 1996)
73
Peter G3RZP
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