Gang,
Almost an oxymoron, ie fans and noise are like ham and eggs, but fans and
quiet are not.
As the local fan guru on repairing computer fans, instrument, or recorder fans
etc. I have learned some truths I eagerly share, as I could do better things
that change out noisey fans, worn out fans, etc.
Most manufacturing is a cost trade off. Given that, if a fan is used it is
often a sleeve bearing fan. These are, or will, become noisey or wear out in
two to five years. Customers become very unhappy with either result.
Customers contribute to the problem by siting equipment in dusty locations
where contamination of the fan bearing and lubricant accelerates the problem.
For slightly more investment, you can buy a ball bearing fan, and I have never
had to change those in computer disk drives, computers, instruments, recorders
etc. where I have used them, and have ten years or more on some of those. Now
I am referring to the so called "muffin" type of fans. Those from say 5
inches square down to less than one inch square. Customer satisfaction with
the main product is enhanced, callbacks to the manufacturer are fewer, and
returns for noise are almost nil. Greater efficiency all around, productivity
and long term cost savings.
Noise reduction in use of Muffin fans, or small blowers: If you have any fan
or blower that mounts by three to four screw holes, you can lessen acoustic
coupling of the basic fan operational noise to the chassis acting as a
sounding and amplification board. One trick from small blower motor days was
to use rubber grommets so the screws pass thru a grommet that isolates the
mounting flange from chassis metal contact. A flat washer under the screw
head and the nut must be used, and the nut should be a locking nut, to
complete this scheme.
Now the mounting of a muffin fan always assumed the fan shroud would make hard
contact with the chassis. This is not a minimum noise design. But at a small
loss of air column coupling , you could use a large "O" ring to the face of
the fan shroud, and rubber grommets on the screw mountings to isolate the
Muffin type fans. If the thickness of the grommet is greater than the "O"
ring, either compress the grommet, or substitute a smaller but flexible washer
or even "O" ring, to acoustically decouple the screws from hard chassis
contact. With the right size binding head screw or washer head screw, the
parts count and labor of installation can be minimum for this. In all
replacement work, I use the nuts with built in lockwasher to lessen the labor
charge for "the washer dropped on the floor search time."
Maybe other flexible mounting ideas that are low cost will come to mind. (RTV
forming a gasket?) Just remember the hard mounting is like a piano sounding
board, and anything you can do to prevent that should keep the fan quiet
longer, no matter the style.
73, Stuart K5KVH
rohre@arlut.utexas.edu
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