Colin,
In a lot of scrap yards they have what's known as alligator shears to cut steel
scrap with. These cut bar stock maybe 1" thick or more like a knife through
paper. All that I've seen use C-660 bronze bearings because of the longevity.
They all generally have an oiler on each sleeve. On most milling machines, the
gibs are bronze for this reason. You would think an alloy of brass and iron
would be week but in reality, that's what's used for heavy loads. Most shaded
pole fan motors use a sintered bronze which has had graphite impregnated into
it. These can run for a good while like you say, even if they go dry of oil.
The same goes with most smaller motors used in blowers, etc, up to about 2 HP.
They use the same sintered bronze, graphite impregnated type. Some have a
spiral groove inside which looks like a figure 8. This is oil paths to
lubricate the shaft. This just goes to show that something more complicated
aint mo-better.
Best,
Will
*********** REPLY SEPARATOR ***********
On 4/25/05 at 12:47 PM Colin Lamb wrote:
>I used to want ball bearing fan motors for computers. However, even
>though they may have a longer period without service, they can become
>noisy. I have found that the sleeve bearing fans can be oiled quite
>easily and continue for a long time. The sleeve bearing depends upon
>lubrication. In effect, the bearing is the oil itself. Without oil,
>there is no bearing. Annual lubrication by removing the label and plug
>covering the bearing can keep the bearing going for a long time. I can
>often bring a seized bearing back to life with a removal of the bearing
>and cleaning of the burned residue and relubrication.
>
>A few years ago, I came upon a small hydroelectric power plant undergoing
>annual maintenance. The generator used sleeve bearings. I asked the
>fellow how long the sleeve bearings lasted at 24/7. His answer was "about
>30 years". But they regularly lubricate them. I no longer make
>slanderous comments about sleeve bearings.
>
>73, Colin K7FM
>
>-----Original Message-----
>From: David Kirkby <david.kirkby@onetel.net>
>Sent: Apr 25, 2005 12:30 PM
>To: Ian White GM3SEK <g3sek@ifwtech.co.uk>
>Cc: "amps@contesting.com" <amps@contesting.com>
>Subject: Re: [Amps] Resistors
>
>Ian White GM3SEK wrote:
>
>> Even a small low-noise fan (ex-PC power supply, for example) will do
>> wonders in keeping the whole thing cool.
>
>Just be aware the mean time before failure (MTBF) of small fans is
>orders of magnitude smaller than most components, and considerably
>shorter than decent fans.
>
>Most PC power supplies have fans with sleeve bearings, which generally
>have even lower MTBF's than those with ball bearings. Couple that with
>the fact the fan is used, and generally made very much to a price, I
>personally I would steer well clear of them.
>
>AC fans normally have much longer lives, but they tend to be bigger and
>more expensive.
>
>I have a PC here, which I bought from work for £25 or so. Two fans had
>failed - one on one of the two 450MHz CPUs, another on the hard drive
>caddy.
>
>On my Sun workstation, two small of its 5 fans have failed on that too.
>One was on the Celeron processor of a "PC" that fits on a PCI slot of
>the Sun (a PC inside a Sun) and the other was on the DC-DC converter
>that supplies power for the CPUs (I think). The former fan I removed
>(decided it was next to useless and Celerons are dirt cheap) and the
>latter I replaced with another fan.
>
>*Generally*, I find Sun workstations run fine for years without fan
>trouble, despite the fact they run 24/7, but fan failure on PCs seems
>very common.
>
>--
>Dr. David Kirkby,
>G8WRB
>
>Please check out http://www.g8wrb.org/
>of if you live in Essex http://www.southminster-branch-line.org.uk/
>
>
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