Having the rotator take all the thrust load doesn't thrill me, but
replacing a thrust bearing is a real pain. I guess I'm a convert to "no
stock thrust bearings". However, my own design....
I just rebuilt a Yaesu G2800 and a HAM-IV, they have same failure modes
as the thrust bearings - steel balls on cast aluminum that make dimples
in the races. It seems to me that what doesn't work for aluminum thrust
bearings also doesn't work for most rotators (well at least Hy-Gain and
Yaesu, I haven't looked inside others). From the rusty balls I found,
these rotator makers didn't use stainless balls in the rotators I've
worked on.
The failure modes can be overloading where the yield strength of the Al
is exceeded by the ball pressure, or corrosion of the balls and
resulting accelerated wear, galvanic corrosion - steel balls against Al,
or fretting/fretting corrosion, or wear from lubrication failure. I
think rotators are particularly susceptible to fretting since they sit
parked for long periods with small wind induced motions. The oil film
breaks down and the fretting process gets underway (see wikipedia
fretting). What K7LXC observed as small flakes of Al is what is
produced as wear material. Bearings work much better when a ball makes
a complete rotation in normal service, this replenishes the oil film on
its surface.
So one way to help your rotator (or thrust bearing) have a long life is
to cycle it through a full rotation on a regular basis. How frequent?
My guess would be once a week or after any wind storm that caused a lot
of parked oscillations. A good grease will also help - full synthetic,
PTFE fortified. Hy-Gain uses RheoLube 362HF, $13/oz from them. Super
Lube with Syncolon is widely available about $5 for a 3oz tube, which I
use. Even with the best grease, expecting it to last for much more than
5 to 7 years is pretty optimistic with the weather exposure at the top
of towers.
I'm thinking that plastic sleeve bearings might be the answer for
handling the lateral mast force. Teflon /Rulon/Torlon are obvious
choices if cost is no object. UHMW (ultra high molecular weight)
polyethylene is a cheap very slippery plastic used for sliding bearings
and low speed rotating bearings. It's cheap but can't handle much UV,
so will need covering up from sunlight. Perhaps a better but somewhat
more expensive choice is oil filled or moly disulfide filled Nylon 6.
3" od material is $35 to $50 per foot at McMaster. The smoother the
outside of the mast where it contacts the plastic, the better, or it
could be sleeved with stainless or the same plastic. Anybody using or
making such bearings?
Grant
KZ1W
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