[TowerTalk] Which Thrust Bearing to Use

[Grant Saviers]

I strongly agree, a UV resistant plastic is a better way to go.  I use 
black UHMW which is UV resistant and is almost as slippery as teflon, 
rulon, torlon or exotics like Vespel and < 1/10 the cost.  I have a 6061 
collar and stainless plate to ride on the UHMW 4" thick block (3" 22' 
alloy mast) but it is set for the prop pitch to handle the axial load 
(500#).  The collar is there as backup and to facilitate work on the PP.

Every rotator or thrust bearing with steel balls on aluminum races I 
have disassembled, resuscitated or trashed shows the results of 
fretting.  When parked the oil film breaks down and fretting digs a 
divot for each ball.  Very small rotation cyclic loads kill ball 
bearings, even instrument grade ones in protected environments (eg disk 
drive rotary actuators).  Very expensive lubricants are often employed 
to lengthen their life. White lithium grease is only slightly better 
than Crisco for lubing your rotator.  Check out DuPont Krytox lubricants 
and others from Nye lubricants.  More easily found are marine grade 
fully synthetic greases with anti corrosion and high pressure additives.

Frequent rotation enough (~ 25-40 degrees depending on the race diameter 
and ball size) to cause a full rotation of the balls brings a fresh oil 
film into the ball-race contact area and is an excellent preventative 
measure.  Several times a week would be ideal.  Parked for weeks is an 
invitation for excessive wear.

Very few hams are "anal" about bearing lubrication, but I am when 
replacing a $600 matched pair of ABEC9 angular contact bearings in a 
machine spindle.

Grant KZ1W



On 12/9/2016 6:14 AM, charlie at thegallos.com wrote:
>> Looks really well made.  I had the original Rohn counterpart for years and
>> it just kept on going.
>> I added a zerk fitting so I could grease it.  They last a very long time
>> dry without lube, but I am anal
>> about lubing everything hihi.
>>
>>
>> Bob
>> K6UJ
>
> Looks nice, but one thing I just have not been able to understand for years
>
> Tower thrust bearings are a LOW rotation speed, high load application,
> probably the WORST place to use ball bearings.  I would expect either
> tapered roller bearings, or today, do what most of industry does, and use
> an engineering plastic bearing.  I mean, we don't need a torlon bearing
> there (the loads are NOT that high)
>
> I mean, a glass reinforced nylon, or a PTFE (Teflon) (say a 25% glass
> filled or molly filled) isn't going to cold flow at ALL under loads a 2"
> mast could sustain, will NEVER need lubrication, will never corrode etc
>
> You either get them molded for you (for some materials would be the
> cheapest way - you do NOT want to know what torlon costs), or you slice it
> from tube, or you even just use end on rods set around the circumference
>
> I mean, today they run the pivot bearings and lower boom bearing on cranes
> in plastic bearings, because they hold up better than metals in those low
> rotation speed, intermittent rotation applications
>
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