[TowerTalk] painting DOM

Fri May 28 02:32:50 PDT 2010


On 5/28/2010 4:55 AM, Jim Thomson wrote:
> Date: Thu, 27 May 2010 02:46:14 -0400
> From: "Roger (K8RI)"<K8RI-on-TowerTalk at tm.net>
> Subject: [TowerTalk] painting DOM
>
> I have three sections of 2" OD DOM to paint. Two sections will be
> spliced in the 45G and run through two sleeve bearings above the rotator
> which will support all the weight.  The paint needs to be really durable
> because of the sleeve bearings, boom to mast clamps, and raising fixtures.
>
> Epoxy paint does not stand up well and the spray on stuff is very fragile.
>
> Rustoleum?  I don't know how mechanically durable it'd be. The sleeve
> bearings will be greased and have rubber gaskets protecting them, but it
> doesn't take much pressure to flake paint off steel.   Also it's amazing
> how much space you have to leave between the OD of the inner sleeve and
> the ID  of the outer sleeve. Just a 1/16" of paint requires an 1/8"
> difference between the two.
>
> Any suggestions for a good strong, long lasting, durable paint.  I do
> have a spray gun.
>
> 73
>
> Roger (K8RI)
>
> ##  This is the one drawback to your  "sleeve bearing scheme"
> You end up with metal rotating on metal..tearing everything off.
>    
Although with a reasonable fit and well lubricated with a lube that 
stands up to the environment, the metal on metal makes a very good, low 
speed bearing. The problem is protecting those bearing surfaces.
> ## yrs ago, when painting steel masts... the paint always came off.  I tried red
> oxide primer, then paint on top... and both the paint and red oxide primer came off.  Then
> with some 5" diam steel guy anchors, I tried several coats of red oxide primer.. and NO paint
> on top of the primer. This works good, and the primer never came off.
"I think" the surface of the primer acts like a lube, but it'd take some 
one with more of a mechanical engineering background to verify that.
>      I also tried ZNC [srpay bombs]
> .. and that stuff lasted 18 x months.  I was going to try zinc chromate... but never did [ yellow in colour]
> Red oxide primer of course is red.
>
>    
I've used a lot of zinc chromate, but never inside a sleeve bearing.  In 
the "old days" we would have used a sleeve with about an 1/8" gap. IOW 
about a 1/4" larger than the mast, placed a flange and seal at the 
bottom and poured it full of "Babbitt" (Mix of zinc and lead) and that 
worked with heavy duty bearings carrying quite a load at 300 to 400 RPM. 
Often they were poured into hardwood pillow blocks and used in both 
combines and thrashing machines.  The most unique bearings I've heard of 
was a guy headed "up North" on vacation when the bearings went out in 
his car.  It was a week end, nothing open, so no parts.  He removed the 
oil pan, pulled the bearings (Rod AND mains IIRC) and replaced them with 
a couple of his belts...Not V-belts, but pants belts...the leather belts 
to hold your pants up.  He drove nearly two hundred miles on those 
leather bearings. Well, not actually that set. He did have to stop and 
replace them once. Now that is really placing a lot of faith in your 
belt...far more than normal<:-))

The main thing here it the protection of those bearing surfaces.   With 
a machine shop and a 1/4 inch clearance, it would be a relatively simple 
job to turn out some graphite impregnated "Delrin" bearings with a 
flange on one end.  Using a spiral split bearing they could be inserted 
in place and if necessary changed with out having to remove the mast. If 
I had it that would be my first choice sans galvanizing.  I've built 
many a bearing using that graphite impregnated Delrin and they worked 
flawlessly. We did drill two holes and also install grease zerks on the 
outside of the sleeve so they did not run dry. They made great, high 
load, low RPM bearings.
> ##  !st choice these days is a hot dipped galvanized mast.
If I had a place nearby that would be my first choice.
>     You can always slop some ZNC on top of
> that if you want.. [and pour some down the inside]. The procedure for the inside of the mast was to seal
> the bottom.. and straddle the mast on a single saw horse... pour the znc /primer/etc into it.. then seal off
> the 2nd end.   Then roll it back and forth on the saw horse.. and also tilt it up/down.. like a teeter/totter.
>
>    
That is the exact procedure we used on the current masting on the 
tower.  I took two, heavy duty "sip loc" (TM) bags and sealed them to 
one end of the mast.  Thined a quart of rustoleum primer 50:50 which is 
just about right for a spray gun. I then poured the whole quart into the 
mast and sealed that end. From there it was a couple minutes of rolling 
and tipping the shaft. Then the bottom end was raised, the seal removed 
and then the end lowered and drained back into the paint can. 
Surprisingly I got more than 3/4 of it back.  The seals were removed 
from the other end and the shaft let set at an angle over a "drip pan".  
The angle along with the heat of the sun dried the primer thoroughly in 
one day.
> ##  A friend in W7 land recently got his new 8.625"  OD guy anchors  hot dipped galvanized at a reasonable cost.
> He also had some other stuff powder coated, and both are holding out.
>    
 From what I've seen the cost is not the problem, but getting three 
20-21' lengths of DOM 20 to 30 miles to the site is.
The galvanizing does need to be smoothed at the contact point although 
if metal to metal it'll take car of that fairly soon.  The sleeve 
bearings should also be Galvanized and add little to the over all cost. 
Again, a good heavy grease is a good idea.
> ## Has anybody used ZNC, or similar, not spray bombs.. but the stuff that comes in gal + pint containers?
>
>    
I wonder if I could spray the powder coat on and heat the mast from the 
inside to bond the powder coat.  Might be kinda tricky.

73

Roger (K8RI)
> later... Jim   VE7RF
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