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G8MNY  > TECHNI   21.11.21 09:50l 130 Lines 5446 Bytes #999 (0) @ WW
BID : 53673_GB7CIP
Read: GUEST
Subj: Corroded & Rusted Up?
Path: PI8DRE<PI8CDR<DB0RES<DB0ERF<DK0WUE<GB7CIP
Sent: 211121/0843Z @:GB7CIP.#32.GBR.EURO #:53673 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To  : TECH@WW

By G8MNY                                (New Oct 09)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

PRECAUTIONS
To stop things rusting/corroding up in the winter, e.g. Nuts & Bolts, PL259s,
rotators, padlocks, generators etc. read on.

You need to protect metal surfaces, from each other & water ingress. Dissimilar
metals on the atomic element table (far apart e.g. Copper & Steel/Ally) produce
a small voltage between them & any electrolyte like water will make a shorted
out battery, which rapidly corrodes one of the metals.

      ___                    ___  More O2
     /H20\                  /H20\/
  ܱ          
    Different            Same metal
 Metals Corrosion

With unprotected metal there is even battery action of a single water droplet
due to the different amount of Oxygen dissolved at the edge of the drop!

BARRIERS
Paint is the normal approach, it adheres to most surface fairly well, but not
always to make a water tight barrier. Some paint are OSMOTIC & allow water
molecules to penetrate under the paint!
  ___                    ___                       ___
 /H20\  Good            /H2O\   Osmotic           /H20\     Flaky
========Paint       = = = = = =  paint          === == ==== paint
                             Ally Metal
  Metal         Corrosion under paint            Corrosion

Aluminium is one metal that is difficult, as it's important tough Oxide
protecting layer also stops paint sticking well, & special etching paints are
best.

For moving metal parts there is nothing like plenty of grease, all greases are
water replant, some are better lubricants than others & the heavier ones are
less likely to be washed away, but also can dry out. For best electrical
insulation use a vaseline, e.g. "N"type & PL259 plugs etc. For padlocks warm
up until quite hot & allow grease to run in. Be aware of some rubber & nylon
gears components may perish/swell with oils or grease, check with the makers
for compatible grease types.

Painting inside thin walled steel aerial poles from each end can be done before
erection with "blown in" spray paint inside the pole while rotating the pole.
                      _______________________
          Blow->> n::::::::::
                /~ ~\ ~~~~~~~~~~~~~~~~~~~~~~~~
                    

The moving air in the pole will thinly deposit the paint several metres inside
the pole & stop rusting. The outside still needs painting of course! With steel
a Zinc primer is best.

Oil spays work for a short time (eg. mower/generator in shed for winter) &
can get to inaccessible parts as the oil "wets" the surface. Painted on old
engine oil also works if you don't mind getting dirty. 

Exposed nut & bolt threads can be greased bolted tight & then cleaned on the
outside & painted. This seals in the grease between the working surfaces
stopping water entry & corrosion where it matters. Many years later it can
easily be undone.

WATER TIGHT
Hermetic seals, these attempt to stop water entering a unit (lock, Preamp etc.)
but usually fail, mainly due to changing air pressure & heat cycles allowing
water to ingress past O ring seals. Then it is too late, you end up with a damp
micro climate inside the unit, causing continuous condensation on all
components.
   ___
  /H20\  SEALED BOX              OPEN BOX
       
  ^SEALS                   Lower vent hole   
     water vapour         lets box breath to 
    trapped in box        dry out any water  
  v                         vapour ingress   
 o      o 
                              ް

The open box approach solves this, with no pressure difference the seals stand
a much better chance of keeping the water out. Insect gauze traps & long tube
breath hole stops most ran & moisture entering.

A rotator normally left on its side unless the mast is up for instance, will
let water inside as the seals are made to only work upright.

  =======================================
    Idle Horizontal Mast         Rotator ====Stub mast
                                     hole^

Drilling a small hole at the lowest point will let more water out than in.

Similar things happen with sealed connector joints, a slight ingress of water
into a clean new PL259 plugs & barrel all taped up will corrode solid under the
tape.
           Amalgamating
         Waterproof Tape
          ___.=========.___Water
  ============[𱱱]=========
          ~~~'========='~~~Ingress
         Corroded inside

Filling the space with vaceline where water could go is the answer here.       

TOO LATE
If it is already too late, there are approaches other than a hack saw or angle
grinder that may recover the situation.

Penetrating oil (eg.WD40) & heat, often works if given time. Work the component
too & throw if there is any movement, not putting too much pressure on it to
shear it off.

       Oil
     /
 Nut۲<Heat 
Bolt   & Rotate

Rusted steel can be partly recovered with painted on Phosphic acid treatments
that convert the flaky rust brown Iron Oxide surface layer to a harder purple
Iron Phosphate. Some rust treatment products are also rubber emulsion paints
that seal the metal from future water at the same time.
    

Why don't U send an interesting bul?

73 De John, G8MNY @ GB7CIP


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