There's lots of things to consider here.
Corrosion: I know that zinc (galvanized steel) and aluminum are pretty
close together on the table of galvanic action so they tend not to corrode
in the weather as much as most other combinations of dissimilar metals. I
have seen stainless steel and aluminum cause the aluminum to turn to white
powder over a period of time. I am not absolutely sure, but I think this is
because the main component of stainless steel is iron, like all steel. Iron
and alumunum are not real close on the table of galvanic action. The basic
principle here is that dissimilar metals that are placed physically against
one another that are close to each other on the galvanic action table tend
to not corrode as much as those that are far apart on that table.
Bolt strength: I have heard that stainless steel is more "brittle" than
most other steels such as the steel that "Grade 5" bolts are made of. Grade
5 galvanized steel bolts is what Rohn recommends for bolting their tower
sections together.
Lock Washers . . . yes or no: Again, looking at steel Rohn tower sections
with tubular legs, Rohn never recommends the use of lock washers at all.
The reason is that the bolt compresses the steel tubular tower leg and
steel, being very elastic, keeps the bolt in constant tension without a lock
washer. On the other hand, if your tower legs are aluminum tubes, aluminum
is not nearly as elastic as steel and tends to take a permanent "set" when
deformed by, say, a bolt through them and tightened. The amount of
elasticity in the aluminum will depend greatly upon the alloy used and some
alloys might even be as elastic as structural steel but you would need to
know the exact allow and then find how its elasticity compares to steel to
know how important this is. Even if you used lock washers with aluminum,
the bolts may loosen up after a period of time as the aluminum tower legs
took a permanent "set". In this case, I would either use nylon insert nuts
which do not depend on tower leg compression to stay put or I would use
longer bolts and "double nut" them to keep them in place without depending
on leg compression to keep them from falling out. If your tower section
legs are more like flat angle material than tubing, lock washers should work
just fine since you will not compress the leg as the bolts are tightened.
But all of this is just my opinon and the guy you should REALLY listen to is
Hank, KR7X . . .
Stan
w7ni@easystreet.com
----- Original Message -----
From: "Jerry Keller" <k3bz@arrl.net>
To: "(Reflector) TowerTalk" <towertalk@contesting.com>
Sent: Tuesday, February 04, 2003 5:40 PM
Subject: [TowerTalk] Nuts & Bolts
> Which is better for the hardware to hold together the legs of my aluminum
> tower sections?
> Galvanized or Stainless steel?
> Finer thread (3/8-24) or courser thread (3/8-16)?
> Flat washers plus lock washers and standard nuts? or flat washers and
> locknuts?
> If Locknuts, should I use the nylon insert type or the type with the
indent?
>
> Advice appreciated.... Jerry K3BZ
>
>
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