[TowerTalk] Hose Clamps

[Patrick Greenlee]

OOPS... Thanks for the correction, Jim.  I wasn't thinking aluminum but 
should have been.

Tighten stainless steel clamps on aluminum tubes when cold!!!!!!!!!!

Thanks again for the correction.

73,
Patrick AF5CK

-----Original Message----- 
From: Jim Lux
Sent: Sunday, January 27, 2013 10:08 AM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Hose Clamps


> As previously posted heat cycling can help get it tight and right.  When
> cycling the clamp (cold-hot,  cold-hot, etc) you should tighten at the
> end of the hot cycle before cooling the clamp to take advantage of the
> expansion and contraction which is the reason for temp cycling.
>

>
> I also found in assembling 3x TH7's and other antennas with hose clamped
> slitted tube sections that 2 or 3 tightening cycles are needed.  After
> some thermal cycles and a few days the stresses redistribute in the
> connection.  If you can create larger thermal cycles on purpose,  it
> helps - e.g. leave the antenna in the sun and then sprinkle with cold
> water.  Then retighten each clamp.  So far, this has worked with no
> loose elements after years of service.  The boom clamps can also benefit
> from this approach.  Retightening bolts after a few thermal cycles is a
> standard manufacturing process when fastening systems are near their
> stress limits.
>
>


CTE of Aluminum is about 13, CTE of stainless is about 6 (ppm/deg C)..

This would imply that you should tighten the clamps at the *coldest*
temperature, not hottest.  As it warms up the aluminum expands more than
the SS, so it will get tighter.
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