From: "Jeffrey R Davis" <jrdavis@crnotes.collins.rockwell.com>
To: towertalk@contesting.com
Date sent: Tue, 23 Mar 1999 08:26:43 -0600
Subject: Re: [TowerTalk] Orion rotator application note
> Although perhaps overkill for the application, if you really, really,
> REALLY don't want bolts to back out, the military and aircraft industry
> way is to safety wire them.
Wait a minute everyone. Everyone is gluing, wiring, locking and
double nutting the bolts.
When a problem gets that severe, you can bet something ELSE is
going on besides the nuts turning. The nylon self-locking nuts by
themselves would totally cure any loosening of the nut by turning,
unless someone is sneaking up your tower at night with a wrench.
Per race cars:
1.) Rod bolts aren't locked, they are lubricated. Almost 10,000
time a minute they go through a complete cycle of full tension
loading and minimum loading with OIL on the threads and NO lock
washers or other hardware.
2.) Bolts that stretch, or can't be properly torqued because the
material is too weak are the ONLY bolts that are locked by
external means. I use locking hardware to fasten fiberglass with
steel bolts, or fasten soft bolts to hard metal, or hard bolts to soft
metal (like soft alloy aluminum) because the materials stretch,
compress, or erode. No way will the bolt stay under tension.
All the locking hardware does is keep the bolt from falling out! It
does NOT keep tension on the bolt. Only stretch of the bolt or
compression of what is under the bolt keeps tension on the bolt.
That's a fact.
I'd suggest you look at the materials used in the area of the bolts
before going wild trying to stop a nut from turning that most likely is
NOT turning in the first place. I've seen this hundreds of times in
race cars, and even in things as small as panel meters. We had a
guy at Prime Instruments who was using locktite, star washers,
compression washers, and eventually wanted to pin meter terminal
to the case of a meter because they kept "getting loose".
Turned out the problem was the case was shrinking from pressure.
Soft plastic. No surface area for the load. Fixing the case cured
the problem.
I'd look at materials. The U-bolts, the saddles, the things that do
the clamping. I'd bet you find a material in the sandwich that is
compressed or stretched beyond the limits where it retains its
ability to return to its original size when the load is relaxed.
If so, you could weld the nuts and the thing would be loose later on.
Proper hardware stacks won't get loose even without locktite
unless something is wrong with the materials for the amount of
applied load. If you don't believe that, look under your cars
hubcaps. You can grease those lugnuts, and they will stay just as
secure (actually more secure if you torque them) as if they were
dry. As a matter of fact, most critical bolts are lubricated before
tightening and locktite and other locking stuff makes them less
reliable.
73, Tom W8JI
w8ji@contesting.com
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