[TowerTalk] Exothermic Welding?

[dlleikis@deseretonline.com (David Leikis)]

The Cadweld area distributor actually came to my home (a 150 mile round
trip) to instruct me on their proper installation.

The reason for the spongy appearance to the metal joint is very simple:
water!  It is strongly recommended and required even to heat the mold
with a torch before use to drive out all trace of water (be it vapor or
condensed).  That is the source of the bubbles.  During the reaction of
the powdered aluminum burning the temperature rapidly (about 1-2
seconds) rises to about 4600 deg. and the tiniest amount of water in the
very porous graphite mold exits in the form of steam directly into the
connection.

I have done several connections and have whacked them (the final
reliability test recommended by the factory, BTW!) with a large hammer
and there has been NO failure.  The distributor told me that it seems
like such a simple procedure overall that very few of the electrical
installers that he has ever instructed believe that this step is
necessary and they don't do it.  Even installers using them for many
years. (Usually the worst offenders!)

The initial purpose of these welds was to hold a large wire (about 4
AWG) onto the adjoining rails for track signaling and I am very
skeptical that they fail with the light tap from a small hammer if done
properly.......  The vibration that a railroad track undergoes is off
the charts in my opinion!

Dave


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