I'm not a metallurgist either. I might have been sold chain link fence
railings, but whatever it was I dragged up 160ft in the air, it work pretty
well. I just googled 4130 and found the text below. All I can tell you is
what I recall from memory of events of nearly 20 years ago. Your results
may vary, good luck, good dx/ -M
4340 (chromoly) Normalized Alloy Steel
Minimum Properties Ultimate Tensile Strength, psi 186,000
Yield Strength, psi 125,000
Elongation 12.2%
Rockwell Hardness B100
Chemistry Iron (Fe) 96%
Carbon (C) 0.37 - 0.43%
Chromium (Cr) 0.7 - 0.9%
Manganese (Mn) 0.7% max
Molybdenum (Mo) 0.2 - 0.3% max
Nickel (Ni) 1.83%
Phosphorus (P) 0.035% max
Sulphur (S) 0.04% max
Silicon (Si) 0.23%
-----Original Message-----
From: Jim Lux
Sent: Thursday, December 27, 2012 1:41 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] mast for two big antennas
On 12/27/12 10:19 AM, Mike Ryan wrote:
This is 4130 chrome molly steel tubing. The word tubing is the primary
descriptor I think, in that there is no seam such as you might find when
using some kind of pipe. I bought a half dozen or so 24 ft lengths from
the Dillsburg Aeroplane Works up in Pennsylvania back in the late '80s
when I was putting together a station in northern Virginia. I had them
galvanized before using them. These were 125,000 psi tubes very similar
to the materials used to build racing car safety cages as I recall.
I'm not a metallurgist, but wonder if the heat from the galvanizing (I
assume it was done hot-dip into molten zinc) affects the heat treatment.
While that might not change the alloy composition, it might change the
yield strength.
My little handbook says 4130 cold-drawn is tensile strength 85-110kpsi,
yield of 70-85kpsi.
My understanding is that non-heat treated CrMo is fairly soft (hence the
low yield strength) and not a whole lot "stronger" than 1XXX type
steels. However, if heat treated it's a whole lot stronger (and more
stiff/brittle, as well) so it gets used for suspension components,
axles, and the like.
I suppose that we're constrained by the OD to fit in clamps, bushings,
bearings and the like, but I wonder if a larger diameter tube of cheaper
thinner steel might not be an easier way to go (lifting a 20 foot stick
of 2" tubing with 1/4" wall is going to be a chore). That r^4 term
really helps a lot..
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