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Posted by Ernie Leimkuhler on March 25, 2007, 6:21 am
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> Ernie Leimkuhler wrote:
>
> > tim124c41@yahoo.com wrote:
> >
>
> > MIG is not an option as it would impart severe distortion to the mast.
>
> Hmm. Why do you say that? These spots are
> typically less than 1/2" in diameter.
>
> Don W.
MIG on aluminum is a very fast process and causes rather extreme
distortion on tubing.
The rapid heating and cooling can warp the crap out of any tubular
extrusion.
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Posted by Bruce on March 25, 2007, 6:35 am
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On Sun, 25 Mar 2007 10:21:49 GMT, Ernie Leimkuhler
>
>> Ernie Leimkuhler wrote:
>>
>> > tim124c41@yahoo.com wrote:
>> >
>
>>
>> > MIG is not an option as it would impart severe distortion to the mast.
>>
>> Hmm. Why do you say that? These spots are
>> typically less than 1/2" in diameter.
>>
>> Don W.
>
>MIG on aluminum is a very fast process and causes rather extreme
>distortion on tubing.
>The rapid heating and cooling can warp the crap out of any tubular
>extrusion.
The original post referred to a 50-something foot mast. Believe me
this is not tubing.
I'm not that familiar with MIG welding but I have successfully stick
welded both masts and boom on a 40 ft. sloop.
Bruce in Bangkok
(brucepaigeatgmaildotcom)
--
Posted via a free Usenet account from http://www.teranews.com
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Posted by on March 25, 2007, 3:28 pm
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> tim124...@yahoo.com wrote:
> > The mast is probably a 6000 series heat treated alloy. Welding heat
> > will drop the strength, perhaps even to half the original. So welding
> > will probably do more damage than it will help.
>
> Um..., wrong.
> 6000 series aluminum alloys and specifically 6061 are precipitation
> hardening alloys.
> To get to the T-6 hardened condition the entire piece is subjected to a
> series of electronically controlled heatings and coolings.
> This is called, euphemistically, "artificial age hardening", and is the
> only way to achieve T-6 hardness and above (T-8 is the hardest).
>
> When you weld 6061 that is T-6 hard, the heat affected zone, will drop
> in hardness to around a T-2 to T-3 hardness.
>
> Over the next few weeks the aluminum will recover some of it's hardness
> through "natural age hardening".
> The hardest it can get to is a T-5.
I dunno Ernie. Everything I've found has said that while some
strength is regained by age hardening, the heat affected zone is still
considerably weaker than a T6 condition. For example, here's a quote
from a Lincoln brochure (http://content.lincolnelectric.com/pdfs/
products/literature/c8100.pdf):
"When T4 or T6 materials are welded, the heat of welding
affects the properties in the HAZ, reducing them.
Properties are usually not reduced all the way down to
the "O" temper. It is difficult to give a general rule
regarding the reduction in properties. The specific value
depends on the alloy and temper under consideration.
However, as an example, 6061-T6 is required to have a
minimum utlimate tensile strength of 40 ksi (276 MPa)
before welding. In the welded condition, most codes
require a minimum tensile stress of 24 ksi (165 MPa), so
that the reduction can be significant."
If 6061 naturally age hardened to regain most of the T6 strength,
wouldn't the welding codes recognize this?
In any event, building up the corroded spots on this mast by welding
is going to be a lot more effort than just using an epoxy filler. All
the rest (corrosion removal, scuffing or removing old paint, priming,
fairing and painting) will be the same either way. Assuming the
corrosion is cosmetic, the mast will look the same in the end.
On the other hand, if the corrosion is bad enough to structurally
weaken the mast, welding will replace lost metal, but it may not add
strength.
Cheers,
Tim
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Posted by Don W on March 25, 2007, 10:14 pm
Please log in for more thread options tim124c41@yahoo.com wrote:
> In any event, building up the corroded spots on this mast by welding
> is going to be a lot more effort than just using an epoxy filler.
Well, maybe not. It may be 4 or 5 hours of
welding and sanding versus 1 hour of epoxy and
sanding. Either way it is about half a day ;-)
> All
> the rest (corrosion removal, scuffing or removing old paint, priming,
> fairing and painting) will be the same either way. Assuming the
> corrosion is cosmetic, the mast will look the same in the end.
True.
> On the other hand, if the corrosion is bad enough to structurally
> weaken the mast, welding will replace lost metal, but it may not add
> strength.
Sounds like a reasonable argument to me. One
thing to consider is that masts are rigged to be
in compression at all times, so the tension specs
on the alloy may not be what is important.
> Cheers,
>
> Tim
Don W.
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Posted by Don W on March 24, 2007, 1:17 am
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tim124c41@yahoo.com wrote:
> The mast is probably a 6000 series heat treated alloy. Welding heat
> will drop the strength, perhaps even to half the original. So welding
> will probably do more damage than it will help.
>
> Ship hulls are usually made from 5000 series aluminum which has better
> weldability and is more corrosion resistant than 6000 series, so you
> can leave a hull unpainted, but you wouldn't want to do the same for
> the mast.
>
> If the pitting isn't very deep and doesn't cover much of the surface,
> I'd say you're better refinishing the mast. With aluminum it's a
> challenge because paint doesn't want to stick to it. Where the
> existing paint is still adhering well you can scuff it and paint over
> it, but you'll be sanding out the corrosion to bare metal. Check with
> Interlux or whoever's paint you want to use for their
> recommendations. You'll probably need an aluminum primer, followed by
> an epoxy primer, then an epoxy filler, another layer of primer, then
> the exterior paint.
>
> If there's just a section of the mast that is badly corroded, you
> might be able to have it replaced. Find a sparmaker and if they can
> find more of that extrusion shape, they can join in a new piece and
> sleeve the inside for reinforcement. In any event, a sparmaker or
> good rigger would be able to look at your mast and give an opinion of
> what should be done.
>
> Good luck,
>
> Tim
Thanks Tim. I'll check with the boat manufacturer
to determine the original manufacturer of the
spar, and then contact them to try to determine
the alloy. If it turns out that it is a heat
treated alloy which will lose strength on re-heat,
I'll drop the welding idea and go to and epoxy
filler for cosmetic repairs.
Don W.
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