Rust Check or Linseed Oil???
R Paul Lumsden
I am in the process of building a tube and fabric aircraft.
Recently, a friend of mine, -an aircraft mechanic with
years and years of experience suggested to me that I
should use Rust Check or some such similar product to
protect the airframe from internal rust instead of the old
tried and true linseed oil and turpentine. "Why not use
these new products', he said, 'they are much improved
over what was used fifty years ago." It seems sensible to
me, but I am very cautious about using products that are
not recommeded.
Does anybody have any opinion on this question???
Paul Lumsden
DC3DRIVER
Linseed oil is perfectly acceptable. However, it needs to be heated prior
to pouring inside the tubing. I prefer to use Tubeseal which is a
Poly-Fiber product. Temperature needs to be above 60 degrees when you put
it in the tubing. Rotate the fuselage or whatever 90 degrees at a time to
insure complete coverage. This product is designed to last for years.
DC3DRIVER
DC3DRIVER
DC3DRIVER
QDurham
I've always wondered why, instead of linseed oil, one didn't weld an inner
tube fitting into the fguselage 4130 tubing, pressurize the thing, check
for leaks with soap, weld off the leaks, and seal the mother up. Rusting
can only occur in the presence of oxygen, and once the available oxygen
trapped inside the tubing has combined with the iron for a trivial coating
of rust, the process stops.
Of course any newly-acquired hole will defeat the process, but it probably
will defeat the Lion-Oil (linseed) process as well.
Hmmmmmmm.
Quent.
QDurham
QDurham
jgraham
Oxidation causes rust. Linseed oil has an abundance of hydrogen groups
that are highly reductive. Reduction is the opposite of oxidation or
rust.
Pressurizing the tubing is a super way to monitor the integrity of
the tube skeleton. Place a fitting and a pressure gauge on the
tubing and you will know that as long as pressure is reasonably
maintained that there are no leaks or cracks.
J. Graham
jgraham
Please see my posting on linseed oil as it opposes the oxidative
process that we call rusting.
J. Graham
Paul Westcott
In article <19970114023...@ladder01.news.aol.com>, dc3d...@aol.com
says...
I'd agree with the above. I've used Polyfiber (nee Stitts) products for
around thirty years and have been happy with their stuff for ragwing
airplanes. I think you get better coverage and capillary action with
tubeseal than linseed. I salvaged some tubing from an airplane that had
been treated with tubeseal before it spent some months submerged and found
the tubing to be in good shape inside. I fly mostly floats here in
Southeastern Alaska, about half fresh and half saltwater operation so I am a
bit compulsive about corrosion control. Nothing wrong with using more modern
products, you weren't thinking of recovering with muslin and varnish ala
Wright Brothers were you?
Paul Westcott
Paul Westcott
In article <19970114153...@ladder01.news.aol.com>, qdu...@aol.com
says...
>
>I've always wondered why, instead of linseed oil, one didn't weld an inn
>er
>tube fitting into the fguselage 4130 tubing, pressurize the thing, check
>for leaks with soap, weld off the leaks, and seal the mother up.
>
One does try to seal the tubing, but it would take a lot of fittings sticking
out of just about everywhere to provide for all the separate pieces of tubing
in a typical fuselage. Next best bet is to squirt in some TUBESEAL or
thinned linseed oil and weld up the tube.
Paul Westcott
ifly
I saw a suggestion somewhere way back that I`m going to use in my fuse.
First, use oil especially formulated for steel, next, weld in a fitting
for a pressure gauge and an air valve, then after you`ve oiled your fuse,
pressurize it with nitrogen. No oxidation, and any cracks that appear
will alert you of damage to your airplane. I believe this has been used
on aerobatic airplanes.
J Morris
William Everett
I've been watching this thread to see if anyone was going to come up with
the most obvious problem. Nobody has.
#1 Each and every joint will require that a hole at least 1/8" or so be
predrilled in the "running" tube to allow either oils or gasses to make it
to all the tubes. Not a big problem if you remember to do it during the
welding. In fact, drilling a hole at each weld joint helps reduce a bit
of the distortion, even if you don't rust proof.
Yes, you can go back and drill completely through the "running" tube to
create this passage, but then you have to weld the outside hole shut. Got
any idea what happens to the oil inside the tubes when you weld on them?
Yep. the oil gets burned off. Besides, there are plenty of places on the
average airframe where this "through drilling" cannot be accomplished.
Now, maybe you can get oil to eventually run all through your frame, and
only have to weld *one* capped tube. (Not great, but a fair idea)
# 2 Pressurizing the frame has one serious draw back. If a leak does
occur, you then have *no* protection till you find that leak... a real
tough job, I might add. Believe it, or not, quite a few welds can be
found to leak, even though you'd swear to look at them they never could.
OMHO, the linseed oil treatment, capped off with a small screw liberally
slopped up with your choice of good sealant is the best bet.
--
Bill Everett
P.O.Box 60038 St. Pete, FL 33784-0038
sfz...@scfn.thpl.lib.fl.us
or try: beve...@juno.com
John Knowles
After drilling holes for all crossmembers on my frame and tack welding,
I took the entire frame to a professional aircraft welding company. This
company does certifcated welding for Aerospatiale Helicopters. They
create some of the most beautiful TIG welded clusters I've seen. Even
with this level of expertise, it took two weeks of soapy water spray and
rewelding to get the frame to hold 10PSI for 4 days. At this point you
had to spray a cluster and wait about 60 seconds for a bubble to show
up. After sand blasting and epoxy primer the frame would hold 10PSI for
5 days. I think I'll live with refilling it with nitrogen until the
linseed oil has a chance to coagulate and seal the remaining pin holes.
Lot's of work but that gauge in the cockpit showing positive pressure
sure does inspire confidence when you're pulling and pushing 9G's.
John Knowles
Chev powered monoplane "Hammerhead"
ifly
I`d like to pick up this thread on the subject of TIG welding. I know
it`s common nowadays, but I understand there are some concerns amongst
some that hydrogen embrittlement can occur due to the very localised
heating of the material. Does anyone have any knowledge on this subject?
I know a lot of kit airplanes are constructed this way with no real
problems yet, but I understand this is a problem that can take many years
to surface.
Jeff Morris
QDurham
<It would only take one fitting, in fact. Since most tube fuses have holes
drilled in every tube joint to allow flow of the oil into all tubes
anyway.>
Additional benefit: I bet the so-so welder would spend an unexpected
number of hours fixing sundryfaulty, leaking joints.
Quent
ifly
It would only take one fitting, in fact. Since most tube fuses have holes
drilled in every tube joint to allow flow of the oil into all tubes
anyway.
Jeff Morris
JaKo
How about another alternative . . .
After all welding is done, drill a couple of little (1/8") holes
in every "enclosed" tube (at opposite ends if possible) and fill
the tubes with polyurethane foam (MONO?), you know the one which
expands about 20 times its original liquid volume. It would
surely affect the resultant strenght of the assembly, but there
are some people who would be willing to make the necessary calc's
and mod's.
And the relevancy to the original post -- no air (water etc.) --
no rust AND with minimum weight increment and, possibly, great
strength improvement -- you all saw the Infinity add -- the one
with the drinking straw breaks easily while empty and doesn't
break *so easily* with polyurethane core inserted).
Cheers,
JaKo, RV-8 hopeful (when the quick built kit ...)
John R. Johnson
Actually, I always understood that the reason you heat the linseed oil
before you pour it into the tubing, was logistic. Then you can feel
the tubing to see where the oil has gone. When all the tubing has been
coated ( is warm ) then you pour OUT as much oil as you can. The
residue that you can't get out will oxidize and use up all the free
oxygen inside the tubing and, viola, no rust!
John
Steve Fribley
I'm not an expert on welding, but understand that MIG/TIG heats a smaller
area, with result that cooldown is faster, and less annealing of the weld
occurs. Common practice with oxy-acetylene welding is to heat the area
after completion of the weld, so that cooling is uniform, and stresses
aren't induced by uneven cooling. You can see warpage if you don't do
this. To really learn nice thinwall techniques, get some 1/8 " or thinner
sheet meatl, shear into 2" wide strips about 8" long, and practice welding
them together. You'll be amazed at the warpage you get! You can also see
how poor your penetration is with quick techniques, and for real fun,
break some on a press & examine the insides of the welds, see how they
fail. (I did take a welding class at Purdue University, and would
recommend a similar course to anyone building an airplane, bicycle,
funnycar, etc.)
Jutka Enochs
This might work to seal out moisture but I'm skeptical that it would add
much stiffness unless the failure mode is expected to be from buckle
failure. i.e. if you have a very large diameter and very thin wall tube,
then the foam will stiffen the tube sufficiently to prevent buckle failure
provided also that the foam has good adhesion with the tubing. Foam is
often used to stiffen composite structures.
Not to discourage you, but I think I'll stick to the line oil.
William Everett
:com>
Distribution:
Yeah, you're sure right about the flame work. So many of us overlook it,
or don't heat the weld (and adjacent areas... about 10" to 12") hot enough
(it needs to be cherry red)nor hold the heat up there at that nice, hot
temperature long enough (should be ten minutes or so) nor cool it all down
slowly enough (five to ten minutes keeping the flame there, but letting it
get progressively cooler) to really give the metal a chance to loose the
build up of stresses incured during the relatively violent process of
welding.
These are, of course, back yard, rule of thumb measurements, and the
results sure aren't going to be thoroughly predictable. But it beats the
daylights out of just yanking the heat off the weld, and hoping for the
best.
You spoke of distortion being seemingly your biggest worry. You'd be
surprised how much distortion can be defeated by the very heat that causes
it. That particular technique takes heaps of experimenting and practice.
Hint: it will go the opposite of what you might expect.
The real devil in welding without relieving stress is the eventual failure
(read: cracking) Yeah, I know you know that. Just harping for the
benefit of all of us who forget.
Now, if you insist on welding without considering any additional heating
IMOH, your best bet is MIG... it's a little quicker on the heat, so less
surrounding metal is effected for a given welded area. (It's also the
easiest)
Charles K. Scott
In article <5bo8ja$d...@news.indigo.ie>
ifly <if...@indigo.ie> writes:
Jeff, it has been suggested many many times in this group that if you
weld your tube fuselage with a TIG welder you should normalize your
welded clusters using a Oxy/Acet torch afterword. This would take care
of any embrittlement. The thing is, if you have to go through the
process of using a torch after welding with a TIG machine, why not just
weld with a torch in the first place? If you use a torch and preheat
the clusters and do all the do's for welding, you really don't have to
normalize afterword because torch welding spreads the heat around so
much anyway. Or so says Tony Bingellis.
In article <5bhe9m$q10$2...@byatt.alaska.net>
av...@alaska.net (Paul Westcott) writes:
> One does try to seal the tubing, but it would take a lot of fittings sticking
> out of just about everywhere to provide for all the separate pieces of tubing
> in a typical fuselage. Next best bet is to squirt in some TUBESEAL or
> thinned linseed oil and weld up the tube.
>
> Paul Westcott
Paul, most of the books and articles on welding tube fuselages call for
a hole to be predrilled in each tube joint prior to welding so as to
facilitate two things: 1. To allow you to flow some type of sealer
throughout the fuselage after welding is completed and 2. To allow an
exit for the air pressurized by the heating of the welding process so
the weld does not have a tendency to blow out on you in short runs of
tubing.
> Yes, you can go back and drill completely through the "running" tube to
> create this passage, but then you have to weld the outside hole shut. Got
> any idea what happens to the oil inside the tubes when you weld on them?
> Yep. the oil gets burned off.
>
> --
> Bill Everett
Bill, if you pre-drill the holes prior to welding, you don't have the
problem you describe. Also, Ron Mason, the designer of the Christavia
series, suggests that every tube be saturated with boiled linseed oil
by soaking a rag and drawing it through the tube, THEN welding it. He
says that the heat of welding evaporates the oil at the weld but then
the oil condenses on the weld as it cools.
Looks like there are lots of ways to successfully weld a tube fuselage
and have a safe airplane.
Corky Scott
John R. Johnson
It is a good point. The linseed oil used should be "raw" linseed oil.
As Jim points out, the "raw" linseed oil will heal uncovered places
inside the tubes. Although he is mistaken is the setting up business.
The advantage of "raw" linseed oil over "boiled" linseed oil is that the
"boiled" linseed oil includes "dryers" which cause it to set up like
varnish. The "raw" linseed oil does NOT contain these dryers and will
take years to solidify to the point where it will not heal over voids.
Even a little welding on the tube, with linseed oil inside, will cause
the linseed oil coating on the inside to burn off. It will quickly
heal and once again provide protection, even if air and moisture have
access to the inside of the tube.
I have used "raw" linseed oil to protect tubing for years, and I have
never had a "rust through" from the inside.
John
On Mon, 20 Jan 1997, Jim VanDervort wrote:
> I think there is still something missing here. I have not seen where it
> was said that you need to use RAW linseed oil. (not boiled) when you heat
> raw linseed oil, and pour it in the tubing, it will "set up"
> and crawl all over everything and dry like paint. You don't need to turn
> the fuselage over to get it everwhere. I have seen it crawl up clear to
> the top of a J-3 Cub tailpost. This is with RAW, heated linseed oil.
> Also, do NOT leave rags wet with raw, heated linseed oil on them in a
> pile anywhere. They will burst into flames in a matter of 2 or 3 hours.
> (just after you have had supper and hit the sack.
>
>
>
John R. Johnson
The REAL problem with MIG/TIG welding of aircraft tubing has nothing to
do with this. 4130 Steel is an "air hardening" alloy. It quenchs in air!
When it quenchs it gets very hard and brittle. When it gets hard and
brittle it cracks. This doesn't usually occur IN the weld, but rather
immediatealy adjacent to the weld, where the hardening occurs.
To avoid this problem you should "normalize" the weld and the surrounding
tubing after welding. This process is very similiar to, but a bit easier
that "annealing" the area of the weld. Annealing an air hardening steel
like 4130 requires heating the entire area to a bright red heat and then
cooling it at about 50 degrees per hour to 1300 or so. Then it can be
allowed to cool slowly to room temperature. The usually way to control
the cooling is to bury it in hot sand.
Normalization is much simpler. Heat the area to a dull red heat and cool
reasonably slowly until the color is gone. Keep it out of drafts and
breezes. A O-A torch is the preferred tool for "normalizing" the weld
area. Since you have the torch there and running for the preheat and the
post weld normalization, it makes sense to go ahead and WELD it with the
torch also. although, if you want to, you CAN spend twice as much money
on welding equipment and switch back and forth in the middle of the weld
so that you can use your nice TIG machine. I do not recommend MIG for
aircraft structures.
John
Jeffrey M. Matthews
In article <5bs51t$e...@ns1.thpl.lib.fl.us>,
William Everett <sfz...@scfn.thpl.lib.fl.us> wrote:
>:com>
>Distribution:
>
>Yeah, you're sure right about the flame work. So many of us overlook it,
>or don't heat the weld (and adjacent areas... about 10" to 12") hot enough
>(it needs to be cherry red)nor hold the heat up there at that nice, hot
>temperature long enough (should be ten minutes or so) nor cool it all down
>slowly enough (five to ten minutes keeping the flame there, but letting it
>get progressively cooler) to really give the metal a chance to loose the
>build up of stresses incured during the relatively violent process of
>welding.
>
Ten or twelve inches? Five to ten minutes? That's not the way I was
taught. You sure you're not an acetlyene salesman?
Jeff Matthews
ifly
>> I`d like to pick up this thread on the subject of TIG welding. I know
>> it`s common nowadays, but I understand there are some concerns amongst
>> some that hydrogen embrittlement can occur due to the very localised
>> heating of the material.
>
>Jeff, it has been suggested many many times in this group that if you
>weld your tube fuselage with a TIG welder you should normalize your
>welded clusters using a Oxy/Acet torch afterword. This would take care
>of any embrittlement. The thing is, if you have to go through the
>process of using a torch after welding with a TIG machine, why not just
>weld with a torch in the first place? If you use a torch and preheat
>the clusters and do all the do's for welding, you really don't have to
>normalize afterword because torch welding spreads the heat around so
>much anyway. Or so says Tony Bingellis.
>
>In article <5bhe9m$q10$2...@byatt.alaska.net>
>av...@alaska.net (Paul Westcott) writes:
>Corky Scott
Corkey,
My understanding of this (think I read it in Sport aviation awhile back)
is that Heating with a oxy-acetylene torch after welding will only
normalize the weld and release stresses built up, wheras hydrogen
embrittlement is a condition where hydrogen molecules are locked into the
metal when it`s molten, and can only be released if the metal is melted
again.
Like so many other things in homebuilding, I`ve read a lot of conflicting
reports and don`t know what to believe, really. I do remember that the
article I read was concerned with the increasingly common practice of TIG
and MIG welding, and the effects of embrittlement in the long term.
Jeff Morris
jj...@dow.com
In article <5c2pnt$c...@news.indigo.ie>, ifly says...
>
>My understanding of this (think I read it in Sport aviation awhile back)
>is that Heating with a oxy-acetylene torch after welding will only
>normalize the weld and release stresses built up, wheras hydrogen
>embrittlement is a condition where hydrogen molecules are locked into the
>metal when it`s molten, and can only be released if the metal is melted
>again.
>Like so many other things in homebuilding, I`ve read a lot of conflicting
>reports and don`t know what to believe, really. I do remember that the
>article I read was concerned with the increasingly common practice of TIG
>and MIG welding, and the effects of embrittlement in the long term.
>
>Jeff Morris
>
Let's make this simple. No matter what process you use, run a nice liquid puddle
around the cluster and you won't have a problem. Just don't undercut the welds
and don't weld in a windstorm.
Cordially
Joe Maj
William Everett
: Ten or twelve inches? Five to ten minutes? That's not the way I was
: taught. You sure you're not an acetlyene salesman?
: Jeff Matthews
Yeah, ten to twelve inches, that'll be about five to six inches to
eitherside of the weld. Now, if you want to see some real long time,
check with one of the places in your area that pop the whole frame in an
oven, and cook it... runs into hours!
And, if you stop to think about it, that slow cooling is the most
important step. If you just let the metal cool off at the same rate it
cooled after you finished welding on it, what have you accomplished in the
reheating? Not too much, you basiclly just repeated the same process all
over a second time, leaving the metal in pretty much the same shape it was
in when you finished welding.
Clarence Snyder
ifly <if...@indigo.ie> wrote:
MIG and TIG welding are both gas sheilded welding processes. If there
is no hydrogen in the welding gas (and i sure hope there is not, with
its flamability), how do you get hydrogen embrittlement in a properly
made TIG or MIG weld?
The job of sheilding gas is to prevent the interaction of
environmental agents with the weld while in process.
>
>>> I`d like to pick up this thread on the subject of TIG welding. I know
>>> it`s common nowadays, but I understand there are some concerns amongst
>>> some that hydrogen embrittlement can occur due to the very localised
>>> heating of the material.
>>
>>Jeff, it has been suggested many many times in this group that if you
>>weld your tube fuselage with a TIG welder you should normalize your
>>welded clusters using a Oxy/Acet torch afterword. This would take care
>>of any embrittlement. The thing is, if you have to go through the
>>process of using a torch after welding with a TIG machine, why not just
>>weld with a torch in the first place? If you use a torch and preheat
>>the clusters and do all the do's for welding, you really don't have to
>>normalize afterword because torch welding spreads the heat around so
>>much anyway. Or so says Tony Bingellis.
>>
>>In article <5bhe9m$q10$2...@byatt.alaska.net>
>>av...@alaska.net (Paul Westcott) writes:
>>Corky Scott
>
>
>Corkey,
>
Jeffrey M. Matthews
In article <5c5h1j$5...@ns1.thpl.lib.fl.us>,
William Everett <sfz...@scfn.thpl.lib.fl.us> wrote:
>: Ten or twelve inches? Five to ten minutes? That's not the way I was
>: taught. You sure you're not an acetlyene salesman?
>
>: Jeff Matthews
>
>Yeah, ten to twelve inches, that'll be about five to six inches to
>eitherside of the weld. Now, if you want to see some real long time,
>check with one of the places in your area that pop the whole frame in an
>oven, and cook it... runs into hours!
>
>And, if you stop to think about it, that slow cooling is the most
>important step. If you just let the metal cool off at the same rate it
>cooled after you finished welding on it, what have you accomplished in the
>reheating? Not too much, you basiclly just repeated the same process all
>over a second time, leaving the metal in pretty much the same shape it was
>in when you finished welding.
>
>
Let's see now--4130 is normalized by heating to 1600 F and cooling in still
air. It's hardened by quenching from 1575 either by water quenching or by
an air blast. I haven't got a reference handy, but it seems to me that's
in the medium orange region. If I haven't heated some area of the part to
at least red heat, I can't have hardened it, and it won't need re-normal-
izing. So we should be talking about an inch at most on either side of the
weld.
If I play the torch flame around the weld as I finish the bead, and let it
take a minute to get from orange to grey, I'll have come pretty close to
re-normalizing the heat affected zone. Anything more might do a better job,
but I doubt there would be any practical difference.
I'm not sure my Smiths will put out enough heat to keep a cluster cherry red
for five inches in all directions--certainly not with any flame I'm going to
be welding with.
Jeff Matthews
John R. Johnson
That sounds like the way I was taught, Jeff. Heat the area around the
weld, a couple of inches, to red and then slowly back away the torch so
that it takes a little while, maybe a minute or so, to cool to dark.
Then go on to the next one. Do your welding someplace protected from
the wind.
John
jd...@lehigh.edu
John R. Johnson writes:
>so that you can use your nice TIG machine. I do not recommend MIG for
>aircraft structures.
>
>John
>
Good post John. Recently I have looked at airframes from two different
manufacturers who advertise the use of 4130N and they were both MIG welded. Is
this the wave of the future to lower manufacturing costs?
John Caffrey
John R. Johnson
It is a wave anyway. MIG is very convenient for production welding.
Almost anyone can make a pretty weld with a MIG with just a little
practice. I found it MUCH easier to learn MIG that either TIG or O-A
welding. Unfortunately, it is also much harder to tell by looking
whether or not you got a good weld. I have seen really pretty MIG welds
that had zippo penetration!
The airframes should be normalized afterward. With a little innovation
you could normalize in the same oven you use to "powder coat" the tubing.
I don't know if anyone is actually doing that. The FAA put out a
service notice not long ago about an aerobatic Decathlon that lost a
wing because the strut fitting was MIG welded and not properly normalized
afterward. It cracked right next to the weld at a much lower than
expected loading.
Stinson pioneered electrically welded airframes in the forties, when
they were a component of Consolidated Vultee. It does lower the cost
for a production welding shop. It would be especially good if you could
oven normalize the entire airframe after welding it entirely up.
I was inspecting an absolutely lovely Waco fuselage that was welded up
entirely electrically. I talked with the welder, who is an old time
aircraft welder. He said he did normalize everything after it was all
welded. It was absolutely beautiful welding. He was restoring a Waco
Taperwing.
John
Bruce A. Frank
John Knowles wrote:
>
> William Everett wrote:
> >
> > I've been watching this thread to see if anyone was going to come up with
> > the most obvious problem. Nobody has.
> >
> > #1 Each and every joint will require that a hole at least 1/8" or so be
> > predrilled in the "running" tube to allow either oils or gasses to make it
> > to all the tubes. Not a big problem if you remember to do it during the
> > welding. In fact, drilling a hole at each weld joint helps reduce a bit
> > of the distortion, even if you don't rust proof.
> >
> > create this passage, but then you have to weld the outside hole shut. Got
> > any idea what happens to the oil inside the tubes when you weld on them?
John,
If your fuselage is sealed up that well there is no reason for tubeseal
of any kind.
--
Bruce A. Frank, "Ford 3.8L Engine and V-6 STOL
BAF...@worldnet.att.net Homebuilt Aircraft Newsletter"
*--------------------------------**----*
\(-o-)/ AIRCRAFT PROJECTS CO.
\___/
/ \
O O
Bruce A. Frank
ifly wrote:
>
> I`d like to pick up this thread on the subject of TIG welding. I know
> it`s common nowadays, but I understand there are some concerns amongst
> some that hydrogen embrittlement can occur due to the very localised
> I know a lot of kit airplanes are constructed this way with no real
> problems yet, but I understand this is a problem that can take many years
> to surface.
>
> Jeff Morris
I don't know where this idea of hydrogen embrittlement got started but
it IS NOT A COMMON PROBLEM- in fact it is NOT AN UNCOMMON PROBLEM- it
just does not happen in normal welding of 4130 tube with oxy/acet, TIG or
MIG.
Hydrogen embrittlement is the process of hydrogen being absorbed into the
molten puddle of metal. When the molten metal solidifies the hydrogen can
no longer stay in solution. At that point you have a bubble of hydrogen
form inside(at a microscopic level) the solidifying metal. This
bubble(and probably several hundred more) is exerting internal stress on
the weld and when combined with others, their combined force can crack a
weld. It is not like nitrogen embrittlement which forms a chemical
nitride to make an extremely hard spot, thus brittle spot.
What is the source of this hydrogen? If you are welding with STICK
electrode( you know, the flux coated type used for structrual work) and
the flux coating has gotten wet in the rain or has drawn moisture from
being stored for years in an unsealed container then there is moisture in
the flux. If the moisture has not damaged the flux you can put them(the
rods) in a rod oven for a day or two and dry them out. Most of todays
rod's coatings(fluxes) are MR type(moisture resistant).
The moisture in the flux is broken into H and O by the electric arc and
it is happening right there at the interface of the rod, the arc and the
molten puddle. So there can be hydrogen absorbsion in that case.
Oil, greese, and paint could be a source of Hydrogen but if such
contamination is present carbon is a much greater problem than any
hydrogen generated. In fact, excess carbon from such contamination is
usually the reason for cracking, not hydrogen.
If the joint to be welded in the tube is clean of oil and paint then
these problems are not likely to take place. When welding with stick,
part of the function of the flux coating is to form a gassious envelope
around the arc and puddle to protect them from contaminants in the
air--oxygen being the primary defect creator. When welding with TIG you
have an gas shield of argon around the molten puddle which protects it
until it solidifies. MIG uses, usually, an argon/co2 mix to accomplish
the same protection. With both MIG and TIG on clean steel with the
shield gas flow adjusted properly, there is no source of hydrogen
contamination.
Oxy/acet also provides the same protective envelope around the molten
puddle with the flame itself. The properly adjusted nutral flame provides
no contamination source either. An excessively oxidizing flame will
oxidize the weld to the point that it will throw sparks like a forth of
July sparkler, leading to a contaminated welding tip which will pop and
blow molten metal away or cause a backfire into the tip. An excessively
carberizing flame can introduce carbon into the weld and cause cracking
from hardness.
With stick electrode you can weld on metal wetted by the rain and not get
hydrogen embrittlement because the generated gas envelope forces the
moisture away. The heat generated by MIG and TIG welding drys the surface
ahead of the weld and also has a gas envelope to protect the molten weld.
TIG and and special water proof flux coated stick can be successfully
used UNDER WATER and no hydrogen embrittlement takes place. Quit worrying
about hydrogen embrittlement with any process you would normally use to
assemble your tube fuselage.
brian whatcott
In article <32F30D...@worldnet.att.net>, BAF...@worldnet.att.net
says...
>
...
>Hydrogen embrittlement is the process of hydrogen being absorbed into
the
>Bruce A. Frank
Hydrogen embrittlement has been implicated in failures of
electro-plated structures too - like chrome-plating....
Regards
brian whatcott <in...@intellisys.net>
altus OK
Bruce A. Frank
True, and the adsorption or desolving of Hydrogen into the crystal
lattice is similar and end results are equal. But the context was
welding.
Sometimes I don't know....
In article <32F30D...@worldnet.att.net> "Bruce A. Frank" <BAF...@worldnet.att.net> writes:
>Path: rtd.com!www.nntp.primenet.com!nntp.primenet.com!enews.sgi.com!news.sgi.com!news.maxwell.syr.edu!worldnet.att.net!newsadm
>From: "Bruce A. Frank" <BAF...@worldnet.att.net>
>Newsgroups: rec.aviation.homebuilt
>Subject: Hydrogen embrit. (Rust Check or Linseed Oil???)
>Date: Sat, 01 Feb 1997 01:30:18 -0800
>
A lot of people wrote a lot of good advise. More than my news reader
would allow me to re-post... However, I was advised by an Acft Welder
to always allow at least a 15-second Post Flow of gas across the hot
joint before pulling the torch away. That was an additional way to
ensure the atmospheric Nitrogen would not combine with the hot puddle.
His reference was to TIG (GTAW) welding, as that was the subject of
conversation at the time.
But, why aren't the common spray-can oils and penetrants used for the
internal rust-proofing of acft. tube frames? Such as the Silicon type
or the use of dilute paraffin based oils.
Shadow
Bruce A. Frank
The advantage of line oil, or linseed oil is its clotting quality. If the
fuselage is welded so well as to have no leaks then there is actually no
need for anything inside the tubes. The little atmospheric oxygen in
there quickly combines with the surface metal to form a very light
frosting of iron oxide and then nothing else happens- rust cannot occure
with out oxygen and none is available.
The linseed oil runs around and fills any pin holes to prevent any more
oxygen entering- stops "breathing" as with barometric pressure changes.
If at some latter date a pin hold does open, the "set up" or
"dried" coating of linseed inside the tubes is then supposed to protect
those surfaces from rust from any new atmospher being introduced.
Linseed oil will not stand up to a heavy introduction of water. I have
cut apart landing gear which was 30 years old which hade no linseed oil
inside and the tube looked brand new. I have also cut apart gear of
similar age which had linseed oil inside emulsified with several ounces
of water and almost rustwed through in several places.
John R. Johnson
Hydrogen embrittlement of steel can occur anytime the steel is immersed
in an environment with free hydrogen ions around. The free ions work
there way into the steel structure. Most electroplating solutions work
by passing current through water, which creates hydrogen ions as a by
product. Baking the part after plating will drive the hydrogen out of
the part and restore its toughness. This baking process is quite
critical and can not be done in your kitchen oven, I fear.
John
Phil Sisson
In my small and humble opinion, The oppinions by Brian and Bruce are the
way I have seen things to be in the last 25 to 30 years of my hobbyist
welding experiences. There are some good books and manuals on this
subject. EAA has some good welding books and Linde also has a gas
welding book that I read alot. Unfortunately, it seems like good TIG
books and information is scattered aound in little bits as it pertains
to 4130 ( all of aircrafting for that matter). This requires some
searching and researching to get what you want to know.
A person who can "type", I can't, could probably contact some of the
manufacturers and present a good bit of information to the newsgroup.
Pitts and many others "TIG" their stuff. Sky Dynamics makes hundreds of
321 SS exhaust systems with TIG.
There is a word "Carbide Precipitation", That I don't understand. I
would like to know if anyone has a very simple and clear explanation of
this, as to its meaning to the sportplane builder. (no bullshit artists
or ten dollar words, please) What is it, how it happens, what will it
do, and how to prevent it.
Build 'em strong and neat and fly 'em safe. Phil