Welding Tips and Tricks

Hi All,

Looks like I need some help here.

I am welding some parts, 4130 steel, for my J3 Cub home-built aircraft. After beading the welds I noticed small black specks that are like glass hard and will not bead off without scraping them. Any suggestions what is causing this or what I am doing to cause these?

I am not a professional welder, just a hobbyist. So, please be kind on the weld appearance .... their not pretty but they work.

Any help would be very appreciative,
Keri-Ann

Using:
L-Tec STW 140i
Foot pedal control @ 30 Amps max set at Welder
CK 130 Flex-Torch ... love this torch.
ER70S-2 filler rod, new.
.06 dia, 2% Cert. electrode. Sharpened to a point, polished.
No.5 stubby cup and gas lens
Agron gas @ 20cfm

Rosie,
What you're seeing is the silicon coming to the surface. Some is picked up from the parent metal but most is from the rod. The designation -S2 (ER70-S2) at the end of the filler rod type is the amount of silicon that's added to the rod. In a perfect world all this would end up at the end of the weld. With practice your welds will become more consistent and it will end up only in the end of the weld. It's nothing to be cocerned about long as it has come to the top though.

Len

Thanks Len for the reply. I am working on that "stack of dimes" look, much more interested in the integrity of the welds at this point.
Glad to hear it is only that. The aesthetics will come with hours of practice, probably the very last weld out of thousands ... LOL!

So, what you are saying is that the weld puddle would keep floating the silicon forward in the weld direction until collecting at the end of the weld .... correct? Is there a way to keep the silicon from separating form the filler matal like this when welding?

Thanks for the reply, much appreciated.
Keri-Ann

Keri-Ann,

The silicon serves a valuable purpose, almost like flux in a solder joint, in that it's intended to carry impurities and oxides to the surface where they can be removed. It should be removed from every stop before you start again.

If it hardens as a light tan color, it indicates you have cleaned/prepped your weld well, and it should chip (or wire-wheel) off with (relatively) little resistance. If it's dark brown to black, and difficult to remove, you are picking up crap from inside the joint, and given the purpose of your welds, you should investigate, if this is happening. The most common cause is prepping the outside and face of the joint, and ignoring the inside of the tube. The first 1/4" or so of the inside of each joint should be sanded with a small sanding roll in a die-grinder to shiny (not aggressively, so you don't reduce wall thickness) and degreased.

BTW, everything reputable I've read in EAA Experimenter and the several books in my library from their publishing division suggest the rod of choice for 4130 is E80-S2, to more closely match the parent metal properties.

I hope some of this is helpful.

Also, nice placement of the TigFinger in the pic!

Steve S

Thanks Steve for the info, very informative.

I have tested a part to destruction and the parent metal tore before the weld let go, good sign. Also cut through the weld and it was solid, looks like it all came to the top. Hard to clean the inside when its half way down a tube, specially on a longeron that is 14 feet long ... LOL! Best I could do was the outside.

I too read that E80-S2 can be used, but E70-S2 is being use on some kit planes an they state it is more ductile. They are so close that I used the E70-S2.

TIG finger ..... I really like Jody and his video's. Love the TIG finger, I purchased 3!

Cheers,
Keri-Ann

What is the thickness of your material? Did you back purge? It's possible your pulling dirt/contaminents from the back of the material.

Your building an aircraft, it's going to be pricey, I would suggest buying about 200' of material same thickness in flat stock in 3" wide. Then weld them up using butt joints, then cut the weld out and do it again, then again. You should get at least three joints out of a 3" piece. That's a lot of practice, then evaluate if your ready for your project, if not do it again. Your only going to get to have one bad landing.

Rosietheriveter wrote:Thanks Steve for the info, very informative.

I have tested a part to destruction and the parent metal tore before the weld let go, good sign. Also cut through the weld and it was solid, looks like it all came to the top. Hard to clean the inside when its half way down a tube, specially on a longeron that is 14 feet long ... LOL! Best I could do was the outside.

I too read that E80-S2 can be used, but E70-S2 is being use on some kit planes an they state it is more ductile. They are so close that I used the E70-S2.

TIG finger ..... I really like Jody and his video's. Love the TIG finger, I purchased 3!

Cheers,
Keri-Ann

You can clean the inside of the mitred joint that is being welded in the center of said tube.

Rosietheriveter wrote:Thanks Steve for the info, very informative.

I have tested a part to destruction and the parent metal tore before the weld let go, good sign. Also cut through the weld and it was solid, looks like it all came to the top. Hard to clean the inside when its half way down a tube, specially on a longeron that is 14 feet long ... LOL! Best I could do was the outside.

I too read that E80-S2 can be used, but E70-S2 is being use on some kit planes an they state it is more ductile. They are so close that I used the E70-S2.

TIG finger ..... I really like Jody and his video's. Love the TIG finger, I purchased 3!

Cheers,
Keri-Ann

I can't argue the E70 too hard

I was referring, on cleaning the backside, to the specific joint you showed. I wasn't suggesting running a brush up a longeron, of course, but rather the open end of the cross-tube or diagonal that meets that longeron, where it is essentially an open-root weld. (No matter how tight you fit it, when you have good penetration, you'll pick up crap from the inside of the cope if you don't dress the inside of it for a short distance).

Keep us updated on this project! I'm interested, and Jody, our host, is also an EAA member, who attends Oshkosh and Sun 'n Fun when he can.

Edit: I think Wes just said the same thing....

Steve S

Hi Wes,

Thanks for tips and possible cause. I possibly did pull some from the .05" wall lower support when welding to the .063" wall square tube. I had cleaned both parts to shiny except the square tube inside. I may have been way to aggressive on the penetration, heat, into the square tube bring the inside contaminates up through the weld puddle to the top.

This is the 2nd plane I am building and these part are way over designed, so a good place to start. Tough to clean all the way down a tube like that an be perfect ... practice, practice and more practice is in order.

Cheers,
Keri-Ann

Steve and Wes your both correct on what happened here. I was joking on the longeron, very dry humor I have

Thanks again.

I appreciate a dry sence of humor, and I apologize for not catching it in the act...

My first reaction when I learn someone is building an airplane is to go into caution mode. I know people building drag-racing cars whom I wouldn't let weld on my grandson's go-kart, and I've known two people who bought aircraft plans AND their first welder at the same time. Never a good combination. I'm pleased to hear this is not your first build, and don't need the "kid-gloves" treatment.

Steve S

Hey Steve,

.... I also know my limits So should I be penetrating the metal to the back side or am I just applying to much heat? Remember most of the welding I am doing is on .035" to .062" wall thickness. If I get a good puddle that is 2/3 into the metal thickness that should be more then adequate for a weld ... yes, no?

Love the bike! I have a HD Heritage Softail.

BTW, kit gloves are always fun! ~ Keri-Ann

LOL! on the bike.

That's the AirGas bike by Orange County Choppers. That bike wasn't done on TV, unfortunately. I did a big job for AirGas, and they threw a picnic/open house near the end. That picture was taken by an executive VP for Airgas.

In an ideal world, you'll be penetrating the intersecting member completely, and teh base metal at that 1/2-2/3. The idea is to eliminate any edges/corners/sharp lines in the metal. These are called stress risers by the engineers. Ideally, every edge should be rounded, even the ones you don't see.

I work with liquid hydrogen (and other liquified gasses) every day, and I can assure you, complete root penetration is very important to a weld that sees stress. I've spent the last 16 hours of work repairing a pressure-building coil. I was replacing previous repairs that were inadequate and cracked.

The most common repair I do in an existing weld is from inadequate penetration, where there is a sharp dividing line left on the backside. Admittedly, your welds don't go instantly from 75* to minus 423*, but they are exposed to stresses of their own.

Steve S

Yes you should be 100% penetrating, which is why I suggested back purging, or aka back up gas in the tube. It will keep your weld clean on both sides. If you don't use a back up the back side of the joint will be grainy or "sugary" and will be a source for failure.

Hi Wes,

You suggestion is very valet. But in all the aircraft welding I have read and seen no one ever back purges the tubes. So there is something else that they are doing not to get these silicon specks.

In Jody's video of him welding a bike frame of 4130 (modified steel) he did not back purge the tube and his welds are perfect with no sign of silicon floaters. So again, what am I doing that is making this happen? ... still on a big learning curve here with simple equipment.

Thanks again for the suggestion,
Keri-Ann

The inside of the tubes need cleaned( ie shined up with a carbide bit or similar) then the back up is for weld integrity on the back side, I'm an aerospace welder, if there's a way to put back up on it you do, if you can't you figure out how. Specks are contamination from somewhere. I can't remember now, did you wipe with acetone after cleaning? What was you prep technique?

Even in aircraft welding (NOT "aerospace" welding"), carbon steels are rarely back-purged.

Even a high-alloy carbon steel like 4130 does not show "sugaring", or heavy oxidation of alloying components, from having atmosphere on the backside.

Backpurge of carbon steel is not required under ASME boiler and pressure vessel codes, nor suggested in any of the aircraft-specific books I've read.

Carbon steels form a scale on the surface only, much as aluminum forms an oxide skin, which protects the metal from further oxidation and does no harm on it's own.

While I agree backpurge will always produce a better product, the means to provide that backpurge in small-bore thin-wall tubing produces weak points I'd opt against.

In an ideal world, each joint in a 4130 airframe will have a small hole drilled connecting each component, so the entire airframe can be evacuated through a single point, and the atmosphere replaced with an inert gas (argon or dry nitrogen) which leaves only one hole external to the welded members to plug. In a practical world, each joint will be a perfectly sealed member with only ambient air and humidity trapped inside, which automatically limits the corrosion that can occur.

Steve S

... nicely said Steve.

Keri-Ann

Otto Nobedder wrote:Even in aircraft welding (NOT "aerospace" welding"), carbon steels are rarely back-purged.

Even a high-alloy carbon steel like 4130 does not show "sugaring", or heavy oxidation of alloying components, from having atmosphere on the backside.

Backpurge of carbon steel is not required under ASME boiler and pressure vessel codes, nor suggested in any of the aircraft-specific books I've read.

Carbon steels form a scale on the surface only, much as aluminum forms an oxide skin, which protects the metal from further oxidation and does no harm on it's own.

While I agree backpurge will always produce a better product, the means to provide that backpurge in small-bore thin-wall tubing produces weak points I'd opt against.

In an ideal world, each joint in a 4130 airframe will have a small hole drilled connecting each component, so the entire airframe can be evacuated through a single point, and the atmosphere replaced with an inert gas (argon or dry nitrogen) which leaves only one hole external to the welded members to plug. In a practical world, each joint will be a perfectly sealed member with only ambient air and humidity trapped inside, which automatically limits the corrosion that can occur.

Steve S

Learn something new everyday, I would think they'd want it back purged. I back purge everything, even my personnel projects. I do not know the codes for this project so I will take your word for it.

I know it's not "sugaring" like stainless, but that's what a lot of people call it regardless, I've forgotten to turn the back up gas on before lol.

So, have you tried again? Did the extra prep solve the problem?

I have more parts to weld up this weekend. Will post some pictures of the welds. I will clean, shine the parts up and wipe down with lacquer thinner. I used Dykes layout dye to mark the steel parts for layout marks, possibly did not get it all off ... ?

Would that cause the black specks?

Thanks for all the help, its my rear up there at 1000 feet!
Keri-Ann

So how'd you make out?

Well no welding do to the fact I had to figure out the aileron pulley height so I would not rub the rear wing spar. So I am going to wait until I have the wing assembled before adding the pulley bracket.

I did over last week talk to a professional welder with 20 years in the Nuclear welding field and has done Chromium-Moly. He stated I had some possible contamination in or on the metal, maybe from the Dykes layout dye or scale and that it came to the surface in the black specks. He said my welds are good and solid, we cross sectioned one test piece, just do not have the stack of dimes look, its there just not standing out ... LOL! He said it does not indicate a bad weld, just shows off ones skill and weld puddle control.

... so practice, practice and more practice. Will post more as I go with the plane project.

Thanks for all the great help guy's.
Keri-Ann