"stick"/SMA - now cellulosic - root fusion, lap and T-joint fillet welds

I learned in an AWS D1.1 Certification class that the filet size code assumes there will NOT be complete fusion in a properly done filet weld. Albeit not impossible, but the normal filet weld won't have it and the thicker the material the harder it becomes. The weld is sized accordingly to account for this.

So, this situation of many problems making desired fillet root fusion ("the sheared edge of the top plate is no longer visible") is not some weird local outbreak... Hmmm...

So chosing cellulosics and getting penetration/fusion at the fillet root each time every time would be pretty A-OK...?

Is this the right scale of the circumstance?

Richard Smith

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I think it would A-OK. Most butted plate filets are basically unprepared joints and by nature of the joint you can't back gouge. If you cut them apart across the weld, you would see a tiny bit of black right at the root. If you open the angle more than 90 or put a gap at the root it will penetrate better approaching 100%. The thinner the plates, the greater chance of melting through the whole thing trying to get complete penetration. As the weld gets hotter, surface tension will pull parent metal into the puddle until you get undercut or a hole. On some joints other than filets, back gouging is mandated for the slag / non-pen we are talking about.

Hi All What is rutile-cellulose? I know that EXX10 & EXX11 (& probably others)are cellulose shielded electrodes. But I don' remember the rutile part. Maybe that's because just about all I've worked with for the last 20 yrs was lo-hi (E-7018)or flux core which is supposed to be lo-hi. If I had seen "rutile" outside of a welding context, I would have thought it had something to do w/ a moose in heat. Best John

Cellulose is vegetable matter in laymans terms. The flux coating is sawdust powder that burns creating a large cloud of protective carbon dioxide. E

6011 and E 6010 are cellulose based Rutile is a titanium oxide based material. ( mineral based) E 6012 and E 6013 are rutile. E 7018 uses flourospar and calcium carbonate making sure to avoid any hydrocarbon based materials. Randy

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Rutile (Titanium dioxide-TiO2) is the mineral in fluxes like the 13's.

This one says that fluxcore is a rutile flux too. I never would have guess that.

John

You are jumping in looking at it the wrong way round. Think of a "6013" rutile rod with a bit of cellulose to give it some penetrating ability. Rutile-cellulose sticks get marked "6013". Still a smooth-running rod, but with a hint of "bite" to get some penetration.

Richard Smith

That is certainly all 100% true. The thing that really sets cellulosics apart is that they generate huge quatities of hydrogen. This has incredible effects on the arc. The voltage drop over the arc something like doubles. So whereas you might be using 90A on another type of rod and struggling, you might be using 70A on a cellulosic and blasting it. Thee arc is also much "stiffer" and more penetrative. That is why you can so readily "keyhole" the root when root-running with cellulosics (you actually control on the arc punching a circular hole through the root).

How much hydrogen? Well, a low hydrogen fluxed process like an oven dried basic stick (xx18?) or flux-cored-wire of the rutile or basic type might give 5mlH2/100g deposited weld metal. Higher hydrogen is given by rutile stick at around 25 to 35mlH2/100g (they have to have moisture to give steam - there is no other shield). "Psychotrodes" (cellulosics, xx10's and 11's) come in at around 100mlH2/100g weld metal. That's a lot!

A rule which comes to you regarding hydrogen when working with welding consumables is "easy come, easy go". To get really high hydrogens you have to get the hydrogen source into the arc before it is driven off by the approching heat source. Cellulose is durable enough to dump its hydrogen into the arc. Leaving your welding rods in a bucket of water for a while does raise the hydrogen level, but the rod will dry as you weld and only a bit of that water will make it into the arc.

When something gets into the arc, its prior state as a compound or whatever is just about irrelevant. The arc is so fierce, at thousands of Celsius (degrees Centrigrade) that everything is dissociated and can be considered solely as amounts of atoms of a particular kind. That is why in welding "hydrogen sources" can be cellulose, moisture, water of crystallisation in the flux materials, oils, etc. - it makes no difference

The hydrogen also shields - keeps out the atmosphere.

Normally hydrogen would be considered undesirable, as it promotes hydrogen cracking. However, the stunning effect of hydrogen on the arc and the handling characteristics of the rod and the welding procedures which go with it make it frequently economic to live with the hydrogen and get lancing holes through the root.

Calcium carbonate = CaCO3

Heat it up: CaCO3 -> CaO + CO2

"lime" (CaO) is a good fluxing agent. CO2 (carbon dioxide) gives shielding. So you have a shielding mechanism needing no recourse to steam. You mustn't dry a rutile stick (xx13) as steam is the only shield it has, but you can bake a basic (xx18) at up to 400C (750F)

Richard Smith