This is probably a great time to clear up some misconceptions on welding that alot of welders have.(Slag inclusion AWS defined): Inclusions are impurites or foreign substances which are forced into a molten puddle during the welding process.
Cause: 1)improper base metal preperation. 2)improper cleaning of slag in a multipass weldment.
3)faulty electrode manipulation. As you can see, all three are caused by welder error. What alot of welders tend to try when inclusions are incurred, is to push the electrode deeper into the weld puddle thus forcing the inclusion out into the slag puddle where it will be removed with the slag. That rarely will happen. What is more likely to occur is the slag will cold fuse to the hole wall, made from the ellectrode, as the electrode is with drawn to noraml arc length thus covering the inclusion with molten metal leaving the welder to believe he has removed the inclusion as the weld puddle will return to look near normal. On a mulitpule pass weldment, the electrode will doposit more slag on top the exisitng slag inclusion but will have a near normal looking molten puddle this time. This inclusion will contiue to grow with-in the weld until the cover pass is put on. During a bend test the slag inclusion will break out and will show the inclusion from the root pass to the cover pass. Under this circumstance this weldment would fail certification.
A welder has a greater risk of a failed weld by not stopping to clean out the inclusion by grinding or other suitable means. Faulty electrode manipulation is mostly from the welder varrying the arc length or too long of arc length or the reverse too sort of arc length as described above. The best improvement a welder will see in his welds is when he learns to control the arc length. It doesn't matter what process is used, arc length is very important. Ever wonder why a machine weld looks so great? It's because of the precise controll of the arc length and electrode speed! On x-rays I've see small slag incusions though out the entire weld shown as small specks on the x-ray. These are usually electrode slag deposits not cleaned off during a multipass weldment but also can be scale and other impurities not cleaned off the base metal before welding. There is a myth that a welder does not have to remove all slag between passes on certian electrodes. This is not true and is what causes all the specks that I see in x-rays. If a welder hurries between electrode changes, he can sometimes restart a rod without chipping the slag without worry of slag and porosity inclusions but this no gaurantee there will not be any slag or porosity inclusions. Another good pratice is to start a bead in a different spot on each pass as this will help elimante any inclusions following though each pass. Depending on the size and spacing of the inclusion, some inclusions are acceptable as sound welds and will certify. Ovehead weldments have a greater tendency to have both slag and porosity inclusions. As an AWS inspector I have seen alot of this and started watching welders during certification tests and found that is from the welder trying to hurry too much as his mindset is the puddle is going to fall if he goes too slow. A overhead weld should be made just like a flat weld with a very slight increase in electrode speed. Vertical up welds are best made with good consentration on the molten puddle. This can best be observed welding in the flat position. The weld puddle will be very shinny and will have some swriling action within the molten puddle. The slag looks dull and lumpy will roll to the back of the weld puddle as the puddle moves forward. As the weld puddle forward speed slows the slag will recombine with molten puddle causing the puddle to splatter and gather inclusions and encase the electrode tip causing the electrode to stick to the base metal. The weld puddle width should be about 2 times the electrode diameter. AWS code calls the maxmium weave bead width of 8 times the electrode diameter in any position as any more width than this will cause slag inclusions because the slag cools too much before the electrode returns to deposit more weld.
The best way that I've taught people to weld is have them try what too many amps does, turn down the amps, move too fast, too slow, too long of arc length, too short of arc length, with stopping inbetween each change to see what the weld looks like. This way the welder learns what each wrong effect has. Then when they make a weld that looks wrong, they will know what caused it and how too correct it. A interesting note, a long arc length with have more uncontrolable heat than a short arc! Back to verical up welding. Now that you've studied weld puddle control, pay close attention to the molten puddle shape and size. There's going to be slag running around the out side edges of the molten puddle but don't pay attention to it as it will go where it goes and the slag distracts your consentration away from the molten puddle. Don't bother to look where your going as that will come with time as you have to look above the electrode to see where your going and at the same time consentrate on the molten puddle. A weld puddle of 1-1/2 times electrode diameter is much easier to consentrate on when first learning vertical up welding. Veritcal down welding should be avoided if possible. AWS code does allow a maxmium 2" of vertical down weld on most electrodes. There is a high risk of slag and porosity inclusions while vertical down welding. The slang "gap rod" will not certifiy under any circumstance. Too wide of a root opening will cause slag inclusions and porosity within root pass of the weld. The proper root opening is 2/3 of electrode diameter with a land thickness 1/4 of electrode diameter. (Land): the flat area between the back of the base metal extending just to where the bevel starts.
(Porosity): Porosity is the formation tiny pinholes generated by atomspheric contamination or gas entrapment during solidification.
(Root Opening): The gap between the base metals to be welded.
(Root Weld): The first weld bead of a weldment.
6010 and 6011 have very different penetration characteristics with 6010 having the best penetration of any stick electrode. All carbon base metals will weld very simular wheather old or new depending on how they are prepared. Alot of welders forget steel on equipment will work harden from viberation thus changing to a tighter grain structure or take on stress. You have to relieve this stress before welding or the weld will soon crack or brake away from the base metal. The easiest way to remove the stress is to heat the base metal to approx 1100F (dull red) and let it cool before welding. This will allow the grain sturcture to return to near normal before welding. As I've stated before Lincoln 6010 is the finest 6010 I've ever used.
Welding galvanized is an art all to it's own. Technique has every thing to do with making a sound weld. As I stated previously 6010 ran DCEN (straight polarity) is a great electrode for welding glavanized. I have ran hundreds of certification tests over the past 35yrs with 6010 and yet to have a test fail because of the electrode. However, I have seen alot welds fail due to welder error. T_Bone
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