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Oct 17 2012, 10:21 PM EDT (current) brandon_a_boyer 995 words deleted, 4 photos deleted
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Shielded Metal Arc Welding (S.M.A.W)Let me begin by clarifying. Anyone who refers to this as "stick welding" needs to be slapped. It's Shielded Metal Arc Welding, hopefully that's not a difficult concept. S.M.A.W is an arc welding process that utilizes a consumable metal electrode which is coated in a layer of protective flux. The flux supplies shielding gas, a protective layer of "slag" and adds alloying elements to the weld metal. First a little history: Shielded Metal Arc Welding (which I am shamefully copying and pasting from wikipedia as most of you won't read this part anyway.)After the discovery of the electric arc in 1800 by Humphry Davy there was little development in electrical welding until Nikolay Benardos developed carbon arc welding, obtaining patents in the 1880s showing a rudimentary electrode holder. In 1888 consumable metal electrode was invented by Nikolay Slavyanov. Later in 1890 C. L. Coffin received U.S. Patent 428,459 for his arc welding method that utilized a metal electrode. The process, like SMAW, deposited melted electrode metal into the weld as filler.[2] Around 1900 A. P. Strohmenger and Oscar Kjellberg released the first coated electrodes. Strohmenger used Clay and lime coating to stabilize the arc, while Kjellberg dipped iron wire into mixtures of carbonates and silicates to coat the electrode.[3] In 1912 Strohmenger released a heavily coated electrode but high cost and complex production methods prevented these early electrodes from gaining popularity. In 1927 the development of an extrusion process reduced the cost of coating electrodes while allowing manufacturers to produce more complex coating mixtures designed for specific applications. In the 1950s manufacturers introduced iron powder into the flux coating, making it possible to increase the welding speed.[4]*Interesting fact for you war buffs out there. It was only due to the advent of Shielded Metal Arc Welding that the British where able to continue to manufacture bombs and torpedoes for the war..Power Sources: Shield Metal Arc Welding power sources operate on a constant current, meaning that you set the machine to a given amperage, and the machine will adjust it's output voltage to stay as close to that current setting as possible. There are three types of current that a SMAW power source can operate on, which current is used depends entirely on the type of electrode being used. Generally speaking DCEP and AC are the most often used, however DCEN can and is used for several electrodes.Electrodes: Electrodes are an important factor in the SMAW process as they control not only the metallurgy of the final weld, but the ease at which it is welded. This is controlled entirely by the flux covering of the electrode.The AWS uses a simple designation system for Carbon steel/low alloy electrodesEXXXX*E - ElectrodeXX - The tensile strength, in KSI of the weld metal (60 = 60,000 lb/in^2 tensile)X - suitable positions, 1 for all positions, 2 for flat and horizontal only.x - covering type - controls how the electrode behaves while welding.* additonal markings can come after these for more advanced electrodes, for the sake of space, we'll avoid them.The three most commonly used electrodes areEXX10 , EXX11, and EXX18The Exx10 and the EXX11 series have virtually the same operating charectoristics, they both have a crisp, penatrating arc that will eat through any level of rust or paint, the only difference is the type of current you use. EXX10 can only be used on DCEP, EXX11 can be used both with AC or DCEP.EXX18 is a special one. As welders we call it the idiot stick because it's user friendly while welding. This electrode operates on DCEP or AC (DCEP preferred) and produces a thick, smooth arc that flows easily. The primary downfall to this electrode is that it is classified as a low-hydrogen electrode. These electrodes come in hermetically sealed containers, once the container is opened you have nine hours to use the electrode at full strength, after you have to put the electrode in a rod oven at 300 degrees for 3 hours to bake out the moisture.Sound complicated? provided you aren't welding bridges or something really heavy and really critical, you'll be ok to use them after nine hours provided they haven't been immersed in water or anything like that.Current settings ChartWelding techniques on steel plate:Starting the arc: the most popular method for new welders to start the arc is the scratch start method, basically you are going to scratch the steel with the electrode like a match, if the electrode sticks, remove it from the electrode holder and snap it off. Once the arc is created, move the electrode to about 1/4" away from the steel with the tip leaning away from the direction travel, making sure that the electrode is at an equal angle to both plates being welded.Continue moving in the direction of travel, maintain your angles and travel speed, consistency is key here, keep your electrode 1/4 away from the plate as you go, when the electrode is close to being used up, give your wrist a flick in the direction of travel and pull the electrode away. Use a slag hammer or other pick to remove the slag from the area that you finished, then replace the electrode and start again.When finished, chip all of the slag away using the hammer or pick and brush the weld clean with a wire brush.Key points - Weld in either the flat or horizontal positions whenever possible- Avoid weaving whenever possible. If you aren't sure what you are doing weaving can result in slag inclusions, if you must a very small, side to side weave is ok, just make sure you maintain a consistent travel speed.- Clean the metal as best you can prior to welding.- don't be afraid to perform multiple passes, just make sure you clean very well in between passes.