From Wikibooks, open books for an open world
Jump to navigation Jump to search

SMAW[edit | edit source]

Introductory arc welding[edit | edit source]

Shielded Metal Arc Welding is often the first welding technique that a welder learns. A machine supplies a negative electrical circuit to the work-piece via a clip and a welding rod is attached to the positive end of the circuit. When the rod is brought close to the work-piece the current connects creating sparks and heat which melts the metal and the rod together. It requires a very steady hand and patience. It is possibly the oldest electrical welding technique still in use. Pre-electrical techniques included 'soldering', 'forging' and 'oxy-acetylene (flammable gas) welding'. It is difficult at first to weld solid bonds without creating bubbles and SMAW is important for this skill as it is easier to feel what the weld is doing (welding is only possible when the eyes are protected by darkened glass so feeling is important). SMAW is preferred in high-strength structure welding, such as construction or pipeline. It generally takes more time and patience to stick weld than it does to MIG or gas weld. SMAW should be the method spent the most time on learning for a beginner welder. Welding practice should begin with an 'E6013' 3mm rod. This is a simple rod to manipulate, and has a medium heat range, with a medium penetration. Amperage for this rod should be set in AC current, working around 85-95 amps. This is an all position rod, suitable for many general applications.

To practice as a beginner, start with a 1/4 inch thickness metal plate around 1ft x 1ft. Do not forget to wear gloves and welders eye protection. If you are right handed start on your left, working to the right, and vis-versa for left handed (MIG welding goes the opposite direction). Try to weld straight lines across your one foot metal plate until it is covered in stripes. Chip off the black residue (slag) with a Chipping Hammer each time you pause and use a wire brush for any smaller pieces of residue. If you allow the plate to cool down (try keeping a container of water nearby to dip your hot work-piece in), you can use both sides of the same plate repeatedly until you are comfortable and steady with the rod. You should learn to hold the tip of the rod around 2mm or less from the work piece and at a 45 degree angle. It is also nessecary to change rods in the middle of a weld without affecting its quality but this should become easy when you get your pace and angle comfortably. The rod will stick to the work-piece a lot at first. You will soon find that arc welding is like blowing hot liquid from a straw in the dark (sounds complicated but is really a matter of a steady hand). You need to learn to make straight, smooth lines (beads).

When you are convinced that your welds are smooth and can maintain the tip of the rod at 2mm from the work-piece, move on to joints. The basic welding joints are T-joints (in the shape of a T, also known as fillet-joints) and lap-joints (overlapping edges, one resting on top of the other). To practice, use metal strips, 1/4 inch thickness, 2 inches wide and 8 - 12 inches long. Place two metal strips together in a T shape or overlapping and 'spot' weld at each end to keep them in place. Now weld from one side of the joint to the other in a careful, small circle motion of the rod, with an angle of 45-65 degrees (in both the up-down direction and left-right direction) keeping a distance of 1-2mm between the rod and the work-piece. It is important to hold the tip of the rod so close to the joint as a good weld will melt and fuse the edges of the original work-piece. The finished weld should look almost smooth and the slag should break off effortlessly (will take at least a few hours practice for most people). The most important part of the weld is inside. Break your finished welds open with a heavy hammer and a vice. Be careful! A good weld is not easy to open and fingers are easily removed against a piece of steel! Try weakening the spot welds with a hacksaw on difficult pieces. A good weld will have decently fused the original edges together. The bead should not cut a groove into the face of the work-piece or leave bubbles and gaps in the weld (the bond should be complete inside leaving no visible straight edge under the weld). This is the requirement to pass a welding examination. Note that a welded piece will lean toward the joint as it cools. Although enough heat is required to fuse the work pieces together, too much heat will make the whole piece red hot, worsening the distortion when it cools so practice is important.

Slightly more difficult to weld correctly without warping is the end-to-end-joint (two pieces beside each other end to end or side by side). This is only slightly more difficult than the previous joints. Practice on two 1/4 inch strips as before but this time take the edges off the strips with a file or rasp so that you are welding into a V-shape. Place together at the edges and weld along the gap. The weld should be done in a careful, small circle motion of the rod, at a slightly more raised angle than before around 60-80 degrees. The finished weld should look like a "stack of dimes" or evenly spaced ripples in the weld. The sides of the weld should be evenly flushed with the base plate raising to a bump in the middle. If the weld looks "stretched", the travel speed should be slower and the tip closer. There will be significant 'slag' and 'spatter' on the sides of the weld, and will be just generally ugly looking. If the build up of the finished weld is higher than about an sixth of an inch, the travel speed was likely too slow. Slightly more difficult again is the corner-joint (end to end in a V or L shape). Do not remove the edges of a corner joint. Instead, weld the inside first which will leave a small "V" shape on the outside for the final weld. The requirements for these welds are the same, properly fused without any bubbles or gaps.

Once these welds have been mastered, play around with welding a plate in a vertical position. Weld vertical beads going up, not down. This is significantly more difficult than a flat position, and can be frustrating to learn, but patience is important. Use a counter-clockwise circle motion, spiralling upwards, pausing at the top of each motion. It may feel more comfortable to pause at the bottom of this motion, but this will cause bad 'undercut', where the sides are not filled in with weld material.

Once this has been mastered, one may choose to continue in SMAW, or move into oxy-fuel welding for a time.

  • Remember that most arc welds shouldn't be cooled in water or cooling oil, but by allowing air access around the whole joint. Cooling, in most cases, changes the way the metal atoms retract and can weaken the weld.

6010 and 6011 Rods[edit | edit source]

E6010 Rods are the most preferred rod for deep 'root' passes, or where a lot of penetration is required. Often, this root pass is covered with two hot passes and a cap or 'face' pass with E7018 rods. This rod has been said to be one of the hardest rods to use, due to the constant attention to rod manipulation, travel speed, and 'arc length'. E6010 is a 'fast-freeze' rod, meaning it is suitable for use in all positions. It is best used with the positive polarity on the rod, or 'reverse polarity', (DC+) with amperage from 75 to 95 being the best (depending on the application). Practice using this rod by cutting (or buying) two 1/4 inch plates with about a 35.5 degree bevel on either side. The bottom of the bevel should be a sharp edge, which will be ground down to about a 3/16 of an inch lands, with either a 3/16 inch gap or 3/32, which ever is more comfortable. Start by simply running a bead down a plain 1/4 inch scrap plate to get the feel of the rod. The flux is cellulose, and is ugly looking at the end; use a wire brush and chipping hammer to clean off. Once comfortable manipulating a straight bead, place the two beveled plates together with the lands facing each other. Make sure that they are perfectly even, as this will cause less grief for the root pass. Use 80 or 85 amps to run the root pass, and start with tacking the two plates together. Weld the root with a 'backhand' motion, (pushing the rod from the base of the weld to the top). Once the root is finished, flip the plate over and wire brush off the bottom; the weld should have fallen through the gap and sealed along both sides evenly if done correctly. If this looks shallow or pitted, turn the amperage up by 5 (but to no more than 90 amps,) and try again, pitching the rod into a sharp 85 to 90 degree angle to the plates. While welding, try to 'dig' the rod into the sides of the bevel, pausing on the sides. If done right, a loud crackling-hissing noise will be heard. This is simply the 'wind' as the weld falls through the bottom of the root. Remember to keep a short arc length with this rod, no longer than the thickness of the rod itself. Otherwise, the weld will be weak, insufficient and contain excessive spatter. Also, consistently weave the rod back and forth, pausing slightly off center, both sides. Once cleaned off, the root pass should be shiny and smooth on the face side, and evenly deep on the bottom. Continue to practice the root weld until it comes naturally and comfortably, as this is a main strength of the whole weld.
Next, a weld will be placed over top the root; a 'hot pass'. Turn the amperage up to 90 or 95 amps (+10% comparing to the root amperage). Weld over top of the root, digging into the sides of the bevel by weaving and pausing on each side momentarily. Minor undercut is normal in this case, and will be filled in by a second hot pass.
The second hot pass should be conducted the same as the first, but the welder may choose to turn the heat down by 5 amps, depending on the joint to be produced. After this, finish with a 'cap' or 'face weld', which must have no undercut on either side. This pass should be done around 85 amps. Use a weaving motion, something like upside down "U's", pausing on either side to allow filler metal to fill in any undercutting. The 6011 rod is essentially the same as a 6010, but is used in AC instead.

6010 and 7018[edit | edit source]

The next thing to practice is a 6010 root pass, with 7018 hot and face passes. This is a common method used often in pipeline and boiler welding. The 6010 will dig into the root pass and cause it to have a higher tensile strength. The 7018 will add more strength to the top than would a 6010 alone. It also has a lesser chance of undercutting the side, which would cause a weaker weld. For the most part, a 7018 rod is easy to manipulate, and deposits nicely. Use DC reverse (DC+) polarity around 105 to 115 amps. The flux on this rod is strange in how it reacts to moisture and humidity. A 'rod oven' is essential if these rods are going to be used in large quantities. The flux must be thoroughly dried out to be used properly, otherwise it will not protect well enough and the weld may look sloppy and weak. If only being used for a personal project, find an old baking sheet, turn up the kitchen oven to around 350 degrees, and bake the required amount of rods for about fifteen minutes. This is far cheaper than a rod oven. To practice with this rod, simply run several beads in the flat, vertical and horizontal position. If control of the 6010 rod has been achieved already, this will not be a big problem. Remember to make small cursive 's' motions on the horizontal weld, pausing at the top, and continuing through quickly on the lower area. Vertical welds should be done in a sort of 'z' motion, pausing on either side, and going quickly over the middle, zigzagging upwards. Once this has been accomplished, practice some more on the 1/4 inch plates in all these positions, welding the root with the 6010. Don't forget to grind lands into the beveled sides (about 3/16 of an inch). Once the root has been cleaned and satisfactory, use the 7018 at 105 amps DC-. For the third pass, turn it up to 115 amps DC-, and finally, for the cap weld use 105 amps again. Remember to clean between each pass, otherwise strength will be decreased. Cool slowly by leaning it somewhere that is not affected by a draft, but where room temperature is stable. Make sure that air has access to the whole plate. You can test these bevel welds by cutting each one down the middle, crossing the weld path. Grind each edge smooth, and the welds should be ground flush to the rest of the plate; both root and face sides. Place in a 50 or 25 ton press, pressing slowly into 'U' shapes. To test the root pass, place the face weld upwards. To test the face weld, simply face the root weld upwards. If there is more than a quarter inch of cracking anywhere on either weld, the weld should be retried.

From here on, any other type of rod can be tried by 'playing around', although if you are unsure, check the rod number on the internet to find the correct voltage and any other applicable setting. This includes travel speed and angle. The next thing to move onto would be MIG welding, but if at all possible (assuming the equipment is available) one should at least understand how to use oxy-fuel welding and cutting methods.