SMAW revisited—You can never know too much

WWW.THEFABRICATOR.COM AUGUST 2002

August 8, 2002

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No matter how much you know about SMAW or any other type of welding, you always can learn more.

Even with all the new welding technologies, shielded metal arc welding (SMAW) still reigns as the most widely used welding process in the country.

In the field, SMAW usually goes by the name of stick welding. My very nonmechanical brother once asked if I was doing SMAW when I used a "sparkler and jumper cables" to weld. That actually is a pretty good analogy for the way stick welding looks to the nonwelder.

First Impressions

One of the first times I observed welding was when I was about 9 years old. I was traveling with my parents to the mountains in Taos, N.M. Ironworkers were constructing a bridge over the Rio Grande Gorge. It is one of the most beautiful bridges in the country. Below is the Rio Grande rushing by. On one side you feel as if you can touch the mountains, and on the other beautiful plains stretch to the horizon.

I heard my mother gasp to her friend, "There are men working out in the middle of the bridge!" I looked out and saw a welder's sparks falling into the abyss below as he stood on a beam 600 feet above the river. Another man was carrying steel out to a perimeter wall. Below was only a black net, which hung underneath the bridge to catch workers in case they "went in the hole."

I can remember that scene as if it were yesterday. I don't know if that in some way influenced my decision to become an ironworker, but I do know that the impression that someone was doing a job that required a lot of skill and daring stayed with me.

Yesterday and Today

They were using stick welding back then, and I am teaching that same welding 40 years later. Although welding technologies have changed, the basics have stayed the same: RELAX YOUR HAND and KEEP YOUR EYE ON THE PUDDLE!

Along with those two basics go:

  1. Work at the correct travel speed.
  2. Use the correct rod angle.
  3. Select the correct temperature.
  4. Choose the proper electrode for the job.
  5. Follow specifications.

In stick welding you use a power source, welding cables, electrode holder (stinger), work clamp (often referred to incorrectly as a ground clamp), and an electrode (or rod, which makes it look like you are welding with a stick).

For years welders, including myself, referred to the work clamp as the ground clamp. However, the actual ground is the wire that grounds the power source in case of an overload or malfunction.

The ground wire allows the electricity to flow to the ground instead of you. Mr. Electricity is always trying to flow back to the ground, and he will gladly use you as the conduit. Humans are made up mostly of water, which conducts electricity quite well. I've seen electricity blast out of the soles of one poor guy's feet; another guy was lucky to live after electricity blasted out of his pelvis!

As risky as welding may sound from those stories, you don't need to worry about getting shocked as long as you take precautions, educate yourself, and use the proper equipment.

Precautions to Take

Chances are you have been shocked already if you've welded for any length of time.

Take a Hint. I never weld without a good pair of dry gloves and try never to put myself in the position of being an electrical conductor. On the job my rule of thumb is the "Three Shock" rule on a drizzly or rainy day. I figure the first shock tells me to be more careful. The second shock tells me it is getting too wet to be welding outside. By the third shock, I'm already two steps toward my pickup and on my way home—Mama didn't raise no fool.

Know Your Polarity. Every welder should know what polarity is and what kind of polarity to use with different thicknesses of steel.

Polarity is the direction current flows. Direct current (DC) electricity always flows from negative to positive. Alternating current (AC) electricity flows back and forth between positive and negative on a sine wave.

AC/DC. DC is used on most construction sites and in most shops because it allows for a smoother and more stable arc. However, I have used a 7018 electrode in a shop with an AC machine because it was cheaper and the welds all were in the flat position.

Working with DC compared to AC is like switching your radio from a Vivaldi to Ozzy Osbourne. AC is louder, sounds more crackly, and sprays out more spatter. An AC arc is way more erratic than DC. Although you can purchase a cheap AC machine at many hardware stores, I would advise putting the extra hundred bucks down to add the DC option.

One advantage of AC is that it doesn't produce arc blow. This is a term for the arc wandering and going everywhere but where the heck you want it to go—usually when you're welding in corners. Arc blow happens only with DC and has something to do with the magnetic field produced during welding. Arc blow still is not totally understood but usually can be corrected by moving the work clamp.

In DC electricity the polarities either are reverse (DC electrode positive [DCEP]) or straight (DC electrode negative [DCEN]). On most structural jobs reverse polarity/DCEP is used. Most steel used in fabrication shops and construction sites is thick, and DCEP provides more penetration into the steel: Two-thirds of the heat is concentrated at the tip of the electrode, because the electricity flows from the machine's negative terminal into the work and then into the electrode and back to the positive terminal.

Straight polarity/DCEN is best for welding on thin material. In this case the electrode is hooked up to the negative terminal. With the electricity flowing out of the welding rod, through the work, and back to the positive terminal, about only one-third of the heat is put out, which prevents you from blowing through the thin stuff.

If you are a beginner and I have thoroughly confused you, don't worry. Polarity is kind of like riding a bike—once you learn it, it comes naturally.

Background on the Process

Volts, Amps, and Circuits. When you stick weld, you are using an electrical circuit to produce heat to melt the base metal and electrode. The heat is produced by generating an arc from your covered metal electrode to the base metal. As enough heat is produced to melt the base metal, small droplets of filler metal are deposited into the molten pool joining the metal.

The power source provides the electrical voltage and amps. The voltage causes the electricity to flow; the amps are the heat produced. With DC, this process is somewhat akin to turning on your garden hose and letting the water flow.

There is an open circuit and a closed circuit. An open circuit occurs when the electricity has no path to flow through. For example, when your bedroom light is switched off, the electricity is there just waiting for you to provide it with a path to travel. When you flip the switch, you complete the circuit and allow the electricity to flow freely, thus making a closed circuit.

Now I know some of my old professors would suffer nervous breakdowns with my layman's explanation of electrical principals and such. But it my defense, I slept through most of their classes anyway.

Flux. Welding rods, or electrodes, are covered with flux. Different rods have different coatings that are weld-specific.

When SMAW was first being used, most welding could only be done in the flat position, because only bare metal rods were used. They stuck constantly and allowed impurities to get into the weld pool, which caused a lot of weld defects.

At some point someone noticed that rusted rods welded better than new ones. After experiments, it was determined that several chemicals—such as calcium and cellulose—produced a cleaning action and shielding gas. This gas surrounded the weld pool and kept impurities in the atmosphere, such as hydrogen and nitrogen, out of the weld pool—thus the term shieldedmetal arc welding.

Common Defects. After the flux cools, it turns into a protective coating called slag that forms over the weld. It is important to chip and brush the slag off of all welds. In welding, the old saying "cleanliness is next to godliness" is applicable. A common weld defect is slag inclusions, which occur when pieces of slag that are not cleaned off are welded over and become trapped in the weld pool, making the final weld susceptible to cracks.

Two other main defects in welding are undercut and porosity.

In an undercut the arc cuts out the steel but no filler metal is deposited, leaving a weak point that is susceptible to cracks and breaks. Porosity occurs when gas pockets form in the weld pool, leaving small holes. These defects leave the weld weak and subject to failure—failed welds can cause property damage, injury, and even death.

I have covered just the tip of the SMAW iceberg. Many books provide excellent references to different welding technologies. Some of these books are way too technical for me; I use them as reference material. I prefer to read some of the more basic, welder-friendly materials out there.

When I need to find something quickly, I refer to one of the walking encyclopedias of welding knowledge, people such as Len Anderson (one of New York City's finest engineers) or AWS President Ernest Levert. One nice thing about welding is that so many people in high positions are willing to help you out, whether you are a beginner or an old journeyman. I can think of few professions, if any, in which the president of an organization as big as the American Welding Society would take time out to help someone just starting out.

The more we know about the basics, the better our skill will be at the advanced level.



High School Career Center in Texas

Marty Rice

Contributing Writer
High School Career Center in Texas
Marty Rice is a welding instructor at a high school career center in Texas. He is an honorary member of the Ironworkers Local 263.

 

Questions for the author can be e-mailed to vickib@thefabricator.com

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