SMAW Basics—How much do you know?

WWW.THEFABRICATOR.COM MAY 2003

May 15, 2003

By:

Image

Editor's Note: This article covers basic SMAW questions and answers. Preceding the SMAW section is the author's opinion about the importance of retaining federal funding for vocational programs. If you would like to express an opinion about this topic, please feel free to do so.

What Are They Thinking?

As I write this article, the rumors are flying from one end of the country to the other. I have heard President Bush has considered cutting federal funding for vocational programs (the Perkins Act). Many schools rely on grants to subsidize their welding programs. I also have heard that President Bush has denied saying he wants to cut these programs. I hope that is true.

Some in the political world feel that our students should be in computer labs rather than in vocational shops. I also believe students need to become computer-literate, but not at the expense of vocational education. Many school districts have shut down vocational programs to put in computer labs. Some of my peers in these districts have told me that this has been a regrettable action because the dropout rate increased almost immediately.

My professional opinion is that cutting vocational programs is a bunch of bunk, as we say in Texas. Shut down vocational education and watch the dropout rate and skilled labor shortage rise! Recently a shipyard had to go to Ireland and India in search of welders. A decrease in craftsmen and -women in all of the construction trades is projected. Who the heck will build the buildings, planes, trains, and automobiles?

Welding is part of our lives from the time we get up until we go to bed at night. Welded pipes bring us water to brush our teeth and remove our sewage. Our houses and apartments are full of welded appliances. Our cars, trucks, and other transportation vehicles are welded. Our roads go over welded bridges, and the traffic lights are fabricated and welded. The buildings we work in, defense hardware, automobiles, and the list goes on and on.

So here's a great idea some genius came up with: Don't train any more welders. This idea gives the word lamebrain new meaning.

More than just a craft is learned in our vocational classes. Work ethics are developed, and social skills are learned. I've taught several female students in the past few years, and it's been great to see them enter a male-dominated trade and find out they can do really well. (I've written before about the women who built the planes, tanks, and ships that kept our country going during World War II.) It's been fantastic the way the men have accepted the women and treated them with respect. Students learn to work cooperatively and develop friendships, while getting a basic idea of some of the different jobs available out there.

Now some might accuse me of being biased (and I am) because of the fact that if vocational programs are cut, so is my job. Yep, that idea doesn't exactly excite me, but I dang sure ain't worried about it either. I've been in dire straits before, but if God's willing and the creek don't rise, I'll be working somewhere else in the field in a flash.

Our vocational classes, what's left of them, prepare students for a productive life even if they never go into that specific craft. I know it because I've seen it, and if we shut 'em down, we are screwing up!

SMAW Basics – The Questions

Now that I've gotten that off of my chest I thought I'd cover a few basic questions about shielded metal arc welding (SMAW or stick welding).

Give the best short answer for the following:

  1. In what direction does current flow in DC electricity?
  2. In what direction does current flow in AC electricity?
  3. What do DCEP and DCEN stand for?
  4. What are the three major weld defects in SMAW?
  5. Why shouldn't you weld with exposed skin?
  6. How can you tell if an unfamiliar machine is set right when welding?
  7. What is the difference between the ground and the work clamp?
  8. You should always relax your hand and do what else when welding?
  9. What is spatter?
  10. List three reasons you should never cut or weld on a used container.

SMAW Basics – The Answers

1. In direct current, electricity always flows from negative to positive. Just like when you turn on your garden hose and the water begins to flow, when you weld with DC, the current flows out of the negative and back into the positive. This makes for a smooth welding current.

2. In alternating current, the electricity flows back and forth from negative to positive and positive to negative on a sine wave. This makes an erratic flow for SMAW, producing more spatter and a more unstable current. I used AC for welding 6011 for a couple of years. The welds were OK, but give me DC anytime.

3. Direct current electrode positive (DCEP) is what we used to call reverse polarity. Direct current electrode negative (DCEN) is what we used to call straight polarity. I suspect the same person who changed the word library to the learning resource center got a hold of these terms.

In DCEP the electricity flows into the tip of the welding rod and concentrates about two-thirds of the heat, which gives good penetration. DCEP is usually used on thicker steels.

In DCEN the electricity flows out of the rod, concentrating about one-third of the heat on the rod. Less penetration makes this a very good choice for thinner steels.

Right about now, some of you are hauling to your e-mail to tell me that I'm wrong about the penetration. Some journals say that DCEN gives better penetration. I had to look through three different journals before I found one that agreed with me. All agree that DCEP has the best weld characteristics. It also has cleaning action that DCEN doesn't have.

Its called welding theory, and my theory is that I've used DCEP on every dang thing from high-rises, nuclear weapons facilities, dams, and a dam power house! Not once did I ever use DCEN. Like the journal that supports my theory, I say that the better weld characteristics and the two-thirds heat at the end of the rod create a force and "there is a jet action and / or expansion of gases in the arc at the electrode tip. This expansion causes the molten metal to be propelled with great speed across the arc. The molten metal impacts the base metal with greater force. This heavy impact on the base metal helps to produce deep, penetrating welds." Modern Welding 1997 Althouse, Turnquist, Bowditch, and Bowditch." Now that is exactly how I would've put it ... well, more or less.

The Hobart School of Welding's Welding Guide also supports my theory: "Electrode negative (straight polarity) often is used when shallower penetration is required. Electrode positive (reverse polarity) generally is used when deep penetration is needed."

We also conducted an experiment by dragging a 1/8-in. rod on an 11-gauge shim. DCEP burned through after one and one-half inches. DCEN did not burn through until about three and a half inches. Now that I have backed up my theory with this highly scientific experiment, I am even more convinced!

I have no problem accepting that DCEN penetrates better in gas tungsten arc welding (GTAW). That's a whole different ball game because of the tungsten electrode. You can't apply much heat on the smaller diameter tungsten rods with DCEP because it melts away the tungsten. You can output more heat with DCEN, allowing for more penetration.

On some machines, a switch is available for changing from AC to DCEP or DCEN; on others, the leads have to be changed.

4. Porosity, slag inclusion, and undercut, the cardinal sin of welding, are defects because they weaken the welded joint and can cause it to fail.

Porosity is wormholes in the weld. It may be caused by moisture in the flux, which is turned into tiny steam explosions, or even minute traces of gas left in the steel when it was formed.

Slag inclusion occurs when the slag is not chipped and cleaned properly and then welded over. A good welder will burn through any exposed slag, but sometimes the slag can be skipped over, leaving it trapped under the bead.

Undercut is the cardinal sin because it occurs when the base metal is penetrated, or cut into, without leaving any filler metal. This usually happens when welders use the wrong rod angle, go too fast, or use amps that are too hot.

5. Welding puts out radiation through ultraviolet light rays. It's like having a little sun at the end of your rod. These rays can sunburn your skin, and eyes and even blister your corneas. Continually welding with your skin exposed can lead to skin cancer, one of the fastest-growing cancers in our country. When the skin is damaged over and over, it is possible for one of the healing cells to be a bad one. Once it starts multiplying, cancer may be present.

Often welders don't want to wear heavy hot leathers or long sleeves on hot days. Do it anyway! Melanoma can be deadly, and even if it isn't, you still might have to have lesions cut out of your skin.

6. I usually don't pay attention to the numbers on the machine. I have eight machines of the same brand in my shop, and all eight of them run a bit differently. I usually set the dial about halfway and then work from there. Run the machine until you get a fluid, steady puddle, and then fine-tune the control.

7. In the field we always called the work clamp the ground, but the ground actually is what gives the electricity an escape route to the ground from the machine if something malfunctions. The work clamp is the part of the circuit that clamps to the piece being welded to complete the circuit.

8. As I've said before and will say a million times again, relax your hand, and watch the puddle. I can still hear Phil Newell yelling in my ear as he stood behind me holding my hands while teaching me to weld. I sure as heck couldn't relax then, but he dang sure got his point across! You have to relax your hand to get good manipulation of the weld puddle. Even the slightest movement will affect it. If you are tense, your movements will be jerky, and the weld pool will be erratic.

You must always watch the puddle to make sure you are feathering into the steel evenly and uniformly. You should see the puddle wash into the steel, thus preventing undercut. After awhile, you should even be able to feel that very subtle give into the steel as the rod fuses into the base metal.

It's OK to take your eyes off the puddle to see where you are as long as you quickly return to watching it. Sometimes you can even lift your rod slightly and lighten up the area around the puddle to see where you're going.

Along with relaxing your hand and watching the puddle, monitor the rod angle, travel speed, and temperature.

9. What is spatter? Spatter is the little molten droplets that stick to the steel around your weld. With 7018 you won't get nearly as much spatter as with 6010 or 6011. If the spatter chips off easily, all is OK. If it doesn't chip off, you're welding too hot.

10. Why do I throw this in? Because every year I hear about a welder who got hurt or killed from welding on a used container. I never weld on used containers, and I never will. You can get burned (flammable), blown up (explosive), or asphyxiated (toxicity) welding on the wrong container. Welding used containers causes many, many accidents. Make it a rule to stay away from them. It doesn't cost that much more to use new steel.

How Do You Score?

All correct—you are in the zone! Ask for a raise.
7 – 9 correct—not bad, you pretty much know your stuff.
4 – 6 correct—study up!
Less than 4 correct—become a carpenter. (Just kidding, keep trying!)


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

More in Arc Welding from TheFabricator.com

Published In...

www.thefabricator.com

Read more from this issue

comments powered by Disqus