Novice welders often wonder if they really need both AC and DC.
They’re confused when they look at the different combinations on the buzz box stick welding machine.
The simple answer is no, you really don’t need AC and DC.
The basic AC machine can produce a good weld if it’s used right. It reliably buzzes away, alternating between positive and negative at a rate of 120 times per second, thus the 60-cycle noise and the buzz box nickname.
Cost is the drawback to straight AC. While it may be the least expensive welding machine to buy, the flip side is that it gobbles up electricity like it’s going out of style. Simply put, AC welding is not efficient.
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The electrical bill isn’t a big factor if you weld only occasionally. How-ever, if you’re welding a couple times a week, your meter readings will really show it with a straight AC machine.
The big step up is the combination AC/DC machine. DC not only makes better use of electricity, but it also provides a much smoother arc, which generally means a better weld.
The AC/DC machine has a rectifier that converts alternating current to direct current, so the current flows in only one direction instead of back and forth. You can still run it as an AC buzz box if you like the sound, but after you’ve tried DC you’ll stay with it. It produces fewer spatters, which means less grinding and trimming. Generally, it’s more welder friendly.
Once you’ve determined you can have the current flowing constantly in one direction, you then have to decide which direction you want. The polarity is up to you.
The important thing to know about current flow is that it changes the ratio of heat in the rod to heat in the base metal. Depending on what you’re welding, sometimes you want the rod hotter and sometimes you want the base material hotter.
In the Direct Current Electrode Positive (DCEP) mode, the stinger is hooked to the positive terminal, which is why it’s also called reverse polarity. When you’re in positive polarity, 70 percent of the amperage flows through the electrode.
That means 70 percent of the heat is in the electrode and 30 percent is in the base material, so you get more penetration.
This is good for “zero gap” weld joints, such as a lap joint, tee joint or a tight butt joint. Just remember that the electrode holder is plugged into the positive terminal and the ground is plugged in the negative terminal.
In the Direct Current Electrode Negative (DCEN) mode, also called straight polarity, 70 percent of the amperage is in the base material and 30 percent is in the stinger.
This means 70 percent of the heat is in the base material and only 30 percent is in the electrode, resulting in less penetration.
This is good for “open root” or if you have a weld joint that has a gap because you will have a little more control of the puddle. Again, remember that the electrode holder will be plugged into the negative terminal and the ground is plugged into the positive terminal.
What about all those numbers on the electrode? They can cause confusion.
The code format is standardized for all rods. Most of it is easy to understand, but some of it needs to be looked up in the book. The legend on a basic E-7018 rod tells us three things.
The first two digits tell us tensile strength, so the 70 in our example means 70,000 pound tensile strength. E-6010 means the electrode has a tensile strength of 60,000 lb., while 10018 has a tensile strength of 100,000 lb., which is an electrode generally used on bridges and large steel structures.
The third digit tells us what welding positions the rod is certified for: flat, horizontal, vertical and overhead.
Number 1 means this electrode is certified for all welding positions. Number 2 tells us the electrode is certified only up to the horizontal position.
Most people don’t even try to memorize the data on the fourth digit, which designates the flux composition, of which there are many. It’s best to just look this up in the book if you’re not sure.
If you keep some 6010 electrodes and some 7018 electrodes, both with 3/32 inch and 1/8 inch diameter, there won’t be much you can’t repair or fabricate.
A future column will explore whether TIG welding is all it’s cracked up to be.
As an aside, Winnipeg Technical College welding students placed gold and bronze in the Skills Manitoba competition this spring. Bronze went to Scott Klassen of Altona, Man., while the gold winner was Merlin Clark, who will compete in the national competition to be held May 19 in Charlottetown. Competition will be hot because Quebec seems to win every year.
Jason Feal is a certified Red Seal journeyman welder with experience in iron working, boiler making and millwrighting. He teaches welding at Winnipeg Technical College. He can be reached at jasfea@wtc.mb.ca.
