7/27/2019 AC_DC Understanding Polarity
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9/29/13 AC/DC Understanding Polarity
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AC/DC: Understanding Polarity
Do you know w hat AC (Alternating Current) and DC (Direct
Current) signify on y our w elder and electrodes? Well, basically
these terms descr ibe the polarity of the electrical current that
is created by the welder and runs through the electrode. Selecting
the electrode w ith the correct polarity has a real effect on
thestrength and quality of y our w eld - so read on and make sure
you know the diff erence! For that extra assuranc e, try the tw o
tests at the end of the article to helpyou deter mine polarity.
The terms "straight" and "reverse" polarity are used around the
shop. They may also be expressed as "electrode-negative" and
"electrode-positive" polarity. Thelatter terms are more descriptive
and w ill be used throughout this article.
Polarity results f rom the fact that an electrical c ircuit has
a negative and a positive pole. Direct c urrent (DC) flow s in one
direction, res ulting in a constant polarity. Alternating current
(AC) flow s half the time in one direction and half the time in the
other, changing its polarity 120 times per second w ith 60-hertz
current.
A w elder should know the meaning of polarity, and recognize w
hat effec t it has on the w elding process. With few exceptions,
electrode-positive (rever sedpolarity) results in deeper
penetration. Electrode-negative (straight polarity) results in
faster melt-off of the electrode and, therefore, faster deposition
rate. Theeff ect of diff erent chemicals in the covering may change
this condition. The high cellulose cov ered mild-steel rod, suc h
as Fleetw eld 5P or Fleetweld 5P+, isrecommended for us e on
positive polarity for general w elding. Some types of shielded
electrodes func tion on either polarity, though some operate on
only onepolarity.
The use of the AC transf ormer-type w elder necessitated the
development of an electrode that w ould wor k on either polarity,
due to the constant-changing of thepolarity in the AC circuit.
Though AC itself has no polarity, w hen AC electrodes are used on
DC they usually operate best on one spec ific polarity. The
covering onthe electrode designates w hich polarity is best and all
manufacturer s spec ify on the electrode container w hat polarity
is recommended.
For proper penetration, uniform bead appearance, and good w
elding results, the correct polarity must be used w hen w elding
with any given metallic electrode.Incorrect polarity w ill cause
poor penetration, irregular bead shape, excessive s patter,
difficulty in controlling the arc, overheating, and rapid burning
of the
electrode.
Most machines are clearly marked as to what the terminals are,
or how they can be set f or either polarity. Some machines have a s
w itch to change polarity,w hereas on others it is necessary to
change the cable terminals. If there is any question as to w hether
or not the correct polarity is being used, or what polarityis set
on the DC machine, there are tw o easily perfor med experiments
that w ill tell you. The first is to use a DC carbon electrode, w
hich w ill work cor rectly only onnegative polarity. The second is
to use Fleetw eld 5P electrode, w hich w orks outstandingly better
on positive polarity than on negative polarity.
Testing Your Polarity :
A. Determine polarity by using the carbon electrode
1. Clean the base metal and position flat2. Shape the points of
the tw o carbon electrodes on a gr inding wheel, so they ar e
identical with a gradual taper running back 2 or 3 inches f rom the
arc tip3. Grip one electrode in the electrode holder close to the
taper 4. Set amperage at 135 to 1505. Adjust to either polarity6.
Strike an arc (use shield) a nd hold for a short time. Change arc
length from short to long, affording an observation of the arc
action7. Observe the arc action. If the polarity is negative
(straight) the arc w ill be stable, easy to maintain, uniform, and
conical in shape. If the polarity is positive
(rever se), the arc w ill be diff icult to maintain and will
leave a black carbon deposit on the surfac e of the base metal8.
Change the polarity. Strike an arc w ith the other electrode and
hold for a similar length of time. Observe the arc action as bef
ore9. Examine the ends of the tw o electrodes and compare. The one
used on negative polarity w ill burn off evenly, keeping its shape.
The electrode used on positivepolarity w ill quickly burn off
blunt
B. Determine polarity by the metallic electrode (E6010)
1. Clean base metal and position f lat2. Set amperage at 130 to
145 f or 5/32" electrode3. Adjust to either polarity4. Strike an
arc. Hold normal arc length and standard electrode angle and run a
bead5. Listen to the sound of the arc. Correct polarity, w ith
normal arc length and amperage, w ill produce a regular "crackling"
sound. Incorrec t polarity, w ith normal
length and amperage setting w ill produce irregular "crackling"
and "popping" with an unstable arc6. See above for characteristics
of arc and bead w hen using metallic electrode on correct and
incorrec t polarity7. Adjust to the other polarity and run another
bead8. Clean beads and examine. With the wr ong polarity, the
electrode negative, you w ill get many of the bad bead
characteristics show n in Lesson 1.69. Repeat several times, until
you can quickly rec ognize corr ect polarity
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