Question: Ed can you describe the difference between straight and
reverse polarity in MIG welding?.
Answer:
As we can all likely do with some humor in our lives, I thought, rather than answer
this common weld question in the traditional manner, that I would tell you about
a welding application I was involved in a few years ago.
A
Midwest company that supplies exhaust systems to the after market had major MIG
welding problems. The owner of the company asked if I would visit his plant and
report on the welding issues. He told me that some of his customers were complaining
that the carbon steel welded flanges were falling of the exhausts while in delivery.
I arrived
at the exhaust manufacturing plant just before lunch. Like many automotive companies,
the plant could not afford an $8 an hour receptionist, and no one answered the
lobby phone. To get access to the plant, I walked around to the back door. I entered
the plant in the weld shop area and my welding senses went immediately on high
alert. The "weld sounds" I heard from the approx. 40 MIG weld booths
were unique, but I had heard them before.
As
I stood in the plant digesting the arc sounds, a six foot four individual with
hair growing in places I had never seen before, walked over to me. This man who
had never seen a Gillette blade was the plant-welding supervisor. Weighing in
at about 300 pounds with his stomach bulging out of his stained black leather
vest and Harley T shirt, he was without question a character to be reckoned with.
The welding supervisor
leaned into my face, and with the smell of stale Budweiser, and deep fried pork
and onions floating from his beard, he snapped, " what dea want". I
told the "gentleman" that the owner of the plant had asked that I examine
the plant's welding issues.
He burped, or it could have been a small
fart and glared down at me, he was obviously not impressed by a weld expert from
out of town. The supervisor spat vile black liquid chewing tobacco close to my
foot and then in his best English politely informed me "there were no f______ing
weld issues in his weld shop".
Having spent my life around interesting
characters, it only took a short conversation with this individual to figure out
that the reason he was made the plant welding supervisor, there was no one in
the plant that could wrestle him.
While
trying to be polite with one of the reasons the welding industry has a poor image,
I wandered off and walked among the weld cells to verify the root cause of the
strange MIG weld sounds. I watched the welders and examined the nearest MIG equipment.
As I suspected it was a polarity issue. I noted the ground cable was attached
to the positive terminal on the MIG equipment. On further examination I noted
that the "straight polarity" was being used by every MIG welder in the
plant.
Straight
polarity when used in the traditional short circuit wire feed range produces
a softer crackle, plopping sound from the formation of larger weld droplets. In
contrast short circuit with reverse polarity (RP) produces a crisp crackle sound
from smaller droplets that transfer in a more rapid manner.
