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Science Forum Index » Engineering - Joining (Welding) Forum » 7018 DC+/AC electrodes
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| Author |
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| Curt Welch |
 Posted: Sun Jan 28, 2007 2:35 pm |
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Ignoramus6496 <ignoramus6496@NOSPAM.6496.invalid> wrote:
Quote: On Sun, 28 Jan 2007 00:24:44 GMT, R. Zimmerman <m-zimmerman@shaw.ca
wrote:
Normally E 7018 is a DC rod. Electrode positive!
You have purchased the AC version of this electrode. It can be used
either on AC or DC. Personally I do not like them. Something in the
flux makes them more susceptible to porosity at the beginning of your
weld bead. They seemed to be even more difficult to strike up again
halfway through than regular DC rods.
In answer to your question: Yes, they will be fine for welding DC on
your trailer.
You can pretty well know if your welds are going to work. A visual
inspection is all you need. You do not want craters at the end of your
beads, undercut or coldlap. If your welds look decent then they will
hold under normal circumstances.
Randy
Randy, thank you. I will try them.
i
"Ignoramus6496" <ignoramus6496@NOSPAM.6496.invalid> wrote in message
news:Y-udnfVVibEmJibYnZ2dnUVZ_r_inZ2d@giganews.com...
I bought some 1/8 7018 electrodes on eBay made by "Washington
Alloy". They turned out to be described as AC/DC+ electrodes. Which
surprised me since most electrodes welding that I have done was with
DC-.
I've just started to learn how to weld so I'm no expert (I've only spent 45
minutes stick welding so far in my life). But 7018 rods were one of the
two I used.  We are using 6010 and 7018 rods in the class at DC+
polarity.
The last digit of the rod numbers identifies the basic type of rod and the
polarity of the current to use with them. ---8 rods are AC or DC+. If I
remember my book correctly, it goes like this:
---0 DC+
---1 AC DC+
---2 AC DC-
---3 AC DC+ DC-
---4 AC DC+ DC-
---8 AC DC+
That's all I remember.
http://www.metalwebnews.com/howto/weldrod.html has a chart as well but it's
a bit different. It's best to always check the manufacture information for
the rod.
I see the Hobart 6011 rods matches what I wrote above, but the Lincoln 6011
rods are for AC DC+ or DC- which matches what is on that web site above.
I see Hobart also makes a 7018AC rod optimized for low voltage AC welders.
Also, if you didn't already know, the 60-- rods have a 60,000 psi tensile
strength and the 70-- rods have a 70,000 psi tensile strength. So your
7018 rods make stronger welds when used correctly.
Quote: My question is, what are they good for, can I use them for
welding my trailer for instance.
They are good rods for that application.
However, 7018 rods are low hydrogen rods which are sensitive to moisture.
You must keep them dry. They should be stored in a rod oven. I've read
that for critical applications like nuclear power plants, if the rods are
not used within something like 8 hours after they are opened or removed
from the oven they must be thrown away (just to demonstrate how important
keeping them dry are). They loose their strength advantage when they get
too much moisture (H20 adds hydrogen to the weld I think).
I believe you will see a problem with porosity if the rods have soaked up
too much moisture from the air (and end up with even weaker welds than a
60* rod). I think you can bake the rods for a few hours at some higher
temp to dry them out again - I think this is something you can do in a home
oven but I'm not sure about that.
Here's a web page I just ran across that talks about problems with porosity
at the start of the weld with low hydrogen rods like the 7018 if you don't
use the correct technique at the start:
http://www.lincolnelectric.com/knowledge/articles/content/e7018.asp
Maybe that was the cause of the porosity problem the other poster was
having at the start of his welds....
It seems that 7018 rods are very common rods which make a stronger and
smoother weld. But they are harder to use correctly and I think it's very
important to make sure you prep the metal correctly and keep everything
clean in order to get the advantage from them.
For thicker material using multiple passes I think it's common to use
something like the 6010 for the root pass because of it's deeper
penetration to make sure you get good penetration on the root pass and then
use something like the 7018 for the cover passes because of the improved
strength and weld quality along with faster application.
The 7018 includes iron powder in the flux coating which makes them a faster
filling electrode.
7018 rods also need higher current than rods like the 6010 or 6013. (20 to
30 amps more I think is typical for a 1/8" rod).
--
Curt Welch http://CurtWelch.Com/
curt@kcwc.com http://NewsReader.Com/ |
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| Richard Smith |
| Posted: Mon Jan 29, 2007 6:24 pm |
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curt@kcwc.com (Curt Welch) writes:
Hydrogen never ever causes porosity in steel under any conditions(?) -
and certainly never under welding conditions. Cellulosics use
hydrogen in hyperdrive to give penetration with no problem.
It does though in metals like Al.
Hydrogen is not rejected from the melt on solidification of iron (and
steel) - as its solubility in the solid is littel different from that
in the melt...
In welding of steels all (?) H problems are cold-cracking.
Richard Smith |
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