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[MW:2734] Re: blow holes in double side welding in H-Beam SAW welding

By Materials & Welding
Three things to look for:

1. Trapped flux, since it is occurring on the second side only.

2. A poor ground, measure the temperature of the ground clamp during
operations, if it heats up significantly the second side weld may not be
receiving enough energy to full melts the metals and flux, resulting in
blowhole. Too much of the voltage drop is happening at the ground clamp. (I
mentioned clamp only but look at the complete ground system.)

3. If it is occurring on both side looks at the electrode spacing.

With a double electrode system if the electrodes do come too close together
the magnetic/electrical field will interfere with other, even if one is AC
and the other DC, and if too fair apart the second electrode will interfere
with the outgassing of the first. At the melt point of the electrode they
should be separated between 15 to 18 mm if you have a single molten puddle.
If you have two molten puddles then make sure that the electrodes are
separated at the melt point by at least 25mm.

The 18 to 25mmm zone is to be avoided, sometimes you get good welds but
many times you will have blowholes.
(The above measurements are for 3.2 mm electrodes 700 Amp 30Vdc, 750 A
32Vac 16mm separation, DC electrode 90deg to base metal, AC electrode
102degree from base metal)

As others have mentioned backchipping or grinding to sound metal, to assure
that all flux/slag is removed prior to welding the second side is important.

Best regards,
Richard Beldyk PhD, PE
AWS CWEng
ASNT NDT Level III


Original Message:
-----------------
From: Rohit Rawat rohit30584@yahoo.co.in
Date: Mon, 20 Jul 2009 23:43:29 +0530 (IST)
To: materials-welding@googlegroups.com
Subject: [MW:2721] Re: blow holes in double side welding in H-Beam SAW
welding


Sir,
This is to inform you that we are using two electrode SAW process.
Thanks,
Rohit Rawat,
Asst.Engg.(QA)

--- On Sat, 18/7/09, welding_engr_rich@charter.net
<welding_engr_rich@charter.net> wrote:


From: welding_engr_rich@charter.net <welding_engr_rich@charter.net>
Subject: [MW:2709] Re: blow holes in double side welding in H-Beam SAW
welding
To: materials-welding@googlegroups.com
Date: Saturday, 18 July, 2009, 6:26 PM

I am assuming that you are using the single electrode SAW process.
Typically blowholes on the second side are a result of flux being trapped
during the root pass on the first side boiling and escaping through the
molten metal of the second side weld. After the first side is done look
carefully at the send side weld prep, look for flux trapped in the root
area,

Wviness control you could try additional preheat this might help.  Contact
Tipmate http://tipmateusa.com/index.html their nozzle extensions might help
the waviness problem with a possible increase in production rates.

Best regards,
Richard Beldyk PhD, PE
AWS CWEng
ASNT NDT Level III

Original Message:
-----------------
From: raw rohit30584@gmail.com
Date: Fri, 17 Jul 2009 22:31:52 -0700 (PDT)
To: materials-welding@googlegroups.com
Subject: [MW:2702] blow holes in double side welding in H-Beam SAW welding

Hi everyone out there,
I am presently working in kirby building systems . we do PEB
fabrication .we use material ASTM A572 typ1 gr50 .the p[roblem is when
we do doubl;e side welding, blow holes occur in second side . what is
the basic reason .allso waviness occurs in flanges of thickness 6mm
and less,
thanks,
rohit rawat
QA(quality assurance)

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