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The Arc Blow Problem

Arc Blow is a problem that exists with most electric welding processes.  It is caused by the preferential magnetic fields developed near the arc.  These are most often caused by the arc current ground path or in the fixture holding the part to be welded.  The fields interact with the self induced field around the electrode.  When employing DC power the external field will be preferentially in one direction.  This builds a stronger field on one side of the arc than the other causing it to move in the direction of the weakened field.  The worse situation is when this movement causes the arc to blow backwards and become unstable.  This can generate gross porosity in the deposit.  See the picture below:

The above sheet metal weld was made at 200 ipm travel speed with the submerged arc welding process and shows classic arc blow porosity at the finish end of the weld.  It is common to have the visual effects of arc blow occur at the end of the plate to be welded.   The magnetic field force line concentrate at the plate end as the arc approaches causing what is often referred to as "back blow" porosity. 

Details of how this problem can be solved in submerged arc welding are discussed in a technical paper on multi-wire multi-power welding.  A recent major porosity problem on an ID weld in a spiral pipe mill was solved with a unique approach.  Details are covered in the paper.  If you are interested in purchasing this technical paper Contact Us.

AC power can not only solve many arc blow problems but also can be shown to produce more penetration that DC under certain conditions.  In fact in two wire systems there are demonstrated benefits of AC-AC versus the more commonly used DC-AC.  These details are covered in the  technical paper.  Want to see an overview of what is included?  Click here.

Multiwire Sub Arc Welding (SAW)

3_wire_OOFMultiwire SAW has a significant arc interaction, which could be considered an Arc Blow problem if when using AC power the system is not phased properly. The photo left was made with a three-wire system operating at high speed and the only difference in the welds was the power phasing. All parameters other than phasing were identical! The research done to define the proper system and increase welding speeds for making large diameter gas and oil pipe is discussed in a free PDF download.

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Another Problem Often Referred to As Arc Blow

Welders often refer to the problem caused by the high gas flow and start gas surge  as "Arc Blow" or the "Gas Blew the Arc Out."  This is especially noticed in TIG welding when you start at low current.  In fact the arc is deflected by the high gas flow.  We have had TIG welders report much better starts when the use out Gas Saver System which reduces the gas surge velocity at the weld start.  SEE DETAILS ON IT'S USE IN TIG WELDING.

Example High Gas Flow With MIG Welding Causing Erratic Arc, Some Might Call Arc Blow

An interesting situation shows what can happen if excess shielding gas flow is used.  An experienced field Welding Engineer was testing a new model multiprocess power source in a fabricators shop.  It worked fine in the Stick and TIG mode.  However when he switched to MIG welding with a cylinder of 75% Argon 25% CO2 gas the arc was harsh, erratic and  the spatter was very high with poor weld surface appearance.  After checking grounding, polarity and making settings changes with no improvement he called the power supply manufactures Product Manager.  After discussing the problem, the Product Manager wondered about the gas flow rate and asked to have it checked.  The field Welding Engineer said it was set for 30 (he assumed CFH.)  The Product Manager had experience with poor performance when flow rates were set excessively high.  He asked the field Welding Engineer to put the MIG gun nozzle up to his cell phone and pull the trigger with the wire disconnected!  The solution was evident from the sound this very experienced Product Manager heard - the flow was excessive!  Sure enough, the distributor salesman who set-up the installation had used a standard inert gas regulator.  It was not a Regulator/Flowgauge with an outlet orifice and flow calibrated pressure gauge.  It was reading 30 psi not 30 CFH!  What flow were they getting?  No doubt over 150 CFH.   Even with a 5/8 inch MIG gun nozzle, much more than about 50 to 60 CFH will cause turbulent flow and mix air into the shielding gas stream!  It takes only a small amount of  air to produce a less stable arc with excess spatter and internal weld porosity-if it is not visible! Very high flows, as in this situation, can cause to arc to "Blow" sideways or erratically. Perhaps more harmful than the visible defects is the effect of Nitrogen on the weld deposit. 

Note: In the above example, when the proper regulator/flowgauge was installed, MIG weld performance was fine!

 See What That Can Cause.

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