Most of the time when welding with open arc or gas shielded hardfacing wires, we don't give the welding polarity much thought.  It is usually Direct Current Electrode Positive (DCEP), or reverse polarity electrode positive.  Rarely do the specs or data sheets call for Direct Current Electrode Negative (DCEN) or straight polarity electrode negative, but occasionally they do. There are some very distinct advantages to DCEN, but there are some consequences as well. Ideally speaking all hardfacing wires should run straight polarity, but they don't and for good reasons. But before we get into the details, it might be helpful to review some of the fundamentals.

When dealing with Direct Current and the welding arc, it may be helpful to think in terms of a gun shot.  When the gun is fired we have the release of a bullet, the reaction of the gun in terms of a kick, and of course the impact of the bullet on the target.  With the welding arc we have a positive (+) pole and a negative (-) pole.  The negative (-) pole always does the shooting, but instead of bullets, it shoots electrons at the positive (+) pole.  The kick in this electron gun is released in the form of excessive heat and pressure on the negative (-) pole, meaning that it is hotter and has more pressure against it than the opposite positive (+) pole.  Just as in any gun shot there is an impact from the bullet, but in the case of the electron gun, the impact results in heating of the positive (+) pole.  Let me interject something here regarding the gun analogy. The analogy implies that the electrons create all the heating at the positive (+) pole, but in fact there are multitudes of reactions that occur at each of the poles as well as within the arc or plasma itself that contribute to heating, melting, etc.  The gun analogy is a very simplified approach to help understand the reactions at each of the poles.  We will see how this affects joining and hardfacing shortly.

Let's examine a welding torch in a GMA welding process. Consider the electrode or wire hooked to the (+) terminal of the power supply, and the work connected to the negative (-) terminal.  This is known as DCEP or Reverse (Polarity) Electrode Positive (REP) and by far the most popular hookup for GMAW.  Switch the connections and we have DCEN or Straight Polarity Electrode Negative or Straight (Polarity) Electrode Negative (SEN), popular for GTAW.  An easy way to remember the connections for each is to think about our government and Congress which is made up of Senators (SEN) and Representatives (REP).   "SEN" is also an acronym for "Straight Electrode Negative" and "REP" is an acronym for "Reverse Electrode Positive". 

Now that we have reviewed the basics let's take a closer look the role of polarity as it pertains to hardfacing. As I mentioned above, most wires run well under Reverse Polarity (REP).  The welding wire in this case is positive (+) and the work is negative (-).  Remember, all electrons are shot from the negative (-) pole, which is the work piece or weld puddle. Since the work is the electron gun and receives the most heat through the "kick", excellent penetration and melting is achieved.  Arc pressure is also directed at the (-) pole or puddle, creating a good mixing action and bead shape. This is great for joining applications, but not great for hardfacing applications where we want low penetration and low dilution. If the poles were switched (SEN), making the welding wire the electron gun, less heat would be generated at the work piece making for shallow penetration and dilution. So let's switch the polarity and try it straight or SEN.  Immediately we see a big difference. Spatter generally goes up and we actually need more wire to keep a stable arc. The reason we see this is because now the electrode or wire is the electron gun and more heat is generated because of the "kick" and more wire is needed to sustain the arc. The ball at the end of the wire is also larger than it was under REP and the pressure against it is great enough to blow it off, causing excess spatter.  Although we achieve lower dilution and penetration with straight polarity (SEN), the arc characteristics are certainly not welcome. 

Ah, but there are exceptions.  When the moon is just right and the planets are aligned, some hardfacing wires do run very well under straight polarity conditions.  This is particularly true with small diameter gas shielded wires as opposed to open arc wires, where the gas can play a major part in the calming of the pressure against the negative (-) pole, thus reducing spatter.  Actually the moon and planets don't have much to do with it, but the gas mixture and wire formulations do.  Some elements can be added to the wire to aid in arc stability and is done whenever possible.  This results in an ideal hardfacing wire having low dilution, low penetration and low spatter.

 Some of the popular Postle wires that do run under straight polarity (SEN) are:

2820 SPL
2832 SPL
2834 SPL
2836 SPL
2842 SPL
Durachrome-G SPL

One very big advantage of running Straight Polarity is the ability to work on thin gage materials or on edges.  There is some sacrifice in bead appearance, but that may be a small price to pay.  If in doubt of whether a wire will run Straight Polarity, give it a try and use different gases.  You may  be surprised.
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