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  • DCEN vs. DCEP....GET IT RIGHT!

    ok in the first welding book i ever bought, Welder's Handbook, by Richard Finch, it states in the arc welding section, page 91, that DCEP, or reverse polarity, gives shallow penetration......then on page 92, it states that DCEN, or straight polarity, gives deep penetration. in DCEN, the work gets hotter than the electrode, and vice versa for DCEP. I've proved this to be true b/c if you try and tig weld mild steel DCEP, the tungsten melts before you get a puddle....now mostly do ac stick welding, and the little bit of DC i've done, was mixed DCEP, or DCEN depending on which machine i was on, but one machine was set DCEN, and the other 3 were set DCEP......so is DCEP better for out of position stuff? Now where i get confused, is on both hobart's and miller's website, they state in black and white, that DCEP gives the most penetration, AC gives medium penetration, and DCEN gives the least....HMMMMMM who's right? personally, i think they're wrong.

    http://www.hobartwelders.com/techtips.html#stick

    http://www.millerwelds.com/education...ips.html#stick

    regards,
    Nathan Hamler.

  • #2
    YJ
    IMO I think Finch is wrong, or got it backwards and missed it in edit. In sheetmetal, everything we did up to 14ga was with DCEN ( straight pol ) to minimize blow-thru. Reverse always blew out eventually. We switched to reverse pol ( DCEP ) on 12ga and up since we actually had something there to take the heat. We also used reverse to certify on all our tests. Most of those were on 10ga. One guy tried it on straight in practice. When the backing plate was ground off, we noticed he didn't penetrate deep enough to fuse the root completely. ( He had a bunch of pinholes. ) The same run on reverse ended in a fused root with no holes.
    I have the same book and noticed that right off.
    Don


    Go Spurs Go!!!!!!

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    • #3
      Electron theroy states that negative flows to positive. In DCEN the electrode is negative and will act as the emitter to release electrons into the work. As I recall about 80% of the energy goes into the work and about 20% into the electrode. The opposite is true for DCEP. A note: The hotter the emitter the easier the electrons will leave. Also electrons like to leave from edges or points. That's why after the tungsten has been balled it is harder to start the arc than before. The newer machines allow for the initial arc to be started DCEP so the arc jumps or is emitted from the work (which is rough and will give up electrons easier than the smooth electrode) it also allows the tungsten to heat quickly making it a good emitter, when the current goes to DCEN a few msec latter. This is why you should size the tungsten to the work or current being used to allow the tungsten to reach the proper temperture as quickly as possible. Too small an electrode will not be able to conduct enough current for the job. Soooo this porridge is to hot, this too cold and so on-------. ****ed if you do, and ****ed if you don't. That's what makes it so much fun.

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      • #4
        That's not the only questionable information in the Welder's Handbook . I bought it from Amazon.com awhile back, and it was so full of inaccurate and incorrect information I sent it back and got my money back. Probably the only book I've ever asked for a refund on in my life. There are much better texts out there.
        Trailblazer 302 * Millermatic 212 * Syncrowave 180SD * X-Treme 12VS Feeder * Spoolmate 3035
        Thermal Dynamics Cutmaster 52 Plasma * Lincoln 175 MIG

        Victor Superrange II * Victor Journeyman

        Hobart HH 125EZ


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        • #5
          yj*,
          I don't have a copy of Finch's book in front of me to check, but I know where your problem lies. The problem is you have assumed that an arc for tig is the same as an arc for stick welding. This is just not the case. The simplest way I can explain this is that for a 'simple' arc, that is one which is created from either a bare piece of tungsten, a stick electrode with it's flux removed, or a carbon electrode, DCEN or DCSP will have the best penetration since more heat is liberated at the positive pole or piece of metal to be welded. This example is for the case of a non-consuming electrode. Tig arcs operate in this category. As has been stated, dopants are added to the tungsten to improve it's emission characteristics.

          Now for stick welding, you are operating a 'consumable electrode'. In this case there is a flux covering which generates gases and fluxing agents which alter the penetration characteristics and movement of metal ions from the electrode tip to the metal being welded. If you have mig welded before with CO2 you will know that this creates the deepest penetration profile. Well,a 6010 rod has a cellulose covering which in turn creates a CO2 gas shield, thus providing a very deep penetration---as long as it is run DCEP or DCRP.

          So in a nutshelll:
          TIG: max penetration with DCEN/DCSP
          STICK: max penetration with DCEP/DCRP

          -dseman
          Last edited by dseman; 04-08-2004, 07:45 AM.

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          • #6
            Everyone is right ( Finch is wrong )

            In MOST processes of consumable electrodes ( stick, MIG, flux cored, gas shield flux cored, submerged arc and SOME self shielded flux cored ) operation on DCEP ( reverse polarity ) generates more heat at the work

            If you run MIG on DCEN the wire ***** like crazy and you get zero penetration. The only wire process that is commonly run on DCEP and DCEN and AC is submerged arc. All other wires processes must be run on the polarity it was designed for

            Whether or not a stick electrode can be run on DCEN as well as DCEP is determined by the coating type ( example : a XX10 cellulose sodium should only be run on DC+ , E6012 should only be run on DC- or AC .

            Where it gets confusing is EXX18 where some 7018 are designed for DC+ only ( not DC- or limited AC ) . A good rule is if it says AC on the rod then you are ok for DC- and AC. If it does not it is best to run on DC+. Even though most low hydrogens can run acceptably on AC the only time you would do this if arc blow is an issue

            The most notable exception is GTAW where a tungsten is used as a cathode. 70% of energy is at work on DCEN , balance at electrode. Another exception is MOST self shielded flux cored wires such as the AWS E71T-11 like Hobart 21B, Lincoln NR211

            These wires are run on DCEN. If you try to run them on DCEP you get poor penetration

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            • #7
              I'd been wondering that ever since I did some reading on tig polarities, and it confused the heck out of me that it was opposite for stick.

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              • #8
                Got Finch's book. Kinda full of Finch, mostly. I liked "Welding Essentials" by Galvery and Marlowe much better.

                Be well.

                hankj
                ...from the Gadget Garage
                MM 210 w/3035, BWE
                HH 210 w/DP 3035
                TA185TSW
                Victor O/A "J" series, SuperRange
                Avatar courtesy of Bob Sigmon...

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                • #9
                  dseman and TRG-42 have given you the correct information

                  This is because of the non-consumable electrode and inert gas vs consumable electrode and active gas or flux

                  GTAW = non consumable electrode with inert gas
                  DCEN = 30% heat on electrode 70% on work
                  DCEP = 70% heat on electrode 30% on work

                  SMAW, GMAW, or FCAW = consumable electrode with active gas and or flux
                  DCEN = 70% heat on electrode 30% on work
                  DCEP = 30% heat on electrode 70% on work

                  Some common examples of this are

                  1. GTAW using DCEP with 3/32" electrode for very thin aluminum, the electrode will ball up before you can establish a puddle on 1/8" aluminum

                  2. SMAW using DCEN with E6012 for thin sheet metal resulting in higher dep. rates with less burn through than on DCEP
                  DrIQ

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                  • #10
                    DCEP vs DCEN for penetration

                    Originally posted by DrIQ View Post
                    dseman and TRG-42 have given you the correct information

                    This is because of the non-consumable electrode and inert gas vs consumable electrode and active gas or flux

                    GTAW = non consumable electrode with inert gas
                    DCEN = 30% heat on electrode 70% on work
                    DCEP = 70% heat on electrode 30% on work

                    SMAW, GMAW, or FCAW = consumable electrode with active gas and or flux
                    DCEN = 70% heat on electrode 30% on work
                    DCEP = 30% heat on electrode 70% on work

                    Some common examples of this are

                    1. GTAW using DCEP with 3/32" electrode for very thin aluminum, the electrode will ball up before you can establish a puddle on 1/8" aluminum

                    2. SMAW using DCEN with E6012 for thin sheet metal resulting in higher dep. rates with less burn through than on DCEP
                    Actually DCEP vs DCEN should be compared including the process.
                    For TIG (non consumable electrode)
                    DCEN : Deeper penetration
                    DCEP : Shallow penetration

                    For stick electrodes, MIG, SAW (consumable electrodes)
                    DCEN : Shallow penetration
                    DCEP : deeper penetration

                    Reason:-

                    For TIG with DCEN.... electrons transfer from W- electrode to the work place. The kinetic energy of electrones are responsible for heating and melting of the base metal. Thus it gives deeper penetration.

                    For MIG or stick electrode with DCEP. ... electrons transfer from work piece to consumable. Majority of the energy of electrones used for melting of consumable (either stick electrode or wire). Now this energy is transgressive melting the base metal, as the molten droplets are propelled by electro magnetic pinch effect to impact the base metal.

                    Comment


                    • #11
                      Originally posted by ronak macwan View Post
                      Actually DCEP vs DCEN should be compared including the process.
                      For TIG (non consumable electrode)
                      DCEN : Deeper penetration
                      DCEP : Shallow penetration

                      For stick electrodes, MIG, SAW (consumable electrodes)
                      DCEN : Shallow penetration
                      DCEP : deeper penetration

                      Reason:-

                      For TIG with DCEN.... electrons transfer from W- electrode to the work place. The kinetic energy of electrones are responsible for heating and melting of the base metal. Thus it gives deeper penetration.

                      For MIG or stick electrode with DCEP. ... electrons transfer from work piece to consumable. Majority of the energy of electrones used for melting of consumable (either stick electrode or wire). Now this energy is transgressive melting the base metal, as the molten droplets are propelled by electro magnetic pinch effect to impact the base metal.
                      Not quite that simple, if you want to explain the "Why?" Was looking for a better answer to this question a few years ago, and here is what I came up with. Feel free to correct me, if I am wrong.

                      "This is my attempt at explaining
                      " Why does SMAW have greater penetration with EP vs GTAW having greater penetration with EN ?"
                      (without much reference to particle physics,since I obviously don't know enough!).

                      First, I think most would agree that a major factor. in achieving penetration, is the heat transmitted to the weld puddle, by various means, through the arc, in both processes. This is called thermal efficiency.

                      In GTAW, the most heat energy is transferred to the weld puddle in EN, making this polarity more thermally efficient. When the polarity is switched to EP, then the major part of the heat energy is focused on the electrode, and this makes the weld puddle cooler and less penetrating than on EP, or less thermally efficient. Also heat energy is dissipated through the electrode into the shielding gas and electrode holder.

                      In SMAW, the most heat energy is transmitted to the weld puddle in EP, because most heat is concentrated on the electrode, as in GTAW, but since the electrode is being consumed, much of this energy is transferred directly back to the weld pool with the molten metal, making the weld pool hotter. In SMAW - EN, the weld pool is cooler since less heat being on the electrode also means less molten metal being transferred to the weld pool, and therefore, EN is less thermally efficient and penetrating.

                      This is also compounded with other factors in SMAW, such as the fact that the plasma column is directed and focused by the coating crater, (coating melting slower than the core metal) in a way similar to a hose nozzle. This is not as efficient in GTAW, which has a sort of pear-shaped column that is controlled mainly by the shape of the electrode. (In some automated GTAW processes, greater plasma control is achieved with a magnetic field). Another factor influencing thermal efficiency in GTAW EN and EP is that the weld pool is cooled by the feeding of the filler rod, and the flow of shielding gas. In SMAW, the slag cover slows the weld pool cooling and increases penetration well. THis is all coupled with the fact that, according to EsabU, there are 9 different purposes for the flux in SMAW, and many hundreds of ingredients which could affect penetration.

                      Given the above, you might expect SMAW to have greater thermal efficiency than GTAW, and in fact, it does."

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                      • #12
                        A three letter acromyme sounds like a word.
                        By that word I recognise it.

                        A four letter acronyme is more profane than a four letter word if ya ask me.
                        Sounds a$$inine. It won't retain at all. Another thing the eggheads
                        just had to fix that wasn't ever broken.

                        We went a long long way just fine without,
                        GTAW SMAW GMAW FCAW FECTAW SCHMUTZTAW and all that [email protected]
                        Last edited by vicegrip; 12-18-2014, 09:28 AM.
                        sigpicViceGrip
                        Negative people have a problem for every solution

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                        • #13
                          Originally posted by vicegrip View Post
                          A three letter acromyme sounds like a word.
                          By that word I recognise it.

                          A four letter acronyme is more profane than a four letter word if ya ask me.
                          Sounds a$$inine. It won't retain at all. Another thing the eggheads
                          just had to fix that wasn't ever broken.

                          We went a long long way just fine without,
                          GTAW SMAW GMAW FCAW FECTAW SCHMUTZTAW and all that [email protected]
                          Didums get up on the wrong side of bed yesterday?

                          I originally wrote the above, and posted it in another forum, and did not feel I had to alter it, to re-post here.
                          Like it or not, it happens to be correct internationally-accepted terminology for weld processes. However, here's a one page chart of the acronyms of all the common current processes to help you out.
                          Attached Files

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                          • #14
                            Gads... How did we ever manage to convey information before we had acronyms...

                            Dale
                            Lives his life vicariously through his own self.

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                            • #15
                              I just invented a new acronym for correct internationally-accepted terminology

                              . . . . Gay . . . .
                              sigpicViceGrip
                              Negative people have a problem for every solution

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