What the big deal with penetration.

admin

Hi Everyone,different arc welding rods give low, medium or high penetration. I read somewhere that penetration is not important but fusion is.Lots of welders however have complained that certain welding rods don't have much penetration. So how does the the amount of penetration affect weld strength. Will you get a better "mixing" of the parent metal with a higher penetration rod, and will this give a stronger joint (assuming identical electrode material).Cheers,Keith.
Reply:Originally Posted by mancavedwellerHi Everyone,different arc welding rods give low, medium or high penetration. I read somewhere that penetration is not important but fusion is.Lots of welders however have complained that certain welding rods don't have much penetration. So how does the the amount of penetration affect weld strength. Will you get a better "mixing" of the parent metal with a higher penetration rod, and will this give a stronger joint (assuming identical electrode material).Cheers,Keith.
Reply:OK.... Just using the slang term "penetration" as it's used in the piping field:"I'm just not getting the penetration I need on this joint". Many times with large diameter pipe... as you weld the root gap, the original gap you had set begins to close up. Soon, you have "metal to metal". With a good rod and a good machine all you have to do is push a bit harder and the root pass will burn through and leave internal reinforcement. If your rod or machine is not up to snuff... you have to stop and run a grinder in the bevel to thin it out. Then continue to weld. Every time you have to stop and restart there is always a chance for something to go wrong (lack of penetration, trap slag, etc).Hope that helps.HoboLincoln SA200's... at least 15 - 20. They come and go. Growing partial to the "Short Hoods" in my old age. Last count on Short Hoods was 13 in possession.
Reply:Weld penetration is the distance that the fusion line extends below the surface of the material being welded.Welding current is of primary importance to penetration. weld penetration is directlyr elated to welding current. An increase or decrease in the current will increase or decrease the weld penetration respectively.However, we have seen that welding current can be varied without changing the wire feed speed; namely,through the variation of the tip-to-work distance. The effect of tip-to-work distance on weld penetration is opposite in nature to that of welding current. An increase in the tip-to-work distance will decrease welding current and penetration. Of course, the converse is also true. In some applications, many operators have found it helpful to use this property to control penetration. Changing the tip-to-work distance while welding prevents burn through when there are discontinuities in material thicknesses or joint gap.Lack of fusion, also called cold lapping or cold shuts, occurs when there is no fusion between the weld metal and the surfaces of the base plate. The most common cause of lack of fusion is a poor welding technique. Either the weld puddle is too large (travel speed too slow) and/or the weld metal has been permitted to roll in front of the arc. Again, the arc must be kept on the leading edge of the puddle. When this is done, the weld puddle will not get too large and cannot cushion the arc.Another cause is the use of a very wide weld joint. If the arc is directed down the center of the joint, the molten weld metal will only flow and cast against the side walls of the base plate without melting them. The heat of the arc must be used to melt the base plate. This is accomplished by making the joint narrower or by directing the arc towards the side wall of the base plate. When multipass welding thick material, a split bead technique should be used whenever possible after the root passes. Large weld beads bridging the entire gap must be avoided.Lack of fusion can also occur in the form of a rolled over bead crown. Again, it is generally caused by a very low travel speed and attempting to make too large a weld in a single pass. However, it is also very often caused by too low a welding voltage. As a result, the wetting of the bead will be poor.When welding aluminum, the common cause of this type of defect is the presence of aluminum oxide. This oxide is a refractory with a melting point of approximately 35000F (19270C). It is also insoluble in molten aluminum. If this oxide is present on the surfaces to be welded, fusion with the weld metal will be hampered.Hope that helps Last edited by Gerry1964; 11-21-2012 at 03:34 PM.
Reply:Damn, I had soo many one liners for this topic..........like; Ask yo mama.... Sorry, tired, long day!
Reply:Question....If my welds are cold with poor penetration and I need to up the heat, when I do, I generally get more arc blow and spatter and still poor welds (or to the other extreme, burn holes).  How to remedy that problem?
Reply:Thanks for the input everyone (I hope you don't type with one finger Gerry, ha ha).Still gets me back to the same question though - does more penetration give a stronger joint, assuming the electrode rod / wire, etc is the same. Does the larger volume of mixing of parent metal and rod create a stronger joint as opposed to a thin depth of fusion with a low penetration rod like 7014.I mean why do some welders complain about an electrode (talking stick welding) not having much penetration. As long as you get fusion why would you need more penetration.I understand about open root and the need to use 6010 or 6011 rods to blast through the root and open a keyhole, but that's a bit different from the fusion / penetration issue I'm trying to understand.
Reply:I look at it lile this.  Fusion is how well the sides of the weld are tied together and is a combination of the parent metal and the electrode/filler.  If this is just laying on the top of the weld joint it will be a weak weld.Penetraton is how deep the fusion goes   A properly fused weld with penetration the entire depth of the material is about as strong as you can get.  This may not happen with one pass so each pass must have the proper fusion to tie in the multiple passes and must have the penetraton to tie each pass together.The first line of Gerry1964's post says it all.  He then goes on to explain what situations cause the problems.  Good informatoin.Dan D.Last edited by DanD78; 11-22-2012 at 06:50 AM.
Reply:Informative thread. Thanks for asking.
Reply:There's a lot more to rod selection than penetration. Joint configuration, ductility of the weld material, tensile strength, ease of use and storage, rod availability etc. all play a part in some way.Everything else being equal, there will be a minimum point where more fusion won't gain you any more strength. At that point, it won't matter how much extra penetration you have. However things are seldom exactly the same in real life. If you are looking for maximum strength, then in general a deeper penetrating rod has a better chance on developing more strength since it will fuse with more material, and thus exceed that minimum fusion level even if the weld is not 100% perfect.In some cases maximum penetration is NOT what you want, for example if doing sheet metal. In that case a shallow penetration rod would be abetter choice. Also some rods are "easier" to weld with. A person might have a better weld with say 7014 then they might with 7018. A "good" 7014 or 7024 weld might have higher strength rating then say a poor 7018 weld with old damp rods and lots of slag entrapped in the weld...In this case it would probably be better for the person to use the rod they run best, even if penetration isn't as good as you might like.CEP did a good "test" that showed how different rods gave different ductility levels, or how well the welds held up under "abuse". Certain welds failed not because they failed to penetrate more, but because the weld material was less ductile and broke rather than bent. Something that becomes more critical as temps drop..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Thanks again everyone.DSW, that's what I was after, cheers. From using 6013 rods on cold metal I would sometimes get beading up on cold steel. I tried preheating another weld and it turned out great so I suppose for a low penetrating rod like a 7014, I could preheat to assist penetration ? (I never get beading up with my beloved 6011 rods )Do 7018 rods have more penetration than 6013. Many welders use only 7018 & 6011. I'm going to some pains to ensure my 7016 / 7018 rods stay very dry and I'm wondering if I'll end up using 7018 instead of 6013 most of the time. I've never used a 7016 or 7018 rod yet (not one that wasn't old and wet that is). Had too much beading up and slag inclusions with 6013 rods. 6013 & 7018 are both classed as medium penetration but does anyone think 7018 does "bite in" better ?Last edited by mancavedweller; 11-22-2012 at 12:53 PM.
Reply:7018 will not do open root joints well. This is because the unprotected back will develop porosity. They combat this several ways. One is to use a backing so you don't have an open root, or adjust joint design so it's not an open root joint. 2nd is that the weld the root pass with 6010/6011. In effect all you are doing is welding in a backing and then running 7018 out. 6010/11 doesn't have the porosity issues with an open root 7018 does. Last option is to back gouge out the root pass and weld it back up with 7018 from the back after the rest of the weld is done.A lot of guys have taken this and simply decided that 6010/11 root, 7018 out is the way to go every time. It's simply because they don't understand the WHY behind the process and simply assume if it works for pipe, then it must work for everything else.Same goes with preheat. There are distinct circumstances where preheat helps, but it can also cause issues as well if you don't understand the WHY behind it's being used. Many times preheat is simply to drive off the moisture that is in the pours of the steel before doing a low hydrogen weld like 7018. As you heat the steel you will see it "sweat" as the moisture comes out. All that moisture defeats the purpose of keeping your rods moisture free. In other cases like high strength steels, the material is very sensitive to temperature changes. Running a hot bead on cold steel will cause cracking issues as the material reacts in the HAZ. Preheat can occasionally help with penetration, but usually that means you really needed more amps or a bigger rod, not preheat. Too much preheat can also be bad. Thin material can warp with too much heat, and as mentioned earlier high strength steels have certain specific temps that need to be maintained to protect the steel. Alum looses a lot of it's strength when heated above a certain point, so too much heat there can be very detrimental.7014, 6013 and 7018 will tell you when you have all your settings and travel speed angle correct. If you are doing a lot of pounding to remove the slag, you don't have things adjusted correctly. When all the stars align, the slag will either peal right off behind you or come of if you simply drag the hammer over the weld. Take a look at the vid Fexal did recently on his tube project. He has his setting pretty near perfect as the slag comes right off when he drags the hammer. I see students having this problem a lot. They can't get good beads on cold steel, but can make nice beads after two or three tries as the material heats up. Most times it's not the amps that are wrong, since we tell them where to set the machine, it's their rod angle, travel speed or arc length that is wrong and causing their issues. From your comments on slag inclusions, that would be my guess at your problem as well.If you want, post up some picts of your welds. Tell us what rod, what size rod, material and thickness, and amps used and we can make a few guesses that may help you. In general all the rods, 7014, 6013, 7018 are drag rods and will run best when the flux is kept in contact with the material. some times some 7018's will like to be held out just a bit though. On average, you will get roughly 6-8" of weld length from a single rod depending on the joint configuration. And longer or shorter, and that means you need to adjust your travel speed accordingly. Rod angle should be maybe 5-10 deg off vertical and with the tip pointed back to the weld so you are dragging. Amps will depend on the rod and size chosen. 7018 1/8" is usually about 125 amps for example, but that can vary slightly depending on your machine and the brand of rod.God luck..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Thanks DSW, some very good information there.I like what you have explained about the open root and how 6010/6011 is basically just to weld a backing strip in. Here in Australia I've seen a couple of 7016 rods that are purposely made for open root welding but I don't know what the welding technique will be. I have a packet of Kobelco (Kobe) LB52-U so I'll probably have a go for the hell of it at some point.I have seen that sweating you mentioned when putting a flame on steel. So that's water, eh. In everything I've read on low hydrogen rods I've never seen that mentioned. I wonder if that could be a cause of porosity that so many welders have experienced with LH rods even when the rods are dried and stored properly. I love what you guys can teach us amateurs.Your mention of getting good beads on cold steel really strikes a chord with me. Just last night I noticed how the start of my 6013 weld bead looked "cold" and humped up then flattened and smoothed out soon after. I tried starting an inch from the weld and long arcing back to the start point and that seemed to help a little, but I'll also try a lower rod angle to penetrate a bit more at the beginning. I wonder if any of the higher end machines have a feature where the first 2 or 3 seconds after striking gives a higher current then tapers off to the set level, or is that just cheating.Keith.
Reply:Originally Posted by DSW7014, 6013 and 7018 will tell you when you have all your settings and travel speed angle correct. If you are doing a lot of pounding to remove the slag, you don't have things adjusted correctly. When all the stars align, the slag will either peal right off behind you or come of if you simply drag the hammer over the weld. Take a look at the vid Fexal did recently on his tube project. He has his setting pretty near perfect as the slag comes right off when he drags the hammer. God luck.
Reply:Originally Posted by mancavedweller I wonder if any of the higher end machines have a feature where the first 2 or 3 seconds after striking gives a higher current then tapers off to the set level, or is that just cheating.Keith.
Reply:Don't know what that would do to the machine, but I've seen three machines get messed up doing that during a weld. It was during arc weld. Personally i would not do that to a machineSent from my DROID RAZR using Tapatalk 2
Reply:Some good replies...................BUTNobody has addressed the issue of admixture/incorporation.Penetration necessarily implies the admixture of the parent metal into the weld pool.  The parent metal mixes with the filler metal.In some cases this a good thing, like increasing ductility etc.  But sometimes it's a bad thing.  In some cases you don't want the metal to mix to a great degree.  So for this situation there are rods/filler metals offered in different penetration levels in the same strength range.Penetration depends on the metal and joint design.  Usually mild steel is forgiving and penetration is allowed, and desired.  Other metals may require different levels of penetration/admixture/incorporation."Any day above ground is a good day"http://www.farmersamm.com/
Reply:Thanks Farmersamm, that's interesting.Anyone got any examples of when more penetration is good and when it's bad.
Reply:One example I can think of is a friend of mine that welds pipe and talked about how they dont want too deep penetration because it will put a crown on the weld inside the pipe and then that will contribute to turbulence in the liquid flowing through it. Probably a bad description dumbed down for me as a hobby welder.  Another example from personal experience would be in doing construction where fit of parts is in close tolerances. f you penetrate to the point you build up bead on the back then you create a build up that has to be ground off to the same tolerace as the original metal and that can be hard. Another reason is tht the stronger the penetration, the harder it is to get a good weld without blasting holes in the metal. Sometimes I would rather do a pass on each side than risk having to figure out how to plug holes.