According to Lincoln Electric "Welding Pressure Pipe Lines & Piping Systems" (Feb 1991, P. 9), regarding cross country pipeline DC- vertical down for E6010, E7010, E8010, "Welding (DC-) (negative polarity) on the root pass will not be harmful to either mechanical or metallurgical properties." Also, "Hot pass and all other passes should be run (DC+) (positive polarity)."
Hey.
If I understand this correctly, you’re wondering broadly if using straight polarity rather than the preferred reverse polarity with 6010/7010 will affect the strength of a weld and will the chemical and mechanical properties change when doing so?
Is this correct? Because if it is, Have I got a story for you.
I took a foods class years ago. Welding came later but I put this together so work with me. Now I mention that because a basic electric oven has a heating element top and bottom. Well if we start splitting the heat of the arc and current flow it's kind of like which element in the oven is giving off the most heat when it's turned on. If we stick with the standard stuff about 70/30, we are on to something.
Now let’s bake a cake. A Betty Crocker cake. Should be simple enough right?
Out on a limb, if the arc energy is being compared to top and bottom elements in an oven, we can relate it to baking the cake.
While both heating elements will heat up to bake the cake, will it be top to bottom or bottom to top? Not to bring up the pan size for even baking, or the size of the oven, but if welding is heat and pressure applied, it is like baking a cake.
With welding, it's the heating and cooling that effects the properties most everyone is worried about protecting. More to that in a moment. Are you concerned with making a big cake light cake or a short dense cake? Which rack in the oven is the cake placed?
The choice of Current flow is akin as well to stirring the mix. Stirring from the bottom gives the best mix. Stirring from the top will mix but takes longer to reach the bottom.
Stir a cake batter long enough and you have pancakes. Keep it up you can get crepes.
Try making waffles with the mix, let me know how that goes.
So... how deep is the mixing bowl and how long do you mix? Its Betty Crocker so don't over think it. But if you did over think it, you’re now forming some opinions. You’re going to think about 70% of the top element hot 30% off the bottom, then the bottom 70% and top 30%. Then you’re going to ask, what's baking what's burning. Maybe what if I preheated the oven before putting the cake in? Did the cake mix change? I don't think so, but how it might bake does.
I would step up on your comment regarding strength. That’s an over rated word. Like saying if you stand enough pancakes high enough you have a real strong cake? I don't think so. How about, what could be done to screw up a perfectly good cake mix and how to prevent it? Simple, follow instructions. Funny thing, girls everywhere baked cakes in their Easy Bake Ovens and 60 watt bulbs.
How about this, it's not the cake mix? It's not the oven. It's the baker.
A good baker knows, does, and is secure in understanding why. A good baker follows the instructions if someone else did the work for him...Like Betty Crocker. Why change what works?
So, in generalities, welding with cellulosic electrodes on DCEN will not cause a major change to composition of the deposit but the deposit will be affected in its metallurgic structure as a result of using a DCEN polarity. How much depends.
Could this result in weld strength change, sure. But in generalities, not as much as you think. Your concern is weld hardness. If you consider droplet size, DCEN causes a spray in a rapid releasing of small wet droplets; the small droplet holds little heat, cools too quickly, causing a harder deposit. Hardness brings an increased degree of toughness. Does that add strength or is it less ductile? Harder to bend or resists being pulled apart? They make graphs to record that stuff but my experience says polarity does not affect tensile strength. Cooling rates do however.
Back in the day, they welded with bare electrodes on DCEN. The problem was resulting hardness, loss of ductility, contracting stress from rapid quenching. As well, back in the day they knew little about Hydrogen gas. Straight polarity and cellulosic electrodes means an increase to those levels.
Not much slag coverage with a 6010 to slow down the heat loss so using straight polarity only adds to this issue of contraction quench, hardness, and hydrogen entrapment. Can it be overcome? Sure, but as material increases in thickness, or the composition of material changes it gets harder to do. That’s not a you can't but it's why you shouldn't.
So, on an x-ray you couldn't tell. The guy who polishes up a sample might raise an eyebrow on what he sees but I doubt he could tell polarity being used? Visually, you might guess but even that would depend on the rod, power source and of course the baker.
You most likely will see it showing up doing mechanical testing, but the results could be somewhat close depending on the skill of the baker and the cake being baked.
But if you need to know all that then you follow the instructions on the box. Closely. It brings about the best results.
On a side note...a rod oven will bake a cake. I don't suggest you do it, but it will. Cup cakes however bake quicker. And cake waffles...that's a mess waiting to be cleaned up so don't bother.
Well that’s my response. Hope it helps.
.
Now that's an interesting comparison. Makes for a good visual aid though. Well put.
And, along with that, since the cake mix maker would know a preferred procedure, so also would the electrode manufacturer who definitely recommends DCEP even though they state that DCEN will work.
As Al states, the WPS, based upon the manufacturer's recommended specifications, are a recipe for a successful operation. Bake it according to the recipe. (not a direct quote)
He Is In Control, Have a Great Day, Brent
Ok, I read the whole thing.
In a single paragraph you pronounced that the smaller DCEN droplets produce a "harder" deposit and also told the OP that tensile strength would not be affected according to your experience.
How dat?
Baking soda?
is it baking soda or baking powder... ?
I can never remember :)
Hi Lawrence,
Is that what I said? Good, because it sounds about right.
To be clear however, I was trying to get across that if buddy thinks about it a bit, polarity isn't the big issue to those properties when compared to what gets hot and how quickly it cools.
I would say in making a most general statement, thats welds completed on straight polarity would tend to be found mildly harder for the reason of polarity. Amplified by other factors more greatly. Material thickness, travel speed, pre-heat temps. On straight polarity energy spent melting the droplet quicker will be lost in material heating to slow the cooling. If the weld cools quicker it becomes harder. We are talking generalities.
In generalities, and with all due respect, polarity is less of an issue in my opinion than heating and cooling rates when it comes to mechanical and chemical properties on a weld deposit.
Long arc short arc. Long arc welds tend to be hard and brittle. Rapid cooling. It stands to reason that if polarity is looked at from a heating view point, the end of that rod is spitting droplets. And while the power source makes this less an issue with inverter power sources, older DC rectified power sources this would be a noticeable issue. We are in clarity discussing the 6010/7010 electrodes. On a roll, If we for a moment bait the discussion we could ask the question again and substitute 6011/7011 and AC current. What's the issue now to changing weld metal chemical and mechanical properties? Still the same, weld metal heating and cooling.
In generalities, if welder 1 was blazing a root in on straight polarity, he's spraying metal and moving quick and steady. The weld goes in thin, lots of side wall pull and the weld cools quicker. That sample would be harder and offer up slightly higher tensile numbers as a result in my experience. Welder 2, uses reverse polarity, his deposits, slightly hotter, impart greater heat input, takes longer to cool and tensile numbers are lower with a more ductile weld deposit. Both will offer the min. on tensile. One might offer more? Or both might? Was that polarity or heat imput and cooling rates?
It's how I see it. Maybe I need glasses?
It's yeast!
