root gap needed for 3mm Mild Steel butt joint?

[L'Andy]

I've had a look through the various thread and tutorials but can't find an answer to my query.

I'm welding up some wheel arches on my trailer using 40x40x3 Angle. Trying to use my new Inverter MMA (Parweld XTI-160 from Weld-equip). I can make a nice looking weld but with little penetration. Using 2.5 and 3.2 rods tried various amp settings. Wedling on the bench horizontally.

Should I be leaving a root gap? I didn't think I would need to at this thickness. If I do need a root gap, how much?

I imagine my technique leaves a lot to be desired! I normally MIG weld but have decided that if I ever want to work with anything thicker than tin then I need to learn MMA. I've had an ancient AC welder in my workshop for years that I had limited success with so finally decided to treat myself to a slightly more modern piece of kit.

Thanks for any advice in advance

 

[zzr1200]

Is the electrode connected to the +ve or -ve, what brand/make of rod (e6013?), ampage setting are you using and are you butting the angle up tight together or leaving a small gap???

 

[L'Andy]

rods- arcweld 6013

supply +ve

amps- 2.5 60 to 100
3.2 vary 80 to 100

Gap- well thats my question really. I've tried butting up and leaving small gap, neither of which seem to make a big difference. So I can only conclude it is my technique rather than the equipment.

But, should I need to leave a gap, and if so, how much?

I know I could MIG weld them no problem and would put a slight bevel edge and 1mm gap on the joint. I just feel it would be a good exercise to do it with MMA.

I will keep trying and post some photos of the results later.

 

[zzr1200]

Try grinding a small 'v' prep on the edge of the angle iron plus leave a 1mm gap, or change the electrode to -ve, but don't try both together.

Work on 40 amps per mm rod diameter approx, your 2.5mm are about right, try upping the 3.2mm 140amp max.

And are your rods dry???

 

[FranV8]

I find if I'm going for a straight prep with TIG, I need a 3mm gap to get full penetration. Vee prep as suggested before would be the best answer though.

 

[L'Andy]

Try grinding a small 'v' prep on the edge of the angle iron plus leave a 1mm gap, or change the electrode to -ve, but don't try both together.

Work on 40 amps per mm rod diameter approx, your 2.5mm are about right, try upping the 3.2mm 140amp max.

And are your rods dry???

So I can use 6013 rods -ve? worth experimenting.

Are my rods dry? Seem dry. They are stored in the open cardboard boxes that they came in, on a mid shelf in an unheated but well ventilated workshop. I didn't think that there was any special storage considerations for 6013's; should I consider storing them in a closed container with a dessicant? I don't do much MMA so they will probably be sat on the shelf for a few years before I use them all up, so it might be a good idea anyway.

One other thing that occurs to me is that the rod holder is a bit cheap and nasty; its the 200amp clamp type and the rod can move in it a bit. Think I'm going to swop it for the one on my old Arc welder, tighten handle to clamp type.

Ultimately I think I need to work on my arc length. I also think I may be being a bit unrealistic thinking that MMA is upto to job at hand, especially considering my skill level. It's only thin stuff and by the time i've tacked in place, I'm only laying a 30-35mm long bead.

 

[zzr1200]

The DC arc has a combined arc temperature of 6000 deg C (4000c on the +ve and 2000c on the -ve) if the electrode is connected to the +ve the electrons travel from the "job" (-ve) to the welding rod, heating up as they cross the arc.

The higher temperature (4000c) causes the rod to melt faster than if it was connected to the -ve (2000c), as the "job" is at 2000c the weld pool is shallower and wider. If the electrode is -ve (2000c) there is less filler burnt off the rod and the weld pool is hotter (4000c), narrower and deeper.

Hence the reason for my suggestion regarding only changing one thing at a time, plus why rod manufacturers state +ve or -ve polarity for their rods.

Check out page 8 on the link below although this is for a tig arc the same basic electrical conditions apply to a dc stick arc, the only real difference is the source of the shielding gas and the source of the filler material.

http://www.r-techwelding.co.uk/Downloads/TIG-WELDER-OWNERS-MANUAL-ACDC-DIGITAL.pdf

Also having damp rods will always effect the weld in some way, just depends on how damp/wet the rods are and the type of rod.

As to welding your angle iron its all down to, practice, practice, practice and even more practice.

hth

 

[rich r]

Try laying a line of weld on some scrap metal with one of your 6013 rods on your AC welder. You should be able to put down a nice neat run at 80A with a 2.5mm rod. Then do the same with your DC welder to see what difference electrode +ve and -ve makes to how the weld pool behaves and compares to AC (where the polarity is obviously swapping 50 times a second)

If you can't lay a neat run on clean, flat metal then practise, practise, practise I know everyone says it, but it's true! Some people pick up the knack of arc welding in a few hours, then refine their technique from there. Some people have to work really hard to get it working for them but in the end it suddenly clicks and becomes natural.

You might want to dry your rods out - in an open box in an unheated workshop they will almost certainly have absorbed some moisture. Just put them in a low oven for a bit.

 

[Alexa]

Angle iron welding. Full versus partial penetration.

"... Try grinding a small 'v' prep on the edge of the angle iron plus leave a 1mm gap, or change the electrode to -ve, but don't try both together. ..."

=====

L'Andy.

You might consider welding out the wheel arches before fitting them up to the trailer frame. In that case you would have access to both sides of the angle iron. Tack welding the angle iron pieces, and then welding first the side of the angle iron that you will not be able to grind. Then go to the opposite side of the joints, grind down to the slag, and weld out them out. Then grind if necessary.

If you do not need a full penetration weld for mechanical strength, as an alternative, consider preparing only a partial penetration joint. You would weld both sides of the joint and not clean out the slag, between them. For corrosion resistance it would be comparable to the full penetration weld.

If you want to only weld from one side, then slightly prep as recommended zzr1200 and weld the joint in two or three passes depending up your rod diameter.

Alexa

 

[L'Andy]

You might consider welding out the wheel arches before fitting them up to the trailer frame. In that case you would have access to both sides of the angle iron.

I am going to pre fab the arches on the bench, so can get to both sides. I was just a little suprised that I should need to weld on both faces; I was assuming that I should be able to get full penetration with a 3.2 rod (or even a 2.5) from one face. I think must be my technique that it at fault, as I think I should be getting full penetration. With some of my last attempts I nearly got full penetration. Unfortunately due to it being mother's day I ran out of time to play yesterday and won't get chance to have another play until later in the week. Oh and it doesn't help that the workshop is currently colder than my fridge really demotivating

I may be being a bit picky, as the welds will not even be under that much stress, so could get away with partial penetration and one face won't even be seen. I'm really using it as an excuse to practice, so I want to get it right.