Arc length
Variable 2 is arc length. A rough guide keeps the arc just shorter than the core wire diameter, i.e. about 0.08" (2mm) for a 3/32" (2.5mm) rod. But this is not a fixed relationship.
Keep your ears and eyes open during work. A good arc has a clear, bright area under the rod tip, and is bordered by a semi-circular curtain of molten slag behind (1.24 B). You’ll know when arc length is right, for its noise hardens from a soft, fluttery sound (arc too long) to a crisp crackle as the right length is found. A good-length arc sounds much like the sizzle of breakfast frying in the pan. When the arc’s too short the rod dips in the molten slag and everything goes quiet, arc light dims and slag wants to run round in front of the tip. This is a perfect scenario for producing slag traps (page 30).
As your confidence grows, arc length can be used to control slag. If you see a violent swirl starting to develop in the slag just behind the rod tip, a trap is imminent: lengthening the arc a little can save the day. But be careful, for an arc that’s too long can itself produce a trap: filler metal lost as spatter means the weld pool isn’t properly filled, so slag gets in instead. This is a common problem in fillet joints, where filler metal can take a shorter path to the vertical and horizontal parent plates. Experimenting with arc length (while keeping the other three variables right) is the best way to get a handle on what’s happening.
1.25 Rod angle during work has a big effect on fusion, penetration and slag trap production. A and C lead to problems, whereas, like Goldilocks’s porridge, B is just right.
Rod angle
Variable number 3 is rod angle, which affects both fusion and penetration (1.25 A-C). Too shallow an angle (C) lets the arc push weld metal along the work’s surface, so there’s not much chance of good fusion or penetration. But too steep an angle risks molten slag running round the rod tip to interfere with the arc, causing slag traps (A). The right rod angle (B) steers between these possibilities.
For work on the flat, an angle of about 70º is right. Some electrode holders come with angled grooves in the jaws. If you put the rod in these and keep the holder’s handle parallel with the work, then the electrode angle won’t be far out for downhand jobs – flat on a bench.
It’s usually best to keep the electrode centered laterally over the joint. Angling the rod toward one plate or the other puts more heat into that plate, which is generally bad for balanced fusion. But deliberately aiming the rod to control heat input can be useful, as when welding thin sections to thick ones - see page 26.
Some rods tolerate operation outside normal limits better than others. So experiment with the rods you use, looking and listening as the angle is changed.
1.26. Going too fast (A) gives no time for fusion or penetration. Travelling too slowly (B) lays down too much metal and the extra heat adds to distortion. Travelling at the right speed leaves a bead that’s about twice as wide as the rod’s core wire (C).
Speed of travel
The final variable is speed of travel. How fast is fast enough? 1.26 shows the differences. Hacking along the joint at a rate of knots (A) leaves no time for weld metal to be deposited and so the bead is stringy and very weak. Travelling too slowly (B) takes longer, wastes rod, increases distortion by increasing heat input and leaves a large humped deposit. But moving along at the right speed (C) leaves a neat, even bead roughly twice as wide as the electrode core wire, i.e. a 5/32-0.2" (4-5mm) deposit from a 3/32" (2.5mm) rod.
Varying your welding speed during a run is bad. Look closely at 1.26 A and you’ll see that even in this acceptable weld, the bead necks down in places along its length. This shows that the speed of travel was not constant. In the fast sections the weld thins out, varying joint strength; surface ripples pulled into Vee-shapes are a giveaway. When welding try to imaging you’re a machine, geared always to travel at a set speed down the joint.
Generally, first-time welders use too little current, work too fast with too long an arc and tend to let rod angle drop during a run until it’s too shallow.
MAKING THE WELD 1
Keep it clean
Now to join some metal. Step one is clean before you weld. Never mind the italics: that should be written in letters of fire. Agriculture produces a fine range of contaminants, ranging from rust and paint to oil and dung. None of these need actually kill the arc to compromise ultimate joint strength: the inclusions or weakening pinholes they leave behind are enough. So sort out contamination before you begin… no matter what the electrode salesman says.
And if preparation isn’t thorough? Rust on the weld area will turn into brittle, weak iron oxide particles in the joint. Grind off (or flame clean/wire brush away) all rust, over and around the weld area.
Paint, oil and animal outfall all vaporize under the arc, leaving blowholes in the weld varying in size from the invisible to the substantial. Normally a run round with the angle grinder is enough to clear crud. But on jobs where oil or other stuff has really penetrated (like an old oil-containing casting) it’s often necessary to make a first run to draw out contamination, then grind that away and weld again.
Whatever the contamination, clean an area about 2" (50mm) wide on either side of the joint. That seems a lot, but it’s the best way to minimize fuming from paint or plating. Grind galvanized steel until it sparks bright, showing that all the plating has gone. Joints should get a lick of paint afterwards, so all this generous preparation won’t be wasted.
We’ve already mentioned metal platings, but they’re serious enough to re-run the subject. Look out for the dull yellow finish of cadmium plating and grind all traces of it away, as heavy metal fumes are really nasty. The zinc in galvanizing makes a mess of a weld, and the dense blue-white smoke produced does you no good at all. Where there’s a risk of fuming, invoke nature’s free ventilation by working in moving air. Indoors, use a fume extractor or the appropriate respirator.
Clean Deviation
A quick philosophical point. To what extent is on-farm welding concerned with ‘ultimate strength’? Such a thing comes only from thorough joint preparation, intelligent rod selection, appropriate plant setting and a high level of operator skill. Top-line work is the province of the trained man working to industrial standards. Lesser mortals don’t have the training or the practice, and may not have the basic hand/eye coordination of a fine welder.
But making a long-lasting, safe job is within most people’s reach. And good preparation is the cornerstone on which such things are built. So go ahead – invest time in removing crud and aligning parts, in grinding and cleaning. It’s always time well spent.
MAKING THE WELD 2
Get set up
Now look to preparing the joint metal itself. Overstating the importance of this stage is hard, but still it’s often skimped on. Think on the following for a moment:
Any joint must be welded to full depth to duplicate the original material’s strength.
So if you’re talking butt joints (i.e. two plates laid side by side to be joined by their edges), welding to full depth almost always involves some sort of edge preparation. That is, cutting or grinding away the edges to let the weld get to the bottom edge