So that’s a fine list of dos and don’ts. But most of it is common sense – try picture 1.15 (page 17) as a test.
1.11. Whether you’re using fume extraction or not, work out of the rising column of smoke.
Self tune-up
In welding (as in life) it’s bad to be tense. Relaxation is central to good control. There are two schools of thought on how to achieve it – either support yourself so only your welding arm needs to move, or develop freestanding control in a legs-spread position (1.12). The first is easier, the second helps you work when there’s nothing to rest on.
Occasional welders prefer the first option. Lean on the bench or machine. Take the welding lead’s drag off your welding arm by pinching the cable between hip and bench or draping it round something handy – but before you do, make sure the cable’s insulation is 100%. A flip-down visor leaves your second hand free to steady the welding arm. Whichever strategy you choose, don’t grip the electrode holder tightly; it’s a sure way to produce wobbles at the rod tip. Try relaxing that iron grip during work and see how control improves!
1.12. A wide stance helps electrode control.
Don’t convert - invert
Traditional power supplies need big, heavy transformers to handle the substantial welding current flows. Inverters stand this notion on its head.
An inverter takes a 60Hz, 230/240V AC supply, rectifies it to DC, and then uses a transistor bank to produce square-wave AC at 8,000-40,000Hz. At these very high frequencies a small transformer can handle the conversion to low voltage/high current welding power, so the physical size and weight of the set can drop dramatically. After transforming, welding-level AC power is rectified back to DC for output, or modified and used as AC. Electronics carry out and control the processes on either side of the transformer, allowing waveforms to be tailored closely to different welding requirements and the set to react very rapidly to changes.
Which rod?
There’s no shortage of electrodes to choose from, varying in core wire make-up, diameter and flux type.
Core wire must match (or be compatible with) the metals to be joined. If you’re not sure on this, ask a welding supplier: your local agricultural dealer may or may not know the real answer.
Mild steel needs a mild steel electrode, fancier stuff needs fancier rods. Be aware that it’s a waste of money using a tough, expensive alloy steel electrode to join mild steel in the hope of getting a stronger result. If the rod is matched to the material and your welds are still failing, then your technique is at fault.
Wire diameter. The narrower the rod, the smaller the arc and the smaller the heating footprint it makes on the metal. Thus thin section steels need skinny rods if arc heat isn’t to burn straight through them. Fusing thick sections needs more heat – a bigger arc from a thicker rod.
While you’re learning, practice with 3/32" (2.5mm) diameter rods. Their short length and small weld pool are relatively easy to control. They’ll do for one-pass welding up to 1/8" (3mm) and can be used for preliminary runs in heavier stuff. As joints get bigger, move up to rod sizes 1/8" and 5/32" (3.25mm and 4mm). These three diameters cover the majority of farm work.
Note: when talking about the capability of a rod or set, thickness refers to the weld’s throat depth – not the thickness of plate that can be joined! (See 1.31).
Flux covering is decided by electrode type and application. Most general-purpose mild steel rods have a flux based on the mineral rutile, with other ingredients to improve arc stability, reduce moisture pick-up in storage and generally make them more sociable to use.
Cellulosic coverings enhance penetration, and are on rods designed for specific purposes like vertical down work and pipe welding.
Low-hydrogen coatings appear on rods intended for high-strength alloy steels, possibly also for service at low temperatures. Very sensitive to moisture content, rods with low-hydrogen coating must be baked before use.
Other electrodes add iron powder to their flux, which bulks the volume of weld metal laid down when compared with normal rods.
So which of this lot do you go for? In practice, rod selection for general farm use is pretty straightforward.
Buying a SMAW Set
Most farm jobs can be handled with 180-200A maximum welding current, which is achievable from a single-phase set. Such units allow mobility around the holding and can be powered by a generator, though some inverters may not like a generator’s potentially spiky output – see below. Higher-output welding sets are more bulky, harder to move and usually need a three-phase supply, though work well within themselves at normal currents.
Oil-cooled, copper-wound units are designed for continuous use, running as long as needed on full blast. A typical AC model has 50V and 80V output lines, allowing most types of electrode to be used (a, left and right terminals). These open circuit voltages (OCVs) are explained on pages 19-20.
Some SMAW sets are fan cooled (b). When the windings get too hot a thermal trip shuts the set down, then after a while it comes back to life. The Murex example shown produces DC output which makes for a consistent and very controllable arc, but it’s more expensive than the many AC alternatives.
The simplest air-cooled sets (c), have no fan, which means a shorter operating period before automatic shut-down and a longer wait before restarting. Consequently, they tend to be DIY items. Although these basic sets can produce acceptable work, the arc is generally not particularly consistent or smooth-running.
A set’s duty cycle should be checked before buying. It’s the length of time within a ten-minute period that the unit can operate at the current quoted. So a duty cycle of 60% at 150A means the set will run for six minutes in ten at 150A. At lower currents it’ll run for longer. The higher the duty cycle, the longer work can go on without the set shutting itself off – important where a lot has to be done.
Three alternative sets, each giving different periods of operation. The oil-cooled, copper-wound set (a) is designed for continuous use: it’ll run as long as needed on full blast. The AC output model shown has both 50V and 80V output lines (bottom, left and right) giving flexibility over electrode type usable; these are open circuit voltages or OCVs.
The fan-cooled set (b) has vents for forced-air passage. It’ll run until its windings get hot, then a thermal trip operates. After a short cool-down period it comes back on stream. This Murex example produces DC output which makes for a smoother-running arc, but it’s more expensive than the AC alternative.
Very common on farms is the simple air-cooled set (c), which is quite capable of producing acceptable work. There’s no forced-air cooling, which means a shorter