1.13. A good habit to cultivate. Laying the electrode holder in your mask or on something insulating (wood is good) means you know where it is (!) and lowers the chance of accidental arcing. Give gas cylinders a wide berth with the electrode, as accidental contact and the resulting arc could be terminal. It follows that chaining gas cylinders to a metal welding bench is not a bright idea.
Inverter sets (d) use electronics to do away with heavy transformer windings, so can be very light for their output current. This makes them ideal for site work or machinery field repair. But the circuits in some designs are easily fried by sustained over-voltage or sharp voltage spikes, both of which mobile generators can produce. As a rule of thumb, an inverter should only be paired with a generator whose capacity is at least 1.5 times the set’s power requirement. For example, a set drawing 5kVA when delivering maximum welding current should only be used with a generator able to deliver at least 7.5kVA. If in doubt, check this with the set’s supplier – better safe than sorry.
An inverter’s electronic control lets the designer add sundry operator-friendly features. These can include:
• Hot starting. To help the arc to start and to boost initial fusion, the welding current is increased automatically for a short while as the arc is struck.
• Anti-stick. If the rod sticks to the work, the set senses the sudden sustained rise in current draw and cuts off after two or three seconds. Saves a lot of agitated hopping about.
• Arc force. The less experienced (or more knackered) the operator, the more arc length varies during a run. The power supply spots the rise and fall in current, and within limits compensates for them. Input current is thus steadier, minimising changes in fusion and penetration and boosting weld quality. This ‘active’ compensation goes beyond what’s provided by a normal, non-electronic SMAW power supply – see pages 37-38.
1.14. Small things can turn out expensive. Clipping the return lead to a bearing housing (A) forces current through ball or roller contact patches (B) on its journey round the circuit. If these burn and/or develop flat spots, the bearing turns to junk. The thoughtful operator also works out how far gas or weld heat is likely to travel: bearing seals are easily cooked.
1.15. Early alternators could be damaged by welding’s relatively high voltages, though modern versions have inbuilt protection. If in doubt, disconnect the battery and alternator before welding on a machine or anything attached to it. Where there are electronic control systems (modern tractors, combines, self-propelled foragers and so on) disconnect the battery and ideally take out any plug-in modules. Alternatively connect a spike catcher (inset) across the battery to damp out surges. Automotive factors stock them.
1.16. How many potential nasties can you spot here? Answer at the foot of page 19.
1.17. Rods from major makers carry full information on the packet and/or product listing. Be sure to check the materials the electrode can weld and the required OCV.
Photo courtesy of ESAB North America.
Find a good specialist supplier and buy mild steel rods from a major maker like ESAB, Murex, Oerlikon or Eutectic. Minor brands can be good (and are usually produced by one of the big makers anyway), but starting with a big-name brand is always a sound idea. The rod packet should list all the info needed to work with the rod (1.17).
Stock up on sizes 3/32, 1/8 and 5/32" (2.5, 3.25 and 4.00mm), adding a pack of 1/16" (1.6mm) ‘sparklers’ if sheet steel work is intended and you don’t have gas or MIG – though these very small rods can be unexpectedly expensive. If vertical down welding is to be done, make sure that the rod flux produces fast freezing slag – see page 31.
For welding anything other than mild steel, check your set’s OCV capability before discussing rod choice with a welding supplier. Firms usually give advice freely, along with lists of electrodes and their applications. As mentioned earlier, ‘dissimilar steels’ rods cover most agricultural eventualities. For instance, some will weld steels of varying carbon content, low alloy and spring steels, ferritic and austentitic stainless steels to themselves…and to each other. And as dissimilar steels rods are relatively hard, most can be used as a ‘buffer’ layer between mild steel and a hard-facing layer, reducing the risk of dilution which can cause the expensive top coat to crack and flake away.
Buy specialist rods only when required, as they’re expensive. Low hydrogen electrodes are a hassle. In non-critical work, dissimilar steels rods will probably cope anyway and are far less trouble to store and use. Cast iron is a law unto itself and needs dedicated rods and technique – see page 103. Building up worn parts or laying hard metal on new soil-engaging bits calls for specialized hard-facing consumables. Tell your rod supplier the application and he’ll recommend something appropriate.
Watch Out
Time to say it again: the cardinal rule is ‘Be cautious’. If in doubt over rod selection or technique, let a specialist do the work. It may be more expensive…but then DIY can sometimes end up very costly in unexpected and unpleasant ways.
Finally, a word on rod storage. Keeping rods in their original packet means you hang on to the information. Although good-quality mild steel rods can survive all year round in the workshop if they must, eventually the damp will get to the coating so it’s best to keep them dry. An old fridge, modified so the bulb always burns, is good. And at least you’ll know the answer to the old question: what happens to the light when you shut the fridge door?
BUILD
Good Technique 1:
Getting Started
Until you get the knack, striking and holding an arc can have you tearing out hair. But there’s a simple way – scratch, tap and lift.
With the right current dialled in on the set, SCRATCH the rod tip near the joint to get it hot. Current flows easier from a warm tip. Be positive with the scratching; use a wide sweep that generates showers of sparks.
Bring the rod quickly into position over the weld area, and in one smooth movement TAP it down and LIFT it just a little (1.18 and 1.19). The arc will establish during the lift and you can weld on.
1.18. Getting the arc started is easier if you warm the tip by scratching it on a plate. A generous sweep (arrow) produces the best effect.
1.19. To