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Farm Welding - the Good, the Bad, the Disastrous

By Graham J Andrews

Published in Town and Country Farmer

Bad welds are a bit like poor building jobs - they're best covered up with a thick coat of paint. Bad welds are best avoided at the best of times; at worst, they can fail and, with large structures or heavy machinery, prove dangerous.

They're unsightly too - something that's hard for anyone to take pride in. That's where the coat of paint comes in handy.

Good welding and bad welding there's about two minutes difference between the two standards. Obviously, the answer is to avoid bad welds.

Look at the causes of bad welds, both in arc welding and in oxy welding. All bad welds can be avoided, or at least minimised, by understanding their causes and knowing the procedures for good welds.

This article applies mainly to steel fabrication - making something from scratch. Good repairs to farm machinery have been covered in a recent issue of Town & Country Farmer magazine.

Dampness

Electrodes should be stored correctly, and they should be handled carefully.

Arc welding electrodes consist of a metal core surrounded by a coating of flux. With careless handling, the flux can break away from the metal. Striking the arc can be rather difficult; maintaining a smooth arc is just about as difficult. The result of broken or deficient flux coating is a weld that has low strength and poor appearance.

If the flux coating is damaged, use up that portion with the damaged flux on scrap steel until solid flux is reached or, better still, throw out the electrode and select one that's in good condition.

Moist electrodes can wreak havoc with welds too. Moisture is readily absorbed by the flux coating. If you know that your electrodes are damp, or suspect that the coating may have absorbed some moisture, dry them out. Drying them in the kitchen oven warmed to about 110-120ºC for one hour will result in dry and usable electrodes. Storing them in a dry spot will obviously be the best solution to this problem.

Using damp electrodes will probably result in a fiery arc - you'll recognise this symptom when it arises! The weld metal will be laid down spasmodically. And you'll recognise the excess splatter when the weld metal, instead of being laid down in a neat row, ends up all over the base metal.

Steam gets into the weld metal and 'explodes', sending the molten metal in all the wrong places. It just isn't possible to get a smooth, even flow of weld metal with damp electrodes. It will look a bit like the effects of chipping away the edge of a concrete slab with a hammer.

Electrical contacts

A problem that's quite often overlooked, yet is common with arc welding, is improper electrical contact, particularly between the clamp and the base metal. A good contact here is essential. If the contact is poor, the arc will be intermittent or non-existent. The weld metal will be laid down in blobs instead of a neat, straight row. The clamp can look firmly attached to the metal, but any grit, even the size of fine sand, under the clamp can prevent electrical contact. The electric circuit - is not completed, and no welding can take place. It's often useful, when attaching a clamp to the metal, to clean the metal itself to remove grime, grit and other electrical insulating materials to allow good contact, and to rub the clamp itself along the area several times where contact is desired.

Contact between the welder and the leads is essential. Loose terminal connections will be the same as having grit under the clamp. Intermittent electrical contact is assured, with intermittent welding too. The connections should be tight, but it isn't necessary to use a large wrench to tighten them. Smaller machines may have finger-grip heads on the terminals. Finger tightness is all that's needed.

Electrodes

Proper electrodes are essential. There are so many types on the market now, that it's reasonable to assume that one was made for every situation anyone could think of. The 'general' electrodes, such as those rated E6012 or E6013, are that - general electrodes. They have their application in general fields, such as with mild steel fabrication. Some electrodes have applications in different positions; some are good for overhead welds, others are not; others are intended for 'vertical down' or 'vertical up'; others aren't. Using one that's designed for downhand welding in an overhead position will give results that the manufacturers wouldn't be impressed with.

Use an electrode intended for the metal you are using - mild steel electrode for mild steel.- 'special' electrode with 'special' steels; cast iron electrodes for cast iron, and so on. While many different electrodes will give at least some results on many different metals, their effectiveness won't necessarily be consistent. Ascertain the base metal you are working with, and select the electrode accordingly. While it is implied that some electrodes have a 'universal' application, that term might be rather like some 'universal' threads I wasted my money on recently - then the term 'universal' meant they didn't fit very much at all.

Of course, there are those 'specials' in electrodes, like the Chinese ones. They will look the same is any other, but (at least my experience has shown) they deposit metal sometimes, will freak out in the middle of a run, and they aren't as strong as better-known ones. They might be a quarter of the price of good quality electrodes, but they're not much good for anything!

Amperage

uccess is assured (with electrode selection, at least) by not only using the correct electrode for the job, but using the correct size electrode, and with the machine set at the right amperage.

Packets of electrodes (except the Chinese packets) will have the recommended amperage set out on them. As a general rule, the range is large, such as those for the 2.5 mm E6013, which suggests a current somewhere between 55-90 amps, or 90-135 amps for the 3.25 mm electrodes. On thick metals, the lowest recommended setting won't achieve much; on thin metal, the highest setting will probably burn right through the steel. It's best to select a current somewhere between the ranges, and raise or lower the amperage according to trial and error in a particular application, and according to your own competence of welding.

A thick electrode (such as 4.O mm) used on thin metals may require a very high current - a small electrode such as 2.5 mm will be too thin to weld thick plate, such as 2 mm thick. Use electrode diameters according to common sense and, again, your competence of welding.

Practice will soon determine what's best for you and for a particular situation. A low amperage with a thick electrode, or a high amperage with a thin electrode - that is, a current that's outside the recommended range for a particular electrode, will result in a welding job that's far from satisfactory. And it's at harvest time that weaknesses will manifest themselves. Again, mid-point between the recommended range is a good starting point, with an adjustment made either side of that current, if necessary.

If the amperage is too high, weld splatter will mess up the work, and the excessively hot arc will result in a poor quality weld. Any operator will know when the current is too low for a particular electrode - the arc cannot be maintained except with great difficulty. The tip of the electrode will stick to the metal - it will melt just slightly enough to melt it onto the base metal, and there it will remain. With a low amperage, only poor weld metal penetration can be achieved - in other words, the weld metal won't flow through to the full thickness of the metal.

Arc Length

You'll soon get the feel of the right arc length to use. It will come with practice. But too long an arc - that is, one where the tip of the electrode is held a long way back from the base metal being welded, will produce lots of heat, arid on thin pieces of metal, may result in burning through - this despite the fact that the same setting, on the same metal, but with the correct length of arc maintained, will give a good weld. But you will be aware of the long arc; just listen to the excessive crackling, and look for the splatter and the blobs of weld metal.

An arc that's too short will also become apparent. The electrode will become buried in the slag and the molten metal.

Rate of Travel

The speed at which the weld metal is deposited into the join will determine its overall characteristics - such as its appearance and strength. If the rate of travel of the electrode is too fast, the weld metal will be spindly and intermittent; if too slow, the pool of weld metal will soon catch up with the tip of the electrode and prevent the arc from doing its job.

The electrode should be held at an angle of about 15-20 degrees to tile vertical, with the tip pointing towards the weld metal pool. A well-formed bead of molten metal should be formed.

just as poor welds can result from too fast a rate of travel and incorrect amperage in arc welding, too hot a flame or incorrect flame adjustment can cause rather poor quality welds with oxy. Of course, even with oxy-welding, poor preparation is no substitute for good work and good results should not be expected. Proper rods for the job in hand must be used at all times. Avoid excess heat (use enough flame for the job, and no more), and adjust the flame to either a neutral, oxidising or reducing flame, according to the rod manufacturer's specifications. And lay down the weld metal or filler rod it a comfortable rate without build-up or without pushing it ahead too fast.

Undercutting

This cause of poor welding and potential weakness is apparent on a close inspection of the weld. The bead of weld metal should slightly bulge above the base metal. With undercutting, the edge of the weld metal bead will be slightly below tile level of the base metal, and it will be seen to have cut into the edges of the join itself.

The causes of this problem are several, their remedies easy; high amperage, too long an arc (causing too much heat), incorrect angle of the electrode, too large an electrode for the base metal, and incorrect deposition of weld metal, especially with wider joins where the electrode needs to be moved back and forth. But sometimes weaving itself can cause undercutting.

With oxy-welding, excessive weaving of the flame, as well as wrong tip size, and insufficient weld metal being added to the molten pool will result in undercutting.

Intrusions

Impurities that can be entrapped in the weld include dirt, grit, or most commonly, slag itself from the electrodes used. Intrusions can severely weaken a weld and should, wherever possible, be cut out and the join re-welded. Intrusions are often caused by improper preparation of the join, such as failure to maintain sufficient gap between the components being welded, or incorrect bevel of the edges of the join. Even using the wrong electrode can be responsible for this potential cause of weakness.

Distortion

his is the factor that will cause more unsightly welds than anything else. Steel that is straight can be easily thrown out of shape by welding.

It's caused by the weld metal contracting on cooling. All metals contract at a set rate for a given drop in temperature; weld metal that is deposited in the flat position when molten will soon shrink when it's cool. When it contracts, it pulls the base metal out of shape, unless the base material is securely clamped down. A welded precision component of some farm machinery that's to fit exactly in place may not, after being welded, fit into its hole. Distortion can, depending on the job being undertaken of course, be overcome by exaggerating the positions of the base metals being welded. In other words, don't weld the join flat, but build into it a slight offsetting so that when cool, the contracted weld metal will pull the pieces of metal together in their correct, flat positions.

Distortions can sometimes be corrected by heating the weld and then beating it heavily with a hammer. This is a good remedy for removing the frustration caused by the distortion too.

Distortion can be even greater when oxy-welding. Intense localised heat is built up due to the welding process; because this heat is unevenly distributed - there will be relatively cool areas of metal, and some very hot sections some parts of the piece of metal will expand a great deal, other parts perhaps very little. One solution here is to preheat the whole of the base metal before oxy-welding it - if this is at all practical. A better solution may be to use arc welding if this is possible.

Improper welding sequences can cause distortions, particularly in large sheets of steel. With oxy-welding, even, it may be impractical to pre-heat the whole sheet of metal. Rather, it would be advantageous to weld in small runs in one direction, then change the direction of the weld for another small run. Use intermittent welding, and skip sections of the join, and step back. This is preferable to laying down one very long run of weld metal, whether with arc or oxy equipment. Altering the direction in which weld metal is deposited will certainly help to overcome distortions, even if it can't eliminate it altogether.

Lack of Fusion

This is a problem that usually manifests itself when the repairs are back in place on the machinery. Again, harvest time is a good time to locate poor-fusion welds!

They're caused by the deposit of too much weld metal without any action being taken to direct the weld metal (electrode or rod) at the base metal itself. This problem can be overcome by using the correct rate of travel, the correct amperage and correctly using the electrode; with oxy-welding, the use of the right size rod with the proper tip for the job in hand will help.

Cracking

Cracks in welds can occur at almost any time - for example if the base metal was clamped too tightly as it was being welded, preventing any 'give'; it can be caused by using damp electrodes, or too high a current, or by slag entrapment, or by using too large an electrode for the base metal, or too slow a rate of travel, or too low a current. And many other causes. Often the crack can be extremely small. If tack welds are not sufficient for the job, they can crack, and here experience will show that the cracks can barely be seen.

Really, good welding isn't at all as difficult to achieve as it's made out to be. Really.