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Grahame Collins
20th Jun 2007, 12:03 PM
The Good, The Bad, and The Dangerous
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I hope this information will help to avoid any dangerous situations cause by poor quality welding.Its not all mine .i have cobbled it together with the intention of applying it to the DIY welding sector.It applies to most welding processes --stick- mig etc.

Bad welds are a bit like poor building jobs – they can be disguised, ground up with an angle grinder and covered up with a thick coat of paint. Bad welds are best avoided at the best of times; at worst, they can fail and catastrophically so.
People have been killed because towing hitches or trailer towbars have failed due to poor welding.
Bad welds are unsightly too – something that's hard for anyone to take pride in. That's where the coat of paint comes in handy.

There is good welding and bad welding there's about a minimum of effort 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 thread applies mainly to diy steel fabrication - making something from scratch.
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.baking 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.I find a length of capped PVC pipe a great way to protect and store them. A moisture absorbent packet is a good idea o keep in there as well.

Using damp electrodes will probably result in a fiery arc - you'll recognize this symptom when it arises! The weld metal will be laid down spasmodically. And you'll identify 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.The little spatter balls from the weld arc are culprits here.
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 beneath with an an angle grinder.
Good 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 and clean , but it isn't necessary to use a large spanner to tighten them. Smaller machines may have finger-grip heads on the terminals. Finger tightness is all that's needed.
Electrodes
Proper electrode selection is 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. 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.
Determine the base metal you are working with, and select the electrode accordingly Of course, there are those 'specials' in electrodes, like the Chinese ones. They will look the same is any other better-known ones.they are like everything else some are good ,some are crap.Look for the Euro standards or Llyods shipping codes compliances that the better ones will have them.

Amperage
Success 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.
Some packets of electrodes 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. 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.
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 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 a deeper thickness of the metal.
Arc Length
You'll soon get the feel of the right arc length to use. It will come with practice. The thickness of the core wire is a rule of thumb as an arc length 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' to tile vertical, with the tip pointing towards the weld metal pool. A well-formed bead of molten metal should be formed.

Grahame Collins
20th Jun 2007, 12:05 PM
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 weaved 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.
Inclusions
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. Inclusions are often caused by the above More often however manipulation technique is the major reason for a slag inclusion. Holding the electrode tip too far away from the parent metal during welding reduces the arc force and molecular attraction to the parent metal
Distortion
This is the factor that will cause more unsightly job than anything else. Steel that is normally supplied straight can be easily pulled out of shape by contraction of the cooling weld. Over welding is quite often the culprit. More welding does not equate with a stronger weld. In the amateur field it is a sign of lack of confidence in the quality ones own work
Distortion is 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 home weldment that's created 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 be prevented by
Presetting the metal
Bracing with a temporary brace.
Minimise weld deposits
Use opposing weld sequences


Lack of Fusion
This is a problem that usually manifests itself when the weld is tested by strain or force against it is the likely time of failure. The weld simply parts company with the parent metal
It is caused by too much weld metal deposited without any action being taken to direct( aiming it) the weld metal (electrode or filler wire) at the base metal itself. This problem can be overcome by using the correct rate of travel, the correct amperage and correctly manipulating the electrode
Cracking
Usually cracking emanates from an unfilled crater at the end of a weld bead. The welded structure usually is under some degree stress or strain for this too occur. A cure to this malady is to finish the bead by coming to a stop and counting 1-2-3-4 and the crater is filled.