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Mig Welding

Mig Welding 101

Here is the description of what MIG welding is, and also there are some usefult tips and tricks.
Metal Inert Gas (MIG) welding, also sometimes called Gas Metal Arc Welding (GMAW) is a process that was developed in the 1940s for welding aluminum and other non-ferrous metals. MIG welding is an automatic or semi-automatic process in which a wire connected to a source of direct current acts as an electrode to join two pieces of metal as it is continuously passed through a welding gun. A flow of an inert gas, originally argon, is also passed through the welding gun at the same time as the wire electrode. This inert gas acts as a shield, keeping airborne contaminants away from the weld zone.
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The primary advantage of MIG welding is that it allows metal to be welded much more quickly than traditional "stick welding" techniques. This makes it ideal for welding softer metals such as aluminum. When this method was first developed, the cost of the inert gas made the process too expensive for welding steel. Over the years, the process has evolved, however, and semi-inert gases such as carbon dioxide can now be used to provide the shielding function, which now makes MIG welding cost-effective for welding steel.

Besides providing the capability to weld non-ferrous metals, MIG welding has other advantages:

* It produces long, continuous welds much faster than traditional welding methods.
* Since the shielding gas protects the welding arc, this type of welding produces a clean weld with very little splatter.
* It can be used with a wide variety of metals and alloys.

The primary disadvantages of MIG welding include the following:

- The equipment is quite complex, as MIG welding requires a source of direct current, a constant source and flow of gas, as well as the continuously moving wire electrode. Plus, electrodes are available in a wide range of sizes and are made from a number of metal types to match the welding application.
- The actual technique used is different from traditional welding practices, so there is learning curve associated with MIG welding, even for experienced welders. - For example, MIG welders need to push the welding puddle away from them and along the seam.
- The necessity for the inert gas shield means that MIG welding cannot be used in an open area where the wind would blow away the gas shield.



Since its development in the middle of the 20th century, MIG welding has become commonplace in many manufacturing operations. For example, it is commonly used in the automobile industry because of its ability to produce clean welds, and the fact that it welds metals quickly.

Mig Welding description

Welding Galvanized Steel

Welding Galvanized Steel

Galvanizing has been used to protect iron and steel from rusting for over a hundred years in places as diverse as the wire rope used for the suspension cables on the Brooklyn Bridge to gutters on houses.
Galvanizing is simply coating of zinc over steel. Like paint, galvanizing protects steel from rusting by forming a barrier between the steel and the environment, but galvanizing goes one giant step further than paint -- it also provides electrochemical protection of the steel. Since zinc is electrochemically more reactive than steel, it oxidizes to protect the steel near it; as a result, even if a galvanized steel surface is scratched down to the bare steel, the galvanizing coating will prevent the steel from rusting. Galvanized steel is, therefore, a superior product to steel with any other type of coating on it since it protects the steel even when the coating is damaged in handling or in service.
Welding of Galvanized Products
Welding of galvanized steel is done almost exactly the same way as welding of the bare steel of the same composition; the same welding processes, volts, amps, travel speed, etc. can be used with little modification when the switch is made from uncoated steel to galvanized steel -- unless the zinc coating is unusually thick.
The difference between welding galvanized steel and welding uncoated steel is a result of the low vaporization temperature of the zinc coating. Zinc melts at about 900˚F and vaporizes at about 1650˚F. Since steel melts at approximately 2,750˚F and the welding arc temperature is 15,000 to 20,000˚F, the zinc that is near the weld does not stand a chance -- it's vaporized!
By the time the weld pool freezes, the zinc is gone. This has two immediate consequences:
• The vaporized zinc increases the volume of welding smoke and fumes.
• The zinc at and near any welds is actually burned off by the heat of the arc, removing the protective zinc coating.
Zinc Fumes -- A Safety Hazard?
When zinc vapor mixes with the oxygen in the air, it reacts instantly to become zinc oxide. This is the same white powder that you see on some noses at the beach and the slopes. Zinc oxide is non-toxic and non carcinogenic. Extensive research into the effects of zinc oxide fumes has been done, and although breathing those fumes will cause welders to think that they have the flu in a bad way, there are no long-term health effects. Zinc oxide that is inhaled is simply absorbed and eliminated by the body without complications or chronic effects. Current research2 on zinc oxide fumes is concentrated in establishing the mechanism by which zinc oxide causes "metal fume fever," how its effects are self-limiting and why zinc oxide fume effects ameliorate after the first day of exposure even though the welder may continue to be exposed to zinc during subsequent days ("Monday-morning fever"). Other research3 is being done using zinc oxide fumes together with various drugs which results in a synergetic effect for treatment of cancer and AIDS. Another area of research is use of zinc compounds as the active ingredients in throat lozengers that are recognized as significantly effective in reducing the duration and intensity of the common cold.
Typical “metal fume fever” begins about 4 hours after exposure, and full recovery occurs within 48 hours. The symptoms include fever, chills, thirst, headache and nausea. All of these symptoms, pain and suffering, as well as lost work (and play) time, can be avoided entirely by simply not inhaling the zinc oxide fumes. This can easily be done using any of the methods described later.
Unlike other heavy metals, such as copper, lead and mercury, zinc is an essential micro nutrient. Zinc is essential to the proper growth of plants and animals. Zinc forms part of the enzyme system that regulates biological processes throughout the body. As shown on any multi-vitamin/mineral bottle, the recommended minimum adult intake is 15 mg/day.
The zinc that is generally used for hot dipped galvanized coating has a naturally occurring lead content around 1/2%. Since lead is not soluble in zinc over 0.9%, it cannot exceed 0.9% concentration. This lead may be vaporized along with zinc during welding. Since lead does not vaporize until it gets over 3000˚F, and since some of it is soluble in steel, proportionately less lead is vaporized than zinc; lead oxide fumes, however, should not be inhaled, and the practices recommended below for avoiding inhaling zinc oxide fumes will also prevent inhalation of lead oxides. There is also some concern about residual lead where galvanized products will be in contact with children, such as when it is used on playground equipment without a high-qualify top coating.
Some galvanized product manufacturers use zinc that is 99.99% pure zinc, so the presence of lead is of no concern when welding these products or due to contact. Similarly, galvanized products that have very thin organic coatings or have been chemically treated to improve the adherence of top coatings are welded safely when the practices recommended below for avoiding inhaling zinc oxide fumes are observed.
The successful welding of galvanized steel is so widely accepted that there is very little recently-published mechanical property data comparing uncoated versus galvanized weld properties. The welding industry recognized fifty years ago that welds on galvanized steel and welds on uncoated steel are of comparable strength if the quality of the welds is comparable.
Recent publications on welding galvanized steels deal with weld toughness, porosity control, weld appearance, restoring corrosion resistance and other issues that are much more complex than the strength of the weld.
When using SMAW ("stick") welding, galvanized steel can be welded in the same manner as uncoated steel. When using MIG or flux cored welding, one may have to adjust the voltage slightly to control spatter, and one may have to clean the welding gun of spatter and zinc oxide deposits more frequently that when welding uncoated steel. Hobart makes a flux cored wire called “Galvacore” that some users have had good success with when welding galvanized steel.
When difficulty is encountered welding galvanized steel that was not encountered during welding uncoated steel, it is usually because the Welding Engineer has not accounted for the volume of gas that is evolved by the vaporization of zinc during welding. The thicker the zinc coating, the more fumes are generated, and those fumes have to be able to escape easily into the atmosphere and not be forced through the liquid weld metal.
For example, welding galvanized plates to form a T-joint is a commonly troublesome situation. Since the galvanized edge of one plate is butted against another galvanized surface, the zinc vapors that are formed at the abutting surfaces will not be able to escape to atmosphere easily as the zinc is vaporized. Instead, they will blow into the weld pool, creating porosity or a poor weld surface. This is aggravated when welding conventionally hot-dipped products, since the edges frequently have excessively heavy zinc coatings. One solution is to separate the parts by 1/16 inch using wire spacers or fixtures which will leave a gap for the zinc vapors to escape easily. Other approaches are to use a slight (15˚) bevel on one member (Figure 1), to remove the zinc from the faying surfaces by shearing or mechanically cuting the plate where the faying surfaces will meet, and to abrasively remove most of the zinc from one or both of the faying surfaces (Figure 2). Any of these methods will significantly reduce the amount of zinc between the parts, and this will reduce the volume of gas evolved, improving weld quality.
The welding engineer should also check the welding electrodes which are being used for high silicon levels. Excessive silicon can cause zinc to penetrate the weld metal, leading to cracking, especially when the zinc coating is thick. The silicon in welding electrodes should not exceed 0.85%; this means that commonly used ER70S-6 filler metals should not be used when welding galvanized steel.
Avoiding and Filtering Fumes
The first line of defense in dealing with zinc oxide fumes is welder training. Welders should be taught -- even when welding uncoated materials -- to keep their heads out of the fume plume and to position themselves relative to the air flow around themselves so fumes and dust do not collect inside their welding shields. If a welder finds white dust inside his welding shield when welding galvanized products, he is not positioning himself properly. When welding galvanized products that have thin, uniform coatings and the process is gas-shielded MIG or flux core, the fumes generated are sparse and the shielding gas blows them away from the welder; this is frequently sufficient to avoid metal fume fever without further action.
To complement proper positioning, a fully effective method to preventing inhaling zinc fumes is to wear a suitable respirator (mask). These masks are similar to a painter’s mask; although there are other larger and more complicated masks, these work, while providing minimal interference and discomfort to the welder. The higher priced masks contain activated charcoal which removes some odors as well as the zinc oxide; welders who use these masks frequently wear them even when they are not welding on galvanized steel, since they make the air smell better and they filter out other particulate matter in the welding fume plume.
Masks that are not properly fitted will not be effective in protecting the welder since the zinc oxide can be pulled through any openings between the mask and the welder's face. Welders who are given masks or any other kind of personal protection equipment have to be trained how to adjust them so that they work correctly.
Institute for Occupational Safety and Health; that the equipment selection be based on the hazard to which the welder is exposed; that only employees who are physically capable of doing the job and know how to use the safety equipment are assigined to perform work; that respirators are cleaned and disinfected regularly, stored in a convenient, sanitary location and kept in good repair; that the work area be monitored for changes in exposure; that the medical status of employees is reviewed regularly; and that the program be reviewed on a regular basis to appraise its effectiveness. OSHA does not currently require periodic medical evaluation of employees, but that is under consideration. Disposable masks eliminate some of the hassle associated with meeting these OSHA regulations.
More complex and expensive than masks are the “personal environment systems” in which the welder has air supplied to a loose-fitting helmet and outer shroud which drapes over the his shoulders. Portable fans or compressed air supply filtered air to each welder under positive pressure, keeping any welding fumes out of his breathing area.

Welding Galvanized Steel