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Understand the process of shielded Metal Arc Welding.

Date:Mar 1,2016

Understand the process of shielded Metal Arc Welding. An electric arc is formed at the tip of the welding rod when a current passes across an air gap and continues through the grounded metal which is being welded. Here are some of the terms and their descriptions used in this article:

Welding machine. This is the term used to describe the machine which converts 120-240 volt AC electricity to welding voltage, typically 40-70 volts AC, but also a range of DC voltages. It generally consists of a large, heavy transformer, a voltage regulator circuit, an internal cooling fan, and an amperage range selector.The term welder applies to the person doing the welding. A welding machine requires a welder to operate it.
Leads, or Welding leads. These are the insulated copper conductors which carry the high amperage, low voltage electricity to the work piece that is being welded.
Rod holder, or stinger is the device on the end of the lead that holds the electrode, which the person welding uses to accomplish the welding task.
Ground and ground clamp. This is the lead that grounds, or completes the electrical circuit, and specifically, the clamp that is attached to the work to allow the electricity to pass through the metal being welded.
Amperage, or amps. This is an electrical term, used to describe the electrical current supplied to the electrode.
DC and reverse polarity. This is a different configuration used in welding with an arc/electrode system, which offers more versatility, especially in overhead welding applications and for use welding certain alloys that do not weld easily with AC voltages. The welding machine that produces this current has a rectifier circuit or has the current supplied by a generator, and is much more expensive than a typical AC welder.
Electrodes. There are many specialized welding electrodes, used for specific alloys and types of metals, such as cast or malleable iron, stainless or chromoly steel, aluminum, and tempered or high carbon steels. A typical electrode consists of the wire rod in the center covered with a special coating (flux)which burns as the arc is maintained, consuming oxygen and producing carbon dioxide in the weld area to prevent the base metal from oxidizing or burning away in the arc flame during the welding process. Here are some common electrodes and their uses:
E6011 electrodes are a mild steel electrode with a cellulose fiber coating. The first two numbers in the electrode identification is the tensile strength, measured in pounds per square inch times 1,000. Here, the yield of the electrode would be 60,000 PSI.
E6010 electrodes are a reverse polarity electrode, commonly used for welding steam and water pipes, and are particularly useful for overhead welding, since the metal holds its position while in a liquid state, being drawn into the molten weld pool by the flow of the direct current from the electrode to the workpiece.
Other specific purpose E60XX electrodes are available, but since E6011s are considered a standard, general purpose rod, and E6010s are considered the standard for reverse polarity DC welding, they will not be covered in detail in this article.
E7018 electrodes are low hydrogenflux coated steel rods, with a high yield tensile strength of 70,000 PSI. These are often used in assembling structural steel used in the construction industry, and in other applications where a strong filler material and higher strength weld is required. Note that, although these rods provide greater strength, they are less forgiving in respect to achieving a clean, high-grade weld at incorrect amperages and with dirty (rusted, painted, or galvanized) steels. These electrodes are called low hydrogen due to every attempt to lower the hydrogen content. These electrodes must be stored in an oven with a temperature between 250ºF and 300ºF. This temperature is above the water boiling point of 212ºF at sea level. This temperature keeps the moisture (dew)(H2O) in the air from collecting in the flux.
Nickel, Castalloy, Ni-Rod electrodes. These are special rods made for welding cast, ductile, or malleable iron, and have more yield, to allow for the expansion and contraction of the iron material being welded.
Dissimilar metals rods. These rods are made from a special alloy and give better results when welding tempered, hardened or alloyed steels.
Aluminum rods. These are a more recent technology and allow arc welding aluminum with a conventional welder, rather than using a special gas-shielded wire feed welder like a MIG (metal, inert gas) or TIG (tungsten, inert gas) welding machine, often referred to as heliarc welding, since helium was the gas used to shield the arc flame while welding. The official names created by the American Welding Society (AWS)for this arc type welding are Shielded Metal Arc Welding (stick), Gas Tungsten Arc Welding (tig)and Gas Metal Arc Welding (mig).
Electrode sizes. Electrodes come in a variety of sizes, measured by the diameter of the metal center of each rod. For mild steel rods, a diameter range of 1⁄16 inch (0.2 cm) to 3⁄8 inch (1.0 cm) is available, and the size used is determined by the amperage of the welder, and the thickness of the material being welded. Each rod performs best at a given amperage range. Selecting the correct amperage range for a given size rod will depend on the base material and the desired penetration, so specific amperages will only be covered for the welding described further in this article.
Safety equipment. A critical part of welding safely is having, and knowing how to use, the correct safety equipment for the job. Here are some typical items that are required for welding safely.
Welding shield (hood). This is the mask which is worn to protect the person welding from the bright flash of the arc, and from sparks being thrown during welding. Standard arc welding lenses are tinted very darkly, since exposure to the arc flash can cause flash burns to the retina of the eye. A level 10 darkness is the minimum for arc welding. Welding hoods with a flip up lens was once preferred, as the dark lens can be lifted up, and a separate clear glass lens will protect the welder from bits of slag while the weld is chipped. The newer self darkening welding shields are the most desirable welding shield now sold. These welding shield lens are very light colored for grinding and torch cutting. When an arc is struck the automatic self darkening lens will change to a preset #10 shade. Even newer on the market are the variable shade automatic self darkening lens.
Welding gloves. These are special, insulated leather gloves that reach about 6 inches (15.2 cm) above the wrists, and protect the hands and lower arms of the welder (the person welding). They also provide limited protection from accidental shock if the person welding comes into contact with the electrode accidentally.
Welding leathers. This is an apron like leather jacket that covers the shoulders and chest of the welder, used for overhead work where sparks might ignite the welder's clothing, or cause burns.
Work boots. The person welding should wear at least a 6 inch (15.2 cm) lace-up type boot to prevent sparks and hot slag from burning his feet. These boots should have insulating soles made from a material which does not melt or burn easily.

TypeInfo: Industry News

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