The electrodes used in MIG welding are wires (or threads) of two types:
- Solid (or solid) wires
- cored wires
Although solids are the most used, partly due to their lower cost, the decision for one or another type will be subject, fundamentally, to the base metal and thickness. The solid wires They are indicated for low carbon steels, they do not leave slag on the cord and the cooling is fast, so their main application is thin materials. The tubular wires they behave similarly to coated electrodes. They consist of a metal casing and a hollow interior filled with a granular flux powder, metallic powder or a mixture of both, which provides alloying elements to the weld bead. They leave slag on the bead and therefore cooling is slow, which is an advantage when working with thick materials.
Both types are generally marketed in diameters of 0.8 / 1.0 / 1.2 and 1.6 mm and are available in coils of varying sizes. It is also common for the wire to have a copper coating, not only to protect it from oxidation, but also to facilitate electrical contact with the nozzle and reduce friction.
Within each type of wire There are a variety of classifications, depending on their composition, the shielding gas used, and the application. Let’s look at this information in detail.
1) Solid or solid wires (GMAW welding)
In general, the composition of the solid wires is very similar to that of the parent metal to be welded, to which variable amounts of deoxidizers, depending on the application and shielding gas.
The most common deoxidizer is silicon, to which small percentages of various metals are added to improve mechanical properties or corrosion resistance. The wires Those with the highest levels of deoxidizers are generally more suitable for CO2 welding because they prevent pinhole formation.
a) Wires for carbon steel
Most of the carbon steel wires are listed under an American Welding Society (AWS) designation of the type ER 70 S-x (imperial system), where:
AND: electrode
R: filler rod
70: minimum tensile strength expressed in thousands of pounds/square inch (psi)
yes: solid
x: digit that represents the chemical composition of the electrode, can be “2”, “3”, “4”, “6” or “7” and corresponds to variable amounts of carbon, manganese and silicon, in addition to fixed amounts of phosphorus, sulfur, nickel, chromium, molybdenum, copper and others.
The properties of each wire, according to this last digit, are as follows:
ER70S-2 wire: it does a good job of welding with C-25 gas (75% argon + 25% CO2), even on rusty steel. Of the entire series, it is the only one that contains titanium, zirconium and aluminum, in addition to all the elements mentioned above. Its main drawback is that it lacks fluidity, the puddle (or pool, or pool of molten metal) does not tend to move laterally and may not stick properly on heavy materials.
ER70S-3 wire: it is one of the most common and least expensive MIG wires, with more deoxidizers and a more fluid puddle that forms a wider bead. It has been used successfully for years in automobiles, agricultural machinery, and household appliances.
ER70S-4 wire: it is a medium priced wire, suitable for almost all steel welding. It offers good flow and better arc characteristics than E70S-3, but has more spatter and is used on structural steel, ships, pipes and boiler vessels.
ER70S-6 and ER70S-7 wires: they are the best performing and highest cost wires, and the ones with the highest levels of silicon and manganese as deoxidizers. They are suitable for welding almost all steels, from thin carbon steel to 1/2-inch plate (with the appropriate wire diameter), work with most commonly used gas mixtures, and have good puddle flow. Its applications include the manufacture of bodies, furniture, fire extinguishers, pressure vessels and pipe welding, among others.
For welding stainless steel you can use the wires mentioned. However, for better corrosion resistance, they should be used. stainless steel wires. There are various alloys of stainless steel. One of the most common varieties is type 304, but the most suitable is the ER308, with variations of increasing silicone content in the types ER308L Y ER308LS. Applications for these wires include: food and chemical processing and storage equipment, corrosive chemical tanks, pumps, heat exchangers, and others.
b) Wires for non-ferrous metals
Non-ferrous metals require different wires. For the aluminum weldingFor example, you need a aluminum wire. There are many aluminum alloy wires and mixtures of various metals, including:
ER-1100 and ER-4043 wires: Primarily used with argon and helium, as well as other commercial gas mixtures, and are ideal for welding thick plates and castings. The main industries that use this type of wire are food, dairy and refrigeration.
ER-5356 wire: With 5% magnesium, this wire works in most situations. Its high tensile strength makes it suitable for the manufacture and repair of rolling-type fuel tanks.
2) Cored wires (FCAW welding)
The materials in which they are used cored MIG welding wires They are, commonly, carbon steels, low alloy steels, stainless steels and cast iron.
The cored wires for carbon steel they are also classified in a series of numbers and letters, according to the mechanical properties of the weld deposit. A typical example of classification based on the imperial system is E 7 1 T – 1 C/M, where:
AND: electrode
7: minimum tensile strength of deposited metal, multiplied by 10,000 psi
one: welding position; can be “0” or “1”. The “0” indicates flat and horizontal position; the “1” indicates any position.
T: tubular
one: indicates the proper use of the electrode, in terms of polarity and general operating characteristics. It can be from “1” to “14” or the letters “G” or “GS”. The letter “G” indicates that the polarity and general operating characteristics are not specified. The letter “S” following the “G” indicates that the electrode is only suitable for one pass.
C/M: indicate the shielding gas required. The letter «C» indicates 100% CO2 and the letter «M» indicates mixture of argon and CO2. If there is no letter, it means the cored wire is self-shielded.
The advantages of cored MIG welding wires are its low levels of splash loss, easy slag removal, and high resistance to impact, temperature extremes, and cracking. The main applications of these wires are found in heavy and industrial machinery, mining equipment and shipbuilding.
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