Types of SMAW Electrode Coating & their various functions.
SMAW Electrodes Coating elements & their roles
Welding rods coatings for mild and low steel alloy have six to twelve ingredients that includes:
- Cellulose– The cellulose disintegrates to produce a gas shield that protects the arc by surrounding it.
- Metal carbonates– It provides a reducing atmosphere and adjusts the basicity of the slag.
- Titanium dioxide– It is helpful in forming a highly fluid and quick-freezing slag and provides ionization of the arc of the welding.
- Ferromanganese and ferrosilicon– This covering helps to deoxidize the molten metal and also supplement the manganese and silicon content in the deposited weld metal.
- Gums and clays– It helps to provide elasticity to the plastic material and provide strength to the coatings.
- Mineral silicate– It helps in slag formation and offers strength to the covering.
- Calcium fluoride– It produces shielding gas to protect the arc, provide fluidity, adjust the basicity of slag, and solubility of metal oxides.
- Alloying metals as nickel, chromium, and molybdenum– It offers alloy content to the deposited metal.
- Manganese or iron oxide– It helps to stabilize the arc and adjust the fluidity and properties of the slag.
- Iron powder– It increases productivity and provides extra metal to the weld zone.
SMAW Electrode Coating types for mild & low alloy steel
- Cellulose sodium (EXX10) – This type of electrode has cellulosic material in the form of reprocessed low alloy with 30% paper, and wood flour. forms a gas shield. The reducing agent carbon dioxide and hydrogen produce a digging arc for deep penetration. The spatter is at the highest in comparison to other electrodes with a rough weld deposit. It offers extremely good mechanical properties even after aging. It is one of the earliest developed electrodes and used widely in countryside pipeline welding. It is used normally with direct current with reverse polarity when the electrode is positive.
- Cellulose potassium (EXX11) –It has similar characters to the cellulose sodium electrode except that here the more potassium is used than sodium. It does ionization of the arc making it suitable to weld with alternating current. The result is similar to cellulose sodium per arc action, penetration, and weld results. A small amount of iron powder is added to E6010 and E6011 for arc stabilization and a better deposition rate.
- Rutile sodium (EXX12) –If the titanium or rutile dioxide is high with respect to other components, the electrode gives an appealing appearance to the user. This electrode offers a quiet arc, low spatters, and a controlled slag. The weld surface gives a smooth appearance but with less penetration, and slightly lower metal properties than with cellulose electrodes. This electrode provides a high deposition rate and a low arc voltage to make it fit for alternating current or direct current with electrode negative.
- Rutile potassium (EXX13) – This coating of electrode acts very similar to rutile sodium except here potassium is used for the arc ionization. This type of coating produces a very quiet, and smooth-running arc that may be used with suitable for alternating current. It can be used with a direct current of either polarity.
- Rutile iron powder (EXXX4) – The coating is very close to a rutile coating with the exception of the iron powder that is included in it. With an iron content of 25-40%, the electrode is EXX14 and 50% or more iron powder makes the electrode EXX24. A lower percentage of iron content makes it suitable for all the positions. The higher percentage of iron makes it suitable for a flat position with horizontal fillet welds. The deposition rate is increased in both cases depending upon the iron content proportion.
- Low hydrogen sodium (EXXX5) –A coating with a high proportion of calcium carbonate or calcium fluoride is called lime ferritic, low hydrogen, or basic type electrode. To ensure the lowest possible hydrogen content in the arc atmosphere, the coating should not have cellulose, clays, asbestos, and other minerals. The coatings are baked at a higher temperature and have superior weld metal properties. They offer the highest ductility, medium to moderate penetration with a medium speed of deposition. These must be stored in a controlled condition and can be used with direct current with electrode positive.
- Low hydrogen potassium (EXXX6)– The characteristics of these coated welding electrodes are similar to the low hydrogen sodium with the exception of the substitution of potassium from sodium for arc ionization. The electrode is used with AC and can be used with a DC electrode positive. Here the arc is smoother but the penetration of the two electrodes remains the same.
- Low hydrogen potassium (EXXX6) – The coating of the electrode here remains similar to the previous one, but the iron powder is added to the electrode in the ratio of 35-40% to name the electrode as EXX18.
- Low hydrogen iron powder (EXX28) –This welding electrode has similar characteristics as EXX18 but has 50% or more iron powder in the coating. It is useful in a flat position and makes a horizontal fillet welding. Here the deposition rate is better than EXX18. The higher alloy electrodes use low hydrogen coatings. We may add specific metal in the coatings to make the electrodes alloy type where suffix letters used to show weld metal compositions. Low hydrogen-type electrodes are used for welding stainless steel.
- Iron oxide sodium (EXX20) –The high content of iron in the coatings produces a weld deposit that generates a bigger slag and is even difficult to control. This coating produces faster deposition with medium penetration and low spatter level and a very smooth finish in welding. These electrodes are fit for a flat position and make horizontal fillet welds. These electrodes can be used with AC or DC with either polarity.
- Iron Oxide Iron power (EXX27) – The features of these electrodes match with iron oxide sodium type electrodes, but it carries 50% or more iron power. This character will improve the deposition rate and can be used with an alternating direct current of either polarity.