Shielding of molten metal - Electrode coating produces shield gas such as carbon dioxide under heat, which can shield molten metal from atmospheric oxygen, nitrogen and hydrogen. This shielding is necessary to ensure no gas pockets in welding and then avoids contamination of the weld joint.
What is the function of the coating on a shielded electrode?
Electrode coatings should provide gas shielding for the arc, easy striking and arc stability, a protective slag, good weld shape, and most important of all a gas shield consuming the surrounding oxygen and protecting the molten weld metal.
What are the functions of coated part of the electrode?
During welding, because of the heat of the arc the flux coating on the electrode melts and perform the following function:It stabilizes the arc.Removes oxide, scale etc. ... It forms a gaseous shield around the arc which protects the molten weld pool from atmospheric contamination.More items...•
What are the functions of coating?
Traditionally, the primary functions of coatings are to protect and decorate substrates. More recently, growth has occurred in the research and development, as well as commercialisation, of coatings which have novel functions in addition to having traditional protection and decoration properties.
What is the purpose of the flux coating on a shielded metal arc welding electrode?
Shielded metal arc welding electrodes have a flux coating. This flux coating is used to protect the molten weld metal from the atmosphere and oxidation. This is necessary because no external shielding gas is used for this welding process. When the flux coating is deposited into the weld, it resurfaces as slag.
What are functions of electrode coating in welding?
The main function of the coating is to shield the arc and molten weld pool from the atmosphere. The shielding gas also helps to protect the weld pool from oxygen and other contaminants. In addition, the coating provides a slag that helps to remove impurities from the weld metal.
What are the types of coatings used in an electrode and its uses?
Shielded Arc/Heavy Coated Electrodes The mineral coatings include sodium silicate, metal oxide clay, and other inorganic substances and combinations. These electrodes generate a slag deposit. The heavy-coated or shielded arc electrodes are employed to weld cast iron, steel, and hard surfaces.
What are the three functions of the electrode covering?
Abdulkader AlshereefA. Protection: It provides a gaseous shield to protect the molten metal from air. ... B. Deoxidation: It provides deoxidizers and fluxing agents to deoxidize and cleanse the weld metal. ... C. Arc Stabilization: It provides arc stabilizers to help maintain a stable arc. ... D.
What is the main function of the flux coating in electrodes?
Flux coating on the electrodes ensures a weld with good mechanical properties, chemical composition and weld metal cleanliness.
What is the main advantage of coating?
Coatings help protect against the damage caused by wear-prone applications. They have been designed to be wear resistant, reduce friction, protect against caustic/acidic materials and cleaning agents, and increase line efficiencies.
What are the advantages of coated welding electrodes?
The coated electrode can be used for the higher welding currents as compared to the bare electrode. The coating of the flux makes the electrode insulated at its outer cover and hence, this electrode can be used at higher welding currents without getting red hot.
What are the parts of coated electrode?
Stick Electrode Coating IngredientsAlloying Elements and de-oxidizers- Alloying elements such as molybdenum, chromium, nickel, manganese and others impart specific mechanical properties to the weld metal. ... Binders- Soluble silicates such as sodium and potassium silicates, are used in the electrode coating as binders.More items...•
What is a coated electrode?
A coated electrode is made of a metallic wire (called core wire) coated uniformly with flux material. While fluxing, the electrode about 20 mm of its length is left bare at one end for mounting it into the electrode holder. The flux material used for coating of the electrode is a bad conductor of electricity.
What are the three functions of the electrode covering?
Abdulkader AlshereefA. Protection: It provides a gaseous shield to protect the molten metal from air. ... B. Deoxidation: It provides deoxidizers and fluxing agents to deoxidize and cleanse the weld metal. ... C. Arc Stabilization: It provides arc stabilizers to help maintain a stable arc. ... D.
What are the functions of electrode coating?
The covering coating on the core wire consists of many materials which perform a number of functions as listed below: 1. Welding electrodes are used to join various similar and dissimilar metals as plain carbon steels, cast iron, copper, aluminium, magnesium and their alloys, ...
Why do we need coatings?
Coating saves the welder from the radiations otherwise emitted from a bare electrode while the current flows through it during welding. 12. Proper coating ingredients produce weld metals resistant to hot and cold cracking. Suitable coating will improve metal deposition rates.
What are the constituents of arc stabilizing?
3. Arc stabilizing constituents like calcium carbonate, potassium silicate, titanates, magnesium silicates, etc.; add to arc stability and ease of striking the same.
What are the ingredients in slag?
Slag forming ingredients, like silicates of magnesium, aluminium, sodium, potassium, iron oxide, china clay, mica etc., produce a slag which because of its light weight forms a layer on the molten metal and protects the same from atmospheric contamination. 3.
Which element refines molten metals?
5. Deoxidizing elements like ferro-manganese, and ferro-silicon, refine the molten metal.
Who wrote the source of basic manufacturing processes and workshop technology?
Source A Textbook of Basic Manufacturing Processes and Workshop Technology by Rajender Songh.
What is the difference between EXX28 and EXX18?
Low hydrogen-iron powder (EXX28). This electrode is similar to the EXX18, but has 50 percent or more iron powder in the coating. It is usable only when welding in the flat position or for making horizontal fillet welds. The deposition rate is higher than EXX18. Low hydrogen coatings are used for all of the higher-alloy electrodes. By additions of specific metals in the coatings, these electrodes become the alloy types where suffix letters are used to indicate weld metal compositions. Electrodes for welding stainless steel are also the low-hydrogen type.
What is low hydrogen?
Low hydrogen-sodium (EXXX5). Coatings that contain a high proportion of calcium carbonate or calcium fluoride are called low hydrogen, lime ferritic, or basic type electrodes. In this class of coating, cellulose, clays, asbestos, and other minerals that contain combined water are not used. This is to ensure the lowest possible hydrogen content in the arc atmosphere. These electrode coatings are baked at a higher temperature. The low hydrogen electrode family has superior weld metal properties. They provide the highest ductility of any of the deposits. These electrodes have a medium arc with medium or moderate penetration. They have a medium speed of deposition, but require special welding techniques for best results. Low hydrogen electrodes must be stored under controlled conditions. This type is normally used with direct current with electrode positive (reverse polarity).
What is rutile iron powder?
Rutile-iron powder (EXXX4). This coating is very similar to the rutile coatings mentioned above, except that iron powder is added. If iron content is 25 to 40 percent, the electrode is EXX14. If iron content is 50 percent or more, the electrode is EXX24. With the lower percentage of iron powder, the electrode can be used in all positions. With the higher percentage of iron paler, it can only be used in the flat position or for making horizontal fillet welds. In both cases, the deposition rate is increased, based on the amount of iron powder in the coating.
What are the ingredients in welding electrodes?
The coatings of electrodes for welding mild and low alloy steels may have from 6 to 12 ingredients, which include cellulose to provide a gaseous shield with a reducing agent in which the gas shield surrounding the arc is produced by the disintegration of cellulose; metal carbonates to adjust the basicity of the slag and to provide a reducing atmosphere; titanium dioxide to help form a highly fluid, but quick-freezing slag and to provide ionization for the arc; ferromanganese and ferrosilicon to help deoxidize the molten weld metal and to supplement the manganese content and silicon content of the deposited weld metal; clays and gums to provide elasticity for extruding the plastic coating material and to help provide strength to the coating; calcium fluoride to provide shielding gas to protect the arc, adjust the basicity of the slag, and provide fluidity and solubility of the metal oxides; mineral silicates to provide slag and give strength to the electrode covering; alloying metals including nickel, molybdenum, and chromium to provide alloy content to the deposited weld metal; iron or manganese oxide to adjust the fluidity and properties of the slag and to help stabilize the arc; and iron powder to increase the productivity by providing extra metal to be deposited in the weld.
How does fluxing affect welding?
The physical characteristics of the weld deposit are modified by incorporating alloying materials in the electrode coating. The fluxing action of the slag will also produce weld metal of better quality and permit welding at higher speeds.
What is covered electrode welding?
The covered electrode is the most popular type of filler metal used in arc welding. The composition of the electrode covering determines the usability of the electrode, the composition of the deposited weld metal, and the specification of the electrode. The type of electrode used depends on the specific properties required in the weld deposited. These include corrosion resistance, ductility, high tensile strength, the type of base metal to be welded, the position of the weld (flat, horizontal, vertical, or overhead); and the type of current and polarity required.
Why do we need a slag cover?
A slag cover is needed to protect molten or solidifying weld metal from the atmosphere. This cover can be obtained from the electrode coating. The composition of the electrode coating determines its usability, as well as the composition of the deposited weld metal and the electrode specification. The formulation of electrode coatings is based on well-established principles of metallurgy, chemistry, and physics. The coating protects the metal from damage, stabilizes the arc, and improves the weld in other ways, which include: