Shielding gas

Shielding gases are inert or semi-inert gases that are commonly used in several welding processes(gas metal arc welding and gas tungsten arc welding ).

protect the weld area from oxygen, and water vapour and improve the quality of the weld or make the welding smoothly.

Improper choice of a welding gas can lead to a porous and weak weld, or to excessive spatter.

Only two of the noble gases, helium and argon, are cost effective enough to be used in welding.

Semi-inert shielding gases, or active shield gases, include carbon dioxide, oxygen, nitrogen, and hydrogen.

Most of these gases, in large quantities, would damage the weld, but when used in small, controlled quantities, can improve weld characteristics.

flux for smelting

Smelting makes use of heat and a chemical reducing agent to decompose the ore, driving off other elements as gases or slag and leaving just the metal base behind.

The reducing agent is commonly a source of carbon such as coke, or in earlier times charcoal.

The carbon (or carbon monoxide derived from it) removes oxygen from the ore, leaving behind the elemental metal.

 The carbon is thus oxidized in two stages, producing first carbon monoxide and then carbon dioxide.

Fluxes are used in smelting for several purposes, chief among them catalyzing the desired reactions and chemically binding to unwanted impurities or reaction products.

 Calcium oxide, in the form of lime, was often used for this purpose, since it could react with the carbon dioxide and sulfur dioxide produced during roasting and smelting to keep them out of the working environment.

fluxes used in welding

fluxes can be defined as a chemical cleaning agent, flowing agent, or purifying agent or for other functions.

flux is used for both metal extraction as well as joining of metals.

Earliest used fluxes were carbonate of soda, potash, charcoal, coke, borax,lime, lead sulfide.

As cleaning agents, fluxes facilitate soldering, brazing, and welding by removing oxidation from the metals to be joined.

Common fluxes are: ammonium chloride or rosin for soldering tin; hydrochloric acid and zinc chloride for soldering galvanized iron (and other zinc surfaces); and borax for brazing, braze-welding ferrous metals, and forge welding.

removes oxidation from the surfaces to be soldered .

seals out air thus preventing further oxidation of the weld pool and enable high productive and robust welding conditions for manufacturing.

facilitating amalgamation improves wetting characteristics of the liquid solder.

It provides a protective barrier against igniting.

It helps with heat transfer from heat source to metal surface and it helps in the removal of surface metal wastes.

It also helps the deposits of metal from the electrode.

electrodes used in welding

Covered electrodes are used extensively in shielded metal arc welding.

Bare electrode wires are used in gas metal arc welding and bare electrode rods are used in gas tungsten arc welding.

Tubular electrode wire is used in flux-cored arc welding.

Filler metal

Filler metal is added to the joint in welding,brazing and soldering.

it is added to supply the material to the joint or to improve the propoties of the joint.
in soldering  lead-tin solder alloy is used in soft soldering.
Filler alloys/metals have lower melting point than the parent metals.for complex shapes like jewellary it is soldered in stages to improve the joint propoties.

kerf of welding

A groove, slit, or notch made by a cutting tool, such as a laser cutter or the width of a groove made by a laser cutting tool. The kerf is dependent upon the properties of the material being cut, the workpiece thickness, the lens focal length, and finally, the type of cutting gas used in the laser.

Laser Beam Cutting

Laser Beam Cutting  is a thermal cutting process that utilizes highly localized melting or vaporizing to sever metal with the heat from a beam of  coherent light, usually with the assistance of a high-pressure gas.

An assist gas is used to remove the melted and volatilized materials from the beam path.

Both metallic and non-metallic materials can be cut by this process. The output beam is often pulsed to very high peak powers in the cutting process, increasing the travel speed of the cutting operation.

The two most common types of industrial lasers are carbon dioxide (CO2) and neodymium-doped yttrium aluminum garnet (Nd:YAG).

A CO2 laser uses a gaseous medium to produce the lasing action while the Nd:YAG use a crystalline material.
CO2 lasers are commercially available in powers up to 6kW and Nd:YAG systems are available up to 6kW.

 Laser cutting delivers highly reproducible results with narrow kerf width, minimal heat-affected zone and little-to-no distortion. The process is flexible, easy to automate and offers high cutting speeds with excellent cut quality. Equipment costs are high but are becoming lower as resonator technology becomes less expensive.

image source:http://www.teskolaser.com/laserglossaryk.html

Submerged arc welding

Submerged arc welding  requires consumable solid or tubular (metal cored) electrode.
The molten weld and the arc zone are protected from atmospheric contamination by being "submerged" under a blanket of granular fusible flux consisting of lime, silica, manganese oxide, calcium fluoride, and other compounds. When molten, the flux becomes conductive, and provides a current path between the electrode and the work. This thick layer of flux completely covers the molten metal thus preventing spatter and sparks as well as suppressing the intense ultraviolet radiation and fumes that are a part of the shielded metal arc welding (SMAW) process.

gas cutting

Gas cutting involves the fuel gases and oxygen to cut the parent metal to be used for jobs.
The gases like acetylene or hydrogen is used for heat generation.
Acetylene reacts with oxygen and it is exothermic reaction

                                          2C₂H₂ + 2O₂ → 4CO + 2H<sub>2+energy

Again the carbon mono-oxide reacts with oxygen and releases energy</sub>

                                 4CO+2H₂ +3O₂ → 4CO₂ +2H₂O+energy

It is economical and can be used for bevel and groove welding.