Group D: Tarang Valecha Dhananjay R. Apurva Mali Prateek Singh WELDING Group D: Tarang Valecha Dhananjay R. Apurva Mali Prateek Singh

List various types of welding used for shipbuilding and with the aid of simple sketches, explain three common types of welding.

Introduction The processes employed in shipbuilding are usually of the fusion welding type. It is achieved by means of a heat source, which is intense enough to melt the edges of the material to be joined as it is traversed along the joint. Gas welding, arc welding and resistance welding all provide heat sources of sufficient intensity to achieve fusion welds.

Various types of welding used in shipbuilding are: Gas welding Electric arc welding Automatic welding with coated wires or cored wires Submerged arc welding Stud welding Tungsten inert gad welding (T.I.G.) Metal inert gas welding

Electro-slag welding Electro-gas welding Thermit welding

Gas welding Oxyacetylene welding, commonly referred to as gas welding, is a process which relies on combustion of oxygen and acetylene. When mixed together in correct proportions within a hand-held torch or blowpipe, a relatively hot flame is produced with a temperature of about 3,200 deg.C. The chemical action of the oxyacetylene flame can be adjusted by changing the ratio of the volume of oxygen to acetylene.

Gas welding Three distinct flame settings are used, neutral, oxidising and carburising. Welding is generally carried out using the neutral flame setting which has equal quantities of oxygen and acetylene. The oxidising flame is obtained by increasing just the oxygen flow rate while the carburising flame is achieved by increasing acetylene flow in relation to oxygen flow. Because steel melts at a temperature above 1,500 deg.C, the mixture of oxygen and acetylene is used as it is the only gas combination with enough heat to weld steel.

Gas welding Neutral flame Carburising flame Oxidising flame

Gas welding However, other gases such as propane, hydrogen and coal gas can be used for joining lower melting point non-ferrous metals, and for brazing and silver soldering. Oxyacetylene equipment is portable and easy to use. It comprises oxygen and acetylene gases stored under pressure in steel cylinders. The cylinders are fitted with regulators and flexible hoses which lead to the blowpipe.

Gas welding The relationship between material thickness, blowpipe nozzle size and welding speed, is shown in the chart.

Tungsten inert gas welding Frequently used in the welding of Aluminium brasses, Cunifer, and stainless steels. This is a particularly effective weld process particularly for the aluminium brasses such as yorcalbro often found in sea water systesm. The small heat effected zone is particularly important as super granulation causes a softening of yorcalbro leading to bulging and failure under pressure

Tungsten inert gas welding The main advantages are : Easy to use in all positions Stable welld directed heat with small heat effected zone and deep penetration Clean smooth welds of high quality

Tungsten inert gas welding Technique-The basic technique is a cross between Stick welding and gas welding. The arc is struck against the surface, the shield gas is ionised and a stable arc is formed. The elctrode must be quickly brought up to the weld height to prevent contaminationof the weld pool. The tungsten electrode does not melt. A filler rod of correct material is introduced in a similar fashion to gas welding. The electrode holder is held at a 75' angle and thefiller rod held at 30' in the direction of the forehand travel.For TIG the shield gas has the added requirement of preventing oxidation and cooling the tungsten electrode.

Metal inert gas welding (M.I.G.) Also called Gas Metal Arc Welding (GMAW). Where CO2 is used as the shielding gas the system may also be known as Metal Active Gas (MAG). Generaically the term MIG is applied to the welding sets.

Metal inert gas welding (M.I.G.) The shield for the arc is formed from a supply of inert gas. Gas stored in a bottle is led via a flow regulator through a tube to the welding torch. When the trigger on the torch is depressed firstly the gas valve is opened and the shield gas emitted from the nozzle. Further depressing the trigger makes an electrical switch and the wire feed is activated and the metal wire electrified. To start the welding operation the torch is held a set distance-sat 10-15mm, from the work piece, the trigger is pressed and the arc established. Note that the arc is not 'struck' in the same way as stick welding. To improve the arc creation is it advisable to sharpen the wire to a point before starting Wire Stick out - The amount of wire sticking out of the holder at startup should be controlled. Too long and the weld arc is cool and may not be properly shielded by the gas. Too short and the holder tip can be overheated and weld spatter may enter the nozzle and cause turbulence in the gas flow

Metal inert gas welding (M.I.G.) Gasses use for different metals: Argon Aluminium Stainless Steel Copper and copper alloys Carbon Dioxide Ferrous metals Argon/CO2 mix Ferrous Metals Stainles steels