WELDING

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WELDING

• Group D Tarang Valecha
• Dhananjay R.
• Apurva Mali
• Prateek Singh

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

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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

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• Electro-slag welding
• Electro-gas welding
• Thermit welding

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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.

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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.

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Gas welding
Neutral flame
Carburising flame
Oxidising flame
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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.

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Gas welding

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

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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

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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

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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.

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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.

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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

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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