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Submerged Arc & Resistance Seam Welding – Engineering

Submerged Arc Welding

  • Uses bare wire electrode.
  • Fed automatically from spool.
  • Generates electric arc to heat metal/
  • Flux in powder form.
  • Fed using a hopper.
  • Electric arc melts joint, flux and electrode.
  • Excess flux is collected and re-used.
  • Fully automated process.
  • Used on Low carbon steels.
  • E.g. Ship building and bridge construction.

Resistance Spot welding

  • Components to be joined are placed between two non consumable electrodes and pressed together.
  • The current is passed through the electrodes which generates the required heat.
  • A nugget weld (circular mark) is formed.
  • It is used on sheet metals.
  • The process is energy efficient and... (More)
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Iron Carbon Equilibrium Diagrams – Engineering Notes

Lower Critical Point

  • Occurs at 723°c.
  • Temperature change occurs.
  • The metal contracts dimensionally, glows less brightly and loses its magnetism.
  • Known as Decalescence.

Upper Critical Point

  • Varies depending on amount of carbon in the steel.
  • Above this point, the metal exists as FCC austenite.

Eutectic Point

  • Liquid to solid
  • Occurs at 1140°C at 4.3% carbon
  • Liquid steel changes to solid austenite and cementite.

Eutectoid Point

  • Solid austenite changes to solid pearlite.
  • Occurs at 723°C at .83% Carbon.


  • Almost Pure Iron.
  • Above a temperature of 1390°C or below 910°C, iron has a BCC lattice.
  • Also known as alpha iron.
  • Contains... (More)
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Heat Treatment – Engineering Notes



  • The piece is heated to a cherry red colour and then cooled rapidly in water oils and brine.
  • At the cherry red colour the steel will have undergone structural changes (FCC to BCC, martensite) and the rapid cooling does not allow it to revert to its original condition.


  • Very hard and Brittle.



  • It is done by heating the article to a suitable temperature (500°C) below the reddening point of steel and then cooling it in oil or water.
  • The higher the temperature the greater the reduction in hardness and brittleness.
  • The temperature is gauged by... (More)
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Polymers – Condensation & Addition Polymerization

Monomer: A monomer is a molecule of a compound which reacts with other monomers to form a polymer.

Mer: A mer is a repetitive unit in a polymer.

Addition Polymerisation of Ethylene (Thermoplastics)

  • Ethylene consists of 4 hydrogen atoms and 2 carbon atoms joined together by a double bond. (Primary and secondary bond)
  • A catalyst is added which introduces a free radical. A free radical is a reactive atom containing an unpaired electron.
  • The free radical joins onto one of the monomers causing the weak secondary bond between the carbon atoms to break.
  • The mer cannot exist on its own... (More)