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)

1. Circuit

Step-down Transformer

Converts high voltage AC to a lower voltage (220V to 80V-100V). This means the
output current is greater than the input current. This is due to the primary coil having
more windings than the secondary coil.

Smoothing Capacitor

Produces a more uniform direct current by smoothing the surges produced by the
rectifier.

Rectifier

• Allows current to flow in one direction only.
• Converts AC to DC.
• Consists of four diodes arranged so to allow current to flow in one direction only.

Circuit for Manual Metal Arc Welding

2. Safety

• Ensure equipment is well maintained.
• Wear protective clothing.... (More)

• Oxy-Acetylene is a Fusion welding process.
• The joint edges are heated until the metals melt.
• The molten metals join and fuse.
• Oxidation is prevented by the envelope of products of combustion.

1. Acetylene

Acetylene would explode if directly compressed. Instead cylinders are filled with
porous acetone which can absorb 25times the amount of acetylene. This is known as
dissolved acetylene.

2. Safety

Colour Coding

The gas cylinders are colour coded for safety as follows:

Oxy-Acetylene welding safety colour coding

Flashback Arrestors

Flashback arrestors are fitted to the regulators to prevent the feedback of flame through the hose.

Gauges

• There are... (More)

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.

Ferrite

• 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)