Welding RevisionLC Engineering

Gas Welding Revision

Stages of combustion

Primary Combustion – Acetylene & Oxygen burn in the primary combustion zone to give off Carbon Monoxide and Hydrogen.

C2H2+O2 2CO+H2

Secondary Combustion – oxygen is sucked in from the weld pool and is burned with Carbon Monoxide & Hydrogen to give off Carbon Dioxide and Water vapour.

CO+H2+O2 CO2+H2O

Types of FlamesThe Oxidising Flame

This is a result of excess Oxygen. Approx 1.5 parts oxygen to 1 part acetylene. If used with steel the excess oxygen would contimnate the joint, so it is used for copper and some bronzes. It has a temp. of about 3500ºC

max temp zoneinner cone

secondary combustion zone

The Carburising FlameThis is a result of excess Acetylene. Approx 0.9 parts oxygen to 1 part acetylene. Has a temp of approx 3150ºC and is used for welding alloy steels and aluminium alloys

max temp zoneinner cone

secondary combustion zone

C

Acetylene feather

Transformer/ RectifierTransformer RectifierDropping Voltage means

current increases current, which is needed for welding.

There is a primary and secondary coil.

The number of windings on each coil controls the output current.

Primary 100 Turns and 220V and 10A

Secondary 200 coils = 110V & 20A

The Rectifier converts AC to DC.

It uses 4 diodes arranged in a diamond shape.

2 diodes conduct in each half-cycle.

The capacitor ensures a smooth output.

Transformer/Rectifier

MIG/MAGSMetal Inert Gas/Metal

Arc Gas Shielded.Semi-automatic ProcessConsumable Electrode

fed automatically.Argon gas protects the

weld pool like a flux.No slag produced.Suitable for steel.

Argon Gas

Wire Feed

Power Plant

Welding Gun

Electrode

NOTE: CO2 welding is a form of MIG/MAGS

TIG/TAGSTungsten Inert GasNon –consumable

Electrode.Filler rod used.Argon gas protects

the weld pool like a flux.

Suitable for Aluminium & Stainless Steel.

Filler Rod

NOTE: Label the diagram using MIG/MAGS as a reference.

A Transformer steps up and down the voltage to set welding currents.

The Rectifier converts AC to DC using a series of diodes.

Resistance Spot Welding

Resistance Seam Welding

Submerged Arc Welding