1. 1131 March 2020 Dr.Abhishek Sharma
By
Dr. Abhishek Sharma
Metal Joining (Gas Welding)
KME-403
Unit - IV
GL BAJAJ INSTITUTE OF TECHONOLOGY & MANAGEMENT
2. 2
Gas Welding:
• Here heat necessary to produce the fusion is obtained by burning some gas issuing
from nozzle of a blow pipe or torch.
• Gas issuing from the nozzle is already mixed with amount of oxygen required to
produce a flame.
• This flame may be chemically oxidizing, neutral or reducing depending on the
requirement of the type of metal or alloy being welded.
Oxy – acetylene welding:
• Gases used are oxygen (O2) and acetylene (C2H2) for producing flame.
•It can be obtained under high pressure (14 MPa and 200C) in cylinders which are
fitted with pressure regulators.
•Acetylene is obtained by dropping lumps of calcium carbide (CaC2) in water.
CaC2 + 2H2O === C2H2 + Ca(OH)2
(Slaked or hydrated lime)
31 March 2020 Dr.Abhishek Sharma
3. 3
• Oxygen Cylinders are painted black.
• Acetylene cylinders are painted maroon.
• Acetylene must be used at low pressure otherwise it may explode.
Gas Flames
Is phenomenon produced at surface of nozzle tip, where two gases meet and
undergo combustion with evolution of heat and some light.
2C2H2 + 5O2 = 4CO2 + 2H2O + Heat
• Heat produced is approximately 53.38 MJ/m3 of acetylene.
• For complete combustion, ratio of O2 to C2H2 is 2.5 to 1.
• Proportion of oxygen to acetylene can be varied to produce carburizing or
oxidizing or neutral flame.
Neutral flame:
• If O2 and C2H2 are used in equal proportion then incomplete combustion of
acetylene occurs at torch tip.
C2H2 + O2 = 2CO + H2 + Heat Energy
• Subsequently CO and H2 produced burn on coming in contact with atmospheric O2
2CO+O2 = 2CO2 + Heat Energy
2H + O = 2H O + Energy
31 March 2020 Dr.Abhishek Sharma
4. 4
• Thus a type of envelope is formed out of combustion of CO on the inner flame
formed due to incomplete combustion of C2H2.
• Inner white and sharply defined central cone referred as luminous cone is at a
temperature around 3300oC.
• No oxidation takes place, thus widely used.
• Used for welding all metals like ferrous materials, Cu and Aluminum except brass.
Carburizing or reducing flame:
• If proportion of acetylene is increased then carburizing flame is achieved.
• Bright luminous inner zone of the flame is at temperature of 31500C.
Oxidizing Flame:
• Is obtained by increasing the oxygen flow rate.
• Here inner pointed cone is at a temperature of about 35000C
31 March 2020 Dr.Abhishek Sharma
5. 5
Equipments:
1. O2 cylinders:
2. C2H2 cylinders:
3. Regulators:
• When acetylene is fully filled it has a
pressure of 250 psi and oxygen cylinder
has 2200 psi.
• Regulator is used to regulate this
pressure and lower it to make usable at
desired working pressure in the torch.
• Single stage and two stage regulators
are used.
4. Welding Hoses:
• Cylinders, torches and regulators are
connected by rubber hoses.
5. Check Valve:
• Mixing of fuel and O2 for combustion should occur in torch mixer or torch tip.
• Check valve is installed b/w hoses and torch to prevent back flow thus avoids combustion in hoses
31 March 2020 Dr.Abhishek Sharma
6. 6
6. Welding torches:
• The assembly consists of handle, O2 and fuel gas valves and mixing chamber.
• Welding tips or cutting attachment may be used with handle.
• O2 and fuel gas flow through tubes inside the handle.
• These gases mix in mixing chamber or at tip.
7. Welding and cutting tips:
The molten pool is generally supplied with additional metal called filler. Filler
material depends upon the metals to be welded.
A stream of oxygen is then trained on the metal, and metal burns in that oxygen
and then flows out of the cut as an oxide slag.
31 March 2020 Dr.Abhishek Sharma
