oxy acetylene welding process

1. Survey of Welding and Allied Processes
 The art of joining metals is about 3000 years
old.
 The origin of welding is probably to be traced
to the shaping of metals.
 The following methods are used for joining
metals:
 joining by screws, bolts, rivets, nails, Soldering
,Brazing, welding

2. Survey of Welding and Allied Processes
Soldering
 This joint is made on thin metals using solder
as a joining medium. The melting point of
solder is less than the metals to be joined.
The joint can be opened by heating up to
the solder melting temperature (below
400°C).
Brazing
 The joint is similar to soldering but has more
strength. The joining medium used is brass,
which has a higher melting temperature than
solder. The joint can also be opened by
heating up to the melting point of brass
(850-950°C).

3. Survey of Welding and Allied Processes
Soldering Brazing

4. Survey of Welding and Allied Processes
Welding
 A metal joining method in which the joining
edges are heated and fused together with or
without filler metal to form a permanent
(homogeneous) bond is known as welding.
or
 Welding is a process of joining two or more
pieces of the same or dissimilar materials
with or without application of heat, with or
without application of pressure, with or
without filler material.

5. COMPARISON BETWEEN WELDING AND OTHER METAL
JOINING METHODS
 Joining methods like riveting, assembling
with bolt, seaming, soldering and brazing all
result in temporary joints.
 Welding is the only method to join metals
permanently
 Welded joints cannot be separated like
soldering and brazing because it is made
homogeneous by heating and fusing the
joining edges together.
 The temporary joints can be separated
if:
 the head of the rivet is cut
 nut of the bolt is unscrewed
 hook of the seam is opened
 more heat is given than that required for
soldering and brazing.

6. Advantages of Welding
Welding is superior to other metal joining
methods because it:
 is a permanent pressure tight joint
 occupies less space
 gives more economy of material
 has less weight
 withstands high temperature and pressure
equal to joined material
 can be done quickly
 gives no colour change to joints.
 It is the strongest joint and any type of metal
of any thickness can be joined.

7. CLASSIFICATION OF WELDING PROCESSES
ACCORDING TO HEAT SOURCE
 According to the sources of heat, welding
processes can be broadly classified as:
 Electric welding processes (heat source is
electricity)
 Gas welding processes (heat source is gas
flame)
 Other welding processes (heat source is
neither electricity nor gas flame)

8. CLASSIFICATION OF WELDING PROCESSES
Electric welding processes
 Electric arc welding
 Electric resistance welding
 Laser welding
 Electron beam welding
 Induction welding
Electric Arc Welding can be further
classified as:
 Metallic arc welding
 Carbon arc welding
 Atomic hydrogen arc welding
 Inert gas arc welding/ TIG welding
 CO2 gas arc welding
 Flux cored arc welding
 Submerged arc welding
 Electro-slag welding
 Plasma arc welding

9. CLASSIFICATION OF WELDING PROCESSES
Electric Resistance Welding can be further
Classified as:
 Spot welding
 Seam welding
 Butt welding
 Flash butt welding
 Projection welding
Gas Welding Processes
 Oxy-acetylene gas welding
 Oxy-hydrogen gas welding
 Oxy-coal gas welding
 Oxy-liquefied petroleum gas welding
 Air acetylene gas welding

10. OTHER WELDING PROCESSES
Solid State Welding
 Forge welding
 Hammer Welding
 Die Welding
 Roll Welding
 Friction welding
 Cold Welding
Ultrasonic Welding
Explosive Welding
 Thermit Welding (Fusion Welding)
 Pressure Thermit
 Non-Pressure Thermit
Arc Welding, Resistance Welding, Gas
Welding, Induction Welding all are Fusion
Welding Processes.

11. Welding Joints

12. Welding Positions

13. GAS WELDING(OXY-FUEL GAS WELDING) AND
CUTTING,PROCESS AND EQUIPMENT
OXYFUEL GAS WELDING(OFW)
 is the term used to describe the group
of Fusion Welding operations that burn
various fuels mixed with oxygen to
perform welding.
 The OFW processes employ several
types of gases, which is the primary
distinction among the members of this
group.
 Oxyfuel gas is also commonly used in
cutting torches to cut and separate
metal plates and other parts
 The most important OFW process
is oxyacetylene welding.

14. OXY-ACETYLENE WELDING
 Oxyacetylene welding (OAW) is performed by a
high temperature flame from combustion of
acetylene and oxygen.
 The flame is directed by a welding torch.
 A filler metal is sometimes added, and pressure
is occasionally applied in OAW between the
contacting part surfaces.
 When filler metal is used, it is typically in the
form of a rod with diameters ranging from 1.6
to 9.5 mm (1/16–3/8 in).

15. OXY-ACETYLENE WELDING
 Composition of the filler must be similar to
that of the base metals.
 The filler is often coated with a flux that
helps to clean the surfaces and prevent
oxidation, thus creating a better weld joint.

16. OXY-ACETYLENE WELDING
 Acetylene (C2H2) is the most popular fuel
among the OFW group because
 it is capable of higher temperatures than
any of the others- upto 3480oC
 The chemical reaction of acetylene and
oxygen in two stages.

17. OXY-ACETYLENE WELDING TOOLS
EQUIPMENTS
 Gas Cylinders
 Pressure Regulators
 Hoses
 Welding Torch
Accessories
 Welding Goggles, Gloves, sleeves, jacket
 Spark lighters, tip cleaners

18. OXY-ACETYLENE WELDING TOOLS
GAS CYLINDERS
 Acetylene and oxygen gas is stored in
compressed gas cylinders. These gas
cylinders differ widely in capacity, design and
colour code.
 Cylinder is painted black for oxygen and
maroon for acetylene.
Oxygen Cylinder
 Three common sizes for cylinders are:
2.27, 3.45 and 6.9 cubic meters.
 Cylinders may vary in size, but they are
all filled to 150 kgf/cm2 at 20oC
 Variations in outside temperatures
change the pressure within the tank.
 Oxygen gas cylinder valves are right hand
threaded.

19. OXY-ACETYLENE WELDING TOOLS
Dissolved Acetylene Cylinders
 The acetylene gas used in gas welding is
stored in steel bottle shaped cylinders
painted in maroon color.
 An acetylene cylinder is filled with some
absorptive material, which is saturated
with a chemical solvent acetone.
 Acetone has the ability to absorb a large
volume of acetylene and release it as the
pressure falls.
 The normal storing capacity of storing acetylene
in dissolved state is 6m3 with the pressure
ranging between 15-16 kg/cm2.
 Acetylene gas is generated by carbide-to-water
method.

20. OXY-ACETYLENE WELDING TOOLS
Oxygen Pressure Regulator
 This is used
 to reduce the oxygen cylinder gas pressure
according to the required working pressure
 to control the flow of oxygen at a constant
rate to the blowpipe.
 The threaded connections are right hand
threaded.

21. OXY-ACETYLENE WELDING TOOLS
Acetylene Regulator
 This is also used
 to reduce the cylinder gas pressure to the required
working pressure
 to control the flow of acetylene gas at a constant
rate to the blowpipe
 The threaded connections are left handed.
 For quickly identifying the acetylene regulator, a
groove is cut at the corners of the nut.
 There are two types of regulators
 single stage regulator
 double stage regulator

22. OXY-ACETYLENE WELDING TOOLS
Rubber Hose Pipes and Connections
 These are used to carry gas from the
regulator to the blowpipe.
 made of strong canvas rubber having good
flexibility.
 Hose-pipes which carry oxygen are black in
colour and the acetylene hoses are of
maroon colour.

23. Welding Torch
 It is a tool for mixing oxygen and
acetylene in correct proportion and burning
the mixture at the end of a tip.
 Gas flow to the torch is controlled with the
help of two needle valves in the handle of
the torch.

24. Accessories
 GOGGLES These are fitted with colored
lenses and are used to protect the eyes
from harmful heat and ultraviolet and
infrared rays.
 SPARK LIGHTER It is used for frequent
igniting the welding torch.
 GLOVES These are required to protect the
hands from any injury due to the heat of
welding process.
 Fluxes are used in gas welding to remove the
oxide film and to maintain a clean surface.
These are usually employed for gas welding
of aluminum, stainless steel, cast iron, brass
and
silicon bronze.
 Gas welding can be done with or without
using filler rod.
 When welding with the filler rod, it should be
held at approximately 900 to the welding tip.
 Filler rods have the same or nearly the same
chemical composition as the base metal.

25. TYPES OF OXY-ACETYLENE FLAME
 NEUTRAL FLAME Oxygen and acetylene are mixed in
equal proportion in the blowpipe and complete
combustion takes place in this flame
 This flame does not have a bad effect on the metal/
weld i.e. the metal is not oxidized and no carbon is
available for reacting with the metal.
 It is used to weld most of the common metals, i.e. mild
steel, cast iron, stainless steel, copper and aluminium.
 temperature 3260oC
 a clear, well defined BLUE inner cone, surrounded by
an outer flame envelope
indicating that the combustion is complete.
 CARBURIZING FLAME It receives an excess of
acetylene over oxygen from the blowpipe
 can be recognized by acetylene feather, which
exists between the inner cone and the outer
envelope.
 Temperature 3038oC
 The flame has a carburizing effect on steel,
causing hard, brittle and weak weld.
 The outer flame envelope is longer than that of
the neutral flame and is usually much brighter in
color.
 This flame is very well used for welding high
carbon steel.

26. TYPES OF OXY-ACETYLENE FLAME
Oxidizing Flame
 It contains an excess of oxygen over acetylene as
the gases come out of the nozzle.
 The flame has an oxidizing effect on metals which
prevents evaporation of zinc/ tin in brass welding/
brazing.
 It is used for welding of brass and for brazing of
ferrous metals
 Can be recognized by the small cone, which is
shorter, much bluer in color and more pointed
than that of the neutral flame.
 Temperature 3300oC

27. Metals and flame to be used are as given below:
 Metal Flame
 Mild steel Neutral
 Copper (de-oxidised) Neutral
 Brass Oxidising
 Cast iron Neutral
 Stainless steel Neutral
 Aluminium (pure) Neutral
 Stellite Carburising

28. OXY-ACETYLENE GAS CUTTING
PRINCIPLE OF GAS CUTTING
 The method can be successfully used to cut ferrous
metals.
 Non-ferrous metals and their alloys cannot be cut
by this process.
 When a ferrous metal is heated to red hot
condition and then exposed to pure oxygen, a
chemical reaction takes place between the heated
metal and oxygen.
 Due to this oxidation reaction, a large amount of
heat is produced and cutting action takes place.
 In oxy-acetylene cutting the combination of red
hot metal and pure oxygen causes rapid burning
and iron is changed into iron oxide (oxidation).
 By this continuous process of oxidation the metal
can be cut through very rapidly. The iron oxide is
less in weight than the base metal.

29. OXY-ACETYLENE GAS CUTTING
CUTTING OPERATION
 There are two operations in oxy acetylene gas
cutting.
 A preheating flame is directed on the metal to be
cut and raises it to bright red hot or ignition point
(900°C app.)
 Then a stream of high pressure pure oxygen is
directed on to the hot metal which oxidizes and
cuts the metal.
 The two operations are done simultaneously with a
single torch.
OXY-ACETYLENE CUTTING EQUIPMENTS
 The oxy-acetylene cutting equipment is similar to
the welding equipment, except that instead of
using a welding torch (blowpipe), a cutting
blowpipe is used.
 Acetylene gas cylinder
 Oxygen gas cylinder
 Acetylene gas regulator
 Oxygen gas regulator (Heavy cutting requires
higher pressure oxygen regulator)
 Rubber hose-pipes for acetylene and oxygen
 Cutting blowpipe