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Welder’s Handbook Published by:
Air Products PLC
Designed and produced by:
PDF Conceptual Design & Marketing
Copyright:
Air Products PLC 1999 – 3rd Edition
For Gas Shielded Arc Welding, Oxy Fuel Cutting & Plasma Cutting
Welder’s
Handbook 1
CONTENTS
Introduction
Fusion welding
2
Why use welding?
3
Arc welding processes
4
Welding terms
5
MIG/MAG welding
6
TIG welding
10
Plasma welding
17
Welding sheet
18
Welding plate
20
Welding pipes
22
Defects in welds
24
The right gas:
MIG/MAG welding
26
TIG welding
29
Welding data:
MIG/MAG welding
30
Flux cored electrodes
33
TIG welding
34
Oxy-fuel gas cutting
37
Plasma cutting
44
Safety always
46
Conversion data
inside back cover
Air Products Welder’s Handbook 2
Air Products Welder’s Handbook
Fusion welding
The most widely used welding proc-
esses rely on fusion of the components
at the joint line.
In fusion welding, a heat source melts
the metal to form a bridge between the
components.
Two widely used heat sources are:
Gas flame
The molten metal must be protected
from the atmosphere - absorption of
oxygen and nitrogen leads to a poor
quality weld.
Air in the weld area can be replaced by
a gas which does not contaminate the
metal, or the weld can be covered with
a flux.
Electric arc
'T' joint
fillet
weld
butt
weld
Butt joint
air must be excluded
from heated area
electrode
arc
high current
low voltage
supply
blowpipe
fuel gas flame 3
Why use welding?
Welding is used because it is:
q
one of the most cost-effective
methods of joining metal
components
q
suitable for thicknesses ranging
from fractions of a millimetre to a
third of a metre
q
versatile, being applicable to a
wide range of component
shapes and sizes
The joints produced by welding are:
q
permanent
q
strong, usually matching the
strength of the components,
q
leak tight,
q
reproducible,
q
readily inspected by non-
destructive techniques.
Welding can be used:
q
in the workshop
q
on site
for
q
sheet
q
plate
q
pipe
q
sections
Which process?
A large number of welding processes
and techniques are available. No
process is universally best. Each has
its own special attributes and must be
matched to the application.
Choosing the most suitable process
requires consideration of a number of
factors.
Factors in choosing
welding process:
q
type of metal
q
type of joint
q
production constraints
q
equipment availability
q
labour availability
q
health, safety and the
environment
q
costs of consumables
q
labour costs
q
material thickness
INTRODUCTION 4
Air Products Welder’s Handbook
ARC WELDING
Arc welding processes
Fabrications involving sheet metal,
plate or pipes are commonly welded
by an arc process.
Two of the most important processes
use a gas shield to protect the weld
metal from atmospheric
contamination. 5
WELDING TERMS
Terms commonly used in
gas shielded welding
arc length Distance between the tip
of the electrode and the surface of the
weld pool.
base metal Incorrectly used to
describe the metal from which the
components of the joint are made.
The correct term is parent metal.
bead A single run of weld metal
deposited onto the surface of the
parent metal.
burn-off rate The rate at which the
wire is melted. Quoted as a linear
measurement - m/min (metres per
minute) or in/min.
deposited metal Material which is
added, either from the electrode or
filler wire, to build up the weld profile.
deposition rate The rate at which
melted electrode metal is added to the
weld pool. Quoted in kg/hr (kilograms
per hour). Sometimes incorrectly
used in reference to the ratio of metal
deposited to the amount of electrode
melted - this is the deposition
efficiency.
electrode The flux coated rod in
manual metal arc welding, the
tungsten in TIG and plasma welding
and the consumable wire in MIG/MAG
welding. The arc is formed between
the parent metal and one end of the
electrode.
filler metal Metal added to the weld
pool during welding. For TIG it is
supplied as cut lengths of wire.
interpass temperature The
temperature of the material adjacent to
the joint between each run is the
interpass temperature. In some
applications, a maximum temperature
is specified to avoid metallurgical
changes in the metal.
melt run Melting the parent metal
by passing a TIG arc along the
surface. Filler metal is not used.
nozzle In TIG and MIG/MAG
welding - A metal or ceramic tube
which confines the shielding gas to
the weld area.
parent metal The metal which is to
be joined by welding. Often incorrectly
called the base metal.
pass or run The metal deposited
during one traverse of the joint by an
arc. In TIG welding without a filler, the
term melt run may be more correct.
preheat temperature The
temperature of the parent metal just
before welding is started. With some
metals the parent metal is heated
before
welding to avoid problems such as
cracking or lack of fusion.
root run The first run deposited in a
joint where further runs are needed to
fill the groove.
sealing run A run of weld metal
deposited on the reverse side of a butt
joint, along the line of the root. 6
Air Products Welder’s Handbook
MIG/MAG welding principles
Gas shielded metal arc welding is a
semi-automatic process which is
suitable for both manual and
mechanised operation.
It is known by a variety of names:
q
MIG - Metal Inert Gas
q
MAG - Metal Active Gas
q
CO
2
- carbon dioxide
A low voltage (18–40V), high current
(60–500A) arc between the end of a
wire electrode and the work provides
the heat needed for the welding
operation. The arc and the weld are
protected from atmospheric
contamination by a gas shield.
The shielding gas can be:
q
pure argon
q
argon mixed with small
amounts of other gases
q
helium or
q
carbon dioxide
according to the metal being welded.
See pages 9 and 26.
nozzle to plate
distance-kept at
about 19-25
mm
arc length
shielding gas
gas nozzle
spool of wire
drive rolls keep constant
wire feed speed
work
power
supply unit
keeps arc
length
constant 7
Operation
An electric motor feeds the wire into
the arc and the power source keeps
the arc length at a preset value leaving
the welder to concentrate on ensuring
complete fusion of the joint.
Power sources for MIG/MAG are
called constant voltage or potential,
known as the self adjusting arc, and
constant current, known as controlled
arc or drooping characteristic units.
Modern power sources combine
constant current and constant voltage
(cc/cv) and are called inverters.
MIG/MAG WELDING
—
MIG/MAG welding with a
Ferromaxx™gas shield gives a low
hydrogen content in the weld. This
means that lower preheat levels are
needed than with MMA welding.
˜
The process can be operated at
currents within the range 280–500A for
welding plates, thick walled pipes and
sections in the flat position. The term
‘Spray Transfer’ is used to describe
this type of operation.
Welds which are located in positions
where the metal tends to run out of the
joint under the action of gravity are
welded at lower currents (60/180A).
joints in flat position
overhead
vertical
vertical
The appropriate technique for these
types of joint is either ‘Dip Transfer’ or
‘Pulse Transfer’.
These two techniques are also used
for welding sheet material.
Synergic MIG/MAG is an advanced
welding system which incorporates
both spray and pulse transfer.
Optimum conditions can be
established for a range of applications
which are readily reproduced by the
welder.
Special equipment is required for
Synergic-MIG/MAG welding.
Welding data for MIG/MAG applica-
tions are given on pages 30 to 33. 8
Air Products Welder’s Handbook
Using MIG/MAG welding
With MIG/MAG, the wire is pointed in
the direction of travel (forehand
technique). This allows the arc to fuse
the parent metal ahead of the weld
pool and gives the best penetration.
The welder controls the speed of travel
to ensure that the weld pool does not
run ahead of the arc as this would
cause lack of fusion.
Weld quality in MIG/MAG welding is
critically dependent on the skill of the
welder and selection of the welding
variables.
Current controls:
q
heat input
q
size of weld
q
depth of penetration
Wire diameter depends on the current
required. The table gives a guide to
the selection of wire diameter but the
exact relationship depends on the
material and the shielding gas.
Voltage controls the profile of the
weld. Inductance (in Dip Transfer)
stabilises the arc and minimises
spatter. Wire feed speed sets the
welding current.
voltage
high
correct
low
75
0
- 80
0
45
0
- 55
0
Current
Wire feed
Diameter
range
speed
(mm)
(A)
(m/min)
0.6
40–100
2–5
0.8
40–150
3–6
1.0
100–280
3–12
1.2
120–350
4–18 9
MIG/MAG WELDING
Flux cored wires
Wires for MIG/MAG welding are
usually solid. For carbon, carbon-
manganese, high strength low alloy
steels and stainless steels,
flux cored wires can be used. These
offer the advantages of higher welding
speeds and easier control of fillet
weld profiles.
Ferromaxx™ Plus is the multi-purpose
gas for welding carbon, carbon-
manganese, high strength low alloy
steels and coated steels of all
thickness’ with solid wires in dip, spray
and pulse transfer and with metal and