Download Arc Welding

Contents
Introduction
3
Arc Welding
4
Theory of operation
4
Equipment
5
Rating of welding power sources
8
Electrical Connections
8
Selecting a current range
10
The arc welding process
12
Arc Welding Safety
13
Electric shock
13
Fumes
13
Hot metal
14
Harmful rays
15
Gas welding equipment
17
Flame types
23
Comparing arc- with oxy-welding
25
Safety
25
Oxyacetylene Welding
29
Uses
29
Technique
29
Consumables
30
Brazing and Soldering
31
Industrial uses
31
Brazing fluxes
31
Brazing alloys
32
Soldering
33
Braze welding
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Safety
Thermal cutting
Cutting equipment
Cutting nozzles
2
37
39
40
42
Oxyacetylene cutting nozzles
42
Safety
43
Cut quality
44
Summary
47
Words you need to know
48
Answers
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Introduction
This section will give you a basic understanding of the equipment,
procedures and processes involved in gas welding and thermal cutting. The
techniques of gas welding, brazing and braze-welding use a hightemperature flame to melt metal and form a metallurgical bond. Thermal
cutting removes metal by burning it away.
At the end of this section, you will be able to:



Describe the various forms of welding
Describe the various forms of brazing and hard soldering
Describe the process of soft soldering
Caution
The information provided here will not equip you to carry out welding and
cutting processes in the workplace. Further specialist training and safety
training is required before you can use this equipment.
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Arc Welding
In manual metal arc (MMA) welding, the electric arc reaches a temperature
of about 6000ºC. This arc provides the heat necessary to melt the electrode,
and fuse it with the parent metal.
Theory of operation
Welding units are essentially sources of high, constant current (~100 A) at a
relatively low voltage (<100 V). The constant current supply produces a
stable arc. Manual metal arc welding machines have an adjustable current
output that can be set to suit the job and the type of electrode.
The current should remain nearly constant during welding where the
operator’s movements tend to vary the arc length. These movements may be
accidental, or deliberate, to control the weld pool. An increase in arc length
will increase the voltage across the arc; however the machine is designed to
control the current close to the amperage set by the operator. Melting of the
electrode is then uniform in spite of the normal variations when welding.
This is achieved as shown in figure 1. The welder makes the arc by striking
the tip of the electrode on the work to cause a momentary short circuit. This
is at the point on the graph where V = O. With current flowing, the electrode
is drawn away by the welder to establish the arc. The amperage and voltage
for a typical arc length are shown at point x. For a longer arc length, there is
significant increase in arc voltage and a small decrease in welding current
(point y). In this way, the welding machine is designed to avoid large
changes in current output when the welder varies the arc length.
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Figure 1: Output curve of welding machine
Equipment
Welding machines operate with either alternating current or direct current.
AC machines are more widely used because they are simpler in design and
cost somewhat less. However the DC arc is much more stable with certain
types of electrode, and is consequently better for working with sheet metal.
There are three types of MMA welding machines commonly available:
AC welding machines
Alternating current welding machines are transformers which step down line
voltage (240 or 415 volts) to provide a low voltage, high current supply. The
welding current supplied by the secondary circuit of the transformer is set
by the operator to suit the type and size of electrode and its use.
DC generators
Engine driven DC models provide welding power where there is no mains
supply available, for example on site work.
Transformer/rectifier units
A transformer/rectifier both transforms an AC input voltage to a lower
voltage AC, and then rectifies that voltage to give DC.
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Transformer/rectifiers have no moving parts and are quiet to operate,
convenient and cost less than motor generator units.
Transformer or rectifiers are often designed to provide either DC or AC
outputs. DC is normally preferred because of its greater arc stability but AC
may be required at higher currents to avoid arc blow.
Figure 2: Arc welding power sources
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Figure 3: mobile engine-driven DC generator
Table 1: AC/DC comparison chart
AC transformer sets
DC motor generator sets
Portability
These machines generally consist
of static step-down transformers
and they are considered as
stationary types.
Most modern types have features
that allow portability (especially
the self contained types). They
have an undercarriage fitted with
wheels.
Power supply
The use of these machines is
restricted to the location of the
nearest alternating current power
point.
Petrol or diesel engine machines
can be used in any location
(special applications may use
generators driven by compressed
air - for example in mining).
Efficiency
70-90 percent electrically efficient.
Many multi operator sets give
higher efficiency.
40-60 per cent electrically
efficient but some modern types
compare with alternating current
efficiency.
Polarity
No polarity
A choice of polarity is obtained
by a simple reversal or a switch
(DC- or DC+)
Arc blow
Unaffected
Arc blow occurs even in normal
currents and they are difficult to
control above 300 amperes.
Maintenance
As there are no moving parts to be
considered, maintenance costs are
very low.
Revolving and wearing parts add
to running costs.
Initial costs
Cheaper plant as less construction
is involved
More costly due to generator and
motor construction.
Electrodes
Restricted to use of electrodes that
are suitable for alternating current
only.
Suitable for all types of
electrodes.
Running costs
Cheaper running costs due to the
use of an installed power supply.
Added costs due to the use of
electric motors or internal
combustion engines.
Voltage control
Constant open circuit voltage.
A variation of open circuit
voltage is possible allowing a
selection of electrode type and
welding technique.
Arc length
Limited arc length.
Greater tolerance in arc length
due to the characteristic of the
machine.
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Rating of welding power sources
Australian Standard AS1966 rates the output (duty cycle) of electric arc
welding power sources. The machines are classified according to the type of
service for which they are designed, for example: continuous duty, heavy
duty, light industrial or limited output cycles.
The standard defines each of the classes according to the output (load
current, load voltage) needed for a nominated duty cycle. The duty cycle
allows for the fact that in any five minute period, current for welding may
be drawn for only part of that time. For example, if welding is for a
maximum of three minutes in any five minute period, the machinery only
operates up 60% duty cycle (3/5 of 5 minutes). A much lower current must
be selected for continuous (100%) operation.
All power sources must display a name plate stating the equipment class and
the rated output and duty cycle for its class (e.g. 300 amps, 23 volts, 605%
duty cycle). The 100% duty cycle output current must also be noted.
Electrical Connections
A multiple-strand insulated flexible copper or aluminium lead conducts the
welding current from the power source to the work. A return clamp is
fastened to the work, and another cable completes the welding circuit
between the work and the power source.
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Figure 4: Cable connections (secondary circuit side)
Electrode holders should suit the minimum output current being used. The
holder should be relatively light, comfortable to hold, fully insulated and
sturdy enough to withstand the wear and tear from constant use. The holder
should be rated to withstand the maximum current required for the activity.
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Figure 5: Electrode holders
Notes regarding polarity:

Output terminals on AC machines are labeled ‘electrode’ and
‘work’.

On a DC machine, the terminals are marked positive (+) and
negative (-) except in the case where the polarity can be changed by
means of a polarity reversing switch. In such cases the terminals are
marked ‘electrode’ and ‘work’ with electrode terminal polarity
indicated at the polarity switch.

Most, but not all, electrodes for DC are designed to be the positive
terminal (+). Refer to manufacturer’s recommendations.
Selecting a current range
Follow the manufacturer’s recommendations on the range of current for
different types and sizes of electrodes. Some typical current ranges for
different electrode types of shown in table 1.
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You should use the recommended procedure and draw on experience to
select the electrode type and size. The choice of current will also depend on
such factors as:

weld position

thickness of the joint parts

root gap

access to the structure.
Typical current ranges for the electrode classifications
Electrode
Diameter = 4.0mm
Diameter = 3.25mm
E4110
130-160
75-125
130-190
90-140
E4114
140-200
95-150
E4814
130-170
100-130
E4818
140-200
105-150
185-235
130-170
E4111
E4112
E4113
E4815
E4816
E4824
E4828
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The arc welding process
The notes below are for general information only, they do not qualify your
to perform arc welding!
Striking the arc
1.
Turn on the power source.
2.
Lightly touch the end of the electrode on to the work and you will
complete the circuit and current will flow.
3.
The electrode end rapidly heats, melting sufficiently to momentarily
weld the electrode on to the work.
4.
Due to the low voltage current you are using, the arc will not jump an
air gap (as in a spark plug). You must therefore establish an arc by first
touching the end electrode onto the work and then immediately,
increasing the distance between end of the electrode and the work
allowing droplets of metal and flux to cross the arc gap (approximately
3 mm) to form a molten pool.
5.
If you fail to do this, droplets will bridge the arc gap, causing a short
circuit and a freezing of the electrode end onto the work.
6.
If your action is incorrect and the electrode freezes onto the work (that
is becomes welded or stuck to it) a sharp backward angling of the
electrode should break it free. When this occurs, keep your head shield
on, as an arc flash will occur as the electrode breaks contact.
Laying down a weld bead
12
1.
Once the arc has been established, the arc length is reduced to about 3
mm
2.
As the molten pool accumulates, the tip of the rod is moved along the
weld slowly, so as to maintain a molten pool approximately 8mm wide
behind the arc.
3.
The electrode is fed in constantly as it burns off, maintaining a steady
rate of consumption by using the correct arc length.
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Arc Welding Safety
Hazards in the welding workshop include electric shock, fumes, heat, glare
and harmful rays.
Electric shock
Electric shocks are possible on the secondary (low voltage) side of the
welding circuit. They may be caused by:

working on wet floors – a shock may be felt when putting an
electrode in the holder. Always stand on insulated mats or wooden
boards to reduce the risk and wear dry leather gloves.

working in a very humid climate or rainy weather – a shock may be
felt when changing electrodes. Keep electrodes and gloves dry.
High voltage shocks shouldn’t happen if precautions are taken such as
ensuring welding machines are maintained by licensed electricians and that
you never interfere with the inside parts of the welding machines.
Fumes
Gases, dusts and vapours are given off during welding. They can cause:

gassing or asphyxiation because the oxygen has been used up in the
work area (common in confined spaces)

build up of poisonous metals in the body, such as lead, cadmium,
zinc, beryllium or mercury

respiratory ailments from wheeziness to serious lung disorders.
Fumes can result from:

the production of oxides and nitrous gases from incomplete
combustion or oxidation of nitrogen from the atmosphere

the surface coating on steel such as galvanizing, cadmium or chrome
plating and paints and solvents such as red oxide parts or degreasing
solvents

elements within the parent metal
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
electrode flux coatings.
Welding should be carried out in well ventilated areas. When welding high
fuming materials such as galvanized steel, use extraction systems to carry
away the fumes.
If an extraction system is not available, an approved respirator should be
used to filter out fumes. Normally, respirators should only be used as a
secondary protection.
Hot metal
Molten droplets from welding spatter can get into boots and clothing. You
can avoid this by wearing protective clothing and footwear. When welding
out of position, wear spats over your boots and under overall legs.
Protective clothing will help to protect you from heat, hot metal and harmful
rays.
Figure 6: Full protective clothing for arc welding
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Harmful rays
Welding arcs give off a broad spectrum of electromagnetic radiation, from
ultraviolet, through visible and infrared wavelengths.
Ultraviolet radiation in particular can damage the skin. Ray burn is like very
severe sunburn; your skin reddens and then peels. If the ray burn is very
severe, there may be blisters and sores.
Rays will harm the eyes, causing a condition called a flash or arc eye. The
first symptom of a flash is an itchy feeling in the eye. Afterwards, a
throbbing pain (much like sand in the eye) may stop you sleeping. There are
eye drops that relieve the pain. Continuous flashes may cause blindness.
The use of filter lenses is essential to protect your eyes from these rays.
Filter lenses
These are specially designed glass lenses to filter out harmful rays and allow
you to see what you’re welding without causing any changes in the pupil
size or damage to your eyes. Filters come in different shade numbers,
according to the current range or type of welding.
The following table indicates the recommended minimum protective filters:
Approximate welding current
(Amperes)
Filter recommended
Up to 100
8
100 – 200
10
200 – 300
11
300 – 400
12
Over 400
13
Protection of others
Welding should be done in special welding bays. When this is not possible,
use portable screens to shield others working in the areas from the rays
generated from the arc. You should also put up signs to warn people that
you are welding.
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Figure 7: Swivel filter and clear glass type visors
Figure 8: Head shield and hand held shield
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Student exercise 1
1.
How does an arc welder melt steel?
_____________________________________________________________________
_____________________________________________________________________
2.
A welder power supply is basically a source of high, constant ________ at a relatively
low _______
3.
Why should a welding unit supply a relatively constant current?
_____________________________________________________________________
_____________________________________________________________________
4.
Name three types of manual metal arc welding equipment.
_____________________________________________________________________
_____________________________________________________________________
5.
Name three hazards that are presented by welding.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
6.
What personal protective equipment should be worn by a welder?
_____________________________________________________________________
_____________________________________________________________________
7.
What hazards exist for bystanders near welding operations, and how can they be
protected?
_____________________________________________________________________
_____________________________________________________________________
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Gas welding equipment
When acetylene is burnt in pure oxygen, the flame temperature is about
3100°C. No other combination of burning fuel gas and oxygen can reach
this temperature. Acetylene (C2H2) is the only fuel gas suitable for fusion
welding carbon steel because it:

burns at the highest temperature in pure oxygen

produces a flame that is least likely to contaminate the weld.
Oxyacetylene equipment includes the gas cylinders, pressure tubing,
welding torches and tips, and consumables such as the gases, and rods.
Figure 9: Oxyacetylene welding equipment
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Oxygen
Oxygen is an odourless, colourless gas which makes combustion (burning)
possible. About 20% of the atmosphere is oxygen, and the other 80% is
mainly nitrogen.
Industrial oxygen is produced by fractional distillation of liquid air. Oxygen
can be supplied as a liquid and takes up very little space compared to a gas.
But more commonly, oxygen comes in cylinders as a compressed gas.
Industrial oxygen cylinders come in three sizes and are filled to a pressure
of 15,000kPa. They are always painted black, and as with all nonflammable gas cylinders, have a right-hand thread on the regulator
connecting outlet.
There is a bursting disc at the tip of the cylinder designed to blow out at a
much lower pressure than the amount that would rupture the cylinder.
Because of this there is less chance of cylinders exploding in fires.
In the illustration below, the letters G, E and D indicate the cylinder size.
These are the typical cylinder sizes you will encounter with G typically
being the largest size cylinder available.
Figure 10: Oxygen cylinders
Figure 11: Oxygen cylinder valve
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Acetylene
Acetylene is highly flammable, colourless and has a strong, odour that is not
pleasant.
Stored acetylene is dissolved under pressure in liquid acetone in special
cylinders. Porous material inside the cylinders is saturated with acetone to
further reduce the risk of free compressed acetylene building up There is no
free gas present in acetylene cylinders. The gas is dissolved under pressure
in acetone. The effective cylinder pressure is 1600 kPa.
Caution!
If acetylene is compressed as a free gas it becomes unstable and may explode.
The cylinders are painted crimson and have more square shoulders than
oxygen cylinders. They have left-hand threads at the regulator outlet and
fusible plugs which will release the gas and stop the cylinder exploding if
the temperature reaches 100°C.
Figure 12: Acetylene cylinders
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Figure 13: Acetylene cylinder valve
Regulators
Regulators are fixed to the gas cylinders for welding and cutting. The
function of regulators is to:



reduce the cylinder pressure to a safe working pressure at the
welding torch
provide a constant gas pressure while the cylinder contents are being
reduced
enable an accurate working pressure to be set and adjusted as
needed.
Caution!
Regulators are the same colours as the cylinders and must not be interchanged.
They are precision instruments and should not be treated roughly.
Figure 14: Acetylene regulator
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Welding torch
The oxy-acetylene welding torch is made to mix oxygen and acetylene in
the proportions needed, and to control the volume of gases burnt at the
welding tip.
Welding tips (jets)
The welding tip screws into the mixer on the end of the torch. The tip directs
the flame where it is wanted and the size of the orifice or hole decides how
much gas is supplied.
Thicker material needs more heat, so a larger tip is used. The image and
chart below show tip sizes used on various thickness of low carbon steel.
Figure 15: Welding torch and tips
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Flame types
By adjusting the mixture of oxygen to acetylene, three basic flame types can
be achieved, which are used for different purposes. There are called neutral,
carburising and oxidising.
Neutral flame
The neutral flame results when the amount of oxygen is just sufficient to
oxidise the acetylene. The neutral flame is therefore ‘balanced’.
A neutral flame is used for fusion welding steel and cast iron. The flame is
relatively harmless to steel, and will neither oxidise it, nor increase its
carbon content. This flame produces an inactive weld pool without sparks.
Carburising flame
When acetylene is in excess of the neutral flame condition, this produces a
carburising flame.
The bright inner cone of the flame is surrounded by a longer white feather.
This type of flame normally damages the weld area. However, a slight
carburising flame is often set for pipe welding to guard against the more
damaging oxidizing flame.
If a highly carburising flame is used, carbon is added to the weld area,
welding is slower and there is sparking.
Oxidising flame
When oxygen is in excess of the neutral flame condition, this produces an
oxidising flame.
The inner cone becomes shorter and pointed. The secondary stage of
combustion is much shorter and there is often a hissing sound. If this flame
is used to weld steel, the weld pool will boil and oxidise, destroying the
properties of the steel.
A slightly oxidising flame is used for braze welding.
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Figure 16: Oxyacetylene welding—flame adjustments
Figure 17: Neutral flame temperature zones
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Comparing arc- with oxy-welding
There are advantages as well as limitations of fusion welding low carbon
steel over other forms of welding. The advantages include:

no electrical supply is needed

equipment is portable and can be taken to the job rather than the job
brought to the workshop

no post-weld cleaning (slag removal) is needed.
Disadvantages of include:

very slow compared to arc processes

requires a lot of skill

heavy welds require heat treatment to normalise the grain structure

there is more distortion because of the high heat input.
Safety
The safety notes are provided for general information, but note again that
you must be specifically qualified and licensed to perform thermal welding
and cutting at work.
Protective clothing
When using oxyacetylene or other oxy-gas equipment, you must protect
yourself from the radiated heat and light, from fumes and from hot objects
and spatter. You also need to handle oxygen, acetylene and your equipment
carefully. Personal protective equipment includes:

Shade 5 or 6 goggles—Australian Standard approved

a shirt and trousers of non-flammable material that is tough and wear
resistant

firm-fitting leather shoes or boots

leather gloves

head covering

appropriate model of respirator where fumes are not completely
extracted from the area.
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Safety with oxygen
Oxygen by itself is not flammable or explosive, but it will support
combustion and cause material to burn rapidly.

Don’t use oxygen other than for its intended purpose. Never use oxygen
as compressed air might be used, for example for blowing out dirt,
powering pneumatic tools, or for spray-painting. Don’t use it to freshen
the air, to clean fumes in a confined space or to cool you on a hot day.

Do not lubricate oxygen connections with petroleum products.
Safety with acetylene

Don’t try to transfer acetylene from one cylinder to another acetylene is
dissolved in liquid acetone in the cylinder.

Always leave the cylinder key in the cylinder when using acetylene.

The fusible plugs on these cylinders melt at 100°C. Store the cylinders
in a cool, well ventilated protected location.
Safety with equipment

Oxyacetylene welding is quite safe if you use the equipment properly
and keep it in good working order.

Report all faulty or damaged equipment.

The work area must be well ventilated.

How work is marked to warn people not to touch it.

Oxy welding equipment is not used in a confined space, as gas leaks can
lead to explosions.
Safety while welding
26

Always wear the required PPE.

The oxy flame is lit with an approved striker flint, or igniter designed for
the purpose.

The burning temperature of the combined oxygen and acetylene gases is
about 3100°C. This flame can burn flesh instantly.

Sparks and spatter move rapidly and will damage unprotected eyes.
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

Heat and light radiation can lead to severe eye damage if you do not
protect your eyes.
Extractors or respirators must be used when there are dangerous fumes
from welding.

Don’t let any flux contact your skin. Be very careful when using acids.
Always wear protective clothing, gloves and goggles when working with
chemicals

You must have adequate ventilation (or other protection such as a
respirator) when brazing. Fumes can come from the flux, from the
parent metal, from the filler rods, or from coatings (eg cadmium or zinc)
on the parent metal. Ventilation is particularly important when the flux
contains fluorides, or when the brazing alloy contains cadmium.
.
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Student exercise 2
1
List four essential component parts required to operate an oxyacetylene welding plant.
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
2
Cylinders are identified by shape and colour. What colour are:
• oxygen cylinders? ____________________________________________________
• acetylene cylinders? __________________________________________________
3
Name two industrial uses for oxyacetylene welding.
_________________________________________________________________________
_________________________________________________________________________
4
List three types of flame settings.
_________________________________________________________________________
5
Briefly describe how the atmosphere is excluded from the weld pool during the
oxyacetylene process.
_________________________________________________________________________
_________________________________________________________________________
6
List three items of clothing you need to protect you when oxy-acetylene welding.
_________________________________________________________________________
Check your answers with those given at the end of the section.
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Oxyacetylene Welding
Oxyacetylene welding is a manual process which combines oxygen and
acetylene gases to give a high temperature flame for welding.
The edges of the parts to be joined are melted and fused together to form a
high-strength joint. Additional weld metal can be added from a hand-held
filler rod.
Uses
Oxyacetylene welding is used for:

light fabrication industry (eg chairs—tubular sheet-metal components)

repairs/reclamation of parts (eg castings), light components (thickness),
automotive body panels/exhausts

farming tasks—because of its portability, it’s often used on site to repair
or build light structures and machinery.
Oxyacetylene welding is often limited by its comparatively slow welding
speed, but because of its ability to weld most metals, this versatile process is
a valuable maintenance tool.
Technique
Two main techniques are used, known as forehand and backhand welding.

In forehand welding, the welding tip point towards the unwelded section
of the joint welding and follows the filler rod along. It is used for most
general welding.

In backhand welding, the welding tip points towards the welded section
of the joint and the filler rod follows the tip along the job. This
technique means better root penetration on thicker sections of material.
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Consumables
Filler rods come in several sizes and different types, made to provide a
range of weld metal properties. Rods must be selected to suit the type of
metal and the service requirements of the job. Manufacturers’ information
sheets give guidance to selection.
Filler rods for low carbon steel are classified in AS1167 Parts 1 and 2:

RG low carbon steel filler rod is for general purpose welding. It has very
low carbon content and produces ductile weld deposits.

R1 low alloy steel filler rod has a much higher tensile strength and is often
used on pressure pipes and for higher strength welds. These rods are copper
coated to avoid oxidation (rusting) during storage. They are often called by
their trade name hi-test.
A flux is not needed for fusion welding low carbon steel. The oxides that
form on low carbon steel have a low melting point and are prevented from
forming by de-oxidisers in the filler rod.
These deoxidisers, sometimes called reducing agents, are usually
manganese, silicon and aluminium all of which join harmlessly with oxygen
at temperatures lower than iron does.
Figure 18: Fusion welding
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Brazing and Soldering
Brazing is similar to soldering because capillary action draws the molten
filler metal between two close-fitting surfaces and joins them. Lap joints and
prepared fillet joints are recommended. However, brazing is much stronger
and more expensive than soft soldering and is done at temperatures above
450°C.
Industrial uses
Brazing is commonly used for:

electrical connections

copper pipes and fittings

furniture

auto fitting
Most ferrous and non-ferrous metals used in industry can be joined with
either copper or silver alloys. You can braze different metals together—such
as copper to steel.
Examples of metals commonly brazed are

steel—most grades and alloys

copper

stainless steel

brass.
Brazing fluxes
Fluxes are used for most brazing operations to:

assist the filler alloy to flow freely

clean the surfaces to be joined

prevent oxides forming on the brazed joint.
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Fluxes are available in a number of forms. The most common fluxes are
powder, liquid or paste. Manufacturers’ information leaflets will help you to
select the most suitable flux for a particular job.
Brazing alloys
Brazing alloys are available in many combinations. Filler metals come in
two main groups:

copper base alloys

silver base alloys.
You must choose the most suitable alloy. Points to consider include:

mechanical strength of the joint

materials involved

finish required

cost

your level of skill

colour of joint—matching the workpieces if required.
Silver alloys are free flowing. They can enter small openings and provide
strong neat-looking joints. Silver brazing is also called silver soldering or
hard soldering, and is used for joining steel, copper, bronze and brass.
For silver brazing you need a filler metal made of silver and copper alloy
and a commercially prepared flux. Silver brazing alloy melts at a lower
temperature than other alloys used for brazing. Common heating gas
mixtures are oxygen and acetylene, and oxygen and LP gas.
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Figure 19: Protective clothing
Soldering
Soldering is a similar process to brazing, except that soldering alloys have a
melting point of less than 450°C. Soldered joints are not as strong as with
brazing. Soldering is used where the lower melting point or the excellent
flowing and wetting ability of solder are important. Applications include
electrical and plumbing work.
In electrical work, soldering is used where a permanent, low-resistance
connection is required, for example in printed circuit boards, and for making
earth connections. The eutectic alloy of 63% tin and 37% lead is used,
which has very specific properties:
 It is the lowest melting point mixture of tin and lead.
 During heating or cooling it transitions directly from solid to liquid, with
no ‘plastic’ phase. This makes it much easier to get good joints, because
movement during the plastic phase will reduce the strength and
conductivity of the joint.
Electrical solder is supplied is wire form, which can easily be fed into a
joint. The wire incorporates about 1% of rosin flux at its core, which helps
to remove oxide from the parent metal, and protects it from rapid oxidation
at soldering temperatures.
To obtain a good soldered joint for earth leads:
 The soldering iron tip should be clean and properly tinned. When the tip
is wiped across a damp sponge, the surface should be bright.
 The parent metal surfaces should be clean and free of oxide, grease or
other contaminants. For wiring joints, you should strip the wire
immediately before soldering and not touch the exposed wire with your
fingers.
 Strip about 20mm of insulation from each wire and twist together with
pliers. Take care not to apply excessive force.
 Apply a small amount of solder to the tip, and then apply the tip to the
work. This gives the best thermal contact, for rapidly heating the work
and avoiding oxidation. Feed in more solder as required as soon as the
work reaches an adequate temperature. You should see the solder wick
quickly into the joint.
 Earth wires may be soldered in a single operation, but thicker wires and
terminals should be individually tinned before making the final joint.
Soldering Safety
Fume from rosin flux is both an allergen and an irritant. Exposure over an
extended period can lead to sensitivity and respiratory problems. Make sure
that soldering is done with good ventilation.
Soldering stations for electronic work should be equipped with extractors or
air filters to remove the soldering fumes.
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Note that lead-free solders have replaced lead solder for all plumbing work,
due to the toxicity of lead.
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Student exercise 3
1
List three metals which can be joined using the brazing process.
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
2
Name two common heating gas mixtures used for brazing.
_________________________________________________________________________
_________________________________________________________________________
3
Name a type of weld joint recommended for brazing.
_________________________________________________________________________
4
What distinguishes soldering from brazing?
_____________________________________________________________________
_____________________________________________________________________
5
Why is it important for the parent metal to be clean and free of oxide?
_____________________________________________________________________
_____________________________________________________________________
6
What is a eutectic mixture?
_____________________________________________________________________
_____________________________________________________________________
Check your answers with those given at the end of this section.
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Braze welding
Braze welding is different from brazing and uses different joint preparation,
filler metal and welding technique. For braze welding you use weld
preparations like the ones used for fusion welding. The weld preparation
allows for a full thickness weld and gives a strong joint.
Braze welding uses an oxyacetylene flame, a flux to clean the surface and a
filler rod made from a copper/zinc alloy (bronze). The filler rod melts at a
much lower temperature than the parts to be joined and the parent metal is
not melted.
Braze welding technique
Molten bronze will flow onto properly heated and fluxed surfaces of metals
with higher melting points. You need to adjust the flame to contain a slight
excess of oxygen. The flux is added to the heated end of the filler rod and
applied to the joint during brazing.
Advantages of braze welding
Braze welding is able to join a greater range of dissimilar metals, including
non-ferrous and ferrous (eg copper tube) steel. It also requires much less
heat input and causes less distortion.
Disadvantages of braze welding
Braze welding has greater consumable costs, and there is a loss of strength
at moderately high temperatures (above 260°C). There is also the change of
a corrosive attack if the weld comes into contact with ammonia.
Braze welding is used for repairing machinery and for fittings in
maintenance work.
Other uses include leak proof joints on tanks and the construction of hollow
section components such as those used for furniture manufacture.
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Safety
Precautions are the same as for brazing:

adequate ventilation

don’t allow fluxes to touch your skin

use flame and other equipment carefully.
Safe clothing
Use the right equipment for the work you have to do. For example for bench
work, use:

overalls

work boots

non-flammable underclothing

oxywelding goggles with standard filter lens.
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Student exercise 4
1
Braze welding is different from brazing because:
_________________________________________________________________________
_________________________________________________________________________
2
Name the two main metals that make up the alloy filler rod for braze welding.
_________________________________________________________________________
_________________________________________________________________________
3
You use a flux in braze welding to give:
_________________________________________________________________________
_________________________________________________________________________
4
List three metals suitable for welding with the braze-welding process.
_________________________________________________________________________
5
Name one use of braze welding.
_________________________________________________________________________
6
(a) List two advantages of braze welding:
___________________________________________________________________
___________________________________________________________________
(b) List two disadvantages of braze welding:
___________________________________________________________________
___________________________________________________________________
Check your answers with those given at the end of this section.
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Thermal cutting
The flame, or thermal, cutting process used for cutting iron and steel
depends on a chemical reaction between heated iron and oxygen.
When a piece of iron or steel is heated to a temperature of 815°C (called the
ignition temperature) the material will burn to form a lower melting-point
substance, called iron oxide.
This chemical reaction generates a great deal of heat, which enables the
cutting to continue. Once the metal begins to burn, the heat generated will
lead to a progressive spread of oxidisation through the material. This
important property of flame cutting allows you to cut and pierce thick steel
without all of the metal heating up.
The ignition temperature is the temperature at which the reaction begins.
The ignition temperature for low carbon steel is 815°C. This is well below
its melting temperature, which is about 1450°C.
The cutting action is a function of the high-speed jet of oxygen. The purpose
of the flame is to heat the metal to its ignition temperature so that the cutting
can begin. Theoretically, once the cutting begins, the flame shouldn’t be
necessary. However heat is lost from the work through conduction so it’s
necessary to keep the pre-heat flame going while you’re working.
The most common gas combinations used for pre-heat are oxyacetylene,
oxy-LPG (liquefied petroleum gas) and oxy-natural gas.
Steps in flame cutting
1 Use the flame to raise a small section of the metal to ignition
temperature.
2 Release a high-speed jet of oxygen onto the heated section.
3 By controlling the direction of the blowpipe nozzle and combining it
with the oxidising action, you can cut through the metal. The width of
the cut through the steel is called the kerf.
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Figure 20: Flame cutting
Limitations
Flame cutting relies on a chemical reaction between heated iron and oxygen,
so you can normally only use it on iron and steel iron. Non-ferrous metals
(copper, brass, aluminium etc) can’t be flame cut.
If a metal is to be readily flame cut it needs:
1. an ignition temperature below its melting point so that the metal can be
cut without being melted by the flame
2. the oxide or slag that forms from the cutting action to have a lower
melting point than the metal being cut.
This method will cut carbon steels and most low-alloy steels commonly
used for construction work. Some high-alloy steels are difficult to cut,
mainly because of the high melting point of the surface oxides that form
under the oxygen jet. Non-ferrous metals (copper, brass, aluminium, etc)
cannot be cut because of the absence of iron content and the formation of
high melting-point oxides.
Cutting equipment
You use the same portable flame-cutting plant as you would for
oxyacetylene welding except for the cutting torch or cutting attachment
connected to the hoses.
The plant consists of:
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
oxygen cylinder

acetylene cylinder

gas regulators

hoses

cutting torch

cutting nozzle

cylinder trolley.
Cutting torches
Types of manual flame cutting torches are:
1. multiple-purpose cutting torches that are heavy duty cutting and gouging
units
2. cutting attachments that are used with a normal welding blowpipe. This
unit is cheaper and offers more versatility than the multi-purpose unit
but is not as robust and does not have the thickness cutting capacity.
Figure 21: Blowpipe attachment with handle
Cutting technique
The torch can be guided by hand (freehand) for normal use. However, there
are aids to steady the cutting torch movement to improve the quality of the
cut (eg a roller guide attachment as shown in Figure 14).
Figure 22: Roller guide attachment
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Cutting nozzles
Cutting nozzles are designed for different thicknesses and applications. Each
nozzle is stamped to indicate the size, type of fuel gas and process.
Oxyacetylene cutting nozzles
Figure 23: Various oxyacetylene cutting nozzles
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Nozzle identification
Every cutting nozzle or tip is stamped for easy identification. The stampings
indicate the type of nozzle, the size of nozzle and special process
identification.
Nozzle type
The first part of the type number gives the form of nozzle connection. The
30 series nozzles are screw-in type with a threaded inlet connection. The 40
series nozzles are the taper seat type.
The second part of the type number indicates the fuel gas used. If the type
number ends in a ‘_1’ the nozzle is used with acetylene, if it ends in ‘_4’ it
is used with LPG (liquefied petroleum gas).
Gas number identification
1
Acetylene
2
Low pressure acetylene
3
Coal gas
4
LPG
5
Hydrogen
Size of nozzle
The size number tells you the diameter of the main bore and is stamped
underneath the type number. The size number is a tenth of a millimetre, for
example a size 12 nozzle has a main bore diameter of 1.2 mm. Typical
nozzle sizes are 6, 8, 12, 15 and 20.
Safety
Be careful when you’re flame cutting as the cutting stream can shower hot
metal sparks over great distances. The protective clothing you need for
flame cutting is the same as for welding:

overalls

goggles (shade 5 filter)

leather gloves

leather apron

steel-capped boots

spats.
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Cut quality
Factors which will affect the quality of the cut are:

metal composition

surface cleanliness—free from paint, oil, grease, etc

cutting nozzle size and condition

gas pressures

size of preheat flame

cutting speed

distance of nozzle from the job.
Figure 24: Effects of variations in flame-cutting procedures
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Student exercise 5
1
Flame cutting requires low carbon steel to be heated to an ignition temperature of:
_____________________________________________________________________
2
List two additional basic steps for flame cutting:
(a) The flame is used to raise a small section of metal to ignition temperature.
(b) ___________________________________________________________________
___________________________________________________________________
(c) ___________________________________________________________________
___________________________________________________________________
3
Name three suitable fuel gases used for oxy-fuel gas cutting.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
4
The gas used to support combustion when flame cutting is:
_____________________________________________________________________
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5
Symbols are used on cutting nozzles. What do the following numbers on a cutting
nozzle indicate?
Type 41: ______________________________________________________________
No. 12: ______________________________________________________________
6
List the factors which will affect a flame cut finish:
(a) Material’s surface should be clean and free from paint, oil, grease, etc.
(b) ___________________________________________________________________
(c) ___________________________________________________________________
(d) ___________________________________________________________________
(e) ___________________________________________________________________
Check your answers at the end of this section.
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Summary
You should now have a basic understanding of the equipment, procedures
and processes involved in thermal welding and cutting. Safety is particularly
important for thermal cutting and joining processes, and we remind you that
specific qualifications and licensing are required for welding and cutting.
Safety area
Protective clothing
Oxygen
Acetylene
Equipment
Brazing and flame
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Safety considerations
•
shade 5 or 6 goggles
•
shirt and trousers of non-flammable material
•
firm-fitting leather shoes or boots
•
leather gloves
•
head covering
•
don’t operate pneumatic tools with oxygen
•
don’t use it for spray painting
•
don’t use instead of compressed air
•
don’t blow out pipes, vessels or containers
•
don’t use to freshen the air, clean fumes or cool yourself
•
don’t try to transfer from one container to another
•
always leave the cylinder key in the cylinder
•
store in a cool, well ventilated, protected location
•
ensure the work area is well ventilated
•
mark finished work hot to warn people not to touch
•
the flame is extremely hot—treat with caution
•
report all faulty/damaged equipment
•
check hoses regularly for leaks
•
fluxing agents contain toxins, so ensure adequate ventilation
•
don’t let flux contact skin
•
when using acids, wear protective clothing, gloves and
goggles
•
for flame cutting, include leather apron, steel-capped boots
and spats
47
Words you need to know
acetone
a flammable and volatile liquid used as a solvent to dissolve and
stabilise acetylene under pressure.
acetylene
a highly combustible gas composed of carbon and hydrogen (C2H2)
and used as a fuel gas in oxyacetylene welding and cutting. When
burnt with oxygen in the correct proportions, it produces a flame
temperature of about 3100°C.
alloy
a mixture of two or more metals in solid solution.
arc
an electric current crossing the gap between an electrode and the
work.
automatic
welding
welding in which the means of making the weld are controlled by
machine.
backfire
a loud snapping or popping noise caused when the blowpipe flame
goes out suddenly or momentarily.
backhand
welding
(rightward, backward) welding with the blowpipe flame pointing in
the opposite direction to that in which the weld progresses—the
opposite of forehand welding.
backing strip
material (metal, carbon etc) used to back up the root of the weld and
retain the molten metal.
blowhole
a cavity in the weld metal caused by a bubble of gas becoming
trapped in the solidifying metal.
blowpipe
an instrument for bringing together and properly mixing fuel gas and
oxygen in such a manner that the mixture, when ignited, will produce
a controlled flame.
bonding
the joining of two or more metals.
braze welding
unlike brazing, does not depend on capillary attraction. The parent
metal is not melted, but the joint design is similar to that which would
be used in fusion welding. The filler metal is a non-ferrous alloy, with
a melting point lower than that of the metal being joined.
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brazing
a joining process in which the molten filler metal is drawn by
capillary action between two closely adjacent surfaces to be joined.
The filler metal is a non-ferrous metal or alloy with a melting point
lower than that of the metal being joined. A process that is more like
soldering than welding.
capillary action
the phenomenon by which the molten filler metal flows between the
properly fitted surfaces of the joint.
Celsius (C)
a temperature scale that registers the freezing point of water as 0°C
and the boiling point as 100°C under normal atmospheric pressure.
combustion
the process of burning.
conduction
the transmission of an electric charge or heat through a medium.
consumable
material that is actually consumed during the welding process (eg
electrodes, filler metals, fluxes, gases).
contamination
the oxidisation of the weld pool or the generation of gas from organic
materials which will cause weakening of the weld.
cover glass
a clear glass used to protect the filter in goggles.
cutting
attachment
an attachment to a welding blowpipe handle to convert it to a cutting
blowpipe.
cutting
blowpipe
equipment used in oxygen cutting. It is designed to control the gases
for pre-heating, as well as the oxygen used for cutting.
cutting oxygen
the jet of oxygen from the central opening of the cutting nozzle which
oxidises the preheated metal, allowing the cutting action to take place.
It shouldn’t be confused with the oxygen that mixes with the
acetylene for the pre-heat flames.
deoxidising
the process of removing oxygen.
deposition rate
the weight of metal deposited in a unit of time.
diameter
a straight line passing through the centre of a circle and touching the
circumference on both sides.
downhand
welding
see flat position.
ductility
the ability to be easily moulded or shaped.
ferrous
a metal that contains iron.
filter (lens)
a filter, usually made of glass, designed to protect a welder’s eyes
from glare and harmful radiation.
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flashback
the burning back of the flame into the blowpipe or the ignition of an
explosive mixture in one of the gas lines.
flat position
the position in which welding is performed from the upper side of the
joint when the weld face is nearly horizontal.
flux
a chemical powder or paste which dissolves oxides, cleans metal and
prevents oxidisation during welding.
flux inclusion
a cavity in the weld metal containing flux caused by a quantity of flux
becoming trapped as the metal hardens.
forehand
welding
(leftward, forward) welding with the blowpipe flame pointing in the
direction of the weld—that is, towards the unfinished seam. The
opposite of backhand welding.
freehand flame
cutting
the cutting process in which the operator both holds and guides the
hand-cutting torch.
fusion
the joining of two metals during the welding process.
gas thermal
cutting
the parting or shaping of materials by the application of heat with a
stream of cutting oxygen.
horizontal
welding
welding in a position in which the line of the weld is horizontal but
the surface of the work is vertical.
ignition
temperature
the temperature at which a material will ignite (eg 815°C for iron).
kerf
the space left during flame cutting by the removal of metal.
manual
working by hand.
non-ferrous
a metal that does not contain iron.
overhead
welding
welding in which the filler metal is deposited from the underside of
the joint and the face of the weld is approximately horizontal.
oxide
a compound of oxygen with another element or substance. Rust and
mill scale are examples of iron oxides.
oxidisation
the process of forming an oxide (eg a section of steel rusting).
oxygen
a colourless and odourless gas which supports combustion and is
present in the atmosphere to the extent of approximately
21 per cent by volume. When the correct mixture of oxygen and
acetylene is burnt, a flame temperature of approximately 3100°C is
obtained.
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parent metal
the metal of the part to be welded as (base metal) opposed to the metal
that is added from the filler rod.
portability
able to be moved easily.
preheat
heat applied before welding or cutting operations begin, used to
prevent distortion, cracking and unwanted hardening.
radiation
the transfer of heat through space by wave motion. All bodies that are
at a higher temperature than their surroundings radiate heat.
semi-automatic
welding
welding in which some of the welding variables are automatically
controlled, but manual guidance is necessary.
shielding
a process in which gases produced are added during the welding to
exclude the harmful elements contained in the atmosphere.
slag
a fused, non-metallic residue produced from some welding processes.
slag inclusion
non-metallic material trapped in a weld.
tack weld
a short weld used for assembly purposes only.
tip
the generally detachable part of a blowpipe from which gas or gases
emerge for welding.
toxic
poisonous.
vertical welding welding in a position in which the axis of the weld is almost vertical.
volatile
evaporating rapidly.
weld
a union between pieces of metal at faces rendered plastic or liquid by
heat pressure or both. Filler metal may be used.
welding hose
reinforced rubber hose strongly built to resist the pressure of the gases
and to withstand constant bending and twisting.
weld metal
metal in a welded joint which has been melted in making the weld.
The weld metal includes the filler and parent metals.
weld pool
the metal pool which is deposited while making the weld. It can
consist of filler metal, plate material or a mixture of both.
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Check your progress
1
State the identifying colours for:
• oxygen cylinders _____________________________________________________
• acetylene cylinders ____________________________________________________
2
What are the pressure gauge settings required when using a size 15 tip?
• oxygen ____________________________________________________________
• acetylene ___________________________________________________________
3
List five important personal safety items that must be worn at all times while operating
oxyacetylene welding equipment.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
4
List four hazards associated with oxyacetylene welding equipment.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
5
What would you do to correct a flame that was producing soot (a carburising flame)?
_____________________________________________________________________
_____________________________________________________________________
6
Why is it necessary to protect the molten puddle with the flame?
_____________________________________________________________________
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7
What are the two functions of a welding torch mixer?
_____________________________________________________________________
_____________________________________________________________________
8
Explain how brazing with oxyacetylene differs from welding with oxyacetylene.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
9
State three reasons for using flux in brazing.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
10 Name two metals used for filler metals in brazing.
_____________________________________________________________________
_____________________________________________________________________
11 What is the parent metal melted during the braze welding process?
_____________________________________________________________________
12 Can ferrous and non-ferrous metals be joined using braze welding?
_____________________________________________________________________
13 What substance is formed when steel is heated to ignition temperature?
_____________________________________________________________________
14 Is the melting point of this new substance higher or lower than that of the parent
metal?
_____________________________________________________________________
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15 What property of the chemical reaction between heated iron and oxygen allows flame
cutting to proceed?
_____________________________________________________________________
_____________________________________________________________________
16 Describe the three basic steps of the flame-cutting operation.
(a) ___________________________________________________________________
(b) ___________________________________________________________________
(c) ___________________________________________________________________
17 Can non-ferrous metals be successfully flame cut?
_____________________________________________________________________
18 Cutting nozzles are stamped with identifying numbers and size numbers. What does
the identifying number tell you?
• First part ___________________________________________________________
• Second part _________________________________________________________
Answers to Check your progress are at the end of the module.
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Answers
Check your progress
1
The identifying colours are:

2
 acetylene cylinder – crimson.
The pressure gauge settings required when using a size 15 tip are:

3
4
oxygen cylinders – black
oxygen–50 KPA
 acetylene–50 KPA.
The five important personal safety items are:

shade 5 lens goggles

gloves

cotton coveralls

leather boots
 leather apron.
The four hazards are:

ultra-violet radiation

heat radiation

flashbacks

burns.
5
Increase oxygen flow
6
Stop atmospheric contamination
7
The two functions of a welding torch mixer are:

mix the gases
8
 join the welding tip to the torch.
Brazing with oxyacetylene differs from welding with oxyacetylene in
that welding is a fusion process (molten parent metal)
9
The three reasons for using flux in brazing are:

clean parent metal

improves filler metal flow

reduces oxidation.
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10 Two metals used for filler metals in brazing are:

silver
 copper
11 Is the parent metal melted during the braze welding process? No
12 Can ferrous and non-ferrous metals be joined using braze welding? Yes
13 The substance formed when steel is heated to ignition temperature is
iron oxide.
14 The melting point of this new substance is lower.
15 The property of the chemical reaction between heated iron and oxygen
which allows flame cutting to proceeds is rapid oxidation.
16
The three basic steps of the flame-cutting operation are:

heat to ignition temperature

introduce cutting oxygen
 move torch.
17 Can non-ferrous metals be successfully flame cut? No
18 The identifying numbers and size numbers tell you:

First part: type of seat (thread or taper).

Second part: fuel gas.
Student Exercise 1
56
1.
The arc is at a very high temperature (~6000 C), and the heat from this
reaches the metal by radiation and conduction.
2.
A welder power supply is basically a source of high, constant current at
a relatively low voltage.
3.
The constant current helps to establish and maintain a stable arc,
allowing weld metal to be deposited evenly.
4.
AC transformers, DC generators, and transformer/rectifier units.
5.
Hazards include exposure of the eyes and skin to UV light and heat
radiation from the arc, exposure to fumes, hot objects and weld spatter.
Electric shocks from the welder supply can be fatal, particularly if
gloves or clothing are wet.
6.
PPI includes welding gloves, visor with glass for arc welding (shade 8
or more, depending upon current), leather apron, long sleeved clothing,
boots, spats. Respirators should only be used in combination with
forced-air ventilation or extraction.
7.
The UV light can cause damage to the eyes including welding flash and
blindness. Bystanders should be protected from the welding light by use
of screens.
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Student exercise 2
1
Any four component parts from the following list:
gas bottles
regulators
valves
valve key
hoses
torch
mixer
tip
2
(a) black
3
(b) crimson
Any two from the following industries:
light fabrication such as sheet metal
repairs to automotive parts
repairs to farm machinery
general ferrous metal joining
4
(a) carburising
5
(b) neutral
(c) oxidising
By keeping the weld pool covered by the flame
6
Any three items of clothing from the following list:
shade 5 or 6 goggles—Australian Standard approved
a shirt and trousers of non-flammable material that is tough and wear
resistant
firm-fitting leather shoes or boots, leather gloves and head covering
Student exercise 3
1
(a) steel and stainless steel
2
(b) copper
(c) brass
(a) oxygen and acetylene
3
(b) oxygen and LP gas
Lap joint or prepared fillet joint.
4
Soldering alloys melt at a lower temperature, typically less than 450°C
EEE022A: 13 Measurement and tolerance
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5
The parent metal needs to make a continuous metallurgical joint with
the soldering alloy. If oxide or other contaminants are present, they will
for a layer which separates the solder from the parent metal and
prevents the ‘wetting’ of the parent metal. This is known as a ‘dry’
joint, and will lead to unreliable electrical connections.
Student exercise 4
1
Different joint preparation, filler metal and techniques.
2
Copper and zinc.
3
A clean surface.
4
Any ferrous and non-ferrous metals including copper, steel, brass, cast
iron etc.
5
Any one of the following typical uses:
leakproof joints
repair of cast iron and light metal parts
joining hollow section furniture parts
6
Advantages and disadvantages:
(a) Two advantages—less distortion, can join a wide range of dissimilar
metals.
(b) Two disadvantages—cost, corrodes in contact with ammonia or loss
of strength above 260°C.
Student exercise 5
1
815°C
2
(a) The flame is used to raise a small section of metal to ignition
temperature.
3
(b) High-speed jet of oxygen.
(c) Moving nozzle and maintenance of heat.
(a) acetylene
4
(b) liquefied petroleum (LPG)
(c) natural gas
Oxygen
5
Type 41: taper seat for LP gas.
No. 12: bore diameter of 1.2 mm.
6
(a) material’s surface—it should be clean and free from paint, oil,
grease, etc
(b) metal composition
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EEE022A: 13 Measurement and tolerance
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(c) cutting nozzle size and condition
(d)
(e)
(f)
(g)
gas pressures
size of preheat flame
cutting speed
distance nozzle is from the job
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