MANUAL METAL ARC WELDING
MANUAL METAL ARC
COURSE INFORMATION
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MANUAL METAL ARC WELDING
SAFETY PRECAUTIONS
1. Safety measures are required to prevent danger from: electric shock: flashes
from the arc: burns caused by the scattering of sparks: pieces of hot or cold
slag: heat and fumes.
2. The ‘mains supply’ to the power unit must comply with electricity regulations
and the framework of the equipment must be earthed.
3. One pole of the welding circuit, the one attached to the work, (return lead)
should be capable of carrying the whole current.
4. The electrode holder should be well insulated, and the cable kept in good
condition, especially where it enters the holder.
5. The operator is protected by a heads screen, fitted with tinted and clear lens
to BS EN 169: 2002. When chipping off slag, the clear screen of the helmet
must be used to protect the eyes.
6. Welding shops must be well ventilated. Where necessary forced ventilation
should be used. When welding galvanised iron, brass or other alloys
containing zinc, the ventilation must be such that the operator cannot inhale
the fumes. If necessary a respirator must be used.
7. Inflammable materials must not be stored near welding equipment.
8. ‘Arc Eye’ is caused by the ultra-violet light radiation from the arc. A few
flashes may produce a feeling of sand in the eyes with pain and perhaps a
headache a few hours later. Recovery takes from one to two days with no
after effects short term. Long term effects could lead to cataracts
Infra-red heat causes burns: Leather gauntlets boiler suit, boots and a leather
apron for additional protection to the body.
9. Welding bays must be separated by screens of brick, wallboard or other
fireproof material. Large work must be screened off from other workers by
using portable screens. The screens should be painted black or pale green
with flat (non-reflective) paint.
10. The maximum voltage output permitted for hand operated welding machines
is 100 volts
11. Do not remove hot electrodes with bare hands.
12. Do not place electrode holder on bare metal surfaces when the machine is
turned on.
13. Do not leave electrode in the electrode holder when you have stopped
welding.
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MANUAL METAL ARC WELDING
ARC WELDING EQUIPMENT
In welding, the relationship between voltage (the pressure) and amperage
(the amount of electricity flowing) is very important. In arc welding, there are
two voltages to be considered: (1) open circuit voltage (OCV) and (2) arc
voltage (AV). OCV is the voltage that exists between the terminals of the
welding machine when there is no welding being performed. AV is the voltage
between the electrode and the base metal during the actual welding
operation. With MMA constant current (CC) is also essential. Due to the
welder’s inconsistences in arc length, it is important there is very little change
in the welding current in order to produce a quality weld.
A.C. TRANSFORMER
An A.C. transformer is an instrument that reduces the voltage of normal mains
electricity to between 60 – 100 volts. This is the maximum voltage permitted
for hand operated welding. These units may be oil or air cooled.
ADVANTAGES
A.C. machines are cheaper to buy: little or no maintenance, as there are no
moving parts.
DISADVANTAGES
Must use coated electrodes: Greater risk of shock: welding of non-ferrous
metal difficult.
D.C GENERATOR
The power for welding is obtained from a generator. A generator is a machine
that generates electricity, and it requires some form of energy to drive the
machine. This may be done using a petrol or diesel engine, or an A.C. or D.C.
electric motor. Where no electrical supply is available (on site or field repairs)
then the petrol or diesel motor is used.
ADVANTAGES
Can be used on ferrous or non-ferrous materials: Good for welding thin
material : safer in damp conditions where there is a high degree of electric
shock.
DISADVANTAGES
More expensive to buy than an A.C. unit: Maintenance is required because of
moving parts.
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MANUAL METAL ARC WELDING
INVERTER TECHNOLOGY
Inverter technology is a control system when applied to welding makes
it possible to develop compact power sources with low energy requirements
and sophisticated controls. The principal operation is shown below.
The mains supply is rectified and filtered converting the supply from AC to DC
(1-2)
The inverter power switch then converts the filtered DC back to an alternating
voltage at a frequency of around 30 Khz. This makes it possible to control
current using much smaller magnetic devices than traditional transformers
and technologies (3)
The transformer then converts the alternating voltage at high frequency to that
required for welding. As a result of the high frequency in the primary the
transformer is not only small in size but low in absorption. The rectifier/filter
then converts the alternating voltage to DC at the required setting (4)
The control system monitors input, output and operator settings to ensure
stable welding characteristics. (5)
This type of system which is fully controlled is precise and offers energy
savings of up to 40% compared with traditional welding machines. The
system also offers input voltage compensation and multi process welding
capabilities.
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MANUAL METAL ARC WELDING
Mosa TS 350 YSX-EL Engine Driven Diesel Welder Generator
The Mosa TS 350 SXC-EL is an
industrial quality, high
specification, engine driven diesel
welder generator for site welding
work. The TS 350 welder provides
350 DC welding output amps
welding output and
110/240/415V/12KVA electrical
auxiliary output, step less welding
power adjustment and a super
silenced canopy. The machine
is suitable for welding
with electrodes sizes between 2 to
6mm diameter. The welder
generator has a Yanmar 4stroke water cooled engine and a 13
hour long run fuel tank.
Fronius: TransPocket 1500
The TransPocket 1500 is a fully
digitally controlled manual electrode
welding machine with resonant
intelligence. The ideal characteristic
ensures the arc is always stable,
even with long mains leads of up to
100 metres or fluctuating mains
voltages.


5
150 A at only 4,7 kg
For portable use
MANUAL METAL ARC WELDING
PROCESS DESCRIPTION
An electric arc is formed when an electric current crosses the gap between
two electrodes. In arc welding the rod forms one electrode, while the work
being welded forms the other. The arc melts the parent metal and the
electrode to form a molten weld pool. This weld pool is protected from the
atmosphere by the liquid slag and a gaseous shield formed by the
vaporisation of the flux coating. The slag formed from the molten flux adheres
to the weld surface, protecting it as it cools, and must be chipped away after
each weld pass. Under no circumstances should you weld over slag.
SHIELDING GAS
The ingress of oxygen and nitrogen from the atmosphere to the weld pool and
arc environment would cause embrittlement and porosity in the weld metal;
this must be prevented. The actual method of arc shielding form atmospheric
nitrogen and oxygen attack varies with different electrode types which are in 2
main categories:
1 Bulk of covering material converts to a gas by the heat of the arc, only
a small amount of slag produced. Depends largely upon a gaseous
shield to prevent atmospheric contamination.
2 Bulk of covering material converts to a slag, only a small volume of
shielding gas produced.
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MANUAL METAL ARC WELDING
WELDING ELECTRODES
Electrodes are sold in packs of only one diameter size per pack,
manufacturers state the optimum welding currents to be used for different
types, thicknesses and lengths of electrode on their electrode packets. Each
diameter and length of electrode has specific limitations on current carrying
capacity. Excessive currents travelling the length of the electrode cause the
covering to overheat and break down which in turn produces poor welds.
2.5, 3.25 or 4mm diameter electrodes are the most commonly used sizes for
welding, the diameter sizing is taken across the bare wire end of the electrode
and not the fluxed part. Electrodes are now available in hermetically sealed
containers. These vacuum packs obviate the need for baking the electrodes in
an oven immediately prior to use. However, if a container has been opened or
damaged, it is essential that the electrodes are re-dried according to the
manufacturer's instructions.
(Ø) DIAMETER mm
AMPS (minimummaximum)
Length of
Electrodes
available
2.5
60-110
350mm
3.25
85-130
375mm
4.0
130-170
375mm
ELECTRODE CLASSIFICATION / IDENTIFICATION
Because there are so many different types of electrodes, the American
Welding Society (AWS) and the British Standards (BS) / European Norm (EN)
have established a numbering system that is used thought the welding
industry. These standards are showing below.
BRITISH STANDARD EUROPEAN NORM BS EN ISO 2560
(SUPERSEDES BS EN 499 – 1995)
The British Standards (BS) / European Norm (EN) specification for mild and
low alloy steel uses codes such as E 420RC11.
E 420RC11 means the following:
E
42
0
RC
1
1
=
=
=
=
=
=
Electrode
Yield strength (420 minimum N/mm²)
Impact energy (0°C for 47 Joules minimum)
Electrode coating type (rutile-cellulosic covering)
Welding current type and polarity (a.c and d.c)
Welding position (all positions)
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MANUAL METAL ARC WELDING
AMERICAN WELDING SOCIETY (AWS) A5. 1 - 91
The American Welding Society A-5.1 specification for mild and low alloy steel
uses codes such as E 6013.
E 6013 means the following:
E
60
=
=
1
3
=
=
Electrode
Tensile strength of the core wire in pounds per square inch (psi)
60,000 psi.
All welding positions
Welding current type and polarity:
Alternating current or Direct current, electrode positive (+), or
negative (-)
TYPES OF FLUX/ELECTRODES
FUNCTION OF THE FLUX:
The flux is there to aid Arc stability, Depth of penetration, Metal deposition
rate. The positional capabilities of the electrode are greatly influenced by the
chemical composition of the flux coating.
ELECTRODES CAN BE DIVIDED INTO FOUR MAIN GROUPS
1.
2.
3.
4.
Cellulosic
Rutile
Basic
Metal Powder
CELLULOSIC ELECTRODES
Cellulosic electrodes contain a high proportion of cellulose in the coating and
are characterised by a deeply penetrating arc and a rapid burn-off rate giving
high welding speeds.
Weld deposit can be coarse with a fluid slag, removing the slag can be
difficult. These electrodes are easy to use in any position and are noted for
their use in the 'stovepipe' (vertical down) welding technique.
Features:
• deep penetration in all positions
• suitability for vertical down welding
• reasonably good mechanical properties
• high level of hydrogen generated - risk of cracking in the Heat Affected
Zone (HAZ)
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MANUAL METAL ARC WELDING
RUTILE ELECTRODES
Rutile electrodes contain a high proportion of titanium oxide (rutile) in the
coating. Titanium oxide promotes easy arc ignition, smooth arc operation and
low levels of spatter. These electrodes are general purpose electrodes with
good welding properties. They can be used with AC and DC power sources
and in all positions. The electrodes are especially suitable for welding fillet
joints in the horizontal/vertical (H/V) position.
Features:
• moderate weld metal mechanical properties
• good bead profile produced through the viscous slag
• positional welding possible with a fluid slag (containing fluoride)
• easily removable slag
BASIC ELECTRODES
Basic electrodes contain a high proportion of calcium carbonate (limestone)
and calcium fluoride (fluorspar) in the coating. This makes their slag coating
more fluid than rutile coatings - this is also fast-freezing which assists welding
in the vertical and overhead position. These electrodes are used for welding
medium and heavy section fabrications where higher weld quality, deep
penetration, good mechanical properties and resistance to cracking (due to
high restraint) are required.
Features:
•
low hydrogen weld metal
•
requires high welding currents/speeds
•
poor bead profile (convex and coarse surface profile) slag removal
can be difficult
METAL POWDER
Metal powder electrodes contain an addition of metal powder to the flux
coating to increase the maximum permissible welding current level. Thus, for
a given electrode size, the metal deposition rate and efficiency (percentage of
the metal deposited) are increased compared with an electrode containing no
iron powder in the coating.
The slag is normally easily removed. Iron powder electrodes are mainly used
in the flat and H/V positions to take advantage of the higher deposition rates.
Efficiencies as high as 130 to 140% can be achieved for rutile and basic
electrodes without marked deterioration of the arcing characteristics but the
arc tends to be less forceful which reduces bead penetration.
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MANUAL METAL ARC WELDING
STORAGE AND DRYING OF WELDING CONSUMABLES
The success of manual metal arc welding depends on the quality of the
electrode coating which often contains ferrous alloys. Because the coatings
play such an important part in the information of the weld deposit no attempt
should be made to weld with electrodes that have their coating wholly or partly
removed.
The efficiency of an electrode will also be impaired if the coating is allowed to
get wet or damp.
Excessive dampness in electrodes may be indicated by:
1.
Fiery arc characteristics.
2.
Excessive spatter.
3.
Porosity or piping in the weld deposit.
4.
Spalling at the electrode tip, blistering and even coating disintegration.
5.
High arc voltage.
6.
Introduction of hydrogen into the weld deposit causing porosity, piping
and heat affected zone cracking.
It is essential therefore that electrode are kept in a dry well-ventilated store
preferably under heated conditions where the humidity is below the general
level. When electrodes are removed from the storage area they will regain
moisture from the surrounding air and it is good practice for unused
electrodes to be returned to the store so that they are not exposed in an
unheated and possibly damp working area.
RUTILE ELECTRODES
Rutile-coated mild steel electrodes of the BS 639 class R types normally
tolerate a limited amount of moisture and may in fact deteriorate slightly, from
the operator’s point of view, if they are over dried.
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MANUAL METAL ARC WELDING
CELLULOSIC ELECTRODES
These electrodes require a definite amount of moisture in the coatings to give
satisfactory results. If over dried the organic content will tend to char with
consequent loss of arc voltage and running properties.
BASIC COATED HYDROGEN CONTROLLED ELECTRODES
Electrodes of this type are specially baked during manufacture to ensure that
the moisture content is extremely low. On exposure to the atmosphere,
however, the moisture pick-up is correspondingly rapid and it is essential that
electrodes of this type are stored under the best conditions and are thoroughly
dried before use.
STAINLESS STEEL AND NON-FERROUS ELECTRODES
These require to be thoroughly dried before use particularly if high
radiographic qualities are to be obtained. Damp electrodes of this type
frequently give porous weld deposits.
STORAGE
Electrodes should be kept in a dry, well ventilated store under heated
conditions where the humidity is below the general level. Preferably the
electrodes should be stored on pallets or racks off the floor. It is good
practice for unused electrodes to be returned to the store so that they are not
exposed to an unheated and possibly damp working area where they can
regain moisture. It is recommended that the relative humidity of welding
consumables storage areas should not exceed 60%. Where the ambient
temperature falls below 15 degrees C, storage temperatures should be
maintained at 2 degrees c, above ambient.
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MANUAL METAL ARC WELDING
REDRYING
Where it is possible to obtain them, ideal drying conditions are where
electrodes are well spaced out in an oven in which the atmosphere circulates
freely. Electrodes must always, of course, be removed from their wrappers or
packets before being placed in a drying oven. If this is not done the moisture
cannot be carried off and will be reabsorbed back onto the coating when the
electrode cools. A longer drying time applies if the air circulation in the drying
oven is sluggish or the electrodes are packed closely together. If it thought
that electrodes have been reasonably well stored but that ideal conditions
have not been achieved, re-drying to the standard conditions given is
recommended.
If the electrodes have become wet and require thorough re-drying before use,
the re-drying time should be extended as indicated. The re-drying period also
varies to a small extent with the size of the electrode, ie. small sizes require
less re-drying time than large ones.
A practical method of finding out whether the electrodes are damp and,
therefore, need re-drying is to shake a small handful between the thumb and
index finger. Dry electrodes give a hard metallic sound, whereas damp
electrodes have a hollow dull sound. “THIS IS ONLY A GUIDE”, however,
and it is emphasises that when at all in any doubt re-drying should be carried
out. It should be noted that no-drying treatment is capable of reclaiming
electrodes which have been stored under conditions sufficiently adverse to
cause a marked deterioration in coating strength or to cause parts of the
coating to break away from the electrode. Electrodes which have deteriorated
in this way should be scrapped.
Occasionally electrodes may become coated with a white furry substance if
stored in damp conditions. This is sodium carbonate which is caused by the
action of CO2 in the atmosphere on the sodium silicate (the coating binder).
The fur coating does not appear to spoil the effectiveness of the electrode but
it is taken as an indication that the storage conditions for the electrode are too
damp.
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MANUAL METAL ARC WELDING
THE NATURE OF THE ARC
An arc is an electric current flowing between two electrodes through an
ionised column of gas called a “plasma”. An arc welding, the space between
the electrode and the work can be divided into three areas of heat generation:
the cathode, the anode and the arc plasma.
The welding arc is characterised as high current, low voltage arc that requires
a high concentration of electrons to carry the current. Negative electrons are
emitted from the cathode and flow (along with negative ions of the plasma) to
the positive anode. Positive ions flow in the reverse direction.
A negative ion is an atom that has picked up one or more electrons beyond
the number needed to balance the positive charge on its nucleus, thus the
negative charge. A positive ion is an atom which has lost one or more
electrons, thus the positive charge. However, just as in a solid conductor, the
principal flow of current in the arc is by electron travel.
Heat generated in the cathode area mostly by the positive ions striking the
surface of the cathode. Heat at the anode is generated mostly by the
electrons. These have been accelerated as they pass through the plasma by
the arc voltage, and they give up their energy as heat when striking the
anode.
The plasma, or arc column, is a mixture of neutral and excited gas atoms. In
the central column of the plasma, electrons, atoms and ions are in
accelerated motion and constantly colliding. The hottest part of the plasma is
the central column, where the motion is most intense. The outer portion or
the arc flame is somewhat cooler and consists of recombining gas molecules
that were disassociated in the central column.
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MANUAL METAL ARC WELDING
THE WELDING CIRCUIT
The basic equipment required for manual metal arc welding is known as the
welding circut:
1. WALL SOCKET AND
MACHINE PLUG
Either 440, 240 or 110 volts may be
supplied to the welding machine.
2. MACHINE POWER CABLE
Carries the current to the welding
machine.
3. WELDING MACHINE
Connected to the power supply and
alters the amperage. This is a
variable transformer.
4. WELDING LEAD
Attached to the electrode holder from
the welding plant.
5. ELECTRODE HOLDER
Connected to the welding plant and
work piece, carries the current back
to the welding plant.
6. RETURN LEAD
Connected to the welding plant the
electrode holder holds the electrode.
7. EARTH CABLE
Acts only when a fault occurs and
protects the welder from severe
shock.
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MANUAL METAL ARC WELDING
SLOPE AND TILT ANGLES FOR FILLET AND BUTT WELDS
The correct angle when welding in the flat position is 60°-70° in the direction
of travel. This is known as the SLOPE angle of the electrode. The arc must
point back towards the weld to ensure good penetration and ensure the flux
does not run forward.
The TILT is the angle that can vary from between 10° - 90°, depending on the
weld positions.
FILLET WELD
BUTT WELD
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MANUAL METAL ARC WELDING
STRIKING THE ARC
Since there must be ionised path to conduct electricity across a gap, the mere
switching on of the welding current with a cold electrode poised over the work
will not start the arc. The arc must first be “ignited”. There are two different
techniques, the touch and withdraw method and the scratching method.
In the touch and withdraw method the electrode is moved downward at 90° to
the plate and withdrawn rapidly after contact with the material. The distance
withdrawn is the diameter of the electrode, it is also necessary to slope the
electrode at 70° in the direction of travel.
In the scratching method the electrode is scratched on the plate. This action is
not unlike striking a match and is easier for beginners. After the arc has been
maintained, the distance of the electrode from the material and the direction of
travel is the same as above.
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MANUAL METAL ARC WELDING
WELDING TERMINOLOGY
BUTT WELD
FILLET WELD
BASE METAL
The metal that is to be welded together
MITRE or FLAT
A weld appearance where the face or reinforcement is a
straight line from toe to toe
TOE
The outside edges of a weld where it fuses with the
parent plate or base metal
CONCAVE
A weld appearance where the face is a curve below the
mitre line
CONVEX
A weld appearance where the face is a curve above the
mitre line
FUSION FACE (or zone)
Where the weld metal interfuses with the parent plate or
base metal
PENETRATION
The distance the weld metal fuses into the root of the
joint
ROOT
The position in a welded joint where the parent plates
come closest together
THROAT THICKNESS
The shortest distance from the root to the mitre line in a
fillet weld or the thickness of the welded plate in a butt
joint
REINFORCEMENT
A surplus deposit of weld metal above the mitre line on a
fillet weld
A surplus deposit of weld metal above the plate
thickness on a butt welded joint.
LEG LENGTH
the width of the fusion face in a fillet or lap joint from the
root to the toes of the weld.
HEAT AFFECTEDZONE
HAZ is the area beyond the fusion line where the
parent material has not melted, but the grain structure
has altered due to the heat input.
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MANUAL METAL ARC WELDING
WELDING VARIABLES
SPECIFIED WELD
VARIABLE
Correct Welding Conditions
Slow Rate of Travel
Fast Rate of Travel
Low Welding Current
High Welding Current
Failure to Remove Slag after
Welding
Too Shallow a Slope Angle
Too Steep a Slope Angle
Arc Length too Short
Arc Length too Long
Depositing a Weld on
Grease, Oil, Paint, Rust or
Scale
Tilt Angle Incorrect
EFFECT OF THE VARIABLE ON WELD
QUALITY
Smooth even weld deposit, stable arc
condition, easily controlled slag, little spatter
produced.
Wide thick deposit, slag floods weld pool
causing difficulty in controlling deposit, on a
root run excessive blowthrough or
penetration.
Narrower thinner deposit, may prevent
adequate fusion with the parent metal.
Weld metal will pile up without adequate
penetration into the parent metal, slag difficult
to control. Poor bead shape,
poor penetration, unstable arc.
Gives a deposit that is flatter and wider than
normal with excessive penetration into the
parent metal, undercut, blowthrough on a butt
weld root run. Excessive spatter.
Slag inclusions in the weld area.
Elongated ripples and weld crater, poor
penetration or excessive spatter.
Weld pool difficult to control, allowing molten
slag and metal to run in front of the electrode.
Arc length difficult to maintain and will cause
irregular piling of the weld metal, the
electrode sticks to the weld pool.
Arc is extremely noisy, large globules of metal
flow between the electrode and workpiece,
coarse ripple, large flat weld deposit,
excessive spatter.
Porous weld (aero bar effect), hydrogen
cracking in the weld metal or heat affected
zone.
Undercutting the opposite side of the weld,
weld metal piling up on the side to which the
electrode is pointed.
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MANUAL METAL ARC WELDING
WELD TESTING AND INSPECTION
1. VISUAL EXAMINATION of all the welds to check for the following:
1. WELD SIZE
2. PROFILE OF WELD SHAPE
3. SLAG INCLUSIONS.
4. UNDERCUT
5. OVERLAP
6. ROOT PENETRATION
WELD DEFECTS
OVERLAP
Overlap is excess weld metal that has flowed on to the parent metal but not
fused to it and is caused by:
1.
Excessive heat
2.
Travelling too slow
3.
Incorrect electrode angle
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MANUAL METAL ARC WELDING
LACK OF SIDE WALL FUSION
Lack of fusion is the failure of the filler metal to fuse with the parent metal and
is caused by:
1.
2.
3.
4.
Current (too low)
Too fast a travel speed
Wrong angle of electrode
Inadequate preparation
POROSITY
Porosity is a group of small holes throughout the weld metal. It is caused by
the trapping of gas during the welding process and it is caused by:
1.
2.
3.
Too rapid cooling of the weld
Flux broken off the end of the electrode
Dampness of electrode and material.
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MANUAL METAL ARC WELDING
UNDERCUT
Undercut is a groove or slot along the toes (edges) of the weld and is caused
by:
1.
2.
3.
Too fast a travel speed
Build up of excess heat
Wrong angle of electrode
LACK OF PENETRATION
The failure of the filler metal to penetrate into the joint and it is caused by:
Incorrect edge preparation
1.
Rate of travel too quick
2.
Current too low
3.
Incorrect electrode angle
4.
Electrode too far away from the joint.
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MANUAL METAL ARC WELDING
INCORRECT PROFILE
Welds that have the appearance of the following are classed as incorrect
profile and are usually caused by the following:
(OVER-FILLING)
1.
Rate of travel to fast
2.
Electrode diameter too small (under-filling)
3.
Current too low
(UNDER-FILLING)
1.
Slow rate of travel
2.
Too large electrode diameter (over-filling)
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MANUAL METAL ARC WELDING
CRACKING
Cracking is the formation of cracks either in the weld metal or the parent metal
and is caused by:
1.
2.
3.
Unsuitable parent metals/consumables used in the weld
Bad welding technique/procedure
Cooling material too fast
SLAG INCLUSION
Slag inclusion is the entrapment of slag in the weld and is caused by the
following:
1.
2.
3.
4.
5.
Slag not cleaned from previous runs
Insufficient cleaning and preparation of the base metal before
welding.
Arc length too long.
Incorrect electrode angles
DC welding machine weld towards the return lead connection
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MANUAL METAL ARC WELDING
BURN THROUGH
Burn through is the collapse of the weld pool and it is caused by:
1.
2.
3.
4.
Too great a heat concentration
Poor edge preparation
Travelling too slow
Incorrect electrode angles
CRATER PIPE
Crater pipe is a hole in the crater of the weld and is caused by:
1. Incorrect finishing technique by the operator
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MANUAL METAL ARC WELDING
EXERCISE 1
LAP WELD
This weld is similar to the fillet weld for the slope and tilt angles.
Electrode: Ø3.25mm
Material:
S235J Low Carbon Steel 150x50x6mm
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MANUAL METAL ARC WELDING
EXERCISE 2
CORNER WELD
In this exercise we join two plates edge to edge at right angles to each other
as shown below. The plates should be dressed by grinding and then tacked at
opposite ends. This is the first part of the exercise and has to be shown to the
lecturer for assessment before welding.
ROOT RUN No: 1
Electrode: Ø2.5mm is used for the first run or as it is more commonly known.
The actual metal upon which the root run is deposited is comparatively thin
compared to the rest of the joint therefore a REDUCED current is used to suit
the electrode.
RUN No: 2
Electrode: Ø3.25mm. The second run and any alternate runs if required may
be produced by WEAVE, SPLIT WEAVE or STRINGER type runs.
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MANUAL METAL ARC WELDING
EXERCISE 3
DOUBLE ‘V’ BUTT WELD
The double ‘V’ butt weld is when two plates are bevelled at 35° giving an
included angle of 70° from both sides. The flat or nose on the angle of
preparation is the ROOT FACE and the space between the root face is known
as the ROOT GAP.
When the material has been prepared by grinding and tacked, it is shown to
the lecturer for inspection as this is the first part of the exercise.
Below is a sequence of drawings showing the run sequence required to
produce the double ‘V’ butt welded joint.
Electrode Ø2.5mm for weld runs 1 & 2
Electrode Ø3.25mm for weld runs 3 & 4
Clean out the slag from weld run 1 before depositing weld run 2
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MANUAL METAL ARC WELDING
EXERCISE & SUMMARY ASSESSMENT
FILLET WELD
In this exercise you join two plates of the right angles to each other as shown
below. The plates should be dressed and then tacked at opposite ends. This
is the first part of the exercise and has to be shown to the lecturer for
assessment before welding can commence.
A 3.25mm electrode is used for the first run and may be sufficient on light
gauge material, however on thicker material a multi-run technique may have
to be used as shown below:
Assessment Material: 150x50x6mm low carbon steel: EN10025: S235
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