Transcript AVOP-STROJ-MAR-011

Tutorial: Engineering technology
Topic: Problems with welding arc – causes and defects´ remove
Prepared by: Ing. Josef Martinák st.
Projekt Anglicky v odborných předmětech, CZ.1.07/1.3.09/04.0002
je spolufinancován Evropským sociálním fondem a státním rozpočtem České republiky.
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Causes:
Too big welding flow
Too long arc
Humidity or dirt on
welded edges
Precautions:
 To decrease welded
flow
 To reduce arc length
 To control right
polarity
 According to electrode
type
 To clean, and dry
welded place
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Causes:
Too low welding flow
Ignition voltage is low
Ignition electrode tip
covers ground
electrodes
Precautions:
 To increase welded flow
 No-load voltage of
welding source is low
for used electrode
types
 To clean grounding
brace surface
 To dust off or grind off
electrode tip gently and
to ignite arc by contact
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Causes:
Low welding flow
Wrong electrode
leading
Too high welding
speed
Small electrode
diameter
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Causes:
Precautions:
Too quick welding
 To fill crater at
shut down (starting
welding finish
fissure in crater
cavity is caused by
shrinkage at welded
metal solidification)
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Causes:
Moving welding
speed is high
Used electrode
diameter is too thick
Space between
welded materials is
too small
Wrong electrode
leading
Precautions:
 To decrease welding
speed
 To choose smaller
electrode diameter
for root weld
 To use right gap
between welded parts
(e.g. By grinding)
 Correct welding
technique
Causes:
Basic material with
higher carbon,
manganese or other
alloyed elements
content
 Quick cooling in
thermally influenced
area of basic
material
 Damp electrodes
( hydrogen
embrittlement)
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Precautions:
To choose welded
material
To decrease cooling
speed by correct
preheating
To use dried alkaline
electrodes
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Causes:
Wrong electrode type
Basic material with high
carbon and sulphur content
Wrong weld geometry
Weld – mainly root layers
and tack welds – if not
sized sufficiently taking
into consideration possible
shrinking effect
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Precautions:
To use electrodes with
alkaline coat whose welded
metal is more resistant to
crack’s development
To use correct electrode
material with good
weldability
To prevent wide spaces
among components and to
ensure right root
penetration
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Causes:
Humidity of wrongly
stored electrodes
Impurities or
protective paint on
welded edges
Precautions:
 To re-dry of electrodes
according to
manufacturer’s
instructions or use new
ones
 To remove paint
impurities and
corrosive products of
welded surfaces, to
remove iron scales and
to dry humidity on
welded surfaces
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Causes:
Electric arc blowing due to
magnetic fields
Appearance mostly at direct
flow welding
It is shown on weldment
edges and in limited space
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Precautions:
To fix ground clamp at the
place of weld
commencement (welding to
proceed from grounding
clamp)
To use alternative current
where possible
To change electrode angle.
If possible, to keep the
shortest arc length.
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Causes:
Slag overtake the welding
arc
Imperfect slag removal
between individual runs
Convex run’s shape makes
´slags´ pockets’
Wrong welding run’s
sequence
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Removal:
To increase welding speed
or to extend electrode
position angle
Accurate slag removal by
grinding, if it is necessary
Use right technique of
welding runs placing
To choose right welding
process
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Describe causes of big spatter.
DILLINGER, Josef. A KOL. Moderní strojírenství pro školu i praxi. 1. Praha: EuropaSobotáles, 2007. ISBN 978-80-86706-19-1.
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M. HLUCHÝ, J. KOLOUCH, R. PAŇÁK. Strojírenská technologie II
Translation:
 www.seznam.cz
 www.slovnik.cz
 JANATA, Petr. Handy slovník technický anglicko-český a česko-anglický. Plzeň:
Nakladatelství Fraus, 2000. ISBN 80-7238-075-3
 Lingea LEXIKON 5, Technický slovník anglicko-český a česko-anglický. 2010.
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