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OPERATION CONTROL AND CONNECTORS
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4.7 Arc Welding Defect and Prevent Method
Defect name
Caused reasons
Prevent methods
Welding
seam
doesn’t
meet the
requirement
The groove angle is not proper
The root face and assembly gap is not equal
Welding
technics
parameters
are
unreasonable
The welder’s operation skill is lower
Choosing the proper groove angle & assembly
gap, improve the assembly quality
Choosing the proper welding parameters
Improve the operation skill of welders
Undercut
Over current
Arc length is too long
The electrode angle is wrong
Manipulation of electrode is not proper
Choosing the proper welding current & speed
The arc can’t be drawn too long
The electrode angle should be proper
Manipulation of electrode should be correct
Incomplete
penetration
The groove angle or gap is too small, the root
face is too big
Welding parameters are not suitable, or the
assembly is not good
The welder’s operation skill is lower
Correctly to choose and process the groove
size
Correctly to assemble and ensure clearance
Choosing the suitable welding current & speed
Improve the operation skill of welders
Incomplete
fusion
The welding thermal input is too low
The arc direction is lean
There are rust & dust on the side of groove
The slag between the layers is not cleared
well
Correctly to choose the welding parameters
Operation seriously
Enhance the clearness of layers
Overlap
The temperature of molten pool is too high
The liquid metal concretes slowly
Choosing parameters based on the welding
different position
Strictly to control the molten hole size
Crater
The crater time lasts too short
Over current in the welding of thin plate
In the crater, electrode should be stayed for a
short time or round to manipulate electrode
after the molten pool is filled in by metal, take
to the side for crater
Blowhole
There are some dust like oil, rust or water on
the work piece surface and groove
The coating of electrode is damped& is not
drying
Under current or over speed in the welding
The arc is too long or lean burning, the
molten pool protection is not good
Over current, the coating of electrode falls
off and lose protection
Manipulation of electrode is not proper
Clear out the dust around groove for about
20
～
30mm
Strictly to dry the electrode according to
manual
Correctly to choose parameters and to operate
Using the short arc operation
Welding operation in the field should have
anti-wind protection
Don’t use the invalid electrode
Inclusion &
slag
inclusion
The slag clears bad in the middle layer in the
welding process
Under current or over speed in the welding
Welding operation is not proper
The welding material can not match the
work piece
The groove design & processing are not
proper
Choosing the electrode of good slag
detachability
Strictly to clear the slag in the layers
Correctly to choose the welding parameters
Adjusting
the
electrode
angle
and
manipulation way
Hot crack
In the process of solidification, the inter
crystal segregation is seriously caused. At the
same time, with the effect of welding stress,
the hot crack is formed.
Strictly control the percentage of S and P in
welding material.
Adjust the structure of welding material.
Adopt the basic electrode.
Cold crack
Three reasons will cause cold crack:
The structure turned from the marten site
The residual stress caused by big restraint
intensity
The residual hydrogen in welding gap.
Adopt low hydrogen type basic electrode.
Bake under the instruction before use.
Remove the feculence before use, reduce the
percentage of hydrogen
Adopt appropriate parameters and heat input
After welding, do dehydrogenation at once.
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