Transcript Course Name

Manufacturing Processes Lab I
MET 1321
Stick Welding part 2
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Electrodes
Use the correct type of electrode for the welding to be
done.
Some electrodes can be used when welding with DC
current, others are only used with AC current.
If welding is to be done using DC current, determine
whether DCEN or DCEP is needed for the particular
electrode to be used.
Select an electrode with a diameter that is about onehalf the thickness of the metal to be welded.
Use electrode until the stub is no longer than 1.5 to 2
inches.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Electrode coatings
Shielded electrode have coatings of various substances such as:
Cellulose sodium, cellulose potassium, titan sodium, titania potassium,
iron oxide, and iron powder, etc.
Roles of the coating in the welding process:
• Acts as a cleaning and deoxidizing agent in the molten crater,
• Releases carbon dioxide to protect the molten metal from
atmospheric oxides and nitrides (excludes oxygen and nitrogen
because these contaminants weaken the weld),
• Forms a slag over the deposited metal that further protects the
weld until the metal cools,
• Provides easier arc starting, stabilizes the arc and reduces the
spatter,
• Permits better penetration and improves the X-ray quality of
the weld.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Identifying electrodes
American Welding Society (AWS) classification:
E- 60 1 3 H4 R
E- identifies electrode for electric arc welding,
60- minimum allowable Tensile Strength in kips (thousands of pounds
per square inch), eg: 60 shows the tensile strength of 60,000 psi.
1- indicates the possible welding location (1 means that electrode can
be used for all positions, 2 for flat or horizontal ones only).
3- shows the special characteristics of the electrode, such as type of
coating, weld quality, type of arc, or amount of penetration.
H4- shows the hydrogen level. H4=hydrogen level less than 4 ml/100 g
H8= hydrogen level of less than 8 ml/100g of electrode.
R- indicates whether the electrode meets the requirements of the
absorbed moisture test.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Sticking an arc
Set the polarity switch to the recommended position,
Do not lay the electrode holder on the bench while
current is flowing,
Release the electrode if it sticks to the workpiece,
Start with the recommended current range and
adjust the current as necessary after welding begins,
Always shut off the welding machine when leaving the
welding bench.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Sticking an arc
Method 2:
Method 1:
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Proper welding
The arc length should be
approximately the
diameter of the electrode,
Use the correct current
for a particular electrode,
Maintain a travel speed
that is just fast enough to
produce evenly spaced
ripples.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Short arc
Sharp cracking sound
Best for most welding
Long arc
Steady hiss allows
Oxidation and spatter
Setting the length of an arc
Proper welding
The depth of penetration should be 1/3 to 1/2 of
the total thickness of the weld bead.
Restart the electrode 1/2 inches from the front
edge of the previously made crater, move the arc
back through the crater to remelt the weld pool,
and continue welding,
When cleaning slag from the weld, using a chipping
hammer or a wire brush, direct chipping away from
the body, eyes and the face.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Electrode angle
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Undercutting
undercutting is a defect that appears as a groove along the edges
of the weld. Undercutting is frequently just an appearance
problem, but it can impair weld strength when the weld is
loaded in tension or subjected to fatigue.
To eliminate undercut:
• Reduce current and slow travel speed, or
• Change the electrode angle so the arc force holds the metal in
the corners.
• Use a uniform travel speed and avoid excessive weaving.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Welding parameters
The current setting for any electrode diameter
influences the fusion rate (deposition rate) and the
penetration.
The voltage varies with the arc length:
- Long arc: higher voltage
- Short arc: low voltage
For direct current (DC), the correct polarity has to be
chosen .
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Amperage
If amperage is too high the following problems may
arise:
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electrode may overheat, possibly damaging the flux coating
oversize of the molten pool
large crater at the end of weld with porosity and crack
formation possible
undercutting
spattering
slag hard to remove
excessive penetration
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Amperage
If amperage is too low the following problems may arise:
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difficulty in striking the arc
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discontinuous fusion of slag (flux coating) due to partial arc
•
poor bonding and slag inclusions
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porosity
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Welding Speed
If the welding speed is too high the
following problems may arise:
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very narrow weld
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discontinuous fusion of slag
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incomplete fusion
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slag inclusions and porosity
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in the weld joints: insufficient
penetration
If the welding speed is too low the
following problems may arise:
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wide weld
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slag inclusion in the weld joint,
•
excessive penetration
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Arc Length
If the arc is too short the following problem may arise:
• the arc chokes
If
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the arc is too long the following problems may arise:
the arc breaks
porosities
undercutting
incomplete fusion
spattering
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Review the imperfections
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri