AME Unit 8 Q7

Covered electrode welding, also known as Shielded Metal Arc Welding (SMAW) or Manual Metal Arc (MMA) welding, is a welding process that uses an electrode coated with a flux to create an arc between the electrode and the workpiece.  

Process Overview:

1. Electrode: A metal rod coated with a flux material is used as an electrode.   1. How It Works: What is a flux in welding and what are the ingredients of fluxes used in the welding of Carbon Steels? | CWB Group www.cwbgroup.org
2. Arc Initiation: An electric arc is struck between the electrode and the workpiece.   1. What is Arc Welding? – Definition and Process Types – TWI Global www.twi-global.com
3. Shielding: The electrode coating melts, forming a protective gas shield around the weld pool.   1. Shielded metal arc welding – Wikipedia en.wikipedia.org
4. Weld Formation: The heat from the arc melts the electrode and the base metal, forming a weld pool.   1. Arc Welding Fundamentals – Lincoln Electric www.lincolnelectric.com
5. Slag Formation: The electrode coating forms a slag covering over the weld pool, protecting it from the atmosphere.   1. Everything You Should Know About Weld Slag (And Why) – Hobart Brothers www.hobartbrothers.com
6. Cooling: The weld pool solidifies, and the slag is removed after cooling.

Advantages of Covered Electrode Welding:

• Versatility: Can be used in various positions and on different types of metals.   1. Everything you need to know about covered electrode welding kurso.eu
• Portability: Requires minimal equipment and can be used in remote locations.
• Low Cost: Relatively inexpensive compared to other welding processes.   1. Comparing the Advantages and Disadvantages of Various Welding Electrodes | L&T-SuFin lntsufin.com

Disadvantages of Covered Electrode Welding:

Operator Skill: Requires more skill and experience compared to some other welding processes.

Slag Removal: Requires additional time and effort to remove slag after welding.

Lower Deposition Rate: Compared to other processes, the deposition rate is slower.

Covered electrode welding, despite its versatility, can produce several types of defects if not performed correctly. Here are some common ones:  

1. Defects encountered when welding with a coated electrode – Techniques de l’Ingénieur

Surface Defects

• Undercut: A groove melted into the base metal adjacent to the weld toe.   1. IM 558, Revised 4/18/17 – Iowa DOT www.iowadot.gov
• Overlap: Excess weld metal deposited beyond the joint faces.
• Craters: A void at the end of a weld pass.
• Spatter: Small molten metal droplets ejected from the weld pool and adhering to the base metal.   1. What is Weld Spatter? (A Complete Guide) – TWI Global www.twi-global.com
• Slag Inclusion: Entrapped slag within the weld metal.

Internal Defects

• Porosity: Gas pockets within the weld metal.   1. The Most Common Welding Defects: Causes and Remedies – Technoweld technoweld.com.au
• Inclusions: Non-metallic inclusions trapped within the weld metal.
• Cracks: Breaks in the weld metal due to excessive stresses or poor weldability.
• Lack of Fusion: Incomplete fusion between the weld metal and the base metal.
• Lack of Penetration: Insufficient penetration of the weld into the base metal.   1. Understanding and preventing common welding defects weldingvalue.com

Understanding these defects is crucial for identifying and preventing them during the welding process. Proper welding techniques, electrode selection, and post-weld inspection are essential for producing high-quality welds.

Surface defects in covered electrode welding are imperfections that occur on the external surface of the weld bead. They can affect the weld’s appearance, strength, and overall quality.

Undercut

• Description: A groove melted into the base metal adjacent to the weld toe.
• Causes: Excessive welding current, incorrect electrode angle, or improper travel speed.
• Consequences: Reduces weld strength and can lead to stress concentration.

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undercut in welding

Overlap

• Description: Excess weld metal deposited beyond the joint faces.
• Causes: Excessive welding current, incorrect electrode angle, or improper travel speed.
• Consequences: Affects weld appearance, can create stress concentrations, and reduce fatigue life.

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overlap in welding

Craters

• Description: A void at the end of a weld pass.
• Causes: Insufficient weld pool cooling before stopping the arc, or excessive travel speed.
• Consequences: Can lead to stress concentration and cracking.

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crater in welding

Spatter

• Description: Small molten metal droplets ejected from the weld pool and adhering to the base metal.
• Causes: Incorrect welding parameters, poor electrode coating, or excessive arc length.
• Consequences: Affects weld appearance and can create potential points for crack initiation.

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spatter in welding

These surface defects can be prevented through proper welding techniques, electrode selection, and equipment adjustment. Regular inspection and cleaning of the weld area are also essential.

Internal defects in covered electrode welding occur within the weld metal and are often invisible to the naked eye. These defects can significantly compromise the strength and integrity of the weld.

Porosity

• Description: Small gas holes within the weld metal.
• Causes: Moisture in the electrode coating, improper electrode storage, insufficient gas shielding, or high welding currents.
• Consequences: Reduces weld strength and fatigue life.

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porosity in welding

Slag Inclusions

• Description: Non-metallic particles trapped within the weld metal.
• Causes: Incomplete slag removal from the previous pass, excessive welding speed, or improper electrode coating.
• Consequences: Reduces weld strength and ductility.

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slag inclusions in welding

Lack of Fusion

• Description: Incomplete fusion between the weld metal and the base metal.
• Causes: Insufficient welding current, improper electrode angle, or poor joint preparation.
• Consequences: Reduces weld strength and can lead to crack initiation.

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lack of fusion in welding

Cracks

• Description: Breaks in the weld metal.
• Causes: Excessive restraint, rapid cooling, or harmful impurities.
• Consequences: Severe reduction in weld strength and potential for catastrophic failure.

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cracks in welding

These internal defects can significantly impact the structural integrity of a weld. To prevent them, it is essential to use proper welding techniques, select appropriate electrodes, and conduct thorough inspections.