(Aktu Btech) Advance Welding Important Unit-1 Welding Arc and Power Sources

Enhance your B.Tech path with quantum notes from Aktu that include critical and commonly repeated questions on advanced welding. Dive into this resource for in-depth knowledge and exam success. Unit-1 Welding Arc and Power Sources

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Important Questions For Advance Welding:
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Q1. What is welding ? Explain the importance of welding.

Ans. A. Welding: 

• 1. The term welding refers to a variety of bonding processes.
• 2. It is defined as a localized coalescence of metals achieved by heating to an appropriate temperature with or without the application of pressure and with or without the use of filler metal. The melting point of the filler metal is similar to that of the base metal.
• 3. A well-welded joint is as durable as the parent metal. Weldment is the name given to this product.

B. Importance of Welding: 

• 1. The welding method is easily adjustable to the structure of a stream line, and the welded seams are extremely tight.
• 2. Welded joints are strong, especially when subjected to static pressure. However, due to stress concentration, residual strains, and numerous weld flaws such as fractures, incomplete fusion, and slag inclusion, they have low fatigue resistance. Yet, all of these disadvantages can be mitigated to a great extent.
• 3. Several welding processes have been developed in recent years, and it is likely that no industry does not use welding procedures in the manufacturing of its products in some form or another.
• 4. Welding is the quickest and easiest method of fabricating and assembling metal parts.
• 5. Welding is widely employed in the automobile sector, aircraft machine frames, structural work, tanks, machine repair work, ship building, and refineries, as well as metal structure fabrication.

Q2. What are the applications of welding ? Give in detail.

Ans. Applications of welding are as follows: 

• i. Automobile and Transport Industries: 
  • 1. Where automobiles, trucks, jeeps, and a variety of other transportation devices and equipment are manufactured.
• ii. Building Construction Industries: 
  • 1. Welding is widely employed in the construction industry for combining door and window frames, reinforcement in concrete works, handrails, and staircases.
  • 2. When a building is a steel frame structure made up of steel roofing frames covered with asbestos sheets or galvanized iron sheets, welding plays an even more important function in combining the structural components for Joining building, frames, and trusses.
• ii. Railroad Industries: 
  • 1. Another important field where welding is used is in the construction of locomotive underframes, bogies, trolleys, railway bridges, electric frame network, signal, equipment, lighting towers, platform shades, and bodies, among other things.
• iv. Pressure Vessels and Tanks Industries: 
  • 1. Pressure vessels and tanks are widely employed in a variety of sectors to transport or store fuel and other liquids.
  • 2. They are created by welding bent steel plates together.
  • 3. Steel is also used to construct oil, gas, and water storage tanks.
• v. Aircraft Industries: 
  • 1. Welding is widely employed in the aircraft industry to join alloy steel, stainless steel, and aluminium alloy aircraft components.
  • 2. Welding is utilised to create auxiliary equipment that aids aircraft operations and maintenance, such as material handling systems and transport means for men and luggage.
• vi. Storage Tank Industries: 
  • 1. Storage tanks are used to hold enormous amounts of liquid or gas.
  • 2. They are so enormous that they cannot be built in a single unit, thus they are created in sections for ease of assembly, after which they can be built in a single unit by welding.
• vii. Pipeline Industries: 
  • 1. The welding procedure is effectively employed in pipeline sectors to generate seamless pipe joints.
  • 2. As compared to riveting, pipe welding lowers joint corrosion.
  • 3. Welding gives the pipes more strength and dependability when compared to other methods of fabrication.
• vii. Petrochemical Industries: 
  • 1. Welding is widely used in the chemical and petroleum sectors for the production of plant and machinery, stainless steel vessels and storage tanks, and a variety of other structures.
• ix. Earth Moving Equipment Industries: 
  • 1. Welding is heavily used in the fabrication of earth moving devices such as bulldozers, loaders, trenches, and drilling ridges for all oil exploration and water tubewells, as well as other related machines.  
• x. Material Handling Equipment Industries: 
  • 1. Welding is employed in this industry to fabricate overhead cranes, jib cranes, and tower cranes, as well as their auxiliary equipment such as trolleys and lifting aids.

Q3. What factors should be considered while selecting a welding process ?

Ans. Factors considered while selecting a welding process are as follows : 

• 1. Metal type and metallurgical properties, joint location and welding position, end use, cost of production, quantity required, product size and location, desired performance, welders skill, training, and experience, joint accessibility, joint design, desired accuracy of assembly, welding equipment available, work sequence, and installation cost.
• 2. The process adopted should meet both technical and financial requirements. These two variables may be incompatible and so necessitate a compromise.
• 3. The welding procedure and filler metal should be chosen in such a way that the weld deposit is compatible with the base metal and has mechanical qualities comparable to or superior to the base metal.

Q4. Describe in detail health and safety measures in welding.

Ans.

• 1. Every welder should be aware of health threats such as fires, explosions, electricity, burns, welder flush, oxygen depletion, toxic fumes/gases particles/vapours, radiation, trips and falls, and take appropriate precautions.
• 2. Welding smoke can irritate the eyes, chest, respiratory tract, and cause lung inflammation.
• 3. Gases and particles in welding fumes may be toxic or non toxic. While particles of size greater than 5 μm are filtered by nose, and less than 0.1 μm are breathed out, particles between size 0.1 and 5 μm are retained in lung. 
• 4. Maximum acceptable concentration (MAC) in general is 6 mg/m³. 
• 5. Welding fume extractor equipment aids in concentration reduction.
• 6. Utilize material safety data sheets to detect dangerous welding materials, such as cadmium-free silver solders and asbestos-free electrodes.
• 7. Welding’s ultraviolet radiation combines with oxygen and nitrogen in the air to generate ozone and nitrogen oxides. Even a concentration of 0.2 mg/m³ is toxic, causing nose and throat discomfort as well as serious lung illnesses.
• 8. Electrical dangers exist in welding, even when the welding source is low voltage.
• 9. To maintain high insulation, keep the electrode holder and cable dry and in good condition. Machinery must meet safety criteria.
• 10. All machinery with moving parts must be guarded for worker safety. To avoid tripping and falls, keep the welding area free of equipment, cables, and hoses.
• 11. Strong light and radiation can harm the retina and cornea of the eye. For the safety of welding operators and others, use an auto-darkening helmet, a welding curtain, and a sound protection curtain.
• 12. All welding operations necessitate safety precautions. Install an extraction hood over the workplace to protect workers from fumes and gases. Employ a welding helmet with overpressure and appropriate ventilation.

Q5. What are the factors affecting arc blow ? Also give its effects. 

Ans. A. Factors Affecting Arc Blow: 

• 1. Magnetic field generated in the workpiece adjacent to the welding arc as a result of current flow across the arc.
• 2. The presence of busbars carrying high-voltage current in the vicinity of the welding site.
• 3. When using several welding heads, the magnetic field of the arc at one electrode may affect the arc at the other electrode.
• 4. The magnetic field created in the workpiece near the earth connection may tend to pull the arc away from the point of connection.

B. Effects of Are Blow: 

• 1. Poor weld bead appearance. 
• 2. Irregular and erratic weld deposition. 
• 3. Undercutting and lack of fusion. 
• 4. Spatter. 
• 5. Uneven and weak welded joint. 
• 6. Slag entrapment and porosity.

Q6. Write short note on use of transformer, rectifier and generators in welding.

Ans. A. Use of Transformer: 

• 1. Welding transformers are used in AC machines to turn the secondary winding’s primary winding’s alternating current from the power line into a low-voltage, high-amperage current.
• 2. It is usual practise to control the secondary voltage and the welding current simultaneously by combining primary and secondary taps on the welding transformer.
• 3. Kilovolt-amperes (kVA) are used to represent transformer ratings for AC machines for a given duty cycle.
• 4. This duty cycle rating, also known as a thermal rating, identifies the maximum amount of energy that a transformer can produce over a set percentage of a given time period, typically one minute, without going over its permitted operating temperature.
• 5. The thickness of the materials that can be welded is indicated by this parameter since heating is a function of the welding current.  

B. Use of Rectifier: 

• 1. The rectifier may be made of silicon diodes or metal plates coated with a selenium compound, each of which has the unique ability to only permit current to flow in one direction.
• 2. Rectifier units are made to offer a choice of low voltage for flux-shielded metal arc for MIG welding, or a high open circuit with drooping voltage characteristics for TIG welding.

C. Use of Generators: 

• 1. Direct current can be produced by a DC welding generator with either straight or reverse polarity. The type of electrode used and the material to be welded determine the polarity that is chosen for welding.
• 2. A diesel engine or an electric motor can power a DC generator. Diesel-powered generator sets are appropriate for outdoor use or other locations without access to electricity.

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