376. Two 8 mm thick steel plates are placed 5 mm apart and welded by a butt joint. Welding is carried out at 20 V and speed of 5 mm/s. Heat transfer efficiency is 0.80. If the heat required to melt steel is 10 J/mm³ and melting efficiency is 0.625. The weld current (in amperes) will be

1. 1. 100

   
   
   

   2. 200

   
   
   

   3. 300

   
   
   

   4. 400

   
   
   

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   t = 8 mm, Gap = 5mm
   V = 20 volts, v = 5 mm/s
   η_Ht = 0.8, H = 10J/mm, η_m = 0.625
   I =?
   Volume of weld pool = 8 × 5 × x
   = 40 x mm³
   Heat Required = 10 × 40 x = 400 x J
   Heat Generated
   

   = ηHtηm	VIx
   	v

   
   

   = 400=	0.625 × 20 × I × x × 0.8
   	5

   
   I = 200 A

   Correct Option: B

   t = 8 mm, Gap = 5mm
   V = 20 volts, v = 5 mm/s
   η_Ht = 0.8, H = 10J/mm, η_m = 0.625
   I =?
   Volume of weld pool = 8 × 5 × x
   = 40 x mm³
   Heat Required = 10 × 40 x = 400 x J
   Heat Generated
   

   = ηHtηm	VIx
   	v

   
   

   = 400=	0.625 × 20 × I × x × 0.8
   	5

   
   I = 200 A

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377. In a fabrication shop, a T-joint is to be made between two plates using a chin intermittent, double fillet weld of 6 mm leg length. The intermittent welds are 40 mm long and spaced 80 mm apart, edge to edge. The welding symbol of the joint is

1. 1. 

   
   
   

   2. 

   
   
   

   3. 

   
   
   

   4. 

   
   
   

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1. View Hint View Answer Discuss in Forum

   

   Correct Option: D

   

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378. The metal powder used in Thermit welding of steel is

1. 1. AI

   
   
   

   2. Cu

   
   
   

   3. Pb

   
   
   

   4. W

   
   
   

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   Exothermic Reaction
   3Fe₃ 0₄ + 8Al → 9Fe + 4 Al₂ 0₃ + Heat

   Correct Option: A

   Exothermic Reaction
   3Fe₃ 0₄ + 8Al → 9Fe + 4 Al₂ 0₃ + Heat

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379. A 900 mm long steel plate is welded by manual metal arc welding process using welding current of 150 A, arc voltage of 20 V and welding speed of 300 mm/min. If the process efficiency of is 0.8 and surface resistance is 36 micro-ohm, the heat input in J/mm

1. 1. 600 J/mm

   
   
   

   2. 480 J/mm

   
   
   

   3. 146 J

   
   
   

   4. 116.5 J

   
   
   

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1. View Hint View Answer Discuss in Forum

   Heat Input to weld
   

   = η	VI	=	0.8 × 20 × 150	= 480 J/mm.
   	V		300/60

   Correct Option: B

   Heat Input to weld
   

   = η	VI	=	0.8 × 20 × 150	= 480 J/mm.
   	V		300/60

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380. A cup of 10 cm height and 5 cm diameter is to be made from a sheet metal of 2 mm thickness. The number of deductions necessary will be

1. 1. One

   
   
   

   2. Two

   
   
   

   3. Three

   
   
   

   4. Four

   
   
   

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1. View Hint View Answer Discuss in Forum

   D = √d² + 4hd = √5² + 4 × 5 × 10 = 15 cm
   first reduction 50%
   Next reduction 30%

   Correct Option: C

   D = √d² + 4hd = √5² + 4 × 5 × 10 = 15 cm
   first reduction 50%
   Next reduction 30%

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