Question

Two steel sheets of 1.0 mm thickness are resistance welded in a projection welding with a current flow time of 0.005 second. The effective resistance of the joint is 100 micro ohms. The joint can be considered as a cylinder of 6 mm diameter and 1.5 mm height. Density of steel is 0.00786 g/mm${}^3$ and heat require for melting steel be taken as 10 J/mm${}^3$ and heat lost to the surrounding is 36 Joules. The current required is ________ (Amperes).

• A. 30,335
• B. 40,335
• C. 25,625
• D. 20,425

Answer 1

The correct option is A 30,335

Heat supplied = $I^{2}R\times t$

Volume of the joint
$=\frac{\pi }{4}\times 6^2\times 1.5=42.41m{m}^3$

Heat required for melting is = 42.41 $\times$10
= 424.1 Joules

Heat lost to surrounding = heat supplied - Actual heat required for melting weld heat supplied = 424 + 36 joules

= 460.11 Joules


$\text{Then, 460.11 =}{I}^2\times 100\times {10}^{-6}\times 0.005$

I = 30,355 Amperes