Low permeability molds and low pouring temperature of the molten metal causes ......................... defect in castings.

Continuous rails for Indian railways are welded by ........ Welding process.

The voltage-arc length characteristic of a $$DC$$ arc is given by $$V=20+40L.$$ where $$L=$$ arc length in $$cm.$$ The power source characteristics can be approximated by a straight line. Open circuit is $$80V$$ and short circuit current $$1000$$Amps. The optimum arc length in $$mm$$

In welding process, penetration is increased by