The optimum pouring time for a casting depends on several factors. One important factor among them is

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 $$mm$$