1
GATE PI 1993
Subjective
+5
-0
The voltage-arc length characteristics of a power source is $$V=20+40L,$$ where $$V=$$ operating voltage in volts and $$L=$$ arc length in $$cm.$$ The open circuit voltage and short circuit current for arc lengths ranging from $$3$$ to $$5mm$$ and current from $$400$$ to $$500$$ amps during welding operation are
2
GATE PI 1992
Subjective
+5
-0
Two sheets of low carbon steel $$1.5mm$$ thick each are spot welded by passing a current $$10000$$ amps for $$5$$ cycles in $$50$$ $$Hz$$ main supply.

i) What is the heat generated due to the supply of power if effective resistance has $$200$$ micro ohms,

ii) The maximum indentation is $$10\% $$ of sheet thickness and density of the spot weld nugget $$8$$ $$gm/cc.$$ If $$1380$$ Joules are required to melt $$1gm$$ of steel, determine heat required for welding operation if $$D=6SQRT$$ $$(t)$$ to determine nugget diameter $$D$$ and assume the nugget size to be equal to metal between the two electrodes

3
GATE PI 1992
Subjective
+5
-0
In $$MIG$$ welding the power source characteristics is $${V_p} = 36 - {\rm I}/60$$ and the arc characteristics is $${V_a} = 2{L_a}\,\,\,\, + 27.$$ Find the change in power of the arc if the arc length changed from $$2mm$$ to $$4mm.$$ If the maximum current capacity of the power source is $$300$$ Amps, the maximum arc length sustainable is
4
GATE PI 1991
Subjective
+5
-0
A resistance welder is rated at $$50$$ $$kVA,$$ at $$50\% $$ duty cycle. Secondary voltage is always constant at $$25$$ volts. If a job requires $$1500$$Amps current, determine the maximum welding time in a total cycle time of $$30$$$$secs$$.
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