1
GATE ME 2000
Subjective
+5
-0
Two different pairs of sheets of same material are welded by resistance-spot welding. In one pair, the average radius $$(r)$$ of each spherical bridge is $$0.2$$ $$mm$$ and the number of bridges per $$c{m^2}\,\,\left( n \right)$$ is $$25.$$ In another pair, the number of bridges per $$c{m^2}$$ is $$50$$ with the same $$'r'$$ of bridge. The contact resistance $${R_c}$$ per unit area is given by $${R_c} = 0.85$$ $$\left( {\rho /n\pi r} \right)$$ where $$'\,\rho \,'$$ is the resistivity of metal. If the voltage applied is $$5$$ volts and the resistivity of metal is $$2 \times {10^{ - 5}}$$ ohm-cm. The rate of heat generated per $$c{m^2}$$ in each case
2
GATE ME 1999
+5
-1.5
For butt welding $$40mm$$ thick steel plates, when the expected quantity of such jobs is $$5000$$ per month over a period of $$10$$ years, choose the best suitable welding process out of the following available alternatives.
A
$$SAW$$
B
Oxy-acytylene gas welding
C
$$EBM$$
D
$$MIG$$
3
GATE ME 1999
+5
-1.5
In butt welding operation on plates, the heat input necessary is given by

$$Q = 8\,K\,{T_c}\,t\,\,\,\left[ {0.2 + {{Vb} \over {4\alpha }}} \right]$$
Where $$K=$$ thermal conductivity,
$${T_c} =$$ temp increases from room temp up to $$MP,$$
$$t=$$ thickness of plate,
$$V=$$ welding speed,
$$b=$$ width of weld,
$$\alpha = thermal diffusivity Two alloy steel plates as shown in fig are to be welded using a power source rated at$$5kVA$$having a duty cycle of$$75\% .$$Using the given data, determine the maximum welding speed for the job given in$$mm/s$$Data :$$K = 45\,W/{m^0}C,\,\,{T_c} = {1450^ \circ }C,$$and$$\alpha = 1.2 \times {10^{ - 5}}\,\,{m^2}/s.$$A$$14.2$$B$$19.0$$C$$10.65$$D none 4 GATE ME 1998 MCQ (Single Correct Answer) +5 -1.5 The voltage-arc length characteristics of a$$DC$$arc is given by$$V=20+4L.$$Where$$L$$is in$$mm$$. During a welding operation arc length is expected to vary between$$4$$and$$6mm$$with the welding current limited between$$450$$and$$550$$amps. The arc power at an arc length of$$5mm$$is A$$10kW$$B$$14kW$$C$$20kW$$D$$80kW
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Medical
NEET