Friday, 27 April 2012

Electric Heating and Welding

Q) What is difference between types of electrical heating?
Ans) Resistance Heating is done at power freq. while Induction Heating and Dielectric Heating is done at high freq.

Q) Why adjustable AC voltage is used for Salt Bath Furnace?
Ans)Slat Bath Furnace ( No oxidation while hardening)  is used for Steel Tools Hardening at 20 V, 3000 V AC ( DCcan cause electrolysis of NaCl solution). Since Resistance drops with temperature, Adjustable voltage is needed.

Q) Why Heating Materal/Element should have high sp. resistance?
Ans) So that short length of wire is enough.

Q)Why heating element should be free from oxidation?
Ans) Otherwise life will be short. ( Iron addition means oxidation)

Q) Why heating element should have low temperature coeff of resistance?
Ans) So that R does not change much with T.

Q) What are common heating materials?
Ans) Ni-Chr, Ni-Chr-Fe, Ni-Chr-Al, Ni-Cu.




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