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Which of the following furnaces is suitable for intermittent work?
Coreless furnace
Indirect arc furnace
Either of the above
Neither of the above
Indirect arc furnace
An indirect arc furnace is ideal for intermittent work because the charge does not come into direct contact with the arc, allowing for rapid starting and stopping without furnace degradation. Unlike coreless induction furnaces which often require a 'heel' (a residual molten metal base) to initiate electromagnetic coupling effectively, the indirect arc furnace relies on radiation, making it flexible for varied melt batches.
An indirect arc furnace is ideal for intermittent work because the charge does not come into direct contact with the arc, allowing for rapid starting and stopping without furnace degradation. Unlike coreless induction furnaces which often require a 'heel' (a residual molten metal base) to initiate electromagnetic coupling effectively, the indirect arc furnace relies on radiation, making it flexible for varied melt batches.
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In an indirect arc furnace, the arc is struck between two carbon or graphite electrodes positioned above the charge. The heat is transferred to the metal primarily through radiation from the arc and reflection from the furnace walls. This allows the furnace to be brought up to operating temperature quickly and shut down immediately after pouring, minimizing idling losses during intermittent operations.
Indirect arc furnaces use radiation for heat transfer.
Coreless induction furnaces work via eddy currents and require a metallic heel to start effectively.
Intermittent work requires equipment that can handle frequent thermal cycling without high standby power consumption.
High temperature control
Rapid start-up and shut-down
Ideal for small batches and intermittent operation
High electrode consumption
Lower thermal efficiency compared to induction furnaces
Potential for uneven heating of the charge
Melting of non-ferrous metals
Small-scale batch casting
Laboratory scale metallurgy
| Feature | Coreless Furnace | Indirect Arc |
|---|---|---|
Starting Requirement | Requires molten heel | No heel required |
Heat Transfer | Induction (Electromagnetic) | Radiation |
Coreless furnaces are highly efficient for continuous production where the furnace is kept hot, but they suffer during cold starts in intermittent use.
Option A is incorrect because coreless induction furnaces are primarily designed for continuous or high-duty cycle operations to maintain magnetic coupling efficiency.
B is correct тАФ Indirect arc furnaces are best suited for intermittent work due to their ability to start and stop without needing a molten metal heel.
In exams, always distinguish between conduction-based heating (like resistance) and induction-based heating; induction typically requires a continuous conductive path or heel to initiate magnetic flux linkage effectively.