HIGH FREQUENCY INDUCTION FURNACE ( ELECTRIC PROCESS OF STEEL MAKING )

The principle of an induction furnace, resembles that of a transformer. It has a primary coil about which an alternating magnetic field is set up with magnetic lines of force of a definite density when an alternating current is passed through the coil. The magnetic field induces alternating eddy currents in the secondary circuits which comprises a crucible containing the metal charge. The eddy currents heat up and melt the metal.

An induction crucible furnace comprises a refractory crucible and a coil or inductor. The latter is made or copper tubing through which cooling water circulates and is arranged inside the refractory crucible. An insulating lining is provided between the coil and the crucible. The metal to be melted is charged into the crucible where it is melted down by the heavy secondary currents induced by the magnetic flux of the primary coil. The crucible can be tilted on horizontal trunnions to pour the molten metal.

Induction furnaces usually operate, on an alternating current with a frequency of 500 to 2500 Hz. The generator rating is selected so as to obtain from 1 to 0.4 KW per kg of the metallic charge.

Induction furnaces are most often employed in making high alloy steels and special purpose alloys. An advantage of these furnaces is that they do not require electrodes. This prevents carburization of the metal and simplifies control of the process. A vigorous stirring action is produced by the electromagnetic force in the crucible. This circulation of the metal accelerates chemical reactions and enables homogenous metal to be obtained.

Induction furnaces are available in a wide range of capacities from 50 kg to 10 tons.

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THROTTLE GOVERNING OF STEAM TURBINES

Steam Pressure at inlet to a steam turbine is reduced by throttling process to maintain the speed of the turbine constant at part load and hence this method of governing is called "Throttle Governing". Construction : Throttle governing system consists of a centrifugal governor, a lever , an oil pump , a pilot piston , control valve , a relay piston and a throttle valve. The throttle valve is moved by a relay piston. The relay piston is actuated by pilot piston control valve. There are two piston valves covering ports in the pilot piston control valve without any overlap. These piston valves are operated by lubricating oil supplied by a gear pump at 2 to 4 bar. The oil returns to the drain from this chamber. Working : When the turbine works on full rated load, the throttle valve will remain open. When the load is decreased, the energy output of the turbine becomes in excess and the turbine shaft speed increases. Hence, governor sleeve will lift. The upward movement of the

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Mechinopedia For Mechanical Engineers

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