At first, on the base unit, several cold rolled steel coils are placed
one above the other. These cylindrical shaped coils are called
charge. After loading the base with the coils, a protective cover is
put in place and hydrogen gas is circulated with in this enclosure.
Then a furnace is placed over this cover. The protective cover is
heated through burners of furnace, and it heats circulating hydrogen
gas, then inner and outer surfaces of the coils get heated by
convection from circulating hydrogen gas and by radiation between
the cover and the coil. The inner portions of the coil are heated by
conduction. The large thermal mass and low conductivity arising
from the air gaps between the sheets result in a large thermal lag
between cylindrical surfaces of the coil and coil core.