Based on the author's own studies, a relationship has been derived tha
t enables the rational heating rate of the thick charge to be theoreti
cally calculated. The rational value of heating rate assures the minim
um process time, the maximum furnace output, and the minimum heat cons
umption to be obtained. The actual value of the rational heating rate
is an individual value for each furnace. The occurrence of the rationa
l heating rate has been confirmed by the results of model studies.