The present invention is characterized in that in a simulation for predicting
a steam pressure setpoint after grade change, an initial moisture percentage is
evaluated from differences between bone-dry basis weights and between machine speeds
before and after grade change; the bone-dry coated weight of a size is evaluated
from the flow rate and concentration thereof; and then the dryer inlet moisture
percentage of a web after a size press is calculated from the coated weight. Thus,
the invention intends to improve the quality of products through precise dryer
control, as well as reduce the time required for grade change, by precisely predicting
the web's initial moisture percentage at the dryer inlet after grade change and
precisely and quickly controlling dryer steam pressure during grade change.
