Abstract:
Apparatus is disclosed for controlling freeness of stock from parallel refiners by controlling the rise in temperature of stock through each refiner. The Delta T setpoint for each refiner is adjusted to compensate for: variations in consistency of stock; maximum power rating of the refiner; weighted average freeness of stock from all refiners; and the composite frheness of stock delivered to a paper machine. Error in the desired temperature rise of a given refiner is employed to control its disc or plug operation. An on-line analyzer is employed to monitor composite freeness. Couch or flatbox vacuum is employed as an alternative measure of composite freeness, but only if intentional paper machine changes which would affect vacuum have not been made. Operator control of composite freeness is also permitted. The composite freeness setpoint is adjusted to maintain a desired paper bursting strength. Power checks are made and instructions are automatically given to adjust flow rate to an individual refiner in order to keep it operating within its maximum power limit and to add or delete refiners for optimum efficiency.
Abstract:
Apparatus is disclosed for controlling the basis weight of double-layer paper from a Fourdrinier machine by: comprising composite dry basis weight from total basis weight and moisture measurements; computing the dry basis weight of the top layer from the composite dry basis weight and the stock flow and consistency data of both layers; correcting the stock flow rate for the top layer to achieve a desired top layer dry basis weight value; and correcting the stock flow for the bottom layer to achieve a desired composite dry basis weight taking into consideration the correction made in the stock flow of the top layer. Composite dry basis weight changes due to changes in machine speed and stock consistency are anticipated and corrected by making a compensating change in stock flow for both layers. The flow rate of fiber onto the wire screen of the machine is controlled by computing headbox total flow setpoints from fiber flow data and desired headbox consistency, and adjusting the headbox slice position accordingly. Speed of the slice jet relative to the wire screen is controlled by controlling headbox head.