Abstract: A method and apparatus for obtaining information, during operation of a headbox for a paper machine, about the size, at one measuring point at least, of a stock discharge slot which is bounded by two structural members comprising two lip members of the headbox of two partitions arranged between the lip members or one of said lip members and one of said partitions. According to the invention, for every such desired information, an ultrasonic transducer means arranged at the measuring point in the headbox and with a combined transmitter and receiver for ultrasound is arranged to transmit an ultrasonic pulse through the stock between two of said structural members within predetermined surface areas of these located in proximity to said discharge slot.

Abstract: In the production of multi-ply paper in a twin-wire former of the kind in which the wires define a curved forming zone, preferably a former of roll type with a smooth-faced forming roll, a substantially improved layer purity is produced in that the discharges from a first and at least succeeding portion of the curved forming zone are collected separately as different fractions. The first fraction collected nearest the multilayer headbox is returned in a first separate circuit to be used for diluting a first high consistency pulp to a first stock of headbox consistency, from which stock a first layer is to be formed directly on the outer wire in relation to the curved forming zone. At least a portion of a second fraction collected at a greater distance from the multilayer headbox is returned in a second separate circuit to be used for diluting a second high consistency pulp to a second stock of headbox consistency, from which a second layer is to be formed superimposed on the first layer.