HEADBOX, SHEET-FORMING UNIT HAVING A HEADBOX AND METHOD FOR OPERATING A SHEET-FORMING UNIT

摘要

The invention relates to a headbox (1) for a machine for producing fibrous material webs from at least one fibrous material suspension (FS), comprising at least one feed device (4) feeding the at least one fibrous material suspension (FS), a nozzle (9) having an outlet gap (12) for dispensing the fibrous material suspension (FS) in a free jet (F), and a turbulence-generating device (7) arranged directly upstream of the nozzle (9) in the flow direction. During operation of the headbox (1), the at least one fibrous material suspension (FS) is guided in the turbulence-generating device in sub-flows through a plurality of turbulence-generating channels (8; 8.1-8.n; 8.11-8.nn). Within the individual turbulence-generating channel (8; 8.1-8.n; 8.11-8.nn) of the turbulence-generating device (7), at least one region forming a fluidisation region (15) is provided, in which a pressure loss (∆p) can be generated in the sub-flow of the fibrous material suspension (FS) guided through said region. The headbox (1) according to the invention is characterised in that the nozzle (9) and the turbulence-generating device (7) arranged directly upstream of the nozzle (9) are designed and dimensioned such that they are suitable for setting a dwell time (TV) of ≤ 200 ms of the fibrous material suspension (FS) flowing through the same from a final fluidisation region (15) of an individual turbulence-generating channel (8; 8.1-8.n; 8.11-8.nn) of the turbulence-generating device (7) before inlet (14) into the nozzle (9) as far as the outlet gap (12) of the nozzle (9), and a pressure loss (∆p) of ≥ 50 mbar in the final fluidisation region (15) upstream of the inlet (14) into the nozzle (9).