Fremstilling av duk med skumprosess med skumfortynning

A nonwoven web of fibrous material is made by the foam process using a manifold of a particular construction. The manifold has a casing with first and second opposite ends including an inlet for a foam-fiber-surfactant slurry at the first end, and optionally a valved outlet at the second end. A center section of the manifold casing has a (e.g. rectangular) cross-section that becomes smaller moving from an inlet toward the outlet. First and second substantially closed side walls, a porous front wall having an effective length, and a back wall opposite the front wall, are provided for the center section, the walls planar or curved. Any suitable structures are provided for introducing a second (e.g. substantially fiber-free, or a fiber-foam slurry) foam into the center section through the back wall. Pressure sensors penetrating one or both of the side walls may sense the pressure within the center section, and automatically control the introduction of slurry into the inlet, withdrawal through the outlet, and/or introduction of the second foam into/through the back wall, so as to maintain the basis weight of the foam-fiber slurry passing through the front wall substantially constant along the effective length of the front wall.