Hybrid former with an mb unit in a paper machine

Abstract

A hybrid former in a paper machine including a lower-wire loop in which there is an initial single-wire portion of a forming zone. In this initial portion, there are draining elements inside the lower-wire loop and thereafter wire-guide and draining elements. The former includes an upper-wire unit in which an upper wire is guided by guide rolls and by a breast roll onto a pulp layer formed on the single-wire portion of the lower wire. In a subsequent twin-wire portion following the single-wire portion, there is a draining and forming unit which includes at least one pressure-loaded press unit and at least one draining-chamber and support unit, which units are arranged inside opposite wire loops. In the units, there are sets of ribs which are pressure-loaded against each other. At the beginning of the twin-wire portion, inside the lower-wire loop, there is a revolving guide and forming roll which is in tangential contact with the lower wire or curves the twin-wire portion at a small angle which is in a range from about 0.degree. to about 5.degree.. The guide and forming roll is substantially immediately followed by the draining and forming unit which includes the sets of ribs. In the area of the draining and forming unit, water is drained primarily through the upper wire while aided by the negative pressures in the draining chamber or chambers in the unit.