FI934667A - Paper machine two-wire guitar former - Google Patents

Abstract

The invention concerns a web forming part with a double screen in a paper machine, which includes a covering screen 10 and a support screen 20, which are guided by guide rolls 12, 22, in which the web W being formed is removed from the support screen to a pickup fabric 30 or the like. The web-forming part includes a forming gap G to which a pulp suspension jet J can be fed from the lip opening of the headbox 32. The forming gap G is determined so that it is controlled by rolls 11, 21 within the loops of said screens 10, 20. The screens 10, 20 delimit a zone with a double screen where there are at least two pressure-loaded pL drainage and forming units 40, 50 after each other. Both of these units contain a support strip system 16, 17; 16, 27 as well as a system of loading strips 26, 27; 26, 17a that function opposite these. A loading pressure is produced with this strip system which forces said screens 10, 20 against each other. The drainage and forming units 40, 50 contain one or more underpressure boxes 15, 29 to which underpressure p1,p2 can be fed. The underpressure boxes 15, 29 of the consecutive drainage and forming units 40, 50, 50A are arranged with an opposite different screen loops 10, 20. The first drainage and forming unit 40 is placed essentially directly at or a short distance from forming gap G so that the thickness k1 of the web W being formed at the input side of said forming unit 40 at the zone with the double screen is not higher than in the range where k1 equals approximately 0.5 to 2.5%. <IMAGE>