GB1376518A - Manufacture of fibre sheet products - Google Patents

Abstract

1376518 Manufacture of fibre sheets KARLSTADS MEKANISKA WERKSTAD AB 13 Oct 1972 [15 Oct 1971] 47235/72 Heading D2A In the manufacture of fibre sheets, e.g. paper, using an initial fibre-stock suspension containing B.O.D., (biochemical oxygen dem- and) substances, the suspension is divided into flows 5, 6, the flow 5 is conveyed to a first sheet forming stage 7 in which a first layer 8 is formed, the flow 6 is subjected to a washing process 9 in which the original B.O.D. substances containing suspension water is replaced by water substantially free of these substances, the washed flow 11 is conveyed to a second sheet forming stage 13 and optionally to a third sheet forming stages 14 where layers are formed which are added to the layer 8, and the water removed in the first sheet forming stage 7 and the original B.O.D. substances containing suspension water from the washing process 9 is recirculated to the initial fibre-stock suspension. Wood associated with water is ground to a pulp at 1; the pulp being then screened at 3 with the recirculated water entering at 4. The water from the second and third forming stages 13, 14 and from a pressing stage 17 is recirculated to the washing process at 10. The three layered web 18 has the layer 8 as the centre layer and passes from the pressing stage 17 to a dryer (not shown). Clean water is supplied at 19 for cleaning, the press felts. Chemical wood-pulp may be added at 20. The layer 8 may be dewatered in forming stage 7 to a value such that its water content does not exceed the total water content of the three layered web 18, to prevent B.O.D. substances reaching the outer surfaces of the web during pressing. A web of more than three layers may be produced and this may be of cardboard or fibreboard. A paper-making machine for forming a three-layered web, Fig. 2 (not shown), has three successively disposed sheet forming double wire sections and a press section, the first forming section having a pervious forming suction roll, and the other two forming sections have impervious forming rolls which avoid dewatering through the first layer containing B.O.D. substances. The headboxes for the second and third forming sections are directed to one side of the previously formed layer or layers so as not to disturb these.