Stock inlet for a papermaking machine has dividers in the second flow path section giving suspension flow channels of the same length and identical cross section to reduce or eliminate tiger stripe effects in the paper

摘要

The stock inlet for a papermaking machine has dividers (3.1-3.3) at the outlet where all have a contour and alignment so that each pulp suspension flow channel (4.1-4.4) has the same length with an identical cross section at the second stage (II) of the pulp flow path where there is a stronger convergence. The cross section of the suspension flow channels (4.1-4.4) expands or is reduced or remains constant in the second path section (II). The second flow path section (II) follows directly after the first path section, where there is an even flow convergence. The pointed structure of the dividers (3.1-3.3) in the second path section (II) is formed by flat surfaces, and the divergence or convergence angle of all the flow channels is identical in the second path section (II). The limit surfaces (5.1-5.8) of the suspension flow channels (4.1-4.4), across the machine width, form an angle at the end zone between 20 deg convergence and 120 deg divergence or 5 deg convergence and 7 deg divergence. The lie of the upper wall (1) and/or the lower wall (2) is in a mirror image to the lie of the surfaces (5.2,5.7) of the facing dividers (3.1,3.3), at least in the second path section (II). The downstream flow ends of the dividers (3.1-3.3) lie on a circular arc (8), where the center point (M) of the radii is on the center line of the suspension stream. The center point (M) for the radii of the circular arc (8) is on the bisection of the angle formed by the surfaces of the upper and lower walls (1,2) in contact with the pulp flow in the second path section (II). The stock inlet has a turbulence generator with a number of diffuser tubes, in rows across the machine width, and the dividers (3.1-3.3) start between the diffuser tube rows. The upper and lower walls (1,2) of the stock inlet have the same length. The second flow path section (II) has a length of 0-4 dm and preferably 0.5-2.0 dm. The stock inlet can be fitted with three dividers (3.1-3.3) and four suspension flow channels (4.1-4.4), where the dividers have a max. thickness of 5 cm and a min. thickness of 0.5 mm and preferably maximum 1 cm and minimum 3 mm. All the suspension flow channels (4.1-4.4) are congruent, at least in the second path section (II). The bisections (6.1-6.4) of all the suspension flow channels in the second path section (II) intersect at one point (A), and the bisections (7.1-7.3) of all the dividers (3.1-3.3) intersect at a point (B). The intersection points (A,B) coincide, on a line with the radius center point (M) of the arc (8), or coincide with the center point (M). At least one of the stock inlet walls (1,2) has a diaphragm to adjust the height of the outlet gap of the stock inlet unit. The lower wall (2) can be longer than the upper wall (1), with the diaphragm at the shorter wall. The walls (1,2) are longer than the dividers (3.1-3.3).