GB1423874A - Headbox for and method of delivering a fibre slurry - Google Patents

Abstract

1423874 Headbox CROWN ZELLERBACH CORP 24 Aug 1973 [12 Oct 1972] 40245/73 Heading D2A [Also in Division Fl] In a method of and headbox for delivering a fibrous slurry to the surface of a forming wire, use is made of the "Coanda effect", i.e. the tendency of a fluid emerging from a slit under pressure to follow an extended lip of the slit which diverges from the flow axis of the fluid. The headbox incorporates an elongate exit aperture and an elongate slit communicating with the flow path of the slurry, the aperture and slit extending substantially parallel. In one embodiment, Figure 1, white or clear water forced along path 74 to emerge at slit 84 follows surface 82 so as to drag slurry in channel 100 to exit A. The ratio of the velocity of the fluid emitted from slit 84 to that of the slurry upstream of the slit 84 is preferably at least 10, this ratio causing total mixing of the fluids and the breaking up any flocs in the slurry. Pivoted members 92, 94 may be adjusted by rams 96a, 96b so as to vary the velocity, degree of turbulence &c of the fluid mixture emitted. Similarly, the configuration of flow path 74 may be adjusted by rams 70. The slurry is delivered to the throat B under a head generated in the headbox, and preferably follows a path prior to throat B which minimises any turbulence. Pivotable baffles 23, (36) (Figure 1, not shown) which may define the flow path, enable the path to be altered within limits. In a further embodiment (Figure 5) the Coanda effect is made use of at surfaces 130, 132 and at the outlet nozzle. Water under pressure enters via conduit 124 to initiate slurry motion, e.g. synthetic fibrous slurry, toward the outlet. Conduifs 118 allow a second fluid under pressure, e.g. a conventional wood pulp, water or a chemical, to generate a further dragging force which moreover also mixes the constituents. Adjacent the variable jaw members 142, 143, a third fluid, e.g. water, enters via conduits 138 at a velocity which brings the slurry velocity up to the value required. A reinforcing scrim of nylon or other material 146 may also be ejected through jaws 142, 143 under the fluid pressure. Other embodiments describe oppositely placed Coanda effect slits which effect slurry motion in adjacent separate channels thereby enabling manufacture of, for example, liner board, since different fibrous slurries may be employed simultaneously. Further, the defining walls of the Coanda slits may be incorporated in a body which may rotate relative to the throat so as to allow the fluid flow parameters to be varied. In the above embodiments the slurry mixture is discharged horizontally onto a horizontal web. In yet a further embodiment, however, (Figure 10, not shown) the slits &c are arranged to discharge the slurry vertically onto a vertical web.