Cae Screenplates Inc.

Advanced Fiber Technologies, Inc.

Ahlstrom Screen Plates Inc.

Frey A Frejborg

Lassi J Halonen

Frank Aaltonen

A screen cylinder () used for screening cellulosic fibrous material pulp in the pulp and paper industry incorporates first () and second () downstream surfaces () having contoured slopes that form a funnel entrance of the grooves () at the screen cylinder slots (). The contoured construction of the screen cylinder () effects greatly enhanced utility compared to conventional milled and discrete element screen cylinders, including substantially avoiding the Coanda effect.

Screen cylinder with performance boosting configuration

A screen cylinder, screen, method of manufacture of the screen cylinder, and method of use of the screen cylinder, allow screen capacity to be maximized without sacrificing screen cylinder strength, and while achieving a clean accepts flow. A screen cylinder is constructed in a conventional manner except that at least one reinforcing ring is permanently fastened (typically by continuous or spot laser or electric beam welding, or direct resistance welding) to at least a majority of (and typically essentially all of) the land areas which separate grooves in a row from each other, at the outlet surface of the cylinder, or at least one spiral ring is applied. In this way effective slot length of screen cylinders may be about 65-90% of the total screen length, compared to only about 45-55% for conventional screen cylinders. The screen cylinders are particularly effective in screening cellulose pulps from the pulp and paper industry.

Screen cylinder with reinforcing rings and method of manufacture thereof

A screen cylinder, screen, method of manufacture of the screen cylinder, and method of use of the screen cylinder, allow screen capacity to be maximized without sacrificing screen cylinder strength, and while achieving a clean accepts flow. A screen cylinder is constructed in a conventional manner except that at least one reinforcing ring is permanently fastened (typically by continuous or spot laser or electric beam welding, or direct resistance welding) to at least a majority of (and typically essentially all of) the land areas which separate grooves in a row from each other, at the outlet surface of the cylinder. The welds each typically have a width of about 1 to 3 mm (that is they are very small), but that width is typically at least about 75% of the width of a land area in which it is formed, and the weld has a length of at least about 50% of the width of the reinforcing ring at the weld. In this way effective slot length of screen cylinders may be about 65-90% of the total screen length, compared to only about 45-55% for conventional screen cylinders. The screen cylinders are particularly effective in screening cellulose pulps from the pulp and paper industry.

Screen and method of manufacture

The differences in performance of a screening cylinder during screening of a fiber suspension (e.g. low consistency paper pulp) at the inlet end compared to the reject end is accommodated by constructing the feed side surface of the screening cylinder so that it induces greater turbulence in the vicinity of the screen cylinder surface adjacent the reject end of the screen than adjacent the inlet end. Typically this increase in turbulence is at least about 10% (preferably at least about 40%, and typically greater than 100%). The turbulence increase can be provided by a substantially smooth screening medium surface at the inlet end and a contoured screening medium surface adjacent the reject end, or by first and second contoured surfaces of different aggressiveness. Contoured surfaces typically include grooves, and variables that may be changed to affect the turbulence include the depth of the grooves, the angle of inclination of the downstream wall of the grooves, the spacing between the grooves, the radius of curvature of the opening (holes or slots) edges, the frequency of openings in grooves, and the dimensions of the openings (holes or slots) in the grooves. The screen cylinder is mounted in a pressure screen housing.

Method and apparatus for screening a fiber suspension

A screen cylinder or plate has a screening surface and accepts surface on opposite faces, and screens pulp flowing in a flow direction to separate accepts from rejects. A number of substantially parallel macro grooves are formed in the screening surface generally transverse to the flow direction, and a number of parallel micro grooves are formed in the screening surface within each macro groove also generally transverse to the flow direction. The macro grooves induce shear stress in the reject material flowing in the flow direction to keep it in constant motion and to prevent it from forming a mat on the screening surface. The micro grooves induce micro turbulence into the pulp at the immediate area of screening openings extending from each micro groove to the accepts surface, to fluidize the pulp so that accepts readily pass through the screening openings toward the accepts surface. Each micro groove within a macro groove is located further away from the accepts surface moving in the flow direction. The contour of each micro groove preferably includes a slightly slanted upstream wall, a sloped downstream wall, and a depression between the upstream and downstream walls. The depression may include a substantially flat surface, or be a continuation of the downstream wall; the slots or holes forming the screening openings are provided in the depression. It is possible to screen with a rejects rate of about 3-10% at debris removal efficiency of above about 85%.

Multiple contour screening

The screen cylinder includes a screening plate having contoured grooves along an inflow side and a backing cylinder having a plurality of openings therethrough and disposed on the outflow side of the screening cylinder. The contoured grooves are elongated in the axial direction and are closely circumferentially spaced one from the other about the screen cylinder. In one embodiment, circumferentially extending grooves are formed along the outflow side of the screening cylinder whereby pulp flows through the contoured grooves into the recesses and then through the openings of the backing cylinder. In another embodiment, the recesses are formed on the inflow side of the backing cylinder, the screening cylinder being provided with elongated slots along its outflow side in registry with the contoured slots. In this manner, increased flow capacity is provided. Additionally, the screening cylinder is removable when worn for replacement by a fresh screening cylinder which may then be secured to the backing cylinder.

Growing community of inventors

Queensbury, NY, United States of America

Frey A Frejborg