CA2302099A1 - Process for the wet screening of stock suspensions in pressure graders and pressure grader screen - Google Patents

Abstract

Process and pressure grader screen for wet screening stock suspensions. The process includes conducting the stock suspension along the screen, so that break-away eddies are formed on an inflow side of the screen, separating portions of the stock suspensions, so that a part of the stock suspension passes through the screen apertures as underflow and an other part is rejected as overflow, and moving the at least one clearer relative to the screen, so that one of pressure- and suction impulses are produced at the screen apertures to form pre- and back flows, In this way, a flow direction of the break-away eddy is reversed by the back flow to rinse a part of the screen lying between the screen aperture with the back flow and an adjacent downstream aperture. The pressure grader screen includes a plurality of bars arranged to form a plurality of essentially parallel grading slots through which an accepted part of the stock suspension passes during the wet screening, The bars have faces located between the grading slots, and the Faces each include a front end and a back end, Each back end includes an extension arranged to cover an adjacent grading slot and at least a part of the front end of the face adjacent the adjacent grading slot. Each extension has an underside, such that the underside and the front end are oriented obliquely to each other.