Pressure screening is the key process in pulp and paper production and is used to enhance the quality of a wide range of pulp and paper products. While theusual goal of screening is to remove oversize contaminants from the pulp with minimal fiber loss and acceptable cost, screening is finding increased use for fiber fractionation which means that the pulp can be split into fiber classes,
which differ in their average properties. For these reasons, pressure screen are an increasingly important unit operation in pulping, recycling and papermaking. In approach flow applications, pressure screening is the final stock cleaning stage before the headbox, and the machine is called headbox screen or machine screen. It is used to protect the headbox and paper machine from foreign material, to remove debris and dirt, to deflocculate the stock and to improve formation.