Headbox with the regulation of the weight per unit area - transverse profile by means of the dilution of the fiber suspension

摘要

The stock inlet for a papermaking machine has a separate distributor for dilution water in a controlled feed near the fibre suspension. This gives local variation of the suspension concentration to control the lateral profile of the paper weight. Turbulence tubes mix the diluting water with the suspension, and the dosed portions of the suspension are delivered to segments of the stock inlet. A feed channel is pref. provided for each stock inlet segment, and the turbulence tubes give stock inlet sections of 50-500 mm wide. The distribution width is determined according to the required accuracy of the lateral profile. The paper weight cross section is cotnrolled by a closed control circuit to regulate the dilution water in a direct injection, to give an even profile with a constant suspension flow. The stock inlet lips are constant, and can be stiffened to give a constant gap across the machine width and prevent paper structure variations. Parts of the stock inlet can be charged solely with water, to prevent paper being formed to give a narrow web width. ADVANTAGE - The system controls the paper weight profile, without altering the paper structure which can happen by adjusting the lips of the stock inlet.