GB825216A - Method of producing wood pulp - Google Patents

Abstract

825,216. Making wood pulp. BAUER BROS. CO. April 20, 1956 [April 21, 1955], No. 12243/56. Class 96. In the production of ground wood pulp from raw uncooked wood, the raw wood is chipped, the chips are fiberized by successive applications and releases of pressure, the fiberized material is refined by further fiberization, and the refined fiberized material is cleaned and screened. In Fig. 1 raw wood passes through a chipper 1 and the chips are introduced into a soaking vat 2. the vat also containing, if desired, a wetting agent or softening agent, e.g. sodium hydroxide. Treatment by soaking may, however, be omitted. The chips are passed to a rotary press 3 in which they are fiberized by successive applications and releases of pressure from a rotating helical feed screw, thereby expelling moisture and natural fluids from the wood, e.g. sap, rosin, which are disposed of as by-products. Material leaving the press 3 is preferably wetted and passed to an attrition mill 4, which may be of the rotary disc type and consisting of a single or double disc mill, and then to a second attrition mill 5 to complete the refining by further fiberization. The pulp passes to a centrifugal cleaner 6 to remove dirt, dark specks, &c., which are rejected as waste, while the pulp is graded by a rotary screen 7 from which any insufficiently fiberized pieces are returned to the rotary press 3. Material passed by the rotary screen comprises finished pulp of the ground wood type. In modifications of the process of Fig. 1, (a) the positions of clearer 6 and screen 7 are reversed; (b) rejects from screen 7 are passed to mill 4 instead of press 3; (c) steps (a) and (b) are combined; (d) screen 7 is interposed between mills 4 and 5 and the acceptable products from screen 7 then by-pass mill 5 to cleaner 6 while rejects from the screen pass to the mill 5, thereby preventing over-refining of pulp material.