The manufacture of pulp and paper - a textbook of modern pulp and paper mill practice (1921) (14598222740)

Identifier: manufactureofpul03join (find matches)
Title: The manufacture of pulp and paper : a textbook of modern pulp and paper mill practice
Year: 1921 (1920s)
Authors: Joint Textbook Committee of the Paper Industry Stephenson, J. Newell
Subjects: Papermaking Wood-pulp
Publisher: New York : McGraw-Hill Book Company
Contributing Library: NCSU Libraries
Digitizing Sponsor: NCSU Libraries



Text Appearing Before Image:
screen plates 12. As the fibers pass over the screenplates, the accepted stock passes through the slots or perforationsand runs into the space between the plates and the diaphragm 22,from whence it gravitates by the way of the passages 16 to theflow box 11, where the adjustable dam 31, 32 regulates the backpressure on stock under the screen plate and varies the effectivehead that induces the flow accordingly. Enough stock isadmitted to the screen to keep the upper surface of the screenplates covered. Then the vibrating motion given to the dia-phragm 22 by the cam mechanism 5, 7, 24, which causes thediaphragm to rise and fall, creates a partial vacuum in the com-partment under the screen plates, thus causing a flow of stockthrough the slots or perforations. A greater volume of stockmust be admitted to the screen than it can possibly accept(screen), because a fairly rapid flow must be maintained over thesurface of the plates, which must be kept covered with a thin §7 FINE SCREENING 29
Text Appearing After Image:
30 TREATMENT OF PULP §7 layer of stock to maintain the vacuum and insure proper opera-tion. For this reason, the rejections, or tailings, from a singlescreen of this type are very large and contain much good fiber.To cut down the final rejections to a reasonable amount, severalscreens are connected, end to end, each delivering the unscreenedpulp to the next in succession. Such a battery of screens (usually3 or 4 screens to a battery) is so arranged that by the addition ofshowers directed either against or with the current of stock acrossthe plates, the fibers are prevented from settling, and good fibersare washed from shives and knots. Finally, the coarse fiber andtailings run out of the battery of screens at the opposite end tothat from which the stock was admitted. The accepted stockis discharged, of course, from flow box 11. 37. The size of the screen box depends upon the size andnumber of screen plates to be used; that is, the box is wide enoughto allow the screen plate to be pla