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Basic study of pulpstone dullness

Pulp & paper Canada, 1996-10, Vol.97 (10), p.27-30

Copyright Southam Business Communications, Inc. Oct 1996 ;ISSN: 0316-4004 ;EISSN: 1923-3515

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  • Title:
    Basic study of pulpstone dullness
  • Author: Lonnberg, B ; Finell, M ; Gros, G
  • Subjects: crushing ; Equipment & supplies ; grinders ; Grinding ; Picea abies ; properties ; Pulp & paper mills ; Pulping ; wood ; wood pulp
  • Is Part Of: Pulp & paper Canada, 1996-10, Vol.97 (10), p.27-30
  • Description: Determination of Dullness: Attempts were made by Finell [16] to quantify the pulpstone surface and the active grits. Casts of the pulpstone were made in Provil M and H silicon rubber that then was cut by a Sorvall TC-2 microtome to about 0.1 mm thin slices. The slices were enlarged and copied on paper for visual evaluation of the grooves. Another method involved pressing a glass plate (Assistent Elka Objekttrager No. 2400) against the slowly moving pulpstone surface. The scratches caused by the active grits of 450 mm pulpstone surface length (half the perimeter) were evaluated by measurement of the light scattering and by weighing. The light scattering was determined by Opton Elrepho 85321 (filter 10) on three scratched glasses piled, with an unscratched glass plate as reference. The silicon rubber method indicated that the groove depth remained constant irrespective of dulling step number. It was, however, difficult slicing the rubber to represent exactly the same position of the pulpstone surface. Further air bubbles captured between rubber and pulpstone caused some disturbances in the surface profile. The glass quantity removed by scratching was small compared with the weight of glass plate, suggesting poor accuracy. The tensile index seemed to correlate with the compression/drag effect ratio (modified friction coefficient) regardless of pulpstone dullness, Fig. 7. The newly sharpened and undulled pulpstone surface produced pulp according to a different mechanism that involved cutting actions rather than viscoelastic behavior. This occurred after ten dulling steps. The coarse fibre fraction was very low at zero dulling steps due to fibre cutting, Fig. 4, and accordingly, the fines fraction was relatively high, Fig. 5. Abstract: Mechanical wood grinding is dependent on the pulpstone dullness that varies in the sharpening interval. Therefore, effects of dulling were studied under laboratory conditions by introducing grinding powder in the grinding. Subsequent to dulling groundwood was produced for testing. It was found that increased pulpstone dullness resulted in: decreased freeness but increased compression force and specific energy; increased shives content, an initial increase in the coarse fibre fraction, which then decreased; an initial stabilisation in the pulp strength, and a decrease in brightness.
  • Publisher: Westmount: Annex Publishing & Printing, Inc
  • Language: English
  • Identifier: ISSN: 0316-4004
    EISSN: 1923-3515
  • Source: ProQuest Central
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