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Standard: |
TAPPI |
Method: |
TAPPI T 261 |
Title: |
Fines fraction by weight of paper stock by wet screening – Britt Jar |
TAPPI T 261 Britt jar measures the weight percent fines content of paper stock or of pulp samples by means of a single-screen classifier. A modified procedure permits the use of the apparatus to measure the tendency of the fines fraction to be retained by the fiber fraction under graduated turbulent conditions. Separation of suspended particles of different shapes and sizes by wet screening may be accomplished using various devices. The apparatus described below is recommended for convenience and accuracy.
Samples of paper stock, particularly those taken from the paper machine circulating system, are characterized by having different proportions of particles generally classified as “fibers” and “fines.” The proportions of these two components may vary greatly, depending upon the furnish, upon stock preparation, and whether mineral fillers are added to the stock. The greater tendency of the fines fraction to pass through the wire during sheet formation and to be recycled leads to an accumulation of fines in the headbox. The extent of this buildup is an indication of the retention performance of the machine and affects, for example, drainage, felt filling, and saveall loading.
A suspension such as paper stock contains a range of solid particles that differ in size by small increments. Any dividing line between what is defined as fiber and as fines is an arbitrary decision. From review of published literature and microscopic examination, it is recommended that the dividing line should be particles that will pass a round hole 76 μm in diameter or a nominally 200 mesh screen. Other hole sizes may be chosen as discussed under Section 4.
This technique may be used to measure the relative tendency of the fines fraction to stay with the fiber rather than to follow the water into the filtrate under graduated turbulence in simulation of paper machine conditions. The determination of fines retention is of particular importance in determining the effect of graduated turbulence in the evaluation of additive materials such as retention aids.
To perform adequate testing the sample must be representative of the system from which it is withdrawn. A minimum of five grams oven-dried pulp is needed to perform duplicate testing on each sample.
SGS-IPS cannot sell or otherwise provide standards, specifications, or test procedures to third parties.