A general purpose practice for screening pulp using a specific screening device is described, which separates from a slurry of pulp fibers a contaminant fraction with size dimensions which are significantly greater than the diameter of a pulp fiber.
Separated contaminants include, but are not limited to, shives in virgin fibers, or stickies and other contaminants in recycled fibers.
There are numerous screening instruments used for separation, classification, or quantitation of contaminants from pulp fibers, or pulp fibers themselves on the basis of size using laboratory screening technology.
These devices include the Valley, Von Alfthan, Somerville, Williamson, and Haindl - type screening devices. Useful methods based on the Valley, Von Alfthan, and Somerville - type devices were a part of the TAPPI Useful Methods procedures which are no longer published. In addition, T 233 Fiber length of pulp by classification describes use of both the Clark and Bauer-McNett - type pulp classifiers which separate pulp fibers into various length classifications by screening. This procedure covers a specific screening procedure to remove contaminants, and does not cover use of screens for pulp size classification.
The specific device described in this practice is the MasterScreen - type instrument.
While this Practice does not describe the specific procedure required to quantitatively measure the contaminant fraction separated, it should be noted that where this is done by the user of this practice, slightly different quantitative results may be found among or between results calculated using the device described in this Practice and the various devices in 1.3.
