Recycled Boxboard Fiber Classification and Mechanical Refining Dynamics
Fractionating recycled furnish prior to low-consistency refining preserves boxboard caliper while meeting internal bond targets at reduced energy consumption.
Bauer-McNett Fractionation
Mechanical Classification
Laboratory classification of pulp fibres by length utilizes a series of wire mesh screens of increasing fineness to divide a slurry into distinct groups. This procedure, known as bauer-mcnett fractionation, separates the stock into four or five fractions to assess the proportion of long reinforcement fibres against short fines. Wet screening through standardised meshes like 14, 28, 48, and 100 mesh yields dry weight percentages for each run.
It stops applying to synthetic or heavily modified binders that do not behave as discrete suspended fibres.
Processing Influence
Refining actions in the mill alter the proportions of these fractions by shortening fibres and generating fine debris. A high proportion of long fibres maintains the tear strength of the finished paperboard, whereas excessive fines slow the drainage of the stock on the forming wire. Modern mills monitor the distribution to adjust the disc gap or rotational speed of refiners.
These changes modify the raw pulp to prevent drainage problems or sheet breaks on the run.
Quality Metric
The weight percentage of the longest fraction dictates the structural strength of packaging grades. A low proportion in this fraction predicts poor performance during carton converting and gluing. Testing verifies that the raw material meets the specified structural threshold.