Fibre Separation
Mechanical separation of long and short cellulose fibres determines the specific sheet strength and opacity of a paper substrate. The sommerville fractionator operates by passing a pulp slurry through a series of increasingly fine screens to isolate fibre classes by physical length. A water flow forces the mixture through each mesh, leaving longer fibres on top and allowing shorter particles to pass into the lower chambers.
Standardised screen apertures define the boundary for each fraction, which manufacturers weigh after drying to establish the fibre length distribution. This measurement provides the basis for predicting tear resistance and bulk in the final paper product.
Grading Protocol
Quality assurance teams use this device to identify batch inconsistencies in recycled or virgin pulp stocks. Variations in the percentage of fines significantly alter the drainage rates on a paper machine wire section. High concentrations of short fibres reduce the bonding surface area available for hydrogen bridges during sheet formation.
Production engineers adjust refining intensity to compensate for identified disparities between target fibre populations and incoming raw material measurements. This adjustment ensures that the finished paper maintains the necessary mechanical integrity for high speed converting lines.
Output Calibration
Each collection chamber recovers specific material fractions that characterise the performance potential of the bulk stock. The top screen captures the long fibres responsible for structural reinforcement while middle screens gather the reinforcing filler stock. Bottom pans retain the fines which fill voids and provide a smooth surface for coating application.
Precise control over these fractions minimises the risk of dusting during the printing process and improves ink transfer consistency. Consistent fibre distribution ensures that paper performance remains stable under different humidity conditions.
