b'WHAT HAPPENS IN REFINING? If the blades The refiner is a hydraulic machineof the refiner with complex flow conditions. TheFibres weakened byare old and main parts of the refiner are a rotorcell wall ruptures worn, the and a stator blades fitted with barsrefining will and grooves. They provide a cyclicCell wall swelling not improve treatment to the pulp fibres. the strength Fibre flexibilityof the fibres.The principal forces involving pulpincreasingrefining include the normal force compressing or crushing the fibre mat, corner forces at the edges of the refiner bars, and the shears forces generatedFigure 3. Refining effectsInternalfibrillation.by bar surfaces.The fibre has a tubular structure. In refining, the fibre structure fibrillates internally and externally. Refining also creates fines, removes primary fibre wall and creates delamination andIncreased area of swelling of fibres. In optimal refining allsurface fibrilsthese phenomenes are optimised.Fibrils increase As a result of refining, fibres are madethe bonding area, more flexible, and their bonding surfaceresulting in greater area is increased. The fibers bond totensile strengthone another better. The amount of refining equals the net refining energySome fibrils are creating finesbeing used. Intensity of refining equals way of directing the energy into the fibres. Figure 4. Refining effectsExternalfibrillation.COMMON PROBLEMS If the blades of the refiner are old and worn, the refining will not improve the strength of the fibres. Problems in refiner passing and product manufacture may occur.An incorrect refining result is often compensated by adding softwood to the furnish. It increases costs but doesnt always generate the desired results and may deteriorate paper quality. The consistency of pulp is not correct. If the pulp consistency is too low, the refining will damage the fibre structure too much. If the consistency is too high, insufficient fibrillation will occur. Figure 5. Example of pulp refining audit.WORLD PULP&PAPER 15'