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REBIRTH OF CONICAL REFINING. Jyhlavara, and then Sunds via their acquisition of Jyhlavara, reintroduced conical refining in the 1980s with its new ConFlo concept- a two-cone refiner with shallow cone angle and lower refining intensities than its ancestors, the Jordans and Claflins. Relative to the ability to provide impacts on the fibers, it was found that centrifugal force and the vortex flows within a conical refiner work to an advantage to force the fibers out of the grooves and into the bar gaps (Figure 1
Initial and continuing field results with the ConFlo showed an ability to provide improved fiber development, more complete and homogenous treatment of the fibers, and improved energy efficiency for identical or better fiber development. One author has suggested that the shallow-angle conical refiner is possibly the most efficient refiner for the treatment of softwood kraft.1
In the mid-1990s, Pilao S.A. of Brazil, a manufacturer of disc type refiners, began a project to improve upon the available designs of conical refiners. The goals were to develop a unit that combined the fiber development and reduced energy characteristics of the new conical refiners with higher capacity and energy efficiency.
The result of the project was a conical refiner with three refining cones. The refining system is a wide-angle, double-flow conical refiner with a double-sided conical rotor and two conical stators. Like a double disc refiner, the rotor floats and is balanced by stock flow and hydrodynamic pressure on both sides. In concept, the refiner can be thought of as a double disc refiner folded back over itself (Figure 1).
FIGURE 1. Diagram of the new triple cone refiner concept.
The design incorporates small diameter cones with a comparatively high refining area. For example, to achieve the same refining area as a 34-in. double disc refiner, the new design requires cone large diameters of only 21.25-in. Since the diameter of the rotor is smaller, the circumferential velocity at the rotor outside diameter for a given RPM is considerably reduced. This permits the maximum allowable RPM of the refiner to be increased, providing for lower refining intensities.
In theory then, the new conical refiner should be better for hardwood and recycled fiber by providing lower intensity refining, equating to better fibrillation and less cutting. Total energy consumption, including no-load power requirements, is also reduced for the equivalent refining area.
Using the existing designs of the refiner body and rotating elements from double disc refiners, the new refiner project team redesigned the refiner door to accommodate the triple-cone tackle concept (Figure 3). The result was a conical refiner with three cones and four refining surfaces, which functions similarly to a double disc refiner. This also was projected to facilitate operation of the new refiner in the mill environment.).2
FIGURE 3. Tackle diameter comparison of a triple conical refiner versus a double disc refiner.
The refining tackle is fabricated, providing greater freedom in bar pattern design to suit various applications. The bars are cold re-rolled steel, which are welded to a fabricated steel cone (Figure 4). The leading edge of each bar is 90 degrees and, due to a unique microstructure, stays at 90 degrees throughout the life of the fill (cast bars generally have a leading edge that is greater than 90 degrees and increases with wear). The geometrical relationship of the bars and the grooves also stays constant over the life of the fill (the bar/groove geometry of cast tackle changes as the bars wear).
The cones are comparatively small and are removed from the door side of the refiner. Filling change from shutdown to startup can be accomplished in one or two hours. When necessary for maintenance, the entire rotating shaft assembly, including bearings, housings, and retainers, can be removed from the door side.