Fiberboards 



2759 



Figure 23-12. — Cross section through a single-revolving-disk refiner. (Drawing courtesy 

 of The Bauer Bros. Co.) 



DISK REFINING 



Southern hardwoods, which have not been successfully stone-ground on a 

 commercial scale, are readily fiberized in disk refiners. Whereas stone grinders 

 must be fed with roundwood, disk refiners are designed to operate on chips — a 

 form of wood more conveniently conveyed and stored. Also, disk refining 

 allows a variety of continuous-flow chip pre-treatments such as water soaking, 

 steam cooking, and chemical digestion, permitting great latitude in pulp manu- 

 facture. In disk refiners chips are sheared, squeezed, cut, and abraded as they are 

 forced through a narrow gap between two textured disks, one or both of which 

 rotate. Resulting pulps are generally superior to stone-ground wood. Most 

 fiberboard pulp is produced by disk refiners. 



Single- and double-disk refiners. — The general design of disk refiners is 

 discussed in section 18-27. A double-disk refiner in which the two disks 

 counter-rotate is shown in figure 18-282, and the action of single- and double- 

 disk machines is compared in related discussion. See figure 18-283 for illustra- 

 tion of profiled cutting elements (disks); these ring segments are bolted to disk or 

 housing. Figure 23-12 shows a single-disk refiner with one stationary and one 

 rotating disk. 



Primary refiners are used to break down chips into fiber bundles, and 

 secondary refiners, which require one-tenth or less of total pulping energy, 

 complete fiberization; the secondary refiners are also called "pump-through" 

 machines (fig. 23-13). Both single-disk and double-disk refiners are used in 

 primary chip breakdown. Secondary refiners are mostly of single-disk design. 



