Smoothing roll

When very high velocities are encountered, metal loss from erosion-corrosion can be general. T ically, however, erosion-corrosion produces localized metal loss in immediate proximity to the disrupted flow. Smooth, rolling, wavelike surface contours are often produced, or distinct, horseshoe-shaped depressions (Fig. 11.1) or comet tails... 

Glattwalze,/. smooth roll(er), plain roll. Gl ttwalze,/. glazing roll. 

Different spectral preprocessing and transformations available in SIMCA P-p (version 10.0, Umetrics, Sweden) were evaluated and the best approach for data handling and manipulation was determined. Data collected on the surrogate tablets were divided into a training set to generate the PLS models, and prediction set to test the PLS models. MCC powder, equilibrated at different RH, was also roller compacted at different roll speeds on a Fitzpatrick IR220 roller compactor fitted with smooth rolls. Powder feed rate and roll pressure were kept constant for all experiments. The key sample attributes measured on the surrogate tablets were also measured for the samples prepared by roller compaction. 

Toothed rolls such as those of Table 12.8(b) can handle relatively large lumps, for example, 14 in. maximum with 24 in. rolls according to the table. To smooth rolls, the feed size is limited by the angle of nip which depends on the surface conditions but often is approximately 16° or arccos 0.961. Accordingly the relation between the diameters of the roll dr and feed df and the gap d0 between the rolls is given by... 

Figure 12.5. Jaw, roll, impact, and tumbling equipment for size reduction, (a) Blake-type jaw crusher operates at 200-300 strokes/min (Allis-Chalmers Co.), (b) Smooth roll crusher, for which operating data are in Table 12.8(b). (c) Swing hammer mill operating data in Table 12.7(a). (d) View of a conical ball mill, showing distributions of balls and material and crusting ranges data in Table 12.6(b) (Hardinge Co.). (e) Tube mill with three compartments, length to diameter ratio 3-5. (f) Rod mill in a cylindrical tumbler, LID = 1.2-1.6 data in Table 12.6(d).

Roll crushers are made either smooth or with teeth. A 24 in. toothed roll can accept lumps 14 in. dia. Smooth rolls effect reduction ratios up to about 4. Speeds are 50-900 rpm. Capacity is about 25% of the maximum corresponding to a continuous ribbon of material passing through the rolls. 

The gear-type pellet mill of Fig. 5.14e is especially useful for difficult applications in which feed material tends to slip away from the nip of smooth rolls [21]. This may occur when the resistance of the die holes is high as with small diameter pellets (e.g. 1 mm diameter). The gear teeth catch the material and force it through the holes higher compaction ratios and more uniform pressure distribution are claimed. 

Noninfectious indolent epithelial ulcers also can occur in HSK.These ulcers, formerly referred to as metaherpetic lesions, tend to be ovoid, 2 to 8 mm in size, with smooth rolled edges. They may be caused by damage to the epithelial basement membrane due to inflammation, tear film abnormalities, neurotropic cornea, or toxicity from antiviral medications. These ulcers may be recalcitrant, resulting in neovascularization and scarring. 

Roll Crushers. Traditional roU emshers effect size reduction by crushing single particles between two counterrotating roUs hence they are emshed between the two surfaces. The rolls can either be smooth or profiled to aid feeding of coarser materials. Figure 6 shows a particle of diameter x being reduced between two rolls of diameter D. For smooth rolls D/x > 17 is usually selected, whereas for profiled roUs this can be varied to D/x < 10. The feed size-to-gap width ratio is essentially limited to approximately 4. 

Roll mills are employed in a wide variety of applications for medium-coarse down to fine size reduction. By far the most prevalent use is in flour milling where banks of roll mills, beginning with coarse profiles and ending with smooth rolls, are used in series with sifting machines to extract the white flour from the associated bran. 

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