Ring roller presses

Pressure and energy requirements to briquet various materials. (Courtesy Bepex Corporation.) 

Low (e.g. 500-20,000 lb/in.2) 2-4 Mixed fertilizers, raw phosphate ore, oil shale, resins Coal, charcoal, coke, animal feedstuffs Crude phosphate 

Medium (e.g. 20-50 X 103 lb/in.2) 4-8 Synthetic resins, plastics, PVC, ammonium chloride, DMT (dimethylterephthalate), inorganic salts, animal feed stuffs Ferrous alloys (in powder form), fluorspar, nickel powder, molybdenum powder Iron, potash salts, glass-maker s sand blends 

High (e.g. 50-80 X 103 lb/in.2) 8-16 Metal powders (zinc, vanadium etc.), calcined dolomite, lime, magnesia, magnesium carbonate, sodium and potash compounds, hay and straw Fly-ash, raw and reduced iron ores Fly-ash, iron oxides, raw and reduced iron ores, scrap 

Very high ( 80 X 103 lb/in.2) 16 All types of metal in powder form, metal swarf Metal swarf 

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Material is compacted as it is carried into the gap between a molding groove on the inner circumference of a ring and a press wheel of smaller diameter running in the groove. As above Ring roller presses... 

Ring roller presses with one or two moulding grooves have been described. Capacity is less than that of the more conventional roll presses described in Section 2.2.1, presumably due to the smaller roll width (and hence total... 

Ring roller presses differ from more conventional roll presses because of the convex-concave relationship of the ring and roller in the former case, compared with the convex-convex relationship of two rolls in contact in the latter case. This means that pressure build-up and release are both more gradual in the ring roller press. The slower pressure release is claimed to avoid crack formation in the agglomerated product as it expands more slowly after passing the nip of a ring roller press. 

Figure 229. Operating principle of the ring roller press...

Fig. 6.10-15 Some typical coal briquettes (bricks) produced with punch-and-die presses Fig. 6.10-16 High-quabty pillow- and egg-shaped coal briquettes Fig. 6.10-17 The operating principle of roller briquetting presses Fig. 6.10-18 The ring roller press" [6.7.3.1] Fig. 6.10-19 Flow diagram of a modem anthracite (hard) coal mixing, drying, conditioning, briquetting, and cooling plant...

Fig. 5.11. Schematic diagram of the ring roller briquetting press [7].

There are variations of the ring-roll type in which the ring is set vertically with rollers pressing against the inner horizontal face of the vertical ring and held there by spring pressure. These variations may have advantages, but such features must be considered with respect to each problem. 

Figure 89 depicts sketches of typical pelleting machines.With the exception of the first method (a), which applies a flat die, all other machines feature cylindrical dies and operate in a very similar manner as roller presses. The general principle is modified such that the material is pulled into the nip but then is extruded through bores in the dies and often scraped off with a knife . Equipment types (b) and (d) represent directly the modified roller press principle. Machine type (c) uses a press roller located within the cylindrical die and therefore resembles ring roll presses (see Section 4.2.2.4.4). To improve the grip and increase densification force gear pelleters (e) are applied which are said to produce pellets of superior quality. 

Figure 285. Vintage (1919) drawing of a Koppern roller press with two rings and mechanical feed distributor. (Courtesy of Koppern, Hattingen, FRG) ... 

Special roller press with one press roller within a large ring-shaped die. (No longer used.)... 

A furrow press is a special type of very heavy ring roller (usually with three or four wheels) used for compressing the furrow slices after ploughing. It is usually... 

Roller cores with integral journals fitted with replacable rings or sleeves as pressing tools. 

Nevertheless, machines with concave die rings and internal press rollers do have advantages. For example, if the feed material exhibits a certain elastic behavior, because the forces in the relatively long and slender nip increase slowly, a more complete conversion of temporary elastic into permanent plastic deformation takes place. Fig. 8.41b is another presentation of the forces at work. Feed, ideally deposited in a uniform layer on the die, is pulled into the space (nip) between roller and die and compressed. Friction between roller, die, and material as well as interparticle friction in the mass are responsible for the pull of the feed into the nip and for densification. Smooth surfaces of roller and/or die may result in slip. Axial grooves in the roller, which may also favor build-up of a thin layer of material, and the above mentioned residual layer of densified feed on the die effectively reduce slip. Low interparticle resistance to flow or a distinct plasticity result in a more or less pronounced tendency of the mass to avoid the squeeze" (back-flow), thus reducing densification and potentially choking the machine (see above). 

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