Briquetting rolls

Figure 12.10. Equipment for compacting, briquetting, and pelleting, (a) Flowsketch of a process for compacting fine powders, then granulating the mass (Allis-Chahners Co.), (b) Integrated equipment for roll compacting and granulating (Fitzpatrick Co.), (c) A type of briquetting rolls, (d) A gear pelleter. (e) A double roll extruder.

Roll pressing 1. Particulate material, with or without binder, is compacted by squeezing as it is carried into the gap between two rolls rotating at equal speed Briquetting, roll compacting Compacting rolls with smooth, corrugated or pocketed surfaces... 

The roll separation or compaction forces are expressed by equation (104) which can be rewritten for briquetting rolls as " ... 

G. Komarek and K. R. Komarek, Briquetting roll structure with mold inserts , US Patent 3 077 634, 1963. 

Roll presses can produce large quantities of materials at low cost, but the product is fess uniform than that from molding or tableting presses. The introduction of the proper quantity of material into each of the rapidly rotating pockets in the rolls is the most difficult problem in the briquetting operation. Various types of feeders have helped to overcome much of this difficulty. 

The impacting rolls can be either solid or divided into segments. Segmented rolls are preferred for hot briquetting, as the thermal expansion of the equipment can be controlled more easily. 

Roll compacting and briquetting is done with rolls ranging from 130 mm dia by 50 mm wide to 910 mm dia by 550 mm wide. Extrudates are made 1-10 mm thick and are broken down to size for any needed processing such as feed to tabletting machines or to dryers. 

Powder compaction may also be achieved in roll processes, including briquetting, in which compression takes place between two rollers rotating at the same speed—that is without producing any shearing action. In pellet mills, a moist feed is forced through die holes where the resistance force is attributable to the friction between the powder and the walls of the dies. 

Figure 12.14. Common shapes and sizes of pellets made by some agglomeration techniques, (a) Sizes and shapes of briquets made on roll-type machines, (b) Catalyst pellets made primarily by extrusion and cutting (Imperial Chemical Industries), (c) Some of the shapes made with tabletting machines.

In the briquetting process, ore fines usually are mixed with a binder and are formed into compact masses between two rotating rolls. The rolls exert pressures of 1.5-4.2 t/cm2 in forming the briquettes. In the nodulizing process, which is relatively uncommon commercially, ore fines are heated in a rotary kiln to a temperature, usually 1250—1370°C, at which the ore begins to melt and bind. The ore balls in the kiln to form nodules that are discharged and cooled. 

Figure 6.2 Dry granulation roll design options briquetting (left) and continuous ribbon (right).

Weggel RW. 1982. The basics of force feed roll briquetting. Manuf. Engng 88(3) 107-109. 

Binderless briquetting of lignite, peat, etc. Development of roll and extrusion presses for fuels. 

Generally less than 5 tons/hr Press wheel may contain projections to form briquets from compressed strip. Pressure build-up and release more gradual than in roll press, claimed to avoid crack formation in agglomerates. Capacity of largest machines machines much less than for roll presses. 

Fig. 5.2. Schematic diagram of a roll compaction and briquetting press [13].

In these machines, granular material is carried into the gap between two opposing counter-rotating rolls as shown in Fig. 5.2. As the feed approaches the smallest gap between the rolls, it is pressed into agglomerates. In briquet-... 

Average briquet thickness, d, for zero roll gap or spacing. This is determined as twice the average pocket depth. 

K = compressibility constant for granular solid L = length of briquet in direction of rolling (in.)... 

Roll diameter, D, is calculated from eqn. (1) where a and Ri are determined from Fig. 5.7 and 5.8 for the given 5, 0 and K. Usually the maximum pressure exerted by the press is set equal to the maximum required briquetting pressure, Pb, to provide a safety factor in the design. A lower applied pressure can be used in press operation, if desirable. Note in Fig. 5.8 a correction may be necessary to Rx if the dimensionless roll gap S/D is different from 0.01. Since D is unknown, an iterative procedure is necessary in its determination. 

J.R. Johanson, Factors influencing the design of roll-type briquetting presses, Proc. Inst. Briquet. Agglom. Bien. Conf., 9 (1965) 17—31. 

Briquetting presses, see Piston presses, Roll presses... 

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