Mechanism compaction

Sintering. Basically a soHd-state process, sintering transforms compacted mechanical bonds between the powder particle into metallurgical bonds (23,34—38). 

Systems with self-loading compactors. Container size and utilization are not as critical in stationaiy-coutaiuer systems using self-loading collec tion vehicles equipped with a compaction mechanism (see Fig. 25-61 and Table 25-59) as they are in hauled-container systems. Trips to the disposal site, transfer station, or processing station are made after the contents of a number of containers have been col-lec ted and compacted and the collec tion vehicle is fuU. Because a variety of container sizes and types are available, these systems may be used for the coUection of all types of wastes. Container sizes vaiy from relatively small sizes (0.6 m ) to sizes comparable to those handled with a hoist truck (see Table 25-58). 

Equipped with self-contained compaction mechanism m 15-30 23 mm 2440 W X 2440 H x 6710 L... 

Stationaiv-contiiiner systems contiiined compaction mechanism Long-lxulv dump tiviiler 15-30... 

Compactors. Large-capacity containers and container-trailers are used in conjunction with stationaiy compactors at transfer stations. In some cases, the compac tion mechanism is an integral part of the container. When containers are equipped with a self-contained compaction mechanism, the moveable bulkhead used to compress the wastes is also used to discharge the compacted wastes. 

Transfer and Transport of Hazardous Wastes The facilities of a hazardous-waste transfer station are quite different from those of an industrial or municipal sohd-waste transfer station. Typically, hazardous wastes are not compacted (mechanical volume reduction). 

Other investigators have evaluated the potential for these indices. In their studies, Williams and McGinnity have concluded that evaluation of single-material systems should precede binary or tertiary powder systems [29]. A full discussion of compaction mechanisms is given later in this chapter. 

Figures 15 and 16 provide a summary of the compression cycles for rotary and single-punch tablet presses. The formation of the tablet compact in these two types of presses mainly differs in the compaction mechanism itself, as well as the much greater speeds achieved with rotary type presses. The single punch basically uses a hammering type of motion (i.e., the upper punch moves down while the lower punch remains stationary), while rotary presses make use of an accordion-type compression (i.e., both punches move toward each other). The former find their primary use as an R D tool, whereas the latter, having higher outputs, are used in most production operations.

N. Kaneniwa, K. Imagaw, and J.-I. Ichikawa, The effect of particle size on the compaction properties and compaction mechanism of sulfadimethoxine and sulfaphenazole, Chem. Pharm. Bull, 36, 2531 (1988). 

Studies involving instrumented compaction equipment can be extremely useful in the development of dosage forms, especially when the amount of drug substance is limited in quantity. Marshall has described a program in which dynamic studies of powder compaction can be used at all stages of the development process to acquire formulation information [63]. The initial experiments include a determination of the intrinsic compactability of the compound. In subsequent work, simple tablets are prepared, and tested for dissolution, potency, and content uniformity. Through studies of the compaction mechanism, it becomes possible to deduce means to improve the formulation under study. 

Indices are dimensionless parameters derived from various mechanical and physical properties of the tablet blend and resulting compacts. Mechanical properties typically measured include indentation hardness (kinetic and static), elastic modulus, and tensile strength (10,11). Physical properties include particle size, shape, and size distribution, density (true, bulk, and tapped), flow properties and cohesive properties. 

The compact mechanical properties of the three grades of mannitol are also shown in Table 7. It should be remembered that compacts of each material were prepared at the standard SF, thus allowing for straightforward comparison between them and other excipients. The rank order of each excipient by the tableting indices mechanical properties is provided in Table 4. 

Hancock BC, Carlson GT, Ladipo DD, Langdon BA, Mullarney MP. The powder flow and compact mechanical properties of two recently developed matrix-forming polymers. J Pharma Pharmacol 2001 53 1193-1199. 

It was demonstrated that dimensional analysis of the tableting process can produce a scientifically reliable way of predicting tablet properties across the range of materials and with diverse compaction mechanisms. A theoretically sound scale-up method is thus readily available for tableting equipment of different capacity. The method can be readily expanded to include other materials and tablet presses and other target quantities, such as tablet stability (disintegration) and bioavailability (dissolution). 

Mullarney, M. P., Hancock, B. C., Carlson, G. T., Ladipo D. D., and Langdon, B. A. (2003), The powder flow and compact mechanical properties of sucrose and three high-intensity sweeteners used in chewable tablets, Int. J. Pharm., 257, 227-236. 

Stationary-container systems contained compaction mechanism Long-body dump trailer 15-30... 

Rue, P.J. Rees, J.E. Limitations of the Heckel relation for predicting powder compaction mechanisms. J. Pharm. Pharmacol. 1978, 30, 642-643. 

McKenna, A. McCafferty, D.F. Effect of particle size on the compaction mechanism and tensile strength of tablets. J.Pharm. Pharmacol. 1982, 34, 347-351. 

The physical strength of a tablet is dependent on the extent and strength of interparticulate bonds and these in turn are related to the compressive force which is applied. Therefore, the relationship between the applied force and some parameter related to tablet strength is a good indication of the ease with which a given substance will form satisfactory tablets, and may also give an insight into the compaction mechanism of the solid and its mechanical properties. 

Radial and axial die-wall force measurements also provide an insight into the compaction mechanism of the material and may indicate a die-wall binding (sticking) that is, in effect, a negative pull on lower punch. The radial die-wall pressure due to friction is material-specific and is more evenly distributed inside the die with an addition of a lubricant. Instrumentation of the die presents a technological challenge because pressure is distributed non-linearly with respect to tablet position inside the die and depends on tablet thickness. " ... 

The phenomenon studied with the help of instrumentation is the so-called lag time (the time difference between peak of compression and maximum punch penetration). The extent of this lag is indicative of compaction mechanisms of the powder being compressed. ... 

Many powders, especially with viscoelastic compaction mechanism, such as starch or avicel, exhibit large degree of stress relaxation (with time-dependent deformation). 

The results with the slabs of monodisperse non aggregated silica spheres (of the same size range than the xerogels and aerogels) which undergo only intrusion during mercury porosimetry implies that the particles need to be aggregated so that the compaction mechanism takes place... 

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