Repose measurement

The angle of repose has been used in several branches of science to characterize the flow properties of solids. Nelson [1] was one of the first to use angle of repose measurements to determine the flow properties of pharmaceutical mate-... 

The weaknesses associated with the flow through an orifice and angle of repose measurements limit their application for powder flow studies and hopper designs. Consequently, several powder shear testers and methods that permit a more thorough and precisely defined assessment of powder flow characteristics were developed. Shear testers that measure the frictional characteristics of a powder bed under load yield valuable information with regard to powder flow in high-speed tablet equipment. A number of types of shear cell testers are available, but the most common types used in the pharmaceutical industry are the Jenike shear cell and the Schulze ring shear tester.61,62... 

The flow through an orifice is an excellenf mefhod fo compare materials with good flow. Pharmacy, however, most often deals with cohesive powders that do not readily flow. The flow of these materials is increased by employing force feeders, resulting in a dynamic process. Angle-of-repose measurements that do not utilize force and that are often a measurement of stagnant powder have therefore limited application. Shear testers, that measure the frictional characteristics... 

Plow chaiacterlstic.s. Angle of repose and flowability are measurable charac teristics for which standard tests are available (e.g., ASTM Test B213-48, Flow Rate of Metal Powders, etc.). A steeper angle of repose would indicate less flowability. The term Hubricity has sometimes been used for solid particles to correspond roughly to viscosity of a fluid. 

Until Jenike developed the rationale for storage-vessel design, a common criterion was to measure the angle of repose, use this value as the hopper angle, and then fit the bin to whatever space was available. Too often, bins were designed from an architectural or structural-engineering viewpoint rather than from the role they were to play in a process. Economy of space is certainly one vahd criterion in bin design, but others must be considered equally as well. Table 21-14 compares the principal characteristics of mass-flow and funnel-flow bins. 

Angle of repose Handling and storage Disposal Direct measurement... 

Most, if not all, velocity measurements in the bulk, other than NMR/MRI, make measurements through dear end-walls of either long or short cylinders. End-walls, because of friction with the particles, change the dynamic angle of repose near the end-wall and can also cause convections in long cylinders with components of velocity in the axial direction [34, 35], NMR/MRI experiments can avoid the end-wall effects by making measurements far from the end-walls in a long cylinder. 

A rapid method of assessing the behaviour of a particulate mass is to measure its angle of repose. If solid is poured from a nozzle on to a plane surface, it will form an approximately... 

The angle of repose may also be measured using a plane sheet to which is stuck a layer of particles from the powder. Loose powder is then poured on to the sheet which is then tilted until the powder slides. The angle of slide is known as the static angle of repose or the drained angle. 

An angle which is similar to the static angle of repose is the angle of slide which is measured in the same manner as the drained angle except that the surface is smooth and is not coated with a layer of particles. 

The powder s flow properties are also important because they control the physical processes that are used to manipulate the material. Carrs s index, which is a measure of powder bulk density and angle of repose, provides information on flow properties, which are important when production utilises high-speed tableting machines. 

The angle of repose of a powder blend, effective angle of internal friction (EAIF) from shear cell measurements, and the mean time to avalanche (MTA) in powder cohesivity tests are useful for assessing the flow of a tableting mixture at various scales (15 18). 

Controlled optimal particle size and size distribution ensures superior flow properties of coprocessed excipients and reduced reliance on addition of glidants. The volumetric flow properties of SMCC were studied in comparison with those of the physical mixture of its parent excipients (42). The particle size range of the two test samples was found to be similar, but the flow of coprocessed excipient was better than that of the physical mixture. A comparison of the flow properties of Cellactose with its parent excipients was also performed (5) by measuring the angle of repose and Hausner ratio, and Cellactose was found to have better flow characteristics than lactose or a physical mixture of cellulose and lactose. The spray-dried coprocessed product had a spherical shape and even surfaces, which resulted in improved flow properties. On similar terms, mechanically coating the 2% CSD over microfine cellulose powder resulted in improving its flow properties (43). 

Angle of repose—a blend is poured through a funnel into a pile and the angle at the base of the cone is measured. 

The angle of repose is a measure of the incline at which conveyors such as screws or belts can carry the material. The tangent of the angle of repose is the coefficient of sliding friction. This property is a factor in the power needed to transfer the material by pushing or dragging as in pneumatic, screw, flight, and Redler equipment. 

The physical properties of granular materials that bear particularly on their conveying characteristics include size distribution, true and bulk densities, and angle of repose or coefficient of sliding friction, but other less precisely measured or described properties are also of concern. A list of pertinent properties appears in Table 5.2. The elaborate classification given there is applied to about 500 materials in the FMC Corporation Catalog 100 (1983, pp. B.27-B.35) but is too extensive for reproduction here. For each material the table also identifies the most suitable design of screw conveyor of this... 

Basal metabolism is the rate of total heat production ol an individual who is awake but in complete mental and physical repose, at comfortable temperature and without having had food for at least 12 hours. See also Basal Metabolism, Under these conditions, oxidation of stored nutrients provides the sole source of energy expended and Ileal is measurable hy calorimetry. See also Digestion. 

Fig. 4.2 The angle of repose. It should be noted that the angle of repose is generally not a measure of flowability of solids, and as Jenike (22) points out, it is strictly useful only to determine the contour of a pile. Its popularity stems from the ease with which it can be measured.

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