Screens particle-size limitations

Screening machines are evaluated on their ability to maximize both prodnct qnality and screening efficiency. One or more of the fractions, or flows, prodnced is considered to be prodnct. This prodnct has imposed on it a quality specihcation defining the acceptable particle size distribution. Often, this specihcation consists simply of particle size limits. For example, in a scalping application, the prodnct quality specihcation may be stated as 0% + 10 U.S. allowable, i.e., a sample of material that passes through the screen should contain no material coarser than a No. 10 U.S. test sieve. Similar specihcations can also be applied to dehne acceptable resnlts of a hnes removal operation. For example, a hnes specihcation of 3% maximnm allowable -60 U.S. means that the analysis of a sample taken from the material that passed over the screen would contain no more than 3% by weight passing the No. 60 U.S. test sieve. 

For granulation work where the objective is to agglomerate particles to form granules, the lower particle size limit may be limited by the screens or filters that confine the particles in the process. If the plate screen does not adequately contain preagglomerated particles, they can be lost from the process. It is also possible for small particles to blind or pass through exhaust filters at the start of a granulation process prior to their incorporation into a granule. 

Therr desorption systems typically have particle size limitations of 2 to 10 cm (0.75 to 4 in.), depending on the components in the system. Soil containing oversized particles must be screened to remove large particles before treatment. The oversized particles can be... 

Early fluorescent pigments were promoted and adopted for use in screen inks for poster boards and paints for safety applications. These thermoset pigments were not well-suited because of their poor fightfastness. Also, because of their relatively coarse particle size, their use in thinner film applications, such as gravure or flexo, was limited. 

The image produced may be viewed either directly by the eye or projected on to a screen. The latter method is usually the more convenient and involves less eyestrain it is less satisfactory than direct observation for fine sizes near the limit of optical resolution. Sizing is commonly achieved by comparison of the particle images with a scale or graticule. Since the process is tedious, sizing is sometimes performed automatically. The smallest resolvable particle size is a function of the wavelength of the light used and varies between 0.5 and 1 p... 

Lu, Vyn, Sandus and Slagg (Ref 17) conducted ignition delay time and initiation studies on solid fuel powder-air mixts in an attempt to determine the feasibility of solid-air detonations. The materials investigated included Al, Mg, Mg-Al alloy, C and PETN. Ignition delay time was used as a method of screening the candidate fuels for further work in initiation studies which determined detonation wave speed, detonation pressure, detonation limits, initiation requirements, and the effect of particle size and confinement. The testing showed the importance of large surface area per unit mass, since the most... 

Another RP-HPLC technique has been applied for the determination of synthetic food dyes in soft drinks with a minimal clean-up. Separation of dyes was obtained in an ODS column (150 x 4 mm i.d. particle size 5 pm). Solvents A and B were methanol and 40 mM aqueous ammonium acetate (pH = 5), respectively. Gradient conditions were 0-3 min, 10 per cent A 3-5 min, to 25 per cent A 5-8 min, 25 per cent A 8-18 min, to 75 per cent A 18-20 min, 75 per cent A. The flow rate was 1 ml/min and dyes were detected at 414 nm. The separation of synthetic dyes achieved by the method is shown in Fig. 3.35. The concentrations of dyes found in commercial samples are compiled in Table 3.21. The quantification limit depended markedly on the type of dye, being the highest for E-104 (4.0 mg/1) and the lowest for E-102 and E-110 (1.0 mg/1). The detection limit ranged from 0.3 mg/1 (E-102 and E-110) to 1.0 mg/ml (E-104 and E-124). It was suggested that the method can be applied for the screening of food colourants in quality control laboratories [113]. 

Results By mass, 99.4 percent of the M28 propellant passed through the /4-inch screen. Owing to a limited supply of M28 propellant, particle size distribution data were collected only for the /4-inch screen. 

Receipts of active ingredient raw materials B1 and B2 are accepted by quality control based on standard tests for potency, chemical attributes, and particle size. Particle size is determined by sieve analysis. Unfortunately, this is a limit test in which 99% of the sample must pass through a certain mesh screen, therefore any influence particle size distribution might have on dosage form potency cannot be examined. 

One efficient removal procedure is to use a 0.45- m filter. There are basically two types of filters depth and screen. Depth filters are randomly oriented fibers that will retain particles throughout the matrix rather than just on the surface. They have a higher load capacity than screen filters. Due to the random nature of the matrix, they have no definite upper-limit cutoff particle size retained. Their porosity is identified as a nominal pore size to indicate this variable. 

In practice, bubble growth is limited not only by the splitting mechanism based on the particle-size distribution of the bed solids, but also by internals (screens, tube bundles, and the like) that cause bubbles to break up. Computational techniques for estimating this process are given in Refs 38 and 39. An example of measured and calculated bubble-growth curve is presented in Figure 6. 

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