Disc screens

The equipment most commonly used for classification involves vibrating screens, rotary screens and disc screens. Air cyclones, which are mostly used as density separation equipment, are described in the corresponding chapter. 

Disc screens are composed of a series of parallel, horizontal, and equally spaced bars or shafts, which are installed perpendicular to the flow of the material. Each shaft is equipped with interlocking serrated or star-shaped discs, installed at equal distances across the width of each bar. Undersized material falls in the space between the discs, while oversized material overflows the discs. The adjustment of the distance between the discs determines the materials size to be separated as underflow. After suitable adjustment, the same screen can be used to separate materials into different size. 

Figure 8 Configuration of patented disc screen. (With permission of Bulk Handling Systems,...

The main advantage of disc screens over vibrating ones is that they do not favor clogging of the apertures. In case that clogging occurs, due to wrapping of materials around the disc, they are usually self-cleaned by rotation. Materials such as metals, glass, and shredded plastic bottles have been separated successfully as undersize. 

The major dasses of antibiotics are secondary metabolic products of micro-organisms. Many were discovered by empirically screening culture filtrates or cell extracts for antimicrobial activity. A range of techniques (examples are methods using, impregnated discs, porous cylinders, cut wells, see Figure 6.2) have been used to carry out such screening. 

Handen, J. S., High throughput screening challenges for the future, Drug. Disc. World 47-50 (Summer 2002). 

Note that the graphics printer is wired into the terminal so that graphics displays on the CRT screen can be dumped directly to the printer. One of the two floppy disc drives is reserved for the minicomputer operating system and the control programs. The other disc drive is used for the user s data. Data files from the user s floppy disc can be read directly by the 32-bit minicomputer. 

Sinko, P. J., Drug selection in early drug development screening for acceptable pharmacokinetic properties using combined in vitro and computational approaches, Curr. Opin. Drug Disc. Dev. 1999, 2, 42-48. 

A soil infiltration test was devised to screen a large number of compounds within a limited time span. The amounts used are far in excess of quantities used in field application. A 5% diamide solution in isopropanol, 15 mL, was added to 50 g soil, air dried overnight, and then placed in a vacuum oven at 50° for 1 hr to remove traces of isopropanol. The treated soil, 10 g, was placed in a 25 X 500 mm glass chromatographic column with a coarse porosity fritted disc on top of a detachable adapter base. The soil was tapped down lightly with a wooden dowel to a depth of 12 mm in order to prevent channeling. Forty-five cm of water covered the soil. The period required for 200 ml distilled water to penetrate through 10 g of treated soil was recorded as the infiltration time. The test was arbitrarily discontinued after 2 weeks. 

Carr, R. Jhoti, H. Structure-based screening of low-affinity compounds. Drug Disc. Today 2002, 7, 522-527. 

Bohm, H.-J. and Schneider, G. (Eds.). Virtual Screening for Bioactive Molecules. Wiley-VCH, Weinheim, 2000. Bajorath, J. Integration of virtual and high throughput screening. Nat. Rev. Drug Disc. 2002, 3, 882-894. 

Schneider, G. and Bohm, H.-J. Virtual screening and fast automated docking methods. Drug Disc. Today. 2002, 7, 64-70. 

Lyne, P.d. Structure-based virtual screening an overview. Drug Disc. 

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