screen
Screen
What does it mean when you dream about a screen?
The dreamer may be needing to “screen out” information that she or he may not be able to assimilate.
screen
[skrēn]screen
screen
ii. In cartography, a sheet of transparent film, glass, or plastic carrying a “ruling” or other regularly repeated pattern, which may be used in conjunction with a mask, either photographically or photomechanically, to produce areas of the pattern.
iii. Refers to Stevenson's screen, which is used to keep meteorological instruments for meteorological data observation.
screen
screen
The display area of a computer monitor, TV set, smartphone, tablet or other electronic device. The terms "screen" and "monitor" are used synonymously, although technically, the screen is the visual display part of a monitor. See touchscreen, flat panel display, automotive display, LCD, OLED and CRT.Screen
a device or machine for the mechanical sorting of bulk materials according to size of particles (pieces). It is used to divide coal, ore, or crushed stone into fragments, and also to dry materials (enriched coals, washed ores, and so on). The screen is one of the basic types of mechanical equipment of crushing and sorting mills and preparation plants. Fixed screens are classified as devices; mobile screens, as machines.
Fixed screens (bar. arc. and conical screens) consist of the working part of a stationary screening surface and its supporting structure. Bar screens have an inclined surface with slots larger than 50 mm and are used for crude sorting of material that comes in large chunks: arc screens are used to dry and sort fine-grain materials (coal or sand); and conical screens are used for drying and crude sorting.
Mobile screens (machines) assure highly efficient screening. They consist of one or more screening surfaces (sieves), their supporting structure, and the drive mechanism for the sieve. In terms of the type of motion of sieves, a distinction is made among screens with rotating surfaces (trommels), shaking screens, and vibrating and semivibrating types. Trommels consist of concentric screening surfaces that rotate about a single axis. They are used mostly for washing materials and for incidental crude sorting. Shaking screens have one or more sieves that are fastened to a rectangular crib linked to a driving mechanism, usually an eccentric. Material moves along the sieve under the force of gravity or inertia. Thanks to the rigid kinematic link between the crib and the eccentric, the scope of vibrations of the sieve is strictly defined and does not depend on the load in the crib. The crib of a vibrating screen is oscillated (vibrated) by the forces created by a vibrator. According to the kind of vibration, screens of this type are classified as linear, elliptical or circular. Unlike shaking screens, the magnitude of the sieve’s vibrations in vibration screens is not constant but depends on the load.
All types of screens are used in industry, but the most promising are the vibrating type (see Table 1). Within this group special attention is due so-called resonance screens, in which the motor’s energy is expended only to overcome resistances to vibration and not to impart kinetic energy to moving masses. Therefore resonance screens require a less powerful drive, and the balanced state of the material makes it possible to build such screens with large screening surfaces.
REFERENCES
Goncharevich, I. F., V. D. Zemskov, and V. 1. Koreshkov. Vibra-tsionnye grokhoty i konveiery. Moscow, 1960.Moliavko. A. R. Zarubezhnye konstruklsii mekhanicheskikh grokho-tov(Obzor). Moscow, 1963.
| Table 1. Specifications of some screens produced in the USSR | ||||||||
|---|---|---|---|---|---|---|---|---|
| Type | Model | Maximum productivity(m3/hr) | Sieve size (mm) | Number of sieves | Size of sieve openings (mm) | Power of electric motor (kW) | Weight (kg) | Use |
| Vibrating inclined................. | GGT-42 | 250 | 1.500 × 3,750 | 2 | 80 × 80 135 × 135 | 17 | 6,615 | Sorting of construction materials up to 400 mm |
| Vibrating inclined................. | GGS-42 | 150 | 1.500 × 3,750 | 2 | 26 × 26 5 × 20 | 13 |  | |
| Vibrating horizontal................. | GSS-42 | 80 | 1,250 × 1,820 | 3 | 11 × 11 26 × 26 5 × 20 | 5.5 | ||
| Two-mass resonance................. | GRL 62–1 | — | 2,000 × 5,000 | 2 | from 6 x 6 to 95 × 95 | 11 | 22,540 | Sorting and drying of anthracite and gas and power coals |
| Flat-shaking tour-crib................. | GPO-4M | 100 | 1,500 × 6,000 | 2 | 1 × 1 | 11 | 10,567 | Drying of construction materials and coal up to 25 mm |
| Arc................. | SD-1 | 200 | 830 × 1.330 | 1 | from 0.5 to 1.5 | — | 350 | Sorting and drying of construction materials and coal up to 6 mm |
Andreev, S. E., V. V. Zverev. and V. A. Perov. Droblenie, iz-mel’chenie i grokhochenie poteznykh iskopaemykh. 2nd ed. Moscow. 1966.
Ponomarev. I. V. Droblenie i grokhochenie uglei. Moscow, 1970.
V. V. BERDUS
Screen
(1) A large operations unit consisting of individual detachments in Soviet Russia in the initial period of the Red Army’s formation, when it was extremely small in size. The screen system was established by the Supreme Military Council to defend the demarcation line established after the Treaty of Brest in March 1918. It included the Northern Sector (March 14-September 11), the Southern Sector (August 5-September 11), and the Western Sector (April 8-September 11) of screen detachments. The screen sectors were headed by military councils, each consisting of a military leader and two political commissars. Small headquarters were established to direct the screen detachments. The screen system later served as the basis for deployment of a number of armies and fronts.
(2) A method of camouflage. The screen is created by smoke or by hanging up authorized (or available) means that conceal the particular military objects (structures, positions, and so on) against visual and air observation by the enemy.
(3) Submarine curtain, a group of submarines formed in general search or combat formation for joint performance of the assigned combat mission.
Screen
In printing, an optical device used in the reproduction of halftones. Such a device consists of a system of opaque elements—most often, parallel lines—that are applied to a nondeforming base, such as glass. Screens differ in the character of the opaque elements (Figure 1) and in the line frequency, that is, the number of such elements per centimeter. Depending on the technique involved, screens may be classified as projection or contact types. Projection types (Figure 1,a-d) are used only in photographic processes. Such a screen is mounted inside the process camera at a small, precalculated distance from the photosensitive layer. The light flux that passes through the screen during exposure is broken up into separate beams of light; these beams have the same dimensions but differ in intensity,
which depends on the brightness of the sections of the original that are being reproduced. The different quantities of light that reach the photosensitive layer cause the formation of exposed sections on the negative in the form of dots or lines of unequal size. The density, structure, and overall dimensions of these dots also depend on the exposure parameters and on the characteristics of the light sources, screen, and photographic material.
Contact screens (Figure 1,e) are used in contact with photosensitive layers. They are employed both in photographic processes and in the transfer of an image from a negative or positive to the printing surface. The formation of the screen image is a result of the absorption of part of the rays coming from the original by the dots on the screen, which are of nonuniform density. There exist gray (silver-containing) and magenta (based on finely dispersed dyes) contact screens. The dyed screens are preferable because of the better quality of the resulting image.
In relief and planographic printing, crossline or autotype screens are generally used. The line frequency in this case ranges from 24 to 60 lines per cm (Figure 1,b). Intaglio printing employs special contact screens with high line frequencies (Figure 1,f). These screens are used in the transfer of the image to the printing plate.
I. A. ZHUKOV