Rotating screens

Direction of Rotation In circle-throw screens somewhat greater efficiency can be obtained by counterflow rotation, that is, having the material move down the screen against the rotation. Screens rotating with the flow of material will hanme greater tonnage and operate at a lower angle. 

Figure 3 (a) Active strand and (b) rotating screen fogwater samplers... 

Liquid-solid mass transfer has also been studied, on a limited basis. Application to systems with catalytic surfaces or electrodes would benefit from such studies. The theoretical equations have been proposed based on film-flow theory (32) and surface-renewal theory (39). Using an electrochemical cell with rotating screen disks, liquid-solid mass transfer was shown to increase with rotor speed and increased spacing between disks but to decrease with the addition of more disks (39). Water flow over naphthalene pellets provided 4-6 times higher volumetric mass transfer coefficients compared to gravity flow and similar superficial liquid velocities (17). 

Sedahmed GH, Al-Abd MZ, El-Taweel YA, Darwish MA. Liquid-solid mass transfer behavior of rotating screen discs. Chem Eng J 2000 76 247-252. 

Printing is most often done with rotary screens etched in the design to be printed. Printing paste is fed constantly to the center of the rotating screen from a nearby supply, and a squeegee pushes the colored paste through the holes in the screen, leaving the dye paste only in the intended areas, a separate screen is required for each color in the pattern. See Fig. 13.27. 

Microscreening is a method of filtration that uses fabric as the filtering medium. Microscreens (microstrainers) usually consist of a special metallic or plastic fabric mounted on the periphery of a revolving drum. The untreated water flows into the drum and radiates outward through the microfabric, leaving behind the suspended solids removed by the cloth. The solids retained on the inside of the rotating screen are carried upward to a row of backwash jets that flush them into a hopper, which is mounted on a hollow axle of the drum, for return to the treatment plant. 

Centrifugal Former. The use of a centrifugal former allows for the preparation of a sheet of paper that posseses a fiber orientation similar to the orientation present in commercial papers. With this apparatus, the fiber suspension is sprayed onto a fast rotating screen. The dynamic motion of the screen mimics the moving wire of the Fourdrinier machine and induces fiber orientation. In addition, by independently varying the flow of the fiber suspension and the speed of rotation of the screen, different degrees of fiber orientation can be obtained. 

Pump the blend over a vibrating or rotating screen to separate all lumps larger than the size that can be sterilized by the time-temperature limitation of the sterilization cycle. Discard the oversized lumps. (Calculate the maximum lump size by the Gurney, Laurie charts. See Perry and Chilton. 1 )... 

Figure 16.21 Schematic diagram of a volumetric display using multiple mini-projectors and a rotating screen. Reproduced with permission from Wiley.

This is a clever modification of flat silk screen printing. The paste adhesive is fed in the center of a rotary perforated drum, it is pumped through a hollow doctor blade into the rotating screen stencil and then through the holes in the drum and applied onto a web or fabric (Fig. 64). The web or fabric is running over a counter roller coated with rubber. 

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