Wedge-wire screen

Metal and plastic wedge wire screens are commonly used in the construction of filters and other separators, as either the support for finer filter media or as the filtering medium itself. The screens have typical aperture sizes of 50 pm with an average tolerance of 10%. Metal, usually steel, screens are used in applications where separator robustness needs to be combined with slurry dewatering duties or when the solids are particularly coarse or abrasive. 

The correct choice of metal must take account of the nature of the solids and liquids to be treated, their temperature and heat cycles and the presence of any other chemical contaminants. The metal must be capable of being drawn and woven. 

Weave choice should take account of both filtration and medium cleaning (see Table 2.9). Mechanical stress during operation or cleaning may require use of higher strength wire cloth, such as the Dutch twill weave. 

Sheet type Typical finest hole size (mm) Approximate open area (%) 

Perforated metals with round holes 0.5-1 (dependent on metal) 27 

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Simple strainers remove gross materials. These should not normally occur in public supply, but strainers are sometimes fitted to protect sensitive equipment or processes against breaks in the main, etc. The commonest form contains a stainless-steel wedge wire screen and is piped with a bypass so that the screen element can be isolated and removed for cleaning when necessary. If the load on the filter makes this kind of cleaning burdensome a self-flushing filter can be used. These can incorporate strainer elements down to 50 pm. 

Fixed, inclined wedge wire screen (sieve bends, DSM) removal of particles >0.15 cm. Variable inclination from 65 to 45° to the horizontal feed concentration 200 mg/L. For dewatering minerals, dewatering particles of diameter >40 pm. Vibrating screens typical exit liquid concentration for <8-mm particle size, 20 to 45 vol% liquid for >40-mm particle size, 2 to 10% v/v liquid. Belt, gravity see Section 16.11.5.13. 

Rapid settling slurries lend themselves to gravity separation or filtering centrifuges with wedge wire screen (like pusher or screen bowl centrifuges). 

Fixed inclined wedge wire screen (sieve bends, DSM) removal of particles... 

Fixed inclined wedge wire screen, sieve bend fluid loading 6.7 to 20 L/s nf or 10 to 40 L/s m of width solids loading 1.4 to 4.2 g/s m exit solids concentration 12 to 15% w/w soUds. For dewatering minerals, fluid capacity of 0.0015 to... 

The grating is the support members that span between the beams and support the media. The grating may be covered with screen to prevent egress of small particles. The screen may be installed in a single or multiple layers of mesh. It can also be covered with a layer of wedge wire screen for file same purpose. The grating must be designed to support the total of all loads. 

Solid fabrications Flat wedge-wire screens 100... 

A wide variety of screens and meshes are available, ranging from fine photoetched or electroformed perforated screens to the heavy duty wedge wire screens used in centrifuge and high pressure screw press construction. Simple sieves and coarse screens were used as early as the sixteenth century for processing metal ores. Modern woven wire screens are precision made cloths with aperture sizes as small as 20 pm (smaller aperture sizes are supplied by some manufacturers) for industrial separations in filtration, clarification and extraction. Plastic meshes and plastic coated metal meshes are finding an increasing number of applications in separation processes. 

A Japanese firm, Kuri Chemical Engineers, has a vertical screw press, with the dewatered solids discharging at the bottom. A scraper part of the screw leaves a thin heel of cake which acts as a precoat, which is either formed directly from the process slurry or from a filter aid such as diatomite. The filtration screen (wedge wire screen of 25 pm aperture) is cleaned automatically by back-washing. The tests reported were with potassium chloride crystals in a solution of PVC in acetone, and with activated carbon in an aqueous solution of alanine. Particle size ranged from 1 to 100 pm. 

To increase the efficiency for the electrochemical treatment of effluents rotating three-dimensional electrodes were also tested. Thus, a rotating packed bed electrode [44] and a vertically moving particle bed electrode were proposed [45, 46]. Plater barrels were also adapted for the removal of metals [47,48]. Likewise, rotating cylinder electrodes made of reticulated vitreous carbon [49], expanded metal sheets [50], woven wire meshes [51] and wedge wire screens [52] were also examined. 

Grau JM, Bisang JM (2007) Electrochemical removal of cadmium from dilute aqueous solutions using a rotating cylinder electrode of wedge wire screens. J Appl Electrochem 37 275-282... 

A particular form of wedge-wire screen is the sieve bend used in the wet classification of slurries. The screen is mounted vertically, with a surface that is flat... 

The lug screen is basically a wire wrap screen located on vertical bars on a perforated pipe, facilitating free entry of fluid over the entire exposed surface of the screen, to increase its efficiency. This principle is further extended in the lug plus version, where the bars are welded to the wedge-wire screen, and the whole is shrink-fitted to the perforated pipe. The slip-on screen is of similar construction, but is a slip on fit. In the weld screen the wedge-wires are welded to vertical rods. The Protecto-Screen mcorpoiates a perforated protective shell guard over the wedge-wire screen. 

Based on the same wedge-wire screen element, the in-line filter shown in Figure 4.9 is self-cleaning and suitable for filtering industrial water as well as small cooling water... 

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