Screw conveyors components

Screw conveyor components (a) flight, (b) screw formed by mounting flights on an axle, and (c) trough. 

Coal fines stored in bins (2) are discharged through several pantlegs (3) into a metering hopper (4). Variable speed discharge belts (8) under the bin (7) and hopper (4) meter the correct amount of each feed into the screw conveyor (9) the binder is pulverized in the hammer mill (10). Both components are premixed in a double screw mixer (11) and elevated (12) into another screw feeder (13). The latter discharges into two vertical pug mills (14) excess feed overflows at the end of the conveyor through a chute (30). 

Fig. 6.4-38 sho vs the functional components. At the inlet on top of the equipment, the slightly pre-mixed feed components enter first a mixing and predensification screw. Pressure builds-up by the changes in shaft diameter, sometimes variable pitch of the screw flights, and by a collar at the end of the screw shaft or a pressure piece , both forming an annular space with reduced area through which the material must pass. Such a screw conveyor, mixer, and processor is often called expander. 

Fig. 6.6-25 Flow diagram of a plant combining fertilizer bulk blending (2-7) and compaction/ granulation (8-27). 1, front-end loader input of components 2, 8, 18, bucket elevators 3, distributor 4, silos for components 5, compounding scale 6, blender 7, bulk blend receiving hopper (courtesy Sackett, Baltimore, USA). 9, mill for feed homogenization 10, feed bin 11, 27, screw conveyors 12, belt mixer 13, metal separators 14, 25,...

Fig. 6.5-7 Components of a ring die pellet mill [B.3, 1971] 1) variable speed screw conveyor, 2) conditioner, 3) ring die and roller (extrusion) section, 4) speed reducer, 5) main motor, 6) machine base Fig. 6.5-8 Schematic of a vertical pellet cooler [B.3, 1971] 1) feed hopper with level sensing device, 2) cooling columns,...

Abrasive or corrosive materials can be handled with suitable construction of the helix and trough. Conveyors using special materials, such as hard-faced cast iron and linings or coatings, on the components that come into contact with the materials can be specified in these applications. The screw conveyor will handle lumpy material if the lumps are not large in proportion to the diameter of the screw s helix. 

Most screw conveyors are mounted above the foundation level on a support structure that generally has a slight downward slope from the feed end to the discharge end. While this improves the operating efficiency of the conveyor, it also may cause premature wear of the conveyor and its components. 

The construction of a basic centrifuge with all its main components is shown in Figure 2.1. The heart of the decanter is the rotating assembly, which comprises a mainly cylindrical bowl housing an Archimedian screw conveyor, with a small clearance between it and the bowl. One end of the bowl is conical in shape, providing the means whereby solids can be removed from it. Affixed to one end of the bow l is usually a gearbox to effect a small differential speed between the conveyor and bowl. 

Required power is made up of two components, that necessary to drive the screw empty and that necessary to move the material. The first component is a function of conveyor length, speed of rotation, and friction in the conveyor bearings. The second is a function of the total weight of material conveyed per unit of time, conveyed length, and depth to which the trough is loaded. The latter power item is in turn a function of the internaf friction and friciion on metal of the conveyed material. 

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