Trough conveying

The other principal technologies that fall into this category are screw conveyors which are covered in Chapter 5 and aeromechanical conveyors which are discussed in Chapter 7. 

Operational difficulties arise, as with most solids handling problems, from a mismatch between bulk material properties and the plant item. Segregation and wear issues are common concerns however, these problems can be mitigated by the correct choice of design and operational parameters. 

Most operations can be completely enclosed providing an environmental advantage and many can combine transport with a process objective such as heating, cooling or screening. 

Bulk Solids Handling Equipment Selection and Operation Edited by Don McGlinchey 2008 Blackwell Publishing Ltd. ISBN 978-1-405-15825-1 

A more complete description of stresses in confined bulk solids is given in Oiapter 3 and is used in the analysis described later in this section. 

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Air Cushion Conveyors. Figure 3a shows an air cushion-supported belt conveyor. The belt and material are supported on an air film created by passing air through small holes or slots in a U-shaped trough beneath the belt. The air film reduces the conveying friction losses, resulting in a reduction in requited... 

Belt Conveying Troughing and Betum Idlers, CEMA Standard502-1980, Conveyor Equipment Manufacturers Association, Rockville, Md., 1980. Conveyor and Elevator Handbook, 3rd ed.. Rubber Manufacturers Association, Washington, D.C., 1988. 

The screw conveyor is one of the oldest and most versatile conveyor types. It consists of a helicoid flight (helix rolled from flat steel bar) or a sectional flight (individual sections blanked and formed into a helix from flat plate), mounted on a pipe or shaft and turning in a trough. Power to convey must be transmitted through the pipe or shaft and is limited by the allowable size of this member. Screw-conveyor capacities are generally limited to around 4.72 mVmin (10,000 ftvh). 

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. 

Processing operations of many types can be carried out in vibrating conveyors because their simple conveying troughs can be modified quite easily. While tube and flat-pan troughs are most common, troughs can be provided in a wide variety of shapes and materials. 

Screw conveyors, also called worm conveyors, are used for materials that are free flowing. The basic principle of the screw conveyor has been known since the time of Archimedes. The modem conveyor consists of a helical screw rotating in a U-shaped trough. They can be used horizontally or, with some loss of capacity, at an incline to lift materials. Screw conveyors are less efficient than belt conveyors, due to the friction between the solids and the flights of the screw and the trough, but are cheaper and easier to maintain. They are used to convey solids over short distances, and when some elevation (lift) is required. They can also be used for delivering a metered flow of solids. 

Belt units are constructed such that the continuous belt is suspended between a driven pulley above the fluid to a lower, idling pulley immersed below the fluid surface. As the belt descends into the liquid, the floating oil adheres to both sides of the belt. Wipers are attached to the upper unit to scrape the oil, which drains into a trough that conveys it to storage containers. 

From these troughs the partly-drained salt is conveyed to the hoppers of a number of adjacent millstones, where it is abraded and given out from the sluice in a pasty state these sluices deliver it into the boxes of other heavier millB placed below the former in a second tier. Finally, the white lead, thus reduced, passes through a third mill, and thence into a deep tub or vat which also receives a stream of water from tho pump and by means of a rotatiag agitator tho load is so mixed with the water, that it is carried off in tho sluice which... 

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