The pipe or tube conveyor solves these problems by transporting the product in a circular cross section formed by overlapping the belt edges and using idlers arranged in a hexagonal pattern to form a tubular shape (see figure #1).
FIGURE No. 1 - Cross Section
The belt encloses the product being conveyed and protects the product from the elements and the environment from the product. The return belt is also formed into a circular cross section, rolled with the carrying side of the belt inward to prevent material clinging to the belt from dislodging at the return idlers.
The only area where the belt is open is at the head and tail end area=s. This limits the possible clean up to the relatively short transition section=s where the belt changes from flat to the circular shape. The most critical area is at the head discharge. This problem can be easily solved by a short Adribble@ collection belt to convey collected material to the discharge chute.
The pipe / tube conveyor also eliminates the need for transfer points to change direction. The pipe / tube conveyor has the ability to form horizontal curves over a much smaller radii than conventional trough belt conveyors, since the belt is constrained on all sides by the idler rolls. This eliminates all the environmental problems and expense of belt cleaners, pulleys, drives, chutes, dust collectors, power distribution and the cost of maintenance associated with transfer points.
For the reasons stated above, the pipe conveyor is an obvious excellent choice for the handling of dusty fly ash, limestone, lime and wet sticky coal, lignite or petroleum coke. What we hope to accomplish in the following pages is to provide sufficient data to allow designers of conventional conveyors familiar with the CEMA method of conveyor belt calculation a method to modify the CEMA equations so they can be used for pipe conveyor preliminary design. The methods outlined in this paper are not meant to influence the pipe/tube conveyor manufacturer=s design and standards but to provide a guideline for preparing a specification.
The power industry has accepted the CEMA handbook (Conveyor Equipment Manufacturers Association) as the standard to use for designing trough belt conveyors. Since pipe conveyors are relatively new and there is no recognized standard, this paper suggests modifications to the CEMA standards for idler selection and horsepower / tension calculations that could be used to specify the minimum requirements for equipment selection.
Frank Loeffler, Jr., PE:
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