How to select and maintain an aeromechanical conveyor

Copyright, CSC Publishing, Powder and Bulk EngineeringFigure 4Rope in contact with sprocket and discs meshing withpockets in sprocket rimSprocketSprocketrimDiscsRopefected by such factors as the conveyor run time, start andstop frequency, the conveyor length, your material’s characteristics,and the solids-to-air ratio. Without regular inspectionand tensioning, the rope can wear and breakprematurely, resulting in unplanned downtime for replacingthe entire rope-and-disc assembly or sections of it.Properly tensioning the rope will ensure that the rope-anddiscassembly has a longer service life. Your operationsand maintenance manual will include detailed instructionsfor tensioning the rope at proper time intervals. The conventionalmanual method for adjusting the rope tensiontypically requires a maintenance worker to check the ropetension at 1-, 4-, 8-, and 50-hour intervals after the conveyoris initially started, and then after every 100 hours ofoperation or as needed. Manually checking the rope tensionis a multistep process: emptying and stopping theconveyor; opening the inlet (bottom) sprocket accessdoor; examining the inlet sprocket to see if the rope is contactingthe sprocket rather than sagging from it; openingthe outlet (top) sprocket access door; and checking the outletsprocket for slippage between the rope and sprocket. Ifthe rope is loose, the worker must tension it manually, typicallyby sliding the outlet sprocket (which is usually therope-tensioning sprocket) housing along the conveyortube to stretch the rope until the rope at the inlet sprocketfits snugly on that sprocket.An alternative to manual tensioning is a recently developedautomatic rope-tensioning system 1 that keeps therope properly tensioned while requiring significantly lesstime and labor than the manual method. The automaticsystem includes a tensioning device (an electric or pneumaticlinear actuator), a load cell that can be integrated intothe conveyor’s control system, and a position control device.The tensioning device is mounted parallel to and betweenthe conveyor tubes near the outlet housing, the loadcell is mounted between one conveyor tube and the tensioningdevice, and the position control device is linked tothe tensioning device. Each time the aeromechanical conveyoris shut down, the load cell automatically measuresthe rope tension, and, when the tension requires adjusting,the tensioning device moves the outlet housing to a positionwhere the rope reaches the correct tension. The positioncontrol device provides feedback about the tensioningdevice’s location and can also be used to indicate when therope is worn. The automatic system’s reduction of ropetensioningtime and labor results in lower conveyor maintenanceand operating costs.Cleaning your conveyor. Periodically, you’ll need toclean out material residue from the empty conveyor. Drycleaning the conveyor with a vacuum cleaning system issuitable in some applications, but in most applications theconveyor must be washed using an integrated clean-inplacesystem with a suitable cleaning fluid, then dried byrunning the conveyor for a period while it’s empty. Theconveyor typically has multiple access panels and doorsthat allow workers to insert dry cleaning equipment orconnect and drain a clean-in-place system. The rope’s constructionof multiple steel strands can make the rope difficultto clean, but this is typically only a concern when youmust frequently change materials and avoid cross-contaminationbetween batches; another type of conveyor canbe better suited to such an application.PBEReference1. Dynamic Automatic Rope-Tensioning (DART) system, available fromSpiroflow Systems Inc., Monroe, N.C. (www.spiroflowsystems.com).For further readingFind more information on aeromechanical conveyors inarticles listed under “Mechanical conveying” in Powderand Bulk Engineering’s comprehensive article index atwww.powderbulk.com and in the December 2006 issue.David Hesketh is vice president of engineering atSpiroflow Systems Inc., 2806 Gray Fox Road, Monroe, NC28110; 704-291-9595, fax 704-291-9594 (davehesketh@spiroflowsystems.com, www.spiroflowsystems.com). He holds a BSc in design and manufacturefrom University of Central Lancashire, England, and has20 years experience in bulk material handling.