The distance between the two sides of the skirtboard is usually determined by belt capacity requirements; the space needed to establish an effective seal on the outside of the skirtboard is too often ignored.
The importance of designing the system so there is enough “free-belt” distance (between the outside of the skirtboard and outer belt edge) should not be understated. A conveyor designer must always consider the effect of possible belt wander on the ability to effectively seal between the stationary skirtboard system and the moving belt. By maintaining the largest possible “free-belt” distance, the designer can help eliminate a great deal of the common spillage and dusting problems often associated with the transfer of bulk materials from one conveyor to another. The benefits realized by maintaining the correct “free-belt” distance to allow a sealable skirtboard system will be further enhanced by incorporating the proper belt support under the skirtboard and by installing a highly effective skirtboard-sealing system.
Because the act of troughing a belt works to diminish a belt’s width, the phrase Effective Belt Width is used to represent the width of a troughed belt. This is not the carrying width (the distance between the skirtboard) but rather the measurement of the horizontal width of a troughed conveyor belt that is measured across the width parallel to the bottom roller.
Several standards are available for setting the distance between the skirtboards and thereby establishing the “free-belt” edge distance. The Conveyor Equipment Manufacturers Association (CEMA) and the Deutsches Institut für Normung (DIN22101) have both established formulas that can be referenced.
Best practice indicates that in order to ensure adequate “free-belt” edge to properly apply edge seals and provide a tolerance for belt mistracking, the skirtboards should be located with a minimum of 115 millimeters (4.5 in.) of actual belt width on each side of the conveyor belt.
The edge distance should be increased to a minimum of 150 millimeters (6.0 in.) when five roll catenary idlers are used in the load zone to compensate for the extra belt misalignment that is a characteristic of belts using catenary idlers.
The width of the skirtboard should be checked to ensure that the height of the material bed exiting the skirting area long with the material’s angle of repose do not combine to create a spillage condition.
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