The distance required for a belt’s transition varies with the amount of troughing required, the belt thickness, the construction of the belt, the type of carcass (steel cable or fabric) and the rated tension of the belt. A transition distance must be selected to provide at least the minimum distance for the belt selected.
The heavier the belt carcass, the more it will resist being placed in a troughed configuration and the longer the required transition distance. This is easy to understand if one remembers that a string stretched down the center of the conveyor will be shorter than the string placed on the outside edge of the idlers. The outer edges of the belt must travel farther than the middle of the belt. The higher the trough angle, the more the edges are stretched and the greater the distance required to reach that angle.
The transition distance required is a function of the construction of a belt. When engineering a new conveyor, the belting should be selected to match the material load and conveyance length characteristics of the conveyor. The transition distance of the system would then be designed to match the requirements of the selected belting. However, a more likely scenario is that, due to space constraints and cost considerations, the belting will be selected to match the transition distance engineered into the steel conveyor structure. Either way, however, the belting manufacturer should be consulted when determining the recommended transition distance.
In the case of replacement belting for existing conveyors, the belt should be selected to match the transition distance provided in the conveyor structure. In no case should a belt be placed on a conveyor where the transition distance is too short for the belt.
Too short of a transition distance from the tail pulley to the first fully-troughed idler can cause junction-joint failure in the belt.
It is highly recommended that the supplier of the belt be contacted to ensure that the transition distance of the existing structure is compatible with the belt. Charts identifying the recommended transition distance as a function of the rated belt tension for both fabric and steel cord belts at the various trough angles are published in manufacturers’ literature and by CEMA in Belt Conveyors for Bulk Materials, Sixth Edition.
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