Strategies to Prevent Sag and Enhance Stability
A flat, sag-free belt line in the skirted area is crucial for effectively sealing the load zone. Ideally, the belting should remain flat, akin to running over a table that restricts movement in all directions except the cargo's intended path. This approach eliminates sagging and simplifies sealing.
Belt sag refers to the vertical deviation of the belt from a straight line drawn across the top of two adjacent idlers, typically forming a catenary curve. When the belt sags or flexes under load, fines and lumps can escape, leading to spillage or airborne dust. Even a slight sag can trap fines, causing abrasive wear on the skirtboard, sealing system, and belt surface.
To reduce sag, increasing belt tension is effective but requires careful adherence to the belt's maximum rated tension to avoid damage. Improving the conveyor's belt-support system is also crucial, ensuring stability throughout the load zone. Adequate support, determined by factors like trough angle, material weight, and loading dynamics, prevents instability and spillage issues.
Stringers, the conveyor's support structure, must be straight and parallel to properly support the belt. Misaligned stringers should be corrected using laser surveying, ensuring they provide rigid support under load. Properly spaced and supported stringers minimize belt deflection and reduce the risk of damage to the conveyor system.
Industry standards, such as those from the Conveyor Equipment Manufacturers Association (CEMA), provide essential guidelines for constructing and maintaining belt conveyors handling bulk materials. Techniques like idlers, belt-support cradles, and impact cradles can be employed to enhance belt support in the loading zone, effectively controlling belt sag.