Each belt is rated as to its strength – the amount of pulling force that it will withstand. The strength of a belt (or more accurately, the tension it is able to withstand) is rated in the United States in Pounds per Inch of Width, commonly abbreviated as PIW. In other parts of the world, the belt is rated in ultimate breaking-strength in the metric units of newtons per millimeter (N/mm) or kilonewtons per meter (kN/m). The strength rating is a function of the reinforcement included in the carcass of the belt and the number of, and type of, material in the fabric plies, or, if it is a steel-cable belt, the size of the cables. As noted above, a belt’s top and bottom covers provide very little of the belt’s strength or tension rating.
The belt’s strength, either carcass tension rating or ultimate breaking-strength, represents the amount of force that can be applied to the belting. Putting greater demands in the form of material load, takeup weight and incline gravity against this belt would cause severe problems, including the possibility of breaking the belt. The higher the rated tension of the belt, the more critical the compatibility of the belt with the structure and rolling components becomes.
Each conveyor structure will require a belt with a specific tension rating. Factors affecting this decision are:
- Length of structure
- Incline angle of the conveyor
- Desired capacity
- Width of belt
- Drag and inertia of rolling components
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