Damage limitation: specifying the right conveyor belt



Larry J. Goldbeck, Manager of Conveyor Technology, Martin Engineering


One of the most common problems in a conveyor system is a belt that is inappropriately matched to the structure, effecting both system efficiency and belt life. It may be tempting to specify a ‘stock’ belt for cost reasons, but understanding a few basic principles of belt/structure compatibility is essential to achieving optimum system performance. Without it, even a new material handling system can be doomed to inefficiency, causing increased maintenance requirements and lost production.

The rated strength of a conveyor belt is expressed in pounds per inch of width (PIW). This rating is based on the type of ply material, number of plies and the size of the reinforcing cables. The higher the rated tension of the belt, the more critical the compatibility of the belt and structure becomes.

A three-ply belt may have each ply rated at 110 PIW (~19.25 N/mm), which translates to a 330 PIW (~57.75 N/mm) belt. This is the maximum rated tension at which the belt can be operated without damage. Over time, exceeding the rated tension of the belt is likely to cause excessive stretch, splice failure, belt cupping and eventual breakage. Factors that affect the rated tension are belt length, width, material of construction and angle of incline; as well as parasitic drags, such as the size and quantity of rolling components, belt cleaners and length of transition sealing systems.

Minimum bend radius
The minimum bend radius of a conveyor belt is determined by the number of plies it has, whether it is steel or fabric reinforced, what the ply material is, the rated tension of the belt and thickness of the top and bottom covers. Bending the belt over a radius that is too small can cause damage such as ply separation or the top cover cracking. This is a common mistake that often occurs if some type of belt damage becomes apparent, as there is tendency is to place a thicker belt on the system to make it last longer. Installing a thicker belt on a system that was designed for a thinner one may require larger pulleys to prevent damage.

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