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for many decades, the coating was used both to protect the drums and to increase the friction available for driving the conveyor belt.. Today, the coating is available in various forms with different capacities and with various characteristics..
A primary consideration when choosing a coating is the coefficient of friction.. Designers use the coefficient of friction in the Euler equation to calculate conveyor transmission capacity., so the friction behavior of the coating under real conditions is of extreme concern. As belt technology innovates with increased tensions and increased energy delivered through drive drums, a correct understanding of the source of friction is required..
There are some established design graphics for friction., as the contents in the CEMA Manual 7º Ed. and the DIN standard 22101, but are widespread, come from best practices and assume a constant coefficient of friction. In contrast, published values by coating manufacturers may vary significantly from charts. Furthermore, there is no standardized test to determine the coating's coefficient of friction or an industry standard to apply a slip safety factor..
Eng. Brett DeVries, through the technical article "VARIANT FRICTION COEFFICIENTS OF LAGGING AND IMPLICATIONS FOR CONVEYOR DESIGN, performed measurements of friction with various coating materials and under the three conditions:
1 – Clean and dry
2 – Wet
3 – Dirty and wet
The results were amazing., as it was found that friction varies depending on the pressure of the belt on the drum, as shown in the chart below, figure 13 of the above-cited article, in dirty and damp condition.
How important is the article "VARIANT FRICTION COEFFICIENTS OF LAGGING AND IMPLICATIONS FOR CONVEYOR DESIGN"?
My focus was to condense the most important information, which is the variation of friction as a function of belt pressure on the drum (see chart above) and the Engineer's versatility in avoiding excessive T1 tension on the belt, increasing the drum diameter or adjusting the type of lining. Since tension T1 normally drives the selection of minimum belt tension, reducing it can save belt costs. Depending on length of conveyor, big savings may be possible, selecting a lower tension belt (and less expensive) and choosing instead to invest in a larger diameter drum and ceramic coating.
The new method is easily adaptable to a spreadsheet format where the conveyor designer can choose the best T1 tension combination, hug angle, drum diameter and liner type to optimize conveyor design.
I recommend reading this article "VARIANT FRICTION COEFFICIENTS OF LAGGING AND IMPLICATIONS FOR CONVEYOR DESIGN by Eng. Brett DeVries, find all friction graphs under other conditions, in addition to the shear stress graph to calculate the slip factor of safety, with simple and clear example.
Also check out other materials and worksheets for the conveyor belt design and FP!