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Rubber Rheology:
There are several computational methods for calculating the power consumption of a conveyor belt. The two most commonly used approaches are the DIN 22101 methodology, and the CEMA method. Although these methods are appropriate for calculating the power of smaller conveyor systems, more advanced methodologies should be used for long overland conveyor designs.
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Historically, there have been numerous papers written on the importance of the belts rubber viscoelastic properties (Spaans, Jonkers, Wheeler). Additionally, the newest (sixth edition) CEMA conveyor design book has also finally embraced this important aspect in conveyor technology. Chapter 16 discusses rubber viscoelasticity, and the new CEMA tension equations have been developed based on a "generic" rubber compound. Rubber viscoelastic properties however, can vary significantly from manufacture to manufacture. Additionally many manufactures have several rubber compounds to choose from.
The viscoelastic loss component of a conveyor is a function of:
- Rubber cover compound (carcass type, cover thickness, etc)
- Ambient temperature
- Idler spacing, troughing angle, and idler diameter
- Material loading
- Belt speed
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| All of the above parameters can effect the rubber indentation as the belt passes over the idler, and thus the rolling resistance losses and power consumption of the conveyor. |
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The importance of this loss varies widely for different types of conveyors. On a relatively short conveyor, idler drag, pulley losses, belt scrapers and other miscellaneous items may comprise the majority of the power consumption. For high lift conveyors 85% or more of the conveyors power may be consumed by elevating the material itself. In theses cases the actual percentage of power consumed by viscoelastic losses is relatively small and thus variations in the the rubber compounds themselves are also less significant.
On long flat overland conveyers however, viscoelastic losses are not only important, but they can be the most significant component in the power calculations. It is these types of installations where accurate power predictions are the most difficult to calculate and can vary significantly from the "basic" calculation methodologies.
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For these reasons, AC-Tek has invested in a Rheometrics RSA Solids Analyzer. This machine is capable of measuring the rubbers viscoelastic properties at various temperatures, frequencies (speeds), and strains (idler normal forces).
A wide range of tests are conducted, and the results compiled into what's know as a rubber viscoelastic "Master Curve".
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These viscoelastic master curves can then be imported in the "Sidewinder" conveyor software in order to accurately predict the power consumption of a particular conveyor system. Using this information allows the conveyor design to be optimized for a specific terrain, regional climate (annual temperature range) and a wide range of other parameters.
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For more information on rubber viscoelasticity, conveyor power consumption, or the "Sidewinder" conveyor design software, please contact us. Our knowledgeable engineers are always happy to discuss how the most "Advanced Conveyor Technologies" can help benefit you!
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