Overland Pipe Conveyor
Conveyor Belts: Save Energy by Minimising Belt Rolling Resistance
An overview of the Low Rolling Resistance Belt Technology is given in Section 2.1. The extension of LRR technology to pipe conveyor and belt is described in Section 2.2.
Rolling Resistance of Trough Conveyor Steel Belt
The components of energy loss of trough conveyors have been well studied. It is shown that the idler indentation rolling resistance can account for approx. 60 % of the total rolling resistance [3,4]. Reducing the indentation rolling resistance is an effective way to reduce conveyor power consumption and the belt tension. The indentation rolling resistance is due to the hysteresis energy loss of the viscoelastic deformation in the belt bottom cover, which is closely related to belt bottom cover properties. The LRR belt has a modified bottom cover rubber with less hysteresis energy loss, compared to the conventional belt bottom cover rubber. Major global belt manufacturers now offer conveyor belts that have low indentation rolling resistance properties, for example, Goodyear’s Easyrider, Phoenix’ EOB (Energy Optimised Belt), and Bridgestone’s Energy Saving Belt.
The question now is how to quantify the low rolling resistance (LRR). It is an important question for conveyor system design, component selection, and cost analysis. The indentation rolling resistance can be determined in a number of ways. Currently three methods are most commonly used: small scale rubber test, medium scale belt test, and full scale conveyor data acquisition.
Small scale rubber test: The viscoelastic properties E’ (elastic modulus) and E” (loss modulus) of a small sample of the bottom cover rubber is measured over a range of temperatures, strains and frequencies using the Dynamic Mechanical Analysis (DMA) machine. The acquired data from DMA testing is post processed to generate master curves and incorporated into mathematical models to calculate the indentation rolling resistance from the conveyor operating conditions. Conveyor Dynamics, Inc. (CDI) has been developing its own proprietary small scale test methodology, applying in conveyor design, and accumulating verification data since 1990s .
Testing Conveyor Belts
Median scale belt sample test: A full size, closed loop belt sample is installed on a 2-pulley test machine, where one pulley is driven and one pulley has variable position to regulate belt tension. The indentation rolling resistance over a range of temperatures, idler diameters, belt loads and belt speeds is measured by a single instrumented idler. University of Hannover, Germany and University of Newcastle, Australia independently developed such testing machines. Currently, one German standard exists (DIN 22123) on the median scale belt sample test. Fig. 1 is University of New Castle’s belt test machine, where the belt sample and the instrumented idler are shown (by permission of Tunra Bulk Solids, University of New Castle). The indentation rolling resistance is expressed in force resistance of the test belt rolling over the instrumented idler, for the particular belt speed, load, idler diameter and temperature. Median scale belt sample test has the benefit of testing an actual belt sample in a controlled lab environment. It can be used to compare different rubber grades from the same or different belt manufacturers to provide meaningful comparative indentation rolling resistance data. The test data can be incorporated into conveyor design tools to predict the power and tension of conveyors.
Full scale conveyor data acquisition: the power consumption and belt tension of an operating conveyor are measured by strain gauges mounted on drive shafts. Other conveyor operating conditions, like belt speed, takeup tension, and material load, can also be measured by instrumentation. This method measures the performance of the actual conveyor system. As a diagnostic tool, the data collected can be used to trouble shoot existing problems, or used in engineering system upgrades. In terms of measuring belt rolling resistance, the conveyor data acquisition is especially insightful on the same conveyor with different types of belt. CDI carried out data acquisition studies on a 7 km long overland conveyor in Ohio, United States between 1999 and 2000 . The conveyor was running with a conventional conveyor belt and then replaced with LRR belt. For both belts, CDI measured the bottom cover viscoelastic properties and compared with actual conveyor operating data. The result is summarized in Fig. 2. It is clear that 1) LRR belt can produce significant power savings of more than 20 %; 2) the small scale rubber test, when coupled with robust mathematical model, can produce accurate results.