The CEMA Horsepower Equation

Belt Conveyor Design

The CEMA Horsepower Equation

Development of a new Conveyor Power Prediction Methodology
The 7th edition of Belt Conveyors for Bulk Materials (known as “The Belt Book”) includes a new con­veyor power prediction methodology using “Large Sample Indentation Test” (LSIT) data. This article provides background and insight into how LSIT data is used to design conveyors, and describes the relation between this and the older conveyor power prediction methods. It also illustrates the use of LSIT data by using it to predict indentation losses in a recently commissioned conveyor system.
(ed. WoMaMarcel - 07/10/2015)
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CDI’s methodology remains largely a trade secret. OCC’s methodology was incorporated into the sixth and seventh editions of The Belt Book. However, programming small sample methods is a daunting task for many users of the Belt Book, and while several companies, including CDI, sell expensive software packages to perform these calculations, many designers still prefer to work with spreadsheets and programs they created themselves. For this reason, the CEMA-6 and CEMA-7 small sample methods are quite controversial.

The Large Sample Method

Before developing our Small Sample Method, CDI and Syncrude Canada built a number of large scale test machines to study the behavior of their conveyors. Two of the machines we built are shown in Fig. 2. Our indentation loss machine directly measured indentation losses for different temperatures, pressures, and speeds. Since the pressure on the idler is uniform, one can divide the measured resistance by the idler roll length to get values with units of [Force/Width]. This is exactly the value calculated using the small sample method.

Fig. 2: CDI’s model validation test machines: trampling and flexure loss test machine (left); indentation loss test machine (right).

We could avoid all the small sample method calculations using machines like this, but these machines require a “Large Sample” of rubber which is expensive to obtain, handle, and store. Having proven that our small sample method yielded the same results as our large sample indentation test (LSIT) machine, we decommissioned the device.

Recently, interest is again growing in LSIT machines. Hannover University in Germany is operating one such machine [17]. To develop new types of low rolling resistance (LRR) belting, CDI, Laing O’Rourke, and Veyance Belting jointly contributed to a grant which the University of Newcastle used to build the large sample test machine shown in Fig. 3 [18]. Both of the Hannover and the Newcastle machines are essentially short flat belt conveyors with uniformly loaded idler rolls creating indentation losses.

Fig. 3: University of Newcastle, large sample testing machine.

The drag measured by large sample test machines is much easier for laymen to understand than master curves produced by small sample test machines. For this reason, mine owners are beginning to require belt manufacturers to submit samples of their LRR belts to large sample testing laboratories so that owners can compare the efficiencies of these belts. Results from LSIT tests are making their way into the industry at large. In recognition of this fact, the German Industrial Norming committee (DIN) recently defined a new standard, DIN-22123:2012, to standardize LSIT test procedures and reports.

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