The CEMA Horsepower Equation
The CEMA Horsepower Equation
Fig. 7 shows a plot of the 20°C LRR data from CEMA7 fitted with the formula Eq. 2.
Fig. 7: Plot of LSIT data included in CEMA7.
According to CEMA7, for an LRR belt at 20°C, ‘a’ = 6.59 · 10^{3} and ‘b’ = 1.28. Since the CEMA test data was measured on a belt with a 7 mm bottom cover and an idler roll diameter of 219 mm, we must scale the CEMA results to model our conveyor. To estimate how much this friction would change if we retested the sample using a different idler diameter and/or belt thickness we multiply constant ‘a’ by the following equation [13]:
where:
 H_{test} = belt bottom cover thickness used to produce the LSIT test
 D_{test} = diameter of the idler roll used to produce the LSIT data
Finally, we substitute Eqs. (4), (5), and (6) into Eq. (2) and integrate the result over the width of the belt as follows:
Thus, using this methodology, the total indentation loss on an idler set is:
Transforming Large Sample Test Data for Use in the Classic CEMA Formulation
For more than half a century conveyor designers used simple friction factor based formulas like Eq. (1) to design conveyors. Experienced conveyor engineers have a “feel” for what friction factors are reasonable on various types of systems, and often the first question auditors ask conveyor engineers is, “what friction factor did you use?”
To get a friction factor, we could simply divide Eq. (3) by the total load on the idler. However, by reconditioning LSIT results in terms of friction factors we can use them in formulas that conveyor engineers are familiar with. This was one of the primary goals of the committee charged with writing the LSIT section in CEMA7.
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