Page 49 - HUB-4 Magazine Issue 89

Quarrying
load capacity to obtain an acceptable life. Consider the life cycle costs of your design and component selections.
Loading and Transition
One of the ways OEMs save money on installation but is one of the biggest contributors to belt damage and the release of fugitive materials is loading the conveyor before the belt is fully troughed, called “loading on the transition.”
Loading on the transition best practices:
• Ifspacepermits,rectifytheloadingsoitstartsatthe second fully troughed idler.
• Verticalcurves,ifproperlydesigned,arenotanissue,but the design calculations need to be verified if the belting or tonnage changes.
• Usingbendpulleysforconvexcurvesratherthanaspaced array of troughing idlers should be avoided, because it is often a source of spillage.
• Diverterplowsandotherdevices,whichtendtoforcethe belt to one side or the other, should be located where the belt has enough distance for returning to running centered in the idlers.
• Whenloadingroundparticlesoroperatinginwet environments, a belt incline of 5 degrees or less will help create a mass that prevents rolling or fluid cargo from flowing backward toward the tail pulley. The best practice is to load horizontally and then transition into the slope.
• Forroundshapedmaterial,considerinstallingcurtains along the slope to knock down bouncing particles and allow them to form into a stable profile.
Curtains can control the bouncing or rollback of round particles.
© 2024 Martin Engineering
Belt Width and Trough Angle
The trough angle is initially selected based on experience or the existing idlers for standardization. Belt width is selected by calculating the cross-sectional area of the bulk material by assuming a troughing angle, an idler with 3 equal roll lengths and the surcharge angle, lump size and flowability of the bulk solid being handled. There are two important cross-sectional areas to consider, CEMA 100% full and full edge-to-edge. The 100% full area is based on a standard belt edge required to prevent spillover between idlers as the belt sags on the carrying run. The full edge-to-edge loading is used to calculate the maximum potential load on the structure. The best practice is to select the belt width based on 85% of the CEMA 100% cross-sectional area to allow for surge loads, off-center loading or normal mistracking. [Fig.2]
Figure 2 – CEMA Standard Belt Edge Distance Recommendations
© 2024 Martin Engineering
Two common techniques can be incorporated into a new or complete conveyor design to make future upgrades less costly. The first technique is changing the trough angle of the idlers to raise the capacity by increasing the cross-sectional area. In new designs, consider using 20-degree idlers. Upgrading to 35-degree idlers is a 27% increase in cross sectional area, and going from 20- to a 45-degree trough angle is a 37% increase. Although 35-degree idlers are fairly standard, it is important to note that for retrofit upgrades, going from 35 to 45-degree idlers is only an 8% cross-sectional area increase. [Fig. 3]
Figure 3 - Comparison of capacity increase by changing idler trough angle © 2024 Martin Engineering
(1200 mm wide belt and 200 surcharge angle)
The second common technique for new construction is to design the structure for the next wider belt width and use CEMA wide-base idlers. The mounting dimensions of the wide-base idlers allow for a future replacement with a wider belt. For example, if the structure for the 1200 mm (48 in.) wide belt and 20-degree surcharge angle using 35-degree trough idlers was designed for wide base idlers, the belt width could be increased to 1400 mm (55 in.), resulting in a 33% capacity increase with the same trough angle and belt speed. Changing from a 35 to 45-degree trough angle and the wider belt and idlers would result in a 90% increase in cross- sectional area. This method is not often used, because there is resistance to increasing capital cost for a wider and higher load-bearing structure, higher material mass and larger drive. However, it is an excellent approach if there is an expectation of increasing capacity in the future.
Belt Speed
CEMA provides some guidance on belt speeds for different classes of material in chapter 4 of Belt Conveyors for Bulk Materials 7th Edition. Generally, a wider belt operating at a
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