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smoothly accelerate the conveyor.
Mass Flow at Transfer Points
One of the reasons for using intermediate drives and running single flight conveyors longer and longer is to eliminate transfer points. Many of the most difficult problems associated with belt conveyors center around loading and unloading. The transfer chute is often sited as the highest maintenance area of the conveyor and many significant production risks are centered here.
Plugging
Belt and Chute Damage and Abrasion
Material Degradation
Dust
Off Center Loading/Spillage
In the past, no analytical tools have been available to the design engineer so trial-and-error and experience were the only design methods available. Today, numerical simulation methods exist which allow designers to “test” their design prior to fabrication.
Numerical simulation is the discipline of designing a model of an actual physical system, executing the model on a computer, and analyzing the results. Simulation embodies the principle of “learning by doing''. To understand reality and all of its complexity, we build artificial objects in the computer and dynamically watch the interactions.
The Discrete Element Method (DEM) is a family of numerical modeling techniques and equations specifically designed to solve problems in engineering and applied science that exhibit gross discontinuous mechanical behavior such as bulk material flow. It should be noted that problems dominated by discontinuum behavior cannot be simulated with conventional continuum based computer modeling methods such as finite element analysis, finite difference procedures and/or even computational fluid dynamics (CFD).
The DEM explicitly models the dynamic motion and mechanical interactions of each body or particle in the physical problem throughout a simulation and provides a detailed description of the positions, velocities, and forces acting on each body and/or particle at discrete points in time during the analysis. 8
In the analysis, particles are modeled as shaped bodies. The bodies can interact with each other, with transfer boundary surfaces and with moving rubber conveyor belt surfaces. The contact/impact phenomena between the interacting bodies are modeled with a contact force law which has components defined in the normal and shear directions as well as rotation. The normal contact force component is generated with a linear elastic restoring component and a viscous damping term to simulate the energy loss in a normal collision. The linear elastic component is modeled with a spring whose coefficient is based upon the normal stiffness of the contact bodies and the normal viscous damper coefficient is defined in terms of an equivalent coefficient of restitution (Figure 29).
Figure 30 shows particles falling through a transfer chute. The colors of the particles in the visualization represent their velocity. The RED color is zero velocity while BLUE is the highest velocity. Perhaps the greatest benefit that can be derived form the use of these tools is the feeling an experienced engineer can develop by visualizing performance prior to building. From this feel, the designer can arrange the components in order to eliminate unwanted behavior.
Other quantitative data can also be captured including impact and shear forces (wear) on the belt or chute walls.
Future
Bigger Belt Conveyors
This paper referenced Henderson PC2 which is one of the longest single flight conventional conveyors in the world at 16.26 km. But a 19.1 km conveyor is under construction in the USA now, and a 23.5 km flight is being designed in Australia. Other conveyors 30-40 km long are being discussed in other parts of the world.
Belt manufacturers have developed low rolling resistance rubber with claims of 10-15% power savings as methods to quantify indentation have become known. Together with improved installation methods and alignment, significant power efficiencies are possible.
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