Overland Pipe Conveyor
Conveyor Belts: Save Energy by Minimising Belt Rolling Resistance
Indentation Rolling Resistance of Pipe Belt
The main difference between pipe belt and trough belt is that the folded pipe belt adds additional contact pressure to idler rolls. The additional contact pressure increases the indentation rolling resistance, causing higher power consumption and belt tension for pipe conveyors. The magnitude of this contact pressure is not only related to the belt weight, material weight, idler spacing, but to a greater extent, affected by the cross sectional bending stiffness of the belt. For trough belt, the cross sectional stiffness can be measured by the troughability test (ISO 703:2007). High belt stiffness decreases troughability, which may cause the empty trough belt not touching the centre roll and belt tracking problem.
The cross sectional stiffness can be modified by the belt construction: belt thickness, rubber modulus, the fabric layer in top and bottom cover. By adjusting the type and spacing of the fabric layer, cover thickness, even the rubber modulus, the pipe belt stiffness can be customized for individual applications.
In general, bigger diameter pipe requires higher stiffness to maintain full pipe shape, and smaller diameter pipe requires lower stiffness. If the stiffness is too high, the pipe belt will have very high indentation rolling resistance. It can even cause the conveyor unable to start an empty belt. If the stiffness is too low, the pipe belt will collapse and not be able to maintain the circular cross section. A collapsed pipe belt also tends to have large rotation and twist during horizontal and vertical curves. Belt tension also affects the belt stiffness design, where high tension would require higher stiffness, because during curves the bending force component is increased.
To analyse all these factors, both experimental testing and finite element analysis (FEA) are developed . The belt bending stiffness is measured by tests: 3 point bending test using a 300 mm × 50 mm belt sample, and 6 point pipe belt stiffness test using full width, folded pipe belt. The bending tests are also simulated in FEA, to establish a correlation with experimental results. After a proper belt construction is designed, the pipe belt FEA model is analyzed for empty and fully loaded condition. Fig. 3 shows the contact pressure of a 350 mm diameter ST1600 pipe belt, in empty and loaded condition. The belt is constructed using the patented Goodyear Confine pipe belt design. It can be seem that the steel cord distribution is different from a conventional trough or pipe belt, where all steel cords have even spacing. The FEA outputs the contact pressure on idler rolls for empty and loaded condition. The pipe belt shape and overlap opening can also be investigated. The contact pressure distribution from FEA is then incorporated into mathematic models to calculate the pipe belt’s indentation rolling resistance. The mathematic models are modified from the ones used to calculate the indentation rolling resistance for trough belt, where the contact pressure distribution is different. The pipe conveyor model is capable of including the rubber viscoelastic properties, to calculate the power consumption and belt tension for different types of belt bottom cover. Now it is possible to study if a LRR pipe belt is used, what kind of power saving benefits, belt tension changes, and related conveyor system changes can be achieved.