Idlers - Troughing
REMA TIP TOP African Group
GERMAN ENGINEERING // MADE IN AFRICA // FOR AFRICA
Exploring the technical background
Sometimes the difficult working conditions of a plant result in lateral movement of the conveyor belt which is termed “mis-tracking”. Mistracking can be caused by many factors, including for example, incorrect tensioning of the take-up, poor alignment of the idler Frames, structural misalignments, worn rollers, and cleanliness of a conveyor belt.
Cost-effective conveyor design and accurate belt selection remains a major cost saver when it comes to designing a conveyor. A modern-day trend is to select higher belt speeds for a narrower conveyor, to achieve a required capacity. Although there is nothing wrong with this practice, the system, including loading and discharge chutes should be designed accordingly. The designer should note the practical limitations of the equipment selected, such as idler rotational speed, and the belt.
Let's consider a deeper insight into how belt selection contributes to adequate troughing within the conveyor design.
Belt selection, the technical summary
Conveyor belting is typically selected by determining a maximum operating tension, multiplying that with an industry-accepted service factor and then dividing this by the belt width.
Simple plant conveyors can thus easily be selected as a class 800/4 (breaking strength per meter/number of plies) and few would realize that when the belt is empty, it is unlikely to trough in a 35° troughed idler set selected for a 1050 mm wide belt. The reason for this is simply because the belt is too stiff, due to carcass thickness and rubber’s natural resistance to bending.
Research conducted at Wrockaw University (Cholodowski and Dudzunski)[1] shows that a significant increase in bending resistance was caused by an increase in sample linear speed.
This phenomenon might be attributed to the viscous elastic properties of rubber. The energy lost due to the deformation of a viscous-elastic body generally increases with an increasing deformation rate. Therefore, an increase in belt speed, using a heavier belt may indeed not be the best idea, as not only does the higher belt speed require power to match, but the power requirement may also be increased even further due to the bending resistance of the belt to trough.
A loaded belt will be forced into the trough, and the operators won’t even notice that the belt carcass is deteriorating. Keep in mind that the bottom ply will be in tension, while the top ply is in compression, which may in the longer term result in ply separation or cover delamination. An empty belt that does not trough, may not track properly, as it is not touching the idlers properly, which in turn may lead to belt edge damage.
What use would all this information be if there was not a technical solution to it? In the next section, we will be evaluating the correct selection of a belt.
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Choosing the right belt
The correct selection for the width would have been a class 800/3 ply, having a thinner carcass, which will be able to trough. There is still a misconception amongst users that the strength of the belt depends on the number of plies. This is not correct as the breaking strength of the belt is defined by the class, 800 in this instance, meaning it has a breaking strength of 800 kN/m width. This can be achieved by almost any number of plies while constructing the belt.
Keep in mind that the same principles apply when the belt goes around a pulley, and a minimum pulley diameter for a class 800/3 ply belt would be smaller than for its 4-ply counterpart, implying a cost saving on the pulleys used.
To conclude, care must be taken when rationalizing belting across several conveyors, to ensure that one stays within the manufacturer's recommendations in terms of pulley diameter selection and correct belt troughing.
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Now that we have covered most aspects relating to Troughing and selection of a belt, to get a quote today call us on 010 880 4744 or email us at [email protected].
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[1] A Method for Experimental Identification of Bending of Reinforced Rubber Belts – Jakub Cholodowski/Piotr Dudzinski (AIP Conference Proceedings – 2019)
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