OPERATIONS MANAGEMENT
Trough Angle Increase in Capacity %
20° to 35° 23%
20° to 45° 37%
35° to 45° 11.5%
Figure 5: Potential capacity increase from just changing the trough angle
the conveyor capacity and speeding up the belt, another approach is to change the trough angle. Using the 1200 mm belt width example the capacity increases compared to a 20-degree trough angle are shown in Figure 5. Figure 5 shows that the FE
allowance for the sealing system is probably adequate at roughly 40 mm but if the trough angle is increased to 35 degrees there is hardly any room for a sealing system. So, this is where the balancing act begins.
Common conveyor system adjustments for increased production include: • Narrowing the skirtboards to increase the height of the material rubbing on the liners • Different trough angles • Different belt widths • Increase/decrease belt speed
One technique that is used is
20-degree idlers in the load zone and then after the load zone transition to 35-degree idlers. The transition must be calculated using the same approach as the transition from the tail pulley to the troughing idlers. This design allows adequate room for belt wander and for a more robust sealing system. The 20-degree configuration gives more room for belt wander and the sealing system. The 35-degree idlers can carry more material. The height of the material rubbing on the skirtboards may cause wear issues. The same concept can be used to help center the load when off center loading causes mistracking in the carrying run.
SERVICE FRIENDLY Making the replacement and adjustment of the seal and liner system easy is important for safety and controlling costs. Mounting the wearliner on the outside of the skirtboards and then placing the seal against the liner does several things. It eliminates the gap, which is the thickness of the skirtboard side wall,
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created by putting the liner on one side of the skirtboard and the seal on the other. This gap can catch and hold material and abrade the belt. Conventional systems weld wearliners onto the inside of the skirtboard making adjustments or replacements require hours of confined space entry involving two or more workers. Moreover, it makes the job more difficult, dangerous and time- consuming than necessary, raising the cost of operation.
Figure 8: Trac-Mount Idlers make replacement easier under the skirtboards
Figure 7 – Wearliner mounted on outside of skirtboard wall
OTHER IDLER CONFIGURATIONS The CEMA method using dimensionless ratios can be used to analyse any three- roll idler sets either fixed or garland by substituting the actual dimensions in place of the CEMA standard assumptions. There are many other idler designs available today to address various needs but all can be studied using basic trigonometry. Typically, the center roll of a set is the most heavily loaded. To increase the load capacity the center roll is often made shorter than the wing rolls. Extending the life of heavily loaded idlers for faster belts can be achieved by widening the diameter of the center roll so it rotates slower. Custom and adjustable trough angles are also available which can be used to help center or recenter the load and help reduce belt mistracking.
CONCLUSION The selection of the trough angle for a new design or retrofit requires a holistic view. When production exceeds the original design or there is a significant material change, operators must confirm the existing belt, idlers and structure can handle the increased load. What seems to be an adequate trough angle for the carrying run may create excessive wear in the loading zone resulting in more frequent spillage, increased clean up and more regular maintenance. Optimising trough angles and skirtboard widths to allow a robust sealing system is critical to reducing belt wear and damage. Similarly, having adequate free belt
edge to accommodate the sealing system and belt wander along with the idler design to handle the load is the path to lower overall costs.
REFERENCES [1] Belt Conveyors for Bulk Materials, 7th edition, Conveyor Manufacturers Association
www.cemanet.org [2] U.S. Occupational Safety and Health Administration (OSHA), ‘OSHA Safety Pay$ Estimator’, Dec. 2023.
https://www.osha.gov/ safetypays/estimator
For more information visit:
www.martin-eng.co.uk
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