The stringers on which the idlers are mounted must be designed, manufactured and installed not only to support the loads but also, and more importantly, to remain within the limits of squareness (3mm), levelness (3mm) and camber/straightness (3mm/12m) specified in the CEMA Standard, Belt Conveyors for Bulk Material, Appendix D, 7th
Edition. If the stringers are not aligned, the idlers will end up misaligned, which in turn will cause belt mistracking.
Furthermore, the pulleys must be installed within 0.8mm of squareness and levelness and, once installed and aligned, must not be used to track a misaligned belt. Instead, the idlers are used to perform the belt tracking.
A team of experienced surveyors are needed to help align the pulleys. Also, pre-operational verifications (POVs) should include validating the correct installation and alignment of pulleys and conveyor stringers.
Poor chute design
It is crucial to design a chute that allows the material to fall onto the belt at its centre line and in the direction of belt travel. Material falling in a direction other than the belt’s centre line and its travel direction will cause belt misalignment.
Material segregation can also lead to belt misalignment, especially when handling lumpy material on conveyors that are installed at or near 90°, where the receiving conveyor belt becomes more loaded on one side of its cross section, thus pushing the belt toward the lighter side.
Lumps that eventually land and block the conveyor feed chute could divert the flow of material, causing misalignment of the receiving belt.
Improper belt handling
Poor splicing, improper belt storage causing a camber beyond 1in/100ft, belt cupping that prevents proper belt-idler contact, inadequate belt troughability and inadequate concave radii preventing proper belt-idler contact will all lead to belt misalignment.
Following splice procedures as per belt manufacturer instructions will avoid belt mistracking.
Storing the belt on a rack will prevent deformation/camber of the belt edge, which usually results from storing the belt on the floor.
Checking the belt’s troughability with the belt manufacturer for the specific application will avoid having a belt that is not in proper contact with the idlers.
Calculating the concave radius based on the worn belt weight will prevent belt lift and ensure proper belt-idler contact.
Using an autostable belt could solve issues for conveyors that are installed on buildings that are too flexible, on reversible conveyors, on conveyors operating at very high speeds, on conveyors that are subject to wind forces and on overland conveyors with mistracking issues.
Uneven drag/friction forces
Seized rollers, misaligned idlers and pulleys, material jammed between the skirt and the belt and uneven or improperly adjusted skirt seals can also steer the belt off-centre.
Proper and even skirt adjustment, careful selection and specification of idlers and their seal systems and good servicing and maintenance will help prevent uneven drag forces causing misalignment.
Material can build up around idler rolls and pulleys, causing belt misalignment and damage to the belt, pulleys and idler rolls.
To prevent build-up, it is crucial to avoid material spillage by properly designing the loading point and the belt transition at the discharge pulley, carefully selecting and installing belt cleaners and V-plows and establishing the right CEMA belt load to maintain an adequate belt-edge distance.
On overland conveyors, performing the turnovers in the return run will protect the return idler rolls from coming into contact with the dirty side of the belt, reducing the risk of build-up around the rolls.