Conveyor belt misalignment can negatively impact production and operating costs

Understanding basic concepts and the root causes of belt misalignment

Belt conveyors are key pieces of equipment in all industrial plants that handle bulk material from point A to point B. They are essentially a belt that is installed over idler rolls and pulleys (see Figure 1).

Basic concepts

The first important concept to understand is that the belt moves in a perpendicular direction to the idler rolls and pulleys (see Figure 2). In other words, idlers and pulleys steer the belt, so it is essential that these components are square and level to ensure the belt runs centrally on them.

The second concept to understand is that, to be properly steered, the belt needs to be in full contact with the idlers and pulleys. A lack of contact or having material in between these components will cause belt mistracking.

Root causes

The main causes of belt misalignment are:

• Lack of squareness and levelness of support structures, pulleys and idlers
• Poor chute design
• Improper belt handling
• Uneven drag/friction forces
• Material build-up

Lack of squareness and levelness of support structures, pulleys and idlers

The main cause of belt misalignment is unaligned structures, pulleys and idlers in relation to the belt conveyor axis and a datum line.

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, 7^th 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 build-up

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.

Conclusion

Notre équipe possède le savoir-faire et la vaste expérience nécessaires pour résoudre et prévenir les problèmes de désalignement des courroies et leurs conséquences. Plus important encore, nous pouvons vous guider dans vos projets de manutention de matériaux en vrac.

N’hésitez pas à communiquer avec notre équipe de manutention de matériaux. Elle saura vous aider à concevoir des systèmes de manutention fiables, à éviter les pertes de production et à réduire vos coûts de maintenance de même que les dommages causés aux structures et aux courroies en raison du mauvais alignement.