Page 41 - HUB-4 Magazine Issue 90

Quarrying
belt’s path will jump quickly to one side as the splice travels
across the pulley.
If it is discovered that these factors are the cause of
mistracking, adjusting the conveyor’s rolling components will
not correct the issue. The only options are either replacing the
belt, or -- in the case of crooked splice(s) -- re-splicing the belt,
assuming there is enough extra belting in the take-up system
to allow removal of the faulty splice section.
During the observation procedure, if the belt moves to one side
and stays there, the problem may be one of three things: the
head pulley lagging is not consistent, the last few carrying
idlers prior to the pulley are out of alignment or the head
pulley itself is not properly adjusted.
Causes
Mistracking just after the head pulley on the conveyor’s return
has two main causes. The first might be that the lagging is
missing on one end of the pulley, so the pulley’s diameter is
off-center, placing uneven pressure on the belt and causing it
to wander. If this is not the case, then the belt cleaning system
may have been mounted slightly askew, putting greater
pressure on one side of the belt and pulley. This uneven
friction can also lead to mistracking.
Once operators and maintenance professionals properly
identify the type of misalignment, they can then seek out the
cause. “We’ve observed that there are three groups of
common causes for mistracking,” Mueller pointed out. “One is
a fault with the belt or splice, another group is the conveyor’s
structure, components or environment, and the last is due to
improper material loading.”
Belt and Splice- If the belt is poorly manufactured or stored
improperly, it can bow or camber. Poor installation of a
vulcanized or mechanical splice can result in a splice that
causes belt tracking problems. Exposure to the elements or to
chemicals can degrade the carcass (plies or cords) and the
cover of the belt. Faults and damage caused by mismatching
the belt to the application and/or operating environment can
require frequent replacement. [Fig. 3]
Figure 3 – Contact with the structure can break mechanical splices with expensive
consequences. Copyright © Martin Engineering 2025
Conveyor Structure - Inaccurate alignment of the conveyor
stringer structure can have subtle but lasting effects on the
belt’s performance. Structural misalignment can happen due
to age, bumped by machinery, affected by seismic activity, or
ground settling.
Outdoor conveyors - High winds require “wind loops” to keep
the belt in line. Exposure to extreme temperatures on one side
of the conveyor can make components expand, causing
changes in friction.
Improper Loading - The load’s center of gravity will seek the
lowest point of the troughing idlers, so if the belt is not center
loaded, the weight of the cargo pushes the belt toward the
conveyor’s more lightly-loaded side. This can be corrected by
installing a central loading transfer chute or by using
deflectors, grids or chute bottoms that can be adjusted to
correct the placement of the load on the belt.
Belt Training
A common procedure to correct the wandering belt is to
slightly adjust the return and carrying idlers against the
direction of the mistracking. Unfortunately, the approach does
not work on reversing belts. An even more serious
consequence is that over time a number of the idlers may be
misaligned, “fighting” each other to correct the alignment.
[Fig. 4]
Figure 4 – Adjusting idlers for tracking can make
correcting the belt for changes in speed or material harder later.
Copyright © Martin Engineering 2025
When idler training is not successful as a long-term solution,
operators may be faced with a situation where the training
procedure is repeated on a frequent (sometimes daily) basis.
At that point, managers should consider installing some form
of engineered training solution to mitigate the problem. [Fig.
5]
Figure 5 – The Torsion Arms sense changes in the belt path and adjust the roller to
compensate. Copyright © Martin Engineering 2025
Engineered training solutions are devices that sense the
position of a belt and, through a mechanism or geometry
change, actively adjust its path. Some of the most common
types include:
Belt Misalignment Switches - The wandering belt pushes a
lever arm and activates a switch, which either sets off an
alarm or stops the system. Costly downtime can result from
these systems.
Vertical Edge Guides - Positioned perpendicular to the belt’s
path to keep the edge away from the conveyor structure and
should not be used to compensate for persistent misalignment
problems. Most practical on short, low-tension systems and
not particularly effective on thin belts, operators have
experienced belt roll over on itself.
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