Page 49 - HUB-4 Magazine Issue 99

Quarrying News
Skirting and Mistracking Allowances
There are many different sealing systems on the market.
Depending on the spacing of the skirtboards and the thickness
of the sealing system, there could be differences in the
amount of free belt edge needed in the design for Allowable
Mistracking in the load zone. [Fig. 5] If there is a history of
Actionable or Critical Mistracking that cannot be mitigated,
then an even wider free belt edge is warranted.
Return trainers act in a very similar fashion but without a
troughed roller. Training idlers are set slightly above the belt
plane allowing the weight of the belt to offer some additional
tension on the roller. As the sensing arm detects the belt drift,
it turns the roller in the opposing direction to train the back
into alignment. Since the low tension belt return can easily
become misaligned, a return tracker is especially effective
when placed near the tail pulley to ensure the belt enters the
loading zone aligned.[Fig.8]
Figure 5 – Determining
conveyor skirtboard
width based on
mistracking and
sealing system
allowances
Belt Training
Accessories to deal with mistracking may come standard with
conveyor systems. These are often “brute force” trainers that
prevent the belt from coming in contact with the structure and
are not actually training systems but merely protective barriers
that lead to system issues and belt wear. When the belt drifts,
the brute force trainers can cause the belt to fold into itself
and fold back into the system. This can permanently damage
the belt and lead to further mistracking and spillage. [Fig. 6]
Figure 8 - It can be argued the return requires just as much training as
the carrying side.
Conclusion
Over the life of a conveyor, it is cost-effective to contact CEMA
member companies for assistance with conveyor design,
component specification, training, or troubleshooting conveyor
belt tracking issues.
References
[ ] Staff, CEMA's System Mistracking Allowance Guide 2023,
Conveyor Equipment Manufacturers Association, Inc. (CEMA),
Bonita Springs, FL.
www.cemanet.org
Figure 6 - Brute force tracking devices treat the symptoms rather than the root
causes of mistracking, often result in belt edge damage.
Modern belt trainers use sensing arms to detect slight
variations in the belt path. These arms are attached to a
pivoting idler that reacts immediately to these variations and
trains the belt back into alignment. If detected early enough,
less force is needed to retrain the belt and ensure alignment
throughout the belt path.[Fig.7]
Figure 7 - The roller arms ride the edges of the belt moving with horizontal variations
off of the center line.
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www.hub-4.com July/August - Issue 99
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