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Preventing Conveyor Belts from
Derailing!
Guest article by Ing. Harry
P.M. Clerx of Centre for Concepts in Mechatronics
 A
flat conveyor belt sometimes has the tendency to transversely
derail. This could lead to higher costs: production stagnation,
repairs and even the replacement of the belt itself. So, it is
of great importance to try and stop the belt from derailing.
There are numerous ways to stop a
conveyor belt from derailing, all of which are described in the book
“Tracking Systems for Conveyor Belts; Existing Systems and New
Developments”. However, almost every one of these tracking
systems, which have been known for quite some time and which will be
referred to as “conventional systems” hereafter, are sensitive to
pollution and tilting between the rolls.
But in this book two completely new
tracking systems are described, which are completely insensitive to
strong pollution, tilting of the rolls and the transverse forces
that are applied to the belt!
These two new systems have been
developed by Centre for Concepts in Mechatronics (CCM web site:
www.ccm.nl) in the Dutch town of
Nuenen, conducted by engineer Harry P.M. Clerx, the author of the
book and the inventor of these new tracking systems.
Flat conveyor belts sometimes have
the tendency to transversely derail – despite of the use of
conventional tracking systems – especially when the conveyor has
been polluted by, for instance, dough, fat, water, oil, earth, clay,
sand or sugar. Other reasons for conveyor belts to derail are
the tilting of the rolls in the conveyor and the transverse forces
the products being transported apply to the belt.
Usually the derailed belt is not
reset until the side of the belt comes in contact with machine
parts. If the belt is extremely damaged, it will need to be
replaced. Replacement costs can get very high, not only
because of loss of production, but also because of the costs of
producing a new customized and endless conveyor belt, and the
demounting and mounting costs. Furthermore, early adjusting of
the derailed belt is expensive too.
Methods
Research shows that the most part of
the annually sold conveyor belts in The Netherlands – approximately
2,700,000 meters – is used to replace worn out belts. For the
most part wear is caused by the derailing of the belt. A well
working tracking system can save a lot of expenses. That is
why, over time, many methods have been developed to keep flat
conveyor belts from derailing.
Some of these methods rigorously
prevent derailment, for instance by using a belt that has a
vulcanized control belt on the bottom side. However, this
method cannot be used on so-called “knife edge belt systems”.
Furthermore, the costs of the belt and the conveyor are much higher.
Other methods do not require the adjustment of the belt, but that of
the features of the drive rolls and reversing rollers, for instance
by using curves and adjustable snub-rollers. However, in
actual practice, such facilities prove not to be sufficient enough
in case of strong pollution or when the rolls are out of true.
Besides these passive tracking
systems, there are also active systems on the market. The
active tracking systems use an optic, pneumatic or electro mechanic
sensor to detect the derailing. If derailing occurs, the
snub-roller will be adjusted (set our of true) by using, for
example, an electro-engine or pneumatic cylinder, so that the belt
is set back after which the same thing will happen on the other side
of the belt after a while. However, these systems are very
costly and sensitive to failure caused by pollution!
New Developments
Polluted rolls, rolls that are out of
true and external transverse forces force the conveyor belt to the
side, causing the belt to spirally derail further and further!
When this happens, the belt cannot be stopped because of the great
friction force between the belt and the rolls.
Centre for Concepts in Mechatronics
(CCM) theoretically researched why it is that a flat conveyor belt
derails under the abovementioned circumstances and then used test
arrangements in their lab to verify their findings. Of course,
CCM also used test arrangements to extensively test the two new
tracking systems. When the belt of a regular conveyor belt
derails, it will continue to cumulatively derail. In other words:
the belt will eventually spirally run off the rolls.
This problem has been rigorously
taken care of in the two new systems!
 In
the first system, side guides (simple, vertically placed pens) keep
the belt in track, forcing the drive roll and/or reversing roller to
either the left or right. So, compared to traditional conveyor
belts, the opposite occurs in this system (all movements are
relative!). In order to realize this, a guiding is used that
allows the rolls to be moved in axial direction across the axel.
The only force the side guiding applies to the belt is the reaction
force of the internal friction of the guiding. As is known,
this friction is very low.
It is obvious that the lateral
movement of the roll can only take a very short while, because the
roll can already come in contact with the frame of the conveyor or
another machine after a few rotations.
The core of this invention is that
the roll is now separated in four segments. These segments
can, loose from each other, use their own side guides to axially
shift (See image).
Side guides are used to keep the belt
itself in track. The image shows how the belt will derail when
the roll is out of true (in the case of the image above, the belt
will derail to the right as seen from the direction of running of
the belt). This causes the belt to come in contact with the
side guiding that applies a force F on the belt. As a
reaction, the belt pushes those segments that are in the angle of
contact spirally to the left until they are out of the angle of
contact.
Next, a feature pushes the released
segments back to their original central position.
 The
second system also uses a belt that is kept in position by simple
side guides. However, now a slack belt part – a “belt loop” -
is included into the belt track.
As soon as the belt in the “tight”
track derails, the side guide pens will reset the “loose” part to
its original central position. The side guides will hardly
apply any force to the belt, because the belt can shift in lateral
direction without any force inside the “loop”. The belt does
derail, but just one belt rotation and not cumulatively as is the
case in conventional conveyors! Tests conducted by CCM and
actual users show that the belt in both new tracking systems remains
exactly in place under all circumstances.
In the meantime, the patents on both
systems have been released so that everyone may apply the systems.
Besides the usual passive and active conventional tracking systems
and the two new tracking systems, the book also describes a few
other special conveyor belt systems. Of course, these systems
are also theoretically well-founded!
The book “Tracking Systems for
Conveyor Belts; Existing Systems and New Developments” (336
pages, 15 pictures and 155 drawings) can be seen as the standard
work on the tracking of conveyor belts. It is published by
Conveyor Belt Tracking Systems (CTS) and can be ordered in three
different languages: Dutch, German and English.
Inclusive is a CD-ROM with several special designs. CTS can
give advice regarding the appliance of the two new revolutionary
systems in existing or new conveyors.
Our Author
For more information, contact our
author:
Ing. Harry P.M. Clerx
Conveyor Belt Tracking Systems
Rodestraat 99
5912 CN Venlo
The Netherlands
E-mail:
HPMClerx@kpnplanet.nl
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