Condition monitoring of belt scraper systems
Report 2006.TL.7042, Transport Engineering and Logistics.
Maintenance, necessary to ensure reliable and safe operation of a belt
conveyor system used to be done by in-house domain specialists of a plant.
Since maintenance costs can be a significant part of the overall plant
costs, companies are searching for alternatives to reduce the total
maintenance costs, and outsourcing of the maintenance to a specialized
maintenance company is one of the possibilities. Due to a number of
problems, such as inexperienced inspectors gathering inaccurate or
inconsistent information about the status of the conveyor system,
companies are looking for other possibilities to reduce their maintenance
costs, and increase the overall performance of their belt conveyor system.
Recently, there is more interest from the bulk solids handling industry in
expert systems that are able to monitor belt conveyor systems (offline and
online) and decide upon maintenance actions. If the inspection is
automated, knowledge of the different components can be built up in a
database with the aim of automated data processing. Newly collected data
can then be analyzed automatically, and an advice can be given to the
operator on appropriate operational actions and maintenance strategies.
One of the main advantages of such system is that the dependability on a
domain expert can be reduced, resulting in a more objective and up-to-date
knowledge on the status of a belt conveyor system and the performance of
the overall belt conveyor system is increased.
This research will be concerned with the viability of implementing a
monitoring system on belt cleaning system and subsequently the
implementation in a knowledge-based expert system of overall belt conveyor
A belt cleaner removes adhered bulk solid material that would stick to the
belt surface after it passed the discharge area of a belt conveyor. This
material is called 'carryback.' As carryback falls off the belt on the
ground or adheres to return idlers, it can cause premature failure of
expensive conveyor components such as the belt or the conveyor
construction. As carryback material piles underneath the belt conveyor
system, it has to be removed by plant personnel, and often separately
processed from the main material flow. This leads to an increase of
maintenance costs, such as extra cleanup costs, but also to the loss of
saleable product. By increasing the performance of belt scraper systems,
the performance of the overall belt conveyor system is increased. There
are many different types of belt cleaning devices, and in this report only
two belt scrapers types are examined. Belt scrapers are the largest group
of belt cleaning devices applied in industry.
The chosen belt scraper consists of a number of scraper blades adjoined on
a shaft that is positioned across the belt in the discharge area. This
shaft is pushed against the belt by a tensioner (air, spring driven). In
order to choice the parameters that can be used to describe and monitor
the belt scrapers' performance, the main failure modes of a belt scraper
system have to be known. These are that 'the cleaning performance of a
belt scraper is insufficient', and 'the wear rate of the scraper blades is
above the nominal wear rate.'
For these failures there are numerous causes that have been identified
(although without extensive research in industry). The amount of carryback
on the belt surface after it passed the belt scraper, the rotation of the
shaft, and tension in the shaft are the three indicators that show a large
number of causes and can be monitored with current sensor technology. The
application of sensors results in a major increase of data that has to be
processed, and combined with (often) linguistic system information of
domain experts. By defining the different behaviour of each indicator a
number of combinations can be made, each describing certain behaviour of
the belt scraper system. Each unique combination is stored in a 'case'
that specifies a certain condition but also gives an operational advice
that adjusts the failure. These cases are structured in the expert system.
Nonetheless, there are still many cases that can not be recognized with
these indicators, and require domain experts.
From this research it is clear that the performance of belt scraper
systems influences the overall performance of belt conveyor systems. How
large this influence is, depends on the operating conditions of each belt
conveyor system. The introduction of condition monitoring on belt scraper
systems can reduce the current maintenance problem experienced in
industry. By implementing the performance data of the condition monitoring
system and knowledge of domain specialist on belt scraper systems in the
general knowledge-based expert system of the belt conveyor system, a more
accurate and consistent image of the status of belt scraper systems is
Condition monitoring requires an initial investment and ongoing
expenditure. A cost û benefit analysis is necessary to quantify the
financial benefits of condition monitoring of belt scraper systems. The
carryback gauge that measures the cleaning performance of a belt scraper
system is not fully automatic and requires a human operator. This prevents
a fully automated functioning of a condition monitoring system on belt
scraper systems. A domain expert stays necessary to monitor the condition
of scrapers blade, the belt, and bulk solid material characteristics.
It is recommended to redesign the ICT carryback gauge such that the condition
monitoring can operate autonomously.
It is recommended to do more research in different bulk solid industries
to get more insight in the failure modes of belt scraper systems,
maintenance procedures and current condition monitoring systems.
Reports on Transport Engineering and Logistics (in Dutch)
, TU Delft