Delft University of Technology
Faculty Mechanical, Maritime and Materials Engineering
Transport Technology

C.R.J. Versteegh Condition monitoring of belt scraper systems
Engineering Assignment, 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 systems.

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 realized.

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)
Modified: 2006.04.12; , TU Delft / 3mE / TT / LT.