The associated test methods and performance standards can also be confusing. Making the correct choice is crucial to improving performance and cost-efficiency. Here, Rob van Oijen, manager of application engineering for Netherlands-based Dunlop Conveyor Belting, begins a series of technical papers for BulkInside that explain what to look for as well as the various test methods and standards, starting with the most commonly used cover grade of all, abrasion.
The wear resistance qualities of a conveyor belt are most likely to be the biggest influence on the length of its operational life and consequently its cost-effectiveness. The two main internationally recognized sets of standards for abrasion-resistant belting are EN ISO 14890 (H, D and L) and DIN 22102 (Y, W, and X). In Europe, it is the longest established DIN standard that is most commonly used. Generally speaking, the abrasion resistance demanded by DIN Y (ISO 14890 L or D) relates to ‘normal’ service conditions and is the most commonly specified abrasion standard. The DIN X (ISO 14890 H) standard is more resistant to abrasive wear than DIN Y and also has other mechanical properties that create good resistance to cutting, impact (from high drop heights), and gouging, usually caused by heavy, sharp materials. DIN W (ISO 14890 D) is the most resistant to abrasion and is therefore well suited for applications where there are particularly high levels of aggressive abrasive wear.
Abrasion – test methods
The test method for abrasion resistance (ISO 4649 / DIN 53516) is carried out by moving a test piece of rubber across the surface of an abrasive sheet mounted on a revolving drum and measuring the amount of rubber that is lost. The measurement is expressed as volume loss in cubic millimeters, for instance, 150 mm³.
The most important thing to remember when looking at abrasion test results is that higher figures represent a greater loss of surface rubber, which means that there is a lower resistance to abrasion. Conversely, the lower the figure the better the rubber will resist day-to-day abrasive wear.
Different kinds of wear and tear
Different causes of wear and abrasion require different kinds of abrasion resistant covers. For example, belts that transport heavy and/or sharp objects such as rocks, timber, or glass that cause cutting and gouging of the belt surface need different resistance properties compared to belts carrying ‘fine’ materials such as cement or sand, which literally act like a piece of coarse sandpaper that is constantly scouring the rubber cover.
As a general rule, 80% of conveyor belt surface wear occurs on the top cover of the belt with approximately 20% of wear on the bottom cover. Wear on the top cover is primarily caused by the abrasive action of the materials being carried, especially at the loading point or ‘station’ where the belt is exposed to impact by the bulk material and the need for the belt to accelerate the material across the belt surface. Aggressive scrapers and skirting will also gradually wear the belt surface.
Belts running on short conveyors (less than 50-meter center-distance) usually wear at a faster rate than those on longer conveyors because they pass the loading point(s) more frequently. For this reason, selecting a good quality belt with a genuinely good level of abrasion resistance becomes even more important than usual. In an effort to extend operational lifetime, many conveyor belt users make the mistake of fitting belts with increasingly thicker covers in order to compensate for poor abrasion resistance. This is not a good idea because belts that are too thick can potentially cause other problems. In reality, the single most important factor is the actual abrasion resistance of the rubber.
Evaluating offers – what to watch out for
Many people are unaware that there is a significant difference between what is simply an approved method of conducting a particular test (test method standard) and the actual performance standards attained during that test. In reality, the fact that a belt has been tested according to a certain method (for example, EN ISO 4649 for abrasion resistance) means very little. What really is important is the actual level of performance achieved during the testing compared against the minimum acceptable level of performance dictated by the test standard. In other words, was the performance standard actually met, and if so, to what degree? In the case of ENISO 4649 abrasion resistance testing, the performance would typically be measured against the standards set within ISO 14890.
It is important to remember that DIN and ISO standards are only the minimum benchmarks of acceptability. Even then, laboratory tests consistently reveal that despite the claims of the manufacturers, more than half of all belts supplied are found to be significantly below those minimum standards.
Comparing (evaluating) one offer from another is made more difficult than it should be because of the potentially misleading technical datasheets supplied by manufacturers and traders. Almost invariably, they only show the minimum standard demanded by a particular test or simply the reference number of the test method rather than the level of performance that the belt should reasonably be expected to achieve. I am proud to say that Dunlop Conveyor Belting is an exception to this often misleading practice because our datasheets also show the actual test performance averages recorded (and regularly updated) during our ongoing quality testing program. Like most things in life, the golden rule when it comes to conveyor belts is that you only get what you pay for.
If you are still unsure of the grade of belting you need or have other doubts such as the correct tensile strength needed on a particular application, then it is best to seek expert advice. At Dunlop for example, we have a team of application engineers and technical advisers who are happy to provide honest advice and guidance on how to make the right choice technically and get not only the best performance but also the best value for money.