Accurate erosive wear testing

June 1, 2016 JESPER AXELSEN

FLSmidth’s erosive wear test procedure helps vertical roller mill operators to reduce maintenance costs and increase equipment lifetime.

Erosive testing of vertical roller mills (VRMs) is an important area in cement production. Together with traditional testing procedures, it can provide vital insight into the expected lifetime of mill equipment and help operating staff prepare effective maintenance plans.

FLSmidth has developed a new erosive test rig to help accurately predict the effects of erosive wear in VRMs. The laboratory-based testing equipment has been proven to accurately test separator return feed from the laboratory VRM. Reflecting FLSmidth’s collaborative approach to meeting market challenges, the test rig is the result of strong teamwork between various departments at FLSmidth, including R&D, Customer Services and the technical department. The test rig has been fully implemented at the Dania R&D centre and is used in designing industrial VRMs, in research projects and for the benefit of cement producers.

Lucas Jensen, Research Engineer at FLSmidth, has been involved in developing the testing rig from the outset. He explains the reason for FLSmidth’s research and development focus on the procedure:

“We felt there was a real need to develop a simple, accurate way of conducting erosive wear testing, because the methods used in the industry to date often produce misleading results. So we have developed a testing system that will enable us to provide better performance guarantees to customers to a greater degree of accuracy.” - Lucas Jensen, Research Engineer at FLSmidth

Abrasive testing insufficient
The problems associated with abrasive wear are well known and abrasion testing is widespread. Abrasion is often the most damaging mechanism occurring in VRMs, contributing to the loss of wear part material on table and roller segments. In contrast to abrasion’s high-pressure wear mechanism, erosion is a low-pressure airborne mechanism occurring primarily on the mill housing and separator.

While the effects of erosive wear can be just as brutally damaging, predicting them is difficult because of the many different determining factors, including the wear part material as well as the abrasive hardness, particle-size distribution, speed, angle of attack and mineralogy.

Abrasive testing is often conducted with a laboratory-scale VRM. Many have adopted the common practise of predicting the effects of erosive wear solely based on results of abrasive testing. This, however, does not provide sufficient insight into erosive wear and can lead to highly inaccurate predictions in an operational environment. FLSmidth’s VRM laboratory mill, for example, shows no signs of erosive wear after many years of operation, whereas in reality, erosive wear will almost certainly occur in a full-size VRM in normal operating conditions.

Determining the erosive wear rate
Used in conjunction with FLSmidth’s laboratory VRM, FLSmidth’s erosive test rig allows research engineers to simulate to a high degree of accuracy the effects of erosive wear within a full-size operational VRM. Testing is based on a two-step process. First, the laboratory VRM is fed with a raw mix with very similar properties to that used in industrial production. FLSmidth’s laboratory VRM has the unique ability to store and remove a large amount of separator return feed from its separator cone. This return feed is a good fingerprint of the material that causes erosive wear within a VRM. Second, the return feed is removed from the cone and put through an accelerated erosive test in the erosive test rig.

The test rig imitates actual erosive VRM situations in a production environment, while also enabling different wear part materials to be tested. All parameters are integrated into a single number, called the erosive wear rate.

Easy to operate
Quartz is the most erosive type of particle occurring in raw material VRMs. Wear is often correlated to the fraction of quartz in a raw mix, which can be measured by means of, for instance, x-ray diffraction or microscopy. But these methods require a sample preparation that destroys the original particle size distribution that is known to be extremely important in erosive wear situations. The erosive wear tester operates with the non-destroyed, original particle-size distribution, while also considering both speed and angle of attack – two properties that are impossible to mimic in x-ray diffraction and microscopy. 

Almost any material can be used in the testing rig. Different wear part materials can be tested to compare their erosive properties. This means wear parts can be replaced with materials less susceptible to erosion, thus improving the VRM’s life expectancy – and allowing better long-term maintenance planning.

The benefits of better erosive testing to cement plant operations are clear. FLSmidth can accurately compare the lifespan of wear parts, depending on the specific material they are made of and the process materials they are exposed to. This helps developing and applying the right wear solutions and thereby reducing maintenance costs and the risk of unexpected equipment failure. Erosive testing is being used in R&D to develop optimal wear resistance solutions for dynamic separators in VRMs.

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