DESIGNING BETTER LINERS WITH DEM SIMULATION TO REDUCE MINING EQUIPMENT WEAR

By Dr Daniel Grasser, Associate Research Fellow (IFM) and

The mineAlloy Industrial Transformation Training Centre (ITTC) is funded by the Australian Research Council (ARC) and operates out of Deakin University's Institute for Frontier Materials (IFM). The Centre represents a consortium of manufacturing companies who supply goods to the mining sector. Target outcomes are job growth, increased efficiency, sustainability, and cost reduction. To reduce wear in the mining sector, the Centre’s research involves efficient alloy development and selection, based on experimental and numerical investigations. This article presents a case study using Discrete Element Modelling (DEM) to simulate the rock flow and wear behaviour of chute liners.

Micro rock-boxes for wear protection – A Discrete Element Modelling (DEM) study

Mining requires processing of solid particles that cause severe wear on the equipment. Every year, wear in mining results in worldwide economic losses of the order of hundreds of billions of dollars and the remanufacturing of worn parts contributes a significant share of this. Chute wear is often a critical issue that affects cost and productivity.

Rock-boxes are a well-known approach to reduce wear in chutes. Here, the chute design aims to trap particles at the wearing surface and form a “box” of rocks that protects the surface during operation. The goal is to foster a flow regime with particles flowing over themselves rather than on the wear surface. The current state of the art for rock-box design is based on trial-and-error approaches. This can result in expensive re-designs, inefficient rock transportation and clogged chutes. Moreover, the application of conventional rock-boxes can be limited due to constraints of the available space within a chute. An alternative approach is to add inserts consisting of highly wear resistant materials. With thoughtful design, the two approaches can be combined with inserts fostering rock-on-rock flow regimes to further reduce wear.

The governing principles for the design of the rock-boxes and the insert placement remain unknown. For this reason, Discrete Element Modelling (DEM) (ESSS Rocky) was used for the investigation of the rock flow inside a transfer chute. DEM is a numerical tool used to investigate the interactions of up to several millions of rocks. Moreover, a wide range of rock shapes can be applied to represent the actual rocks found on mine sites. In addition to chutes, DEM has been used to investigate mining applications including bins, hoppers and diggers exposed to abrasive wear. Using DEM allowed the systematic comparison of 35 wear plates with inserts and a conventional wear plate. A benefit of DEM is that the important rock flow parameters such as the sliding and rolling velocity, and most importantly, the effectiveness of an evolving protective rock layer (which is an important measure for the micro rock-box design), can be assessed. A non-spherical particle shape representing the rock shape was used as shown in Figure 1. The sieve size of the investigated cases ranged from 3.5mm to 32mm.

A 65⁰ transfer chute was implemented in the DEM model (Figure 2). The input velocity of the rocks falling into the chute was 12m/s, which is approximately equal to the velocity occurring at the exit zone of a chute with a head height of 10m. Wear plates consisting of a matrix (i.e. base plate) and inserts (i.e. reinforcements) were investigated (Figure 2). Different numbers of inserts have been investigated. Where an increasing number of inserts decreased the spacing between them, and a wear plate fully consisting of inserts represented a conventional wear liner. Moreover, the size (diameter of the circular inserts) and exposure height of the inserts from the matrix were studied. An example of an investigated chute with a wear liner with inserts is shown in Figure 2.

The resulting rock flow was then analysed for the representative crosssection (Figure 3) in the centre of the wear plates. A special focus was set on the rocks in contact with the wearing surface. Interestingly, an optimum wear liner design was derived when the inserts were placed in geometrical relationships in respect to the size of the processed rocks. It was found that a spacing between the inserts approximately equal to the rock size was most beneficial. Other important geometrical parameters of the inserts are the diameter and the exposure height of the inserts from the matrix. The sieve size (50 per cent passing) of the rocks was seen to be an important parameter to represent the size of the cohesionless rocks. For the optimum wear liner with inserts, the rocks in contact with the wearing surface possessed the lowest sliding velocity as shown in Figure 3.

In this case, a protective rock layer acted as a protective cushion on top of the wear surface. Moreover, the optimum wear liner with inserts showed a tendency to change the mechanism from rock sliding against the chute liner towards a mechanism where the rocks rolled over themselves at a slower velocity. The sliding velocity of the rocks near the wear surface was up to 6x slower for the wear liner with inserts. The sliding velocity is well-known to be the main contributor to abrasive wear, thus, this indicated a change of the rock flow near the wear surface into a significantly less severe wear regime. In contrast, the build-up of a protective rock layer did not occur for the conventional wear liner.

Rocks partly flowing over themselves and not on the wear surface of the chute provides a significant benefit. As a result, the simulations indicated that the optimum insert design offers a longer service life than conventional wear liners. Most importantly, the optimum wear liner required only a reduced vol% of insert material (<50 vol%) compared to a conventional wear liner fully (100 vol%) consisting of insert material. This implies benefits in terms of economic use of materials and sustainability.

In summary, Discrete Element Modelling (DEM) was used to compare different wear plate designs with inserts. Using DEM, the rock flow was analysed, which is difficult to assess experimentally. The benefits of wear plates with inserts are attributed to the development of protective micro rock-boxes evolving between the inserts and temporarily locking rocks between them. The inserts can thus be placed to foster a less severe wear regime by sustaining this protective rock layer. The design principles thus developed are providing extended wear life in experimental trials.

The study was conducted as part of a PhD project at Deakin University under the supervision of Associate Professor Michael Pereira (School of Engineering), Professor Matthew Barnett and Dr Santiago Corujeira Gallo (Institute for Frontier Materials (IFM)).