Australasian Mining Review
Issue link: http://ebook.aprs.com.au/i/37922
270 Wear Protection and Prevention Modes of Wear In the world of mining materials handling, whether it is mobile or fi xed plant, it is necessary to protect expensive capital equipment from wear to prevent premature failures which lead into extended periods of downtime. The protection systems available for equipment are many and varied and can lead to confusion in determining the right system for the right location. One of the easiest ways to establish the most appropriate form of protection for each piece of equipment, is to develop a basic understanding of the modes of wear that cause material loss. This basic understanding of how material is removed will narrow down the choice of what is available for each mode and make selection of products or systems signifi cantly quicker. T he three main modes of wear/material removal faced by most mining operations today are 1. Impact, 2. Abrasive and 3. Erosive. Each of these modes can occur individually or in most cases there is a combination of one or two that creates the problems. 1. Impact – impact wear can be categorised as “the gradual wastage of material due to repeated impact by particulate streams or by continued hammering with a hard object (percussive wear)”. In more relevant terms it is the striking or battering contact of one object against the other that creates deformation of the material. These deformations may then be removed by ploughing wedging or cutting (in the more ductile materials) or by fracture (in the brittle materials). Examples of impact wear are – jaw, gyratory and cone crushers, mine truck bodies (which also suffer abrasive). In the majority of instances the preferred materials to protect components against impact wear are cast manganese steels and medium hardness quench and tempered plates. 2. Abrasive – abrasive wear can be categorised as “the gradual wastage of material when hard asperities or third party particles rub under load against a relatively softer surface”. In mining operations this generally takes the form of two-body abrasive wear where loose abrasive particles roll over the equipment surface. Depending on the angle of attack, three modes of abrasive wear usually occur on the more ductile materials. Ploughing; where ridges form alongside a track of wear. Wedging; a short wedge forms in front of the abrading asperity. Cutting; a ribbon like chip forms in front of the abrading asperity. In all cases wear particles form when ridges, wedges or chips fracture and detach from the underlying surface, perhaps by a process of delamination. Examples of abrasive wear are – mining shovel and loader buckets, conveyor transfer chutes and bins and hoppers. Materials used to protect components from abrasive wear include high hardness cast white irons, chromium carbide overlay plate and in cases of higher impact lower abrasiveness, medium hardness quench and tempered plate. 3. Erosive – erosive wear (or erosion) can be categorised as “the gradual wastage of material due to the impact of abrasive particulates in a fl uid stream”. Erosive wear can also be described as an extremely short sliding motion and is usually executed within a short time interval. The impacting particles then gradually remove material from the surface through repeated deformations and cutting actions. Examples of erosive wear are slurry pump impellers and casings, slurry transfer piping, cyclones and cyclone launders. Materials used to protect components from erosive wear are generally higher in hardness due to the reduced occurrence of severe impact. Materials such as ceramic, basalt and high chrome cast white irons. Once the relevant mode of wear is established for each circumstance, it is easier to determine the most appropriate material/product for the duty. Wear prevention in mining operations can be divided into two segments (in the view of the author), 1. Engineering and 2. Condition Monitoring. [Wear Protection and Prevention] _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _