REQUIREMENTS TO BE FULFILLED BY EXISTING BWES WORKING IN HARD TO EXCAVATE ROCK FORMATIONS.

One of the frequent problems that needs to be addressed when mining coal deposits is the presence in the working face of cohesive materials having high mechanical strength in relation to the average rock to be excavated. These are generally called "hard formations" or "hard inclusions" and are in the form of either continuous layers or boulders. This problem is of particular importance in Europe where lignite deposits are exploited in large opencast mines utilizing Bucket Wheel Excavators (BWEs) as the main means of excavation. Often it is difficult or impossible to excavate these hard inclusions with BWEs. If their location has been previously determined by exploration, they are usually blasted. But it is not uncommon to discover them when it is too late, that is when the BWE actually digs into them. The actually operating of BWEs are designed to excavate materials with an "earthy" texture with low mechanical strength. Dynamic and stochastic impact loads exerted on the machine during these encounters are the most common causes of major BWE component failures leading to downtime, production disruption, and high-cost repairs. [ABSTRACT FROM AUTHOR]

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