Rock particles flowing through an ore pass incur an enormous number of collisions until all the rock particles involved come to a rest. An ore pass has three major components including the lined or unlined walls of the ore pass, rock fragments, and the gate assembly at the bottom end of the pass. Recent statistical analysis indicated that a significant number of injuries and fatalities to miners have occurred in or near an ore pass including failure of the chute gate assembly. Due to high impact energy on the chute gate, this may be the main cause of gate assembly failure. To improve the safety of the miner working near an ore pass, it is very important to understand the collisions that take place during the travel as the energy regime of the bulk of materials, especially near the chute gate assembly.
1. Coefficient of Restitution and Collisions
The most fundamental question is how a collision of rock impacting rock and rock impacting steel structures is defined and what happens after a collision takes place? In general, collisions involve two or more objects (at least one of the objects must be a moving object) impacting each other. Every earthy object, whether static or dynamic, has some form of energy stored in it. Collisions involving two or more objects can be defined as a phenomenon that results into exchanging or transferring energy. From both the definitions (general and physics), it is evident that collisions result in energy transfer between bodies and in turn depend on some more fundamental properties including masses of the objects, impact velocities, and the ambient atmosphere in which the collisions take place.
The after-effects of a collision depend on other physical and mechanical properties of the objects that are involved in the collision. The amount of energy that remains in the object after the collision is totally dependent on its deformation characteristics. Some energy loss as heat and sound from the impact, but the elastic properties and strength of the objects dictate the energy stored or lost in fracturing of the object. A parameter known as Coefficient of Restitution (hereafter COR) is a measure of the energy loss in fracturing or energy loss in rebounding of the objects after an impact or collision. This paper deals with coefficient of restitution, its role in defining the mechanism of bulk solid flow, and specifically the collision of rock on the gate of an ore pass chute.
When collisions involve two objects, there are two possibilities; (1) both the objects are moving and collisions occur between rock fragments on the move, and (2) one object is moving and the other one is static and collisions occur between either rock fragment and inner wall of ore pass or rock fragment and the ore chute gate. In both the cases, the law of conservation of momentum governs the collisions. For an object with mass, m, and moving with a velocity, v, the momentum is given by
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For a collision involving two objects, the law of conservation of momentum can be written as
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