外文翻译 隧道窑
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- 外文翻译 隧道窑 The physical and mechanical characteristics of intact rocks depend on the way of their formation, sustained deformations and the process of wearing a specific rock has been exposed to. These characteristics have a rather high influence on the technological process of extraction and dressing of mineral raw materials. However, the mechanical characteristics of rocks due to use of explosives for their extraction in the open pit have a more significant impact. The rock blocks extracted by blasting which are larger than the opening of the primary crusher are usually fragmented by hydraulic hammer. The paper presents the results of the testing of impact of rock hardness on fragmentation of rocks by means of hydraulic hammer and during crushing in jaw crusher. The testing was carried out on the rock samples from five quarries. According to the obtained results the hardness has a considerably larger impact on the fragmentation energy by hydraulic hammer than on the crushing energy in jaw crusher.
Introduction
The production of building crushed stone represents a considerable part of the production of mineral raw materials in the Republic of Croatia. Building crushed stone was until 2004 extracted on 250 exploitation fields according to the records of the Ministry of Economy, Labour and Entrepreneurship .Principally,it is extracted from rock massif by blasting. The blasted rock mass is transported to separation where the stone is usually beneficiated by the crushing and sieving processes. The
blasted rock mass contains oversized rock blocks, which are actually stone pieces larger than the opening of the primary crusher and which should have been fragmented before rushing. Oversized blocks are today almost always fragmented by hydraulic hammers.They have been frequently applied due to their numerous advantages compared to the secondary blasting – there is no stoppage of the working process, there is no stone scattering, the costs are lower, etc. However, since the beginning of their application there have been almost no testing, neither any attempts to better understanding and determination of the mechanical characteristics of rocks, which affect the use of energy upon crushing of oversized blocks.
Crushing is the process of fragmentation mineral grain aimed at achieving a certain grain size distribution,grain shape and mineral liberation The quality of building crushed stone is evaluated on the basis of the physical and mechanical characteristics, the grain size distribution and the grain shape. The co-efficient of energy use is rather low and rarely reaches 1% (Slokan, 1969), whereas the rest of the energy is used for elastic and plasticdeformation and the loss of energy in crusher.Accordingly, the fragmentation process is very expensive and affects the complete mining activities. Therefore, the attempts of better understanding of the affecting values on the processes of stone fragmentation are justifiable.
Theoretical consideration
The rock characteristics largely affect the energy needed for their fragmentation from blasting, subsequent fragmentation of oversized blocks by hydraulic hammers to crushing in the process of stone refining. The explosive energy during blasting is used up on fragmentation vibration (seismic waves) and forward movement of blasted rock mass. It has been proved in practice that blasting affects the further processing of mineral raw materials. The use of larger quantities of explosives and the explosives with a higher detonation speed will reduce the resistance of raw materials to crushing and fragmentation
There are two important impacts of blasting on fragmentation. The first‘visible’ one is the grain size distribution of the blasted rock mass and the second ‘invisible’ one is the creation of micro-cracks in some stone pieces (Workman & Eloranta, 2003). The efficient blasting in terms of energy use includes the use of a small quantity of explosives, which at the same time will result in the optimum rock fragmentation and thus enable higher security due to the minimum loss of energy on seismic waves and forward movement of material. However, such a process results in a smaller number of micro-cracks within the bullet of the blasted stone material, which means higher energy use for further fragmentation. Accordingly, it is obvious that the fragmentation processes of stone Material are affected by the physical and mechanical characteristics of intact rock material and even more by the changed physical and mechanical characteristics of stone due to its extraction by blasting.
The number and size of micro-cracks within the rock material caused by the energy of explosives directly affects the reduction of all mechanical characteristics of the material. A large number of authors have tested the impact of various mechanical characteristics of rocks on the fragmentation energy The researches of impact were conducted in order to find a specific rock characteristic which would enable easier choice and dimensioning of machinery for fragmentation taking into consideration the determined efficiency.
The Schmidt rebound hardness of rocks is the characteristic which is due to its speed and simplicity of testing often applied in practice. Besides, in many papers the Schmidt rebound hardness has been directly linked with the efficiency of the mechanical conmunication of rock upon excavation。
The paper presents the results of the testing of hardness impact on...
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