花岗岩采石场某些岩石强度特性对颚式破碎机性能的影响外文翻译资料

Influence of some rock strength properties on

jaw crusher performance in granite quarry

OLALEYE B M*

Department of Mining Engineering, Federal University of Technology, Akure, Nigeria

Abstract: The influence of rock strength properties on Jaw Crusher performance was carried out to determine the effect of rock strength on crushing time and grain size distribution of the rocks. Investigation was conducted on four different rock samples namely marble, dolomite, limestone and granite which were representatively selected from fragmented lumps in quarries. Unconfined compressive strength and Point load tests were carried out on each rock sample as well as crushing time and size analysis. The results of the strength parameters of each sample were correlated with the crushing time and the grain size distribution of the rock types. The results of the strength tests show that granite has the highest mean value of 101.67 MPa for Unconfined Compressive

Strength (UCS) test, 6.43 MPa for Point Load test while dolomite has the least mean value of 30.56 MPa for UCS test and 0.95 MPa for Point Load test. According to the International Society for Rock Mechanic (ISRM) standard, the granite rock sample may be classified as having very high strength and dolomite rock sample, low strength. Also, the granite rock has the highest crushing time (21.0 s) and dolomite rock has the least value (5.0 s). Based on the results of the investigation, it was found out that there is a great influence of strength properties on crushing time of rock types.

Keywords: rock strength; jaw crusher; crushing time; grain size distribution; efficiency

1 Introduction

The strength of a material refers to the materials ability to resist an applied force. Strength property of rock is the ability of the rock material to resist failure when load is applied without yielding or fracture. The mechanical properties of rock depend upon the interaction between the crystals, particles and cementation material of which it is composed. The yield strength of a material is an adequate indicator of the materials mechanical strength and is the parameter that predicts plastic deformation in the material, from which one can make informed decisions on how to increase the strength of a material depending on its micro-struc- tural properties and the desired end effect. Strength is considered in terms of compressive strength, tensile strength, and shear strength, namely the limit states of compressive stress, tensile stress and shear stress, respectively. According to Reference, the effect of dynamic loading is probably the most important practical part of the strength of materials, especially the problem of fatigue. Repeated loading often initiates brittle cracks, which grow slowly until failure occurs.

It is of paramount importance to first carryout size reduction of an ore or rock material on a laboratory scale for the ore or rock material to be profitably and economically processed industrially. This permits the determination of parameters such as liberation size, grindability, coarse to medium to fine proportion in any product of the crushing and grinding equipment and the proportion of values of gangues in the fines. Jaw Crusher is used for crushing rock material in mines and quarries. It provides the latest technology in heavy duty crusher design that delivers high production, infinite setting adjustment, larger feed opening bolted mainframe, cast swing, jaw holder and optional positioning of the crusher support feet to suit installation requirement. This crusher is designed for exceptional heavy and continuous application with heavy duty part for optimum operation and long life and this can be influenced by the strength properties of the rock. The influence of rock strength property can result to the loss of capacity to perform the stipulated function for which jaw crusher was designed. The UCS was the main quantitative method for characterizing the strength of rock materials. Point load test is used to determine rock strength indexes in geotechnical practice. Rock lithologies were classified into general categories and conversion factors were determined for each category. This allows for intact rock strength data to be made available through point load testing for numerical geotechnical analysis and empirical rock mass classification systems such as the Coal Mine Roof Rating (CMRR).

Crushing is an integral portion for mineral processing operations and is critical for the preparation of ore for downstream process for mineral processing operations. Crushing of quarried rock is carried out in stages, with the primary crushing stage typically carried out using Jaw crusher and subsequent (secondary and tertiary). From field observation, the greater the number of crushing stage, the higher the amount of fine produced as a proportion of total plant throughout. The type of crusher used also directly controls the amount of fines produced. A recent study of quarry fines looked at possible relationship between quarry plant operation and the generation of quarry fines. The conclusion drawn have been critically revealed that hard rock aggregate plant production is directly proportional to the number of crushing stages; it increases with an increase in production stage. Low reduction fines generation at each stage especially where the rock or mineral are fragile, however, the cumulative fines production may be higher than a process using fewer stages with higher reduction.

The particle size analysis is the method used to determine the particle size distribution or the grain size distribution of rock/ore materials. In practice, close size control of feed to mineral processing equipment is required in order to reduce the size effect and make the relative motion of the particles separation dependent[9]. The particle size distributio

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