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1、 Received 29 August 2009; accepted 12 November 2009 *Corresponding author. Tel: 86 516 83885948 E-mail address: L doi: 10.1016/S1674-5264(09)60185-X Influence of some rock strength properties on jaw crusher performance in granite quarry OLALEYE B M* Department of Mining Engineering, Federal Universi

2、ty 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

3、, dolomite, limestone and granite which were representatively selected from fragmented lumps in quarries. Uncon- fined 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

4、 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 3

5、0.56 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

6、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

7、 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 inte- raction between the cryst

8、als, particles and cementa- tion material of which it is composed1. 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

9、 strength of a material depending on its micro-struc- tural properties and the desired end ef- fect. 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, respectively2. According

10、 to Refer- ence 3, 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 siz

11、e 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 a

12、nd grinding equipment and the proportion of values of gangues in the fines4. 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 pro- duction, infinite setting adjustment, larger feed open- ing bolted

13、 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 prop

14、erties of the rock. The influence of rock strength property can result to the loss of capacity to perform the stipu- lated function for which jaw crusher was designed. The UCS was the main quantitative method for cha- racterizing the strength of rock materials5. Point load test is used to determine

15、rock strength indexes in geotechnical practice. Rock lithologies were classi- fied into general categories and conversion factors were determined for each category. This allows for intact rock strength data to be made available through Mining Science and Technology 20 (2010) 02040208 MINING SCIENCE

16、AND TECHNOLOGY OLALEYE B M Influence of some rock strength properties on jaw crusher performance in granite quarry 205 point load testing for numerical geotechnical analysis and empirical rock mass classification systems such as the Coal Mine Roof Rating (CMRR)6. Crushing is an integral portion for

17、mineral processing operations and is critical for the preparation of ore for downstream process for mineral processing opera- tions. Crushing of quarried rock is carried out in stages, with the primary crushing stage typically car- ried out using Jaw crusher and subsequent (secondary and tertiary).

18、From field observation, the greater the number of crushing stage, the higher the amount of fine produced as a proportion of total plant through- out. The type of crusher used also directly controls the amount of fines produced. A recent study of quarry fines looked at possible relationship between q

19、uarry plant operation and the generation of quarry fines7-8. 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 ea

20、ch 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/

21、ore materials. In practice, close size control of feed to mineral processing equipment is required in order to reduce the size ef- fect and make the relative motion of the particles se- paration dependent9. The particle size distribution of a material is important in understanding its physical and c

22、hemical properties. It affects the strength and load bearing properties of rocks. The easiest conven- tional method of determining mineral particle size is sieve analysis, where grain size is separated on sieve of different sizes/apertures using Sieve Shaker. Thus, the particle size distribution is

23、defined in terms of discrete size ranges and measured in micron (m). It is usually determined over a list of size ranges that covers nearly all the sizes present in the sample. Some methods of determination allow much narrower size ranges to be defined that can be obtained by use of sieves and are a

24、pplicable to particle sizes outside the range available in sieves. However, the idea of notional sieve that retains particles above a certain size and passes particles below that size is univer- sally used in presenting particle size distribution data of all kinds. The size distribution may be expre

25、ssed as a range analysis, in which the amount in each size range is listed in order of fineness of particles. It may also be presented in cumulative form in which the total of all sizes retained or passed by a single no- tional sieve is given for a range of sizes. Range analysis is suitable when a p

26、articular ideal mid-range particle size is being sought while cumulative analy- sis is used where the amount of under-size or over-size must be controlled. 2 Materials and method 2.1 Sample collection, preparation and testing The rock samples used for the investigation were obtained from different q

27、uarries in Nigeria. Dolomite, limestone and marble samples were collected from Edo State and granite rock samples from Ondo State, Nigeria. Five boulders of each rock type of dimension 90 cm50 cm50 cm were representatively selected from recently blasted portion of the rocks which were free from natu

28、ral defects, that is, discontinuities such as cracks, joints, fractures etc were packed properly to avoid damage during transportation. For the un- confined compressive strength test, the rock sample was cut into square shape with dimension of 60 mm60 mm with masonry saw and Vernier caliper was used

29、 to measure the dimension. Also, for the point load test, the rock samples were broken into irregular shape with sledge hammer. Vernier caliper was used to measure the diameter and length of irre- gular shaped rock samples from the different loca- tions. The mean value for length ad diameter was det

30、ermined The rock samples were prepared and tested in the laboratory to International Society for Rock Mechan- ics Standard for each strength test carried out using Masonry Saw Machine and Compression Testing Machine and Point Load Tester respectively10. The readings were taken and recorded. The size

31、 reduction of equal weighed of the rock samples was done using Laboratory Jaw Crusher and the particle size distribu- tion was carried out in notional set of sieves using Sieve Shaker. The crushing times were taken and recorded and the weights of samples retained on the sieves recorded for size dist

32、ribution. The rock sample were cut into square shape by using masonry cutting machine, the cut samples were smooth, free of abrupt irregularities and strength. Five specimen of each of the rock samples were tested and the failure load was recorded for each test as the failure was observed axially in

33、 the compressive testing machine. Some lumps of the different rock types were then crushed using the Laboratory Jaw Crusher and taken record of the crushing times. The screening of the crushed rock samples was carried out in a set of sieve using the Laboratory Sieve Shaker. The sieve was arranged in

34、 the order of decreasing aperture: 4700, 2000, 1700, 1180, 850, 600, 425, and 212 m by placing the sieve that has the largest opening at the top and the least opening at the bottom. A tight fitting pan or receiver was placed below the bottom sieve to receive the finest grained which is referred to a

35、s un- dersize. The crushed sample was placed on the top sieve and a lid was used to cover it to prevent escape of the rock sample during the process. The set of the sieve was then placed in a sieve shaker which vi- brates the sieve for proper screening. This operation Mining Science and Technology V

36、ol.20 No.2 206 was carried out on each of the rock sample for five minutes. This was achieved by using the automatic control timer of the sieve shaker. After the screening analysis, the retained sample on each sieve was measured on weigh balance and recorded to the cor- responding sieve opening size

37、. 3 Results and discussion Tables 16 are the results of unconfined compres- sive strength tests, crushing time and particle size distribution of the different rock samples while Figs. 1 and 2 are the plots of the compressive strength val- ues and the logs of the size distribution of the rock types r

38、espectively. Table 1 Results of unconfined compressive strength tests of rock samples Rock samples Mean UCS (MPa) Mean PLI (MPa) Marble 86.11 5.28 Dolomite 34.72 1.98 Limestone 81.94 3.68 Granite 125.00 8.61 Table 2 Results of crushing time of rock samples Rock samples Quantity crushed (kg) Crushing

39、 time (s) Marble 5 14.0 Dolomite 5 5.0 Limestone 5 11.0 Granite 5 21.0 Table 3 Results of particle size distribution of marble sample Sieve range (m) Nominal aperture (m) Sieve fraction Cumulative undersize (%) Cumulative oversize (%) logN logM Wt (g) Wt (%) +4700 4700 2420 40.33 59.67 40.33 3.68 1.

40、78 4700 +2000 2000 696 11.60 48.07 51.93 3.30 1,68 2000 +1700 1700 546 9.10 38.97 61.03 3.23 1,59 1700 +1180 1180 600 10.00 28.97 71.03 3.07 1.46 1180 +850 850 576 9.60 19.37 80.63 2.93 1.29 850 +600 600 610 10.17 9.20 90.08 2.78 0.96 600 +425 425 192 3.20 6.00 94.00 2.63 0.78 425 +212 212 140 2.33

41、3.67 96.33 2,33 0.56 212 220 3.67 Table 4 Results of particle size distribution of dolomite sample Sieve range (m) Nominal aperture (m) Sieve fraction Cumulative undersize (%) Cumulative oversize (%) logN logM Wt (g) Wt (%) +4700 4700 2340 39.00 61.00 39.00 3.68 1.79 4700 +2000 2000 830 13.83 47.17

42、52.83 3.30 1.67 2000 +1700 1700 380 6.33 40.84 59.16 3.23 1.61 1700 +1180 1180 410 6.83 34.01 65.99 3.07 1.53 1180 +850 850 190 3.17 30.84 69.16 2.93 1.49 850 +600 600 230 3.84 27.00 73.00 2.78 1.43 600 +425 425 280 4.67 22.33 77.67 2.63 1.35 425 +212 212 380 6.33 16.00 84.00 2.33 1.20 212 960 16.00

43、 Table 5 Results of particle size distribution of limestone sample Sieve range (m) Nominal aperture (m) Sieve fraction Cumulative undersize (%) Cumulative oversize (%) logN logM Wt (g) Wt (%) +4700 4700 4300 71.67 28.33 71.67 3.68 1.45 4700 +2000 2000 570 9.50 18.83 81.17 3.30 1.27 2000 +1700 1700 1

44、00 1.67 17.16 82.84 3.23 1.23 1700 +1180 1180 190 3.16 14.00 86.01 3.07 1.15 1180 +850 850 110 1.83 12.17 87.84 2.93 1.09 850 +600 600 130 2.17 10.00 90.01 2.78 1.00 600 +425 425 160 2.67 7.33 92.68 2.63 0.87 425 +212 212 245 4.08 3.25 96.76 2.33 0.51 212 195 3.25 OLALEYE B M Influence of some rock

45、strength properties on jaw crusher performance in granite quarry 207 Table 6 Results of particle size distribution of granite sample Sieve range (m) Nominal aperture (m) Sieve fraction Cumulative undersize (%) Cumulative oversize (%) logN logM Wt (g) Wt (%) +4700 4700 3800 63.33 36.67 63.33 3.68 1.5

46、6 4700 +2000 2000 940 15.67 21.00 79.00 3.30 1.32 2000 +1700 1700 118 1.97 19.03 80.97 3.23 1.28 1700 +1180 1180 210 3.50 15.53 84.47 3.07 1.19 1180 +850 850 160 2.67 12.86 87.14 2.93 1.11 850 +600 600 200 3.33 9.53 90.47 2.78 0.98 600 +425 425 170 2.83 6.70 93.30 2.63 0.83 425 +212 212 210 3.50 3.2

47、0 96.80 2.33 0.51 212 190 3.20 Note: logN and logM are the logs of sieve range and cumulative oversize (retained) respectively. 0 20 40 60 80 100 120 140 MarbleDolomiteLimestoneGranite UCS PLI UCS and PLI (MPa) Fig. 1 Plot of strength values of the rock samples LogM Fig. 2 Plots of logN against logM

48、 of the size distribution of the rock types The analysis of the tests results in Table 1 shows the mean Unconfined Compressive Strength values of 86.11, 34.72, 81.94 and 125.00 MPa for marble, do- lomite, limestone and granite respectively; and mean point load index of 5.28, 1.98, 3.68 and 8.61 MPa

49、for marble, dolomite, limestone and granite respectively. The crushing time of the rock samples as shown in Table 2 indicates 14.0 seconds for marble, 5.0 seconds for dolomite, 11.0 seconds for limestone and 21.0 seconds granite. From the results, it was ob- served that granite has the highest stren

50、gth value and crushing time while dolomite has the least of the val- ues. The compressive strength and crushing time fol- low an increasing trend and implies that the crushing time is directly proportional to the compressive strength of the rocks, that is, the harder the rock, the more the crushing

51、time under the impact of the jaw crusher. The general size distribution plot in Fig. 2 is the upward trend of each plot and the line variation of each plot is as a result of grain size retained on each sieve during the screen analysis. From the Figure, it would be observed that the size distribution

52、 of the weight retained and other parameters followed a sim- ilar trend, that is, there is a good correlation between the log plots of the rock samples. Also, this is an in- dication that size analysis of the products can be used to determine the optimum size of the feed to the process for maximum e

53、fficiency and to determine the size range at which much fine occur in the plant so that it can be minimized. The effects of rock strength on the crusher performance can be attributed to the stiffness of rock and also refer to the state of stress at which a rock specimen or rock mass element ruptures

54、. Rock strength generally influenced the performance of crusher in an aggregate quarry. The influence of rock strength based on the crushing time and size distribution affect crusher performance. Also, the strength parameters will indicate the rock type that has less influence on the crusher performance during crushing operation. 4 Conclusions In correlating the strength parameters of the rock types with the corresponding crushing times, the work revealed that the higher the strength value the higher the crushing of the rock under the influence of a crusher. Ac