英文文献翻译.docx

1、英文文献翻译Experimental results of a low-power roadheader driving a gallery with different types of rock at the faceAbstractIn this paper , the experimental results of a 45-kW and 15-t roadheader excavating a gallery with two different types of rock at the face using two different cutting heads are shown

2、. It is proved that the roadheader works properly with both cutting heads. In comparison with other results in the literature, the principal parameters, i.e. specific energy, cutting rate and tool wear, are at a level that can be considered satisfactory taking into account the low power of the roadh

3、eader. On the other hand, the influence of the number of picks, which is the main difference between the two cutting heads, on the operational parameters is shown.Keywords: Roadheaders; Cutting head design; Specific cutting energy; Cutting rate; Tool wear1. Test description1.1. Test objectivesThe ai

4、m was to determine the possibility of driving these galleries by means of a 45-kW roadheader, comparing two different cutting heads excavating the same type of rock in similar operating cycles. The main difference between the two cutting heads was the number of picks: the first cutting head had 36 p

5、icks, while the new one had only 24 (Fig. 5). Because of the lower number of cutting tools in contact with the rock, the torque transmitted by the motor was transformed to a larger tangential force in the pick, which allows higher -strength rock to be cut. Stress concentration is the major factor in

6、 rock fragmentation.The parameters to measure (according to classic studies on this theme; Fowell and McFeat-Smith, 1976;Gehring, 1989) are the cutting rate (volume of rock excavated per time unit in m/s), specific energy (energy necessary to excavate a unit of volume in MJ/m ) and the tool wear or

7、specific pick consumption (picks or pick mass lost excavating a unit of volume of rock in picks/mor g/m). All parameters were measured when the roadheader was excavating coal and rock, as well as when it was performing other parts of the cycle. 1.2. Description of the excavated face.The coal seam mi

8、ned by the sublevel caving method was vertical and its average thickness was2.0 m. With the aim of carrying out the test in the worst conditions, the test zone used was in an area with a seam thickness of less than 2.0 m. A three-segment steel set support was used, the gallery being of 2.50 m in wid

9、th at the low part and 3.0 m high. In Fig. 6 sketches of the excavated faces with the 36-pick (7.74 m ) and 24-pick cutting heads (7.97 m ) are shown. The coal seam was 1.70 and 1.90 m thick, respectively. It was formed by two veins: on the right the coal was soft (5 MPa), while on the left the coal

10、 was strong (1015 MPa) without rock between them. The left wall was of siltstone (sometimes sandstone) with a compressive strength of 60 MPa, fracture spacing of S 1015 cm and an RMR (Rock Mass Ratio, Bieniawski, 1976) value of approximately 3540. The SiOcontent in the rock was18% and the mean grain

11、 size 18. The Schimazek index was at an average value of F=0.194 N/mm. The right wall was also sandy siltstone, but more fractured and it broke because of the discontinuities rather than the pick action. Fig. 7 shows the roadheader and the gallery.1.3. Test and measurementsThe test for each of the t

12、wo cutting heads consisted of advancing 1.35 m (equal to the distance between steel sets) in three passes of 0.45 m each, since this was the dimension of the cutting head. While the road- header was excavating, the instantaneous power and other electrical parameters were recorded by means of a data

13、logger . In each case, the cross-section was measured and the excavated volume was calculated in order to determine the energy consumption and tool wear. All the picks were changed for new ones in each test and were weighed before and after the trial in order to determine the tool consumption during

14、 excavation. The pick mass lost in each test is more realistic than the number of picks changed for a longer period, because many picks can be lost due to other causes. The operating method was as follows: in the first pass (cutting the first 0.45 m) the different types of rock were cut separately;

15、after this, the next two passes were carried out as in a typical cycle in the mine. Thus, the results for the two cutting heads could be compared in the ideal case, in which rock was cut separately, or in the other case of a more realistic excavation. Information about the cutting of two coal veins

16、and the left rock wall can be obtained from the first pass. The resultsfor cutting of the right rock wall were less interesting because of its tendency to fall down due to discontinuities, which made its excavation easier.1.4. Tese with 36-pick cutting headThe record of the instantaneous power consu

17、mption during the complete trial with the 36-pick cutting head is shown in Fig. 9.The total-interval average power is approximately 35kW (less than the nominal power of the motor),although there are periods of 2-3 s during which values of 60 kW, representing an overload of more than 30%, are reached

18、. Moreover, peaks of 100 kW are also observed. However, these peaks, produced when a pick hits on a hard rock zone, areinstantaneous and are not significant. The cycle started with cutting of the soft coal vein, working from top to bottom. This is common, because the first cut is the most difficult

19、one due to the rock being more confined, and thus the soft rock is selected for starting the operation.This first cut then allows easier excavation of the other parts of the face, starting with the right rock wall, followed by the hard coal vein and finishing with the left rock wall.When the cutting

20、 head is working, two different parts can be observed in the recording. One, for which high power is required, corresponds to the typical cutting operation (the head is against the face, cutting a significant volume of rock), the results of which are easy to compare in different tests. The other par

21、t corresponds to periods during which the head is carrying out other operations that require lower power. In this case, the results are not easily comparable because the power is only slightly higher than the power required for head rotation. These operations involve, for example, moving waste to he

22、lp the conveyor work, attacking local points without excavating a significant volume of rock in order to give the final gallery profile, or moving the machine arm without contacting the face (in this case, head rotation is the only movement).These operations are developed according to the conditions

23、 and can be carried out during excavation of part of the face, or after excavating the complete section. In this study, the power consumption in cutting and other operations has been evaluated separately.The new 36 picks placed on the cutting head weighed 30 017 g before the trial and 30 001 g after

24、wards, i.e. the overall mass loss was16 g.1.5. Test with new 24-pick cutting head.The complete power record of the 24-pick head test is shown inFig.10.The average power for the complete period is similar to the other case, 35 kW, but the time spent at work is less (30 vs. 35 min, without computing s

25、top periods).It can also be observed that the overloads endure for a longer time.In this case, the excavation cycle was slightly different, having worked the right rock wall in two phases: the first after excavating the soft coal vein and the second at the end of the cycle, when the final gallery pr

26、ofile was cut. The 24 new picks weighed 19 985 g before the trial and 19 961 afterwards, i.e. mass loss was 24 g.2. Results2.1 Tool wear (pick conumption)In this trial it was not possible to determine directly the pick consumption, because no pick was totally worn when cutting this small volume of r

27、ock. Nevertheless, the mass loss during the test allows us to estimate the rate at which one head would wear out a larger number of picks than the other. The results are shown in Table5.From Table 5 it is inferred that the tool consumption would be approximately 45% greater using the 24-pick head co

28、mpared to the 36-pick head.Taking into account the pick weight (approx. 833 g) and assuming that it is not useful after losing 510%of its mass, then consumption of 1.53 and 2.23 g/m is equivalent to 0.0360.018 and 0.053-0.026 picks/m, in accordance with other published results (when the specific ene

29、rgy required is 1015 MJ/m, tool consumption of 0.0400.050 picks/mis common ). These results are in accordance with the day-to-day work of this roadheader: the number of tools lost is nearly 45% greater with the 24-pick head than with the 36-pick head, as shown in Table 6.This level of pick wear is h

30、igh compared to soft mineral excavation (mining potash, Ortega, 1996, or mining coal, Bermudez, 1995). Nevertheless, it is not excessive in the case of excavating rock (Anon., 2000), which demonstrates againthat it is possible to use this kind of roaheader in advancing this type of gallery.3. Conclu

31、sionsFrom the tests carried out and from experiences in the mine, the following conclusions can be inferred: Analysing only the excavation of rock (the most critical material), the cutting rate using the 24-pick head is approximately 1020% greater than for the 36-pick head and the specific energy is

32、 clearly lower. Analysing a normal working cycle, in which the complete face is excavated, the cutting rate reached with the 24-pick head is 20% greater, with less specific energy needed. One disadvantage is that cutting tool consumption is 4050% greater with the 24-pick head. Another disadvantage observed, for which the effectswere not quantified, is the greater level of vibrations in the roadheader.In general, the use of a head with a lower number of picks would involve a balance between greater advancement in the rock and greater pick consumption. In the cas