ARTICLE

J. Cent. South Univ. (2019) 26: 1619-1636

DOI: https://doi.org/10.1007/s11771-019-4117-4

Factors affecting thin coal seam shearer drum coal-loading performance by a model test method

GAO Kui-dong(高魁东)^{1, 2}, XU Wen-bo(徐温博)¹, JIANG Shou-bo(江守波)¹, DU Chang-long(杜长龙)²

1. College of Mechanical & Electrical Engineering, Shandong University of Science and Technology,Qingdao 266590, China;

2. Jiangsu Key Laboratory of Mine Mechanical and Electrical Equipment, China University of Mining and Technology, Xuzhou 221116, China

Central South University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2019

Abstract: To solve the problem of a low coal-loading rate being exhibited by the drum shearer on Chinese thin coal seams, systematic tests and research were performed to study the pivotal factors’ influences on drum coal-loading rate using a model test method. The effects of the drum hub diameter, cutting depth, vane helix angle, drum rotation speed and hauling speed on drum coal-loading rate were determined under circumstances of coal-loading with drum ejection and pushing modes, and reasons for these phenomena were analyzed. The results indicate that the influence of the drum cutting depth on the drum coal-loading rate is the most significant. The parameters of hub diameter, drum rotation speed and hauling speed can influence the drum coal-loading rate by cutting the coals’filling rate in the drum. The parameters of vane helix angle and drum rotation speed can influence drum coal-loading rates by influencing the ratio of cutting coals’ tangential and axial speed in the drum. The coal-loading rate with drum ejection is clearly higher than that observed with drum pushing. Research in this study can provide support to design the drum structure and select drum operational parameters for a thin coal seam shearer.

Key words: thin coal seam; shearer; cutting; drum; coal-loading rate; model test

Cite this article as: GAO Kui-dong, XU Wen-bo, JIANG Shou-bo, DU Chang-long. Factors affecting thin coal seam shearer drum coal-loading performance by a model test method [J]. Journal of Central South University, 2019, 26(6): 1619-1636. DOI: https://doi.org/10.1007/s11771-019-4117-4.

1 Introduction

Since the 1980s, in order to improve coal mining range and make better use of coal resources, coal production enterprises in China have listed thin coal seams as their mining objects while being occupied in the mining of thick and medium-thick coal seams. In China, coal reserves on thin coal seams reach approximately 6150 Mt, which occupies approximately 20% of total coal reserves; mining yield on thin coal seams occupies approximately 10.4% of total coal mining yield [1–3]. In recent years, since coal resources on medium-thickness coal seam in certain mining areas in China have continuously reduced, input of Chinese coal production enterprises on thin coal seams has been increasing. Yield on thin coal seams has continuously increased. Such high coal mining yield on thin coal seams is usually achieved with drum shearers. As the main equipment used in coal mining at present, drum shearers have been widely applied to mining on thick, medium-thickness and thin coal seams in China. The drum is the main operating mechanism, and drum performance can directly influence mining efficiency and the reliability of the shearer.

Drum performance mainly includes cutting performance and coal loading performance. Recently, many scholars have performed research on drum cutting performance. SHEN et al [4] used acoustic emission techniques to study the relationship between coal crushing characteristics and pick cutting parameters. HEKIMOGLU et al [5] studied the relationship between the wrap angle of shearer drum vanes and drum cutting performance. These researchers noted that the cutting load was at the minimum when the slant angle of cutting pick on the drum was approximately 10°. QAYYUM [6] used an automated rotary coal cutting simulator (ARCCS) to study the difference in the specific energy consumptions of the drum under five different types of cutting picks. MISHRA et al [7, 8] used the finite element method and an ARCCS test-bed to study the influences of design of cutting pick and drum on heat transfer on the cutting pick, stress-bearing trend of the cutting pick, cutting specific energy consumption and absorbable dust. ZENG et al [9] established a theoretical model of the cutting pick and water jet while rock breaking, based on mining seepage catastrophe theory and confirmed optimal location parameters under the cutting pick and water jet while rock breaking through the test. REID et al [10] gave a prediction method of the drum cutting force based on an extended Kalman filter. DEWANGAN et al [11] focused on the analysis of the different wear mechanisms of conical picks in the coal cutting process and pointed out the main causes for failure of the cemented carbide head. et al [12] used the finite element method to establish a numerical model of coal cutting with a drum and constructed a mechatronic model of the drum driveline with a reference to simulation results of the drum cutting force. LIU et al [13] used theoretical calculation and test methods to study the influence rules of pick arrangements, helix angle, advancing velocity and the cutting line space on the size of coal fragments. SI et al [14] used five different recognition methods to perform drum cutting pattern recognition tests and the results certified that the least squares support vector machine coupled with improved fly optimization algorithm(IFOA-LSSV) method was the most effective. HUANG et al [15] used the finite element method to simulate rock cutting process under confining pressure and obtained influence of confining pressure on the cutting force. However, there are relatively few studies on the drum coal loading performance, and many research studies were conducted in the last century. PENG [16] gave several main factors influencing the drum coal-loading effect of the shearer. BROOKER [17] summarized research achievements of previous British scholars and obtained influences of structural and operating parameters for the drum on drum coal-loading performance and gave value ranges of parameters and their mutual relationships as well as a calculation method of the relevant structure parameters. Combining computer technology, MORRIS [18] gave a prediction model of coal-loading performance of the shearer drum under different working conditions. HURT et al [19] pointed out in their research that the main factors influencing the shearer drum coal-loading performance included the number of vane threads, helix angle, vane depth, size of coal-loading port and drum rotation speed. Using theoretical analysis and test methods, LUDLOW et al [20] pointed out that too large a wrap angle of the shearer drum would form circling coal and increase dust capacity, while too small a wrap angle was adverse for crushing coal to be conveyed on the scraper conveyer. Through underground tests, AYHAN et al [21] pointed out that the coal-loading effects of a conical drum hub were better than that of a cylindrical drum hub. BOOZ [22] designed a type of longwall shearer, which was applicable to mining thin hard coal seams, and this shearer operation technology and possible daily output achievement was introduced in his study in detail. In 2015, WYDRO [23] researched the influences of filling rate and coal plate on the transport rate of bulk coal with the help of a self-developed drum test bench for coal transport. In 2016, the coal loading process of a shearer was simulated by GOSPODARCZYK [24] using PFC3D, and the drum transport effect and coal particle movements under circumstances of cutting top coal, cutting bottom coal, with and without coal plate were studied. As coal resource mining in European and American countries does not involve or scarcely involves thin coal seams; the aforementioned research on drum coal loading performance mostly examines medium-thickness coal seam shearers. As the height of the shearer surface on the thin coal seam is low and the drum diameter is small, space for coal to pass through in the shearer body is small; the drum vane depth is shallow, and the drum coal-loading space is small, and the coal-loading rate of the drum shearer on thin coal seam is low. Moreover, the Chinese definition of a thin coal seam is somewhat different from that in European and American countries; thin coal seams defined in European and American countries mostly refer to coal seams with thicknesses smaller than 1.7 m, while those in China generally refer to coal seams with mining heights being smaller than 1.3 m. Hence, the heights of shearer surface on thin coal seams in China are lower, the drum diameter is smaller and the drum coal loading rate is lower, that is, less than 70%. The coal not conveyed onto the scraper conveyer becomes float coal on the machine road, which affects normal operation of the shearer and requires artificial clearing to ensure that labour intensity and working risks are not aggravated. Therefore, drum coal-loading rate becomes a key factor restricting the promotion and application of drum shearers on thin coal seams and improvement of thin coal seam productivity in China.

Chinese researchers have used theoretical analysis, analogue simulation, orthogonal simulation tests and other methods to perform research and make advances [25–27], but the following problems still exist: 1) Research from Chinese scholars mainly stresses the theoretical analysis of the shearer drum coal-loading performance with a lack of relevant experimental verification, meaning that great errors exist in shearer application; 2) recently, most research on drum coal-loading performance involves one factor influencing drum coal-loading performance without comprehensive consideration of all the main factors; 3) most model experimental research in China, at present, uses orthogonal tests with few influential factors being studied; these experimental research studies are implemented under one drum coal- loading form such that comparative conclusions of two coal-loading forms of the drum cannot be given. Therefore, with the help of a coal-rock cutting test-bed after transformation, an experimental method was used in this study to conduct detailed research on the influences of structural parameters (drum hub diameter, cutting depth and vane helix angle) and motion parameters (hauling speed and drum rotation speed) on the drum coal-loading rate. Two coal-loading modes, namely, coal-loading with drum pushing mode and ejection mode, were taken into consideration in this study.

2 Experimental design and its equipment

In terms of the shearer drum, the parameters influencing drum coal-loading performance are mainly the drum diameter, vane depth, cutting depth, vane helix angle, hauling speed and drum rotation speed. When the drum diameter is certain, vane depth is mainly influenced by the drum hub diameter; therefore, influences from drum hub diameter, cutting depth, vane helix angle, hauling speed and drum rotation speed on the drum coal-loading performance were taken as study objects in this study. Laboratory testing methods have been widely used in coal or rock cutting [23, 28], and laboratory model test methods will be adopted in our research, which is similar to the research of LIU et al [25]. Figure 1 shows the coal-rock cutting test-bed used in this test. It mainly consisted of a main drive system, auxiliary drive system, hydraulic control system, signal acquisition system and drum. Its cutting power was 30 kW, the range of rotation speed was 0–135 r/min and the hauling speed was 0–10 m/min. Figure 2 shows the drums used in this test, and Table 1 shows the main structural parameters of the drums. In Figure 2(a), the drum was mainly used to study the influence of cutting depth on drum coal-loading performance. The hub diameter of this drum was large, the vane depth was small, and its structure was the most similar to the drum structure used in present thin coal seam mining. Hub diameters of drums Figures (b), (c) and (d) were different, vane helix direction of Figure (d) drum was contrary to those Figures (b) and (c). Their other structural parameters were identical, and they together with Figure (a) drum were used to study the influence of the rules of drum hub diameter (vane depth) on coal-loading performance. The vane helix angles of drums in Figures (e), (f), (g) and (h) were different but their other parameters were identical, and they were mainly used to study the influence of the vane helix angle on drum coal-loading performance. In the test, structural parameters and installation angles of the cutting picks used by all drums were identical. The compressive strength of the prepared artificial coal wall was 1.06 MPa, the elasticity modulus was 102.4 MPa, the density was 1204.4 kg/m³ and the coefficient of volumetric expansion was 1.27.

Figure 1 Cutting test-bed

Figure 2 Test drums

Table 1 Structure parameters of drums

The test was mainly used to study influential rules of the drum structural parameters on drum coal-loading performance; therefore, the calculation of coal-loading rate was especially crucial. The test-bed used in the test was somewhat different from actual working environments of a shearer drum on thin coal seams; distribution of cutting coals after being loaded and transported could not be calculated according to real coal mining situations. Through systematic analysis, the statistical area of effective coal-loading capacity in the test was specially divided in order to reduce test errors. The effective coal-loading area started from the drum coal cutting side of the bearing pedestal in the hauling direction and from the coal wall edge in the axial direction of the drum (Figure 3(a)). The difference between this division method and actual situations lies in the negligence of the distance from coal exit to the middle trough of the scraper, but its advantage is that it reduced the statistical error caused by the difference in coal mass stacking at coal exit. Moreover, this division method also neglected coal quantity falling outside of the drum cutting depth from half of the rear side and float coal area at the rear side of the drums. The drum diameter of the shearer on the thin coal seam was small, and the thickness of the range arm was relatively large, and during the coal cutting and loading process of the front drum, coal output from half of the rear side of the drum and float coal from the rear side of the drum could not enter the scraper conveyer due to obstruction from range arm. Therefore, test results obtained through this division method were more approximate to working conditions of the front drum of the shearer. From the previous section, the test-bed after transformation could realize cutting feed at left and right sides of the drum and could simulate the process of coal-loading with drum ejection and pushing. Figures 3(b) and (c) show coal-loading modes with pushing and ejection modes, and it could be seen that the drum coal-loading mode was mainly decided by the rotary direction of the helix vane and direction of hauling speed.

3 Test results and discussion

3.1 Influence of drum hub diameter on drum coal-loading performance

Drum hub diameter is the main factor influencing the drum hub vane depth and drum coal-loading capacity and it is decided by the structure of the output end of the range arm. The study of the influential rule of drum hub diameter on drum coal-loading performance is of great significance for improving drum coal-loading rates and guiding the structural design of range arm. Therefore, four types of designed and researched & developed drums were used in this paper, as shown in Figuer 4(a). The coal-loading performances of the four types of drums were studied when drum rotation speed was 45 r/min and the cutting depth was 0.45 m. Figure 4(b) shows drum torques acquired by a test-bed data acquisition system under coal-loading with a drum ejection condition.Table 2 shows the coal-loading with drum ejection effects for the drums with four different drum hub diameters.

As shown in Figure 4(b), the rotation speeds of the four drums were identical; periods of fluctuations of torques generated by coal cut using the four drums were basically identical. However, their amplitudes were somewhat different. It could be seen from Table 2 that the average torques of the four drums were different. According to the drum coal cutting and loading process, the drum torque included cutting torque and loading torque. Although there is a number of cutting picks in the endplates, the number of cutting lines inside the cutting depth, the pick-line spacing of the vanes, the number of cutting picks on each cutting line, and the installation angle of cutting picks in corresponding position and structural size of the cutting picks for the four drums were identical. The circumferential angles between neighbouring cutting picks were different. Figure 5 shows a schematic diagram of the helix vane expansion, as it is only ensured in the design that the average helix angles of the vanes in the four drums were identical. The difference between the hub diameters of the drums would result in great differences for the vanes of the four drums with respect to the outer helix angle and inner helix angle. It could be deduced from Figure 5 that the outer helix angle α_y and inner helix angle α_g of the drums met the following:

                (1)

According to Eq. (1), the outer helix angle α_y and inner helix angle α_g could be obtained as:

 (2)

Figure 3 Two coal-loading modes:

Figure 4 Four different hub diameter drums (a) and torques of four different hub diameter drums (b) (coal-loading with drum ejection)

Table 2 Test results of coal-loading with drum ejection by four different hub diameter drums

Figure 5 Unfold scheme of drum helix vane (D_g—Drum hub diameter; D_i—Helix vane diameter; D_y—Mean diameter of helix vane; L_i—Length of vane; α_g—Inner helix angle of vane; α_i—Mean helix angle of vane; α_y—Outer helix angle of vane)

The drum vane diameter and drum hub diameter in the tests were substituted into Eq. (2), the inner helix angle and the outer helix angle values of the vanes in the four types of drums could be obtained as shown in Table 3.

Table 3 Inner and external helix angles of four different drum vanes

As the pick pedestal was welded at the outer vane edge, the circumferential angles of the cutting picks in the neighbouring cutting lines in the same vanes of the four drums would certainly be different, and consequently, the torque of the drum coal- loading under this test condition could not be independently separated out. In addition, according to the structure of the test drums, frequency components of the torque during the drum cutting and loading were mainly caused by installed eccentricity, vanes number and cutting picks number. The frequency component caused by the installed eccentricity was identical with the rotating frequency; the frequency component caused by the vanes was a product of rotating frequency and the number of vanes. The frequency caused by pick cutting was related to the number of cutting lines on the vanes, the number of picks on each cutting line, the circumferential angle between neighbouring picks on the same vane and the number of pick groups at the endplate. As cutting picks on the vanes in the four drums were sequentially arranged, and the number of vane picks on each cutting line was identical to the number of vanes, it is impossible to separate out the coal-loading torques of the drum vanes even with the frequency analysis method. The number of vanes for the four test drums used in the test was 2 and the drum rotation speed was 45 r/min. Thus, it could be observed that the rotating frequency of the drums was 0.75 Hz, and both the frequency caused by vanes and that caused by the cutting picks on the same cutting line were 1.5 Hz. Figure 6 shows the change curves of torques of the four drums after the frequency components ranging from 1 to 2 Hz were filtered. From the figure, the curves of the four drums after filtering did not have any special rule, which further demonstrated that it is difficult to study acting torques of the vanes through the frequency analysis method. It could be shown from the above analysis that due to the particularities of the shearer drum structure and its working mode, the coal-loading torques can not be separated out from the vane coal-loading and pick-cutting joint torques, and the research emphasis was laid on the coal-loading performance of the drum. Therefore, a detailed analysis of drum torques would not be made in a follow-up study.

Figure 6 Drum torque after filtering with different drum hub diameters:

Figure 7 shows the change in the drum coal-loading rate and the change of drum torque with drum hub diameter. It could be seen from Figure 7(a) that the drum coal-loading rate presented first a rising trend and then a declining trend as the drum hub diameter increased, and the torque presented an increasing trend. The drum coal-loading rate suddenly decreased by a large margin when the drum hub diameter was 240 mm, mainly because the volume of the coal cut from the artificial coal wall exceeded the quantity of coal that the drum could contain such that coal-blocking phenomenon appeared inside the drum, which influenced axial movement of the excavated coal. Hence, in order not to influence the drum coal- loading performance and increase the drum load, first it should be ensured that the coal blocking phenomenon would not happen to the shearer drum on the thin coal seam during its application.

Table 4 shows the test results of coal-loading with the drum pushing mode with four different drum hub diameters when the drum rotation speed was 45 r/min. From a comparison between Table 2 and Table 4, the coal-loading rate with drum pushing under the same conditions was obviously lower than that with the ejection, and coal-loading rate presented an increasing trend as the drum hub diameter increased. Figure 7(b) shows the influences of the drum hub diameter on the coal-loading rate and torque under drum pushing mode. It could be seen that the drum coal-loading rate had an increasingly smaller amplitude as the drum hub diameter increased. With a reference to the analysis of the influence of the drum hub diameter on coal-loading with drum ejection, it could be speculated that, under coal-loading with drum pushing conditions, the coal blocking phenomenon should appear when the drum hub diameter was 240 mm. However, it could be seen from Figure 7(b) that this phenomenon did not happen, mainly because under the coal-loading with drum pushing condition, some of the coal at the front of the drums would be easily carried to the rear side of the drums to reduce the loading quantity of coal mass in the drum coal cutting area. Then, there was enough space inside the drums to contain excavated coal mass, which guaranteed axial movement of the excavated coal. It could be seen from the change of torques with the drum hub diameter that coal-loading with drum pushing torque was obviously higher than coal-loading with drum ejection torque, which was mainly decided by the coal-loading form of the drum vanes and coal cutting form of cutting picks.

Figure 7 Influence of drum hub diameter on drum torque and coal-loading rate:

Table 4 Test results of coal-loading with drum pushing by four different hub diameter drums

3.2 Influence of drum cutting depth on drum coal-loading performance

The drum cutting depth generally refers to the drum mining depth and its value is smaller than the drum width. When the hauling speed of the shearer remains unchanged, the greater the drum cutting depth is, the higher the shearer’s mining efficiency becomes. As the diameter of the shearer drum on the thin coal seam at present is seriously restricted by the height of the coal seam, the cutting depths of most shearers on the thin coal seam are greater than the cutting depths of those at medium-thickness coal seams, ranging from 600 to 1000 mm. The cut and falling coal belong to the bulk materials whose stacking is related to their stacking space and stacking quantity. The reduction of the drum mining diameter and increasing of the drum cutting depth will degrade the coal-loading effect generated by crushed coal mass depending on its own stacking effect. As a result, the requirement of shearer on thin coal seam for drum coal-loading performance is more rigorous. Therefore, conducting a study of influence of the cutting depth on the drum coal-loading performance is of great significance to improve the shearer mining efficiency and guide the structural design of the shearer drum on the thin coal seam. To study the influence of the cutting depth on drum coal-loading performance, the drum coal-loading test was carried out when cutting depths were respectively 300, 350, 400, 450, 500, 550 and 600 mm, with the researched & developed drums (width of 650 mm, see Figure 8), and the nature of the coal wall was identical with the last section. The test results are shown in Table 5.

According to Table 5, the drum coal-loading rate basically presented a decreasing tend with the cutting depth, and the average torque of the drums basically presented a decreasing trend with the cutting depth. Figure 9(a), drawn according to Table 5, shows the change curves of the coal-loading rate and the torque with the cutting depth under coal-loading with the drum ejection condition, and these curves could more intuitively reflect the relationships between the cutting depth with coal-loading rate and torque. It could be seen from Figure 9(a) that the drum coal-loading rates were largely identical when the drum cutting depths were 0.3 m and 0.35 m and presented a decreasing trend at 0.4 m. It is possible that the main reason for this is that when this drum was used for cutting and cutting depth was within 0.35 m, which was small, the excavated coal in the tangential direction were already transported to the statistical area before being carried by the vanes to the rear side of the drum under this test condition so that coal-loading rate almost did not change; when the cutting depth was 0.4 m, a portion excavated coal already moved to half of the rear side of the drum in a tangential direction before moving to the statistical area in the axial direction. The coal became unloaded coal, and this phenomenon was more obvious as the cutting depth further increased. Also, because the cutting depth was >0.45 m, the drum would experience a coal blocking phenomenon, which hindered the drum rotation so that the drum coal-loading torque increased, and due to the increment of cutting torque itself, the total drum torque presented exponential growth.

Figure 8 Photo of 650 mm width test drum

The drum torque value was 1840.24 N·m, which was very close to the maximum torque of the output by the motor when the drum cutting depth was 0.6 m. According to the difference value between coal-loading with drum ejection and pushing modes in the torque values mentioned in the previous section, it could be seen that if coal-loading test in drum pushing mode with the cutting depth of 0.6 m was implemented, the cutting torque would exceed the maximum torque of the motor. To avoid the reappearance of the coal blocking phenomenon, the drum rotation speed in the test was set to 75 r/min to research the influence of cutting depth on coal-loading with drum pushing. Table 6 shows the test results of coal-loading with drum pushing.

Table 5 Influence of cutting depth on mean torque and coal-loading rate (coal-loading with drum ejection, rotation speed of 45 r/min)

Figure 9 Effects of drum cutting depth on drum torque and coal-loading rate:

According to Table 6, the change in the curves of influence from the drum cutting depth on the drum torque and coal-loading rate with drum pushing condition could be drawn. It could be seen from Figure 9(b) that the drum coal-loading rate presented a decreasing linear trend with the drum cutting depth, and the drum torque presented a nonlinear growth trend with the drum cutting depth. Figure 10 shows test pictures of coal-loading with drum pushing under 0.6 m cutting depth, and it could be seen from the figure that a large quantity of coal was carried to the rear side of the drum in area A, but only scarce coal was output in area B position.

3.3 Influence of vane helix angle on drum coal-loading performance

The vane helix angle is the most important parameter in the drum structure. From the above analysis, it can be seen that the vane helix angle not only influences the arrangement mode of drum picks but also influences the drum coal-loading performance. Studying the influence rules of the helix angle on the drum coal-loading performance is of great significance to guide the structural design of the drum and selection of working parameters. Figure 11(a) shows drums with four different vane helix angles used in this test; their drum hub diameter, vane diameter, drum diameter and drum width were identical, respectively 200, 420, 530 and 330 mm, and the cutting depth adopted in the test was 0.3 m. Table 7 shows the coal-loading rates of four types of drums during coal-loading with the drum ejection process when the rotation speed was respectively 45, 70 and 105 r/min.

Figure 11(b) shows the change curves of drum coal-loading rate with the vane helix angle under coal-loading with the drum ejection condition as drawn according to Table 7. It could be seen that when the drum rotation speed was low, the drum coal-loading rate increased with the vane helix angle, and it reduced with the vane helix angle when the drum rotation speed was high; the drum coal-loading rate basically presented as first increasing and then a decreasing trend with the drum rotation speed, except for the drum with a helix angle of 24°. It is known from Ref. [29] that the tangential speed and axial speed of the material under the effect of the helix vane increased with a vane helix angle. Therefore, under the low rotation speed in this test, the coal mass could obtain a high axial speed and tangential speed under the effect of the vane with the large helix angle so that the coal flow could obtain favourable output paths and the drum coal-loading rate could be slightly improved. However, as drum rotation speed continued to increase, the coal quantity fell when the drum rotated and the cut for one circle decreased and got smaller. The coal quantity inside the drum also decreased, and the centrifugal force borne by the coal mass increased. As the distance between the bearing pedestal and drum end was large, some of the coal was cast to the left side of the bearing pedestal at the drum exit under the effects of centrifugal force and vane tangential speed, but this side belonged to the non-statistical area. The coal located in this area was not within statistical range, therefore the drum coal-loading rate calculated in this test decreased with the drum rotation speed. Further, according to the analysis on the influence of drum hub diameter on coal-loading with drum ejection, it could be observed that the radial movement ability of the coal inside the drum was enhanced as the coal quantity inside the drum was reduced. A portion of the coal was cast to the pick position or the coal wall under the effect of centrifugal force. Under the interference of the pick pedestal, the new cutting coal and coal wall, the axial movement of coal flow was restricted, which was one of the reasons why the drum coal-loading rate decreased as the rotation speed increased. The greater the vane helix angle, then the greater the tangential speed of the drum and the greater the centrifugal force borne by the drum. Therefore, the drum coal-loading rate reduced as the vane helix angle increased under high rotation speed, which was rightly proved by the change rules of the three curves in Figure 11(b).

Table 6 Influence of cutting depth on mean torque and coal-loading rate (coal-loading with drum pushing, rotation speed 75 r/min)

Figure 10 Photo of coal-loading test with drum pushing (cutting depth 0.6 m)

Figure 11 Influence of drum vane helical angle on coal-loading rate:

Table 7 Influence of vane helical angle on coal-loading rate (coal-loading with drum ejection, cutting depth of 0.3 m)

Table 8 shows the coal-loading rates of four types of drums under coal-loading with drum pushing condition when the rotation speeds were respectively 45, 70 and 105 r/min. Figure 11(c) shows the change curves of the drum coal-loading rate with the vane helix angle under coal-loading with the drum pushing condition as drawn according to Table 8.

It could also be seen from Figure 11(c) that under coal-loading with the drum pushing condition, the drum coal-loading rate was reduced as the drum rotation speed increased, and the value of the difference between the drums with different helix angles in the coal-loading rate would increase with the drum rotation speed. Thus, it could be seen that when coal-loading with the drum pushing mode was adopted by the drum shearer on the thin coal seam, the drum rotation speed should not be too high, and the helix angle should be selected according to the actual situation of the drum. It is noteworthy that the results of this test were greatly different from test results in Ref. [26] also written by these authors, mainly because the two tests had a great difference with respect to the test method and statistical method. First, the full-drum cutting method was adopted in Ref. [26], but the cutting depth used in this test was smaller than the drum width, so the flow obstruction suffered by the coal mass at the exit of the drum cutting depth in this test was reduced. Second, there was a certain distance between the statistical area of the coal-loading quantity and coal wall in Ref. [26] (as shown in Figure 12); coal within this distance was not within the statistical range of Ref. [26] and the effective coal-loading quantity in this test included this part of the coal. This was the main reason for the great difference in results of the two tests.

Furthermore, it could be seen from the influence rules of the drum cutting depth and vane helix angle on the coal-loading rate that an inappropriate selection of drum structure parameters would result in significant degradation of the drum coal-loading rate. When drum cutting depth was large, the small helix angle or large average vane diameter could be selected to improve the drum coal-loading rate, but restricted by mining conditions on thin coal seam, the method of increasing the vane diameter was not applicable. Therefore, only the method of reducing the vane helix angle could be used to improve the drum coal-loading rate.

3.4 Influence of hauling speed on drum coal- loading performance

Drum hauling speed is an important factor influencing the shearer mining efficiency and it together with drum rotation speed influences the cutting torque and cutting efficiency of the drum. Under different hauling speeds, the coal cutting quantity of the drum within unit time will be different, which will influence the quantity of the coal mass filling inside the drum to influence the performance of drum coal-loading. To study the influence rules of the hauling speed on drum coal-loading performance, the drum, as shown in Figure 13(a), was used to carry out coal-loading with drum ejection and drum pushing tests. The cutting depth was set to 450 mm and the drum rotation speed was 45 r/min. The test results are shown in Table 9.

Table 8 Influence of vane helix angle on coal-loading rate (coal-loading with drum pushing, cutting depth 0.3 m)

Figure 12 Available zone scheme of loaded coal in Ref. [26]

The change curves of the drum torque and coal-loading rate, with hauling speed being presented in Figure 13(b), as drawn according to Table 9, show that the drum torque increases with the hauling speed under both of the coal-loading modes. The growth trend of coal-loading with drum ejection torque was approximately linear to growth while that of coal-loading with drum pushing torque was approximate to exponential growth. From Figure 13(b), drum coal-loading rate first presented an increasing trend and then a decreasing trend with the hauling speed under coal-loading with drum ejection situation and presented an increasing trend with the hauling speed under coal-loading with the drum pushing situation. When the hauling speed was small, coal quantity cut by picks using the coal-loading with drum ejection method was small; coal quantity inside the drum was small, and the arrangement of the coal mass in radial direction of the drum was relatively sparse. The ability of coal masses in overcoming centrifugal force was not strong and they would easily move towards the outer vane edge and then reach the pick position or coal wall, which was adverse to drum coal loading. As the hauling speed increased, the coal quantity inside the drum increased and the ability of the frictional force of the coal mass in the overcoming centrifugal force was enhanced such that the movement of the coal mass in the radial direction of the drum was reduced and the influence on the pick pedestal and coal wall was avoided. As the hauling speed continued to increase, the coal mining quantity within unit time was greater than the volume of the drum so that coal discharge was created and the drum coal-loading rate was degraded. Under the coal-loading with drum pushing situation, coal mass would generate movement under the effect of the drum vanes. First, vanes should generate pressure on the internal surface of stacked coal and the pressure transferred towards the exit of the drum, thus it could be seen that the best position in which vanes generated an axial driving effect on coal mass was at the first half of the drum. To reach this requirement, sufficient coal falling was needed inside the drum. As the rotation speed of the drums used in the test was low, there should be enough space inside the drum for coal loading, and these factors resulted in improvement of the drum coal-loading rate with hauling speed under coal-loading with the drum pushing situation.

Figure 13 Influence of hauling speed on drum torque and coal-loading rate:

Table 9 Influence of hauling speed on drum torque and coal-loading rate

4 Conclusions

1) Influence rules of the drum hub diameter, drum cutting depth, vane helix angle, drum rotation speed and hauling speed on the coal-loading rate with drum ejection and pushing modes are studied through a test method. The results of the study show that under the test conditions, the coal-loading rate with drum ejection presents a rising trend first followed by a descending trend with drum hub diameter, while the coal-loading rate with the drum pushing increases with drum hub diameter, and both largely present a decreasing trend with the drum cutting depth. The coal-loading rate with drum ejection increases with the vane helix angle under low rotation speed while decreasing with the vane helix angle as the drum rotation speed increases. The higher the drum rotation speed, the greater the decreasing amplitude of the coal-loading rate with drum ejection with a large helix angle; the coal-loading rate with drum pushing decreases as the drum vane helix angle and drum rotation speed increase. The higher the drum rotation speed, the more obvious the decreasing amplitude of coal-loading rate with drum pushing as the helix angle increases; the coal-loading rate with drum ejection presents an increasing trend first and then a decreasing trend with the hauling speed while the coal-loading rate with drum pushing increases with the hauling speed.

2) When the drum cutting depth is large, coal-loading with drum ejection should use vanes with a helix angle as small as possible to increase the ratio of axial velocity to tangential speed of coal mass to improve drum coal-loading rate. When coal-loading with the drum pushing mode is adopted, the quantity of coal stacked under vanes should be increased by increasing the drum hauling speed on the condition that enough vane depth is ensured to improve the drum coal-loading performance. In the thin coal seam mining process, the shearer should use the mining mode of coal-loading with a drum ejection of the front drum and coal-loading with the drum pushing to the rear of the drum as much as possible. Centrifugal force generated by coal mass with tangential movement of the vanes is one of the main factors influencing the drum coal-loading rate with drum ejection. When the drum rotation speed is high, the hauling speed should be increased as much as possible to increase the coal filling rate inside the drums and reduce radial movement generated by the coal mass under the effect of centrifugal force to ensure that no blocking phenomenon will occur inside the drums.

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(Edited by FANG Jing-hua)

中文导读

薄煤层采煤机滚筒装煤率影响因素的模化试验研究

摘要：针对中国薄煤层开采中滚筒采煤机装煤率低这一问题，本文利用模化试验的方法对影响滚筒装煤率的几个关键因素展开了系统的试验研究。通过试验获得了滚筒筒毂直径、截深、叶片螺旋升角、滚筒转速和牵引速度在抛射装煤和推挤装煤条件下对滚筒装煤率的影响规律，并分析了产生这些现象的主要原因。通过研究发现：滚筒截深对滚筒装煤率的影响最为显著；筒毂直径、滚筒转速、牵引速度通过影响滚筒内截落煤体的填充率而影响滚筒装煤率；叶片螺旋升角和滚筒转速通过影响滚筒内煤体的切向速度和轴向速度比值而影响滚筒装煤率；滚筒抛射装煤率要明显高于推挤装煤。上述研究结论能够为指导薄煤层采煤机滚筒的结构设计和运行参数选择提供帮助。

关键词：薄煤层；采煤机；截割；滚筒；装煤率；模化试验

Foundation item: Project(2012AA062104) supported by the National High Technology Research and Development Program of China; Project(51704178) supported by the National Natural Science Foundation of China; Project(ZR2017MEE034) supported by Natural Science Foundation of Shandong Province, China; Project(2018T110700) supported by China Postdoctoral Science Foundation

Received date: 2018-01-22; Accepted date: 2018-07-26

Corresponding author: GAO Kui-dong, PhD, Lecturer; Tel:+86-15954827709; E-mail:gaokuidong22@163.com; ORCID: 0000-0002- 8303-5991