Method for caving top coal in front of coal face frame

Abstract

The invention belongs to the field of coal mining, and particularly discloses a coal mining method for caving top coal in front of a coal face frame, which comprises the following steps of: S1, extending a telescopic beam to a coal wall support top plate, paving a metal net along a coal wall, and binding and connecting the metal net with a hydraulic support side protection plate to form a metal net false top; s2, a hydraulic support side protection plate above a front roller of the coal mining machine is contracted in advance, a coal seam at the bottom of the working face is cut according to the mining and caving ratio, and a coal caving opening is located at the front end of a hydraulic support telescopic beam; s3, the top coal seam is slowly released to a scraper conveyor to be conveyed out under the shielding action of a metal net and a hydraulic support side protection plate by stretching out and retracting a hydraulic support telescopic beam front and back; the coal discharging port is located in front of the support, top coal is slowly discharged to the scraper conveyor to be conveyed out from the side protection plate in front of the telescopic beam under the shielding effect of the laid metal net false roof, and the method has the advantages of being high in coal resource recovery rate, simple in construction organization and high in hydraulic support applicability.

Description

Technical Field

[0001] The present invention belongs to the field of coal mining, and particularly relates to a top coal caving mining method in front of the support in a coal mining face. Background Art

[0002] With the continuous development and utilization of coal resources in China, improving coal recovery efficiency, reducing production costs and ensuring production safety have become the focus of attention in the coal industry. As the main mining method for thick coal seams, top coal caving mining has the characteristics of high-efficiency mining, strong adaptability, high cost-effectiveness, etc., and has been widely used in the coal seam mining of mines in China.

[0003] At present, the rear coal caving technology in the fully mechanized caving face is generally adopted, that is, a scraper conveyor is installed at the rear end of the hydraulic support. As the working face advances, the coal seam at the top of the support naturally breaks under the action of mine pressure or artificial loosening blasting, and the broken coal is discharged from the coal discharge port behind the support and transported out through the scraper conveyor.

[0004] However, in actual application, due to the limitation of the rear space, there are particularities and complexities such as large coal dust which is easy to cause fires, insufficient fragmentation of the top coal resulting in reduced extraction rate, high requirements for equipment performance, and high equipment investment cost. Therefore, the top coal caving technology in front of the support in the working face is proposed in this paper to improve the top coal caving recovery efficiency in the working face, and thus meet the production requirements of high yield, high efficiency and safety. Summary of the Invention

[0005] The purpose of the present invention is to provide a top coal caving mining method in front of the support in a coal mining face to solve the problems of particularities and complexities in the traditional top coal caving mining technology, such as large coal dust which is easy to cause fires, insufficient fragmentation of the top coal resulting in reduced extraction rate, high requirements for equipment performance, and high equipment investment cost, as mentioned in the above background art.

[0006] To achieve the above purpose, the present invention provides the following technical solutions:

[0007] A top coal caving mining method in front of the support in a coal mining face, comprising:

[0008] S1. In the mining preparation stage, retract the rib protection plate of the hydraulic support, extend the telescopic beam to the coal wall to support the roof, then lay a metal mesh along the coal wall, and tie and connect the metal mesh with the rib protection plate of the hydraulic support to form a metal mesh false roof;

[0009] S2. In the mining stage, along the running direction of the shearer, contract the rib protection plate of the hydraulic support above the front drum of the shearer in advance, and then cut the bottom coal seam of the working face according to the mining and caving ratio. The hydraulic support follows the shearer to move the support and push the scraper conveyor, so that the coal discharge port is located at the front end of the telescopic beam of the hydraulic support;

[0010] S3. During the coal caving stage, extend the rib protection plate of the hydraulic support behind the shearer to closely adhere to the coal wall. By extending and retracting the telescopic beam of the hydraulic support forward and backward, the top coal seam is slowly released under the cover of the wire mesh and the rib protection plate of the hydraulic support and transported out by the scraper conveyor.

[0011] Preferably, the wire mesh is composed of double-layer wire mesh and steel wire ropes. After laying one row of the wire mesh, hang the steel wire ropes. Two steel wire ropes are laid on each row of the wire mesh, and the steel wire ropes and the wire mesh are tied and tightened with iron wires, and then the laying work of the next row of the wire mesh is carried out until the wire mesh and the steel wire ropes are laid in place on the entire mining face.

[0012] Preferably, the wire mesh is 2000 mm long, 800 mm wide, with a mesh size of 20 mm×20 mm, and the spacing of the steel wire ropes is 400 mm.

[0013] Preferably, the wire mesh and the rib protection plate of the hydraulic support are connected by tying with iron wires.

[0014] Preferably, the moving step distance of the hydraulic support following the shearer is 800 mm, the scraper conveyor is pushed 15 m behind the moving of the support, and the scraper conveyor is sequentially pushed after the support is moved.

[0015] Preferably, after cutting the bottom coal seam of the cutting working face, the coal caving operation is carried out at a position 10 - 15 m behind the rear drum of the shearer. If the scraper conveyor stops running, the coal caving operation is synchronously stopped.

[0016] Preferably, when the coal seam is thick and the hardness of the roof structure is high during the coal caving stage, the hydraulic support is repeatedly lifted and lowered to collapse and break the top coal and release it. When the top coal is emptied until gangue appears, the telescopic beam of the hydraulic support is extended to maintain the coal rib and roof. After the coal caving is completed, the end face distance is not greater than 200 mm.

[0017] Preferably, the formula for the mining - caving ratio is as follows:

[0018] h1 = h2(k s - 1)

[0019] Wherein, h1 is the mining height, obtained according to the diameter of the shearer drum; h2 is the height of the top coal, with the unit of m; ks is the coal seam loose coefficient, taking 1.2 - 1.3.

[0020] Preferably, the calculation formula for the load of the hydraulic support is as follows:

[0021]

[0022] Wherein, M1 is the thickness of the top coal, with the unit of m; γ1 is the bulk density of the coal seam; γ is the bulk density of the rock stratum, with the unit of kN / m3; Σh is the thickness of the immediate roof, with the unit of m; L is the periodic weighting interval, with the unit of m; H is the thickness of the first caving of the main roof, with the unit of m; l is the roof control distance, with the unit of m.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] In the present invention, the coal discharge opening is located in front of the support, that is, on the telescopic beam. Under the cover of the false roof made of metal mesh, the top coal is slowly discharged from the rib protection plate in front of the telescopic beam to the scraper conveyor for transportation. It has the characteristics of high recovery rate of coal resources, simple construction organization, and strong applicability of hydraulic supports. It reduces the engineering quantity of production systems such as construction transportation lanes, return air lanes, and cutting eyes during the slicing mining of traditional thick coal seams and the re-cementation time of the lower slice roof, reduces production costs, and improves production efficiency; since one less scraper conveyor is installed behind the support, the difficulty of equipment management is reduced; at the same time, the top coal is discharged from in front of the support, making it easier to control the fragmentation and discharge of the top coal and avoiding the risks existing in the operation behind the support; using the supported shield type hydraulic for top coal caving mining operations can not only be used in a single longwall coal mining face, but also in top coal caving faces, increasing the applicability of the support and saving equipment investment costs for mining enterprises.

[0025] By analyzing the relevant technical parameters of top coal caving in front of the support, the present invention obtains a reasonable top coal caving height and mining-drawing ratio, and adopts the single-wheel sequential coal discharging method. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for description in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts. Among them:

[0027] Figure 1 is the overall structural schematic diagram of the mining stage of the present invention;

[0028] Figure 2 is the structural schematic diagram of the coal discharging stage of the present invention;

[0029] Figure 3 is the mechanical structural schematic diagram for calculating the load of the hydraulic support of the present invention;

[0030] Figure 4 is the pressure monitoring diagram of the hydraulic support of the present invention.

[0031] In the figure: 1. Hydraulic support; 2. Metal mesh; 3. Rib protection plate; 4. Telescopic beam; 5. Shearer; 6. Scraper conveyor. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] In order to make the above objects, features, and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention will be made in conjunction with the drawings in the specification.

[0033] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, the present invention may be practiced in other ways than those specifically described herein, and those skilled in the art can make similar extensions without departing from the spirit of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0034] Secondly, the so-called "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation manner of the present invention. The phrase "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor is it an individual or alternative embodiment that is mutually exclusive with other embodiments.

[0035] As shown in the attached Figure 1 to the attached Figure 4 as follows:

[0036] Embodiment 1:

[0037] A certain mine has a production capacity of 4 million tons per year. The main mined coal seam is the 17# coal seam. The fully mechanized mining face has a buried depth of 163 - 256 m, a coal seam thickness of 2.3 - 18.7 m, an average thickness of 10.6 m, an inclination angle of 12° - 23°, and an average inclination angle of 17°. The strike length of the working face is 489 m, the length of the open-off cut is 122 m, and the mining height is 3 m. The coal seam structure is simple, with 0 - 2 layers of parting, and it is a relatively stable coal seam, and most of it is recoverable. The lithology of the roof and floor is shown in Table 1.

[0038] Table 1 Lithology of the roof and floor of the working face

[0039]

[0040]

[0041] This embodiment provides a top coal caving mining method in a coal mining face, including:

[0042] S1. In the mining preparation stage, retract the rib protection plate 3 of the hydraulic support 1, extend the telescopic beam 4 to the coal wall to support the roof, and then lay a metal mesh 2 along the coal wall and tie and connect the metal mesh 2 with the rib protection plate 3 of the hydraulic support 1 to form a false roof of the metal mesh 2, as Figure 1 shown;

[0043] Specifically, the metal mesh 2 is composed of a double-layer wire mesh and steel wires. After laying one row of wire mesh, hang the steel wires. Two steel wires are laid on each row of wire mesh, and the steel wires and the wire mesh are tied and tightened with iron wires, and then the laying work of the next row of wire mesh is carried out until the wire mesh and steel wires of the entire mining face are laid in place.

[0044] Specifically, the wire mesh is 2000 mm long, 800 mm wide, with a mesh size of 20 mm × 20 mm, and the wire rope spacing is 400 mm.

[0045] Specifically, the wire mesh 2 and the rib protection plate 3 of the hydraulic support 1 are tied and connected by double hoop 12# iron wire.

[0046] S2. During the coal mining stage, along the running direction of the shearer 5, contract the rib protection plates 3 of 3 - 5 hydraulic supports 1 connected with the wire mesh 2 above the front drum of the shearer 5 in advance. Then, cut the bottom coal seam of the working face according to the mining - caving ratio. The hydraulic support 1 follows the shearer 5 to move the support and push the scraper conveyor, so that the coal discharge opening is located at the front end of the telescopic beam 4 of the hydraulic support 1.

[0047] When the shearer 5 cuts coal, it cuts triangular coal at the upper and lower ends and performs an oblique cutting feed. The oblique cutting length is not less than 30 m. It cuts coal back and forth for two passes; the drum cutting depth is 800 mm, the drum diameter is 2.0 m, the applicable mining height is 1.5 - 3.5 m, the cycle progress is 0.8 m, and the shearer 5 uses the spiral blade of the drum to automatically load coal. The support moving lags behind the rear drum of the shearer 5 by 3 - 5 supports, the support moving step is 800 mm, and the support is moved in the way of moving with pressure and rubbing the roof. After the support moving is completed, ensure that the support engineering quality standard meets the requirements of the operation regulations. After the support moving, the scraper conveyor 6 is pushed in sequence. The scraper conveyor pushing lags behind the support moving by 15 m, the bending section length shall not be less than 30 m, the pushing step is 800 mm, and the scraper conveyor is pushed in sequence to avoid opposite - direction operation.

[0048] S3. During the coal caving stage, extend the rib protection plate 3 of the hydraulic support 1 behind the shearer 5 to closely adhere to the coal wall. By extending and retracting the telescopic beam 4 of the hydraulic support 1 forward and backward, the top coal seam is slowly discharged under the protection of the wire mesh 2 and the rib protection plate 3 of the hydraulic support 1 to the scraper conveyor 6 for transportation, as Figure 2 shown. At this time, a coal cutting and coal caving cycle is completed.

[0049] During the coal caving operation, extend the telescopic rib protection beam 4 with the wire mesh hung, make the rib protection plate 3 closely adhere to the coal wall, and through repeatedly extending and retracting the telescopic beam 4, the top coal seam is broken under the action of the mine pressure and discharged from the front of the rib protection plate 3.

[0050] Specifically, after cutting the bottom coal seam of the working face, the coal caving operation is carried out at a position 10 - 15 m away from the rear drum of the shearer 5. If the scraper conveyor 6 stops running, the coal caving operation is stopped synchronously.

[0051] The coal caving method is to carry out coal caving for every pass of coal cutting.

[0052] Specifically, when encountering a relatively thick coal seam and a high - hardness roof structure during the coal caving stage, repeatedly raise and lower the hydraulic support 1 to collapse and break the top coal and discharge it. When the top coal is emptied until gangue appears, extend the telescopic beam 4 of the hydraulic support 1 to maintain the coal rib and roof. After the coal caving is completed, the end face distance is not greater than 200 mm.

[0053] When the coal seam is relatively thick and the hardness of the roof structure is high, it will prevent the coal from being released. At this time, the top coal is collapsed and broken by repeatedly raising and lowering the hydraulic support 1 and then released. During the coal caving process, the situation of coal gangue gushing out is observed at all times. When the top coal is emptied until gangue appears, the telescopic beam 4 is extended to timely maintain the coal rib roof and ensure its integrity.

[0054] In the fully mechanized mining face, the MG500 / 1170-WD1 shearer 5 is used to cut coal, and the SGZ-800 / 800 double-strand scraper conveyor 6, SZZ764 / 315 loader, PLM1000 crusher, and DSJ-100 / 2×75 belt conveyor are used to transport coal. The ZY6000 / 15 / 35D shield electro-hydraulic control hydraulic support 1 is used to support the roof. This fully mechanized mining system mainly consists of the electro-hydraulic control system of the hydraulic support 1, the video monitoring system, the electric control system of the shearer 5, the centralized control system of the three-machine pump station, and the gateway centralized control system. After using this system, in the fully mechanized mining face, during the normal coal mining production process, the shearer 5 mainly performs memory cutting with manual intervention as a supplement; the hydraulic support 1 mainly follows the shearer 5 to perform automatic actions with manual intervention as a supplement; the fully mechanized mining transportation equipment mainly performs centralized automatic control with local control as a supplement; the fully mechanized mining equipment mainly performs data monitoring with video monitoring as a supplement; that is, an automated production mode of "mainly automatic control of the working face with manual intervention control as a supplement" is achieved, and safe and efficient mining with fewer people at the working face is achieved.

[0055] The ZY6000 / 15 / 35D shield hydraulic support 1 adopts a partial electro-hydraulic control operation mode, which can realize self-frame, adjacent-frame or skip-frame control. One hydraulic support 1 serves as a coal caving port. After the shearer 5 cuts the bottom coal, the coal caving work is carried out at a position 10 - 15 m away from the rear drum. If the scraper conveyor 6 stops running, the coal caving operation needs to be stopped in time. The coal caving method is to cut and cave coal once for each pass.

[0056] Example 2: This example is basically the same as the previous example. The difference is that the coal output in the fully mechanized top coal caving mining face consists of two parts: the coal cutting amount of the shearer 5 and the top coal caving amount. The release of the top coal utilizes the action of mine pressure to loosen, break and naturally collapse the top coal, and it is released by its own weight. A certain space is required during the release process. Therefore, a reasonable proportional relationship needs to be determined between the mining height and the top coal height to improve the coal recovery rate. Increasing the mining height can increase the coal cutting amount of the shearer 5, increase the mining-to-caving ratio, and is beneficial to the collapse and release of the top coal, but it intensifies the manifestation of mine pressure, makes the stability of the support worse, and is not conducive to roof management; reducing the mining height improves the stability of the support, but it will reduce the release space of the top coal, and the top coal cannot be fully recovered. The reasonable mining height h1 and the top coal height h2 should conform to the following formula.

[0057] The mining-to-caving ratio formula is as follows:

[0058] h1 = h2(ks -1)

[0059] Among them, h1 is the mining height, obtained according to the drum diameter of the shearer 5; h2 is the height of the top coal, with the unit of m; ks is the coefficient of loose coal seam, taking 1.3.

[0060] Calculation shows that the height of the top coal is 8 m and the mining-drawing ratio is 1:3.

[0061] In the support system composed of the support, the top coal and the immediate roof, the support controls the top coal so that the pressure of the immediate roof is transmitted to the support through the top coal. During the process of pressure transmission, the roof also moves, deforms and fails accordingly. The fragmentation of the top coal is accompanied by the expansion and penetration of the original coal seams. The cracks in the top coal start from the peak area of the abutment pressure in front of the coal wall. Under the action of the abutment pressure, the top coal undergoes shear and tensile failures, and new cracks are generated due to the expansion of the original cracks. As the working face advances, the roof rotates and subsides. The coal body cut by these new cracks and weak joints is in a plastic state under the action of the mining stress field. When the top coal enters above the support and loses the lateral constraint, it will gradually collapse under the action of the roof pressure and the self-weight of the top coal, and accumulate above the support or on the shield beam to form a loose body.

[0062] The displacement of the top coal reflects the degree of fragmentation of the top coal. A large displacement indicates that the top coal is fully fragmented with small fragmentation size and is easy to be discharged, while a small displacement indicates that the top coal is not fully fragmented. As the distance from the working face gets closer, the displacement of the top coal gradually increases. In the initial stage of the top coal movement, the horizontal displacement is the main one. As the working face continues to advance, the vertical displacement gradually increases. Above the working face support, the vertical displacement exceeds the horizontal displacement, which varies according to the hardness coefficient of the coal seam. For soft coal, it is near the front of the coal wall, while for hard coal, it is 0.5 - 1 m behind the coal wall.

[0063] Regarding the top coal and the immediate roof strata above it as the immediate roof, after being affected by the advanced abutment pressure in front of the working face, the immediate roof is in a plastic state. The immediate roof above the support fractures along the coal wall, and the other end rotates and subsides and touches the gangue in the goaf. Therefore, the magnitude and load distribution of the support force depend on the overall mechanical properties of the immediate roof and its interaction with the support.

[0064] The number of dirt bands in the top coal of the fully mechanized mining face is 0 - 2 layers, showing muddy strip shapes, with a thickness of 200 - 300 mm. The caving index is 0.61 - 0.8, belonging to a coal seam with general caving property. The roof is siltstone mudstone, belonging to Class III moderately stable strata. After the previous cycle of operation, due to the relatively thin main roof, the main roof above it can collapse in layers, forming a "rock - gangue" transfer beam structure in a semi - arch caving state, as Figure 3 shown; at this time, the load transfer of the support load is the load of the top coal and the immediate roof transferred to the support, as shown in the following formula.

[0065] Specifically, the load calculation formula of the hydraulic support 1 is as follows:

[0066]

[0067] Among them, M1 is the thickness of the top coal, with the unit of m; γ1 is the bulk density of the coal seam; γ is the bulk density of the rock stratum, with the unit of kN / m3; Σh is the thickness of the immediate roof, with the unit of m; L is the periodic weighting interval, with the unit of m; H is the thickness of the first caving of the main roof, with the unit of m; l is the roof control distance, with the unit of m.

[0068] Support test: According to the mine pressure observation results of the working face of this mine, it can be known that the periodic weighting interval L of the working face is 15 m, the thickness H of the first caving of the main roof is about 5 m, the roof control distance l is 6.3 m, the thickness M1 of the top coal is 7 m, the thickness Σh of the immediate roof is 3 m, the bulk density γ1 of the coal seam is 14.2 kN / m3, and the bulk density γ of the rock stratum is 25 kN / m3. Substituting the actual observation data of the above working face into the formula for calculation, the support load P is 351.2 kN / m2.

[0069] The ZY6000 / 15 / 35D shield type caving hydraulic support 1 is adopted in this working face, and its rated parameters are the support area of 6.75 m2 per support, the working resistance of 6000 kN, and the initial support force of 5064 kN. When the working face is under pressure, the measured average working resistance is 2665 kN per support, and the calculated working load of the support is 2792 kN per support, which is 55% of the rated initial support force. Therefore, when the caving coal mining operation is carried out, the support can effectively control the roof and meet the requirements of stability and support safety.

[0070] Result analysis: The fully mechanized caving coal mining method with pre-mining caving in the fully mechanized mining face has been normally mined and completed. From the construction effect, in the process of coal caving, except for the relatively large coal dust in the working face, the top coal has been effectively broken and recovered, and the manifestation of mine pressure in the mining process has been significantly reduced, and the on-site application effect is remarkable;

[0071] During the mining period, the pressure of the hydraulic support 1 was monitored, as Figure 4 shown. The results show that the maximum pressure value of the support reaches 31.3 MPa, the minimum pressure value is 24.2 MPa, and the average pressure value is 27.7 MPa. The pressure change is not large and is overall stable. It can be seen that there is no large-area pressure coming in the roof, and the support effectively controls the roof, ensuring the normal mining of the working face.

[0072] Importantly, it should be noted that the construction and arrangement of the present application shown in multiple different exemplary embodiments are merely illustrative. Although only a few embodiments are described in detail in this disclosure, those who refer to this disclosure should easily understand that many modifications are possible without materially departing from the novel teachings and advantages of the subject matter described in this application (e.g., changes in the dimensions, scales, structures, shapes and proportions of various elements, as well as parameter values (such as temperature, pressure, etc.), installation arrangements, use of materials, colors, orientations, etc.). For example, an element shown as integrally formed may be composed of multiple parts or elements, the position of the element may be inverted or otherwise changed, and the nature, number or position of discrete elements may be altered or changed. Accordingly, all such modifications are intended to be included within the scope of the present invention. The order or sequence of any process or method steps may be changed or reordered according to alternative embodiments. In the claims, any "means plus function" clauses are intended to cover the structures that perform the recited function herein, and not only structural equivalents but also equivalent structures. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the exemplary embodiments without departing from the scope of the present invention. Therefore, the present invention is not limited to specific embodiments, but extends to various modifications that still fall within the scope of the appended claims.

[0073] In addition, in order to provide a concise description of the exemplary embodiments, all features of the actual embodiments may not be described (i.e., those features that are not relevant to the currently contemplated best mode of carrying out the present invention or those features that are not relevant to the implementation of the present invention).

[0074] It should be understood that in the development of any actual implementation, as in any engineering or design project, numerous specific implementation decisions may be made. Such development efforts may be complex and time-consuming, but for those of ordinary skill in the art who benefit from this disclosure, without undue experimentation, such development efforts will be a routine task of design, manufacturing and production.

[0075] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention may be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A coal caving mining method in front of the support in a coal mining face, characterized in that, Including: S1. In the mining preparation stage, retract the rib protection plate of the hydraulic support, extend the telescopic beam to the coal wall to support the roof, then lay a metal net along the coal wall, and tie and connect the metal net with the rib protection plate of the hydraulic support to form a false roof of the metal net; S2. In the mining stage, along the running direction of the shearer, retract the rib protection plate of the hydraulic support above the front drum of the shearer in advance, and then cut the bottom coal seam of the working face according to the mining and caving ratio. The hydraulic support follows the shearer to move the support and push the scraper conveyor, so that the coal discharge opening is located at the front end of the telescopic beam of the hydraulic support; S3. In the coal caving stage, extend the rib protection plate of the hydraulic support behind the shearer to closely adhere to the coal wall, and slowly discharge the top coal under the cover of the metal net and the rib protection plate of the hydraulic support to the scraper conveyor by extending and retracting the telescopic beam of the hydraulic support forward and backward and then transporting it out.

2. A coal caving mining method in front of the support in a coal mining face according to claim 1, characterized in that The metal net is composed of a double-layer wire mesh and steel wire ropes. After laying a row of the wire mesh, hang the steel wire ropes. Two steel wire ropes are laid on each row of the wire mesh, and the steel wire ropes and the wire mesh are tied and tightened with iron wires, and then the laying work of the next row of the wire mesh is carried out until the wire mesh and the steel wire ropes of the whole mining face are laid in place.

3. A coal caving mining method in front of the support in a coal mining face according to claim 2, characterized in that, The wire mesh is 2000 mm long, 800 mm wide, and the mesh size is 20 mm×20 mm, and the spacing of the steel wire ropes is 400 mm.

4. A top coal caving mining method in front of the support in a coal mining face according to claim 1, characterized in that, The metal net is tied and connected with the rib protection plate of the hydraulic support by iron wires.

5. A top coal caving mining method in front of the support in a coal mining face according to claim 1, characterized in that, The moving step distance of the hydraulic support following the shearer is 800 mm, the scraper conveyor is pushed 15 m behind the support moving, and the scraper conveyor is sequentially pushed after the support is moved.

6. A top coal caving mining method in front of the support in a coal mining face according to claim 1, characterized in that, After cutting the bottom coal seam of the working face, carry out the coal caving operation at a position 10 - 15 m away from the rear drum of the shearer. If the scraper conveyor stops running, stop the coal caving operation synchronously.

7. A coal caving mining method in front of the support in a coal mining face according to claim 1, characterized in that, When the coal seam is thick and the hardness of the roof structure is high during the coal caving stage, repeatedly lift and lower the hydraulic support to collapse and break the top coal and discharge it. When the top coal is emptied until gangue appears, extend the telescopic beam of the hydraulic support to maintain the coal rib roof. After the coal caving is completed, the end face distance is not greater than 200 mm.

8. A top coal caving mining method in front of the support in a coal mining face according to claim 1, characterized in that The formula for the mining and caving ratio is as follows: h1 = h2(k s - 1) Among them, h1 is the mining height, which is obtained according to the diameter of the shearer drum; h2 is the height of the top coal, with the unit of m; ks is the loose coefficient of the coal seam, taking 1.2 - 1.

3.

9. A coal caving mining method in front of the support in a coal mining face according to claim 1, characterized in that, The calculation formula for the load of the hydraulic support is as follows: Among them, M1 is the thickness of the top coal, with the unit of m; γ1 is the bulk density of the coal seam; γ is the bulk density of the rock stratum, with the unit of kN / m3; Σh is the thickness of the immediate roof, with the unit of m; L is the periodic weighting interval, with the unit of m; H is the thickness of the first caving of the main roof, with the unit of m; l is the roof control distance, with the unit of m.

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