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Hydraulic support technology is one of the key technologies necessary to realize mining, steel, tunnel construction, etc. The development of its technology has always been widely concerned by the industry.

1 Status quo of foreign hydraulic supports

Since the 1980s, various industries such as mining and iron and steel have actively developed new technologies for high-performance and high-reliability hydraulic supports. These new technologies generally use electro-hydraulic control valves driven by micro-motors or electromagnets, and displacement sensors are applied to pushing jacks. Infrared sensors are installed in coal shearers, and the diameter of some pillars even exceeds 400 mm. The bracket uses a high-strength steel plate with a yield strength of 800-1000 Mpa. This steel plate has the characteristics of high strength, high hardness, strong toughness, and outstanding cold welding performance.

2. Development status of hydraulic support technology in my country

2.1 Domestic hydraulic support technology

After 1990, the domestic hydraulic support has been fully developed. After more than 50 years of technical accumulation and development, my country’s hydraulic support technology has made great progress, and gradually formed a backbone support manufacturer design institute and a professional coal science institute. The support research and design team represented by the research institute has maturely used computer CAD and finite element analysis software for design calculations. The research results represented by the classification of the roof of the gently inclined working face provide a strong support for the design, selection, manufacture and use of the support.

2.2 Materials used in hydraulic supports

After the mid-1990s, China began to study the welding process of high-strength plates, especially the welding process of steel plates below 1000 Ma grade, and made a breakthrough. Up to now, the main bracket manufacturers in my country have basically possessed the production capacity of Φ400 mm columns with independent intellectual property rights, and the working pressure of the two-column shielded brackets has reached more than 10,000 kN.

3 Problems and solutions of hydraulic support technology in coal mining

3.1 Problems of hydraulic support technology in coal mining

At present, the single hydraulic column used in domestic coal mines generally has poor initial support force and insufficient rigidity of the column, resulting in a worrying safety hazard in the coal mine working face. The main factors are:

(1) The location of the hydraulic pump station is improperly selected, resulting in the pressure output of the nozzle of the pressure gun not meeting the rated working requirements. In addition to being related to the model, the initial support force of the coal mine hydraulic prop is also directly related to the output pressure of the pump station. Some mine hydraulic pump stations are more than 1000 m away from the mining face, and the output pressure loss of the pump station is relatively large, resulting in insufficient initial support force during pillar driving, which seriously affects the control of the composite roof.

(2) The base area of the hydraulic column is small, and the rigidity of the support system is insufficient. The base of the hydraulic column, especially the ring-shaped base, is greatly affected by the floor rock formation. With the mining of the coal seam, the settlement of the roof makes the pillar drill the bottom and the shrinkage of the live column is small. The volume pressure increase of the liquid in the hydraulic column cylinder decreases, and the support The resistance drops, the rated working resistance cannot be reached, and the support effect cannot meet expectations. Therefore, when the old roof is pressed periodically, the roof will sink and break, which will easily cause the working face to cut the roof along the coal wall.

3.2 Solutions to the problems of hydraulic support technology in mining

(1) Reasonable site selection for hydraulic pumps and reasonable selection of buoyancy pumps. The rated working pressure of the emulsification pump should be greater than 15M a, and the location should not exceed 100m from the working face to ensure that the working pressure at the farthest liquid supply point reaches above 9.8M a. If conditions permit, a mobile hydraulic pump station can be built.

(2) Appropriately increase the area of the bottom of the pillar to prevent bottom drilling. The matrix of some regional coal seams in China is silty clay rock, which has a high expansion coefficient when it meets water, and the bottoming of pillars occurs from time to time. During the work, the area of the bottom of the pillar can be appropriately increased, and the base of the pillar can be used as an “iron shoe”, with a size of 200×200×15 mm. Remember, try not to use wooden bases to reduce the risk of failure due to the low strength of wooden shoes and easy fracturing and breaking.

(3) Reasonable selection of pillars and three-purpose valves. Regularly inspect the hydraulic system to prevent leakage and damage. If there is any problem, repair or replace the failed original in time to prevent the hydraulic system from working with problems; the cylinder of the hydraulic prop newly entered into the well should be emptied before use to avoid mixing gas into the emulsion , thereby reducing the pressure and stiffness of the support system.

4 The development trend of support equipment such as bearing instrument at home and abroad

At present, improving the supporting capacity of hydraulic supports, improving their adaptability to geological conditions, expanding the scope of use in mines, and improving working life are the main development directions of hydraulic supports:

(1) Vigorously develop and apply shield-type and support-shield-type brackets, and reduce the use of other types of brackets. At the 16th China International Coal Mining Technology Exchange and Equipment Exhibition held in Beijing China International Exhibition Center in 2015, a total of 89 hydraulic supports were exhibited, of which 73 were cover supports, accounting for 82% of the total. The main common features of these brackets are: using four-link or other mechanisms to maintain a basic safe distance between the beam break and the coal wall; using an integral self-moving structure and an intelligent automatic control system to facilitate bracket operation, automatic control and remote control.

(2) Expand the scope of use of hydraulic supports. At present, all major mining countries are developing hydraulic supports that can be applied to large mining heights, large cutting depths, large dip angles, and thin coal seams, and pay attention to the coordinated linkage and cooperation between supports and shearers

(3) Further increase the working pressure of the emulsion pump to improve the initial support force of the hydraulic support. At present, the working pressure of many over-pressed hydraulic pump stations including the United States can reach more than 300Kg/cm2.

(4) Use the control method based on the “multi-core tube” pilot-operated adjacent frame control to simplify the hydraulic support piping system and facilitate operation and maintenance.

(5) Increase the moving speed of the hydraulic support and improve the operating conditions. The hydraulic support is developing in the direction of electromechanical-hydraulic integration, and AI automatic control is the main development direction. Group program control has been widely used, and further develops towards intelligent control and fully automatic control.