Introduction

 

    With the development of rock bolt support technology, roof bolters, as the main mechanical equipment in the rock bolt support process, have developed from the initial single function, poor reliability, low technical content, and poor safety to today's new drilling rigs with high reliability, good safety, and high degree of automation. At present, the use of roof bolters in some mines is not very good. Often, a new drilling rig is used underground for less than two months before it needs to be repaired on the surface, seriously affecting normal production. Whether the roof bolter can work normally and whether faults can be accurately and promptly eliminated is the key to improving support effects, accelerating roadway completion speed, reducing labor intensity, improving production efficiency, and increasing equipment utilization. Therefore, it has received widespread attention from coal-producing enterprises in various regions and is being adopted competitively, representing the main development direction of roadway support technology. Based on the author's practical work experience, this paper puts forward the following views on the problems and maintenance methods in the use of pneumatic roof bolters, for the exchange and reference of peers.

 

    China began importing Australian pneumatic roof bolters in 1987. After more than 20 years of development, there are many models of domestic pneumatic roof bolters, from MQT-50C to MQT-120C, and there are also many manufacturers. The performance of the roof bolters has reached the international level of the 1990s. They are suitable for drilling roof bolt holes and anchor cable holes in rock strata with a rock firmness coefficient f≤8 in underground engineering such as coal mine roadways. They can integrate mixing, nut tightening, and bolt installation, featuring simple operation, multiple functions, and convenient maintenance.

 

    1.1 Causes and Troubleshooting of Insufficient Motor Power

 

    1.1.1 Low air source pressure and small air volume: Check whether the air supply valve is fully open and whether the air supply hose is damaged; if the inlet pipe diameter is too small, increase the inlet pipe diameter; if the inlet hose is too long, shorten the inlet hose length; if the oil cup is blocked, clean the oil cup to eliminate the fault; if the air compressor is not working properly, solve the problem to make it work normally; if the bearing is damaged, replace the bearing; if the pressure reducing valve is in the closed position, close the pressure reducing valve; if there is air leakage at the joint, tighten the joint to ensure it is well sealed; if there are debris in the motor reduction gearbox, remove the debris.

 

    1.1.2 Clogged filter screen and muffler: Disassemble the filter and clean the filter screen; if there is excessive lubricating oil, disassemble and clean the filter and adjust the oil supply. If the muffler is frozen, take it out and clean it; it is recommended to use antifreeze lubricating oil.

 

    1.1.3 Wrench not pressed in place: Check the motor valve; if it cannot be fully opened, replace with a new valve.

 

    1.1.4 Air leakage at the three-way shaft: Check the "O" rings and replace damaged "O" rings.

 

    1.1.5 Low motor driving torque: The gap between the motor rotor and the casing is too large, and the seals of the cylinder directional valve are worn, causing a large amount of compressed air leakage. This makes the motor speed normal when idling, but after drilling, the motor speed drops rapidly or loses speed, and stops when mixing anchoring agent.

 

    1.2 Causes and Troubleshooting of Insufficient Leg Thrust: ① The compressed air pressure at the working face is low and does not meet the requirements of the drilling rig; it is recommended to use 0.4-0.65MPa air pressure; ② The filter is blocked by pollutants, increasing pipeline pressure loss and reducing air pressure; check and clean it; ③ The air supply valve is not fully open, the air supply pipeline is damaged and leaking, the pipe joints leak, the air supply hose is bent, coiled too much, or the pipe diameter is too small, etc., which increase pipeline pressure loss and cause low compressed air pressure supplied to the cylinder; ④ The oil injector is blocked, increasing pipeline pressure loss and reducing air pressure; ⑤ The seals of the cylinder directional valve are worn, causing air leakage; ⑥ The leg seals are damaged; replace with new seals; ⑦ There is too much oil dirt in the leg, causing excessive resistance; clean the leg, lubricate appropriately, and reduce resistance.

 

    1.3 Causes and Troubleshooting of Slow Leg Retraction: When the drilling rig is working, improper placement causes uneven force on the machine, bending the telescopic tube; dust enters the cylinder; clean it, lubricate appropriately, reduce resistance, and check whether the dust ring is damaged; if damaged, replace it immediately; the inner wall of the steel outer casing is rusted, making the rubber bowl move poorly and accelerating the wear of the rubber bowl; the exhaust valve is blocked; clean the exhaust valve.

 

    1.4 Causes and Troubleshooting of Slow Drilling Speed: ① Insufficient cylinder thrust: The compressed air pipeline exceeds the rated load, pipeline leakage, valve wear cause low working air pressure, and insufficient cylinder thrust. ② The drill pipe specifications are unqualified or already bent and deformed: Check whether the drill pipe is bent; if bent, straighten it before use; check whether the drill bit specifications are correct and use a suitable drill bit. Check whether the drill bit is sharp and use a sharp drill bit; if the central hole of the drill pipe is blocked, check and clean the central hole of the drill pipe. ③ Insufficient water supply: The drilling rig water valve cannot be fully opened, and the water flow is not smooth; the water source pressure is low; keep the water pressure within the range of 0.6-1.2MPa; the water supply valve is not fully open, the water supply pipe is blocked, the pipeline is damaged, and the joints leak, causing low water pressure and small flow.

 

   2 Points to Note in the Use of Pneumatic Roof Bolters

 

    2.1 Sufficient water pressure is required during operation. The pneumatic roof bolter must have sufficient water pressure during operation, maintained at 0.6MPa-1.2MPa, and the water quality must be clean. In actual use, there are often cases where the drilling rig continues to be used with insufficient water pressure. In this case, a large amount of heat is generated by friction between the output shaft and the water sleeve and seals, causing the water sleeve and seals to age quickly, damaging the seal and causing premature damage to the drill bit. Therefore, in use, be sure to supply water before drilling, stop drilling when water stops, and do not drill when water pressure is insufficient. In addition, the drill pipe and drill sleeve sealing rings should be replaced frequently. The water leakage at the connection between the drill sleeve and the drill pipe underground is very serious, which not only makes operation inconvenient for workers but also causes water loss so that the pressurized water cannot fully flush the drill bit, resulting in insufficient cooling and chip removal.

 

    2.2 The oil mist lubricator of the drilling rig must not be short of oil, ensuring that the roof bolter receives sufficient lubrication. The lubrication and cooling of the motor part all rely on high-pressure gas passing through the oil mist lubricator to bring oil into the motor. If the oil mist lubricator is short of oil, the pneumatic motor will not be lubricated, and the temperature of the gear tooth surface of the motor will rise rapidly, greatly reducing the efficiency of the pneumatic motor. If the motor is not lubricated and cooled, the burned area will continue to expand, and the motor will soon be scrapped, making the roof bolter unable to work. Therefore, during the use of the pneumatic roof bolter, the oil mist lubricator must not be short of oil. In addition, before use, apply lubricating grease to the part of the drill pipe inserted into the drill sleeve, which can extend the service life of the drill pipe and drill sleeve and make assembly and disassembly more convenient.

 

    2.3 Sufficient air pressure and air volume must be provided when the roof bolter is working. The normal control air pressure of the pneumatic roof bolter is 0.4-0.63MPa, and the diameter of the compressed air pipeline is not less than Φ25. Only when the above conditions are met can the roof bolter work under rated conditions. When the air pressure is insufficient, it is forbidden to use the roof bolter; otherwise, it will accelerate the damage of the drilling rig parts. Be sure to keep the compressed air clean and dry. If the water content is too high, it will wash away and destroy the oil film on the surface of the parts in the pneumatic motor, and cause scale in the muffler, blocking the exhaust passage and preventing the drilling rig from operating normally.

 

    2.4 The torque and thrust of the roof bolter should match during operation. During drilling, the drilling rig often gets stuck, greatly reducing drilling efficiency. Therefore, when selecting the model, according to the average hardness of the roof in the mine, since prestressed bolts are currently being promoted, the requirements for the selection of roof bolters will be higher. When selecting a roof bolter, first consider the hardness value of the roof, and secondly, understand the failure value of the nut stop plate of the prestressed bolt used in the mine. The maximum torque of the selected roof bolter must be greater than this value.

 

 

    Pneumatic roof bolters are the most widely used rock bolt support equipment in coal mines in China. Scientific management, maintenance, and correct use of roof bolters are important factors in improving the efficiency and quality of rock bolt support, improving the accuracy of fault diagnosis of roof bolters, and improving the speed and quality of drilling rig maintenance. From the perspective of the development of high-yield and high-efficiency mines in China's coal mine construction, the development of roof bolters in China has hindered the pace of building high-yield and high-efficiency mines. Our country should, according to its own conditions, conduct research on existing single roof bolters to enhance their reliability, increase output power, reduce weight, and improve service life to meet the needs of underground coal mine use.