Abstract: The widespread application of anchor net support technology has enabled some equipment to be put to use. Pneumatic roof bolters have advantages such as high reliability, long service life, high work efficiency, low noise, wide application range, light weight, small size, easy movement, simple operation, and easy disassembly and maintenance. However, in actual production practice, it has been found that pneumatic roof bolters, constrained by the underground coal mine environment, are frequently damaged, causing both economic losses and adverse effects on normal production. Now, combined with practice, the common faults, damage causes, and troubleshooting of pneumatic roof bolters are discussed one by one.
1 Overview
The MQT series pneumatic roof bolters used in our mine consist of three parts: rotation mechanism, propulsion mechanism, and operation mechanism, mainly including: gearbox, motor, head, air leg, control arm, water chamber, muffler, and other components. Its working principle: the drill uses compressed air as power, and controls the rotation of the motor and the extension and retraction of the leg through the motor valve and air valve respectively. Open the motor valve, compressed air drives the gear to rotate, and after deceleration, drives the main shaft to rotate, thereby driving the drill bit to work.
2 Cause Analysis and Troubleshooting of Common Faults in Pneumatic Roof Bolters
According to on-site observation and analysis, the common fault phenomena of pneumatic roof bolters are: (1) insufficient motor power and abnormal noise; (2) insufficient leg thrust; (3) slow leg retraction speed; (4) slow drilling speed; (5) insufficient water flow.
2.1 Cause Analysis and Troubleshooting of Insufficient Motor Power
⑴ Low air pressure, small air volume; air pressure should be 0.4-0.65MPa.
Check whether the air supply valve is fully open; it should be fully open. Check whether the air supply hose is damaged; if damaged, replace the water supply hose; if the intake hose is too long, shorten it; if the intake pipe diameter is too small, increase it. If the air compressor is not working properly, solve the problem to make it work normally. If the pressure reducing valve is not in the closed position, close it. If there is air leakage at the joint, tighten the joint to ensure it is well sealed. If the oil cup is blocked, clean it to eliminate the fault. If the bearing is damaged, replace it. If there are debris in the motor reduction gearbox, remove them.
⑵ Filter screen blocked: disassemble the filter and clean the filter screen.
⑶ Muffler blocked
Excessive lubricating oil: disassemble and clean the filter, adjust the oil supply. If the muffler is frozen, take it out and clean it; it is recommended to use antifreeze lubricating oil.
⑷ Wrench not pressed in place: check the motor valve; if it cannot be fully opened, replace with a new valve.
⑸ Air leakage at the three-way shaft: check the "O" rings and replace damaged "O" rings.
2.2 Cause Analysis and Troubleshooting of Insufficient Leg Thrust
⑴ Low air pressure: it is recommended to use air pressure of 0.4-0.65MPa.
⑵ Adjustment rod not in place: adjust to the appropriate position.
⑶ Leg seal damaged: replace with new seals.
⑷ Leg control valve leaking: replace damaged "O" rings.
⑸ Intake filter blocked: check and clean.
⑹ Leg damaged: replace the damaged leg.
⑺ Too much oil dirt inside the leg, excessive resistance; clean the leg, lubricate appropriately to reduce resistance.
2.3 Cause Analysis and Troubleshooting of Slow Leg Retraction Speed
⑴ Exhaust valve blocked: clean the exhaust valve.
⑵ Leg seal damaged: check and replace.
⑶ Dust entered the cylinder: clean the cover and check whether the dust ring is damaged; if damaged, replace immediately.
⑷ Too much oil dirt inside the leg, excessive resistance; clean the leg, lubricate appropriately to reduce resistance.
2.4 Cause Analysis and Troubleshooting of Slow Drilling Speed
⑴ Drill pipe and drill bit.
Check whether the drill pipe is bent; if bent, straighten it before use. Check whether the drill bit specification is correct; use a suitable specification drill bit. Check whether the drill bit is sharp; use a sharp drill bit. If the center hole of the drill pipe is blocked, check and clean it.
⑵ Insufficient water pressure causes the borehole to be blocked by drill cuttings.
If water pressure is insufficient, keep it within the range of 0.6-1.2MPa. If the water circuit or water valve is damaged, repair the water circuit or replace the water valve.
⑶ Filter blocked: check and clean the filter.
⑷ Insufficient leg thrust: check the causes related to leg faults and eliminate the faults.
2.5 Causes and Troubleshooting of Insufficient Water Flow
⑴ Insufficient water supply pressure: water supply pressure should be maintained between 0.6-1.2MPa.
⑵ Water valve damaged or not fully open: replace the water valve or fully open it.
⑶ Water supply pipeline damaged and leaking: repair or replace the damaged part to eliminate leakage.
⑷ Water filter blocked: clean the water filter.
⑸ Debris in the center hole of the drill pipe: clean the center hole of the drill pipe.
3 Compliance with Regulations
In order to fully utilize the working performance of the pneumatic roof bolter and reduce the accident rate (such as roof bolter failures and personal accidents), operators must comply with the following regulations.
3.1 Preparation before use
⑴ Operators must carefully study the "Pneumatic Roof Bolter Operation Manual" and master the performance and operation methods of the roof bolter. Establish an operation responsibility system for the roof bolter, with dedicated personnel operating it.
⑵ Establish an operation responsibility system for the roof bolter, with dedicated personnel operating it.
⑶ Before going underground, conduct a trial run on the surface. The procedure is as follows: connect the water and air pipes, press the motor control handle, and let the motor run from low speed to high speed for two minutes; exhaust gas and oil droplets should be discharged from the muffler; open the air valve knob to make the leg extend and retract quickly twice; after closing the air valve, the leg should retract under its own weight; open the water valve control knob, and water should spray from the main shaft hole; only after the above actions are normal can underground operations begin.
⑷ Transport the roof bolter underground in a wooden box.
⑸ Carefully check all parts of the roof bolter; all parts should be complete, fasteners should not be loose, and operation switches should be in the "closed" position.
⑹ Check all water and air pipelines to ensure they are clean.
⑺ It is strictly prohibited to place wood or other materials under the drill.
⑻ Before starting each shift, be sure to check the oil level in the atomizing oil cup; appropriate lubrication must be provided to the motor, and No. 20 or No. 30 lubricating oil must be used; hydraulic oil is strictly prohibited.
⑼ Check the air supply and water systems to ensure the supplied air is clean and dry, with pressure controlled between 0.4-0.65MPa and water pressure between 0.6-1.2MPa.
⑽ Add appropriate amount of grease and No. 20 or No. 30 engine oil to the reduction gearbox monthly; the temperature of the reduction gearbox body should not exceed 65℃.
3.2 Precautions during operation
⑴ It is strictly prohibited to touch the rotating drill pipe with hands. When drilling, do not wear gloves to hold the drill pipe.
⑵ After the drill pipe reaches the roof, press down the motor wrench and simultaneously open the water control knob to start drilling. Adjust the motor and water controls to gradually increase the rotation speed and propulsion speed to the maximum; the propulsion speed and force should be moderate. Also note that under soft rock conditions, the roof bolter requires a higher rotation speed and lower thrust. Under hard rock conditions, the roof bolter requires a lower rotation speed, and the leg thrust should be slowly increased to obtain the optimal drilling speed. When drilling in argillaceous rock, special attention should be paid to water pressure; if the water output is small, stop the motor and flush for a while before drilling.
⑶ When the drill suddenly gets stuck, a large reaction torque will be generated; the operator should operate carefully to prevent sprains.
⑷ When the leg retracts, do not put your hand on the cylinder to prevent pinching.
⑸ During drilling, the drill pipe and the drill must not be relatively inclined; the water flow must not be interrupted; no one is allowed to stand in front of the drill to prevent accidents from broken rods.
⑺ The operator should stay away from the center line of the borehole to prevent accidents when the drill rod breaks.
3.3 After operation
⑴ When drilling is completed, reduce the rotation speed, first close the leg air source, and rely on its own weight and manual assistance to smoothly push the drill pipe out of the borehole. Stop the motor and close the water valve.
⑵ After each hole is drilled and anchoring is completed, rinse the exterior of the drill with water and run it idle to remove moisture; check whether all fastening bolts are loose and handle them promptly; check that the oil level in the oil cup is sufficient for the next use, and place it in a safe location to prevent accidental damage from other falling, hitting, or bumping; after multiple cycles of operation, if the drill is not used for a long time after stopping, partial disassembly and maintenance can be performed, wearing parts replaced, and rust prevention treatment applied.
4 Correct Maintenance and Care Help Reduce Drill Failures
(1) Before repairing the roof bolter, use a water gun and cleaning agent to thoroughly clean dust and dry it.
(2) When it is necessary to remove the shaft pin in the head, special care must be taken not to damage or destroy the mating surface of the head and the pin. When removing or assembling the pin, special care must be taken not to rotate or operate the control handle, otherwise the O-ring will be damaged when the pin passes through several grooves. Note that the pin must be thoroughly cleaned, coated with grease, and gently tapped in straight.
(3) When repairing the air leg, it should be fixed in a soft clamp; do not use a vise, pipe wrench, or chain to fix the air leg; do not use hot steam or solvents to clean the air leg; use the specified cleaning agent and high-pressure water gun to clean the air leg, and alternately clean with hot water below 90℃ and cleaning agent. Replace all seals of the air leg with correct gas seals; incorrect use of seals will cause poor operation of the air leg.
5 Recommendations
(1) According to actual observation, there are many types of roof bolters; after a period of use, the drill model cannot be distinguished, causing mismatches when replacing wearing parts. It is recommended to engrave the drill model on the drill body.
(2) Strengthen the training of employees on operating procedures, drill performance, maintenance, and use, and educate employees on responsibility to develop a good habit of caring for equipment.
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