The three-arm hydraulic drilling rig is equipped with a high-performance imported rock drill. If the rock drill fails frequently during tunnel excavation, it will seriously affect the construction schedule and increase the construction cost. The working principle and common failure causes of COP1838 three-arm hydraulic drilling rig of Atlas Boomer are analyzed, and the treatment measures and precautions are put forward.

1.1 Structure composition

COP1838 rock drill is mainly composed of head, gear box, intermediate, cylinder block, rear end body, impact piston, bit tail, accumulator and other parts, as shown in Figure 1.

1. Impact piston 2. Drive sleeve 3. Stop ring 4. Bit tail 5. Flushing head 6. Drive gear 7. Drill tail thrust ring 8. Buffer piston 9. Drive shaft 10. Low pressure accumulator 11. Impact piston front guide sleeve 12. Cylinder block 13. Rotary motor 14. Shock piston rear guide bushing 15. Rear end body 16. Return oil accumulator 17. Reversing spool 18. High pressure accumulator 19. Drill tail oil passage

Figure 1 Structure and working principle of rock drill

1.2 Working principle of rock drill

Figure 1 is a schematic diagram of the working principle of the rock drill. The high pressure oil enters the piston cylinder through the high pressure accumulator 18, and under the action of the reversing valve core 17, the piston 1 does a high frequency round-trip movement to hit the drill tail and provide the impact energy of breaking rock. The buffer system is composed of a low pressure accumulator 10, a buffer piston 8 and a bit tail thrust ring 7. When the impact piston 1 hits the bit tail 4, the bit tail bounces back and pushes the bit tail thrust ring 7. The thrust ring pushes the buffer piston 8 to move backward, and after the two-stage buffer, the rear hydraulic oil absorbs its pressure and releases it through the low pressure accumulator 10 to achieve the buffer effect.

The rotary power is provided by the hydraulic rotary motor 13, and the torque is transmitted to the gear box through the drive shaft 9, and then the torque is transmitted to the drill tail 4 through the internal drive sleeve 2, to achieve the role of driving the drill pipe rotation. Under the action of 0.3 ~ 0.4MPa air pressure, the drill tail oil passes through the drill tail oil channel 19 to each lubrication surface.

2 Common Fault Causes Analysis and treatment

2.1 Accumulator Fault Analysis and treatment

The main reason for the rupture of the diaphragm of the accumulator is the high nitrogen charging pressure of the accumulator. When the nitrogen charging pressure is too high, the diaphragm will be close to the bottom of the accumulator, resulting in reduced movement space of the diaphragm, and the hydraulic oil will be trapped between the diaphragm and the bottom plate of the accumulator, forming several small oil cavities. The pressure will gradually increase, resulting in the diaphragm cracking and pipeline vibration. The main reason for the rupture of the accumulator shell is that the accumulator has been working in a state of no air or insufficient air pressure for a long time, resulting in the maximum hydraulic oil pressure and the stress concentrated in the accumulator shell.

If the sound of the rock drill is changed from crisp to dull or hoarty, the impact system cannot reach the high impact pressure, the pressure is about 14MPa, and the pressure gauge pointer wobbles and the oil pipe vibrates violently, that is, the accumulator is broken. During normal use, the pressure of the accumulator should not be too high. The charging pressure of the high pressure accumulator should be lower than the rock drill hole impact pressure of 3 ~ 4MPa, the maximum should not exceed 11MPa, and the nitrogen charging pressure of the low pressure accumulator should be controlled at 2 ~ 2.5MPa. It is necessary to check the accumulator charging valve spool frequently and check whether the valve spool leaks. Accumulator core installation torque control should be controlled at 300N· m or so.

2.2 Flushing head fault analysis and treatment

Corrosion and cracking is a common failure of the washing head. The making material of the washing head has low strength and poor corrosion resistance, so it can not work in the corrosive water environment for a long time, otherwise it will produce cracks. After the nose is corroded, the wash head will move forward and transfer the impact force to the nose through the thrust ring, resulting in stress concentration.

The treatment measures are as follows: The processing material of the washing head is made of stainless steel with high strength and strong corrosion resistance; When installing the flushing seal, ensure that the position is accurate, ensure that the impact force is transmitted to the flushing head through the thrust ring, and reduce the loosening of the flushing head; Replace the drill tail and wash head seal in time.

2.3 Head Fault Analysis and treatment

The main failure form of the head is the head fracture, the main reason is a long time empty play. When all the pressure is released, the propulsion force is lost, and the impact force generated by the impact piston is transmitted to the thrust ring and the washing head, and the most front-end pressure reaches its maximum. If a corrosive wash water is used, the corroded crack will slowly increase with the impact stress until the entire front end breaks. The handling measures and precautions are as follows: It is strictly forbidden to play empty, ensure that the bit tail, washing seal and bonding surface are intact, and replace the worn washing head and the bit tail guide sleeve in time.

2.4 Impact Piston Fault analysis and treatment

Common faults of impact piston include: bolt loosening; Impact sealer wear; The local temperature of the piston surface rises due to the prolonged impact of the drill pipe. The piston contact surface and cylinder block are stuck, which causes the impact piston contact surface to break suddenly. The main reasons include: cracks have occurred on the piston; The lubricating oil is contaminated; The impact piston alignment size deviation is large; Rock drill bolt fastening force is too large and piston guide sleeve is worn. The main reason for the damage of the percussion surface of the impact piston is water leakage or oil leakage to the piston area, resulting in corrosion or cavitation, as shown in Figure 2 and Figure 3.

Figure 2 Radioactive strip cracks on the end surface caused by water erosion

Figure 3 Cavitation caused by the end of the block

Treatment measures and precautions: Ensure that the impact piston is neutral, and do not drill for a long time; Strictly implement the mandatory maintenance regulations of the rig, timely replace the worn piston front and rear guide sleeves, Sterseal, etc.; Ensure that the hydraulic oil is clean, and prevent gravel from entering when replacing the rock drill pipe or maintaining the rock drill; Prevent cavitation and water erosion, check and replace the water seal regularly; Lubricating oil input is maintained at 20 ~ 25 drops/min; Timely replacement of worn sterseal; Prevent impurities from entering the rock drill. After the metal parts inside the rock drill are damaged, the rock drill must be disassembled and cleaned before it can be reassembled.

2.5 Impact piston guide Bush Fault Analysis and treatment

The main reasons for the failure of impact piston guide sleeve include: impact piston joint surface or piston fracture; Cavitation of the impact piston guide sleeve: it is in the state of low propulsion or empty punching for a long time, resulting in the mismatch between the impact piston and the reversing valve and the rock drill design; Misuse of a damaged or wrong type accumulator.

Handling measures and precautions are as follows: When a fault occurs, stop the machine immediately for inspection to prevent secondary damage to internal components; During operation, try to avoid empty beating, and adjust the appropriate pushing pressure according to the strength of surrounding rock; The accumulator should be replaced in time after failure, and ensure that the inflation pressure is correct; There are cavitation marks on the internal guide surface, which can not be replaced, and cavitation marks on the external guide sleeve surface, which can be rotated and continued to be used.

2.6 Fault Analysis and Treatment of drill tail thrust ring

The common failure form of the drill tail thrust ring is the rotating bushing crack, the main reason is insufficient lubricating oil and fatigue damage, as shown in Figure 4. Treatment measures and precautions: ensure the normal supply of drill tail lubricating oil, check whether there is lubricating oil discharge at the oil outlet and drill tail at each shift, if no lubricating oil discharge must be stopped for inspection; The rotating bushing is replaced once according to 400h; Ensure that the wear of the cone of the rotating bushing does not exceed 1mm.

▲ Figure 4 Rotary bushing broken

2.7 Drive Sleeve Fault Analysis and treatment

The main failure form of the drive sleeve is the drive sleeve wear, the main reasons include: lack of lubricating oil, or lubricating oil model does not meet the requirements; Drilling large diameter holes beyond the limits of the rock drill design; The treatment measures and precautions for missing meshing teeth inside the drive sleeve are as follows: Ensure that the drilling tail oil is sufficient and the air pressure is moderate, and the use of non-special lubricating oil is strictly prohibited; The optimum drilling hole size of COP1838 rock drill is 43 ~ 89mm, and the maximum drilling hole size cannot exceed 102mm. The drill tail guide sleeve must be replaced when it is worn more than 1mm.

2.8 Buffer Piston Fault analysis and treatment

The common cavitation of the buffer piston is mainly caused by the wrong pressure setting and the poor stability of the constant flow valve. The handling measures and precautions are as follows: record the operating parameters of the rock drill every shift, and adjust in time when the impact pressure, pushing pressure, rotating pressure and buffer pressure do not match; Ensure that the charging pressure of the high and low pressure accumulator is correct. If the accumulator is found to be faulty, it must be shut down immediately. Ensure the hydraulic oil is clean, check the constant flow valve in time and deal with seal wear; During the maintenance of the rock drill, the wear condition of the buffer piston and the cavitation condition should be judged and analyzed, and the causes should be found and dealt with in time to prevent secondary damage to other parts of the rock drill.

3 Summary

The most common failure of the rock drill is mainly caused by too high rebound pressure and too low propulsive pressure. At the same time, the operator's standard operation is also crucial, non-standard operation will lead to a variety of damage inside the drill. Advance prevention of specific faults can prevent the expansion of accidents and cause greater economic losses. Making and strictly implementing the operation and maintenance procedures can effectively extend the service life of the rock drill.