A low impact frequency of a pneumatic impact bolter directly affects rock breaking efficiency and support effectiveness. So, what causes a low impact frequency of a pneumatic impact bolter? A low impact frequency of a pneumatic impact bolter is typically caused by issues with the air source, mechanical components, or operation and maintenance. This can be diagnosed through multi-dimensional troubleshooting and testing with specialized tools. The following is a detailed analysis and solution:

   I. Core Causes of Low Impact Frequency

   1. Air Source System Abnormality

   ① Insufficient Air Pressure: The air compressor output pressure is lower than the equipment requirement (typically 0.4-0.63 MPa). This may be caused by a compressor malfunction, an air supply valve not fully open, or a pipe blockage or leak (such as a damaged hose or loose connector). For example, an air inlet pipe that is too small or too long will significantly increase pressure loss and needs to be replaced with a pipe that meets specifications.

   ② Limited air volume: Insufficient air compressor capacity or clogged filters can result in insufficient air flow to meet equipment requirements, especially when multiple devices are operating simultaneously.

   ③ Poor air quality: Moisture or impurities in the compressed air can cause valve corrosion and piston seal failure, reducing the impact frequency.

   2. Wear or malfunction of mechanical components

   ① Failure of piston and cylinder seals: After long-term use, seals such as piston rings and O-rings wear, leading to compressed air leakage and reduced impact energy. For example, if the clearance between the piston and cylinder of the ZSTD-150 anchor bolter is excessive, replacement is required.

   ② Spring fatigue or breakage: The return spring of the impact mechanism loses its elasticity or breaks due to high-frequency vibration, hindering the piston's return stroke and reducing the frequency. Spring fatigue can be caused by material defects, surface wear, or overload.

   ③ Stuck or damaged air valves: Clogged with oil, impurities, or worn valve discs in the reversing and exhaust valves prevents them from properly controlling the airflow direction, resulting in a disrupted impact rhythm. For example, a clogged exhaust valve can prevent timely release of pressure within the cylinder, affecting the piston's reciprocating speed.

   3. Inadequate Lubrication and Cooling

   ① Insufficient or deteriorated lubricating oil: Failure to add lubricating oil as specified (e.g., using No. 20 mechanical oil in summer and No. 10 mechanical oil in winter), or oil contamination or emulsification, can increase friction between the piston and cylinder and reduce the impact frequency.

   ② Inadequate Cooling: Prolonged high-load operation without timely cooling can cause thermal expansion and deformation of components, affecting fit accuracy.

   4. Improper Operation and Maintenance

   ① Excessive Load: The drill bit becomes stuck in rock or the drilling depth exceeds the equipment's capacity, overloading the impact mechanism and reducing the frequency.

   ② Chronic Empty Drilling: Activating the impactor without tightening the anchor bolt causes the hammer to strike empty, damaging internal components.

   ③ Lack of Preventive Maintenance: Failure to regularly clean filters and replace wearing parts (such as seals and springs) can lead to accumulated faults.

   II. Determining if the Impact Frequency is Too Low

   1. Abnormal Drilling Efficiency

   Consult the equipment manual to confirm the rated impact frequency (e.g., 800 times/minute for the ZSTD-150). An abnormality can be identified if the actual frequency is less than 80% of the rated value.

   2. Directly Measuring the Impact Frequency

   ① Professional Instrument Testing: Use a pressure sensor and a single-chip microcomputer measuring instrument (such as the device described in Abstract 9) to collect the air pressure fluctuation signal during impact and calculate the frequency with an accuracy of ±1%.

   ② Vibration Counter: Secure the vibration sensor to the impactor housing and analyze the vibration waveform to obtain the frequency.

   ③ Simple Timing Method: Manually count the number of impacts in 10 seconds and multiply by 6 to obtain the frequency per minute. This method is suitable for preliminary troubleshooting.

   3. Observe the Drilling Status and Sound

   ① Decreased Drilling Efficiency: Under the same rock formation conditions, the drilling speed slows significantly, possibly accompanied by drill bit jamming.

   ② Abnormal Noise: The impact sound becomes muffled and intermittent, or is accompanied by air leaks, indicating seal failure or air valve malfunction.

   4. Inspecting Key Components

   ① Air Pressure Test: Use a pressure gauge to measure the actual pressure at the equipment's air inlet. It should meet the specifications in the manual (e.g., 0.63 MPa ± 0.015 MPa).

   ② Sealing Performance Check: After shutting off the air supply, observe the rate of pressure drop. If the pressure drops by more than 0.05 MPa per minute, a leak is present.

   ③ Spring Elasticity Test: Remove the spring and measure its free length. Compare it to the original specifications. If it decreases by more than 3%, it should be replaced.

   5. Simulated Load Test

   Measure the impact frequency under no-load and load conditions. If the frequency drops by more than 15% under load, it may be due to insufficient power or mechanical wear.

   III. Troubleshooting and Maintenance Recommendations

   1. Air Supply System Inspection

   ① Clean or replace the air filter to ensure clean and dry air supply.

   ② Check the air compressor output pressure and repair or replace if necessary.

   ③ Check the pipeline section by section, using soapy water to check for leaks at the joints, and replace damaged hoses.

   2. Mechanical Component Inspection

   ① Disassemble the impactor and inspect parts such as the piston, seals, and springs. Replace any parts that show excessive wear. For example, if the clearance between the piston and cylinder exceeds 0.3mm, replace the entire assembly.

   ② Clean the valve assembly to remove oil and impurities, and repair or replace any stuck valve discs.

   3. Lubrication and Cooling Optimization

   ① Refill lubricant at the specified intervals to ensure sufficient oil in the oil cup and unobstructed oil flow.

   ② Avoid prolonged continuous operation of the equipment and allow for appropriate downtime and cooling.

   4. Strengthening Operating Procedures

   ① Before drilling, confirm that the drill bit is aligned with the anchor bolt to avoid eccentric loading.

   ② Never operate the impactor without tightening the anchor bolt to prevent dry drilling and component damage.

   ③ Perform regular preventive maintenance, cleaning the impactor and replacing seals every 200 hours of operation.

   The above methods can systematically analyze the root cause of low impact frequency and carry out targeted repairs and maintenance to ensure the efficient and stable operation of the pneumatic impact bolter. For complex faults, it is recommended that professional technicians use specialized tools (such as oscilloscopes and micrometers) to conduct in-depth inspections.