| As a core equipment of top hammer drilling,hydraulic rock drills have been widely used in many applications,such as mining,coal mine roadway excavation,railway tunnel,highway tunnel and rock excavation projects.Especially the heavy hydraulic rock drill with high-frequency and high-power becomes the first choice facing the scale of mining and the larger-scale tunneling.Meanwhile,a higher requirement on the damper system is put forward.Then the double damper system emerges as the times require.It is an inevitable trend to develop high-power hydraulic rock drills with the double damper system.For the key problems existing in the development of hydraulic rock drills with double damper system,a coupling model including percussion system,double damper system and rock was established.The comprehensive performance test for hydraulic rock drills was conducted.The influence of floating characteristic of the double damper system,the opening type of reversing valve and the dynamic characteristics of accumulator on the percussion characteristics of rock drills was researched.The cavitation erosion and impact powerless of the hydraulic rock drill with double damper system were analyzed and solved.The mechanism of percussion drilling was described.The structure and operating principle of percussion system with no constant-pressurized chamber were introduced.A coupling model including the impact piston,reversing valve,high-pressure accumulator and connecting pipelines was established considering the compressibility and leakage of hydraulic oil and the rebound of impact piston.Calculation formulas of drill bit's chiseling depth and rebound velocity of damping piston were established based on the stress wave theory.A coupling model of double damper system including the damping piston,damping valve,damping accumulator and connecting pipelines was established considering oil compressibility,oil leakage and pressure drop in valve ports.The comprehensive performance test for hydraulic rock drills with double damper system was conducted considering the structure characteristics.The pressure in the chambers of percussion system and double damper system's were measured and analyzed.The impact point was judged.The velocity curve of impact piston was acquired.The simulation and experimental results had consistency.The numerical model was verified.Based on the operation principle,the damping piston's statics equations were established by law of orifice flow.The key indicator parameters of double damper system's floating characteristic were ascertained,which were damper flow rate and feed force.Their effects on the percussion performance were researched by experiment.The reasonable range of matching parameters was given.The overlap value of reversing valve was designed considering the time variation of the leads of stroke reversing.The advantages of the overlapped reversing valve were analyzed by contrasting the pressure pulsation in the impact system and motion law of the impact piston with different opening types.For the cavitation erosion of impact piston and guide sleeve in the percussion system with no constant-pressurized chamber,the mechanism was revealed by simulation results.The oil-return accumulator was designed and installed.Combining the mathematical models of oil-return accumulator and percussion system,the influence of inflation pressure on the cavitation was researched by simulation.For the cavitation erosion of damping piston,the cavitation erosion mechanism was revealed by the simulation results.The critical influencing factors of the cavitation erosion were determined.The influence on system cavitation of damping valve structure and connecting pipeline types was discussed,and the reasonable range of matching parameters was given.Pressure curves in the primary,secondary damping chamber and noise spectra of cavitation were obtained by the field rock drilling test.The simulation and experimental results had consistency.The system cavitation was detected by the high-frequency pulsating pressure signal and its power spectral density analysis.This detection method provides a new approach for studying the cavitation behavior of hydraulic rock drills.An overall model of damper accumulator was established considering the inlet pipe characteristics.The relationships between system's natural characteristic and precharge pressure,damper pressure were analyzed.The step response was simulated under different precharge pressures.Then experiments were conducted.The pressures in damper chamber and accumulator's air-chamber were tested synchronously.The optimum working parameters were obtained.In order to find the impact powerless and airframe fever reasons of a certain domestic heavy hydraulic rock drill with double damper system,its impact energy was measured by the stress wave test.And on this basis the comprehensive performance test was conducted.The impact piston's moving law was obtained,the damper system's working condition and the damping piston's equilibrium position were inferred,too.The causes of problems were found.An improved method of shortening the bushing length was proposed.Then the improved rock drill's property was verified through experiment.The comprehensive performance test provides an effective means for hydraulic rock drills' troubleshooting and the development of new products. |
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