| Hydraulic impact machinery(hydraulic breaker,hydraulic rock drill,etc.)is a construction machinery device that performs crushing operations.It is widely used in mining,municipal construction,highways and railways at home and abroad,and hydraulic impactor is the core work of hydraulic impact machinery.Due to the high frequency and long-term repeated impact of the hydraulic impactor,the oil flow in the inner flow channel is complex,and the vortex generated in the flow field and the scouring of the oil make the inner wall of the cylinder easily damaged.In this paper,a certain type of gas-liquid combined hydraulic breaker is taken as the research object.Aiming at the phenomenon that the inner wall of the impactor is damaged during the working process,the numerical simulation of its internal flow field is studied.Firstly,the hydraulic impactor system is modeled and simulated to determine the boundary conditions of the flow field in the impactor;secondly,the numerical simulation of the flow field in the impactor is carried out to analyze the dynamic characteristics of the flow field and generate vortices and oil shocks in the inner flow channel.The optimization was carried out,and it was found in the flow field that the flow velocity at the outlet of the fitting clearance between the cylinder and the piston suddenly increased when the impactor hits,which is easy to cause impact damage to the cylinder.Using the orthogonal test and the control variable method to analyze the weight of different factors affecting the flow velocity at the exit of the gap,the conclusions drawn from the two analysis methods show that the size of the gap has the greatest influence on the flow velocity at the exit of the gap;The flow field simulation and system simulation were carried out to explore the relationship between the size of the impactor gap and the outlet flow velocity at the end of the fitting gap,so as to reduce the flow velocity and suppress the damage.Through the above research,the purpose of improving the flow field characteristics of the impactor,reducing the impact velocity of the oil in the impactor cylinder,and guiding the subsequent design of the impactor is achieved.Specifically,there are the following aspects of work:(1)Modeling of hydraulic impactor system and determination of boundary conditions of internal flow fieldIn this paper,numerical simulation is used to analyze the characteristics of the flow field in the cylinder to study the damage of the cylinder.Therefore,the boundary conditions of the flow field in the cylinder of the hydraulic impactor and the parameters of the piston motion are first determined.According to the working principle of the hydraulic impactor,combined with the specific parameters of this type of hydraulic impactor in this research,the AMESim system simulation model of the impactor is built,and the simulation results of the model are described.The AMESim-PumpLinx co-simulation required for the field provides dynamic mesh motion constraints and boundary conditions for each port.(2)Simulation analysis and optimization of the flow field in the hydraulic impactorBased on the AMESim-PumpLinx co-simulation technology,the characteristics of the flow field in the cylinder were analyzed,so as to find out the reason and time point of the damage to the inner wall of the cylinder.Firstly,the flow field model of the hydraulic impactor is established,and the flow field pressure and flow characteristics of the hydraulic impactor are described.Secondly,it was found that when the hydraulic impactor hits,there is a sudden increase in the flow velocity at the end of the gap between the cylinder and the piston,which is consistent with the damaged position of the inner wall of the impactor cylinder,indicating that this phenomenon is easy to cause the cylinder to be damaged by the impact of oil.(3)Influencing factors and weight analysis of the flow velocity at the outlet of the hydraulic impactor with the clearanceAiming at the problem that the high flow velocity at the end of the fitting clearance at the time of the hydraulic impactor’s impact is likely to cause damage to the cylinder,the main influencing factors are the size of the clearance,the taper of the clearance,the length of the seal and the pressure difference,and an orthogonal test is designed based on these factors.The software simulates and analyzes the fitting clearance of each group of hydraulic impactors with different test parameters,and explores the influence and weight of these factors on the flow velocity at the outlet of the fitting clearance.Secondly,relying on the control variable method to analyze the influence of each single factor and the outlet flow velocity of the fitting clearance,the conclusions obtained by the orthogonal test and the controlled variable method show that the influencing factors on the outlet velocity of the fitting clearance between the cylinder block and the piston of the hydraulic impactor The weights are: gap size > seal length > differential pressure > gap taper.(4)Analysis of the influence of different gap sizes on the outlet flow rate of the hydraulic impactor gap and the impact performance of the systemBased on the conclusion that the gap size has the greatest influence on the flow velocity at the outlet of the hydraulic impactor,the PumpLinx flow field simulation and the AMESim system simulation were carried out for four groups of hydraulic impactor models with clearances of 0.04 mm,0.05 mm,0.06 mm,and 0.07 mm,respectively.The simulation results show that the reduction of the clearance from 0.07 mm to 0.04 mm will reduce the outlet flow rate of the fit clearance when the impactor piston hits by 7.85%;at the same time,the working frequency of the impactor will be slightly increased by 0.5%,and the impact energy will be reduced by 1.21%.Therefore,reducing the size of the gap can effectively reduce the flow velocity at the outlet of the fitting gap without causing too much impact on the impact performance of the impactor. |
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