Cluster down-the-hole (DTH) hammers are often used in large-diameter hard rock drilling operations. Due to complex rock formation conditions, cluster DTH hammers cannot adjust the working airflow in time according to rock formation conditions, resulting in frequent damage to cluster DTH hammers and low work efficiency. Aiming at this problem, this paper proposes an airflow adjustment mechanism as a solution. In this paper, the operation stability and airflow adjustment characteristics of the adjustment mechanism are studied. The impact characteristics and driving force variation characteristics of the adjustment mechanism under different speeds and loading modes are analyzed, and the results show that the movement impact of the adjustment mechanism increases with the increase of the movement speed of the driving actuator under the same loading mode. With the increase of the eccentric load, the critical movement speed of the driving actuator decreases when the adjustment mechanism moves without impact. The test verifies the synchronization characteristics of the adjustment mechanism under different load modes and different control valves. The results show that, under the condition of uniform load, the synchronization accuracy of the dividing/focusing valve and the proportional valve is good. With the increase of the eccentric load difference, the synchronization performance of the dividing/focusing valve becomes worse, and the average error increases. The test results in this paper are of great significance for guiding the engineering design of cluster DTH hammers.
During hard rock excavation in the process of tunnel construction, the hard rock excavator wears seriously and quickly and reduces its excavation efficiency. Aiming at this problem, this paper proposes a composite rock breaking method by impact rolling and cutting as a solution. In this paper, the composite rock breaking characteristics of impact hob are studied. The impact cutting load of the hob was analyzed, and the hobbing force equation and the rock crushing volume equation were established. The effects of different impact frequencies and impact loads on the cutting force and rock crushing characteristics of the hob were analyzed by experiments. The results show that under a certain thrust and hob spacing, with the increase of the impact frequency, the rock ridge between the two hobs gradually decreases, while the crushed volume of the rock increases gradually. Under the same axial load and cutter spacing conditions, with the increase of the impact frequency, the hob shear force decreases significantly. Under a certain axial load and impact frequency, with the increase of impact load, the crushing volume of rock and the hob shear force decrease significantly. These test results are of great significance for guiding the efficient excavation of hard rock tunnels.
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