In mining, tunneling, and underground construction using the drilling and blasting method, hydraulic rock drills play a crucial role. Their performance stability and reliability directly influence construction progress and quality. The shank adapter, a key component of the hydraulic rock drill, operates under high-frequency, high-impact tensile, compressive, bending, and torsional cyclic stresses. It transfers energy from the drill to break the rock while withstanding immense impact loads, severe abrasive wear, and the corrosive effects of rock, dust, and water in the working environment. Consequently, shank adapter failure and fracture remain an industry concern. This article explores the causes of shank failure and proposes preventive measures to ensure safe and efficient construction.
Working Environment of the Shank Adapter
The shank adapter connects the hydraulic rock drill to the drill rod. During operation, it transmits the rock drill’s impact energy and torque to the drilling tools to break the rock via the drill bit. The shank adapter ensures high-frequency impacts, powerful torque, and environmental corrosion from water and debris. Such harsh working conditions make the shank susceptible to failure and fracture under combined cyclic stresses.
Causes of Shank Adapter Failure and Fracture
Material Factors
Shank adapters are usually constructed from 23CrNi3Mo steel, which undergoes carburizing, quenching, and tempering. These treatments result in a surface hardness of 52–58 HRC, offering exceptional wear resistance and toughness. However, the sulfur (S) content in the material has a significant impact on its corrosion resistance and fatigue properties. High sulfur levels lead to sulfide inclusions, which form lamellar structures during forging and rolling, reducing fracture toughness and fatigue performance. Furthermore, sulfur accelerates corrosion, creating pits that weaken the shank adapter’s strength.
Corrosive Effects
In mining and tunneling, shank adapters are exposed to corrosive working media such as rock dust, water, and slurry containing acids, bases, and salts. These substances accelerate the corrosion process, especially when sulfur inclusions are present. Localized corrosion, or pitting, often initiates near these inclusions. The acidic environment around the inclusions dissolves sulfides, producing H₂S and HS⁻ ions that exacerbate pitting. The friction and wear caused by rock debris further intensify this damage, creating surface pits that act as origins for fatigue cracks.
Stress Concentration
The piston’s cyclic impacts create high-stress areas, particularly at the root of the helical grooves, where fatigue cracks are prone to develop. Surface defects such as pits and corrosion marks exacerbate stress concentration, accelerating crack initiation and propagation.
Improper Usage
Operational errors, overuse, or lack of regular maintenance can also contribute to shank failure. Misuse accelerates wear and corrosion, shortening the shank adapter’s service life.
Preventive Measures for Shank Adapter Failure
Optimize Material Selection
Reduce sulfur content to minimize sulfide inclusions and improve corrosion resistance. Increase chromium (Cr) and nickel (Ni) content to enhance mechanical properties and corrosion resistance. These elements form a protective passivation layer on the steel surface, reducing corrosion rates significantly.
Surface Treatment Technologies
Apply chromium plating to the shank adapter’s surface to improve wear and corrosion resistance. The chromium layer acts as a barrier, isolating the base material from corrosive substances while increasing surface hardness and durability.
Regular Inspections
Conduct routine inspections to identify defects such as pits, corrosion marks, and excessive wear. Check for tight connections between the shank and the drill. Address identified issues promptly through repairs or replacements to prevent further damage.
Proper Operation and Usage
Train operators to follow correct handling techniques, avoid excessive use, and ensure optimal operation. Manage work schedules to prevent prolonged high-load operation, allowing the shank to rest and cool.
Use Compatible Tools
Select and install tools matching the hydraulic rock drill’s specifications and operating conditions. Properly matched tools ensure efficient operation and reduce the risk of shank adapter failure.
Conclusion
Shank adapter failure in hydraulic rock drills is a complex yet critical issue. By deeply analyzing the causes and taking effective preventive measures, we can significantly reduce the risk of shank adapter failure and fracture, prolong its service life, and provide a strong guarantee for the project’s construction. At the same time, it also helps to improve the efficiency and quality of rock drilling and reduce the construction cost and safety risks. Therefore, we should attach great importance to the failure of shank adapters, strengthen the research and application work, and promote the continuous progress and development of hydraulic rock drill technology.
