Failure Analysis of the Shank Adapter

When the drill bit shank is in operation, its tail end face directly bears the impact contact of the rock drill piston, transmitting the impact energy of the piston movement from the tail end to the drill rod and drill bit, thus performing the drilling operation. Simultaneously, the spline of the drill bit shank transmits torque under the drive of the rock drill's rotating sleeve , causing the entire drill bit system to rotate. The inner bore of the drill bit is also subject to erosion from rapidly flowing water and the humid environment of mining, meaning the drill bit operates under corrosive conditions caused by molten rock. Therefore, the failure modes of the drill bit shank are quite complex, and the main failure modes are as follows.

 

 1. Fracture

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The shank is the last section of the drill bit assembly. During rock drilling, it inevitably bears bending moments. Simultaneously, due to wave reflection from the impact compression wave at the free end and at points of cross-sectional change, tensile stress waves are generated inside the shank. This alternating action of impact compression and tensile stress, coupled with the corrosive effect of the mine water, will cause impact corrosion fatigue fracture of the shank. Multiple mining tests have shown that the most vulnerable area for shank fracture is the eccentric relief groove at the end of the wavy thread, followed by the rounded transition at the corner of the sealing ring groove not far from the shank end face in the inner hole. Therefore, it is essential to improve the impact fatigue resistance of these two weak points. As for the occasional fractures caused by the development of corrosion fatigue cracks in the smooth inner hole and outer surface, these are rare, and the shank often fails in other ways before they are exposed.

 

 

2. Damage to the tail end face

 

Damage to the end face of the drill bit tail under the impact and compressive stress of the piston generally occurs as follows: The end face of the drill bit tail directly bears the impact contact of the rock drill piston, and end face spalling is a common form of damage. More serious damage occurs when large, deep spalling occurs on the end face, which will worsen the contact between the piston and the drill bit tail, and may even cause piston damage.

 

3. Wear of wave-shaped threads

 

During rock drilling, each piston impact on the drill bit causes a rebound motion in the wavy thread clearance between the drill bit and the drill sleeve , resulting in impact wear on the wavy thread. When the wear reaches a certain level, the clearance between the drill bit and the drill sleeve thread becomes too large, causing thread misalignment and severe "stuck-in" phenomena, making it difficult to load and unload the drill rod. Therefore, improving the wear resistance of the wavy thread is also an important issue, in addition to addressing the first two failure modes.

 

 

Luoyang Golden Egret Geotools co., Ltd. specializes in the processing and manufacturing of shank adapter. By studying shank adapter failures, they strictly control the processing precision of each process during manufacturing, resulting in products with long service life, fewer problems, and greater peace of mind and effort.