Analysis of Working Environment and Failure Mode of Drill Shank Adapter

In the construction of rock drilling operations in mines and quarries, rock drilling shanks adapter is one of the vulnerable parts of rock drilling tools. The shank adapter is an important part of the threaded connection rock drilling tool. It directly bears the high-frequency impact and strong torsion of the rock drill during work, and transmits the impact energy of the piston movement of the rock drill from the tail end of the shank adapter to the drill rod and bit for rock drilling. At the same time, the torque is transmitted under the drive of the rotating sleeve of the rock drill, so that the entire drilling tool system rotates. The inner hole of the shank adapter is also scoured by fast flowing water and corroded by mineral water. The harsh working environment and the complexity of the load put forward higher requirements for the performance of the shank adapter. The shank adapter is to transmit the impact energy of the piston to the drill rod and the drill bit to achieve the effect of breaking the rock. The main damage forms of the shank adapter are the fracture, the damage of the end face, the wear of the thread, and the breakage of the drill lug.

1. Fracture of the drill shank adapter

In the rock drilling operation of threaded drilling tools, the shank adapter inevitably bears impact, torsion, bending, etc., which is easy to cause fracture. Fracture is the fatigue damage that often occurs during the working process of the shank adapter, and it occurs at the water injection port of the shank adapter. In addition, when the shank adapter is in the corrosive medium of the coal mine, it is also easy to produce corrosion pits at the water injection port. Under the action of impact load, stress concentration occurs in the corrosion pits and develops into fatigue cracks. Under the joint action of corrosion and fatigue stress, cracks Extend until broken.

2. The damage of the end surface of shank adapter

The end face of the tail of the shank adapter directly bears the impact contact of the piston of the rock drill, and peeling off of the end face is a common damage method. After most of the shank  shank adapters are used, there are small shallow peelings on the end face of the tail, and they look like a relatively shallow "small pits" by naked eyes. This kind of peeling has little effect on the use. The contact of relatively serious large pieces of deep peeling with the piston may cause damage to the piston and cause economic losses to the user. This large deep spalling is caused by cracks perpendicular to the end surface. It is mainly caused by local overheating or overburning of the shank adapters during heat treatment, quenching cracks or excessive internal stress.

3. Wear of shank thread and breaking of shank lug

During the drilling process of the shank adapter, its external thread is connected with the internal thread of the coupling sleeve, and it is subjected to impact, torsion, bending, etc. during use, and the thread is easy to wear due to insufficient hardness. The shank lug cooperates with the spline of the inner sleeve of the rock drill, and mainly bears the torsional stress. During the rock drilling process, the axial tensile and compressive stress and torsional stress cause the drill tool to rotate through the drill ear, and transmit the impact energy to the drill bit to achieve the effect of breaking the rock. Therefore, the alternating stress that the shank lug can withstand is very large, and broken teeth often occur here. After the shank lug is broken, the torsional stress of the rock drill cannot be transmitted to the drill tool and fails.