The main working parameters of the down-the-hole drill are drilling speed, torque, and shaft thrust. The size and matching of these parameters directly affect the rock drilling tools rotation speed and perforation cost. Therefore, reasonable selection of these parameters is the key to the correct and effective use of the down-the-hole drill.

1. Rotational speed of rock drilling tools

The reasonable selection of the speed of rock drilling tools plays a great role in reducing machine vibration, improving drill bit life, and accelerating drilling speed. The size of the rotating speed should be able to ensure the optimal rotation angle of the drill bit between two adjacent impacts. At this time, the amount of rock broken by a single impact of the drill bit is the largest, and the cutting speed is the fastest. The size of the optimal angle of rotation depends on the diameter of the hole, the structure of the drill bit, and the nature of the rock. Therefore, the selection of drilling speed must be based on the diameter of the borehole, the structure of the drill bit, the frequency of the hammer, and the nature of the rock.

During the drilling operation, the rotary speed of the rock drilling tool must be correctly selected. If the rotary speed is too high, the amount of rock fragmentation in a single impact will be reduced, which will not only lead to lower drilling speed but also accelerate the wear of the drill bit; if the rotary speed is too small, the impact work will be wasted and the crushing work ratio will be increased, which will also reduce the drilling speed.

2. Torque

During the normal drilling process, the rotary torque of the rock drilling tool is mainly used to overcome the frictional resistance and shearing resistance between the drill bit and the bottom of the hole, as well as the frictional resistance between the rock drilling tool and the hole wall. The resistance moment of the rock drilling tool is proportional to the diameter and depth of the hole. In rocks with relatively good integrity, the torque required for normal drilling is not large. Drills usually have much more torque than that it is mainly for unloading rods and preventing sticking. The greater the torque, the easier it is to unload the drill pipe, the better the ability to prevent jamming, and the deeper the hole can be drilled.

For drilling in the fracture zone where joints are more developed, you must choose a rig with higher torque; for large-hole diameter deep-hole drilling operations, you should also choose a higher rotary torque.

3. Shaft thrust

Shaft thrust is a very important parameter of DTH rock drilling, whether it is properly selected or not, not only has an impact on the service life of the drill bit but more importantly, directly affects the drilling speed. If the shaft thrust is too large, it will not only lead to discontinuous rotation and rotary impact, but also lead to excessive crushing of drill chips at the bottom of the hole, which will waste energy and affect the drilling speed, and accelerate the wear of the drill bit; if the shaft thrust is too small, the backlash of the rock drilling tool will increase, and the drill bit will not be able to stick to the bottom of the hole, so that the impact energy cannot be effectively applied to the rock at the bottom of the hole, which will affect the rock drilling efficiency and accelerate the damage of the drilling rig and rock drilling tool.