Button bit has the advantages of fast and smooth rock drilling speed and long service life, and is widely used in coal mine rock tunneling and other fields. It is the main tool used by hydraulic rock drills and other high-powered machines, and its consumption is very high. Most of the blunted button bits are discarded, and a few of them are ground by hand with flake grinding wheels. It is not only laborious and time-consuming, but also difficult for the resharpened drill bit to reach the original performance, and the repair rate of drill bit is very low, resulting in a large amount of wasted drill bit. Therefore, the correct use and reasonable grinding of button bit can prolong its service life and increase the rock drilling speed.

Principle of correct use of button bit

1. To obtain a good rock drilling effect, in addition to supplying enough pressure air to clean the blast hole, drill bit must be continuously pressed on the new surface of the rock. Otherwise, the drill will produce empty drilling, and its impact energy will remain in the rock drilling tools, which will cause fatigue damage to rock drilling tools and cause the button to fall off due to its continuous vibration.

2. Pay attention to control of rock drilling speed. Too high speed will accelerate the wear of the drill bit and increase the risk of breaking the buttons, especially the buttons on the outer edge of drill bit.

3. It is recommended to check the drill bit regularly after each blast hole is drilled so that problems on the button can be found and dealt with in time.

4. When the rock powder is in a suspended state, never turn off the compressed air (such as connecting drill rod or replacing drill bit). Otherwise, it will affect the cleaning of the blast hole and cause an accident.

5. Do not limit the air volume and pressure.

Principle of grinding button bit

To improve the service life of drill bit, it is not possible to wait until the drill bit wears down to a very low drilling speed. Instead, the principles of “early repair and less grinding” and “frequent repair and fine grinding” should be adopted, and the drill bit should be ground in time after wear. When the button wears to 1/3~1/2 of its column diameter, or when the surface of button shows hotlines and a “snakeskin” phenomenon,  it should be ground in time to ensure the drilling speed and rock drilling performance of drill bit and avoid drill bit from breaking button due to stress concentration. When necessary, the outer cylindrical working surface of the grinding drill bit can be used to grind the outer cone of drill bit and the shallower powder discharge groove.

Precautions for grinding the button bit

1. Reasonably arrange the grinding time

① Determine whether the button bit needs to be ground. It is generally determined by the size of the worn surface of the button. When the drill bit is worn, the resistance to rock penetration increases, the energy transfer rate decreases, the drilling rate decreases, and the stress on the drill rod increases accordingly. Therefore, when the drilling rate drops sharply, drill bit should be reground in time to restore its original shape and reduce the rock penetration resistance to a predetermined level.

② Since the rock drilling conditions vary greatly, the grinding interval of the drill bit cannot be fixed, but we can make reference to the resharpening interval according to the production experience and the hardness of the ore rock, formulate a reasonable drill bit grinding plan, and resharpen the drill bit regularly. For example, according to the degree of wear of the drill bit, the dull drill bit should be removed and ground every 5~10 holes. Adopting this mandatory system of regular grinding of drill bits can avoid economic losses caused by human factors and bring many economic benefits, such as prolonging the service life of drill bits, drill rods, and coupling sleeves, increasing the drilling speed, reducing the working stress of rock drilling tools and drilling rig parts, reducing the chance of failure of rock drilling tools, and improving the straightness quality of drilling. In addition, on-site operators should also closely observe the rock drilling conditions and replace in time those drill bits that do not work properly during the planned grinding period.

2. Correctly master the grinding method

The direct purpose of grinding the button bit is to restore it to its original geometry. The correct grinding process and method are not only the quality assurance of drill bit grinding but also the basic functional requirements for grinding tools and equipment.

When grinding, pay attention to the following matters.

①Since the wear of button is greater than the drill bit body when drilling rock when grinding the drill bit, part of drill bit body at the head end should be removed first, to restore the height of the button protruding from the drill bit body.

② Select suitable abrasive materials according to different carbide button grades, and pay attention to the metallographic organization of the abrasive materials, especially do not choose abrasives with too hard a texture.

③ Pay attention to cooling when grinding the drill bit.

④ During the grinding, pay attention to the measurement of drill bit with the button sample to ensure the correct geometric dimensions of the drill bit and timely adjustment of the machine parameters.

⑤  For the completely failed button, remove them completely with an ordinary grinder.