Tungsten Carbide Button Distribution Optimization on Drills (2/2)

In the early 1980s, some researchers have proposed the distribution of the drill bit buttons should follow three guidelines: 1. each cutting button has equal rock breaking volume; 2. equal wear rate; 3. equal rock consumption. Meet these three criteria in order to ensure rock breaking energy evenly distributed on each cutting tooth, so as to obtain the best rock-breaking effect. Theoretically, the process of tungsten carbide buttons for rock breaking can be divided in to three steps: elastic deformation (when the force is released, the rock surface can restore the status), fatigue process (also known as pressure crushed stage, surface cracks do not disappear and fracture rock surface) and volume breaking (The formation of shear body, under increasing pressure formed pit crushing).

When the adjacent tungsten carbide buttons impact the rock at the same time, the overall crushing effect depends on the nature of the deformation of the cross-belt. Reasonable button spacing will produce elastic deformation energy to rupture and push the rocks out with the increasing load; if the spacing of two buttons is too narrow, it will make the compacting zone too close to increase the difficulty of the shear rock; if the spacing of two buttons is too wide, the rock in the middle part will not be cracked and form rock ridges. Viewed from the impact energy, for the drills fixed diameter, the less number of buttons, the more impact energy of each button endure and the rock crushing volume will also increase accordingly. However, if the number of button is too small, which over the stress fracture of a single button, tungsten carbide button will be broken.

Buttons distribution firstly depends on the shape of the bit end face, which includes flat-shaped, arc-shaped, protruding, concave shape, and so on. The most used are flat-shaped and arc-shaped. Generally, tungsten carbide drill bit with large diameter usually uses arc end face and the small diameter often uses the flat-shaped. In intermediate buttons distributed in the cross section perpendicular to the bit axis, while the button are located on the inclined face of the drill bit. The outermost edge of buttons not only has to be mechanical support, but also should withstand the crushing function so that it has a greater amount of consumption than the buttons middle. Furthermore, it has high speed of linear velocity and requires a larger diameter, wider distribution and excellent quality.

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