From the bit point of view, most Tophammer drilling operations need to spend the least amount of money per millimeter of bit diametral wear. Reason being that the hole being drilled is only allowed to vary X amount of mm from the nominal hole size. Hence, if nothing else happens to the bit the bit life will end when the diameter of the hole reaches the minimum allowed size.
The classic approach to increasing the amount of meters it takes to reach the minimum allowed hole size, and hence also the service life, is to fit the bit with larger carbide buttons in the gauge. This gives the bit more carbide to wear during its degradation journey to the minimum diameter. The biggest drawback of doing this is that it will increase the frontal contact area with the rock which is a large factor in determining the resistance against penetrating the rock. Thus the penetration rate will go down.
This is the classical compromise of bit design, larger carbide buttons will give more bit wear life but it will at the same time slow down the drilling.
To crush this age-old compromise Epiroc R&D invented the Trubbnos button shape that have many benefits and of which the two most important are:
1. It increases the radial contact area with the rock hole wall and by doing this it gives the bit more carbide volume to wear during its journey towards minimum allowable bit size. This increased contact area also allows the rock hole wall to push harder against the button, helping the button to withstand the bending moment created by the impact forces.
2. It decreases the frontal contact area with the rock hole bottom. This makes the rock penetration resistance smaller and increases the drilling speed.
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