Check your buttons: Proven tips for more meters per bit

This article originally appeared in International Mining’s November 2017 issue

Drilling contractors and mining companies rely on their tooling to get the highest productivity and the lowest cost per meter for every project.

When purchasing top hammer button bits, for example, choosing a high-quality product designed for the specific ground conditions is only the first step to achieving more meters per bit. Ensuring bits are properly used and maintained is critical to realizing a high return on investment.

Why button bit wear is important

When a top hammer button bit is sharp, the percussive energy transferred into the rock is at its optimum, resulting in effective rock fracture and a maximum penetration rate for the given drilling parameters.

As flats develop on the buttons (tungsten carbide inserts), energy utilization is no longer optimized, leading to a lower penetration rate and reduced productivity. As buttons wear, the bit is less effective at fracturing the rock and the energy is dispensed over a larger surface area. Instead, rock is ground, rather than cut, producing smaller cuttings and energy (no longer used for breaking virgin rock) is reflected back up the drill string. This reflective energy contributes to increased loads on the tooling, drifter, and rig. As a general guideline, refurbishing the buttons before the flats reach 1/3 of the button diameter will maintain penetration/productivity, provide maximum bit utilization and help extend the life of all drill string components.

If the button flats are allowed to develop further to where they are considered over-drilled, productivity and the rate of penetration deteriorates. In this situation, much of the rock in contact with the buttons is re-drilled and the steel bit face may make contact with the bottom of the hole. Fewer and smaller rock chips are produced and much of the energy is reflected back up the drill string. This sacrifices the life of all the drill string components is a major contributor to hole deviation, increases wear and tear on drill rig components and results in higher operational costs overall. Top hammer button bits that are over-drilled exhibit broken buttons and impact drilling productivity.

Recommendations

To get the most out of top hammer button bits, training drillers and mining management on bit care, maintenance and identifying excessive wear can increase the return on investment.

1. Inspect bits frequently

Understand the ground conditions and regular inspections of a button bit are necessary to prevent over drilling. To ensure optimal performance and life, bits require sharpening before the flat exceeds 1/3 of the button diameter. Working with a technical representative is recommended to establish specific guidelines since the maximum suggested wear before reshaping will depend on the button profile.

Drilling in non-abrasive ground can give rise to ‘snakeskin’ (small cracks) on the button surface. If it is not removed by grinding, button fatigue failure still occurs.

2. Grind protruding inserts

Drilling in non-abrasive rock results in the bit face wearing faster than the inserts. Excessive insert protrusion, lacking sufficient steel support, can easily break while drilling and when retracting the bit from the hole. To prevent this from occurring, grind the buttons to restore the protrusion height.

3. Button sharpening and reshaping

If button protrusion is adequate, satisfactory re-sharpening can be achieved by use of a preformed diamond faced tool (‘cups’). Sharpening is performed by holding the tool firmly against the button and orbiting the machine in a circle to achieve a uniform surface finish. Diamond faced tools are designed to cut carbide and not steel. It is therefore recommended to have enough protrusion of the button from the face to avoid damage to the cup, bit or grinding machine.

Over Drilling

The detrimental effects of over drilling button bits may not be immediately apparent. However, running dull bits not only slows down drilling rates but escalates costs by reducing the life of the drill string components, the rock drill and the rig components. Premature button bit insert failures are substantially reduced when over drilling is eliminated and correct sharpening procedures are performed.

Add it up

· The approximate cost of maintaining the performance of a drill bit is only 2% of the total drilling cost.

· Use of state of the art grinding systems in combination with a comprehensive, regular maintenance plan can reduce your overall drilling costs by up to 40%.

· A state of the art grinding system can restore your carbide button bits to near-new condition, increasing your net penetration by as much as 35%.

That’s a significant ROI – contact us to explore the cost reductions and performance improvements that your operation could be achieving.