When it comes to hard rock, its Mohs scale of hardness should be higher than six. This typically includes kimberlite, granite, chert, quartz, and silicified rock. Before beginning, the drilling company should conduct a hardness test on the site, which is a fairly simple process.
Generally, a scratch test is performed on the ground using an etcher kit. The result is then compared with the Mohs scale to determine the hardness of the ground. This information helps in selecting the appropriate tools for the task.
Choosing and Maintaining the Right Bit
Typically, the harder the ground, the more challenging it is to drill through. To make things easier, it’s important to select the right bit. For penetrating hard rock, diamond drilling is essential.
When drilling through such material, it’s crucial to use a core bit with a higher number, a free-cutting edge, and a softer matrix. Keep in mind that the higher the bit’s number designation, the more exposed the encrusted diamonds are, providing greater cutting power. When choosing bits for hard rock, opt for those with self-sharpening capabilities.
Another important factor is the configuration of the bit face, as it greatly impacts penetration and performance. For very hard rock, the turbo configuration is a good choice. It offers a free-cutting bit with less surface area contact with the rock. Additionally, the turbo configuration ensures that the bit head is properly cooled and flushed during operation.
It’s also crucial to monitor drilling parameters when working in hard rock. Everything should remain within tolerance, including water flow, feed pressure, and rotation speed. These details are essential. If water flow is insufficient, the bit may overheat, while excessive water flow can prevent the blade from sharpening.
Bit wear is another important consideration. Ideally, the diamonds and matrix should wear evenly throughout the depth of impregnation. Overexposing the diamonds can risk them breaking off or polishing the bit’s face prematurely.
If the rotation speed is too low, it can put undue strain on the matrix. Conversely, if the speed is too high, it may damage the bit by polishing the diamonds too quickly.
Finally, if drilling slows or fails to advance, the bit is already polished. In this case, you’ll need to sharpen it before using it again. Sharpening exposes the impregnated diamonds on the surface, which requires expert skill. Since each bit is unique, it’s important to adjust your sharpening techniques to fit the specific bit.
Hardness And Type of The Rock
When choosing the best drill bit to use, the first step is to determine the hardness and type of the rock you’ll be drilling through. Keep in mind that each rock’s properties differ, including porosity, fracturing, abrasiveness, and compressive strength.
All of these factors can affect the durability and performance of the drill bit. For instance, drilling through abrasive, hard rock such as granite will require different bits compared to drilling through a ductile, soft rock like shale.
Various techniques can be used to determine the hardness and type of rock, such as drillability tests, drill cuttings analysis, logging data, and core samples.
Design Of the Bit
Choosing the appropriate bit design is also a crucial step in selecting the best drill bits. This includes considering the cutter geometry, bit shape, bit size, and bit type.
Each bit design has its own pros and cons when drilling through hard rock. For example, roller cone bits, which consist of tungsten carbide or steel teeth, can roll and smash the rock, making them ideal for drilling through abrasive, hard rocks.
However, they generate higher torque and have lower penetration compared to other bit types. On the other hand, for drilling through non-abrasive but hard rocks, fixed cutter bits are more suitable as they have polycrystalline or diamond compact cutters that can slice through the rock.
Keep in mind that these tend to be more expensive and less durable than other bit types.
Drilling Parameters
Optimizing drilling parameters is crucial when selecting the best drill bits. This includes considering hydraulic horsepower, flow rate, rotary speed, and weight on the bit.
These factors significantly impact bit efficiency, lifespan, and rate of penetration. It’s essential to balance these parameters to achieve optimal drilling performance and avoid failures.
For instance, applying excessive weight on the bit can cause vibrations or damage to the bit teeth, while using an extremely low rotary speed might increase bit wear and reduce cleaning efficiency.
Depending on the hardness and type of rock you’re drilling, there are various software, charts, and formulas available to help adjust the drilling parameters.
Bit Wear
To ensure you’re using the best drill bits, it’s important to efficiently evaluate and monitor bit wear. Bit wear occurs when the bit’s cutting elements deteriorate due to corrosion, erosion, impact, or friction.
Bit wear can affect drilling costs and bit performance, so it’s vital to replace the bit before it becomes inefficient or excessively worn. Several indicators can help measure bit wear, including bit run length, weight loss, dull characteristics, and dull grade. Additionally, methods such as bit protection, stabilization, cleaning, and cooling can help reduce wear.
Drilling Objectives
Finally, be sure to choose the bit that satisfies your drilling objectives, including the environmental impact, the budget, the required hole quality, and the preferred penetration rate.
There are different criteria that you can use in evaluating your bit options, like the bit reliability, the bit availability, the bit cost, and the bit performance. You can also refer to other sources to obtain more information, such as the bit feedback, the bit records, the bit catalog, and the bit manufacturer.
If you require hard drilling for hard rock, then you can get in touch with Hard Rock Drilling LLC at
