what diamond concentration is used in impregnated core bits

What Does Diamond Concentration Actually Mean?

In the diamond tool industry, concentration is a standardized measure of how much diamond grit is embedded in the metal matrix of a core bit. The industry convention defines a concentration of 100 as equivalent to 4.4 carats of diamond per cubic centimeter of the impregnated matrix layer. This corresponds to roughly 25% diamond by volume, with the remaining 75% being the metal binder — typically a blend of cobalt, bronze, iron, or tungsten carbide alloys.

Concentration is expressed as a percentage relative to this baseline. A concentration of 50 means 2.2 carats/cm³ (about 12.5% diamond by volume). A concentration of 125 means 5.5 carats/cm³ (about 31% diamond by volume). The most common range used in impregnated core bits spans from 50 to 150, though the exact number should always be matched to the rock formation at hand.

It is important to understand that concentration is not a quality grade — higher is not automatically better. Diamond concentration must work in balance with matrix hardness, diamond mesh size, and formation characteristics. A concentration that works brilliantly in hard granite will cause a bit to glaze and fail in soft limestone, and vice versa.

Recommended Diamond Concentration by Rock Formation

The single most important factor in determining diamond concentration is the type of rock you are drilling. The table below summarizes the recommended concentration ranges for common formation types.

The logic behind these ranges is straightforward. In soft, non-abrasive formations, the rock does not wear down the matrix quickly enough to expose fresh diamonds. If you use too high a concentration, the bit surface becomes crowded with diamonds that are never fully exposed — a condition called glazing. The bit skids across the rock face instead of cutting, and penetration rates ｄｒｏｐ dramatically. A lower concentration with a soft matrix allows the matrix to wear at a controlled rate, continuously exposing sharp diamonds.

In hard, abrasive formations, the opposite is true. The rock aggressively erodes the matrix, and if the diamond concentration is too low, the bit runs out of cutting points before the matrix wears away. A higher concentration ensures that enough diamonds are present to handle the abrasive wear, extending bit life and maintaining consistent penetration.

For fractured or heterogeneous formations, the challenge is impact resistance rather than pure abrasion. A moderate concentration paired with a tough, ductile matrix absorbs vibrations and prevents diamond fracture, keeping the bit intact through unpredictable conditions.

Concentration by Bit Size: NQ, HQ, and PQ

In addition to rock type, the size of the impregnated core bit itself influences the optimal diamond concentration. Larger bits generate more heat and cutting torque, and they require more diamonds to maintain an even cutting surface across the wider crown. Here is how concentration typically scales with the three most common wireline sizes:

NQ bits, being the smallest of the three, operate with a moderate concentration of 75–100%. This provides enough cutting points for medium-hard formations while keeping the bit cost-effective for projects that require frequent bit changes in mixed ground conditions.

HQ bits step up to 100–125% concentration. The larger crown area needs more diamonds to distribute the cutting load evenly, especially in deep drilling where rotational speeds are high and the bit must maintain aggressive penetration through alternating hard and soft layers.

PQ bits demand the highest concentration — 125–150% — because of their large diameter and the extreme conditions they face. Deep oil and gas wells, hard granite, and highly abrasive formations all require the additional cutting points that a high concentration provides. At this level, the matrix is typically reinforced with tungsten carbide to withstand the intense wear.

The Concentration-Matrix Balance: Why Both Matter

Diamond concentration cannot be selected in isolation. It must be paired with the correct matrix hardness for the bit to perform as intended. The matrix is the metal alloy that holds the diamonds in place, and its wear rate determines how quickly fresh diamonds are exposed. The relationship works as follows:

Getting the concentration-matrix balance wrong is one of the most common causes of poor bit performance. A bit with the right concentration but the wrong matrix will still fail — either glazing over (matrix too hard) or shedding diamonds before they are fully used (matrix too soft).

Common Mistakes When Selecting Diamond Concentration

Mistake 1: Assuming Higher Concentration Is Always Better

Many buyers treat concentration as a quality grade and assume that a 150% concentration bit is automatically superior to a 75% concentration bit. This is incorrect. In the right formation, a lower concentration bit will outperform a higher one because it avoids glazing and maintains better penetration rates. The goal is to match concentration to the rock, not to chase the highest number.

Mistake 2: Ignoring Diamond Mesh Size

Concentration and diamond mesh size are interdependent. A high concentration of coarse diamonds (20/30 mesh) behaves very differently from the same concentration of fine diamonds (100/120 mesh). Coarse grit cuts faster but leaves a rougher surface; fine grit cuts more slowly but produces smoother cores and handles hard rock better. When selecting concentration, always consider the diamond mesh size that your formation requires.

Mistake 3: Using One Concentration for Mixed Formations

Geological formations are rarely uniform. A borehole may pass through shale, sandstone, and granite in a single run. Using a single bit with a fixed concentration across all three will compromise performance in at least one of them. If you know your project involves mixed formations, either plan to switch bits at formation boundaries, or choose a medium concentration (75–100%) with a balanced matrix as a compromise that works adequately across the range.

How to Choose the Right Concentration for Your Project

Selecting the correct diamond concentration for an impregnated core bit comes down to a systematic evaluation of your drilling conditions. Follow these steps:

Conclusion

Diamond concentration in impregnated core bits typically ranges from 50 to 150 (equivalent to roughly 2.2 to 6.6 carats/cm³), with the exact value dictated by rock formation hardness, abrasivity, and bit size. For soft non-abrasive formations, stay in the 50–75% range. For medium-hard sandstone and siltstone, use 75–100%. For hard, abrasive granite and quartzite, push to 100–150%. And always pair the concentration with the correct matrix hardness — the two parameters work together, and a mismatch in either direction will compromise bit performance.

At TY Drill Bits, we manufacture a full range of impregnated core bits in NQ, HQ, and PQ sizes, with customizable diamond concentration and matrix formulations to match your specific drilling conditions. Whether you are exploring for minerals, drilling geothermal wells, or conducting geotechnical surveys, having the right concentration makes the difference between a smooth, cost-effective operation and a frustrating, expensive one. Contact our team to discuss your project requirements and find the optimal bit configuration for your next drilling campaign.