Wear Patterns

When an impregnated core bit is removed from the drill-hole after use, the resulting wear pattern on the bit face is an important source of information for the operator. By “reading” the bit face, the operator can frequently troubleshoot problems by simply altering the drill’s operating parameters or by changing the bit to a matrix type or waterway configuration that is better suited to the ground conditions.

Click on any of the illustrations below to view actual photos of the corresponding wear pattern. (Image size ranges from 88kb to 115kb.)

New Condition

For reference purposes, this graphic illustrates the appearance of a new, unused impregnated diamond core bit crown.

Ideal Wear Pattern

The observed mid-life wear pattern on a properly used impregnated diamond core bit should be relatively flat with slightly chamfered sides.

Normal Retirement

The full depth of diamond impregnation is evenly consumed.

Outside Diameter Gauge Loss

Possible causes and solutions:

  • Vibration - Lower the rotational speed.
  • Lack of in-hole fluid circulation - Increase the pump rate.
  • The bit is reaming an undersized drill hole - Check the gauge diameter of the reaming shell in use and replace if found to be undersized.

Inside Diameter Gauge Loss

Possible causes and solutions:

  • Overfeeding the bit - Reduce the penetration rate.
  • Damage from drilling into highly unconsolidated material - Cement the drill hole or change to a harder (lower number) Dimatec “D-Series” or “HR-Series” matrix type.
  • Drilling over lost core - Examine the core tube contents.
  • Lack of fluid circulation - Check the inner tube length adjustment to ensure that there are no fluid restrictions within the core barrel assembly. Also check the in-hole circulation pump rate and the drill rod string for leaks.

Cracked Waterways

Possible causes:

  • An excessive bit load was applied.
  • The bit, core barrel and drill rod string were accidentally dropped in the drill hole.
  • The wireline inner tube assembly was accidentally allowed to free fall through the drill rod string in a dry hole.
  • The bit was accidentally crushed by the rod holder or foot clamp

Concave Face Wear

This wear pattern frequently results from the use of a penetration rate that is too high for the rotational speed being used (overfeeding). This wear pattern is also caused by “grinding core”.

Convex Face Wear

Possible causes and solutions:

  • Insufficient fluid circulation across the bit face - Check the circulation pump and drill rod string for leaks; increase the pump rate.
  • Repeated in-hole “dry-stripping” in hard, non-abrasive formations - Change to a softer (higher number) Dimatec “D-Series” or “HR-Series” matrix type

Excessive Diamond Exposure

In this wear pattern, the metal-bond matrix abrades away before the diamond crystals have become worn. As there is insufficient metal-bond matrix material to support the over-exposed diamond crystals on the bit face, the diamonds are released from the matrix material prematurely resulting in low bit life. Possible causes and solutions:

  • The penetration rate is too high for the rotational speed in use (overfeeding) - Reduce the penetration rate or increase the rotational speed.
  • The matrix type is too soft for the ground conditions - Change to a harder (lower number) Dimatec “D-Series” or “HR-Series” matrix type

Glazed Bit Face

In this condition, the diamond crystals on the bit face have become completely embedded in the metal-bond matrix. Sandblast the bit face in order to re-expose the diamond crystals. Try drilling with a slower rotational speed and/or a lower in-hole fluid circulation rate in an effort to cause the metal-bond matrix to abrade at a higher rate that will cause the diamond crystals to become exposed more readily. If the bit face glazes repeatedly, change to a softer (higher number) Dimatec “D-Series” or “HR-Series” matrix type.

Burnt Bit Crown

This condition is the result of a significant loss of fluid circulation across the bit face. Possible causes for this condition include:

  • The operational failure of the fluid circulation pump.
  • Excessive circulation fluid leaks in the drill rod string, water swivel or hoses.
  • Internal core barrel fluid restrictions resulting from the incorrect adjustment of the wireline inner tube assembly.
  • One or more waterway canals on the bit crown are blocked by pebbles or other debris.