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Where the matrix type and waterway configuration
have been correctly selected for a drilling job, an impregnated
core bit should drill steadily with an even wear pattern
until the matrix layer is totally consumed. At this point,
the circulating pump pressure will usually increase due
to the fluid restriction caused by the diminished waterway
depth on the bit face.
If the matrix type and/or waterway configuration
is not exactly suited to the formation conditions, it may
become necessary to sharpen the bit face in the event that
the penetration rate becomes unacceptably low. A decrease
in penetration rate is usually caused by the diamond crystals
on the bit face becoming blunt. The metal bond matrix is
probably too hard for the formation conditions and will
not erode at a controlled rate to expose new layers of diamond
crystals. If possible, change to another D-Series or HR-Series
bit with a softer (higher number) matrix type and/or a bit
with a lower face contact area that has a more open waterway
configuration such as the ‘Turbo’ style.
If it is not possible to change the
bit, it will be necessary to sharpen the bit face using
one of the following methods. Bit sharpening techniques
should only be used when absolutely necessary as they tend
to have an adverse effect on overall bit life.
Method 1 – Bit
Face Dressing (Preferred Method)
Remove the bit from the drill hole and sandblast the face
with an abrasive media such as Aluminum-Oxide or Silicon-Carbide
grit. If sandblasting equipment is not available on site,
use a tapping action with a flat file to roughen the surface
of the bit.
Method 2 – In-Hole
Method
With the bit on the bottom of the drill hole and with the
drill string rotating, reduce the rotational speed to about
50% to 75% of the normal rotational speed. Try to maintain
a constant rate of penetration for a distance of 6 to 50
mm (0.25 to 2 inch) allowing the bit load to gradually increase
and then suddenly decrease thus indicating that the bit
face has sharpened and will now cut freely. IMPORTANT: It
is imperative that at the instant this sharpening (bit load
decrease) occurs, the applied bit load must be decreased
and the rotational speed must be increased to their original
values. Failure to make this adjustment will result in further
stripping and could cause a premature failure of the bit
crown.
In extremely hard formations with a high Silicate
content, it may be necessary to reduce the fluid circulation
rate below recommended values in order to maintain bit sharpness.
THE FLUID CIRCULATION MUST NEVER BE COMPLETELY
CUT-OFF TO A BIT ROTATING UNDER LOAD AND IS NOT AN ACCEPTABLE
METHOD OF SHARPENING ANY DIMATEC IMPREGNATED DIAMOND BIT. |
