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 This
group of products are similar to surface-set
diamond bits in that they
are set with a single layer of cutters mounted on the
face of the bit in a pre-determined pattern. Instead
of natural drill diamond however, the cutting media
used on geotechnical bits are synthetic polycrystalline
diamond elements. These elements are composed of micron-sized
particles of synthetic diamond that have been formed
into various geometric shapes. Like surface-set diamond
bits, geotechnical bit crowns consist of a tough wear
resistant matrix body that as a minimum includes natural
diamond gauge protection setting. In most cases, the
gauge protection setting is augmented with seismic grade
tungsten-carbide pads and/or polycrystalline diamond
elements.
Shear is the mechanism by which geotechnical
bits cut the formation being drilled. In softer formations,
these bits are capable of very high rates of penetration
when compared to surface-set diamond bits due largely
to their high degree of cutter exposure.
Geotechnical bits are divided into two
categories:
’TSP Type’ (Thermally Stable
Polycrystalline) bits that use smaller triangular and
cubic shaped cutters that are composed entirely of micron-sized
synthetic diamond particles:
  
Triangular-TSP & Cubic-TSP
’Pax Type’ or ‘PCD Type’
(Polycrystalline Diamond) bits that use larger cylindrical
shaped cutters that consist of a layer of micron-sized
synthetic diamond particles that are mounted on a tungsten-carbide
substrate:
  
R-Pax, T-Pax & H-Pax
Geotechnical bits are recommended
for use when drilling relatively soft, abrasive, unconsolidated
sedimentary formations that are not effectively drilled
by surface-set diamond bits. The formation types may
range from very soft Clay, Gypsum or Talc to harder
types of Sandstone. The difference between the various
types of geotechnical bits is in the degree of cutter
exposure and the density (or number) of cutters mounted
on the face of the bit.
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