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 The
application of hard-metal strips to the steel body of
most types of diamond tools is available and recommended
when drilling in highly abrasive formations. These strips
aid in the prevention of premature erosion of the steel
tool shank. In most cases, three equally spaced strips
are applied to the steel tool shank. The approximate
dimensions of each strip are 12mm (0.50 inch) wide by
0,5mm (0.02 inch) thick. The length of the strips varies
according to the type of tool and typically covers the
area indicated in the illustration below.
The hard-metal strips
are composed of micron-sized tungsten-carbide particles
that are suspended in a metal alloy and are applied
using a plasma spray technique. Due to the elevated
fusion temperatures that are required for this process,
the application of hard-metal strips on some thin-wall
diamond tools is not possible.
With the exception
of “Heavy Duty Reaming Shells”, hard-metal
strips are provided only on request. Pricing for this
option varies by tool type. Contact Dimatec for a quotation.
This type of bit is identical to
those with standard set diameters with the exception
of the outside set diameter. Generally, these units
are manufactured with an outside set diameter that is
equivalent to that of the reaming shell driving the
bit. These bits are commonly referred to as “RSG”
(Reaming Shell Gauge) core bits. This configuration
has an advantage over bits manufactured with standard
set diameters in that the bit does the bulk of the cutting
and thus reduces the amount of wear on the reaming shell.
The disadvantage of this configuration is that there
is a greater tendency for the drill hole to deviate,
particularly under higher bit loads.
A second group of common oversize set
diameters exists in the B, N, HXB and HQ size ranges.
These set diameters are 2.400 inches (60,96mm), 3.032
inches (77,00mm), 3.750 inches (95,25mm) and 3.830 inches
(97,28mm) respectively. Bits manufactured with these
oversize outside set diameters provide a substantially
larger annular area between the wall of the drill hole
and the drill string. They are particularly well suited
to conditions where ground swell tends to jam the drill
string in the hole or where relatively large cuttings
must be transported to the surface. High volume pumping
equipment is recommended in this case. A reaming shell
with an equivalent outside set diameter should be used
in this arrangement.
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