As the name suggests, the
surface-set diamond bit differs from the impregnated diamond type in that they
are set with a single layer of natural drill diamond on the working surfaces of
the bit crown in a pre-determined pattern.
The diamonds are mounted
in a bit crown powdered metal matrix body that is fused to a steel tool body or
shank. Unlike impregnated diamond bits where the controlled erosion of the
powdered metal bit crown is desirable to expose new diamond crystals, the metal
bond matrix used for all IDP surface-set bits is extremely tough and
wear-resistant. The function of the bit crown matrix body on a surface-set bit
is to securely hold the diamonds in position throughout the operational life of
the bit.
Surface-Set diamond bits
are primarily recommended for use in drilling relatively soft, abrasive,
unconsolidated formations that are not effectively drilled by impregnated
diamond bits. They are also recommended for use in drilling harder formations
where the available rotational speeds and bit loads are insufficient to use
impregnated diamond bits due to drilling equipment limitations.
In most cases, surface-set
diamond bits will provide higher rates of penetration than impregnated diamond
bits in softer formations due largely to the greater degree of exposure of the
individual diamond crystals. However, as they are set with only a single layer
of diamond crystals, surface-set diamond bits will generally yield a lower
overall bit life than impregnated diamond bits.
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