The DTH drilling method is growing in
popularity, with increases in all application
segments, including blasthole, water well,
foundation, oil & gas, cooling systems and
drilling for heat exchange pumps.
DTH is short for
“down-the-hole”. Since the DTH method was
originally developed to drill large-diameter
holes downwards in surface-drilling
applications, its name originated from the fact
that the percussion mechanism followed the bit
down into the hole. Applications were later
found for the DTH method underground, where the
direction of drilling is generally upwards
instead of downwards.
In DTH drilling, the percussion mechanism –
commonly called the hammer – is located directly
behind the drill bit. The drill pipes transmit
the necessary feed force and rotation to hammer
and bit plus compressed air for the hammer and
flushing of cuttings. The drill pipes are added
to the drill string successively behind the
hammer as the hole gets deeper. The piston
strikes the impact surface of the bit directly,
while the hammer casing gives straight and
stable guidance of the drill bit. This means
that the impact energy does not have to pass
through any joints at all. The impact energy
therefore remains constant, regardless of the
hole depth. |
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Secoroc COP 54
Gold Express: Raising the bar for DTH
drilling. |
DTH Drilling features
In the hole range 100-254 mm, DTH drilling is the dominant drilling
method today (especially when the hole depth is greater
than 20 metres). The main features of DTH drilling in
this hole range are: excellent hole straightness within
1.5% deviation without guiding equipment; good hole
cleaning, with plenty of air for the hole cleaning from
the hammer; good hole quality, with smooth and even hole
walls for easy charging of explosives; deep hole
drilling capacity, with constant penetration and no
energy losses in joints; and efficient energy
transmission.
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