pneumatic impact equipment in China. The large diameter pneumatic DTH hammer
designed in this case is used for rapid drilling in various complex geological
conditions, such as filling stratum, clay stratum, pebble stratum, and weathered sand
stratum, to form large bearing capacity rock entry pile and anti-slide pile to prevent
geological hazards. Drilling diameter ! 600 mm requires high-pressure impact
equipment to form large bearing capacity. Combined with ISO5941-1979, the
tentative design pressure is 1:6 MPa.
(2) Estimation of impact energy e
For the DTH impactor used for drilling large holes, its design impact energy
fluctuates widely, generally more than 100 J. This is related to the use of
high-pressure air handling equipment in DTH impactor. The design impact energy
can be pre-calculated according to the following empirical formulas:
e ¼ 21K
p
p p
e
0:152D
ð11:1Þ
where
p Supply pressure of DTH hammer (Pa);
p p Standard design pressure, p p ¼ 5 Â 10
5 Pa;
K Amplitude modulation coefficient, K value fluctuates in the range of 1 $ 1:17,
when the supply pressure of pneumatic circuit is 5 Â 10
5 Pa, K ¼ 1;
D Drilling diameter (cm).
(3) Impact frequency
Choosing the impact frequency is an important work in the design of large diameter
pneumatic DTH hammer impactor. The output power of DTH hammer can be
directly increased by increasing the impact frequency when the impact energy e is
selected. In terms of the structure of impactor, to increase the impact frequency, the
piston stroke must be reduced, which will reduce the impact energy of a single
impact. When the impact energy of a single impact decreases to a certain extent, no
matter how to increase the impact frequency, there will be no good drilling effect.
On the contrary, increasing piston stroke can improve the single impact energy and
reduce the impact frequency. Therefore, the selection of impact frequency is
restricted by impact energy.
The design frequency of pneumatic DTH hammer is generally lower than that of
other percussive drilling machines. Usually, when the design pressure is 0:5 MPa, it
is not more than 16:6 Hz. However, the design pressure of large diameter pneumatic
DTH hammer used in complex geology such as fill, pebble, and sand layers is far
more than 0:5 MPa, so the impact frequency fluctuation range of its equipment is
11.3 Principle and Parameter Design of Large Diameter …
209
designed in this case is used for rapid drilling in various complex geological
conditions, such as filling stratum, clay stratum, pebble stratum, and weathered sand
stratum, to form large bearing capacity rock entry pile and anti-slide pile to prevent
geological hazards. Drilling diameter ! 600 mm requires high-pressure impact
equipment to form large bearing capacity. Combined with ISO5941-1979, the
tentative design pressure is 1:6 MPa.
(2) Estimation of impact energy e
For the DTH impactor used for drilling large holes, its design impact energy
fluctuates widely, generally more than 100 J. This is related to the use of
high-pressure air handling equipment in DTH impactor. The design impact energy
can be pre-calculated according to the following empirical formulas:
e ¼ 21K
p
p p
e
0:152D
ð11:1Þ
where
p Supply pressure of DTH hammer (Pa);
p p Standard design pressure, p p ¼ 5 Â 10
5 Pa;
K Amplitude modulation coefficient, K value fluctuates in the range of 1 $ 1:17,
when the supply pressure of pneumatic circuit is 5 Â 10
5 Pa, K ¼ 1;
D Drilling diameter (cm).
(3) Impact frequency
Choosing the impact frequency is an important work in the design of large diameter
pneumatic DTH hammer impactor. The output power of DTH hammer can be
directly increased by increasing the impact frequency when the impact energy e is
selected. In terms of the structure of impactor, to increase the impact frequency, the
piston stroke must be reduced, which will reduce the impact energy of a single
impact. When the impact energy of a single impact decreases to a certain extent, no
matter how to increase the impact frequency, there will be no good drilling effect.
On the contrary, increasing piston stroke can improve the single impact energy and
reduce the impact frequency. Therefore, the selection of impact frequency is
restricted by impact energy.
The design frequency of pneumatic DTH hammer is generally lower than that of
other percussive drilling machines. Usually, when the design pressure is 0:5 MPa, it
is not more than 16:6 Hz. However, the design pressure of large diameter pneumatic
DTH hammer used in complex geology such as fill, pebble, and sand layers is far
more than 0:5 MPa, so the impact frequency fluctuation range of its equipment is
11.3 Principle and Parameter Design of Large Diameter …
209