large. The impact frequency of DTH hammer equipment can be estimated
according to the following empirical formulas:
f ¼ 10:4 þ 7:6p
ð11:2Þ
In the formula, the unit of frequency f is Hz and the unit of design pressure p of
DTH hammer is MPa.
(4) Output Power
After choosing the impact energy and frequency, the output power of the equipment
can be obtained by taking the product of the impact energy and the impact frequency, whose unit is kW.
11.3.4 Calculation Method of Performance Parameters
When DTH hammer impactor works, its internal dynamic process is very complex.
It is assumed that the pressure of the air chamber and the atmosphere in the exhaust
stage of the impactor is one atmosphere in a working cycle. When the air chamber
is connected with the compressor pipeline, the pressure is the supply pressure.
When the air chamber is disconnected from the atmosphere and the compressed gas
pipeline, the process of an adiabatic expansion or adiabatic compression should be
considered.
11.3.4.1 Calculation Method for General Design of Performance
Parameters
A modified coefficient is used to generalize the effects of mechanics and thermodynamics, which is called the total coefficient method. The basic idea of calculating
the total coefficient is the gas pressure in the piston is nonconstant, and the actual
stroke of the piston is less than the structural stroke. The weight of the moving
parts, the mechanical friction resistance, and the rebound force after collision have a
great influence on the performance parameters.
(1) Calculation of impact energy
The work done by the piston of the impactor to the drill bit can be expressed as the
product of the force P and the distance s experienced, i.e.,
e ¼ Ps ¼ p w A k s
ð11:3Þ
210
11 Pneumatic Down-the-Hole Hammer
according to the following empirical formulas:
f ¼ 10:4 þ 7:6p
ð11:2Þ
In the formula, the unit of frequency f is Hz and the unit of design pressure p of
DTH hammer is MPa.
(4) Output Power
After choosing the impact energy and frequency, the output power of the equipment
can be obtained by taking the product of the impact energy and the impact frequency, whose unit is kW.
11.3.4 Calculation Method of Performance Parameters
When DTH hammer impactor works, its internal dynamic process is very complex.
It is assumed that the pressure of the air chamber and the atmosphere in the exhaust
stage of the impactor is one atmosphere in a working cycle. When the air chamber
is connected with the compressor pipeline, the pressure is the supply pressure.
When the air chamber is disconnected from the atmosphere and the compressed gas
pipeline, the process of an adiabatic expansion or adiabatic compression should be
considered.
11.3.4.1 Calculation Method for General Design of Performance
Parameters
A modified coefficient is used to generalize the effects of mechanics and thermodynamics, which is called the total coefficient method. The basic idea of calculating
the total coefficient is the gas pressure in the piston is nonconstant, and the actual
stroke of the piston is less than the structural stroke. The weight of the moving
parts, the mechanical friction resistance, and the rebound force after collision have a
great influence on the performance parameters.
(1) Calculation of impact energy
The work done by the piston of the impactor to the drill bit can be expressed as the
product of the force P and the distance s experienced, i.e.,
e ¼ Ps ¼ p w A k s
ð11:3Þ
210
11 Pneumatic Down-the-Hole Hammer