passages depending on the motion of the piston itself. Finally, the exhaust is carried
out through the central exhaust passage. Valveless DTH hammer has only piston as
a moving part, and its overall structure is simple.
(2) Central exhaust DTH impactor
Large diameter pneumatic DTH hammer impactor adopts central exhaust structure,
as shown in Fig. 11.7. The central exhaust impactor refers to the working exhaust
gas of the impactor and a part of compressed air, which directly enters the bottom of
the hole from the hollow passage of the piston and the drill bit. The exhaust gas and
some compressed air from the side exhaust impactor are discharged from the special
holes on the impactor cylinder body to the hole wall and then to the bottom of the
hole.
11.3.3 Selection of Working Parameters
The drilling parameters of DTH hammer mainly include drilling diameter, drilling
depth, drilling direction, and rock firmness coefficient. They are all determined by
the construction technology. These parameters are the original parameters for
designing large diameter pneumatic DTH hammer impactor. According to these
original parameters, the main working parameters of impact equipment, namely
working gas pressure, impact energy, impact frequency, and output power, can be
determined.
(1) Working gas pressure p of DTH hammer
To select and determine the design pressure of DTH hammer, it is necessary to
consider the use of DTH hammer and its operation mode, as well as the ability to
manufacture compressed air equipment at present, such as whether high-pressure air
compressor can be manufactured or not. The international standard ISO5941-1979
has stipulated the design pressures to be used in priority, as detailed in Table 11.5.
At present, 0:49 MPa %0:5 MPa
ð
Þ is widely used as the design pressure of
Table 11.5 Priority design pressure for pneumatic tools and pneumatic machinery
Priority design
pressure (MPa)
Examples of application occasions
0.4
Rock drills and other equipment for coal mines
0.63
General rock drilling machinery, road construction and construction
equipment, machine shop, sheet metal industry, shipyard engineering
tools, etc.
1
Sandblasting equipment for mass production; DTH impactor
equipment
1.6
Heavy-duty DTH impactor
2.5
Pressure to be used later
208
11 Pneumatic Down-the-Hole Hammer
out through the central exhaust passage. Valveless DTH hammer has only piston as
a moving part, and its overall structure is simple.
(2) Central exhaust DTH impactor
Large diameter pneumatic DTH hammer impactor adopts central exhaust structure,
as shown in Fig. 11.7. The central exhaust impactor refers to the working exhaust
gas of the impactor and a part of compressed air, which directly enters the bottom of
the hole from the hollow passage of the piston and the drill bit. The exhaust gas and
some compressed air from the side exhaust impactor are discharged from the special
holes on the impactor cylinder body to the hole wall and then to the bottom of the
hole.
11.3.3 Selection of Working Parameters
The drilling parameters of DTH hammer mainly include drilling diameter, drilling
depth, drilling direction, and rock firmness coefficient. They are all determined by
the construction technology. These parameters are the original parameters for
designing large diameter pneumatic DTH hammer impactor. According to these
original parameters, the main working parameters of impact equipment, namely
working gas pressure, impact energy, impact frequency, and output power, can be
determined.
(1) Working gas pressure p of DTH hammer
To select and determine the design pressure of DTH hammer, it is necessary to
consider the use of DTH hammer and its operation mode, as well as the ability to
manufacture compressed air equipment at present, such as whether high-pressure air
compressor can be manufactured or not. The international standard ISO5941-1979
has stipulated the design pressures to be used in priority, as detailed in Table 11.5.
At present, 0:49 MPa %0:5 MPa
ð
Þ is widely used as the design pressure of
Table 11.5 Priority design pressure for pneumatic tools and pneumatic machinery
Priority design
pressure (MPa)
Examples of application occasions
0.4
Rock drills and other equipment for coal mines
0.63
General rock drilling machinery, road construction and construction
equipment, machine shop, sheet metal industry, shipyard engineering
tools, etc.
1
Sandblasting equipment for mass production; DTH impactor
equipment
1.6
Heavy-duty DTH impactor
2.5
Pressure to be used later
208
11 Pneumatic Down-the-Hole Hammer