The unit of diameter D in Eq. (11.22) is m. Considering that DTH hammer
impactor is limited by mining technology and borehole size, cylinder diameter, and
stroke can be selected according to the following equation:
D ¼ kD K ¼ 0:57 $ 0:68
ð
Þ D K
ð11:24Þ
where
D K Drilling diameter.
Normally, the valve rod size of the central exhaust impactor is estimated by the
following equation:
d ¼ 0:32 $ 0:42
ð
Þ D
ð11:25Þ
The model of the outer cylinder of large diameter pneumatic DTH hammer is
shown in Fig. 11.9, and the sectional drawing of the outer cylinder is shown in
Fig. 11.9a.
11.3.5.2 Piston Design
Piston is the main moving part of DTH hammer impactor. Viewed from the
function of piston in valve distribution and the load it bears in operation, the piston
should have high dimensional accuracy and surface roughness, so that it can adapt
to high-frequency up-down reciprocating motion and good airtightness.
In the pneumatic DTH hammer, the piston large diameter matches with the outer
cylinder and the small diameter matches with the inner cylinder. After the inner and
outer cylinder dimensions are determined, the piston large and small diameters are
also determined. The piston weight is estimated by the following equation:
G k ¼ 0:0205D
2:84
ð11:26Þ
The upper equation is obtained when the diameter unit of cylinder block is cm,
in which the G k unit is kg. The piston model of large diameter pneumatic DTH
hammer is shown in Fig. 11.10.
Fig. 11.9 Outer cylinder model. a Sectional drawing of outer cylinder; b outer cylinder shape
11.3 Principle and Parameter Design of Large Diameter …
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