seen from the isostress curve Fig. 11.40b that the fatigue failure zone of rock is still
in a large coincidence state after one impact. The spacing between the two spherical
teeth continues to increase (t ¼ 1:5D). It can be seen from the isostress curve
Fig. 11.40c that the fatigue failure zone of rock has begun to separate after one
impact. If the tooth spacing is increased to t ¼ 2D (Fig. 11.40d), it can be seen that
the fatigue failure zone of the damaged rock has basically separated.
From the stress nephrogram, it can be more intuitively observed that when
t ¼ 1D (Fig. 11.41a), the stress waves overlap in the middle of the spherical teeth,
which results in a high stress in the middle. As shown in Fig. 11.41b, when
t ¼ 1:5D, the most superficial rock in the middle of the spherical teeth has begun to
appear nondestructive zone. When t ¼ 2D, the non-damaged zone in the middle can
be clearly seen from the stress nephrogram of Fig. 11.41c. In this case, the rock
between the two spherical teeth will produce a “ridge” because of not reach the
failure strength, which will undoubtedly reduce the drilling efficiency. From the
analysis of isostress diagram and the comparison of Fig. 11.41, it can be concluded
that when the spacing of spherical teeth is slightly larger than t ¼ 1:5D, the spacing
is reasonable. The calculation in this case is only a reasonable pitch under this kind
of rock and working condition. According to the specific rock characteristics and
working conditions, the appropriate parameters can be set in the simulation analysis, so as to get a reasonable pitch.
(5) Spherical Tooth Layout of Large Diameter DTH Bit
Based on the above basic layout principles and the simulation results—reasonable
spacing of spherical teeth, combined with the structure of the bit itself, such as the size
and location of exhaust holes and slag suction holes, a reasonable layout of spherical
teeth of a 600 mm DTH hammer bit can be designed, as shown in Fig. 11.42.
Fig. 11.42 1/4 diagram of
reasonable layout of a
600 mm pneumatic DTH
hammer bit
260
11 Pneumatic Down-the-Hole Hammer
in a large coincidence state after one impact. The spacing between the two spherical
teeth continues to increase (t ¼ 1:5D). It can be seen from the isostress curve
Fig. 11.40c that the fatigue failure zone of rock has begun to separate after one
impact. If the tooth spacing is increased to t ¼ 2D (Fig. 11.40d), it can be seen that
the fatigue failure zone of the damaged rock has basically separated.
From the stress nephrogram, it can be more intuitively observed that when
t ¼ 1D (Fig. 11.41a), the stress waves overlap in the middle of the spherical teeth,
which results in a high stress in the middle. As shown in Fig. 11.41b, when
t ¼ 1:5D, the most superficial rock in the middle of the spherical teeth has begun to
appear nondestructive zone. When t ¼ 2D, the non-damaged zone in the middle can
be clearly seen from the stress nephrogram of Fig. 11.41c. In this case, the rock
between the two spherical teeth will produce a “ridge” because of not reach the
failure strength, which will undoubtedly reduce the drilling efficiency. From the
analysis of isostress diagram and the comparison of Fig. 11.41, it can be concluded
that when the spacing of spherical teeth is slightly larger than t ¼ 1:5D, the spacing
is reasonable. The calculation in this case is only a reasonable pitch under this kind
of rock and working condition. According to the specific rock characteristics and
working conditions, the appropriate parameters can be set in the simulation analysis, so as to get a reasonable pitch.
(5) Spherical Tooth Layout of Large Diameter DTH Bit
Based on the above basic layout principles and the simulation results—reasonable
spacing of spherical teeth, combined with the structure of the bit itself, such as the size
and location of exhaust holes and slag suction holes, a reasonable layout of spherical
teeth of a 600 mm DTH hammer bit can be designed, as shown in Fig. 11.42.
Fig. 11.42 1/4 diagram of
reasonable layout of a
600 mm pneumatic DTH
hammer bit
260
11 Pneumatic Down-the-Hole Hammer