A new face drilling rig for narrow tunnels and ... - Advanced Mining
A new face drilling rig for narrow tunnels and ... - Advanced Mining
A new face drilling rig for narrow tunnels and ... - Advanced Mining
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Table 8: Time change of the third-octave<br />
spectrum of a pipe conveyor<br />
the measuring result, because the A-weighting even gets<br />
here maximally. Having treated the belt edge with talcum<br />
powder, the noise level did directly sink by the difference<br />
of 10.3 dB(A). After an operation of approx. 2 months, <strong>and</strong><br />
without further treatment with talcum, the sound level get<br />
levelled out at Lw=69.9 dB(A), <strong>and</strong> it could sink further in<br />
fact.<br />
All belt conveyor drives have sound protection hoods.<br />
Nevertheless, the sound power taken at the pipe conveyor<br />
drive unit in the corner station North-West exceeded the<br />
value planned. That was caused due to the instruction,<br />
providing <strong>for</strong> a mounting of the drive unit on a base plate.<br />
This plate was set vibrating by the drive unit, a condition<br />
audible <strong>and</strong> measurable in the <strong>for</strong>m of airborne sound.<br />
With a view to reducing the sound, the base plate was put<br />
into an off-tuned state by fixing steel cubes to the points<br />
exposed to the highest particle velocity.<br />
To determine the positions where the steel cubes have<br />
to be welded on, one draws on the discovery made by Ernst<br />
Florens Friedrich Chladni at the end of the 18th century,<br />
furnishing proof of the fact that it comes to a characteristic<br />
spreading of s<strong>and</strong>, having uni<strong>for</strong>mly sprinkled with s<strong>and</strong><br />
plates <strong>and</strong> membrane elements <strong>and</strong> set into natural<br />
vibration then. The s<strong>and</strong> is carried away from the areas<br />
exposed to the highest particle velocity, the bulges, <strong>and</strong> it<br />
accumulates on st<strong>and</strong>ing nodal lines <strong>and</strong> points exposed<br />
to lowest particle velocity. The nodal lines are function of<br />
the plate <strong>for</strong>m <strong>and</strong> the type of holder.<br />
If a driving plate is sprinkled with s<strong>and</strong> <strong>and</strong> put into<br />
operation <strong>for</strong> some time, it will come to figured effects that<br />
are similar to the Chladni’s figures. Now, the steel cubes<br />
have to be fixed by welding to the points presenting a small<br />
quantity of s<strong>and</strong>.<br />
Issue 04 | 2010<br />
Fig. 15:<br />
Chladni’s figures<br />
TRANSFER OF TECHNOLOGY<br />
Fig. 14:<br />
Acoustic off-resonance of a drive frame<br />
www.advanced-mining.com<br />
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