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The coupling hoods, screw-connected to
the same base plate, got uncoupled with the
aid of plastic elements. For such hoods, whose
primary function consists in a protection against
accidental contact, the obvious thing to do
would be to use perforated plates or expanded
metal or similar instead of solid sheet metal.
A perforated portion of 30 % makes it already
possible to reduce the sound radiation by 80 %.
The two actions mentioned before could help
to minimize the sound power level of the drive
unit from at first LWA = 101,9 dB(A) to LWA = 99,2
dB(A). Thus, the sound power level has almost
halved.
Material flow divider
Issue 04 | 2010
Fig. 16:
Corner station North-East with material flow
divider and bifurcated chute
We follow the coal on its further way and get through
the cross conveyor No. 8 to the corner station North-East.
This corner station accommodates a material flow divider,
enabling the coal to be transported through the feeding belt
conveyor No. 10 to the stacker. Or alternatively, to guide
the material flow through the reclaiming belt conveyor No.
12 towards the coking plant. The distance between the
two belt conveyors and the minimally possible inclination
of the chutes, lead to a relatively high minimum fall of the
material at the cross conveyor.
Due to the high fall and dependent on the nature of
coal (grain size, moisture, etc.) the sound power level
produced by the material flow divider experiences a
change. On the chutes, there occurs an acoustic pattern,
very similar to the white noise, featuring a large bandwidth
of frequencies. Because of the equipartition of the energy
density for the frequencies, the human ears regard this
noise as very unpleasant. The large dimensions of the
chute and, consequently, the large enveloping surface
result in remarkable sound power levels.
It follows for the material flow divider a total sound
power level of:
TRANSFER OF TECHNOLOGY
The dependence of the sound power level on the
enveloping surface is made clear with the help of this
example. An area with a low sound pressure level at
its top can produce a considerably high sound power,
provided that the area is sufficiently large. That is a clear
demonstration of the analogy to the thermodynamics. A
heating unit is able to warm up a room in spite of its low
surface temperature. The human can touch the heating
unit without getting burnt the fingers. But we cannot touch
the match flame whose energy is not sufficient enough to
warm up the room.
Possible actions to help to reduce the sound power of
the chute are:
Table 9:
Sound pressure level of bifurcated
chute on in different heights
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