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The total sound power is inversely
calculated on the basis of the specific
sound power
To convert a known (measured) sound
power of a belt conveyor to another belt
speed, we apply the following empirical
formula:
In accordance with the following
diagram, it is enabled the specific sound
power level to be derived from the
sound pressure measuring by adding the
distance.
Many tests made in the last 20 years on belt conveyors
we built, where a belt speed of 2.0 m/s has been taken as
standard, allow to tell the difference between the following
two sound power groups on idlers:
• quiet idlers L` = 60 dB(A)/m bis 75 dB(A)/m
W
• standard idlers L` = 70 dB(A)/m bis 80 dB(A)/m
W
As a function of the highly estimated sound power
and the weather conditions, the pipe conveyor has been
equipped with a single-layer trapezoidal sheet wall
cladding and a single-layer trapezoidal sheet roof, in order
to get a shielding in direction of the Rhine river and the test
point that is located there.
On the basis of the sound pressure measurements taken
along the closed side of the pipe conveyor, there could be
calculated a sound power level of LWA = 85,2 dB(A), and
on the open side, there has been calculated, considering
the reflection resulting from the cladding, a sound power
level of LWA = 98,4 dB(A).
The idlers are considered the main noise source on
belt conveyor systems. That is the reason why special
attention must be turned to the selection of correct and
appropriate idlers. Comparison measurements made on
a test carrier have shown that the sound pressure levels
taken at a distance of 1m from a belt conveyor system did
vary between 68dB(A) and 72dB(A), dependent on idlers of
different manufacturers and type.
When use is made of plastic bushes between the idler
axle and the idler support, particular attention must be
directed towards the electrical conductivity of the bushes
within the EX-zone.
Issue 04 | 2010
TRANSFER OF TECHNOLOGY
Fig. 12:
Distance for linear sources of sound
Fig. 13:
Cross-section of the belt bridge of the pipe conveyor
Because of the large number of idlers installed, pipe
conveyors also emit a higher sound power than comparable
troughed belt conveyors. As the pipe conveyor does not
require transfer stations, it is enabled the belt bridges to
be a tighter type, a fact simplifying actions in the matter of
sound insulation. So, the rating of the pipe conveyor is as
bad or as good as that of a troughed belt conveyor, seen
from a sound-specific point of view.
From the following table can be seen a further, interesting
effect. At the start of the pipe conveyor operation, the
sound power level taken at the belt route was higher (by
10,3dB(A)) than after an operation of 2 months. The reason
is probably a micro-motion of the inner belt edge against
the outer belt surface within the lap joint of the belt. Since
the maximum level was 2,5kHz, the effect, that could be
very strongly noticed, had a considerable influence on
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