Retsch AS 300 - Manual (Page 17)

07/02/2012 Retsch GmbH
17
Time correction
Our investigations have shown that the switch to specifying the
sieve plate acceleration instead of the amplitude is the
most significant influencing variable when sieving at varying
frequencies. Nevertheless, it is clear that an equal sieving time
at 60Hz will involve 20% more sieve strokes than at 50Hz,
which basically is on a par with an extension to the sieving
time. Especially when short sieving times are selected, we ac-
cordingly recommend that the sieving time is corrected with
the help of EasySieve
®
Acceleration guidelines
The relevant specialist textbooks, e.g. "Zerkleinerungs- und
Klassiermaschinen" (Crushers and Classifiers) by Prof. Dr. Karl
Höffl, designate sieve plate acceleration in "g" with the letter K
and describe the relationship between this and the sieving ef-
fect as follows:
K
(„g“)
Movement of charge Sieve performance Associated
amplitude at
50 Hz
Associated
amplitude at
60 Hz
1,0 No throw, flow or slip Very sluggish,
sieve plate clogs up quickly 0.2 mm 0.14 mm
1,5 Gradual lift Sluggish,
sieve plate clogs up slowly 0.3 mm 0.21mm
1,8 Very flat throw Very gentle action for material
which is easy to screen 0.36 mm 0.25mm
2,3 Flat to slightly steep
throw
Gentle action for material which is
less easy to screen 0.46 mm 0.32mm
3,5 Steep throw Brisk action 0.7 mm 0.5 mm
4 Very steep throw Very brisk action with strong
separation 0.8 mm 0.55 mm
We have added the last two columns to show the associated
amplitudes for the two most common mains power frequencies
in the world.
These particulars should only be regarded as rough values ap-
plicable to small charges, when the material to be screened can
generally move around the sieve plate as discrete grains due to
its distribution.
In the laboratory, however, the pulse transmitted by the sieve
plate are usually muffled by thick layers of charge and the
sieve plate of the analytic sieve itself vibrates. Accordingly,
higher K-factors are required in everyday laboratory practice
than those resulting from the dynamics of individual grains.
Thus for everyday practice, the aforesaid recommendations
need to be multiplied by a factor of 1.5 - 2.