2040 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
amount of oversize material OS [t/h] from each of the cal-
culation elements.
As the feed material enters the calculation element, it is
evenly distributed. BD is the material bed depth in each of
the calculation elements and W is the width of the effective
screening area. Apl is the actual passage layer, which deter-
mines the thickness of the material bed from which the
undersized material can pass the screen. In the actual pas-
sage layer, undersized material has the probability for pas-
sage with one attempt. The length of the effective screening
area and the length of the material throw LT determine the
theoretical number of attempts that the screened material
must pass through the screen.
LIMITATIONS OF THE FUNCTIONS IN
THE PASSING PROBABILITY MODEL
The probability function works with certain limitations
in the new model. It calculates the passing probability for
each of the fractions mean sized particles, if the determined
aperture size in the calculation element is larger than the
particle. Otherwise, the passing probability is zero.
The height of the actual passage layer, Apl, is calculated
from two different blockage functions. If the second func-
tion turns down to zero, there is always the first blockage
function calculating the height of the bed where material
can pass the screen deck. Another limitation considers
the layers in the model. If the material bed on the screen
decreases so low that it is equal to the actual passage layer,
the thickness of the actual passage layer is the thickness of
the material bed on the screen. In this case, the whole ton-
nage of the material bed in the calculation element is mul-
tiplied by the probability of passage to obtain the amount
of undersize material.
MODEL IMPLEMENTATION AND
VERIFICATION
Testing of the passing probability model was done with the
1998s test results made by the Nordberg-Lokomo company.
The initial purpose of the tests was to ensure the mechani-
cal strength of the prototype Trible Slope screen TS18.60.
Other targets were to measure the screening capacity and
the screening efficiency in different cases. Also, there was
a desire to determine the optimal settings for the screen
and to generate a screen calculation theory for multi-slope
screens at the time (Viilo, 1998).
The implementation and verification of the passing
probability model were done in Microsoft Excel, where it
was built and tested with 10 test results from 1998. The
compared results were the passing probability model results
and the 1998s test results. The compared factors were the
screening efficiency, the throughput rate, the material bed
depth, and the distribution of the oversize material.
THE 1998S TESTS, VERIFICATION
PROCESS AND MODEL EVALUATION
As shown in Figure 2, the 1998s tests were executed so that
different feed materials were fed to the closed test circuit
consisting of a feeder, four conveyors, B280T screen and
Figure 1. The principle of the passing probability model represents its basic functions
amount of oversize material OS [t/h] from each of the cal-
culation elements.
As the feed material enters the calculation element, it is
evenly distributed. BD is the material bed depth in each of
the calculation elements and W is the width of the effective
screening area. Apl is the actual passage layer, which deter-
mines the thickness of the material bed from which the
undersized material can pass the screen. In the actual pas-
sage layer, undersized material has the probability for pas-
sage with one attempt. The length of the effective screening
area and the length of the material throw LT determine the
theoretical number of attempts that the screened material
must pass through the screen.
LIMITATIONS OF THE FUNCTIONS IN
THE PASSING PROBABILITY MODEL
The probability function works with certain limitations
in the new model. It calculates the passing probability for
each of the fractions mean sized particles, if the determined
aperture size in the calculation element is larger than the
particle. Otherwise, the passing probability is zero.
The height of the actual passage layer, Apl, is calculated
from two different blockage functions. If the second func-
tion turns down to zero, there is always the first blockage
function calculating the height of the bed where material
can pass the screen deck. Another limitation considers
the layers in the model. If the material bed on the screen
decreases so low that it is equal to the actual passage layer,
the thickness of the actual passage layer is the thickness of
the material bed on the screen. In this case, the whole ton-
nage of the material bed in the calculation element is mul-
tiplied by the probability of passage to obtain the amount
of undersize material.
MODEL IMPLEMENTATION AND
VERIFICATION
Testing of the passing probability model was done with the
1998s test results made by the Nordberg-Lokomo company.
The initial purpose of the tests was to ensure the mechani-
cal strength of the prototype Trible Slope screen TS18.60.
Other targets were to measure the screening capacity and
the screening efficiency in different cases. Also, there was
a desire to determine the optimal settings for the screen
and to generate a screen calculation theory for multi-slope
screens at the time (Viilo, 1998).
The implementation and verification of the passing
probability model were done in Microsoft Excel, where it
was built and tested with 10 test results from 1998. The
compared results were the passing probability model results
and the 1998s test results. The compared factors were the
screening efficiency, the throughput rate, the material bed
depth, and the distribution of the oversize material.
THE 1998S TESTS, VERIFICATION
PROCESS AND MODEL EVALUATION
As shown in Figure 2, the 1998s tests were executed so that
different feed materials were fed to the closed test circuit
consisting of a feeder, four conveyors, B280T screen and
Figure 1. The principle of the passing probability model represents its basic functions