2038
Passing Probability Model for Non-Uniform Screen Deck
Eero Pohjasenaho, Keijo Viilo
Metso, Finland
Maria Sinche-Gonzalez
University of Oulu, Oulu Mining School, Finland
ABSTRACT: Several apertures are employed on a single screen deck in the mining and aggregate industries. This
work presents i) the development of a passing probability simulation model for a single screen deck with varying
aperture size and ii) the development of a continuous model that can forecast screening efficiency, throughput
rate, material bed depth along the screen deck, and particle size distributions of undersize and oversize material.
Those were integrated into Microsoft Excel so that the model could be used to select appropriately sized apertures
for the screening media. According to the results, the passing probability model is most precise when the rate
of fine material fed to the screen is controlled so that it is not overloaded. The new model was verified with a
multi-slope vibrating screen type.
INTRODUCTION
Variables that influence the screening performance are
numerous and they can be divided into three larger groups
(Metsälä, 2008). The first group is the characteristics of the
screened material. In this group, the distribution is a partic-
ularly important factor that determines the difficulty level
of screening. For example, particle shape and humidity
influence the passage. Feed rate influences the capacity. The
surface structure and physical properties of the feed mate-
rial influence screening performance. The second group is
the screening media, where the aperture size is based on
the required cut point and the aperture shape is considered
when the product has shape-based quality requirements.
The screen effective open area and thickness of the screen-
ing media are also related to each other. The material of the
screening media is important considering the effective open
area and lifetime of the screen. The third group is screen-
ing mechanical parameters, which have factors like angular
rotation speed, stroke, deck inclination angle and dimen-
sions of screening area.
According to the Vibrating Screen Manufacturers
Association (VSMA, 1998), ten different variables, such as
basic capacity, amount of oversize material, amount of half
size material, deck location, wet screening, material bulk
density, effective open area, aperture shape and screening
efficiency, have been used in the sizing of vibrating screens.
Manufacturers have been using the same widely known
theory and variables presented in the VSMA manual.
Despite the research, there are no other widely used models
for screen sizing than the VSMA model (1998).
The problem is that vibrating screens are designed and
sized nowadays with one aperture size, but in the indus-
try, there are many applications where multiple different
sized apertures on the screens are used, for example, in
banana screens, where different sized apertures can be used
in multi-deck applications. These applications are obtained
with experimental methods.
The objectives of this work were to introduce a model
for passing probability of screened material to simulate dif-
ferent sized apertures on the same screen deck. The second
Passing Probability Model for Non-Uniform Screen Deck
Eero Pohjasenaho, Keijo Viilo
Metso, Finland
Maria Sinche-Gonzalez
University of Oulu, Oulu Mining School, Finland
ABSTRACT: Several apertures are employed on a single screen deck in the mining and aggregate industries. This
work presents i) the development of a passing probability simulation model for a single screen deck with varying
aperture size and ii) the development of a continuous model that can forecast screening efficiency, throughput
rate, material bed depth along the screen deck, and particle size distributions of undersize and oversize material.
Those were integrated into Microsoft Excel so that the model could be used to select appropriately sized apertures
for the screening media. According to the results, the passing probability model is most precise when the rate
of fine material fed to the screen is controlled so that it is not overloaded. The new model was verified with a
multi-slope vibrating screen type.
INTRODUCTION
Variables that influence the screening performance are
numerous and they can be divided into three larger groups
(Metsälä, 2008). The first group is the characteristics of the
screened material. In this group, the distribution is a partic-
ularly important factor that determines the difficulty level
of screening. For example, particle shape and humidity
influence the passage. Feed rate influences the capacity. The
surface structure and physical properties of the feed mate-
rial influence screening performance. The second group is
the screening media, where the aperture size is based on
the required cut point and the aperture shape is considered
when the product has shape-based quality requirements.
The screen effective open area and thickness of the screen-
ing media are also related to each other. The material of the
screening media is important considering the effective open
area and lifetime of the screen. The third group is screen-
ing mechanical parameters, which have factors like angular
rotation speed, stroke, deck inclination angle and dimen-
sions of screening area.
According to the Vibrating Screen Manufacturers
Association (VSMA, 1998), ten different variables, such as
basic capacity, amount of oversize material, amount of half
size material, deck location, wet screening, material bulk
density, effective open area, aperture shape and screening
efficiency, have been used in the sizing of vibrating screens.
Manufacturers have been using the same widely known
theory and variables presented in the VSMA manual.
Despite the research, there are no other widely used models
for screen sizing than the VSMA model (1998).
The problem is that vibrating screens are designed and
sized nowadays with one aperture size, but in the indus-
try, there are many applications where multiple different
sized apertures on the screens are used, for example, in
banana screens, where different sized apertures can be used
in multi-deck applications. These applications are obtained
with experimental methods.
The objectives of this work were to introduce a model
for passing probability of screened material to simulate dif-
ferent sized apertures on the same screen deck. The second