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Vibration Diagnosis of Sand Units in Stone Crusher Plant On-site Field Test

02 Jun 2020-

TL;DR: The vibration caused from the beating is significantly reduced by adjusting the driving frequencies for the sand units so that they are sufficiently scattered to avoid the beating.
Abstract: Due to limitation of natural sand from rivers and seas, artificial sand production from large stones or rocks is being increased. However, this sand manufacturing process is dangerous and causes several social problems such as high level of unwanted vibrations or noises. This study investigates vibration characteristics of sand and screen units in artificial sand production plant whose actuating operation is multiple with several different exciting frequencies. As a first step, vibration levels are measured at the sand and screen unit positions using accelerometers in time and frequency domains. The measurement is carried out at two different conditions: activating sand unit only and operating entire facilities such as stone crusher. Vibration signals acquired from several locations of the sand and screen units of the plant are collected and analyzed from waveforms and spectrums of the signals. It is identified that the vibration acceleration level of the screen unit is higher than that of the sand unit. In addition, it is found from the acceleration signals measured at plant office and shipping control center those places are far away from the plant location that the beating phenomenon is occurred by close driving frequencies for several sand units. In this work, the vibration caused from the beating is significantly reduced by adjusting the driving frequencies for the sand units so that they are sufficiently scattered to avoid the beating.
Topics: Crusher (54%)

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applied
sciences
Article
Vibration Diagnosis of Sand Units in a Stone Crusher
Plant: An On-Site Field Test
Seong-Hwan Kim
1
, Bo-Gyu Kim
1
, Dong-Soo Jung
1,
*, Seung-Bok Choi
1,
* , Jong-Mu Lee
2
and
Kyu-Bong Lee
2
1
Smart Structure Systems Laboratory, Department of Mechanical Engineering, Inha University,
Incheon 22212, Korea; neumann9177@naver.com (S.-H.K.); kims21006@nater.com (B.-G.K.)
2
Maleun Environment Industrial Co. Ltd., Incheon 21687, Korea; ljmsim@naver.com (J.-M.L.);
sa@maleun.co.kr (K.-B.L.)
* Correspondence: dsjung@inha.ac.kr (D.-S.J.); seungbok@inha.ac.kr (S.-B.C.)
Received: 1 June 2020; Accepted: 18 June 2020; Published: 24 June 2020


Abstract:
Due to the shortage of natural sand from rivers and seas, artificial sand production from
large stones or rocks is being increased. However, this sand manufacturing process is dangerous
and causes several social problems such as a high level of unwanted vibrations or noises. This study
investigates the vibration characteristics of sand and screen units in an artificial sand production
plant whose operation is multiple with several actuators dierent exciting frequencies. As a first
step, vibration levels are measured at the sand and screen unit positions using accelerometers in time
and frequency domains. The measurement is carried out at two dierent conditions: activating only
the sand unit and operating entire facilities such as a stone crusher. Vibration signals acquired from
several locations of the sand and screen units of the plant are collected and analyzed from waveforms
and spectrums of the signals. We identified that the vibration acceleration level of the screen unit is
higher than that of the sand unit. In addition, it is found from the acceleration signals measured at the
plant oce and shipping control center (which are far away from the plant location) that the beating
phenomenon arose due to close driving frequencies for several sand units. In this work, the vibration
caused from the beating is significantly reduced by adjusting the driving frequencies for the sand
units so that they are suciently scattered to avoid the beating.
Keywords:
artificial sand plant; stone crusher; screen unit and sand unit; beating phenomenon;
vibration measurement and reduction
1. Introduction
Natural sand has been formed through the normal erosion process of exposed rocks. Sands of
various configurations, dierent sizes, and dierent non-rock inclusions of organic material are lined
on the beach or with rivers or lake shores. Therefore, sand can be easily found in our surrounding
natural environment, such as rivers and seas. Over the past decades, humans have been required large
amounts of sand for social overhead capital (SOC) facilities and infrastructure, including large-scale
construction of buildings, roads, bridges, airports, and harbors. However, as most natural sand
is obtained from rivers and seas, its availability in the natural environment is limited. Moreover,
indiscriminate collection of sand from rivers causes flooding and destruction of the natural environment
such as river ecosystems, leading to various social issues. In the case of sand collected from the sea,
it must proceed by removing the salt and undergoing a drying process. Therefore, a method for
manufacturing artificial sand using a stone or rock grinding mechanism is used as a solution to prevent
environmental destruction and sand depletion problems caused by massive natural sand production.
In contrast, artificial sand is essentially manufactured or processed to have appropriate particle sizes
Appl. Sci. 2020, 10, 4327; doi:10.3390/app10124327 www.mdpi.com/journal/applsci

Appl. Sci. 2020, 10, 4327 2 of 17
required for the intended utilization. Most studies related to artificial sand in civil engineering have
focused on the comparison of strength property between natural sand-based concrete and artificial
sand-based concrete [
1
7
]. In addition, several works on the equipment design and analysis have been
reported to enhance the production eciency of an artificial sand manufacturing facility [
8
11
]. A few
works on the vibration problem of artificial sand manufacturing facilities have been introduced by
carrying out transverse and longitudinal oscillation analysis of screen units [
12
,
13
]. Recently, in order
to improve the screening eciency of the vibration screen and make the vibration process smoother,
a new type MR damper was proposed and evaluated at a laboratory level [
14
]. Furthermore, shape
memory alloy (SMA) is applied to the screen unit to properly achieve a sucient spring constant by
controlling the operating temperature [15].
The rock (or stone) breaking and crushing process plays an important role in minimizing the
particle size of stone or rock for various construction activities, such as building bridges or infrastructure.
They can be obtained in large quantities from artificial sand production plant facilities such as jaw
crushers, vibration screen units and sand units. In the manufacturing process of an artificial sand,
relatively large stones or rocks are first crushed, then screened, washed, and fine-sized [
16
21
]. An
artificial sand production system consists of large motors with high power output and jaw crusher or
impact crusher to break rocks or large stones. In addition, a hopper and cone crusher are required to
break large stones into small sized stones or gravels. Then, the gravel and sand which are respectively
transferred to the vibrating screen unit and sand unit are sorted by particle size by a washing and
screening process. Subsequently, the fine sand is moved to a designated storage place Thus, the artificial
sand production from crushed stones or rocks requires various types of equipment related to the full
manufacturing processes. These facilities are large and hence inevitably have a significant impact,
generating a high level of vibration and noise. Therefore, an artificial sand manufacturing plant should
be built on large plains or mountain entrances which are far from densely populated residential areas
and industrial complexes. Otherwise, if an artificial sand plant is located close to a densely populated
area such as a residential complex or an industrial complex, then there will exist significant noise and
vibration issues when the artificial sand manufacturing facilities are operating in such sites. Many
complaints are also related to the transmission of such vibrations, shock, and noise by the residents in
the adjacent areas.
Most of the artificial sand manufacturing facilities include vibration isolating devices that are
operated by simply installing several coil spring parallelly around the device, and most structures
comprise simple steel structures connected by welding H-beams (Maleun Environmental Co. Ltd.
made by artificial sand facilities Manufacturer). Therefore, the vibration generated in the facility is
transmitted to the ground through the vibration isolating device and supporting structures. The noise
generated during the operation of the manufacturing facility is at a loud level, exceeding 90 dB. Thus,
it is impossible to communicate with another operator. It is well known that vibration is measured as
three physical parameters: displacement, velocity, and acceleration. Among these three parameters,
the acceleration is frequently adopted to analyze vibration intensity. Since the main issue of this
work is to investigate the vibration intensity that occurs in an artificial sand production plant, we
used several accelerometers. However, it is noted that displacement sensors such as linear variable
dierential transducer (LVDT) are also used for vibration control focusing on the displacement of
flexible structures. The vibration level of an artificial sand facility plant is severe, and this vibration is
propagated to the surrounding through floors and structures. This vibration can be also detected in
nearby oces and residential areas located several hundreds of meters away. In addition, many social
issues of environments are caused by complaints regarding discomfort caused by the propagation of
the vibration-induced high noise level to the surroundings. Despite the discomfort to the residents,
research reports into the reduction of the unwanted vibration from artificial sand plants are considerably
rare. In particular, vibration measurement and reduction of an artificial sand manufacturing plant has
not been reported so far.

Appl. Sci. 2020, 10, 4327 3 of 17
Consequently, the main technical contribution of this work is to experimentally investigate the
vibration characteristics of the artificial sand production plant through on-site measurement. More
specifically, from the analysis of the measured signals in time and frequency domains, vibration
isolations of the sand and screen units are evaluated, and vibration sources are identified. To achieve
this contribution, accelerometers are located on the sand and screen units by operating only the
sand unit actuators and the entire facilities of the plant. Subsequently, collected acceleration signals
from various locations are analyzed in the time and frequency domains. In particular, vibration
acceleration level (VAL), the vibration isolation level dierence (
VAL), percent isolation rate, and
vibration transmissibility of the sand and screen units are calculated to evaluate the vibration isolation
system. In addition, to find out the vibration source at the shipping control center and plant oce
located far away from the plant site, acceleration signals are measured and analyzed. From the analysis,
it is identified that the main vibration source is the beating phenomenon caused by multiple operations
of the motors to activate sand units which have close driving frequencies. In other words, close driving
frequencies for the simultaneous operation of three motors for the sand units cause the beating and
hence large vibration occurs [
22
31
]. In this work, the driving frequencies are adjusted to be suciently
separated so that the beating is avoided in the multiple operations of several actuating motors. Then, it
is shown that unwanted vibrations are significantly reduced by the adjustment of driving frequencies
of the sand units [23].
2. Artificial Sand Production Plant
2.1. Overall Structure
To understand the artificial sand manufacturing production facilities, we overview the stone
crusher plant shown in Figure 1 which includes various manufactural equipment. Stone crushing
plays a key role in the reduction of particle size of rocks or stones [
8
21
]. The jaw crusher is defined as
a device for crushing large rocks or stones. The crushed rocks and stones from the jaw crusher are
screened on a dry type vibration screen and transported through a conveyor belt to a cone crusher.
The barmac is defined as a device for crushing stones conveyed from a cone crusher into smaller pieces.
The operation of the artificial sand manufacturing production process using these facilities generates a
significant level of impulse or shock and vibration. The wet type vibration screen unit and sand unit
are defined as a device for screening (or sorting) and washing the stones using the water, and it is
transported from the barmac into fine sized sand. In case of the vibration screen unit, two wet type
vibration screen units are operated by connecting them to an H-beam welded in parallel, and three
wet type vibration sand units are also operated by connecting them to H-beam welded in parallel,
respectively. The moving paths of the raw materials (i.e., rocks, stones, or sands) are denoted by a red
arrow in Figure 1b. In the figure, the blue points denote vibration isolation representing the coil spring
for screen units and sand units.

Appl. Sci. 2020, 10, 4327 4 of 17
Appl. Sci. 2020, 10, x FOR PEER REVIEW 3 of 17
isolations of the sand and screen units are evaluated, and vibration sources are identified. To achieve
this contribution, accelerometers are located on the sand and screen units by operating only the sand
unit actuators and the entire facilities of the plant. Subsequently, collected acceleration signals from
various locations are analyzed in the time and frequency domains. In particular, vibration
acceleration level (VAL), the vibration isolation level difference (ΔVAL), percent isolation rate, and
vibration transmissibility of the sand and screen units are calculated to evaluate the vibration
isolation system. In addition, to find out the vibration source at the shipping control center and plant
office located far away from the plant site, acceleration signals are measured and analyzed. From the
analysis, it is identified that the main vibration source is the beating phenomenon caused by multiple
operations of the motors to activate sand units which have close driving frequencies. In other words,
close driving frequencies for the simultaneous operation of three motors for the sand units cause the
beating and hence large vibration occurs[2231]. In this work, the driving frequencies are adjusted to
be sufficiently separated so that the beating is avoided in the multiple operations of several actuating
motors. Then, it is shown that unwanted vibrations are significantly reduced by the adjustment of
driving frequencies of the sand units [23].
2. Artificial Sand Production Plant
2.1. Overall Structure
To understand the artificial sand manufacturing production facilities, we overview the stone
crusher plant shown in Figure 1 which includes various manufactural equipment. Stone crushing
plays a key role in the reduction of particle size of rocks or stones [821]. The jaw crusher is defined
as a device for crushing large rocks or stones. The crushed rocks and stones from the jaw crusher are
screened on a dry type vibration screen and transported through a conveyor belt to a cone crusher.
The barmac is defined as a device for crushing stones conveyed from a cone crusher into smaller
pieces. The operation of the artificial sand manufacturing production process using these facilities
generates a significant level of impulse or shock and vibration. The wet type vibration screen unit
and sand unit are defined as a device for screening (or sorting) and washing the stones using the
water, and it is transported from the barmac into fine sized sand. In case of the vibration screen unit,
two wet type vibration screen units are operated by connecting them to an H-beam welded in parallel,
and three wet type vibration sand units are also operated by connecting them to H-beam welded in
parallel, respectively. The moving paths of the raw materials (i.e., rocks, stones, or sands) are denoted
by a red arrow in Figure 1b. In the figure, the blue points denote vibration isolation representing the
coil spring for screen units and sand units.
(a)
Appl. Sci. 2020, 10, x FOR PEER REVIEW 4 of 17
(b)
Figure 1. Artificial sand manufacturing plant and process: (a) Photograph of the artificial sand
manufacturing plant; (b) Overall process of manufacturing in artificial sand production.
2.2. Vibration Isolation
Vibration isolation is a procedure by which undesirable vibrations are eliminated or reduced.
Basically, it involves the insertion of a resilient member (or isolator) between the vibrating mass (or
equipment or payload) and the source of vibration so that the reduction in the dynamic response of
the system can be achieved under specified vibration excitation conditions. Therefore, this can be
achieved using not only passive but also controllable vibration isolators. It is well known that the
isolation system can be classified into passive, active and semi-active. The passive isolator consists of
a resilient material (stiffness), an energy dissipator (damper) and mass as a single degree of freedom
of the mechanical system. The example of passive isolators in a mechanical system includes metal
coil spring, cork, felt, pneumatic springs and viscoelastic material, such as elastomer or rubber
springs. Among the passive isolators, the rubber springs have been popularly used in terms of the
shear mode, or combinations of the shear and compression modes along with sophisticated
viscoelastic elements. The active vibration isolator features actuators with a closed-loop feedback
control system. Thus, the isolation performance of the active isolation is high, but it requires high cost
and sophisticated sensors and control algorithms. The semi-active vibration isolation is featured by
addition of damping property in real time manner. This method is known to be simple, but very
effective. Among three vibration isolation approaches, the passive method is mostly used in the
production of the artificial sand or in the building of the civil engineering structures. The vibration
isolation for the artificial sand production plant is mainly achieved by utilizing rubber mounts and/or
coil springs. More specifically, many rubber mounts and coil springs are installed under the
structures of screen and sand units to reduce the vibration caused from driving (or exciting) actuators
such as large-sized motors. Therefore, this isolation system is weak to external disturbances and time-
varying uncertainty of the driving frequencies. This isolation system is normally designed to protect
against the lowest frequency of the system since it causes the highest vibration amplitude. To achieve
the vibration transmissibility of the artificial sand production plant, a single degree of freedom (DOF)
model shown in Figure 2 can be considered.
Figure 1.
Artificial sand manufacturing plant and process: (
a
) Photograph of the artificial sand
manufacturing plant; (b) Overall process of manufacturing in artificial sand production.
2.2. Vibration Isolation
Vibration isolation is a procedure by which undesirable vibrations are eliminated or reduced.
Basically, it involves the insertion of a resilient member (or isolator) between the vibrating mass (or
equipment or payload) and the source of vibration so that the reduction in the dynamic response of
the system can be achieved under specified vibration excitation conditions. Therefore, this can be
achieved using not only passive but also controllable vibration isolators. It is well known that the
isolation system can be classified into passive, active and semi-active. The passive isolator consists of a
resilient material (stiness), an energy dissipator (damper) and mass as a single degree of freedom of
the mechanical system. The example of passive isolators in a mechanical system includes metal coil
spring, cork, felt, pneumatic springs and viscoelastic material, such as elastomer or rubber springs.
Among the passive isolators, the rubber springs have been popularly used in terms of the shear mode,
or combinations of the shear and compression modes along with sophisticated viscoelastic elements.
The active vibration isolator features actuators with a closed-loop feedback control system. Thus,
the isolation performance of the active isolation is high, but it requires high cost and sophisticated

Appl. Sci. 2020, 10, 4327 5 of 17
sensors and control algorithms. The semi-active vibration isolation is featured by addition of damping
property in real time manner. This method is known to be simple, but very eective. Among three
vibration isolation approaches, the passive method is mostly used in the production of the artificial
sand or in the building of the civil engineering structures. The vibration isolation for the artificial sand
production plant is mainly achieved by utilizing rubber mounts and/or coil springs. More specifically,
many rubber mounts and coil springs are installed under the structures of screen and sand units to
reduce the vibration caused from driving (or exciting) actuators such as large-sized motors. Therefore,
this isolation system is weak to external disturbances and time-varying uncertainty of the driving
frequencies. This isolation system is normally designed to protect against the lowest frequency of the
system since it causes the highest vibration amplitude. To achieve the vibration transmissibility of
the artificial sand production plant, a single degree of freedom (DOF) model shown in Figure 2 can
be considered.
Appl. Sci. 2020, 10, x FOR PEER REVIEW 5 of 17
Figure 2. Single degree of freedom (DOF) vibration isolation model on rigid foundation.
The resilient material is assumed to have both elasticity and damping and modeled as a spring
k and a dashpot c, respectively. It is assumed that the operation of the sand manufacturing plant is
undertaken by applying a harmonically varying force
0
() cos
F
tF t
ω
=
. Then, the governing equation
of the machine sand unit (or screen unit) body is given by
0
cosmx cx kx F t
ω
++=

(1)
Using the steady state solution of the above equation, the magnitude of the total transmitted
force is determined by [32–37]
222
0
22 22
()
T
Fk c
F
km c
ω
ωω
+
=
−+
(2)
Thus, the transmissibility of the vibration isolation model is defined as the ratio of the magnitude
of the force transmitted to the exciting force [32–37]:
22
22 2 2
0
()
T
Fkc
T
F
km c
ω
ωω
+
==
−+
2
22 2
1(2 )
(1 ) (2 )
r
rr
ζ
ζ
+
=
−+
(3)
In the above, F
T is the amplitude of the force transmitted to the sand unit, F0 is amplitude of the
excitation force from the sand unit body and r is the frequency ratio. It is defined by f/f
n. Here, f is the
exciting (or driving) frequency of the vibration source and f
n is the natural frequency of the sand unit
which is mainly influenced by the stiffness of the sand unit structure. In Equation (3), ζ is the damping
ratio, which depends on the damping property of the system structures of the sand unit [32–38]. The
vibration isolation design has three criteria or requirements as follows [32–38]: (i) the frequency ratio
should be more than three (f/f
n = r 3), (ii) the vibration transmissibility (or percentage isolation)
should be below 0.1 (%I 90%, where, %I represents the vibration isolation rate percentage) (iii) the
minimum value of the vibration isolation efficiency should be under 12.5%. In order to meet the above
requirements, most artificial sand production devices including screen and sand units are built by
coil springs to achieve vibration isolation as well as avoid the resonance phenomenon. In this plant,
the coil springs are installed on each sand unit and screen unit, as shown in Figure 3. The detained
specifications of the coil springs used in this plant are given as follows. The outer diameter is 212 mm,
the diameter of the coil spring itself is 32 mm, the number of coil turn is 7.5, the static deflection is
25.3 mm, the maximum load is 2950 kgs and the material is stainless steel.
Figure 2. Single degree of freedom (DOF) vibration isolation model on rigid foundation.
The resilient material is assumed to have both elasticity and damping and modeled as a spring
k and a dashpot c, respectively. It is assumed that the operation of the sand manufacturing plant is
undertaken by applying a harmonically varying force
F(t) = F
0
cos ω t
. Then, the governing equation
of the machine sand unit (or screen unit) body is given by
m
..
x + c
.
x + kx = F
0
cos ω t (1)
Using the steady state solution of the above equation, the magnitude of the total transmitted force
is determined by [3237]
F
T
=
F
0
k
2
+ ω
2
c
2
q
(k m ω
2
)
2
+ ω
2
c
2
(2)
Thus, the transmissibility of the vibration isolation model is defined as the ratio of the magnitude
of the force transmitted to the exciting force [3237]:
T =
F
T
F
0
=
k + ω
2
c
2
q
(k mω
2
)
2
+ ω
2
c
2
=
q
1 + (2ζr)
2
q
(1 r
2
)
2
+ (2ζr)
2
(3)
In the above, F
T
is the amplitude of the force transmitted to the sand unit, F
0
is amplitude of
the excitation force from the sand unit body and r is the frequency ratio. It is defined by f /f
n
. Here,
f is the exciting (or driving) frequency of the vibration source and f
n
is the natural frequency of the
sand unit which is mainly influenced by the stiness of the sand unit structure. In Equation (3),
ζ
is the damping ratio, which depends on the damping property of the system structures of the sand

Figures (8)
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Zhao Yuemin1, Liu Chusheng1, He Xiao-mei1, Zhang Cheng-yong1  +2 moreInstitutions (1)
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Abstract: Use of springs made of an alloy with shape memory (SMA) to shape the dynamic characteristics of a resonance vibration screen is proposed in this paper. These springs change spring constant as a result of temperature changes. Thus it is possible to change their resonance frequency in real time. In the paper a mathematical model of a controlled SMA spring was formulated and its parameters were identified. In the model both the effect of spring coefficient changes and damping changes depending upon alloy temperature and spring vibration frequency were taken into consideration. Experimental investigations of the examined spring and screen physical model were carried out and selected characteristics were also included. The investigations were carried out at the Dynamics and Control of Structures Laboratory of AGH University of Science and Technology. The control law was formulated. Simulation investigations of the mathematical vibration screen model in both open and closed loop systems were made. It was shown ...

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TL;DR: The comparison shows that the most conservative Justervesenet vibration criterion is stricter with respect to high- frequencies than are the others, but it is less strict for low-frequency vibrations.
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