Vibration Diagnosis of Sand Units in Stone Crusher Plant On-site Field Test
Summary (2 min read)
1. Introduction
- Natural sand has been formed through the normal erosion process of exposed rocks.
- It is well known that vibration is measured as three physical parameters: displacement, velocity, and acceleration.
- 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.
- The main technical contribution of this work is to experimentally investigate the vibration characteristics of the artificial sand production plant through on-site measurement.
2.1. Overall Structure
- To understand the artificial sand manufacturing production facilities, the authors overview the stone crusher plant shown in Figure 1 which includes various manufactural equipment.
- The jaw crusher is defined as a device for crushing large rocks or stones.
- 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.
- In the figure, the blue points denote vibration isolation representing the coil spring for screen units and sand units.
- Water, and it is transported from the barmac into fine sized sand.
2.2. Vibration Isolation
- 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.
- The passive isolator consists of a resilient material , an energy dissipator and mass as a single degree of freedom of the mechanical system.
- The semi-active vibration isolation is featured by addition of damping property in real time manner.
- 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.
2.3. Vibration Sources
- Vibration sources of the artificial sand production plant are very difficult to find.
- As a power source, a largecapacity four-phase induction motor with 60-200 horsepower is used and its operating speed ranges from 800 to 1800 rpm.
- The power is transmitted to the drive shaft via a belt pulley.
- The construction and installation of the vibration isolation system in the screen and sand units is described in the next section.
- To identify the vibration problem that occurred in the artificial sand manufacturing plant, the authors visited the field site several times to feel the vibration levels.
3.1. Vibration Level
- To investigate the vibration level of the screen unit (600 ton) and sand unit (600 ton) during normal operation, two measurement positions of the screen unit and sand unit are fixed as shown in Figure 5 .
- Thus, the percent isolation rate is calculated as 96.4%, which indicates high performance of the vibration isolation even if entire facilities of artificial sand production plant are activated with multiple operating modes.
- Figure 7 presents vibration results of the coil spring installed at the top and bottom positions of the screen unit when the entire manufacturing components including jaw crushers, cone crushers, barmacs, and screen unit and sand units are operated.
- The vibration acceleration level (VAL) at the upper point of the coil spring is calculated by 150 dB, and the VAL at the bottom point of the coil spring is by 140 dB, respectively.
- The beating frequency is equal to the complete value of the alternation in the frequency of the two waves or frequencies.
4. Vibration Reduction
- As observed from the measured vibration signals shown in Figure 8a , the beating occurred due to close driving (or exciting) frequencies of actuating motors during multiple operation of the artificial sand manufacturing plant.
- It is well known that the beating phenomenon is frequently observed when two harmonic motions with frequencies close to each other are combined.
- To avoid the beating behavior, the operating speed (or driving frequency) of the sand unit is adjusted.
- More specifically, the power spectrum is remarkably reduced; ∆VAL is 28 dB, and the transmissibility is 0.04.
- The beating at the shipping control center is more rigorous than that occurred at the plant office.
5. Conclusions
- Vibration levels of an artificial sand manufacturing plant are measured and evaluated in time and frequency domains.
- It is identified from the vibration analysis that the isolation system of the sand unit is much better than that of the screen unit.
- The beating is caused by the close driving frequencies of several sand units during simultaneous multiple operation of several motors.
- The results and analysis presented in this work have considered the real site of the plant and hence can be effectively used for several plants where multiple operations of several actuators such as motors are to be simultaneously carried out.
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Frequently Asked Questions (14)
Q2. What is the role of the rock breaking and crushing process?
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.
Q3. What is the vibration transmission principle of the screen and sand production plant?
The vibration that occurred during the operation of the screen unit and sand units is transmitted the power to the shaft through the belt pulley directly related to the excitation force generated by actuating motors.
Q4. What is the vibration isolation for the artificial sand production plant?
The vibration isolation for the artificial sand production plant is mainly achieved by utilizing rubber mounts and/or coil springs.
Q5. What is the main reason for the lack of sand in the natural environment?
indiscriminate collection of sand from rivers causes flooding and destruction of the natural environment such as river ecosystems, leading to various social issues.
Q6. How many dB are calculated for the sand unit?
More specifically, for the sand unit, VAL, ∆VAL, transmissibility and percent isolation are calculated by 116 dB, 31 dB, 0.028, and 97.2%, respectively.
Q7. What is the fundamental frequency of the sand and screen unit actuators?
In this work, the beating phenomenon can occur by resonance when the fundamental frequencies corresponding to the driving frequencies of sand and screen unit actuators are close.
Q8. What is the definition of passive isolators?
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.
Q9. How many dB is the VAL at the upper point of the coil spring?
The vibration acceleration level (VAL) at the upper point of the coil spring is calculated by 150 dB, and the VAL at the bottom point of the coil spring is by 140 dB, respectively.
Q10. What is the minimum value of the vibration isolation efficiency?
The vibration isolation design has three criteria or requirements as follows [32–38]: (i) the frequency ratio should be more than three (f /fn = 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%.
Q11. What is the main technical contribution of this work?
Appl. Sci. 2020, 10, 4327 3 of 17Consequently, the main technical contribution of this work is to experimentally investigate the vibration characteristics of the artificial sand production plant through on-site measurement.
Q12. How many dB is the VAL at the top point of the coil spring?
Based on Equation (4), the calculated VAL at the top point of the coil spring is 147 dB, and the calculated VAL at the bottom point of the coil spring is 116 dB, respectively.
Q13. What is the reason why the vibration is so high?
the occurrence of the beating behavior is seriously considered as one of the main reasons which can cause high vibration levels.
Q14. How many isolations of the sand and screen units are evaluated?
Appl. Sci. 2020, 10, 4327 4 of 17Appl. Sci. 2020, 10, x FOR PEER REVIEW 3 of 17 isolations of the sand and screen units are evaluated, and vibration sources are identified.