Belt conveyors are an integrated transmission and carrying mechanism with length sometimes extending several thousand meters. In traditional design and analysis of belt conveyors, vibration and impact are usually ignored and only static design is considered. However, to ensure the safety of conveyor operation for this restricted analysis, designers must increase the safety factor, which increases production costs.
Many research groups have conducted dynamic analysis of large belt conveyors to reduce production cost and optimize conveyor performance. The conveyor belt was first modeled as an elastic body and then a viscoelastic body to incorporate viscoelastic characteristics of belt cover layer.
In the early 1960s, the former Soviet Union began to study conveyor dynamics. However, due to the limited science and technology at that time, the starting characteristics for constant acceleration or AC motors were studied by using impulse principles and stress wave propagation in the conveyor belt on the basis of a simplified mechanic model. A series of later studies at Hannover University of Technology in Germany established the traveling wave theory. Further studies investigated conveyor dynamic characteristics.
Harrison, Robert, and James amongst others investigated starting and braking characteristics of steel wire rope core conveyors and lateral bending vibration of the conveyor belt. They also analyzed stress wave propagation speed in the conveyor belt based on the theory of elastic and stress waves and developed various relevant models.
Computer simulation of belt conveyor dynamic characteristics was presented by the Taiyuan University of Science and Technology using a Kelvin viscoelastic model, and belt conveyor stability was analyzed in terms of the transverse vibration. Transverse vibration was also studied at Xi’an University of Science and Technology and Shandong University of Science and Technology, obtaining the relationship between transverse vibration and speed and belt conveyor tension to provide a theoretical basis belt conveyor development.
The transverse vibration frequency of conveyor belts is an important parameter describing the dynamic characteristics of a belt conveyor. This parameter is most often identified from theoretical relationships, which are derived on the basis of an assumption that the belt is a stationary elastic string.
Belt vibrations have a number of analogies to other tension member systems, such as, for example, power transmission belts. Some research findings suggest that in the case of a limited length of the belt section, a more accurate description of its vibration can be obtained with a beam model rather than with a string model. Experimental research has so far mostly revolved around measurements of stationary belts.
Starting and braking curves, horizontal turning, and broken band detection of belt conveyors were studied in the Liaoning Technical University using finite element analysis. A model of the whole belt conveyor was established using the discrete dynamic method and dynamic simulation software was constructed at Northeastern University. The conveyor dynamic characteristics under different boundary conditions were studied experimentally, and the conveyor dynamic tension under different conditions was simulated.
Modern conveyor design methods were proposed on the basis of analysis of the vibration characteristics by the Shanghai Jiao Tong University and Shanghai Normal University.
The hall sensor used to measure the belt running speed - the Shanghai Jiao Tong University
However, previous and current researches have mainly focused on discrete conveyor models and one thing is clear, conveyors are not immune to failure. Issues with components such as pulleys and their bearings can trigger unexpected shutdowns and create logistical problems that impede the productivity of busy sites. By employing advanced technology to conduct conveyor vibration analysis on its pulleys can ensure the products are optimised for an extended service life.
The most common causes of failure identified through conveyor vibration analysis
Conveyor vibration analysis offers an opportunity to understand the health of a pulley before it ever enters a live production system. Anomalous vibrations introduced into a conveyor’s frames can indicate a problem with the pulley which could include:
Pulley defects – a lapse in tolerance can introduce undesirable changes in operation
Bearing failures – vibrational analysis can uncover bearing defects undetectable through a visual inspection
Miscellaneous failure modes – it can be investigated any deviation from the required operational specifications.
Even brand-new bearings sometimes feature imperfections that ultimately cause failure. The manufacturers need to undertake extensive testing of components before delivery, to ensure correct operation immediately from installation.
Let’s take as an example the noise and vibration measurement of a conveyor belt. Tube and belt conveyors are most commonly used for transporting loose and small solid materials. Like any machinery, even belt and tube conveyors are the source of noise. An important source of noise is the roller, which leads the conveyor belt. Another noise is emitted by the roller itself, the other roller, after which the belt is guided. The belt can be made of rubber, metal, textiles, etc. Therefore, it is necessary to reduce noise and hence the vibration of all parts of the conveyor. The conveyor belt was supported on six rollers fixed on three plates of stand, return and drive drum. These six rollers were produced in two sets (convectional tube and accurate tube). Rollers were driven by a rubber belt. The noise was measured and evaluated on both sides of the conveyor. Vibration of the conveyor was measured at four locations of the conveyor construction. All measurements were performed in an unloaded condition. The results of the analysis showed that the vibration of the conveyor is comparable in both cases, however, the rollers from accuracy tube excite the construction less, and this results in a lower total noise. By comparing the acceleration to the dominant frequency, it is obvious that the noise and the vibration of the belt conveyor construction were reduced by using rollers from accuracy tube. This are very useful information in preventing problems and delivering better solutions.
Another example, analysis of overturning and vibration during field operation of a tractor-mounted 4-row radish collector that has been done in order to ensure the user safety during radish collection.
The overturning stability and vibration of upland crop machinery under development are important issues for analysis because farms for upland crops are usually uneven, which may cause work-related fatalities, and vibration affects user comfort and reduces the durability of components. To analyze lateral stability, the center of gravity (CG) of the tractor-mounted radish collector system was calculated mathematically. Then, a simulation was performed to determine the lateral overturning angles at different folding positions of the radish conveyor belt and load conditions, and the results were validated through tests.
Frequency of belt transverse vibrations as a function of two measured parameters: belt tensile force and spacing between the idler supports
Vibration sensors were used to measure the vibration levels and the power spectrum density (PSD) was obtained to check the cyclic apparatuses of the major frequencies. The load conditions, different conveyor speeds, and locations were considered as factors affecting the vibration levels. Vibration affects user comfort and machinery durability, and also partially affects the stability. Excessive vibration impedes the collection of crops. It usually occurs due to rapid forward, backward, or oscillating movement of the mechanical components. The vibration level may differ as a result of component speed, position, loading condition, operational site, and environmental factors. The measurement of vibration is essential for maintaining stability (static, couple, dynamic, and overhung); reducing dynamic stress; preventing misalignment (belt and shaft), looseness, and resonance; and improving the overall working environment and maintaining the safety of off-road agricultural machinery or vehicles.
The vibration level was greater under the unloaded conditions and increased with an increase in the conveyor speed. Vibrations under the loaded condition satisfied the ISO standard (except the first conveyor belt). According to the PSD analysis, high magnitude peaks (>25 dB) appeared frequently in all directions, which indicates a high possibility of damage to the first conveyor belt. This analysis provides useful information for improving the safety and durability of agricultural machinery for uneven and sloped field conditions.
Avoid design and quality issues and deliver better solutions
By conducting vibration analysis of conveyors, the manufacturers can meet only the highest standards and benefit from advantages in the form of:
Lowered maintenance costs accompanying a reduction in pulley replacements
Smooth, seamless integration of new components into older systems
Confidence in the quality, durability, and value of this conveyor hardware.
Belt Conveyor
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