Literature Review

Literature Review

Introduction

Conveyors are large complex motorized objects, which are useful in many industries. They are common and they are present in every industry. They move different materials from one location to the other. They are important in every industry, and are especially useful in the production process. There are different types of conveyors, including overhead conveyors, belt, roller, and floor conveyors. People use conveyors in almost all the processes of production. Some people use them all the time, for many hours on end. They are therefore at risk of different health hazards. In most cases, people who use conveyors use a lot of physical exertion, and they normally use them while standing. They are therefore at risk of getting physical body problems such as back and leg problems. Another major health risk that may result is hearing loss or damage. Conveyors are often noisy machines. People who are used to working with them often say that they are used to the noise, and it does not affect them. This is a risky assumption, and there is always the chance that most people will develop hearing problems later. The noise levels increase because there are other machines working in the background, and products and materials flow through the systems. It is important to understand different sources of conveyor noise generation, as this will help in finding ways to reduce the noise levels.

Discussion

Generally, people do not understand the mechanisms of conveyor noise generation, and this is clear from the little published information regarding the subject. The roller, chains and bearings are some of the main sources of noise. There are different ways of reducing the noise levels of the conveyors. Improving the idler roll surface and implementing the damping treatments helps to reduce some of the noise. However, researchers do not agree on these proposals of noise reduction, with those opposing arguing that they do not help to reduce the levels of noise. Others propose the idea of using idler rolls, which have low indicator run-out values because they produce quiet conveyors. There are several advantages of using conveyors. People prefer them because they operate continually, handle a variety of materials, are easy to configure, saves labor cost, eases workload, and transports materials quickly. However, they have several limitations and drawbacks. For instance, they occupy considerable space, and they require heavy maintenance. They are a heavy investment and they pose several health risks. The noise levels can be dangerous to people’s heath. It is more dangerous than water and air pollution, as it is a slow and insidious killer (Bhatia, 2007). It is therefore important to understand the mechanisms behind conveyor noise generation.

Noise Pollution and Control

In order to control noise, it is important to understand how it occurs. Some of the main contributors of noise include compressors and gas turbines, airplanes and motor vehicles, and high-speed machine tools. Noise sources are categorized into motor, drive train, cutting head and conveyor. Conveyor and cutting head are the dominant sources of noise. Conveyor noise occurs as the top and bottom decks, chain and tail roller, sidewalls under the horizontal pivot and the flex plates collide. With the increase in urbanization and industrialization, noise levels have continued to increase (Bhatia, 2007). Most of the machines, devices and gadgets are noisy to some extent. A lot of research done on engineering controls for noise reduction focused on the mining industry in the US. The government took the issue of noise pollution in the mining industry seriously, and it awarded contracts to determine what equipment produced more noise than the allowed federal regulation levels. The federal regulations permit noise levels of not more than 90 dBA for eight hours (Durr et al, n. d.). The Occupational Safety and Health Administration sets the standards for noise levels. It has identified that workers who are exposed to a time weighted average level of 85 dBA for an eight-hour period are within the cautionary noise zones. The government intended to develop the engineering noise controls for all the equipments, and evaluate them to establish that they attained the quality required. Some people enjoy loud machinery noises, and this exposes them to various health risks such as hearing damage or hearing loss. They also determined the dominant noise sources in all the equipment. Employees working in noisy environments need audiograms to check whether there is any damage to their hearing. They also need to use hearing protectors to minimize any risks (Timmerman, 2011).

Controlling noise levels does not have to be a complicated and costly investment. However, some people go to the extreme when they are trying to reduce noise levels, and they end up using a lot of money by conducting unsuccessful experiments and coming up with solutions which are practical, or which are expensive to implement. Some of the methods proposed for reduction and control of noise include using silencers, mufflers, shields, barriers, improvement in the design of the machinery, and the reduction of noise at source (Bhatia, 2007). Different industries use different control measures because they have different processes. The control measures used in the paper, metal, rubber, plastic, and food processing industries vary in some ways because these industries produce different noise levels. Educating people about noise pollution through different media channels such as television and newspapers can help to reduce noise pollution, as people will become more aware of the dangers of noise. Industry players need to coordinate with the planners and the concerned environmental authorities so that they can come up with practical ways of dealing with noise pollution. Some of the treatments for noise control include retrofitting the chain conveyor with a urethane coating or a urethane sleeve on the tail roller, constrained layer damping, and using a modified take up plate (Durr et al., n. d.). The different methods of controlling noise will depend on the conveyor system. The materials used to make the conveyors determine the levels and the kind of noise they produce. Using the conveyors in unintended manner might result to noise increase.

Classification of conveyors depends on the type of the materials or products transported the location of the conveyors, or the accumulation of loads on the conveyor. Some types of conveyors include belt, roller, chain, screw, vibrating, overhead, pneumatic, and gravity conveyors among others. The choice of the conveyor depends on the capacity, distance, and configuration. The peripherals surrounding the conveyors are a source of noise generation. An effective method of ensuring that the noise levels reduce is to deal with the noise production at different peripherals. Rollers, bearing, chains and shafts are possible noise generators. Drives such as belts, power trains, sprockets, motors, whines, mounts, gearboxes, and guards also produce noise (Timmerman, 2011). The materials used to manufacture the drives and other components matter, because they can influence the noise levels. Conveyor frames generate a lot of noise because they are made of steel. Another possible source of noise generation is the building used to place the conveyors. It is important to check the conveyors regularly, and to ensure that they are in good working conditions. Lubricating the conveyors, isolating the vibration, dampening and using acoustic energy are some of the ways to ensure noise control and noise reduction.

Conveyor Bearings

The bearing construction and design is a comprehensive subject. One of the major concerns in the design, application, implementation and usage of the bearing is the noise generation. Bearings produce a lot of noise, although some seem to produce more noise. Using high noise bearings in a particular application can have disastrous effects. When some parts in a bearing are misaligned, the bearing produces excessive noise. The periodic deformation of a bearing rotation result to noise generation. Bearing imbalances, which occur because of imperfections and inaccuracies are a source of noise. Clearance is one of the most important factors, which influence the level of noise in bearings. Applications with more clearance generate a lot of noise. Manufacturers can use angular ball bearings, which make clearance adjustment possible, and this makes it possible for a person to control the level of noise (It’s All Ball Bearings, 2011). Using lubricants can help to reduce or eliminate bearing noise. Some of the most effective lubricants contain lithium or calcium, although the most effective ones for ball bearings are sodium based.

Industries need to implement a bearing fault-detection technique that will be reliable. This will help to prevent malfunction, performance degradation, and catastrophic failures. It is challenging to develop such techniques because most of the bearing fault related signatures are non-stationary. Some researchers have proposed the use of detrended fluctuation analysis (DFA) of vibration signals to deal with this challenge. Unlike the traditional spectral analysis method, the DFA deals with non-stationary signals. Most people prefer the DFA because it does not rely on the mother functions as the wavelet transform does. The DFA is able to detect the faulty conditions of bearings by analyzing its power-law characteristics. It is important to understand the different bearings, and know how they relate to the vibration system. An Anderson meter is one of the commonly used instruments for testing vibrations because it only picks information from the bearing, and not from the surroundings.

Chain Conveyors

There are different chain designs, depending on their application. Chain designs can be vertical, sliding, pusher, or rolling. The most common ones are the sliding chains, although they cannot transport heavy goods for long distances. They are noisier because the person using them has to drag them on the surface. Conveyor chains can be a source of noise, especially when using high-speed conveyors. They are especially useful when lifting and transporting materials continuously, and in all directions. The chain conveyors can transport materials vertically or horizontally. They can transport materials in inclined, curved, or straight paths. Either the materials are transported openly, or they are enclosed in toughs or troughs. Some of the chains are detachable, while others are hooked. Most of the conveyor chains are made of malleable cast iron, and they are not smooth. They generate a lot of noise, and they require lubrication. Lubricating the chains will not only help to reduce the noise, but it will also help to reduce corrosion, resistance, and minimize the power used. Lubricating is therefore an important process because it helps to maintain the chains, and they last longer.

Chains can also be made of other materials such as different varieties of steel including cast, manganese and welded steel, or chilled and usable iron. The type of material used determines the level of noise generated. The block chains produce noise when the teeth and the links rub against each other. They produce a squeaking noise when the links pivot horizontally and vertically in a concurrent manner because of the differences of the link and the bearing surface materials. People use chain conveyors with other types of conveyors and other material-holding equipment. When considering the different ways to reduce noise, it is important to consider the details of all the other interfaces (Gunal et al., 1996).  The assembly system reduces determines the level of noise. For instance, designers have discovered that chains with plastic bolt on flights have significant low noise levels compared to the ones joined by welding.

Roller Conveyors

Roller conveyors are popular because of their flexibility. Roller conveyors transport materials and products of different shapes and sizes. Rollers move materials in horizontal and vertical directions. Rollers move every type of load. They can move smooth as well as rigid loads. Some roller conveyors use power, while others use gravity. Gravity rollers can be stationary or mobile. All roller conveyors have rollers, stands, and a supporting frame. Some rollers are cylindrical while others have a disc shape. There are different types of powered rollers. Some are gear driven and others are chain or belt driven.

Powered rollers are especially noisy. Noise generation can occur because of the conveyor roller surfaces. Most of the noise generated by conveyor rollers occurs when the conveyor belt contact the surface of the rollers. Changing one of the materials will therefore reduce the noise. The rollers can be aluminum, steel, or galvanized steel. It is possible to reduce the noise levels by ensuring that the Maximum Indicator Slope and the Total Indicator Reading attain the specified limits. The rate of change over the diameter has an influence on the roll noise. The noise levels increase if the total indicator readings occur within a short distance. The speed of the rollers can also increase the noise levels by increasing the vibration. Ensuring the correct balance of the rotational speed will reduce the vibration, and this will in turn reduce the noise levels (Sandvik, 2008).

Mechanical Vibration Analysis       

In some cases, vibration is a desirable effect, as it indicates that an instrument is working. In other cases, vibration often has undesirable consequences as it results to noise production, and energy wastage. Some of the reasons for the noise might include uneven friction and meshing of gear teeth among others. Many scientists and researchers have studied the subject of vibration for a long time. Many people do not view acoustics and vibration as part of the same subject although they overlap considerably. Mathematicians and physicians have conducted most of the studies and research on vibration over the past four centuries. However, many academic and industrial researchers have intensified their research on the subject (Benaroya, 2004).

Design and Analysis of Experiments (DOE)

The Design of Experiments Techniques makes it possible for designers to determine how different factors affect the results of any design. People use different methods and techniques, when they are designing and analyzing experiments. They emphasize the connection between the experiment and the model that the person conducting the experiment can develop from the results of the experiment. Researchers have to understand how they can achieve optimal industrial experimentation in the best way. Factorial and fractional factorial design and the presentation of new analysis techniques, such as the generalized linear model, are some of the factors to consider in the design, conduct and analysis of experiments. Researchers are now able to use computers when designing and analyzing experiments. One of the most effective ways of reducing the noise levels is by ensuring that the design does not encourage noise production.

Some of the most powerful software tools that the researchers can incorporate in experimental design are the Design-Expert (r) and Minitab (r). Design of Experiments (DOE) techniques enables designers to determine simultaneously the individual and interactive effects of many factors that could affect the output results in any design. DOE also provides a full insight of interaction between design elements; therefore, it helps turn any standard design into a robust one. DOE helps designers to identify the sensitive parts and areas in designs that affect the results in a negative way. By identifying these areas, the designers are able to fix the problems and thus realize higher yields. It eliminates wastage because designers are able to fix these problems before production (Agilent, n. d.).

 

References:

Agilent (n. d.). design of experiment (DOE) tutorial. Retrieved from http://www.home.agilent.com/upload/cmc_upload/All/DesignOfExperimentsTutorial.pdf?&cc=US&lc=eng

Benaroya, H. (2004). Mechanical vibration: Analysis, uncertainties, and control, volume 1. New York, NY: Marcel Dekker

Bhatia, S.C. (2007). Textbook of noise pollution and its control. New Delhi, India: Atlantic Publishers & Distributors (P) Ltd.

Brown, S. C. (2004). Conveyor noise specification and control. Proceedings of ACOUSTICS. Retrieved from http://www.acoustics.asn.au/conference_proceedings/AAS2004/ACOUSTIC/PDF/AUTHOR/AC040002.PDF

Bruun, E. B. (1996). Noise properties of CMOS current conveyors. Proceedings of the 1996 IEEE International Symposium on Circuits and Systems, 144-147

Durr, M. T., Kovalchik, P., & Kwait, E. (n. d.). evaluation of engineering noise controls for a continuous miner conveyor system. retrieved from http://www.cdc.gov/niosh/mining/pubs/pdfs/eoenc.pdf

Gunal, A.K., Williams, E.J., and Sadakane, S. (1996). Modeling of chain conveyors and their equipment interfaces. Proceedings of the IEEE  Simulation Conference, 1107 – 1114

Huang, H. M. (2010). Vibration measurement and structural optimization simulation of a boom type tunneller.  IEEE ICCA 2010, 1120-1123 

It’s All Ball Bearings (2011). The impact of bearing noise on project applications. Retrieved from http://www.its-all-ball-bearings.com/the-impact-of-bearing-noise-on-project-applications

Liu, J. L. (2011). Detrended fluctuation analysis of vibration signals for bearing fault detection. Proceedings of the IEEE Conference on Prognostics and Health Management (PHM), 1-5

Montgomery, D. C. (1996).Mechanical vibration design and analysis of experiments, (4th ed.).  New Jersey, NJ: John Wiley & Sons Inc

Rao, S. S. (2010). Mechanical vibration, (5th ed.). New Jersey, NJ: Prentice Hall.

Sandvik. (2008). Conveyor components: HA100 Roller. Retrieved from http://www.construction.sandvik.com/sandvik/0120/Internet/Global/S003713.nsf/Alldocs/Products*5CConveyors*and*conveyor*components*5CRollers*2AImperial*Heavy*duty/$FILE/DataBrochureLowNoiseRollersV1.pdf

Tempest, W., and Bryan, M.E. (1976). Noise measurement and evaluation. Proceedings of the Institution of IEEE Electrical Engineers, 1113 – 1137

Timmerman, P. (2011). Convetor noise: Dampening distraction. Retrieved from http://www.plastics.com/content/articles/44660/1/Conveyor-Noise—Dampening-Distraction/Page1.html

Wahren, E. M. (1990). Conveyor belt chain. Retrieved from http://www.google.com/patents?hl=en&lr=&vid=USPAT4895248&id=VDMBAAAAEBAJ&oi=fnd&dq=conveyor+belt+noise+issues&printsec=abstract#v=onepage&q=conveyor%20belt%20noise%20issues&f=false

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