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| {{expert|Materials science|date=November 2013}}
| | Let's have an appear on world's internet hosting business: Thousands and thousands of web hosts spread around the world and their company objective is easy - to get recognized and make revenue. If you have any concerns concerning wherever and how to use [http://ccucontest.commons.co.kr/?document_srl=1818162 Cheap Hostgator Hosting], you can get in touch with us at our internet site. With so much sound around the web hosting market, it is a hard job for us to pick up the right hosting.<br><br><br><br>[http://www.google.de/url?url=https://www.facebook.com/Hostgator1CentCoupon&rct=j&q=&esrc=s&sa=U&ei=LvDeVI-RMMqVatbqgvgD&ved=0CDYQFjAD&usg=AFQjCNEmrJtPnGYOMTYp0NFKNQckzrNzxg google.de]In any internet company, we depend on great internet hosts to offer stable and reliable webhosting services. Hostgator provides timely and promising qualities. They invested a lot of money for its servers which each of them utilizing Dual Xeon servers with 4GB memory and IDE hard disk drives. These high rate servers offer high responsive uptime of up to 99.9 % without failure.<br><br>Hostgator offers a bunch of plans to clients. Almost all the packages provided are cost effective. Hostgator shared hosting are charged $4.95 regular monthly for the basic shared hosting packaged. At charges which begin from $9.95 yearly, you can delight in even more compact packages which truly include a great deal of stuffs. Although there still have a lot plans which offering less costly rates, however if you begin to study and attempt Hostgator, you will feel that every dollar and cent you invested is just not lost. Do your own study on the attributes consisted of in every packages Hostgator providing, then you can distinguish the distinctions with others packages offered by various other web hosts.<br><br>For exaple, Hostgator helps you to back up the internet sites quickly and safely. You have the option to host limitless domains, sub domains and FTP accounts. Of source, the attribute which pointed out simply now will not be readily available if you are the basic hosting bundle customer.<br><br>Hostgator provides control panel. This attribute assists individuals to handle their domains and sub domains in even more versatile way. Besides, the control board demo which is available in standard offers the helpful aid devices to brand-new individuals. Out of a lot of webhosting around the world, Hostgator's cpanel can be stated winning the top ranking amongst them.<br><br>In regard to [http://dictionary.reference.com/browse/consumer?s=ts consumer] supports, Hostgator has an extremely strong client care group which working 24/7 to assist you take on all kinds of problems relevant to their products. You can either call them through phone or live chat with them with web. You can also email your troubles to them. They will response quickly without taking any fees. This is why till now, Hostgator still the best option for consumers.<br><br>A final words for those who are getting began - do not be scare by exactly what you are reading as constructing a great internet site is not that difficult. The work is in truth pretty easy and direct as long as you're getting the right info. To obtain begun, you'll initially require a domain name and a trustworthy hosting service. |
| {{copyedit|date=November 2013}}
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| A '''circle-throw vibrating machine''' is a [[Mechanical screening|screening]] machine employed in processes involving particle separation. In particle processes screening refers to separation of larger particles from smaller in a given feed stream, using only the physical properties of the material. Circle throw machines have simple structure with high screening efficiency and volume of output however holds limitations to the types of feed that can be processed smoothly. Some characteristics of circle-throw machines, such as [[frequency]], [[amplitude]] of vibration and angle of incline deck also affect the unit output. When designing a circle throw vibrating screen, aside from the rotation inducing motor, specific consideration must be devoted to control of the vibration principles employed in the separation, in terms of structural stability and bearing stress and how suitable the feed is to use a circle-throw vibrating screen.
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| ==Range of application==
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| Circle-throw vibrating screens are relatively new, multilayer, high efficiency mechanical screening equipment for material classification. They are widely used for screening stone stock of quarry, and classifying products in mining, sand, gold, energy and chemical [[industrial processes]].<ref> Interval Equipment, ‘Separating Different Materials’, U.S.A., 2013 [Accessed: 13th October 2013] http://www.intervalequipment.com/contact.html</ref> The targeted substance of screening is predominantly the finer particles, which can then be directed into a separation unit capable of further extraction e.g. hydrocyclones or are materials which can be removed and used. Removed materials are often formed intentionally and are classified into various categories by their shape, size and [[physical properties]]. For example, construction wastes are sorted and sieved of the by circular vibrating screen into coarse and fine particles, then the particles are taken to make concrete, architectural bricks and road base materials.<ref name=two> Siebtechnik Gmbh, ‘Screening Machines Process Equipment – Circular and elliptical motion screens, Double counterweight screens’, Germany, 3rd 2013 </ref>
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| ==Advantages and limitation over competitive processes==
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| Circle-throw vibrating screens operate on an inclined surface using a deck moving in circular motion presents an advantage over the typical flat vibrating screens as feed can be fed into the screen in a continuous matter rather than batch, leading to much greater product output. Having an incline overcomes the transport issue within the unit. A use of both circular motion and vibration is to separate particles delivers very high sieving efficiency.
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| Disadvantages are that circle-throw machine have a large physical dimensions, and may require larger plots to place than other screening units, however as circle –throw screen are predominantly used in heavy-duty separations, large unit sizes are expected. Furthermore, the machine has a less efficient towards fine wet and sticky materials unless the water spraying method is used. Water spraying process is to wash fine materials under spray bars.<ref>Crushing Plant Grinding Mill, ‘Circular Vibrating Screen’, China, 15th February 2012 [Accessed : 09th October 2013] http://www.coal-crusher.net/equipment/circular-vibrating-screen.html</ref> Another drawback is to have a large [[stroke]] and allow heavy component to circulate and throw up in the screen box, a high horsepower motor is needed, which is a limitation over separators not requiring large motor action.
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| Circle throwing vibrating screens are usually engaged after a grinding process. There is no waste stream obtained from this unit, rather the feed is separated into ‘upper deck’ and ‘lower deck’ streams, the number of exit streams correspond to the number of decks. Quantity of product exiting from the unit is dependent on size distribution of the particles. Upper deck streams are can be immediately re-fed into the grinding units due to the continuous nature, thus greatly reducing transport time and costs.
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| ==Designs available==
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| The standard circle-throw vibrating is a single shaft, double bearing unit constructed by sieving box, mesh, vibration exciter and damper spring. The screen framing is steel side plates and cross-members that brace static and dynamic forces produced when the machine operates. At the center of the side plates, two roller bearings with counterweights are connected for running the drive. Four sets of springs are fixed on the base of the unit to overcome the lengthwise or crosswise tensioned from sieves and panels and dampen movements.<ref name = two/> An external vibration exciter (motor) is mounted on the lateral (side) plate of the screen box with a cylindrical eccentric shaft and stroke adjustment unit. At the screen outlet, the flows are changed in direction, usually to 90 degrees or alternate directions, which reduces the stream speed upon exiting.<ref name = four>PT. Rutraindo Perkasa, ‘Round (Circular) Vibrating Screen/ Single Eccentric vibrating screen’, Indonesia, 2000 [Accessed: 09th October 2013]
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| http://www.rutraindo.com/stonecrusher/round-circular-vibrating-screensingle-eccentric-vibrating-screen | |
| </ref> High strength [[bolts]] and ring-grooved lock bolts are used to connect components.<ref name = five>ZhengZhou YiFan Machinery Co. LTD, ‘YK Series Inclined Vibrating Screen’, China, 2009</ref>
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| [[File:Circle-throw Vibrating Screen T-class.png|thumb|Circle-throw Vibrating Screen T-class<ref name = un>W.S. Tyler, ‘Technical Specification F-Class Four Bearing Vibrating Screen’, 2012</ref>]]
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| Variations available in this design regard the positioning of the vibration components. One of them is top mounting vibration, which the vibrators are attached to the top of the unit frame and produces an elliptical stroke, this decreases the efficiency of the unit but will increase capacity by increasing the rotational speed, which is required for rough screening procedures where a high flow rate must be maintained.<ref name = six>FUERSTENAU, M.C. and HAN, K.N., Principles of Mineral Processing. Society for Mining, Metallurgy, and Exploration (SME).</ref>
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| This can be varied to a counter-flow top mounting vibration, in which the sieving is more efficient as the material bed is deeper and feed is held on the screen for a longer time and would be employed in processes where a higher separation efficiency per pass is required.
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| If particularly loose particles are present in the feed, a dust hood or enclosure can be mounted. Water sprays may be attached above the top deck and the separation can be converted into a wet screening process.<ref name = two/>
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| ==Characteristics and assessment== | |
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| ===Screen deck inclination angle=== | |
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| The circular-throw vibrating screen generates a rotating acceleration vector and the screen must maintain a steep throwing angle to prevent transportation along the screen deck.<ref name = eight>L. Zhao, Y. Zhao, C. Liu, J. Li and H. Dong, ‘Mining Science and Technology (China)’, Vol 21, pp. 677-680, 2011</ref> The screen deck is commonly constructed to have an angle within the range of 10° to 18°, in order to develop adequate particle transportation. An Increase of deck angle speeds the motion of particle with proportional relationship to particles size.<ref name = nine>STANDISH, N., BHARADWAJ, A.K. and HARIRI-AKBARI, G., 1986. A study of the effect of operating variables on the efficiency of a vibrating screen. Powder Technology, 48(2), pp. 161-172.</ref> This decreases ranges of residence time and fine particles place in bottom and rough particles set at top (stratification) along the mesh screen faster.<ref name = six /> However, if the angle is bigger than 20°, efficiency would decrease due to reduction of effective mesh area. Effect of deck angle on efficiency is also influenced by particle density. In the mining industry where the optimal screen deck inclination angle is investigated to be about 15°. <ref name = eight /> Exceptions are the dewatering screens at 3° to 5° and steep screens at 20° to 40°.
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| ===Short distribution time===
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| On average, 1.5 seconds is required for the screen process reach a [[steady state]] and particles to cover the entire screen.<ref name = eight /> This is induced by the circular motion, the rotary acceleration has a loosening effect on the particles on the deck. [[Centrifugal]] forces spread particles across the screen. With the combination of the gravitational component, the efficiency of small particle passing through aperture is improved, and large size particles are carried forward to discharge end.<ref name = eight />
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| ===Vibration separation===
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| Under vibration, particle mixtures of different sizes segregate ([[Brazil nut effect]]). Vibration is an important characteristic of this type of screen as it lifts and segregates particles on the inclined screen It is suggested that when vibration amplitude is within the range of 3 to 3.5mm, equipment segregates the large and small particles with best efficiency.<ref name = eight /> If the amplitude is too high, the contact area between particles and screen surface is reduced and energy is wasted; if too low, particles will block the aperture, causing poor separation.<ref name = six />
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| Higher frequency of vibration improves component stratification along the screen and leads to better separation efficiency.<ref name = six /> Most of circle throw screening equipment are designed with 750 ~to 1050 rpm, which is used to screen large materials. However, too high frequency vibrates particles excessively; therefore the effective contact area of mesh surface to particles will again decrease.<ref name = nine />
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| ===Characteristics of feed===
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| Presence of [[moisture]] in the feed cause formation of larger particles by [[coagulating]] small particles onto oversized particles, and this effect will reduce efficiency of sieving.<ref name = six /> However the centrifugal force and vibration and acts to prevent blockage of aperture and formation of agglomerated particles. Sizes of feed particles are distinguished into fine, near-sized and oversized particles; most near-sized and fines particles pass through aperture rapidly. Therefore ratio of fine and near-size particles to oversize should be maximized to obtain high screening rates.<ref name = six />
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| Rate of feed is proportional to efficiency and capacity of screen; high feed rate reaches steady state and results better screening rates. However, there is an optimum bed thickness that should be maintained for consistent high efficiency of sieving.<ref name = six />
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| ===Stable efficiency===
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| The steady state screening efficiency is greatly affected by the vibration amplitude. A good screening performance usually occurs when the amplitude is 3-3.5mm. The [[particle velocity]] should be no bigger than 0.389 m/s, if the speed is too big, poor segregation will occur, consequently low efficiency.
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| Eo shows the efficiency of undersize removal from the oversize at steady state.
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| <math>E_o=100{ {mass\ flow\ rate\ of\ solids\ coarser\ than\ screen\ size\ in\ feed\ stream} \over {mass\ flow\ rate\ of\ solids\ in\ the\ oversize\ stream}}</math> | |
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| <math>E_o=100{\left [ \frac{F(1-f_x)}{O} \right ]}=100(1-o_x)</math>
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| Where F is stph(short ton per hour) of feed ore, O is stph of oversize solids discharging as screen oversize, fx is cumulative weight fraction of feed finer than ‘x’ and ox is cumulative weight fraction of oversize finer than ‘x’. Eu shows the efficiency of undersize recovery. U is mass rate of solids in the undersize stream.
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| <math>E_u=100{ {mass\ flow\ rate\ of\ solids\ in\ the\ undersize\ stream} \over {mass\ flow\ rate\ of\ solids\ finer\ than\ screen\ size\ in\ feed\ stream}}</math>
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| Thus
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| <math>E_u=100{\left ( \frac{U}{Ff_x} \right )}=100{\left [ \frac{f_x-o_x}{f_x(1-o_x)} \right ]}= \frac{E_o-(1-f_x)}{E_o f_x}</math>
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| ==Heuristics/design considerations==
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| ===Vibration design===
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| Circle-throw vibrating units rely on the screen component being operated at a resonant frequency in order to achieve efficient sieving of particles. While properly selected vibration frequencies drastically improve the filtration abilities of the screen, a static deflection factor in introduced. A deflection factor occurs as the vibrations causes smaller particles to displace thus not properly passing through the screen due to excess movement and is a property of the system natural frequency. The natural frequency that a system will preferably vibrate at F<sub>n</sub> is 188(1/d)<sup>2</sup> (cycles per min) where d = (188/F<sub>n</sub>)<sup>2</sup> (inches). Static deflection corresponding to this frequency. Vibration isolation is a control principle employed to mitigate the transmission of vibrations. On circle-throw vibrating screens, passive vibration isolation in the form of mechanical springs and suspension are employed at the base of the unit, which provides stability for the unit and control of the vibration generated by the motor. A general rule of thumb regarding the amount of static deflection minimization that should be targeted with respect to operating RPM is provided in the table below.<ref name = ten>Engineering Cookbook- A handbook for the Mechanical Designer. 1999. 2nd edn. Springfield, MO: Loren Cook Company</ref>
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| [[File:Critinstallation.png|thumb|Critical vibration isolation installations<ref name= ten />]]
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| Critical installations refer to roof mounted whilst non-critical refers to base mounted installations. Weight, loading and weight distribution are all elements which must be considered.
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| [[File:Vibrationchart12.png|thumb|Common rule of thumb table for vibration isolation design<ref name = ten />]]
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| ===Heuristic on the roller bearing design===
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| {{seealso|Heuristics}}
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| Whilst designing a circle-throw vibrating screen with a shaft and [[bearing]] system, consideration must be made regarding the loading the unit will undergo as well as extra loading to the screen box created by the centrifugal force, due to the circular motion of the load as it passes through the unit. Bearings must be designed to accommodate for the extra stress.
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| Bearing load due to screen box centrifugal force (F<sub>r</sub>) is
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| <math>F_r={\frac {1}{z} \times \frac {G}{g} \times r \times (\pi \times \frac {n}{30})^2 }</math> | |
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| Supplementary factor of F<sub>z</sub> = ~1.2 is used to account for unfavorable dynamic stressing:
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| <math>P = F_z \times F_r</math>
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| Index of dynamic stressing F<sub>L</sub>, speed factor Fn are used to calculate minimum required dynamic loading (kN)
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| <math>C = P \times \frac{F_L}{F_n} </math>
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| F<sub>L</sub> is taken between 2.5-3 generally as to correspond to a nominal fatigue life of 11,000-20,000 hours as part of a usual design.<ref name = eleven>The Design of Rolling Bearing Mountings [Homepage of FAP Group], [Online]. Available: http://www.m3.tuc.gr/ANAGNWSTHRIO/STOIXEIA%20MHXANWN/PDF%20APO%20FAG/WL_00200_5_T6-8_de_en.pdf[10/12, 2013]</ref>
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| ===Structural support of vibrating equipment===
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| As the processing ability of the unit is related to the vibration, a high level of care must extend to the design of the structural and support aspects. If the structural design does not meet the requirements to stabilize the unit (e.g. too resonant will lead to extreme vibrations) then excessive vibrations may be introduced, again leading to higher deflection or reducing the effectiveness of installed isolation.
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| [[File:Masssprings14.png|thumb|Unit loading with total spring stiffness 2k <ref name = twelve>SAYER, R.J., The effect of structural support conditions on the vibration characteristics of machinery. Medina, Ohio: Sayer & Associates Inc</ref>]]
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| Taking in total static force applied to the unit and stiffness of the springs used in the design:
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| <math>Deflection = \frac {Force}{Stiffness} = \frac {F_{static}}{2k} </math>
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| When the dynamic forces of the loading is taken into account,an amplitude magnification factor (MF) must be considered:
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| <math>Amplitube = MF \left ( \frac{F_{dynamic}}{2k} \right ) </math>
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| An estimation of the magnification factor for a system with one degree of freedom may be gained using:<ref name = twelve />
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| <math>MF = \frac {1}{\left [ 1- \left ( \frac{f_d}{f_n} \right ) ^2 \right ]^2 + \left [ 2 \zeta \left ( \frac {f_d}{f_n} \right )^2 \right ]^{\frac {1}{2}} }</math>
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| Most structural mechanical systems are lightly damped. If the [[damping]] term is neglected:
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| <math>MF = \frac {1}{ \left [ 1 - \left ( \frac{f_d}{f_n} \right )^2 \right ] ^2}</math>
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| where f<sub>d</sub>/f<sub>n</sub> represents frequency ratio (frequency due to dynamic force, f<sub>d</sub>, and natural frequency of the unit, f<sub>n</sub>).
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| [[File:Freratiomf14.png|thumb|the relationship between amplitude magnification factor of vibrations to the amount the unit has been dampened to resist natural frequencies (lower denominator in ratio thus higher ratio, and lower MF) <ref name = twelve />]]
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| ===Length/width for the circle-throw vibrating screen===
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| Once the area of the unit is known, as a general vibrating screen design rule the length and width must be calculated so that a ratio of 2-3 width(W) to 1 length (L) is maintained. Capacity is controlled by width adjustment and efficiency by width.<ref name = third>MULAR, A.L., 2003. Size Separation. In: M.C. FUERSTENAU and K.N. HAN, eds, Principles of Mineral Processing. Littleton, Colorado, USA: Society for Mining, Metallurgy and Exploration;, pp. 119</ref>
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| <math>W = \frac {400F}{DT \times (bulk\ density)}</math> | |
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| <math>T = -120 + 10 \times (inclination\ angle)</math>
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| The bed depth D must be lesser or equal to
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| <math>D^* = [2+0.2 \times (bulk\ density)] \times X_s</math>
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| Xs is desired cut size.
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| <math>Length = \frac {A}{W} </math> (ft)
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| Starting deck angles can be estimated from
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| <math>A = 15.5 \sqrt {\frac {F}{W}}</math>
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| F= ideal oversize flowrate, standard widths for circle-throw machines are 24,36,48,60, 72, 84, 96 inches. Measurements should be matched to available “on-shelf” units to reduce [[capital cost]].
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| ===Aperture size and shape===
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| At a fixed screen capacity, efficiency is more likely to decrease with as the aperture size decreases. The aperture shape strongly influences screen performance, in general, particles are not required to be separated precisely at their aperture size when using circle-throw vibrating screen. However efficiency is improved if the screen is designed to filter at as close to the intended cut size as possible. The selection of aperture type is generalized by the table below:
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| [[File:Aperturesize9.png|thumb|Rules of thumb equations for screen aperture design<ref name = six />]]
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| ==New developments==
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| In previous years most processes have employed two-bearing circular vibrating screens. Two- bearing circular vibrating screens with a screen box weight of 35 kN and speed of 1200RPM. The centroid axis of the screen box and unbalanced load does not change during rotation. After adopting traditional screens advantages and absorbing technology from abroad, a four-bearing vibrating screen (F- Class) was developed.<ref>Canada’s National Equipment Newspaper Equipment Journals, No. 4, pp. B9 25th March 2013</ref> This development is meets demands especially for iron ore, phosphate and limestone production industries. F-Class features a HUCK-bolted screen body that is connected for extra strength and rigidity and carbon steel is used for building the side plates to give a high strength. The shaft is strengthened with a reinforcing plate, which attaches to the slide plate and screen panels.
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| Four-bearing screen provide much greater unit stability thus higher vibration amplitudes and/or frequencies may be used without excess isolation or dampening; overall plant noise emission. The new design gives an accurate, fast sizing classification with materials ranging in cut size from 0.15 to 9.76 inches and high tonnage output where it can process up to 5000 tons per hour.<ref name = un />
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| ==References==
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| {{reflist}}
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| [[Category:Mechanics]]
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| [[Category:Materials science]]
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