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Thread: Discharge from conveyor belts

  1. #1
    Peter Brown Guest

    Discharge from conveyor belts

    What is the best practical approach to use when calculating the throw off trajectory from conveyor belts? Are there any references comparing calculation with actual performance.

  2. Dear Mr. Brown:

    There are a number of references that you can use for trajectory calculation. One of the most useful is the CEMA (Conveyor Equipment Manufacturers Associatyion) publication BELT CONVEYORS FOR BULK MATERIALS.

    This book indicates that the calculations offered are in close agreement with actual observed trajectories.

    Good luck with your calculations.
    Dave Miller
    ADM Consulting
    10668 Newbury Ave., N.W.,
    Uniontown, Ohio 44685 USA
    Tel: 001 330 265 5881
    FAX: 001 330 494 1704
    E-mail: admconsulting@cs.com

  3. #3
    Author Guest

    Discharge Trajectory

    A search in the eLibrary on this website resulted in this hit:

    Name of Author:***Arnold, P.C., Hill, G.L.
    Company Affiliation:***University of Wollongong
    Title of Article:***Predicting the Discharge Trajectory from Belt Conveyors
    Published in Journal:***bulk solids handling
    Year:**1990*****Volume:**10*****Number:**4*****Page:**379*****
    Type of Article:***Original Article
    Fields of Interest:***Belt Conveying
    Article published in 'The Best of ...' book:***I/94*(Belt Conveyor Technology)

    In the Bookstore you can check all articles published in the
    Best of Belt Conveyor Technology books published by Trans Tech Publications, virtually hundreds of them, and perhaps you find more references to discharge trajectories.

    Reinhard H. Wohlbier
    The Powder/Bulk Portal
    wohlbier@bulk-online.com

  4. #4
    Dear Mr. Brown,

    The best approach to predicting conveyor belt material discharge trajectories depends on what you want to use the information for. The CEMA approach offers a very simple method of calculation which gives you a reasonable approximation quickly. If, however, you require a more precise approximation to the trajectory, you would be better off to use another method, such as the Dunlop conveyor design method, the Stephens-Adamson method or the Probelt method. All three calculation methods effectively provide the same results.

    The main difference between the CEMA method and the others occurs when the belt speed is not high enough to cause the material to leave the belt at the point of tangency of the belt and the pulley. CEMA assumes, in this case, that the material will accelerate to match the tangential velocity of the discharge pulley. In fact, this only occurs on very slow conveyors. This is an extremely simplified method of approximating the frictional forces between the material and the belt.

    None of these methods take other factors into account, such as wind currents, adhesive properties of the material and the cohesiveness of the material. However, these methods are generally accurate enough to provide sufficiently accurate predictions.

    According to Hill and Arnold (BSH Vol. 10 No. 4 10-1990), the Dunlop method is more accurate than the CEMA method, as proven by testing.

    L.P. Huitema
    EMS-Tech Inc.
    www.ems-tech.net

  5. #5
    Author Guest

    Discharge Trajectory

    Dear Sir/Madam,

    I have not seen any record to help me answer your question nor do I have the resources to verify my conceptions, but coming from the engineering
    background I can share the following:

    The trajectory of material from the conveyor belt will be affected by its
    adhesion to the belt, the belt velocity and the incline or decline of the
    belt. All these factors will be accounted for in the calculations by using
    the balanced force relations or Newton's second law of motion. The
    trajectories of each material can then be observed for the MAXIMUM SPEED of
    the belt.

    For this speed a possible range of trajectories can PHOTOGRAPHICALLY be
    captured, and a distinction for various materials be made on at least one
    chart. Ideally for conveyed material the higher the adhesion properties the
    more likely is the material carry-back at the head-pulley, and the higher
    the speed of the belt the farther the trajectory of material.

    Thank you.

    > Mr. Iti Modipane
    > Sales & Marketing Director
    > Brelko Engineering C.C.
    > P.O. Box 62392
    > 2107 Johannesburg
    > Republic of South Africa

    iti@brelko.com

  6. #6

    trajectory program

    Peter

    I have a very simple excel program that I use for calculating trajectories from belts. It gives me the X & Y coordinates to plot from 0,0 in auto cad or on a graph. I use Pline in autocad and then transfer the pline to the appropriate point on the pulley.

    The program is based on formulas from CEMA and I have found it to be quite accurate for my chute designs working with road salt.

    Send me your e-mail and I will forward it to you if you like.

    Regards, Gary Blenkhorn
    blenkhor@compassminerals.com

  7. #7

    Discharge from conveyor belts

    Dear Mr Brown,
    CEMA or MHEA graphical methods are sufficient for most situations with the hope that most of the elaborate attention devoted to slow conveyors is no longer of much importance. Admittedly some material characteristics do require slower belts but they should never be so slow that material slides off the end of the belt and so increase top cover wear at the region of maximum tension. Surely that defeats the object of slowing the belt down in the first place.
    During transition a lot of material accelerates sideways in a very short time. That is why we have to have liners on the sides of chutes. Present 2 dimensional analyses of conveyor discharge do not consider this lateral disturbance of the cross section except to describe the material cross section at discharge in terms of an arc sector.
    By confining the examination to a 2D situation the present methods seem to contradict the Conservation of Energy. Since many particles are given a lateral velocity during transition then they probably cannot be moving ahead at exactly the same speed as the belt.
    In 2002 we ought to be examining conveyor discharge trajectories using the particle dynamics add ins of CFD packages. This would be the most reliable and practical approach. With reference to photographic data; I can only imagine conventional photography providing 2D data with the complication of providing a backlight source when taking head on shots.

  8. #8

    Material Trajectory

    I had occasion to test the accuracy of the trajectory calculations, according to Newtons Laws without regard to air friction, adhesion or other complications (this is the CEMA method). In a coal unloading upgrade project our conveyor to the plant had the options of transfer to the the plant bunker feeding conveyor, or to stackout. to complicate matters the plant system was not upgraded and could not handle the new 1000 stph rate, it is limited to 800 stph design rate. When feeding to the plant we were required to deflect the trajectory to skim the excess 200 stph from the trajectory's underside, to stackout. The existing chute design and the new deflector required accurate prediction of the trajectory in order to accomplish the material deflection (only above the 800 stph rate) and the precise split in very limited space (with limited adjustment because of space). Our calculations (an excel program that produces x/y coordinate points and a trajectory plot) proved very accutate with little adjustment required and mission accomplished.

    Joe Dos Santos
    Dos Santos International
    531 Roselane St NW
    Suite 810
    Marietta, GA 30060
    USA
    Tel: 1 770 423 9895
    Fax 1 866 473 2252
    Email: jds@ dossantosintl.com
    Web Site: www.dossantosintl.com

  9. #9
    Peter Brown Guest
    Thanks to all who bothered to reply. I have looked at those methods I can easily find and read a paper on the subject by Professor P. C. Arnold.

    Reading the CEMA method I had difficulty in accepting its method for 'high speed' conveyors and found it intersting that Prof. Arnold reported this method overestimated the distance the material would be thrown. Also on very 'slow speed' conveyors it seemed to me most unlikely that the material would stay on the belt as far as predicted. Again Prof. Arnolds results reported this.

    I have been unable to read in detail the Dunlop/Booth method, but have found an alternative method contained in the the MHEA 'Guide to the Design of Transfer Chutes' 1989 (not to be confused with 'Recommended Practice for Trough Belt Conveyors').

    The upshot of all this is I now have a programme that produces dxf or dwg drawings of tracectories based on either CEMA, MHEA(1989) or Stephens-Adamson. I can then take my pick!!

    Thanks again

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