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Thread: Selection of Motors

  1. #1
    Divya Pandya Guest

    Question Selection of Motors

    How we select the motor rating for screening applications. For example how do I know whether to select a 1440rpm/ 1000rpm/ 720 rpm motor?

  2. You should select the motor based on the oscilating frequency that you desire.
    The size of the motor or motor/gear reducer is selected based on the power required to move the load and the rpm's based on how fast you want it to be oscilated.
    Antonio Reis
    www.vitrom.com

  3. Please refer my reply dated 26 Jul 03 in the thread "Vibrating Screen Design" in the Forum "Vibrating Screens & Feeders", which does not provide direct answer to your question, but provides some related information, which may be of use to you.

    Regards,
    Ishwar G Mulani.
    Author of Book : Engineering Science and Application Design for Belt Conveyor.
    Advisor / Consultant for Bulk Material Handling System & Issues.
    Email : parimul@pn2.vsnl.net.in
    Tel.: 0091 (0)20 5882916.

  4. #4
    George Baker

    George Baker

    Vice President- Corporate Communications

    Assinck Ltd. [eDir]

    Assinck Ltd.

    Professional Experience 39 Years / 9 Month George Baker has 39 Years and 9 Month professional experience

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    Know-How Screening (373) George Baker used this tag 373 times, Manufacturer (110) George Baker used this tag 110 times, Conveying (28) George Baker used this tag 28 times

    MOTOR Choices

    Hello: motor rpm is dependant on the application data, which dictates the size of the screen body and static weight of same and type of material being handled.

    If we run too fast, we create HIGH accelerating forces and we basically cause the screening device to BREAK APART due to operating over the design parameters.

    If we run too slow, it does not screen good and carrys fines over the deck and IS IN-efficient.

    The assumption is always: the material if moving over the vibrating screen is NOT a static load. If RPM is not correct on the motor in conjunction with the slope and stroke the material will in fact become a STATIC load and create a problem.

    Please refer to VSMA rules of vibrating equipment (Vibrating Screen Manufacturing Association) guidelines under the sub heading called: SPEED, STROKE, SLOPE.

    Regards, GEORGE BAKER, Moderator

  5. #5
    George Baker

    George Baker

    Vice President- Corporate Communications

    Assinck Ltd. [eDir]

    Assinck Ltd.

    Professional Experience 39 Years / 9 Month George Baker has 39 Years and 9 Month professional experience

    Discussions 883 George Baker acceded to 883 discussions, Articles 0 George Baker wrote 0 articles, Publications 0 George Baker Baker released 0 publications

    Searching nothing specified

    Know-How Screening (373) George Baker used this tag 373 times, Manufacturer (110) George Baker used this tag 110 times, Conveying (28) George Baker used this tag 28 times

    Another tip on motor sizing for vibrating screens

    TYPICALLY: for conventional circle throw or horizontal or flat type vibrating screens the motors are twice the size needed.

    UMMMMMMMMM........why would be the question......well...

    When we used "bellied or counterweighted shafts" we need momentary extra HP to PULL the heavy weighted shaft from the 6 oclock position over the 12 o'clock position. Once we get the heavy portion over the 12 o'clock position we are off and running.

    SO....if you have a 30 hp motor......say 575/60/3ph hi eff motor on a vibrating screen ..........say 6x16 3 deck. That size is needed only to START THE screen......after is starts, you can put an amp meter on the motor........and you will actually see the screen motor will basically be pulling half OR 15 amps basically.

    We could use a HI TORQUE motor in lieu of above, but not as accessible from stock and more expensive.

    GEORGE BAKER

  6. #6
    Join Date
    Feb 05
    Posts
    25

    Screen Speed Amplitude

    Divya,

    The Screen can be theoritically any combination of speed & Amplitude.

    But it is necessary to Harmonise the weight to the amplitude.

    So it normal practice to give higher amplitude to bigger screens and eventually lower speeds. High amplitude also mean more time to go up the sinusoidal - stop to change direction and - move downward.

    Static moment is the basic parameter (Kg-m) you know the weight of the screen and the displacement in meters and you can design you screen.

    Higher amplitudes give better stratification and screening become easy.

    higher RPM mean more rapid flow of material.

    When y0ou have material of more consisent size you can have a fast screen than when you have a widw varition in the particle size distribution.

    Rough thumb rule :

    Amplitude up to 16 750 rpm
    12 1000
    4 1500

    Trust this was of help

    Jacob
    B. J. Jacob
    Chennai

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