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Thread: Rock Bouncing on Inclined Conveyor

  1. #1
    Join Date
    Feb 04

    rock bouncing on incline conveyor

    I am interested in how to control rocks which are rolling and bouncing back down an inclined conveyor. They damage idlers and cause spillage which must be cleaned up.

  2. Hello Jeff,

    If I understand your problem correctly, the rocks are becoming dislodged after they have settled from the load zone and only present a problem once they are in the incline.

    This sounds as if your belt is overloaded or too steep; or some of your conveyor idlers are (vertically).

    If overloaded, reduce the loading and speed up the belt to get the same output. There are limits to this as your loading zone "settle" time will be reduced, your idlers will wear faster, and you will probably have to change your discharge chute geometry.

    If too steep, you may have to change the system to one which can hold the rocks (Muli-Fold, Pipe, Square, Corrugated Sidewall, or Cleated belt). Alternatively, you could change the angle of the present system, if space allows.

    If some of your carry idlers are too high (vertical misalignment), the rocks can be jostled and start their freefall (roll/bounce back). You should be able to ascertain if this is the case by visual inspection or by tracking where the problem starts. If the rocks come loose always at or near the same point, a high idler could well be the cause. If so, you can correct the problem by aligning the system (bringing all idler and pulley heights to the same incline plane).

    Hope this helps.
    Dave Miller
    ADM Consulting
    10668 Newbury Ave., N.W.,
    Uniontown, Ohio 44685 USA
    Tel: 001 330 265 5881
    FAX: 001 330 494 1704

  3. Dear Mr. Jeff,

    It would be better if you mention the following parameters :
    1) Belt width
    2) Troughing angle
    3) Carrying idlers type (3 equal / unequal rollers)
    4) Belt speed
    5) Lump size distribution percentage, from maximum to minimum
    6) Material name
    7) Conveyor maximum inclination angle

    As a general rule, material roll back etc would be less when material cross section on belt is reasonably full. In case of dribble feed chances of material movement on belt is more. You can check when the roll back slide back is occurring.

    Ishwar G Mulani.
    Author of Book : Engineering Science and Application Design for Belt Conveyors.
    Email :
    Tel.: 0091 (0)20 25882916

  4. #4
    Join Date
    Feb 04

    rock bouncing on incline conveyor

    Thanks for your responses, this is a pet project of mine.

    A few details will probably help. We have 12" minus gypsum coming from a primary roll crusher at rates up to 2000 tph. Several times a day the feed hopper goes empty between trucks. It is thought the rolling and bouncing rocks normally occur near the end of a run. The belt is 48" wide, 1000 ft long, 35 degree idlers, 3 equal width idlers, incline 18 degrees, speed 630 fpm, wrap drive, gravity takeup, 500 Hp.

  5. Jeff,

    From the information supplied, it appears that your rollback problem is directly related to the light loading which is normal at the tail end of a run. There are not enough rocks and fines to support each other on the relatively steep incline. The incline angle, belt width, speed, et cetera are not out of line, and appear to work well for you under full load situations.

    You can address the maintenance annoyance and expense by one of the following:

    [1] Reduce the incline angle of your conveyor. This alternative has the cost of extra structure and belt; and requires additional floor or ground space that you may not have.

    [2] Alter the system to semi-sandwich one by installing another belt over the existing one. This alternative is relatively expensive, but less costly than replacing the system.

    [2] Change the system to a Multi-Fold, Pipe, Square Belt, or Sandwich belt system. This alternative will correct the problem, but it is the most expensive choice.

    [3] Install cleats or pegs that will act as holders in low load situations. This alternative is a quick fix that will create other maintenance and clean-up problems, as well as having a possible negative impact on your full load production rates.

    [4] Install over belt rollback checking devices to catch the rocks before they damage idlers. This option is another quick fix ? involving rubber or metal flaps suspended over the belt (but not touching it) which will deflect forward to allow full loads to pass and drop down under low or no load situations. The problem with this choice is the extra maintenance costs associated with changing the flaps as they wear.

    Hope this helps.
    Dave Miller
    ADM Consulting
    10668 Newbury Ave., N.W.,
    Uniontown, Ohio 44685 USA
    Tel: 001 330 265 5881
    FAX: 001 330 494 1704

  6. #6
    David Beckley Guest
    Hi Jeff,

    The problem of rocks bouncing off lightly loaded inclined conveyors is universal and as you point out it can create a serious risk to personnel and equipment. The only method that I have seen used to prevent it from happening is to totally enclose the carry side of the belt using continuous skirts and a hood.

    The problems with this system when fitted to a conveyor using conventional foot mounted idlers are that the design must allow the idler wing rollers to be removed and replaced when failures occur and the belt must be suitably supported between the idlers to prevent material escaping under the skirts during deceleration, when belt sag will increase. If material does escape under the skirts, this material will be crushed between the belt and the skirt as it approaches the next idler. The increased drag at the skirts from the crushing of material at every idler may make restarting difficult.

    Sorry that I can't offer a low cost miracle cure.


    Dave Beckley
    Conveyor Design Consultants of WA
    Perth, Western Australia.

  7. #7
    Lawrence K. Nordell

    Lawrence K. Nordell

    President and CEO

    Conveyor Dynamics Inc.

    Conveyor Dynamics Inc.

    Professional Experience 59 Years / 11 Month Lawrence K. Nordell has 59 Years and 11 Month professional experience

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    The degree and manner of rollback containment depends on rock shape, size distribution, and moisture influence.

    1. Conventional conveyors are capable of carrying some materials up or down slopes of 25-30 degrees.

    2. Rock shape such as slabby granular material is more stable than cubical material.

    3. Some cohesive materials can negotiate steeper slopes

    4. Larger to medium rock sizes can be contained when using both bagger side boards, interval rubber cross belt aprons, and a restraining mess above the bagger boards which arrests the spin momentum.

    Your noted observation of spillage is typical, for an 18 degree belt slope and lumpy ore.

    Your speciifications, I believe, are suitable for restraint per item 4.
    Key to success is to not allow spin momentum to develop.

    Lawrence NOrdell
    Conveyor Dynamics, Inc.

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