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Distance, Angle, and Overlap between Conveyors

Ideally, all belt-to-belt transfers would be in-line: The discharging and receiving belts would run in the same direction. This type of transfer allows for sufficient belt overlap in order to avoid loading on the transition area of the receiving belt, where the belt goes from flat at the tail pulley to its full trough angle. Transitioning in this manner also makes it relatively easy to place the material on the receiving belt with the load moving in the direction of the belt, thus reducing unnecessary wear and spillage. In-line transfers are to reduce the length of the conveyor when insufficient drive power or tension is available for a single belt, to extend the length of the conveyor system or to accommodate mechanisms to blend, crush or separate the material.

Three conveyors are in-line with each other, one dumping onto the next.
With in-line conveyor transfers, the discharging and receiving belts would run in the same direction.

More typically, a change in the direction of the material movement is required as one conveyor loads onto another. A non-linear transfer may be required to accommodate changes in material flow direction, to allow for diverting the material for stockpiling, or for splitting the material for separation.

Problems associated with non-linear transfer points include: difficulty in maintaining the material's proper speed, trajectory, and angle; problems controlling dust and spillage; and issues of increased wear on (and the resulting higher cost for replacement of) transfer-point components.

If material is loaded on the belt in a direction that is not in line with movement of the receiving belt, wear patterns may become visible on the inside of the head (discharge) chute. These patterns will correspond to the path the material takes as it bounces off the inside of the chute as it tries to attain the direction and speed of the moving belt. Although turbulence may not be visible as the load exits the skirted area, the ricocheting movement of the material within the transfer chute accelerates wear on liners, skirtboard, and sealing systems. The force of the loading material may mistrack the belt and push it out from under the skirting on one side of the belt, allowing the sealing strip to drop down and preventing the belt from returning to its centered position. The belt will attempt to return to its center as material loading changes, forcing the belt into contact with the sealing strip and cutting through the strip, resulting in significant spillage opportunities.

Fortunately, a number of strategies and components can be employed to guide the flow of material into the desired direction of travel and load it onto the center of the receiving belt.

The most common mistakes made in the transfer chute design stage include not providing enough overlap of the conveyors. This leads to loading on the belt transition and not allowing enough room for installing belt cleaners. Without attention to proper conveyor design, including sufficient overlap, the operation is burdened with a conveyor that plugs often, generates loads of fugitive material, and creates excessive wear problems.

Loading in the transition area of the receiving belt is done in an attempt to reduce costs by saving a few meters of conveyor length. It is recognized that this practice creates numerous problems in loading, sealing, and belt wear and should be avoided.

It should be noted that in order to reduce the load absorption requirements and dust creation opportunities of a conveyor transfer system, drop height should be kept at a minimum; however, engineered hood and spoon designs use gravity to maintain material flow speed and often require greater drop heights in order to implement them. Engineered spoons provide many benefits and should be considered as part of the original design or as part of the requirement of a future retrofit.

Topics: Conveyor Belt Mistracking, Conveyor Belt Component Damage, Material Flow Problems, Basics of Belt Conveyor Systems, Material Spillage

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