With continuous bucket elevators (or bucket conveyors as they are often called), the term “Carryback” is used to describe the incomplete emptying and discharge of material from the buckets. Incomplete emptying of buckets results in material remaining in the bucket following discharge and being “carried back” through the elevator. Carryback material eventually deposits on ledges and surfaces within the conveyor frame, while traces may also remain in the buckets. Accumulation of the material within the conveyor frame can lead to potential mechanical problems such as off-tracking or in severe cases damage to the buckets or other components.
Addressing carryback, when it occurs, requires first determining the cause. When buckets do not discharge completely, and material is being carried back through the elevator, it could be due to the following reasons:
• The material being moved adheres to the elevator buckets. Materials which are prone to static, or are sticky or tacky in nature, may adhere to the bucket walls, resulting in incomplete discharge.
• The material being moved has a tendency to cake and pack once loaded into the elevator buckets. When handling these types of materials, it is not uncommon for some residual material which has become caked or packed to remain within a bucket following discharge.
Solutions to the causes of carryback include the following:
• Different bucket plastic materials can be selected to provide the best product release properties while still maintaining other requirements such as conductivity, extreme temperature or abrasion resistance.
• When handling materials which are prone to accumulating a static charge, causing it to adhere to the buckets, consider using elevators with fully conductive bucket assemblies. Conductive bucket assemblies help discharge static, allowing material to fully release from the buckets.
• Applicable flow aids such as a bucket discharge assist device (“bucket thumper” or “bucket knocker”), whose pendulum mechanically impacts each bucket at discharge, thereby loosening material and directing it back into the discharge flow of the elevator.
• As with any equipment, routine inspections are required. As most Bucket elevators are fully enclosed for safety reasons; Inspection windows, doors and removable cover panels in strategic locations allow your maintenance personnel to perform these routine inspections and provide the necessary access for cleaning.
• Clean-out drawers are also available to allow for some accumulation of the carryback material which can then be easily emptied.
The above tips will help to troubleshoot bucket elevator carryback when it occurs. Implementing many of these solutions onto an existing installation will likely require retrofit assistance from the OEM who supplied the elevator. However, an ounce of prevention is always worth a pound of cure. Reducing bucket elevator carryback requires working with equipment suppliers who have the know-how and equipment solutions to properly address the issues and reduce the frequency thereby preventing serious issue from happening in the future.
At UniTrak, we have over 45 years’ experience in helping customers to move even the most difficult-handle materials effectively and efficiently. TipTrakTM bucket elevators from UniTrak have design features and options to successfully prevent and address bucket elevator carryback. In every project requiring a bucket elevator, we carefully review the application requirements and, where appropriate, conduct material tests to determine the risk of carryback occurring. From there, we propose an equipment solution which includes specific options to prevent carryback. These options may include the provision of buckets especially designed to prevent material adherence and the inclusion of suitable flow aids where needed.
To find out more about UniTrak can solve your conveying challenges, please contact our sales team directly.
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