A bucket elevator is used to transit bulk materials along a vertical or an inclined path. This equipment can easily be found in most industries as they are essentials to the production process.
A typical bucket elevator manufacturer keeps the mechanism similar in operation to conveyor belts, with the main difference being that the bucket elevators use buckets attached to a rotating chain or belt to move the materials.
There are three classes of bucket elevators. The classification is based on the spacing of buckets and modes of discharge.
Centrifugal Discharge Elevators
In this type, the buckets are placed at regular intervals on the belts or chains. This allows for easy loading and displacement of materials. Centrifugal discharge elevators are primarily used for hauling materials in a vertical path.
Materials to be pulled are fed into the boot of the elevator, after which the buckets scoop them up as they pass under the bottom wheel. The discharge of materials happens due to the impact of the centrifugal action when buckets go over the head pulley.
Centrifugal discharge elevators are used to haul relatively free flowing materials as the loading of the materials is done by scooping the buckets at the boots. Lump size below 50 mm is usually not used for this type of bucket elevator as this could result in damage to the buckets.
Also, it is not advisable to use lump size finer than 200 mesh size, as bigger sizes are often aerated and cause wastage and jamming problems.
The speeds at which centrifugal discharge elevators operate are higher than other types. Their speed falls between the range of 70 to 125 m/min.
Continuous Discharge Elevators
The continuous discharge elevator is designed in such a way that the buckets are fixed on the chain or belt without any space between them. Materials with larger lump sizes can be handled by a continuous discharge elevator, which otherwise would be difficult when using a centrifugal discharge elevator.
Buckets used with continuous discharge elevators are usually given shapes that allow the belt or chain to pass over the head wheel. Also, the buckets have a flanged end that serves as a conduit leading the materials to the discharge spout.
In continuous discharge elevators, the materials are not fed by the scooping action of the buckets passed the stack of materials. The speed of operation of this elevator type range from 30 to 50 m/min. This rate is much lower than that of centrifugal discharge elevators.
The loading and unloading take place slowly and gently. This makes them appropriate for material that is fragile, fluffy or pulverised. Continuous discharge elevators can operate in both vertical and inclined conditions.
Positive Discharge Elevators
Positive discharge elevators are similar to the centrifugal discharge elevators; there are, however, some notable differences. Here the spacing in the buckets are at regular intervals and are mounted on two strands of chains.
There is a snub wheel under the head sockets so that the buckets are inverted to ensure complete discharge. The buckets operate at low speeds between the range of 35 – 40 m/min.
These elevator types are used for handling materials that are light, fluffy, dusty and sticky. In positive discharge elevators, materials are fed by the scooping or digging action of the buckets.
In summary, in a bucket elevator, several options of buckets (in malleable iron, plastic, and fabricated options) are made available by the manufacturer. Also, in bucket elevator system venting is an option to ensure an efficient bucket filling and discharging.