6.3.4 Continuous Bucket Unloader Chain
Large conveyance: For conveyance of iron, stone, coal, and rock salt
Continuous Bucket Unloader Chain is used to remove large quantities of material, like iron, stone, coal, or rock salt from a ship's cargo hold (Figure 6.19). This application originally used a cable-driven bucket on a crane rather than chains. However, there were several problems with the original design—contamination of the environment by conveyed material, difficulty with automation, inability to scoop material in hard-to-reach areas, and short working life of wire rope. Because of these problems, chain has become the design of choice in current applications.
Figure 6.19 Continuous Bucket Unloader Chain
In this conveyor form, buckets that scoop conveyed objects are installed between two chains. Mobility and flexibility make this equipment different from the conventional bucket elevator. The conveyor system can be moved to different locations, and the equipment can be transformed from an L-shape to an I-shape to get to hard-to-reach areas.
The maximum conveyance capacity: 3,000 ton/h.
The maximum chain speed: about 100 m/min.
Some types of flow conveyors are used for unloaders.
Construction and Features
Chains used in continuous bucket unloaders are exceptionally large, even when compared to other large pitch conveyor chains. Average tensile strengths are 3,040 kN, 3,630 kN, and 4,460 kN for some of the heaviest chains. Usually N-rollers are used in the chain.
The sprockets are exposed to high speeds, heavy shock loads, and corrosive and abrasive materials. Special sprockets with more than 12 teeth and with a noise-reduction factor should be used. Wear-resistant, detachable-tooth sprockets are frequently used.
Selection and Handling
- The chain must have exceptional wear resistance because it is exposed to high speeds, heavy shock loads, and conveyed materials that are corrosive and abrasive. For example, in the case of coal, the corrosiveness varies with each coal mine.
- Chain attachments should have high strength to support large bucket loads.
- Noise and abrasion of sprockets are important considerations.
- Choose chain from a manufacturer with a lot of experience and known to produce a high-quality product. Select the chain only after communicating application requirements to the manufacturer.
- Assembly of large pitch conveyor chain on the equipment can be an enormous task. There are special tools available that can assist in connecting the chain.
Manufacturers are working to develop relatively light-weight chain for the load it carries, and sprockets that can provide long-term performance with low noise levels.