Fig:self unloader boom installation
The advantages of the Lift Belt System are:
- It occupies less space in the vessel than any other elevator belt system, as the angle of the elevation is vertical.
- It requires a smaller number of rollers to support the belt.
The disadvantages of the Lift Belt System are:
- High Cost
- Long belt change-out time required i.e. three to four weeks and this can only be performed in a shipyard with sufficient crane height, and capacity.
- The belts are prone to damage from cargo falling from the upper part of the system.
- The belts are prone to damage if the side guide wheels become
- seized. The resultant edge damage lays open the steel cables to corrosion which will eventually result in the belt being scrapped.
Important note: the side guide wheels must be inspected during and after each discharge. Any seized guide wheels must be repaired immediately. Any edge damages on the lift belt must be repaired using cold cure procedures immediately.
- Hotwork in the lift belt casing is extremely hazardous as hot material can lodge in the pockets.
- Lift belts are susceptible to stalling, if the system is shut down during high rates of discharge.
The loop belt elevator
The loop-belt arrangement is housed in the Loop-Belt Casing of the self unloading bulk carriers cargo transfer system and found normally just in front of the ships bridgefront bulkhead. The loop belt elevates cargo material using two belts arranged in a C form, with one driven outer belt, and one non-driven inner belt. These belts turn on trough section rollers the outer edges of which contain the cargo material within the belts.
The cargo material is lifted in the sandwich formed between the two belts the tension of which creates the clamping force and resultant friction necessary to lift the material.
The system is driven by electric motors at each end of the outer belt using fluid couplings and reduction gearboxes. Speed sensing ensures that the speed of the inner belt which is driven by the friction between the two belts, does not fall below a pre-set level. This is to avoid a reduction in the transfer of cargo material and resultant build up of cargo material at the bottom of the loop elevator. If slippage does occur to the extent that the pre-set level is exceeded then the tunnel and transfer belts will automatically stop.
In the event of a stoppage, the loop belt system is prevented from running backwards under the forces of gravity, by two backstops fitted inside each reduction gearbox.
The hydraulic tensioning of the loop belt system is critical, and the design specifications must be complied with.
The advantages of a Loop Belt Elevating System are as follows:
- High cargo handling capacity
- A relatively small volume of the vessel is occupied by the Loop System with its near vertical lift.
- Belts can be completely changed out in a short period of time i.e. three to five days.
- Easy to maintain.
- Belting material is available from several manufacturers at competitive prices.
- Simple and robust drive system.
- A minimum of automation is required.
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Self unloaders various cargo handling gears
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Various type boom conveyor belts - How the belt sytem practically works ?
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Dealing with self unloaders stalled lift belt
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Conveyor belt construction & troubleshoot guide
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Conveyor belt installation guide
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Conveyor belt repair & maintenence guide
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Safe working practice onboard self unloading bulk carriers
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Preventing conveyor belt fire onboard self unloading bulk carriers
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Cargo work safety precautions
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Various bulk cargoes - free flow ability
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Various bulk cargoes & dealing with cargo hang ups
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Preparations for cargo planning, handling & stowage
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Preparations for discharging & related guideline
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self-unloaders-discharging-operation
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Safety precautions for boom operation
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Directing gate operation, gate problems & crew duties
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Cargo holds/ tunnels cleaning, maintenance and check items
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Procedure for transporting coal on self- unloading bulk carriers
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Instructions for dealing with a stalled lift belt
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