Self- unloading bulk carriers various cargo handling gears

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Self- unloading bulk carriers various cargo handling gears

The fluidrive
: The ‘Fluidrive’ is a coupling, which is situated between a driving motor and reduction gear box. Using hydraulic fluid as the transmission medium, it allows the electric drive motor to reach running speed before the driving force is passed to the reduction transmission.

Fig:self unloader standby for cargo

The amount of oil in a fluidrive coupling is critical. Reference is to be made to the manufacturer’s instructions for the amounts to be used in each size of coupling.

Note: fluidrive couplings do not provide a variable speed drive for conveyor belts. Their sole purpose is to allow the driving motor to reach running speed before any load is applied.

If there is an imbalance between the ammeters on the two motors driving on a common shaft the oil levels are to be checked in the fluidrive couplings.

Reduction gear

Reduction gearboxes are used on the belt drives of various configurations, and can be either splash lubricated or fitted with a forced lubrication system. The reduction gearboxes are fitted with a Backstop, which is usually mounted internally on the input shaft. In some cases the Backstop is mounted externally on the intermediate shaft.

Fig: Self unloader with excavating system for cargo handling

The oil level in each reduction gearbox must be checked before unloading. When a gearbox is slowing down, after the motor has been stopped, a clicking sound should be heard coming from the gearboxes. This is the sound of the pawls inside the backstop contacting the ratchet teeth. If this sound cannot be heard, then there is a problem with the backstop, and it must be examined.

Couplings

Steelflex Falk Couplings are used between the reduction gearbox and the fluid drive.

Belt tensioning (Take ups)

Conveyor belts must be kept under constant pre-set tensions at all times particularly when unloading. Lack of tension will result in belt slippage which has the knock on effect of damaging the drive pulley lagging, and wearing away the top cover on the non-load side of the belt.

Smaller belts such as transfer belts are tensioned by means of jacking screws, which are attached to the tail pulley pillow block bearings.

Scrapers or cleaners

The purpose of the belt cleaner, is to remove any material which may be adhering to the belt surface.

The straight blade scraper.
The plough scraper.

Straight blade scrapers are mounted in pairs (primary and secondary) at the head pulley of each belt. Presently, the most widely used product is the Gordon Sabre Scraper, which has a urethane blade mounted on a steel rail and has a twist tensioning system. The amount of tension in the blade of a scraper is important as it determines the efficiency of the scraper. However, too much tension will cause the blade to wear out prematurely.

It should also be noted that too little tension of the scraper can lead to serious belt damage, as pieces of cargo can lodge between the moving belt and the scraper blade resulting in scoring or even tearing of the belt.

Plough scrapers are mounted on the return strand of each belt, and their function is to remove any material which has fallen onto the return strand, before it is carried back through the carriage frames.

Carriages or under carriage

Steel frames, which carry idler rollers are known as tunnel belt carriages, and tensioning carriages are sometimes referred to as carriage frames.

Pulleys

The term is applied to large diameter rollers, which are set in various parts of the belt systems, e.g. head pulley, bend pulley, tension pulley.

Vibrators

The type used on CSL vessels are all of the rotary type. They work by means of a rapidly rotating outof- balance weight, which induces vibration into the steelwork in the area of its attachment. There are three methods of driving vibrators i.e. hydraulic motor, pneumatic motor and electric motor. The most commonly used are the hydraulic type.

When using vibrators care must be taken with the hydraulic type to open the oil return valve before opening the oil inlet valves, otherwise the motor seals will be blown out. Vibrators are mounted above the tunnel belts, and attached to the undersides of the saddleback steelwork.

The vibration that they induce disturbs the cargo above, and thus speeds the flow of cargo. They are effective in shifting hang-ups in cargo holds, and are very useful when cleaning out the last remaining cargo from a hold. Vibrators are to be checked as part of the planned maintenance of the unloading system after each discharge. Vibrators may tend to work loose from their brackets during unloading, and must be re-secured at the first opportunity.

The ends of the securing bracket of each vibrator, and the saddleback steelwork must be regularly inspected. Note: the chief engineer on each vessel is to maintain an adequate level of spare parts ,and must set up a programme of regular maintenance for the vibrators fitted to the vessel. All vibrators must be run on test as part of the post unloading checks carried out after each voyage and defective vibrators must be changed immediately.

CCTV

Closed circuit televisions are provided in the cargo control room (CCR) of vessels, to continuously monitor certain positions within the SUL system.

Ship specific critical spares and tools for the SUL system

Each vessel carries an inventory of critical spares and tools for the SUL system. The Chief Engineer and Head Tunnel man must ensure that this inventory is maintained.

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