What advantages do diesel-hydraulic grabs offer?Orts GmbH Maschinenfabrik Ltd
Radio-controlled diesel-hydraulic grabs are, in terms of advantages, a combination of mechanical single-rope grabs and electro-hydraulic grabs.
Like a mechanical single-rope grab, the radiocontrolled diesel-hydraulic grabs from German grab manufacturer Orts can operate on every crane. Just ‘hook on’ and go. It doesn’t matter if on shore crane, mobile harbour crane, ships deck-crane or auto-crane (truck-crane). These grabs can work everywhere at once.
In contrast to mechanical single-rope grabs, dieselhydraulic grabs are powerful with high closing force on the knives. They are able to handle heavy bulk cargo, like iron ore, without problems and a best grade of filling of the clamshells. With a 7m 3 capacity, the diesel-hydraulic grab offers a rate of over 300tph handling iron ore, and the same goes for clinker stone with a 12m 3 -capacity grab.
Because of the optimized construction and kinematics of the grab (especially the clamshells), diesel-hydraulic grabs are fast and effective.
With radio-controlled diesel-hydraulic grabs, the owner does not have to invest in crane equipment which would otherwise be necessary to operate electro-hydraulic grabs, so there are no installation costs for crane equipment, and no maintenance and spare parts.
Deadweight and Payload:
A radio-controlled single-rope grab for a average piled density of 1.8t/m 3 and with 12m 3 capacity has a dead weight of around 10.5 to 11 tonnes. A radio-controlled diesel-hydraulic grab with a capacity of 12m 3 for the same density has a dead weight of 7. 8 tonnes. This means for a vessel with 30- tonne cranes on board, which has to discharge e.g. clinker stone (density 1.6 t/m 3 ):
12m 3 (capacity) x 1.6t/m 3 (density) + 7.8-tonne (grab) = 27 tonnes
Mechanical single-rope grab
12m 3 (capacity) x 1.6t/m 3 (density) + 10.5-tonne (grab) = 29.7 tonnes
The SWL (safe working load) of the crane for normal cargo is 30t. As manufacturers of cranes recommend that operators lower the SWL for grab operation by approximately 10–12%, this means that a 30-tonne crane has a SWL for grab operation of 26.4 to 27 tonnes.
The diesel-hydraulic grab fits; the mechanical single-rope grab is too heavy. If possible, the volume of the single-rope grab has to be reduced down to 10m 3 before the operation can start. The radio controlled diesel- hydraulic grab is faster (more cycles per hour) and he can handle 2m 3 more bulk.
Other advantages are:
These grabs can come on board of a vessel temporarily for a new contract and switched to another vessel when the contract is over. Other customers put stationary diesel-hydraulic grabs in a port for unloading their own vessels. Then the shipping company can save money on the charter-rates, because there is no need to charter vessels which are equipped with grabs. In the meanwhile, between the arrivals of the vessels, the owner can rent out the grabs to other companies and earn additional money.
With mechanical single-rope grabs it can happen that the unloading of a vessel must be stopped, because of low tide in the port which means that hoppers are out of reach for single-rope grabs, as they are too high. The closing rope gives a fixed working height; the average for a 12m 3 single-rope grab is approximately 10–12 metres (depending on how the rope is reeved within the grab).
For heavy bulk the closing rope has to be reeved more than 3x in a single-rope grab. With a 4x folded closing rope, the working height increases and the time for closing the grab also. A further problem for single-rope grabs is that the working height also limits the minimum distance between the jibhead and grab, so the crane driver must compensate this 10–12 metres working height with the jib.
And lifting the jib costs valuable time. Orts GmbH has been manufacturing radio-controlled diesel-hydraulic grabs for ten years now. With the help of long-term customers, improvements have been made over the years. The grabs are in operation in the Black Sea Area, Southern Africa, Far East, Baltic Countries, Saudi Arabia, Australia and on board of vessels. The grabs are available in two models — clamshell for bulk, and orange peel design for, e.g. scrap.
They are also available as custom designed models for, for example, timber logs and woodchips. The diesel engine emissions are all within to the latest European regulation.