Kristiansund Kranservice orders radio-controlled bulk grab from Port-Trade:
Demag MC 300 to be fitted with 4.3 m3 MRS grab for rehandling of salt
Single-line, radio-controlled grabs enable cranes with only one winch to handle bulk materials efficiently.
Grabs of this type are fitted with a closing rope in the same way as traditional 2-rope grabs.
Thus, when the open grab is lowered into the bulk material, the grab will close as the winch takes in the closing rope.
As the grab closes, a piston rod is pushed into a hydraulic cylinder, which is fitted between the lower grab traverse and the grab head.
The crane driver can, at the moment of his own choosing, open a valve in the cylinder’s oil line by means of a radio signal from the cab, thereby allowing the piston rod to be pulled out by the weight of the grab shell halves as they move apart.
The driver can stop the opening movement of the grab at any point and thereby easily control the outflow of bulk material from the grab, e.g. when discharging directly onto a lorry.
The driver cannot reverse the opening movement of the grab, only stop it.
Old type single line grabs have a wire from the grab, that the driver has to pull in order to release a locking mechanism, allowing the grab to open in one continuous movement, unstoppable once started.
Alternative old designs require that the full grab is lowered onto the bulk heap or onto the ground so that the hoist rope becomes slack, automatically releasing the locking mechanism.
The older designs have slow down cycle times, whereas the new radio-controlled design works at the same speed as a normal 2-rope mechanical grab.