Mastering Crane Breaking Advanced Technology can Reduce Loss

Many authorities begin to think about emergency brakes for High compensation claims when happened injury or cargo damage. Because this is the high torque side of the hoist drive train, it requires brakes of a much higher capacity than those installed between crane motor and gearbox. As an example, the main boom hoist on a typical 70 ton container crane would require two emergency brakes, each capable of generating a braking force of 119kN.

These brakes need to be “fail safe,” which means that a nest of powerful springs are used to generate the required force and hydraulic pressure in excess of 160 bar is needed to compress the springs in order to effect brake release.

This hydraulic pressure is provided by a small power pack which typically consists of a 1.5 kW motor mounted on a tank top driving a positive displacement pump. This discharges its flow through a check valve to an accumulator and is automatically switched off when the system pressure is reached.

Two solenoids are employed: one on the flow line into the brake and the other on the discharge side. In normal operation with the drive hoist energized, the discharge valve would be closed and the input flow valve open. This condition permits the oil to maintain pressure on the springs and effect brake release.

The solenoids are connected to the crane motor circuitry and when de-energized open the discharge valve and close the input flow valve. This immediately releases the oil from the calipers and arrests the input flow allowing the springs to force the pads against the flange of the drum.

Failure of the transmission drive or normal service brake will activate an overspeed switch mounted on the drum shaft. This will then trip the power supply and consequently automatically apply the emergency brakes.

An alternative to an overspeed switch is a “mis-matched” control which constantly monitors the crane motor speed relative to the drum speed. The ratio of these speeds will always be constant parameters determined by gear backlash.

Many new cargo handling cranes are installed with the latest in superior braking technology, making braking and load holding safer and more controllable.