Robust outdoor safety brakes for harbour crane systems

There is always a rush of activity at the entrance to Singapore Harbour. Hundreds of ships stand daily in front of the harbour basin, waiting to be let in. Here, in the second-largest container harbour in the world, over 30 million standard container units (TEUs) were handled in the year 2015. The loading and unloading of the ships generally takes place mostly land-side via harbour crane systems, so-called container gantry cranes, with load capacities of up to several hundred tonnes.

In order to cope with the uninterrupted handling of sea-borne goods, all components in these systems must function particularly efficiently and reliably. Renowned manufacturers therefore place their trust in the robust and high-performance ROBA-stop-S safety brakes by mayr power transmission for their travel and hoist drives. These brakes have been especially developed for outdoor applications with extreme ambient conditions, and convince customers through their simple assembly and handling as well as long maintenance intervals.

The brakes in the travel and hoist drives of harbour crane systems fulfil two functions: on the one hand, they function in normal operation as holding brakes. This means they have to hold the system safely in the approached position once the drives have been switched off - even in wind and storm.

On the other hand, in critical operating situations, during emergency stops or power failure, the ROBA-stop-S safety brakes are dimensioned to adsorb peak loads with very high friction work. This is, for example, the case when loads moved downwards by hoist drives have to be braked whilst moving at full speed.

The ROBA-stop-S safety brakes are electromagnetic safety brakes. They work according to the fail-safe principle, which means they are fail-safe. They are closed in de-energised condition, meaning also in case of a power failure or emergency stop. In this condition, the screw springs press against the armature disk. The friction linings of the rotor, which is connected with the drive shaft via a toothed hub, are clamped between the armature disk and the mounting surface of the brake. When the power is switched on, a magnetic field is built up in the brakes. In this way, the armature disk is pulled against the spring pressure towards the coil carrier. The rotor with the friction linings is free and the brake is released.

Even in adverse conditions and during operational malfunctions, the braking effect is always ensured: even if the brake is damaged, caused for example through cable breakage or failure of the magnetic coil, the braking torque is retained.

Performance around the clock

When loading and unloading ships, harbour crane systems must be able to provide high performance around the clock. The pre-requisite for this is high operational safety with minimum standstill times for maintenance and repair work. In addition, extreme ambient conditions such as the salty environment, varying air humidity values, wind and storm have to be weathered. All components, and in particular safety-relevant ones such as brakes, therefore have to be robust and resistant. Only sealed brakes with high-quality corrosion protection can survive here long term without incurring damage.

With the ROBA-stop-S, mayr power transmission has developed a safety brake especially for critical ambient conditions and outdoor applications. It accords with Protection IP 67 and is therefore completely dust-tight and waterproof. The compact and solid housing with an integrated terminal box and without any pockets and grooves makes the brake resistant to damage caused by external influences. In addition, the high-quality primer on the brake body, the chrome or nickel coating of the inner components or the manufacture in rustproof stainless steel provide permanent protection against corrosion. A microswitch for release monitoring is integrated into the terminal box and thus optimally protected, which guarantees that the motor only starts up when the brake is released.

This terminal box also features sufficient space to hold a rectifier for the brake's magnetic coil. In addition, a further microswitch can be integrated which inspects the wear on the friction linings.

On the ROBA-stop-S safety brake, it is possible to mount a speedometer on the brake body. If no speedometer is used, the coil carrier is sealed with a cover. In addition, the brake has an emergency hand release, using which it can be mechanically released via two screws. If the brake is used at temperatures below zero degrees Celsius or in high air humidity, an anti-condensation heating system is recommended. This heating system prevents condensation from forming within the brake interior.

In particular in difficult installation positions, criteria such as simple installation and handling and long maintenance intervals are particularly important. Through their compact construction and small outer diameter, the safety brakes are easy to handle and can be quickly and easily installed. The high-quality friction material of the brake linings with high wear resistance also substantially reduces the number of inspections necessary, and therefore the failure times. If the friction linings wear down, the maintenance effort is minimal: only the air gap has to be readjusted or, at the end of its service lifetime, the rotor has to be replaced along with the friction linings. A threaded bore which is tightly sealed during operation permits quick inspection of the air gap without having to de-install the brake. This low-maintenance effort and the high operating safety avoid expensive downtimes on harbour crane systems and substantially reduce operating costs.

Please go to www.mayr.co.uk to learn more about ROBA-stop-S safety brakes.