Variable frequency drive technology are helping to optimise crane brakes

 For lifts where additional security is required, such as lifting molten metal in foundries or projects in the nuclear sector, a secondary brake can be added. “The old-style system is a ratchet and pawl, but the industry is moving away from that; there are numerous types of brakes that can be added on the drum,” says Comiono. “On engineered or built-up hoists for specialised applications, customers may prefer shoe brakes or band brakes for ease of maintenance. Some sectors such as mills want an open design, again making it easier to service.

“And for handling really fragile, expensive or dangerous loads, an emergency lowering brake might be added, usually on the drum or gearbox shaft. Using this, the operator can get on the crane and lower the load in a controlled manner.”

At Turkey-based crane manufacturer CMAK, the company typically uses either electromagnetic brakes or electrohydraulic brakes, depending on environmental conditions, application type and customer requests, says Oguzhan Gülerci, exports specialist at CMAK—as well as additional drum brakes for enhanced safety and redundancy.

“We use electromagnetic brake systems in our standard cranes. However, if the environmental temperature in which the crane will operate is constantly over than 55 °C, these electromagnetic brakes may start to lose performance, and this is not a case in which we can take risk,” says Gülerci.

“Therefore, in such circumtances we prefer to use electrohydraulic brake sytems in our cranes. In addition to this, we also prefer to use electrohydraulic brake sytems in custom-made open winches with high capacity or high lifting speeds, or those suitable for special applications in foundries, mines, hydroelectric power plants and so forth.

“For example, we are about to complete a project which includes one 100t + 25t and one 80t + 15t capacity custom-made open winches for one of our clients in Mexico, and these cranes will operate in a crushing mill plant. Therefore, we used a pair of electrohydraulic brakes to ensure the safety. In addition to this, we used emergency drum brakes to take a step further for safety and to create redundancy.”

Both electromagnetic and electrohydraulic brake systems have different advantages depending on their design and the intended purposes of them, adds Gülerci. “Briefly stated, the main advantages of electromagnetic brake systems are durability, compact design, easy assembly and maintenance, silent operation, and asbestos-free brake pads. Regarding electrohydraulic brake systems, of course these brakes are more powerful and suitable for high capacites and lifting speeds, and they are also long-lived, and durable against high environmental temperature and dusty conditions.”

Specialised solution

Sheffield, UK-based SCX Special Projects, part of Street CraneXpress, specialises in innovative lifting equipment systems for bespoke applications. To maximise failsafe capabilities, the company established a partnership with Bulgarian company Siguren, the manufacturer of the MotoSuiveur hoist safety device.

“For our failsafe hoisting solutions, we had to explore beyond traditional calliper emergency brakes as their performance can often fall short,” says Dave Little, SCX Special Projects’s Nuclear sales manager. “That led to a partnership with Siguren and its innovative MotoSuiveur system.

“The MotoSuiveur’s design will never allow a free-fall condition to develop in the event of a mechanical or electrical failure of the hoist drive or gearbox. It doesn’t depend on the friction of brake pads to arrest the load: instead, it brings it to a rapid and safe stop through an ingenious damped, interlocking worm and wheel mechanism.

“In practice, this means that the load is arrested in less than 50mm of vertical hook drop, a level of performance that is simply unachievable with traditional calliper hoist brakes.”

The system’s worm and wheel drive is mounted directly to the hoist drum, explains SCX. In normal operation, the unit simply ‘follows’ the rotation of the hoist drum—hence the name MotoSuiveur or ‘motor follower’. The hoist arrest action is purely mechanical and based on the principle of non-reversibility of worm and wheel drives. Should any unexpected movement outside normal parameters take place, for any reason, the worm makes mechanical contact with the drum, and locks the system. Using a patented design, the worm then slides and is damped by an oil-filled chamber, preventing any shock loading of the hoist, the supporting structures, or the load itself.

“As far as hoist safety developments go, the MotoSuiveur device is a big step forward. It totally redefines the way that load safety is addressed.”

The MotoSuiveur’s near-instantaneous detection of overspeed makes it react much faster, and therefore significantly reduce load drop, compared to calliper brakes, says SCX, with calliper brakes normally dependent on reaching a defined overspeed before the system is triggered. “By the time that overspeed is detected and the load arrested, rope pay-outs of between 1.5m and 2m are not uncommon. Certain closed loop safety systems can overcome this, but they introduce other areas of complexity.

“Another significant difference between MotoSuiveur and an emergency calliper brake is that MotoSuiveur delivers ‘permissive safety’. It’s a principle where the safety device must be functioning correctly before machinery can be operated. MotoSuiveur’s intrinsic self-checking and auto-diagnostics ensure the system is ready before any hoist movements are permitted.”

Little continues: “The purely mechanical action of MotoSuiveur does not depend on the integrity of the hoist it protects. It is an open loop, mechanically failsafe system. So, it cannot be caught out by a seized calliper piston, for example.

“MotoSuiveur addresses hoist safety issues such as brake failure, motive drive failure, gearbox failure, overspeed protection, overload protection—all in a single, compact unit. And at the same time, it provides that quick load arrest capability.”

The compact design of the system facilitates retrofitting into some hoists that do not have room for a standard calliper disc-style brake, adds SCX.

The MotoSuiveur unit reduces reliance on the integrity of the hoist motor, gearbox, and couplings. This allows for the incorporation of a torque limiter between the motor and gearbox, giving mechanical protection against any overload—for example in the event of a snagged load or double blocking.

The device can also be configured to provide an independent recovery option for arrested loads. By reverse driving the worm against the drum, an additional motor is able to remotely raise or lower the arrested load. This allows the load to be released so that the crane and hoist can be taken into maintenance.

MotoSuiveur was initially developed for the high-integrity nuclear crane market, and already in use on many of the UK’s Nuclear Licenced Sites, says SCX. Its benefits are now being recognised in other industries where personnel safety, highvalue or high-sensitivity payloads, or asset protection are key drivers. In total, there are more than 70 MotoSuiveur installations worldwide, over 30 of which have been installed by SCX Special Projects in the UK.

“We’ve already installed cranes featuring the MotoSuiveur device into numerous nuclear sites to be used for decommissioning,” says Little. “We are now also integrating it into solutions for other safety-critical industries, such as aerospace, for handling valuable jet engines, or defence for handling munitions.”

Driving factors

For VFD systems to provide reliable and advanced braking capabilities, the technology behind it has to be sound. Chicago-based Power Electronics International (PE), established in 1969, specialises in the technology, producing the Micro-Speed range of VFDs. These are used for overhead cranes as well as other cranes and hoists, in a full range of industries including nuclear, foundries, and industrial plants.

Variable frequency drive technology are helping to optimise crane brakes