Tour de force

Despite technological advances fluid-powered hydraulics systems are still the best way to lift and manoeuvre large, heavy objects, from aircraft parts to film industry special effects, says Colin Carter.

Although there have been some amazing advances in automation over the past 25 years, hydraulics is still the best way to supply forces for large-scale movement jobs.

And the technology looks set to remain viable for years to come because it is safe, reliable — especially when it comes to moving large objects — and most importantly is cost-efficient to install and maintain.

At the Airbus facility at Filton, near Bristol, for example, Bosch Rexroth supplied complete hydraulic systems for lifting and manoeuvring Airbus A400m wings during assembly.

The systems, comprising 16 separate hydraulic platforms for two wing jigs, were designed to lift the 23m-long carbon fibre reinforced composite wings. The lifting process has to be level, so the synchronisation of the lifting cylinders has to be a very high degree.

Control of the platforms is by Rexroth HNC100 digital axis controllers with linear transducers, which provide the accurate positional feedback necessary to synchronise the two cylinders. This system has proved to be capable of lifting the wings in place to an accuracy of +/- 2mm over a stroke length of around 3.5m using linear slides.

Another example of using hydraulic systems to lift aircraft and associated parts — although the objects to be lifted are far less technologically advanced — is the World War II B25 Mitchell Bomber owned by the historic Duke of Brabant Air Force.

Here, jacks are needed for under-wing lifting and raising the fuselage at the nose end. Allspeeds of Greater Manchester supplied Tangye aluminium hydraulic jacks for the job, along with a wheeled steel tripod frame which supports the load firmly when in position. The jacks have a lifting capacity of 12 tonnes and operate over an extended height of 3.25m.

Aircraft are not the only military transport to benefit from hydraulics. In an even larger example, sections of the ‘Daring’ class Type 45 destroyer are moved using a programmable logic controller (PLC) for assembly and as part of the production process. The PLC system, provided by Enerpac, is again controlled so that the destroyer parts move synchronously.

Six of these destroyers are being built for the Royal Navy at BAE Systems shipyards at Govan and Scotstoun — with the bow sections, masts and funnels being made in Portsmouth. The ships, the first of which is due to enter service in May 2009, are just over 150m long with a displacement of 7,350 tonnes — and the individual sections (blocks) of the hull that need to be moved into position weigh up to 1,400 tonnes.

The hull is made up of five of these blocks, which are moved to a slipway by purpose-built multi-wheeled vehicles for assembly. Once on the slipway Enerpac’s system lifts the blocks so the vehicles can be removed. The synchronous system then moves the hull sections in place so they can be welded together. accuracy and even load distribution are essential as the outer ‘skin’ of the hull is relatively thin and easily damaged.

Large, delicate structures are often moved to create special effects in the film industry too. For example, hydraulics were used in a huge rig designed to simulate the sinking of a whole building in Venicefor the James Bond film Casino Royale.

The rig, custom built by Moog Controls and Sick (UK), was based at Pinewood studios, and had to lift three motion bases — one of which weighed approximately 80 tonnes — precisely to provide the sinking building effect.

The system was controlled by Moog’s M3000 system operating the company’s digital axis control valves, with positional feedback coming from a set of hydraulic actuators operated by Sick wire-driven encoders.

Elsewhere, hydraulics are also essential for milking cows. Parker Hannifin has supplied a hydraulic control system to Fullwood, manufacturer of milking machines and milk storage equipment.

Fullwood’s rotary milking machines enable cows to be milked in their own areas and rely on Parker’s hydraulic power packs to operate the drive system, which comprises fully floating hydraulic motors, planetary gearboxes and compression drive wheels.

Here, using hydraulic rather than electric power packs resulted in considerable cost savings. Fullwood’s system is driven by a single 3kW motor rather than three electric ones. The other big advantage is that the hydraulic system can be safely used in wet areas or places that have to be cleaned regularly.

And finally, even beer is touched by fluid power on its way to your glass. Fuller’s brewery has specified the use of Penny Hydraulics’ Cellar Lift and installed them in pubs where barrels have to be lifted between floors.

The lifts, according to Penny, can be installed however access to the cellar is arranged. A vertical unit can lift a 300kg barrel, containing some 54 gallons of beer up and down, meaning fewer staff are required which in turn leads to improved cost efficiency.