Giant steel ball joints play an important role in operating the Maeslant storm surge barrier in the Netherlands. For problem-free interaction of the ball and shell segments weighing hundreds of tonnes that bring the colossal barrier gates reliably into position, large "cushioning pads" made from GUR® provide ideally smooth, low-wear operating conditions.
To have any concept of the gigantic dimensions of the Maeslant barrier, you would have to compare it with the 300-m-high Eiffel Tower. The barrier's two movable gates or retaining walls, which close the Nieuwe Waterweg (New Waterway) at the Hook of Holland in the event of a storm surge and so prevent Rotterdam and the surrounding area from flooding, are moved by two trusses approximately the same size as the Eiffel Tower but in the horizontal direction. The retaining walls themselves, 22 meters high and 210 meters wide, are also enormous. They transmit the water pressure via the trusses to a 680-tonne, steel ball joint resting on foundations that comprise 52,000 tonnes of concrete.
The two ball joints are the pivotal point of the entire monumental barrier structure, both literally and metaphorically speaking. The designers based the concept on the human shoulder joint, because the barrier gates, too, have to be capable of movement in three directions. The ball-shaped elements made of cast steel, which were produced by Skoda in the Czech Republic, rotate in eight shell segments (also made of steel). To improve slip properties in the ball joint and reduce wear, the steel shell plates were originally coated with MoS² coating and PTFE powder. The barrier, which was completed in 1997, undergoes an annual closure test and this revealed that the coating could not cope with the load over a prolonged period. In the quest for a better solution to the problem, the Dutch engineers from the Ministerie van Verkeer en Waterstaat Rijkswaterstaat turned to GUR. This ultrahigh-molecular-weight polyethylene (UHMW-PE) from Ticona has already proved its worth in other large-scale projects involving high-tonnage stresses – for example as guides for the vertical-lift gates in the River Ems barrier.
As a result of its exceptionally high molecular weight (between 3.9 and 10.5 million g/mol), GUR is extremely wear-resistant, while also possessing excellent impact strength, outstanding chemical resistance and very good sliding properties. Suitable sliding partners for GUR include not only other plastics but also metals such as cast steel. Because of these special material properties, components made from GUR have long been used successfully in machine construction (e.g. castors, chain guides), the chemical industry (e.g. centrifugal pumps, silo linings) and mining (e.g. linings for conveyor chutes, wagons).
The large GUR "cushioning pads" that were inserted into the steel shell segments of the ball joint consist of a circular UHMW-PE core held by a carbon fiber ring. On this GUR "cushion", the giant steel ball can slide smoothly and bring the barrier gate into the required position. A trial run in September 2003 proved that this system not only functions in theory but also performs successfully in practice. Ever since then this vital flood protection barrier structure has passed all closure tests with no damage whatsoever to the GUR "cushions".
http://www.ticona.com
Posted 13th February 2006
