Rolling bearings improve life of crane cable sheaves
Over many centuries, block-and-tackle systems, or rope and pulley systems as they are more commonly known, have been used to help construct a variety of famous buildings, including the Colosseum in Rome. These devices have also helped generations of students to understand the basics of mechanics and were even sketched by Leonardo da Vinci in some of his famous detailed engineering drawings.
Today, these simple systems are critical when it comes to the lifting or hoisting of heavy loads. However, rather than rely on the physical power of humans to operate these systems, the latest systems utilise electric motors, gearboxes, steel cables instead of ropes, and sheaves made from synthetic materials or steel rather than wooden rollers.
Rolling bearings too play a vital role in supporting the latest cable pulley systems. Indeed, rolling bearings from the Schaeffler Group are being utilised in a number of different applications, including heavy-duty crawler cranes, floating cranes and lifting bridges.
Used for the first time to construct and erect a wind turbine in Cuxhaven, Germany, Liebherr’s new LR 11350 crawler crane sets new standards in terms of its lifting capacity (up to 1,350 tonnes) and has a maximum lift height of 223 metres.
Driven by a six-cylinder turbo diesel engine, the LR 11350 is one of the largest crawler cranes in the world. The design principle of the crane enables economical and straightforward transportation of the crane components and rapid set-up time. The diesel engine, hydraulics, electrical systems and crane cab are transported as a complete unit. A wide range of boom systems gives the crane excellent versatility, with or without a derrick system.
To date, Schaeffler’s Power Transmission Group has supplied more than 100 cylindrical roller bearings for the LR 11350’s cable sheave supports. The heavy duty SL04 bearings have a 160mm bore, an outside diameter of 220mm and a width of 80mm. These bearings provide high load carrying capacity and long service life and are protected by Corrotect®. This coating, specially developed by engineers at Schaeffler, prolongs the life of the bearing and prevents, for example, corrosion underneath the sealing lips. In turn, this prevents premature wear of the lips and ingress of dirt and water to the bearing.
Most of the sheaves used in today’s mobile and crawler cranes are manufactured from synthetic materials such as cast polyamide. These materials offer the required elasticity, high wear resistance, high durability (even at low temperatures), good resistance to lubricants and to the often-harsh outdoor conditions (i.e. weatherproof).
When selecting bearings for these types of applications, a range of design factors should be considered, including whether the bearings are maintenance-free; how easy they are to assemble; and their static and dynamic load carrying capacity. Due to the different coefficients of expansion of the plastic sheave and the steel bearing, it is also important to carefully examine and select a suitable bearing fit and internal clearance.
In another application, Schaeffler’s SL04 bearings (260mm bore, 400mm outside diameter, 160mm width) are being utilised to support the ‘Hermod’ crane ship or floating crane.
With a crew of more than 300, the semi-submersible Hermod crane vessel is designed for offshore operations, including bridge construction projects and the erection of oil drilling platforms. Used in tandem, these types of crane can lift up to 8,100 tonnes and a radius of 39 metres.
The Corrotect® coated bearings also have special seals that protect the bearings from salt-water corrosion and temperature fluctuations.
Vertical Lift Bridges
On the ‘Kampenbrug’ 400-metre long, 20 metre-wide lifting bridge in The Netherlands, the cable sheaves are actually gold-plated. This is to provide better protection against rust and corrosion.
Schaeffler’s double row spherical roller bearings with a cylindrical bore transmit the enormous loads from the 30-metre moving section of the bridge, which is lifted and lowered at regular intervals through the day, to enable ships to pass through.
The SL04 range of cylindrical roller bearings with snap ring grooves is a full complement, double row unit that comprises solid outer and inner rings with ribs, rib-guided cylindrical rollers and sealing rings. The outer rings have grooves for retaining rings. The inner rings are axially split, are 1mm wider than the outer rings and held together by a rolled-in steel strip.
Due to their snap ring grooves, the bearings are locating bearings, providing high rigidity and supporting axial forces in both directions, as well as high radial forces.
The full complement design (i.e. the bearings have the maximum possible number of rolling elements) means the units offer maximum basic dynamic and static load ratings.
Sealing rings on both sides protect the running system against contamination and moisture. The cylindrical roller bearings are greased with lithium-based soap grease and can be relubricated via the outer and inner ring.
Grooves in the outer rings mean the bearings can be easily axially located, making them ideal for cable sheave applications.
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