Bronze replaced by post-cured composites in power station vanes

Written by: Tom Shelley | Published:

A post-curing process has solved a problem, with composite bearings replacing bronze at the Dinorwig Hydro pumped storage power station

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The bearings are used on the guide vane shafts, where First Hydro replaced the original bronze bearings with Orkot TXMM bearings in 1999. The material is a composite incorporating solid lubricants.
After two years, some bearings had become tight on the guide vanes due to a change in their inside dimensions, reducing their inside diameters by up to 0.05mm in some cases. This has been overcome using a new post-curing process, machining to size and then fitting into bearing houses supplied by First Hydro. No significant changes in dimension have since been found over a two-year period.

Water toughness
Fatigue life of bearings used in water contaminated environments, such as roll neck bearings in steel mills is increased three times by adopting super clean steel for raceway rings.
The resulting range has been designated Water Tough WTF. The steel also contains tightly controlled levels of surface retained austenite. The need for extra cleanliness was revealed by laboratory experiments that conclusively showed that failures resulted from pits in raceway surfaces that were caused by the spalling of non-metallic oxide inclusions.


Improved split roller bearing
Revolvo has come up with a number of improvements to split roller bearings.
First, its designers have found that by incorporating two ribs on the pedestal cap casting, it significantly improves rigidity. To assist inspection, they have provided ‘Pry’ slots to enable disassembly of the cartridge and pedestal, reducing the likelihood of components being broken. In addition, they have come up with a new cage clip, which is retained by spiral pins to one half of the cage during assembly and disassembly.
The bearings are designed to be statically self aligning, and can accept up to 3 degrees of shaft misalignment. The rolling elements are specially profiled to minimise edge stresses that can occur under conditions of dynamic misalignment. These are able to displace slightly, and so prevent potential damage to the bearing raceway and rolling elements. The cages have CNC bored pockets that are optimised to give accurate roller guidance to prevent skewing. Being made of brass, they allow operation at up to 140 deg C without problems.
Sealing systems are available to protect the cartridge bearing units in aggressive environments, including ‘Viton’ high temperature seals, aluminium triple labyrinth seals for high speeds with high contamination, ‘Kevlar’ packing seals for aggressive environments, seals for use in very wet environments, and Laminar Seal rings to deny ingress to fine particles such as cement or ash.
Products includes Light, Medium and Heavy series in sizes from 35mm to 600mm in diameter plus imperial equivalents and larger non catalogue sizes up to 1400mm outside diameter


Cutting backlash
Ball bearing disc springs from Bauer Springs are designed to pre-load ball bearings. Unlike other springs, where a progressive force/deflection characteristic is the best that can be achieved, disc springs give very little pre-load variation, covering a wide range of spring deflections. Both plain and slotted disc springs can be supplied, with slots in either inner or outer rim diameters. Materials thicknesses are from 0.15 to 3mm, outside diameters are from 9.8 to 358mm, and inside diameters are from 6.2 to 242mm.
Special materials include; corrosion resistant or non magnetic steel; spring bronze CuSn8, copper beryllium alloy and Nimonic 90.

Main shaft bearings pass on Airbus
The maiden test run of the Airbus turboprop engine for the A400M military transport aircraft has been successfully completed. The test was undertaken complete with gearbox and propeller, with the turbine main shaft bearings and gearbox bearings developed and supplied by FAG Aerospace, the Schaeffler Group’s aerospace bearing division. The three shaft TP400 engine has a maximum shaft output of 11,000 HP. It was developed by Industria de Turbo Propulsores (Spain), MTU Aero Engines (Germany), Rolls Royce (UK) ad Snecma (France), as members of the Europrop Engine Consortium.
Schaeffler UK

Plastic bearings replace bronze at the docks
A maker of equipment for loading and unloading at docks has solved a problem of cracking bronze bushings by switching to Spyraflo bearings made of ‘Delrin’ AF and ‘Permaglide’ ‘Teflon’ Bronze.
The problem centred on companies that used gangways to load and transport dry powdered cement. The 18mm diameter Teflon Bronze and 16mm Delrin self-clinching/self aligning bearings are said to have “completely eliminated” failures in the field.
Installation time is less and performance is better and the clinching feature provides a secure mount.


Hybrids combat current effects
New Insocoat and hybrid bearings from SKF combat the effects of electric currents on bearing surfaces and lubricants used in motors and generators.
Insocoat bearings feature a specially developed surface coating just 50 microns in thickness that acts as an electric insulator to provide protection against flashovers of up to 500V. Thicker coatings are available to withstand discharges of up to 1000V. The coating is unaffected by extremes of temperature or humidity and can be used with all common lubricants. The bearings are available in shaft diameters from 55 to 150mm. They can be supplied with brass or steel cages, and used in applications with dynamic loads of up to 276kN and shaft speeds of up to 6,700rpm, depending on the lubricants used.
The hybrid bearings use silicon nitride rolling elements to provide insulation properties.


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