Tube roller bearing prevents slippage in wind turbine gearboxes

A novel design of rolling bearing for wind turbine gearboxes has been developed, which is not only resistant to the effects of slippage, but actually prevents slippage from occurring in the first place.
 
Rather than utilising conventional rolling elements, Schaeffler's FAG tube roller bearing incorporates three tube rollers. These tube rollers enable the bearing to rotate without slippage under all load conditions. At the same time, the load rating and rating life are unaffected.
 
Slippage is the natural enemy of all rolling bearings. The life and performance of a rolling bearing will suffer if it is overloaded or under-loaded. This is because rolling bearings are designed with a minimum load requirement in order to function optimally. If this minimum load is not met, slippage will occur. This means that the rolling elements not only rotate, but also slide on the bearing raceways. Eventually, this can lead to surface damage such as increased wear or smearing, particularly in critical lubrication conditions.

A novel design of rolling bearing for wind turbine gearboxes has been developed, which is not only resistant to the effects of slippage, but actually prevents slippage from occurring in the first place.

In wind turbines, rolling bearings have to meet special performance requirements. The bearings must be designed to withstand extremely low and high loads that act on the bearing during calm or strong wind conditions. The risk of damage to a bearing increases significantly when the roller set of a rolling bearing with high slippage is suddenly subjected to extremely high acceleration forces. For this reason, Schaeffler has developed the tube roller bearing, which completely eliminates the problem of slippage.
 
Hollow tube rollers with interference
The FAG tube roller bearing is a conventional cylindrical roller bearing that incorporates three cylindrical rollers with a slightly increased diameter. These three rollers have a hollow design and are supported by a support roller in the inner bore. These rollers with a slightly increased diameter generate preload in the bearing and drive the bearing cage (and therefore the entire roller set) at low loads.
 
At higher loads, the bore of the cylindrical rollers ensures sufficient deflection of the larger rollers so that that they are not overloaded. This means that the load is evenly distributed to all the rolling elements, similar to a conventional rolling bearing.
 
The support roller in the inner bore of the tube roller has a slight clearance to ensure that the roller is less rigid (more flexible) at higher loads. At the same time, this also prevents excessive deflection of the tube roller. Together, the tube roller and support roller provide increased fatigue strength to the bearing, which results in a rigid rolling element that withstands peak load conditions.
 
The tube roller bearing is not available from Schaeffler's standard catalogue but is custom designed for specific customer projects and applications. Initial prototypes have already been manufactured and tested. Pilot applications in wind turbine gearboxes are planned for the end of 2010.
 
For further information on Schaeffler's tube roller bearing, e-mail: info.uk@schaeffler.com  Refer to page 78

Cropico microhmmeter digs deep
at quarry electrical safety testing house

A high performance Cropico microhmmeter is being used by certification, testing and inspection house Bureau Veritas to test the safety of cables installed in quarries operated by contractors across Britain.

Bureau Veritas has extensive UK coverage, providing safety testing and risk assessment services for national and international manufacturing and industrial clients. The company has been used by organisations since 1828 to ensure compliance with health and safety regulations and to manage risk factors on work sites.

Electrical circuits installed within quarries, must be tested in order to ensure no damage during installation and in service. A low resistance microhmmeter, with a 10A test current, is essential for testing such as this, due to the low resistance of the cables, which cannot be accurately tested using a regular ohmmeter.

Bureau Veritas has specified the DO7010 to inspect the safety of these circuits because if left unchecked, they can continue to function but offer a high risk of fire or electric shock - extremely dangerous to those working on site.

Mahendra Mistry, electrical engineering specialist at Bureau Veritas, said: "The accuracy of the DO7010 was a key factor in my decision to use it for testing the quarry installations.

It's also an extremely reliable instrument while being portable and easy to use.  It meets all of our requirements."

The DO7010 has been developed for a wide range of electronic engineering, design and manufacturing applications requiring accurate low resistance measurement.
With a measuring range of 600µΩ to 60Ω with 0.1 and 10mΩ resolution respectively, the instrument can measure with switchable current levels of 1A or 10A on all except the highest range. Externally recharged NiMh battery packs can be replaced quickly via the front panel to ensure minimum downtime anywhere.

An LCD panel displays full information on measurement configuration and a single start button ensures ease of use while the ability to trigger measurements by lead contact to the test device provides fast single-person operation. A remote hand terminal is also available to fully control the tester at up to 15m distance.

Other features include a robust design, true 4-terminal measurement to eliminate lead resistance errors, auto average of forward/reverse measurement and sequence testing with memory for 1000 readings.

The instrument's data logging function also permits downloading of test sequences from a spreadsheet and uploading of test results back to the data records. The DO7010 forms part of a comprehensive range of precision measurement instruments available from Cropico, part of the Seaward Group.

For further information, view website: www.cropico.com   Refer to page 260   

Metering valves cut lubricant consumption
by 25 per cent on linear guidance systems

By incorporating special lubricant metering discs on its range of linear recirculating roller bearings and guideway assemblies, Schaeffler has reduced lubricant consumption by more than 25 per cent compared to conventional designs.

A range of linear recirculating roller bearings and guidance systems are now available with special lubricant metering valves, which provide precise doses of lubricant to the linear guides, reducing lubricant consumption by more than 25 per cent compared to standard designs, reducing maintenance and servicing costs and preserving resources for the customer.

Schaeffler's RUE-E range of roller monorail guidance systems can now be fitted with special lubricant metering valves to ensure that the lubricant is precisely metered under all operating conditions, regardless of the guide's mounting position. This is made possible because of several key design factors.

First, Schaeffler uses a patented injection moulding technology to produce the saddle plate, which, combined with the various connection options for relubrication at the front, rear and side of the carriage end, and the special design of the end pieces - the lubricant is directed precisely at the rolling elements. This not only minimises relubrication quantities, but also improves the reliability of the guide and is kinder to the environment.

John Loonam, Linear Product Specialist at Schaeffler UK comments: "Basically, the O rings in a standard linear guidance system are replaced with the SMDS metering valves. A paper seal is placed between the end plate and the lubrication duct, which prevents leakage of the lubricant from the ends, resulting in a reduction of more than 25 per cent in lubricant consumption compared to standard designs. Only one valve per side and rolling element loop is required and one lubrication connector per carriage."

Several years ago, Schaeffler's Linear Technology specialists developed a relubrication and sealing component kit that contained a metering system for minimising lubricant quantities and various sealing elements. These provided optimal sealing of the lubricant duct for the standard INA-branded roller monorail guidance systems.

The latest SMDS integrated metering valve option offers high reliability with only one lubrication hole per carriage, independent of the roller monorail guidance system's mounting position and operating conditions.

With conventional roller monorail guidance systems, the relubrication duct between the lubrication hole on the linear guide and the rolling elements can become empty, depending on the mounting position and operating conditions. This means more lubricant is required during relubrication to ensure reliable operation and because it takes the lubricant longer to reach its desired destination. With centralised lubrication systems, only one specific dose is provided per impulse, which can be a problem. This can lead to the lubricant arriving late in the rolling elements or, at worst, lubricant starvation. This problem is exacerbated when the guide is mounted at an angle of 90 degrees, often resulting in insufficient supply of lubricant to the upper rolling element rows. In extreme cases, this can cause damage to the rolling elements and raceway, leading to the complete failure of the linear system.

The new SMDS metering valves replace the standard O-ring seals. These prevent the lubricant duct from running dry, avoid inadequate lubrication or over metering, and allow precise relubrication with very small, precise quantities. The linear guides have only one valve per side and function irrespective of mounting position.

For further information, e-mail: info.uk@schaeffler.com  or view website: www.schaeffler.co.uk    Refer to page 75