Super precision bearings for air handling systems
05-11-2010 | BARDEN CORPORATION | PLYMOUTH UK
Custom-designed, super precision bearings are critical to a wide variety of high performance air handling systems, from vacuum pumps, fans and air conditioning systems, through to the latest advanced cooling systems for military aircraft, says Gary Hughes of The Barden Corporation (UK) Limited.
Certain technologies demand custom-engineered, high precision bearings rather than standard catalogue bearings. Air handling or air movement systems, for example, often require high precision bearings, especially if the application is critical or requires a bearing solution that offers long life, high reliability and high speeds.
Other factors that make high precision, custom bearings essential to many applications are high temperatures, high pressures, poor lubrication, low vibration levels or abnormal contamination levels.
Air handling systems are commonly found in every industry sector. Examples include axial and radial flow fans, compressors, turbomolecular pumps, dry pumps, emergency magnetic touchdown systems, turbochargers, air conditioning systems and cooling systems used on military aircraft for engine, avionics or infrared weapon systems.
Barden's manufacturing plant in Plymouth boasts more than 1,700 square metres of clean cleanrooms for contaminant-free assembly and inspection of bearings. The company designs and manufactures super precision bearings to a minimum of P4/ABEC 7 quality standards. Bearing sizes range from 5mm to 180mm outside diameter. Most bearing solutions are angular contact or deep groove and are available as hybrid (steel races with ceramic balls) depending on the individual application.
Barden is capable of manufacturing bearings to a geometric tolerance of P2 or better, and envelope dimensions to P4 or better. Raceway roundness is better than half a micron, with raceway surface finish better than 1 micro inch Ra.
Aerospace & Defence Applications
For the aerospace and defence sector, Barden provides bearing solutions for the relatively small fans that are used in electronics cooling systems on aircraft, as well as bearings for the larger, more powerful axial and radial flow fans, which are frequently found in military aircraft start-stop air handling applications. Super precision angular contact and deep groove ball bearings are also used in cooling systems for avionics bays and for military aircraft and helicopter engines.
On military aircraft, Barden bearings are also being used on the latest advanced weapons ejection systems. The bearing solution, which may include special flanges, threads or tapped holes, is custom engineered for the specific application, enabling the customer to quickly and easily fit the bearing assembly into their own pneumatic ejection system. Often, the bearing assembly is so critical to the overall product that none of the system can be assembled without the bearing.
Multiple bearing solutions may need to be engineered to suit the customer's different product variants. The bearing solution may also help reduce the customer's overall design and assembly costs.
Air conditioning systems on aircraft also use super precision bearings. Bleed valves, which are designed for flow and pressure regulation, take the air from the aircraft engines and move hot or cold air around the aircraft. Whilst this particular application may not require the very high precision levels offered by Barden, they benefit from unique material combinations such as Cronidur/ceramic in order to survive their arduous operating conditions. Once the bleed air has been used to control the temperature of the cabin air, it must then be moved around the aircraft. The fan speeds here are moderate but the bearings are critical in ensuring that the fan can deliver the correct mixture of hot or cold air to the required location on the aircraft at the right time.
Bearings for Turbochargers and Fuel Cells
Turbochargers are another important application area for super precision bearings. Barden is currently producing a high speed ball bearing cartridge for use in automotive turbochargers. The bearing itself incorporates two rows of balls built to a controlled end float. The design of the cartridge includes features for delivery of lubricating oil directly to the raceways and also for an oil film around the outside diameter of the bearing, which provides damping from high levels of vibration. The high speed of the turbocharger creates its own challenges and requires a bearing cage that is mechanically strong in order to resist the high ball-to-cage contact loads, but which is suitably compliant to ensure that wear is not a limiting factor.
Another growing air handling application for super precision bearings is in fuel cell technologies, where the fuel cell requires a compressor for the hydrogen used in the reaction.
Bearings for Vacuum Pumps
Barden engineers bearing solutions for a number of different high performance pump manufacturers, for use in extreme, hostile environments. By using new materials, special coatings and by adding real value to the customer's own design, Barden can help the customer reduce design costs, minimise component count, reduce assembly time, as well as optimise the overall efficiency and reliability of the air handling system.
In turbomolecular pumps, for example, the most important requirements are long life, reliability and high speed performance. Used predominantly to create high vacuum conditions for semiconductor, analysis and SEM applications, these bearings typically require a solution that comprises ceramic balls, a special coating, is greased-for-life and that has a special high quality raceway finish.
Semiconductors, solar panels and flat panel displays all require a production process that is clean and free of any contaminants that may adversely affect the process. Working chambers are normally flooded with gas and evacuated using dry pumps to create a working vacuum. In semiconductor manufacturing, the etching tools need to operate in a vacuum chamber whilst they etch miniature grids of electronic circuitry onto silicon wafers. This type of operation is so intricate that all contaminants must be removed from the production chamber before work can begin. It is therefore common to see rows of dry vacuum pumps installed under production floors in many semiconductor-manufacturing plants.
Another example of where high precision customer bearings are used for air handling is in emergency touchdown bearings for active magnetic bearings (AMBs). AMBs use actively controlled electromagnetic forces to control the motion of a rotor or other ferromagnetic body, providing a practical method of suspending shafts (both axially and radially) in numerous applications, including compressors, blowers, air conditioning systems, gas expanders (used as venting devices in gas pipelines) and in energy storage systems as emergency back up power. However, as most AMBs require continuous power input and an active control system to hold the load stable, if this system fails then high performance rolling element back up bearings, such as those produced by Barden, are needed to help control the system and bring it safely to a stop.
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