Fag Bearings India Limited, India Connaught Place, Delhi

The superior engineering that goes into the design and production of Barden bearings makes them an obvious choice for advanced X-ray and medical scanner applications. The bearings, typically used to support the spinning X-ray anode, operate at speeds of up to 13,000 rpm under extremely harsh conditions. In addition to withstanding the passage of high voltage, the bearing must also operate in a vacuum environment down to 10-8 torr and at temperatures of 400 - 500˚C. They are full complement bearing designs, incorporating a flanged shaft with integral races to which the target anode is attached. A separate flange made of lower thermal conductivity material can be welded to the shaft in order to reduce heat transfer from the anode. The bearings are built with controlled axial clearance in order to compensate for thermal growth at the operating temperature. Conventional outer rings are separated by spacers with either solid or spring X-Raypreloading designed to meet specific application requirements. Barden utilises advanced surface engineering technologies such as plasma and ion-beam assisted deposition to provide effective lubrication. With this application in mind, development of a range of advanced solid lubricants 2,000 times thinner than the human hair is in progress. Barden also has a dedicated in-house testing facility to enable the evaluation and performance verification of its X-ray tube bearing designs under simulated thermal-vacuum test conditions.

One major contributing factor to a bearing's reliability is proper lubrication. Selecting the correct lubricant and maintaining it appropriately will significantly decrease the risk of premature bearing failure and running interference. There are three main categories of bearing lubrication; oils, greases and solid dry film. Selection of the most appropriate lubricant is generally governed by the operating system and limitations of the bearing system. Selecting the right lubricant for a specific bearing and application can: Reduce friction and wear by supporting the load and separating the balls from the raceways. Minimise cage wear. Prevent oxidationcorrosion of the balls. Act as a barrier to contaminants. Conduct heat away from the bearing.

Full complement ball bearings capitalise on the space usually occupied by the ball retainer, as removing the retainer enables additional balls to be fitted. This increase in ball complement allows for significant increases in bearing capacity in either axial or radial directions. Barden offers two basic designs of full complement bearings, each with different capabilities, limitations and fields of application.

Deep groove ball bearings have full shoulders on both sides of the raceways of the inner and outer rings and can accept radial loads, thrust loads in either direction, or a combination of loads.

Ceramic hybrid bearings also run at significantly lower operating temperatures, allowing running speeds to increase by as much as 40 to 50 per cent. Lower operating temperatures help extend lubricant life and bearings with ceramic balls have been proven to last up to five times longer than conventional steel ball bearings. Systems equipped with ceramic hybrids show higher rigidity and higher natural frequency making them less sensitive to vibration

Selection of a suitable standard bearing - or the decision to use a non-standard bearing - must take performance requirements and operating limitations into consideration. This may involve conflicts which must be resolved to reach a practical solution. Each performance requirement, such as speed, torque or load rating, usually generates its own specifications which can be compared with available bearing characteristics. If a standard bearing does not meet the requirements, a design compromise will be necessary in either the assembly or the bearing. At this point, the creation of a special bearing should be explored. Among the most important application considerations which need to be evaluated are speed and load conditions. Specific bearing design choices should be based on anticipated operating conditions. Design choices include: Materials (balls and rings - hybrid bearings) Bearing type Bearing size and capacity Closures Internal design perameters Cages Preloading (duplexing) Lubrication Tolerances and geometric accuracy

Bearing closures are available in two basic types - shields and seals. Both closure types are generally ordered as integral components of deep groove bearings. Closures serve the same purposes with varying effectiveness - they exclude contamination, contain lubricants and protect the bearing from internal damage whilst being handled. Closures are attached to the outer ring of the bearing. Seals are defined as closures which contact the inner ring, while shields clear the inner ring. Both are designed so that the stringent precision tolerances are not affected by their use.

In any application proper attention to cage design and materials selection is essential to ensure reliable and long-term bearing performance. The role of cages, or separators as they are sometimes known, covers: They space the rolling elements apart equally and help lubricant distribution within the bearing. Separating the elements halves their running contact speed, allowing higher bearing speeds. They facilitate handling and installation of separable type bearings. Since they may be required to accelerate rapidly, bearing cages should be lightweight and be manufactured from materials that have superior strengthweight ratios. Traditionally used brass or bronze cages have good wear characteristics but steel cages are offered which provide excellent service but at a lower cost. They are favoured in applications for harsh environmental conditions or where bearings are subject to very high levels of vibration or extremes of heat. Alternatively, in some price sensitive applications, cages manufactured from high performance plastics are preferred.

The Barden product line encompasses predominantly radial, single row, super precision angular contact and deep groove ball bearings, incorporating full complement bearings and hybrid bearings as well as standard designs and materials. Bearings come in inch or metric dimensions with diameters ranging from 4mm (0.16") outer diameter (OD) up to 180mm (approx 7") OD and operate comfortably at speeds of 2 million dN (bore in mm x RPM) or above. A variety of bearing seals, shields and metallicnon-metallic cage designs are available for all products.

Angular contact bearings have one ring shoulder removed, either from the inner or outer ring. This allows a larger ball complement than is found in comparable deep groove bearings, giving a greater load capacity. Speed capacity is also greater. Barden's angular contact bearings have a nominal contact angle ranging from 10° to 25°. they can be used in pre-loaded duplex sets, back to back (DB), face to face (DF) for supporting thrust loads in both directions, or in tandem (DT) for additional capacity. Angular contact bearings support thrust loads or combinations of radial and thrust loading. They cannot accept radial loads alone. A single angular contact bearing can be loaded in one thrust direction only, this may be an operating load or pre-load. Separable and non-separable types are both available. Separable bearings are useful where bearings must be installed in blind holes or where press fits are required on the shaft and in the housing. The separable feature also permits dynamic balancing of the rotating components with the inner ring mounted in place without the outer ring and housing.

BardenFAG offer an extensive global network of aerospace bearing repair facilities. Based on the understanding that modern aerospace applications demand bearings that combine the highest quality and reliability, the Barden and FAG repair stations can restore bearings to as-new condition in less time and for less cost, all to the high standards expected from aerospace experts. With facilities located in Germany, Canada and the USA, and with a new site soon to open in Singapore, superior repair services are offered worldwide.