September 23, 2003

By: Mark Harris
Website: http://www.bearing-n-bearings.com

“Totally unique” super precision hybrid bearings operate at speeds up to 30% faster than standard hybrids & offer longer life

FAG/Barden have combined unique Cronidur 30Ô bearing steel, exclusive, non-contact sealing technology and ceramic rolling elements to produce advanced hybrid bearings that can operate at speeds up to 30% higher than standard hybrid bearings. The synergy achieved with the unique advanced design also enables the FAG/Barden hybrids to offer the user reduced wear, longer life, enhanced stiffness and improved reliability.

Ideally Suited To Machine Tools & New Technology Applications

The superior speed and life characteristics of new hybrid bearings mean that they are ideally suited to high speed machining operations (up to a maximum of 3 x 106 dmN) where conventional angular contact bearings - and those employing smaller balls - would be beyond their operating limits. The same advanced levels of performance also provide the ideal solution in new technology applications such as turbomolecular vacuum pumps, critical aerospace applications and in Formula 1 racing cars.

Higher Speed For Enhanced Spindle Performance

The major factor in the exceptional speed performance of the hybrid bearings is FAG/Barden's unique Cronidur 30Ô, a new bearing steel that has been used successfully in the engines of the NASA space shuttle. Cronidur 30Ô exceeds the speeds and fatigue life available from other bearing steels, with the added benefits of superior corrosion and wear resistance.

Proof of the superior speed characteristics of Cronidur 30Ô has been provided in comparative testing. A grease-lubricated (70mm ID) Cronidur 30Ô bearing installed in the spindle of a machining centre ran at a constant speed of 20,000 rpm while exhibiting good even temperature behaviour. This contrasts with the 15,000 rpm achieved in the same test by an SAE52100 (100Cr6) bearing with identical dimensions. The importance of the higher achievable speeds with Cronidur 30Ô is that they provide machine tool builders, rebuilders and machine users with a relatively simple and low cost method of achieving greater performance from their machine spindles. Added to this, the even temperature operation at higher speeds of the Cronidur 30Ô bearings provides opportunities for substantial cost savings on spindle systems, simply by changing from air-oil to grease lubrication.

The second significant factor contributing to the higher speed performance of Cronidur 30Ô hybrid bearings is the use of Silicon Nitride (ceramic) balls which are 2.5 times lighter than steel. The use of ceramic rolling elements improves, significantly, the kinematics of the bearing. Centrifugal force is reduced dramatically and the lower inertia enables substantially higher acceleration to be achieved, together with operating speeds up to 15% higher than equivalent steel-balled high-speed bearings, and an astonishing 55% faster than traditional angular contact bearings of similar size.

Lower Wear and Longer Operating Life

In addition to higher speeds, the service life of the hybrid bearings, both with grease and oil lubrication, is several times that achieved by bearings with steel balls. There are a number of reasons for this. Firstly, the superior load and fatigue life characteristics (the latter 10 x that of 100CR6 bearings) of the Cronidur 30Ô bearing rings. Secondly, friction and adhesion between the ceramic balls and steel bearing rings (and, consequently, wear) is very low, especially at cold starts.

Thirdly, the superior tribological properties of the ceramic ball material enable "cool running" which can extend the working life of the grease, and hence, the life of the hybrid bearing, by a factor of five. Finally, the presence of unique non-contact seals which perform the dual function of excluding contaminants, whilst retaining grease within the contact area of the bearing rolling elements - even in the face of damaging airflows.

Improved Operating Reliability

As well as ensuring longer service life, the excellent running conditions (i.e. lower friction and heat generation) in the rolling contact zone of the hybrid bearings, combined with the beneficial effects of the seals, add up to greatly improved operating reliability for the bearing user. This is evident even under conditions of marginal lubrication where the bearings are protected against seizure by their emergency running properties of low adhesion and friction.

High Levels Of Stiffness Improve Machining Precision & Surface Quality

The improved thermal stability of the ceramic balls has another implication for bearing performance, beyond its role in providing improved reliability. It is also one of the major contributory factors to the exceptional running accuracy of the hybrid bearings. Another, and probably the most important factor, is the stiffness of the ceramic material itself. This characteristic, combined with the extremely fine grain structure of the Cronidur 30Ô bearing steel, also provides additional operating benefits to the bearing user in terms of reduced vibration and noise.

Unprecedented Levels Of Running Accuracy

FAG/Barden hybrid spindle bearings offer users unprecedented levels of running accuracy, within ISO P2 (Abec 9). To enable problem-free changeovers the hybrids are designed to be totally inter-changeable with high speed steel-balled spindle bearings. One of the benefits of this is that they provide a cost effective method of achieving significantly higher performance from a machine tool spindles without expensive redesigning and remanufacturing of spindle housings.

The use of FAG/Barden hybrid bearings can also help users to overcome the costs incurred with oil/air systems in applications where standard bearings with steel balls are required to run at higher speeds. Above a certain speed, steel bearings have to be lubricated with oil. In contrast, hybrid spindle bearings operate with grease lubrication even at extremely high speeds. The grease lubrication, via FAG/Barden's new Arcanol L75, is fully efficient, and offers the additional benefits of economy, easy maintenance and environmental friendliness.

About The Author:

Mark Harris is a successful author and regular contributor to http://www.bearing-n-bearings.com.  Keep things running smoothly with ball bearings, roller bearings, ball thrust bearings and tapered bearings.