Ceramic - Hybrid Bearings

Technical information on Hybrid bearings

Properties of ceramic are excellent for use in precision ball bearings. A comparison between silicon nitride and conventional bearing steel 100 Cr6 is shown in the diagram: Further advantages of ceramic are: Low chemical affinity to 100 Cr6 Low friction coefficient Little heat transfer Corrosion resistant Non-magnetic Electrically isolating

Advantages for the user

Longer service life
The service life of a hybrid bearing can be up to 40% longer than for a conventional bearing.

Reasons:
	Low surface adhesive wear The lower affinity to steel reduces the adhesive wear, which is caused by the cold welding effect on irregularities in the raceway and ball surface.
	Low abrasive wear out With steel balls, contaminants and particles from the process of running in are embedded into the surface. With every revolution of the ball, these foreign particles damage the raceway. These particles make little impact on the extremely hard ceramic ball.
	Insensitivity to poor lubrication Low adhesion and friction allow the hybrid bearing to perform well even under poor lubrication.
	Longer grease service life Lower operating temperature and favorable tribologic features, extend the service life of the grease.

Higher speeds
The attainable speed depends on the thermal conditions in the bearing. Because of lower friction, the hybrid bearing generates less power loss, therefore the speed limit is increased dramatically.

Low rolling friction The rolling friction is reduced, as the centrifugal force of the lighter ceramic ball is less. The contact ellipse is less because of the higher Young's modulus. Low sliding friction between ball and raceway At high speeds, sliding friction is responsible for most of the total friction. One of the criteria for the sliding friction is a low spin/roll ratio. The service life is effected by values above 0,25. The diagram shows the advantages of ceramic balls.

Avoid ball skidding The balls skid on the raceway if the preload between the rings is too small. This process usually occurs in case of an insufficient preload of the bearing or an excessive acceleration. With hybrid bearings the minimum preload can be reduced as they have a smaller inertia and generate a smaller spinning moment.

Low cost lubrication
	Grease lubrication can be used in higher speed ranges.
	The limiting speed for minimum oil lubrication increases significantly. In many cases, it can replace the expensive oil jet lubrication.

The possible increase of the speed depends on different factors, such as the allowed speed factor of the grease used, temperature and the concept of the bearing fittings. Therefore, GMN does not publish a standard additional factor for the limiting speed, but offers an individual check of your construction. For contact, please click here.

Higher rigidity The radial rigidity of hybrid bearings is approximately 15% higher at low speeds because of the higher Young's modulus. With higher speeds, the centrifugal force affects the internal load distribution and the dynamic rigidity is reduced. The diagram shows reduced loss of rigidity for hybrid bearings. A high rigidity improves the accuracy and shifts the critical fundamental frequency of the bearing arrangement.

Improved machining accuracy

The following factors lead to an improvement of the surface quality and accuracy of machined parts.
	Higher rigidity of bearing arrangement
	Small thermal expansion
	Low vibration impulse by ceramic balls

Examples of application

	Spindles for machine tools: State of the art machining processes like high speed milling require a new concept of bearing arrangement for spindles. The application of hybrid bearings has resulted in a remarkable improvement in performance. For some years we at GMN have successfully used many spindles with hybrid bearings for our own production processes.
	Special bearing arrangements: With vacuum pumps, reliability of the bearings is of utmost importance, as breakdown can result in high costs.

More applications are:
	Medical equipment like X-ray tube bearings
	Emergency bearings for magnetic bearings
	Bearings for aeronautic and aerospace

Summary

When conventional bearings fail, the solution is often to use hybrid bearings. It is important always to take the whole system into consideration and to carry out a "weak point" analysis. Our experience in operating these bearings is at your service.

For the selection and interpretation of the hybrid bearings, please contact our application consultancy.