Properties of Ceramic Ball Material
Ceramic (silicone nitride Si3N4) is an excellent choice for ball material in precision bearings. A comparison between ceramic ball material and conventional bearing steel 100 Cr6 is shown in the chart.
A few other advantages of ceramic ball material is:
- Low chemical affinity to 100 Cr6
- Low friction coefficient
- Little heat transfer
- Corrosion resistant
- 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.
- Low surface adhesive wearThe 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 outWith 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 lubricationLow adhesion and friction allow the hybrid bearing to perform well even under poor lubrication.
- Longer grease service lifeLower operating temperature and favorable tribologic features, extend the service life of the grease.
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 frictionThe 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 racewayAt 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 skiddingThe 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.
- 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
- 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
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 us.