Ceramic Hybrid Ball Bearings
Today, hybrid ceramic ball bearings with steel rings and ceramic balls have become indispensable for many advanced applications. The advantages have been clearly demonstrated by numerous trials and successful use in the field.
All GMN bearings are available in hybrid design on request. Please contact us for information.
Properties of ceramic
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
- 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 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 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 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.
- 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
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.
Examples & Applications
GMN spindle HCS 170-24000/27 with ATC and HSK A 63
HY SM 6014 17° TA UP DDT, spring preloaded.
Speed with oil-air lubrication 24.000 rpm
Floating bearing HY SM 6010 17° TA UP DDT spring preloaded
Ceramic Bearing Applications
- Aircraft generators
- Biotechnology equipment
- High speed machining and grinding spindles
- high speed mills
- Precision instruments
- Pumps and compressors
To obtain the best possible performance of the bearings, installation must be performed very carefully in ultra clean conditions.
Errors during fitting of ball bearings can jeopardize the best design and create high repair and maintenance costs. We would like to give some advise for proper mounting of bearings:
The workshop should be dust free with low humidity, no compressed air or machining is allowed.
Only unpack bearings immediately before installation. If grease is required it should be applied at this time, with a syringe. Do not use fingers or a spatula.
The use of a syringe is recommended to inject the grease right between the balls into the ball/raceway area. Nearly all standard greases are compatible to our rust preventive, so in most cases it is not necessary to wash the bearings prior to greasing. The only exceptions are special greases, based on silicone or fluorocarbon oils or PTFE-thickeners. They require a clean oil free surface to obtain good adhesion of the grease.
Never clean the bearings in ultra sonic devices! Allow the rust preventive to dissolve in a gasoline bath by slowly moving the bearings.
It is recommended to use filtered cleaning gasoline type 100/140 (max. filter 0.45 microns). Drying of the bearings should take place under a dust cover. Bearings should never be dried by blowing with compressed air because of environmental dust and moisture!
Finally the bearings, ready for installation, can be mounted by adequate means. It is of utmost importance to avoid misalignment of the bearings in the seats and that mounting loads never be applied through the balls.
The following pictures illustrate the correct installation:
The red lines show the line of force while pressing the bearings onto their seats.
The sketch on the right shows the mounting forces passing through the balls. This leads to indentations in the raceways hence the bearings run noisy and the service life will be reduced. This sketch shows the correct mounting of a bearing with a tight bore fit onto the shaft.
Mounting forces are conveyed through the inner ring only, balls and races remain free and undamaged. Very few applications call for tight fits on both bearing seats. In this case a bearing can be mounted by pressing both rings simultaneously. As a result, balls and raceways remain undamaged.
In general, there are no particular running-in specifications for oil lubed bearings, nevertheless it proved advantageous when
- lubricant is available prior to start up. Consider length of feed pipes to avoid insufficient lubrication,
- when performing a short running-in procedure to allow the bearings to settle in their seats.
Grease lubrication calls for running-in of the bearings. Even when a reduced grease pack is applied to the bearing, a certain amount of surplus grease causes additional friction. A complete grease film must cover all contact surfaces.
GMN recommends the following procedure for the majority of applications:
- Starting sequence at 10 per cent of operating speed followed by a stop to allow the bearings to cool off to ambient temperature.
- Distribution sequence at 50 per cent of operating speed where actual operating temperature slightly exceeds final operating temperature. When the temperature has reached a maximum, the unit is stopped to cool off again to ambient temperature. Test sequence, first operate at nominal speed. If target operating temperature is exceeded, the distribution sequence should be repeated.
- Length and number of sequences depend on specific properties of the application. Grease reservoirs, limited space, operating speed and environmental media have a strong effect on the distribution of the grease.
How long and how often this procedure is to be repeated depends on the properties of the application. To optimize the running-in process for your specific application, please contact our application engineers.