Spindle
Accessories
Types of high speed spindles bearings
The type of bearings available for spindles are as follows:
- Angular contact ball bearings: These are the most commonly
used bearings today in very high speed spindle designs. Also known as
precision ball bearings, they provide the precision, load carrying
capacity ( both axial and radial load carrying capacity ) and speed
required for metal cutting spindles.
- Roller bearings: The roller bearings, also called cylindrical
bearings offer higher load carrying capacity and greater stiffness than
angular contact ball bearings. They are applicable in spindles with
specific rpm requirements and applications.
- Tapered roller bearings: These bearings are used, because of their higher load capacity and greater stiffness over ball bearings. But they do not allow the high speeds required by many spindles.
Characteristics of spindle bearings
- Axial load supported in one direction only.
- Necessary of adjustment against a second bearing.
- Compared to deep groove ball bearings, spindle bearings have extended ball complement.
- High rigidity and loading capacity.
Spindles bearings : Types of Mounting
| Types | Explanation |
| Face to Face/DF X Configuration Bearing Mounting | Referred as "Face-to Face" or "X" configuration,it means bearings are mounted face to face . Here, the outer races are relieved. The relief clearance is removed when the outer races are clamped together. This results in the correct pre-load. The bearing pair is capable of withstanding both axial and radial loading in this type of configuration. |
| Back to Back/DB/O Configuration Bearing Mounting | Also known as "O", or "DB " mounting, this is the most common mounting method. In back-to-back configuration, the inner races are relieved. The relief clearance is removed, resulting in the correct pre-load when the inner races are clamped together. This is suitable for most applications and provides good rigidity and accuracy. |
| Tandem/DT Configuration Bearing Mounting | This is a combination of two or more mounting techniques. This mounting does not allow forces in both directions, unless and until there is another pair of bearings used on the spindle shaft, facing in the opposite direction. |
Bearing Construction: Hybrid ceramic
The ball bearings affect vibration levels, temperature and the spindle's life and this is dependent on the materials used in the making of ball bearings. However, the most popularly used ball bearings are hybrid ceramic as they offer distinct advantages over typical steel ball bearings.
- Less mass: The hybrid ceramic balls have 60% less mass than
steel balls. This becomes important because as a ball bearings operate,
centrifugal forces push the balls to the outer race, and can deform the
shape of the ball which leads to rapid wear and bearing deterioration.
Ceramic balls because of less mass will not be affected even at the same
speed. Moreover, the use of ceramic balls allows speed to go up 30% for
a given ball bearing size, without sacrificing any bearing life.
- Elimination of cold welding: Ceramic balls eliminate cold
welding which is a major cause of bearing failure. They can do this
because they do not react with the steel raceways, thereby resulting in
longer bearing life.
- Operate at lower temperatures: Because of the nearly perfect
round shape of the ceramic balls, hybrid ceramic bearings operate at
lower temperatures compared to steel ball bearings, which results in
longer life for the bearing lubricant.
- Lower vibration levels: Spindles with ceramic bearings have higher rigidity and higher natural frequencies, which makes them less sensitive to vibration.
Lubrication of bearings
For proper functioning of spindles, proper lubrication of bearings is very essential. To keep the bearings properly lubricated, machine tool manufacturers use several systems like oil-mist, oil-air, oil-jet, pulsed oil-air etc. Such systems become very necessary if bearing spindle speeds are more than 18,000 rpm. These lubrication systems must be thoroughly monitored so that the ratio and the amount of oil and air and/or mist are correct. Permanent lubricated bearings are the best option for keeping replacement costs lower and maintenance costs down . Lubrication helps to form a microscopic film between the rolling elements and it prevents skidding and abrasion. Besides that lubrication in spindles also protects the surfaces from corrosion, and protects the area from particle contamination.
Bearing life
The durability of bearings used in spindles in general is affected by the following factors:
- Bearing Loads, Axial and Radial
- Vibration Levels
- Quality of Lubrication
- Quantity of lubrication
- Maximum Speed
- Average Bearing Temperature
