Cancel
Super-Precision Contact Ball Bearings Designs And Variants
Single row super-precision angular contact ball bearings are non-separable and, like all angular contact ball bearings, have raceways in the inner and outer rings that are displaced relative to each other in the direction of the bearing axis. This means that in addition to radial loads, these bearings can also accommodate axial loads in one direction. Radial loads induce axial forces in these bearings that need to be balanced by counterforces. An angular contact ball bearing is, therefore, always adjusted against a second bearing or used in sets.
Bearing series
The assortment of super-precision angular contact ball bearings includes bearings in the following dimension series:
- Ultra light 718 series
- Extremely light 719 series
- Light 70 series
- Robust 72 series
The cross sections of the four bearing series are compared in for the same bore and same outside diameters. Each bearing series has characteristic features that make it particularly suitable for certain bearing applications.
Where a low cross-sectional height is a critical design parameter, bearings in the 718 series should be selected. If more radial space is available, and loads are not very heavy, bearings in the 719 or 70 series could be used. Bearings in the 72 series have the largest cross-sectional height for a given bore diameter and are suitable for heavy loads at relatively low speeds.
If a high degree of stiffness is required, bearings in the 718 and 719 series are typically used. Bearings in these two series contain the largest number of balls, relative to the selected bore size, and can also accommodate the largest shaft diameter, relative to their outside diameter. Both characteristics are particularly important for system rigidity, as the rigidity of a spindle increases with its shaft diameter, and the rigidity of a bearing arrangement increases with the number of balls.
Contact angles
Super-precision angular contact ball bearings are manufactured with the following contact angles :
- A 15° contact angle, designation suffix C
- A 25° contact angle, designation suffix AC
For S70 W series bearings, the contact angle is 18° (designation suffix F). For other series, bearings with an 18° contact angle (designation suffix F), are available on request.
A larger contact angle provides a higher degree of axial stiffness and a higher axial load carrying capacity. However, speed capability, radial stiffness, and radial load carrying capacity are reduced.
Designs
High-capacity D design bearings
D design bearings are designed to accommodate heavy loads at relatively high speeds under low to moderate operating temperatures. When compared to other precision angular contact ball bearings, D design bearings contain the maximum number and size of balls. Their close osculation provides a relatively high degree of stiffness and the highest possible load carrying capacity.
Typical applications for bearings in the 718 .. D series include:
- Machine tools, e.g. multispindle drilling heads
- Robotics
- Printing
- Measuring systems
- Racing car wheels
Typical applications for bearings in the 719 .. D and 70 .. D series include:
- Machining centres (horizontal and vertical)
- Milling machines
- Lathes
- External and surface grinding machines
- Boring machines
- Machines for cutting or polishing stones and glass
- Semiconductor industry, e.g. units for detecting defects on silicon wafer chips
- Boat gyrostabilizers
- Telescopes
- Microturbines
- Racing/super car wheels
- Medical equipment
Typical applications for bearings in the 72 .. D series include:
- Machine tool spindles e.g. live centre spindles
- Lathes (main spindles, tailstock)
- Grinding machines
- Boring machines
- Parallel Kinematic Machines (PKM)
- Dynamometers for engine testing
- High-speed turbochargers
High-speed E design bearings
E design bearings when compared to D design bearings, have a more open osculation and a maximum number of smaller balls. They can therefore accommodate very high speeds but do not have the same high load carrying capacity as D design bearings. Compared to B design bearings, E design bearings have a slightly higher speed capability and can accommodate heavier loads.
Typical applications for bearings in the 719 .. E and 70 .. E series include:
- Electro-spindles
- High-speed machining centres (horizontal and vertical)
- High-speed milling machines
- High-speed internal grinding machines
- High-speed spindles for PCB drilling
- Woodworking machines
High-speed W design bearings
W design bearings when compared to D design bearings, have a more open osculation and a maximum number of smaller balls. They can therefore accommodate very high speeds but do not have the same high load carrying capacity as D design bearings.
W design bearings are only available as hybrid (balls made of bearing grade silicon nitride), sealed and lubricated for life, angular contact ball bearings with an 18° contact angle. Their new cage design has a very high stability at low and medium speeds for reduced noise and vibration levels. They are available as single bearings for universal matching or as matched sets of two bearings arranged back-to-back or in tandem.
Typical applications for bearings in the S70 .. W series include medium-high volume production machines such as:
- Woodworking machines
- Transfer machines
- Small machining centres
- Tool grinding machines
High-speed B design bearings
B design bearings are designed for high-speed operation and are best suited for lighter loads and lower operating temperatures. When compared to E and D design bearings, B design bearings are equipped with the maximum number of very small balls. The smaller, lighter balls reduce the centrifugal loads acting on the outer ring raceway and therefore reduce the stresses on the rolling contact surfaces. As smaller balls require less space, the bearing rings have a larger cross-sectional height, making them less susceptible to distortion resulting from irregularities of the bearing seat, either on the shaft or in the housing.
Typical applications for bearings in the 719 .. B and 70 .. B series include:
- Electro-spindles
- Metal cutting machines
- Woodworking machines
- Milling machines
- Machining centres
Sealing solutions
The most common bearings can be supplied with an integral seal fitted on both sides (designation prefix S). The seal forms an extremely narrow gap with the inner ring shoulder and therefore speed capability is not compromised.
The seals are made standard of an oil- and wear-resistant NBR and are reinforced with sheet steel. On request, bearings can be supplied with seals made of FKM.
Sealed bearings are filled as standard with a high-quality, low-viscosity grease that has a lithium soap thickener and a synthetic ester base oil. The quantity of grease fills ~ 15% of the free space in the bearing. The temperature range for the grease is –55 to +110 °C (–65 to +230 °F). On request, the bearings can be supplied with other greases. For additional information, contact the application engineering service.
When compared to bearing arrangements with open bearings and external seals, sealed bearings can provide a number of advantages, including:
- Potential for extended bearing service life
- Extended maintenance intervals
- Reduced inventory
- Reduced risk of lubricant contamination during mounting and operation
Sealed bearings are lubricated for life. They should not be washed or heated to temperatures above 80 °C (175 °F). If a sealed bearing is to be heated for mounting, an induction heater must be used and the bearing should be fitted immediately to minimize the time that the bearing is exposed to high temperatures.
WARNING
Seals made of FKM (fluoro rubber) exposed to an open flame or temperatures above 300 °C (570 °F) are a health and environmental hazard! They remain dangerous even after they have cooled.
Read and follow the safety precautions under this WARNING.
Direct oil-air lubrication
Some very high speed applications require open bearings in the 719 .. D and 70 .. D series, 719 .. E and 70 .. E series, and 719 .. B and 70 .. B series to be lubricated with minimal amounts of oil, directly through their outer rings.
On request, bearings can be supplied with two lubrication holes in their outer rings. Bearings with an annular groove or an annular groove and two annular O-ring grooves, complete with O-rings to seal to the bearing housing bore, are also available The positions of these features are listed in the product table